Late stage modification of peptides via CH activation reactions

Recently developed strategies for late stage modification of peptides through CH activation, an arena of contemporary interest in chemical biology and drug discovery, are discussed. Through this tactic, non-polar amino acids in peptides have been selectively functionalized and CH activation enabled new CC and CX bond formations (arylation, alkynylation, fluorination, hydroxylation, azidation, etc.) are documented. Significant advances have been made in Pd or Au-catalyzed, racemization-free, tryptophan specific modifications of large peptides via CH arylation and alkynylation reactions without any protecting group requirement. Development of a new biaryl stapling technique for complex peptides, 18F radiofluorine introduction and diversity oriented post synthetic applications on bio-active cyclopeptides like valinomycin and aureobasidin are additional highlights which underscores the vast potential of late stage CH activation reactions in peptide based therapeutics research.     

The low frequency behaviour in high frequency capacitance–voltage characteristics due to contribution of band-to-band tunnelling and generation–recombination in Hg0.75Cd0.25Te MIS capacitors

Hg_1−xCd_xTe Metal–Insulator–Semiconductor (MIS) capacitors were studied both experimentally and theoretically to investigate the capacitance contributions due to band-to-band (btb) tunnelling and generation–recombination (gr) of carriers to inversion layer capacitance. A good fit to the data has been obtained by including the btb contributions rather than gr contributions.     

Constraints on dark matter annihilation from M87

As the largest mass concentrations in the local Universe, nearby clusters of galaxies and their central galaxies are prime targets in searching for indirect signatures of dark matter annihilation (DMA). We seek to constrain the dark matter annihilation emission component from multi-frequency observations of the central galaxy of the Virgo cluster. The annihilation emission component is modeled by the prompt and inverse-Compton gamma rays from the hadronization of annihilation products from generic weakly interacting dark matter particles. This component is fitted to the excess of the observed data above the spectral energy distribution (SED) of the jet in M87, described with a best-fit synchrotron-self-Compton (SSC) spectrum. While this result is not sufficiently significant to claim a detection, we emphasize that a dark matter “double hump signature” can be used to unambiguously discriminate the dark matter emission component from the variable jet-related emission of M87 in future, more extended observation campaigns.     

Effect of thermal annealing on the formation of silicon nanoclusters in SiOX films grown by PLD

Silicon nanoclusters formation in pulsed laser deposited (PLD) silicon suboxide (SiO_X) films by thermal annealing is reported. The SiO_X films are prepared by ablation of silicon target at different oxygen partial pressures. The different deposition conditions are employed to study the effect of oxygen concentration on the size of the nanoclusters. Post deposition thermal annealing of the films leads to the phase separation in silicon suboxide films. Fourier transform infrared spectroscopy, micro-Raman spectroscopy and UV-vis absorption spectroscopy studies were carried out to characterize the formation of silicon nanoclusters in SiO_X films.     

Cryopreservation of shoot tips and cotyledons of the north american ginseng (Panax quinquefolius l.)

North American ginseng (NAG) (Panax quinqueolius L.) is a medicinal plant in high demand due to its health benefits. Cryopreservation is a good alternative for long-term conservation of NAG germplasm. Pretreatments of shoot tips (0.8-1 mm) and cotyledons (1-2 mm) on sucrose and abscisic acid (ABA) enriched medium were tested to determine the effects on regrowth following cryopreservation in liquid nitrogen. The maximum regrowth (60 percent) following PVS2 vitrification occurred with shoot tips after three weeks of cold acclimation and pretreatment on sucrose (0.3 M) or a combination of ABA (0.1 M) and sucrose in the third week. Cotyledon recovery was best with the combination pretreatment. Shoot tips showed normal development and cotyledons produced embryogenic callus after the cryopreservation process. This is the first report on cryopreservation of shoot tips and cotyledons of Panax species. This cryopreservation protocol provides a safe long-term storage method for important NAG selections and makes it possible to use cryopreservation for improving the security of NAG germplasm.     

Dielectric relaxation in polyvinylidenefluoride–polysulfone blends

Dielectric properties of polymer blend of polyvinylidenefluoride (PVDF) and polysulfone (PSF) of different wt. % have been studied to understand the molecular motion and their relaxation behavior in the frequency range of 100 Hz to 10 kHz at different temperatures between 30 and 190 °C. The dielectric constant of the blend decreased with frequency and increased with the increasing temperature and PSF content in the blend. The magnitude of dielectric loss also increased with increase in temperature and PSF content. The observed characteristic has been consistently explained in terms of dipolar motions and the plasticization effect brought about by blending of PSF with PVDF. At constant frequency and temperature, the blend follows a linear relationship between logarithm of their dielectric constant and different ratios of blend. The appearance of a peak for each concentration in dielectric loss suggests the presence of relaxing dipoles in the blend. In addition of PSF with PVDF, the peak shifts toward higher frequency side suggesting the speed up the relaxation process. AC dielectric data is also combined with thermally stimulated depolarization current (TSDC) data which is generally studied for low-frequency dielectric properties of polymers blends so as to produce the results in a wide frequency range. The glass transition temperature (T_g) of the blend was studied by differential scanning calorimetric technique (DSC), the T_g was compared and correlated with TSDC peak. The blend samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to study the formation of blend and micro structural properties of the materials. The shifting of peak toward lower diffraction angle side confirms the reduction in particle size with increasing amorphous content in the blend.     

A new volumetric method for microdetermination of tellurium or mercury

Summary A volumetric method for the determination of tellurium(IV) or mercury(II) in the mg range is proposed by using the redox process. Reduction is effected by boiling with an excess of reducing sugar in alkali solution. The metals obtained are re-oxidised by means of ferric chloride solutions. The ferrous ions formed are titrated against a standard solution of ceric sulphate using N-phenyl anthranilic acid as indicator. The interference due to various cations has been investigated.

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Zusammenfassung Ein neues oxydimetrisches Verfahren zur Bestimmung von Tellur(IV) oder von Quecksilber(II) im Milligrammaßstab wird vorgeschlagen. Die mit einem Überschuß von reduzierendem Zucker in alkalischem Milieu bei Siedehitze reduzierten Metalle werden mit Eisen(III)-chlorid reoxydiert. Das dabei entstandene Eisen(II) wird mit Cersulfat gegen N-Phenylanthranilsäure als Indikator titriert. Die Störung durch verschiedene Kationen wurde untersucht.

     

First observation of a smectic A-cholesteric phase transition in a thermotropic liquid crystal consisting of a rigid-rod helical polysilane

A smectic A-cholesteric phase transition for a rigid-rod helical polymer, poly[n-decyl-(S)-2-methylbutylsilane] (PD2MBS), with a narrow molecular weight distribution, has been observed for the first time. Polarizing optical microscopy showed that the fan-shaped texture of the smectic A phase turned into the characteristic planar texture of the cholesteric phase upon heating. The positive CD band, which corresponds to the reflection band of the cholesteric phase, gradually decreased in intensity within a range 30°C below the transition temperature on cooling, while the peak maximum shifted towards shorter wavelengths. It was concluded that the system has a very wide temperature region over which the cholesteric-smectic A phase transition occurs and in which the cholesteric pitch varies with temperature.     

THE ESTIMATION OF PRIOR FROM FISHER INFORMATION

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New cyclopentadienylzirconium(IV) complexes of N-phthaloyl amino acids

Transition Metal Chemistry - Cyclopentadienylzirconium(IV) complexes of N-phthaloyl amino acids of general formulae Cp2Zr(L)nCl2?n (n = 1 or 2) and CpZrCl(L)2 (LH = N-phthaloyl derivatives of...