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71.
Gray M Cuello AO Cooke G Rotello VM 《Journal of the American Chemical Society》2003,125(26):7882-7888
Two receptors, a diaminotriazine derivative (DAT) and diamidopyridine (DAP), are complementary to the electroactive naphthalimide (N) through three-point hydrogen bonding. The association constants of the two receptors were evaluated for both the fully oxidized and the radical anion forms of N. In the oxidized state, the two receptors displayed identical binding constants. Diamidopyridine, however, lowers the reduction potential of naphthalimide to a far greater extent than does diaminotriazine, indicating a greater affinity for diamidopyridine by naphthalimide in the radical anion form. This behavior was mirrored by EPR experiments that showed small deviations from the hyperfine coupling pattern of N(red) in the presence of DAT, with greater effects seen for the N(red).DAP complex. Computational simulations using the UB3LYP/6-311+G(d,p)//UHF/6-31G(d) hybrid gave theoretical hyperfine constants in good quantitative agreement with the experimental results. Using this correlation, we determined that electrostatics and hydrogen bond polarizability play key roles in controlling redox-modulated molecular recognition. 相似文献
72.
Matthias Schüler Thomas Kovar Hans Lischka Ron Shepard Robert J. Harrison 《Theoretical chemistry accounts》1993,84(6):489-509
Summary In this work a parallel implementation of the COLUMBUS MRSDCI program system is presented. A coarse grain parallelization approach using message passing via the portable toolkit TCGMSG is used. The program is very well portable and runs on shared memory machines like the Cray Y-MP, Alliant FX/2800 or Convex C2 and on distributed memory machines like the iPSC/860. Further implementations on a network of workstations and on the Intel Touchstone Delta are in progress. Overall, results are quite satisfactory considering the complexity and the prodigious requirements, especially the I/O bandwidth, of MRCI programs in general. For our largest test case we obtain a speedup of a factor of 7.2 on an eight processor Cray Y-MP for that section of the program (hamiltonian matrix times trial vector product) which has been parallelized. The speedup for one complete diagonalization iteration amounts to 5.9. An absolute speed close to 1 GFLOPS is found. Results for the iPSC/860 show that ordinary disk I/O is certainly not sufficient in order to guarantee a satisfactory performance. As a solution for that problem, the implementation of a fully asynchronous distributed-memory model for certain data files is in preparation.
On leave from: Bereich Informatik, Universität Leipzig, Augustusplatz 10/11, O-7010 Leipzig, Germany 相似文献
73.
Ron S. Dickson Rhonda J. Nesbit Helen Pateras Jennifer M. Patrick Allan H. White 《Journal of organometallic chemistry》1984,265(2):c25-c28
Complexes of formula (η-C5H52Rh2{CF3C2CF3 · RNCO} have been prepared by three methods, from reactions between organic isocyanates and (η-C5H5)2Rh2(CO)(CF3C2CF3) or (η-C5H5)2Rh2(CO)2(CF3C2CF3); by treatment of (η-C5H5)2Rh2(CO)(CF3C2CF3) with organic azides; and by oxidation with Me3NO of the organic isocyanide in (η-C5H5)2Rh2(CO)(CNR)(CF3C2CF3). The crystal and molecular structure of the complex (η-C5H5)2Rh2{CF3C2CF3 · RNCO} with R = Ph has been determined from single crystal X-ray diffraction data. This reveals that the isocyanate has condensed with the hexafluorobut-2-yne to form an amide ligand of the form C(CF3)C(CF3)C(=O)N(R); this bridges the two rhodium atoms in a μ2η3-manner. 相似文献
74.
A range of mixed ether-esters of cellulose was prepared from partially substituted ethylcellulose and methylcellulose. The 13C-NMR analysis of ethylcellulose with a DS of 2.5 indicated that the hydroxyl groups at carbon six of anhydroglucose units were completely substituted. Acetylation of the ethylcellulose under different conditions yielded (acetyl) (ethyl) cellulose (AEC) samples with acetyl degree of substitution ranging from 0 to 0.5. Fully substituted (propionyl) (ethyl) cellulose (PEC) and (acetyl) (methyl) cellulose (AMC) were also prepared. Chiral nematic liquid crystals were formed in these mixed ester/ethers of cellulose in concentrated solutions of acidic solvents. The critical concentration for the phase separation of the cellulosic solutions depended on the nature of the substituent, the degree of substitution, and the solvent at a given temperature. Methylcellulose solutions in trifluoroacetic acid and dichloroacetic acid form chiral nematic liquid crystals with a left-handed helicoidal structure. The acetylated methyl cellulose samples did not show the reversal of handedness with increasing acetyl content that was previously observed for the corresponding ethylcellulose samples. © 1994 John Wiley & Sons, Inc. 相似文献
75.
Ron Orlando Catherine Fenselau Robert J. Cotter 《Journal of the American Society for Mass Spectrometry》1991,2(3):189-197
Endothermic ion-molecule reactions in a tandem mass spectrometer have been used for a number of years for determining thermodynamic quantities, such as heats of formation and proton affinities, for gaseous ions. Recently, the reactive, endothermic collision has been exploited as an analytical technique for the structural analysis of peptides and other biomolecules. The technique is based upon the endothermic transfer of protons associated with amide bonds to ammonia. This reaction proceeds via a long-lived collision complex. When additional beam energy is supplied, other dissociation channels are opened up, leading to the production of sequence ions for the mass-selected, protonated analyte that are normally observed in high energy collision-induced dissociation spectra. The advantage, however, is that such spectra can be produced at very low beam energies. In this article, the rationale for developing this scheme, and its roots in previous ion-molecule studies, are explored. 相似文献
76.
Fulton R Jensen T Johnson DR Kagan H Kass R Morrow F Whitmore J Wilson P Bortoletto D Chen W Dominick J McIlwain RL Miller DH Ng CR Schaffner SF Shibata EI Shipsey IP Yao W Battle M Sparks K Thorndike EH Wang C Alam MS Kim IJ Li WC Romero V Sun CR Wang P Zoeller MM Goldberg M Haupt T Horwitz N Jain V Mestayer MD Moneti GC Rozen Y Rubin P Sharma V Skwarnicki T Thulasidas M Zhu G Csorna SE Letson T Alexander J Artuso M Bebek C Berkelman K Browder T Cassel DG Cheu E Coffman DM Crawford G DeWire JW 《Physical review D: Particles and fields》1991,43(3):651-663
77.
The approximation order provided by a directed set {S
h
}
h>0 of spaces, each spanned by thehZ
d
-translates of one function, is analyzed. The nearoptimal approximants of [R2] from eachs
h
to the exponential functions are used to establish upper bounds on the approximation order. These approximants are also used on the Fourier transform domain to yield approximations for other smooth functions, and thereby provide lower bounds on the approximation order. As a special case, the classical Strang-Fix conditions are extended to bounded summable generating functions.The second part of the paper consists of a detailed account of various applications of these general results to spline and radial function theory. Emphasis is given to the case when the scale {s
h
} is obtained froms
1 by means other than dilation. This includes the derivation of spectral approximation orders associated with smooth positive definite generating functions. 相似文献
78.
79.
Straub PB Jaffe DE Glass HD Adams MR Brown CN Charpak G Cooper WE Crittenden JA Finley DA Gray R Hemmi Y Hsiung YB Hubbard JR Jonckheere AM Jöstlein H Kaplan DM Lederman LM Luk KB Maki A Mangeot P McCarthy RL Miyake K Plaag RE Rutherfoord JP Sakai Y Santiard JC Sauli F Smith SR Yoshida T Young KK 《Physical review letters》1992,68(4):452-455
80.
Amber L. H. Gray Aleksandra Antevska Benjamin A. Link Bryan Bogin Susan J. Burke Samuel D. Dupuy J. Jason Collier Zachary A. Levine Michael D. Karlstad Thanh D. Do 《Chemical science》2021,12(16):5853
Despite being relatively benign and not an indicative signature of toxicity, fibril formation and fibrillar structures continue to be key factors in assessing the structure–function relationship in protein aggregation diseases. The inability to capture molecular cross-talk among key players at the tissue level before fibril formation greatly accounts for the missing link toward the development of an efficacious therapeutic intervention for Type II diabetes mellitus (T2DM). We show that human α-calcitonin gene-related peptide (α-CGRP) remodeled amylin fibrillization. Furthermore, while CGRP and/or amylin monomers reduce the secretion of both mouse Ins1 and Ins2 proteins, CGRP oligomers have a reverse effect on Ins1. Genetically reduced Ins2, the orthologous version of human insulin, has been shown to enhance insulin sensitivity and extend the life-span in old female mice. Beyond the mechanistic insights, our data suggest that CGRP regulates insulin secretion and lowers the risk of T2DM. Our result rationalizes how migraine might be protective against T2DM. We envision the new paradigm of CGRP : amylin interactions as a pivotal aspect for T2DM diagnostics and therapeutics. Maintaining a low level of amylin while increasing the level of CGRP could become a viable approach toward T2DM prevention and treatment.CGRP concentration is elevated in migraine conditions. The protective effect of migraine against type 2 diabetes is attributed to the ability of CGRP to remodel human amylin aggregation and to suppress the secretion of mouse insulin 2 (the orthologue of human insulin). 相似文献