Artificial neural networks for quantification in unresolved capillary electrophoresis peaks

The application of the combination of experimental design (ED) and artificial neural networks (ANNs) for the quantification of overlapped peaks in capillary zone electrophoresis is described. When the total separation cannot be achieved by separation techniques, the use of ED-ANN can be a suitable approach. The unstability of EOF causes peak shift that has to be corrected in order to apply ED-ANN methods. In this work, normalization procedure of electropherograms with consequent application of ANNs for quantification purpose was developed. Both, spectra and electropherograms can be used as multivariate data. In general, both kinds of data were found to be suitable for unresolved peaks quantification by ED-ANN approach.     

Chelating Behaviour of Substituted 1-Benzoyl-4-Phenylthiosemicarbazide

The preparation and characterization of a series of new coordination compounds of Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) containing o-methyl- or o-chlorobenzoyl-4-phenyl-3-thiosemicarbazide (HMBPT, HCBPT=HL) are reported. The reaction products were investigated by analyses, electrolytic conductance, magnetic susceptibility, reflectance and IR spectral studies. The IR spectra show that HMBPT and HCBPT coordinate with the metal ions via different coordination sites (NS and/or NO). The spectral data support the suggestion that the ligands form his-chelates with Ni(II) and Cu(II) of square planar stereochemistry and of general formulae ML₂·H₂O, where L is the uninegatively charged bidentate ligand. The Co(II) ion forms octahedral and tetrahedral structures with HMBPT and HCBPT, respectively. The ligand field parameters (D₄, B and β) for the Co(II) chelates were calculated using the averaged-ligand-field approximation. The influence of the benzene ring substituents (o-chloro or o-methyl) on the stereochemistry are discussed. Also, the formation of the complexes in solution was tested by the pH-metric method.     

四核钴羰基簇合物Co4(CO)8(μ-CO)2(μ4-PSR)2的合成和晶体结构

The title compounds Co4(CO)8(μ-CO)2 (μ4-PSR) [R=-CH3, -C2H5, -C(CH3)3,-(CHa)4CH3] were synthesized by the reaction of Co2(CO)8 with RSPCl2. They were characterized by IR, 1HNMR, elemental analysis. The crystal and molecular structure of Co4(Co)8(μ-CO)2 (μ4-PSC2H5) has been determined by single crystal diffraction method. Crystal data: monoclinic, space group P21 /c, with a=8-445(3), 6=8.562(3), c= 17.125(6)Å, β=104.26 (3)' 9 V=1200.1Å3, Z=2, Dc=1.937gcm-3. Its molecular structure contains an octahedral Co4P2 skeleton which consists of a rectangular four cobalt atoms core and the Co4 core is capped above and below by two quadruply bridging PSR ligands.     

A genetic algorithm for structure-based de novo design

Genetic algorithms have properties which make them attractive in de novo drug design. Like other de novo design programs, genetic algorithms require a method to reduce the enormous search space of possible compounds. Most often this is done using information from known ligands. We have developed the ADAPT program, a genetic algorithm which uses molecular interactions evaluated with docking calculations as a fitness function to reduce the search space. ADAPT does not require information about known ligands. The program takes an initial set of compounds and iteratively builds new compounds based on the fitness scores of the previous set of compounds. We describe the particulars of the ADAPT algorithm and its application to three well-studied target systems. We also show that the strategies of enhanced local sampling and re-introducing diversity to the compound population during the design cycle provide better results than conventional genetic algorithm protocols.     

Flow injection system for hydrolysable tannin determination

A flow injection system was proposed to evaluate the transient product of a colorimetric reaction between hydrolysable tannin and potassium iodate (KIO₃) solution. The system optimization was accomplished by using statistical methods based on experimental design. Flow rate of KIO₃ solution, sample volume, carrier flow rate, and reaction coil were the selected factors for evaluation. On screening step, complete factorial 2⁴ was used and two levels for each selected factor were studied. For the optimization phase, a centered face composite design 2² + star was employed to evaluate sample volume and flow rate of KIO₃ solution, which were the factors identified in the screening phase as having more influence on the absorbance signal. After optimization, the proposed system was compared with batch determination. Some characteristics, such as analytical frequency, reagent consumption and chemical residues generation presented better results by the use of the proposed system if compared with batch method. The system presented good repeatability with standard deviation lower than 3%, for n = 10, linearity (R² = 0.9974) for tannic acid standard, analytical frequency of 15 injections h^− 1 and limit of quantification of 24 mg L^− 1 of tannic acid. Good results were obtained when the proposed system was applied to hydrolysable tannin determination in Stryphnodendron barbatimão, Eucalyptus citriodora and Phyllanthus niruri, samples of plants commonly used in popular medicine.     

Copolymerization of butadiene and styrene with a gadolinium tricarboxylate catalyst

Homo- and copolymerizations of butadiene (BD) and styrene (St) were carried out by gadolinium catalysts having various tricarboxylate ligands [Gd(OCOR)₃: R = CH₃, CH₂Cl, CHCl₂, CCl₃, and CF₃], to investigate the effects of ligands and discuss the cis polymerization mechanism. Polymerization of BD with Gd(OCOR)₃—(i—Bu)₃Al—Et₂AlCl catalysts was carried out in hexane at 50°C. By each catalyst, poly(BD) having a high cis content (cis = 97–99%) in 22–85% yields for 2–24 h were obtained. The ligands with low pKa values increased the polymerization activity as follows: R of Gd(OCOR)₃: CF₃ > CCl₃ > CHCl₂ > CH₂Cl ～ CH₃. On the other hand, in the polymerization of St or copolymerization of BD and St under similar conditions, the highest activity was attained by a Gd(OCOCCI₃)₃- based catalyst. The difference in the optimum ligand among the homo- and copolymerization of BD and St was discussed on the basis of energy levels of the catalysts. In the copolymers of BD and St, the cis-1,4 content of the BD unit decreased with increasing St content. Furthermore, according to the diad analysis of copolymers (St content ～ 14.5 mol %) by ¹³C NMR spectroscopy, the low cis value of the BD unit was observed in the St-BD diad (cis/trans/vinyl = 24/53/23), while the high cis value of the BD unit remained in the BD-BD diad (cis/trans/vinyl = 89/10/1). These results suggest that the terminal BD unit is controlled by the cis configuration by the coordination between the penultimate cis vinylene unit and the gadolinium metal catalyst, whereas the presence of the penultimate St unit interferes with cis polymerization of the terminal BD unit. The difference in the coordination mechanism in the course of polymerization between rare earth metal and transition metal catalysts such as the Ni(acac)₂ and Co(acac)₃-based catalyst was also discussed. © 1995 John Wiley & Sons, Inc.     

Synthesis and Characterization of Fluoro- and Chloro- bimetallic Alkoxides as Precursors for Luminescent Metal Oxide Materials via Sol-Gel Technique

Heterobimetallic alkoxides are broadly recognized as versatile precursors for luminescence materials, and efforts are being made to develop novel routes by applying the concept of geometrical molecular design, for their synthesis and to design a single source precursor suited to photoluminescent materials. Novel and new series of bimetallic alkoxides has been prepared by metathesis route. They exhibit a lower sensitivity towards hydrolysis and so they are easier to handle as compared to other alkoxides. All the compounds were characterized by elemental analysis, FT-IR and multinuclear NMR spectroscopies. FT-IR revealed that the molecular structure of these metal alkoxides was retained to a large extent in 4 ： 1 halogenated alcohol-benzene solution. The heteronuclear NMR spectroscopy provided useful information about chemical shifts for better understanding the likely structure based on interactions with their coordinate metals. The mass spectra show similar types of fragmentation pattern. SEM-EDS analyses showed consistency with the formulation. XRD patterns show an enhanced homogeneity at high temperature. TGA measurements show that thermal decomposition occured in steps that depended entirely on the chemical compositions and the synthesis routes. SEM observation reveals that the morphology and particle size strongly depend on synthesis routes for their precursors.     

Calculating the knowledge-based similarity of functional groups using crystallographic data

A knowledge-based method for calculating the similarity of functional groups is described and validated. The method is based on experimental information derived from small molecule crystal structures. These data are used in the form of scatterplots that show the likelihood of a non-bonded interaction being formed between functional group A (the `central group') and functional group B (the `contact group' or `probe'). The scatterplots are converted into three-dimensional maps that show the propensity of the probe at different positions around the central group. Here we describe how to calculate the similarity of a pair of central groups based on these maps. The similarity method is validated using bioisosteric functional group pairs identified in the Bioster database and Relibase. The Bioster database is a critical compilation of thousands of bioisosteric molecule pairs, including drugs, enzyme inhibitors and agrochemicals. Relibase is an object-oriented database containing structural data about protein-ligand interactions. The distributions of the similarities of the bioisosteric functional group pairs are compared with similarities for all the possible pairs in IsoStar, and are found to be significantly different. Enrichment factors are also calculated showing the similarity method is statistically significantly better than random in predicting bioisosteric functional group pairs.     

Synthesis and structural characterization of ferrocene-based bis(pyrazol-1-yl)borate ligands: FcB(Me)pz2K, Fc2Bpz2K, and 1,1′-fc[B(Me)pz2]2K2 (Fc: ferrocenyl, fc: ferrocenylene, pz: pyrazolyl)

Reaction of the ferrocenyl(dimethylamino)boranes FcB(Me)NMe₂, Fc₂BNMe₂, and 1,1′-fc[B(Me)NMe₂]₂ with 1:1 mixtures of pyrazole and potassium pyrazolide in refluxing THF gave the potassium salts of the ferrocene-based bis(pyrazol-1-yl)borate ligands FcB(Me)pz₂K, Fc₂Bpz₂K, and 1,1′-fc[B(Me)pz₂]₂K₂ in good yield (Fc: ferrocenyl, fc: ferrocenylene, pz: pyrazolyl). In the solid state, FcB(Me)pz₂K and Fc₂Bpz₂K form centrosymmetric dimers with short K?Cp contacts suggesting an η⁵ coordination mode of the potassium ion. The crystal lattice of the ditopic ligand 1,1′-fc[B(Me)pz₂]₂K₂ consists of coordination polymer strands featuring essentially the same structural motif that has been observed for the monotopic derivatives. All three scorpionate ligands are thus promising building blocks for the preparation of ferrocene-containing multiple-decker sandwich complexes.     

Surface diffusion in reversed-phase liquid chromatography using silica gels bonded with C1 and C18 ligands of different densities

Surface diffusion in reversed-phase liquid chromatography (RPLC) using silica gels bonded with C₁ and C₁₈ alkyl ligands of different densities was studied from the viewpoints of two extrathermodynamic relationships, i.e., enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). First, according to the four methods proposed by Krug et al., the values of surface diffusion coefficient (D_s) were analyzed to confirm that an actual EEC resulting from substantial physico-chemical effects takes place for surface diffusion. Then, it was also demonstrated that a LFER is observed between surface diffusion and the retention equilibrium. The establishment of EEC and LFER suggests a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length and the densities of C₁ and C₁₈ ligands. Finally, a thermodynamic model for the LFER based on the real EEC was used to estimate D_s values under various RPLC conditions. The D_s values can be estimated with a mean square deviation of about 25–30%. The agreement between the D_s values estimated and those experimentally measured suggests that the total mass flux by surface diffusion consists of the two contributions due to C₁ and C₁₈ ligands and that the contribution of each ligand is proportional to the ligand density.