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101.
102.
Francisco M. García Olmedo Antonio J. Rodríguez Salas 《Mathematical Logic Quarterly》1995,41(1):24-38
In this paper the structure of pretemporal algebra is used to study some aspects of temporal algebras and modal algebras. The paper contains a computational approach to finite temporal algebras and a general splitting theorem for finite temporal algebras. 相似文献
103.
Remsing LL González AM Nur-e-Alam M Fernández-Lozano MJ Braña AF Rix U Oliveira MA Méndez C Salas JA Rohr J 《Journal of the American Chemical Society》2003,125(19):5745-5753
To gain initial structure-activity relationships regarding the highly functionalized pentyl side chain attached at C-3 of mithramycin (MTM), we focused on a post-polyketide synthase (post-PKS) tailoring step of the MTM biosynthesis by Streptomyces argillaceus ATCC 12956, which was proposed to be catalyzed by ketoreductase (KR) MtmW. In this last step of the MTM biosynthesis, a keto group of the pentyl side chain is reduced to a secondary alcohol, and we anticipated the generation of an MTM derivative with an additional keto group in the 3-side chain. Insertional inactivation of mtmW, a gene located ca. 8 kb downstream of the mithramycin-PKS genes, yielded an S. argillaceus mutant, which accumulated three new mithramycin analogues, namely mithramycin SA, demycarosyl-mithramycin SK, and mithramycin SK (MTM-SK). The structures of these three compounds confirmed indirectly the proposed role of MtmW in MTM biosynthesis. However, the new mithramycin derivatives bear unexpectedly shorter 3-side chains (ethyl or butyl) than MTM, presumably caused by nonenzymatic rearrangement or cleavage reactions of the initially formed pentyl side chain with a reactive beta-dicarbonyl functional group. The major product, MTM-SK, was tested in vitro against a variety of human cancer cell lines, as well as in an in vitro toxicity assay, and showed an improved therapeutic index, in comparison to the parent drug, MTM. 相似文献
104.
Sybil O’Reilly Sonia Erazo Victoriano Campos Erika Salas Jaime Baeza AndrÉ Ferraz Jaime Rodriguez Nelson DurÁn 《Applied biochemistry and biotechnology》1991,27(3):267-276
The single cell protein and extracellular enzyme production from a lignocellulolytic fungus,Chrysonilia sitophila, using different carbon sources were evaluated. The mycelial dry mass composition showed a high protein (39.2%) and low nucleic
acid content (3.3%), as well as carbohydrate, fatty acid, fiber, and ash levels comparable with single cell proteins currently
studied. Mycelial protein showed amino acid content similar to or higher than FAO standard requirements. The amino acid, fatty
acid, and carotenoid composition, as well as mycelial mass yield and enzyme production, were dependent on the carbon source
used. Glucose, saccharose, cellobiose, cellulose, microcrystal-line cellulose, lactose, and rice hull as carbon sources were
studied. 相似文献
105.
Barea E Quiros M Navarro JA Salas JM 《Dalton transactions (Cambridge, England : 2003)》2005,(9):1743-1746
One-pot reaction of CuX2 salts (X = NO3, Cl, ClO4, AcO, SO(4)/2), 2-Hydroxypyrimidine hydrochloride (2-Hpymo.HCl) and 4,4'-bipyridine (4,4'-bpy), in H2O : ethanol : ammonia (20 : 10 : 5) solution, leads to isomorphous extended layered materials of type [Cu3(mu-OH)2(mu-Cl)2(mu-2-pymo)(mu-4,4'-bpy)3]nXn.mH2O (X = NO3 (1a), Cl (1b), ClO4 (1c), AcO (1d), SO(4)/2 (1e)). The single crystal X-ray crystallographic analysis performed on species exemplifies that it is built by 2D [Cu3(mu-OH)2(mu-Cl)2(mu-2-pymo)(mu-4,4'-bpy)3]n(n+) cationic sheets, which pack in a staggered fashion, with non coordinated NO3- anions and crystallisation water molecules included in the interlayer voids. XRPD studies performed on the species show a swelling response along the crystallographic a axis concomitant to aliphatic alcohol inclusion. Additionally, we have also studied the magnetic properties of , which show that its magnetic behaviour is dominated by the strong antiferromagnetic interactions taking place in the Cu3(mu-OH)2(mu-Cl)2 trinuclear cores. 相似文献
106.
beta-lactam ring formation in carbapenem and clavam biosynthesis proceeds through an alternative mechanism to the biosynthetic pathway of classic beta-lactam antibiotics. This involves the participation of a beta-lactam synthetase. Using available information from beta-lactam synthetases, we generated a probe for the isolation of the thienamycin cluster from Streptomyces cattleya. Genes homologous to carbapenem and clavulanic acid biosynthetic genes have been identified. They would participate in early steps of thienamycin biosynthesis leading to the formation of the beta-lactam ring. Other genes necessary for the biosynthesis of thienamycin have also been identified in the cluster (methyltransferases, cysteinyl transferases, oxidoreductases, hydroxylase, etc.) together with two regulatory genes, genes involved in exportation and/or resistance, and a quorum sensing system. Involvement of the cluster in thienamycin biosynthesis was demonstrated by insertional inactivation of several genes generating thienamycin nonproducing mutants. 相似文献
107.
AbstractThe chemical analyses of ethyl acetate-methanol (EtOAc-MeOH) extract of muricid gastropod mollusk, Chicoreus ramosus from the southeastern coast of Indian peninsular led to the identification of unprecedented cembrane-type diterpenoid, which was characterized as (3E, 6E, 10E)-8a-butoxy-17(15→14), 20(12→11)-bis-abeo-cembra-3,6,10,14(17),15-pentaene (1). The structure of the studied cembrane was unambiguously assigned through the extensive spectroscopic experimentations. The antioxidant potentials of the bis-abeo cembrane as determined by in vitro 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis-3-ethylbenzothiozoline-6-sulfonic acid diammonium salt radical quenching potentials were greater (IC50?<?0.40?mg/mL) related to α-tocopherol (IC50?>?0.60?mg/mL). The pro-inflammatory anti-5-lipoxygenase potential of studied cembrane was higher (IC50?<?0.80?mg/mL) related to those demonstrated by ibuprofen and sodium salicylate (IC50?>?0.90?mg/mL). 相似文献
108.
The biosynthetic gene cluster of the aureolic acid type antitumor drug chromomycin A3 from S. griseus subsp. griseus has been identified and characterized. It spans 43 kb and contains 36 genes involved in polyketide biosynthesis and modification, deoxysugar biosynthesis and sugar transfer, pathway regulation and resistance. The organization of the cluster clearly differs from that of the closely related mithramycin. Involvement of the cluster in chromomycin A3 biosynthesis was demonstrated by disrupting the cmmWI gene encoding a polyketide reductase involved in side chain reduction. Three novel chromomycin derivatives were obtained, named chromomycin SK, chromomycin SA, and chromomycin SDK, which show antitumor activity and differ with respect to their 3-side chains. A pathway for the biosynthesis of chromomycin A3 and its deoxysugars is proposed. 相似文献
109.
M. A. Valenzuela P. Bosch G. Aguilar-Rios B. Zapata H. Armendariz P. Salas I. Schifter 《Reaction Kinetics and Catalysis Letters》1992,48(1):121-126
The effect of the support preparation technique (solgel and coprecipitation) on the final Pt/ZnAl2O4 catalyst is presented. The structural properties of the solids obtained are correlated to the selectivity and activity for isobutane dehydrogenation in H2 and He reaction media. If a highly dispersed catalyst is suitable, the support has to be prepared by the sol-gel method.
( — ) Pt/ZnAl2O4. H2 He. , — .相似文献
110.
Génesis Adilene Grijalva Bustamante Brianda María Salazar Salas María Mónica Castillo Ortega José Carmelo Encinas Dora Evelia Rodríguez Félix Lerma Hanaiy Chan-Chan Rosa Elena Navarro Gautrín Jorge Romero García Teresa del Castillo Castro 《先进技术聚合物》2023,34(2):621-633
The development of electro-stimulated drug release devices is an innovative approach to attain the drug delivery in accurate doses at target sites in a programmed manner. In this work, novel electroactive nanocomposite hydrogels were prepared by encapsulating green-synthesized polypyrrole (PPy) colloids within chondroitin sulfate (CS) networks during the self-crosslinking of CS via N-ethyl-N′-(3-dimethylaminopropyl) carbodiimide chemistry. The structural and morphological properties of CS/PPy hydrogels were studied by Fourier-transformed infrared spectroscopy, scanning electron microscopy, and swelling kinetic measurements. The chemotherapeutic agent 5-fluorouracil (5-FU) was loaded into CS/PPy samples by hydrogel swelling method, or alternatively, by pre-incubating the drug in polymer mixture before crosslinking. Different electrical stimulations can be used to switch ON and accurately tune the 5-FU delivery from GG/PPy hydrogels. A single pulse potential of 5 V switched on the drug delivery up to 90% from nanocomposite hydrogel, in contrast to the low 5-FU amount released in a passive form (< 20%). PPy electroactive behavior played a determining role as the main driving force in 5-FU release activation. Cytotoxicity of hydrogels with and without 5-FU was examined in normal and cancer cells. Considering the high cytotoxicity of 5-FU, the ON/OFF 5-FU release patterns evidenced the potential of CS/PPy hydrogels for electrically controlled drug delivery in implantable or transdermal drug release devices. 相似文献