Molecular mobility and transport in polymer membranes and polyelectrolyte multilayers

Polyelectrolyte multilayers prepared by the layer-by-layer technique provide an efficient way to generate planar structures of tailored surface charge and hydrophobicity, which are used as membranes for pervaporation. The use of polyelectrolyte multilayers to form the membrane permits tailoring the surface charge of the membrane and, thus, selectivity; at the same time, it reduces fouling of the membrane by adsorption of organic matter. Pulsed field gradient (PFG) nuclear magnetic resonance has been used to investigate the diffusion of probe molecules into polymer systems. Evaluation of the apparent diffusion coefficient in porous poly(amide) results in a pore size of 4 microm, as found in electron micrographs. For the pore size obtained for polyelectrolyte multilayers, no equivalent pores could be found in microscopy. Propagators for the diffusion of propanol and propanol-water mixture into multilayers reveal that there might be selective interaction of probe molecules with the polyelectrolyte system.     

Transversals in Uniform Hypergraphs with Property (p,2)

Dedicated to the memory of Paul Erdős Let f(r,p,t) (p > t >= 1, r >= 2) be the maximum of the cardinality of a minimum transversal over all r-uniform hypergraphs possessing the property that every subhypergraph of with p edges has a transversal of size t. The values of f(r,p,2) for p = 3, 4, 5, 6 were found in [1] and bounds on f(r,7,2) are given in [3]. Here we prove that for large p and huge r. Received September 23, 1999 RID="*" ID="*" This work was partially supported by the grant 99-01-00581 of the Russian Foundation for Fundamental Research and the Dutch–Russian Grant NWO-047-008-006.     

Synthesis and characterization of mono beta-diketiminatosamarium amides and hydrocarbyls

Reaction of SmCl3 with 1 eq of KL (L =[DippNC(Me)CHC(Me)NDipp]; Dipp = 2,6-i-Pr2C6H3) in THF afforded the dimeric samarium dichloride LSmCl2(THF)Cl2SmL (1) in high yield. Reactions of 1 with NaN(SiMe3)2, KNHAr (Ar = 2,4,6-t-Bu3C6H2), KBHEt3, and KCp*(Cp*= C5Me5) yielded various new complexes: LSmClN(SiMe3)2 (2), LSm[N(SiMe3)2]2 (3), LSmNHAr(HBEt3) (4), LSm(NHAr)2 (5), and LSmCp*Cl (6). Reaction of 1 with one eq of NaN(SiMe3)2 followed by treatment with excess AlMe3 afforded a unique bimetallic samarium tetramer Cl3L2Sm2(AlMe4)2Sm2L2Cl3 (7). Reaction of 6 with LiMe or LiCH2SiMe3 afforded LSmCp*Me (8) and LSmCp*CH2SiMe3 (9) in excellent yield. Methyl abstraction from with B(C6F5)3 in toluene yielded the cationic borate species (LSmCp*)[MeB(C6F5)3] (10). Molecular structures of 1-7 and 9 were determined by X-ray single crystal analysis.     

Selective synthesis of the C3v isomer of C60h18

[chemical structure: see text]. C60H18 has been produced by hydrogenation of C60 at 100 bar H2 pressure and 673 K for 10 h. We have investigated the crude material without any purification by use of 1H NMR, 13C NMR, and IR spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. We show that the crude material consists of 95% of the C3v isomer of C60H18.     

A modified HPLC method for the determination of aspartic acid racemization in collagen from human dentin and its comparison with GC

The D/L ratio of aspartic acid enantiomers in proteins of low turnover is generally accepted as a reliable procedure for age determination. In our study, twelve samples of eyetooth dentin were analyzed for age determination. The pure insoluble collagen isolated from eyetooth dentin was obtained by an EDTA demineralization process. Free amino acids obtained after collagen hydrolysis were converted into o-phthaldialdehyde-N-acetyl-L-cysteine (OPA-NAC) derivatives for HPLC analysis under modified conditions and into trifluoroacetic acid isopropyl esters for GC analysis, respectively. The modified HPLC procedure used phosphate buffer and acidified sample matrix prior to injection which resulted in suppression of peak tailing of both diastereomers, thus allowing achievement of both good selectivity and good resolution. To ensure the high accuracy of the developed method the other parameters, i.e. specificity, precision, linearity, LOD, and LOQ, were also determined. Nine collagen samples covering the age range of 18 to 84 years were used for the determination of coefficient of racemization (KR) and calculation of parameters for age estimation. The regression equations for the data set analyzed were as follows: KR= 0.0005 x age + 0.0262 (R2 = 0.9639) for HPLC, and KR= 0.0006 x age + 0.0319 (R2 = 0.9374) for GC, respectively.     

Three-dimensional tracking of fluorescent nanoparticles with subnanometer precision by use of off-focus imaging

We show that the position of a fluorescent nanoparticle can be measured in three dimensions with subnanometer precision and 100-ms temporal resolution by use of standard epifluorescence video imaging in off-focus mode. The particle can be tracked without feedback in a volume of at least 40 microm x 60 microm x 3 microm. With the technique presented, the structure-mobility relationship of 216-nm latex particle in a porous polymer network was studied in three dimensions.     

Density Conditions for Panchromatic Colourings of Hypergraphs

Let be a hypergraph. A panchromatic t-colouring of is a t-colouring of its vertices such that each edge has at least one vertex of each colour; and is panchromatically t-choosable if, whenever each vertex is given a list of t colours, the vertices can be coloured from their lists in such a way that each edge receives at least t different colours. The Hall ratio of is . Among other results, it is proved here that if every edge has at least t vertices and whenever , then is panchromatically t-choosable, and this condition is sharp; the minimum such that every t-uniform hypergraph with is panchromatically t-choosable satisfies ; and except possibly when t = 3 or 5, a t-uniform hypergraph is panchromatically t-colourable if whenever , and this condition is sharp. This last result dualizes to a sharp sufficient condition for the chromatic index of a hypergraph to equal its maximum degree. Received November 10, 1998 RID="*" ID="*" This work was carried out while the first author was visiting Nottingham, funded by Visiting Fellowship Research Grant GR/L54585 from the Engineering and Physical Sciences Research Council. The work of this author was also partly supported by grants 96-01-01614 and 97-01-01075 of the Russian Foundation for Fundamental Research.     

Development and Validation of an LC–ESI-MS Ion-Trap Method for Analysis of Impurities in Transkarbam 12, a Novel Transdermal Accelerant

A new, sensitive LC–MS method for evaluation of the purity of Transkarbam 12 (T12), a novel and highly effective accelerant of transdermal penetration, has been developed and validated. T12 and its impurities (6-aminohexanoic acid, AH, ε-caprolactam, CA, and dodecyl 6-(6-aminohexanamido)hexanoate, DAH) were characterized by MS and MS–MS analysis. Separation was achieved on a 150 mm × 3 mm, 5-μm particle, phenyl–hexyl column. The mobile phase was a gradient prepared from water, formic acid, and acetonitrile. The method was validated within the concentration range 50–250 ng mL^?1; correlation coefficients were >0.998. The accuracy of the method was from 98.6–105.0% for AH, 102.6–104.8% for CA, and 97.9–100.9% for DAH. Precision was in the range 3.19–4.42% for AH, 3.22–5.81% for CA, and 4.8–8.78% for DAH. The selectivity of the method and sample stability were also confirmed. The practical applicability of the method was proven by analysis of T12 bulk substance.