Pai-H-AgNP SERS-DFT Chem Phys Lett, 2013, 586, 132-137.pdf (original) (raw)
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SERS and DFT study of silver nano particle induced dark isomerisation in 1H-2(Phenylazo) imidazole
Chemical Physics Letters, 2013
Raman spectra and SERS of 1H-2(Phenylazo) imidazole (PaiH) adsorbed on silver nano particles are reported. Monomolecular layer is formed at a concentration of 5 Â 10 À6 M. A trans-to-cis isomerisation of PaiH is suggested by the cis-signature peak at 570 cm À1. In absorption spectra a single p-p ⁄ band at 358 nm is observed at higher concentrations whereas the p-p ⁄ and the n-p ⁄ bands appear at 370 nm and 456 nm, respectively, at a concentration of 5 Â 10 À6 M. This is in support of the hypothesis of trans-to-cis-isomerisation with lowering of concentration. DFT calculations are shown.
Revista de Chimie -Bucharest- Original Edition-
A thoroughly experimental and theoretical spectroscopic study (Surface-enhanced Raman Spectroscopy (SERS), Raman and FT-IR) concerning the structure of N-(2-cyanoethil)-imidazole have been performed. Limited information is bringing by Raman Spectroscopy, but when absorbed on the surface of the silver nanoparticles, strong vibrational signals were recorded. The influence of aggregation ions (F -, Cl -, Br -, I -) and the influence of pH on the adsorption mechanism was investigated. Ab initio HF and density functional theory calculation were carried out to compute the wavenumbers of N-(2-cyanoethil)-imidazole. All theoretical and experimental vibrational frequencies for N-(2-cyanoethil)-imidazole were carefully assigned, and are in agreement to each other.
Chemical Physics, 2006
The adsorption of biologically important 2-amino-6-methylbenzothiazole (2A-6MBT) molecule on silver colloids has been investigated by Surface Enhanced Raman Scattering (SERS) study. The SERS spectra of 2A-6MBT at different adsorbate concentrations are compared with its Fourier transform infrared spectrum and normal Raman spectrum in varied environments. Concentration-dependent SERS spectra of the molecule reveal the existence of two types of adsorbed species on colloidal silver particles, whose relative population varies with adsorbate concentrations. The experimentally observed SERS spectra are compared with the theoretically modeled surface complexes using density functional theory calculations. The appearance of Ag–N stretching mode at around 212 cm−1 in the SERS spectra along with theoretically calculated atomic charge density, force us to believe that the molecules are adsorbed through the lone pair electrons of the nitrogen (N9 and N10) atoms with the molecular plane tilted or remain pendant on the colloidal silver surface. The direction of charge transfer contribution to SERS has been discussed from the frontier orbital theory.
Vibrational spectral and DFT studies of 7-azaindole adsorbed on silver nanometal surface
2007
Surface Enhanced Raman Scattering (SERS) studies of 7-azaindole (7-AI) adsorbed on silver nanometal surface are reported here. The observed SERS spectra have been compared with the normal Raman spectral assignments. From the assignment of the observed SERS bands, possible orientation of the 7-AI adsorbed on the metal surface is presumed. DFT studies have been undertaken and normal mode displacements analysed for 7-AI for better assignment of normal Raman and SERS bands.
The Journal of Physical Chemistry B, 2006
In this work piperazine-1-carbodithioic acid (PZCDT) and piperazine-1,4-dicarbodithioic acid (PZbCDT) were synthesized. These analytes PZCDT and PZbCDT have chair conformations, which is expected to give specific surface-enhanced Raman scattering (SERS) effects on individual bands. SERS, UV-Visible, TEM and DFT methods have proved that the dithiocarbamate moiety is a potential and suitable functional group for silver and ZnO nanoparticles (AgNPs and ZnONPs). The enhancement mechanism and enhancement factors in both SERS@AgNPs and SERS@ZnONPs are also discussed. Two new strong bands appear at 1630, 1286 cm À1 with very large intensity in SERS@AgNPs, which signifies the conversion of the C-N bond of the dithiocarbamate moiety into C]N bonds. The SERS signatures that are observed are quite different in SERS@AgNPs and SERS@ZnONPs. PAPER adenine, benzenethiol derivatives etc. The -N site of the PZ ring (aer removal of H atom) is associated to the -dithiocarbamate moiety.
Surface enhanced Raman scattering of pyrazole adsorbed on silver colloids
Journal of Molecular Structure, 1999
SERS spectra of pyrazole adsorbed on silver hydrosol at different pH values and on silver colloidal substrate deposited on filters were obtained and interpreted on the basis of the existence of three forms in equilibrium, cationic, neutral and anionic. SERS data indicate that the neutral molecule is preferentially adsorbed in acidic environment, pyrazolide anion is instead favoured over all the other pH values. Addition of chloride anions induces the formation of reaction products when pyrazole is adsorbed on silver hydrosols, while this effect is missing on dry silver substrate. ᭧
Vibrational Spectroscopy, 2016
Surface-enhanced Raman scattering (SERS) was used to obtain adsorption isotherms for two types of SERS-active substrates: silver nanoparticles (AgNPs) dispersed in water (AgNP/sol); and AgNPs dispersed in agarose gel (AgNP/Agar). Rodhamine 6G (R6G) was chosen as the probe molecule to evaluate the two substrates. R6G adsorbs on both substrates following Langmuir isotherms with very similar adsorption constants. The SERS from R6G in AgNP/Agar is ca. 10 times more intense than in AgNP/sol due to the confinement of the R6G molecules within the gel matrix. The AgNP/Agar was further evaluated for the adsorption of methylene blue (MB), crystal violet (CV) and benzotriazole (BTA). The results showed that, for lower surface coverages (u < 0.1), the observed SERS (or SERRS) spectra corresponded to single molecule events. In this case, each single spectrum presented different relative intensities than from the ensemble averaged spectrum. On the other hand, for higher coverages (u % 1), the relative intensities of a single spectrum were quite similar to those of the ensemble average. Single molecule SERRS events were well identified for MB, because the spectra of the monomer and of the aggregated state differ considerably for this dye. The results also indicate that R6G and CV adsorb on the SERS-active sites forming ion pairs with the adsorbed chloride, while MB and BTA form covalent bonds with Ag atoms on the AgNP surface. In all cases the Gibbs free energy of adsorption were below À30 kJ mol À1 , characterizing chemical adsorption.
Journal of Physical Chemistry B, 2009
Surface-enhanced Raman scattering (SERS) spectra from phosphonate derivatives of N-heterocyclic aromatic compounds immobilized on an electrochemically roughened silver electrode surface are reported and compared to Raman spectra of the corresponding solid species. The tested compounds contain imidazole [ImMeP ([hydroxy-(1H-imidazol-5-yl)-methyl]-phosphonic acid) and (ImMe) 2 P (bis[hydroxy-(1H-imidazol-4-yl)methyl]-phosphinic acid)]; thiazole [BAThMeP ((butylamino-thiazol-2-yl-methyl)-phosphonic acid) and BzAThMeP ((benzylamino-thiazol-2-yl-methyl)-phosphonic acid)]; and pyridine ((PyMe) 2 P (bis[(hydroxypyridin-3-yl-methyl)]-phosphinic acid) aromatic rings. Changes in wavenumber, broadness, and the enhancement of N-heterocyclic aromatic ring bands upon adsorption are consistent with the adsorption primarily occurring through the N lone pair of electrons with the ring arranged in a largely edge-on manner for ImMeP and BzAThMeP or in a slightly inclined orientation to the silver electrode surface at an intermediate angle from the surface normal for (ImMe) 2 P, BAThMeP, and (PyMe) 2 P. A strong enhancement of a roughly 1500 cm-1 SERS signal for ImMeP and (PyMe) 2 P is also observed. This phenomenon is attributed to the formation of a localized CdC bond, which is accompanied by a decrease in the ring-surface π-electrons' overlap. In addition, more intense SERS bands due to the benzene ring in BzAThMeP are observed than those observed for the thiazole ring, which suggests a preferential adsorption of benzene. Some interaction of a phosphonate unit is also suggested but with moderate strength between biomolecules. The strength of the PdO coordination to the silver electrode is highest for ImMeP but lowest for BzAThMeP. For all studied biomolecules, the contribution of the structural components to their ability to interact with their receptors was correlated with the SERS patterns.
The Journal of Physical Chemistry C, 2017
We present a combined experimental and theoretical study dedicated to analyze the surface enhanced Raman spectra of solutions of citrate-covered silver nanoparticles (NP) in the presence of acetil-neuraminic acid (Neu5Ac). The Raman signals from Neu5Ac(particularly the bands located at 1002 and 1237 cm-1) can easily be detected for concentrations as low as 1 mg/dl, providing outstanding molecular sensing properties for our synthesized Ag-NP. When compared to its solid phase, Neu5Acadsorption on citratecovered Ag particles leads to enhanced Raman intensities, many vibrational frequencies are shifted, and relative intensities undergo significant changes. These variations in the spectra complicate molecular identification, especially in mixed over-layers as the ones considered in this work. Consequently, experimental results are discussed on the basis of extensive density functional theory (DFT) calculations on model citrate-covered silver clusters with co-adsorbed Neu5Acspecies. Several citrate-Neu5Ac-cluster complexes are optimized and the Raman spectra of every stable structure are calculated. The theoretical data reveals a