Synthesis and properties of tialite, beta-AL2TIO5

Tialite, beta-Al2TiO5, a low expansion material, has been synthesised by the combustion of corresponding metal nitrates and carbohydrazide (CH) or urea redox mixtures at 500-degrees-C. As prepared powders contained tialite, rutile, and corundum in the mole ratios of 50:25:25 (CH) and 20:40:40 (urea). The combustion derived powders, when calcined 30 min at 1300-degrees-C, gave single phase beta-tialite having a surface area of 20-25 m2 g-1 and a particle size of 0.79-1.03 mum.

Synthesis based on cyclohexadienes. Part 15. Total synthesis of (±)-prezizaene, (±)-prezizanol and (±)-jinkohol II

A new methodology for the synthesis of the complex ring system tricyclo[6.2.1.0(1.5)]undecane. present in the zizaene group of sesquiterpenes, is described. Acid-catalysed rearrangement of the endo alcohol 20 afforded the enone 12, which was transformed stereoselectively into the key intermediate. (+/-)-norprezizanone 10. The features of the synthesis are the transformation of a bicycle[2.2.2] octane framework into a bicycle[3.2.1] octane system by an acid-catalysed rearrangement and a stereoselective conjugate addition of a methyl group on an alpha,beta-unsaturated keto ester at -100 degrees C. Norprezizanone was converted into the sesquiterpenes (+/-)-prezizanol 5 and(+/-)-prezizaene 4. The first total synthesis of (+/-)-jinkohol II 6 is also presented.

Transformation of 16-dehydroprogesterone and 17?-hydroxyprogesterone by Mucor piriformis

Mucor piriformis was used to study the mode of transformation of 16-dehydroprogesterone (I, pregna-4, 16-diene-3, 20-dione) and 17 alpha-hydroxyprogesterone (II, 17 alpha-hydroxypregn-4-ene-3, 20-dione). Biotransformation products formed from I were 14 alpha-hydroxypregna-4, 16-diene-3, 20-dione (Ia), 7 alpha, 14 alpha-dihydroxypregna-4 16-diene-3, 20-dione (Ib), 3 beta, 7 alpha, 14 alpha-trihydroxy-5 alpha-pregn-16-en-20-one (Ic), and 3 alpha, 7 alpha, 14 alpha-trihydroxy-5 alpha-pregn-16-en-20-one (Id). Metabolites Ic and Id appear to be hitherto unknown. Timecourse studies suggested that the transformation is initiated by hydroxylation at the 14 alpha-position (Ia) followed by hydroxylation at the 7 alpha-position (Ib). Microsomes (105,000 g sediment) prepared from 16-dehydroprogesterone-induced cells hydroxylate I to its 14 alpha-hydroxy derivative (Ia) in the presence of NADPH. Incubation of Ia with the organism resulted in the formation of Ib, Ic and Id. Biotransformation products formed from compound II were 17 alpha, 20 alpha-dihydroxypregn-4-en-3-one (IIa), 7 alpha, 17 alpha-dihydroxypregn-4-ene-3, 20-dione (IIb), 6 beta, 17 alpha, 20 alpha-trihydroxypregn-4-en-3-one (IIc) and 11 alpha, 17 alpha, 20 alpha-trihydroxypregn-4-en-3-one (IId). Time-course studies indicated that IIa is the initial product formed, which is further hydroxylated either at the 6 beta or 11 alpha position. Incubation of IIa with the organism resulted in the formation of IIc and IId. Reduction of the 4-en-3-one system and 20-keto group has not been observed before in organisms of the order Mucorales. In addition, M. piriformis has been shown to carry out hydroxylation at the C-6, C-7, C-11 and C-14 positions in the steroid molecules tested.

Application of microwave heating technique for rapid synthesis of ?,?-unsaturated esters

The use of microwave heating technique for the acceleration of ortho ester Claisen rearrangement (a three step transformation) is described. Irradiation of a DMF solution of the allyl alcohol 5, triethyl orthoacetate and propionic acid (catalytic) in an Erlenmeyer flask for 10 minutes in a microwave oven generated the ester 8 in 83% yield. Analogously, ortho ester Claisen rearrangement of a variety of allyl and propargyl alcohols (9, 12-22) were achieved. The formation of the diester 10 from 2-butyne-1,4-diol (9) via the ortho ester Claisen rearrangement of two allyl alcohol moieties (involving sh steps) in 15 minutes, demonstrates the versatility of the microwave heating technique.

Characterization of the DNA-binding domain of beta protein, a component of phage lambda Red-pathway by UV catalyzed cross-linking

beta protein, a key component of Red-pathway of phage lambda is necessary for its growth and general genetic recombination in recombination-deficient mutants of Escherichia coli. To facilitate studies on structure-function relationships, we overexpressed beta protein and purified it to homogeneity. A chemical cross-linking reagent, glutaraldehyde, was used to stabilize the physical association of beta protein in solution. A 67-kDa band, corresponding to homodimer, was identified after separation by SDS-polyacrylamide gel electrophoresis. Stoichiometric measurements indicated a site-size of 1 monomer of beta protein/5 nucleotide residues. Electrophoretic gel mobility shift assays suggested that beta protein formed stable nucleoprotein complexes with 36-mer, but not with 27- or 17-mer DNA. Interestingly, the interaction of beta protein with DNA and the stability of nucleoprotein complexes was dependent on the presence of MgCl2, and the binding was abolished by 250 mM NaCl. The K-d of beta protein binding to 36-mer DNA was on the order of 1.8 x 10(-6) M. Photochemical cross-linking of native beta protein or its fragments, generated by chymotrypsin, to 36-mer DNA was performed to identify its DNA-binding domain. Characterization of the cross-linked peptide disclosed that amino acids required for DNA-binding specificity resided within a 20-kDa peptide at the N-terminal end. These findings provide a basis for further understanding oi the structure and function of beta protein.

Chemo- and stereoselective reduction of alpha,beta-epoxyketones with diisopropoxytitanium(III) tetrahydroborate

Reduction of alpha,beta-epoxyketones with diisopropoxytitanium(III) tetrahydroborate in dichloromethane under mild conditions (-78 degrees--> -20 degrees C) provides anti- (or erythro-) alpha,beta-epoxy alcohols in high yields with high degree of chemo- and stereoselectivity. Copyright (C) 1996 Elsevier Science Ltd

Helix termination and chain reversal: Crystal and molecular structure of the alpha,beta-dehydrooctapeptide Boc-Val Delta Phe-Phe-Ala-Leu-Ala-Delta Phe-Leu-OH

The crystal structure of the dehydro octapeptide Boc-Val-Delta Phe-Phe-Ala-Leu-Ala-Delta Phe-Leu-OH has been determined to atomic resolution by X-ray crystallographic methods. The crystals grown by slow evaporation of peptide solution in methanol/water are orthorhombic, space group P2(1)2(1)2(1). The unit cell parameters are a = 8.404(3), b = 25.598(2) and c = 27.946(3) Angstrom, Z = 4. The agreement factor is R = 7.58% for 3636 reflections having (\F-o\) greater than or equal to 3 sigma (\F-o\). The peptide molecule is characterised by a 3(10)-helix at the N-terminus and a pi-turn at the C-terminus. This conformation is exactly similar to the helix termination features observed in proteins. The pi-turn conformation observed in the octapeptide is in good agreement with the conformational features of pi-turns seen in some proteins. The alpha(L)-position in the pi-turn of the octapeptide is occupied by Delta Phe(7), which shows that even bulky residues can be accommodated in this position of the pi-turns. In proteins, it is generally seen that alpha(L)-position is occupied by glycine residue. No intermolecular head-to-tail hydrogen bonds are observed in solid state structure of the octapeptide. A water molecule located in the unit cell of the peptide molecule is mainly used to hold the peptide molecule together in the crystal. The conformation observed for the octapeptide might be useful to understand the helix termination and chain reversal in proteins and to construct helix terminators for denovo protein design.

Temperature-dependent photoluminescence of GaN grown on beta-Si3N4/Si (111) by plasma-assisted MBE

Photoluminescence (PL) of high quality GaN epitaxial layer grown on beta-Si3N4/Si (1 1 1) substrate using nitridation-annealing-nitridation method by plasma-assisted molecular beam epitaxy (PA-MBE) was investigated in the range of 5-300 K. Crystallinity of GaN epilayers was evaluated by high resolution X-ray diffraction (HRXRD) and surface morphology by Atomic Force Microscopy (AFM) and high resolution scanning electron microscopy (HRSEM). The temperature-dependent photoluminescence spectra showed an anomalous behaviour with an `S-like' shape of free exciton (FX) emission peaks. Distant shallow donor-acceptor pair (DAP) line peak at approximately 3.285 eV was also observed at 5 K, followed by LO replica sidebands separated by 91 meV. The activation energy of the free exciton for GaN epilayers was also evaluated to be similar to 27.8 +/- 0.7 meV from the temperature-dependent PL studies. Low carrier concentrations were observed similar to 4.5 +/- 2 x 10(17) Cm-3 by measurements and it indicates the silicon nitride layer, which not only acts as a growth buffer layer, but also effectively prevents Si diffusion from the substrate to GaN epilayers. The absence of yellow band emission at around 2.2 eV signifies the high quality of film. The tensile stress in GaN film calculated by the thermal stress model agrees very well with that derived from Raman spectroscopy. (C) 2010 Elsevier B.V. All rights reserved.

Influence of glycosidic linkage on the nature of carbohydrate binding in beta-prism I fold lectins: An X-ray and molecular dynamics investigation on banana lectin-carbohydrate complexes

The three crystal structures reported here provide details of the interactions of mannose and the mannosyl-alpha-1,3-mannose component of a pentamannose with banana lectin and evidence for the binding of glucosyl-alpha-1,2-glucose to the lectin. The known structures involving the lectin include a complex with glucosyl-beta-1,3-glucose. Modeling studies on the three disaccharide complexes with the reducing end and the nonreducing end at the primary binding site are also provided here. The results of the Xray and modeling studies show that the disaccharides with an alpha-1,3 linkage prefer to have the nonreducing end at the primary binding site, whereas the reducing end is preferred at the site when the linkage is beta-1,3 in mannose/glucose-specific beta-prism I fold lectins. In the corresponding galactose-specific lectins, however, alpha-1,3-linked disaccharides cannot bind the lectin with the nonreducing end at the primary binding site on account of steric clashes with an aromatic residue that occurs only when the lectin is galactose-specific. Molecular dynamics simulations based on the known structures involving banana lectin enrich the information on lectin-carbohydrate interactions obtained from crystal structures. They demonstrate that conformational selection as well as induced fit operate when carbohydrates bind to banana lectin.

Novel reduction (Zn-AcOH) of DDHQ esters - A new route to tropone synthesis

Zn/acetic acid reaction of DDHQ esters 1 a-d gave the saturated acids 3 a-d and the hydrocarbons 7 a-d. The intermediacy of the aldehydes 10 and 11 in the formation of the products has been established. Oxidation of hydrocarbons 7a and 7b gave the corresponding tropones (5a and 5b).

Oxygenation of alkenes with t-BuOOH catalysed by beta-cyclodextrin borate

beta-Cyclodextrin borate catalyses oxygenation of aryl substituted alkenes in the presence of t-BuOOH to afford beta-dioxy alcohols in good yields (63-86%). Copyright (C) 1996 Published by Elsevier Science Ltd

Sintering of beta titanium: Role of dislocation pipe diffusion

Sintering of titanium in its high temperature beta phase was studied by isothermal dilatometry. The sintering shrinkage y did not follow the normal time exponent type of behaviour, instead being described by the equation y = Kt(m)/[1-(A+Bt)(2)], where m = 1.93 +/- 0.07, with an activation energy of 62-90 kJ mol(-1). A detailed analysis of these results, based on the 'anomalous' diffusion behaviour reported for beta titanium, is carried out. It is shown that the generation of a high density of dislocations during the alpha --> beta phase transformation, coupled with sluggish recovery at the sintering necks, enables sintering mass transport by pipe diffusion through dislocation cores from sources of matter within the particles to become dominant.

Reduction of DDHQ and TCC esters by NaBH4-its specificity in the presence of Alkyl/Aryl esters

DDHQ/TCC esters 3a–f, 7a–g were prepared either by oxidation of spiroketones 1 with DDQ/Image -chloranil or by condensation of acid chloride with DDHQ/TCC. NaBH4 reduction of unsaturated DDHQ 3a–b and TCC 7a–c esters gave the corresponding allylic alcohols in good yield without any observable 1,4-addition products. Reduction of saturated esters 3e, 7d, gave the corresponding alcohols. Alkyl esters 5 and 6, methyl benzoate and phenyl benzoate remained unaffected under these reduction conditions. In the reduction of compound 7e containing both alkyl and TCC esters, TCC ester is selectively reduced. Reduction of TCC mono esters 7f–g gave the lactones. The observed facile reduction has been rationalised.