G. B. Talapatra

Hemoglobin−Silver Interaction and Bioconjugate Formation: A Spectroscopic Study

In this article, we report the results of the extent of interaction as well as the formation of a bioconjugate of human hemoglobin (Hb) with silver (Ag). The complexation process and conformational changes are characterized using different spectroscopic and microscopic techniques. The UV-vis study demonstrates the perturbation of the soret/heme band and generates conformational heterogeneity within the heme group in the presence of silver. A fluorescence study suggests that the Tryptophan (Trp) residues of Hb are in a more polar environment after conjugation. Initial fluorescence enhancement with addition of silver is due to metal-enhanced fluorescence. Moreover, the fluorescence quenching after the formation of the Hb-Ag bioconjugate follows the modified Stern-Volmer (S-V) plot. The S-V plot along with the time-resolved fluorescence study indicates the presence of both static and dynamic types of quenching. In addition, the reduction potential values of the entities (Hb-heme, Ag(+), and Trp) indicate the possible electron transfer. The secondary structure calculation from CD and FTIR spectra indicate alpha-helix to beta-sheet conversion, and unfolding of Hb is also responsible for the bioconjugate formation. In addition, FE-SEM, phase contrast inverted microscopy (PCIM) images demonstrate the formation of the silver-protein bioconjugate. The overall data show that there is a change in the secondary as well as the tertiary structure of Hb after conjugation with silver.

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.

The formation of pepsin monomolecular layer by the Langmuir-Blodgett film deposition technique.

We report herein the formation of pepsin monomolecular layer by the Langmuir-Blodgett film deposition technique. An effort was made to find an optimal subphase by adjusting the concentration of salt (KCl) and pH by monitoring the growth kinetics of pepsin for the formation of Langmuir monolayer by using as little as possible pepsin molecules to build up ultra thin film and to measure the extent of denaturation. Significant changes of area/molecule, compressibility, rigidity and unfolding of pepsin are observed at optimized subphase than pure water subphase. Observations at optimal subphase are explained in context of the modified DLVO theory and the site dissociation model. FTIR analysis of amide band together with the observed surface morphology of pepsin film in FE-SEM images indicate that at optimal subphase the pepsin molecules modify their structures by incrementing the beta-structure, resulting into larger unfolding and inter-molecular aggregates.

On the origin of iron-oxide nanoparticle formation using phospholipid membrane template

In this report, we have studied the formation of iron-oxide nanoparticle at biologically relevant phospholipids, DPPC Langmuir monolayer at air/water interface. Water subphase contains FeCl(3). Adsorption and agglomeration of Fe(3+) ions at DPPC head group have being monitored by Langmuir and Langmuir Blodgett (LB) technique. Adsorption kinetics (pi-t) as well as the surface pressure area (pi-A) isotherms measurement demonstrate the incorporation of Fe(3+) ion at DPPC monolayer. The amount of incorporation of Fe(3+) to the DPPC monolayer is FeCl(3) concentration and time dependent. This reaction kinetics is well fitted by single exponential association equation. The composite monolayers transferred to different substrates are characterized by UV-vis absorption spectroscopy and electron microscopy (FE-SEM and HR-TEM). Study shows the formation of monodisperse Fe(3)O(4) nanoparticle having size approximately 20 nm coated with DPPC mono or multilayer. The overall study indicates that the formation as well as assembly of iron-oxide nanoparticle in two dimensions is possible using lipid monolayer as a template.

Synthesis of Amphiphilic Azo‐Anion‐Radical Complexes of Chromium(III) and the Development of Ultrathin Redox‐Active Surfaces by the Langmuir–Schaefer Technique

Neutral tris-chelated chromium complex [Cr(L(a))(3)] (1a), and its surfactant derivatives [Cr(L(b))(3)] (1b), [Cr(L(c))(3)] (1c), and [Cr(L(d))(3)] (1d) (where L(a)=2-(4-methoxyphenylazo)pyridine, L(b)=2-(4-butyloxyphenylazo)pyridine, L(c =2-(4-octyloxyphenylazo)pyridine, and L(d)=2-(4-dodecyloxyphenylazo)pyridine) were synthesized. The molecular structure of compound 1a, determined by X-ray diffraction, showed that the local geometry around the metal center is a distorted octahedral with meridional coordination of the ligands. The structural parameters, spectroscopic data, and density functional theory (DFT) calculations on representative complex 1a suggest that ligand L(a) is predominantly an azo-anion-radical-type, and so the complex can be represented as [Cr(III)(L(a.-))(3)]. An assessment of their physicochemical and surface properties was performed with the aim of using these triple-tailed metallosurfactants as precursors for redox-responsive films. The surface-pressure-molecular-area isotherm measurement for compound 1d shows that the complex forms a stable Langmuir film at the air/water interface. The monolayer and multilayers were successfully transferred onto the quartz substrate and the platinum working electrode at a surface pressure of 10 mN m(-1) by the Langmuir-Schaefer (LS) technique. The LS films were studied by UV/Vis spectrometry, infrared spectroscopy, field-emission scanning electron microscopy, and atomic force microscopy. A good linear relationship between the absorbance at 370 nm and the thickness of the layers against the number of deposited layers indicated the uniformity and reproducibility of this transfer process. Voltammograms for platinum-surface-bound LS film of compound 1d showed that the redox response owing to the first oxidation is stable and reproducible after many cycles (>300 cycles). Spectroscopic studies and electrochemical measurements of compound 1d on the LS films revealed that these complexes are potential candidates for molecular devices.

Adsorption of pepsin in octadecylamine matrix at air–water interface

The incorporation/entrapment of water-soluble surface-active enzyme, pepsin (PEP) within an insoluble cationic octadecylamine (ODA) monolayer is studied by Langmuir-Blodgett technique. The observation suggests that the incorporation of PEP is less preferable at compressed region (~30mN/m). The electrostatic interaction plays a significant role for the greater incorporation of PEP in cationic ODA monolayer. The surface pressure-area isotherms along with FE-SEM analysis indicates the squeezing out of PEP from the monolayer at higher surface pressure. This will assist to select the optimum surface pressure to obtain a good quality and well-ordered Langmuir monolayer. FTIR study of amide bands together with FE-SEM imaging of ODA-PEP mixed film indicates that ODA perturbs the PEP by the increment of beta-structure resulting into larger unfolding, intra, and intermolecular aggregates.

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.

Incorporation of pepsin within zwitterionic, anionic, and cationic lipid monolayers: A comparative study

The incorporation of water-soluble surface-active enzyme pepsin (PEP) within insoluble zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and anionic stearic acid (SA) monolayer is studied. Furthermore, the results are compared with cationic octadecylamine (ODA). Adsorption of PEP is found to be higher in ODA as compared to that of DPPC and SA. PEP adsorption kinetics in lipids monolayer follows two-step process: diffusion and unfolding. The unfolding of PEP is lower in the case of DPPC than in SA and ODA. π-A isotherm together with high-resolution field emission scanning electron microscope (FE-SEM) images indicate that at higher pressure, PEP molecules tend to squeeze out from the lipids monolayer. PEP forms larger irregular intermolecular aggregates by increment of β-component on SA and ODA monolayer. However, in zwitterionic (DPPC) matrix the α-helix increases with smaller intermolecular aggregates. The overall results specify that zwitterionic (DPPC) monolayer is better choice to obtain protein lipid mixed film than anionic (SA) and cationic (ODA) monolayer.

Monte Carlo simulation of organic light-emitting devices under alternating applied field

A Monte Carlo method has been employed to simulate electroluminescence (EL) from organic light-emitting devices (LEDs) under an alternating applied field. EL responses under forward and reverse bias modes have been simulated with different experimental parameters. Dependences of EL on the frequency of an applied field, electrode work function, band gap and film thickness of the active organic material, etc., have been studied. The origin of EL under alternating current (ac) mode has been explained in terms of radiative recombination of excitons formed via injected holes and electrons present from the previous cycle of ac voltage. The time response of EL intensity and its profile during forward and reverse bias half-cycles has been found to depend on carrier injection and also on their temporal and spatial distribution along the thickness of the emitting material. Efforts have been made to match a simulated EL response with representative experimental results. The Monte Carlo simulation results presented here provides a way to select certain parameters to fabricate efficient ac LEDs.

QM/MM simulation of the amide-I band in the Raman spectrum of insulin

ABSTRACT Raman spectroscopy is an effective tool to detect conformational changes and secondary structures of biological molecules. The amide-I band representing the amide carbonyl (C=O) stretching, with smaller contributions of C–N stretching and N–H bending is a signature band for protein secondary structure conformation. We have simulated the Raman spectra of insulin by a hybrid quantum-mechanics and molecular-mechanics (QM/MM) method with an aim to provide an accurate description of the amide-I band. To fulfil this aim we have considered three different QM/MM models with increasingly accurate description of the electrostatic environment for tyrosine (TYR), phenylalanine (PHE) and cystine (CYS) residues of insulin. All three models successfully describe the experimental Raman spectral features associated with the vibrational modes of the amino acid side chains. However, an accurate simulation of the amide-I band is achieved only in one of the three models, where the peptide backbone atoms together with its hydrogen bonding partners are treated with QM method. This work indicates that the accurate treatment of electrostatic interactions of the peptide backbone is crucial for correct simulation of the amide-I region, which acts as a spectral signature of proteins.