Pt- (and Co-) Promoted Molybdena-Alumina Catalysts: Analysis of the Impregnation Steps

The equilibrium parameters for the adsorption of Mo(VI) on gamma-Al(2)O(3) and of Co(II) and Pt(IV) on MoO(3)/gamma-Al(2)O(3) were determined. The adsorption isotherms were performed from aqueous solutions of the corresponding precursors on two different alumina supports. According to the classification given by Giles, L-type-shaped, subgroup 2, adsorption curves were found for the system Mo on gamma-Al(2)O(3), L-type, subgroup 1, for the Pt on MoO(3)/gamma-Al(2)O(3), and S-type for Co on the MoO(3)/gamma-Al(2)O(3) system. Numerical calculations were carried out for all the isotherms to find the equilibrium parameters. These constants are being used to model the development of Pt, Co, and Mo profiles on MoO(3)/gamma-Al(2)O(3) or gamma-Al(2)O(3) extrudates, respectively, which belong to the new generation of noble-metal-MoO(3)/gamma-Al(2)O(3)-supported catalysts to be used in oil-refining processes. Copyright 2001 Academic Press.     

d-xylose transport by Candida succiphila and Kluyveromyces marxianus

The kinetics and regulation of d-xylose uptake were investigated in the efficient pentose fermentor Candida succiphila, and in Kluyveromyces marxianus, which assimilate but do not ferment pentose sugars. Active high-affinity (K _m ∼ 3.8 mM; V _max ∼ 15 nmol/[mg·min]) and putative facilitated diffusion low-affinity (K _m ∼ 140 mM; V _max ∼ 130 nmol/[mg·min]) transport activities were found in C. succiphila grown, respectively, on xylose or glucose. K. marxianus showed facilitated diffusion low-affinity (K _m ∼ 103 mM; V _max ∼ 190 nmol/[mg·min]) transport activity when grown on xylose under microaerobic conditions, and both a low-affinity and an active high-affinity (K _m ∼ 0.2 mM; V _max ∼ 10 nmol/[mg·min]) transport activity when grown on xylose under fully aerobic conditions.     

Novel photopolymerizable biodegradable triblock polymers for tissue engineering scaffolds: synthesis and characterization

For use in micro-patterned scaffolds in tissue engineering, novel diacrylated triblock macromers (PLA-b-PCL-b-PLA, PGA-b-PCL-b-PGA and PCL-b-PEO-b-PCL) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). All diacrylated polymers were designed as triblock copolymers and involved biodegradable blocks of relatively non-polar epsilon-caprolactone (CL) and polar monomers such as glycolide (GA), lactide (LA) or ethylene oxide (EO). All triblock polymers were prepared in molecular weights of a few kilo daltons via the anionic ring-opening polymerization (ROP) of the corresponding lactide, glycolide or caprolactone using stannous octoate [Sn(Oct)(2)] as catalyst. The polymers had low polydispersity indices, ranging from 1.23 to 1.56. Biodegradable polymeric networks were prepared with conversions of 72-84% via photopolymerization of the triblock diacrylated polymers with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. PLA-b-PCL-b-PLA copolymers crumbled easily and were not suitable for micro-patterning. PGA-b-PCL-b-PGA copolymers had higher water contact angles than PCL-b-PEO-b-PCL and were also cytocompatible with Fibroblasts 3T3.     

Evaluation of the immobilized artificial membrane phosphatidylcholine: Drug discovery column for high-performance liquid chromatographic screening of drug–membrane interactions

Chromatographic retention factors (k′) of a series of eight β-adrenoceptor antagonist compounds (β-adrenolytic drugs) were determined employing an immobilized artificial membrane column (IAM.PC.DD). The influence of mobile phase pH, ionic strength, and organic modifier composition was studied in order to examine column performance. After the IAM.PC.DD columns were exposed to approximately 7000 column volumes of a 0.01 M PBS mobile phase, five out of six columns tested showed significant peak broadening and decreased k′ values indicative of premature column failure. The data suggested that the immobilized phospholipids stationary phase was removed by the 0.01 M PBS mobile phase. The β-adrenolytic drug's log k′_IAM values obtained with an IAM.PC.DD column were compared to an ^esterIAM.PC.MG column for predicting drug membrane interactions. For the linear regression analysis between log k′_IAM and the logarithm of the n-octanol–water partition coefficients (r_IAM.PC.DD=0.8710 vs. r_IAM.PC.MG=0.9538), the C₁₈ HPLC retention factors (r_IAM.PC.DD=0.8408 vs. r_IAM.PC.MG=0.9380), the liposome partition coefficients (r_IAM.PC.DD=0.8887 vs. r_IAM.PC.MG=0.9187), and various pharmacokinetic parameters, significantly better correlations were obtained with the ^esterIAM.PC.MG column than the IAM.PC.DD column.     

Immunoassay of P-glycoprotein on single cell by capillary electrophoresis with laser induced fluorescence detection

The cellular mechanism based on P-glycoprotein (PGP) for its drug pump function has become very important in multidrug resistance (MDR) research. A method has been established to characterize PGP on single K562 cell by coupling capillary electrophoresis with laser induced fluorescence detection. A permeable intact cell after the immunoassay binding with fluorescence labeling antibody was injected into the capillary and directly separated without lysis. It was found that once 5-10 optional cells were detected in batch, the PGP amount on this cell line could be outlined and calculated clearly. The PGP amount on K562 MDR cell line is 3.88 times higher than that on K562 sensitive cell line. These two cell lines with immunoassay binding were also analyzed by injection of multi-cells in order to improve the throughput. A resistance factor so called multidrug resistance multiple (MRM) was introduced to evaluate the MDR difference between cell lines. The MRM values of the cell line K562 measured by single cell analysis are well correlated with those by flow cytometry, which also prove the validity of our method in single cell analysis for the possibility of cancer diagnosis, pharmacokinetics and drug screening in future.     

Self-assembly via ionic interactions of calix[6]arene-based receptors displaying remarkable host-guest properties toward neutral guests

The association of a C_3v-symmetrical calix[6]tris-amine with different concave tris-carboxylic acids of various degrees of flexibility has been explored by ¹H NMR spectroscopy. In all cases, self-assembled structures directed by the selective inclusion of a neutral guest molecule were obtained, the more preorganized being stable in protic solvents. With a rigid C₃-symmetrical cap, chiral guest recognition in the calixarene cavity resulted. A large tris-acidic partner gave a unique molecular ditopic receptor that is able to simultaneously accommodate two neutral molecules in two distinct hydrophobic cavities with different binding processes.     

Perfluormethyl-Element-Liganden. XXIX. Darstellung und spektroskopische Untersuchungen von M(CO)4L2-Komplexen (M = Cr,Mo, W; L = Me2PSMe,Me2PSeMe, (CF3)2PSMe, (CF3)2PSeMe)

Perfluoromethyl Element Ligands. XXIX. Preparation and Spectroscopic Investigation of M(CO)₄L₂ Complexes (M ? Cr, Mo, W; L ? Me₂PSMe, Me₂PSeMe, (CF₃)₂PSMe, (CF₃)₂PSMe) The complexes M(CO)₄L₂ (see Inhaltsübersicht) have been prepared by the reaction of tetracarbonyl norbornadiene metal compounds M(CO)₄NBD with L at room temperature or 35°C, respectively. The cis-complexes formed in the first step undergo rearrangement to trans-isomers at higher temperatures. New compounds have been characterized by analytical and spectroscopic (IR, NMR, MS) methods.     

Optimization of matrix-assisted laser desorption/ionization time-of-flight collision-induced dissociation using poly(ethylene glycol)

Details of the optimization of the collision-induced dissociation (CID) process, using a collision cell on a matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer, are described using poly(ethylene glycol) 1000 (PEG 1000) as a model analyte. The effects of collision gas identity (helium, air, and argon), as well as collision gas pressure, on the resulting MS/MS data were investigated. With PEG 1000, helium was found to give the best results with respect to signal-to-noise (S/N) ratio. The optimum pressure for each gas was found to be in the range where the precursor ion signal was attenuated to approximately 30-50% for helium and 40-60% for argon. The effect of cation choice (Li, Na, and K) on the CID of PEG was also studied. CID spectra were produced for each, but PEG cationized with lithium was found to produce the spectra with the highest S/N ratio. The MALDI-TOF CID spectra that were generated for PEG were compared with the high-energy and low-energy MS/MS spectra obtained from a sector mass spectrometer and from a triple quadrupole mass spectrometer, respectively. The results observed for PEG confirm that CID on a MALDI-TOF mass spectrometer is a high-energy MS/MS technique.     

The chemistry of fluorine containing phosphaalkenes, arsaalkenes and selenocarbonyls

This review covers our extensive research activities in the area of fluorine containing phospha- and arsaalkenes as well as selenocarbonyls, which differ considerably in their properties and reactivities from their alkyl and aryl counterparts and thus contribute in a gratifying manner to the still growing field of unsaturated element-carbon compounds of 3rd and 4th row main group elements E. Of particular interest is the influence of the fluorine substituents and other small groups (OR, NR₂) with either inductive and/or mesomeric effects on the polarity and reactivity of the EC bond. Addition reactions of proton acidic and hydridic polar HX reactants as well as [2+2], [3+2] and [4+2] cycloadditions have been thoroughly studied. The results obtained allow a classification of the EC systems within five different types, A to E, and prove a change from “normal” to “inverse” heteroalkenes in this sequence. The ligand properties of some derivatives have also been investigated in some detail.     

Channel flow cell studies on the evaluation of surface pretreatments using phosphoric acid or polymaleic acid for calcite stone protection

The dissolution kinetics of surface-pretreated and weathered calcite was investigated in dilute acid using a channel flow cell with microdisk detection. Two pretreatments were studied, polymaleic acid and phosphoric acid. Treatment with polymaleic acid was shown to significantly passivate calcite but to a lesser extent than the phosphoric acid and the former coating was found to be less effective for protection of calcite from acid attack. However, treatment of calcite with phosphoric acid resulted in the passivation of calcite from acid attack which strongly inhibited dissolution, an effect that was enhanced even further after exposure to the environment.