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Least Stable (least + stable)
Selected AbstractsAb initio conformational study of the P6 potential surface: Evidence for a low-lying one-electron-bonded isomerHETEROATOM CHEMISTRY, Issue 2 2007Philippe C. Hiberty The low-lying isomers of the P6 species are investigated at various levels of calculations, ranging from MP2/6-31G(d) to CCSD(T) in triple-zeta basis set involving polarization functions up to f. In addition to the five possible normal-valent isomers, which obey the octet rules, several other conformations are found to be stationary points on the potential energy surface. Among the five normal-valent isomers, the benzvalene structure is found to be the most stable one, in agreement with former studies. The benzene-like D6h planar hexagon is the least stable one, lying 32.3 kcal/mol over benzvalene, and spontaneously distorts to a less symmetrical, nonplanar six-membered ring. Above the benzvalene structure, and lying, respectively, 5.8 and 15.8 kcal/mol higher, the two lowest lying isomers are the prismane and the chair-like forms. This latter conformation, which does not obey the octet rule, exhibits two one-electron PP hemibonds and can be considered as a generic model for a new category of heterobenzene analogs, among which is the recently discovered dimer of diphosphirenyl radical. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:129,134, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20324 [source] TEXTURE STABILITY OF HYDROGEL COMPLEX CONTAINING CURDLAN GUM OVER MULTIPLE FREEZE,THAW CYCLESJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2009PATRICK D. WILLIAMS ABSTRACT The texture stability of hydrogel complexes containing curdlan gum over multiple freeze,thaw cycles (FTCs) was investigated. The hydrogels formed by curdlan and xanthan gum, locust bean gum, carrageenan or guar gum at various combinations were stored at 4C for 24 h before subjected to five FTCs alternating between,16 (18 h) and 25C (6 h). Xanthan/curdlan hydrogels showed the highest freeze,thaw stability in terms of syneresis, heat stability and adhesiveness. The viscosity of xanthan/curdlan combination was the lowest among all samples studied yet the most stable over the five FTCs, whereas significant changes were observed with locust bean/curdlan hydrogels. The guar/curdlan combination before freeze,thaw treatments exhibited predominant elasticity; however, as the cycles progressed the elasticity decreased. The most stable gel strength was achieved when curdlan was combined with guar or xanthan at 2% (w/v) total concentration, while carrageenan/curdlan gels were the least stable. PRACTICAL APPLICATIONS Texture instability remains the most significant challenge for frozen food products, especially with inevitable post-production temperature fluctuations. Loss of moisture and changes in textural attributes often results in significant reduction of product quality. Precise control of hydrogel complexes that provide texture stabilization over multiple freeze,thaw cycles will enhance the quality of existing products while enabling the development of new ones. [source] Composition and Oxidative Stability of a Structured Lipid from Amaranth Oil in a Milk-Based Infant FormulaJOURNAL OF FOOD SCIENCE, Issue 2 2010Ashanty M. Pina-Rodriguez ABSTRACT:, Amaranth oil can be enzymatically modified to match breast milk fat analog requirements. We have developed a structured lipid (SL) from amaranth oil that, in combination with milk fat, delivers recommended amounts of docosahexaenoic acid (DHA) with palmitic acid specifically esterified at the,sn- 2 position of the triacylglycerol (TAG) backbone. The aim of this study was to study the final fatty acid (FA) contribution and oxidation stability of an infant formula prepared using the structured lipid DCAO (DHA-containing customized amaranth oil). DCAO was included as complementary fat in a "prototype" infant formula, and prepared in parallel with a "control" infant formula under the same processing conditions. The same ingredients but different complementary fat sources were used. A blend of the most commonly used vegetable oils (palm olein, soybean, coconut, and high-oleic sunflower oils) for infant formula was used instead of DCAO in the "control" formula. Additionally, "prototype" and "control" infant formulas were compared to a "commercial" product in terms of FA composition. The oxidative stability index (OSI) of the extracted fats from "prototype,""control," and "commercial" infant formulas were evaluated and compared to the OSI of the substrate fat replacers used. DCAO was the least stable compared to other fat analogs. The use of commercial antioxidants in DCAO containing products should prevent oxidation and therefore increase their stability. [source] Evolving patterns of tobacco use in northern SwedenJOURNAL OF INTERNAL MEDICINE, Issue 6 2003B. Rodu Abstract., Rodu B, Stegmayr B, Nasic S, Cole P, Asplund K (University of Alabama at Birmingham, Birmingham, AL, USA; Umeå Hospital, Umeå, Sweden). Evolving patterns of tobacco use in northern Sweden. J Intern Med 2003; 253: 660,665. Background and objectives., Cross-sectional data from northern Sweden suggest that the increased use of Swedish moist snuff (snus) may have contributed to a decline in the prevalence of smoking, especially amongst men. This study describes the evolving patterns of tobacco use in this population over the period 1986,1999. Design., This is a prospective follow-up study of 1651 men and 1756 women, aged 25,64 years, who were enrolled in the northern Sweden MONICA project (entry in 1986, 1990, 1994) and who were followed-up in 1999. Information on tobacco use at entry and at follow-up was used to describe the stability of tobacco use over a period of 5,13 years ending in 1999. Results., Snus was the most stable form of tobacco use amongst men (75%); only 2% of users switched to cigarettes and 20% quit tobacco altogether. Smoking was less stable (54%); 27% of smokers were tobacco-free and 12% used snus at follow-up. Combined use (smoking and snus) was the least stable (39%), as 43% switched to snus and 6% switched to cigarettes. Former users of both products were much less stable than former users of either cigarettes or snus. The stability of smoking amongst women was 69%, which was higher than that amongst men (P < 0.05). Conclusions., The use of snus played a major role in the decline of smoking rates amongst men in northern Sweden. The evolution from smoking to snus use occurred in the absence of a specific public health policy encouraging such a transition and probably resulted from historical and societal influences. [source] ORDOVICIAN,PERMIAN PALAEOGEOGRAPHY OF CENTRAL EURASIA: DEVELOPMENT OF PALAEOZOIC PETROLEUM-BEARING BASINSJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2003V. A. Bykadorov In this paper, we discuss three petroleum-bearing basins of Palaeozoic age in Central Eurasia,the Precaspian, Tarim and Chu-Sarysu Basins. We make use of recently-published palaeogeographic maps of the Central Eurasian region, six of which are presented here (Late Ordovician, Early-Middle Devonian, Late Devonian, Early Carboniferous, Early Permian and Late Permian). The maps illustrate the development through the Palaeozoic of the Palaeoasian and Palaeotethys Oceans; of the East European, Siberian and Tarim cratons; and of the Kazakhstan and other microcontinental blocks. The Kazakhstan block formed during the Late Ordovician and is a collage of Precambrian and Early Palaeozoic microcontinents and island arcs. It is surrounded by collisional foldbelts (Ob-Zaisan, Ural-Tianshan and Junggar-Balkhash) which formed in the Late Carboniferous , Permian. We believe that the formation of a stable Kazakhstan block is not consistent with the existence of the previously-identified "Kipchak arc" within the Palaeoasian ocean, or (as has previously been proposed) with activity on this arc up to the end of the Palaeozoic. The oil and gas potential of the Precaspian, Tarim and Chu-Sarysu Basins depends to a large extent on their tectonic stability during the Palaeozoic and subsequent time. The Precaspian Basin has been stable since the Cadomian orogeny (Early Cambrian) and is known to have major hydrocarbon potential. The Tarim Basin (NW China) has somewhat lower potential because the margins of the Tarim continental block have been affected by a series of collisional events; that margin with the Palaeotethys Ocean, for example, was active during the Late Palaeozoic. The Chu-Sarysu Basin on the Kazakhstan block is the least stable of the three and contains only minor gas accumulations. [source] Loss of tocopherols and formation of degradation compounds at frying temperatures in oils differing in degree of unsaturation and natural antioxidant contentJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 14 2002Daniel Barrera-Arellano Abstract Samples of oils of different degrees of unsaturation, namely palm olein, olive oil, high-linoleic sunflower oil, high-oleic sunflower oil, rapeseed oil and soybean oil, were heated at 180,°C for 2, 4, 6, 8 and 10,h in the presence or absence of their natural antioxidants. Also, tocopherol-stripped oils were supplemented with ,-tocopherol (500,mg,kg,1), ,-tocopherol (500,mg,kg,1) or a mixture of ,-, ,-, ,- and ,-tocopherols (250,mg,kg,1 each) and heated under the same conditions. Losses of tocopherols and formation of polymeric triacylglycerols were followed. Total polar compounds were also evaluated after 10,h of heating. Results demonstrated that tocopherols were lost very rapidly, in the expected order, with ,-tocopherol being the least stable. Polymeric and polar compound formation during heating was inhibited to a variable extent, being more dependent on the natural content and type of tocopherols than on the degree of unsaturation of the oil. For example, polymeric and polar compound contents in soybean oil were significantly lower than those found in high-linoleic sunflower oil. However, the expected influence of the degree of unsaturation was evident when oils were unprotected or possessed identical initial antioxidant contents. Finally, levels of degradation compounds after 10,h of heating were not dependent on the remaining content of antioxidants. © 2002 Society of Chemical Industry [source] Effects of Drug Hydrophobicity on Liposomal StabilityCHEMICAL BIOLOGY & DRUG DESIGN, Issue 1 2008David R. Khan A major obstacle in drug delivery is the inability to effectively deliver drugs to their intended biological target without deleterious side-effects. Delivery vehicles such as liposomes can minimize toxic side-effects by shielding the drug from reaction with unintended targets while in systemic circulation. Liposomes have the ability to accommodate both hydrophilic and hydrophobic drugs, either in the internal aqueous core or the lipid bilayer, respectively. In the present study, fluorescein and rhodamine have been used to model hydrophilic and hydrophobic drugs, respectively. We have compared the stabilities of liposomes encapsulating these fluorophores as a function of lipid content, time, and temperature. At 25 and 37 °C, liposomes containing distearoyl phosphatidylcholine as the major phospholipid component were found to be more stable over time than those containing dipalmitoyl phosphatidylcholine, regardless of the fluorophore encapsulated. Liposomes loaded with fluorescein were found to be more stable than those with rhodamine. Dipalmitoyl phosphatidylcholine liposomes that encapsulated rhodamine were the least stable. The results indicate that the physical properties of the drug cargo play a role in the stability, and hence drug delivery kinetics, of liposomal delivery systems, and desired drug release times can be achieved by adjusting/fine-tuning the lipid compositions. [source] | ||||||||||