Facilitated SO4(2-) transfers by hydrogen bond-forming ionophores are investigated across the nitrobenzene (NB)-water interface by using polarography with a dropping electrolyte electrode. Bis-thiourea 1, alpha,alpha'-bis(N'-p-nitrophenylthioureylene)-m-xylene, is found to significantly facilitate the transfer of the highly hydrophilic SO4(2-) whereas its counterpart, N-(p-nitrophenyl)-N'-propylthiourea (ionophore 2), cannot. In contrast to the predominant formation of a 1:1 complex with SO4(2-) in the bulk NB phase, the SO4(2-) transfer assisted by 1 is indeed based on the formation of a 1:2 complex between SO4(2-) and ionophore, even under the condition of [SO4(2-)]aq > [1]org. Such an exclusive formation of the 1:2 (SO4(2-) to ionophore) complex at the NB-water interface is not observed with structurally similar bis-thiourea 3, alpha,alpha'-bis(N'-phenylthioureylene)-m-xylene, where p-nitrophenyl moietes of bis-thiourea 1 are simply replaced by phenyl groups. The facilitated transfer of SO4(2-) with bis-thiourea 1 is further compared to that of HPO4(2-) and H2PO4- across the NB-water interface, which was previously shown to be assisted by 1 through the formation of the 1:1 and 2:1 (anion to ionophore) complexes, respectively. On the basis of these examinations, unique binding behaviors of hydrogen bond-forming ionophores at the NB-water interface are discussed, with a view towards development of ionophore-based anion-selective chemical sensors. 相似文献
A new method for the construction of the AB-ring core of Taxol was developed utilizing a new skeletal transformation protocol as a pivotal step. The acid-catalyzed rearrangement of the cyclopentenone-allene photoadduct gave a bridged seven-membered ketone, which was easily transformed, using the intramolecular Suzuki reaction and the oxidative cleavage of the vicinal diol, to the bicyclic diketone. 相似文献
GABA is a major neurotransmitter in the central nervous system. Data on GABA and its analogues calculated by using the ab initio and the MNDO method were compared with data obtained experimentally. The structures of GABA analogues calculated by the ab initio method agree well with the experimental data. This finding suggests the high reliability of this method. However, the structures of GABA analogues calculated by the MNDO method reflect only some aspects of the experimental data. Therefore the MNDO method should be used only for carefully selected chemical compounds.
The amino group in GABA and its analogues was proved to be the major active site. The electrostatic potential around the amino group in these compounds seems to be related to their biological activity. The difference in the electrostatic potential between the receptor binding molecules and the neuronal uptake molecules suggests that the structure of post-synaptic receptors might differ from that of uptake receptors. This finding suggests that there are at least two GABA-A receptors. GABA molecules seem to have a high potential for binding to the two receptors because they are highly flexible and can readily change their conformation. These results indicate a high reliability of the data calculated by the molecular orbital method and suggest that this method provides us with useful information that cannot be obtained experimentally. 相似文献
Spectrally resolved infrared stimulated vibrational echo data were obtained for sperm whale carbonmonoxymyoglobin (MbCO) at 300 K. The measured dephasing dynamics of the CO ligand are in agreement with dephasing dynamics calculated with molecular dynamics (MD) simulations for MbCO with the residue histidine-64 (His64) having its imidazole epsilon nitrogen protonated (N(epsilon)-H). The two conformational substate structures B(epsilon) and R(epsilon) observed in the MD simulations are assigned to the spectroscopic A(1) and A(3) conformational substates of MbCO, respectively, based on the agreement between the experimentally measured and calculated dephasing dynamics for these substates. In the A(1) substate, the N(epsilon)-H proton and N(delta) of His64 are approximately equidistant from the CO ligand, while in the A(3) substate, the N(epsilon)-H of His64 is oriented toward the CO, and the N(delta) is on the surface of the protein. The MD simulations show that dynamics of His64 represent the major source of vibrational dephasing of the CO ligand in the A(3) state on both femtosecond and picosecond time scales. Dephasing in the A(1) state is controlled by His64 on femtosecond time scales, and by the rest of the protein and the water solvent on longer time scales. 相似文献
In situ synchrotron X-ray powder diffraction patterns of porous coordination polymers [[Cu(2)(pzdc)(2)(bpy)].G] have been measured (pzdc = pyrazine-2,3-dicarboxylate, bpy = 4,4'-bipyridine) (where G = H(2)O for CPL-2 superset H(2)()O, G = benzene for CPL-2 superset benzene, and G = void for the apohost). The structures of apohost and CPL-2 superset benzene were determined from Rietveld analysis. Adsorption of benzene in the channels induced a remarkable contraction in the crystal (b axis; 6.8%, volume; 4.9%), although the channels were occupied by the benzene molecules. This crystal transformation provides a new pore structure that is well suited for benzene molecules, and we denote it as a "shape-responsive fitting" transformation. This type of pore gives rise to a new guideline: frameworks can be composed of flexible motifs that are linked via strong bond and/or stiff motifs that are connected via weaker bonds. 相似文献
The intercalation of 4-phenylazoaniline (PAA) in supercritical carbon dioxide (SC-CO(2)) into montmorillonite (TMA-Mnt) pillared with tetramethylammonium ions at 313 K and 15 MPa was investigated. The adsorption rate and equilibrium PAA uptake were compared with those in n-hexane, CCl(4) and benzene solutions at 313 K. The XRD and N(2) adsorption/desorption analyses showed that TMA-Mnt after adsorption of PAA in SC-CO(2) had the same pore structure as after adsorption of PAA in normal solvents. SC-CO(2) was found to be a good medium for PAA adsorption owing to its having a relatively high adsorption rate and the highest adsorptivity at the same PAA concentration. The properties of PAA adsorption on TMA-Mnt could be well elucidated by the difference in solubility parameters between liquid and solid phases. 相似文献
The reversible transportation of droplets was realized by spatiotemporal control of the wetting gradient. The surface wetting was reversibly regulated by using electrochemical reactions of the ferrocenyl (Fc) alkanethiol monolayer, and the wetting gradient was generated by the application of the in-plane bias voltage to the substrate. The back-and-forth motion of the wetting boundary, where the surface changed from wetting to repulsive, sequentially caused a droplet unidirectional spreading and shrinking on the surface. These unidirectional deformations resulted in the net transport of the droplet in an inchwormlike manner. The droplet moved backward when the direction of the in-plane bias voltage was reversed. 相似文献
The molecular recognition of catecholamines by hydrindacene-based receptors 1 and 2, as well as the durene-based receptor 3, and the guest-induced conformational changes are reported. These receptors selectively bind adrenaline and dopamine salts through the guests' ammonium group and 3-hydroxyl group on the aromatic ring. In the case of adrenaline, an additional hydrogen bond with a benzylic hydroxyl group is formed. In 2 % CD3CN/CDCl3, the association constants are of the order of 10(4) M(-1), which is much larger than with guests without the 3-hydroxyl groups (10(3) M(-1)). The two amide groups of receptor 1 can rotate freely around the C(aromatic)--C(amide) bond, whereas the tert-amide in 2 changes between two stable conformations at a slow enough rate to allow detection by (1)H NMR spectroscopy. In the absence of a guest molecule, the syn-conformer is less stable than the anti-conformer. On complex formation with adrenaline, the syn-conformer becomes dominant due to an intramolecular dipole-reversal effect in addition to multipoint hydrogen bonding. 相似文献