Morphology and micromechanical behavior of blends of ethene/1-hexene copolymers

Using (Me₅Cp)₂ZrCl₂ and Et(Ind)₂ZrCl₂ activated by methylaluminoxane (MAO), ethene/1-hexene copolymers of markedly different densities were produced under the same conditions. Binary blends were produced by melt blending of a high-density ethene/1-hexene copolymer with an elastomeric ethene/1-hexene copolymer. Transmission electron microscope (TEM) investigations of ultrathin sections of samples stained with ruthenium tetroxide revealed the morphology of the different blends. Depending on the blend composition, the degrees of segregation differed. An analysis of the TEM micrographs shows that increasing the segregation of the elastomeric blend component seems to be accompanied by an increase of the mean thickness of the crystalline lamellae of the matrix. Corresponding to the TEM results, typical morphological structures were also revealed by scanning force microscope (SFM) investigations using the tapping mode and a force modulation mode. Furthermore, these SFM techniques were applied to study in situ local deformations and changes in the morphological structures in a certain specimen position while the external stress was successively increased. Results of these experiments, as well as those from additional TEM in situ tensile tests of thin sections, show that the deformation that appears homogeneously down to the micron range is strongly inhomogeneous in the submicron range.     

Universal scaling in BCS superconductivity in three dimensions in non-s waves

The solutions of a renormalized BCS equation are studied in three space dimensions in s, p and d waves for finite-range separable potentials in the weak to medium coupling region. In the weak-coupling limit, the present BCS model yields a small coherence length and a large critical temperature, , appropriate for some high- materials. The BCS gap, , and specific heat as a function of zero-temperature condensation energy are found to exhibit potential-independent universal scalings. The entropy, specific heat, spin susceptibility and penetration depth as a function of temperature exhibit universal scaling below in p and d waves. Received: 18 July 1997 / Revised: 8 September 1997 / Accepted: 29 September 1997     

On the existence and stability of double-walled armchair silicon carbide nanotubes

A systematic study of type 1 armchair double-walled SiC nanotubes (DWNTs) (n,n)@(m,m) (3≤n≤6;7≤m≤12) using the finite cluster approximation is presented. The geometries of the tubes have been spin optimized using the hybrid functional B3LYP (Becke’s three-parameter exchange functional and the Lee-Yang-Parr correlation functional) and the all-electron 3-21G* basis set. The study indicates that the stabilities of the double-walled SiC nanotubes are of the same order as those of single-walled SiC nanotubes suggesting the possibilities of experimental synthesis of both single-walled and double-walled SiC nanotubes. The binding energy per atom or the cohesive energy of the double-walled nanotubes depends not only on the number of atoms but also on the coupling of the constituent single-walled nanotubes. The formation energy of the DWNTs is found to be maximum when the interlayer separation is about 3.5 Å. The DWNTs (n,n)@(n+4,n+4) are found to have large formation energies. In particular, (5,5)@(9,9) DWNT is the most stable tube in our study with a binding energy per atom of 5.07 eV, the largest formation energy of 12.39 eV, an interlayer separation of 3.58 Å and a “band gap” of 1.97 eV. All double-walled SiC nanotubes are found to be semiconductors, with the band gaps decreasing from single-walled nanotubes to double-walled nanotubes.     

Stereoselective Synthesis of α-Digitoxosides and α-Boivinosides via Chelation-Controlled Anomeric O-Alkylation

A chelation-controlled anomeric O-alkylation has been developed for the stereoselective synthesis of α-digitoxosides and α-boivinosides bearing a C3-free hydroxyl group. Due to chelation via sodium ion, the anomeric alkoxides are locked in the axial configuration, which leads to the selective production of α-glycosides.     

Neutral and cationic half‐sandwich arene d6 metal complexes containing pyridyl and pyrimidyl thiourea ligands with interesting bonding modes: Synthesis,structural and anti‐cancer studies

The reaction of [(p‐cymene)RuCl₂]₂ and [Cp*MCl₂]₂ (M = Rh/Ir) with benzoyl (2‐pyrimidyl) thiourea (L1) and benzoyl (4‐picolyl) thiourea (L2) led to the formation of cationic complexes bearing formula [(arene) M (L1)к² _(N,S) Cl]⁺ and [(arene) M (L2)к²_(N,S)Cl]⁺ [(arene) = p‐cymene, M = Ru, ( 1 , 4 ); Cp*, M = Rh ( 2 , 5 ) and Ir ( 3 , 6 )]. Precursor compounds reacted with benzoyl (6‐picolyl) thiourea (L3) affording neutral complexes having formula [(arene) M (L3)к¹_(S)Cl₂] [arene = p‐cymene, M = Ru, ( 7 ); Cp*, M = Rh ( 8 ), Ir ( 9 )]. X‐ray studies revealed that the methyl substituent attached to the pyridine ring in ligands L2 and L3 affects its coordination mode. When methyl group is at the para position of the pyridine ring (L2), the ligand coordinated metal in a bidentate chelating N, S‐ mode whereas methyl group at ortho position (L3), it coordinated in a monodentate mode. Further the anti‐cancer studies of the thiourea derivatives and its complexes carried out against HCT‐116, HT‐29 (human colorectal cancer), Mia‐PaCa‐2 (human pancreatic cancer) and ARPE‐19 (non‐cancer retinal epithelium) cell lines showed that the thiourea ligands are inactive but upon complexation, the metal compounds displayed potent and selective activity against cancer cells in vitro. Iridium complexes were found to be more potent as compared to ruthenium and rhodium complexes.     

Structural exploration of hydroxyethylamines as HIV-1 protease inhibitors: new features identified

The current study deals with chemometric modelling strategies (Naïve Bayes classification, hologram-based quantitative structure–activity relationship (HQSAR), comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA)) to explore the important features of hydroxylamine derivatives for exerting potent human immunodeficiency virus-1 (HIV-1) protease inhibition. Depending on the statistically validated reliable and robust quantitative structure–activity relationship (QSAR) models, important and crucial structural features have been identified that may be responsible for enhancing the activity profile of these hydroxylamine compounds. Arylsulfonamide function along with methoxy or fluoro substitution is important for enhancing activity. Bulky steric substitution at the sulfonamide nitrogen disfavours activity whereas smaller hydrophobic substitution at the same position is found to be favourable. Apart from the crucial oxazolidinone moiety, pyrrolidine, cyclic urea and methyl ester functions are also responsible for increasing the HIV-1 protease inhibitory profile. Observations derived from these modelling studies may be utilized further in designing promising HIV-1 protease inhibitors of this class.     

RhCl3-assisted C-H and C-S bond scissions: isomeric self-association of organorhodium(iii) thiolato complex. synthesis, structure, and electrochemistry

The ligating properties of alkyl 2-(phenylazo)phenyl thioether 1 (HL(R); R = Me, CH(2)Ph) toward Rh(III) have been examined. A novel hexacoordinated orthometalated rhodium(III) thiolato complex trans-[Rh(L)Cl(PPh3)2] 5 has been synthesized from 1 and RhCl(3).3H(2)O in the presence of excess PPh(3) via in situ C(sp(2))-H and C(sp(3))-S bond scissions, which is the first example for a coordination compound of [L](2-). We were also able to isolate the intermediate organothioether rhodium(III) compound trans-[Rh(L(R))Cl(2)(PPh(3))] 6 with 1 equiv of PPh(3) relative to both 1 and RhCl(3).3H2O in the course of the synthesis of the S-dealkylated product. PPh(3) plays a crucial role in the C(sp(3))-S cleavage process. A plausible mechanistic pathway is presented for C-S bond cleavage, and reductive cleavage by single-electron transfer mechanism is likely to be operative. The electronically and coordinatively saturated thiolato complex 5, indefinitely stable in the solid state, undergoes spontaneous self-dimerization in solution via dissociation of one coordinated PPh3 molecule to afford edge-shared bioctahedral anti-[Rh(L)Cl(PPh(3))]2 7 and syn-[Rh(L)Cl(PPh(3))]2 8 isomers. All the synthesized organosulfur rhodium(III) compounds were isolated as both air- and moisture-stable solids and spectroscopically characterized in both solution and solid states. In addition, all the representative members have been authenticated by single-crystal X-ray structure analyses. Availability of the isomeric dimers provides an opportunity to recognize the presence of noncovalent intramolecular "metallochelate-metallochelate" interaction in the sterically encumbered syn isomer. Unlike other organosulfur rhodium complexes, the monomeric thiolato complex 5 exhibits a fully reversible oxidative wave at 0.82 V vs Ag/AgCl, which is supposed to be primarily centered on the thiolato sulfur atom, and such perception is consistent with the DFT study. Formation of rhodium-bound thiyl radical cation 5(*+) by electrochemical oxidation was scrutinized by EPR spectroscopy.     

Femtosecond solvation dynamics in different regions of a bile salt aggregate: excitation wavelength dependence

Solvation dynamics of coumarin 480 (C480) in the secondary aggregate of a bile salt (sodium deoxycholate, NaDC) is studied using femtosecond up-conversion. The secondary aggregate resembles a long (approximately 40 A) hollow cylinder with a central water-filled tunnel. Different regions of the aggregate are probed by variation of the excitation wavelength (lambdaex) from 375 to 435 nm. The emission maximum of C480 displays an 8 nm red shift as the lambdaex increases from 345 to 435 nm. The 8 nm red edge excitation shift (REES) suggests that the probe (C480) is distributed over regions of varied polarity. Excitation at a short wavelength (375 nm) preferentially selects the probe molecule in the buried locations and exhibits slow dynamics with a major (84%) slow component (3500 ps) and a small (16%) contribution of the ultrafast component (2.5 ps). Excitation at lambdaex=435 nm (red end) corresponds to the exposed sites where solvation dynamics is very fast with a major (73%) ultrafast component (相似文献