Thermal radiation effects on MHD flow of a micropolar fluid over a stretching surface with variable thermal conductivity

In this paper, the effects of variable thermal conductivity and radiation on the flow and heat transfer of an electrically conducting micropolar fluid over a continuously stretching surface with varying temperature in the presence of a magnetic field are considered. The surface temperature is assumed to vary as a power-law temperature. The governing conservation equations of mass, momentum, angular momentum and energy are converted into a system of non-linear ordinary differential equations by means of similarity transformation. The resulting system of coupled non-linear ordinary differential equations is solved numerically. The numerical results show that the thermal boundary thickness increases as the thermal conductivity parameter S$S$ increases, while it decreases as the radiation parameter F$F$ increases. Also, it was found that the Nusselt number increases as F$F$ increases and decreases as S$S$ increases.     

Synthesis of tacrine derivatives under solventless conditions

Effects of microwave irradiation on the solid‐phase synthesis of tacrine and its derivatives have been evaluated. Preparation of tacrine analogues under conventional conditions suffers from poor synthetic efficiency and usually gives low yield. Reaction of substituted anthranilonitrile with cyclohexanone under microwave irradiation gave a good to excellent yield of the corresponding substituted 9‐amino‐1,2,3,4‐tetrahydroacridines.     

Sculpting the bicyclo[3.1.0]hexane template of carbocyclic nucleosides to improve recognition by herpes thymidine kinase

The replacement of the furanose ring by a cyclopentane in nucleosides generates a group of analogues known generically as carbocyclic nucleosides. These compounds have increased chemical and enzymatic stability due to the absence of a true glycosyl bond that characterizes conventional nucleosides. The additional fusion of a cyclopropane ring to the cyclopentane produces a bicyclo[3.1.0]hexane system that depending on its location relative to the nucleobase is able to lock the embedded cyclopentane ring into conformations that mimic the typical north and south conformations of the furanose ring in conventional nucleosides. These bicyclo[3.1.0]hexane templates have already provided important clues to differentiate the contrasting conformational preferences between kinases and polymerases. Herein, we describe the design, synthesis, and phosphorylation pattern of a new bicyclo[3.1.0]hexane thymidine analogue that seems to possess an ideal spatial distribution of pharmacophores for an optimal interaction with herpes simplex 1 thymidine kinase. The bicyclo[3.1.0]hexane template represents a privileged rigid template for sculpting other carbocyclic nucleosides to meet the demands of specific receptors.     

Complex formation reactions of lanthanum(III), cerium(III), thorium(IV), dioxouranyl(IV) complexes with tricine

Equilibrium studies for the heavy metal ions La(III), Ce(III), Th(IV) and UO2(IV) (M) complexes of the zwitterionic buffer tricine (L) in aqueous solution are investigated. Stoichiometry and stability constants for the different complexes formed as well as hydrolysis products of the metal cations are determined at 25 degrees C and ionic strength 0.1 M NaNO3. The stability of the formed complexes are discussed in terms of the nature of the heavy metal cation. The solid complexes are synthesized and characterized by means of elemental analysis, FTIR, and TG analysis. The general molecular formulae of the obtained complexes is suggested to be [M(L)2](NO3)n-2(H2O)x, where n = the charge of the metal cation, x = no. of water molecules.     

Organocatalytic enantioselective conjugate addition of aldehydes to maleimides

The highly enantioselective direct organocatalytic conjugate addition of aldehydes to maleimides is presented.     

Biosynthesis of gold nanoparticles using Pseudomonas aeruginosa

Pseudomonas aeruginosa were used for extra-cellular biosynthesis of gold nanoparticles (Au NPs). Consequently, Au NPs were formed due to reduction of gold ion by bacterial cell supernatant of P. aeruginosa ATCC 90271, P. aeruginosa (2) and P. aeruginosa (1). The UV-vis and fluorescence spectra of the bacterial as well as chemical prepared Au NPs were recorded. Transmission electron microscopy (TEM) micrograph showed the formation of well-dispersed gold nanoparticles in the range of 15-30 nm. The process of reduction being extra-cellular and may lead to the development of an easy bioprocess for synthesis of Au NPs.     

A new germacranolide-type sesquiterpene lactone from Tanacetum santolinoides

A new germacranolide-type sesquiterpene lactone, 1alpha-hydroxy-3-oxo-7alpha,11betaH-germacra-4Z,9Z-dien-12,6alpha-olide (1), was isolated from the CH2Cl2--MeOH extract of the aerial parts of Tanacetum santolinoides. Its structure was determined by spectroscopic techniques including, IR, high-resolution-EIMS, and extensive 400 MHz one- and two-dimensional NMR-analysis (1H, 13C-NMR, DEPT, 1H--1H COSY, HMQC, HMBC, and NOE experiments).     

A new steroid glycoside and furochromones from Cyperus rotundus L

Further phytochemical investigation of the aerial parts of Cyperus rotundus L. afforded a new steroid glycoside named sitosteryl (6'-hentriacontanoyl)-beta-D-galactopyranoside (4) in addition to three furochromones, khellin (2), visnagin (3) and ammiol (9). Furthermore, benzo-alpha-pyrone (coumarin) (1), salicylic acid (5), caffeic acid (6), protocatechuic acid (7), p-coumaric acid (8), tricin (10) and isorhamnetin (11) were isolated. The structures of these compounds were established by spectroscopic methods. The isolated furochromones were tested for insect antifeedant activity against larvae Spodoptera littoralis when incorporated in artificial diet and offered to larvae in a chronic feeding bioassay. Also, visnagin, khellin and sitosteryl (6'-hentriacontanoyl)-beta-D-galactopyranoside showed strong cytotoxic activity against L5178y mouse lymphoma cells and were also active in the brine shrimp lethality test.     

Vibrational analysis of amino acids and short peptides in hydrated media. II. Role of KLLL repeats to induce helical conformations in minimalist LK-peptides

Aqueous solution secondary structures of minimalist LK-peptides, with the generic sequence defined as KLL(KLLL)nKLLK, have been analyzed by means of circular dichroism (CD) and Raman scattering techniques. Our discussion in the present paper is mainly focused on four synthetic peptides (from 5 to 19 amino acids), KLLLK, KLLKLLLKLLK, KLLKLLLKLLLKLLK, and KLLKLLLKLLLKLLLKLLK, corresponding to the repeat unit, and to the peptide chains with the values of n = 1-3, respectively. CD and Raman spectra were analyzed in order to study both structural features of the peptide chains and their capability to form aggregates. On the basis of the obtained results it was concluded that the conformational flexibility of the shortest peptides (5-mer and 11-mer) is high enough to adopt random, beta-type, and helical chains in aqueous solution. However, the 11-mer shows a clear tendency to form beta-strands in phosphate buffer. The conformational equilibrium can be completely shifted to beta-type structures upon increasing ionic strength, i.e., in PBS and tris buffers. This equilibrium can also be shifted toward helical chains in the presence of methanol. Finally, the longest peptides (15-mer and 19-mer) are shown to form alpha-helical chains with an amphipathic character in aqueous solution. The possibility of bundle formation between helical chains is discussed over the temperature-dependent H-D exchange on labile hydrogens and particularly by considering the particular behavior of an intense Raman mode at 1127 cm-1 originating from the leucine residue side chain. The conformational dependence of this mode observed upon selective deuteration has never been documented up to now.     

How many conformers determine the thymidine low-temperature matrix infrared spectrum? DFT and MP2 quantum chemical study

A comprehensive conformational analysis of isolated 2'-beta-deoxy-thymidine (T), canonical DNA nucleoside, has been performed by means of ab initio calculations at the MP2/6-311++G(d,p)//DFT B3LYP/6-31G(d,p) level of theory. At 298.15 K, all 92 conformers of isolated dT are within a 7.49 kcal/mol Gibbs energy range. Syn orientation for the base and South (S) conformers for the sugar dominate at this temperature: syn/anti = 61.6%:38.4% and S/N = 74.5%:25.5%. However, at 420 K, the majority of conformers contain anti base and the population of North (N) sugars increases: syn/anti = 38.0%:62.0% and S/N = 59.5%:40.5%. The whole conformational parameters (P, chi, gamma, delta, beta, epsilon, nu max) were analyzed as well as the energies of the OH...O intramolecular H-bonds on the basis of nu(OH) stretching vibrations. Convolution of calculated IR spectra of all of the T conformers appears consistent with its low-temperature matrix spectrum (Ivanov et al. Low Temp. Phys. 2003, 29, 809). The maximal discrepancy in frequencies between calculated and experimental spectra is less than 1%. A conclusion was made that for reliable reconstruction of the isolated nucleoside IR spectrum the quasi whole set of conformers should be taken into consideration. In essence, this result opens up a possibility to reconstruct IR spectra of isolated nucleosides at physiological temperatures with rather satisfactory probability.