Buckling and enforced stretching of bio-filaments

We examine the force needed to extend/compress a bio-filament, a key issue in the study of cytoskeleton mechanics and polymer physics, by considering both the associated stretching and bending deformations. Specifically, closed form relationships are derived to predict the buckling of stiff filaments such as F-actin and microtubules. Our results clearly demonstrate that the maximum force a 2D filament can sustain is higher than the Euler buckling load whereas the force in a 3D filament is always below it, and hence clarify some of the ambiguities in the literature. In addition, analytical expression is also obtained to describe how the extensional force increases when a flexible molecule, like DNA, is stretched close to its contour length, which has been shown to fit a variety of experimental data very well. Our theory provides important corrections/improvements to several well-known existing models.     

Embedded silicon nanocrystal interface structure and strain

The structure of nanocrystal-matrix interface and strain in embedded nanocrystals are studied using large-scale atomistic simulations, with the examples of Si nanocrystal embedded in amorphous matrix of SiO₂. Photoluminescence from silicon nanocrystals embedded in a dielectric matrix like SiO₂ and Si₃N₄ are promising for Si-based optical devices. The nanocrystal-matrix interface plays a crucial role in understanding its optical and electrical properties. Nanocrystals with diameters varying from 2.17 to 4.56 nm are studied. A detailed quantitative analysis of the variation of Si/SiO₂ interface structure and strain distribution with nanocrystal diameter is reported. A linear variation of the interface width with nanocrystal diameter is observed with thinner interfaces for larger nanocrystals. Local deformation analysis reveals that the smaller nanocrystals are highly strained, whereas the strain in the larger ones shifts to the interface. This is in accordance with observed increase in total percentage of defect states in the interface from 39 to 70% for diameter increasing from 2.17 to 4.56 nm. Moreover, based on the atomic arrangements at the interface, optically active defects like Pb centres, E centres and non-bridging oxygen centres are identified and a dominance of Pb centres is observed for all the nanocrystals. The detailed structural characterization-related investigations using the proposed simulation approach will find useful application in designing system-level response of embedded nanocrystals and also to correlate various experimental observations.     

Investigation of covalency in CrI3 using Mössbauer spectroscopy of129I

The principal components of the electric field gradient tensor, the transferred hyperfine magnetic field and the isomer shift have been measured in ferromagnetic CrI₃ using the 27.8 keV Mössbauer resonance in¹²⁹I. From these hyperfine parameters we have determined the electron transfer and spin transfer coefficients for CrI₃ and compared these with the ones deduced for other Cr compounds.     

Condensed Heterotricycles. Synthesis and Reactions of b-Fused 1(2H)-Isoquinolinones with unusual enaminic properties

Homophthalic acid ( 1 ) undergoes reaction with 1,2-, 1,3-, and 1,4-diamines to give condensed 1(2H)-isoquinolinones like 2 , 4 , 13 , and 25 , which exhibit marked enamine character. These are attacked by electrophiles at the N or C terminus. Some notable reactions of imidazoisoquinolone 2 are those with maleic and acrylic acids to form the tetracycles 48 and 51 , respectively. With propiolic acid, 5 underwent an interesting reaction to form the benzimidazonaphthyridine 53 . An equally interesting behaviour was elicited from 2 in its reaction with formaldehyde, when in addition to the expected methylene-bridged molecule 59 , the novel spiro derivative 60 was formed by the dimerisation of a presumed azadiene intermediate 63 .     

Moment collapse in the Ce(Rh1−xOsx)3B2 system

The compound CeRh₃B₂ orders magnetically with a low saturation moment of about 0.4 micro_B per formula unit but a very high Curie temperature of 115 K. On replacing Rh with Os, it is observed that in the Ce(Rh_1?xOs_x)₃B₂ (0 ? x ? 0.167) series, both the magnetic moment and the Curie temperature decrease rapidly with increasing x. The compound CeRh_2.5Os_0.5B₂ (x = 0.167) does not appear to be ordered magnetically down to 5 K. This behavior is thought to arise from the changes in the hybridization of Ce 4f levels with sp type conduction electrons and/or with Rh and Os derived d bands.     

A Novel Architecture of a Heptadentate Macroacyclic 2,6-Bis [(3-methoxy salicylidene) Hydrazino carbonyl] Pyridine Towards Lanthanides: A Synthetic and Structural Studies of Dinuclear Lanthanide (III) Complexes

Reaction of Ln(NO₃)₃ with 2,6-bis[(3-methoxysalicylidene)hydrazino carbonyl]pyridine (BMSPD) afforded binuclear complexes of the type [Ln₂(BMSPD)(NO₃)₂(H₂O)₅]·3H₂O in case of La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III) and Dy(III), and [Ln₂(BMSPD)(NO₃)₂(H₂O)₅] in case of Y(III). The mode of coordination of ligand and the conformational changes on complexation with lanthanides was studied based on elemental analysis, magnetic studies, TG/DTA, IR, ¹H-NMR, Electronic, EPR and Fluorescence spectral studies. The ligand coordinates to one metal centre through enolized deprotonated carbonyls and pyridine nitrogen whereas doubly deprotonated phenolate oxygens and two hydrazonic nitrogens ligate to another lanthanide centre. Both the metal ions are in eight-coordination environments. The ligand and complexes were further tested for antifungal and antibacterial activities.     

Synthesis and Spectral Investigation of Some Transition Metal Complexes Containing Pentadentate Macroacyclic <Emphasis Type="Italic">NNNNN</Emphasis>-donor Schiff Base Ligands

A new Schiff base, 2,6-diacetylpyridine bis(2-hydrazinobenzothiazole) (DPHB), has been designed, and synthesized by the condensation of 2,6-diacetylpyridine with 2-hydrazinobenzothiazole, and structurally characterized. Copper(II), cobalt(II), nickel(II), manganese(II), zinc(II), cadmium(II) and oxovanadium(IV) complexes of DPHB have been synthesized for the first time. Their structures have been elucidated on the basis of elemental analyses, conductance measurements, magnetic properties, spectral (i.r., ¹H-n.m.r., u.v.–vis., e.p.r. and FAB-mass) and thermal studies. The complexes exhibit an octahedral geometry around the metal centre. The conductance data of all the complexes suggest them to be 1:1 electrolytes. The X-band e.p.r. spectra of the copper(II) and oxovanadium(IV) complexes in the polycrystalline state at room (300 K) and liquid nitrogen temperature (77 K) were recorded and their salient features are reported. Thermal stabilities of the manganese(II) and zinc(II) complexes have been studied.     

Crystal Structure of 2-thiophene-2-yl-3(thiophene-2-carboxylideneamino)-1, 2-dihydroquinazolin-4(3H)-one and the Synthesis, Spectral and Thermal Studies of its Transition Metal(II) Complexes

The synthesis of manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes of a new ligand 2-thiophene-2-yl-3(thiophene-2-carboxylidene-amino)-1,2-dihydroquinazolin-4(3H)-one (TTCADQ) is described. The ligand and metal complexes were characterized by elemental analysis, conductivity measurements, spectral (u.v.–vis., i.r., 1D n.m.r., 2D hetcor and e.p.r.) and thermal studies. The formation of 1,2-dihydroquinazolin-4(3H)-one rather than hydrazone, in the reaction of aromatic aldehyde and o-aminobenzoylhydrazide is proved by single crystal X-ray diffraction and 2D hetcor n.m.r. studies. On the basis of elemental analysis, u.v.–vis.spectroscopy and magnetic moment studies, six coordinate geometry for all the complexes was proposed. The i.r. spectral studies reveal the bidentate behaviour of the ligand.     

N-(salicylidene)nitrosophenylglycine Schiff base as NOOO-donor towards transition metal ions

A new tetradentate NOOO-donor ligand, N-(salicylidene)nitrosophenylglycine (H₂snpg) has been designed, synthesized and structurally characterized. Copper(II), nickel(II), cobalt(II), manganese(II) and zinc(II) complexes of H₂snpg have been prepared for the first time. The authenticities of the ligand and its metal complexes have been established on the basis of elemental analyses, molar conductance measurements, magnetic properties, spectral (i.r., ¹H-n.m.r., u.v.–vis. and mass) studies. The i.r. spectral studies of all the complexes exhibit a similar feature about the ligating nature of the ligand to the metal ions and revealed that the ligand has coordinated through the carbonyl oxygen, azomethine nitrogen, nitroso oxygen and deprotonated hydroxyl oxygen. The molar conductance data suggest them to be non-electrolytes. The antimicrobial activity of all the compounds was studied against Escherichia coli, Bacillus cirroflagellosus, Aspergillus niger and Candida albicans. All the complexes have shown a moderate to high fungal activity compared to the ligand.