Stabilization of p-block organoelement terminal hydroxides, thiols, and selenols requires newer synthetic strategies

Metal hydroxides represent a very interesting and highly useful class of compounds that have been known to chemists for a very long time. While alkali and alkaline earth metal hydroxides (s‐block) are commonplace chemicals in terms of their abundance and their use in a chemical laboratory as bases, the interest in Brønsted acidic molecular terminal hydroxides of p‐block elements, such as aluminum and silicon, has been of recent origin, with respect to the variety of applications these compounds can offer both in materials science and catalysis. Moreover, these systems are environmentally friendly, relative to the metal halides, owing to their ‐OH functionality (resembling that of water). Design and conceptualization of the corresponding terminal thiols, selenols, and tellurols (M? SH, M? SeH, and M? TeH) offer even more challenging problems to synthetic inorganic chemists. This concept summarizes some of the recent strategies developed to stabilize these otherwise very unstable species. The successful preparation of a number of silicon trihydroxides a few years back resulted in the generation of several model compounds for metal–silicates. The recent synthesis of unusual aluminum compounds such as RAl(OH)₂, RAl(SH)₂, and RAl(SeH)₂ with terminal EH (E=O, Se, or Se) groups is likely to change the ways in which some of the well‐known catalytic conversions are being carried out. The need for very flexible and innovative synthetic strategies to achieve these unusual compounds is emphasized in this concept.     

Extracellular pH influences the mode of cell death in human colon adenocarcinoma cells subjected to photodynamic treatment with chlorin p6

Effect of varying extracellular pH on mode of cell death induced by photodynamic action of chlorin p6 was investigated in human colon carcinoma (Colo-205) cells. At an extracellular pH of 7.4, compared to cells treated with chlorin p6 in dark, the photodynamically treated cells showed reduction in mitochondrial membrane potential, an increase in ADP/ATP ratio (1:2) and a large percentage of cells with chromatin condensation. In contrast, when photodynamic treatment and post irradiation incubation was carried out in acidic medium (pH 6.5), total loss of mitochondrial membrane potential, a marked increase in ADP/ATP ratio (1:33) and increased damage to plasma membrane were observed. Further, cells subjected to photodynamic treatment in a medium of pH 7.4 showed twofold increase in caspase-3 activity as compared to photodynamic treatment at pH 6.5. These results suggest that chlorin p6 mediated photodynamic action induces apoptotic cell death when extracellular pH is 7.4 whereas necrosis is more predominant under condition when extracellular pH is 6.5.     

Monomeric, tetrameric, and polymeric copper di-tert-butyl phosphate complexes containing pyridine ancillary ligands

The reaction of di-tert-butyl phosphate (((t)BuO)(2)P(O)(OH), dtbp-H) with copper acetate in the presence of pyridine (py) and 2,4,6-trimethylpyridine (collidine) has been investigated. Copper acetate reacts with dtbp-H in a reaction medium containing pyridine, DMSO, THF, and CH(3)OH to yield a one-dimensional polymeric complex [Cu(dtbp)(2)(py)(2)(mu-OH(2))](n) (1) as blue hollow crystalline tubes. The copper atoms in 1 are octahedral and are surrounded by two terminal phosphate ligands, two pyridine molecules, and two bridging water molecules. The mu-OH(2) ligands that are present along the elongated Jahn-Teller axis are responsible for the formation of the one-dimensional polymeric structure. Recrystallization of 1 in a DMSO/THF/CH(3)OH mixture results in the reorganization of the polymer and its conversion to a more stable tetranuclear copper cluster [Cu(4)(mu(3)-OH)(2)(dtbp)(6)(py)(2)] (2) in about 60% yield. The molecular structure of 2 is made up of a tetranuclear core [Cu(4)(mu(3)-OH)(2)] which is surrounded by six bidentate bridging dtbp ligands. While two of the copper atoms are pentacoordinate with a tbp geometry, the other two copper atoms exhibit a pseudooctahedral geometry with five normal Cu-O bonds and an elongated Cu-O linkage. The pentacoordinate copper centers bear an axial pyridine ligand. The short Cu.Cu nonbonded distances in the tetranuclear core of 2 lead to magnetic ordering at low temperature with an antiferromagnetic coupling at approximately 20 K (J(P) = -44 cm(-1), J(c) = -66 cm(-1), g = 2.25, and rho = 0.8%). When the reaction between di-tert-butyl phosphate (dtbp-H) and copper acetate was carried out in the presence of collidine, large dark-blue crystals of monomeric copper complex [Cu(dtbp)(2)(collidine)(2)] (3) formed as the only product. A single-crystal X-ray diffraction study of 3 reveals a slightly distorted square-planar geometry around the copper atom. Thermogravimetric analysis of 1-3 revealed a facile decomposition of the coordinated ligands and dtbp to produce a copper phosphate material around 500 degrees C. An independent solid-state thermolysis of all the three complexes in bulk at 500-510 degrees C for 2 days produced copper pyrophosphate Cu(2)P(2)O(7) along with small quantities of Cu(PO(3))(2) as revealed by DR-UV spectroscopic and PXRD studies.     

Controlled induction, enhancement, and guidance of neuronal growth cones by use of line optical tweezers

We report an optical tweezers based approach for efficient and controlled manipulation of neuronal growth cones. The approach exploits asymmetric transverse gradient force created in a line optical tweezers to transport actin monomers in the desired growth direction. With this approach induction of artificial growth cones from the neuronal cell body and enhancement of the growth rate of the natural growth cones have been achieved. The use of this approach to bring two growth cones into close proximity for establishing a neuronal connection is also discussed.     

Vibrational markers of structural distortion in adenine nucleobases upon DNA damage

Oxidation is one of the common causes of chemical damage of DNA. Among the oxidized nucleobases in DNA, 8-oxoadenine (8-oxoA) and 4,6-diamino-5-formamidoadenine (FaPyA) are two of the most commonly found lesions. Relatively little information has been published so far on these lesions compared to the more mutagenic modified purines like 8-oxoguanine. In this study, we investigate the structure and vibrational spectra of these two lesions using Density Functional Theory relative to the parent compound adenine. In addition, we have incorporated a solvent environment through the Polarizable Continuum Model (PCM), as well as explicit solvent model calculations to test for the best prediction of the vibrational wavenumbers of adenine. We find that, while the explicit solvent model predicts the structure of the lesions better with respect to published X-ray diffraction structures, they do not reproduce the vibrational wavenumbers as accurately. In comparison, PCM predicts the wavenumbers better with less of the typical overestimation seen in the absence of solvent effects. Intriguingly, uniform linear scaling of the 'gas phase' calculations provides the best agreement with published experimental spectra. Finally, we demonstrate that 8-oxoA and FaPyA have unique spectral features compared to adenine by characterizing the differences in their normal modes. We propose the use of their distinct spectra as site-specific Raman probes of systems such as base-specific local probing of a DNA strand and DNA-enzyme active site interactions where the substrate can be used as an in situ probe.     

Theoretical study of small clusters of manganese-doped gallium oxide: Mn(GaO)n and Mn2(GaO)n with n?=?1?7

Structures, electronic and magnetic properties of Mn and Mn₂ doped stoichiometric (GaO) _n clusters with n = 1−7 are studied in the framework of density functional theory. Doping of a Mn atom is found to be energetically favorable in (GaO) _n clusters and the equilibrium configurations are found to be determined by the metal–oxygen interactions. Mn prefers to maximize the number of Mn–O bonds by selecting a Ga site in the cluster which increases its coordination with oxygen. Addition of a Mn atom in Mn(GaO) _n clusters results into the ground state to be either ferromagnetic or antiferromagnetic depending on the Mn coordination number and the Mn–Mn bond-length in the given Mn₂(GaO) _n cluster.     

Molecular zinc phosphonates: synthesis and X-ray crystal structures of [[(ZnMe)4(THF)2][tBuPO3]2] and [[(ZnEt)3(Zn(THF))3][tBuPO3]4[mu3-OEt]

The reactions of zinc alkyls with tert-butylphosphonic acid in 2 : 1 and 1 : 1 molar ratios afforded [[(ZnMe)(4-)(THF)2][tBuPO3]2] (2) and [[(ZnEt)3(Zn(THF))3][tBuPO3]4[mu3-OEt]] (3), respectively. Compounds 2 and 3 have been fully characterised by means of spectroscopic and analytical methods. Single-crystal X-ray diffraction studies revealed that zinc phosphonates 2 and 3 are tetra- and hexa-nuclear, respectively. This is in contrast to the dodecanuclear zinc phosphonate [[Zn2(THF)2(ZnEt)6Zn4(mu4-O)][(tBuPO3)8]] (1) obtained in a 1.5 : 1 reaction between zinc alkyls and tBuP(O)(OH)2.     

Studies in reduction of molecular weight of polypropylene

Polypropylene (PP) is the most widely used polyolefin, due to its high mechanical strength and better processability in comparison to the others in its group. Conventional methods of polymerisation result in high molecular weights of PP. However, high molecular weights are not required for several applications. To overcome this problem controlled reduction in molecular weight of PP in presence of free radicals, in solution, is proposed. Four commonly available free radical generators viz: benzoyl peroxide (BPO), azo- iso-bis butyronitrile (AIBN), t-butyl hydroperoxide (TBHP) and dicumyl peroxide (DCP) were used to bring about reduction in molecular weight of PP. Effect of the free radical generator concentration, reaction time, reaction temperature and reaction medium (toluene, xylene and decalin) on the extent of molecular weight reduction was studied. The effect of this molecular weight reduction on mechanical, thermal, rheological and crystalline properties of the polymer was also studied. With proper selection of initiator and reaction conditions, it was possible to obtain low molecular weight branched PP with improved mechanical and thermal properties.     

Simultaneous Determination of Diclofenac Sodium and Rabeprazole Sodium in Bulk and Pharmaceutical Dosage Form by LC

A simple, selective, rapid, precise and accurate reverse phase high pressure liquid chromatographic method has been developed for the simultaneous estimation of diclofenac sodium and rabeprazole sodium from pharmaceutical formulations. The method was developed using a HiQ SiL C18 (250 mm × 4.6 mm i.d.) column with a mobile phase consisting of methanol:water, (80:20 v/v), at a flow rate of 1.25 mL min⁻¹. Detection was carried out at 284 nm. Indapamide was used as an internal standard. The developed method was validated for linearity, accuracy, precision, limit of detection and limit of quantitation. The proposed method can be used for the estimation of these drugs in combined dosage forms.