Thermotropic poly(azomethine-urethane)s with non linear optical properties: Synthesis and characterization

Two series of the thermotropic main chain poly(azomethine-urethane)s were synthesized by the polyaddition of azadiol, 1,8-octandiol with methylene bis(phenyl isocyanate) (MDI) and tolylene 2,4-diisocyanate (TDI) respectively. The mesomorphic properties and phase transition temperature of the polymers were characterized by differential scanning calorimetry and hot stage polarizing microscopy. These polymers showed nematic messophase. The non linear optical (NLO) activity of the polymers was also investigated.     

Three ginkgolide hydrates from Ginkgo biloba L.: ginkgolide A monohydrate,ginkgolide C sesquihydrate and ginkgolide J dihydrate,all determined at 120 K

A low‐temperature structure of ginkgolide A monohydrate, (1R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐dimethylethyl)‐hexa­hydro‐4,7b‐di­hydroxy‐8‐methyl‐9H‐1,7a‐epoxymethano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclopenta­[1,2‐d]­furan‐5,9,12(4H)‐trione monohydrate, C₂₀H₂₄O₉·H₂O, obtained from Mo Kα data, is a factor of three more precise than the previous room‐temperature determination. A refinement of the ginkgolide A monohydrate structure with Cu Kα data has allowed the assignment of the absolute configuration of the series of compounds. Ginkgolide C sesquihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11S,11aR)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b,11‐tetrahydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclopenta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione sesquihydrate, C₂₀H₂₄O₁₁·1.5H₂O, has two independent diterpene mol­ecules, both of which exhibit intramolecular hydrogen bonding between OH groups. Ginkgolide J dihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b‐tri­hydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]furo[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione dihydrate, C₂₀H₂₄O₁₀·2H₂O, has the same basic skeleton as the other ginkgolides, with its three OH groups having the same configurations as those in ginkgolide C. The conformations of the six five‐membered rings are quite similar across ­ginkgolides A–C and J, except for the A and F rings of ginkgolide A.     

Surfing π Clouds for Noncovalent Interactions: Arenes versus Alkenes

A comparative study of molecular balances by NMR spectroscopy indicates that noncovalent functional‐group interactions with an arene dominate over those with an alkene, and that a π‐facial intramolecular hydrogen bond from a hydroxy group to an arene is favored by approximately 1.2 kJ mol^?1. The strongest interaction observed in this study was with the cyano group. Analysis of the series of groups CH₂CH₃, CH?CH₂, C?CH, and C?N shows a correlation between conformational free‐energy differences and the calculated charge on the C^α atom of these substituents, which is indicative of the electrostatic nature of their π interactions. Changes in the free‐energy differences of conformers show a linear dependence on the solvent hydrogen bond acceptor parameter β.     

Natural Products Inhibitors of Monoamine Oxidases—Potential New Drug Leads for Neuroprotection,Neurological Disorders,and Neuroblastoma

Monoamine oxidase inhibitors (MAOIs) are an important class of drugs prescribed for treatment of depression and other neurological disorders. Evidence has suggested that patients with atypical depression preferentially respond to natural product MAOIs. This review presents a comprehensive survey of the natural products, predominantly from plant sources, as potential new MAOI drug leads. The psychoactive properties of several traditionally used plants and herbal formulations were attributed to their MAOI constituents. MAO inhibitory constituents may also be responsible for neuroprotective effects of natural products. Different classes of MAOIs were identified from the natural product sources with non-selective as well as selective inhibition of MAO-A and -B. Selective reversible natural product MAOIs may be safer alternatives to the conventional MAOI drugs. Characterization of MAO inhibitory constituents of natural products traditionally used as psychoactive preparations or for treatment of neurological disorders may help in understanding the mechanism of action, optimization of these preparations for desired bioactive properties, and improvement of the therapeutic potential. Potential therapeutic application of natural product MAOIs for treatment of neuroblastoma is also discussed.     

Inelastic incoherent neutron scattering studies of water interacting with biological macromolecules.

The interaction between water and biological macromolecules in living organisms is of fundamental importance in a range of processes. We have studied water-DNA and water-proteolipid membrane systems over a range of hydration states using inelastic incoherent neutron scattering. We find a relatively sharp transition for both systems at a water concentration above which bulk solvent can be detected. Below this concentration, bulk water is essentially absent, i.e., all the water in the system is interacting with the biological macromolecules. This water is strongly perturbed as judged by its energy transfer spectrum, with a broader and lower energy transition than bulk water in the 50-75 meV (approximately 400-600 cm(-1)) range. Taking into account the differing geometry of (cylindrical) DNA and (planar) membranes, the number of water shells perturbed by each system was estimated. A conclusion is that in living organisms a large proportion of the cellular water will be in a state quite distinct from bulk water. The data add to the growing evidence that water structure in the vicinity of biological macromolecules is unusual and that the proximal water behaves differently compared to the bulk solvent.     

Pyrimidine Derivatives and Related Compounds II: Synthesis of some derivatives of pyrimido[1,2:2′,3′]pyrazolo[1,5-a]pyrimidines,a new ring system

3,5-Diamino-4-phenylazo-pyrazoles ( 1a–1c ) react with acetylacetone and with ethyl acetoacetate to yield the corresponding pyrazolo[1,5-a]pyrimidine derivatives 2a–2c and 3a–3c , respectively. Whereas 1a–1c add readily to methyl acrylate yielding the 4,5,6,7-tetrahydropyrazolo[1,5-a]-pyrimidine derivatives 5a–5c, 1a–1c add to methylacrylonitrile or methyl methacrylate only under drastic conditions to yield 5d–5f . The pyrimido[1,2:2′,3′]pyrazolo[1,5-a]pyrimidine derivatives 10a–10c are prepared by the action of acrylonitrile on 2a–2c . Compounds 10a–10c are readily converted into the corresponding oxo derivatives 12a–12c on treatment with acetic acid-hydrochloric acid mixture.     

Electrochemical Detection of Metals Using Thick Nanofibrous Nafion Web Modified Electrodes

In this work, GC electrodes modified with thick electrospun nanofibrous Nafion webs were characterized using scanning electron microscopy (SEM) and cyclic voltammetry (CV) and used for the extraction and electrochemical detection of cadmium by differential pulse voltammetry. Cadmium was detected after 10 min incubation at open circuit followed by anodic stripping using 60 s reduction at ?1.4 V. The electrode yielded well‐defined, undistorted and reproducible (RSD of 7.0 % based on 10 measurements) voltammetric response with two linear ranges from 0.1 to 3 µM (R²=0.994 ) and from 3 to 10 µM (R²=0.977) and a detection limit and sensitivity of 0.01 µM and 32 and 7.725 µA/µM for both linear portions of the curve respectively.