d9配合物MOSE曲面和几何构型的研究

d~9电子构型的金属离子所形成的配合物几何构型一般为拉长八面体或平面正方形,晶体场理论和角重叠模型都对此作出了较满意的描述,但就该电子构型的中心离子与指定配体配位时易形成配合物的配位数、配体所处的位置等问题,至今尚无满意解释.本文通过分子轨道稳定化能(MOSE)的计算及其曲面的绘制,形象地解释了上述问题.     

The absolute sign of J coupling constants determined using the order matrix calculation

A novel methodology using the order matrix calculation to determine the absolute sign of spin-spin couplings based on the structure of organic compounds is presented. The sign of the residual dipolar coupling (RDC) depends on the sign of corresponding scalar spin-spin coupling constant and the sign of the RDC has a dramatic influence on the order matrix calculation. Therefore, the sign of the spin-spin coupling constant can be obtained by an order matrix calculation through the corresponding RDC. Six types of spin-spin coupling constants, including 2J(H,H), 1J(C,F), 2J(C,F), 3J(C,F), 2J(F,H) and 3J(F,H), were obtained simultaneously. Except for 3J(C,F) where the measured RDCs have very small magnitudes, the signs were determined unambiguously.     

Partial-filling affinity capillary electrophoresis

Partial-filling affinity capillary electrophoresis (PFACE) is used to examine the binding interactions between two model biological systems: D-Ala-D-Ala terminus peptides to the glycopeptide antibiotic vancomycin (Van) from Streptomyces orientalis, and arylsulfonamides to carbonic anhydrase B (CAB, EC 4.2.1.1, bovine erythrocytes). Using these two systems, modifications in the PFACE technique are demonstrated including flow-through PFACE (FTPFACE), competitive flow-through PFACE (CFTPFACE), on-column ligand synthesis PFACE (OCLSPFACE), and multiple-step ligand injection PFACE (MSLIPFACE). In PFACE small plugs of sample are injected into the capillary column and an equilibrium is established between receptor and ligand during electrophoresis. Binding constants are then obtained by Scatchard analysis using changes in the migration time of the receptor/ligand on changing the concentration of the ligand/receptor. Data demonstrating the quantitative potential of these methods are presented. This review focuses on the unique capabilities of the different PFACE techniques as applied to two model biological systems.     

Equilibrium and spectral studies of putrescine complexes with copper(II)

Summary It has been found that in the putrescine-copper system several types of complex compounds (MHL,ML,ML ₂,ML ₂OH) are formed. In thepH range of 7–9, despite a multiple excess of ligand, a precipitation occurs. When adenosine is introduced to the system, the ability to observe the complexation reaction in solution is largely increased, because the additional ligand prevents precipitation. On the basis of computer analysis of potentiometric titration data the stability constants of the compounds have been determined. The coordination mode of the complexes is discussed.

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Gleichgewichte und spektroskopische Untersuchungen an Putrescin-Komplexen mit Kupfer(II)

Zusammenfassung Es wurde festgestellt, daß sich im Putrescin-Kupfer System einige Typen von Komplexen bilden (MHL,ML,ML ₂ andML ₂OH). ImpH-Bereich von 7–9 tritt trotz eines mehrfachen Ligandenüberschusses ein Niederschlag auf. Bei Einführung von Adenosin in das System wird die Beobachtbarkeit der Komplexreaktion verbessert, da der zusätzliche Ligand die Niederschlagsbildung verhindert. Mittels Computeranalyse der potentiometrischen Titrationsdaten wurden die Stabilitätskonstanten der Verbindungen ermittelt. Die Art der Komplexierung wird ebenfalls diskutiert.

     

Determination of pKa values of some hydroxylated benzoic acids in methanol-water binary mixtures by LC methodology and potentiometry

An accurate estimation of pK_a values in methanol-water binary mixtures is very important for several separation techniques such as liquid chromatography and capillary electrophoresis that use these solvent mixtures. In this study, the pK_a values of 11 polyphenolic acids have been determined in methanol-water binary mixtures (10%, 20% and 30% (v/v)) by potentiometry, liquid chromatography (LC) and LC-DAD methodology.The results show a similar trend for the pK_a values of all the studied compounds, as they increase with increasing concentration of organic modifier, which allows a linear relationship between pK_a values and mole fraction of methanol to be obtained. The pK_a values obtained in aqueous medium have been compared with those given in the literature, and also with the values predicted by the SPARC on-line pK_a calculator. The data obtained have been used to test the feasibility of an estimation of dissociation constants in a methanol-water medium from the relationship between pK_a values and the organic cosolvent fraction in the mixtures.     

Retention of ionizable compounds on HPLC. Modelling retention for neutral and ionizable compounds by linear solvation energy relationships

Summary A global LSER model that relates HPLC retention to mobile phase composition and pH is tested for a varied group of solutes, both neutral and ionizable, in a polymeric column and methanol-water mobile phases. It is compared to the local LSER model developed only for a given mobile phase, i.e., a fixed organic modifier content, and to the global LSER model set only for neutral solutes. The global LSER model for neutral and ionizable solutes requires a few supplementary parameters over the other models tested, but it accounts for retention under any experimental conditions for a given column and methanol-water mobile phases, describing properly the interactions established in the HPLC system (hydrophobicity, hydrogen-bond acidity and basicity, dipolarity/polarizability…). This paper is number 13 of a series with the same general title: “Retention of Ionizable Compounds on HPLC” published in various journals.     

Binary and Ternary Complexes Between Lauryl Hexaoxyethylene, Benzoate and Cyclodextrin. Part II. β-CD

The characterization of binary and ternary complexes of benzoate, lauryl hexaoxyethylene (C₁₂E₆) and -CD is presented. The complexation equilibrium was characterized by UV-Vis spectrophotometry, titration microcalorimetry, capillary electrophoresis, and 2D ROESY ¹H-NMR. Results suggested that -CD forms one complex with C₁₂E₆in the stoichiometric ratio of -CD : C₁₂E₆1.5 : 1, with a stability constant 1.3 × 10⁵ M^-1.5. The 2-D ROESY ¹H-NMR spectrum indicated that C₁₂E₆is included inside the -CD cavity. The primary binding site of C₁₂E₆ is on the lauryl subunit of this molecule. Analogous to a previously reported study of -CD, the combination of -CD and C₁₂E₆precipitated from the solution. Addition of benzoate seemed to dissolve the precipitate and nearly doubled the apparent stability constant of the complex. Results from the various techniques supported formation of ternary complexes between -CD, C₁₂E₆, and benzoate.     

Electrical Conductance Studies in Aqueous Solutions of Glutaric Acid,Disodium Glutarate and Sodium Hydrogen Glutarate

Conductivity measurements of glutaric acid and disodium glutarate in dilute aqueous solutions were performed in the 288.15 to 323.15 K temperature range. The limiting equivalent conductances of glutarate anions, λ ^o(HGlut⁻,T) and λ ^o(1/2Glut²⁻,T), and the dissociation constants of glutaric acid, K ₁(T) and K ₂(T), were derived by the use of the Onsager and the Quint and Viallard conductivity equations. The applied molecular model was successfully confirmed by analyzing the conductivities of sodium hydrogen glutarate at 298.15 K.     

Synthesis and supramolecular properties of molecular clips with anthracene sidewalls

Novel molecular clips with anthracene sidewalls (1 a-c) were synthesized; they form stable host-guest complexes with a variety of electron-deficient aromatic and quinoid molecules. According to single-crystal structure analyses of clip 1 c and 1,2,4,5-tetracyanobenzene (TCNB) complex 14@1 b, the clips' anthracene sidewalls have to be compressed substantially during the complex formation to provide attractive pi-pi interactions between the aromatic guest molecule and the two anthracene sidewalls in the complex. The compression and expansion of aromatic sidewalls are calculated by molecular mechanics to be low-energy processes, so the energy required for compression of the anthracene sidewalls during complex formation is apparently overcompensated by the gain in energy resulting from the attractive pi-pi interactions. The finding that complexes of the clips 1 a-c are more stable than those of the corresponding clips 2 a-c can be explained in terms of the larger van der Waals contact surfaces of the anthracene sidewalls in 1 a-c (relative to the naphthalene sidewalls in 2 a-c). Color changes resulting from charge-transfer (CT) bands are observed in complex formation by 1 a-c: from colorless to red or purple with TCNB (14), and from yellow to green with 2,4,7-trinitro-9-fluorenone TNF (17). Independently, the host 1 b and guest 14 fluoresce from their respective excited singlet states, whilst in the complex 14@1 b the charge-transfer state quenches the higher-energy singlet states of the two components, and as a result luminescence is only observed from this new CT state. To the best of our knowledge, complex 14@1 b is the first example of CT luminescence from a host-guest complex. The binding constant determined for the formation of the TCNB complex 14@1 b from a UV/Vis titration experiment (Ka = 12 400 m(-1)) agrees well with the value (K(a) = 12 800 m(-1)) obtained by 1H NMR titration.     

Molecular recognition of biotin, barbital and tolbutamide with new synthetic receptors

We have measured, by means of NMR titrations, the binding constants for the complexes between hosts N,N′-bis(6-methylpyridin-2-yl)-1,3-benzenedicarboxamide (7) and 4-chloro-N,N′-bis(6-methylpyridin-2-yl)-2,6-pyridinedicarboxamide (8, hydrated) with biotin methyl ester (1), N,N′-dimethylurea (2), 2-imidazolidone (3), N,N′-trimethylenurea (4), barbital (5) and tolbutamide (6) as guests. Molecular Mechanics calculations (Monte Carlo Conformational Search, AMBER and OPLS force fields, MacroModel v.8.1) on the complexes formed between the foregoing guests and hosts 7 and 8, comparatively with 4-oxo-N,N′-bis(6-methylpyridin-2-yl)-1,4-dihydro-2,6-pyridinedicarboxamide (9a) have been carried out in order to determine the correlation between experimental and theoretical results and to understand the behaviour of the designed new hosts. Finally we have performed single point DFT [B3LYP/6-31G(d,p)] calculations on the optimised Molecular Mechanics geometries for the complexes between hosts 7-9 and water.