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Showing papers in "Pure and Applied Chemistry in 1994"


Journal Article•DOI•
TL;DR: In this article, the authors present a tool for the selection and appraisal of the methods of characterization of porous solids, and also give the warnings and guidelines on which the experts generally agree.
Abstract: These recommendations aim to be a tool for the selection and appraisal of the methods of characterization of porous solids, and to also give the warnings and guidelines on which the experts generally agree. For this purpose, they successively consider the description of a porous solid (definitions, terminology), the principal methods available (stereology , radiation scattering, pycnometry, adsorption, intrusion, suction, maximum buble pressure, fluid flow, immersion or adsorption calorimetry, thermoporometry , size exclusion chromatography, Xenon NMR and ultrasonic methods) and finally the general principles which are worth being followed in the selection of the appropriate method.

3,257 citations




Journal Article•DOI•
TL;DR: In this paper, the Commission on Atomic Weights and Isoto- ic Abundances recommended at the 37* General Assembly at Lisbon, Portugal that (i) 'H/H relative ratios of all substances be expressed relative to VSMOW (Vienna Standard Mean Ocean Water) on a scale such that 2H/'H of SLAP (Standard Light Antarctic Precipitation) is 0.572 times that of VPMW, (ii) 13C/'2C relative ratios for all substances was expressed relative with VPDB on a level such that
Abstract: To eliminate possible confusion in the reporting of isotopic abundances on noncorresponding scales, the Commission on Atomic Weights and Isoto ic Abundances recommended at the 37* General Assembly at Lisbon, Portugal that (i) 'H/ H relative ratios of all substances be expressed relative to VSMOW (Vienna Standard Mean Ocean Water) on a scale such that 2H/'H of SLAP (Standard Light Antarctic Precipitation) is 0.572 times that of VSMOW, (ii) 13C/'2C relative ratios of all substances be expressed relative to VPDB (Vienna Peedee belemnite) on a scale such that 13C/12C of NBS 19 carbonate is 1.00195 times that of VPDB, and (iii) l8O/l6O ratios of all substances be expressed relative to either VSMOW or VPDB on scales such that 180/160 of SLAP is 0.9445 times that of VSMOW. P COMMENT Abundances of stable hydrogen, carbon, and oxygen isotopes in geochemical and environmental studies are generally expressed in parts per thousand (k or per mil) difference from a standard. Thus, for the oxygen isotopic composition of a sample x , we have r 1 The standard may be an actual reference material or a hypothetical material whose isotopic abundance is set by assigning an isotopic composition to an existing reference material. Irregularities concerning the choice of the standard have arisen for hydrogen, carbon, and oxygen isotopes (refs. 1 & 2). Friedman and O'Neil (ref. 1) point out that some laboratories are \"tied\" to each other by acceptance of the 6 values of certain comparison materials. The situation for the SMOW (Standard Mean Ocean Water) standard has become increasingly aggravated. The SMOW standard was originally a hypothetical water sample with abundances of stable hydrogen and oxygen isotopes similar to those of average ocean water (ref. 3). Its abundances of stable hydrogen and oxygen isotopes were defined in terms of NBS 1 water distributed by the U.S. National Bureau of Standards (now National Institute of Standards and Technology): ( 2H/'H) SMOw 1.050( 2W1H) ms 1 and ( l80/l6O) SMOW = l.O08( 180/'60)ms Subsequently, H. Taylor and S. Epstein of the California Institute of Technology used a hypothetical standard that they also called SMOW and defined it by assigning a 6 l 8 0 value of +15.5% to their laboratory reference material, a sample of Potsdam Sandstone (ref. 1). Thus, their oxygen isotope scale is defined by 18 oPotsdam SandstonelSMOW = +15*5%* Ym = parts per thousand 274 Stable hydrogen, carbon, and oxygen isotopic abundances 275 Additionally, the International Atomic Energy Agency (IAEA) distributed a water sample they named SMOW. This sample was near (but not the same) in isotopic composition to the original SMOW defined in terms of NBS 1 water. Thus, there are three independent usages of SMOW that we observe today, leading to three differing 2W1H and l80/l6O abundances with the same name. The IAEA recognized the dilemma of naming a reference water as SMOW and subsequently changed the name to VSMOW (Vienna Standard Mean Ocean Water). Furthermore, they recommended that abundances of hydrogen and oxygen isotopes of all materials (except marine carbonates) be expressed using VSMOW rather than SMOW (refs. 2, 4 & 5). However, these recommendations have not received wide distribution and may be unknown to numerous producers of data on abundances of oxygen and stable hydrogen isotopes, particularly in the rapidly expanding fields of environmental and climate studies. A second standard is used for reporting abundances of oxygen isotopes of marine carbonates and is named PDB (Peedee belemnite). Because the su ply of this material is exhausted, some laboratories have \"tied\" themselves to each other by adopting 6l 0 values of various carbonate reference materials. The IAEA recognized the potentially serious problem that oxygen isotopic scales in different laboratories might not correspond. They recommended that abundances of oxy en isotopes of carbonates be expressed relative to VPDB (Vienna Peedee belemnite) by adopting a 6 0 consensus value of -2.2% for NBS 19 carbonate relative to VPDB at a meeting in 1983 in Vienna (ref. 2). Thus, P

674 citations



Journal Article•DOI•
TL;DR: In this paper, the palladium-catalyzed cross-coupling reaction of 1-alkenylboron compounds with various vinylic or aryl halides in the presence of base provides the corresponding coupling products.
Abstract: It was previously reported that the palladium-catalyzed cross-coupling reaction of 1-alkenylboron compounds with various vinylic or aryl halides in the presence of base provides the corresponding coupling products in high yields, stereoand regioselectively. The recent progress of such reactions, including the reaction of sterically hindered arylboronic acids with sterically hindered haloarenes, the palladium-catalyzed carbonylative cross-coupling to provide a versatile ketone synthesis, the synthesis of functionalized organotin compounds, the stereoselective synthesis of exocyclic alkenes, and the syntheses of allylic and benzylic boronates, is described. INTRODUCTION The cross-coupling reactions of various organoboranes with a number of organic halides in the presence of a catalytic amount of palladium complexes and bases were reported to give versatile and useful synthetic methods for conjugated alkadienes and alkenynes, arylated alkenes, 1.4-alkadienes, allylic benzenes, a$-unsaturated carboxylic acids, and 2,4-alkadienoates (ref. 1). Thereafter, a modified method for the synthesis of conjugated alkadienes, syntheses of stereodefined trisubstituted alkenes, benzo-fused heteroaromatic compounds, and a,&unsaturated ketones were presented (ref. 2). Although the palladium-catalyzed cross-coupling reactions of 1-alkenyland arylboranes with organic halides proceed readily and stereoand regioselectively to give expected coupling products in high yields, organoboranes with alkyl groups on boron were not used successfully for the coupling under similar conditions. Recently, it was found that the reaction between 9-alkyl-9-BBN derivatives and l-halo-lalkenes or haloarenes in the presence of dichloror l,l'-bis(diphenylphosphino)ferrocene]palladium(II) and base, such as sodium hydroxide, potassium carbonate, and phosphate gives the corresponding alkenes or arenes in excellent yields (ref. 2). By using the reaction, cycloalkenes, benzo-fused cycloalkenes, and exccyclic alkenes are readily synthesized (ref. 2). The palladium-catalyzed coupling reactions of 1-alkenyl-, aryl-, and alkylboron compounds with aryl or 1-alkenyl triflates, instead of organic halides, take place with ease to give expected coupling products in high yields under mild conditions (ref. 2). Most recently, we have found new synthetic methods related to the palladium-catalyzed cross-coupling reactions of organoborane derivatives, which are described in this review. CARBONYLATIVE CROSS-COUPLING OF 9-ALKYL-9-BBN DERIVATIVES WITH 1-HALO-1-ALKENES (ref. 3) AND IODOALKANES (ref. 4) Carbonylative cross-coupling of organometallic compounds with organic halides are reported to give a method for the synthesis of ketones. Among a variety of organometallic reagents, a method using organoboron compounds was first examined by Kojima and his coworkers (ref. 5 ) for the synthesis of 213

276 citations


Journal Article•DOI•
TL;DR: The biological properties of carotenoids can be divided into functions, which are essential to the well-being of organisms, and actions or associations,Which are either responses to the administration of carOTenoids, or are phenomena which still lack evidence of a causal relationship to the presence of the substance.
Abstract: The biological properties of carotenoids can be divided into functions, which are essential to the well-being of organisms, and actions or associations, which are either responses to the administration of carotenoids, or are phenomena which still lack evidence of a causal relationship to the presence of carotenoids. Regardless of the strength of the evidence for these various biological properties, there must be either a physical or chemical basis that will serve to explain these phenomena. Many of the reported effects still require further investigations to help us understand the relationship between chemical properties and biological activity.

258 citations




Journal Article•DOI•
TL;DR: In this paper, the synthesis of organosilicon compounds with fluoride ion produces a transient pentacoordinate silicate, which is capable of transmetalation with a catalytic organopalladium complex and achieves cross-coupling reaction.
Abstract: Activation of organosilicon compounds with fluoride ion produces a transient pentacoordinate silicate, which is capable of transmetalation with a catalytic organopalladium complex and achieves cross-coupling reaction. Mono-, di- or trifluorosilanes can deliver alkenyl, aryl, or alkyl group, respectively. The reaction, characterized by high chemo- and stereoselectivity, was successfully applied to synthesis of HMG-CoA reductase inhibitor NK-104 and functionalized biaryls for liquid crystals. The stereochemical aspects are discussed.

229 citations


Journal Article•DOI•
TL;DR: Diamond-like carbon (DLC) is a dense, partially sp3 bonded form of amorphous carbon prepared by ion beam or plasma deposition and frequently used as a hard coating material as discussed by the authors.
Abstract: Diamond-like carbon (DLC) is a dense, partially sp3 bonded form of amorphous carbon prepared by ion beam or plasma deposition and frequently used as a hard coating material. Its sp3 bonding arises from C+ ions penetrating surface layers and giving a quenched-in density increase. The formation of DLC can be viewed as a phase transition to a denser metastable phase. The atomic structure of DLC consists of a network of sp3 and sp2 sites. The ?r states of sp2 sites control the electronic properties and the connectivity of sp' sites controls the mechanical properties.

Journal Article•DOI•
TL;DR: In this article, an inventory of the parameters that are in use to describe impedances of electrochemical cells is provided, as well as recommendations for their terminology and nomenclature.
Abstract: This document provides an inventory of the parameters that are in use to describe impedances of electrochemical cells. The definitions of these parameters are given, as well as recommendations for their terminology and nomenclature. Where relevant, experimental determination of a parameter and limitations to its validity are briefly discussed.

Journal Article•DOI•
TL;DR: The cleavage and addition of ortho C-H bonds in various aromatic compounds such as ketones, esters, imines, imidates, nitrile, and aldehydes to olefins and acetlylenes can be achieved catalytically with the aid of ruthenium catalysts.
Abstract: The cleavage and addition of ortho C-H bonds in various aromatic compounds such as ketones, esters, imines, imidates, nitrile, and aldehydes to olefins and acetlylenes can be achieved catalytically with the aid of ruthenium catalysts. The reaction is generally highly efficient and useful in synthetic methods. The coordination to the metal center by a heteroatom in directing groups such as carbonyl and imino groups is the key. The reductive elimination to form a C-C bond is the rate-determining step.

Journal Article•DOI•
TL;DR: In this paper, discharge physics and plasma chemistry of dielectric barrier discharges (silent discharges) are discussed and numerical models describing electrical breakdown, microdischarge formation and the ensuing free radical chemistry are presented.
Abstract: The discharge physics and plasma chemistry of dielectric barrier discharges (silent discharges) is discussed. Numerical models describing electrical breakdown, microdischarge formation and the ensuing free radical chemistry are presented. Applications ranging from ozone generation, excimer UV lamps and C02 lasers to surface treatment and pollution control are described. Experimental and modelling results on C@ hydrogenation in dielectric barrier discharges are also presented.

Journal Article•DOI•
TL;DR: In this article, the concepts of short synthesis, high selectivity and reduce effluent for industrial processes in the field of vitamin A and E synthesis were illustrated, and four reactions were selected to demonstrate how organometallic chemistry can improve industrial synthesis.
Abstract: This paper illustrates the concepts of short synthesis, high selectivity and reduce effluent for industrial processes in the field of vitamin A and E synthesis. We have selected four reactions to demonstrate how organometallic chemistry can improve industrial synthesis : isomerisation of methylbutynol 1 to prenal 2 ; Carbon - Carbon coupling and new access to geranylacetone ; Hydrogenation of a p-unsaturated aldehydes ; Oxidation and access to trimethylhydroquinone.

Journal Article•DOI•
TL;DR: In this paper, the photosynthetic reaction center (RC) was modeled as an octaalkyl- substituted zinc porphyrin (MJ) subunit with octa-alkyl substituted zinc (Z) pigments.
Abstract: Phenylene-bridged zinc diporphyrin (D)-monoporphyrin (h4)-pyro- mellitimide (I) triads were prepared as models for the photosynthetic reaction center (RC). With D and I fmed, the central monoporphyrin subunit is tuned from octaalkyl- substituted zinc porphyrin (MJ to a doubly strapped metal-free porphyrin (SH), a p- unsubstituted metal-free porphyrin (H), and a p-unsubstituted zinc porphyrin (Z) in order to achieve a RC-type sequential ET relay. In &%-I and D-SH-I, the charge separation (CS) between 'M,,* and I or 'SH* and I and a subsequent hole transfer to D provide D+-&--I' and IT-SH-I-, respectively. Upon excitation of D-H-I, an effective CS between the porphyrin pigments provides D+-H--I which is converted to D+-H-I by a subsequent charge shift reaction in 0.8 overall quantum yield in a manner analogous to that in RC. D-Z-I gives D+-Z-I in 0.4 overall quantum yield both in DMF and THF but the transient absorption spectra revealed that a stepwise ET relay of 'P-2-1 -+ IT-Z-I +D+-Z-I in DMF, while superexchange mediated long-distance electron transfer is suggested in THF.

Journal Article•DOI•
TL;DR: Carotenoids are found in nearly all tissues, but, particularly, in the liver and adipose tissue, and each carotenoid shows individual features relative to its absorption, transport and metabolism as mentioned in this paper.
Abstract: Vitamin A, which is an essential nutrient for humans, may be provided in the diet either as preformed vitamin A or as provitamin A carotenoids. The bioavailability of carotenoids in foods varies greatly, depending on many factors. Carotenoids are emulsified and then are solubilized in micellar form within the intestine with an absolute requirement for conjugated bile salts. Dietary carotenoids are absorbed as part of chylomicra, but in the steady state they are primarily constituents of low density and high density lipoproteins. Carotenoids are metabolized in many different ways, depending on their structure. particular importance nutritionally is the conversion of provitamin A carotenoids to vitamin A. Carotenoids are found in nearly all tissues, but, particularly, in the liver and adipose tissue. Each carotenoid shows individual features relative to its absorption, transport, and metabolism. Of

Journal Article•DOI•
TL;DR: Palladium-catalyzed cyclizations of aryl halides, vinyl halides and vinyl mflates with tethered alkenes have proven to be powerful reactions for forging congested quaternary carbon centers in complex organic molecules as mentioned in this paper.
Abstract: Palladium-catalyzed cyclizations of aryl halides, vinyl halides and vinyl mflates with tethered alkenes have proven to be powerful reactions for forging congested quaternary carbon centers in complex organic molecules. I'n some cases, the use of enantiopure ligands allows the new quaternary center to be formed with excellent enantioselectivity. The scope, stereochemical nuances and power of this organometallic chemistry is illustrated by briefly considering our recent total syntheses of (*)- pretazettine, (2)-tazettine, (-)- and (+)-morphine, (-)- and (+)-physostigmine, (&)- scopadulcic acid A and (*)-scopadulcic acid B.

Journal Article•DOI•
TL;DR: Svehla et al. as discussed by the authors proposed a committee for the first time, which consisted of C. G. Svehla (UK), S. P. Perone (USA), C. A. Doerffel (GDR), I. N. Giolito (Brazil), E. E. Grushka (Israel), W. Frei (Netherlands), R. W. Harris (Canada), H. H. Horwitz (USA) and W. M.
Abstract: Chairman: G. Svehla (UK), Secretary: S . P. Perone (USA). Titular Members: C. A. M. G. Cramers (Netherlands), R. W. Frei (Netherlands), R. E. van Grieken (Belgium), D. Klockow (FRG). Associate Members: L. Currie (USA), L. S . Ettre (USA), A. Fein (USA), H. Freiser (USA), W. Horwitz (USA), M. A. Leonard (UK), D. Leyden (USA), R. F. Martin (USA), B. Schreiber (Switzerland). National Representatives: K. Doerffel (GDR), I. Giolito (Brazil), E. Grushka (Israel), W. E. Harris (Canada), H. M. N. H. Irving ( S . African Republic), D. Jagner (Sweden), W. Rosset (France), J. Stary (Czechoslovakia).

Journal Article•DOI•
TL;DR: Projections are for global aquaculture output to exceed 20 million MT by the year 2000, comprising about 25% of the world's seafood, especially for salmonids and marine shrimp species.
Abstract: Aquaculture is a rapidly growing global industry, comprising cultivation of various freshwater and marine species of finfish, shellfish, molluscs, and ornamental fish. By the year 2000, as much as 20% of the world production of fish will be based on aquaculture. Properly formulated feeds are a significant part of successful aquaculture. Carotenoids play a major role in culture of salmonids such as Atlantic salmon and rainbow trout. Various biological and nutritional roles for carotenoids in salmonids are documented along with the effect of biotic and abiotic factors on astaxanthin transport and retention and final flesh pigmentation. Relevant recent feeding results are presented. INTERNATIONAL DIMENSIONS OF AQUACULTURE Global moduct ion and growth Aquaculture, involving farming of a variety of freshwater and marine species of finfish, shellfish, molluscs, and ornamental fishes, is a rapidly growing global industry with a broad range of technological and managerial practices. In 1990 (ref. l), world aquaculture reached 15.3 million metric tons (MT), or 12.1 million MT, if aquatic plants were excluded. This is more than double that reported for the year 1975. Of this, approximately 50% was of freshwater origin, largely cyprinid species, while 6% was of marine origin. As much as 80% of aqua- culture production is centered in Asia, particularly in China and Southeast Asia. During the 1984-89 period, capture fisheries expanded only about 14%, while aquaculture rose nearly 70%. Furthermore, the total value of world aquaculture production averaged an annual increase of 15% during the 1984-90 period. Market demand for quality product has stimulated much of the growth in aquaculture, especially for salmonids and marine shrimp species. The total world aquatic harvest in 1991, including aquaculture, was about 96 million MT of which aquaculture comprised about 16% (ref. 2). Harvest limitations in global fisheries suggest that further growth in aquatic production will depend upon aquaculture. Projections are for global aquaculture output to exceed 20 million MT by the year 2000, comprising about 25% of the world's seafood. Of cultured finfish, 85% are nonsarnivorous species, mostly cyprinids of various Chinese and Indian carp species. Almost half of the carnivorous species are salmonids, a ratio of about 50:50 salmon and trout. In the period 1986 to 1989, increases of 100-180% occurred in production of farmed Atlantic and Pacific salmon, while increases of 20-70% were recorded for common carp, tilapias, channel catfish, rainbow trout, and various species of marine shrimp, the latter comprising nearly 88% of crustacean aquaculture production. Global shrimp production alone in 1989 was over 530,000 MT, varying in volume and particular species with specific country. Successful cultivation of other marine finfish includes that of yellowtail, sea bass, sea bream, flatfish, grouper, and snapper. Numerous other marine and freshwater finfish are in various stages of evaluation for commercial aquaculture purposes. Salmonid broductim In 1991, the worldwide annual harvest of salmon was approximately 720,000 MT, of which 25- 30% were produced in a variety of aquaculture facilities and encloske designs. This includes such salmonid species as rainbow trout, Atlantic salmon, chinook salmon, and coho, pink, and chum salmon. The most spectacular growth has been with Atlantic salmon, notably in Norway

Journal Article•DOI•
TL;DR: In this article, a titration microcalorimetric measurement of poly(n-vinylpyrrolidone) PEO with nominal molar masses of 4 000,8 000 (two different samples ), 20 000, 100 000, and 1 500 000 were used without further treatment.
Abstract: The interaction between ionic surfactants and uncharged polymers in dilute aqueous solution has been studied by titration microcalorimetry. The resulting enthalpic titration curves give detailed information about polymer - surfactant interactions. While sodium dodecylsulfate interacts strongly with poly(ethy1ene oxide) and poly(viny1-pyrrolidone), the micelle formation of the cationic surfactants dodecyl-, tetradecyl-, and hexadecyl-trimethylammonium bromide is not measurably perturbed by the presence of these polymers. However, there is no significant difference between the interaction of the anionic and cationic surfactants with ethyl(hydroxyethy1)cellulose ethers. The aggregation of surfactants in polymer solutions shows clear similarities to the solubilization of small, polar molecules in ionic micelles. Preaggregation between surfactant monomers and polymers can be significant as indicated by sizeable endothermic enthalpy contributions from hydrophobic pair-wise interaction. Systems containing surfactants and water-soluble polymers are of great interest both for their widespread applications and for their inherently interesting properties. Polymer - surfactant complexes are used for instance in paints and coatings, in laundry detergents, cosmetic products, and in tertiary oil recovery. Systems containig nonionic polymers and ionic surfactants have been studied quite extensively during the last couple of decades so much is known about them. The various studies are summarized and discussed in several review articles ( ref 1-5 ). However, fundamental questions such as why and how surfactants form aggregates in the presence of polymers and how the polymer is involved in the aggregate formation are still unanswered.We became interested to see if results of calorimetric measurements could help to answer these questions and therefore, we started a study of some typical polymer - surfactant systems by titration microcalorimetry. EXPERIMENTAL Materials. Sodium dodecylsulfate SDS (BDH, 99%), dodecyltrimethylammonium bromide DoTAB (Aldrich, 99%), tetradecyltrimethylammonium bromide TTAB ( Sigma,99% ), and hexadecyltrimethylammonium bromide CTAB (Sigma, 99%) were used as received.Samples of poly(ethy1ene oxide) PEO with nominal molar masses of 4 000,8 000 ( two different samples ), 20 000, 100 000, and 1 500 000 were used without further treatment. Poly(N-vinylpyrrolidone) PVP with an average molar mass of 40 OOO ( Aldrich, special grade) and poly(propy1ene oxide) PPO with molar mass of 1 000 (Aldrich) were used as received. Samples of ethyl (hydroxy-ethy1)cellulose EHEC E230G and EHEC CST 103 ( Berol Nobel AB, Sweden) were dialyzed before use. The calorimetric measurements were made using the commercial microcalorimetric measuring channel of the 2277 TAM Thermal Activity Monitor system ( ThermoMetric AB, JMiilla, Sweden ) in a homebuilt high-precision thermostat bath (ref 6). The calorimetric titration experiments consisted of series of consecutive additions of concentrated surfactant solution to the calorimeter vessel initially containing 2.7 g of polymer solution. In some of the experiments concentrated polymer solution was added to surfactant solution in the vessel.The liquid samples were added in portions of 7 - 15 mg from a gas-tight Hamilton syringe through a thin stainless-steel capillary tube. A microprocessor-controlled motor-driven syringe drive was used for the injections. The fast titration procedure was used with six minutes between each injection (ref 7). The dynamic correction method used to deconvolute the potential signals was based on the simple Tian equation.

Journal Article•DOI•
TL;DR: In this article, the authors propose the design of systems undergoing molecular self-organisation, i.e. systems capable of spontaneously generating a well-defined supramolecular architecture by self assembling from their components in a given set of conditions.
Abstract: Supramolecular chemistry has relied on more or less preorganised molecular receptors for effecting molecular recognition, catalysis and transport processes. A step beyond consists in the design of systems undergoing molecular self-organisation, i.e. systems capable of spontaneously generating a well-defined supramolecular architecture by self assembling from their components in a given set of conditions.

Journal Article•DOI•
TL;DR: In this article, the interleukin-4 receptor was used to predict protein structure using a neural network, which was then applied to predict the relative potency of different chiral forms of drugs.
Abstract: Two distinct approaches are possible in the area of computer-aided drug design. If the molecular structure of the target macromolecule is known the methods are obvious and direct and have achieved a high level of sophistication. That area may be extended by using computational techniques to predict protein structure as illustrated here by the interleukin-4 receptor. When the only lead is a set of known active compounds or knowledge of a biochemical transformation which is to be interrupted, then the path is less direct. Currently favoured tactics include the use of molecular similarity methods and the employment of neural networks. Recent advances include the prediction of the relative potency of different chiral forms of drugs.


Journal Article•DOI•
TL;DR: Epidemiological studies show consistent decreased risk of lung cancer and certain other cancers, cataracts, age-related macular degeneration, and coronary heart disease in populations with the highest intakes of carotenoid-rich diets.
Abstract: Epidemiological studies show consistent decreased risk of lung cancer and certain other cancers, cataracts, age-related macular degeneration, and coronary heart disease in populations with the highest intakes of carotenoid-rich diets. Intervention studies show reductions in precancerous oral lesions, enhancement in immune parameters, and reduced incidence of cardiovascular events in individuals supplemented with A- carotene.

Journal Article•DOI•
TL;DR: In this article, the authors define phase transitions that relate specifically to the solid state and various types of transition have been defined; they include structural transitions of the solid states, transitions related to the change in the state of matter, i.e., from a solid phase to either a gaseous phase, or vice-versa.
Abstract: Definitions of phase transitions that relate specifically to the solid state are presented. Various types of transition have been defined; they include: (i) structural transitions of the solid state, (ii) transitions related to the change in the state of matter, i.e., from a solid phase to either a liq. or gaseous phase, or vice-versa, (iii) transitions related to changes in compn., (i.v.) metallurgical transitions, (v) transitions related to changes in the electronic structures of crystals, (vi) transitions that change thermodn. properties or the disorder of a system, and (vii) liq.-crystal transitions. [on SciFinder (R)]

Journal Article•DOI•
TL;DR: Chiral chelated lithium amides were designed and synthesized in this article for enantioselective reactions such as deprotonation of prochiral cyclic ketones, kinetic resolution of racemic 2-substituted cyclohexanones, and deracemization of chiral ketones by protonation.
Abstract: Chiral chelated lithium amides were designed and synthesized. Studies have been done to explore the use of these lithium amides or their corresponding amines for enantioselective reactions such as deprotonation of prochiral cyclic ketones, kinetic resolution of racemic 2-substituted cyclohexanones by deprotonation, regioselective deprotonation of optically active 3-keto steroids, alkylation of achiral ketones, and deracemization of chiral ketones by protonation. Approaches to catalytic asymmetric deprotonation and alkylation are also attempted.

Journal Article•DOI•
TL;DR: Recent studies concerning the origin of bioactive metabolites from lithistid sponges, some of which contain filamentous micro-organisms, are presented.
Abstract: From both ecological and biomedical viewpoints, it has become important to know whether the metabolites isolated from sponges are produced by symbiotic micro-organisms. Certain halogenated metabolites from Dysidea herbacea are localized in the symbiotic cyanobacterium Uscillatoria spongeliae. Recent studies concerning the origin of bioactive metabolites from lithistid sponges, some of which contain filamentous micro-organisms, are presented.

Journal Article•DOI•
TL;DR: In this article, the enantioselective electrophilic substitution of 1-methylindene was investigated and a qualitative transition state model was proposed, in which the stereoselection was kinetically controlled and the competition between external and internal competition was investigated in few cases.
Abstract: The deprotonation of achiral akyl carbamates with sec-butyllithium/(-)sparteine proceeds with a high degree of chiral recognition to form substituted alcohols usually with 2 95 76 ee after reaction with electrophiles followed by deprotection. The stereoselection is kinetically controlled and a qualitative transition state model is proposed. Some studies, concerning the discrimination between both enantiomers of stereogenic akyl carbamates and on its utilization for the kinetic resolution are reported. The competition between external and internal competition was investigated in few cases. Finally, we disclose a short report on the enantioselective electrophilic substitution of 1-methylindene; here the origin of stereoselection is an thermodynamically driven epimerization of diastereomeric indenyllithium sparteine complexes. INTRODUCTION Many methods for the enantioselective synthesis are based on the selection of a chiral reagent or of a reagent under the influence of a chiral catalyst between the enantiotopic faces of a trigonal carbon moiety. In only a few cases, an efficient selection between enantiotopic groups at a tetragonal carbon atom has been verified (Scheme 1). Scheme 1 Select ion between Enant iotopic Faces Select ion between Enant io top ic Groups Widely used in synthesis Impressive examples of the latter type have been reported (ref. 1) independently by the research groups of Koga and Simpkins: CSubstituted cyclohexanones are deprotonated by chiral lithium amides, derived from

Journal Article•DOI•
TL;DR: The only catalysts available until a few years ago were "classical" catalysts (usually containing Mo, W, or Re), i.e., catalysts that were simple to make, but whose nature was not known in detail and whose activity therefore could not be controlled to a degree to which we have become accustomed in modern day catalysis chemistry as mentioned in this paper.
Abstract: Olefin metathesis (equation 1; = some ligand coordination sphere) has been known for -35 years (ref. l), but until a few years ago the only catalysts available were "classical" catalysts (usually containing Mo, W, or Re), i.e., catalysts that were simple to make, but whose nature was not known in detail and whose activity therefore could not be controlled to a degree to which we have become accustomed in modern day catalysis chemistry. Such "black box" catalysts in general will not tolerate many donor functionalities, perhaps in part because little metal is actually active in such systems and absolute activity therefore has to be exceedingly high. Side reactions associated with "co-catalysts" such as aluminum halides are another significant complication. L,M=CHR' + RCH=CHR (1) LxM ITR LM=CHR + RCH=CHR'