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1.
Vinyl and diene derivatives of thiolactomycin have been prepared via Horner-Wadsworth-Emmons olefination from protected 5-formyl-3,5-dimethylthiotetronic acid. Several 4-position protecting groups and a variety of phosphonates were evaluated, with MOM protection and β-ketophosphonates yielding the highest ratio of the desired product to deformylated product. 相似文献
2.
Nicolò Giovannelli Giuseppe Rao Calogero Vetro 《Rendiconti del Circolo Matematico di Palermo》2005,54(3):443-450
In this paper we consider a definition of essentialK-variation for real functions which gives information on the absolute integrability of its approximate derivate on a measurable
set. 相似文献
3.
Cynthia J. Burrows Richard A. Sauter 《Journal of inclusion phenomena and macrocyclic chemistry》1987,5(1):117-121
New synthetic hosts have been designed incorporating two molecules of cholic acid linked by a rigid diamine. Proton NMR studies indicate that the compounds exist in a rigid conformation with the steroid hydroxyl groups intramolecularly hydrogen-bonded. Heat or addition of methanol leads to conformational isomerism due to insertion of methanol into the cavity.A preliminary report of this work was presented at the 4th International Symposium on Inclusion Phenomena, July 20–25, 1986, Lancaster, U.K. 相似文献
4.
5.
Nicolás Andruskiewitsch 《Selecta Mathematica, New Series》2005,11(2):203-246
Quivers over a fixed base set form a monoidal category with tensor product given by pullback. The quantum Yang–Baxter equation,
or more properly the braid equation, is investigated in this setting. A solution of the braid equation in this category is
called a “solution” for short. Results of Etingof–Schedler–Soloviev, Lu–Yan–Zhu and Takeuchi on the set-theoretical quantum
Yang–Baxter equation are generalized to the context of quivers, with groupoids playing the role of groups. The notion of “braided
groupoid” is introduced. Braided groupoids are solutions and are characterized in terms of bijective 1-cocycles. The structure
groupoid of a non-degenerate solution is defined; it is shown that it is a braided groupoid. The reduced structure groupoid
of a non-degenerate solution is also defined. Non-degenerate solutions are classified in terms of representations of matched
pairs of groupoids. By linearization we construct star-triangular face models and realize them as modules over quasitriangular
quantum groupoids introduced in papers by M. Aguiar, S. Natale and the author. 相似文献
6.
Angle-resolved low-energy ion scattering is a valuable technique for examining the topmost surface layers of materials. Using this technique, information about both composition and structure can be obtained. We discuss the physical basis of this technique and present our findings for the fivefold surface of icosahedral (i-) Al–Pd–Mn. Our results clearly show that the exposed surface has a higher Al content than the bulk and can have fivefold periodicity. Information about frequently occurring interatomic distances on the surface can also be obtained by this technique. We discuss the results and compare them to recent scanning tunneling microscopy studies and to bulk structure models. 相似文献
7.
The rhetoric surrounding integration of mathematics and science abounds. Professional organizations’ standards and recommendations for reform in mathematics and science education each point out the need to make connections among various disciplines. However, some remain unconvinced, citing a lack of research supporting the assertion that integration improves student achievement. This article examines the current situation, discusses the growing body of related research, and examines the implementation issues related to integrated curriculum projects. The conclusion calls for mathematics and science educators to work collaboratively to address implementation issues surrounding reform of any kind and to explore further the possibilities of integration. 相似文献
8.
Cynthia Kolb Whitney 《Foundations of Physics》2007,37(4-5):788-812
This paper revisits the historical sequence in which some of the major developments of 20th-century physics occurred, and
explores how theories could have turned out differently, if the sequence of developments had been different. It shows how
a delay in founding special relativity theory until after (1) at least one puzzling problem in electromagnetic theory could
be acknowledged, and (2) sat least some of the experimental observations pertinent to the development of quantum mechanics
had become well known, could have resulted in a larger theory that covers both domains in a manner quite different from that
of any of the theories we use today. The revised theory dispenses with a separate postulate introducing Planck’s constant
h, identifying instead a physical mechanism that implies the constant. Some important aspects of quantum chemistry then follow.
Editor, Galilean Electrodynamics, Proceedings of the Natural Philosophy Alliance; Visiting Industry Professor, Tufts University,
retired 相似文献
9.
Cynthia M. Allen Joseph M. Weber Johan E. van Lier 《Photochemistry and photobiology》1995,62(1):184-189
Abstract— Transmission of infectious diseases through blood transfusions is well known. Ultraviolet irradiation, solvents and detergents provide a means of sterilizing noncellular blood components. However these harsh methods are not applicable to cellular blood products. Recently, attempts have been made to sterilize biological fluids using photodynamic treatment and phthalocyanine (Pc) dyes have been advanced as photosensitizers for this purpose. We have evaluated a series of water-soluble Pc, chelated with different central metal ions, substituted to different degrees with sulfonato and r-butyl groups, for their effectiveness to reduce virus infectivity in red blood cell suspensions. Vaccinia virus cytopathogenicity was determined by endpoint serial dilutions in the CV-1 cell line. Anti-viral activity increased with the central metal ion in the following order: Ga(III) < Al(III) < Zn(II), and varied inversely with the degree of sulfonation. Furthermore, addition of a t -butyl group onto the trisulfonated dyes (PcS3 [ t -Bul) resulted in a 5–40-fold increase in anti-viral potency, suggesting that amphiphilicity enhances the photodynamic activity of the dye. Strong anti-viral photosensitizing properties cannot be the sole selection criterion. Of equal importance is the preservation of blood component integrity. Accordingly, the photohemolytic activity of the dyes was evaluated using the rate of hemolysis as a parameter and a toxicity index was defined. Among the most active dyes, the AlPcS3 ( t -Bu) complex exhibited the most favorable anti-viral properties combined with a low toxicity index. Our results suggest that trisulfophthalocyanines, bearing an additional t -butyl group to enhance amphiphilicity, are particularly promising dyes for photodynamic blood sterilization. 相似文献
10.
Paul Jara Montserrat Justiniani Nicolás Yutronic Isabel Sobrados 《Journal of inclusion phenomena and macrocyclic chemistry》1998,32(1):1-8
We report the syntheses and structural aspects of cyclodextrin host–guest inclusion compounds containing linear secondary alkylamines (dipropyl, dibutyl, dipentyl, dihexyl, and dioctyl) at 25 °C. Elemental analysis, 13C CP-MAS NMR spectroscopy, and powder X-ray diffraction analysis confirm the inclusion process. The basic host structure of the products is similar to that of typical cyclodextrin inclusion systems. 13C MAS NMR experiments show a different resonance pattern for the confined guest molecules with respect to the amine in the liquid phase. The presence of different resonance signals for the homologous carbon atoms of both dialkylamine branches is evidence for the non-symmetric location of the amine in the cyclodextrin channels. 相似文献