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971.
Mixtures of diblock co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides have been found to be amphiphilic, as reported before. In order to clarify
their accurate amphiphilic property, diblock co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides with monodispersity, methyl β-d-glucopyranosyl-(1→4)-2,3,6–tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6–tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-d-glucopyranoside (1, pentamer), methyl β-d-glucopyranosyl-(1→4)- β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-d-glucopyranoside (2, hexamer), and methyl β-d-glucopyranosyl-(1→4)-2,3,6-tri-O-methyl-β-d-glucopyranosyl-(1→4)- 2,3,6-tri-O-methyl-d-glucopyranoside (3, trimer) were synthesized independently. These compounds had higher surface activities compared to the mixture of diblock
co-oligomers of tri-O-methylated and unmodified cello-oligosaccharides and commercially available methylcellulose (MC) SM-4. This paper describes
the methods of synthesis of these compounds, and the influence of amphiphilic character on their surface activity. A new class
of carbohydrate-based nonionic surfactant without long alkyl chain was discovered. 相似文献
972.
Two solid phase transitions of [Cd(H2O)6](BF4)2 occurring on heating at TC2=183.3 K and TC1=325.3 K, with 2 K and 5 K hysteresis, respectively, were detected by differential scanning calorimetry (DSC). High value of entropy changes indicated large orientational disorder of the high temperature and intermediate phase. Nuclear magnetic resonance (1H NMR and 19F NMR) relaxation measurements revealed that the phase transitions at TC1 and TC2 were associated with a drastic and small change, respectively, of the both spin-lattice relaxation times: T1(1H) and T1(19F). These relaxation processes were connected with the “tumbling” motions of the [Cd(H2O)6]2+, reorientational motions of the H2O ligands, and with the iso- and anisotropic reorientation of the BF4− anions. The cross-relaxation effect was observed in phase III. The line width and the second moment of the 1H and 19F NMR line measurements revealed that the H2O reorientate in all three phases of the title compound. On heating the onset of the reorientation of 3 H2O in the [Cd(H2O)6]+2, around the three-fold symmetry axis of these octahedron, causes the isotropic reorientation of the whole cation. The BF4− reorientate isotropically in the phases I and II, but in the phase III they perform slow reorientation only about three- or two-fold axes. A small distortion in the structure of BF4− as well as of [Cd(H2O)6]2+ is postulated. The temperature dependence of the bandwidth of the O-H stretching mode measured by Fourier transform middle infrared spectroscopy (FT-MIR) indicated that the activation energy for the reorientation of the H2O did not change much at the TC2 phase transition. 相似文献
973.
Jing?Zhou Yuqi?Liu Liming?Tang Xinchen?Teng Ning?Tang Zhongxian?HuangEmail author 《中国科学B辑(英文版)》2003,46(1):64-74
Two mutants of the zinc finger protein, ZNF191 (243–368) I323W and R327W, are successfully obtained by site-directed mutagenesis.
The fluorescence spectrum is used to study the interaction between these two mutants and the oligonucleotides. The influence
of the mutation on the interaction has been studied using ethidium bromide (EB) as the fluorescence probe. The binding constants
of the I323W-DNA and R327W-DNA have been calculated and the possible binding models have been discussed. 相似文献
974.
Centrosymmetric linear [Ar-H-Ar]+ and asymmetric linear [Ar---Ar-H]+ are two stable configurations of [Ar2H]+. Based on the global potential energy surface of [Ar2H]+ provided by our group recently, we calculated the vibrational spectra of [Ar---Ar-H]+ with total angular momentum J = 0 by time-dependent quantum mechanical method, and the influence of quantum tunneling effect on vibrational spectra was
found. With the help of the observation on the eigenstate functions and the modified potential energy surface, assignments
were made to the spectra. The strong coupling between the excited bending mode of [Ar-H-Ar]+ and the vibrational states of [Ar---Ar-H]+ was discussed. 相似文献
975.
976.
Thermodynamic studies of clathrate hydrates, mainly of structures I and II, are considered in this review which is based on 147 references. There are two main subjects. The first is the host lattice energy and the guest-host interaction energy, both of these quantities being related to the enthalpy of dissociation and composition of the hydrates. The second subject concerns orientational ordering phenomena occurring in both host and guest, as reflected in the low temperature heat capacity. The classical theoretical treatment of clathrate formation has been reconsidered on the basis of recent experimental results. Particular emphasis has been given to orientational ordering since this topic is undoubtedly central to clarifying the nature of clathrate hydrates.Ausgehend von 147 Literaturangaben wurden in diesem Review thermodynamische Untersuchungen von Klathrathydraten hauptsächlich der Struktur I und II betrachtet. Es gibt zwei Hauptaugenmerke. Als erstes die Wirtsgitterenergie und die Gast-Wirt-Wechselwirkungsenergie, beide bezogen auf die Dissoziationsenthalpie und die Bildungsenthalpie der Hydrate. Das zweite Hauptaugenmerk betrifft Orientierungs-Konditionierungserscheinungen sowohl in Wirt als auch Gast, wie in den Wärmekapazitäten bei niedrigen Temperaturen widergespiegelt wird. Auf der Basis jüngster experimenteller Ergebnisse wurde die klassische theoretische Betrachtung über die Bildung von Klathraten überprüft. Der Orientierung-Konditionierung wurde besonderer Nachdruck verliehen, da dies zweifellos eine entscheidende Rolle bei der Klärung der Natur der Klathrathydrate spielt. 147 I II. . «» « — », . «» « », . . , .
Contribution No. 155 from the Chemical Thermodynamics Laboratory. 相似文献
Contribution No. 155 from the Chemical Thermodynamics Laboratory. 相似文献
977.
Ryo HorikoshiTomoyuki Mochida Hiroshi Moriyama 《Journal of solid state chemistry》2002,164(2):320-325
A series of ionic 4-(4′-pyridylthio)-1-methylpyridinium salts with different counteranions (1, I−; 2, BF−4; 3, PF−6; and 4, OTf−, where OTf=trifluoromethanesulfonate) have been prepared. Structural analysis reveals that the cation exhibits a variety of stacking structures dependent on the anion. Compound 1 crystallizes in space group P21/n (#14), with a=10.764(3) Å, b=9.601(5) Å, c=13.105(3) Å, β=108.35(2), V=1285.4(8) Å3, and Z=4. In this compound, each cation moiety is stacked in a helical arrangement along the c-axis. Compound 2, which is isomorphous to 1, has space group P21/n (#14), with a=11.647(2) Å, b=9.203(3) Å, c=13.232(2) Å, β=108.42(2), V=1345.6(5) Å3, and Z=4. Compound 3 crystallizes in space group P21/n (#14), with a=8.06(1) Å, b=17.43(1) Å, c=10.30(1) Å, β=103.0(1), V=1410(3) Å3, and Z=4. In this salt, the cation molecules assume a head-to-tail stacking arrangement, forming a polar pseudo 1-D chain. Compound 4 crystallizes in space group Pb? (#2), with a=7.585(4) Å, b=15.443(7) Å, c=6.775(4) Å, α=99.33(4), β=108.35(2)o, γ=98.37(4), V=756.6(7) Å3, and Z=2. The structure of 4 consists of a columnar stacking of pyridine moieties, with the cation moieties surrounded by the counteranions. Calculations show that the 4-(4′-pyridylthio)-1-methylpyridinium cation may be a good building block for second harmonic generation (SHG) materials, even though salts 1-4 crystallized in centrosymmetric structures and were SHG inactive. 相似文献
978.
Makoto Karakawa Yuji Mikawa Hiroshi Kamitakahara Fumiaki Nakatsubo 《Journal of polymer science. Part A, Polymer chemistry》2002,40(23):4167-4179
Seven possible regioselectively methylated cellulose acetates (RS‐MCAs)—2,3,6‐tri‐O‐methyl cellulose acetate, 3,6‐di‐O‐methyl cellulose acetate, 2,6‐di‐O‐methyl cellulose acetate, 2,3‐di‐O‐methyl cellulose acetate, 6‐O‐methyl cellulose acetate, 3‐O‐methyl cellulose acetate, and 2‐O‐methyl cellulose acetate—were prepared for the first time from chemically synthesized cellulose derivatives obtained by cationic ring‐opening polymerization and then were analyzed by 1H and 13C NMR spectroscopy. The chemical shifts of ring protons and carbons were influenced by substituent groups (methyl or acetyl) and clearly reflected the pattern of substituent distribution in anhydroglucose units. These data may conveniently be used for the determination of the substituent distribution of methyl cellulose. The synthesized RS‐MCAs also may be used for the elucidation of the structure–property relationship. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4167–4179, 2002 相似文献
979.
Pre-column labelling techniques are described for the determination of S-carboxymethyl-L-cysteine (CMC) and its metabolites in urine and plasma samples by high-performance liquid chromatography (HPLC) without prior extraction. All substances containing an amino group were converted into fluorescent fluorenylmethyl derivatives with 9-fluorenylmethyloxycarbonyl chloride (FMOC). Deaminated or N-acetylated carbocysteine metabolites were coupled with 1-pyrenyldiazomethane (PDAM) to give fluorescent PDAM esters. Similar results were obtained with the two commercially available and stable diazomethane derivatives PDAM and 9-anthryldiazomethane (ADAM). Following double derivatization with PDAM and FMOC, in a single chromatographic run with two fluorescence detectors connected in series, amines and amino(carboxylic) acids could be detected by their FMOC residues and, simultaneously, carboxylic acids were detected as fluorescent PDAM esters. The (R) and (S) enantiomers of the sulphoxides of CMC, of methylcysteine and of N-acetyl CMC were separated, although the reversed-phase HPLC system did not contain a chiral additive or stationary phase designed for the separation of enantiomers. The methods do not include liquid extraction steps and can therefore be performed either manually or automatically using an HPLC autosampler. These methods were used for the investigation of a disputed pharmacogenetic polymorphism of S-oxidation of CMC in humans, which until now has most often been studied using paper chromatography. The described techniques were applied to the determination of CMC and its metabolites in human urine and plasma samples. 相似文献
980.
Noritaka Ohtani Yukihiko Inoue Hiroshi Mizuoka Kenya Itoh 《Journal of polymer science. Part A, Polymer chemistry》1994,32(13):2589-2595
Dilute-solution viscosities of polystyrene-based cationic ionomers containing ammonio or phosphonio groups were measured in several solvents. In polar solvents with dielectric constant (εr) beyond 10, the ionomers showed a typical polyelectrolyte behavior, indicating that a large part of ionic groups were dissociated into ions. In nonpolar solvents with low εr, the reduced viscosity of the ionomers linearly decreased with a decreasing ionomer concentration. At low polymer concentrations, every ionomer gave a reduced viscosity lower than that of the corresponding chloromethylated polystyrene. With an increasing ion content, the intrinsic viscosity progressively decreased if the nonpolar solvents had a low acceptor number (AN), such as toluene or tetrahydrofran (THF). In the halogenated solvents with high AN value, such as chloroform, however, the intrinsic viscosity was hardly dependent on the ion content. This indicates that the intramolecular aggregation among the ionic groups is inhibited in the halogenated solvents due to a strong anion solvation. An addition of a protic solvent to a nonpolar solvent eliminates the aggregation between ionic groups and leads to polyelectrolyte behavior. © 1994 John Wiley & Sons, Inc. 相似文献