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Int. J. Mol. Sci., Volume 4, Issue 10 (October 2003) – 2 articles , Pages 537-561

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302 KiB  
Article
An Acid Exchanged Montmorillonite Clay-Catalyzed Synthesis of Polyepichlorhydrin
by Ahmed Yahiaoui, Mohammed Belbachir and Aïcha Hachemaoui
Int. J. Mol. Sci. 2003, 4(10), 548-561; https://doi.org/10.3390/i4100548 - 30 Sep 2003
Cited by 54 | Viewed by 10874
Abstract
“Maghnite”, a montmorillonite sheet silicate clay, exchanged with protons to produce “H-Maghnite” is an efficient catalyst for cationic polymerisation of many heterocyclic and vinylic monomers (Belbachir, M. U.S. Patent. 066969.0101 –2001). The structural compositions of both “Maghnite” and “H-Maghnite” have already been determined. [...] Read more.
“Maghnite”, a montmorillonite sheet silicate clay, exchanged with protons to produce “H-Maghnite” is an efficient catalyst for cationic polymerisation of many heterocyclic and vinylic monomers (Belbachir, M. U.S. Patent. 066969.0101 –2001). The structural compositions of both “Maghnite” and “H-Maghnite” have already been determined. Epichlorhydrin monomer, which is polymerizable by a cationic process (Odian,G. La Polymerisation: Principes et Applications; Ed.Technica: New York, 1994; pp 222-226), was used to elucidate the polymerization cationic character. The polymerization was performed under optimum conditions at 20°C. Experiments revealed that the polymerisation induced by “H-Maghnite” proceeds in bulk. In bulk polymerization, Epichlorhydrin conversion increases with increasing “H-Maghnite” concentration and temperature. Full article
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266 KiB  
Article
Structure of Stacked Dimers of N-Methylated Watson–Crick Adenine–Thymine Base Pairs
by Oleg V. Shishkin, Marcus Elstner, Thomas Frauenheim and Sándor Suhai
Int. J. Mol. Sci. 2003, 4(10), 537-547; https://doi.org/10.3390/i4100537 - 29 Sep 2003
Cited by 21 | Viewed by 10484
Abstract
The structure of two isomeric stacked dimers of Watson-Crick 9-methyladenine-1-methylthymine pairs was fully optimized using an approximate density functional theory (DFT) method augmented with an empirical dispersion interaction. The results of the calculations reveal that head-to-tail (AT-TA) and head-to-head (AT-AT) dimers possess a [...] Read more.
The structure of two isomeric stacked dimers of Watson-Crick 9-methyladenine-1-methylthymine pairs was fully optimized using an approximate density functional theory (DFT) method augmented with an empirical dispersion interaction. The results of the calculations reveal that head-to-tail (AT-TA) and head-to-head (AT-AT) dimers possess a significantly different geometry. The structure of both complexes is stabilized by vertical CH…O and C-H…N hydrogen bonds with the participation of the hydrogen atoms of the methyl groups. The energy of hydrogen bonding and stacking interactions was additionally calculated using the MP2/6-31G*(0.25) method. Differences in the mutual arrangement of the base pairs in two isomeric dimers lead to significant changes of intra and interstrand stacking interaction energies. Full article
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