Synthesis of modular building blocks using glycosyl phosphate donors for the construction of asymmetric N-glycans

Glycosyl phosphates are known as versatile donors for the synthesis of complex oligosaccharides both chemically and enzymatically. Herein, we report the stereoselective construction of modular building blocks for the synthesis of N-glycan using glycosyl phosphates as donors. We have synthesized four trisaccharide building blocks with orthogonal protecting groups, namely, Manβ2GlcNAc(OAc)₃β6GlcNAc (9), Manβ2GlcNAc-β6GlcNAc(OAc)₃ (15), Manβ2GlcNAc(OAc)₃β4GlcNAc (18) and Manβ2GlcNAcβ4GlcNAc(OAc) (22) for further selective elongation using glycosyltransferases. The glycosylation reaction using glycosyl phosphate was found to be high yielding with shorter reaction time. Initially, The phthalimide protected glucosamine donor was exploited to ensure the formation of β-glycosidic linkage and later converted to the N-acetyl group before the enzymatic synthesis. The selective deprotection of O-benzyl group was performed prior to enzymatic synthesis to avoid its negative interference.     

Metastable surface alloys produced by ion implantation,laser and electron beam treatment

Ion Implantation, Laser and Electron-beam Treatment (LET) of metals have been employed extensively to produce metastable surface alloys. Recent published work on implanted alloys is reviewed first. The dilute implanted alloys (solute concentration <10 at. %) are shown to lead to crystalline metastable solid solutions. At higher solute concentrations, an amorphous phase has been observed for several binary systems and recently for a ternary system. The physical mechanisms at play, are discussed in detail. A review of the surface alloys produced by LET of metals is then presented—with an emphasis on the mechanisms involved. In particular, general criteria governing formation of metastable solid solutions under LET are proposed and shown to have excellent agreement with available data on metals and Si.     

Rheology of semi-dilute solutions of calf-thymus DNA

We study the rheology of semi-dilute solutions of the sodium salt of calf-thymus DNA in the linear and nonlinear regimes. The frequency response data can be fitted very well to the hybrid model with two dominant relaxation times τ₀ and τ₁. The ratio (τ₀/τ₁) ∼5 is seen to be fairly constant on changing the temperature from 20 to 30°C. The shear rate dependence of viscosity can be fitted to the Carreau model.     

Ultra thin films of nanocrystalline Ge studied by AFM and interference enhanced Raman scattering

Initial growth stages of the ultra thin films of germanium (Ge) prepared by ion beam sputter deposition have been studied using atomic force microscope (AFM) and interference enhanced Raman scattering. The growth of the films follows Volmer-Weber growth mechanism. Analysis of the AFM images shows that Ostwald ripening of the grains occurs as the thickness of the film increases. Raman spectra of the Ge films reveal phonon confinement along the growth direction and show that the misfit strain is relieved for film thickness greater than 4 nm. Dedicated to Professor C N R Rao on his 70th birthday     

Temperature dependence of infrared and Raman modes in polymeric RbC60

Temperature dependence of the intra-molecular vibrational modes of C₆₀ in the quasi-1D polymeric RbC₆₀, across the low temperature transition at ∼50 K, has been probed through infrared (IR) and Raman spectroscopies. With the lowering of temperature, the split IR modes of RbC₆₀ are seen to harden but below 50 K a small but definitive signature of an anomalous softening is observed. In addition, the background IR transmission shows an increase below 50 K with the opening of a well defined gap in the electronic spectrum. The implications of these results, along with those of Raman measurements, are discussed in terms of the interaction of intra-molecular phonons with electrons and spin excitations in the system.     

Event-by-event study of DCC-like fluctuation in ultra-relativistic nuclear collisions

A method based on sliding window scheme is developed to search for patches in the pseudorapidity-azimuth plane, on an event-by-event basis, having unusual fluctuation in the neutral pion fraction which may arise due to the formation of Disoriented Chiral Condensates (DCC) in high energy nuclear collisions. The efficiency of the method to extract the patches and the purity of the extracted sample are studied for possible experimental situations.     

Influence of organic solvents and temperature on the micellization of conventional and gemini surfactants: a conductometric study

The micellar behaviour of similar hydrophobic chain length conventional (cetyltrimethyl ammonium bromide, CTAB; cetyl pyridinium chloride, CPC; cetyldimethylbenzyl ammonium chloride, C16BCl) and gemini surfactant (16-2-16) in water and polar non-aqueous solvents has been investigated in the temperature range 288.15–318.15 K with the help of conductivity measurements. The method proposed by Carpena et al. has been used to analyse the conductivity–concentration to determine the micellization parameters using critical micelle concentration (CMC) and degree of counter-ion dissociation (α) of the micelle. It shows much better performance than the conventional methods and the effect of experimental errors on the evaluation of the micellization parameters has been shown to be minimal by using this procedure. It was observed that the micellization tendency of the surfactant decreases in the presence of solvents. Thermodynamic parameters were also evaluated from the temperature dependence of the CMC values.     

Role of Macrophage (M1 and M2) in Titanium-Dioxide Nanoparticle-Induced Oxidative Stress and Inflammatory Response in Rat

Titanium-dioxide nanoparticles (TNP) are used in various consumable goods. Evidence has demonstrated the cytotoxicity of TNPs, but exact mechanism is yet to be elucidated. The present study has been aimed at finding out the mechanism of TNP-induced toxicity in biological system. Different doses of anatase-TNPs administrated intravenously to Wistar rats for once a week for 1 month and properties of T_H cells, macrophages, cytokines secretion, oxidative damage, apoptotic pathway, and hematological and pathological changes were investigated as downstream events of TNP-mediated cytotoxicity. Result suggests that TNPs induce T_H1 and T_H2 response as measured by immunophenotyping (interferon gamma (IFN-γ) and interleukin (IL)-4) of T_H cells, causing induction of M1 (nitric oxide (NO), nitric oxide synthase (iNOS), NF-kappaB (NF-κB), cyclooxygenase-2 (COX-2), IL-1, IL-6, and TNF-α) and M2 (Arg-1, Ym1) macrophages response. At lower dose, T_H1 or M1 response counteracted by T_H2 or M2 response, resulting in insignificant oxidative damage. However, with increasing dose of TNPs, the M1 response was increased over M2 response resulting in significant tissue damage. The M1-induced inflammatory response was found to cause DNA and chromosomal damage resulting apoptosis induction via upregulation of Bax/Bcl-2 ratio and subsequent loss of mitochondrial membrane potential and cyto c release in splenocytes. The TNP-led inflammatory response also causes damage at different tissue levels.