Development of an in Situ NMR Photoreactor To Study

Development of an in Situ NMR Photoreactor To Study Environmental Photochemistry ..... cryoprobe systems, it involves developing custom flow cells as ...
2 downloads 0 Views 2MB Size
Subscriber access provided by UNIV OF NEBRASKA - LINCOLN

Article

The development of an in-situ NMR photoreactor to study environmental photochemistry Liora Bliumkin, Rudraksha Dutta Majumdar, Ronald Soong, Antonio Adamo, Jonathan P.D. Abbatt, Ran Zhao, Eric J Reiner, and Andre J Simpson Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b00361 • Publication Date (Web): 12 May 2016 Downloaded from http://pubs.acs.org on May 24, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

Environmental Science & Technology

The Development of an in-situ NMR Photoreactor to Study Environmental Photochemistry

1 2 3 4

Liora Bliumkin,†,‡ Rudraksha Dutta Majumdar,† Ronald Soong,† Antonio Adamo,§ Jonathan P.D.

5

Abbatt,‡ Ran Zhao,‡ Eric Reiner,∥ and André J. Simpson*,†,‡

6 7



Environmental NMR Centre, Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4, Canada

8 9



Department of Chemistry, University of Toronto, Toronto, Ontario, M5S 3H6, Canada

10

§

Teaching and Research in Analytical Chemical and Environmental Science (TRACES),

11

Department of Physical and Environmental Sciences, University of Toronto Scarborough,

12

Toronto, Ontario, M1C 1A4, Canada

13



Ontario Ministry of the Environment, Toronto, Ontario, M9P 3V6, Canada

14 15 16

*Corresponding

author.

17

[email protected]

Phone

+1

416-287-7547.

Fax

18 19 20 21 22 23

ACS Paragon Plus Environment

+1

416-287-7279.

E-mail:

Environmental Science & Technology

24

ABSTRACT: Photochemistry is a key environmental process directly linked to the fate, source,

25

and toxicity of pollutants in the environment. This study explores two approaches for integrating

26

light sources with nuclear magnetic resonance (NMR) spectroscopy: sample irradiation using a

27

“sunlight simulator” outside the magnet, versus direct irradiation of sample inside the magnet.

28

To assess their applicability, the in-situ NMR photoreactors were applied to a series of

29

environmental systems: an atmospheric pollutant (paranitrophenol), crude oil extracts, and

30

groundwater. The study successfully illustrates that environmentally relevant aqueous

31

photochemical processes can be monitored in-situ and in real-time using NMR spectroscopy. A

32

range of intermediates and degradation products were identified and matched to the literature.

33

Preliminarily measurements of half-lives were also obtained from kinetic curves. The “sunlight

34

simulator” was shown to be the most suitable model to explore environmental photolytic

35

processes in-situ. Other light sources with more intense UV output hold potential for evaluating

36

UV as a remediation alternative in areas such as wastewater treatment plants or oil-spills.

37

Finally, the ability to analyze the photolytic fate of trace chemicals at natural abundance in

38

groundwater, using a cryogenic probe, demonstrates the viability of NMR spectroscopy as a

39

powerful and complementary technique for environmental applications in general.

40 41 42 43 44 45 46 47

ACS Paragon Plus Environment

Page 2 of 36

Page 3 of 36

48

Environmental Science & Technology

TOC ART:

49 50 51

KEYWORDS. Nuclear Magnetic Resonance Spectroscopy, Environmental Photochemistry,

52

Photolysis, Degradation, In-situ, Kinetics

53 54

INTRODUCTION

55

Environmental photochemistry involves the transformation of compounds, found on

56

Earth’s surface and in the atmosphere, due to the absorption of photons between 290-600 nm.1

57

The absorption of photons provides sufficient energy for electrons to be excited from the ground

58

state into an excited state (commonly π→π∗ or n→π∗).1 In order for the excited electrons to return

59

to ground (stable) state, they must release the excess energy. One way this can be achieved is

60

through the initialization of a chemical reaction that requires an input of energy.1 These

61

photochemical reactions can then result in mineralization (conversion to CO2 and H2O) or

62

generation of new compounds via bond cleavage, isomerization, rearrangement or intermolecular

63

reactions, and can take place in both the aqueous (atmospheric aerosols or surface water) and

64

solid phases (plant and soil surface).2 Generally, photochemical reactions (photolysis) can be

ACS Paragon Plus Environment

Environmental Science & Technology

65

direct or indirect. In direct photolysis, a chromophore directly absorbs a photon and becomes

66

excited.1 Conversely, indirect photolysis involves a photosensitizer, that upon absorption of

67

photons, transfers the energy to initiate a chemical reaction in nearby compounds.1 Not only does

68

solar radiation play a pivotal role in the composition and fate of both natural and anthropogenic

69

chemicals in the environment, much of the life on Earth also relies on it as its source of energy.3

70 71

Current techniques used in photochemical analysis

72

Photochemistry is commonly studied using fluorescence, optical spectroscopy, and mass

73

spectrometry (MS) due to the high temporal resolution and sensitivity of the techniques.4

74

Chemical properties such as quantum yields can be obtained using optical spectroscopy.

75

However, it becomes challenging to elucidate such information from complex samples due to

76

spectral overlap, as in the case of polycyclic aromatic hydrocarbons (PAHs) in cosmic water ice.5

77

Other studies have demonstrated that UV-Vis spectrometry provides more ambiguous

78

information relative to higher resolution techniques such as NMR spectroscopy.6 Fluorescence is

79

a highly sensitive alternative, but is restricted to only a small fraction of molecules that fluoresce

80

and thus provides only limited information with respect to chemical structure. Mass spectrometry

81

(MS) is arguably one of the most efficient and informative techniques and can characterize

82

photoproducts in a complex mixture based on their fragmentation patterns.7 High Performance

83

Liquid Chromatography (HPLC) and Gas Chromatography (GC) are generally coupled with MS

84

to enhance selectivity and reduce spectral overlap.8 Nonetheless, MS may require extensive

85

sample preparation that can potentially lead to the introduction of variability and artifacts.9 For

86

example, many free radicals (such as nitroxides) can be detected in solution using fluorescence

87

while much of this information is lost with MS if the preparation time is too long.10 Furthermore,

ACS Paragon Plus Environment

Page 4 of 36

Page 5 of 36

Environmental Science & Technology

88

while MS provides critically needed molecular formulae information, identification of exact

89

structures may not be possible if novel structures are formed (i.e. library fragmentation not

90

available). As such, there is need for complementary techniques, especially those that can

91

provide high resolution isomeric information required to solve de-novo molecular structure.

92 93

NMR Spectroscopy as a tool in environmental research

94

In recent years, NMR spectroscopy has emerged as an important complementary tool in

95

environmental research as it can provide unprecedented information regarding molecular

96

structures, mechanisms, and kinetics that are key in the elucidation of photochemical reactions.4

97

Moreover, it is a non-selective, versatile, robust, and highly reproducible technique that offers

98

efficient and indiscriminate information that can be missed by conventional methods.11,12

99

Simpson et al. have previously provided a detailed review of the applicability of NMR

100

spectroscopy to environmental research.13 A brief overview of the unique advantages afforded by

101

NMR spectroscopy as it pertains to environmental studies is provided in Table S1, with the

102

appropriate examples and references.14–31

103

The ability of NMR spectroscopy to analyze a sample in its natural state and in a non-

104

invasive manner is a very important factor in environmental studies. The technique has been

105

shown to be a useful tool to follow the progress of chemical reactions. An excellent example is

106

the study of trifluralin degradation by using 19F NMR spectroscopy where samples in NMR tubes

107

were placed outside in direct sunlight and then periodically brought in for NMR analysis.32 The

108

study identified a range of degradation products and reaction mechanisms. However, while such

109

studies are accessible and easy to perform, periodic sampling only provides information on the

110

sample at discrete points in time. Determining the correct sampling frequency and timing for

ACS Paragon Plus Environment

Environmental Science & Technology

111

each sample becomes essential to minimize over- and under-estimations and bias on the complex

112

chemistry taking place inside the NMR tube.33 The lack of high temporal resolution is

113

specifically problematic if reactive short-lived intermediates or rapid reactions occur. These can

114

be avoided using near real-time measurements, as demonstrated with the application of in-situ

115

NMR analysis to study reactive organometallic structures with short lifetimes.34 Similarly,

116

Henjum et al.33 have shown the importance of in-situ analysis as they compared pollutant

117

loadings in streams from near real-time measurements and periodic sampling. It was

118

demonstrated that larger calculation errors arise from periodic sampling and that identifying

119

pollution sources and sinks are more feasible using near real-time monitoring.33 Thus, in-situ

120

monitoring has the capability to improve quantitative analyses, reduce the loss of valuable

121

information between sampling points, and follow the fate, source, and toxicity of pollutants in

122

the environment for a more comprehensive understanding on environmental processes.35

123

In this article, we explore and develop various approaches for performing in-situ

124

photochemical NMR spectroscopy to study environmental photochemistry. These include

125

comparison of light sources, from relatively cheap xenon arc lamps to more realistic “sunlight

126

simulators”, as well as comparing flow systems (light source outside the spectrometer) to optical

127

fiber (light directly into the NMR magnet). Three different light setups are tested on a range of

128

media including individual compounds, crude oil extracts, and groundwater to test the

129

applicability to a wide range of environmental systems. This study demonstrates that

130

environmentally relevant photochemical processes in the aqueous phase can be monitored in-situ

131

and in real time using NMR spectroscopy. Once constructed, the photochemical NMR systems

132

are relatively easy to operate permitting studies with high temporal resolution in an automated

133

fashion without user intervention. Considering the highly complementary nature of NMR

ACS Paragon Plus Environment

Page 6 of 36

Page 7 of 36

Environmental Science & Technology

134

spectroscopy to MS,36 especially in terms of structural elucidation, in-situ photochemical NMR

135

will likely play an important role unraveling photochemical processes especially in more

136

complex system where MS alone is insufficient.

137 138

EXPERIMENTAL SECTION

139

Light Sources and Optical Fiber (for full details see Supporting Information) OceanOptics HPX-2000: 35 W continuous xenon light source (main output: 290-800 nm.

140 141

Figure S1a) OceanOptics PX-2: a pulsed xenon lamp, wavelength range from 220-750 nm (Figure

142 143 144 145

S1b). Original Hanau Suntest: a xenon burner with daylight filter, specifically designed to mimic the spectrum of sunlight received at the Earth’s surface (Figure S2).

146 147

Chemical Actinometry and Calibration of the Suntest

148

The average global shortwave (SW) downward surface radiation (DSR) reported in the

149

literature is ~17 mW/cm2, while the average global net absorbed surface shortwave radiation flux

150

is ~15 mW/cm2.37 Nuclear magnetic resonance spectroscopy based chemical actinometry using a

151

2 mM solution of 2-nitrobenzaldehyde38 in 70% D2O and 30% H2O was used to measure the

152

average radiation flux between 290-380 nm reaching the reaction vessel inside the Suntest by

153

monitoring the NMR peaks of the protons attached to C(3) and C(6). The radiation flux exposed

154

to the reaction vessel inside the Suntest was calculated to be ~8.53 mW/cm2 with an average

155

photon flux of 2.46 × 1014 s-1·cm-2·nm-1 which was consistent with that reported by Zhao et al.39

156

This is ~2 times lower than the average global SW-DSR and ~1.75 times lower than the net

ACS Paragon Plus Environment

Environmental Science & Technology

157

absorbed radiation flux reported in the literature and is consistent with the net absorbed

158

shortwave radiation in New Orleans, Casablanca, and Beijing in January and Paris and Berlin in

159

October.37 No attempts were made to calibrate the HPX-2000 or PX-2 light sources in relation to

160

natural sunlight since their spectral output differs greatly from sunlight, and numerous

161

disadvantages observed in this work make them less suitable for photochemical studies that aim

162

to mimic the natural environment.

163 164

Experimental Summary (see Supporting Information for full details)

165

Samples were prepared as described in the Supporting Information. For both the HPX-

166

2000 and PX-2 light was transferred via an optical fiber and data were collected on the most

167

sensitive 5 -mm cryogenically cooled NMR probe (see Supporting Information for details and

168

Figure 1 for schematic). The polyamide coating was removed from a ~ 10 cm section at the end

169

of the fiber that entered the NMR tube to increase light transmittance into the sample.40 The

170

optical fiber OD was 1 mm, and it was connected to the 4.2 mm ID NMR tube such that it does

171

not form a gas tight seal, allowing air exchange. No spinning was performed on the NMR tube.

172

Due to the different design of the Suntest (a sunlight chamber, rather than a light source with an

173

optical fiber connector), a looped flow system was employed. The easiest integration was via a

174

standard, commercial NMR flow probe that permits the sample to be directly flowed through the

175

spectrometer. All studies with the Suntest light source were performed using a 1H, 13C, 15N, TXI

176

(Triple resonance Inverse) z-gradient 250 µL injection NMR flow probe with the exception of

177

the groundwater. For groundwater, while a lot more challenging due to the low concentration, a

178

cryogenic probe was employed fitted with a custom designed flow cell as previously described

179

by Soong et al.17 All other experimental details are provided in the Supporting Information.

ACS Paragon Plus Environment

Page 8 of 36

Page 9 of 36

Environmental Science & Technology

180 181 182 183

RESULTS AND DISCUSSION

184

Comparison of different light sources

185

Riboflavin represents a simple, cheap and well characterized photosensitive compound

186

ideal for investigating the basic performance of the in-situ NMR photoreactors before application

187

to more environmentally relevant systems later in this paper. Riboflavin is highly sensitive to UV

188

and visible light, and forms reactive oxygen species (ROS) upon light exposure.41 Absorption

189

maxima have been reported around 224, 268, 373, and 445 nm.42,43 The photodegradation of

190

riboflavin has been extensively studied, and is known to form two main photoproducts:

191

lumichrome and lumiflavin.41

192

HPX-2000, PX-2, and Suntest light systems were selected for comparison. These are

193

discussed more in the Supporting Information. Figure 1 provides the schematics, NMR spectra

194

and kinetic curves for the degradation of riboflavin using the three different light sources.

195

Expanded NMR spectra including detailed assignments and various controls are provided in the

196

supporting section (Figures S3 through S8), along with specific assignments of the degradation

197

products. The controls included light-off before exposure (to ensure no change prior to analysis),

198

light-off after exposure (to ensure changes halt when light is removed), and dark controls (to

199

demonstrate that changes are caused by the light). No changes were observed in any of the

200

controls, confirming all reactions to be photolytic.

201

On light exposure of riboflavin using both PX-2 and HPX-2000, the two singlet (methyl)

202

peaks at 2.05 and 2.17 ppm and aromatic peaks at 7.09 and 7.19 ppm decreased in intensity.

ACS Paragon Plus Environment

Environmental Science & Technology

Page 10 of 36

203

Eight new peaks appeared between 6-8.5ppm along with two large signals at 3.61 and 3.77 ppm

204

(Figure 1, S3, S4). The solution changed from light to a dark orange, and a dark, orange-brown

205

precipitate was formed inside the NMR tube (more visible with HPX-2000, see Figure S3). The

206

NMR products were not consistent with products expected to be formed from riboflavin in

207

sunlight.41,44 The alkyl region resembled the spectrum of erythritol (Figure 1) and indicates the

208

polar branch from riboflavin is cleaved. The aromatic region (Figure S3) exhibited similarities to

209

spectra of riboflavin derived polymers previously reported in the literature,45 and constituted a

210

very small fraction of the overall spectrum. However, in-depth identification is beyond the scope

211

of this paper and was not attempted.

212

The results with the Suntest were significantly different. The peaks at 7.09 and 7.19 ppm

213

were replaced by five new singlet peaks between 6.7-8.5 ppm. Also, new peaks between 3.4–3.8

214

ppm were observed. These are all consistent with the main photoproducts of riboflavin reported

215

in the literature for > 254 nm light, namely lumichrome, lumiflavin, erythrose, and 1-deoxy-

216

xylulose (Figure 1).41,44 Detailed assignments are provided in Figure S8. The occurrence of

217

different photoproducts between the light systems are likely due to the different spectral output.

218

While not clear from Figure S1, the manufacturer reports wavelengths down to 185 nm for the

219

HPX-2000 and 220 nm for the PX-2. Riboflavin is known to contain several chromophores

220

ranging between 200-500 nm, including a chromophore at 224 nm.42,43

221

The kinetics also highlighted differences between the light systems. The PX-2 and HPX-

222

2000 show unusual sigmoidal curves (Figure 1). However, these are likely result of how the

223

optical fiber was placed within the NMR tube. To avoid shimming problems, the end of the

224

stripped fiber was placed in the reaction solution but above the detection coil. It appears that the

225

light induces photolytic reactions, but the products take time to diffuse into the detection coil

ACS Paragon Plus Environment

Page 11 of 36

Environmental Science & Technology

226

region. The lack of an immediate and prominent reaction suggests that the light cannot penetrate

227

directly into the coil region due to self-absorption from the sample itself. This clearly highlights

228

the difficulties in distributing light uniformly through any sample based on an optical fiber,

229

which in turn would complicate calculating kinetic parameters such as half-lives.46 To test this

230

hypothesis of delayed onset of product detection, the experiment was repeated with the fiber

231

completely stripped of polyamide coating and submerged to the bottom of the NMR tube.

232

However, this was done using a room temperature probe, since the heating from the fiber may

233

adversely affect the cryoprobe detection coil that has cryogenically cooled electronics at very

234

close proximity to the sample. It could potentially cause the cryogens to become gaseous and

235

crack probe components.

236

immediately with the compound completely degrading within 1 hour (Figure S5), thus validating

237

our hypothesis that when the fiber is above the coil region, the products take time to diffuse

238

downwards for detection.

It was observed that the riboflavin signals started attenuating

239

The Suntest system, which is based on a flow design, produces a logical decay profile

240

indicating that the reaction starts immediately after light exposure and continues in a two-step

241

first-order mechanism,39,44 initial rapid degradation followed by slower degradation. The half-life

242

was calculated as ~1.88 h. Based on chemical actinometry (see experimental section), the Suntest

243

system produces light that is consistent with that measured in New Orleans, Casablanca, and

244

Beijing in January and Paris and Berlin in October which is ~ 1/2 of the global solar average.37

245

The average half-life of riboflavin in the environment can be measured by accounting for the

246

difference in radiation flux (a factor of two) between the Suntest and the environment. Previous

247

kinetic studies suggest a linear relationship between photon flux and the rate of riboflavin

248

photodegradation.39,44 Once the reduced light output from the Suntest (~50% compared to

ACS Paragon Plus Environment

Environmental Science & Technology

Page 12 of 36

249

average global net) is accounted for, the global average half-life of riboflavin is ~0.94 h. This is

250

consistent with previous reports of riboflavin photodegradation in milk.47 Considering this along

251

with the fact that Suntest produced the expected degradation products,41,44 and is fundamentally

252

designed to simulate sunlight, it is clear that this approach is best suited to investigate and

253

monitor environmental photochemistry. That said, the drawbacks of such a flow system include

254

the requirement for larger volumes of sample, the rigorous cleaning required between samples to

255

prevent carry over, the cost of a Suntest simulator, and the need to design a NMR flow cell or

256

have access to an NMR flow probe. Arguably, the HPX-2000 and PX-2 may have use if reactions

257

in the deep UV range are of interest, for instance, the photoremediation of contaminants.

258 259

Photooxidation and phototransformation of p-nitrophenol, an atmospheric pollutant

260

Solar radiation is known to be the driving force behind several atmospheric processes and

261

responsible for the generation of atmospheric radicals which are considered “cleansers” of the

262

atmosphere.48–50 Nitrophenols are introduced into the atmosphere via biomass burning emissions,

263

as well as the atmospheric oxidation of aromatic pollutants.51 Nitrophenols are phytotoxic;52 and

264

therefore, their photochemistry and decay products are of great interest to the atmospheric

265

chemistry community. In particular, p-nitrophenol is sufficiently water-soluble and consequently

266

subject to aqueous-phase photooxidation and phototransformation in cloud and fog waters.53

267

Hence, the phototransformation of p-nitrophenol was monitored here to demonstrate the

268

phototransformation process of a simple environmentally relevant compound using in-situ NMR

269

photoreactors.

270

In-situ and real time information from NMR spectroscopy enabled the identification of

271

p-nitrophenol degradation products, as shown in Figure 2, along with the kinetic curve for the

ACS Paragon Plus Environment

Page 13 of 36

Environmental Science & Technology

272

phototransformation using the Suntest as a light source. The various control spectra collected

273

under the light-off conditions (see Supporting Information, Figure S9) confirmed the spectral

274

changes as photolytic.

275

The signals from the parent compound and photoproducts decrease over the course of

276

light exposure, suggesting either phototransformation to CO2 or release of small volatile organic

277

products (Figure 2). As stated in the literature, the major photoproducts of p-nitrophenol are

278

hydroquinone and 4-nitrocatechol (4-nitrobenzene-1,2-diol).54 These primary intermediates

279

reacted further with hydroxyl radicals leading to ring-opening products and formation of

280

oxygenated aliphatic compounds such as 2-butenedioic acid (fumaric acid).54,55 Additionally,

281

benzoquinone was formed from hydroquinone while terephthalic acid, and 5-nitrobenzene-1,2,3-

282

triol were detected based on their chemical shifts (Figure 2).56 The ability to monitor a reaction’s

283

progress with high temporal resolution using in-situ NMR spectroscopy and NMR’s highly

284

complementary nature to MS should prove useful in the elucidation of reaction mechanisms in

285

general. The half-life of p-nitrophenol was determined to be 2.47 h (Figure 2). Unlike riboflavin,

286

estimating the half-life of p-nitrophenol in the environment has proven to be more challenging

287

with a wide range of half-lives reported since the photooxidative degradation of p-nitrophenol is

288

highly dependent on ·OH and substrate concentrations as well as the light source used.54

289

In contrast, only slight phototransformation was observed with HPX-2000 as the light

290

source (Figure S10). This is most likely related to the spectral output of the two sources. The

291

Suntest produces 90 µW/cm2/nm (converted from ~0.9 W/m2/nm, Figure S2) which is ~9 times

292

more intense than the ~10 µW/cm2/nm for the HPX-2000. Furthermore, loss in the optical fibers

293

and low surface area exposure would render an external optical fiber solution, such as the HPX-

294

2000, less appealing for most environmental applications. A schematic summarizing the

ACS Paragon Plus Environment

Environmental Science & Technology

295

photodegradation behavior of riboflavin and p-nitrophenol under the different light sources is

296

shown in Fig S11.

Page 14 of 36

297 298 299 300

Oil spills: the fate of Water Soluble Fraction of crude oil upon exposure light

301

To demonstrate the application of photochemical NMR spectroscopy to a more complex

302

environmental mixture, the water soluble fraction (WSF) of crude oil was studied. Crude oil is a

303

complex heterogeneous mixture containing > 30,000 different hydrocarbon molecules57

304

(saturates, aromatics, resins and asphaltenes)58 some of which contain aromatic rings and

305

heteroatoms, as observed by Fourier transform ion cyclotron resonance mass spectrometry

306

(FTICR-MS).57,59–61 Oil spills are a significant environmental problem where toxic chemicals are

307

released into the environment.62–64 Certain gasoline components are resistant to biodegradation,

308

but are photoliable.65 Here, the fate of water soluble oil components upon light exposure using

309

the HPX-2000 and the Suntest light sources was investigated.

310

Sodium dodecyl sulfate (SDS) was added to simulate the use of surfactants which are

311

often used to help disrupt large oils spills and disperse oil components into the aqueous phase.66

312

H2O2, an oxidant, was also added as an essential catalyst in the photodegradation of the WSF.

313

Photooxidation in the presence of H2O2 has been proven to be an important remediation

314

technique involving the generation of reactive hydroxyl radicals that are capable of degrading a

315

wide range of organic pollutants.67 An SDS control experiment containing H2O2 confirmed that

316

SDS is not photolabile (Figure S12). Other controls, including light-off prior and following

317

photoirradiation and dark controls containing H2O2, confirmed all reactions to be photolytic

ACS Paragon Plus Environment

Page 15 of 36

Environmental Science & Technology

318

(Figures S13, S14, S18). With both models, new peaks were observed between 0.7-1.5 ppm,

319

suggesting the formation of aliphatic compounds (Figure 3B, pink),68,69 but to a greater extent

320

with Suntest. Furthermore, new photoproducts between 3.5-3.8 ppm hint at hydroxylation of

321

crude oil precursors (Figure 3B orange).61,68,69 This trend is in agreement with previous

322

observations on photo-degraded and weathered oil by Islam et al. using FT-ICR MS.60

323

Two-dimensional (2D) Distortionless Enhancement by Polarization Transfer -

324

Heteronuclear Single Quantum Coherence (DEPT-HSQC) Spectroscopy provides additional

325

spectral dispersion and 1H-13C connectivity over one bond (1JCH). The DEPT component encodes

326

CH3/CH and CH2 with opposite phases based on the difference in evolution behaviour of these

327

units during the experiment. In simple terms, DEPT-HSQC provide a high dispersion map of the

328

H-C units in the mixture with the CH2 units phased negative (coloured green, Figure S15) and

329

the CH/CH3 units phased positive (coloured blue, Figure S15). Region 6 in the DEPT-HSQC

330

data (Figure S15) supports the production of a small quantity of hydroxylated products.

331

Additional naphthenic acid moieties were observed for the Suntest system (~2.7 ppm, Figure 3B,

332

green),70 but no corresponding change was detected for the HPX-2000. A notable reduction in

333

aromaticity between 6.5-8.0 ppm following light exposure (Figures 3C&D) was also observed,

334

as previously noted by other groups.60,71,72 The aromaticity decreased by ~13% with HPX-2000

335

and by ~35% with the Suntest model (Figure 3). Based solely on the spectral output of the lamps,

336

the Suntest is ~9 times more intense than HPX-2000 between 300-800 nm and likely explains the

337

increased breakdown down of more aromatic structures (Figures 3C&D). It is proposed that

338

photooxidation of aromatic compounds was initiated by ring oxidation followed by ring-opening

339

reactions that yielded a range of oxygenated compounds,60 mainly aldehydes and acids, and

340

unsaturated products (Figures 3B&D).57,61,71–73 The clearest indicators are the new signals

ACS Paragon Plus Environment

Environmental Science & Technology

341

between 5.0-6.0 ppm (HC=C) region following irradiation with HPX-2000 further, which are

342

consistent with the formation of double bonds (Figure 3D, green and HSQC region 5, Figure

343

S15).

Page 16 of 36

344

Other protons in the same 1H-1H spin system can be isolated using selective TOCSY. In

345

this experiment the double bond signals are selectively excited and then a homonuclear spinlock

346

transfers the magnetization down the chain to other protons within the same 1H-1H spin system.

347

The result is a sub-spectrum of the structural motif that contains the double bonds (Figure S16).

348

The units are consistent with linear aliphatic constructs and are most likely the result from

349

aromatic ring opening reactions. Interestingly, these products are more intense with the HPX-

350

2000. One argument is that the deeper UV offered by this lamp leads for enhanced degradation

351

of the aromatics. However, the overall aromatic region decreases more with the Suntest (Figure

352

3D). Double bonds are seen to form with the Suntest system (Figure 3D) but they do not appear

353

to accumulate. These unsaturated products are known to be photolabile, and hence, can further

354

react via oxidative cleavage of double bonds to form saturated aldehydes, ketones and

355

acids.60,71,74 Figure S15 (HSQC) also supports the production of a small quantity of hydroxylated

356

products. Hydroxylated products associated with long chain aliphatics are further confirmed by

357

2D 1H-1H TOCSY (Figure S17). The singlet peak at ~8.3 ppm in Fig. 3C (purple, likely formic

358

acid or alkyl formate) was shifted to a slightly lower frequency (~8.2 ppm, Fig. 3D), and the

359

singlet at ~9.6 ppm in Fig. 3D (brown, an aldehyde) was formed following photoirradiation, with

360

both the Suntest and HPX-2000. However, signals corresponding to -CH2-/-CH- signals adjacent

361

to carboxylic groups at ~2.5 ppm (red) following irradiation were larger with the Suntest model

362

(Figure 3B). The kinetic profile of this region shows that carboxylic groups accumulated over

363

time with the Suntest while it remained relatively the same with HPX-2000 (Figure S19). This

ACS Paragon Plus Environment

Page 17 of 36

Environmental Science & Technology

364

provides further evidence that ring-opening products continue to degrade further with the Suntest

365

model due to greater light intensity, forming acidic end products. These are further confirmed by

366

1

H-1H TOCSY (see Figure S17).

367

In summary, NMR is a useful tool to help explain the overall changes occurring during

368

photochemical process, for example, the formation of new structural categories (double bonds)

369

and the degradation of aromatics. With additional assignments from a list of specific compounds

370

of interest (for example benzene, xylene, ethylbenzene, xylene or BTEX) it should be possible to

371

combine both non-targeted and targeted analysis and extract a wealth of process information in a

372

relatively short amount of time and in a non-invasive fashion.

373

In this study, 1H NMR data of the crude oil WSF using HPX-2000 as the light source was

374

acquired with a cryogenically cooled probe while the 1H NMR data using the Suntest system was

375

acquired with a room temperature flow injection probe, as the latter is much easier to integrate

376

into a flow system. However, as can be seen from Figure 3C, the sensitivity of the cryoprobe

377

(HPX-2000, right) is ~2 times that of the flow probe (left). While it is possible to integrate flow

378

into cryoprobe systems it involves developing custom flow cells as previously reported by Soong

379

et al.17 To demonstrate a flow-application taking advantage of additional sensitivity of the

380

cryoprobe, the next section deals with the flow analysis of a low concentration environmental

381

sample, at natural abundance.

382 383

Monitoring photochemical changes of groundwater at natural abundance

384

The final example demonstrates the application of cryogenically cooled NMR probe for

385

analysis of complex environmental samples. For centuries, groundwater has been used as a main

386

source of drinking water. Today, it is still a favorable source of drinking and agricultural water.75

ACS Paragon Plus Environment

Environmental Science & Technology

Page 18 of 36

387

There has been a growing interest in evaluating the application of sunlight in water treatment as a

388

result of groundwater contamination originating from leeching of industrial chemical waste

389

discharge and pesticides through the soil.76 Aquatic organic matter ranges in complexity and

390

heterogeneity. At one extreme over 80% of the total organic carbon in Antarctic glacial ice can

391

be assigned to simple biomolecules77 while at the other extreme 100,000’s of structures have

392

been demonstrated in river, lake and ocean samples by both NMR and FT-ICR.28,78–80 These

393

humic substances can be divided into 4 main classes: material derived from linear terpenoids

394

(MDLT), carboxyl-rich alicyclic molecules (CRAM), carbohydrates, and aromatics.81 In this

395

manuscript, groundwater was analyzed at its natural state and in a non-invasive manner, a key

396

factor in environmental studies, using a sunlight simulator. Dissolved organic carbon (DOC)

397

concentration in groundwater in North America can be as low as 1-2 ppm depending on the

398

season.82 The total organic carbon (TOC) of the groundwater discussed in this paper was 1.96

399

ppm. Considering the total volume of the NMR is ~300 µL, there is only ~588 ng of total organic

400

matter in the coil with many species in the low ng range. The ground water here, is consistent

401

with previous natural abundance NMR of ground water83 (see supporting Figure 2 in reference

402

81) that demonstrates strong biological inputs. However, it has a very low concentration in

403

comparison and is at the limits of NMR detection. As such it is possible that a more

404

characteristic broad profile for more heterogeneous “humic/fulvic” mixtures that can be observed

405

by natural abundance NMR (see Figure 4 ref. 83) is present but below detection limits in this

406

particular sample. As such, this analysis which uses a relatively low number of scans (4096) will

407

be biased towards the more homogeneous components with any heterogeneous “broad profile”

408

potentially lost in the baseline. Future studies could use more concentrated ground water, more

409

scans, or higher magnetic fields to achieve more comprehensive detection.

ACS Paragon Plus Environment

Page 19 of 36

Environmental Science & Technology

410

Control experiments confirmed all reactions to be photolytic (Figure S20). The chemical

411

fingerprints of groundwater prior to light exposure were relatively easy to identify as it consisted

412

of mostly biological molecules that are well represented in bio-reference NMR databases (Figure

413

4). The molecular composition of groundwater was shown to contain many similarities to the

414

spectral composition of DOM in glacial ice. It was found to consist of: acetic acid, alanine,

415

glycerol, glycine, lactic acid, pyruvic acid, and short chain organic acids (SCA) (Figure 4).84 The

416

degradation products were more challenging to identify using the NMR database alone (Figure

417

4B). Acetone is a likely mineralization intermediate of an oxygenated precursor while formic

418

acid, at ~8.1 ppm, is a general breakdown product found in many DOM samples.85 Other

419

possible photodegradation products of DOM reported in literature are: methylglyoxal, glyoxal,

420

acetaldehyde, formaldehyde, pyruvate, glyoxylate,85 malonate,86 succinate, oxalate, acetate,

421

formate87 and ammonium,88 but the signal to noise ratio is too low here to make unambiguous

422

assignments. Figure S21 provides a kinetic profile of the photodegradation of lactic acid and

423

dual photogeneration and consumption of acetone over the course of light exposure,

424

demonstrating the viability of in-situ NMR analysis in understanding photochemical processes of

425

environmental samples taken directly from the environment and analyzed at natural abundance.

426

Additional information such as diffusion, connectivity information, dynamics, and

427

conformation, could not be obtained as the trace amounts of organic material in groundwater

428

prevent 2D NMR analysis at natural abundance. This stated it should be possible to concentrate

429

(freeze dry, speed vacuum) the sample and run 2D NMR at high concentration to elucidate

430

structures. Proton NMR can then be used to follow these assigned molecules at natural

431

abundance. Interestingly, the flow system employed using the Suntest could theoretically permit

432

a small flow to split to MS. The direct combination of NMR and MS is proving very powerful in

ACS Paragon Plus Environment

Environmental Science & Technology

433

metabolic research, where the co-variance between signals over time in the two instruments can

434

be used to statistically correlate peaks in NMR and MS.15 Such applications in environmental

435

research could be very powerful and should directly relate molecular formulae (MS) and

436

isomeric information (NMR) to provide an unrivalled combination in terms of identifying new

437

species. The looped photochemical NMR reactor described here paves the way to make such

438

future studies possible.

Page 20 of 36

439 440

The study has successfully demonstrated that photolytic reactions in the aqueous phase

441

can be explored in-situ and in real time using NMR spectroscopy. It provides unambiguous

442

information on kinetics and structural identification of intermediates and degradation products

443

which can be further used to elucidate reaction mechanisms. It was determined that the Suntest

444

light source in combination with a loop flow system is the most suitable model to explore

445

environmental photolytic processes using in-situ NMR spectroscopy. Its application to a range of

446

environmental systems have illustrated that NMR is a powerful complementary tool that can be

447

used to study simple chemical transformations down to groundwater at natural abundance. The

448

isomeric information provided by NMR spectroscopy is extremely complementary to MS and

449

has an important role in unraveling photochemical processes in complex environmental systems.

450 451

ASSOCIATED CONTENT

452

Supporting Information

453

Additional 1H NMR spectra for riboflavin, p-nitrophenol, WSF of crude oil, and groundwater are

454

provided, including a detailed experimental section. This material is available free of charge via

455

the Internet at http://pubs.acs.org.

ACS Paragon Plus Environment

Page 21 of 36

Environmental Science & Technology

456 457

AUTHOR INFORMATION

458

Corresponding Author

459

* Corresponding author phone: 416-208-4798; email: [email protected]

460

Notes

461

The authors declare no competing financial interest.

462 463

ACKNOWLEDGMENTS

464

A.J.S. thanks NSERC (Strategic and Discovery Programs), the Canada Foundation for

465

Innovation (CFI), the Ministry of Research and Innovation (MRI), and the Krembil Foundation

466

for providing funding. A.J.S. also thanks the Government of Ontario for an Early Researcher

467

Award.

468 469

REFERENCES

470

(1)

Chemistry; John Wiley & Sons: New York, 1993.

471 472

(2)

(3)

Chaudhry, G. R. Biological degradation and bioremediation of toxic chemicals, 1st ed.; Timber Pr: London, 1994.

475 476

Larson, R. A.; Weber, E. J. Reaction mechanisms in environmental organic chemistry, 1st ed.; CRC Press: USA, 1994.

473 474

Schwarzenbach, R. P.; Gschwend, P. M.; Imboden, D. M. Environmental Organic

(4)

Lankadurai, B.P.; Nagato, E.G.; Simpson, M.J. Environmental metabolomics: an

477

emerging approach to study organism responses to environmental stressors. Environ. Rev.

478

2013, 21 (3), 180-205.

ACS Paragon Plus Environment

Environmental Science & Technology

479

(5)

Bouwman, J.; Cuppen, H. M.; Steglich, M.; Allamandola, L. J.; Linnartz, H.

480

Photochemistry of polycyclic aromatic hydrocarbons in cosmic water ice. Astron.

481

Astrophys. 2011, 529, A46.

482

(6)

Closs, G. L.; Miller, R. J. Laser flash photolysis with NMR detection. Submicrosecond

483

time-resolved CIDNP: kinetics of triplet states and biradicals. J. Am. Chem. Soc. 1981,

484

103 (12), 3586-3588.

485

(7)

Page 22 of 36

Douki, T.; Court, M.; Cadet, J. Electrospray-mass spectrometry characterization and

486

measurement of far-UV-induced thymine photoproducts. J. Photochem. Photobiol., B

487

2000, 54 (2-3), 145-154.

488

(8)

Karonen, M.; Mattila, H.; Huang, P.; Mamedov, F.; Styring, S.; Tyystjärvi, E. A tandem

489

mass spectrometric method for singlet oxygen measurement. Photochem. Photobiol. 2014,

490

90 (5), 965-971.

491

(9)

pharmaceuticals in the environment. TrAC, Trends Anal. Chem. 2007, 26 (6), 486-493.

492 493

Petrovic, M.; Barceló, D. LC-MS for identifying photodegradation products of

(10)

Moad, G.; Shipp, D. A.; Smith, T. A.; Solomon, D. H. Measurements of primary radical

494

concentrations generated by pulsed laser photolysis using fluorescence detection. J. Phys.

495

Chem. A. 1999, 103 (33), 6580-6586.

496

(11)

Comel, A.; Guiochon, G. The chemical composition of mixed wastes: analysis of the

497

photolysis products of organic ligands. J. Radioanal. Nucl. Chem. Art. 1994, 181 (2), 373-

498

384.

499

(12)

Smith, M.E.; van Eck, E.R.H. Recent advances in experimental solid state NMR

500

methodology for half-integer spin quadrupolar nuclei. Prog Nucl Mag Res Sp, 1999, 34

501

(2), 159-201.

ACS Paragon Plus Environment

Page 23 of 36

502

Environmental Science & Technology

(13)

Simpson, A. J.; McNally, D. J.; Simpson, M. J. NMR spectroscopy in environmental

503

research: from molecular interactions to global processes. Prog. Nucl. Mag. Resp. Sp.

504

2011, 58 (3-4), 97–175.

505

(14)

Robertson, D. G. Metabonomics in toxicology: a review. Toxicol. Sci. 2005, 85, 809-822.

506

(15)

Pan, Z.; Raftery, D. Comparing and combining NMR spectroscopy and mass spectrometry in metabolomics. Anal. Bioanal. Chem. 2007, 387 (2), 525-527.

507 508

(16)

27 (3), 228-237.

509 510

Wishart, D. S. Quantitative metabolomics using NMR. TrAC, Trends Anal. Chem. 2008,

(17)

Soong, R.; Nagato, E.; Sutrisno, A.; Fortier-McGill, B.; Akhter, M.; Schmidt, S.;

511

Heumann, H.; Simpson, A. J. In vivo NMR spectroscopy: toward real time monitoring of

512

environmental stress. Magn. Reson. Chem. 2015, 53 (9), 774-779.

513

(18)

Bunescu, A.; Garric, J.; Vollat, B.; Canet-Soulas, E.; Graveron-Demilly, D.; Fauvelle, F.

514

In vivo proton HR-MAS NMR metabolic profile of the freshwater cladoceran Daphnia

515

magna. Mol. BioSyst. 2010, 6 (1), 121–125.

516

(19)

Akhter, M.; Dutta Majumdar, R.; Fortier-McGill, B.; Soong, R.; Liaghati-Mobarhan, Y.;

517

Simpson, M.; Simpson, A. J. Identification of aquatically available carbon from algae

518

through solution-state NMR of whole

519

early access]. DOI: 10.1007/s00216-016-9534-8. Published Online: Apr 13, 2016.

520

http://link.springer.com/article/10.1007%2Fs00216-016-9534-8 (accessed Apr 20, 2016).

521

(20)

13

C-labelled cells. Anal. Bioanal. Chem. [Online

Kelleher, B. P.; Simpson, M. J.; Simpson, A. J. Assessing the fate and transformation of

522

plant residues in the terrestrial environment using HRMAS NMR spectroscopy. Geochim.

523

Cosmochim. Acta. 2006, 70 (16), 4080–4094.

524

(21)

Palmer, A. G III. NMR probes of molecular dynamics: overview and comparison with

ACS Paragon Plus Environment

Environmental Science & Technology

other techniques. Annu. Rev. Biophys. Biomol. Struct. 2001, 30 (1), 129–155.

525 526

(22)

Simpson, A. J.; Kingery, W. L.; Spraul, M.; Humpfer, E.; Dvortsak, P.; Kerssebaum, R.

527

Separation of structural components in soil organic matter by diffusion ordered

528

spectroscopy. Environ. Sci. Technol. 2001, 35 (22), 4421–4425.

529

Page 24 of 36

(23)

Šmejkalová, D.; Piccolo, A. Aggregation and disaggregation of humic supramolecular

530

assemblies by NMR diffusion ordered spectroscopy (DOSY-NMR). Environ. Sci.

531

Technol. 2008, 42 (3), 699–706.

532

(24)

Shirzadi, A.; Simpson, M. J.; Kumar, R.; Baer, A. J.; Xu, Y. P.; Simpson, A. J. Molecular

533

interactions of pesticides at the soil–water interface. Environ. Sci. Technol. 2008, 42 (15),

534

5514–5520.

535

(25)

science. Environ. Sci. Technol. 2002, 36 (7), 154 A–160 A.

536 537

Nestle, N.; Baumann, T.; Niessner, R. Magnetic resonance imaging in environmental

(26)

Viant, M. R.; Bearden, D. W.; Bundy, J. G.; Burton, I. W.; Collette, T. W.; Ekman, D. R.;

538

Ezernieks, V.; Karakach, T. K.; Lin, C. Y.; Rochfort, S.; de Ropp, J. S.; Teng, Q.;

539

Tjeerdema, R. S.; Walter, J. A.; Wu, H. International NMR-based environmental

540

metabolomics intercomparison exercise. Environ. Sci. Technol. 2009, 43 (1), 219-225.

541

(27)

Brown, S. A. E.; Simpson, A. J.; Simpson, M. J. Evaluation of sample preparation

542

methods for nuclear magnetic resonance metabolic profiling studies with Eisenia fetida,

543

Environ. Toxicol. Chem. 2008, 27 (4), 828–836.

544

(28)

Woods, G. C.; Simpson, M. J.; Simpson, A. J. Oxidized sterols as a significant component

545

of dissolved organic matter: evidence from 2D HPLC in combination with 2D and 3D

546

NMR spectroscopy. Water Res., 2012, 46 (10), 3398-3408.

547

(29)

Haiber, S.; Herzog, H.; Burba, P.; Gosciniak, B.; Lambert, J. Quantification of

ACS Paragon Plus Environment

Page 25 of 36

Environmental Science & Technology

548

carbohydrate structures in size fractionated aquatic humic substances by two-dimensional

549

nuclear magnetic resonance. Fresenius’ J. Anal. Chem. 2001, 369 (5), 457-460.

550

(30)

Woods, G. C.; Simpson, M. J.; Kelleher, B. P.; McCaul, M.; Kingery, W. L.; Simpson, A.

551

J. Online high-performance size exclusion chromatography-nuclear magnetic resonance

552

for the characterization of dissolved organic matter. Environ. Sci. Technol. 2010, 44 (2),

553

624–630.

554

(31)

Courtier-Murias, D.; Farooq, H.; Masoom, H.; Botana, A.; Soong, R.; Longstaffe, J. G.;

555

Simpson, M. J.; Maas, W. E.; Fey, M.; Andrew, B.; Struppe, J.; Hutchins, H.;

556

Krishnamurthy, S.; Kumar, R.; Monette, M.; Stronks, H. J.; Hume, A.; Simpson, A. J.

557

Comprehensive multiphase NMR spectroscopy: Basic experimental approaches to

558

differentiate phases in heterogeneous samples. J. Magn. Reson. 2012, 217, 61-76.

559

(32)

research. J. Agric. Food Chem. 1995, 43 (7), 1845-1848.

560 561

Mabury, S. A.; Crosby, D. G. 19F NMR as an analytical tool for fluorinated agrochemical

(33)

Henjum, M. B.; Hozalski, R. M.; Wennen, C. R.; Novak, P. J.; Arnold, W. A. A

562

comparison of total maximum daily load (TMDL) calculations in urban streams using near

563

real-time and periodic sampling data. J Environ Monit. 2010, 12 (1), 234-241.

564

(34)

Spectrosc. Prop. Inorg. Organomet. Compd. 2010, 41, 262-287.

565 566

Ball, G. E. In situ photochemistry with NMR detection of organometallic complexes,

(35)

MacLeod, S. L.; McClure, E. L.; Wong, C. S. Laboratory calibration and field deployment

567

of the polar organic chemical integrative sampler for pharmaceuticals and personal care

568

products in wastewater and surface water. Environ Toxicol Chem. 2007, 26 (12), 2517-

569

2529.

570

(36)

Hertkorn, N.; Ruecker, C.; Meringer, M.; Gugisch, R.; Frommberger, M.; Perdue, E. M.;

ACS Paragon Plus Environment

Environmental Science & Technology

571

Witt, M.; Schmitt-Kopplin, P. High-precision frequency measurements: indispensable

572

tools at the core of the molecular-level analysis of complex systems. Anal Bioanal Chem.

573

2007, 389 (5), 1311-1327.

574

(37)

Hatzianastassiou, N.; Matsoukas, C.; Fotiadi, A.; Pavlakis, K. G.; Drakakis, E.;

575

Hatzidimitriou, D.; Vardavas, I. Global distribution of Earth's surface shortwave radiation

576

budget. Atmos. Chem. Phys. 2005, 5(10), 2847-2867.

577

(38)

Kuhn, H. J.; Braslavsky, S. E.; Schmidt, R. Chemical actinometry (IUPAC Technical Report). Pure Appl. Chem. 2004, 76 (12), 2105-2146.

578 579

(39)

Zhao, R.; Lee, A. K. Y.; Huang, L.; Li, X.; Yang, F.; Abbatt, J. P. D. Photochemical

580

processing of aqueous atmospheric brown carbon. Atmos. Chem. Phys. 2015, 15(2), 2957-

581

2996.

582

(40)

Feldmeier, C.; Bartling, H.; Riedle, E.; Gschwind, R. M. LED based NMR illumination

583

device for mechanistic studies on photochemical reactions – Versatile and simple, yet

584

surprisingly powerful. J. Magn. Reson. 2013, 232, 39-44. DOI: 10.1016/j.jmr.2013.04.011

585

(41)

Jung, M. Y.; Oh, Y. S.; Kim, D. K.; Kim, H. J.; Min, D. B. Photoinduced generation of 2,3-butanedione from riboflavin. J. Agric. Food Chem. 2007, 55 (1), 170-174.

586 587

Page 26 of 36

(42)

Cheng, C. W.; Chen, L. Y.; Chou, C. W.; Liang, J. Y. Investigations of riboflavin

588

photolysis via coloured light in the nitro blue tetrazolium assay for superoxide dismutase

589

activity. J. Photochem. Photobiol. B Biol. 2015, 148, 262-267.

590

(43)

Drössler, P.; Holzer, W.; Penzkofer, A.; Hegemann, P. pH dependence of the absorption

591

and emission behaviour of riboflavin in aqueous solution. Chem. Phys. 2002, 282 (3), 429-

592

439.

593

(44)

Ahmad, I.; Fasihullah, Q.; Vaid, F. H. M. Effect of light intensity and wavelengths on

ACS Paragon Plus Environment

Page 27 of 36

Environmental Science & Technology

594

photodegradation reactions of riboflavin in aqueous solution. J. Photochem. Photobiol. B.

595

2006, 82 (1), 21–27.

596

(45)

Iida, H.; Iwahana, S.; Mizoguchi, T.; Yashima, E. Main-chain optically active riboflavin

597

polymer for asymmetric catalysis and its vapochromic behavior. J. Am. Chem. Soc. 2012,

598

134 (36), 15103-15113.

599

(46)

Kuprov, I.; Hore, P. J. Uniform illumination of optically dense NMR samples. J. Magn. Reson. 2004, 171 (1), 171-175.

600 601

(47)

Wishner, L. A. Light-induced oxidations in milk. J. Dairy Sci. 1964, 47(2), 216-221.

602

(48)

Zhang, W.; Xiao, X.; An, T.; Song, Z.; Fu, J.; Sheng, G.; Cui, M. Kinetics, degradation

603

pathway and reaction mechanism of advanced oxidation of 4-nitrophenol in water by a

604

UV/H2O2 process. J. Chem. Technol. Biotechnol. 2003, 78 (7), 788-794.

605

(49)

experiments, and applications; Academic Press: San Diego, 2000.

606 607

Finlayson-Pitts, B. J.; Pitts, J. N. J. Chemistry of the upper and lower atmosphere: theory,

(50)

Volkamer, R.; Jimenez, J. L.; San Martini, F.; Dzepina, K.; Zhang, Q.; Salcedo, D.;

608

Molina, L. T.; Worsnop, D. R.; Molina, M. J. Secondary organic aerosol formation from

609

anthropogenic air pollution: rapid and higher than expected. Geophys. Res. Lett. 2006, 33

610

(17), L17811.

611

(51)

phenols in the atmosphere: a review. Atmos. Environ. 2005, 39 (2), 231-248.

612 613

(52)

616

Rippen, G.; Zietz, E.; Frank, R.; Knacker, T.; Klöpffer, W. Do airborne nitrophenols contribute to forest decline? Environ. Technol. Lett. 1987, 8 (1-12), 475-482.

614 615

Harrison, M. A. J.; Barra, S.; Borghesi, D.; Vione, D.; Arsene, C.; Olariu, R. I. Nitrated

(53)

Vione, D.; Maurino, V.; Minero, C.; Marius, D.; Olariu, R. I.; Arsene, C. Assessing the transformation kinetics of 2- and 4-nitrophenol in the atmospheric aqueous phase.

ACS Paragon Plus Environment

Environmental Science & Technology

617

Implications for the distribution of both nitroisomers in the atmosphere. Atmos. Environ.

618

2009, 43 (14), 2321-2327.

619

(54)

Daneshvar, N.; Behnajady, M. A.; Asghar, Y. Z. Photooxidative degradation of 4-

620

nitrophenol (4-NP) in UV/H2O2 process: influence of operational parameters and reaction

621

mechanism. J. Hazard Mater. B. 2007, 139 (2), 275-279.

622

(55)

Kamps, J.; Belle, R.; Mecinović, J. Hydroxylamine as an oxygen nucleophile: substitution

623

of sulfonamide by hydroxyl group in benzothiazole-2-sulfonamides. Org. Biomol. Chem.,

624

2013, 11 (7), 1103-1108.

625

(56)

Liu, Y.; Wang, D.; Sun, B.; Zhu, X. Aqueous 4-nitrophenol decomposition and hydrogen

626

peroxide formation induced by contact glow discharge electrolysis. J. Hazard Mater.,

627

2010, 181 (1), 1010-1015.

628

(57)

McKenna, A. M.; Nelson, R. K.; Reddy, C. M.; Savory, J. J.; Kaiser, N. K.; Fitzsimmons,

629

J. E.; Marshall, A. G.; Rodgers, R. P. Expansion of the analytical window for oil spill

630

characterization by ultrahigh resolution mass spectrometry: beyond gas chromatography.

631

Environ. Sci. Technol. 2013, 47 (13), 7530-7539.

632

(58)

(59)

Marshall, A. G.; Rodgers, R. P. Petroleomics: Chemistry of the underworld. Proc. Natl. Acad. Sci. 2008, 105 (47), 18090-18095.

635 636

Fan, T.; Buckley, J. S. Rapid and Accurate SARA Analysis of Medium Gravity Crude Oils. Energy Fuels 2002, 16 (6), 1571-1575.

633 634

Page 28 of 36

(60)

Islam, A.; Cho, Y.; Yim, U. H.; Shim, W. J.; Kim, Y. H.; Kim, S. The comparison of

637

naturally weathered oil and artificially photo-degraded oil at the molecular level by a

638

combination of SARA fractionation and FT-ICR MS. J. Hazard Mater. 2013, 263, 404-

639

411.

ACS Paragon Plus Environment

Page 29 of 36

640

Environmental Science & Technology

(61)

Ray, P. Z.; Chen, H.; Podgorski, D. C.; McKenna, A. M.; Tarr, M. A. Sunlight creates

641

oxygenated species in water-soluble fractions of Deepwater Horizon oil. J. Hazard Mater.

642

2014, 280, 636-643.

643

(62)

Bhattacharya, P.; Geitner, N. K.; Sarupria, S.; Ke, P. C. Exploiting the physicochemical

644

properties of dendritic polymers for environmental and biological applications. Phys.

645

Chem. Chem. Phys. 2013, 15, 4477-4490.

646

(63)

Alves Filho, E. G.; Alexandre e Silva, L. M.; Ferreira, A. G. Advancements in waste water

647

characterization through NMR spectroscopy: review. Magn. Reson. Chem. 2014, 53(9),

648

648-657.

649

(64)

using TiO2 nanopowder film. Environmental Technology, 2013, 34 (9-12), 1183-1190.

650 651

Fard, M. A.; Aminzadeh, B.; Vahidi, H. Degradation of petroleum aromatic hydrocarbons

(65)

Saeed, T.; Ali, L. N.; Al-Bloushi, A.; Al-Hashash, H.; Al-Bahloul, M.; Al-Khabbaz, A.;

652

Ali, S. G. Photodegradation of volatile organic compounds in the water-soluble fraction of

653

Kuwait crude oil in seawater: effect of environmental factors. Water, Air, Soil Pollut.

654

2013, 224 (6), 1584-1598.

655

(66)

Simpson, A. J.; Mitchell, P. J.; Masoom, H.; Liaghati Mobarhan, Y.; Adamo, A.; Dicks,

656

A. P. An oil spill in a tube: an accessible approach for teaching environmental NMR

657

spectroscopy. J. Chem. Educ. 2015, 92 (4), 693-697.

658

(67)

seawater. Chinese J. Oceanol. Limnol. 2006, 24 (3), 264-269.

659 660

(68)

Altgelt, K. H.; Boduszynski, M. M. Composition and analysis of heavy petroleum fractions. Marcel Dekker: New York, 1994.

661 662

Yang, G.; Zhang, L.; Sun, X.; Jing, W. Photochemical degradation of crude oil in

(69)

Frena, M.; Oliveira, C. R.; da Silva, C. A.; Madureira, L. A. S.; Azevedo, D. A.

ACS Paragon Plus Environment

Environmental Science & Technology

663

Photochemical degradation of diesel oil in water: a comparative study of different

664

photochemical oxidation processes and their degradation by-products. J. Braz. Chem. Soc.

665

2014, 25 (8), 1372-1379.

666

(70)

Frank, R. A; Fischer, K.; Kavanagh, R.; Burnison, B. K.; Arsenault, G.; Headley, J. V;

667

Peru, K. M.; Van Der Kraak, G.; Solomon, K. R. Effect of carboxylic acid content on the

668

acute toxicity of oil sands naphthenic acids. Environ. Sci. Technol. 2009, 43 (2), 266-271.

669

(71)

671

Maki, H.; Sasaki, T.; Harayama, S. Photo-oxidation of biodegraded crude oil and toxicity of the photo-oxidized products. Chemosphere. 2001, 44 (5), 1145-1151.

670

(72)

Boukir, A.; Aries, E.; Guiliano, M.; Asia, L.; Doumeng, P.; Mille, G. Subfractionation,

672

characterization and photooxidation of crude oil resins. Chemosphere. 2001, 43 (3), 279-

673

286.

674

(73)

Huang, M.-Q.; Zhang, W.-J.; Hao, L.-Q.; Wang, Z.-Y.; Zhao, W.-W.; Gu, X.-J.; Fang, L.

675

Low-molecular weight and oligomeric components in secondary organic aerosol from the

676

photooxidation of p-xylene. J. Chin. Chem. Soc. 2008, 55(2), 456-463.

677

(74)

679

(75)

Protti, S.; Fagnoni, M. The sunny side of chemistry: green synthesis by solar light. Photochem. Photobiol. Sci. 2009, 8 (11), 1499-1516.

680 681

Ehrhardt, M. Photo-oxidation products of fossil fuel components in the water of Hamilton harbor, Bermuda. Mar. Chem. 1987, 22(1), 85-94.

678

(76)

Matamoros, V.; Duhec, A.; Albaigés, J.; Bayona, J. M. Photodegradation of

682

carbamazepine, ibuprofen, ketoprofen and 17 α-ethinylestradiol in fresh and seawater.

683

Water Air Soil Pollut. 2009, 196, 161-168.

684 685

(77)

Page 30 of 36

Pautler, B. G.; Simpson, A. J.; Simpson, M. J.; Tseng, L. H.; Spraul, M.; Dubnick, A.; Sharp, M. J.; Fitzsimons, S. J. Detection and structural identification of dissolved organic

ACS Paragon Plus Environment

Page 31 of 36

Environmental Science & Technology

686

matter in antarctic glacial ice at natural abundance by SPR-W5-WATERGATE 1H NMR

687

spectroscopy. Environ. Sci. Technol. 2011, 45 (11), 4710-4717.

688

(78)

Gonsior, M.; Hertkorn, N.; Conte, M. H.; Cooper, W. J.; Bastviken, D.; Druffel, E.;

689

Schmitt-Kopplin, P. Photochemical production of polyols arising from significant photo-

690

transformation of dissolved organic matter in oligotrophic surface ocean. Mar. Chem.

691

2014, 163, 10-18.

692

(79)

Stenson, A. C.; Marshall, A. G.; Cooper, W. T. Exact masses and Chemical Formulas of

693

Individual Suwanee River Fulvic Acids from Ultrahigh Resolution Electrospray Ionization

694

Cyclotron Resonance Mass Spectra. Anal. Chem. 2003, 75 (6), 1275-1284.

695

(80)

Tfaily, M. M.; Chu, R. K.; Tolić, N.; Roscioli, K. M.; Anderton, C. R.; Paša-Tolić, L.;

696

Robinson, E. W.; Hess, N. J. Advanced solvent based methods for molecular

697

characterization of soil organic matter by high-resolution mass spectrometry. Anal. Chem.

698

2015, 87 (10), 5206-5215.

699

(81)

Cottrell, B. A.; Gonsior, M.; Isabelle, L. M.; Luo, W.; Perraud, V.; McIntire, T. M.;

700

Pankow, J. F.; Schmitt-Kopplin, P.; Cooper, W. J.; Simpson, A. J. A regional study of the

701

seasonal variation in the molecular composition of rainwater. Atmos. Environ. 2013, 77,

702

588-597.

703

(82)

Hendry, M. J.; Wassennar, L. I. Origin and migration of dissolved organic carbon

704

fractions in a clay-rich aquitard: 14C and δ13C evidence. Water Resour. Res. 2005, 41 (2),

705

W02021.

706

(83)

natural waters. Analyst 2008, 133 (2), 263-269.

707 708

Lam, B.; Simpson, A. J. Direct 1H NMR spectroscopy of dissolved organic matter in

(84)

Pautler, B. G.; Woods, W. C.; Dubnick, A.; Simpson, A. J.; Sharp, M. J.; Fitzsimons, S. J.;

ACS Paragon Plus Environment

Environmental Science & Technology

Page 32 of 36

709

Simpson, M. J. Molecular characterization of dissolved organic matter in glacial ice:

710

coupling natural abundance 1H NMR and fluorescence spectroscopy. Environ. Sci.

711

Technol. 2012, 46 (7), 3753-3761.

712

(85)

Kieber, R. J.; Zhou, X.; Mopper, K. Formation of carbonyl compounds from UV-induced

713

photodegradation of humic substances in natural waters: fate of riverine carbon in the Sea.

714

Limnol. Oceanogr. 1990, 35 (7), 1503-1515.

715

(86)

Brinkmann, T.; Hörsch, P.; Sartorius, D.; Frimmel, F. H. Photoformation of low-

716

molecular-weight organic acids from brown water dissolved organic matter. Environ. Sci.

717

Technol. 2003, 37 (18), 4190-4198.

718

(87)

irradiation. Environ. Int. 1994, 20 (1), 97-101.

719 720

Allard, B.; Borén, H.; Petterson, C.; Zhang, G. Degradation of humic substances by UV

(88)

Bushaw, K. L.; Zepp, R. G.; Tarr, M. A.; Schulz-Jander, D.; Bourbonniere, R. a.; Hodson,

721

R. E.; Miller, W. L.; Bronk, D. A.; Moran, M. A. Photochemical release of biologically

722

available nitrogen from aquatic dissolved organic matter. Nature 1996, 381, 404-407.

723

ACS Paragon Plus Environment

Page 33 of 36

Environmental Science & Technology

724 725 726 727 728 729 730

Figure 1. Schematics, 1H NMR data (500 MHz), preliminary assignments, and kinetic information for the photodegradation of the reference sample, 34.52 mM riboflavin solution (in 70% D2O and 30% H2O; pH 11.43) at 296 K, using three different light sources. A: lumiflavin, B: lumichrome, C: 1-deoxy-xylulose, D: erythrose. For detailed assignments and control experiments, see Supporting Information. The blue highlights indicate structure units and NMR signals arising from the riboflavin aliphatic “sidechain” and its derivatives.

ACS Paragon Plus Environment

Environmental Science & Technology

731 732 733 734 735 736 737 738 739 740

Page 34 of 36

Figure 2. 1H spectra (500 MHz, at 296 K) of p-nitrophenol solution (7.74 mM p-nitrophenol with 38 mM H2O2 in 70% D2O and 30% H2O solution; pH 5.40) and its photoproducts at three different time points during the light exposure inside the Suntest. The percentages represent the relative distribution of the observable photodegradation products, calculated by integrating the areas under the peaks corresponding to the individual products, and then normalizing to the number of protons in each peak such that the percentages between different the products are directly comparable. The products in bottom panel represent ~75% of the NMR signal with ~25% of the parent compound remaining.

ACS Paragon Plus Environment

Page 35 of 36

741 742 743 744 745

Environmental Science & Technology

Figure 3. 1H spectra (500 MHz, at 296 K) showing the phototransformation of the WSF of crude oil (extracted from a mixture of 4 mL crude oil : 1 mL of 17.51 mM SDS dissolved in 70% D2O and 30% H2O) containing 68 mM H2O2 with Suntest (left) and HPX-2000 (right) light sources. A (aliphatic) and C (aromatic) are prior to light exposure and B (aliphatic) and D (aromatic) are

ACS Paragon Plus Environment

Environmental Science & Technology

746 747 748 749

750 751 752 753

Page 36 of 36

following light exposure. 1: CH/CH2 adjacent to –OH or carboxylic groups; 2: naphthenic acid CH2 groups; 3: CH/CH2 adjacent to carboxylic groups; 4: CH3 groups attached to aromatic rings; 5: aliphatic CH2; 6: aliphatic CH3. The vertically truncated aliphatic signals are from SDS.

Figure 4. 1H spectrum (500 MHz, at 296 K) of A: groundwater sample (TOC: 1.96 ppm; pH = 7.91; conductivity: 1448 µS/cm) after 6 hours in the dark (0-4.5 ppm region), B: after the sample was exposed to light for 1 d 12 h inside the Suntest solar simulator.

ACS Paragon Plus Environment