Honeycomb nets with interpenetrating frameworks involving iminodiacetato-copper(II) blocks and bipyridine spacers: syntheses, characterization, and magnetic studies

Three coordination polymers of copper(II), viz. ([Cu(ida)(4,4'-bipyH)]ClO(4))( proportional, variant ) (1), ([Cu(2)(ida)(2)(micro-4,4'-bipy)].2H(2)O)( proportional, variant ) (2), and [Cu(2)(ida)(2)(bpa)]( proportional, variant ) (3) have been synthesized by the process of self-assembly using Cu(ida) [ida = iminodiacetate(2-)] as the building block and 4,4'-bipyridyl and 1,2-bis(4-pyridyl)ethane (bpa) as linkers. Crystals of 1 are orthorhombic, of space group Pna2(1), with a = 13.8956(12) A, b = 16.3362(16) A, c = 7.3340(12), and Z = 4. Both compounds 2 and 3 crystallize in monoclinic space group P2(1)/a with a = 10.1887(8) A (9.6779(10) A for 3), b = 8.0008(11) A (9.1718(10) A), c = 11.6684(9) A (12.9144(12) A), beta = 98.307(11) degrees (102.796(18) degrees ), and Z = 2 (2). Compound 1 has a zigzag chain structure with an extensive hydrogen-bonded network while compounds 2 and 3 are honeycomb (6,3) nets with interpenetrating structures. Variable temperature (2-300 K) magnetic study indicates the presence of weak antiferromagnetic interactions (J = 0.82 +/- 0.01 cm(-)(1)) in 1 and ferromagnetic in 2 (J = -0.45 +/- 0.05 cm(-)(1)) and 3 (J = -0.21 +/- 0.02 cm(-)(1)). The extent of planarity of the bridging "Cu-O-C-O-Cu" moiety, acting as the super-exchange pathway between the neighboring copper centers, probably controls the sign of the magnetic exchange coupling in these compounds.     

A family of mixed-ligand oxovanadium(V) complexes incorporating tridentate ONO donor hydrazone ligands derived from acetylhydrazide and 2-hydroxybenzaldehyde/2-hydroxyacetophenone

In the title family the tridentate ONO donor ligands are the fully deprotonated forms of acetylhydrazones of 2-hydroxybenzaldehyde (H₂L¹) and 2-hydroxyacetophenone (H₂L²) (general abbreviation H₂L), while bidentate mononegative OO donor ligands are the deprotonated salicylaldehyde (Hsal), vanillin (Hvan) and monodeprotonated 1,2-ethanediol (H₂ed) (general abbreviation HB). The reaction of V^IVO(acac)₂ with H₂L and Hsal or Hvan in equimolar ratio in MeOH afforded the complexes of the type [V^VO(L)(B)], (1)–(4). The reaction of V^IVO(acac)₂ with H₂L¹ (in an equimolar ratio) and an excess of H₂ed in MeOH yielded the complex [V^VO(L¹)(Hed)], (5) but the similar reaction with H₂L² ligand failed to produce such a type of complex. Complexes have been characterized by elemental analyses and by i.r., n.m.r. and u.v.-vis. spectroscopies. All the complexes are diamagnetic and display only LMCT bands. ¹H-n.m.r. spectral data indicate that complexes (1)–(4) exist in two isomeric forms [(1A), (1B); (2A), (2B); (3A), (3B) and (4A), (4B)] in different ratios in CDCI₃ solution. Complexes (1)–(4) display a quasi-reversible one electron reduction peak in the −0.06 to +0.05 V versuss.c.e. region in CH₂CI₂ solution and (5) displays an irreversible reduction peak at −0.46 V versuss.c.e. in DMF solution. The trend in the redox potential values has been correlated with the basicity of both the primary and auxiliary ligands.     

Finite Inhomogeneous Radial Expansion (Contraction) and Longitudinal Shearing of an Isotropic Compressible Elastic Circular Cylindrical Shell

We have first obtained that the equations of equilibrium governing the finite radial expansion (contraction) and longitudinal shearing of a circular cylindrical shell become uncoupled for a class of harmonic materials (a class of isotropic homogeneous compressible elastic materials). Next it has been assumed that the dilatation is uniform. Following this the exact solutions of the uncoupled equations of equilibrium have been obtained for a simple harmonic material which is reduced to the Neo-Hookean material for the incompressible case. The deformation is nonhomogeneous in nature. The stresses have been obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diversity-oriented synthesis of amino acids using chiral enolates

We report a facile diversity oriented synthesis of α- and β-amino acids, by utilizing the pluripotent α-methylene group in a chiral bicyclic lactam as our key point of transformation.     

Topological alterations in human spermatozoa associated with the polyelectrolytic effect of RISUG

A new method of male contraception has been developed which results in long-term infertility and has the potential advantage of being reversible. The contraceptive, given the name RISUG (an acronym for Reversible Inhibition of Sperm Under Guidance) is a polyelectrolytic compound and when injected into the lumen of the vas deferens, induces a surface charge imbalance on the sperm membrane system leading to its destabilization. In the present study, morphological and topological alterations in human spermatozoa induced by RISUG have been investigated using atomic force microscopy (AFM). Complete disintegration of the plasma membrane with subsequent rupture and dispersion of the acrosomal contents is observed on treatment with RISUG in vitro. Considerable damage to the midpiece region with significant clustering of the mitochondria and its fusion with the head region is also observed. These observations are in agreement with the significant increase in the volume of RISUG-treated sperm-head region. Topological alterations in the flagellar and midpiece region of RISUG-treated spermatozoa have also been studied.     

Covalently functionalized single-walled carbon nanotubes at reverse micellar interface: a strategy to improve lipase activity

The present work reports covalent functionalization of single-walled carbon nanotubes (f-SWNTs) to introduce hydrophilicity to the otherwise amphiphobic nanotubes. The charge and spacer length of the functional moiety were varied by using quaternized ethylene diamine, 6-aminocaproate, quaternized (ethylenedioxy)bis(ethylamine), and a poly(ethylene glycol) (PEG) unit (f-SWNT-1 to f-SWNT-4, respectively). These f-SWNTs with varying degrees of hydrophilicity were incorporated within cetyltrimethyl ammonium bromide (CTAB) reverse micelles to develop stable self-assembled nanohybrids. An optimum hydrophilicity on the SWNT surface led to interfacial localization of f-SWNTs resulting in the augmentation of space at the interface. A surface-active enzyme, lipase, localized at this enhanced interface of f-SWNT-containing CTAB reverse micelles exhibited significant activation (2.5-fold) compared to that in the absence of the nanoconstructs. This improvement in lipase activity was mainly due to the smooth occupancy of lipase and also presumably because of the increase in the concentrations of both substrate and the enzyme at the augmented interface. Interestingly, the f-SWNTs that activate lipase in reverse micelles deactivate the same enzyme in water. The dispersion of f-SWNTs in water and its matching integration at the interface of reverse micelles were confirmed through transmission electron microscopic (TEM) investigations. The interfacial localization of these nanoconstructs was also established from the distinct fluorescence behavior of a hydrophobic fluorescent probe, fluorescein isothiocyanate (FITC), adsorbed onto the f-SWNT surface. In concurrence with the observed lipase activity, the corresponding changes in the enzyme conformation within f-SWNTs integrated reverse micelle as well as in aqueous medium were studied by circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy.