Gurinder Singh

Understanding the mechanism of replacement of citrate from the surface of gold nanoparticles by amino acids: a theoretical and experimental investigation and their biological application

The present study explores the physicochemical aspects needed for the appropriate in vitro synthesis and surface modification behavior of gold nanoparticles (AuNPs) in the presence of amino acids (AA). AAs replace citrate (Cit) from surface of citrate-coated AuNPs (Cit-AuNPs) depending upon their structural variations at different pH values. This behavior is further supported by molecular simulation studies, in which we have measured the effectiveness of different AAs in replacing the Cit from the gold (Au) surface. Within the limitations of the approach, the results indicate that cysteine (Cys) is most effective in replacing the Cit, arginine (Arg) is least effective, with glutamic acid (Glu) being intermediate. The UV-vis and FT-IR studies are employed to monitor the simultaneous synthesis and interactions of AA coated AuNPs over a range of pH values from 3.5 to 11. AA coated AuNPs are characterized by XRD and TEM studies. Cysteine coated AuNPs (Cys-AuNPs) show remarkable pH responsive behavior as compared to Glu and Arg coated AuNPs (Glu-AuNPs/Arg-AuNPs). Moreover, all AA coated AuNPs show little hemolysis with Arg-AuNPs having the least hemolytic effect. Thus, AA coated AuNPs are considered to be best vehicle for drug release and other biomedical applications.

Production of bacteriocin by isolates ofYersinia enterocolitica from fresh buffalo milk

Fifty isolates ofYersinia enterocolitica from fresh buffalo milk were screened for the production of bacteriocin using isolates as indicators. Seven isolates (14%) were bacteriocin producers at 22°C which had more bacteriolytic activity at 37°C. Only one isolate produced bacteriocin at both temperatures.

Identifying the preferred interaction mode of naringin with gold nanoparticles through experimental, DFT and TDDFT techniques: insights into their sensing and biological applications

In this work, the binding behaviour of naringin – a flavonoid with AuNPs is explained by combining experimental and theoretical approaches. We have systematically analysed the effect of temperature and concentration of naringin and gold (Au) in the formation of naringin stabilized Au nanoparticles (N-AuNPs). The interaction of naringin with gold nanoparticles (AuNPs) is investigated by various techniques such as UV-visible spectroscopy, TEM, FT-IR, XRD and gel electrophoresis. These studies indicate that naringin acts as a reducing and stabilizing agent. Further, we have modelled the two side chains of naringin with the functional groups [C10H7O2] and [C6H5O]−, and identified the lowest energy configurations of these groups with AuNPs with the help of density functional theory (DFT). The [C10H7O2]–Au13 has higher binding energy than [C6H5O]−–Au13 and it is attributed to delocalized molecular orbitals in [C10H7O2], hence higher charge transfer to the Au13 cluster. On the basis of the resulting structures, we examine the optical properties using time-dependent density functional theory (TDDFT). We observe significant changes in the optical spectra of the representative structures of side chains with the AuNPs. The peak in the spectra of the Vis region of [C10H7O2]–Au13 undergoes a shift towards lower wavelength in comparison to [C6H5O]−–Au13. Natural transition orbitals (NTOs) of hole and particle states of the [C10H7O2]–Au13 conjugate system are localized on [C10H7O2] and Au13, respectively, whereas for the [C6H5O]−–Au13 both hole and particle states are localized on the Au13 cluster. These N-AuNPs show their applicability as a sensor for detecting aluminium ions (Al3+) in aqueous solution. These NPs are also found to be biocompatible with normal red blood cells and MDAMB-231 breast carcinoma cell lines, as evaluated from hemolysis and cytotoxicity assays. Thus, naringin offers non-toxic and bio friendly N-AuNPs, which are considered to be the best vehicle for drug release and other possible biomedical and sensing applications.

Understanding of ZnO morphologies in the presence of surfactants

Zinc oxide (ZnO) nanostructures (dumbbell, flower and tablets) are synthesized using zinc precursor, anionic surfactant Sodium Dodecyl Sulphate (SDS) and cationic surfactant Dodecyl Trimethyl Ammonium bromide (DTAB) by chemical route. Inadequate covering of ZnO with SDS leads to ZnO dumbbells, which are assembled to form flower like geometry. Mixture of SDS and DTAB retards the growth along polar planes i.e. (0001) and (0001¯) respectively, resulting in the formation of tablets. The experimental results are studied by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and UV-Vis spectroscopy (UV-Vis), which indicates that chemical nature of surfactants, is responsible for the variation of ZnO morphologies.

Theoretical investigation of Sn-doped Ge2Sb2Te5 alloy in crystalline phase

Ge2Sb2Te5 (GST) is technologically important for phase-change random access memory applications. It has been shown that the 2.2 atomic % doping of Sn weakens the Ge–Te bond strength while maintaining the symmetry of stable phase of GST. The influence of Sn doping upon the phase change characteristics of the crystalline GST alloy has been investigated by ab initio calculations. The lattice parameter, average interface distances between two adjacent (111) layers, equilibrium volume, metallic character and electrical resistance has been calculated for the stable phase of GST and Sn-doped GST.

Drug resistance and lecithinase activity of Yersinia enterocolitica isolated from buffalo milk

Two-hundred-and-seven samples of raw buffalo milk and 60 samples of pasteurized buffalo milk were screened for presence of Yersinia enterocolitica. The prevalence of Y. enterocolitica was found to be 24.1% in raw milk, however, no isolation could be made from the pasteurized milk samples. Cold enrichment in trypticase soy broth and alkali treatment methods were followed in this study. The majority of the isolates (62%) were found sensitive to all the antibiotics used and only a few (16%) were resistant to two or more than two antibiotics. The incidence of Y. enterocolitica showed seasonal variations. Incidence was much higher (25-50%) during the winter season as compared to the summer (0-17%). The incidence of lecithinase production was high (40-50%) in Yersinia isolates resistant to one or two antibiotics.

Study of Pb-doped Ge2Sb2Te5 in crystalline phase using first principle calculations

To improve the phase change characteristics of Ge2Sb2Te5 (GST), doping is used as one of the effective methods. 4.4 atomic % of Pb doped GST has been studied using first principle calculations. No effect of doping on Te-Ge and Te-Sb bond length has been observed, but the Te-Te bond gets shrink with Pb doping. Due to which the Sb2Te3 segregates as a second phase, with increased doping concentration of Pb in GST alloy. Using such type of calculation, we can calculate the desirable concentration of dopant atoms to prepare the desired material. We can control any segregation in required material with pre-theoretical calculations. The metallic nature of Pd doped GST has been discussed with band structure plots. The metallic character of alloys calculated as in this paper will be helpful to understand the tuning of conductivity of phase change materials, which helps to enhance the phase change properties.

EFFECT OF ALUMINIUM IONS ON COVALENT BEHAVIOUR OF Li2CO3-B2O3 GLASSES

The paper undertakes the preparation of Aluminium oxide doped Lithium borate glasses and characterizes to investigate the physical and optical studies of these glasses using density and UV-Visible spectroscopy. Results had been obtained with the help of FTIR Spectra in our previous work which indicate that Al2O3 acts as a network modifier by converting three coordinated boron atoms [BO3] to four coordinated boron atoms [BO4]. The effect of aluminium content on the optical properties of the present glass system has been studied from the optical absorption spectra. It shows the shifting of the band edge towards the higher wavelength and that there is corresponding decrease in the band gap, which is due to the conversion of BO3 to BO4 units. The evaluation of the compact structure of prepared glass samples with the presence of [BO4] groups has been made in terms of the physical properties such as density and molar volume. It is also confirmed by average boron-boron separation results. The research findings confirm that the addition of Aluminium oxide increases the covalent value and corresponding decrease in ionicity behaviour.

Amino acid-assisted synthesis of zinc oxide nanostructures

In this manuscript we have used experimental approach that can provide a fundamental knowledge about the role played by biomolecules in designing the shape of nanostructure (NS) at a microscopic level. The three different amino acids (AAs) – Arginine (Arg), Aspartic acid (Asp) and Histidine (His) coated Zinc oxide (ZnO) NSs to explain the growth mechanism of nanoparticles of different shapes. Based on the experimental methodology we propose that AA-ZnO (Asp and Arg) nanomaterials could form of rod like configuration and His-ZnO NPs could form tablet like configuration. The synthesized samples are characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results reveal that AAs are responsible for formation of different NSsIn this manuscript we have used experimental approach that can provide a fundamental knowledge about the role played by biomolecules in designing the shape of nanostructure (NS) at a microscopic level. The three different amino acids (AAs) – Arginine (Arg), Aspartic acid (Asp) and Histidine (His) coated Zinc oxide (ZnO) NSs to explain the growth mechanism of nanoparticles of different shapes. Based on the experimental methodology we propose that AA-ZnO (Asp and Arg) nanomaterials could form of rod like configuration and His-ZnO NPs could form tablet like configuration. The synthesized samples are characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Results reveal that AAs are responsible for formation of different NSs

Study of structural and conformational change in cytochrome, C through molecular dynamic simulation in presence of gold nanoparticles

Proteins are the most abundant organic molecules in living system having diverse structures and various functions than the other classes of macromolecules. We have done Molecular Dynamics (MD) simulation of the Cytochrome,C (Cyt,c) protein found in plants, animals and many unicellular animals in the presence of gold nanoparticles (Au NPs). MD results helped to recognize the amino acids that play important role to make the interaction possible between protein and gold surface. In the present study we have examined the structural change of protein in the presence of gold surface and its adsorption on the surface through MD simulations with the help of Gold-Protein (GolP) force field. Results were further analyzed to understand the protein interaction up to molecular level.