Kinetics of Surfactant-induced Aggregation of Lysozyme Studied by Fluorescence Spectroscopy

The study of protein conformational changes in the presence of surfactants and lipids is important in the context of protein folding and misfolding. In the present study, we have investigated the mechanism of the protein conformational change coupled with aggregation leading to size growth of Hen Egg White Lysozyme (HEWL) in the presence of an anionic detergent such as sodium dodecyl sulphate (SDS) in alkaline pH. We have utilized intrinsic protein fluorescence (tryptophan) and extrinsic fluorescent reporters such as 8-anilinonaphthalene-1-sulfonic acid (ANS), dansyl and fluorescein to follow the protein conformational change in real-time. By analyzing the kinetics of fluorescence intensity and anisotropy of multiple fluorescent reporters, we have been able to delineate the mechanism of surfactant-induced aggregation of lysozyme. The kinetic parameters reveal that aggregation proceeds with an initial fast-phase (conformational change) followed by a slow-phase (self-assembly). Our results indicate that SDS, below critical micelle concentration, induces conformational expansion that triggers the aggregation process at a micromolar protein concentration range.     

The role of N dopant in inducing ferromagnetism in (ZnO)n clusters (n = 1-16)

The effect of nitrogen doping on the magnetic properties of (ZnO)(n) clusters (n = 1-16) has been investigated using spin polarized density functional theory. The total energy calculations suggest that N is more stable at the O site than at the Zn site in (ZnO)(n) clusters and induces a magnetic moment of 1 μ(B)/N atom. The N-Zn-N configuration is more stable than isolated N for 3D structures. The N dopants do not show any tendency for clustering. The binding energy is found to decrease with the increase in the number of N dopants. The magnetic moment increases gradually with the increase in the number of atoms with 1 μ(B)/N atom for n ≤ 4 and less than 1 μ(B)/N for n > 4. The local magnetic moment is mainly localized at the N site with a small magnetic moment induced at the O site. The presence of a Zn vacancy (V(Zn)) induced an additional magnetic moment of 2 μ(B) on the nearest O atoms. The N dopant prefers to form a N-V(Zn) pair. The combination of N and V(Zn) in 3D structures leads to a total magnetic moment of 3 μB. The Mulliken charge transfers from Zn to N and O in all N doped (ZnO)(n) clusters. The calculated results are consistent with existing experimental and theoretical results.     

Effect of WO3 on EPR, structure and electrical conductivity of vanadyl doped WO3·M2O·B2O3 (M=Li, Na) glasses

Glasses with composition xWO₃·(30−x)M₂O·70B₂O₃ (M=Li, Na; 0≤x≤15) doped with 2 mol% V₂O₅ have been prepared using the melt-quench technique. The electron paramagnetic resonance spectra have been recorded in X-band (ν≈9.14 GHz) at room temperature (RT). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) only due to V⁴⁺ ions, which exist as VO²⁺ ions in octahedral coordination with a tetragonal compression in the present glass system. The tetragonality increases with WO₃:M₂O ratio and also there is an expansion of 3d_xy orbit of unpaired electron in the vanadium ion. The study of IR transmission spectra over a range 400-4000 cm⁻¹ depicts the presence of WO₆ group. The DC conductivity (σ) has been measured in the temperature range 423-623 K and is found to be predominantly ionic.     

Quantitative Analysis of Flavonoids in Annona squamosa Leaf Extracts and Its Pellet Formulation by Validated High-Performance Thin-Layer Chromatographic Technique

JPC – Journal of Planar Chromatography – Modern TLC - Annona squamosa, commonly known as custard apple, possesses various medicinal properties such as antimicrobial, insecticidal,...     

Separation of Aminoglycosides by Normal- and Reversed-Phase TLC

JPC – Journal of Planar Chromatography – Modern TLC - The normal-phase (NP) and reversed-phase (RP) thin-layer chromatographic separations of aminoglycosides (streptomycin, kanamycin,...     

Numerical and experimental analysis of large passivation opening for solder joint reliability improvement of micro SMD packages

In this paper, using a recently developed solder fatigue model for wafer level-chip scale package (WL-CSP), we investigated the improvement on solder joint reliability for a 8-bump micro SMD package by enlarging the passivation layer opening at the solder–die interface. The motivation to enlarge the passivation opening is to reduce the severity of the stress concentration caused by the original design, and also to increase the contact area between the solder bump and aluminum bump pad. It was confirmed in the thermal shock test that with the new design, package fatigue life improved by more than 70%. To numerically predict this improvement represents a unique challenge to the modeling. This is because in order to capture the slightest geometrical difference on the order of a few microns between the two designs, the multiple-layer solder-die interface needs to be modeled using extremely fine mesh, while the overall dimensions of the package and the test board are on the order of millimeters. To bridge this tremendous gap in geometry, a single finite element model that incorporates all necessary geometrical details is deemed computationally prohibitive and impractical. In this paper, we applied a global–local modeling scheme that was also suggested by others [1, 2 and 3]. The global model contains the complete package with much simplified solder–die interface whereas the local model includes only one solder joint, but with detailed solder–die interface. Unlike most global–local models proposed by others, we included time-independent plasticity and temperature-dependent materials in the global model. This greatly improved model correlation accuracy with only moderate increase in run time. Energy-based solder fatigue model was used to correlate the inelastic strain energy with the package fatigue life. In an earlier study [4], we have found that Darveaux’s equations tended to be conservative when applied to the micro SMD, and hence new correlations based on curve-fitting the test data were derived. In this paper, we used the newly derived equation and achieved less than 20% error in N₅₀ life for both designs, which is on par with Darveaux’s equations when used for BGAs. The analysis also revealed two factors that may account for the life improvement. First, a slight decrease in inelastic energy dissipation after enlarging the passivation opening. Second, the shift of the crack initiation location which leads to longer crack growth length for the new design. The second factor was also independently confirmed by the failure analysis.     

Effect of nuclei concentration on cavitation cluster dynamics

Cavitation cluster dynamics after the passage of a single pressure wave is studied for different concentrations of artificial cavitation nuclei (30 to 3x10(5) nuclei/ml). With increasing concentration of cavitation nuclei the lifetime of the cavitation cluster is prolonged. Additionally, it is found that the spatial extent of the cluster decreases with higher nuclei concentration. The experimental data for concentrations less than 400 nuclei/ml are compared to simulations with a Rayleigh-Plesset-type equation, taking into account bubble-bubble interaction. For higher concentrations (more than 1000 nuclei/ml) the observed radial cluster dynamics is compared with calculations from an axisymmetric cavity-collapse model.     

DFT studies on the acid-catalyzed Curtius reaction: the Schmidt reaction

The Schmidt reaction is the acid-catalyzed analogue of the Curtius reaction and is extensively used in organic synthesis. In this work, the mechanism of this reaction has been explored using DFT calculations at the B3LYP/6-311+G(d,p) level. Protonated formyl azide may undergo rearrangement to the product, protonated isocyanic acid, with simultaneous extrusion of molecular nitrogen (concerted mechanism), or undergo rearrangement to the anti conformer, followed by removal of nitrogen to form the nitrenium ion, which then rearranges to the final product, protonated isocyanic acid (step-wise mechanism). Like the Curtius reaction, it is found that the concerted pathway is definitely preferred. The key role of acidification in decreasing the overall energy barrier is more highlighted in case of phenyl substitution, with negligible effect on the lower homologues. For methoxy and amine substituents, there is very little difference in the activation energies of the concerted and step-wise reactions, with the former being still slightly preferred. Unlike the parent compound, the rearrangement of substituted nitrenium ion in some cases involves side reactions like C-H insertion and cyclization.     

Density of solutions to quadratic congruences

A classical result in number theory is Dirichlet’s theorem on the density of primes in an arithmetic progression. We prove a similar result for numbers with exactly k prime factors for k > 1. Building upon a proof by E.M. Wright in 1954, we compute the natural density of such numbers where each prime satisfies a congruence condition. As an application, we obtain the density of squarefree n ≤ x with k prime factors such that a fixed quadratic equation has exactly 2 ^k solutions modulo n.     

A visual strip sensor for determination of iron

A visual strip has been developed for sensing iron in different aqueous samples like natural water and fruit juices. The sensor has been synthesized by UV-radiation induced graft polymerization of acrylamide monomer in microporous poly(propylene) base. For physical immobilization of iron selective reagent, the in situ polymerization of acrylamide has been carried out in the presence of 1,10-phenanthroline. The loaded strip on interaction with Fe(II) in aqueous solution turned into orange red color and the intensity of the color was found to be directly proportional to the amount of Fe(II) in the aqueous sample. The minimal sensor response with naked eye was found for 50 ng mL⁻¹ of Fe in 15 min of interaction. However, as low as 20 ng mL⁻¹ Fe could be quantified using a spectrophotometer. The detection limit calculated using the 3s/S criteria, where ‘s’ is the standard deviation of the absorbance of blank reagent loaded strip and ‘S’ is the slope of the linear calibration plot, was 1.0 ng mL⁻¹. The strip was applied to measure Fe in a variety of samples such as ground water and fruit juices.