Multiple-injection affinity capillary electrophoresis to estimate binding constants of receptors to ligands

Multiple-injection affinity capillary electrophoresis (MIACE) is used to determine binding constants (K _b) between receptors and ligands using as model systems vancomycin and teicoplanin from Streptomyces orientalis and Actinoplanes teichomyceticus, respectively, and their binding to D-Ala-D-Ala peptides and carbonic anhydrase B (CAB. EC 4.2.1.1) and the binding of the latter to arylsulfonamides. A sample plug containing a non-interacting standard is first injected followed by multiple plugs of sample containing the receptor and then a final injection of sample containing a second standard. Between each injection of sample, a small plug of buffer is injected which contains an increasing concentration of ligand to effect separation between the multiple injections of sample. Electrophoresis is then carried out in an increasing concentration of ligand in the running buffer. Continued electrophoresis results in a shift in the migration time of the receptor in the sample plugs upon binding to their respective ligand. Analysis of the change in the relative migration time ratio (RMTR) or electrophoretic mobility (μ) of the resultant receptor–ligand complex relative to the non-interacting standards, as a function of the concentration of ligand yields a value for K _b. The MIACE technique is a modification in the ACE method that allows for the estimation of binding affinities between biological interactions on a timescale faster than that found for standard ACE. In addition sample volume requirements for the technique are reduced compared to traditional ACE assays. These findings demonstrate the advantage of using MIACE to estimate binding parameters between receptors and ligands.     

Electronic structures of 4d transition metal monoxides by density functional theory

Bond distances, dissociation energies, ionization potentials and electron affinities of 4d transition metal monoxides from YO to CdO and their positive and negative ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91, B3P86, BP86, SVWN, MPW1PW91 and PBE1PBE. It was found that calculated properties are highly dependent on the functionals employed, especially for dissociation energy. For most neutral species, pure density functionals BLYP, BPW91 and BP86 have good performance in predicting dissociation energy than hybrid density functionals B3LYP, B3PW91 and B3P86. In addition, BLYP gives the largest bond distance compared with other density functional methods, while SVWN gives shortest bond distance, largest dissociation energy and electron affinity. For the ground state, the spin multiplicity of the charged species can be obtained by ± 1 of their corresponding neutral species.     

Determination of Tetracyclines in Honey Using Liquid Chromatography with Ultraviolet Absorbance Detection and Residue Confirmation by Mass Spectrometry

A determination method has been optimized and validated for the simultaneous analysis of tetracycline （TC）, oxytetracycline （OTC）, chlortetracycline （CTC） and doxycycline （DC） in honey. Tetracyclines （TCs） were removed from honey samples by chelation with metal ions bound to small Chelating Sepharose Fast Flow columns and eluted with Na2EDTA-Mcllvaine pH 4.0 buffers. Extracts were further cleaned up by Oasis HLB solid-phase extraction （SPE）, while other solid-phase extraction cartridges were compared. Chromatographic separation was achieved using a polar end-capped C 18 column with an isocratic mobile phase consisting of oxalic acid, acetonitrile and methanol. LC with ultraviolet absorbance at 355 nm resulted in the quantitation of all four tetracycline residues from honey samples fortified at 15, 50, and 100 ng/g, with liner ranges for tetracyclines of 0.05 to 2 μg/mL. Mean recoveries for tetracyclines were greater than 50% with R.S.D. values less than 10% （n= 18）. Detection limits of 5, 5, 10, 10 ng/g for oxytetracycline, tetracycline, chlortetracycline and doxycycline, respectively and quantitation limits of 15 ng/g for all the four tetracyclines were determined. Direct confirmation of the four residues in honey （2-50 ng/g） was realized by liquid chromatography-tandem mass spectrometry （LC/MS/MS）. The linear ranges of tetracyclines determined by LC/MS/MS were between 5 to 300 ng/mL, with the linear correlation coefficient r〉 0.995. The limits of detection of 1 to 2 ng/g were obtained for the analysis of the TCs in honey.     

Crystal chemistry of protonated 1,2-bis(di-R-aminomethyl)benzenes. Part V. [1,2-bis(diethylaminomethyl)-3,6-dichlorobenzene:1,2-bis(diethylaminomethyl)-3,4,6-trichlorobenzene]perchlorate mixed crystals

The mixed crystals of 1,2-bis(diethylaminomethyl)-3,6-di- and 3,4,6-trichloro-benzene perchlorate at 0.5:0.5 ratio have been studied using X-ray diffraction and FT-IR spectroscopy. The molecules of di- and tri-chloro derivatives are distributed randomly in the crystal lattice; however, this disorder manifested mainly by a partial occupation of the chlorine atom at C(4) and by relatively big atomic temperature parameters even at 99 K, particularly for the oxygens of the perchlorate anion. The proton in the [NHN]⁺ bond refined close to the equidistant position between the nitrogens. The conformations of the diethylaminomethyl substituents are pseudo-symmetrical relative to the plane and twofold axis passing through the midpoint of the hydrogen bond. The IR spectrum of the crystals shows a broad intense band and an intense continuous absorption indicating relatively high proton polarizability in the intramolecular hydrogen bond. In acetonitrile and in chloroform, the proton in the intramolecular hydrogen bond also shows a very high proton polarizability demonstrated by the continuous absorption in the IR spectrum.     

Proton transfer reactions from N-H acid [5,10,15,20-tetrakis(pentafluorophenyl)-21-H, 23-H-porphyrin] to strong bases in acetonitrile

Deprotonation of 5,10,15,20-tetrakis(pentafluorophenyl)-21-H, 23-H-porphyrin (PhF₅PorH₂) by various bases has been studied by ¹H NMR and kinetic methods. The kinetic parameters in acetonitrile were defined for proton transfer reactions yielding [NH]⁺ protonated bases and [NHN]⁻ anions with intramolecular hydrogen-bonded chains.     

Structure refinement and chemical analysis of Cs3Li(DSO4)4, formerly ‘Cs1.5Li1.5D(SO4)2’

An accurate structure refinement of the deuterated analog of the cesium lithium acid sulfate, formerly identified as ‘Cs_1.5Li_1.5H(SO₄)₂’, has been carried out using neutron diffraction methods. Like the protonated material reported earlier (Merinov et al., Solid State Ionics 69 (1994) 53), the compound is cubic, , however, the correct stoichiometry is Cs₃Li(DSO₄)₄. There are four formula units per unit cell and six atoms in the asymmetric unit. The lattice constant measured in this work is a=11.743(2) Å, comparable to the earlier results. The structure contains one disordered hydrogen bond, formed between O(2) atoms and located on two of the edges of the single LiO₄ tetrahedron. The Li site occupancy is , as is that of the deuterium site. This level of site occupancies is consistent with a structure in which hydrogen bonds are formed only when the lithium site is unoccupied, and explains the otherwise close proximity of the Li and D atoms, 1.394(10) Å. This unusual structural feature furthermore leads to a fixed stoichiometry, as confirmed here by chemical analysis of both the deuterated and protonated materials, despite the partial occupancy of the lithium and deuterium (hydrogen) atom sites.     

磺化酚酞型聚醚砜膜的制备及其阻醇和质子导电性能

直接甲醇燃料电池 (Directmethanolfuelcell,DMFC)以高效、清洁和燃料储运方便等优点适宜于作为各种用途的可移动动力源 ,成为 2 0世纪 90年代以来研究与开发的热点[1,2 ] .目前 ,这种电池的研究难点主要集中在催化剂不稳定和质子交换膜透醇上 .一张好的DMFC膜不但要可传递质子、绝缘电子 ,还应具有良好的阻醇性能 .如果膜的阻醇性能不好 ,甲醇会穿过膜到达阴极 ,与氧直接反应而不产生电流 ,不但造成燃料的浪费 ,同时也影响阴极的正常反应 ,使电池效率下降[3 ] .目前广泛应用于燃料电池中的Nafion 系列膜是由美国DuPont公司生产的一种…     

质子化硼烷正离子体系电子结构的理论研究

本文用a b initio计算法和近似a b initio计算法(PRDDO)研究了质子化硼烷正离子体系的电子结构,给出了一些正离子体系的优化几何构型并讨论了它们的成键情况。计算的硼烷分子质子亲和势与实验值相当吻合。     

Vertical proton affinities of CH2O and CH2OH+ in their ground singlet,excited triplet and ionized doublet states

Vertical proton affinities were calculated with closed and open shell direct SCF-MO methods for the ground, excited triplet and ionized doublet states of CH₂O and CH₂OH⁺.The computed gas phase basicity of CH₂O follows the order: CH₂O(¹ A ₁) > CH₂O*(³ A ₁ or ³ A ₂) > CH₂O⁺(² B ₂ or ² B ₁).