Synthesis of Some Novel Class of Peptides from α‐Amino Nitrones and Their Potential Biological Activities

α‐amino nitrones are found to have a great significance in the synthesis of peptides. Simple reaction methodology, high yield, and atom efficiency in these reactions have made this protocol highly attractive. The synthetic route may be extended to the synthesis of dipeptides in enantiomerically pure form. Potential biological activity of the newly synthesized peptides is the major application in this new methodology.     

Specular X-ray reflectivity study of interfacial SiO2 layer in thermally annealed NiO/Si assembly

Present report details an analysis of X-ray reflectivity (XRR) for solution processed NiO thin films on Si (100) substrates. The films were annealed at 700–1,000 °C for 1 h in air. XRR data indicated growth of SiO₂ layer from ~8 nm at 700 °C to ~66 nm at 1,000 °C along with significant variation of electron density profile. X-ray photoelectron spectroscopy and X-ray diffraction studies were used as supporting studies for phase purity and oxidation states of the NiO thin films as well as interfacial SiO₂ layer.     

L-shell ionization of atoms by relativistic electrons

A theoretical study of theL-shell ionization of atoms by relativistic electrons is made for atomic numbers in the range 47 to 92. A new potential model recently proposed by Das and Chakraborty dealing with atomic screening effect in a better way has been used. The results are in satisfactory agreement when compared with some available experimental results and also with the theoretical results of Scofield.     

Environmental DNA-encoded antibiotics fasamycins A and B inhibit FabF in type II fatty acid biosynthesis

In a recent study of polyketide biosynthetic gene clusters cloned directly from soil, we isolated two antibiotics, fasamycins A and B, which showed activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis. To identify the target of the fasamycins, mutants with elevated fasamycin A minimum inhibitory concentrations were selected from a wild-type culture of E. faecalis OG1RF. Next-generation sequencing of these mutants, in conjunction with in vitro biochemical assays, showed that the fasamycins inhibit FabF of type II fatty acid biosynthesis (FASII). Candidate gene overexpression studies also showed that fasamycin resistance is conferred by fabF overexpression. On the basis of comparisons with known FASII inhibitors and in silico docking studies, the chloro-gem-dimethyl-anthracenone substructure seen in the fasamycins is predicted to represent a naturally occurring FabF-specific antibiotic pharmacophore. Optimization of this pharmacophore should yield FabF-specific antibiotics with increased potencies and differing spectra of activity. This study demonstrates that culture-independent antibiotic discovery methods have the potential to provide access to novel metabolites with modes of action that differ from those of antibiotics currently in clinical use.     

Heteroleptic FeII Complexes of 2,2′‐Biimidazole and Its Alkylated Derivatives: Spin‐Crossover and Photomagnetic Behavior

Three iron(II) complexes, [Fe(TPMA)(BIM)](ClO₄)₂?0.5H₂O ( 1 ), [Fe(TPMA)(XBIM)](ClO₄)₂ ( 2 ), and [Fe(TPMA)(XBBIM)](ClO₄)₂ ?0.75CH₃OH ( 3 ), were prepared by reactions of Fe^II perchlorate and the corresponding ligands (TPMA=tris(2‐pyridylmethyl)amine, BIM=2,2′‐biimidazole, XBIM=1,1′‐(α,α′‐o‐xylyl)‐2,2′‐biimidazole, XBBIM=1,1′‐(α,α′‐o‐xylyl)‐2,2′‐bibenzimidazole). The compounds were investigated by a combination of X‐ray crystallography, magnetic and photomagnetic measurements, and Mössbauer and optical absorption spectroscopy. Complex 1 exhibits a gradual spin crossover (SCO) with T_1/2=190 K, whereas 2 exhibits an abrupt SCO with approximately 7 K thermal hysteresis (T_1/2=196 K on cooling and 203 K on heating). Complex 3 is in the high‐spin state in the 2–300 K range. The difference in the magnetic behavior was traced to differences between the inter‐ and intramolecular interactions in 1 and 2 . The crystal packing of 2 features a hierarchy of intermolecular interactions that result in increased cooperativity and abruptness of the spin transition. In 3 , steric repulsion between H atoms of one of the pyridyl substituents of TPMA and one of the benzene rings of XBBIM results in a strong distortion of the Fe^II coordination environment, which stabilizes the high‐spin state of the complex. Both 1 and 2 exhibit a photoinduced low‐spin to high‐spin transition (LIESST effect) at 5 K. The difference in the character of intermolecular interactions of 1 and 2 also manifests in the kinetics of the decay of the photoinduced high‐spin state. For 1 , the decay rate constant follows the single‐exponential law, whereas for 2 it is a stretched exponential, reflecting the hierarchical nature of intermolecular contacts. The structural parameters of the photoinduced high‐spin state at 50 K are similar to those determined for the high‐spin state at 295 K. This study shows that N‐alkylation of BIM has a negligible effect on the ligand field strength. Therefore, the combination of TPMA and BIM offers a promising ligand platform for the design of functionalized SCO complexes.     

Improvement in nanoscale contact resistance of alumina

In all contact-related applications such as the wear-resistant inserts, biomedical implants, high strain rate impact-resistant plates, etc., nanohardness, i.e. the intrinsic contact resistance at the nano scale, plays a major role. In spite of the wealth of literature, the studies on nanohardness of dense, coarse-grain alumina ceramics which represent many commercial varieties; have reasonably good hardness at the macro scale and characteristically exhibit R-curve behaviour, are far from significant. Here, to the best of our knowledge, we report for the first time the experimental observations of the increase in intrinsic contact resistance at the nano scale with the loading rate applied to a high-density (～95?% of theoretical) coarse-grain (～20?μm) alumina ceramics. These observations were explained in terms of the initiation of nanoscale plasticity and maximum shear stress generated just underneath the nanoindenter.     

Monotonicity testing and shortest-path routing on the cube

We study the problem of monotonicity testing over the hypercube. As previously observed in several works, a positive answer to a natural question about routing properties of the hypercube network would imply the existence of efficient monotonicity testers. In particular, if any set of source-sink pairs on the directed hypercube (with all sources and all sinks distinct) can be connected with edge-disjoint paths, then monotonicity of functions $f:\{ 0,1\} ^n \to \mathcal{R}$ can be tested with O(n/∈) queries, for any totally ordered range $\mathcal{R}$ . More generally, if at least a µ(n) fraction of the pairs can always be connected with edge-disjoint paths then the query complexity is O(n/(∈µ(n))). We construct a family of instances of Ω(2 ⁿ ) pairs in n-dimensional hypercubes such that no more than roughly a $\frac{1} {{\sqrt n }}$ fraction of the pairs can be simultaneously connected with edge-disjoint paths. This answers an open question of Lehman and Ron [16], and suggests that the aforementioned appealing combinatorial approach for deriving query-complexity upper bounds from routing properties cannot yield, by itself, query-complexity bounds better than ≈ n ^3/2. Additionally, our construction can also be used to obtain a strong counterexample to Szymanski’s conjecture about routing on the hypercube. In particular, we show that for any δ > 0, the n-dimensional hypercube is not $n^{\tfrac{1} {2} - \delta }$ -realizable with shortest paths, while previously it was only known that hypercubes are not 1-realizable with shortest paths. We also prove a lower bound of Ω(n/∈) queries for one-sided non-adaptive testing of monotonicity over the n-dimensional hypercube, as well as additional bounds for specific classes of functions and testers.     

An ab-initio study of silicon adsorption on metallic surfaces (Au/Ag): Novel perspective to explore chemical bonding

We analyzed localized charge time evolution in the system of two interacting quantum dots (QD) (artificial molecule) coupled with the continuous spectrum states. We demonstrated that Coulomb interaction modifies relaxation rates and is responsible for non-monotonic time evolution of the localized charge. We suggested new mechanism of this non-monotonic charge time evolution connected with charge redistribution between different relaxation channels in each QD.     

Photophysical and photodynamical study of fluoroquinolone drug molecule in bile salt aggregates

Photophysical properties of two widely used antibiotic fluoroquinolone drugs, namely Norfloxacin (NOR) and Ofloxacin (OFL) have been investigated in biomimicking environments formed by bile salts. Experimental results demonstrate that photophysical enhancement and fall of a particular prototropic species are sensitive to the excitation wavelength in bile salt aggregates. Excitation at shorter wavelengths reveals quenching of fluorescence of these fluoroquinolone with addition of sodium deoxycholate (NaDC), sodium taurocholate (NaTC) and sodium glycodeoxycholate (NaGDC). On the contrary, we observe a steady increase in the fluorescence intensity with a continuous redshift upon excitation at longer wavelength. The experimental results were rationalized in terms of the fact that, neutral and zwitterionic species of fluoroquinolone molecules in bile salt aggregates are selectively excited at shorter wavelength while the cationic form of fluoroquinolone molecules are excited at longer wavelength. The excess hydronium ions in the hydrophilic surface of bile salt aggregates convert the neutral species of NOR and OFL into cationic species causing an enhancement in the emission intensity. We found that NaGDC and NaTC because of the conjugate head group are more effective in converting the neutral species of fluoroquinolones into a cationic species than NaDC. The quenching order is in accordance with hydrophobicity indices of bile salt.