Reductive amination using ammonia borane

A variety of primary, secondary, and tertiary amines were prepared in 84-95% yields using ammonia borane for the reductive amination of aldehydes and ketones in the presence of titanium isopropoxide.     

Identification and Characterization of the Yellow Pigment Synthesized by Cupriavidus sp. USMAHM13

Microbial pigments are gaining intensive attention due to increasing awareness of the toxicity of synthetic colours. In this study, a novel polymer-producing bacterium designated as Cupriavidus sp. USMAHM13 was also found to produce yellow pigment when cultivated in nutrient broth. Various parameters such as temperature, pH and ratio of culture volume to flask volume were found to influence the yellow pigment production. UV-Visible, Fourier transform infrared and ¹³C-nuclear magnetic resonance analyses revealed that the crude yellow pigment might probably represent new bioactive compound in the carotenoid family. The crude yellow pigment also exhibited a wide spectrum of antimicrobial activity against Gram-negative and Gram-positive bacteria with their inhibition zones and minimal inhibitory concentrations ranged from 25 to 38 mm and from 0.63 to 2.5 mg/ml, respectively. To the best of our knowledge, this is the first report on the identification and characterization of yellow pigment produced by bacterium belonging to the genus Cupriavidus.     

Synthesis and Biological Evaluation of Amide Derivatives of Imidazopyridine as Anticancer Agents

A series of new amide derivatives of imidazopyridine is synthesized and structures of the products are confirmed by ¹H and ¹³C NMR, and mass spectral data. The synthesized derivatives are screened for their anticancer activity against four human cancer cell lines: lung cancer (A549), breast cancer (MCF-7), melanoma cancer (A375), and colon cancer (HT-29). Six synthesized compounds exhibit more potent activity than the control drug.

     

THE 31P NMR SPECTRA OF ISOMERIC DIAMINOHEXA-CHLOROCYCLOTETRAPHOSPHAZATETRAENES; EXAMPLES OF A2B2 AND AA'BB' SPIN SYSTEMS

Abstract

The ³¹P nmr spectra of 2,4- and 2,6-diamino-derivatives of octachlorocyclotetraphosphazatetraene, N₄P₄Cl₆(NR¹R²)₂ (R¹ = H, R² = Bu^t; R¹ = H, R² = CH₂Ph; R¹ = Me, R² = Ph), have been measured. The 2,4- and 2,6-isomers were analysed as AA'BB' and A₂B₂ spin systems respectively. In the 2,4-isomers the spin-spin couplings ²J(PNP) and ⁴J(PNPNP) were of opposite sign.     

Quantum and quasiclassical studies of the O(3P)+HCl-->OH+Cl(2P) reaction using benchmark potential surfaces

We have performed quantum mechanical (QM) dynamics calculations within the independent-state approximation with new benchmark triplet A" and A' surfaces [B. Ramachandran et al., J. Chem. Phys. 119, 9590 (2003)] for the rovibronic state-to-state measurements of the reaction O(3P)+HCl(v=2,j=1,6,9)-->OH(v'j')+Cl(2P) [Zhang et al., J. Chem. Phys. 94, 2704 (1991)]. The QM and experimental rotational distributions peak at similar OH(j') levels, but the QM distributions are significantly narrower than the measurements and previous quasiclassical dynamics studies. The OH(low j) populations observed in the measurements are nearly absent in the QM results. We have also performed quasiclassical trajectory with histogram binning (QCT-HB) calculations on these same benchmark surfaces. The QCT-HB rotational distributions, which are qualitatively consistent with measurements and classical dynamics studies using other surfaces, are much broader than the QM results. Application of a Gaussian binning correction (QCT-GB) dramatically narrows and shifts the QCT-HB rotational distributions to be in very good agreement with the QM results. The large QCT-GB correction stems from the special shape of the joint distribution of the classical rotational/vibrational action of OH products. We have also performed QM and QCT calculations for the transition, O+HCl(v=0,T=300 K)-->OH(v'j')+Cl from threshold to approximately 130 kcal mol(-1) collision energy as a guide for possible future hyperthermal O-atom measurements. We find in general a mixed energy release into translation and rotation consistent with a late barrier to reaction. Angular distributions at high collision energy are forward peaked, consistent with a stripping mechanism. Direct collisional excitation channel cross sections, O+HCl(v=0,T=300 K)-->O+HCl(v'=1), in the same energy range are large, comparable in magnitude to the reactive channel cross sections. Although the (3)A" state dominates most collision processes, above approximately 48 kcal mol(-1), the (3)A' state plays the major role in collisional excitation.     

Theory of heteronuclear decoupling in solid-state nuclear magnetic resonance using multipole-multimode Floquet theory

A formal theory for heteronuclear decoupling in solid-state magic angle spinning (MAS) nuclear magnetic resonance experiments is presented as a first application of multipole-multimode Floquet theory. The method permits a straightforward construction of the multispin basis and describes the spin dynamics via effective Floquet Hamiltonians obtained using the van Vleck transformation method in the Floquet-Liouville space. As a test case, we consider a model three-spin system (I2S) under asynchronous time modulations (both MAS and rf irradiation) and derive effective Hamiltonians for describing the spin dynamics in the Floquet-Liouville space during heteronuclear decoupling. Furthermore, we describe and evaluate the origin of cross terms between the various anisotropic interactions and illustrate their exact contributions to the spin dynamics. The theory presented herein should be applicable to the design and understanding of pulse sequences for heteronuclear and homonuclear recoupling and decoupling.     

Water clusters in a confined nonpolar environment

The stability and structure of water clusters in a confined nonpolar environment is investigated theoretically by examining the encapsulation of water molecules inside a fullerene (C₆₀) cage. While the Hartree–Fock (6-31G) calculations suggest H₂O@C₆₀ to be marginally more stable (−0.5 kcal/mol) than the isolated water and C₆₀ molecules, second order Møller–Plesset perturbation theory suggests it to be much more stable (−9.9 kcal/mol). It is shown that encapsulation results in the breaking of hydrogen bonds and rearrangement of water clusters. The tetramer inside the cage, for example, is tetrahedral in arrangement, in contrast to a square planar geometry observed in the gas phase.     

An improved spectrophotometric determination of silicate in water based on molybdenum blue

Silicate in water is determined by a heteropoly blue method with ascorbic acid and antimony as reducing agents; antimony does not participate in the complex but enhances the absorbance. The method is comparatively fast and sensitive. Beer's law is obeyed for 0.02–1.2 μg ml^?1 silica. Interferences are discussed.