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141.
Complete Carbon-13 magnetic resonance spectral assignments of cocaine and atropine were made.13C Nmr spectra of atropine provides an interesting example of long range coupling on chemical shifts. 相似文献
142.
Percec V Mitchell CM Cho WD Uchida S Glodde M Ungar G Zeng X Liu Y Balagurusamy VS Heiney PA 《Journal of the American Chemical Society》2004,126(19):6078-6094
Structural analysis of three libraries of up to five generations of self-assembling dendrons based on AB(3), AB(2), and combinations of AB(3) with AB(2) building blocks (Percec et al. J. Am. Chem. Soc. 2001, 123, 1302) facilitated the discovery of several nanoscale lattices previously unknown for organic compounds (3-D Pm3n cubic, 3-D P4(2)/mnm tetragonal, and a crystallographically forbidden 12-fold symmetry liquid quasicrystal) and provided fundamental correlations between the molecular structure of the dendron and the shape and the diameter of the supramolecular dendrimers which, in these experiments, were limited to less than 75 A. That study concluded that alternative design principles should be elaborated for the assembly of supramolecular dendrimers of larger dimensions. Here we report design principles, synthesis and analysis of first and higher generations AB(3) and AB(2) self-assembling dendrons, based on various primary structures, and combinations of (AB)(y)-AB(3) and (AB)(y)-AB(2) (i.e., from nondendritic AB where y = 1 to 11 and dendritic AB(3) and AB(2)) building blocks that produced the largest structural (including six new lattices) and dimensional (100 to 217 A diameter) diversity of supramolecular dendrimers. 相似文献
143.
Virgil Percec Monika J. Sienkowska 《Journal of polymer science. Part A, Polymer chemistry》2009,47(2):628-634
Pentaerythritol tetrakis(2‐iodopropionate) was used as a tetrafunctional initiator for the Na2S2O4 catalyzed SET‐DTLRP of n‐butyl acrylate in water at room temperature. The resulting tetrafunctional poly(n‐butyl acrylate) macroinitiator with Mn = 14,864 or Mn = 3627 per arm was used to initiate the SET‐DTLRP of vinyl chloride and provide the first examples of four‐arm star‐block copolymers [PVC‐b‐PBA‐CH(CH3)? CO? O? CH2]4C. The Mn of the PVC segment from each arm of the four‐arm star‐block copolymer varied between 353 and 33,622. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 628–634, 2009 相似文献
144.
Virgil Percec Shigeru Okita 《Journal of polymer science. Part A, Polymer chemistry》1993,31(4):877-884
4,4?-Dichloro-1,1′ : 2′,1″ : 2″,1?-quaterphenyl ( 9 ), 4,4?-dichloro-1,1′ : 3′,1″ : 3″,1?-quaterphenyl ( 10 ), and 4,4?-dichloro-1,1′ : 4′,1″ : 4″,1?-quaterphenyl ( 11 ) were synthesized by Pd (0) catalyzed cross-coupling reaction of 4-chlorobenzeneboronic acid with 2,2′-, 3,3′-, and 4,4′-bis (trifluoromethanesulfonyloxy)biphenyl respectively. 4,4?-Dichloro-1,1′ : 2′,1″ : 2″,1?-quaterphenyl ( 9 ) and 4,4?-dichloro-1,1′ : 3′,1″ : 3″,1?-quaterphenyl ( 10 ) were oligomerized by Ni(0) catalyzed homocoupling reaction to yield white and soluble oligophenylenes. © 1993 John Wiley & Sons, Inc. 相似文献
145.
Gerard Lligadas Janine S. Ladislaw Tamaz Guliashvili Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2008,46(1):278-288
The single‐electron transfer living radical polymerization (SET‐LRP) of methyl acrylate initiated with bromoform (CHBr3) and iodoform (CHI3) and catalyzed by Cu(0)/Me6‐TREN in DMSO at 25 °C provides a reliable method to prepare poly (methyl acrylate) (PMA) with active chain ends and controlled structure that can undergo subsequent functionalization to provide strategies for the synthesis of different block copolymers and other complex architectures. A detailed kinetic and structural analysis was used to assess the scope and the limitations of CHBr3 and CHI3 as initiators under SET‐LRP conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 278–288, 2008 相似文献
146.
147.
Virgil Percec 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):1479-1496
Abstract This paper reviews the principles of self-assembly of rodlike viruses, such as tobacco mosaic virus (TMV), and discusses with selected examples the strategy used in our laboratory to produce synthetic systems which self-assemble via related principles. 相似文献
148.
Nga H. Nguyen Brad M. Rosen Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2011,49(5):1235-1247
Computational studies on the heterolytic bond dissociation energies and electron affinities of methyl 2‐bromopropionate (MBP) and ethyl 2‐bromoisobutyrate (EBiB) in the dissociative electron transfer (DET) step of single electron transfer living radical polymerization (SET‐LRP) of methyl acrylate (MA) combined with kinetic experiments were performed in an effort to design the most efficient initiation system. This study suggests that EBiB is more effective than MBP in the SET‐LRP of acrylates catalyzed by Cu(0) wire, thus being a true electronic mimic of the dormant PMA species. EBiB allows for a more predictable dependence of the molecular weight evolution and distribution. This is exemplified by the absence of a deviation in the PMA molecular weight from theoretical values at low conversions, as a result of a faster SET activation with EBiB than with MBP. The enhanced control over molecular weight evolution was also observed in the SET‐LRP of MA initiated with bifunctional initiators similar in structure to MBP and EBiB, suggesting a higher reactivity than MBP in the SET activation, which matches closely that of the polymer dormant chains. The use of bifunctional initiators in conjunction with activated Cu(0) wire in SET‐LRP allows for dramatically accelerated polymerizations, although still providing for exceptional control of the molecular weight evolution and distribution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
149.
V. Franco A. Conde V. Provenzano R.D. Shull 《Journal of magnetism and magnetic materials》2010,322(2):218-223
The field dependence of the magnetic entropy change has been studied for a series of doped Gd5Si2Ge2 alloys, which possess a magnetic phase transition that is either entirely second order or a combination of primarily second-order mixed to a very minor degree with a first-order transition arising from a magneto-structural phase change. By analyzing the field scaling of the refrigerant capacity as well as of the reference temperatures used for constructing a universal scaling curve, a procedure for estimating the values of the critical exponents for the alloys was developed. For the cases where the transition is entirely second order, the results obtained from this procedure are comparable to the values obtained from the Kouvel–Fisher method. For the case of Fe-doped alloys which partially possess a first-order phase change, the Kouvel–Fisher method is inapplicable. However, their critical exponents determined by our developed procedure can be used to estimate the Curie temperature of the orthorhombic majority phase. 相似文献
150.
Sven Fleischmann Brad M. Rosen Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2010,48(5):1190-1196
Single Electron Transfer‐Living Radical Polymerization (SET‐LRP) represents a robust and versatile method for the rapid synthesis of macromolecules with well defined topology. In SET‐LRP, certain combinations of solvents and ligands facilitate the disproportionation of in situ generated Cu(I) species into “nascent” Cu(0) and Cu(II) species. A combination of heterogeneous and “nascent” Cu(0) activation yields polymers with very high chain end functionality. Under suitable conditions the tolerance toward oxygen must be increased since Cu(0), the activator in SET‐LRP, acts as an oxygen scavenger in all inert gas purification systems. Here we demonstrate that SET‐LRP of methyl acrylate can be conducted in the presence of air. The addition of a small amount of reducing agent hydrazine hydrate to the reaction mixture reduces Cu2O generated by the oxidation of Cu(0) with air, regenerating Cu(0) and allowing for the synthesis of polymers with predictable molecular weight and perfect retention of chain end functionality. The kinetics plots obtained under these conditions were identical to these generated by degassed samples. High conversions were achieved within a very short reaction time. In these SET‐LRP experiments, the reagents were not deoxygenated or subjected to standard degassing procedures such as freeze‐pump‐thaw or nitrogen sparging. This simple SET‐LRP procedure provides an efficient and economical approach to the synthesis of functional macromolecules. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1190–1196, 2010 相似文献