FT‐IR,FT‐Raman and SERS spectra of anilinium sulfate

The FT‐IR and FT‐Raman spectra of anilinium sulfate were recorded and analyzed. The surface‐enhanced Raman scattering (SERS) was recorded from a silver electrode. The vibrational wavenumbers of the compound have been computed using the Hartree‐Fock/6‐31G* basis and compared with the experimental values. The molecule is adsorbed on the silver surface with the benzene ring in a tilted orientation. The presence of amino and sulfate group vibrations in the SERS spectrum reveal the interaction between amino and sulfate groups with the silver surface. The direction of the charge transfer contribution to SERS has been discussed from the frontier orbital theory. Copyright © 2009 John Wiley & Sons, Ltd.     

IR,Raman and SERS spectra of ethyl salicylate

The IR and Raman spectra of ethyl salicylate were recorded and analyzed. The surface enhanced Raman scattering (SERS) spectrum was recorded in a silver colloid. The vibrational wavenumbers of the compound have been computed using the Hartree‐Fock/6‐31G* basis. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface and the presence of ring vibrations and out‐of‐plane ring modes in the SERS spectrum suggests a flat orientation of the molecule on the silver surface. The first hyperpolarizability is calculated and the calculated molecular geometry has been compared with the reported similar structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectroscopic investigations and computational study of sulfur trioxide–pyridine complex

The Fourier transform infrared (FT‐IR) and FT‐Raman spectra of sulfur trioxide‐pyridine complex were recorded and analyzed. The potential‐dependent surface‐enhanced Raman scattering (SERS) was recorded from an electrochemically roughened silver electrode. The vibrational wave numbers of the compound were computed using the Hartree–Fock/6‐31G* basis and compared with the experimental values. The presence of strong pyridine ring vibrations in the SERS spectrum reveals the interaction between the pyridine ring and the silver surface. The molecule is adsorbed on the silver surface with the pyridine ring in a tilted orientation. The direction of charge‐transfer contribution to the SERS is discussed from the frontier orbital theory. The value of the calculated first hyperpolarizability is comparable to those reported for similar structures, which makes this molecule an attractive object for future studies of nonlinear optics. The optimized geometrical parameters of the title compound are in agreement with similar reported structures. Copyright © 2011 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman,SERS spectra and computational calculations of 4‐ethyl‐N‐(2′‐hydroxy‐5′‐nitrophenyl)benzamide

Fourier transform infrared (FT‐IR) and FT‐Raman spectra of 4‐ethyl‐N‐(2′‐hydroxy‐5′‐nitrophenyl)benzamide were recorded and analyzed. A surface‐enhanced Raman scattering (SERS) spectrum was recorded in silver colloid. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red shift of the NH stretching wavenumber in the infrared spectrum from the computational wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO stretching mode gives the charge transfer interaction through a π‐conjugated path. The presence of methyl modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface, which affects the orientation and metal molecule interaction. The first hyperpolarizability and predicted infrared intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive subject for future studies of nonlinear optics. Optimized geometrical parameters of the title compound are in agreement with reported structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies and computational study of methyl(2‐methyl‐4,6–dinitrophenylsulfanyl)ethanoate

FT‐IR and FT‐Raman spectra of methyl(2‐methyl‐4,6–dinitrophenylsulfanyl)ethanoate (MDIE) were recorded and analyzed. Surface‐enhanced Raman scattering (SERS) spectra were recorded in silver colloid and silver electrode. The vibrational wavenumbers were computed using HF/6‐31G* and B3LYP/6‐31G* basis. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in infrared and Raman spectroscopies as well as in SERS of the studied molecule. The first hyperpolarizability and infrared intensities are reported. The geometrical parameters of the title compound are in agreement with the reported similar derivatives. The presence of new bands at 1045 and 948 cm⁻¹ in the SERS spectrum in silver electrode is related to the change in orientation of the molecule with respect to the metal surface. In silver colloid SERS spectrum, the methyl group attached to the methoxy carbonyl group is close to the metal surface, whereas on silver electrode the methyl group attached to the phenyl ring is close to the metal surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Concentration and pH dependent SERS spectra of sulfanilic acid sodium salt on colloidal silver particles

IR, Raman and surface‐enhanced Raman scattering (SERS) spectra of sulfanilic acid sodium salt (SANA) were recorded and analysed. The vibrational wavenumbers were computed by the density functional theory method using the B3LYP/6–31G* basis and found to be in good agreement with the experimental values. The effect of concentration and pH dependence on the SERS intensity of the molecule was also studied. The molecular plane assumes a tilted orientation with respect to the silver surface. The observed changes of the relative intensities of some enhanced bands and the presence of in‐plane and out‐of‐plane modes of the phenyl ring suggest that the molecule assumes a more tilted orientation upon lowering the concentration of the adsorbate. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering and density functional theory studies of bis(4‐aminophenyl)sulfone

Raman and surface‐enhanced Raman scattering (SERS) spectra of dapsone by using colloidal silver nanoparticles have been recorded. Density functional theory was used for the optimization of ground state geometries and simulation of the vibrational spectrum of this molecule. The SERS spectrum with a large silver cluster as a model metallic surface was simulated for the first time. Taking into account the experimental and calculated Raman as well as the SERS normal modes and the corresponding assignments, along with the modeling of the free dapsone and the one in the presence of the colloidal silver nanoparticles, the importance of the sulfone group on the SERS effect in dapsone was inferred. Copyright © 2009 John Wiley & Sons, Ltd.     

FT‐IR,FT‐Raman,and computational calculations of 4‐chloro‐2‐(3‐chlorophenyl carbamoyl)phenyl acetate

FT‐IR and FT‐Raman spectra of 4‐chloro‐2‐(3‐chlorophenylcarbamoyl) phenyl acetate were studied. Vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes and the normal modes are assigned by potential energy distribution (PED) calculations. Simultaneous IR and Raman activation of the CO stretching mode shows the charge transfer interaction through a π‐conjugated path. Optimized geometrical parameters of the title compound are in agreement with the reported values. Analysis of the phenyl ring modes shows that C C stretching mode is equally active as strong bands in both IR and Raman, which can be interpreted as the evidence of intramolecular charge transfer via conjugated ring path and is responsible for hyperpolarizability enhancement leading to nonlinear optical activity. The red‐shift of the NH‐stretching wavenumber in the infrared spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman and surface‐enhanced Raman studies of α‐aminophosphinic inhibitors of metalloenzymes

Here, we report the nature of new di‐α‐amino (L¹–L³) and α‐amino‐α‐hydroxyphosphinic (L⁴–L⁶) acids, which are considered potential inhibitors of the aminopeptidase N, adsorbed on a colloidal silver surface by means of surface‐enhanced Raman scattering (SERS) spectroscopy. In order to reveal the adsorption mechanism of these species from their SERS spectra, Fourier‐transform Raman (FT‐RS) spectra of these nonadsorbed molecules were measured. By examining the enhancement, shift in wavenumbers, and changes in breadth of the SERS bands due to the adsorption process, we revealed that the tilted compounds interact with the colloidal silver substrate mainly through the benzene ring, amino group, and phosphinic moiety in the following way. The benzene ring of L² and L³ is ‘standing up’ on the colloidal silver surface, and the C N bond is almost vertical to it, while the tilt angle between the O PO bond and this surface is greater than 45°. On the other hand, for L¹, L⁴, and L⁵, the aromatic ring and C N bond are arranged more or less tilted, and the tilt angle between the O PO bond and the silver substrate is smaller than 45°. The elongation of the bond to the benzene ring, the L⁶ case, produces an almost horizontal orientation of the benzene ring and the O PO bond on the silver nanoparticles. For these ligands, the complement inhibition IC₅₀ tested in vitro using porcine kidney leucine aminopeptidase was correlated mainly with the behavior of the O PO and C CH N fragments on the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies and DFT calculations of 4‐fluoro‐N‐(2‐hydroxy‐4‐nitrophenyl)benzamide

Fourier transform infrared (FT‐IR) and FT‐Raman spectra of 4‐fluoro‐N‐(2‐hydroxy‐4‐nitrophenyl)benzamide were recorded and analyzed. The vibrational wavenumbers and corresponding vibrational assignments were examined theoretically using the Gaussian03 set of quantum chemistry codes. The red‐shift of the NH‐stretching wavenumber in the infrared (IR) spectrum from the computed wavenumber indicates the weakening of the NH bond resulting in proton transfer to the neighboring oxygen atom. The simultaneous IR and Raman activation of the CO‐stretching mode gives the charge transfer interaction through a π‐conjugated path. Copyright © 2008 John Wiley & Sons, Ltd.     

Visible laser–induced photoreduction of silver 4‐nitrobenzenethiolate revealed by Raman scattering spectroscopy

We have investigated the photochemical characteristics of silver 4‐nitrobenzenethiolate (Ag‐4NBT) by means of Raman spectroscopy. When Ag‐4NBT is irradiated with an argon ion laser at 514.5 nm, its Raman spectrum changes over time, resulting in the production of 4NBT‐capped silver nanoparticles. The surface‐enhanced Raman scattering (SERS) spectrum of 4NBT adsorbed on those Ag nanoparticles is subsequently converted to that of 4‐aminobenzenethiol (4ABT). These surface‐induced photoreduction characteristics were investigated by monitoring the growth of Raman peaks of 4ABT as a function of the laser exposure time. Water vapor or ambient conditions were more effective than vacuum conditions for the photoreduction of 4NBT to 4ABT. Nonetheless, the occurrence of photolysis even under vacuum conditions suggests that the benzene ring hydrogen atoms might be the H‐atom source of the nitro‐to‐amine group conversion although in ambient conditions water or solvent molecules trapped inside the Ag‐4NBT should be the primary H‐atom source and facilitate the transfer of electrons, as well as the diffusion of Ag atoms to form highly SERS‐active nanoaggregates. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering study of human serum on PVA?Ag nanofilm prepared by using electrostatic self‐assembly

Polyvinyl alcohol (PVA)‐protected silver nanoarchitecture (PVA Ag nanofilm) on the surface of the glass substrate was prepared by using electrostatic self‐assembly at a proper voltage. The two‐dimensional morphology of the PVA Ag nanofilm has been examined by scanning electron microscopy (SEM). The surface‐enhanced Raman scattering (SERS) spectra of human serum (HS) on PVA Ag nanofilms were recorded. The results show that the Raman scattering of HS can be enhanced efficiently based on these PVA Ag nanofilms. However, it also can be seen that the effect of sodium citrate (SC) acting as anticoagulant on the SERS spectrum of HS is unnegligible, which has not been discussed adequately in the previous reports. To discuss the effect of SC on the SERS spectrum of HS, we have studied the normal Raman spectra of solid SC and the SERS spectra of 1.0 × 10⁻³ mol/l aqueous solution of SC adsorbed on the PVA–Ag nanofilms. Meanwhile, Raman wavenumbers of the SC molecule were calculated by using the method of DFT‐B3LYP/6‐31G*, and the dominant assignations of the calculated wavenumbers were performed. It was found that the density functional theory (DFT) calculation of SC Raman spectrum matches well with the experimental results. With the perfect reproducibility and high SERS activity, this method will be useful in the development of HS detection methods. Copyright © 2010 John Wiley & Sons, Ltd.     

DFT,FT‐Raman,FT‐IR and NMR studies of 2‐fluorophenylboronic acid

The experimental and theoretical vibrational spectra of 2‐fluorophenylboronic acid (2fpba) were studied. The Fourier transform Raman and Fourier transform infrared spectra of the 2fpba molecule were recorded in the solid phase. The structural and spectroscopic analysis of the molecule was carried out by using Hartree‐Fock and density functional harmonic calculations. For the title molecule, only one form was found to be the most stable structure, by using B3LYP level with the 6‐31++G(d,p) basis set. Selected experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumbers by their total energy distribution (TED). The ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts of the 2fpba molecule were calculated using the Gauge‐Invariant‐ atomic orbital (GIAO) method in DMSO solution using IEF‐PCM model and compared with the experimental data. Finally, geometric parameters, vibrational wavenumbers and chemical shifts were compared with available experimental data of the molecule. Copyright © 2009 John Wiley & Sons, Ltd.     

IR,Raman and SERS spectra of 3,5‐dinitrosalicylic acid

IR, Raman and surface enhanced Raman scattering (SERS) spectra of 3,5‐dinitrosalicylic acid (DNSA) were recorded and analysed. The vibrational wavenumbers were computed by the ab initio method using RHF/6–21G* basis and they were found to be in good agreement with the experimental values. The effect of the concentration dependence on the SERS intensity of the molecule was studied. The molecular plane assumes a tilted orientation with respect to the silver surface. Copyright © 2006 John Wiley & Sons, Ltd.     

Adsorption of 1,2,4‐triazole on a silver electrode: surface‐enhanced Raman spectroscopy and density functional theory studies

The pH‐dependent surface‐enhanced Raman scattering (SERS) of 1,2,4‐triazole adsorbed on silver electrode and normal Raman (NR) spectra of this compound in the aqueous solutions were investigated. The observed bands in the NR and SERS spectra were assigned with the help of density functional theory calculations for model molecules in the neutral, anionic, and cationic forms and their complexes with silver. The Raman wavenumbers and intensities were computed at the optimized molecular geometry. Vibrational assignments of the SERS and NR spectra are provided by calculated potential energy distributions. The combination of experimental SERS results and density functional theory calculations provide an insight into the molecular structure of adlayers formed by 1,2,4‐triazole on a silver surface at varying pH values and enable the determination of molecular orientation with respect to the surface. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman and SERS study of metoclopramide at different pH values

Conjugate acid–base forms of the drug metoclopramide were investigated by Raman spectroscopy in aqueous solutions and by surface‐enhanced Raman scattering (SERS), when the molecules were adsorbed on colloidal silver surfaces. Raman spectra were recorded at pH values below 8, metoclopramide being poorly water soluble at higher pH values. The SERS spectra of metoclopramide were recorded in the 3–11 pH range, even in spite of its low solubility at basic pH values. The Raman and SERS spectra were assigned by means of density functional theory (DFT) calculations. By monitoring several SERS marker bands, the protonated, neutral or the coexistence of both molecular species adsorbed on the colloidal silver particles could be evidenced. The adsorbate orientation was deduced to be perpendicular to the metal surface for the protonated molecular species and tilted for the neutral metoclopramide molecular species. Copyright © 2009 John Wiley & Sons, Ltd.     

Visible light response of silver 4‐aminobenzenethiolate and silver 4‐dimethylaminobenzenethiolate probed by Raman scattering spectroscopy

Silver thiolate is a layered compound with a Raman spectrum that is known to change with time, becoming the same as the surface‐enhanced Raman scattering (SERS) spectrum of the parent thiol molecule adsorbed on Ag nanoparticles. On this basis, the Raman scattering characteristics of silver 4‐aminobenzenethiolate (Ag‐4ABT) compounds were investigated to determine whether certain peaks that are identifiable in the SERS spectrum of 4‐aminobenzenethiol (4‐ABT) but absent in its normal Raman spectrum were also apparent in the Ag salt spectrum. For comparative purposes, the Raman scattering characteristics of silver 4‐dimethylaminobenzenethiolate (Ag‐4MABT) were also examined. Raman spectra acquired while spinning the sample were typified by only a₁‐type vibrational bands of Ag‐4ABT and Ag‐4MABT, whereas in the static condition, several non‐a₁‐type bands were identified. The spectral patterns acquired in the static condition were similar to the intrinsic SERS spectra of 4‐ABT or 4‐dimethylaminobenzenethiol (4‐MABT) adsorbed on pure Ag nanoparticles. Notably, the CH₃ group vibrational bands were observable for Ag‐4MABT irrespective of the sample rotation. In addition, no decrease in intensity during irradiation with a visible laser was observed for any of the bands, suggesting that no chemical conversion actually took place in either 4‐ABT or 4‐MABT. The preponderance of evidence led to the conclusion that the non‐a₁‐type bands observable in the SERS spectra must be associated with the chemical enhancement mechanism acting on the Ag nanoparticles. The chemical enhancement effect was more profound at 514.5 nm than at 632.8 nm, and was more favorable for 4‐ABT than 4‐MABT at both wavelengths. Copyright © 2012 John Wiley & Sons, Ltd.     

Structure and conformation of Arg8 vasopressin modified analogs

Fourier‐transform Raman and infrared spectra were acquired for four arginine vasopressin (AVP) analogs containing L ‐diphenylalanine (Dpa): [Dpa²]AVP, [Cpa¹,Dpa²]AVP, [Dpa³]AVP, and [Cpa¹,Dpa³]AVP (where Cpa denotes 1‐mercaptocyclohexaneacetic acid). We compared and analyzed these spectra. In addition, the Raman spectra were compared to the corresponding surface‐enhanced Raman scattering spectra recorded in an aqueous silver colloidal dispersion. Silver colloidal dispersions prepared by the simple borohydride reduction of silver nitrate were used as substrates. The geometry of these molecules etched on the silver surface was deduced from the observed changes in the intensity enhancement, breadth, and shift in wavenumber of the Raman bands in the spectra of the bound versus free species. Based on the obtained data, adsorption mechanisms were proposed for each case, and the suggested adsorbate structures were compared. All the molecules were thought to adsorb onto a silver surface via a phenyl ring, free electron pairs on the sulfur atom, and CO and  CONH‐bonds. However, the orientation of these fragments on the colloidal silver surface and the strength of the interactions with this surface are different. For [Dpa³]AVP and [Cpa¹,Dpa³]AVP, a strong interaction among the—CCN‐peptide fragment and the colloidal silver surface occurs. Copyright © 2011 John Wiley & Sons, Ltd.     

Vibrational spectroscopy and density functional theory calculations of poly‐D‐mannuronate and heteropolymeric fractions from sodium alginate

The tetrasaccharide of 1 → 4β‐D‐mannopyranuronate (MM) and the alternating tetrasaccharide of 1 → 4 b‐D‐mannopyranuronate and 1 → 4α‐L‐gulopyranuronate (MG) were analyzed based on density functional theory (DFT) by employing the Gaussian 03 W package. The molecular geometries were fully optimized by using the Becke's three‐parameter hybrid exchange functional combined with Lee–Yang–Parr correlation functional (B3LYP) and using a 6‐31G(d,p) basis set. The calculated IR spectrum of MM presents a band at 1093 cm⁻¹ for C C stretching vibration, which is in good agreement with the experimental observation (1096 cm⁻¹) for the polymannuronate fraction obtained by partial hydrolysis of sodium alginate extracted from the hybrid brown seaweed Lessonia–Macrocystis. The calculated value at 826 cm⁻¹for MM is in close agreement with the experimental value and confirms that this band is characteristic of polymannuronate blocks. Most of the bands in the IR spectrum are also present in the observed Raman spectrum of the polymannuronate fraction. The experimental IR spectrum of heteropolymeric fraction obtained by partial hydrolysis of sodium alginate shows absorbances similar to those calculated for the model tetrasaccharide (MG). Surface‐enhanced Raman scattering (SERS) allows differentiation between the homopolymeric and heteropolymeric fractions of sodium alginate. The SERS spectrum of the heteropolymeric fraction shows an enhanced signal at 731 cm⁻¹which is present in the calculated Raman spectrum of the tetrasaccharide MG at 729 cm⁻¹. This band is assigned to the ring‐breathing deformation of the β‐D‐mannopyranuronate and α‐L‐gulopyranuronate residues. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering (SERS) spectra of hemoglobin on nano silver film prepared by electrolysis method

Nano silver films were prepared by the electrolysis method. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to detect the morphology of the silver particles. The surface‐enhanced Raman scattering (SERS) spectra of the hemoglobin on nano silver film were recorded. It is seen from the SERS spectra that the nano silver films can enhance the Raman signals of the hemoglobin efficiently, and sodium citrate and phosphate buffered saline have no influence on the SERS spectra of hemoglobin. The electrolysis technique to fabricate this highly bioactive, stable, reusable, and low‐cost SERS substrate will be useful in the development of hemoglobin detection methods. Copyright © 2009 John Wiley & Sons, Ltd.