The Linear Tripeptide L-Alanylglyeyl-L- alanine

L-Alanylglycyl-L-alanine, C8H15N3O4, exists as zwitter-ion in the crystal with the N terminus protonated and the C terminus in an ionized form, Both the peptide units are in trans configurations and deviate significantly from planarity. Backbone torsion angles are psi(1)=172.7(2), omega(1)=-178.2(2), phi(2)=91.7(2), phi(2)=-151.9(2), omega(2)=-176.9(2), phi(3)=-71.3(2), phi(31)=-7.0(3) and psi(32) 172.4(2)degrees. The protonated NH3+ group forms three hydrogen bonds with atoms of symmetry-related molecules.

A note on mass transfer in turbulent wall jets

THE PROCESS of mass transfer from saturated porous surfaces virtual origin ; exposed to turbulent air streams finds many practical applitransverse coordinate; cations. In many cases, the air stream will be in the form of a height of nozzle above flat plate--radial wall jet; wall jet over the porous surface. The aerodynamics of both plane and radial wall jets have been investigated in detail and a vast amount of literature is available on the subject [l-3].

A Raman study of multiferroic LuMnO3

Magnetic and dielectric measurements confirm the multiferroic nature of LuMnO3. Raman spectra of LuMnO3 have been recorded in the 77-800 K range covering both the antiferromagnetic transition at 90 K and the ferroelectric-paraelectric transition at 750 K. The changes in the phonon modes frequencies and band-widths indicate the presence of phonon-spin coupling in the antiferromagnetically ordered phase. The ferroelectric-paraelectric transition is accompanied by the broadening and disappearance of many of the phonon modes. Some of the phonon modes also show anomalies at the ferroelectric transition.

Mechanical properties of nanodiamond-reinforced polymer-matrix composites

Poly(vinyl alcohol)-matrix reinforced with nanodiamond (ND) particles, with ND content up to 0.6 wt%, were synthesized. Characterization of the composites by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) reveal uniform distribution of the ND particles with no agglomeration in the matrix. Differential scanning calorimetry reveals that the crystallinity of the polymer increases with increasing ND content, indicating a strong interaction between ND and PVA. Nano-indentation technique was employed to assess the mechanical properties of composites. Results show that even small additions of ND lead to significant enhancement in the hardness and elastic modulus of PVA. Possible micromechanisms responsible for the enhancement of the mechanical properties are discussed.

Diphenyl sulphoxide complexes of some divalent metal ions*1

Diphenyl sulphoxide (DPSO) complexes of some divalent metal perchlorates and chlorides are prepared The perchlorates of Mn, Co, Ni, Zn and Cd have the general formula [M(DPSO)6](CIO4)2. The Cu(II) complex is found to have the composition [Cu(DPSO)4] (CIO42. The chloro complex having the formula ZnCl2. 2DPSO, CdCl2.DPSO, HgCl2. DPSO and PdCl2. 2 DPSO have also been obtained. Infrared spectra indicate that the DPSO complexes of Mn, Co, Ni, Cu and Zn are oxygen-bonded while those of Cd, Hg and Pd are sulphur-bonded. The magnetic susceptibility and the optical spectral data reveal octahedral coordination for Mn, Co and Ni complexes. From the electronic spectra of Co and NI complexes, the ligand field parameters, Dq and β, are calculated.

Potentiometric and spectrophotometric investigations of nickel-triethanolamine complexes

A detailed study of nickel-triethanolamine complexes has been made employing potentiometric and spectrophotometric methods. The potentiometric method has been used to investigate the conditions for the formation of both mono- and polynuclear complexes. The formulae and the stability constants of the following complexes have been determined Ni(TEA)2+, Ni(TEA)22+, and Ni2(TEA)24+. Absorption spectra of pure mononuclear complexes have been computed by the combination of potentiometric and spectrophotometric methods. The results are discussed on the basis of ligand field theory. Comparison of the step constants of the nickel-ethanolamines (mono-, di- and tri-) shows a slight chelate effect in these complexes due to coordination through hydroxyl oxygen. In the case of polynuclear complexes it is likely that bridging occurs through hydroxyl oxygen.

Electron-beam melting and centrifugal splat-quenching technique for rapid solidification of titanium alloys

An electron-beam melting and centrifugal splat-quenching technique for the production of microflakes of Ti-6A1-4V (wt%) alloy quenched at an average cooling rate of about 105 K sec–1 is described. The effect of substrate angle on the shape, size, microstructure and average cooling rate of the flakes of major sieve fractions is discussed. Morphologies of particles of minor sieve fractions are dealt with briefly.

Crystallographic characterization of the conformation of the 1-aminocyclohexane-1-carboxylic acid residue in simple derivatives and peptides

The crystal structures of 1-aminocyclohexane-1-carboxylic acid (H-Acc6-OH) and six derivatives (including dipeptides) have been determined. The derivatives are Boc-Acc6-OH, Boc-(Acc6)2-OH, Boc-L-Met-Acc6-OMe, ClCH2CO-Acc6-OH, p-BrC6H4CO-Acc6-OH oxazolone, and the symmetrical anhydride from Z-Acc6-OH, [(Z-Acc6)2O]. The cyclohexane rings in all the structures adopt an almost perfect chair conformation. The amino group occupies the axial position in six structures; the free amino acid is the only example where the carbonyl group occupies an axial position. The values determined for the torsion angles about the N–Cα(φ) and Cα–CO (ψ) bonds correspond to folded, potentially helical conformations for the Acc6 residue.

First total synthesis of a natural thapsane

A stereospecific first total synthesis of a natural thapsane 1, from the readily available cyclogeraniol 8, is described.

b-Turn conformations in crystal structures of model peptides containing a,a-di-n-propylglycine (Dpg) and a,a-di-n-butyl-glycine (Dbg).

The crystal state conformations of three peptides containing the a,a-dialkylated residues, a,adi n-propylglycine (Dpg) and a,@-di-n-butylglycine (Dbg), have been established by x-ray diffraction. Boc-Ala-Dpg-Ala-OMe ( I ) and Boc-Ala-Dbg-Ala-OMe (III) adopt distorted type II @-turn conformations with Ala ( I ) and Dpg/Dbg (2) as the corner residues. In both peptides the conformational angles at the Dxg residue (I: 4 = 66.23 J/ = 19.3'; III: 4 = 66S0, J. = 21 .la)deviate appreciablyfrom ideal values for the i + 2 residue in a type II @-turn. In both peptides the observed(N. 0) distances between the Boc CO andAla(3) NHgroups are far too long (I:3.44 k; III: 3.63 k) for an intramolecular 4 + 1 hydrogen bond. Boc-Ala-Dpg-Ala-NHMe (II)crystallizes with two independent molecules in the asymmetric unit. Both molecules IIA and IIB adopt consecutive @-turn (type III-III in IIA and type III-I in IIB) or incipient 3,,,-helical structures, stabilized by two intramolecular 4 --t I hydrogen bonds. In all four molecules the bond angle N-C"-C' ( T ) at the Dxg residues are 2 1109 The observation of conformational angles in the helical region of 4,J/ space at these residues is consistent with theoretical predictions

Synthetic and physicochemical studies of uranium complexes with semicarbazone and hydrazone

Uranyl complexes of two Schiff bases, semicarbazone and hydrazone containing OON donor atoms have been synthesized and characterized on the basis of NMR, IR and electronic spectral studies, conductance, magnetic susceptibility and thermogravimetric data. The 1H NMR spectrum of the semicarbazone complex shows low field signals due to OH, NH and ---CH=N groups at 10.23, 9.31 and 8.17 ppm, respectively. The aromatic protons appear in the range 7.74–7.40 ppm. On complexation with U(VI) the signals due to OH and NH disappear evidently due to their participation in coordination. The coordination number of the o-vanillin semicarbazone (oVSC) complex is 6 whereas, that of the o-vanillin isonicotinic acid hydrazone (oVINAH) complex is 8, in addition to the two oxygen atoms already bonded to U(VI) in each species. The thermograms show the presence of 3 and 2 water molecules in these complexes, respectively and the IR spectral data also support the above conclusion. Suitable structures have been assigned.

Structural effects on the vaporization of high molecular weight esters

To understand the effect of molecular weight and branching on the heats of vaporization (AH,) and their flow behavior, AH, and viscosity (7) were measured at different temperatures in the high molecular weight ester series: linear flexible di-n-alkyl sebacates and compact branched triglycerides with molecular weight ranging from 300 to 900. AHv" values (AHv corrected to 298 K) have been obtained with experimental AH, and also computed according to the group additivity method; a smaller-CH,- group value of 3.8 kJ mol-' compared to the normal value of 5.0 kJ mol-' is found to give good agreement with the experimental data (within 2-5% error). Both ester series have the same AH," irrespective of their molecular features, namely,shape, flexibility, and polarity, suggesting the coiling of the molecules during vaporization. The segmental motion of these ester series during their flow and its dependence on their molecular features unlike AH,' are demonstrated by the correlation of the enthalpy of activation for viscous flow (AH*) and the ratio AE,/AH* = n (AE, is the energy of vaporization) with molecular weight.