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81.
Mohammad A. Khadim Lawrence D. Colebrook Laurance D. Hall 《Journal of heterocyclic chemistry》1980,17(4):651-656
Proton spin-lattice relaxation rates (R1 values) have been measured, at 270 MHz, for a series of N-aryl isoindolinones. A normalization procedure has been used to enable comparison of R1 values in different compounds by minimizing the effects on relaxation rates of changes in motional correlation times accompanying changes in substitution patterns. A substantial (4.3-fold) dynamic range of R1 values has been observed, and individual values have been correlated with the molecular environments of the nuclei. There is evidence for an interring relaxation process. 相似文献
82.
Austen K FlattShawn M Dirk Jay C HendersonDwanleen E Shen Jie SuMark A Reed James M Tour 《Tetrahedron》2003,59(43):8555-8570
Several new classes of oligomers have been synthesized with functionalities designed to aid in the understanding of molecular device behavior, specifically when molecules are interfaced between proximal electronic probes. The compounds synthesized are series of azobenzenes, bipyridines and oligo(phenylene vinylene)s that bear acetyl-protected thiols for ultimate attachment to metallic surfaces. Some initial electrochemical and solid-state test results are also reported. 相似文献
83.
Gas-phase activation energies were calculated for three lithium enolate reactions by using several different ab initio and density functional theory (DFT) methods to determine which levels of theory generate acceptable results. The reactions included an aldol-type addition of an enolate to an aldehyde, a proton transfer from an alcohol to a lithium enolate, and an S(N)2 reaction of an enolate with chloromethane. For each reaction, the calculations were performed for both the monomeric and dimeric forms of the lithium enolate. It was found that transition state geometry optimization with B3LYP followed by single point MP2 calculations generally provided acceptable results compared to higher level ab initio methods. 相似文献
84.
A series of gold(III) cations of the type cis-[CH3)2AuL2]+ X? where L Ph3, PMePh2, PMe2Ph, PMe3, AsPh3, AsPh3, SbPh3, H2NCH2CH2NH2, Ph2PCH2CH2-PPh2, Ph2AsCH2CH2AsPh2, and o-C6H4(AsMe2)2 and X BF4?, PF6?, ClO4?, and F3CSO3? has been prepared. In addition, the cis complexes [(CH3)(CD3)-Au(PPh3)2]F3CSO3, [(C2H5)2Au(PPh3)2]F3CSO and [(n-C4H9)2Au(PPh3)2]F3-CSO3 have been synthesized. All have been characterized by PMR, Raman and infrared spectroscopy. These [R2AuL2]X compounds yield only ethane, butane, or octane via reductive elimination, and no disproportionation is observed. The alkane eliminations have been studied in CHCl3, CH3Cl2, and CH3COCH3 solution as a function of temperature, concentration of the complex, and concentration of added ligand L. Elimination is fastest when L is bulky (PPh3 > PMePh2 > PMe2Ph > PMe3), decreases in the sequence SbPh3 > AsPh3 > PPh3, is slow with chelating ligands, is inhibited by excess ligand, and there is small anion effect as X is varied. As R is varied, the rate of elimination decreases Bu ? Et > Me. An intramolecular dissociative mechanism is proposed which involves rapid elimination of alkane from an electron deficient dialkylgold(III) complex with nonequivalent gold—carbon bonds and produces the corresponding [AuL2]X complex. 相似文献
85.
Abstract— The lowest-lying triplet states of a variety of aromatic molecules and complexes have been generated by the irradiation of these compounds in solvent glasses with plane-polarized light. Measurements of the allowed (Δ M=± 1) ESR transitions clearly demonstrate that the triplets so formed are oriented with respect to the external magnetic field. By this method the triplet zero-field splitting parameters, D and E , can be evaluated simply and reliably. Intramolecular energy transfer is postulated to explain the triplet spectra of Zn( o -phen)2 (NO3 )2 and Zn( o -phen)3 (NO3 )2 . It was observed that in triplet-triplet energy transfer from benzophenone to naphthalene there is no apparent orientation requirement between the donor and acceptor molecules. Further areas of significance and application of this technique are suggested. 相似文献
86.
R. A. Loghry S. Kasina S. H. Simonsen Jay Nematollahi 《Journal of heterocyclic chemistry》1976,13(4):931-932
The structures of two of the three isomeric products of the reactions between cis- and trans-cyclohexanedicarboxylic anhydrides and methylhydrazine were determined by single-crystal X-ray methods to ascertain their tautomeric forms and stereochemistries. One product was found to be cis-N-methylamino-1,2-cyclohexanedicarboximide and the other trans-hexahydro-2-methylcyclohexa[d]pyridazine-1,2-dione. 相似文献
87.
The photophysical properties of CdSe and ZnS(CdSe) semiconductor quantum dots in nonpolar and aqueous solutions were examined with steady-state (absorption and emission) and time-resolved (time-correlated single-photon-counting) spectroscopy. The CdSe structures were prepared from a single CdSe synthesis, a portion of which were ZnS-capped, thus any differences observed in the spectral behavior between the two preparations were due to changes in the molecular shell. Quantum dots in nonpolar solvents were surrounded with a trioctylphosphine oxide (TOPO) coating from the initial synthesis solution. ZnS-capped CdSe were initially brighter than bare uncapped CdSe and had overall faster emission decays. The dynamics did not vary when the solvent was changed from hexane to dichloromethane; however, replacement of the TOPO cap by pyridine affected CdSe but not ZnS(CdSe). CdSe was then solubilized in water with mercapto-acetic acid or dihydrolipoic acid, whereas ZnS(CdSe) could be solubilized only with dihydrolipoic acid. Both solubilization agents quenched the nanocrystal emission, though with CdSe the quenching was nearly complete. Additional quenching of the remaining emission was observed when the redox-active molecule adenine was conjugated to the water-soluble CdSe but was not seen with ZnS(CdSe). The emission of aqueous CdSe could be enhanced under prolonged exposure to room light and resulted in a substantial increase of the emission lifetimes; however, the enhancement occurred concurrently with precipitation of the nanocrystals, which was possibly caused by photocatalytic destruction of the mercaptoacetic acid coating. These results are the first presented on aqueous CdSe quantum dot structures and are presented in the context of designing better, more stable biological probes. 相似文献
88.
To explore tertiary contact formation in alpha-synuclein, a natively unfolded protein implicated in Parkinson's disease, we have measured the rates of reaction between a powerful electron donor, the tryptophan (W) triplet excited state, and an acceptor, 3-nitro-tyrosine (Y(NO2)) in six different variants, probing loop sizes between 15 and 132 residues. Electron transfer rates decrease with loop size with the fastest contact time of 140 ns for the N-terminal pair and the slowest of 1.2 mus for the N- to C-terminal pair. Diffusion coefficients ranging from approximately 2 x 10-6 to approximately 10-5 cm2 s-1 were extracted from simultaneous fits of the W to Y(NO2) electron (triplet excited state) and energy transfer (singlet excited state) kinetics. 相似文献
89.
L. G. Chalmet R. L. Francis J. F. Lawrence 《Journal of Optimization Theory and Applications》1980,32(2):135-149
An example of design might be a warehouse floor (represented by a setS) of areaA, with unspecified shape. Givenm warehouse users, we suppose that useri has a known disutility functionf
isuch thatH
i(S), the integral off
iover the setS (for example, total travel distance), defines the disutility of the designS to useri. For the vectorH(S) with entriesH
i(S), we study the vector minimization problem over the set {H(S) :S a design} and call a design efficient if and only if it solves this problem. Assuming a mild regularity condition, we give necessary and sufficient conditions for a design to be efficient, as well as verifiable conditions for the regularity condition to hold. For the case wheref
iis thel
p-distance from warehouse docki, with 1<p<, a design is efficient if and only if it is essentially the same as a contour set of some Steiner-Weber functionf
=1
f
1++
m
f
m
,when the
i
are nonnegative constants, not all zero.This research was supported in part by the Interuniversity College for PhD Studies in Management Sciences (CIM), Brussels, Belgium; by the Army Research Office, Triangle Park, North Carolina; by a National Academy of Sciences-National Research Council Postdoctorate Associateship; and by the Operations Research Division, National Bureau of Standards, Washington, D.C. The authors would like to thank R. E. Wendell for calling Ref. 16 to their attention. 相似文献
90.
Lawrence E. Thomas 《Communications in Mathematical Physics》1980,77(3):211-218
Let 1 and 2 be thermodynamic Gibbs measures on
m
and
n
, respectively. Diffusions are constructed having 1, and 2 as invariant measures. These diffusions are then coupled; inequalities between expectations of certain random variables on the two spaces result.Partially supported by NSF-MCS 74-07313-A03 相似文献