Stabilization of α-nickel hydoxide in the presence of organic additives: chemical route to bulk synthesis

Organic molecules such as glucose or lactose mediate the synthesis and stabilize alpha-nickel hydroxide in a simple precipitation reaction, while, in the absence of these additives, beta-nickel hydroxide is formed. The additives are not incorporated in the product phase.

Structure of Nonplanar Octabromotetraphenyl Porphyrin and Kinetics of Rapid Metalation Reactions

Octabromotetraphenylporphyrin adopts a severe saddle-shaped distorted structure owing to the steric crowding of heavy bromine substituents. The rate enhancement of porphyrin metalation reaction is primarily due to the nonplanarity of the ring while the electronic effect diminishes the affinity of the porphyrin towards metal ions.

DNA Compaction by a Dendrimer

At physiological pH, a PAMAM dendrimer is positively charged and can effectively bind negatively charged DNA. Currently, there has been great interest in understanding this complexation reaction both for fundamental (as a model for complex biological reactions) as well as for practical (as a gene delivery material and probe for sensing DNA sequence) reasons. Here, we have studied the complexation between double-stranded DNA (dsDNA) and various generations of PAMAM dendrimers (G3-05) through atomistic molecular dynamics simulations in the presence of water and ions. We report the compaction of DNA on a nanosecond time scale. This is remarkable, given the fact that such a short DNA duplex with a length close to 13 nm is otherwise thought to be a rigid rod. Using several nanoseconds long MD simulations, we have observed various binding modes of dsDNA and dendrimers for various generations of PAMAM dendrimers at varying charge ratios, and it confirms some of the binding modes proposed earlier. The binding is driven by the electrostatic interaction, and the larger the dendrimer charge, the stronger the binding affinity. As DNA wraps/binds to the dendrimer, counterions originally condensed onto DNA (Na+) and the dendrimer (Cl-) get released. We calculate the entropy of counterions and show that there is gain in entropy due to counterion release during the complexation. MD simulations demonstrate that, when the charge ratio is greater than 1 (as in the case of the G5 dendrimer), the optimal wrapping of DNA is observed. Calculated binding energies of the complexation follow the trend G5 > 04 > 03, in accordance with the experimental data. For a lower-generation dendrimer, such as G3, and, to some extent, for G4 also, we see considerable deformation in the dendrimer structure due to their flexible nature. We have also calculated the various helicoidal parameters of DNA to study the effect of dendrimer binding on the structure of DNA. The B form of the DNA is well preserved in the complex, as is evident from various helical parameters, justifying the use of the PAMAM dendrimer as a suitable delivery vehicle.

Nano structured carbon nitrides prepared by chemical vapour deposition

Nanostructured carbon nitride films were prepared by pyrolysis assisted chemical vapour deposition(CVD). A two zone furnace with a temperature profile having a uniform temperature over a length of 20 cm length has been designed and developed. The precursor Azabenzimidazole was taken in a quartz tube and evaporated at 400 degrees C. The dense vapours enter the pyrolysis zone kept at a desired temperature and deposit on the quartz substrates. The FTIR spectrum of the prepared samples shows peaks at 1272 cm(-1) (C-N stretching) and 1600 cm(-1) (C=N) confirms the bonding of nitrogen with carbon. Raman D and G peaks, are observed at 1360 cm(-1) and 1576 cm(-1) respectively. XPS core level spectra of C 1s and N 1s show the formation of pi bonding between carbon and nitrogen atoms. The size of the nano crystals estimated from the SEM images and XRD is similar to 100 nm. In some regions of the sample a maximum of 57 atom % of nitrogen has been observed.

Chemical communication in Ropalidia marginata: Dufour's gland contains queen signal that is perceived across colonies and does not contain colony signal

Queens of the primitively eusocial wasp Ropalidia marginata appear to maintain reproductive monopoly through pheromone rather than through physical aggression. Upon queen removal, one of the workers (potential queen, PQ) becomes extremely aggressive but drops her aggression immediately upon returning the queen. If the queen is not returned, the PQ gradually drops her aggression and becomes the next queen of the colony. In a previous study, the Dufour's gland was found to be at least one source of the queen pheromone. Queen-worker classification could be done with 100% accuracy in a discriminant analysis, using the compositions of their respective Dufour's glands. In a bioassay, the PQ dropped her aggression in response to the queen's Dufour's gland macerate, suggesting that the queen's Dufour's gland contents mimicked the queen herself. In the present study, we found that the PQ also dropped her aggression in response to the macerate of a foreign queen's Dufour's gland. This suggests that the queen signal is perceived across colonies. This also suggests that the Dufour's gland in R. marginata does not contain information about nestmateship, because queens are attacked when introduced into foreign colonies, and hence PQ is not expected to reduce her aggression in response to a foreign queen's signal. The latter conclusion is especially significant because the Dufour's gland chemicals are adequate to classify individuals correctly not only on the basis of fertility status (queen versus worker) but also according to their colony membership, using discriminant analysis. This leads to the additional conclusion (and precaution) that the ability to statistically discriminate organisms using their chemical profiles does not necessarily imply that the organisms themselves can make such discrimination. (C) 2010 Elsevier Ltd. All rights reserved.

Large negative magnetoresistance and metal-insulator transition observed in MnO/C composite coatings grown on ceramic alumina by metalorganic chemical vapor deposition

MnO/C composite coatings were grown by the metalorganic chemical vapor deposition process on ceramic alumina in argon ambient. Characterization by various techniques confirms that these coatings are homogeneous composites comprising nanometer-sized MnO particles embedded in a matrix of nanometer-sized graphite. Components of the MnO/C composite coating crystalline disordered, but are electrically quite conductive. Resistance vs. temperature measurements show that coating resistance increases exponentially from a few hundred ohms at room temperature to a few megaohms at 30 K. Logarithmic plots of reduced activation energy vs. temperature show that the coating material undergoes a metal-insulator transition. The reduced activation energy exponent for the film under zero magnetic field was 2.1, which is unusually high, implying that conduction is suppressed at much faster rate than the Mott or the Efros-Shklovskii hopping mechanism. Magnetoconductance us. magnetic field plots obtained at various temperatures show a high magnetoconductance (similar to 28.8%) at 100 K, which is unusually large for a disordered system, wherein magnetoresistance is attributed typically to weak localization. A plausible explanation for the unusual behavior observed in the carbonaceous disordered composite material is proposed. (C) 2010 Elsevier Ltd. All rights reserved.

DNA Binding, Coprotease, and Strand Exchange Activities of Mycobacterial RecA Proteins: Implications for Functional Diversity among RecA Nucleoprotein Filaments

One of the fundamental questions concerning homologous recombination is how RecA or its homologues recognize several DNA sequences with high affinity and catalyze all the diverse biological activities. In this study, we show that the extent of single-stranded DNA binding and strand exchange (SE) promoted by mycobacterial RecA proteins with DNA substrates having various degrees of GC content was comparable with that observed for Escherichia coli RecA. However, the rate and extent of SE promoted by these recombinases showed a strong negative correlation with increasing amounts of sequence divergence embedded at random across the length of the donor strand. Conversely, a positive correlation was seen between SE efficiency and the degree of sequence divergence in the recipient duplex DNA. The extent of heteroduplex formation was not significantly affected when both the pairing partners contained various degrees of sequence divergence, although there was a moderate decrease in the case of mycobacterial RecA proteins with substrates containing larger amounts of sequence divergence. Whereas a high GC content had no discernible effect on E. coli RecA coprotease activity, a negative correlation was apparent between mycobacterial RecA proteins and GC content. We further show clear differences in the extent of SE promoted by E. coli and mycobacterial RecA proteins in the presence of a wide range of ATP:ADP ratios. Taken together, our findings disclose the existence of functional diversity among E. coli and mycobacterial RecA nucleoprotein filaments, and the milieu of sequence divergence (i.e., in the donor or recipient) exerts differential effects on heteroduplex formation, which has implications for the emergence of new genetic variants.

A New Era for Chemical Superconductors

A review of the development of ceramic superconductors and the steady increase in the superconducting transition temperature which currently stands at 135 K or about 164 K under pressure.

Binding of active site directed ligands to phospholipase A2: Implications on the molecular constraints and catalytic mechanism

Molecular constraints for the localization of active site directed ligands (competitive inhibitors and substrates) in the active site of phospholipase A2 (PLA2) are characterized. Structure activity relationships with known inhibitors suggest that the head : group interactions dominate the selectivity as well as a substantial part of the affinity. The ab initio fitting of the amide ligands in the active site was carried out to characterize the head group interactions. Based on a systematic coordinate space search, formamide is docked with known experimental constraints such as coordination of the carbonyl group to Ca2+ and hydrogen bond between amide nitrogen and ND1 of His48. An optimal position for a bound water molecule is identified and its significance for the catalytic mechanism is postulated. Unlike the traditional ''pseudo-triad'' mechanism, the ''Ca-coordinatedoxyanion'' mechanism proposed here invokes activation of the catalytic water to form the oxyanion in the coordination sphere of calcium. As it attacks the carbonyl carbon of the ester, a near-tetrahedral intermediate is formed. As the second proton of the catalytic water is abstracted by the ester oxygen, its reorientation and simultaneous cleavage form hydrogen bond with ND1 of His48. In this mechanism of esterolysis, a catalytic role for the water co-ordinated to Ca2+ is recognised.

Characterization of the zinc-metalloprotein nature of rat spermatidal protein TP2

Spermatidal transition protein, TP2, was purified from rat testes by Hg-affinity chromatography. The present study reports the details of the zinc-metalloprotein nature of TP2 by employing the Zn-65-blotting technique. Chemical modification of cysteine by iodoacetic acid, and histidine by diethylpyrocarbonate, resulted in a near complete inhibition of Zn-65-binding to TP2. The (65)Zinc-binding was localized to the V8 protease-derived N-terminal two-third polypeptide fragment. Circular dichroism spectroscopy studies of TP2 (zinc pre-incubated) and its V8 protease-derived polypeptide fragments revealed that the N-terminal fragment has a Type I-beta-turn spectrum, while the C-terminal fragment has a small but significant alpha-helical structure. EDTA altered the circular dichroism spectrum of TP2 and the N-terminal fragment (zinc binding domain) but not that of the C-terminal fragment.

Chemical Approaches to the Design of Oxide Materials.

Chemical methods of synthesis play a crucial role in designing and discovering new and novel materials and in providing less cumbersome methods for preparing known materials. Chemical methods also enable the synthesis of metastable materials which are otherwise difficult to prepare. In this presentation, the various innovative chemical methods of synthesising oxide materials will be briefly reviewed with emphasis on soft-chemical routes. Electrochemical synthesis, ion-exchange method, alkali-flux method and some of the interaction reactions will be highlighted, besides topochemical aspects of solid state synthesis. Cuprate superconductors as well as intergrowth structures will also be examined.

Synthesis of Nano Structured Carbon Nitride by Pyrolysis Assisted Chemical Vapour Deposition

Nanostructured carbon nitride films were prepared by pyrolysis assisted chemical vapour deposition. A two zone furnace with a uniform temperature over a length of 20 cm in both the zones was built. The precursor Azabenzimidazole (C6H5N3) taken in a quartz tube was evaporated at zone A and pyrolysed at zone B at a temperature of 800 degrees C. The FTIR spectrum of the prepared sample shows peaks at 1272 cm(-1) and 1591 cm(-1) corresponding to C-N stretching and C=N respectively, which confirms the bonding of nitrogen with carbon. Raman D and G peaks are observed at 1357 cm(-1) and 1560 cm(-1) respectively. X-ray photoelectron spectroscopy (XPS) shows the formation of pi bonding between carbon and nitrogen atoms. These observations along with XRD analysis show the formation of crystallites of alpha-C3N4 and beta-C3N4 in the background of graphitic C3N4. The size of the nanocrystals estimated from the SEM images is similar to 100 nm.

DNA Photocleavage and Cytotoxic Properties of Ferrocene Conjugates

Ferrocenyl conjugates 2-ferrocenylimidazophenanthroline (1) and 2-ferrocenylimidazophenanthrene (2) were prepared, characterized, and their photoinduced DNA cleavage and photocytotoxic activity were studied. 2-Phenylimidazophenanthroline (3) was used as a control species. Compound 2 was characterized by X-ray crystallography. The interaction of the compounds with double-stranded calf thymus DNA (CT DNA) was studied. The compounds show good binding affinity to CT DNA with K-b values of approximately 10(5) M-1. Thermal denaturation data suggest the groove binding nature of the compounds. The redox-active compounds show poor chemical nuclease activity in the presence of hydrogen peroxide and glutathione (GSH). Compound 1 exhibits significant DNA photocleavage activity in visible light of 476 and 532 nm. Compound 3 shows only moderate DNA cleavage activity. The positive effect of the ferrocenyl moiety is demonstrated by the DNA photocleavage data. Mechanistic investigations reveal the formation of superoxide as well as hydroxyl radicals as the active species. The photocytotoxicity of the compounds in HeLa cells was studied upon irradiation with visible light (400-700 nm). Compound 1 shows efficient photocytotoxic activity with an IC50 value of 13 mu M, while compounds 2 and 3 are less active with IC50 values of > 50 and 22 mu M, respectively.

Calcium/Calmodulin Dependent Protein Kinase II Bound to NMDA Receptor 2B Subunit Exhibits Increased ATP Affinity and Attenuated Dephosphorylation

Calcium/calmodulin dependent protein kinase II (CaMKII) is implicated to play a key role in learning and memory. NR2B subunit of N-methyl-D-aspartate receptor (NMDAR) is a high affinity binding partner of CaMKII at the postsynaptic membrane. NR2B binds to the T-site of CaMKII and modulates its catalysis. By direct measurement using isothermal titration calorimetry (ITC), we show that NR2B binding causes about 11 fold increase in the affinity of CaMKII for ATP gamma S, an analogue of ATP. ITC data is also consistent with an ordered binding mechanism for CaMKII with ATP binding the catalytic site first followed by peptide substrate. We also show that dephosphorylation of phospho-Thr(286)-alpha-CaMKII is attenuated when NR2B is bound to CaMKII. This favors the persistence of Thr(286) autophosphorylated state of CaMKII in a CaMKII/phosphatase conjugate system in vitro. Overall our data indicate that the NR2B- bound state of CaMKII attains unique biochemical properties which could help in the efficient functioning of the proposed molecular switch supporting synaptic memory.