Examination of the statistical method in the conjugated circuit theory

Summary The recently proposed statistical method for the calculation of resonance energies in the conjugated circuit theory is tested on the example of polyacenes. It is found that for the estimation of the resonance energy with a 10% average error, the method requires a sample consisting of about 20 (randomly chosen) Kekulé structures. Further increase of the sample size gives no significant gain in the accuracy of the method.

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Überprüfung der statistischen Methode in der Konjugierten-Ring-Theorie

Zusammenfassung Die unlängst vorgeschlagene statistische Methode in der Konjugierten-Ring-Theorie (conjugated circuit theory) wird am Beispiel der Polyacene getestet. Es wurde festgestellt, daß für die Abschätzung der Resonanzenergien bei einem mittleren Fehler von 10% für diese Methode ungefähr 20 (willkürlich gewählte) Kekulé-Strukturen nötig sind. Weitere Erhöhung dieser Anzahl bringt keine signifikante Verbesserung der Genauigkeit der Methode.

     

Theoretical Study on the Hetero-Diels-Alder Reactions between 3-Pyridinedithioesters and 1-Phenylsulfanylbutadiene

The mechanism, catalytic effect and solvent effect of the hetero-Diels-Alder reac- tions between 3-pyridinedithioesters and 1-phenylsulfanylbutadiene have been studied theoretically using density functional theory (DFT) at the B3LYP/6-31G(d) level. The results show that all of these reactions proceed in a concerted but asynchronous way. In some reactions the formation of C-S bond is prior to that of C-C bond and the opposite results are found in other reactions. The BF3 catalyst may lower the activation barriers by changing the energies of LUMO for 3-pyridine- dithioester. THF solvent has trivial influence on the potential energy surface of these reactions. With the BF3-catalyzed reactions, regioselectivity and stereoselectivity observed experimentally were predicted correctly by calculations and these results originate probably from C-H···F interaction in two transition states.     

Theoretical Study of the Low-Lying Excited States of Butoxy Radicals and Non-Radiative Decay Routes

The potential energy surfaces for the butoxy radical dissociation into R·＋O on the six low-lying electronic states have been determined with the combined CASSCF and MR-CI methods. The isomerization reactions between the different conformers of 1- and 2-butoxy radicals at the X and B states have been also investigated with the MP2, B3LYP, and CASSCF methods. The non-radiative decay mechanisms of butoxy radicals at the B state have been characterized with the computed potential energy surfaces and intersections. Supported by recent LIF experimental results, it was predicted that the t-butoxy radical would predissociate via the B/C intersection. As to 1- and 2-butoxy radicals, the relative energies of the transition states for the isomerization reactions between conformers at the B state are much lower than those of the B/C intersections, resulting in the predominance of the isomerization in the decay of the B state for 1- and 2-butoxy radicals.     

高效液相色谱/电化学法测定大鼠血液和脑组织中单胺类物质的含量

建立了高效液相色谱／电化学检测法测定大鼠脑组织和血液中单胺递质及其代谢产物的方法。能同时测定去甲肾上腺素（NE）、肾上腺素（E）、3，4-二羟基苯乙酸（DOPAC）、多巴胺（DA）、高香草酸（HAV）、5-羟色胺（5-HT），并能和内标3，4-二羟卞胺（DHBA）分离良好。本方法快速、简便，回收率为92％-105％，线性范围2．8-680ng／mL，检出限为0．05ng（S／N=3）。本方法已应用在服用中药的大鼠下丘脑组织及血液的测定中，数据显示，本法能满足测定要求。     

Synthesis and spectroscopic analysis of tetraphenylporphyrinatoantimony(V) complexes linked to boron-dipyrrin chromophore on axial ligands

Tetraphenylporphyrinatoantimony(V) complexes, linked to boron-dipyrrin chromophores on axial ligands, were synthesized. The fluorescence spectra of 1a, 1b and 1c (3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo(methoxo)antimony(V) tetraphenylporphyrin bromide (1a); 6-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]hexyloxo(methoxo)antimony(V) tetraphenylporphyrin bromide (1b); bis{3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo}antimony(V) tetraphenylporphyrin bromide (1c)) were analyzed under the excitations of N,N′-difluorobornyl-5-dipyrrinylphenyl (Bdpy) and tetraphenylporphyrinatoantimony(V) (Sb(TPP)) chromophores. Under the irradiation of Bdpy chromophore, the excitation energy was transferred from Bdpy chromophore to the Sb(TPP) moiety at 0.13–0.40 of the quantum yields, even in a polar solvent. On the other hand, the emission of Sb(TPP) chromophores was quenched by Bdpy chromophores at rate constants of 10⁸–10⁹ s⁻¹, independent of on the solvent polarity. Under the excitation of the Bdpy chromophore of 1d (3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo(phenyloxo)antimony(V) tetraphenylporphyrin bromide) involving both the Bdpy and the phenoxy chromophores on the axial ligands, the excited singlet state of the Sb(TPP) chromophore generated by the energy transfer from the Bdpy chromophore was quenched by the phenoxy ligand via non-radiative processes involving electron transfer. However, rapid back electron-transfer may occur because no absorption of the anion radical of Sb(TPP) was observed by nanosecond laser photolysis.     

Analysis of critical points on the potential energy surface

A simple classification scheme is proposed for critical points, based only on rankr and signatures of the (n,n)-matrixG of harmonic force constants. The determination ofr ands, e.g. by the well-known factorizationG=L ^T gL (L: triangular matrix,g: diagonal matrix), has several theoretical as well as practical (computational) advantages over the inspection of eigenvalues ofG, so far used in quantum chemistry. The eigenvalues are sufficient butnot necessary for a classification whereas rank and signature are the only necessary and sufficient prerequisites for solving the task. For the purpose of presenting a working example, by calculating only a 2×2 torque constant matrix, it is shown that the coplanar ethylbenzene is unstable in the CNDO/2 picture.     

Surface free energies of styrene-acrylic acid copolymer plates prepared in various frames

Styrene (St)-acrylic acid (AA) copolymer plates were synthesized in the frames made of glass, aluminum (Al) and poly(difluoroethylene) (PDFE). Surface properties of the prepared copolymer plates were characterized with regard to critical surface tension ( _C ), chemical components by IR analysis and surface energies (total energy, _S ; dispersion force components, _S ^d ; polar component, _S ^p ; hydrogen bonding component, _S ^h ) and the following results were obtained.The _C values of the copolymer plates increased with AA content and also depended on the sort of the used frame. The increasing order of the _C values of the copolymer plates corresponded to those of the used frames, namely, PDFE frame < Al frame < Glass frame.The prepared copolymer plates with low AA contents (ca. 10 mol%) were enriched in the AA moiety in the surface layer regardless of the kind of the used frame.The total and the individual components of the surface free energies of the copolymer plates were largely affected by the property of the used frame. The glass frame gave the plate with higher _S ^h values suggesting preferential orientation of the polar site of AA component.     

Quantitation of agmatine by liquid chromatography with laser-induced fluorescence detection

A high performance liquid chromatography (HPLC) method is described for the determination of agmatine, an endogenous neuromodulator. The method involves pre-column derivatization of the sample with a fluorescent tagging reagent, 7-fluoro-4-nitrobenzoxadiazole (NBD-F). The resulting agmatine derivative is stable and can be readily extracted into ethyl acetate at pH 8.5. The extraction enhances the quantification of low level agmatine because it eliminates chromatographic peaks caused by endogenous amino acids. The HPLC separation is carried out on a C₈ reversed phase column and completed in less than 10 min. With laser-induced fluorescence (LIF) detection, the detection limit is 5×10⁻⁹ M agmatine. Method precision (coefficient of variation) is 5% for agmatine in human plasma at the sub-μM level. This method has been validated by determination of agmatine in biological samples including human plasma and rat brain and stomach tissues.     

Determination of rimantadine in pharmaceutical preparations by capillary zone electrophoresis with indirect detection or after derivatization

Summary Rimantadine is synthetic analog of amantadine; both are antiviral agents used for prophylaxis and treatment of influenza A. A capillary zone electrophoretic (CZE) procedure for the determination of rimantadine has been developed. As the direct determination of rimantadine is poorly sensitive because the compound is almost transparent in the UV/Vis range, several indirect methods were studied. Two were found to be the particularly useful: (a) indirect detection using 5 mM 4-methylbenzylamine in 1:4 methanol-water as absorbing background electrolyte, with detection at 210 nm, and (b) derivatization of rimantadine with 1,2-naphthoquinone-4-sulfonic acid in alkaline medium and subsequent determination of the derivative by CZE (40 mM tetraborate, pH 9.2, detection at 280 nm). Uncoated capillary tubing, 44 cm length ×75 μM i.d., was used for both determinations. The detection limits were 0.1 and 2 ppm for methods a and b, respectively. The methods were used to determine rimantadine in pharmaceutical products and for dissolution testing of Flumadin^? tablets.     

Analysis of carbohydrates by anion exchange chromatography and mass spectrometry

A versatile liquid chromatographic platform has been developed for analysing underivatized carbohydrates using high performance anion exchange chromatography (HPAEC) followed by an inert PEEK splitter that splits the effluent to the integrated pulsed amperometric detector (IPAD) and to an on-line single quadrupole mass spectrometer (MS). Common eluents for HPAEC such as sodium hydroxide and sodium acetate are beneficial for the amperometric detection but not compatible with electrospray ionisation (ESI). Therefore a membrane-desalting device was installed after the splitter and prior to the ESI interface converting sodium hydroxide into water and sodium acetate into acetic acid. To enhance the sensitivity for the MS detection, 0.5 mmol/l lithium chloride was added after the membrane desalter to form lithium adducts of the carbohydrates. To compare sensitivity of IPAD and MS detection glucose, fructose, and sucrose were used as analytes. A calibration with external standards from 2.5 to 1000 pmole was performed showing a linear range over three orders of magnitude. Minimum detection limits (MDL) with IPAD were determined at 5 pmole levels for glucose to be 0.12 pmole, fructose 0.22 pmole and sucrose 0.11 pmole. With MS detection in the selected ion mode (SIM) the lithium adducts of the carbohydrates were detected obtaining MDL's for glucose of 1.49 pmole, fructose 1.19 pmole, and sucrose 0.36 pmole showing that under these conditions IPAD is 3-10 times more sensitive for those carbohydrates. The applicability of the method was demonstrated analysing carbohydrates in real world samples such as chicory inulin where polyfructans up to a molecular mass of 7000 g/mol were detected as quadrupoly charged lithium adducts. Furthermore mono-, di-, tri-, and oligosaccharides were detected in chicory coffee, honey and beer samples.