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51.
Matthew Myers Eric F. Connor Thierry Glauser Andreas Mck Gregory Nyce James L. Hedrick 《Journal of polymer science. Part A, Polymer chemistry》2002,40(7):844-851
A new metal‐free synthetic approach to the controlled ring‐opening polymerization (ROP) of lactide with nucleophilic phosphines as transesterification catalysts is described. P(Bu)3, PhPMe2, Ph2PMe, PPh3, and related phosphines are commercially available, inexpensive catalysts that generate narrowly dispersed polylactides with predictable molecular weights. These organic catalysts must be used in combination with an initiator, such as an alcohol, to generate an alcoholate ester α‐end group upon ROP. A likely polymerization pathway is through a monomer‐activated mechanism, with minimal active species, facilitating narrow molecular weight distributions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 844–851, 2002; DOI 10.1002/pola.10168 相似文献
52.
Bismuth triflate catalyzes the allylation of a variety of in situ generated protected aldimines using aldehydes, primary carbamates, and allyltrimethylsilane in a three-component reaction. The reaction proceeds rapidly and affords the corresponding protected homoallylic amine in good yield (up to 86%). Scope and limitations of the aldehyde and carbamate components are reported. 相似文献
53.
Investigation of the Interactions of β‐Peptides with DNA Duplexes by Circular Dichroism Spectroscopy
Kenji Namoto James Gardiner Thierry Kimmerlin Dieter Seebach 《Helvetica chimica acta》2006,89(12):3087-3103
The interaction of β‐peptides with the DNA duplexes of dA20dT20 and a GCN4‐binding CRE sequence was examined. To gauge the factors that govern these interactions, two β‐pentadecapeptides, 1 and 2 , a β‐dodecapeptide, 3 , three β‐decapeptides, 4 – 6 , three β‐heptapeptides, 7 – 9 , and β‐octaarginine 10 were designed and synthesized. The β‐peptides were conceived to adopt a β‐peptide 314 helix, in which the side chains at position i and i + 3 are aligned vertically along one side of the helix. The side chains of Lys, Asn, and Arg were positioned such that potential H‐bonding sites were created for a helical conformation to interact with the base pairs of DNA. CD Analysis showed that β‐peptides 1, 2 , and 10 interacted with dA20dT20. In addition, β‐peptides 1 and 2 showed significant interaction with a DNA‐duplex 20mer containing the ATF/CREB recognition sequence for the regulatory protein GCN4. It is impossible, at this stage of the investigation, to make a safe proposal about the actual nature of the interaction of the structures(s) of the complexes, the formation of which is suggested by the CD spectra reported herein. 相似文献
54.
Thierry Boulanger Christine Evrard Daniel P. Vercauteren Guy Evrard François Durant 《Journal of chemical crystallography》1991,21(3):287-295
The crystal structures ofp-methoxyphenyl-3-triazolo [4,3-a] isoquinoline (SR95926),p-methoxyphenyl-3-triazolophtalazine (CMW1842), andp-methoxyphenyl-3-N-dimethoxyethylamino-6-triazolophtalazine (L16317) have been solved by direct methods from single-crystal X-ray diffraction data, and refined by full-matrix least squares. SR95926: monoclinic,P21/n,a=20.950(3),b=6.769(1),c=9.465(2) Å,=100.90(1)°. CMW1842: triclinic,P¯1,a=8.784(1),b=9.160(4),c=8.555(1) Å,=99.10(2),=93.90(1), =106.77(1)°. L16317: monoclinic,P21/n,a=20.124(3),b=9.586(1),c=10.788(1) Å,=91.91(1)°. FinalR factors are 0.034, 0.037, and 0.053, respectively. Experimental geometries were used to perform STO-3Gab initio molecular-orbital calculations. A relationship between the electronic pattern within the molecules and the affinity of the benzodiazepine receptor sites is pointed out. 相似文献
55.
Thierry Coquand 《BIT Numerical Mathematics》1992,32(1):10-14
We show how to represent a paradox similar to Russell's paradox in Type Theory withW-types and a type of all types, and how to use this in order to represent a fixed-point operator in such a theory. It is still open whether such a construction is possible without theW-type.This research was partly supported by ESPIRIT Basic Research Action Logical Frameworks. 相似文献
56.
Thierry Coulhon 《Potential Analysis》1992,1(4):343-353
One shows the equivalence between an abstract form of a Gagliardo-Nirenberg inequality and an estimate of the decay of the L
1–L
norm of a semigroup of operators. This equivalence, contrary to the one with the classical Sobolev inequalities, allows the treatment of situations where the decay is exponential. Related results and applications are given.
Cet article a pu être terminé pendant un séjour de l'auteur à l'université d'Edimbourg. 相似文献
57.
We consider global solutions of the nonlinear Schrödinger equation
相似文献
58.
Tae-Kyu Ha Urs P. Wild Ren O. Kühne Charles Loesch Thierry Schaffhauser Johanna Stachel Alexander Wokaun 《Helvetica chimica acta》1978,61(3):1193-1199
Ab initio SCF and CI calculations on the cationic and neutral complexes of formaldehyde and lithium are reported. For the cationic complex CH2O/Li+, the stabilization energy of 41.7 kcal/mol obtained from the SCF calculation increases to 51.6 kcal/mol if a configuration interaction is introduced. For the neutral complex CH2O?/Li+, the C2v-conformer of the 2A1-state with the equilibrium bond distances of d(C? O) = 1.23 Å and d (O? Li) = 1.90 Å is calculated to be more stable than the 2B1-state with d (C? O) = 1.34 Å, and d (O? Li) = 1.65 Å. Charge transfer and polarization effects upon complex formation are discussed. 相似文献
59.
Tetraphenylmethanes with multiple hydrogen-bonding sites are known to associate to form robust porous supramolecular networks. Analogous anionic networks can be built from the corresponding tetraphenylborates. Crystallization of the tetraphenylphosphonium salt of tetraphenylborate 2 produces an anionic network in which 74% of the volume is available for including cations and neutral guests. Other salts of anion 2 with diverse cations crystallize consistently to form the same network, whereas a neutral analogue of anion 2, tetraphenylmethane 1, produces an uncharged network that is far less open. Cations can be exchanged in single crystals of salts of tetraphenylborate 2 with retention of crystallinity and with selectivities similar to those observed in typical zeolites. Together, these observations provide new strategies for making ordered molecular materials by design, and they reveal that constructing such materials from charged subunits offers special advantages. 相似文献
60.
Amgoune A Thomas CM Roisnel T Carpentier JF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):169-179
A series of new alkoxy-amino-bis(phenols) (H2L 1-6) has been synthesized by Mannich condensations of substituted phenols, formaldehyde, and amino ethers or diamines. The coordination properties of these dianionic ligands towards yttrium, lanthanum, and neodymium have been studied. The resulting Group 3 metal complexes have been used as initiators for the ring-opening polymerization of rac-lactide to provide poly(lactic acid)s (PLAs). The polymerizations are living, as evidenced by the narrow polydispersities of the isolated polymers, together with the linear natures of number average molecular weight versus conversion plots and monomer-to-catalyst ratios. Complex [Y(L6){N(SiHMe2)2}(THF)] (17) polymerized rac-lactide to heterotactic PLA (Pr = 0.90 at 20 degrees C) and meso-lactide to syndiotactic PLA (Pr = 0.75 at 20 degrees C). The in situ formation of [Y(L6)(OiPr)(THF)] (18) from 17 and 2-propanol resulted in narrower molecular weight distributions (PDI = 1.06). With complex 18, highly heterotactic PLAs with narrow molecular weight distributions were obtained with high activities and productivities at room temperature. The natures of the ligand substituents were shown to have a significant influence on the degree of control of the polymerizations, and in particular on the tacticity of the polymer. 相似文献
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