Showing papers in "ChemInform in 1995"
TL;DR: In the twelve years since the first review article dealing with chemical constituents of the Hepaticae appeared in this series as Volume 42 (19), several short reviews concerned withchemical constituents of bryophytes have been published.
Abstract: In the twelve years since the first review article dealing with chemical constituents of the Hepaticae appeared in this series as Volume 42 (19), several short reviews concerned with chemical constituents of bryophytes have been published (22, 96, 144, 265, 271, 647, 649, 650) In 1988, a Symposium on Chemistry and Chemical Taxonomy of Bryophytes was organised on the behalf of the Phytochemical Society of Europe; the proceedings of this meeting appeared as a book entitled Bryophytes: Their Chemistry and Chemical Taxonomy (651) The symposium concerned itself with phytochemical, biochemical, botanical, chemotaxonomical, pharmaceutical, biotechnological and environmental aspects of bryophytes as well as with the synthesis of the terpenoids and aromatic compounds bryophytes elaborate The physiological and biochemical aspects of bryophytes have also been described in a recent book Bryophytes Development: Physiology and Biochemistry (139)
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TL;DR: In this paper, the authors present a method analogous to a mechanism of antibody formation proposed earlier, by which in the presence of interacting monomers a cross-linked polymer is formed around a molecule that acts as a template.
Abstract: Can binding sites be produced in organic or inorganic polymers—similar to those in antibodies—which are able to recognize molecules and which may have catalytic action? In this article we review a method, analogous to a mechanism of antibody formation proposed earlier, by which in the presence of interacting monomers a cross-linked polymer is formed around a molecule that acts as a template. After removal of the template, an imprint containing functional groups capable of chemical interaction remains in the polymer. The shape of the imprint and the arrangement of the functional groups are complementary to the structure of the template. If chiral templates are used, the success of the imprinting process can be assessed by the ability of the polymer to resolve the racemate of the template molecule. Through optimization of the process has led to chromatographic separation factors of α = 4–8, and to base line separations. There is also great interest in the surface imprinting of solid materials and monolayers. In all cases, the structure of the polymeric matrix in the imprinted materials and the function of the binding groups are of crucial importance. The mechanisms of imprinting and molecular recognition of substrates are by now well understood. A large number of potential applications for this class materials are being intensively developed, for example in the chromatogrphic resolution of recemates, and as artificial antibodies, chemosensors, and selective catalysts. The use of similarly produced materials as enzyme models is also of great interest.
157 citations
TL;DR: Inducible nitric oxide synthesis after appropriate stimuli has regulatory, cytostatic and/or toxic consequences and may play an important role in the pathophysiology of several diseases.
Abstract: More and more attention is paid to the radical nitric oxide which is now known to be part of the mammalian physiology and immune system. Nitric oxide is synthesized by one of the most complicated and fascinating enzyme families identified so far. Inducible nitric oxide synthesis after appropriate stimuli has regulatory, cytostatic and/or toxic consequences and may play an important role in the pathophysiology of several diseases.
146 citations
TL;DR: In this article, the authors propose a new algorithm called 1.8.1.1-2.0-1.8-1/2.8/1/1.
Abstract: 8.
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127 citations
TL;DR: Transparent polycrystalline YAG with nearly the same optical characteristics as those of a single crystal were fabricated by a solid-state reaction method using high-purity powders (>99.99 wt% purity) as discussed by the authors.
Abstract: Transparent polycrystalline YAG with nearly the same optical characteristics as those of a single crystal were fabricated by a solid-state reaction method using high-purity powders (>99.99 wt% purity). The average grain size and relative density of the 1.1 at.% ND:YAG ceramics obtained were about 50 {micro}m and 99.98%, respectively. An oscillation experiment was performed on a cw laser by the diode laser excitation system using the fabricated ceramics. The experimental results indicated an oscillation threshold and a slope efficiency of 309 mW and 28%, respectively. These values were equivalent or superior to those of the 0.9 at.% ND:YAG single crystal fabricated by the Czochralski method.
TL;DR: The complete active space (CAS) SCF method in conjunction with multiconfigurational second-order perturbation theory has been used to study the electronic spectra of a large number of molecules, including polyenes from ethene to octatetraene (cis-and trans-forms); a number of cyclic pentadienes; norbornadiene; benzene, phenol, phosphabenzene, and the azabenzenes; free base porphin; and the nucleic acid base monomers cytosine
Abstract: The complete active space (CAS) SCF method in conjunction with multiconfigurational second-order perturbation theory (CASPT2) has been used to study the electronic spectra of a large number of molecules. The wave functions and the transition properties are computed at the CASSCF level, while dynamic correlation contributions to the excitation energies are obtained through the perturbation treatment. The methods yield energies, which are accurate to at least 0.2 eV, except in a few cases, where the CASSCF reference function does not characterize the electronic state with sufficient accuracy. The applications comprise: the polyenes from ethene to octatetraene (cis- and trans-forms); a number of cyclic pentadienes; norbornadiene; benzene, phenol, phosphabenzene, and the azabenzenes; free base porphin; and the nucleic acid base monomers cytosine, uracil, thymine, and guanine. Finally, the photochemistry of the molecules aminobenzonitrile (ABN) and dimethylaminobenzonitrile (DMABN) has also been studied, in particular the double fluorescence that occurs in DMABN. Taken together these studies comprise large amounts of new spectroscopic data of high accuracy, which either confirm existing assignments of experimental data or lead to new predictions and qualitative as well as quantitative understanding of a large number of electronic spectra. Most studies are restricted to ground state geometries (vertical energies), but in a few cases (octatetraene, ABN, and DMABN) also excited state geometries have been determined, thus yielding 0-0 transition energies and emission spectroscopic data.
TL;DR: In this paper, the authors tried to describe perhaps the most important solid acids based on inorganic oxides, going from their preparation procedures and characterization, to their catalytic activity for a series of hydrocarbon reactions.
Abstract: It is possible to say that solid acid catalysis involves the largest amounts of catalysts used and the largest economical effort in the oil refining and chemical industry. In this review the author has tried to describe perhaps the most important solid acids based on inorganic oxides, going from their preparation procedures and characterization, to their catalytic activity for a series of hydrocarbon reactions. The review starts with an introductory part in where the nature of the acid sites and their physicochemical characterization is described. Then the classification to the different catalysts is initiated with the older amorphous silica-alumina and aluminum phosphates and followed by catalysts with more interest at present which are discussed in order of increasing acid strength: zeolites, heteropoly acids, and sulfated metal oxides. The aim of this review is to present an extended summary of the state of the art and the current and the future tendencies in the field. 720 refs.
TL;DR: A large cross-section of degradable polymeric delivery systems for protein and peptide pharmaceuticals is reviewed in this article, which includes monolithic type devices in which the drug is dispersed throughout the polymer and protein-polymer conjugates where the drugs are covalently bound to the polymer.
Abstract: We have reviewed a large cross-section of degradable polymeric delivery systems for protein and peptide pharmaceuticals. These systems include monolithic type devices in which the drug is dispersed throughout the polymer and protein-polymer conjugates where the drug is covalently bound to the polymer. These delivery systems have unique challenges associated with their development that are related to both protein stability and protein release kinetics. Despite numerous reports in the scientific literature which include many encouraging results in preclinical models, very few of these systems have been developed into viable products. The products that have made it to market, however, have proven to be very successful and demonstrate the significant advantages that these systems can provide. The continuous advances in biotechnology will produce more proteins and peptides that will be difficult to administer by conventional means, and an increased demand for controlled or site-specific delivery systems is anticipated.
TL;DR: The crystal structure of urease from Klebsiella aerogenes has been determined at 2.2 A resolution and refined to an R factor of 18.2 percent as discussed by the authors.
Abstract: The crystal structure of urease from Klebsiella aerogenes has been determined at 2.2 A resolution and refined to an R factor of 18.2 percent. The enzyme contains four structural domains: three with novel folds playing structural roles, and an (alpha beta)8 barrel domain, which contains the bi-nickel center. The two active site nickels are 3.5 A apart. One nickel ion is coordinated by three ligands (with low occupancy of a fourth ligand) and the second is coordinated by five ligands. A carbamylated lysine provides an oxygen ligand to each nickel, explaining why carbon dioxide is required for the activation of urease apoenzyme. The structure is compatible with a catalytic mechanism whereby urea ligates Ni-1 to complete its tetrahedral coordination and a hydroxide ligand of Ni-2 attacks the carbonyl carbon. A surprisingly high structural similarity between the urease catalytic domain and that of the zinc-dependent adenosine deaminase reveals a remarkable example of active site divergence.
TL;DR: In this paper, a review of the existing published experimental evidence for ageing mechanisms in zirconia ceramics is presented and discussed and attention is drawn to the contradictions between the theories.
Abstract: This paper critically reviews the existing published experimental evidence for ageing mechanisms in zirconia ceramics. The first part of the paper is concerned with the material and environmental variables affecting the kinetics of the transformation. The current ageing mechanisms are presented and discussed and attention is drawn to the contradictions between the theories. Finally, techniques to retard or prevent the tetragonal-monoclinic phase transformation are presented.
TL;DR: In this article, the template synthesis of electronically conductive polymer nanostructures has been studied and shown to have interesting and unusual electronic properties and provide an opportunity for exploring how molecular and supermolecular structure affect conductivity in conductive polymers.
Abstract: : Nanochemistry is an emerging subdiscipline in the chemical and materials sciences that deals with the development of methods for synthesizing nanoscopic bits of a desired material and with chemical and other investigations of the nanomaterial obtained. My research group has been exploring a general method, called "template-synthesis," for preparing nanomaterials. This method entails synthesizing the desired material within the pores of a nanoporous membrane. The membranes employed have cylindrical pores of uniform diameter. In essence, we view each of these pores as a "nanobeaker" in which a piece of the desired material is synthesized. We have used this method to prepare nanostructures composed of electronically conductive polymers, metals, semiconductors, and other materials. In this Accounts article, I discuss my work on template synthesis of electronically conductive polymer nanostructures. I will show that these conductive polymer nanostructures have interesting and unusual electronic properties and that these nanostructures provide an opportunity for exploring how molecular and supermolecular structure affect conductivity in conductive polymers.
TL;DR: In this article, a new family of inorganic-organic hybrid materials that are assembled by sol-gel polymerization of polyfunctional molecular building blocks is presented, bridged polysilsesquioxanes, which are distinguished by incorporation of an organic fragment as an integral component of the network.
Abstract: This contribution reviews a new family of inorganic-organic hybrid materials that are assembled by sol-gel polymerization of polyfunctional molecular building blocks. These bridged polysilsesquioxanes are three-dimensional network materials that are distinguished by incorporation of an organic fragment as an integral component of the network. The intimate association of the organic and inorganic phase, a true molecular composite, coupled with the variability of the organic component, permits engineering of both chemical and physical properties of the material. The paper reviews bridged polysilsesquioxanes, arylene-bridged polysilsesquioxanes, alkylene-bridged polysilsesquioxanes; and their applications.
TL;DR: In this paper, the authors provide a rationale for each reader to answer the following rhetorical questions: what are the properties which determine the performance of a catalytic material; how can these properties be introduced, developed, and/or improved during preparation?
Abstract: To establish guidelines for the development of a scientific basis for catalyst preparation is perhaps a very ambitious goal. One would re required first to answer the following rhetorical questions: what are the properties which determine the performance of a catalytic material; how can these properties be introduced, developed, and/or improved during preparation? The answer to these questions involves a comprehensive discussion of the theories of catalysis, which is beyond the scope of this review. The authors will attempt, instead, to provide a rationale for each reader to answer these questions on the basis of his/her own interests. They start the discussion by describing the fundamental steps in producing bulk catalysts and/or catalyst supports. The fundamental processes involved are those derived from traditional three-dimensional chemistry. The topic areas will include single-component and multicomponent metal oxides. Unsupported metallic catalysts are formed by transformations involving physical or chemical processes, and the preparation methods for this class of materials will be discussed next. Attention will then turn to the preparation of supported catalytic materials. The main topics to be discussed will be those related to the interaction between the support and the active phase when they are put together to generate the catalyst.more » In this approach, the authors exploit the virtually unexplored field of surface, or two-dimensional, physical chemistry. The materials considered include dispersed metals and alloys and composite oxides. 366 refs.« less
TL;DR: FTY720 (2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol hydrochloride), a novel synthetic immunosuppressant led by modification of ISP-I (myriocin, thermozymocidin) displayed potent immunoSuppressive activity both in vitro and in vivo.
Abstract: FTY720 (2-amino-2-[2-(4-octylphenyl)ethyl]-1,3-propanediol hydrochloride), a novel synthetic immunosuppressant led by modification of ISP-I (myriocin, thermozymocidin) displayed potent immunosuppressive activity both in vitro and in vivo.