Total synthesis of (-)-ent-pachastrissamine (ent-Jaspine B)

The total synthesis of the enantiomer of the tetrahydrofuran containing natural product Jaspine B is reported. The key reactions in the synthesis include formation of the tetrahydrofuran unit by an acid mediated Williamson etherification and a subsequent elaboration with an olefin cross metathesis reaction. (C) 2011 Elsevier Ltd. All rights reserved.

Synthesis of benzofuran based 1,3,5-substituted pyrazole derivatives: As a new class of potent antioxidants and antimicrobials-A novel accost to amend biocompatibility

In search for a new antioxidant and antimicrobial agent with improved potency, we synthesized a series of benzofuran based 1,3,5-substituted pyrazole analogues (5a-l) in five step reaction. Initially, o-alkyl derivative of salicyaldehyde readily furnish corresponding 2-acetyl benzofuran 2 in good yield, on treatment with 1,8-diaza bicyclo5.4.0]undec-7-ene (DBU) in the presence of molecular sieves. Further, aldol condensation with vanillin, Claisen-Schmidt condensation reaction with hydrazine hydrate followed by coupling of substituted anilines afforded target compounds. The structures of newly synthesized compounds were confirmed by IR, H-1 NMR, C-13 NMR, mass, elemental analysis and further screened for their antioxidant and antimicrobial activities. Among the tested compounds 5d and 5f exhibited good antioxidant property with 50% inhibitory concentration higher than that of reference while compounds 5h and 5l exhibited good antimicrobial activity at concentration 1.0 and 0.5 mg/mL compared with standard, streptomycin and fluconazole respectively. (C) 2012 Elsevier Ltd. All rights reserved.

Analysis of Parameter Values in the van der Waals and Platteeuw Theory for Methane Hydrates Using Monte Carlo Molecular Simulations

The van der Waals and Platteuw (vdVVP) theory has been successfully used to model the thermodynamics of gas hydrates. However, earlier studies have shown that this could be due to the presence of a large number of adjustable parameters whose values are obtained through regression with experimental data. To test this assertion, we carry out a systematic and rigorous study of the performance of various models of vdWP theory that have been proposed over the years. The hydrate phase equilibrium data used for this study is obtained from Monte Carlo molecular simulations of methane hydrates. The parameters of the vdWP theory are regressed from this equilibrium data and compared with their true values obtained directly from simulations. This comparison reveals that (i) methane-water interactions beyond the first cage and methane-methane interactions make a significant contribution to the partition function and thus cannot be neglected, (ii) the rigorous Monte Carlo integration should be used to evaluate the Langmuir constant instead of the spherical smoothed cell approximation, (iii) the parameter values describing the methane-water interactions cannot be correctly regressed from the equilibrium data using the vdVVP theory in its present form, (iv) the regressed empty hydrate property values closely match their true values irrespective of the level of rigor in the theory, and (v) the flexibility of the water lattice forming the hydrate phase needs to be incorporated in the vdWP theory. Since methane is among the simplest of hydrate forming molecules, the conclusions from this study should also hold true for more complicated hydrate guest molecules.

Influence of Sn doping on structural, optical and electrical properties of ZnO thin films prepared by cost effective sol-gel process

Tin (Sn) doped zinc oxide (ZnO) thin films were synthesized by sol-gel spin coating method using zinc acetate di-hydrate and tin chloride di-hydrate as the precursor materials. The films were deposited on glass and silicon substrates and annealed at different temperatures in air ambient. The agglomeration of grains was observed by the addition of Sn in ZnO film with an average grain size of 60 nm. The optical properties of the films were studied using UV-VIS-NIR spectrophotometer. The optical band gap energies were estimated at different concentrations of Sn. The MOS capacitors were fabricated using Sn doped ZnO films. The capacitance-voltage (C-V), dissipation vs. voltage (D-V) and current-voltage (I-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated. The porosity and surface area of the films were increased with the doping of Sn which makes these films suitable for opto-electronic applications. (C) 2012 Elsevier B.V. All rights reserved.

Novel De-Acylative Ring Opening of 3-Acetyl and 3-Bromo Acetyl Coumarins

Reaction of 3-acetyl and 3-bromoacetyl coumarins with hydrazine hydrate has resulted in the ring opening of the coumarin moiety. The reaction was attempted with a view to obtain some new pyridazinones and pyrazolones. The reaction did not proceed via the expected pathway instead led to the formation of salicyl azines, the structure of which has been confirmed by single crystal X-ray studies.

Polymorphs and hydrates of Etoricoxib, a selective COX-2 inhibitor

The crystal structures of two polymorphs and two polymorphic hemihydrates of Etoricoxib are reported. Etoricoxib is a non-steroidal anti-inflammatory drug (NSAID) that is a selective inhibitor of COX-2. It is used in the treatment of various types of inflammation, pain and fever. Clas et al. have reported four polymorphs (labeled I through IV) and two solvates (hemi-and sesquihydrate) of the API in US patent 6,441,002 (Clas et al, US patent 6,441,002, 2002). However, no crystal structures have been reported for any of these forms. A comparison was made between the PXRD patterns reported in patent `002 and the powder spectra simulated from single crystal data. The two polymorphs characterized here correspond to form I and form IV of the patent. Form II of the patent could not be obtained by us with a variety of experimental conditions. Form III of the patent corresponds to hemihydrate II of this study. Form III is therefore not a polymorph of form I and form IV. What we have termed hemihydrate I in this study is obtained under a wide variety of conditions and it is also the only hemihydrate reported as such in the patent. Because the Etoricoxib molecule contains no conventional hydrogen bond donors, there cannot be any strong hydrogen bonds in the crystal structures of forms I and IV. The packing is accordingly characterized by weak hydrogen bonds of the C-H center dot center dot center dot O=S and C-H center dot center dot center dot N type. Thermal data were collected for form I, form IV and hemihydrate I to shed some light on relative stabilities. PXRD diffractograms show the transformation of form IV to form I at elevated temperature, indicating that form I is more stable than form IV. However, this transformation occurs only in samples of form IV that contain some form I; it does not occur in pure form IV. The formation of the two hemihydrates could follow from the known tendency of an acceptor-rich molecule to crystallize as a hydrate.

An approach toward the synthesis of PPAP natural product garsubellin A: construction of the tricyclic core

In a study directed toward the bioactive natural product garsubellin A, an expedient route to the bicyclo 3.3.1]nonan-9-one bearing tricyclic core, with a bridgehead anchored tetrahydrofuran ring, is delineated. The approach emanating from commercially available dimedone involved a DIBAL-H mediated retro aldol/re-aldol cyclization cascade and a PCC mediated oxidative cyclization as the key steps. (C) 2013 Elsevier Ltd. All rights reserved.

Calculation of Chemical Potentials and Occupancies in Clathrate Hydrates through Monte Carlo Molecular Simulations

The flexibility of the water lattice in clathrate hydrates and guest-guest interactions has been shown in previous studies to significantly affect the values of the thermodynamic properties, such as chemical potentials and free energies. Here we describe methods for computing occupancies, chemical potentials, and free energies that account for the flexibility of water lattice and guest-guest interactions in the hydrate phase. The methods are validated for a wide variety of guest molecules, such as methane, ethane, carbon dioxide, and tetrahydrodfuran by comparing the predicted occupancy values of guest molecules with those obtained from isothermal isobaric semigrand Monte Carlo simulations. The proposed methods extend the van der Waals and Platteuw theory for clathrate hydrates, and the Langmuir constant is calculated based on the structure of the empty hydrate lattice. These methods in combination with development of advanced molecular models for water and guest molecules should lead to a more thermodynamically consistent theory for clathrate hydrates.

Iodo( trisyl) sulfane: Reactivity of a Stable Alkanesulfenyl Iodide towards Antithyroid Drugs

Iodination of tris(trimethylsilyl)methanethiol (trisylthiol, TsiSH) in tetrahydrofuran provides the new thermally stable alkanesulfenyl iodide iodo(trisyl)sulfane, TsiSI] as a violet solid. Iodo(trisyl)sulfane exhibits iodine-iodine contacts between pairs of TsiSI molecules in the solid state. Properties of TsiSI were studied by vibrational spectroscopy and with the help of density functional calculations. TsiSI reacts in the presence of triethylamine with the antithyroid drugs 6-n-propyl- and 6-methylthiouracil (PTU, MTU) and with N-methylmethimazole (MMI) to form unsymmetric disulfides that were investigated by means of X-ray crystallography. In the solid state, the PTU and MTU derivatives exist as hydrogen-bonded centrosymmetric dimers, whereas the MMI-derived disulfide is an unsymmetric monomer.

Polymorphism and Phase Transformation Behavior of Solid Forms of 4-Amino-3,5-dinitrobenzamide

We report the preparation, analysis, and phase transformation behavior of polymorphs and the hydrate of 4-amino-3,5-dinitrobenzamide. The compound crystallizes in four different polymorphic forms, Form I (monoclinic, P2(1)/n), Form II (orthorhombic, Pbca), Form III (monoclinic, P2(1)/c), and Form IV (monoclinic, P2(1)/c). Interestingly, a hydrate (triclinic, P (1) over bar) of the compound is also discovered during the systematic identification of the polymorphs. Analysis of the polymorphs has been investigated using hot stage microscopy, differential scanning calorimetry, in situ variable-temperature powder X-ray diffraction, and single-crystal X-ray diffraction. On heating, all of the solid forms convert into Form I irreversibly, and on further heating, melting is observed. In situ single-crystal X-ray diffraction studies revealed that Form II transforms to Form I above 175 degrees C via single-crystal-to-single-crystal transformation. The hydrate, on heating, undergoes a double phase transition, first to Form III upon losing water in a single-crystal-to-single-crystal fashion and then to a more stable polymorph Form I on further heating. Thermal analysis leads to the conclusion that Form II appears to be the most stable phase at ambient conditions, whereas Form I is more stable at higher temperature.

Synthesis and antioxidant activity study of pyrazoline carrying an arylfuran/arylthiophene moiety

A novel series of N-acetyl-3-aryl-5-(5-(p/o-nitrophenyl)-2-furyl//thienyl)-substituted pyrazolines (3a-o) were synthesized by the reaction of 1-aryl-3-(5-(p/o-nitrophenyl)-2-furyl/thienyl)-2-propene-1-ones with hydrazine hydrate in acetic acid medium. The structures of the newly synthesized compounds were established by IR, H-1-NMR, mass spectra and a single-crystal X-ray study. The antioxidant activities of the synthesized compounds were determined using the DPPH scavenging assay. The compounds 3a, 3f, 3h and 3o showed moderate activity.

A versatile, RCM based approach to eudesmane and dihydroagarofuran sesquiterpenoids from (-)-carvone: a formal synthesis of (-)-isocelorbicol

An enantiospecific and diversity oriented approach to a range of functionalized eudesmane, nor-, iso-, and dihydroagarofuran frameworks from (-)-carvone is delineated. The cornerstone of this approach is the installation of the quaternary carbon center through reductive opening of the carvone epoxide and setting-up of RCM reaction to generate the bicyclic eudesmane framework. Various options like carbocation mediated oxycyclization and intramolecular hydroxy directed epoxide opening have been explored for the construction of the bridged tetrahydrofuran moiety. Among the several eudesmane and dihydroagarofurans accessed during the present study, one has been previously elaborated to iso-celorbicol, thus constituting its formal synthesis. (C) 2015 Elsevier Ltd. All rights reserved.

BIMODAL NANOINDENTATION RESPONSE OF THE (001) FACE IN CRYSTALLINE SODIUM SACCHARIN DIHYDRATE

The nanoindentation response of the (001) face of sodium saccharin dihydrate is examined. The structure can be demarcated into regular and irregular regions or domains. The regular domains have solid-like and the irregular ones have liquid-like characteristics. Therefore, these domains impart a microstructure to the crystal. The indent face (001) is prominently developed in this crystal and unambiguously presents the regular and irregular regions to nanoindention. Average values of elastic modulus and hardness show a distinct bimodal mechanical response. Such a response has been observed in the case of intergrown polymorphs of aspirin and felodipine. We examine two possible reasons as to why the responses could be for bimodal in this crystal. The first possibility could be that the two domains correspond to regions of the original dihydrate and a lower hydrate that is obtained by the loss of some water. The second possibility could be that these responses correspond to regular and irregular regions in the structure. Nanoindentation is a very useful technique in the characterization of molecular solids, as a complementary technique to X-ray crystallography, because it samples different length scales.

Yellow-red luminescence in ZnO nanoparticles synthesized from zinc acetylacetonate phenanthroline

ZnO powders/thin films/coatings when excited by a suitable excitation source, usually yield green luminescence in the visible wavelength range along with characteristic ultra-violet emission. We report yellow-red emission from ZnO nanoparticles synthesized within 5 min of microwave irradiation by using zinc acetylacetonate phenanthroline as the starting precursor material. The emission is strongly dependent on the typical structure of the starting precursor for ZnO synthesis, where one phenanthroline moiety is attached with zinc acetylacetonate hydrate complex. These ZnO nanoparticles could be potentially suitable phosphor for white light generation when excited by a blue laser. In contrast, the ZnO nanoparticles obtained from zinc acetylacetonate by similar method yield weak green emission. (C) 2015 Elsevier B.V. All rights reserved.

开采地层中的天然气水合物的数学模型

目前从天然气水合物中开采天然气的方法,主要有热激发法、化学试剂法和减压法.文章通过适当简化,从理论上推导出减压法开采天然气的数值模型和水合物分解前缘边界曲面离井筒距离表达式,并对推导出的偏微分方程经过线性简化和自相似原理,推导出多孔介质水合物地层中压力和温度的分布方程和天然气产量方程.通过实例,研究了多孔介质水合物地层中压力和温度的分布规律,即离井筒越近,压力和温度越小.进行了影响水合物分解前缘边界曲面离井筒距离各影响因素的敏感性分析,得到了减小井筒压力和增大地层温度可以使离井筒越远地方的水合物层分解释放出天然气,天然气的产量随着开采时间的增大而逐渐减小但最终趋于一稳定值的结论。