02715nas a2200253 4500008004100000022001400041245012000055210006900175260006800244300001400312490000700326520180900333653001302142653002802155653002502183653001002208653001902218653001802237653001902255100001702274700002802291700001602319856012602335 2005 eng d a0887-624X00aStructure of poly(L-lactic acid)s prepared by the dehydropolycondensation of L-lactic acid with organotin catalysts0 aStructure of polyLlactic acids prepared by the dehydropolyconden a111 RIVER ST, HOBOKEN, NJ 07030 USAbJOHN WILEY & SONS INCcMAY a2164-21770 v433 a

The synthesis of low-molecular-weight (weight-average molecular weight < 45,000 g/mol) lactic acid polymers through the dehydropolycondensation of L-lactic acid was investigated. Polymerizations were carried out in solution with solvents (xylene, mesitylene, and decalin), without a solvent using different Lewis acid catalysts (tetraphenyl tin and tetra-n-butyldichlorodistannoxane), and at three different polymerization temperatures (143, 165, and 190 degrees C). The products were characterized with differential scanning calorimetry, size exclusion chromatography, vapor pressure osmometry, C-13 NMR, and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). The resulting polymers contained less than 1 mol % lactide, as shown by NMR. The number-average molecular weights were calculated from the ratio of the area peaks of ester carbonyl and carboxylic acid end groups via C-13 NMR. The stereosequences were analyzed by C-13 NMR spectroscopy on the basis of triad effects. Tetraphenyl tin was an effective transesterification catalyst, and the randomization of the stereosequence at 190 degrees C was observed. In contrast, the distannoxane catalyst caused comparatively less transesterification reaction, and the randomization of the stereosequences was slow even at 190 degrees C. The L-lactic acid and D-lactic acid isomers were added to the polymer chain in a small, blocky fashion. The MALDI-TOF spectra of poly(L-lactic acid) (PLA) chains doped with Na+ and K+ cations showed that the PLA chains had the expected end groups. The MALDI-TOF analysis also enabled the simultaneous detection of the cyclic oligomers of PLA present in these samples, and this led to the full structural characterization of the molecular species in PIA. (c) 2005 Wiley Periodicals, Inc.

10aC-13 NMR10adehydropolycondensation10aLewis acid catalysts10aMALDI10apolymerization10arandomization10astereosequence1 aShyamroy, S.1 aGarnaik, Baijayantimala1 aSivaram, S. uhttp://library.ncl.res.in/content/structure-polyl-lactic-acids-prepared-dehydropolycondensation-l-lactic-acid-organotin-002178nas a2200241 4500008004100000022001400041245011500055210006900170260006800239300001400307490000700321520131700328653001001645653002401655653001801679653002101697653001801718653002201736653001801758100001401776700001901790856012701809 2008 eng d a0887-624X00aSolvent-free and nonisocyanate melt transurethane reaction for aliphatic polyurethanes and mechanistic aspects0 aSolventfree and nonisocyanate melt transurethane reaction for al a111 RIVER ST, HOBOKEN, NJ 07030 USAbJOHN WILEY & SONS INCcAPR a2445-24580 v463 a

A novel melt transurethane polycondensation route for polyurethanes under solvent-free and nonisocyanate condition was developed for soluble and thermally stable aliphatic or aromatic polyurethanes. The new transurethane process was investigated for A + 13, A-A + B, and A-A + B-B (A-urethane and B-hydroxyl) type condensation reactions, and also monomers bearing primary and secondary urethane or hydroxyl functionalities. The transurethane process was confirmed by H-1 and C-13 NMR, and molecular weight of the polymers were obtained as M-n = 10-15 X 10(3) and M-w = 15-45 X 10(3) g/mol. The mechanistic aspects of the melt transurethane process and role of the catalyst were investigated using model reactions, H-1 NMR, and MALDI-TOF-MS. The model reactions indicated the occurrence of 97% reaction in the presence of catalyst, whereas its absence gave only less than 2% of the product. The polymer samples were subjected for end-group analysis using MALDI-TOF-MS, which confirms the Ti-catalyst mediated nonisocyanate pathway in the melt transurethane process. Almost all the polyurethanes were stable up to 280 degrees C, and the T-g of the polyurethanes can be easily fine-tuned from -30 to 120 degrees C by using appropriate diols in the melt transurethane process. (C) 2008 Wiley Periodicals, Inc.

10aMALDI10amelt polymerization10anonisocyanate10aPolycondensation10apolyurethanes10athermal stability10atransurethane1 aDeepa, P.1 aJayakannan, M. uhttp://library.ncl.res.in/content/solvent-free-and-nonisocyanate-melt-transurethane-reaction-aliphatic-polyurethanes-and-001626nas a2200229 4500008004100000022001400041245007400055210006900129260006100198300000900259490000700268520085000275653002101125653001001146653002001156653003101176653001901207100001501226700002501241700002601266856010401292 2008 eng d a1572-388700aStudy of papain-cystatin interaction by intensity fading MALDI-TOF-MS0 aStudy of papaincystatin interaction by intensity fading MALDITOF a233 SPRING STREET, NEW YORK, NY 10013 USAbSPRINGERcJAN a7-120 v273 a

Intensity fading (IF) matrix assisted laser desorption ionization (MALDI) time of flight (TOF) mass spectrometry (MS ) has become an alternative screening approach for the affinity-binding analysis of proteins and peptides with molecular ligands. In this investigation an attempt has been made to study the protein ligand interaction by intensity fading (IF) MALDI-MS using papain and cystatin as model system for protein-ligand interactions. The intensity fading of cystatin was monitored using various concentration of cystatin ranging from (1 to 8.6 mu M) in presence of target protein, papain. The results indeed indicate that the intensity of cystatin decreases upon addition of papain. Furthermore, for the first time we have used IF-MALDI-MS for determining the number of binding sites for cystatin on papain by Scatchard analysis.

10aintensity fading10aMALDI10apapain-cystatin10aprotein-ligand interaction10aScatchard plot1 aShabab, M.1 aKulkarni, Mahesh, J.1 aKhan, Mohammad, Islam uhttp://library.ncl.res.in/content/study-papain-cystatin-interaction-intensity-fading-maldi-tof-ms-0