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71.
Santini Jr Richards AC Scheidt R Cima MJ Langer R 《Angewandte Chemie (International ed. in English)》2000,39(14):2396-2407
Controlled-release systems are common in a number of product areas, including foods, cosmetics, pesticides, and paper. Microencapsulated systems, for example, are used for the release of flavors and vitamins in foods, fragrances in perfumes, and inks in carbonless copy paper. Controlled-release systems for drug delivery first appeared in the 1960s and 1970s. In the past three decades, the number and variety of controlled release systems for drug-delivery applications has increased dramatically. Many of these use polymers having particular physical or chemical characteristics such as biodegradability, biocompatibility, or responsiveness to pH or temperature changes. However, recent advances in the field of microfabrication have created the possibility of a new class of controlled-release systems for drug delivery, namely, that of small, programmable devices. Their small size, potential for integration with microelectronics, and ability to store and release chemicals on demand could make controlled-release microchips useful in a number of areas, including medical diagnostics, analytical chemistry, chemical detection, industrial process monitoring and control, combinatorial chemistry, microbiology, and fragrance delivery. More importantly, drug-delivery microchips resulting from this convergence of controlled release and microfabrication technologies may provide new treatment options to clinicians in their fight against disease. 相似文献
72.
P. G. Mendoza Jr D. D. Jackson T. M. Niemczyk 《Journal of Radioanalytical and Nuclear Chemistry》1990,141(2):357-371
The uranium spectrophotometric measurement using the uranylnitrate-quaternaryamine solvent extraction method is investigated to identify factors that affect precision and accuracy of the uranium determination. The inherent spectrophotometric precision was measured with neutral density filters in the sample light path and was found to be <0.1% relative standard deviation (RSD). Under selected experimental conditions, temperature instability has a –0.02% effect on the extraction, and a –0.4% effect on the absorbance of the uranium extract in 2-nitropropane (2-NP) or methyl isobutyl ketone (MIBK) solvents. Under optimum conditions at the 10 mg uranium level, RSDs of 0.1% resulted. 相似文献
73.
An ab initio molecular orbital study, using a Gaussian basis set, of the geometries of Li2O2 and LiO2H is presented. Consistent with the experimental data available, Li2O2 is found to have a rhombic structure; the O-Li-O configuration in LiO2H is found to form an acute triangle. The bonding in these species is discussed to terms of Mulliken population analyses. 相似文献
74.
Three theories which have been proposed to explain the observed shortening of a single bond when it is adjacent to a double bond are discussed. Possible predictions from these theories are examined, especially for comparison with various quantities measurable by microwave spectroscopy. It is concluded that the steric theory is probably untenable, that some conjugation appears necessary to explain observed barries to internal rotation, and that it is difficult to find testable predictions from the hybridization theory. 相似文献
75.
C. P. Boyer E. G. Kalnins Willard Miller Jr. 《Communications in Mathematical Physics》1978,59(3):285-302
We present a complete list of all separable coordinate systems for the equations
and
with special emphasis on nonorthogonal coordinates. Applications to general relativity theory are indicated. 相似文献
76.
Thermal studies have been carried out on trans-[Co(NH3)4Cl2]X · YH2O complexes (whereX=IO3, BrO3, NO3, or NO2 andY=0, 1, or 2) in an effort to find cases of trans to cis isomerization as occurs for the iodate. No evidence of isomerization was found for any of the other compounds. The complexes decompose in a series of steps and these reactions have been identified and kinetic parameters determined. 相似文献
77.
The wavefunctions and various partitions of the energy are examined for a variety of small molecules (H2, H3, H4, HeH, HeH2, He2, LiH, and BH) in order to isolate the factors crucial for bond formation. We find that a natural partition of the energy leads to the conclusion that the crucial factor is the exchange, or nonclassical, part of the kinetic energy, T
x. The change in T
xupon pushing the atoms towards one another is the dominant term in the binding energy; it is negative when the resulting molecule is stable and positive when it is unstable. We show that T
x is related to the interference kinetic energy considered by Ruedenberg.
Partially supported by a grant (GP-15423) from the National Science Foundation. This paper is based on a portion of the PhD thesis (California Institute of Technology, 1970) by CWW.
National Science Foundation Predoctoral Trainee.
Alfred P. Sloan Foundation Research Fellow.
Contribution No. 3917. 相似文献
Zusammenfassung Die Wellenfunktionen und verschiedene Zerlegungen der Energie werden für eine Reihe kleiner Moleküle untersucht (H2, H3, H4, HeH, HeH2, He2, LiH und BH), um die Faktoren zu finden, die für die Bindungsbildung ausschlaggebend sind. Die natürliche Zerlegung der Energie läßt die Folgerung zu, daß der bestimmende Faktor der Austauschanteil T x(oder nichtklassische Anteil) der kinetischen Energie ist. Die Änderung von T xbeim Zusammenführen der Atome ist der dominierende Term für die Bindungsenergie; er ist negativ, wenn das resultierende Molekül stabil ist, und positiv, falls es instabil ist. Es wird gezeigt, daß T x im Zusammenhang zum Wechselwirkungsanteil der kinetischen Energie nach Ruedenberg steht.
Partially supported by a grant (GP-15423) from the National Science Foundation. This paper is based on a portion of the PhD thesis (California Institute of Technology, 1970) by CWW.
National Science Foundation Predoctoral Trainee.
Alfred P. Sloan Foundation Research Fellow.
Contribution No. 3917. 相似文献
78.
Marcelo O. Santiago Alzir A. Batista Marcio P. de Araújo Claudio L. Donnici Icaro de S. Moreira Eduardo E. Castellano Javier Ellena Sauli dos Santos Jr Salete L. Queiroz 《Transition Metal Chemistry》2005,30(2):170-175
A series of cis-{RuCl2(PPh3)2[4,4-(X)2-2,2-bipy]} [cis-chlorines; X=-H, -Me, -SMe, and (-Cl,-Me)] complexes have had their structures determined by single crystal X-ray diffraction. The geometry of these complexes, also determined in CH2Cl2 solution by 31P{1H}-n.m.r. spectroscopy, showed that the chemical shifts for the phosphorus atoms are slightly dependent on the pKa of the 4,4-(-X)2-2,2-bipy ligands. 相似文献
79.
Kathleen V Kilway Keith A Lindgren James A Watson Jr. Robert D Ingalls Robert A Pascal Jr. 《Tetrahedron》2004,60(10):2433-2438
Oxygenation of 2,5,9,12-tetra(tert-butyl)diacenaphtho[1,2-b:1′,2′-d]-thiophene (1, C40H44S) by peracids gave the cyclic sulfonic ester 4 (2,7,10,13-tetra(tert-butyl)diacenaphtho[1,2-c:1′,2′-e]oxathiin 5,5-dioxide, C40H44O3S) which, when heated in nitrobenzene, is converted into a complex, macrocyclic anhydride 3 (C80H88O3), which is derived from two molecules of 4. Further investigation found a likely intermediate in this reaction, 4,4′,7,7′-tetra(tert-butyl)-1,1′-biacenaphthylenylidene-2,2′-dione (5, C40H44O2), apparently formed from 4 by additional oxidation. Anhydride 3 plausibly arises by Diels-Alder reaction of 4 and 5 followed by several ring fragmentations. The structures of 3, 4, and 5 were unambiguously established by X-ray crystallography. 相似文献
80.
Rafael Fogel Rafaela Rodrigues Garcia Rebeca da Silva Oliveira Denise Neves Menchero Palacio Luciana da Silva Madeira Nei Pereira Jr. 《Applied biochemistry and biotechnology》2005,122(1-3):741-752
The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates
containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t
C) to 75 h (without nitrogen source addition t
C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions,
resulted in enhanced conversion rates, reducing t
C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation. 相似文献