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91.
92.
E. Rodrigues S. Vaz V.M.S.S. Gil M. Caldeira A.M.G. Moreira Da Silva 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):395-397
A 1H-NMR study of the interactionsbetween -cyclodextrin (-CD) and included phenolic molecules (chloragenic acid and caffeic acid ) in aqueous medium is reported. The results confirm that inclusion occurs. Data analysis by the continuous variation method shows that all the complexes have 1 : 1 stoichiometries. Values for the apparent association constants of the inclusion compounds are estimated and compared with previously reported values. 相似文献
93.
We describe measurements of colloidal transport through arrays of micrometer-scale potential wells created with holographic optical tweezers. Varying the orientation of the trap array relative to the external driving force results in a hierarchy of lock-in transitions analogous to symmetry-selecting processes in a wide variety of systems. Focusing on colloid as a model system provides the first opportunity to observe the microscopic mechanisms of kinetic lock-in transitions and reveals a new class of statistically locked-in states. This particular realization also has immediate applications for continuously fractionating particles, biological cells, and macromolecules. 相似文献
94.
Aida Moreira Da Silva José Empis José J.c. Teixeira-Dias 《Journal of inclusion phenomena and macrocyclic chemistry》1999,33(1):81-97
In aqueous solution, the apparent association constant at room temperature for the 1 : 1 inclusion of S-(+)-carvone in - cyclodextrin is double of that for R-(-)-carvone, whereas, at 45 °C, both enantiomers have association constants two orders of magnitude smaller, with the S-(+) inclusion being then slightly weaker than the R-(-) encapsulation. Calculations carried out at the molecular mechanics, AM1 and STO-3G levels confirm the preferential inclusion of the S-enantiomer and provide important clues for understanding chiral discrimination by -cyclodextrin. 相似文献
95.
Onody RN de Medeiros NG 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3234-3238
We introduce an age-structured asexual population model containing all the relevant features of evolutionary aging theories. Beneficial as well as deleterious mutations, heredity, and arbitrary fecundity are present and managed by natural selection. An exact solution without aging is found. We show that fertility is associated with generalized forms of the Fibonacci sequence, while mutations and natural selection are merged into an integral equation which is solved by Fourier series. Average survival probabilities and Malthusian growth exponents are calculated and indicate that the system may exhibit mutational meltdown. The relevance of the model in the context of fissile reproduction groups like many protozoa and coelenterates is discussed. 相似文献
96.
Fajardo M. Pérez Alcázar G. A. Moreira A. M. Speziali N. L. 《Hyperfine Interactions》2004,158(1-4):395-400
The local environment of implanted 111Ag (t
1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following
the 60 keV low dose (1 × 1013 cm−2) 111Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps,
at temperatures ranging from 200 to 1050°C. The results revealed that 42% of the probes are located at defect-free SZn sites (ν
Q ∼ 32 MHz, η = 0) in the as-implanted state and that this fraction did not significantly change with annealing. Moreover, a progressive
lattice recovery in the near vicinity of the probes was observed. Different EFGs assigned to point defects were furthermore
measured and a general modification of their parameters occurred after 600°C. The 900°C annealing induced the loss of 30%
of the 111Ag atoms, 7% of which were located in regions of high defects concentration. 相似文献
97.
Douglas J. Raber Milton D. Johnston Catherine M. Campbell Christopher M. Janks Pamela Sutton 《Magnetic resonance in chemistry : MRC》1978,11(7):323-328
The use of lanthanide shift reagents (LSR's) to obtain additional structural information from nuclear magnetic resonance studies has gained widespread acceptance. However, there has not been general agreement with regard to the most appropriate methodology for analysis of the shifted NMR spectra. We present arguments that only the bound shifts (Δ1) corresponding to the LS complex should be used for correlation of lanthanide-induced shifts with molecular structure by means of the pseudocontact equation. Several examples are discussed of compounds for which the relative induced shifts are dependent on the concentration of LSR. For such cases it is not possible for both Δ1 and Δ2 (the bound shift corresponding to the LS2 complex) to correlate successfully with the correct structure. Alternative methods of obtaining bound shifts are critically evaluated. 相似文献
98.
99.
Abstract— Near ultraviolet (365 nm) and green-yellow (546-579nm) radiations repress the growth of liquid cell cultures of Ginkgo pollen and of monolayer cultures of HeLa. The deleterious effects of green-yellow wavelengths can be negated by red radiation; near-u.v.-induced growth repressions are insensitive to visible light photorestoration. These wavelengths do not interact synergistically and evoke different kinetics of response. 相似文献
100.
Jordan P Leach J Padgett M Blackburn P Isaacs N Goksör M Hanstorp D Wright A Girkin J Cooper J 《Lab on a chip》2005,5(11):1224-1228
We report the creation of permanent 3D configurations of cells, at predefined positions, within a gelatin matrix. The technique used holographic optical tweezers to manipulate individual E. coli within a solution comprising monomer precursors. The matrix was then set and after the laser beam was removed, we were able to demonstrate that the structures remained intact for many days. We were also able to demonstrate that, in the presence of appropriate nutrients, the E. coli survived within the gelatin matrix for several days. The technique could have a number of potential future applications, including the arrangement of a variety of different cell types in complex architectures, as motifs for promoting tissue differentiation and growth within the field of cell engineering. 相似文献