Sarathi Kundu

Fluorescence behavior of globular proteins from their bulk and thin film conformations in presence of mono-, di- and tri-valent ions

Photoluminescence behavior of globular proteins, lysozyme and bovine serum albumin (BSA), from their bulk and thin film conformations have been studied in presence of mono-, di- and tri-valent ions by using fluorescence and UV-Vis spectroscopy at two different temperatures and the morphology of the protein thin films have been studied by using atomic force microscopy. Protein- and ion-dependent dynamic and static quenching behaviors have been identified. While dynamic quenching is observed for lysozyme for all the three different valent ions, BSA shows no quenching for mono-valent (Na(+)) ions, dynamic quenching for di-valent (Ni(2+)) ions and static quenching for tri-valent (Fe(3+)) ions at pH≈5.5. After heat treatment, as the conformation of the protein molecules changes, the quenching efficiency for lysozyme in presence of ions decreases but shows enhancement for BSA. In thin film geometry, the molecular conformation of both lysozyme and BSA modifies on the solid surfaces and hence quenching efficiency also modifies in comparison with that of bulk and as a result the quenching efficiency for lysozyme increases but decreases for the BSA film.

Cation-induced monolayer collapse at lower surface pressure follows specific headgroup percolation

A Langmuir monolayer can be considered as a two-dimensional (2D) sheet at higher surface pressure which structurally deform with mechanical compression depending upon the elastic nature of the monolayer. The deformed structures formed after a certain elastic limit are called collapsed structures. To explore monolayer collapses at lower surface pressure and to see the effect of ions on such monolayer collapses, out-of-plane structures and in-plane morphologies of stearic acid Langmuir monolayers have been studied both at lower (≈6.8) and higher (≈9.5) subphase pH in the presence of Mg^{2+},Ca^{2+},Zn^{2+},Cd^{2+}, and Ba^{2+} ions. At lower subphase pH and in the presence of all cations, the stearic acid monolayer remains as a monolayer before collapse, which generally takes place at higher surface pressure (π_{c}>50mN/m). However, at higher subphase pH, structural changes of stearic acid monolayers occur at relatively lower surface pressure depending upon the specific dissolved ions. Among the same group elements of Mg^{2+},Ca^{2+}, and Ba^{2+}, only for Ba^{2+} ions does monolayer to multilayer transition take place from a much lower surface pressure of the monolayer, remaining, however, as a monolayer for Mg^{2+} and Ca^{2+} ions. For another same group elements of Zn^{2+} and Cd^{2+} ions, a less covered bilayer structure forms on top of the monolayer structure at lower surface pressure, which is evidenced from both x-ray reflectometry and atomic force microscopy. Fourier transform infrared spectroscopy confirms the presence of two coexisting conformations formed by the two different metal-headgroup coordinations and the monolayer to trilayer or multilayer transformation takes place when the coverage ratio of the two molecular conformations changes from the critical value (p_{c}) of ≈0.66. Such ion-specific monolayer collapses are correlated with the 2D lattice percolation model.

Variation in surface plasmonic response due to the reorganization of Au nanoparticles in Langmuir-Blodgett film

Layer-by-layer structures of dodecanethiol-encapsulated Au nanoparticles have been formed on Si(001) and quartz substrates at different surface pressures by Langmuir-Blodgett method. Optical absorption spectra and out-of-plane structural information have been obtained from UV-Vis spectroscopy and X-ray reflectivity measurements, respectively. With time the thickness of the film decreases keeping the layered structure unchanged but finally monolayer like structure forms. Localized surface plasmon resonance peaks obtained from the UV-Vis spectra show that coupling between Au nanoparticles occurs at the initial stage of the reorganization process as the interparticle distance decreases and as a result, a redshift in the plasmon peak wavelength takes place. Maximum redshift occurs for the monolayer and the peak shift linearly decreases for the multilayer structures. After prolonged reorganization when all layered structures transform into monolayer like structure again redshift occurs but in this process the ...

Effect of water and air-water interface on the structural modification of Ni-arachidate Langmuir-Blodgett films

Nickel arachidate (NiA) Langmuir-Blodgett (LB) films have been deposited on hydrophilic Si(0 0 1) substrates by three (up-down-up) and five (up-down-up-down-up) strokes. During deposition, substrates were kept inside the water subphase for different times after each down stroke. Structural information of all the LB films have been obtained from X-ray reflectivity (XRR) studies. One and two symmetric monolayer (SML) was deposited on top of the asymmetric monolayer (AML) in three and five stokes respectively. All the preformed LB films were then used to go through the air-water interface with the same speed that was used at the time of film deposition. Structural information obtained from the XRR studies show that mainly the top layer density decreases after passing through the air-water interface but the layered structure remains the same. Information obtained from both the XRR and atomic force microscopy (AFM) studies suggest that molecules peeled from the top SML layer do not reincorporate with the LB film through tail-tail hydrophobic interaction. Our study shows that NiA LB film has better stability compared with cadmium arachidate LB film inside the water subphase without forming any out-of-plane molecular reorganization.

Functionalization of β-lactam antibiotic on lysozyme capped gold nanoclusters retrogress MRSA and its persisters following awakening

In this study we have reported an efficient antibacterial hybrid fabricated through surface functionalization of lysozyme capped gold nanoclusters (AUNC-L) with β-lactam antibiotic ampicillin (AUNC-L-Amp). The prepared hybrid not only reverted the MRSA resistance towards ampicillin but also demonstrated enhanced antibacterial activity against non-resistant bacterial strains. Most importantly, upon awakening through cis-2-decenoic acid (cis-DA) exposure, the MRSA persister got inhibited by the AUNC-L-Amp treatment. Intraperitoneal administration of this hybrid eliminates the systemic MRSA infection in a murine animal model. Topical application of this nano conjugate eradicated MRSA infection from difficult to treat diabetic wound of rat and accelerated the healing process. Due to inherent bio-safe nature of gold, AUNC-L alone or in the construct (AUNC-L-Amp) demonstrated excellent biocompatibility and did not indicate any deleterious effects in in vivo settings. We postulate that AUNC-L-Amp overcomes the elevated levels of β-lactamase at the site of MRSA antibiotic interaction with subsequent multivalent binding to the bacterial surface and enhanced permeation. Coordinated action of AUNC-L-Amp components precludes MRSA to attain resistance against the hybrid. We proposed that the inhibitory effect of AUNC-L-Amp against MRSA and its persister form is due to increased Amp concentration at the site of action, multivalent presentation and enhanced permeation of Amp through lysozyme-mediated cell wall lysis.

Thin film of polyelectrolyte complex nanoparticles for protein sensing

Polyelectrolyte complex nanoparticles (PEC NPs) are prepared using two polyelectrolytes poly(Na-4-styrene sulphonate) (PSS) and poly(diallyldimethylammoniumchloride) (PDADMAC) at a molar mixing ratio of n-/n+ ≈ 0.67 by consecutive centrifugation. PEC NPs formation is investigated through dynamic light scattering (DLS) and atomic force microscopy (AFM). Optical behaviors of PEC NPs in thin film confirmation are studied using UV-Vis and photoluminescence spectroscopy. Although absorption peaks of PSS occurs at the same position before and after the formation of PEC NPs but emission peaks are found at ≈ 278 and 305 nm whereas for pure PSS emission peaks exist at ≈ 295 and 365 nm. Hence, thin film of PEC NPs can be applied as very sensitive material for protein sensing since absorption of protein is occurred at ≈ 278 nm. Protein sensing behavior of such PEC NPs thin film is studied using photoluminescence spectroscopy.

Studies on surface morphology and electrical conductivity of PEDOT:PSS thin films in presence of gold nanoparticles

PEDOT:PSS is a water soluble conducting polymer consists of positively charged PEDOT and negatively charged PSS. However, this polymer suffers low conductivity problem which restrict its use. In this paper, electrical conductivity of PEDOT:PSS thin films is improved by using charged gold nanoparticles. The nanoparticles used are synthesized using lysozyme protein. The nanoparticles coated with lysozyme protein possess positive zeta potential. In the presence of gold nanoparticles due to electrostatic interaction between positively charged nanoparticles and negatively charged PSS chains, modification takes place in the surface morphology and electrical behaviors of PEDOT:PSS thin films. The changes in the polymer matrix conformations in the presence of nanoparticles are studied by Fourier transformed Infra-red (FTIR) spectroscopy, whereas the surface morphology of prepared thin films before and after interaction with nanoparticles is investigated through atomic force microscopy (AFM). Four probe method is used to measure the variation of electrical conductivity from I-V characteristics curves.PEDOT:PSS is a water soluble conducting polymer consists of positively charged PEDOT and negatively charged PSS. However, this polymer suffers low conductivity problem which restrict its use. In this paper, electrical conductivity of PEDOT:PSS thin films is improved by using charged gold nanoparticles. The nanoparticles used are synthesized using lysozyme protein. The nanoparticles coated with lysozyme protein possess positive zeta potential. In the presence of gold nanoparticles due to electrostatic interaction between positively charged nanoparticles and negatively charged PSS chains, modification takes place in the surface morphology and electrical behaviors of PEDOT:PSS thin films. The changes in the polymer matrix conformations in the presence of nanoparticles are studied by Fourier transformed Infra-red (FTIR) spectroscopy, whereas the surface morphology of prepared thin films before and after interaction with nanoparticles is investigated through atomic force microscopy (AFM). Four probe method is ...

A comparative study on intrinsic fluorescence of BSA and lysozyme proteins in presence of different divalent ions from their solution and thin film conformations

Optical emission behaviours of lysozyme and bovine serum albumin, from bulk and thin film geometry, were studied in the presence of three different divalent ions (Mg2+ , Ca2+ or Ba2+ ) using different spectroscopic [steady-state fluorescence, UV-Vis and Fourier transform infra-red (FTIR)] techniques. Additionally, protein thin films on silicon surfaces were prepared and morphological studies were carried out using atomic force microscopy. Dynamic quenching was mainly identified for both proteins in the presence of Mg2+ , Ca2+ and Ba2+ ions. The molecular conformation of the proteins was modified in thin films compared with that in solution, consequently quenching efficiencies also varied. ATR-FTIR studies confirmed the conformational changes of proteins in the presence of all divalent ions. All metal ions used were divalent in nature and belonged to the same group of the periodic table but, depending on their individual characteristics such as electron affinity, ionic radius, etc., the magnitude of the protein and hydrated ion interaction varied and accordingly the quenching efficiency was modified. Quenching was maximum for Ca2+ ions, followed by the other two ions. Our study clearly illustrates the geometry-dependent physical and biological functions of proteins.

Optical and structural behaviors of crosslinked polyvinyl alcohol thin films

Polyvinyl Alcohol (PVA) has excellent properties like uniaxial tensile stress, chemical resistance, biocompatibility, etc. The properties of PVA further can be tuned by crosslinking process. In this work, a simple heat treatment method is used to find out the optimum crosslinking of PVA and the corresponding structural and optical responses are explored. The PVA crosslinking is done by exposing the films at different temperatures and time intervals. The optical property of pure and heat treated PVA films are investigated by UV-Vis absorption and photoluminescence emission spectroscopy and structural modifications are studied by Fourier Transform Infrared Spectroscopy (FTIR). The absorption peaks of pure PVA are observed at ≈ 280 and 335 nm and the corresponding emission is observed at ≈ 424 nm. The pure PVA showed modified optical behaviors after the heat treatment. In addition, dipping the PVA films in hot water (85°C) for nearly 20 minutes also show impact on both structural and optical properties. From...

Glycogen–gold nanohybrid escalates the potency of silymarin

In this study, a glycogen–gold nanohybrid was fabricated to enhance the potency of a promising hepatoprotective agent silymarin (Sly) by improving its solubility and gut permeation. By utilizing a facile green chemistry approach, biogenic gold nanoparticles were synthesized from Annona reticulata leaf phytoconstituents in combination with Sly (SGNPs). Further, the SGNPs were aggregated in glycogen biopolymer to yield the therapeutic nanohybrids (GSGNPs). Transmission electron microscopy, UV–Vis spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis confirmed the successful formation and conjugation of both SGNPs and GSGNPs. The fabricated nanohybrids showed significant protection against CCl4-induced hepatic injury in Wistar rats and maintained natural antioxidant (superoxide dismutase and catalase) levels. Animals treated with GSGNPs (10 mg/kg) and SGNPs (20 mg/kg) retained usual hepatic functions with routine levels of hepatobiliary enzymes (aspartate transferase, alanine transaminase, alkaline phosphatase, and lactate dehydrogenase) and inflammatory markers (interleukin-1β and tumor necrosis factor-α) with minimal lipid peroxidation, whereas those treated with 100 mg/kg of Sly showed the similar effect. These results were also supported by histopathology of the livers where pronounced hepatoprotection with normal hepatic physiology and negligible inflammatory infiltrate were observed. Significant higher plasma Cmax supported the enhanced bioavailability of Sly upon GSGNPs treatment compared to SGNPs and free Sly. Graphite furnace atomic absorption spectrophotometry analysis also substantiated the efficient delivery of GSGNPs over SGNPs. The fabricated therapeutic nanohybrids were also found to be biocompatible toward human erythrocytes and L929 mouse fibroblast cells. Overall, due to increased solubility, bioavailability and profuse gut absorption; GSGNPs demonstrated tenfold enhanced potency compared to free Sly.