02716nas a2200253   4500008004100000022001400041245012000055210006900175260006800244300001400312490000700326520180900333653001302142653002802155653002502183653001002208653001902218653001802237653001902255100001702274700002802291700001602319856012702335       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<p>The synthesis of low-molecular-weight (weight-average molecular weight &lt; 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.</p>10aC-13 NMR10adehydropolycondensation10aLewis acid catalysts10aMALDI10apolymerization10arandomization10astereosequence1 aShyamroy, S.1 aGarnaik, Baijayantimala1 aSivaram, S.  uhttps://library.ncl.res.in/content/structure-polyl-lactic-acids-prepared-dehydropolycondensation-l-lactic-acid-organotin-002215nas a2200277   4500008004100000022001400041245010800055210006900163260007300232300001000305490000900315520124800324653001301572653000801585653002101593653002301614653001401637653001501651100002101666700002401687700002201711700002301733700002601756700002701782856012801809       2015                        eng d  a0022-286000aFirst naphthosemiquinone complex of K+ with vitamin K3 analog: experiment and density functional theory0 aFirst naphthosemiquinone complex of K with vitamin K3 analog exp  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcMAY  a56-630 v10883 a<p>Synthesis and characterization of potassium complex of 2-hydroxy-3-methyl-1,4-naphthoquinone (phthiocol), the vitamin K3 analog, has been carried out using FT-IR, UV-Vis, H-1 and C-13 NMR, EPR, cyclic voltammetry and single crystal X-ray diffraction experiments combined with the density functional theory. It has been observed that naphthosemiquinone binds to two K+ ions extending the polymeric chain through bridging oxygens O(2) and O(3). The crystal network possesses hydrogen bonding interactions from coordinated water molecules showing water channels along the c-axis. C-13 NMR spectra revealed that the complexation of phthiocol with potassium ion engenders deshielding of C(2) signals, which appear at delta = similar to 14.6 ppm whereas those of C(3) exhibit up-field signals near delta similar to 6.9 ppm. These inferences are supported by the M06-2x based density functional theory. Electrochemical experiments further suggest that reduction of naphthosemiquinone results in only a cathodic peak from catechol. A triplet state arising from interactions between neighboring phthiocol anion lead to a half field signal at g = 4.1 in the polycrystalline X-band EPR spectra at 133 K. (C) 2015 Elsevier B.V. All rights reserved.</p>10aC-13 NMR10aDFT10ahydrogen bonding10aNaphthosemiquinone10aPhthiocol10aVitamin K31 aKathawate, Laxmi1 aGejji, Shridhar, P.1 aYeole, Sachin, D.1 aVerma, Prakash, L.1 aPuranik, Vedavati, G.1 aSalunke-Gawali, Sunita  uhttps://library.ncl.res.in/content/first-naphthosemiquinone-complex-k-vitamin-k3-analog-experiment-and-density-functional-0