Fourier Transform Infrared and Raman and Surface-Enhanced Raman

Article pubs.acs.org/JPCA

Fourier Transform Infrared and Raman and Surface-Enhanced Raman Spectroscopy Studies of a Novel Group of Boron Analogues of Aminophosphonic Acids Natalia Piergies,† Edyta Proniewicz,*,† Andrzej Kudelski,‡ Agata Rydzewska,§ Younkyoo Kim,∥ Marcin Andrzejak,† and Leonard M. Proniewicz†,⊥ †

Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30-060 Krakow, Poland Faculty of Chemistry, University of Warsaw, ul. L. Pasteura 1, 02-093 Warsaw, Poland § Department of Bioorganic Chemistry, Faculty of Chemistry, Wrocław University of Technology, Wybrzeże Wyspianskiego 27, 50-370, Wrocław, Poland ∥ Department of Chemistry, Hankuk University of Foreign Studies, Yongin, Kyunggi-Do, 449-791, Korea ⊥ The State Higher Vocational School, ul. Mickiewicza 8, 33-100 Tarnów, Poland ‡

S Supporting Information *

ABSTRACT: Five analogues of a novel group of boron derivatives of aminophosphonic acidsN-benzylamino-(3boronphenyl)-S-methylphosphonic acid (m-PhS), N-benzylamino-(4-boronphenyl)-S-methylphosphonic acid (p-PhS), Nbenzylamino-(2-boronphenyl)-R-methylphosphonic acid (oPhR), N-benzylamino-(3-boronphenyl)-R-methylphosphonic acid (m-PhR), and N-benzylamino-(4-boronphenyl)-R-methylphosphonic acid (p-PhR)were studied using Fourier transform infrared (FT IR), Fourier transform Raman (FT RS), and surface-enhanced Raman (SERS) spectroscopies. Analysis of obtained FT IR and FT RS spectra show that all investigated compounds in the solid state exist as dimeric species formed by an H-bonding interaction between −B(OH)2 moieties of each monomer. In addition, comparison of the wavenumbers, intensities, and broadness of bands from the FT Raman and SERS spectra allowed information to be obtained regarding the adsorption geometry of the investigated compounds immobilized onto an electrochemically roughened silver substrate.

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as potential diol10 and saccharide receptors11−13 and as enzyme inhibitors. Boron analogues of amino acids have also proven useful as protease14−16 and kinase enzymes17,18 inhibitors. These two groups of enzymes play essential roles in the growth, progression, and metastasis of tumors.19−22 A great deal of research has been conducted on the use of enzyme inhibitors, particularly kinases, in cancer therapy, with excellent results.23−25 The potent biological activity of boronic acid is due to the boron atom’s vacant orbital that provides an easy transition between the neutral sp2 and the anionic sp3 hybridization states. This transition allows for covalent bonding between a donor molecule and the boron atom.17 Interactions with target enzymes through covalent and hydrogen bonding imbue boron compounds with unique properties.17,26,27 We present the first vibrational characteristics for a group of N-benzylamino(boronphenyl)methylphosphonic acids, includ-

INTRODUCTION The increasing interest in amino acid analogues in pharmaceutical drug design can be attributed to their ability to easily move deeper into an affected cell than into a normal cell.1 For this reason, these compounds are commonly used as enzyme inhibitors or antibacterial agents.2−5 Aminophosphonic acids (phosphorus analogues of amino acids), in which the carboxylic acid group is replaced by a phosphonic acid moiety, exhibit an inhibitory effect that is primarily due to the strong electrostatic binding of the phosphonate dianion by the active site of the enzyme.6 Therefore, aminophosphonic acids are commonly known as potential enzyme inhibitors and are considered promoters of tumor cell growth and invasion.6,7 Modifying aminophosphonic acids to (N-benzylamino)benzylphosphonic acids produces the most effective phosphatase inhibitors; phosphatase is an enzyme that catalyzes the dephosphorylation process.8,9 Additional introduction of a boronic acid group to the biologically active (N-benzylamino)benzylphosphonic acid opens new possibilities for its application. Boronic acid compounds have attracted recent attention because of their biomedical functions: they are used © 2012 American Chemical Society

Received: July 17, 2012 Revised: September 9, 2012 Published: September 18, 2012 10004

dx.doi.org/10.1021/jp307064p | J. Phys. Chem. A 2012, 116, 10004−10014

The Journal of Physical Chemistry A

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Table 1. Molecular Structures of m-PhS, p-PhS, o-PhR, m-PhR, and p-PhR Dimers

analogues,37−40 in good agreement with the experimental data. The benefits of applying theoretical analysis led us to perform theoretical calculations using the B3LYP hybrid density functional theory method for the investigated compounds to compare the calculated spectra with the experimental FT IR and FT Raman spectra. In this work, we also present surface-enhanced Raman (SERS) spectra of the investigated compounds adsorbed onto an electrochemically roughened silver substrate to study the behavior of these molecules at the solid/liquid interface. The influence of the position of the boronic acid group (ortho, meta, or para) and the absolute conformation (R or S) of the investigated phosphonic acids on their interaction with the substrates was analyzed. SERS combines the specificity of vibrational spectroscopy with ultra high sensitivity at the molecular level.41 Because of these features SERS can be used, for example, in biotechnology and medicine, in the cases were small concentrations of the investigated materials and rapid and nondestructive analytical methods is needed. In addition, the method can be employed for qualitative and quantitative measurements.42,43 The specificity of this method is related to the fact that only vibrations of these groups of molecules, which are attached or are in contact with the SERS-active substrates, are observed in SERS spectra.42 By comparison of Raman and SERS spectra some changes can be noted in band wavenumbers and enhancement. Creighton has described selection rules for determining the orientation of aromatic molecules adsorbed

ing N-benzylamino-(3-boronphenyl)-S-methylphosphonic acid (m-PhS), N-benzylamino-(4-boronphenyl)-S-methylphosphonic acid (p-PhS), N-benzylamino-(2-boronphenyl)-R-methylphosphonic acid (o-PhR), N-benzylamino-(3-boronphenyl)R-methylphosphonic acid (m-PhR), and N-benzylamino-(4boronphenyl)-R-methylphosphonic acid (p-PhR) (see Table 1 for molecular structures). Absorption infrared and Raman spectroscopies provide the characteristic vibrations (vibrational fingerprints) of the molecules and supply information regarding their structure and composition.28,29 These methods are commonly used for qualitative and quantitative analysis and to study different types of samples over a wide range of temperatures and physical states.29 The development of Fourier transform techniques helps to reduce the fluorescence background,30 which allows for analyses that were previously impossible.31,32 In many cases, the experiments are extended by theoretical analysis using advanced methods of computational quantum chemistry because interpreting correlations between measured spectra and molecular structures can be difficult and can lead to erroneous conclusions.33 Theoretical calculations are helpful and provide unambiguous and reliable interpretation of the obtained results.34−36 Density functional theory (DFT) calculations at the B3LYP hybrid level of theory have become a popular approach for computing molecular structures, vibrational frequencies, and the energies of chemical reactions. B3LYP has been employed to calculate the vibrational spectra of many molecules, especially peptides, amino acids, and their 10005



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onto SERS-active substrates.42−44 These selection rules are connected with the mode intensities belonging to the one of the three classes of symmetry: A2, B1, and B2. The ratios of the surface enhancement factors for the A2, B1, and B2 vibrations are 4:1:1 for the horizontal orientation and 1:1:4 for the vertical orientation on the substrate. These enhancements can be understood by taking into account the nature of the vibrations; the “out-of-plane” (A2) vibrations for a horizontal orientation have a larger polarizability tensor component normal to the surface than the “in-plane” (B2) vibrations. The opposite should be true for the vertical orientation.44,45 However, for highly symmetric molecules, the Herzberg−Teller selection rules have been shown to be a better approach for correctly predicting SERS intensities.46 On the basis of the relative intensities, the wavenumbers, and the bandwidth changes in the SERS spectra in comparison with the Raman spectra, one can determine the adsorption geometry structure of investigated molecules and the distance of the functional groups with respect to the substrate.47,48 The study of molecular interaction mechanisms at the solid/solution interface may play a significant role in understanding in vivo behavior.48 For this reason, SERS is becoming increasingly popular, especially in research concerning protein interactions49 and the inhibitions of some enzymes.50,51 Some evidence exists to promote the theory that the interaction between a molecule and a metal substrate (under SERS conditions) can mimic the mechanism of a substrate−receptor bond.47,52−54

cell was equipped with a large platinum sheet as the counter electrode, a silver/silver chloride electrode (Ag|AgCl, 1 M KCl) as a reference electrode (all potentials are quoted vs this electrode), and a silver working electrode. The silver was roughened by three successive negative−positive−negative cycles from −0.3 to 0.3 V at a sweep rate of 5 mV/s. The roughening was performed in an aqueous KCl solution at a concentration of 0.1 M. The cycling ended at −0.3 V. Then, the electrode was held at −0.4 V for 5 min. Next, the silver electrode was carefully removed at an open circuit potential and rinsed with water. The SERS spectra for the compounds immobilized onto the as-prepared silver electrode were recorded using an ISA T64000 (Jobin Yvon) Raman spectrometer with Kaiser SuperNotch-Plus holographic filters, a 600 grooves/mm holographic grating, an Olympus BX40 microscope with a 50× long-distance objective and a 1024 × 256 pixel nitrogencooled charge-coupled device detector. A Laser-Tech (LJ-800) mixed argon/krypton laser with excitation at 514.5 nm was used as the radiation source. The measurements were performed on 10−4 M samples with a laser power of 1 mW (∼104 W/cm2). No spectral changes associated with sample decomposition or desorption were observed. Theoretical Analysis. The Gaussian 03 suite57 was employed to optimize the geometry of the investigated molecules and to calculate their vibrational wavenumbers and Raman and IR intensities. According to the literature26,27 and our analysis (theoretical calculations for different types of Nbenzylamino(boronphenyl)methylphosphonic acid dimers), the most stable structure for boronic acid derivatives is a cyclic dimer created by a pair of intermolecular hydrogen bonds between the boron hydroxyl groups of two monomers (present in solid state). Therefore, all calculations were performed for dimers. We also calculated the vibrational structures of proper monomers (not shown). The difference in energy between monomers and formed by them dimers was calculated (stabilization of energy) based on the method proposed by Dr. Paweł Dziekoński (Ph.D. Thesis, Technical University of Wroclaw, Wroclaw 2003). Our calculations show that investigated in this work dimers are more stable than monomers: m-PhS by 12 kcal/mol, p-PhS by 6 kcal/mol, oPhR by 22 kcal/mol, m-PhR by 5 kcal/mol, and p-PhR by 8 kcal/mol. Optimization was carried using the DFT method at the B3LYP theory level. The triple-split valence basis with a polarization function on heavy atoms and hydrogens (6-311 G(d,p)) was applied as the basis set.58 This type of basis is approved for the calculations of similar molecules and provides reliable results.26,59 During optimization, no imaginary wavenumbers were obtained showing that the calculated structures correspond to energy minima on the potential energy surface for nuclear motion. Because of the results of the Gaussian Raman scattering, the Raint program was required to obtain theoretical Raman intensities. The intensities were calculated using the following relationship, which is connected with the intensity theory of Raman scattering60

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EXPERIMENTAL AND THEORETICAL METHODS Phosphonic Acid Synthesis. The group of Nbenzylamino(boronphenyl)methylphosphonic acidsN-benzylamino-(3-boronphenyl)-S-methylphosphonic acid (m-PhS), Nbenzylamino-(4-boronphenyl)-S-methylphosphonic acid (pPhS), N-benzylamino-(2-boronphenyl)-R-methylphosphonic acid (o-PhR), N-benzylamino-(3-boronphenyl)-R-methylphosphonic acid (m-PhR), and N-benzylamino-(4-boronphenyl)-Rmethylphosphonic acid (p-PhR)were synthesized according to the previously described procedure.55 The purity and chemical structures of the investigated compounds were confirmed using 1H, 13C, 31P, and 11B NMR spectroscopy (Bruker Avance DRX 300 MHz spectrometer, Bruker Polska, Poznań) and electrospray ionization mass spectrometry (ESIMS, Bruker MicrOTOF-Q spectrometer, Bruker Polska, Poznań). FT IR Measurements. Pellets containing 1.0 mg of each sample dispersed in 200 mg of KBr were used for the infrared measurements. The spectra were recorded at room temperature as an average of 30 scans using a Bruker FT IR spectrometer (EQUINOX 55) equipped with a Nernst rod as the excitation source and a deuterated triglycine sulfate (DTGS) detector in the 400−4000 cm−1 range. Spectral resolution was set at 4 cm−1. FT Raman Measurements. A Nicolet spectrometer (model NXR 9650) equipped with a liquid-nitrogen-cooled germanium detector was used for the FT Raman measurements to investigate the phosphonic acids on a glass plate. The 1064nm line from a continuous-wave Nd3+:YAG laser was used as an excitation source with a power output of 500 mW. During the measurements, 1000 scans were collected with a resolution of 4 cm−1. SERS Measurements. SERS active silver substrates were electrochemically roughened according to the standard procedure56 using a conventional three-electrode cell. The

Ii =

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C(ν0 − νi)4 Si −hν c ⎤ ⎡ νi−1⎢⎣1 − exp kTi ⎥⎦

( )



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Figure 1. FT Raman spectra (black solid line, experimental spectra; red dashed line, theoretical spectra) of m-PhS, p-PhS, o-PhR, m-PhR, and p-PhR in the range of 3650−400 cm−1.

in which Ii is given in arbitrary units, C is a constant equal to 10−12, ν0 is the laser excitation wavenumber (cm−1, 9398.5 cm−1 for a Nd:YAG laser), νi is the frequency of the normal mode obtained from the DFT calculation, Si is Raman scattering activity of the normal mode Qi calculated by DFT calculation, c is the speed of light, T is the temperature in Kelvin, and h and k are the Planck and Boltzmann constants, respectively. The calculated frequencies were scaled with scaling factor of 0.987 to better reproduce the experimental spectra. The GaussSum 0.8 free software package was used to check the outputs and generate theoretical Raman and IR spectra.61 The final step was to determine the potential energy distribution for all optimized structures with the Gar2ped freeware program62 implemented by additional program that took under consideration formation of H-bonding between two −B(OH)2 fragments (the 8-member atomic ring since one of the proton from each of −B(OH)2 moiety is not involved in the Hbonding; see structures of the dimers in Table 1) in conjunction with a specially written visualization script. The theoretical spectra were plotted by setting the fwhm (full width at half-maximum) to 11 cm−1, the average value of a typical fwhm for these compounds in the condensed phase with a 50%/50% Gaussian/Lorentzian band shape. While comparing the theoretical and experimental spectra, some shortcomings were observed because of the difference between the conditions included in the calculations and those in the experimental measurements. The spectra were measured for compounds in the solid state, and the calculations were performed for compounds in a vacuum. Despite these shortcomings, the approximation was sufficient to yield results comparable to the

experimental spectra, and the wavenumbers and intensities obtained from the experimental and theoretical spectra were in good agreement. Deconvolution Procedure. Deconvolution of the 1020− 950 cm−1 spectral region for the SERS spectra of the investigated compounds was conducted using a GRAMS/AI program (Galactic Industries Co., Salem, NH). A 50/50% Lorentzian/Gaussian band shape was assumed and fixed for all bands.

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RESULTS AND DISCUSSION FT Raman and DFT Studies. Figures 1 and 1S (see Supporting Information) show experimental (black solid lines) and theoretical (red dashed lines) FT Raman and FT IR spectra, respectively, of m-PhS, p-PhS, o-PhR, m-PhR, and pPhR in the spectral range between 400 and 3650 cm−1. According to the literature26,27 and our theoretical analysis of the N-benzylamino(boronphenyl)methyl-phosphonic acids, the most stable structure for the boronic acid derivatives is a cyclic dimer created by a pair of intermolecular hydrogen bonds between the boron hydroxyl groups of two monomers. Therefore, all calculations were performed and are presented for the dimers (red dashed line spectra in Figures 1 and 1S of Supporting Information). Table 1S in Supporting Information lists the experimental and calculated wavenumbers with the obtained potential energy distribution (PED, in %). As shown in Figures 1 and 1S of Supporting Information, the calculated wavenumbers and intensities for the investigated Nbenzylamino(boronphenyl)methylphosphonic acid dimers are in good agreement with the experimental values. In addition, 10007



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these, according to Y. Erdougdu and co-workers70 and S. Ayyappan and co-workers71 (theoretical calculation for phenylboronic acid derivative monomers using B3LYP hybrid density functional theory with 6-31++G(d,p) and 6-31G(d), 6-311+ +G(d,p) basis sets, respectively), the B−O stretching vibrations [ν(BO)] are expected to be enhanced in the spectrum at 1453−1450, 1384, and1369−1361 cm−1. Our calculations for dimers, using DFT/B3LYP at the 6-311G(d,p) level of theory, indicated that these vibrations appear at 1453−1450, 1445− 1440, 1434−1427, 1415−1404, 1401, and 1384−1383 cm−1. The ν(BO) vibrations also influence the bands at 1369−1360, 1349−1345, and 1010−1009 cm−1 (Table 1S of Supporting Information). As previously mentioned, in the solid state, the most stable structure of phenylboronic acid derivatives is a dimer that is formed by two hydrogen bonds between the boron hydroxyl groups of two monomers. These hydrogen bonds are manifested in the spectra by the deformation and torsion vibrations of the HOBO···H bridge. These bands are observed at 1369−1360, 1349−1343, 1338−1333, 1283−1279, 1178− 1168, 887, 879, 809−797, 778−776, 764−763, 745−735, 724− 721, 647−642, 639−632, 607−600, 599−582, 555−553, 536− 525, and 459−456 cm−1. In addition, the ρr(BO(H)H)bridge mode is enhanced at 1010−1009 and 999−996 cm−1, whereas the deformation vibrations of the HOBO···H fragment [δoop(BO(H)H)bridge] influence the 496−487 cm−1 band. The bands related to the −BOH deformation vibrations [δ(BOH)] (according to the literature70,71) appear in the spectral ranges of 1110−1090 and 1010−1009 cm−1. Our calculations indicated that bands observed in these ranges are due to the deformation/torsion vibrations of the HOBO···H bridge coupled with the ν(NC/CαN) mode [δ/γ(bridge)] + ν(NC/CαN)] and to the bending vibrations of the HOBO···H bridge [ρr(BO(H)H)bridge], respectively. S. Ayyappan and coworkers70 also suggested that bands due to the coupling of the B−C and B−O stretching vibrations [ν(BC/BO)] are observed at 809−797 cm−1. However, the calculations performed for dimers indicate that these bands can be assigned to the [δ/ γ(bridge)] vibrations. In contrast, Y. Erdougdu and co-workers70 indicated that the torsion vibrations from OBCC and HOBC/ OBCC fragments [γ(OBCC) and γ(HOBC/OBCC)] are present in the ranges of 738−735, 639−632, and 591−582 cm−1, respectively. Theoretical calculations provide evidence that the bands occurring in these spectral ranges are connected with torsion and deformation vibrations of the HOBO···H fragment. Additionally, according to the literature,70,71 the 536 cm−1 band may be assigned to the torsion vibrations of the −HOBC−, −HOBH−, and −HOBO− fragments [γ(HOBC)/ (HOBH)/(HOBO)], whereas our calculations indicated that these bands are due to the torsion vibrations of HOBO···H [δ(bridge)], the deformation of HOBO···H [γ(bridge)], and δoop(BO(H)H)bridge. The discrepancies in the band assignments may be due to the fact that Y. Erdougdu and co-workers70 and S. Ayyappan and co-workers71 presented results for phenylboronic acid derivative monomers, while we performed theoretical calculations for dimers. Imine Group Vibrations. In the FT IR spectra of the investigated molecules (Figure 1S of Supporting Information), the broad, strong band due to the imine group vibrations appears in the range of 3500−3437, 3337 cm−1. This band is associated with the N−H stretching mode [ν(NH)]. The broadness of this spectral feature can be explained by the

most of the FT Raman and FT IR bands for these compounds matched the spectral features of monosubstituted benzene and phenylboronic acids. Therefore, the literature data for the Raman and absorption infrared spectra of aromatic phosphonodipeptide analogues,63−66 benzene derivatives,67,68 and phenylboronic acid derivatives69−71 were also considered. We briefly discuss the FT Raman and FT IR bands that provide information regarding the molecular structures of the investigated compounds. This analysis is crucial for interpreting the SERS spectra discussed later in this work because the clear assignment of the SERS bands allows us to suggest an adsorption mode for the N-benzylamino(boronphenyl)-methylphosphonic acids onto an electrochemically roughened silver surface. Aromatic Vibrations. As expected, the FT Raman spectra (Figure 1) are dominated by bands arising from the aromatic ring vibrations. Some of these bands are seen in the corresponding FT IR spectra (Figure 1S of Supporting Information). These bands are associated with the ν2, ν8a, ν8b, ν18a, ν12, ν4, and ν6b modes (according to the Wilson numbering scheme)72 and appear at 3067−3044, 1634−1607, 1587−1574, 1038−1030, ∼1003, 700−698, and 630−619 cm−1, respectively (see Table 1S in the Supporting Information for the precise wavenumbers of these bands). For molecules that contain the boronic acid group in the meta position (m-PhS and m-PhR) a weak band is also observed at ∼1184 cm−1 due to the ν9a vibration (Figure 1S of Supporting Information). Because these bands are well described in the literature,45,63−66,73−75 we omitted a detailed discussion here. However, significant changes can be observed in the relative intensities of the three bands assigned to the ν8a, ν18a, and ν12 modes. For o-PhR, the ν8a mode exhibited the weakest relative intensity compared with other molecules, whereas the band characteristics for ν18a and ν12 had the strongest intensities in the spectrum. For mPhS and m-PhR, the relative intensity of ν18a was noticeably lower compared with that of o-PhR, but the relative intensities of ν8a and ν12 were strengthened. The same situation can be found for p-PhS and p-PhR. However, for p-PhS the ν12 band exhibited only a slight relative intensity. In Table 1S of Supporting Information we showed proposed assignments of the bands based on our calculations. From this table it is clearly seen that there are several vibrations with different PEDs (this is due to phenyl rings substituted in orto, meta, or para positions plus different conformations of each dimer) that have almost the same frequencies in each of the investigated compound. Thus, observed Raman (as well as SERS bands) are the results of overlapping of existing in these regions vibrations. Please note that each dimer consists of a mono- (N-benzylamino-) and disubstistuted benzene ring besides of a spacer (i.e., methylphosphonic acid). This complexity causes not only frequency but also intensity changes of certain (normal) Raman bands of each compound. This situation influences strongly SERS band intensities and frequencies due to selective (different) enhancement of these Raman (IR) “component” vibrations that will be discussed further in the paper. To simplify this situation we assigned frequencies in the 1634−1607, 1587−1574, and 1005−995 cm−1 ranges to the most recognizable ν8a, ν18a, and ν12 modes of phenyl ring. Boronic Acid Group Vibrations. In the vibrational spectra of the investigated N-benzylamino(boronphenyl)methylphosphonic acids, several medium- and weak-intensity bands appeared due to the boronic acid group vibrations. From 10008



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Figure 2. SERS spectra of m-PhS, p-PhS, o-PhR, m-PhR, and p-PhR adsorbed onto an electrochemically roughened silver surface in the range of 1850−400 cm−1 (inset: deconvolution of the ν12 band with a summary of the deconvoluted wavenumbers and fwhm).

Methylene and Methine Group Vibrations. The CH2 and CH groups’ stretching vibrations exhibit strong spectral features in the high wavenumber range of the vibrational spectra (3079, 3034−3024, 3011−2983, 2959− 2929, and 2900−2895 cm−1 for the ν(CH) of CH2; 3017, 3004−2999, 2990, 2942, 2919−2909, and 2878−2873 cm−1 for the ν(CαH) of CαH). The twisting vibrations of the NC(H)2CL fragment [ρt(NC(H)2CL)] appear at 1246− 1243 and 1232−1230 cm−1. In contrast, the twisting and rocking modes of this molecular fragment [ρt/ρr(NC(H)2CL)] contributed to the 1331−1328 and 1325−1316 cm−1 bands and the 1040−1037, 918, 884, 899−897, and 894 cm−1 bands, respectively. In addition, the scissoring vibrations of the same fragment [ρs(NC(H)2CL)] were observed at 1506−1503, 1473, 822, 816−814, and 602−597 cm−1. SERS Studies. Figure 2 shows the SERS spectra of the investigated N-benzylamino(boronphenyl)methyl-phosphonic acidsm-PhS, p-PhS, o-PhR, m-PhR, and p-PhRadsorbed onto an electrochemically roughened silver surface. The spectra, taken with 514.5-nm excitation in the spectral region of 1850−500 cm−1, were normalized to the most intense band. The proposed SERS band assignments to the normal coordinates, based on the DFT calculations, are given in Table 2 together with the observed wavenumbers. To support the discussion of the results, we have considered a number of related adsorbate systems to allow for the identification of a mode of interaction for the investigated molecules with the electrochemically roughened silver substrate. In particular, a

formation of intermolecular and/or intramolecular hydrogen bonds between the −PO3H2, −NH−, and −BOH groups. The C−N stretching vibrations [ν(NC) and ν(CαN)] were observed at 1110−1089 cm−1 in the FT Raman (Figure 1) and FT IR (Figure 1S of Supporting Information) spectra (Table 1S of Supporting Information). The deformation modes of the CαN(H)C fragment are also enhanced at 1050−1036 cm−1. In contrast, the bending vibrations of the CαN(H)C fragment [ρr(CαN(H)C)] contribute to the bands at 1506− 1503 and 1235−1230 cm−1. In addition, the ν(NC) and ν(CαN) vibrations influence the bands at 1086 and 1076−1063 cm−1. Phosphonate Group Vibrations. The presence of the −PO3H2 group is manifested in the vibrational spectra at 1270−1269, 1264−1252, 1048, 1018−1011, 918, 899−897, 877−859, 840, 833−824, 496−487, 481−478, 474, 460, and 724−717 cm−1 (Figure 1 and Figure 1S of Supporting Information). The 1270−1269 and 1264−1252 cm−1 bands are primarily due to the PO stretching vibrations [ν(PO)], whereas the 1048 and 1018−1011 cm−1 bands are assigned to the ν(PO) + ρb(POH) modes. In contrast, δs(CαPO3) was enhanced at 496−487, 481−478, 474, and 460 cm−1. The coupled ν(PO) + ρb(POH) + ν(CαP) vibrations are present at 840 and 833−824 cm−1. The ν(PO) vibrations appear at 918 and 877−859 cm−1 and contributed to the band at 899−897 cm−1. Moreover, the ν(CαP) mode was observed at 724−717 cm−1. 10009



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Table 2. Wavenumbers and Suggested Band Assignments for the SERS Spectra of m-PhS, p-PhS, o-PhR, m-PhR, and p-PhR Adsorbed onto an Electrochemically Roughened Silver Substrate wavenumbers/cm−1

assignments based on work

m-PhS

p-PhS

o-PhR

m-PhR

582 630 688

578

561 628

556 630 689

703

699

715 786

786

825 991 1034 1086

845 992 1032

854 999 1042

991 1034 1078

997 1031 1072

1142 1161 1190 1210 1301

1186 1225 1271

1287 1338

1215 1300

1283

1364 1398 1451

1405 1475 1568 1601

1473 1503 1567 1599

1572 1607

DFT/B3LYP calculation of Raman spectra, this worka

p-PhR

1567 1601

1572 1606

literature63−72

δp/δs/δas/γs/γas(bridge), δas(ϕ)B δas(ϕ), δp(bridge) δas(ϕ)B/δp(ϕ), δoop(CC(H)C)ϕ δoop(CBO2), δp(bridge), δas/δp(ϕ)B, δoop(CLCB(OH)2(B)C)ϕB, ν(CB) δp(ϕ)B, δoop(CB(OH)2CL(Cα)C)ϕB, δoop(CLCB(OH)2(B)C)ϕB ν(PO), δoop(CC(H)C)ϕB δoop(CLC(H)C)ϕ/(CC(H)C)ϕ δtrig(ϕ)B/δtrig(ϕ), ν(CC)ϕB/ν(CC)ϕ ν(CC)ϕ, δtrig(ϕ), ρr(CC(H)C)ϕ/(CLC(H)C)ϕ ν(CC)ϕB, ν(NC)/(CαN), ρr(CB(OH)2C(H)C)ϕB/(CC(H)CL)ϕB ν(CαN)/(NC), δoop(CαN(H)C) ρb(POH), ν(PO), ρr(CC(H)C)ϕB/(CC(H)CL)ϕB/ρr(CB(OH)2C(H)C)ϕB, ν(CC)ϕB, ρr(CC(H)C)ϕB/(CC(H)CL)ϕB/(CB(OH)2C(H)C)ϕB, ν(CC)ϕB/(CCL)ϕB ρr(CB(OH)2C(H)C)ϕB, ν(PO), ν(CLCα)/(CC)ϕB/(CCL)ϕB, δtrig(ϕ)B ν(PO), δp/γas/γs(bridge), ν(CC)ϕB δp/γs/γas(bridge) ρw(NC(H)2CL), δp/γas/(bridge), ν(BO) ν(BO), ρr(CC(H)CL)ϕB, ν(CC)ϕB ν(BO), ν(CCL)ϕB, ρr(CC(H)CL)ϕB ρr(CC(H)CL)ϕB, ν(CCL)ϕB ρr(CαN(H)C) ν(CC)ϕB,ρr(CC(H)C)ϕB ν(CC)ϕB, ρr(CC(H)C)ϕB/ ν(CC)ϕ, ρr(CLC(H)C)ϕ

γ(HOBC)/ (HOBO) Phe(ν6b) Phe(ν4) Phe(ν1) ν(PO) and/or Phe(ν10a) Phe(ν12) Phe(ν18a) Phe(ν18b), and/or ν(NC) Phe(ν9b) and/or ν(PO) Phe(ν9a/15) Phe(ν7) Phe(ν4) ν(BO), ν(BC), δ(BOH), and/or ρb(HOB) ρw(CH2) and/or ν(BO) ν(BO) Phe(ν19b) and/or ν(BO)

Phe(ν8b) Phe(ν8a)

a Abbreviations: ν, stretching; ρb, bending; ρs, scissoring; ρt, twisting; ρw, wagging; δ, deformation; γ, torsion; p, puckering; δtrig, trigonal deformation; s, symmetric; as, antisymmetric; oop, out-of-plane; i.p., in-plane; ϕ, aromatic ring; B, phenylboronic acid ring; bridge, hydrogen bonds HOBO···H; CL, carbon atom of the aromatic ring connected to the aliphatic chain.

Table 3. Summary of Wavenumbers and Full Width at Half Maximum for the Phenyl FT Raman and SERS Bands of m-PhS, pPhS, o-PhR, m-PhR, and p-PhR Adsorbed onto an Electrochemically Roughened Silver Substrate m-PhS

p-PhS

RS

SERS

RS

fwhm [cm−1]

ν [cm−1]

fwhm [cm−1]

ν [cm−1]

fwhm [cm−1]

620 1003 1030 1184 1586 1607

4 7 6 13 8 10

630 991 1034

20 21 26

1568 1601

52 39

631 1003 1031 1191 1587 1611

4 4 6 7 6 7

ν6b ν12 ν18a ν9a/15 ν8b ν8a

o-PhR

ν [cm−1]

SERS

RS

SERS

fwhm [cm−1]

992 1032 1190 1572 1607 p-PhR

m-PhR

RS

ν6b ν12 ν18a ν9a/15 ν8b ν8a

SERS

ν [cm−1]

18 30 25 21 24

RS

SERS

ν [cm−1]

fwhm [cm−1]

ν [cm−1]

fwhm [cm−1]

ν [cm−1]

fwhm [cm−1]

ν [cm−1]

fwhm [cm−1]

ν [cm−1]

fwhm [cm−1]

ν [cm−1]

fwhm [cm−1]

620 1003 1038 1191 1587 1608

4 9 12 13 5 8

628 999 1042

17 16 31

17 21 26

9 11

4 4 6 11 6 10

630 991 1034

1567 1599

620 1003 1031 1185 1586 1607

1567 1601

51 28

619 1003 1031 1191 1586 1613

4 4 6 10 4 6

997 1031 1186 1572 1606

27 27 30 16 19

phenylboronic acid derivatives69−71 served as a reference system for the interaction of the investigated compounds with the substrate. Group theory provides the most elegant framework for applying the metal−surface selection rule to the adsorbed molecules.76 We can make the following two assumptions: (1)

comparison with the constituent functional groups enables us to characterize important changes in the bonding properties of the larger system. Thus, the phenylalanine phosphonodipeptide molecules deposited onto the same substrate provide information on the how the ring and methyl groups interact with the substrate.63−67 Finally, benzene derivatives67,68 and 10010



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position of the phenyl ring is directed out of the substrate surface. Some differences were also observed among the SERS spectra in the relative intensities of the ν6b, ν8a, ν8b, ν9a/15, ν18a, and ν12 signals (Figure 2). The relative intensity variations were also noticed between the corresponding SERS and FT Raman spectra. For example, the ν12 SERS signal (the A1 point symmetry group) decreased in relative intensity in comparison with that in the corresponding m-PhS, m-PhR, and p-PhR FT Raman spectra (the relative intensity of ν12 (Iν12) decreased in the following order: m-PhR > m-PhS > p-PhR), whereas p-PhS and o-PhR exhibited comparable SERS and FT Raman scattering. This result may indicate a surface interaction in accordance with the somewhat vertical orientation of the phenyl ring(s) of p-PhS and o-PhR on the silver surface and with a tilted arrangement of the phenyl ring(s) of m-PhR, mPhS, and p-PhR with respect the substrate. This conclusion is supported by the stronger SERS enhancement of the ν6b mode (630 cm−1, B2) in comparison with the FT Raman enhancement of this spectral feature for m-PhR, m-PhS, and p-PhR. In addition, based on the alterations in the relative intensity of ν12 between m-PhR, m-PhS, and p-PhR, the angle at which the phenyl ring tilts from the substrate normal was found to increase in the following order: p-PhR > m-PhS > m-PhR. The ν8a (1607−1599 cm−1, A1) and ν8b (1572−1567 cm−1, B2) SERS and FT Raman spectral features (see Table 2 for precise band wavenumbers) also indicated the comparable relative intensities for m-PhS and p-PhS. For p-PhR and m-PhR, the ν8a and ν8b SERS bands were stronger that those in the FT Raman spectra. In the SERS spectrum of p-PhR, the 1572-cm−1 band distinctly increased in its relative intensity in comparison with the corresponding FT Raman signal and became the strongest band in the spectrum. Therefore, given the SERS excitation profiles of the monosubstituted benzene that show that the enhancement of the ring vibrations may be due to both electromagnetic (EME) and chemical mechanisms (CE),76 one can conclude that the CE mechanism plays an essential role in p-PhR. Given the selection rules of the EME mechanism, the completely symmetric ring modes should be most enhanced when the Phe ring is nearly perpendicular to the metal surface. In contrast, the contribution of the CE mechanism to the enhancement is manifested by the strong band enhancement of the ν8 mode. Among several bands of the phosphonate group that our calculations located in the 1850−400 cm−1 spectral region, three are enhanced in the o-PhR and p-PhS SERS spectra (Figure 2)the PO stretching at higher and lower wavenumbers, the −POH bending, and the P−O stretching. These modes, observed at ∼1271, ∼1225, ∼1161, and ∼854 cm−1, respectively, are relatively weak indicating that oxygen (O) and hydroxyl (OH) groups of the phosphonate groups of o-PhR and p-PhS only assist in the molecular interactions with the substrate and the phosphonate groups of m-PhS, m-PhR, and p-PhR are moved away from the silver substrate. Similarly, the o-PhR SERS spectrum indicates that the B−O stretching (1451, 1398, and 1364 cm−1) is weakly enhanced, suggesting that the −B(OH)2 group of only o-PhR is in proximity to the substrate. This is the first report of such enhancement and will be further investigate in the future. Additionally, the presence of the CαN(H)C fragment is manifested in the o-PhR spectra by a medium-intensity band at ∼1503 cm−1 [ρr(CαN(H)C)] suggesting that the NH

the surface selection rules and (2) the vibrations involving atoms close to the silver surface will be enhanced due to their interactions with the metal surface, and this enhancement will affect the observed SERS signal of the adsorbed molecule, leading to the possibility of significant shifts. Under these assumptions, the analysis of the intensities, broadness, and position shifts of most of the visible SERS spectral features, assigned to fundamental vibrations as shown in Table 2, can be used to predict the geometries of the adsorbed N-benzylamino(boronphenyl)methyl-phosphonic acids. For example, for a perpendicular phenyl ring orientation, the in-plane vibrations should be enhanced to a greater extent than the out-of-plane vibrations. Therefore, for a flat ring orientation, the A2 symmetry vibrations will contain a larger polarizability tensor component normal to the surface than the B2 modes, whereas the opposite should be the case for the vertical adsorption geometry. In addition, for π adsorption, the bands of the phenyl ring that involve the C−C stretching vibrations move to lower frequencies due to the anticipated back-donation of electron density from the metal surface to the π* antibonding orbitals of the phenyl ring.77 Gao and Weaver reported that the ν12 and ν18a modes of alkylobenzenes shift down by 10−15 cm−1 upon adsorption. In contrast, the observed downshift by 4−5 cm−1 for the corresponding modes of halogenobenzenes was interpreted as evidence of no direct interaction between the π-electron systems and the metal surface. In addition, significant band broadening for the phenyl ring modes was reported in the case of π adsorption caused by an interaction between the phenyl ring and the metal surface.77 The SERS spectra presented for the N-benzylamino(boronphenyl)methylphosphonic acids show an analogy in the types of enhanced bands, which are mainly due to the phenyl ring vibrations, i.e., the ν6b, ν8a, ν8b, ν9a/15, ν18a, and ν12 modes, potentially indicating that the investigated compounds interact with the substrate through the phenyl ring(s). The broadening of the bandwidths for these modes and the downshifting in these bands’ wavenumbers in comparison with those in the FT Raman spectra (provided in Table 3) support this statement. The especially high bandwidth of the ν12 spectral feature (fwhm = 16−27 cm−1) implies that the π-electron system of the benzene ring(s) is adsorbed onto the electrochemically roughened silver surface. However, the asymmetric shape of this band for p-PhS, o-PhR, and p-PhR implies that two phenyl rings participate in the interaction with the silver substrate. This observation was confirmed by the deconvolution procedure of the ν12 band (see inset in Figure 2) that indicated the presence of two sub-bands at ∼990 (fwhm = ∼15 cm−1) and ∼1002 cm−1 (fwhm = ∼11 cm−1) that could be assigned to both the phenyl and boronphenyl rings interacting with the silver substrate. In the case of o-PhR, the 990-cm−1 sub-band (Δν12 = −13 cm−1 and Δfwhm = +6 cm−1 for FT Raman → SERS) is connected to the adsorbed boronphenyl ring on the electrochemically roughened silver substrate, whereas the 1002-cm−1 sub-band (Δν12 = −1 cm−1 and Δfwhm = +2 cm−1 for FT Raman → SERS) is due to the interaction between the phenyl ring and this substrate (inset in Figure 2). This conclusion was based on the observed features in the oPhR SERS spectrum arising from the boronic acid group (see below) present at the ortho position of the phenyl ring. For the remaining compounds, distinguishing which ring adsorbs and which interacts with the silver substrate surface is difficult because the boronphenyl ring could be oriented onto the substrate such that the boronic acid group at the meta or para 10011



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Figure 3. Suggested orientations for m-PhS, p-PhS, o-PhR, m-PhR, and p-PhR on an electrochemically roughened silver surface.

metal surface. For o-PhR, an interaction between the  B(OH)2 group and the substrate was also suggested.

groups of o-PhR are in close proximity to the electrochemically roughened silver substrate. A possible manner of binding between the electrochemically roughened silver surface and m-PhS, p-PhS, o-PhR, m-PhR, and p-PhR is provided in Figure 3.

■

ASSOCIATED CONTENT

S Supporting Information *

■

A figure depicting the FT IR spectra of m-PhS, p-PhS, o-PhR, m-PhR, and p-PhR in the range of 3650−400 cm−1 and a table depicting the calculated and experimental wavenumbers and the potential energy distribution for the FT Raman and FT IR spectra of the investigated compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

CONCLUSIONS We presented the first detailed vibrational characterization of five analogues of N-benzylamino(boronphenyl)methylphosphonic acids based on DFT calculations (B3LYP theory level with the 6-311G(d,p)) and the literature.63−71 We also discussed the mode of adsorption for the investigated compounds immobilized onto an electrochemically roughened silver surface. We demonstrated that the investigated molecules interact with the silver substrate surface through both aromatic rings. In the case of o-PhR, the boronphenyl ring adsorbed onto the substrate, whereas the phenyl ring interacted with it. For the remaining compounds, distinguishing between which ring adsorbed and which interacted with the silver substrate surface was difficult because the boronphenyl ring could be oriented onto the substrate in such a way that the boronic acid group at the meta or para position of the phenyl ring was directed out of the substrate surface. For the investigated compounds, the orientation of the aromatic rings onto the silver surface was also determined. For m-PhS, m-PhR, and p-PhR the adsorbed aromatic ring was tilted with regard to the silver surface, although with different angles between the planes of the aromatic rings and the surface. The angles increased in the following order: p-PhR > m-PhS > m-PhR. In contrast, the aromatic ring(s) of p-PhS and o-PhR adopted more or less vertical orientations onto the metal surface. Although the interaction of o-PhR and p-PhS with the electrochemically roughened silver surface was suggested by the phenyl rings, the phosphonate oxygen O and hydroxyl OH groups assisted in the adsorption process. For m-PhS, m-PhR, p-PhS, and pPhR, the phosphonate group was located at a distance from the

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +48-12-6632077. Fax: +48-12-634-0515. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Research Center of the Ministry of Science and Higher Education (Grant No. N N204 544339 to E.P.). Y. Kim gratefully acknowledges HUFS for financial support. The authors kindly acknowledge the Academic Computer Center “Cyfronet” in Krakow for computational facilities.

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REFERENCES

(1) Bandurina, T. A; Konyukhov, N. V.; Ponomareva, O. A.; Barybin, A. S.; Pushkareva, Z. V. Pharm. Chem. J. 1978, 11, 1428−1431. (2) Mucha, A.; Drag, M.; Dalton, J. P.; Kafarski, P. Biochimie 2010, 92, 1509−1529. (3) Kettner, Ch. A.; Shenvi, A. B. J. Biol. Chem. 1984, 259, 15106− 15114. (4) Lejczak, B.; Kafarski, P.; Sztajer, H.; Mastalerz, P. J. Med. Chem. 1986, 29, 2212−2217. 10012



Article

(39) Podstawka, E.; Kafarski, P.; Proniewicz, L. M. J. Phys. Chem. A 2008, 112, 11744−11755. (40) Podstawka-Proniewicz, E.; Piergies, N.; Skołuba, D.; Kafarski, P.; Kim, Y.; Proniewicz, L. M. J. Phys. Chem. A 2011, 115, 11067−11078. (41) Cialla, D.; Marz, A.; Bohme, R.; Theil, F.; Weber, K.; Schmitt, M.; Popp, J. Anal. Bioanal. Chem. 2011, 403, 27−54. (42) Koglin, E.; Sequaris, J.-M. Top. Curr. Chem. 1986, 134, 1−57. (43) Nabiev, I. R.; Sokolov, K. V.; Manfait, M. In Biomolecular spectroscopy part A; Clark, R. J. H., Hester, R. E., Eds.; John Willey and Sons: New York, 1993, p 267. (44) Creighton, J. A. Surf. Sci. 1983, 124, 209−219. (45) Gao, X.; Davies, J. P.; Weaver, M. J. J. Phys. Chem. 1990, 94, 6858−6864. (46) Lombardi, J. R.; Birke, R. L. J. Phys. Chem. C 2008, 112, 5605− 5617. (47) Podstawka-Proniewicz, E.; Sobolewski, D.; Prahl, A.; Kim, Y.; Proniewicz, L. M. J. Raman Spectrosc. 2012, 43, 51−60. (48) Podstawka, E.; Ozaki, Y.; Proniewicz, L. M. Appl. Spectrosc. 2004, 58, 1147−1156. (49) Kaminska, A.; Inya-Agha, O.; Forster, R. J.; Keyes, T. E. Phys. Chem. Chem. Phys. 2008, 10, 4172−4180. (50) Liron, Z.; Zifman, A.; Heleg-Shabtai, V. Anal. Chim. Acta 2011, 703, 234−238. (51) Li, T.; Liu, D.; Wang, Z. Biosens. Bioelectron. 2009, 24, 3335− 3339. (52) Podstawka, E. J. Raman Spectrosc. 2008, 39, 1290−1305. (53) Podstawka, E.; Kudelski, A.; Olszewski, T. K.; Boduszek, B. J. Phys. Chem. B 2009, 113, 10035−10042. (54) Podstawka, E.; Drąg, M.; Oleksyszyn, J. J. Raman Spectrosc. 2009, 40, 1564−1571. (55) Młynarz, P.; Rydzewska, A.; Pokładek, Z. J. Organomet. Chem. 2011, 696, 457−460. (56) Podstawka, E.; Kudelski, A.; Drąg, M.; Olekszyszyn, J.; Proniewicz, L. M. J. Raman Spectrosc. 2009, 40, 1578−1584. (57) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision A.01; Gaussian, Inc.: Wallingford, CT, 2004. (58) Jensen, F. Introduction to Computational Chemistry; John Wiley and Sons, Ltd.: Chichester, ; p 192. (59) Jezierska, A.; Panek, J. J.; Ż ukowska, G. Z.; Sporzyński, A. J. Phys. Org. Chem. 2010, 23, 451−460. (60) Michalska, D.; Wysokiński, R. Chem. Phys. Lett. 2005, 403, 211− 217. (61) O’Boyle, N. M.; Vos, J. G. GaussSum 0.8, Dublin City University: Dublin, 2004. Available at http://gausssum.sourceforge. net. (62) Martin, J. L. M.; Van Alsenoy, C. Gar2ped; University of Antwerp: Antwerp, 1995. (63) Podstawka, E.; Kozłowski, H.; Proniewicz, L. M. J. Raman Spectrosc. 2006, 37, 574−584. (64) Podstawka, E.; Borszowska, R.; Grabowska, M.; Drąg, M.; Kafarski, P.; Proniewicz, L. M. Surf. Sci. 2005, 599, 207−220. (65) Podstawka, E.; Kudelski, A.; Proniewicz, L. M. Surf. Sci. 2007, 601, 4971−4983.

(5) Skinner-Adams, T. S.; Stack, C. M.; Trenholme, K. R.; Brown, Ch. L.; Grembecka, J.; Lowther, J.; Mucha, A.; Drag, M.; Kafarski, P.; McGowan, S.; Whisstock, J. C.; Gardin, D. L.; Dalton, J. P. Trends Biochem. Sci. 2009, 35, 53−61. (6) Pawełczak, M.; Nowak, K.; Kafarski, P. Phosphorus Sulfur 1998, 132, 65−71. (7) Lejczak, B.; Kafarski, P. Top Heterocycl. 2009, 20, 31−63. (8) Beers, S. A.; Schwender, C. F.; Loughney, D. A.; Malloy, E.; Demarest, K.; Jordan, J. Bioorg. Med. Chem. 1996, 4, 1693−1701. (9) Vovk, A. I.; Mischenko, I. M.; Tanchuk, V. Yu.; Kachkovskii, G. A.; Sheiko, S. Yu.; Kolodyazhnyi, O. I.; Kukhar, V. P. Bioorg. Med. Chem. Lett. 2008, 18, 4620−4623. (10) Tomsho, J. W.; Benkovic, S. J. J. Org. Chem. 2012, 77, 2098− 2106. (11) Dowlut, M.; Hall, D. G. J. Am. Chem. Soc. 2006, 128, 4226− 4227. (12) Sharrett, Z.; Gamsey, S.; Levine, P.; Cunningham-Bryant, D.; Vilozny, B.; Schiller, A.; Wessling, R. A.; Singaram, B. Tetrahedron Lett. 2008, 49, 300−304. (13) Adamczyk-Woźniak, A.; Brzózka, Z.; Cyrański, M. K.; Filipowicz-Szymań s ka, A.; Klimentowska, P.; Ż u browska, A.; Ż ukowski, K.; Sporzyński, A. Appl. Organomet. Chem. 2008, 22, 427−432. (14) Leung, D.; Abbenante, G.; Fairlie, D. P. J. Med. Chem. 2000, 43, 305−341. (15) Zhong, S.; Haghjoo, K.; Kettner, Ch.; Jordan, F. J. Am. Chem. Soc. 1995, 117, 7048−7055. (16) Katz, B. A.; Finer-Moore, J.; Mortezaei, R.; Rich, D. H.; Stroud, R. M. Biochemistry 1995, 34, 8264−8280. (17) Asano, T.; Nakamura, H.; Uehara, Y.; Yamamoto, Y. Chem. Bio. Chem. 2004, 5, 483−490. (18) Nakamura, H.; Horikoshi, R.; Usui, T.; Ban, H. S. Med. Chem. Commun. 2010, 1, 282−286. (19) Zhang, J.; Yang, P. L.; Gray, N. S. Cancer 2009, 9, 28−39. (20) Tsatsanis, Ch.; Spandidos, D. A. Int. J. Mol. Med. 2000, 5, 583− 590. (21) Giles, N. M.; Giles, G. I.; Jacob, C. Biochem. Bioph. Res. Co. 2003, 300, 1−4. (22) Watson, Ch. J.; Kreuzaler, P. A. J. Mammary. Gland. Biol. Neoplasia 2009, 14, 171−179. (23) Bell-McGuinn, K. M.; Garfall, A. L.; Bogyo, M.; Hanahan, D.; Joyce, J. A. Cancer Res. 2007, 67, 7378−7385. (24) Pearson, M. A.; Fabbro, D. Expert Rev. Anticancer Ther. 2004, 4, 1113−1124. (25) Gorzalczany, Y.; Gilad, Y.; Amihai, D.; Hammel, I.; SagiEisenberg, R.; Merimsky, O. Cancer Lett. 2011, 310, 207−215. (26) Cyrański, M. K.; Jezierska, A.; Klimentowska, P.; Panek, J. J.; Sporzyński, A. J. Phys. Org. Chem. 2008, 21, 472−482. (27) Sporzyński, A. Pol. J. Chem. 2007, 81, 757−766. (28) Kneipp, K. Phys. Today 2007, 60, 40−46. (29) Larkin, P. J. IR and Raman spectroscopy. In Principles and spectral interpretation; Elsevier: Amsterdam, 2011; p 1. (30) Agarwal, U. P.; Atalla, R. H. In Surface analysis of paper; Conners, T. E., Banerjee, Sukit, Eds.; CRC Press: Boca Raton, 1995, p 152. (31) Geiman, I.; Leona, M.; Lombardi, J. R. J. Forensic. Sci. 2009, 54, 947−952. (32) Moricz, A. M.; Horvath, E.; Ott, P. G.; Tyihak, E. J. Raman Spectrosc. 2008, 39, 1332−1337. (33) Kubelka, J.; Keiderling, T. A. J. Am. Chem. Soc. 2001, 123, 12048−12058. (34) Bichara, L. C.; Bimbi, M. V. F.; Gervasi, C. A.; Alvarez, P. E.; Brandan, S. A. J. Mol. Struct. 2012, 1008, 95−101. (35) Wei-Ning, W.; Guo, W.; Yan, Z. Chin. Phys. B 2011, 20, 1−5. (36) Fu, A.; Du, D.; Zhou, Z. Spectrochim. Acta A 2003, 59, 245−253. (37) Baek, K. Y.; Fujimura, Y.; Hayashi, M.; Lin, S. H.; Kim, S. K. J. Phys. Chem. A 2011, 115, 9658−9668. (38) Podstawka-Proniewicz, E.; Andrzejak, M.; Kafarski, P.; Kim, Y.; Proniewicz, L. M. J. Raman Spectrosc. 2011, 42, 958−979. 10013



Article

(66) Podstawka, E.; Kudelski, A.; Kafarski, P.; Proniewicz, L. M. Surf. Sci. 2007, 601, 4586−4597. (67) Varsanyi, G. Assignments for Vibrational Spectra of Seven Hundred Benzene Derivatives; Academic Kiado: Budapest, 1973; Vol. 1. (68) Chalmers, J. M.; Griffiths, P. R. Handbook of Vibrational Spectroscopy; John Wiley & Sons, Ltd.: Chichester, 2002; Vol.3, Chapter 9, pp 1885−1892. (69) Kurt, M.; Sertbakan, T. R.; Ozduran, M. Spectrochim. Acta A 2008, 70, 664−673. (70) Erdogdu, Y.; Gulluoglu, M. T.; Kurt, M. J. Raman Spectrosc. 2009, 40, 1615−1623. (71) Ayyappan, S.; Sundaraganesan, N.; Kurt, M.; Sertbakan, T. R.; Ozduran, M. J. Raman Spectrosc. 2010, 41, 1379−1387. (72) Wilson, E. B., Jr. Phys. Rev. 1934, 45, 706−714. (73) Bae, S. J.; Lee, Ch.; Choi, I. S.; Hwang, Ch.-S.; Gong, M.; Kim, K.; Joo, S. W. J. Phys. Chem. B 2002, 106, 7076−7080. (74) Joo, S. W.; Han, S. W.; Kim, K. J. Phys. Chem. B 1999, 103, 10831−10837. (75) Moskovits, M.; DiLella, D. P.; Maynard, K. J. Langmuir 1988, 4, 67−76. (76) Castro, J. L.; Lopez Ramirez, M. R.; Lopez Tocon, I.; Otero, J. C. J. Col. Interf. Sci. 2003, 263, 357−363. (77) Gao, X.; Weaver, M. J. J. Phys. Chem. 1985, 89, 5040−5046.

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