De novo asymmetric syntheses of muricatacin and its analogues via dihydroxylation of dienoates

A short and highly efficient route to both enantiomers of muricatacin as well as the C-5-epimer has been developed. The key to the overall transformation is the highly regio- and enantioselective Sharpless asymmetric dihydroxylation of an (E,Z)-dienoate. The highly efficient stereoselective synthesis prepares (-)-muricatacin in seven steps and 66% overall yield.     

Some aromatic hydrazone derivatives as inhibitors for the corrosion of C-steel in phosphoric acid solution

The effect of furfural benzoylhydrazone and its derivatives (I-VII) as corrosion inhibitors for C-steel in 1M phosphoric acid solution has been studied by weight-loss and galvanostatic polarization techniques. A significant decrease in the corrosion rate of C-steel was observed in the presence of the investigated inhibitors. This study revealed that, the inhibition efficiency increases with increasing the inhibitor concentration, and the addition of iodide ions enhances it to a considerable extent. The effect of temperature on the inhibition efficiency of these compounds was studied using weight-loss method. Activation energy (E(a)*) and other thermodynamic parameters for the corrosion process were calculated and discussed. The galvanostatic polarization data indicated that, the inhibitors were of mixed-type, but the cathode is more polarized than the anode. The adsorption of these compounds on C-steel surface has been found to obey Frumkin's adsorption isotherm. The mechanism of inhibition was discussed in the light of the chemical structure of the undertaken inhibitors.     

Capillary waves at the liquid-vapor interface and the surface tension of water

Capillary waves occurring at the liquid-vapor interface of water are studied using molecular dynamics simulations. In addition, the surface tension, determined thermodynamically from the difference in the normal and tangential pressure at the liquid-vapor interface, is compared for a number of standard three- and four-point water models. We study four three-point models (SPC/E, TIP3P, TIP3P-CHARMM, and TIP3P-Ew) and two four-point models (TIP4P and TIP4P-Ew). All of the models examined underestimate the surface tension; the TIP4P-Ew model comes closest to reproducing the experimental data. The surface tension can also be determined from the amplitude of capillary waves at the liquid-vapor interface by varying the surface area of the interface. The surface tensions determined from the amplitude of the logarithmic divergence of the capillary interfacial width and from the traditional thermodynamic method agree only if the density profile is fitted to an error function instead of a hyperbolic tangent function.     

Synthesis of conformationally constrained lysine analogues

The synthesis of two conformationally constrained lysine analogues is reported. The synthesis of the novel analogue 1 based on the 3-aza-bicyclo[3.1.0]hexane system is accomplished from the known tricycle 3 in eight steps. The synthesis of the analogue 2 is accomplished in eight steps from 4-hydroxy proline. Both analogues are synthesized appropriately protected for Fmoc/Boc solid-phase peptide synthesis.     

Precipitate flotation-separation, speciation and hydride generation atomic absorption spectrometric determination of selenium(IV) in food stuffs

A method for flotation and determination of selenium(IV) in foodstuffs using p-chlorophenylthiosemicarbazide (HCPT) was investigated. At pH  2, selenium(IV) forms a 1:1 reddish-brown precipitate with HCPT easily floated using oleic acid (HOL) surfactant. The separated complex was dissolved in 4 M HCl and diluted in 10-ml double-distilled water (DDW). Selenium(IV) content in the eluate was determined by hydride generation atomic absorption spectrometry (HG-AAS) at 196.4 nm using sodium borohydride. The HCPT–Se(IV) complexes formed in absence and presence of oleic acid were characterized by elemental analysis, mass and infrared spectral studies. The mode of chelation between Se(IV) and HCPT is proposed to be through S and N coordination. Interferences, on the flotation process, from various foreign ions were avoided by adding excess HCPT. The proposed flotation methodology was successfully applied to the analysis of selenium in real foodstuffs and natural water spiked with known amounts of Se(IV) with a preconcentration factor of 100 and a detection limit of 20 pg. Application was also extended to separate Se(IV) successfully from Se(VI) in their synthetic mixtures. The separation mechanism is proposed to be due to hydrogen bond formation between the COOH group of HOL and –NH of the HCPT–Se(IV) complex.     

Total synthesis of (±)-pentenomycin

A concise stereoselective route to (±)-pentenomycin 1 in 33% overall yield starting from the readily accessible Diels-Alder adduct 4 is reported. The key reaction involves decarbonylation of β-methoxy-α,β-unsaturated aldehyde 8 obtained from β-hydroxy-dimethylketal 6.     

Gold(I) and silver(I) mixed-metal trinuclear complexes: dimeric products from the reaction of gold(I) carbeniates or benzylimidazolates with silver(I) 3,5-diphenylpyrazolate

Trinuclear mixed-metal gold-silver compounds are obtained by the reaction of gold(I) carbeniate [Au(mu-C(OEt)=NC6H4-p-CH3)]3, TR(carb), or gold(I) imidazolate [Au-mu-C,N-1-benzyl-2-imidazolate]3, TR(bzim), with silver(I) pyrazolate [Ag(mu-3,5-Ph2pz)]3. The crystalline products are mixed-ligand, mixed-metal dimeric products [Au(carb)Ag2(mu-3,5-Ph2pz)2], [Au2(carb)2Ag(mu-3,5-Ph2pz)].CH2Cl2, [Au(bzim)2Ag2(mu-3,5-Ph2pz)], and [Au2(bzim)2Ag(mu-3,5-Ph2pz)]. They have been characterized by elemental analysis and 1H NMR and mass spectrometry. The X-ray structure of [Au(carb)Ag2(mu-3,5-Ph2pz)2] shows it to be a dimer with two Ag...Au contacts between the trinuclear units of 3.083(2) and 3.310(2) A and with average intramolecular Ag...Ag and Au...Ag distances of approximately 3.3 and 3.2 A, respectively. The structure of [Au2(carb)2Ag(mu-3,5-Ph2pz)].CH2Cl2 is a dimer with one intermolecular Au...Au attraction of 3.3354(10) A and a short Ag...Au distance of approximately 3.42 A and intramolecular Ag...Au and Au...Au contacts of approximately 3.2 and approximately 3.3 A, respectively. Packing diagrams of both complexes show that the dimeric units are independent, similar to their parent molecules. The dimers of trinuclear [Au(carb)Ag2(mu-3,5-Ph2pz)2] and [Au2(carb)2Ag(mu-3,5-Ph2pz)].CH2Cl2 crystallize in the triclinic space group P (Z = 2), a = 9.688(3) A, b = 15.542(4) A, c = 23.689(6) A, alpha = 82.560(5) degrees , beta = 87.887(6) degrees , gamma = 78.060(5) degrees , and the orthorhombic space group Pca2(1) (Z = 4), a = 29.644(4) A, b = 7.4582(10) A, c = 30.473(4) A, respectively. The structure of [Au(bzim)Ag2(mu-3,5-Ph2pz)2] is a dimer with two metallophilic Ag...Au interactions of 3.14 A. The complex crystallizes in the monoclinic space group C2/c (Z = 4), a = 26.368(5) A, b = 15.672(3) A, c = 17.010(3) A, beta = 102.206(3) degrees .     

Microwaves in organic synthesis: Synthesis of pyridazinones,phthalazinones and pyridopyridazinones from 2‐oxo‐arylhydrazones under microwave irradiation

The phenylhydrazones 1a‐d condensed with ethyl cyanoacetate to yield pyridazinones 2a‐d that reacted with sulphur in presence of piperidine to yield the aminothienopyridazineones 3a,b that reacted with electron poor olefins and acetylenes to yield phthalazines 10‐12. The condensed aminothiophenes 3a,b reacted with dimethylformamide dimethylacetal to yield amidines 13a,b. Compounds 2a,b condensed with dimethylformamide dimethylacetal to yield the trans enamines 16a,b that cyclized readily into the pyridopyridazinones 17a,b on treatment with ammonium acetate in presence of acetic acid. Compounds 2a‐d reacted also with benzylidenemalononitrile to yield the phthalazinones 21a‐d. The reactions were conducted both by microwave heating and conventional heating. Better yields in much shorter reaction times were achieved by microwave heating.     

Synthesis of oligo(ethylene glycol) toward 44-mer

A synthetic method for oligo(ethylene glycol) toward 44-mer (FW = 1956.35) is described. Reiteration of Williamson's ether synthesis and hydrogenation to remove protecting benzyl group affords desired oligo(ethylene glycol) toward 44-mer in moderate yields. The advantages in this method are use of commercially easily available materials as starting materials and procedures avoiding difficulty in purification of the products as much as possible.     

Artifact-free black-blood cine cardiac imaging in a single breath-hold

Fast imaging using the STimulated Echo Acquisition Mode (STEAM) sequence can produce cine images of the heart with black-blood contrast. Nevertheless, correction of deformation-related artifacts is required in order to maintain myocardial signal throughout the cardiac cycle. Recent work by our group has eliminated this artifact by combining two STEAM sequences acquired with two different demodulation gradients. Unfortunately, these two STEAM sequences were acquired on two separate breath-holds; thus, scan time doubled. In this work, we present a technique to reduce the total scan time by one half, without sacrificing image quality. The technique is based on interleaving two demodulations within one acquisition in order to obtain quality cine images of the heart in a single breath-hold. The technique was tested on animal models and human subjects, and the impact of interleaved acquisition on image quality was studied using quantitative and qualitative measures.