Siderophores in Cloud Waters and Potential ... - ACS Publications

Subscriber access provided by Northern Illinois University

Article

Siderophores in cloud waters and potential impact on atmospheric chemistry: Photoreactivity of iron complexes under sun-simulated conditions Monica Passananti, Virginie Vinatier, Anne-Marie Delort, Gilles Mailhot, and Marcello Brigante Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b02338 • Publication Date (Web): 03 Aug 2016 Downloaded from http://pubs.acs.org on August 10, 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 31

1 2 3

Environmental Science & Technology

Siderophores in cloud waters and potential impact on atmospheric chemistry: Photoreactivity of iron complexes under sun-simulated conditions

4 5

Monica Passanantia,b, Virginie Vinatiera,b, Anne-Marie Delorta,b, Gilles Mailhota,b, Marcello Brigantea,b*

6

a

7

F-63000 CLERMONT-FERRAND, FRANCE

8

b

Université Clermont Auvergne, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448,

CNRS, UMR 6296, ICCF, F-63171 AUBIERE, FRANCE

9 10 11

* Corresponding author MB: University Blaise Pascal, Institute of Chemistry of Clermont-Ferrand, avenue des Landais 63171 Aubière, France; Phone +33 0473405514 e-mail: [email protected]

12 13

Submitted to Environmental Science and Technology

14 15 16 17

1 ACS Paragon Plus Environment


Page 2 of 31

18

Abstract

19

In the present work, the photoreactivity of a mixture of iron(III)-pyoverdin (Fe(III)-Pyo) complexes was

20

investigated under simulated cloud conditions. Pyoverdins are expected to complex ferric ions naturally

21

present in cloud water, thus modifying their availability and photoreactivity. The spectroscopic properties

22

and photoreactivity of Fe(III)-Pyo were investigated, with particular attention to their fate under solar

23

irradiation, also studied through simulations. The photolysis of the Fe(III)-Pyo complex leads to the

24

generation of Fe(II), with rates of formation ( RFe( II ) ) of 6.98 and 3.96 × 10-9 M s-1 at pH 4.0 and 6.0,

25

respectively. Interestingly, acetate formation was observed during the iron-complex photolysis, suggesting

26

that fragmentation can occur after the ligand-to-metal charge transfer (LMCT) via a complex reaction

27

mechanism. Moreover, photogenerated Fe(II) represent an important source of hydroxyl radical via the

28

Fenton reaction in cloud water. This reactivity might be relevant for the estimation of the rates of

29

formation and steady-state concentrations of the hydroxyl radical by cloud chemistry models and for

30

organic matter speciation in the cloud aqueous phase. In fact, the conventional models, which describe the

31

iron photoreactivity in terms of iron-aqua and oxalate complexes, are not in accordance with our results.

f

32 33

TOC/Abstract


Page 3 of 31


34

Introduction

35

Clouds play a key role in the atmospheric system and may indeed influence the troposphere composition,

36

the oxidizing capacity of the atmosphere and radiation phenomena (such as light diffusion). Therefore,

37

clouds have a strong impact on the climate. It is well known that the aqueous phase in clouds is an

38

important medium for chemical reactions, in which the fate of organic and inorganic constituents is

39

strongly dependent on the oxidative capacity and cloud water composition.1, 2 The determination of cloud

40

composition has become a popular subject of research in recent years.3, 4 While the inorganic composition

41

of clouds has been well elucidated,5,

42

characterized due to its complexity.7, 8

43

Only 25-30% of the organic components of clouds have been characterized, while the remaining 70-75% is

44

unidentified.9-11 The identified compounds are mainly acetic, formic and oxalic acids and other small chain

45

acids10, 12 or aldehydes.13 A recent study reported the molecular weight distribution for the organic fraction

46

of cloud samples and showed that the main compounds have molecular weights between 50 and 2500

47

Da.14 The small chain carboxylic acids are derived from anthropogenic and biological emission and from

48

chemical transformation in the atmosphere and in clouds. The higher molecular weight material (> 500 Da)

49

could be humic-like substances (also called HULIS), macromolecules and biogenic nanoscale material

50

(BONM)

51

water.14, 17, 18 Indeed the presence of microorganisms such as bacteria and fungi has been reported mainly

52

in the last decade.19-21 Bauer and coworkers reported that microorganisms can contribute to the organic

53

carbon (OC) content of cloud water: in particular bacteria and fungi account for 1.7% of the OC (in mgC/L).9

54

Living microorganisms can have a direct effect on the chemical composition of cloud water via

55

biocompound production and/or by the degradation of species present in atmospheric water including

56

carboxylic acids, aldehydes, sugars and H2O2.22-24 The chemical species produced by microorganisms can

57

also interact with the species present in atmospheric water. In a companion paper it has been shown that a

58

large number of bacteria and yeasts isolated from cloud waters are able to produce siderophores which are

59

strong complexing agents that uptake iron from the extracellular environment. These molecules have been

15, 16

6

the composition of the organic fraction has not been fully

and this organic fraction is an important portion of the organic matter present in cloud



25 26, 27

Page 4 of 31

60

shown to modify iron speciation and photostability in oceanic systems,

61

occur in atmospheric waters. Barbeau and co-workers investigated the photostability of different Fe(III)-

62

siderophores and suggested that their photostability depends strongly on the chemical structure of the iron

63

binding groups.28 In fact, the presence of specific groups such as catechols and α-hydroxy carboxylates can

64

possibly lead to the photooxidation of the iron complexes and reduction of Fe(III) into Fe(II) in aquatic

65

media.

66

Iron (Fe(II) and Fe(III)) that is naturally present in the atmosphere has been considered as one of the most

67

important sources of the hydroxyl radical (HO•) in cloud water, via the Fenton and Fe(III) photolysis

68

processes (R1 and R2).29, 30

69

Fe( II ) + H2O2 → Fe( III ) + HO− + HO•

(R1)

70

hν Fe( III ) + H2O  → Fe( II ) + H + + HO•

(R2)

71

HO• is a strong and non-selective photooxidant and reacts with a wide variety of compounds at nearly

72

diffusion-controlled rates leading to the oxidation of organic compounds present in natural water.31 The

73

photoinduced generation of hydroxyl radicals plays a key role in the oxidative capacity of the cloud aqueous

74

phase. Therefore, its formation mechanism needs to be investigated.

75

Fenton and photo-Fenton reactions refer to free iron and have been extensively studied in atmospheric

76

waters.32,

77

models represent iron as free ions, aquo-complexes or Fe-oxalate complexes.34 As recently shown,

78

atmospheric aqueous models tend to overestimate hydroxyl radical formation from iron species, probably

79

due to an incorrect modeling of iron (free or Fe-oxalate complexes).35

80

The photoreactivity and impact on the oxidative budget of iron complexes with the most abundant

81

carboxylic acids found in cloud water (oxalate, formate, etc.) have been extensively studied.34, 36 However,

82

to the best of our knowledge, the fate (under environmental conditions) of iron complexes in the presence

83

of large and functionalized molecules (i.e. polycarboxylic acids, siderophores, etc.) is not yet understood.

33

and the same could thus

To evaluate the contribution of iron to hydroxyl radical formation, atmospheric chemistry


Page 5 of 31


84

The photoreacctivity of iron-siderophore complexes in the aqueous phase of clouds could be substantially

85

different from that of Fe-oxalate or Fe-aqua complexes and should therefore be evaluated to assess the

86

contribution of the source to the generation of Fe(II) and the hydroxyl radical in cloud water.

87

In the companion paper of this work, 450 microbial strains isolated from cloud waters were screened for

88

their production of siderophores. Of these strains, 43% are able to produce siderophores and among them

89

36% belong to the genus Pseudomonas. This genus is the major group present in cloud waters

90

known to produce pyoverdins, which are siderophores containing both hydroxamate and catechol-

91

chelating functions.37 These molecules are strong iron complexants containing a chromophore and,

92

consequently, may impact photoreactivity of iron in clouds. In this paper, we examined a pyoverdin

93

mixture produced by Pseudomonas fluorescens 36b5, a bacterial strain isolated from the aqueous phase of

94

clouds. Microorganisms are metabolically active and are also able to grow at low temperatures in clouds as

95

recently demonstrated using in situ measurements performed directly in cloud water and in lab cultures.24,

96

38, 39

97

The aforementioned pyoverdin mixture (Pyo) was purified and characterized by spectroscopic tools, and

98

the photochemical behaviour of iron(III)-pyoverdin complexes (Fe(III)-Pyo) was studied under simulated

99

solar irradiation. In particular, the rates of formation of Fe(II) and the hydroxyl radical were measured to

100

21

and is

assess the impact of the Fe(III)-Pyo complex on the oxidative capacity of the aqueous phase of clouds.

101 102

Materials and methods

103

Pyoverdin purification

104

Pyoverdins were produced by the bacterial strain Pseudomonas fluorescens 36b5 (JF706586) isolated from

105

cloud water collected at the puy de Dôme station.21 The bacteria were grown at 25°C under shaking for 24

106

h in a 1 L of distilled water with 6.0 g of K2HPO4, 3.0 g of KH2PO4, 1.0 g of (NH4)2SO4, 0.2 g of MgSO4•7H2O

107

and 4.0 g of succinic acid. The pH was adjusted to 7.0 with NaOH before sterilisation.



Page 6 of 31

108

After centrifugation the supernatant was filtered on a 0.2 µm Polyethersulfone (PES) membrane and loaded

109

on a 120 g Puriflash IR-C18 (50 µm) cartridge (Interchim). The cartridge was placed on a Spot II (Armen)

110

flash chromatography system and rinsed 5 times with of water to remove mineral compounds. The

111

pyoverdin mixture was then eluted with H2O/methanol with a linear gradient from 5 to 25% methanol over

112

10 minutes. After HPLC analysis, the fractions containing pyoverdins were evaporated. Further purification

113

was carried out with the same gradient on a higher-resolution cartridge with smaller particles

114

(InterchimPuriflash C18-HQ-15 µm-35 g). Pure fractions were freeze, dried and stored under argon in a

115

polypropylene

116

No additive was added to the mobile phase during purification to avoid eventual artefacts. Plasticware was

117

used to avoid complexation with iron, and pyoverdins were obtained in the free form.

centrifuge

tube.

118 119

Determination and analysis of chemical and physicochemical parameters

120

All chemicals were used without further purification: iron(III) perchlorate (Fe(ClO4)3) (98%), nitrobenzene (>

121

99 %), potassium oxalate (> 99%) (Sigma-Aldrich) and acetonitrile (chromasolv) were obtained from Sigma

122

Aldrich. GPR Rectapur methanol was purchased from VWR. All solutions were prepared in water purified by

123

a Millipore milli-q device (Millipore αQ, resistivity 18 MΩ cm, DOC < 0.1 mg L-1). The pH was modified by the

124

addition of HClO4 or NaOH.

125

Fluorescence measurements were performed using a Varian Cary Eclipse fluorescence spectrofluorimeter,

126

adopting a 5 nm bandpass on both excitation and emission. The fluorescence excitation–emission matrix

127

(EEM) was obtained from 250 to 460 nm for excitation and from 250 to 600 nm for emission. UV-vis spectra

128

were acquired with a Varian Cary 300 UV–vis spectrophotometer.

129

Mass spectrometry was performed by mixing pyoverdin samples (1:1) with R-cyano-4-hydroxycinnamic acid

130

(7 mg mL-1 in 30% acetonitrile/0.1% trifluoroacetic acid) and spotting them on a MTP384 Ground Steel

131

plate. MALDI-TOF-TOF analyses were performed on an Autoflex Speed (Bruker) in the positive reflectron

132

mode. The LIFT technique was used for MS/MS.


Page 7 of 31


133

A Perkin Elmer series 200 HPLC system equipped with a DAD detector was used for pyoverdin

134

quantification and to check purity. Samples were injected on a Varian Polaris amide C18 column (150 × 4.6

135

mm; 5 µm). Solvent A contained 1 mM ethylenediaminetetraacetic acid in 0.1% formic acid. Solution B was

136

acetonitrile. Elution was performed at 1 mL min-1 with a linear gradient from 0 to 60 % B starting 5 minutes

137

after injection.

138

Iron (II) was quantified using a colorimetric complexant (ferrozine,3-(2-pyridyl)-5,6-bis(4-phenylsulfonic

139

acid)-1,2,4-triazine) coupled with UV/vis spectrophotometric detection at λmax = 562 nm 40. The well-known

140

molar absorption coefficient of the complex between ferrozine and Fe(II) (ε562nm = 27900 M-1 cm-1) was used

141

to calculate the Fe(II) concentration.

142

Ion chromatography analyses were performed for the quantification of carboxylic acids (material: Dionex

143

DX320, column AS11 for anions, eluent KOH). The elution method has been previously described.2 The

144

method adopted to calculate the Fe(III)-Pyo transformation ( RFe(III )−Pyo ) and Fe(II) ( RFe( II ) ) formation rates

145

as well as quantum yields are described in the Supplementary Materials section.

146

The stoichiometry of the Fe(III)-Pyo complex was investigated using Job’s method in a buffer solution

147

(phosphate buffer) at pH 4.0.41 The complex formation was monitored by spectroscopic analysis following

148

the absorption peak at 480 nm characteristic of the Fe(III)-Pyo complex. At pH 4.0, complex absorbance

149

shows a maximum at XFe(III) (Fe(III) molar fraction) of 0.5, corresponding to a Fe(III):Pyo stoichiometry of 1:1.

d

f

150 151

Irradiation experiments

152

Aqueous solutions were irradiated in a 40 mL cylindrical reactor at a constant temperature (278 ± 2

153

K) controlled by water circulation. The reactor was located at the focal point of the lamp to ensure a

154

constant irradiation of the whole sample, and was equipped at the top with a Pyrex filter to remove

155

wavelengths lower than ~290 nm. Samples were continuously stirred with a magnetic stirrer and a

156

Teflon bar to ensure homogeneity. 7 ACS Paragon Plus Environment


Page 8 of 31

157

The emission spectrum of the Xenon lamp reported in Figure 1 was recorded using an optical fiber coupled

158

with a CCD spectrophotometer (Ocean Optics USD 2000+UV-VIS). A reference lamp (DH-2000-CAL, Ocean

159

Optics) was used for calibration. The energy was normalized to the actinometry results obtained using a

160

paranitroanisole (PNA)/pyridine actinometer.42 A total flux of 34 W m-2 was measured over the wavelength

161

range 290-400 nm. As shown in Figure 1, the intensities are similar to those measured in cloudy conditions

162

at the top of the puy de Dôme mountain in autumn 2013.

163 164

Detection of hydroxyl radicals

165

Hydroxyl radicals (HO•) were quantified using nitrobenzene (NB) as a trapping molecule. Nitrobenzene,

166

which reacts directly with photogenerated hydroxyl radicals to produce different nitrophenols and 1,3-

167

dinitrobenzene,43 was measured by HPLC. Further details about the detection method are reported in the

168

Supporting Information (Text S1).The kinetic approach to estimate the rate of hydroxyl radical formation is

169

obtained from the following equation (eq.1)

170

d f RNB = RHO − •

k NB ,HO• [NB]

(eq. 1)

k NB ,HO• [NB] + ∑ k i [Si ] i

d

171

f where RNB is the rate of degradation of nitrobenzene (M s-1), RHO • is the formation rate of the hydroxyl

172

radical (M s-1), k NB, HO • the second order rate constant for the reaction between nitrobenzene and the

173

hydroxyl radical (3.9 × 109 M-1 s-1)

44

and

∑k [S ] i

i

is the pseudo-first-order rate constant (s-l) for HO•

i

174

scavenging by all constituents (i.e., Fe-complexes) of the solution except for the probe NB.

175

In the presence of Fe(III)-Pyo a competition to react with HO• between iron-complex and NB was

176

f considered to determine RHO k NB,HO• [NB] and k NB,HO• [NB] • . Under adopted conditions,

177

estimated to be 1.17 × 106 s-1 and 1.0 × 106 s-1 respectively indicating that 54 % of photogenerated hydroxyl

178

radicals react with NB probe (see Text S1 and figures S1-2 for details).

can be


Page 9 of 31


179 180

Results and discussion

181

Production, isolation and structural characterization of pyoverdins

182

Pseudomonas fluorescens 36b5 was grown in a succinate minimal medium for 24 h. Separation of the

183

supernatant components by reverse phase chromatography showed the presence of two major and two

184

minor products with spectra characteristic of pyoverdins. Longer incubations increased the yield, but

185

degradation products appeared as the pH of the medium was increased.

186

Pyoverdin was extracted and pre-purified from the supernatant in a single step by ultraperformance flash

187

chromatography on a C18 cartridge. Further purification was performed on a high quality column with a

188

smaller particle size (15 µm). The global yield of the culture medium was 50 mg L-1. HPLC analyses showed

189

that the major components were present in identical proportions and represented 91% of the total

190

pyoverdin (Figure S3).

191

Experiments were performed on a mixture of pyoverdins to take into account the diversity of

192

pyoverdins in the environment. Exact molecular masses of various pyoverdins were determined by

193

MALDI-TOF. The two major compounds had molecular weights of 1142.6 and 1160.6 Da. Minor

194

compounds had molecular masses of 1171.6 and 1188.6 Da. As the masses of the major compounds

195

differ by 18u, they probably share the same peptide chain in a linear and a cyclic form. Indeed,

196

cyclisation has already been described in terms of ester bond formation between a carboxylic acid

197

and the alcohol function of serine 45 with a loss of H2O.

198

Structural investigation of the major linear form was performed by fragmentation of the [M-H2O+H]+ ion

199

(m/z = 1143) by MALDI-TOF-TOF. The major ion corresponds to the A1 fragment (m/z = 417) with a loss of

200

H2O (m/z = 399) which indicates that serine is the first amino acid linked to the chromophore (Figures S4, S5

201

and Table S1) associated with a succinic acid side chain.46 Retro-Diels-Alder opening of the chromophore

202

gives characteristic fragments (m/z = 286 and 204). Loss of 74u due to the elimination of COOH-CHO by a

203

Mc Lafferty rearrangement indicates the presence of a hydroxyaspartic acid residue. The presence of an N9 ACS Paragon Plus Environment


Page 10 of 31

204

acetyl-N-hydroxyornithine residue is suggested by the loss of 73u (-NOH-COCH3). A hypothetical structure

205

matching the exact mass and the fragmentation pattern can then be proposed as follows: Chr-Ser-

206

AcOHOrn-Pro-Val OHAsp-Ala-Lys. (Figure 2).

207 208

Spectroscopic analyses of pyoverdin and Fe(III)-pyoverdin complex

209

Pyoverdins are strong Fe(III) complexing agents. Therefore, it is highly probable that in atmospheric water

210

they may exist in the form (Fe(III)-Pyo). A spectroscopic analysis of pyoverdin and the Fe(III)-pyoverdin

211

complex (Fe(III)-Pyo) was carried out in water at pH 4.0 and pH 6.0 (with addition of HClO4), considered as

212

the typical pH range values of cloud water.12 The pyoverdin mixture solution (~100 µM, without iron) was

213

found to be stable in water in the dark for more than 72 h. The natural pH of the solution was 8.3 and the

214

UV-vis spectrum in Figure S6 shows an absorption band at 230 nm [ε230 = (2.00 ± 0.02) × 104 M-1 cm-1] with a

215

shoulder at 280 nm and a band centred at 408 nm [ε408 = (9.18 ± 0.09) × 103 M-1 cm-1]. The UV-vis spectrum

216

was observed to change with pH. In particular, a hypochromic shift was observed at more acidic pH values.

217

The pyoverdin solution at pH 4.0 was not stable, and the UV-vis spectrum changed during 72 h (in the dark),

218

as reported in Figure S7. When the solution was returned to its natural pH (~ 8.0), a bathochromic shift in

219

the UV-vis spectrum was observed. In aqueous solution, pyoverdin acts as a buffer, and its pH slowly

220

changes towards the natural pH (~ 8.3). Pyoverdins are fluorescent molecules containing a chromophores,

221

generally a catechol, that is responsible for colour and fluorescence.47 A fluorescence excitation−emission

222

matrix (EEM) of pyoverdin was recorded at natural pH (Figure 3). Pyoverdin excited at λex= 408 nm emits at

223

a maximum (λem) centred at 460 nm. The measurement of fluorescence is a sensitive method for detecting

224

pyoverdin (detection limit estimated to be approximately 0.3 µM), and a linear correlation between

225

fluorescence intensity and concentration was observed up to 40 µM (Figure S8). After this concentration

226

corresponding to Abs > 0.2, fluorescence quenching was observed.48 The 1:1 Fe(III):Pyo stoichiometry of the

227

Fe(III)-Pyo complex was confirmed using Job’s method in buffer solution (phosphate buffer) at pH 4.0


Page 11 of 31


228

(Figure S9). Pyoverdins have three bidentate chelating groups (a catechol and two hydroxamate functions)

229

and form strong 1:1 complexes with iron (III), in agreement with the results reported in the literature.49, 50

230

A spectroscopic analysis of Fe(III)-pyoverdin shows that the complex formation can be confirmed by

231

fluorescence loss. Indeed, the Fe(III)-Pyo complexwas found not to be fluorescent, and in the EEM of the

232

complex solution, only Rayleigh and Raman scattering were observed (Figure S10).51

233

The UV-vis spectrum of the complex at pH 4.0 shows a shoulder at 273 nm and a band centred at 386 nm

234

[ε3869 = (1.52 ± 0.09) × 103 M-1 cm-1] with a tail extending to 700 nm (Figure 1). The UV-vis spectrum at pH

235

6.0 has an absorption band at 230 nm [ε230 = (4.04 ± 0.10) × 103 M-1 cm-1], a shoulder at 273 nm and the

236

same absorption band at 386 nm as that observed for the complex at pH 4 [ε386 = (1.46 ± 0.11) × 103 M-1 cm-

237

1

238

observed after 2 h.

]. The stability of the complexes was investigated in the dark, and no change in the UV-vis spectra were

239 240

Photochemical behaviour of pyoverdin and the Fe(III)-pyoverdin complex

241

The photoreactivity of Fe(III)-Pyo was investigated at pH 4.0 and 6.0 under polychromatic irradiation with,

242

particular attention to the generation of Fe(II) and small carboxylic acids. Fe(III)-Pyo under simulated solar

243

irradiation undergoes a ligand-to-metal-charge-transfer (LMCT) leading to the formation of Fe(II) and

244

organic ligand radicals.52 The quantity of Fe(II) produced during the irradiation is directly proportional to

245

the Fe(III)-Pyo concentration (see the Supporting Information for the method adopted to measure the

246

formation/loss rates).

247

at pH 6.0 (3.96 ×10-9 M s-1) (Table 1), as shown in Figure 4A. The evaluated quantum yields are 1.9 × 10-4

248

and 5.5 × 10-5 respectively for pH 4.0 and 6.0. The difference of

249

considering the spontaneous oxidation of Fe(II) to Fe(III) by oxygen in waters at pH > 4, as previously

250

reported by Morgan and Lahav.53

RFef ( II ) at pH 4.0 is 6.98 ×10-9 M s-1 and is approximately two times the value observed

RFef ( II ) at pH 4 and 6 can be explained by



Page 12 of 31

251

Photolysis was performed on Fe(C2O4)2- and on a mixture of Fe(C2O4)2-/Fe(C2O4)33- (50/50) to compare the

252

formation rates of Fe(II) with those reported for Fe(III)-Pyo. Iron-oxalate complexes were prepared as

253

reported in the Supporting Information (Text S4 and Figures S11-12 ), and the pH was fixed at 2.5 and 3.8 to

254

obtain the maximum concentration of the desired stoichiometry of the complex or mixture. RFe( II ) were

255

estimated to be 5.35 ± 0.60 ×10-7 M s-1 for Fe(C2O4)2- and 1.88 ± 0.29 ×10-7 M s-1 for the Fe(C2O4)2–/

256

Fe(C2O4)33– mixture under polychromatic irradiation. These values are approximately two orders of

257

magnitude higher than the RFe( II ) found for the Fe(III)-Pyo complexes. This difference could explain the

258

overestimation of iron reactivity by cloud chemistry models. Indeed, it has been observed that cloud

259

chemistry models tend to overestimate the contribution of iron to the oxidative capacity of clouds,

260

probably due to the incorrect description of iron in this complex medium.35 The iron is generally described

261

as iron oxalate and iron aquo-complexes, whereas strong iron-organic complexes (like Fe(III)-Pyo) are not

262

taken into account in the models. In presence of Fe(III)-Pyo complexes in cloud waters the Fe(III) photo-

263

reduction rate and associated free radical production decrease compared to the iron-oxalate and iron

264

aqua-complexes.

265

The photolysis of Fe(III)-organic complexes produces radical compounds that might generate reactive

266

oxygenated species such as HO2•/O2•–, H2O2 and HO•.54-56 In the case of iron aqua complexes, the photolysis

267

directly leads to the formation of Fe(II) and the hydroxyl radical, while in the case of Fe(III)-oxalate

268

complexes ([Fe(C2O4)]+, [Fe(C2O4)2]– and [Fe(C2O4)3]3–), the so-called LMCT involving nonbonding p-orbitals

269

of the coordinating O-atom and empty d-orbitals of the metal ion leads to the generation of an oxalate

270

radical followed by its reaction with molecular oxygen (expected to have a reaction rate of ~2 × 109 M-1 s-1)

271

57

272

more complicated due to the chemical structure of the organic ligand. In the Fe(III)-Pyo complex the LMCT

273

mechanism can occur by two different reaction pathways, A) and B) (see Figure 5). According to A), photo-

274

dissociation of the complex from the carbonyl binding group can lead to the formation of ferrous ions

275

(Fe(II)) and a carbonyl radical (1). The carbonyl radical undergoes a decarboxylation resulting in the

f

f

and the formation of CO2 and O2•–. In the case of Fe(III)-Pyo the photolysis mechanism is found to be


Page 13 of 31


276

formation of an unstable carbon-centred radical (2) that reacts with molecular oxygen to generate a

277

peroxide radical (3). The intermediate 3 can decompose into the hydroperoxide radical (HO2●) and a

278

derivative (4). Such a mechanism has been previously suggested for other Fe(III)-polycarboxylated

279

complexes in water under irradiation.58 Finally, hydroperoxide radical disproportionation leads to the

280

formation of hydrogen peroxide, which can react with ferrous ions to generate hydroxyl radical in water.

281

In the second pathway (B), the LMCT reaction can occur, leading to the oxidation of the N-hydroxylamine

282

functional group. In this way, the radical cation (5) leads to the protonated nitroxide radical (6a) via an

283

intramolecular hydrogen shift. Nitroxide radicals are stable. Thus, their formation is favoured, and they are

284

often used in organic synthesis and for their redox properties.59, 60 Radical 6a is in equilibrium with its basic

285

form 6b, with a pKa estimate of approximately 5.5 on the basis of reported values for dialkylnitroxide.61

286

Different pathways have been suggested for the nitroxide radical transformation: one possible mechanism

287

involves hydrogen transfer between the protonated (6a) and deprotonated (6b) forms of the nitroxide

288

radical, 62, 63 which yields hydroxylamine (7) and the N-oxoammonium cation (8). The latter can lead to the

289

formation of acetic acid (9) and pyoverdin product (10) via hydrolysis, acetic acid could be also produced by

290

reaction of 8 with hydroxyl radical that could lead to formation of 9 and a nitro derivative. Another possible

291

transformation pathway has been suggested by Goldestein and co-workers, who investigated the effect of

292

the hydroperoxide radical/superoxide radical anion couple (HO2•/O2•–, pKa = 4.8) on the stability of

293

nitroxides. These authors showed that the formation of the N-oxoammonium cation (8) is enhanced by the

294

presence of HO2•, while the back reaction (i.e., oxidation of oxoammonium cations to the nitroxide radical)

295

is promoted by O2•–.64 The suggested mechanism is also supported by experimental data, which show a

296

faster formation of acetic acid at pH 4.0 than at pH 6.0 (see Figure 4B). Acetate formation at pH 4.0 is found

297

to be approximately two times higher compared to that at pH 6.0 during the first 10 minutes.

298

The formation rate of the hydroxyl radical ( RHO• ) was measured to evaluate the impact of the photolysis of

299

Fe(III)-Pyo on the cloud chemistry oxidative budget. The

300

9

f

f RHO • value was on the order of magnitude of ~10

‒10-8 M s-1 under simulated solar irradiation of Fe(III)-Pyo (100 µM for both pH 4.0 and 6.0), showing that 13 ACS Paragon Plus Environment


Page 14 of 31

301

secondary species such as HO2•/O2•– and H2O2 can be generated during iron complex photolysis, leading to

302

the formation of the hydroxyl radical.

303

In Figure S13, Fe(III)-Pyo (100 µM at pH 6.0) was irradiated for 1 hour, and Fe(II) and acetate were

304

quantified. The data show that the Fe(III)-Pyo is photolysed faster at pH 4.0 (Figure 4A) compared to pH 6.0,

305

and in stronger acidic conditions, the formation rates of Fe(II) and acetate are approximately 2 times

306

greater than those at pH 6.0 (Figure 4B). Hydroxyl radical formation rates were measured to be 9.6 × 10-9

307

and 7.8 × 10-9 M s-1 at pH 4.0 and 6.0, respectively (see Supporting Information Text S1).

308 309

Atmospheric implications

310

This work reports the first investigation of the photochemical behaviour Fe(III)-pyoverdin complex, in which

311

the pyoverdin mixture produced by a bacterium isolated from the cloud aqueous phase is shown to

312

complex with ferric ions. Particular attention was paid to the generation of Fe(II) and HO• under aqueous

313

phase conditions of clouds. Additionally, the stability constants of Fe(III)-Pyo (log K) were estimated to be

314

20-27 times higher than those reported for other Fe(III)-carboxylate complexes. Hence, pyoverdins and

315

carboxylic acids, naturally present in the aqueous phase of clouds, can compete for Fe(III) complexation and

316

the formation of Fe(III)-Pyo can be considered as relevant.

317

Previous studies have not reported any data on the concentration of pyoverdins in cloud water, although

318

siderophores have been quantified in rain water. Cheize and coworkers have reported that the

319

concentrations of siderophores in rainwater are in the range of 0.104 to 0.366 µM equivalent of Fe(III), with

320

the dissolved Fe (dFe) concentrations being in the range of 0.073 to 0.988 µM.

321

dissolved iron concentrations in cloud samples are on the same order (µM) and much more concentrated

322

than those in sea waters (nM). Furthermore, concentrations of compounds found in rain water are

323

estimated to be between 2 and 23 times more diluted that the corresponding concentrations in cloud

324

water 66. Therefore, the siderophore concentration is expected to be in the same range as that of dissolved

325

iron in cloud water. Considering a reasonable concentration of Fe(III) 2 µM 35, 67 and Pyo ranging from 0.5 to 14 ACS Paragon Plus Environment

65

Measurements of

Page 15 of 31


326

2 µM, we can estimate the competition between Pyo and oxalate (Ox) to complex Fe(III) at a pH of 4.0 (see

327

text S4). Due to the high complexation constant between Fe(III) and Pyo, the complex Fe(III)-Ox2 is expected

328

to be predominant for [Ox]/[Pyo] ratios greater than 200 (see figure S14). In Figure 6, the expected

329

concentrations of Fe(III)-Pyo and Fe(III)-Ox2 (Fe(C2O4)2-) complexes are determined as a function of oxalate

330

concentration in cloud water.2,12 As expected, all Pyo is complexed with iron and Fe(III)-Ox2 concentration

331

becomes relevant only when Pyo concentration is lower than iron concentration. In fact, in the presence of

332

0.5 µM of Pyo (and 2 µM of Fe(III)), Fe(III)-Ox2 concentration increases up to 1.5 µM, when reaches a

333

plateau due to the complete Fe(III) complexation. This estimation suggests that the presence of Fe(III)-Pyo

334

complex (and as consequence the relevance of this complex) depends on the relative Pyo/Fe(III)

335

concentrations ratio. However, our estimation is performed considering only one type of siderophores that

336

is expected to be produced by bacteria in cloud water. Therefore more siderophores are expected to be

337

present in cloud waters.

338

The presence of pyoverdins in the aqueous phase of clouds can impact the composition and oxidative

339

capacity of this medium via the following:

340

i) Iron cycle modification leading to the complexation of ferric ions and their increased availability 68 and

341

photochemistry.

342

ii) Formation of new ferric ion complexes from the pyoverdin oxidative products (after LMCT reaction), as

343

shown for marine siderophores.27, 69 These species can be attributed to the formation of new complexes

344

between Fe(III) (still present in solution under its soluble form) and degradation products of pyoverdin).

345 346

iii) Scavenging of the hydroxyl radical in cloud water (pyoverdins’ reactivity with the hydroxyl radical has been estimated to be approximately 1010 M-1 s-1).70

347

iv) Decrease the Fe(III) photo-reduction rate and consequently the associated free radical production.

348

v) Formation of low molecular weight organic compounds, such as carboxylic acids, under solar irradiation.

349

Finally, the iron chemistry and its photoreactivity in cloud water should be deeply investigated in the

350

future, and the related impact on the oxidative capacity of cloud water must be reconsidered by cloud 15 ACS Paragon Plus Environment


Page 16 of 31

351

chemistry models. In fact, cloud chemistry models are generally restricted to iron oxalate and iron aqua

352

complexes and tend to overestimate the contribution of iron to the oxidative capacity of this complex

353

medium. This work considers only one type of siderophores, the pyoverdins, but the real environment can

354

have many other biological or anthropogenic compounds with a strong affinity to iron (e.g.,

355

aminopolycarboxylic acids). It is likely that other Fe(III)-siderophore complexes may have a similar reactivity

356

to Fe(III)-Pyo, but this hypothesis should be confirmed through future studies. In summary, other studies

357

are needed to better investigate the photoreactivities of other strong Fe(III)-organic complexes.

358 359

Acknowledgements

360

Authors acknowledge financial support from the Regional Council of Auvergne and from the "Fédération de

361

Recherches en Environnement" through the CPER “Environnement” founded by the “Région Auvergne,” the

362

French government, FEDER from the European community, and the ANR BIOCAP (ANR-13-BS06-0004).

363

AMD and VV gratefully acknowledge Christophe Chambon and Didier Viala (INRA, Plateforme d'exploration

364

du métabolisme, F-63122 Saint-Genès Champanelle, France) for mass spectrometry analysis.

365 366

Associated content

367

Supporting information. Experimental setups details and formation rates calculations, Table S1 and Figures

368

S1-14.

This

information

is

available

free

of

charge

via

Internet

at

http://pubs.acs.org/


Page 17 of 31

369


REFERENCES

370 371

1. Marinoni, A.; Parazols, M.; Brigante, M.; Deguillaume, L.; Amato, P.; Delort, A.-M.; Laj, P.; Mailhot, G.,

372

Hydrogen peroxide in natural cloud water: Sources and photoreactivity. Atmos. Res. 2011, 101, (1–2),

373

256-263.

374

2. Charbouillot, T.; Gorini, S.; Voyard, G.; Parazols, M.; Brigante, M.; Deguillaume, L.; Delort, A.-M.;

375

Mailhot, G., Mechanism of carboxylic acid photooxidation in atmospheric aqueous phase: Formation,

376

fate and reactivity. Atmos. Environ. 2012, 56, (0), 1-8.

377

3. Collett Jr, J. L.; Bator, A.; Sherman, D. E.; Moore, K. F.; Hoag, K. J.; Demoz, B. B.; Rao, X.; Reilly, J. E., The

378

chemical composition of fogs and intercepted clouds in the United States. Atmos. Res. 2002, 64, (1–4),

379

29-40.

380

4. Guo, J.; Wang, Y.; Shen, X.; Wang, Z.; Lee, T.; Wang, X.; Li, P.; Sun, M.; Collett Jr, J. L.; Wang, W.; Wang,

381

T., Characterization of cloud water chemistry at Mount Tai, China: Seasonal variation, anthropogenic

382

impact, and cloud processing. Atmos. Environ. 2012, 60, (0), 467-476.

383

5. Chandler, A. S.; Choularton, T. W.; Dollard, G. J.; Gay, M. J.; Hill, T. A.; Jones, A.; Jones, B. M. R.; Morse,

384

A. P.; Penkett, S. A.; Tyler, B. J., A field study of the cloud chemistry and cloud microphysics at Great Dun

385

Fell. Atmos. Environ. 1988, 22, (4), 683-694.

386 387 388 389 390 391

6. Collett Jr, J.; Iovinelli, R.; Demoz, B., A three-stage cloud impactor for size-resolved measurement of cloud drop chemistry. Atmos. Environ. 1995, 29, (10), 1145-1154. 7. Herckes, P.; Valsaraj, K. T.; Collett Jr, J. L., A review of observations of organic matter in fogs and clouds: Origin, processing and fate. Atmos. Res. 2013, 132–133, (0), 434-449. 8. Marinoni, A.; Laj, P.; Sellegri, K.; Mailhot, G., Cloud chemistry at the Puy de Dôme: variability and relationships with environmental factors. Atmos. Chem. Phys. 2004, 4, (3), 715-728.

392

9. Bauer, H.; Kasper-Giebl, A.; Löflund, M.; Giebl, H.; Hitzenberger, R.; Zibuschka, F.; Puxbaum, H., The

393

contribution of bacteria and fungal spores to the organic carbon content of cloud water, precipitation

394

and aerosols. Atmos. Res. 2002, 64, (1–4), 109-119.

395 396

10.Benedict, K. B.; Lee, T.; Collett Jr, J. L., Cloud water composition over the southeastern Pacific Ocean during the VOCALS regional experiment. Atmos. Environ. 2012, 46, (0), 104-114.



397 398

Page 18 of 31

11.Fuzzi, S.; Facchini, M. C.; Decesari, S.; Matta, E.; Mircea, M., Soluble organic compounds in fog and cloud droplets: what have we learned over the past few years? Atmos. Res. 2002, 64, (1–4), 89-98.

399

12.Deguillaume, L.; Charbouillot, T.; Joly, M.; Vaitilingom, M.; Parazols, M.; Marinoni, A.; Amato, P.; Delort,

400

A. M.; Vinatier, V.; Flossmann, A.; Chaumerliac, N.; Pichon, J. M.; Houdier, S.; Laj, P.; Sellegri, K.; Colomb,

401

A.; Brigante, M.; Mailhot, G., Classification of clouds sampled at the puy de Dôme (France) based on 10

402

yr of monitoring of their physicochemical properties. Atmos. Chem. Phys. 2014, 14, (3), 1485-1506.

403

13.Houdier, S.; Barret, M.; Dominé, F.; Charbouillot, T.; Deguillaume, L.; Voisin, D., Sensitive determination

404

of glyoxal, methylglyoxal and hydroxyacetaldehyde in environmental water samples by using

405

dansylacetamidooxyamine derivatization and liquid chromatography/fluorescence. Anal. Chim. Acta

406

2011, 704, (1-2), 162-173.

407

14.Wang, Y.; Chiu, C.-A.; Westerhoff, P.; Valsaraj, K. T.; Herckes, P., Characterization of atmospheric organic

408

matter using size-exclusion chromatography with inline organic carbon detection. Atmos. Environ. 2013,

409

68, (0), 326-332.

410 411 412 413 414 415 416 417

15.Graber, E. R.; Rudich, Y., Atmospheric HULIS: How humic-like are they? A comprehensive and critical review. Atmos. Chem. Phys. 2006, 6, (3), 729-753. 16.Wang, Y. Characterization of atmospheric organic matter and its processing by fogs and clouds. Ph.D. Arizona state University, 2014. 17.Feng, J.; Moller, D., Characterization of water-soluble macromolecular substances in cloud water. J. Atmos. Chem. 2004, 48, (3), 217-233. 18.O'Sullivan, D.; Murray, B. J.; Ross, J. F.; Whale, T. F.; Price, H. C.; Atkinson, J. D.; Umo, N. S.; Webb, M. E., The relevance of nanoscale biological fragments for ice nucleation in clouds. Sci. Rep. 2015, 5, 8082.

418

19.Santl-Temkiv, T.; Finster, K.; Dittmar, T.; Hansen, B. M.; Thyrhaug, R.; Nielsen, N. W.; Karlson, U. G.,

419

Hailstones: A Window into the microbial and chemical inventory of a storm cloud. PLoS One 2013, 8, (1),

420

e53550.

421 422

20.Kourtev, P. S.; Hill, K. A.; Shepson, P. B.; Konopka, A., Atmospheric cloud water contains a diverse bacterial community. Atmos. Environ. 2011, 45, (30), 5399-5405.

423

21.Vaitilingom, M.; Attard, E.; Gaiani, N.; Sancelme, M.; Deguillaume, L.; Flossmann, A. I.; Amato, P.; Delort,

424

A.-M., Long-term features of cloud microbiology at the puy de Dôme (France). Atmos. Environ. 2012, 56,

425

(0), 88-100.


Page 19 of 31


426

22.Delort, A.-M.; Vaïtilingom, M.; Amato, P.; Sancelme, M.; Parazols, M.; Mailhot, G.; Laj, P.; Deguillaume,

427

L., A short overview of the microbial population in clouds: Potential roles in atmospheric chemistry and

428

nucleation processes. Atmos. Res. 2010, 98, (2–4), 249-260.

429

23.Matulová, M.; Husárová, S.; Capek, P.; Sancelme, M.; Delort, A.-M., Biotransformation of various

430

saccharides and production of exopolymeric substances by cloud-borne Bacillus sp. 3B6. Environ. Sci.

431

Technol. 2014, 48, (24), 14238-14247.

432

24.Vaitilingom, M.; Deguillaume, L.; Vinatier, V.; Sancelme, M.; Amato, P.; Chaumerliac, N.; Delort, A.-M.,

433

Potential impact of microbial activity on the oxidant capacity and organic carbon budget in clouds. Proc.

434

Natl. Acad. Sci. 2013, 110, (2), 559-564.

435 436 437 438 439 440

25.Gledhill, M.; Buck, K. N., The organic complexation of iron in the marine environment: a review. Front. Microbiol. 2012, 3, (69), 1-17. 26.Barbeau, K., Photochemistry of organic iron(III) complexing ligands in oceanic systems. Photochem. Photobiol. 2006, 82, (6), 1505-1516. 27.Barbeau, K.; Rue, E. L.; Bruland, K. W.; Butler, A., Photochemical cycling of iron in the surface ocean mediated by microbial iron(III)-binding ligands. Nature 2001, 413, (6854), 409-413.

441

28.Barbeau, K.; Rue, E. L.; Trick, C. G.; Bruland, K. W.; Butler, A., Photochemical reactivity of siderophores

442

produced by marine heterotrophic bacteria and cyanobacteria based on characteristic Fe(III) binding

443

groups. Limnol. Oceanogr. 2003, 48, (3), 1069-1078.

444

29.Arakaki, T.; Faust, B. C., Sources, sinks, and mechanisms of hydroxyl radical (OH) photoproduction and

445

consumption in authentic acidic continental cloud waters from Whiteface Mountain, New York: The role

446

of the Fe(r) (r = II, III) photochemical cycle. J. Geophys. Res. 1998, 103, (D3), 3487-3504.

447

30.Arakaki, T.; Kuroki, Y.; Okada, K.; Nakama, Y.; Ikota, H.; Kinjo, M.; Higuchi, T.; Uehara, M.; Tanahara, A.,

448

Chemical composition and photochemical formation of hydroxyl radicals in aqueous extracts of aerosol

449

particles collected in Okinawa, Japan. Atmos. Environ. 2006, 40, (25), 4764-4774.

450

31.Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A. B., Critical review of rate constants for reactions

451

of hydrated electrons, hydrogen atoms and hydroxyl radicals (•OH/•O−) in aqueous solution. J. Phys.

452

Chem. Ref. Data 1988, 17, 513-886.

453

32.Deguillaume, L.; Leriche, M.; Desboeufs, K.; Mailhot, G.; George, C.; Chaumerliac, N., Transition metals in

454

atmospheric liquid phases: Sources, reactivity, and sensitive parameters. Chem. Rev. 2005, 105, (9),

455

3388-3431. 19 ACS Paragon Plus Environment


Page 20 of 31

456

33.Harris, E.; Sinha, B. r.; van Pinxteren, D.; Tilgner, A.; Fomba, K. W.; Schneider, J.; Roth, A.; Gnauk, T.;

457

Fahlbusch, B.; Mertes, S.; Lee, T.; Collett, J.; Foley, S.; Borrmann, S.; Hoppe, P.; Herrmann, H., Enhanced

458

role of transition metal ion catalysis during in-cloud oxidation of SO2. Science 2013, 340, (6133), 727-

459

730.

460

34.Long, Y.; Charbouillot, T.; Brigante, M.; Mailhot, G.; Delort, A.-M.; Chaumerliac, N.; Deguillaume, L.,

461

Evaluation of modeled cloud chemistry mechanism against laboratory irradiation experiments: The

462

HxOy/iron/carboxylic acid chemical system. Atmos. Environ. 2013, 77, (0), 686-695.

463

35.Bianco, A.; Passananti, M.; Perroux, H.; Voyard, G.; Mouchel-Vallon, C.; Chaumerliac, N.; Mailhot, G.;

464

Deguillaume, L.; Brigante, M., A better understanding of hydroxyl radical photochemical sources in cloud

465

waters collected at the puy de Dôme station: experimental vs. modeled formation rates. Atmos. Chem.

466

Phys. 2015, 15, (10), 13923-13955.

467

36.Weller, C.; Tilgner, A.; Brauer, P.; Herrmann, H., Modeling the impact of iron-carboxylate

468

photochemistry on radical budget and carboxylate degradation in cloud droplets and particles. Environ.

469

Sci. Technol. 2014, 48, (10), 5652-5659.

470 471

37.Visca, P.; Imperi, F.; Lamont, I. L., Pyoverdine siderophores: from biogenesis to biosignificance. Trends Microbiol. 2007, 15, (1), 22-30.

472

38.Amato, P.; Ménager, M.; Sancelme, M.; Laj, P.; Mailhot, G.; Delort, A.-M., Microbial population in cloud

473

water at the Puy de Dome: Implications for the chemistry of clouds. Atmos. Environ. 2005, 39, (22),

474

4143-4153.

475

39.Hill, K. A.; Shepson, P. B.; Galbavy, E. S.; Anastasio, C.; Kourtev, P. S.; Konopka, A.; Stirm, B. H. C. D.,

476

Processing of atmospheric nitrogen by clouds above a forest environment. J. Geophys. Res., Atmos.

477

2007, 112, (D11).

478 479 480 481 482 483 484

40.Stookey, L. L., Ferrozine - A new spectrophotometric reagent for iron. Anal. Chem. 1970, 42, (7), 779781. 41.Vosburgh, W. C.; Cooper, G. R., Complex Ions. I. The identification of complex ions in solution by spectrophotometric measurements. J. Am. Chem. Soc. 1941, 63, (2), 437-442. 42.Dulin, D.; Mill, T., Development and evaluation of sunlight actinometers. Environ. Sci. Technol. 1982, 16, 815-820. 43.Bhatia, K., Hydroxyl radical induced oxidation of nitrobenzene. J. Phys. Chem. 1975, 79, (10), 1032-1038.


Page 21 of 31


485

44.Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A. B., Critical review of rate constants for reactions

486

of hydrated electrons, hydrogen atoms and hydroxyl radicals (•OH/•O−) in aqueous solution. J. Phys.

487

Chem. Ref. Data 1998, 17, 513-886.

488

45.Khalil-Rizvi, S.; Toth, S. I.; van der Helm, D.; Vidavsky, I.; Gross, M. L., Structures and characteristics of

489

novel siderophores from plant deleterious Pseudomonas fluorescens A225 and Pseudomonas putida

490

ATCC 39167. Biochemistry 1997, 36, (14), 4163-4171.

491

46.Budzikiewicz, H.; Schafer, M.; Fernandez, D. U.; Matthijs, S.; Cornelis, P., Characterization of the

492

chromophores of pyoverdins and related siderophores by electrospray tandem mass spectrometry.

493

BioMetals 2007, 20, (2), 135-144.

494 495

47.Fuchs, R.; Schäfer, M.; Geoffroy, V.; Meyer, J., Siderotyping - A powerful tool for the characterization of pyoverdines. Curr. Top. Med. Chem. 2001, 1, (1), 31-57.

496

48.Zwinkels, J. C.; DeRose, P. C.; Leland, J. E.; Thomas A. Germer, J. C. Z. a. B. K. T., Chapter 7 - Spectral

497

Fluorescence Measurements. In Experimental Methods in the Physical Sciences, Academic Press: 2014;

498

Vol. 46, pp 221-290.

499

49.Albrecht-Gary, A.-M.; Blanc, S.; Rochel, N.; Ocaktan, A. Z.; Abdallah, M. A., Bacterial iron transport:

500

Coordination properties of pyoverdin PaA, a peptidic siderophore of Pseudomonas aeruginosa. Inorg.

501

Chem. 1994, 33, (26), 6391-6402.

502 503 504 505 506 507

50.Parker, D. L.; Sposito, G.; Tebo, B. M., Manganese(III) binding to a pyoverdine siderophore produced by a manganese(II)-oxidizing bacterium. Geochim. Cosmochim. Acta 2004, 68, (23), 4809-4820. 51.Lapp, M.; Penney, C. M.; Emrich, R. J., 3.2. Analysis of Raman and Rayleigh Scattered Radiation. In Methods in Experimental Physics, Academic Press: 1981; Vol. 18, Part B, pp 408-433. 52.Wang, Z.; Chen, C.; Ma, W.; Zhao, J., Photochemical coupling of iron redox reactions and transformation of low-molecular-weight organic matter. J. Phys Chem. Lett. 2012, 3, (15), 2044-2051.

508

53.Morgan, B.; Lahav, O., The effect of pH on the kinetics of spontaneous Fe(II) oxidation by O2 in aqueous

509

solution - basic principles and a simple heuristic description. Chemosphere 2007, 68, (11), 2080-2084.

510

54.Wang, L.; Zhang, C.; Mestankova, H.; Wu, F.; Deng, N.; Pan, G.; Bolte, M.; Mailhot, G., Photoinduced

511

degradation of 2,4-dichlorophenol in water: influence of various Fe(III) carboxylates. Photochem.

512

Photobiol. Sci. 2009, 8, (7), 1059-1065.



Page 22 of 31

513

55.Zhang, X.; Gong, Y.; Wu, F.; Deng, N.; Pozdnyakov, I. P.; Glebov, E. M.; Grivin, V. P.; Plyusnin, V. F.;

514

Bazhinb, N. M., Photochemistry of the iron(III) complex with pyruvic acid in aqueous solutions. Russ.

515

Chem. Bull. 2009, 58, (9), 1828-1836.

516 517 518 519

56.Zhou, D.; Wu, F.; Deng, N., Fe(III)-oxalate complexes induced photooxidation of diethylstilbestrol in water. Chemosphere 2004, 57, (4), 283-291. 57.Adams, G. E.; Willson, R. L., Pulse radiolysis studies on the oxidation of organic radicals in aqueous solution. Trans. Faraday Soc. 1969, 65, (0), 2981-2987.

520

58.Abida, O.; Mailhot, G.; Litter, M.; Bolte, M., Impact of iron-complex (Fe(III)-NTA) on photoinduced

521

degradation of 4-chlorophenol in aqueous solution. Photochem. Photobiol. Sci. 2006, 5, (4), 395-402.

522

59.Hodgson, J. L.; Namazian, M.; Bottle, S. E.; Coote, M. L., One-electron oxidation and reduction potentials

523 524 525

of nitroxide antioxidants: A theoretical study. J. Phys. Chem. A 2007, 111, (51), 13595-13605. 60.Volodarsky, L. B.; Reznikov, V. A.; Ovcharenko, V. I., Synthetic Chemistry of Stable Nitroxides, CRC Press. 1994.

526

61.Malatesta, V.; Ingold, K. U., Protonated nitroxide radicals. J. Am. Chem. Soc. 1973, 95, (19), 6404-6407.

527

62.Ma, Y. Nitroxides in mechanistic studies: Ageing of gold nanoparticles and nitroxide transformation in

528 529 530 531 532

acids. PhD thesis. 2010. 63.Ma, Y.; Loyns, C.; Price, P.; Chechik, V., Thermal decay of TEMPO in acidic media via an N-oxoammonium salt intermediate. Org. Biomol. Chem. 2011, 9, (15), 5573-5578. 64.Goldstein, S.; Merenyi, G.; Russo, A.; Samuni, A., The Role of oxoammonium cation in the SOD-mimic activity of cyclic nitroxides. J. Am. Chem. Soc. 2003, 125, (3), 789-795.

533

65.Cheize, M.; Sarthou, G. r.; Croot, P. L.; Bucciarelli, E.; Baudoux, A.-C.; Baker, A. R., Iron organic speciation

534

determination in rainwater using cathodic stripping voltammetry. Anal. Chim. Acta 2012, 736, 45-54.

535

66.Lin, N.-H.; Peng, C.-M., E

536

stimates of the contribution of below-cloud scavenging to the pollutant loadings of rain in Taipei, Taiwan.

537 538 539

Terr. Atmos. Ocean. Sci. 1999, 10, 693-704. 67.Parazols, M.; Marinoni, A.; Amato, P.; Abida, O.; Laj, P.; Mailhot, G., Speciation and role of iron in cloud droplets at the puy de Dome station. J. Atmos. Chem. 2006, 54, (3), 267-281.


Page 23 of 31

540 541 542 543 544 545 546 547 548


68.Kraemer, S., Iron oxide dissolution and solubility in the presence of siderophores. Aquat. Sci. 2004, 66, (1), 3-18. 69.Vraspir, J. M.; Butler, A., Chemistry of marine ligands and siderophores. Ann. Rev. Mar. Sci. 2009, 1, (1), 43-63. 70.Hoe, S.; Rowley, D. A.; Halliwell, B., Reactions of ferrioxamine and desferrioxamine with the hydroxyl radical. Chem.-Biol. Interact. 1982, 41, (1), 75-81. 71.Ongena, M.; Jacques, P.; Delfosse, P.; Thonart, P., Unusual traits of the pyoverdin-mediated iron acquisition system in Pseudomonas putida strain BTP1. BioMetals 2002, 15, (1), 1-13. 72.Smith, R. M.; Martell, A. E., Critical Stability Constants. Springer US: 1977; Vol. 3-6.

549



Page 24 of 31

550

RFef ( II ) (M s-1)

φFe ( II )

Stability constant (log K)

Fe(III)-Pyo pH 4.0

6.98 ± 0.07 ×10-9

1.9 × 10-4

19.7-21.2 * (at pH 5)71

Fe(III)-Pyo pH 6.0

3.96 ± 0.04 ×10-9

5.5 × 10-5

25.5-27.1 * (at pH 7)71

Fe(III)-oxalate complexes [Fe(C2O4)2]–

5.35 ± 0.60 ×10-7

16.2 72

[Fe(C2O4)2]–/ [Fe(C2O4)3]3–

1.88 ± 0.29 ×10-7

16.2 / 26.2 72

50/50 551 f

552

Table 1. Fe(II) formation rate ( RFe( II ) ) and Fe(II) quantum yield formation ( φFe ( II ) ) of the 100 µM Fe(III)-Pyo

553 554 555 556

complex at pH 4.0 and 6.0 and 100 µM Fe-oxalate complexes (di-oxalate : [Fe(C2O4)2]– and a mixture of di and tri-oxalate [Fe(C2O4)2]–/ [Fe(C2O4)3]3–) obtained in this work under simulated solar irradiation. Stability constants (log K) of [Fe(C2O4)2]– and [Fe(C2O4)3]3– are reported from the literature. * Data are taken from other iron(III)-pyoverdins.

557


Page 25 of 31

558


Figure Caption

559 560 561 562 563 564 565 566 567 568 569 570 571 572 573

1)

2) 3) 4) 5) 6)

Emission spectrum of Xenon lamp (solar simulator), sun emission spectrum measured at the top of puy de Dôme mountain in autumn 2013 during cloudy conditions and molar absorption coefficients of the aqueous Fe(III)-Pyo complexes at pH 4.0 and 6.0. Proposed structure for the linear form of the major pyoverdin. A, B and Y indicate the identified fragmentations reported in Figure S3 Fluorescence excitation-emission matrix (EEM) of pyoverdin. Fe(II) (A) and acetate (B) formations from Fe(III)-Pyo (100µM) irradiation in water at pH 4.0 and 6.0 at 278 ± 2 K. The lines are the exponential rise fits of data. Proposed reaction mechanisms from the LMCT reaction of Fe(III)-Pyo under polychromatic irradiation The Fe(III)-Pyo and Fe(III)-Ox2 complexes concentration are reported as a function of oxalate concentration. The competition between Fe(III)-Pyo and Fe(III)-Ox2 complexes is calculated at pH 4.0, considering 2 µM of Fe(III) in the presence of Pyo 0.5µM (dashed lines) and 2 µM (continuous lines). The shaded region of the graph highlights the most significant concentration range of oxalate found in cloud waters.

574



Page 26 of 31

575 576

Figure 1

577


Page 27 of 31


578 579

580 581

Figure 2

582



Page 28 of 31

583 584

Figure 3

585 586


Page 29 of 31


587

588 589

Figure 4 29 ACS Paragon Plus Environment


Page 30 of 31

590 591

592 593

Figure 5

594 595 596 597 598


Page 31 of 31


599 600

Figure 6


Siderophores in Cloud Waters and Potential ... - ACS Publications

Recommend Documents