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Chemical Diversity (chemical + diversity)

Distribution by Scientific Domains

Chemistry	62%
Life Sciences	25%

Selected Abstracts

Chemical Diversity in Himalayan Elsholtzia Species

CHEMISTRY & BIODIVERSITY, Issue 12 2009
Chandra
Abstract The terpenoid composition of essential oils from the leaves of five Elsholtzia species, viz., E. eriostachyaBenth., E. cristataWilld., E. polystachyaBenth., E. flavaBenth., and E. pilosaBenth., collected from the Himalayan region (India), was examined by GC, GC/MS, and NMR analyses. Comparison of the results with previous reports revealed new chemotypes. Cluster analysis was carried out in order to discern the similarities and differences within the essential-oil compositions at their subspecies/chemotype level. Based on the major constituents of the essential oils, six chemical groups were obtained. [source]

Atomic Diversity, Molecular Diversity, and Chemical Diversity: The Concept of Chemodiversity

CHEMISTRY & BIODIVERSITY, Issue 8 2009
Bernard Testa
Abstract This minireview is meant as an introduction to the following paper. To this end, it presents the general background against which the joint paper should be understood. The first objective of the present paper is thus to clarify some concepts and related terminology, drawing a clear distinction between i) atomic diversity (i.e., atomic-property space), ii) molecular or macromolecular diversity (i.e., molecular- or macromolecular-property spaces), and iii) chemical diversity (i.e., chemical-diversity space). The first refers to the various electronic states an atom can occupy. The second encompasses the conformational and property spaces of a given (macro)molecule. The third pertains to the diversity in structure and properties exhibited by a library or a supramolecular assembly of different chemical compounds. The ground is thus laid for the content of the joint paper, which pertains to case ii, to be placed in its broader chemodiversity context. The second objective of this paper is to point to the concepts of chemodiversity and biodiversity as forming a continuum. Chemodiversity is indeed the material substratum of organisms. In other words, chemodiversity is the material condition for life to emerge and exist. Increasing our knowledge of chemodiversity is thus a condition for a better understanding of life as a process. [source]

Chemical diversity of zeolite catalytic sites

AICHE JOURNAL, Issue 6 2008
Raul Lobo
First page of article [source]

Molecular recognition: Identifying compounds and their targets

JOURNAL OF CELLULAR BIOCHEMISTRY, Issue S37 2001
Prabhavathi B. Fernandes Ph.D.
Abstract As a result of gene sequencing and proteomic efforts, thousands of new genes and proteins are now available as potential drug targets. The milieu of these proteins is complex and interactive; thousands of proteins activate, inhibit, and control each other's actions. The effect of blocking or activating a protein in a cell is far-reaching, and can affect whole, as well as adjacent pathways. This network of pathways is dynamic and a cellular response can change depending on the stimulus. In this section, the identification and role of individual proteins within the context of networked pathways, and the regulation of the activity of these proteins is discussed. Diverse chemical libraries, combinatorial libraries, natural products, as well as unnatural natural products that are derived from combinatorial biology (Chiu [2001] Proc. Natl. Acad. Sci. USA. 98:8548,8553), provide the chemical diversity in the search for new drugs to block new targets. Identifying new compounds that can become drugs is a long, expensive, and arduous task and potential targets must be carefully defined so as not to waste valuable resources. Equally important is the selection of compounds to be future drug candidates. Target selectivity in no way guarantees clinical efficacy, as the compound must meet pharmaceutical requirements, such as solubility, absorption, tissue distribution, and lack of toxicity. Thus matching biological diversity with chemical diversity involves something more than tight interactions, it involves interactions of the compounds with a variety host factors that can modulate its activity. J. Cell. Biochem. Suppl. 37: 1,6, 2001. © 2002 Wiley-Liss, Inc. [source]

Preferential flow and aging of NAPL in the unsaturated soil zone of a hazardous waste site: implications for contaminant transport

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2003
Kai U. Totsche
Abstract Flow of non-aqueous phase liquids (NAPL) in the unsaturated zone is thought to be driven by gravity with a dominant vertical flow direction, and lateral spreading to be limited to the gradient of the relative permeabilities. The effect of soil profile build-up, preferential flow, aging, and groundwater level fluctuations is mostly neglected. The objective of our study was to check the effects of such processes on the fate of NAPL in the unsaturated soil zone. At a hazardous waste site, we conducted a field survey of the unsaturated soil zone and monitored the groundwater for a two year period. We conducted spatially resolved and depth dependent soil sampling and analysis and the evaluation of former ram and core drilling protocols. The samples were analyzed for the 16 EPA PAH and alkanes with GC-MS and GC-FID. 13C-NMR spectroscopy was used to assess structural changes of the NAPL phase. Flow of bulk NAPL along macropores and along preferential permeability structures, like sedimentation discontinuities, are the dominant transport pathways which cause large lateral spreading beyond those expected by the relative permeability gradient. Accumulation of NAPL was found at locations with abrupt textural changes and within the zone of capillary rise. Aging of NAPL results in the depletion in soluble and volatile compounds but also in oxidation and polymerization. It increases the chemical diversity and decreases the mobility of the NAPL. Thus, NAPL flow ceases much earlier than expected from the capillary forces. As chemical transformation is restricted to the NAPL water/air interface, a skin-like thin film is formed which encapsulates and preserves the bulk NAPL from further hardening, limiting contaminant mass transfer from the NAPL to the aqueous phase. Präferenzieller Fluss und Alterung nichtwässriger flüssiger Phasen (NAPL) in der ungesättigten Bodenzone eines Altlastenstandortes: Bedeutung für den Stofftransport Bei der Abschätzung der Tiefenverlagerung von nichtwässrigen Phasen (NAPL) in der ungesättigten Bodenzone ging man bisher davon aus, dass der Fluss im Boden eine dominante vertikale Fließkomponente besitzt. Die Bedeutung bevorzugter Fließwege, des Bodenprofils und der Alterung für die Ausbreitung der NAPL wurde bisher nicht untersucht. Ziel unserer Arbeiten war es daher, die Gültigkeit der Vorstellungen zum Transport von NAPL in der ungesättigten Bodenzone zu überprüfen. Hierzu wurde die ungesättigte Bodenzone an einem ehemaligen Teerwerkstandort untersucht und ein zweijähriges Grundwassermonitoring durchgeführt. Es wurde eine tiefendifferenzierte und räumlich aufgelöste Probenahme mit Rammkernsondierungen und Linern durchgeführt, sowie Bohrprotokolle vorhandener Gutachten ausgewertet. In den Proben wurden Alkane mittels GC-FID und PAK mittels GC-MS bestimmt. NAPL wurden 13C-NMR-spektroskopisch untersucht. Der Fluss von NAPL entlang präferenzieller Fließpfade ist der dominante Prozess der Tiefenverlagerung. Dabei kommt es zu einer starken lateralen Ausbreitung von NAPL weit über den Bereich hinaus, der aufgrund der heterogenen Verteilung der relativen Permeabilitäten erwartet werden würde. Innerhalb des Bodenprofils reichern sich NAPL oberhalb der Grenzflächen mit abruptem Texturwechsel und innerhalb der kapillaren Aufstiegszone an. Alterung der NAPL führt zu einer Zunahme der chemischen Diversität und zu einer Abnahme der Mobilität. Die Tiefenverlagerung von NAPL kommt viel früher zum Erliegen als durch Viskosität und Kapillarkräfte zu erwarten wäre. Die strukturchemischen Veränderungen beschränken sich jedoch auf die Grenzfläche NAPL/Wasser bzw. NAPL/Bodenluft: Es bildet sich eine dünne, verhärtete Grenzschicht aus, die die NAPL umhüllt, die weitere Alterung verlangsamt und den Stoffaustausch zwischen NAPL und Bodenwasser bzw. der Bodenluft verringert. [source]

Exploring pathways to reduce the distribution of active sites in the Ziegler,Natta polymerization of propylene

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2007
David Ribour
Abstract Chemical treatments of classical supported Ziegler,Natta precatalysts were conducted by using additional bulky ligands to attempt to narrow and homogenize the active sites distribution in propylene polymerization. Additions of monodentate ligands such as bis(trimethylsilyl)amide, cyclopentadienyl derivates or triphenylsilanol were seen to slow down the polymerization without modifying the distribute properties of polypropylenes. In the case of multidentate ligands (porphines or biquinolines), in addition to the poisoning of active sites, an extraction of titanium from the catalyst surface is observed. A decrease of both melting point and isotacticity (II%) of polymers using these compounds suggest that the most isospecific titanium sites are first extracted from the MgCl2 -surface. The narrowing of the molecular weight distribution confirms that the highly isospecific sites are the most active sites, producing the higher molecular weight polymers. Moreover, this study shows that the distributed properties of polymers are due to the chemical diversity of the active sites with various steric and electronic environments at the catalyst surface and not to mass transfer limitations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3941,3948, 2007 [source]

The evolution of secondary metabolism , a unifying model

MOLECULAR MICROBIOLOGY, Issue 5 2000
Richard D. Firn
Why do microbes make secondary products? That question has been the subject of intense debate for many decades. There are two extreme opinions. Some argue that most secondary metabolites play no role in increasing the fitness of an organism. The opposite view, now widely held, is that every secondary metabolite is made because it possesses (or did possess at some stage in evolution) a biological activity that endows the producer with increased fitness. These opposing views can be reconciled by recognizing that, because of the principles governing molecular interactions, potent biological activity is a rare property for any molecule to possess. Consequently, in order for an organism to evolve the rare potent, biologically active molecule, a great many chemical structures have to be generated, most of which will possess no useful biological activity. Thus, the two sides of the debate about the role and evolution of secondary metabolism can be accommodated within the view that the possession of secondary metabolism can enhance fitness, but that many products of secondary metabolism will not enhance the fitness of the producer. It is proposed that secondary metabolism will have evolved such that traits that optimize the production and retention of chemical diversity at minimum cost will have been selected. Evidence exists for some of these predicted traits. Opportunities now exist to exploit these unique properties of secondary metabolism to enhance secondary product diversity and to devise new strategies for biotransformation and bioremediation. [source]

Addressing chemical diversity by employing the energy landscape concept

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010
Martin Jansen
Exploring the structural diversity of a chemical system rests on three pillars. First, there is the global exploration of its energy landscape that allows one to predict which crystalline modifications can exist in a chemical system at a given temperature and pressure. Next, there is the development of new synthesis methods in solid-state chemistry, which require only very low activation energies such that even metastable modifications corresponding, for example, to minima on the landscape surrounded by low barriers can be realized. Finally, there is the theoretical design of optimal synthesis routes, again based on the study of the system's energy landscape. In this paper the energy landscape approach to the prediction of stable and metastable compounds as a function of temperature and pressure is presented, with a particular focus on possible phase transitions. Furthermore, several examples are presented, where such predicted compounds were subsequently successfully synthesized, often employing a newly developed synthesis method, low-temperature atom-beam deposition. [source]

A validated spectrophotometric method for quantification of prenylated flavanones in pacific propolis from Taiwan

PHYTOCHEMICAL ANALYSIS, Issue 2 2010
Milena Popova
Abstract Introduction , Because of its chemical diversity, the only way to standardise propolis is to specify multiple standards for different propolis types according to the corresponding chemical profile. So far, this has been done only for European propolis. Objective , To develop a rapid low-cost spectrophotometric procedure for quantification of bioactive prenylated flavanones in Taiwanese propolis. Methodology , The proposed method quantifies the total flavanones on the basis of their absorption as coloured phenylhydrazones formed by interaction with 2,4-dinitrophenylhydrazine. The procedure was validated through model mixture of compounds representing the composition of Taiwanese propolis according to previous studies. The major flavanones of the propolis samples (propolins C, D, F and G) were quantified by HPLC. Antiradical activity against DPPH was also measured. The DNP (dinitrophenylhydrazine) spectrophotometric method is applied for the first time for quantification of prenylated flavanones. Results , Spectophotometric procedure applicable to new type propolis (Macaranga type) was developed with recovery between 105 and 110% at the concentration range of 0.573,1.791,mg/mL. Six propolis samples were analysed by spectrophotometry using the procedure developed and validated, and by HPLC as the results demonstrated satisfactory agreement. Neither the spectrophotometric data nor the values measured by HPLC showed significant correlation with the antiradical activity against DPPH. Conclusion , The proposed spectrophotometric procedure is useful for routine analyses of Macaranga -type propolis, because of its simplicity, repeatability and acceptable accuracy. Its application to a number of commercial samples could be used as a basis for standardisation and quality control of Pacific propolis. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Direct metabolic fingerprinting of commercial herbal tinctures by nuclear magnetic resonance spectroscopy and mass spectrometry,

PHYTOCHEMICAL ANALYSIS, Issue 4 2009
Matteo Politi
Abstract Introduction Tinctures are widely used liquid pharmaceutical preparations traditionally obtained by maceration of one or more medicinal plants in ethanol,water solutions. Such a process results in the extraction of virtually hundreds of structurally diverse compounds with different polarities. Owing to the large chemical diversity of the constituents present in the herbal tinctures, the analytical tools used for the quality control of tinctures are usually optimised only for the detection of single chemical entities or specific class of compounds. Objective In order to overcome the major limitations of the current methods used for analysis of tinctures, a new methodological approach based on NMR spectroscopy and MS spectrometry has been tested with different commercial tinctures. Methodology Diffusion-edited 1H-NMR (1D DOSY) and 1H-NMR with suppression of the ethanol and water signals have been applied here for the first time to the direct analysis of commercial herbal tinctures derived from Echinacea purpurea, Hypericum perforatum, Ginkgo biloba and Valeriana officinalis. The direct injection of the tinctures in the MS detector in order to obtain the corresponding metabolic profiles was also performed. Results Using both NMR and MS methods it was possible, without evaporation or separation steps, to obtain a metabolic fingerprint able to distinguish between tinctures prepared with different plants. Batch-to-batch homogeneity, as well as degradation after the expiry date of a batch, was also investigated. Conclusion The techniques proposed here represent fast and convenient direct analyses of medicinal herbal tinctures. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Development and validation of a liquid chromatography/tandem mass spectrometric method for the determination of 39 mycotoxins in wheat and maize

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2006
Michael Sulyok
This paper describes the first validated method for the determination of 39 mycotoxins in wheat and maize using a single extraction step followed by liquid chromatography with electrospray ionization triple quadrupole mass spectrometry (LC/ESI-MS/MS) without the need for any clean-up. The 39 analytes included A- and B-trichothecenes (including deoxynivalenol-3-glucoside), zearalenone and related derivatives, fumonisins, enniatins, ergot alkaloids, ochratoxins, aflatoxins and moniliformin. The large number and the chemical diversity of the analytes required the application of the positive as well as the negative ion ESI mode in two consecutive chromatographic runs of 21,min each. The solvent mixture acetonitrile/water/acetic acid 79,+,20,+,1 (v/v/v) has been determined as the best compromise for the extraction of the analytes from wheat and maize. Raw extracts were diluted 1,+,1 and were injected without any clean-up. Ion-suppression effects due to co-eluting matrix components were negligible in the case of wheat, whereas significant signal suppression for 12 analytes was observed in maize, causing purely proportional systematic errors. Method performance characteristics were determined after spiking blank samples on multiple levels in triplicate. Coefficients of variation of the overall process of <5.1% and <3.0% were obtained for wheat and maize, respectively, from linear calibration data. Limits of detection ranged from 0.03 to 220,µg/kg. Apparent recoveries (including both the recoveries of the extraction step and matrix effects) were within the range of 100,±,10% for approximately half of the analytes. In extreme cases the apparent recoveries dropped to about 20%, but this could be compensated for to a large extent by the application of matrix-matched standards to correct for matrix-induced signal suppression, as only a few analytes such as nivalenol and the fumonisins exhibited incomplete extraction. For deoxynivalenol and zearalenone, the trueness of the method was confirmed through the analysis of certified reference materials. Copyright © 2006 John Wiley & Sons, Ltd. [source]

A systems biology investigation of the MEP/terpenoid and shikimate/phenylpropanoid pathways points to multiple levels of metabolic control in sweet basil glandular trichomes

THE PLANT JOURNAL, Issue 3 2008
Zhengzhi Xie
Summary The glandular trichome is an excellent model system for investigating plant metabolic processes and their regulation within a single cell type. We utilized a proteomics-based approach with isolated trichomes of four different sweet basil (Ocimum basilicum L.) lines possessing very different metabolite profiles to clarify the regulation of metabolism in this single cell type. Significant differences in the distribution and accumulation of the 881 highly abundant and non-redundant protein entries demonstrated that although the proteomes of the glandular trichomes of the four basil lines shared many similarities they were also each quite distinct. Correspondence between proteomic, expressed sequence tag, and metabolic profiling data demonstrated that differential gene expression at major metabolic branch points appears to be responsible for controlling the overall production of phenylpropanoid versus terpenoid constituents in the glandular trichomes of the different basil lines. In contrast, post-transcriptional and post-translational regulation of some enzymes appears to contribute significantly to the chemical diversity observed within compound classes for the different basil lines. Differential phosphorylation of enzymes in the 2- C -methyl- d -erythritol 4-phosphate (MEP)/terpenoid and shikimate/phenylpropanoid pathways appears to play an important role in regulating metabolism in this single cell type. Additionally, precursors for different classes of terpenoids, including mono- and sesquiterpenoids, appear to be almost exclusively supplied by the MEP pathway, and not the mevalonate pathway, in basil glandular trichomes. [source]

Cloning large natural product gene clusters from the environment: Piecing environmental DNA gene clusters back together with TAR

BIOPOLYMERS, Issue 9 2010
Jeffrey H. Kim
Abstract A single gram of soil can contain thousands of unique bacterial species, of which only a small fraction is regularly cultured in the laboratory. Although the fermentation of cultured microorganisms has provided access to numerous bioactive secondary metabolites, with these same methods it is not possible to characterize the natural products encoded by the uncultured majority. The heterologous expression of biosynthetic gene clusters cloned from DNA extracted directly from environmental samples (eDNA) has the potential to provide access to the chemical diversity encoded in the genomes of uncultured bacteria. One of the challenges facing this approach has been that many natural product biosynthetic gene clusters are too large to be readily captured on a single fragment of cloned eDNA. The reassembly of large eDNA-derived natural product gene clusters from collections of smaller overlapping clones represents one potential solution to this problem. Unfortunately, traditional methods for the assembly of large DNA sequences from multiple overlapping clones can be technically challenging. Here we present a general experimental framework that permits the recovery of large natural product biosynthetic gene clusters on overlapping soil-derived eDNA cosmid clones and the reassembly of these large gene clusters using transformation-associated recombination (TAR) in Saccharomyces cerevisiae. The development of practical methods for the rapid assembly of biosynthetic gene clusters from collections of overlapping eDNA clones is an important step toward being able to functionally study larger natural product gene clusters from uncultured bacteria. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 833,844, 2010. [source]

Biotechnological studies in the Far-Eastern Region of Russia

BIOTECHNOLOGY JOURNAL, Issue 7 2007
Valentin A. Stonik Professor
Abstract Achievements and problems in both the studies on natural bioactive compounds from the Far-Eastern higher plants and marine invertebrates and development of the corresponding biotechnologies concerning new drugs and food supplements, as well as pharmaceutical leads are discussed. Special emphasis is made on recent results from the Far-eastern Institutions belonging to the Russian Academy of Sciences, and their application in both medicine and the food industry, as well as on peculiarities of biological and chemical diversity in the North-Western part of Asia and adjoining seas. [source]

Atomic Diversity, Molecular Diversity, and Chemical Diversity: The Concept of Chemodiversity

Comparative performances of selected chiral HPLC, SFC, and CE systems with a chemically diverse sample set

CHIRALITY, Issue S1 2003
Phil Borman
Abstract Pharmaceutical companies have a continuous need to resolve new racemates. Analysis may be required in aqueous and nonaqueous media, or in the presence of several different sets of potentially interfering compounds. There is often a preparative requirement. For these reasons analysts may require a number of different separation systems capable of resolving a given pair of enantiomers. We wished to improve upon existing approaches that address this situation and undertook a program of work to screen over 100 racemates, selected for their chemical diversity, on over 100 different chiral HPLC, SFC, and CE systems. Here we report results of this comparison and illustrate the use of rapid gradient screening as a valuable tool for chiral method development. Chirality 15:S1,S12, 2003. © 2003 Wiley-Liss, Inc. [source]