Ligand-exchange chromatography of racemates, 9. Ligand-exchange chromatography of amino acid enantiomers on asymmetric sorbents with polydentate sulfur containing groupings

The paper describes the syntheses of four asymmetric sorbents, which contain S-(2-aminoethyl)-L -cysteine ( 1a ), S-(carboxymethyl)-L -cysteine ( 1c ), S,S′-(ethylene)-bis(L -cysteine) ( 2a ), and N,N′-(ethylene)-bis(D-methionine) ( 3a ) groupings as the chiral fixed ligands in a cross-linked polystyrene matrix. The sorbents were used for ligand-exchange chromatography of amino acid enantiomers in the presence of Cu(II) and Ni(II) ions. Enantioselective effects in the formation of mixed-ligand complexes consisting of a fixed ligand, a metal ion, and an amino acid enantiomer were determined. The highest values of enantioselectivity reaching 1 300 to 1 890J/mol were found in mixed-ligand complexes containing histidine or β-phenyl-α-alanine.     

High resolution of oligosaccharide mixtures by ultrahigh voltage micellar electrokinetic capillary chromatography

Oligosaccharide mixtures released from ribonuclease B and human IgG have been separated using micellar electrokinetic capillary chromatography operated at 100 kV. The resolution of these closely related analytes at this high voltage was found to be superior to that obtained at 20 kV, a voltage which is ordinarily used in most capillary electrophoresis separations.     

Improved method for simultaneous determination of L-arginine and its mono- and dimethylated metabolites in biological samples by high-performance liquid chromatography

An improved method has been developed for the determination of L-arginine and its methylated metabolites, N(G)-monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (asymmetric DMA, ADMA) and N(G),N(G)'-dimethyl-L-arginine (symmetric DMA, SDMA) in biological samples. Extraction of these compounds with a strong cation-exchange resin AG50W-X8 with L-homoarginine (2-amino-6-guanidinohexanoic acid) as an internal standard gave a recovery of more than 70% except for SDMA from plasma samples. After extracted samples were converted to fluorescent derivatives with o-phthalaldehyde (OPA) in an alkaline medium, the following high-performance liquid chromatographic separation with a ODS column (wide-pore size, 300 A) was successfully performed with an isocratic mobile phase system. The method permits quantitative determination of L-arginine and its methylated metabolites at concentrations as low as 4 microM and 0.18 microM, respectively. Using this method, the levels of L-arginine, L-NMMA, ADMA and SDMA in human plasma, urine and rat tissue were determined.     

Enzyme-analogue built polymers, 4. On the synthesis of polymers containing chiral cavities and their use for the resolution of racemates

With the aid of a chiral template molecule functional groups could be placed in a highly crosslinked polymer in such a way that they are present in a chiral cavity in a given stereochemistry. By this method methyl, resp. 4-nitrophenyl α-D -mannopyranoside-2,3; 4,6-di-O-(4-vinylphenylboronate) ( 1a , resp. 1b ) were copolymerized to macroporous polymers from which the templates methyl, resp. 4-nitrophenyl α-D -mannopyranoside ( 2a , resp. 2b ) could be split off in return. It could be shown that such polymers with two boronic acid groupings within the chiral cavity possess a good ability for the resolution of racemates of the template used. In the case of the separation of the enantiomers of 2b separation factors up to 2,27 could be obtained. The overall optical enrichment in a chromatographic separation amounted to 87%.     

Thermal and mesogenic properties of semirigid polyamides based on mono- or trimethylsubstituted 1,3-diaminobenzenes

Thermal and mesogenic properties of semirigid polyamides composed of one benzene ring with a kinked linkage and various aliphatic chains in the repeating unit, which are derived from three 1,3-diaminobenzenes and aliphatic dicarboxylic acids, were examined. Only two polyamides with a long aliphatic chain (C₁₈H₃₆), based on 4-methyl- and 2,4,6-trimethyl-1,3-diaminobenzenes, form mesophases although the polymers exert nontraditional mesogenic units. Formation of the mesophase in the latter case depends on the inherent viscosity, i.e., polymers with lower inherent viscosity (?1,47 dL/g) form a layered structure by intermolecular interaction via hydrogen bonding of the amide linkage.     

Novel one-pot polymer syntheses based on dithiols obtained from a five-membered cyclic dithiocarbonate and diamines

Novel one-pot syntheses of sulfur-containing polymers from a five-membered cyclic dithiocarbonate (5-phenoxymethyl-1,3-oxathiolane-2-thione ( 1 )) and diamines were examined. Polydisulfides with M̄_n 5400 ∼ 15800 were obtained in the oxidation polymerization of dithiols 2 , which were obtained in situ by the reactions of 1 and diamines. When 1,12-dodecanediamine was employed, a polydisulfide with relatively high M̄_n was obtained, while in the case of m-xylylenediamine, the polymerization was accompanied by intermolecular cyclization to give a polydisulfide with low M̄_n. Polythiourethanes with M̄_n 6500 ∼ 17200 were obtained in the polyaddition of 2 with 4,4′-methylenebis(phenyl isocyanate). The yields and M̄_n values increase with increasing methylene chain length of 2 . Polythioethers with M̄_n 2600 ∼ 19900 were obtained by the polycondensations of 2 with α,α′-dibromo-p-xylene. The glass transition temperature (T_g) of the polymer decreases with increasing methylene chain length in the main chain.     

Separation of some mono-, di- and tri-unsaturated fatty acids containing 18 carbon atoms by high-performance liquid chromatography and photodiode array detection

Positional and geometric isomers of mono-, di- and tri-unsaturated fatty acids containing 18 carbon atoms were separated on commercially available reversed-phase columns in gradient systems composed of acetonitrile and water, utilizing photodiode array detection. The biological samples were hydrolyzed with 2 M NaOH for 35-40 min at 85-90 degrees C. After cooling, the hydrolysates were acidified with 4 M HCl and the free fatty acids were extracted with dichloromethane. The organic solvent was removed in a gentle stream of argon. The fatty acids were determined after pre-column derivatization with dibromacetophenone in the presence of triethylamine. The reaction components were mixed and reacted for 2 h at 50 degrees C. Separations of derivatized fatty acids were performed on two C18 columns (Nova Pak C18, 4 microm, 250x4.6 mm, Waters) by binary or ternate gradient programs and UV detection at 254 and 235 nm. The geometric and positional isomers of some unsaturated fatty acids were substantially retained on the C18 columns and were distinct from some saturated fatty acids, endogenous substances in biological samples or background interference. Only slight separation of critical pairs of cis-9 C18:1/cis-11 C18:1 and cis-6 C18:1/trans-11 C18:1 was obtained. A ternate gradient program can be used for complete fractionation of a mixture of conjugated linoleic acid isomers (CLA) from cis-9, cis-12 and trans-9, trans-12 isomers of C18:2. The CLA isomers in the effluent were monitored at 235 nm. The CLA isomers were differentiated from saturated and unsaturated fatty acids using a photodiode array detector. The utility of the method was demonstrated by evaluating the fatty acid composition of duodenal digesta, rapeseed and maize oils.     

Crystallization during polymerization of L-alanine N-carboxy anhydride initiated by diamines

Polymerization of L-alanine N-carboxy anhydride (4-methyl-2,5-dioxo-1-oxa-3-azacyclopentane) was carried out in acetonitrile using hexamethylene diamine (HM), ethylene diamine (ED) and bis(4-aminophenyl) ether (AP) as initiators, in order to investigate the effect of diamines on the crystallization mechanism during polymerization in comparison with that for butylamine already reported. The resultant polymers obtained here had wider molecular weight distributions than those obtained with butylamine, indicating the occlusion of some active growing chain ends into the precipitate during polymerization. The relative width of the molecular weight distribution of the polymers formed in the later stages of the polymerization was larger in the following order as compared among the initiators: HM<ED<AP. The oligomer chains formed in the beginning of the polymerization crystallized into the antiparallel β-structure and thereafter the β-helical chains grew from the active sites of the β-chains. However, it is likely that, in the later stages of the polymerization, the α-helical chains grew from one of the amino groups of a diamine molecule but most of the other amino groups were inactive, since the ends of the β-chains were occluded into the precipitate due to the antiparallel nature of the β-chains precipitated. The morphologies of the resultant polymer crystals were in good agreement with the results obtained from the intrinsic viscosities (molecular weights), conformations, and structures.     

Synthesis of high-molecular-weight polysuccinamides by polycondensation of active succinates with diamines

High-molecular-weight, film- and fiber-forming polysuccinamides were synthesized by polycondensation of active diesters of succinic acid with hexamethylenediamine or dodecamethylenediamine under mild conditions. By kinetic investigations it was established that the formation of high-molecular-weight polysuccinamides is connected with a low rate of chain-terminating formation of a cyclic imide and its nearly complete suppression by chain-growth aminolysis reaction.     

New copolyamides based on adipic acid,aliphatic diamines and amino acids: Synthesis,characterization and biodegradability, 5

Novel series of biodegradable copolyamides were synthesized via melt copolymerization. The statistical copolymides were produced by reaction of the salt of adipic acid (AA) and bis(para-aminocyclohexyl)methane (PACM) or isophoronediamine (IPD)/α-amino acids at 250°C. Elemental analyses, density, viscosity, differential thermal analysis (DTA) and gelpermeation chromatography (GPC) measurements and FT-IR spectroscopy were employed for the characterization of these copolyamides. The semicrystalline (AA/PACM/α-amino acids) or amorphous (AA/IPD/α-amino acids) nature of these copolyamides was shown with DTA and wide angle X-ray diffraction patterns. Several methods were used in order to investigate and assess their biodegradability such as alkaline hydrolysis (10% w/v NaOH, 80°C), burial in soil (microbial and bacterial attack) and enzymatic hydrolysis (α-trypsin and α-chymotrypsin). The degradation of the copolyamides was evaluated with the aid of GPC and DTA measurements and correlated to the α-amino acid content. These copolyamides could eventually find applications in the field of food packaging and agriculture (disposable plastics) and medicine (sutures).     

基于高精度断层图片数据集的大鼠动脉血管重建

目的基于微米级大鼠断层图片数据集,建立高精度的大鼠动脉血管的三维模型,为各种监测鼠血管组织形态变化的试验提供客观依据。方法采用一套高分辨率大鼠断层切片图像数据集,使用半自动交互方法对动脉血管进行分割,使用改进的移动立方体(marching cube,MC)算法,在一台IBM图形工作站上对80 GByte大小的血管图片数据集进行重建。结果建立了完整的高精度大鼠动脉血管的三维表面模型,能显示出0.4mm大小的微细血管。结论该大鼠动脉血管三维模型可以为观测试验鼠血管组织形态变化提供一个立体的空间比较标准。     

Synthesis of polyureas by polycondensation of diamines with active derivatives of carbonic acid

New polycondensation reactions of active diphenyl carbonates and diphenyl carbamate with diamines were developed for the synthesis of high-molecular-weight polyureas. The kinetics and mechanism of carbonic acid active esters aminolysis model reactions were studied. Possible side reactions including nucleophilic substitution reaction were investigated as well. It is shown that novel methods advantageously distinguish from traditional methods of polyureas synthesis by low tendency to side reactions and facilitate the synthesis of linear polyureas and copolyureas. It is found that N,N′-bis(trimethylsilylated) diamines and salts of diamines as monomers can be successfully used in these reactions. Bioanalogous polymers promising for biomedical application — polyureas based on L -lysine — were synthesized using novel polycondensation reactions.     

Micromechanics of bone tissue-engineering scaffolds,based on resolution error-cleared computer tomography

Synchrotron radiation micro-computed tomography (SRμCT) revealed the microstructure of a CEL2 glass–ceramic scaffold with macropores of several hundred microns characteristic length, in terms of the voxel-by-voxel 3D distribution of the attenuation coefficients throughout the scanned space. The probability density function of all attenuation coefficients related to the macroporous space inside the scaffold gives access to the tomograph-specific machine error included in the SRμCT measurements (also referred to as instrumental resolution function). After Lorentz function-based clearing of the measured CT data from the systematic resolution error, the voxel-specific attenuation information of the voxels representing the solid skeleton is translated into the composition of the material inside one voxel, in terms of the nanoporosity embedded in a dense CEL2 glass–ceramic matrix. Based on voxel-invariant elastic properties of dense CEL2 glass–ceramic, continuum micromechanics allows for translation of the voxel-specific nanoporosity into voxel-specific elastic properties. They serve as input for Finite Element analyses of the scaffold structure. Young's modulus of a specific CT-scanned macroporous scaffold sample, predicted from a Finite Element simulation of a uniaxial compression test, agrees well with the experimental value obtained from an ultrasonic test on the same sample. This highlights the satisfactory predictive capabilities of the presented approach.     

Spike sorting based on multi-class support vector machine with superposition resolution

A new spike sorting method based on the support vector machine (SVM) is proposed to resolve the superposition problem. The spike superposition is generally resolved by the template matching. Previous template matching methods separate the spikes through linear classifiers. The classification performance is severely influenced by the background noise included in spike trains. The nonlinear classifiers with high generation ability are required to deal with the task. A multi-class SVM classifier is therefore applied to separate the spikes, which contains several binary SVM classifiers. Every binary SVM classifier corresponding to one spike class is used to identify the single and superposition spikes. The superposition spikes are decomposed through template extraction. The experimental results on the simulated and real data demonstrate the utility of the proposed method.     

Cytostatic effect of DL-α-difluoromethylornithine against Plasmodium falciparum and its reversal by diamines and spermidine

DL--difluoromethylornithine (DFMO) inhibited ornithine decarboxylase (ODC) activity and arrested the growth of Plasmodium falciparum at the early trophozoite stage. The inhibition of ODC activity did not result in the formation of an alternative diamine such as cadaverine. When putrescine or spermidine were added to the parasites grown in culture, the arrest was reversed, and normal schizogony was completed even in the presence of DFMO. Some reversal of the inhibition was achieved with cadaverine at high concentrations, while 1,3-diaminopropane and spermine failed to restore the development. Resumption of growth could be detected when putrescine was added even after 67 h of DFMO treatment. Electron microscopy did not reveal any changes in the morphology of parasites treated for 47 h, while 73 h of treatment with DFMO induced massive accumulation of pigment. Death was observed a few hours later. These results suggest that DFMO acts as a cytostatic rather than as a cytocidal agent. The four carbon diamine restored cell growth while the shorter or the longer homologous compounds showed little activity.     

The synthesis of polymers from phenylphosphonic diisocyanate and diamines

Phenylphosphonic diisocyanate has been prepared and polymers from its condensation with diamines using the interfacial technique are reported. The polymers are believed to contain the following repeating structure:      

Cyclotrimerization reactivities of mono- and difunctional cyanates

The influence of substituents of several mono- and difunctional cyanates on their cyclotrimerization behaviour has been studied by several methods. Shifts of gel point and gel fractions at full conversion in dependence on the substituent were detected for coreactions of a dicyanate with monofunctional cyanates. Critical fractions of monocyanate groups in the range of 50 mol-% for the absence of gelation were measured and could be described quantitatively by a model that is based on reaction kinetics and network statistics. Reactivity differences in dependence on substituents are also reflected in the distribution of homo- and mixed trimers at full conversion of paris of different monofunctional cyanates as measured by high-performance liquid chromatography (HPLC). This distribution follows a simple binomial scheme for cyanates with equal reactivity, whereas remarkable deviations occur, if one of the monomers reacts faster than the other. Besides, a qualitative reactivity gradation of the used cyanates was found on the basis of differential scanning calorimetry (DSC) peak temperatures, where the reaction of each cyanate was catalyzed by the same amount of a certain phenol. Finally, the shift of the OH band of several phenols caused by association with cyanate groups, measured by FTIR, was related to the data obtained from gelation, trimer distribution and DSC experiments to establish an easy and reproducible method for comparing the reactivity of cyanate monomers.     

基于焦区积分的高分辨率光声变焦显微成像

光声显微成像兼具高光学组织对比度,以及超声的高穿透深度和高空间分辨率的优点。但一方面在光声显微成像中,组织深层目标易被浅表目标屏蔽,另一方面其横向分辨率与焦深的矛盾一直限制了光声显微的成像质量。针对这两个问题,本实验搭建了一套基于超声分辨的光声显微成像系统。其采用一种非共轴的照明-探测方式来减少浅层组织对深层信息的影响,并且采用一种新的焦区积分算法来进行数据的处理,结合多次纵向变焦扫描来实现深层组织的高分辨探测。仿体实验表明,该方法可以在不同纵向深度上保持约0.6 mm的横向分辨率,与理论值相接近。裸鼠肿瘤成像结果表明,本文所提出的方法可以比普通的背向探测声聚焦光声显微成像方法在深度方向上获取更多的信息。随着超快脉冲激光和高速扫描方式的发展,本文所提出的方法有望在脑部血管成像、宫颈癌内窥成像、浅表肿瘤成像等方面得到较好的应用。