Manash Ghosh

Study of silver nanoparticle–hemoglobin interaction and composite formation

Nanoscience is now an expanding field of research and finds potential application in biomedical area, but it is limited due to lack of comprehensive knowledge of the interactions operating in nano-bio system. Here, we report the studies on the interaction and formation of nano-bio complex between silver nanoparticle (AgNP) and human blood protein hemoglobin (Hb). We have employed several spectroscopic (absorption, emission, Raman, FTIR, CD, etc.) and electron diffraction techniques (FE-SEM and HR-TEM) to characterize the Hb-AgNP complex system. Our results show the Hb-AgNP interaction is concentration and time dependent. The AgNP particle can attach/come closer to heme, tryptophan, and amide as well aromatic amine residues. As a result, the Hb undergoes conformational change and becomes unfolded through the increment of β-sheet structure. The AgNP-Hb can form charge-transfers (CT) complex where the Hb-heme along with the AgNP involved in the electron transfer mechanism and form Hb-AgNP assembled structure. The electron transfer mechanism has been found to be dependent on the size of silver particle. The overall study is important in understanding the nano-bio system and in predicting the avenues to design and synthesis of novel nano-biocomposite materials in material science and biomedical area.

Concentration-dependent surface-enhanced resonance Raman scattering of a porphyrin derivative adsorbed on colloidal silver particles

Surface-enhanced Raman spectra (SERS) of 5,10,15,20-tetrakis(1-decylpyridium-4-yl)-21H,23H-porphintetrabromide or Por 10 (H(2)Tdpyp) adsorbed on silver hydrosols are compared with the FTIR and resonance Raman spectrum (RRS) in the bulk and in solution. Comparative analysis of the RR and the FTIR spectra indicate that the molecule, in its free state, has D(2h) symmetry rather than C(2v). The SERS spectra, obtained on adsorption of this molecule on borohydride-reduced silver sol, indicate the formation of silver porphyrin. With the change in the adsorbate concentration, the SERS shows that the molecule changes its orientation on the colloidal silver surface. The appearance of longer wavelength band in the electronic absorption spectra of the sol has been attributed to the coagulation of colloidal silver particles in the sol. The long wavelength band is found to be red-shifted with the decrease in adsorbate concentration. The excitation profile study indicates that the resonance of the Raman excitation radiation with the original sol band is more important than that with the new aggregation band for the SERS activity. This indicates a large contribution of electromagnetic effect to surface enhancement.

CRYSTALLINE STATE PHOTOREACTION IN 4-METHYLCINNAMIC ACID : A RAMAN PHONON SPECTROSCOPIC STUDY

The solid-state photodimerization reaction mechanism in 4-methylcinnamic acid crystal was investigated. Raman and infrared spectroscopy were used to study the intramolecular vibrations of the reactant and the product in order to characterize them. The absence of any large Stokes shift between the excitation and emission bands of the monomer crystal shows that the exciton–phonon coupling is weak. Raman phonon spectroscopic studies reveal that the reaction proceeds by a homogeneous mechanism in the initial stage and subsequently by a heterogeneous mechanism. The appearance of new sharp phonon bands suggests that the product lattice is ordered. No mode softening is observed. Hence the reaction seems to be topochemically controlled and lattice phonons do not take part in the reaction.

Topochemically controlled solid state photoreaction in 7-acetoxy coumarin : A Raman phonon spectroscopic study

The solid state photodimerization reaction mechanism in 7-acetoxy coumarin (7AC) crystal has been investigated. Raman phonon spectroscopic studies reveal that the reaction mechanism is homogeneous and the lattice becomes disordered with the increase of product concentration. No mode softening is observed. Electronic excitation and emission spectra show that exciton-phonon coupling is weak in the monomer crystal. Thus the reaction seems to be topochemically controlled and lattice phonons do not take part in the reaction. Formation of cyclobutane rings through the > CC < of the pyrone moiety is established by infrared and Raman spectroscopy.

Quantum-mechanical DFT calculation supported Raman spectroscopic study of some amino acids in bovine insulin.

In this article Quantum mechanical (QM) calculations by Density Functional Theory (DFT) have been performed of all amino acids present in bovine insulin. Simulated Raman spectra of those amino acids are compared with their experimental spectra and the major bands are assigned. The results are in good agreement with experiment. We have also verified the DFT results with Quantum mechanical molecular mechanics (QM/MM) results for some amino acids. QM/MM results are very similar with the DFT results. Although the theoretical calculation of individual amino acids are feasible, but the calculated Raman spectrum of whole protein molecule is difficult or even quite impossible task, since it relies on lengthy and costly quantum-chemical computation. However, we have tried to simulate the Raman spectrum of whole protein by adding the proportionate contribution of the Raman spectra of each amino acid present in this protein. In DFT calculations, only the contributions of disulphide bonds between cysteines are included but the contribution of the peptide and hydrogen bonds have not been considered. We have recorded the Raman spectra of bovine insulin using micro-Raman set up. The experimental spectrum is found to be very similar with the resultant simulated Raman spectrum with some exceptions.

Phonon participation in solid state photoreaction in 6-bromocoumarin : Laser Raman spectroscopic study

Abstract The photodimerization reaction in 6-bromocoumarin in the crystalline state is shown to be mediated by lattice phonon. Significant overlap between the electronic absorption and emission spectra suggests that the exciton-phonon coupling is not very strong in the monomer crystal. Raman phonon spectra show softening of a specific phonon mode with photoreaction progress. This suggests that phonon participation in the reaction is through a mode softening in the excited state of the crystal on photoirradiation, not via strong exciton-phonon coupling. Raman phonon spectroscopic study also reveals that the reaction mechanism is homogeneous in the initial stage of reaction when the reactant and the product form solid solution and is heterogeneous in the later stage when the product segregates out. IR and Raman spectroscopy are used to characterize the reactant and the product, and the results confirm that reaction occurs by cyclobutane ring formation through the > C  C

Excited Electronic States and Raman Spectra of 2-Benzoylpyridine

Raman excitation profiles of several normal modes of 2-benzoylpyridine were measured, and the structural changes encountered on excitations, excited state symmetries, and vibronic couplings among various excited electronic states of the molecule were investigated. Vibrational spectroscopic studies of the molecule were done in detail, and critical investigation on the electronic spectra of the molecule was also carried out. It is shown that the experimentally allowed transitions, corresponding to the band around 262 and 238 nm, occur to the excited states, where the major geometry changes involve both ring CC/CN and CO stretching vibrations. An excited state lying around 185 nm above the ground state was also found to play an important role in the scattering process. All necessary and valuable quantum chemical calculations accompany the presented spectral studies.

Spectroscopic study of photoreaction dynamics inp-bromo cinnamic acid

The photodimerization reaction inp-bromocinnamic acid (p-BCA) in the crystalline state has been probed by Raman phonon spectroscopy. Monotonic redshift of the phonon bands and nonappearance of any new phonon bands on reaction progress suggest that the reaction is homogeneous and the reactant and the product form a solid solution. It is further observed that a low frequency phonon at 18·6 cm−1 softens on photoexcitation and progress of reaction. The photoreaction inp-BCA crystal therefore seems to be mediated by the lattice phonon. In the IR spectrum disappearance of the aliphatic > C=C < stretching frequency and appearance of cyclobutane ring deformation and ring stretching modes on reaction confirm photodimerization by cyclobutane ring formation. Considerable overlap between the absorption and emission bands shows that the exciton-phonon coupling is not very strong in the monomer crystal.

Magnetic measurements, Raman and infrared spectra of metal–ligand complex derived from \(\hbox {CoCl}_{2}\cdot \hbox {6H}_{2}\hbox {O}\) and 2-benzoyl pyridine

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