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41.
New asymmetric bent-shaped molecules were synthesised and their mesomorphic properties and phase structures investigated by means of electro-optical measurements. All of the compounds formed fluid smectic phases and showed the homochiral antiferroelectric (SmCAPA) ground structure of the B2 phase. Comparing the new molecules with the previously reported classical symmetric bent-shaped molecules, we concluded that the modification of the chemical structure, especially the asymmetrical design of the bent-shaped molecules, is very significant for the interlayer interaction, influencing the formation of a specific polar order in banana phases. 相似文献
42.
In this communication, several sliding friction formulations used in spur gear dynamics are examined and compared in terms of the predictions of interfacial friction forces and off-line-of-action motions. Competing friction formulations include Coulomb models with time-varying friction coefficients and empirical expressions based on elasto-hydrodynamic and/or boundary lubrication regime principles. Predicted results compare well with friction force measurements. 相似文献
43.
Kang S Saito Y Watanabe N Tokita M Takanishi Y Takezoe H Watanabe J 《The journal of physical chemistry. B》2006,110(11):5205-5214
Bent-shaped molecules based on the oxadiazole central core with various side wings and terminal chain groups have been synthesized, and their liquid-crystalline behavior was investigated by optical microscopic, X-ray, and electrooptic measurements. These molecules exhibit liquid-crystal polymorphism including both the calamitic and banana phases. Such a characteristic polymorphism is attributable to the larger bend angle of the oxadiazole core compared to that of the resorcinol core used in conventional banana molecules. Only one type of banana phase, designated as the Bx phase, is formed. It appears upon cooling from the nematic and smectic liquid crystals and exhibits chiral domains with a very weak birefringence (apparently optically isotropic). By applying an electric field, the Bx phase is altered to a high-birefringence B2 phase with a homochiral SmC(A)P(A) structure that exhibits an antiferroelectric response. From detailed analyses of the optical texture and X-ray patterns through the transformation from well-oriented calamitic phases, the Bx phase was found to exhibit a helical structure, which arises as a frustration from the ground-state B2 phase in such a manner that the blocks of B2 layers are twisted with respect to each other in a direction parallel to the layer plane similarly to the twisted grain boundary (TGB) phase. 相似文献
44.
Laurie J. Burn Jean-Pierre Candelone Graeme R. Burton Vin I. Morgan Sungmin Hong 《Analytica chimica acta》2009,634(2):228-20
Measurements of Pb isotope ratios in ice containing sub-pg g−1 concentrations are easily compromised by contamination, particularly where limited sample is available. Improved techniques are essential if Antarctic ice cores are to be analysed with sufficient spatial resolution to reveal seasonal variations due to climate. This was achieved here by using stainless steel chisels and saws and strict protocols in an ultra-clean cold room to decontaminate and section ice cores. Artificial ice cores, prepared from high purity water were used to develop and refine the procedures and quantify blanks. Ba and In, two other important elements present at pg g−1 and fg g−1 concentrations in Polar ice, were also measured. The final blank amounted to 0.2 ± 0.2 pg of Pb with 206Pb/207Pb and 208Pb/207Pb ratios of 1.16 ± 0.12 and 2.35 ± 0.16, respectively, 1.5 ± 0.4 pg of Ba and 0.6 ± 2.0 fg of In, most of which probably originates from abrasion of the steel saws by the ice. The procedure was demonstrated on a Holocene Antarctic ice core section and was shown to contribute blanks of only ∼5%, ∼14% and ∼0.8% to monthly resolved samples with respective Pb, Ba and In concentrations of 0.12 pg g−1, 0.3 pg g−1 and 2.3 fg g−1. Uncertainties in the Pb isotopic ratio measurements were degraded by only ∼0.2%. 相似文献
45.
Kristine Prendergast Kym Adams William J. Greenlee Robert B. Nachbar Arthur A. Patchett Dennis J. Underwood 《Journal of computer-aided molecular design》1994,8(5):491-512
Summary A systematic search has been used to derive a hypothesis for the receptor-bound conformation of A-II antagonists at the AT1 receptor. The validity of the pharmacophore hypothesis has been tested using CoMFA, which included 50 diverse A-II antagonists, spanning four orders of magnitude in activity. The resulting cross-validated R2 of 0.64 (conventional R2 of 0.76) is indicative of a good predictive model of activity, and has been used to estimate potency for a variety of non-peptidyl antagonists. The structural model for the non-peptide has been compared with respect to the natural substrate, A-II, by generating peptide to non-peptide overlays. 相似文献
46.
Flow injection analysis with electrospray ionization mass spectrometry was used to investigate borate-nucleotide complex formation. Solutions containing 100 microM nucleotide and 500 microM boric acid in water-acetonitrile-triethylamine (50:50:0.2, v/v/v; pH 10.3) showed that borate complexation with nicotinamide nucleotides was significantly influenced by the charge on the nicotinamide group and the number of phosphate groups on the adenine ribose. Borate binding decreased in the order of NAD(+), NADH, NADP(+) and NADPH. To investigate the relationship between complex formation and phosphorylation, association constants (K(A)) of borate-adenine (AMP, ADP, ATP), -guanine (GMP, GDP, GTP), -cytidine (CMP, CDP, CTP) and -uridine (UMP, UDP, UTP) complexes were compared. The results showed that the number of nucleotide phosphate groups was inversely proportional to the relative abundance of the borate complexes, with the K(A) of borate-nucleotide complex decreasing in the order mono-, di- and tri-phosphates (AMP approximately GMP approximately CMP approximately UMP > ADP approximately GDP approximately CDP approximately UDP > GTP > ATP approximately CTP approximately UTP). At pH 7.4, using ammonium bicarbonate buffer, only borate-NAD(+) complex was observed. This indicates that the borate-NAD(+) complex may be the most physiologically relevant of those studied. 相似文献
47.
Ashwell GJ Wierzchowiec P Phillips LJ Collins CJ Gigon J Robinson BJ Finch CM Grace IR Lambert CJ Buckle PD Ford K Wood BJ Gentle IR 《Physical chemistry chemical physics : PCCP》2008,10(14):1859-1866
The properties of self-assembled molecules may be tuned by sequentially coupling components on a gold surface, the molecular electronics toolbox of chemically reactive building blocks yielding molecular wires with diode-like current-voltage (I-V) characteristics. The bias for rectification in each case is dependent upon the sequence of electron-donating and electron-accepting moieties and similar behaviour has been achieved for four different contacting techniques. 相似文献
48.
Hong S Jauregui LA Rangel NL Cao H Day BS Norton ML Sinitskii AS Seminario JM 《The Journal of chemical physics》2008,128(20):201103
1 microm double-stranded DNA molecules are immobilized between pairs of gold and pairs of platinum microelectrodes with gaps of 0.4 and 1 microm, respectively, and their electrical characteristics are determined under the application of constant and sinusoidal bias voltages. Due to their extremely high impedance for constant voltage bias, the samples of DNA are excellent insulators; however, their impedances show strong frequency dependence in the range of 10 Hz-7.5 MHz. Favorable response in the gold electrodes is attributed to the higher ability of DNA molecules to bridge the narrower gold electrode gaps in contrast to that in the wider platinum junctions. 相似文献
49.
Two‐Dimensional Skyrmion Lattice Formation in a Nematic Liquid Crystal Consisting of Highly Bent Banana Molecules 下载免费PDF全文
Prof. Dr. Sungmin Kang Dr. Eun‐Woo Lee Tianqi Li Prof. Dr. Xiaobin Liang Prof. Dr. Masatoshi Tokita Prof. Dr. Ken Nakajima Prof. Dr. Junji Watanabe 《Angewandte Chemie (International ed. in English)》2016,55(38):11552-11556
We synthesized a novel banana‐shaped molecule based on a 1,7‐naphthalene central core that exhibits a distinct mesomorphism of the nematic‐to‐nematic phase transition. Both the X‐ray profile and direct imaging of atomic force microscopy (AFM) investigations clearly indicates the formation of an anomalous nematic phase possessing a two‐dimensional (2D) tetragonal lattice with a large edge (ca. 59 Å) directed perpendicular to the director in the low‐temperature nematic phase. One plausible model is proposed by an analogy of skyrmion lattice in which two types of cylinders formed from left‐ and right‐handed twist‐bend helices stack into a 2D tetragonal lattice, diminishing the inversion domain wall. 相似文献
50.
Christopher M. Ryan Puneet Souda Frederic Halgand David T. Wong Joseph A. Loo Kym F. Faull Julian P. Whitelegge 《Journal of the American Society for Mass Spectrometry》2010,21(6):908-917
A hybrid linear ion-trap Fourier-transform ion cyclotron resonance mass spectrometer was used for top-down characterization
of the abundant human salivary cystatins, including S, S1, S2, SA, SN, C, and D, using collisionally activated dissociation
(CAD) after chromatographic purification of the native, disulfide intact proteins. Post-translational modifications and protein
sequence polymorphisms arising from single nucleotide polymorphisms (SNPs) were assigned from precursor and product ion masses
at a tolerance of 10 ppm, allowing confident identification of individual intact mass tags. Cystatins S, S1, S2, SA, and SN
were cleaved of a N-terminal 20 amino acid signal peptide and cystatin C a 26-residue peptide, to yield a generally conserved
N-terminus. In contrast, cystatin D isoforms with 24 and 28 amino acid residue N-terminal truncations were found such that
their N-termini were not conserved. Cystatin S1 was phosphorylated at Ser3, while S2 was phosphorylated at Ser1 and Ser3,
in agreement with previous work. Both cystatin D isoforms carried the polymorphism C46R (SNP: rs1799841). The 14,328 Da isoform
of cystatin SN previously assigned with polymorphism P31L due to a SNP (rs2070856) was found only in whole saliva. Parotid
secretions contained no detectable cystatins while whole saliva largely mirrored the contents of submandibular/sublingual
(SMSL) secretions. With fully characterized cystatin intact mass tags it will now be possible to examine the correlation between
the abundance of these molecules and human health and disease. 相似文献