联二炔囊泡的光致聚合、热致变色及应用

物理化学实验为各大高校本科化学教学的主干实验课程之一。虽然各高校的物理化学实验内容已十分丰富,但仍然缺乏将不同章节知识点融会贯通以及与学科前沿密切联系的综合型实验内容。我们根据南开大学郭东升教授课题组发表的一篇有关联二炔程序性响应检测胆碱酯酶的工作设计了“联二炔囊泡的光致聚合、热致变色及应用”的物理化学实验,涉及到联二炔缔合胶体的制备、联二炔的紫外光致聚合反应和聚联二炔的热致变色,进而显示其在防伪领域的潜在应用价值。希望通过此实验,使学生对物理化学中的缔合胶体、光化学、热力学、动力学等章节有更深一步的贯通性掌握,并了解自组装、光聚合、变色材料和防伪等相关研究领域的前沿动态。     

Hydrothermal synthesis, crystal structures and luminescent properties of two new Ln(III)–succinate (Ln=Eu, Tb) complexes exhibiting three dimensional networks

Two new coordination polymers, [Eu₂(L)₃(H₂O)₂]_n 1 and {[Tb₂(L)₃(H₂O)₂]·H₂O}_n 2, (H₂L=succinic acid) have been synthesized by the reaction of H₂L with nitrate salts of Eu(III) or Tb(III) under hydrothermal conditions. The X-ray diffraction analysis reveals that the two complexes are constructed by L bridging the chains of edge-sharing EuO₈(H₂O) or TbO₈(H₂O) polyhedra to form 3D network structure. 1 and 2 possess different topological structures due to the difference in the conformations of L. The solid photoluminescence of 1 and 2 was also investigated in room temperature.     

One-dimensional coordination polymers containing penta-supertetrahedral sulfide clusters linked by dipyridyl ligands

Three new one-dimensional coordination polymers [Zn8S(SC6H5)14.C12H10N2](1), [Zn7CoS(SC6H5)14.C13H14N2](2) and [Zn8S(SC6H5)14.C13H14N2](3) have been prepared containing penta-supertetrahedral clusters and linear crosslinking dipyridyl ligands; the two complexes show optical transitions with band gaps of approximately 3.44 eV (1) and approximately 3.54 eV (2).     

Theoretical prediction of the contact distance dependence of the electron transfer reactivity of the ClO/ClO− coupling system

On the basis of the structures and properties of the ClO/ClO^? system obtained at the density functional theory (DFT) (UB3LYP) level, employing the 6‐311+G(3df) standard basis set, the electron transfer reactivity of this system is investigated. The results indicate that there are five possible stable coupling complexes that correspond to the generous minima on the global potential energy surfaces (PES). The most stable coupling complex is planar EC4, in which there is a O? O linkage with two trans‐Cl atoms. Their stabilization energies are calculated to be 20.57 (EC1: C₁), 20.54 (EC2: C₂, ²B), 20.69 (EC3: C₁), 20.70 (EC4: C_s, ²A′), and 20.69 (EC.5: C_2h, ²B_u) kcal/mol at the B3LYP/6‐311+G(3df) level; with the correction of the basis set superposition error (BSSE), the stability order of these encounter complexes is EC4 > EC.5 > EC3 > EC1 > EC2. Based on the five encounter complexes, five coupling modes are designed for the study of the electron transfer reactivity of this system. The dissociation energy curves at the activated states and the corresponding activation energies of these five coupling modes are obtained and are compared at the B3LYP/6‐311+G(3df) and MP2/6‐311+G* levels. The inapplicability of DFT methods has also been discussed in this article in predicting the energy curves, especially with a long contact distance, in which DFT methods give the abnormal behavior for the dissociations of the complexes caused by the “inverse symmetry breaking” problem. On the basis of the golden rule of the time‐dependent perturbation theory, the electron transfer reactivity and the contact distance dependence of the various electron transfer kinetics parameters (e.g., activation energy, coupling matrix element) have been analyzed at the UMP2(full)/6‐311+G* level. The electron transfer can take place over a range of contact distances, but the most effective coupling distance corresponds to only a small range. The coupling orientation analyses also indicate that the most favorable coupling mode to the electron transfer does not always correspond to the most stable encounter complex mechanism. Some highly energetic coupling modes are more favorable for the electron transfer. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Synthesis of gramicidin S and its analogues via an on-resin macrolactamization assisted by a predisposed conformation of the linear precursors

A simple and efficient preparation of gramicidin S and its analogues is described. It involves solid-phase peptide synthesis and on-resin macrolactamization without side chain protection, affording cyclic products in high yield and high purity. The high specificity of the cyclization reaction was shown to originate in the formation of a pre-organized conformation of the linear biosynthetic precursor of gramicidin S. This facile method will provide convenient access to the analogues of the natural product for functional optimization to counter microbial resistance.     

High-throughput cytochrome P450 inhibition screening via cassette probe-dosing strategy. IV. Validation of a direct injection on-line guard cartridge extraction/tandem mass spectrometry method for simultaneous CYP3A4, 2D6 and 2E1 inhibition assessment

A highly efficient direct injection on-line guard cartridge extraction/tandem mass spectrometry (DI-GCE/MS/MS) method has been validated for high-throughput evaluation of cytochrome P450 (CYP) 3A4, 2D6 and 2E1 inhibition potential via cassette dosing of midazolam, dextromethorphan and chlorzoxazone using human hepatic microsomes and 96-well microtiter plates. Microsomal incubations were terminated with formic acid, centrifuged, and the resulting supernatants were injected for analysis by DI-GCE/MS/MS. Due to the novel use of an extremely short C(18) guard cartridge (4 mm in length), this method exhibits several advantages such as no sample preparation, excellent on-line extraction, short run time (2.5 min), and minimized source contamination and performance deterioration. The DI-GCE/MS/MS method demonstrates acceptable accuracy and precision for the simultaneous quantification of 1'-hydroxymidazolam, dextrorphan and 6-hydroxychlorzoxazone in microsomal incubations. The inhibition potential of CYP3A4, 2D6 and 2E1 has been evaluated using their known selective inhibitors. The IC(50) values measured by the cassette dosing approach (high-throughput) are consistent with those observed by an individual dosing regimen (conventional) and are all in good agreement with the literature values. The results suggest that the cassette probe-dosing strategy may provide an in vitro approach to minimize cost while maximizing throughput of CYP inhibition evaluation of new chemical entities in support of drug discovery and development.     

Double proton transfer behavior and one-electron oxidation effect in double H-bonded glycinamide-formic acid complex

The behavior of double proton transfer occurring in a representative glycinamide-formic acid complex has been investigated at the B3LYP/6-311 + + G( * *) level of theory. Thermodynamic and, especially, kinetic parameters, such as tautomeric energy, equilibrium constant, and barrier heights have been discussed, respectively. The relevant quantities involved in the double proton transfer process, such as geometrical changes, interaction energies, and intrinsic reaction coordinate calculations have also been studied. Computational results show that the participation of a formic acid molecule favors the proceeding of the proton transfer for glycinamide compared with that without mediate-assisted case. The double proton transfer process proceeds with a concerted mechanism rather than a stepwise one since no ion-pair complexes have been located during the proton transfer process. The calculated barrier heights are 11.48 and 0.85 kcal/mol for the forward and reverse directions, respectively. However, both of them have been reduced by 2.95 and 2.61 kcal/mol to 8.53 and -1.76 kcal/mol if further inclusion of zero-point vibrational energy corrections, where the negative barrier height implies that the reverse reaction should proceed with barrierless spontaneously, analogous to that occurring between glycinamide and formamide. Furthermore, solvent effects on the thermodynamic and kinetic processes have also been predicted qualitatively employing the isodensity surface polarized continuum model within the framework of the self-consistent reaction field theory. Additionally, the oxidation process for the double H-bonded glycinamide-formic acid complex has also been investigated. Contrary to that neutral form possessing a pair of two parallel intermolecular H bonds, only a single H bond with a comparable strength has been found in its ionized form. The vertical and adiabatic ionization potentials for the neutral complex have been determined to be about 9.40 and 8.69 eV, respectively, where ionization is mainly localized on the glycinamide fragment. Like that ionized glycinamide-formamide complex, the proton transfer in the ionized complex is characterized by a single-well potential, implying that the proton initially attached to amide N4 in the glycinamide fragment cannot be transferred to carbonyl O13 in the formic acid fragment at the geometry of the optimized complex.     

Synthesis, crystal structure and properties of the Cu complex of a tetradentate imidazole-functionalized diazamesocyclic ligand, 1,4-bis(N-1-methylimidazol-2-yl-methyl)-1,4-diazacycloheptane

A new potential tetradentate ligand, 1,4-bis(N-1-methylimidazol-2-ylmethyl)-1,4-diazacycloheptane (l), together with its Cu^II complex [CulCl]ClO₄ (1), has been reported. The crystal structure of 1, determined by single-crystal X-ray analysis, shows that it is in chiral P2₁2₁2₁ space group. The Cu^II centre is penta-coordinated in square pyramidal geometry and the diazacycloheptane (DACH) ring adopts normal boat configuration. The most striking feature of this complex is the formation of a 3D network bridged through the C-H?Cl hydrogen bonds with the perchlorate anions in the cavities, and stabilized via π-π stacking interactions along the a-direction. The solution behaviour of 1 has been further investigated by UV/Vis and ESR techniques.     

Exploration on regulating factors for proton transfer along hydrogen-bonded water chains.

Proton transfer along a single-file hydrogen-bonded water chain is elucidated with a special emphasis on the investigation of chain length, side water, and solvent effects, as well as the temperature and pressure dependences. The number of water molecules in the chain varies from one to nine. The proton can be transported to the acceptor fragment through the single-file hydrogen-bonded water wire which contains at most five water molecules. If the number of water molecule is more than five, the proton is trapped by the chain in the hydroxyl-centered H(7)O(3) (+) state. The farthest water molecule involved in the formation of H(7)O(3) (+) is the fifth one away from the donor fragment. These phenomena reappear in the molecular dynamics simulations. The energy of the system is reduced along with the proton conduction. The proton transfer mechanism can be altered by excess proton. The augmentation of the solvent dielectric constant weakens the stability of the system, but favors the proton transfer. NMR spin-spin coupling constants can be used as a criterion in judging whether the proton is transferred or not. The enhancement of temperature increases the thermal motion of the molecule, augments the internal energy of the system, and favors the proton transfer. The lengthening of the water wire increases the entropy of the system, concomitantly, the temperature dependence of the Gibbs free energy increases. The most favorable condition for the proton transfer along the H-bonded water wire is the four-water contained chain with side water attached near to the acceptor fragment in polar solvent under higher temperature.     

Zinc-bound thiolate-disulfide exchange: a strategy for inhibiting metallo-beta-lactamases

The mononuclear zinc thiolate complexes [(Tp(PhMe))Zn(S-R)], where Tp(PhMe) is hydrotris((3-methyl-5-phenyl)pyrazolyl)borate and (S-R) is benzyl thiolate, 4-nitrophenylthiolate, 4-trifluoromethylphenylthiolate, 4-chlorophenylthiolate, phenylthiolate, 2-methylphenylthiolate, 4-methylphenylthiolate, 4-methoxyphenylthiolate, or 4-hydroxyphenylthiolate, were synthesized. Representative members of the class were also characterized structurally. The benzyl thiolate complex undergoes a thiolate-disulfide exchange reaction with a variety of diphenyl and dipyridyl disulfides. Kinetic studies revealed that the reaction shows saturation behavior in both complex and disulfide for most of the disulfides studied. Combined with studies of the lability of the coordinated thiolate, a mechanism is proposed where the reactive species is the zinc-coordinated thiolate. When the free benzyl thiol was allowed to react with the same disulfides, the reaction was slower by a factor of 20-200 than that for the zinc-thiolate complex, depending on the particular disulfide employed. Since most metallo-beta-lactamases contain one or more cysteine residues, the one in the active site being coordinated to zinc, the present study was extended to examine whether disulfides can be used as inhibitors of these enzymes by selective oxidation of the metal-bound cysteine. Several disulfides allowed to react with metallo-beta-lactamase CcrA from Bacteroides fragilis were moderate to potent irreversible inhibitors of the enzyme.