Self-Assembling Synthetic Oligopeptide-Based Gelators

Synthetic self-assembling oligopeptide gelators are an important class of compounds which form thermoreversible gels in various organic solvents as well as in aqueous medium. These gels are soft, viscoelastic materials which are envisaged for useful applications in biological and material sciences. The terminally protected self-assembling synthetic tripeptide Boc-Ala-Aib-β-Ala-OMe 1 (Aib: α-aminoisobutyric acid i.e. dimethyl glycine and β-Ala: β-Alanine) forms gels in various organic solvents, whereas its structural analog i.e. the peptide Boc-Ala-Gly-β-Ala-OMe 2 (another self-assembling synthetic tripeptide) fails to form gels under similar conditions and this issue has been addressed. The terminally protected tripeptide Boc-Ala-Val-Ala-OMe 3 has been found to form gels in different aromatic organic solvents. Several structural analogs of peptide 3 [using small structural changes either in protecting groups (at the N or C-terminal position) or in amino acid side chains] have been synthesized, characterized and studied for gelation to address the question how structural changes can regulate the gelation property. Results of the gelation studies indicate that some structural changes are useful to make new peptide gelators with some variations in gelation property and efficiency, while a few structural changes in the protecting groups are really detrimental, leading to abolition the gelation property. These gels are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-Transform Infrared (FT-IR) spectroscopy and ¹H NMR studies.     

Enhanced non-metallic behavior on the verge of magnetic instability in Fe2V1−xNbxAl Heusler alloys

Structural, magnetic and transport behavior of Nb substituted Fe₂VAl alloys have been investigated in the present work. From the detailed analysis of these data it is observed that Nb content promotes a lattice expansion in L2₁ super-structure of Fe₂VAl. Magnetization data suggest that un-doped Fe₂VAl exhibits cluster glass behavior with a bimodal distribution of superparamagnetic clusters at lower temperatures, developed possibly due to the cluster size distribution. However, in Nb-substituted alloys, cluster size reduces and cluster density increases, which further reduces coupling between the clusters, resulting in a state of increased magnetic disorder up to a plausible 20% substitution. Concurrently resistivity increases at lower temperatures and shows a deviation from semiconductor like transport, which can be explained in terms of increasing spin dependent scattering and decreasing inter cluster interaction due to iso-electronic-but-larger-sized Nb substitution at V site. Present experimental results corroborate well with the theoretical predictions made in the literature.     

Photophysical properties of the 8-phenyl analogue of PM567: A theoretical rationalization

The absorption and emission spectroscopic investigations of the C-8-phenyl substituted analogue of the pyrromethene dye PM567 in various polar, non-polar as well as protic and aprotic solvents are reported. The solvatochromic shifts of the spectral bands were studied in a multitude of polar, non-polar and protic, aprotic solvents followed by a multilinear regression in which several solvent parameters were simultaneously analysed. Comparison of the experimental results with those obtained by gas phase ab initio computation with CIS, TD-HF and TD-DFT theories using 6-31G* basis set reveal an overestimation of the experimentally measured excitation parameters by all these theoretical models. However, the trends in the experimental results agree with those calculated theoretically.     

Uniqueness and set sharing of derivatives of meromorphic functions

We prove some uniqueness theorems concerning the derivatives of meromorphic functions when they share two or three sets which will improve some existing results.     

Synthesis and Characterization of 2-Aminobenzothiazol and 1-Methylisatin Co-Сrystal

Crystallography Reports - A co-crystal of 2-aminobenzothiazol and 1-methylisatin (III) was synthesized and characterized by elemental analysis, Fourier-transform infrared spectroscopy, nuclear...     

Ordering in alloys

Abstract

The continuous ordering process can be viewed as a development and a gradual amplification of concentration modulations with wave lengths of the order of a few lattice spacings. How the development of different concentration modulaltions leads to different superlattice structures in cubic systems is explained with the help of some illustrative examples. The importance of concentration modulations with special point wave vectors in the stability of the various coherent superlattice structures is discussed. Experimental evidences for such continuous ordering is cited from recent results on ordering in Ni-Mo alloys.

The evolution of ordering in some systems can also be viewed as progressively tiling the disordered lattice by superlattice tiles. When more than one type of coherent superlattice tiles compete, juxtaposition of different types of tiles can occur during the course of ordering. The transitional states between the short range and the long range ordered Ni-Mo alloys indeed exhibit such structures where different types of superlattice tiles decorate the fcc lattice. The role of special point concentration waves in the development of such structures will be discussed in relation to the secondary ordering processes involving two perpendicular ?1 ½ 0? waves and a combination of an ?1 ½ 0? and an appropriate ?100? wave.