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101.
Jain V Harris FA Aderholz M Aggarwal MM Akbari H Allport PP Baba PV Badyal SK Barth M Baton JP Bingham HH Brucker EB Burnstein RA Campbell JR Cence RJ Chatterjee TK Clayton EF Corrigan G Coutures C Deprospo D Devanand De Wolf E Faulkner PJ Fretter WB Gupta VK Guy J Hanlon J Harigel GG Jabiol MA Jacques P Jones GT Jones MD Kafka T Kalelkar M Kasper P Kaul GL Kaur M Kohli JM Koller EL Krawiec RJ Lauko M Lys J Marage P Milburn RH Miller DB Mittra IS Mobayyen MM Moreels J Morrison DR Myatt G 《Physical review D: Particles and fields》1990,41(7):2057-2073
102.
Polyketides and nonribosomal peptides constitute a large and diverse set of natural products with biological activity in microbial survival and pathogenesis, as well as broad pharmacological utility as antineoplastics, antibiotics or immunosupressants. These molecules are biosynthesized by the ordered condensation of monomer building blocks, acyl-CoAs or amino acids, leading to construction of linear acyl chains. Many of these natural products are constrained to their bioactive conformations by macrocyclization whereby, in one of the terminal steps of biosynthesis, parts of the molecule distant in the constructed linear acyl chain are covalently linked to one another. Typically, macrocyclization is catalyzed by a thioesterase domain at the C-terminal end of the biosynthetic assembly line, although alternative strategies are known. The enzymology of these macrocyclization catalysts, their structure, mechanism, and catalytic versatility, is the subject of this review. The diversity of macrocyclic structures accessed by enzyme catalyzed cyclization of linear acyl chains as well as their inherent substrate tolerance suggests their potential utility in reprogramming natural product biosynthesis pathways or accessing novel macrocyclic structures. 相似文献
103.
Summary New carbodithioate complexes of the oxovanadium(IV), manganese(II) and manganese(III) ions have been prepared and studied by i.r. and electronic spectral and variable temperature magnetic susceptibility (77K to room temperature) measurements. The carbodithioate ligands, 4-methylpiperazine-1-carbodithioate (4-MPipzcdt) and 4-phenylpiperazine-1-carbodithioate (4-PPipzcdt), were derived from heterocyclic secondary amines. The VO(4-MPipzcdt)2 and VO(4-PPipzcdt)2 complexes possess C
4v
symmetry; Mn(4-PPipzcdt)2 is tetrahedral and Mn(4-PPipzcdt)3 is octahedral. All exhibit abnormal room temperature magnetic moments and the variable temperature magnetic moments suggest antiferromagnetism for the oxovanadium(IV) and the manganese(II) complexes and the occurrence of low spin (3
T
1g
) high spin (5
E
g
) equilibrium in addition to antiferromagnetic interactions in the manganese(III) complex. The spin-spin exchange parameter (-2J) value for the VO(4-MPipzcdt)2 complex has been calculated using variable temperature magnetic susceptibility data. 相似文献
104.
Induction of phr gene expression in E. coli strain KY706/pPL-1 by He-Ne laser (632.8 nm) irradiation
Kohli R Bose B Gupta PK 《Journal of photochemistry and photobiology. B, Biology》2001,60(2-3):136-142
We have observed that He–Ne laser irradiation of E. coli strain KY706/pPL-1 leads to induction of photolyase gene, phr. The magnitude of induction was found to depend on the He–Ne laser fluence, fluence rate and post-irradiation incubation period in the nutrient medium. The optimum values for fluence and fluence rate were 7×103 J/m2 and 100 W/m2, respectively, and the induction of phr gene was observed to saturate beyond an incubation period of 2 h. Experiments carried out with singlet oxygen quenchers and with D2O suggest that the effect is mediated via singlet oxygen. Photoreactivation studies carried out after UVC exposure of both the He–Ne laser-exposed as well as unexposed cells showed a larger surviving fraction in the He–Ne laser pre-irradiated cells. This can be attributed to He–Ne laser irradiation-induced induction of phr expression. However, since even without photoreactivating light He–Ne laser pre-irradiated cells show higher survival against UVC radiation it appears that He–Ne laser irradiation induces both light-dependent as well as dark DNA repair processes. 相似文献
105.
The pinkish-violet complex developed on interaction of ruthenium(III) with 3-nitroso-4-hydroxy-5,6-benzocoumarin (NHBC) in the pH range 5.5-8.0 can be extracted into n-butanol. The complex has an absorption maximum at 520 nm. Maximum colour development takes place after heating for 20 min on a steam-bath and the extracted complex is stable for at least 92 hr. Beer's law is followed up to 7.4 ppm of ruthenium. The molar absorptivity is 1.04 x 10(4) 1.mole(-1).cm(-1). The composition of the complex is 1 : 2 (ruthenium: NHBC). None of the other platinum metals was found to interfere in the determination of ruthenium, even though present in large excess. 相似文献
106.
107.
The conformational isomerism, relative stabilities of isomeric forms, acid–base behavior, and hydrogen bonding of formylphosphinous acid (FPA), an isostere of formohydroxamic acid (FHA) and its tautomer formylphosphine oxide have been analyzed in the present study. Molecular orbital and density functional theory methods in conjunction with 6-31+G* basis set have been employed. The protonation, deprotonation, and hydrogen bonding abilities of FHA and FPA have been compared. FPA has P as preferred site of deprotonation like N in FHA, but they differ in their preferred site of protonation. With similar nature and orientation of H-bond donor and acceptor atoms, stabilization energy of most stable aggregate of FHA with water is 0.99 kcal/mol higher than that of similar aggregate of FPA with water. In addition, FPA is more stable than its corresponding oxide form in gas phase as well as on H-bonding interaction with single water molecule. 相似文献
108.
N. Srinivasan S. Thirumaran Sabeta Kohli Rajnikant 《Journal of chemical crystallography》2010,40(6):505-509
109.
We report here a novel system where the rate of energy transfer is based on changes in the spectral overlap between the emission of the donor and the absorption of the acceptor (J) as well as changes in the quantum yield of the acceptor. We use the fluorophore dansyl as the donor and polydiacetylene (PDA) as the acceptor to demonstrate the modulation of FRET through conformationally induced changes in the PDA absorption spectrum following thermal treatment that converts the PDA backbone of the liposome from the blue form to the red form. Energy transfer was found to be significantly more efficient from dansyl to the red-form PDA. These findings support the basis of a new sensing platform that utilizes J-modulated FRET as an actuating mechanism. 相似文献
110.
Charoo NA Shamsher AA Kohli K Pillai K Rahman Z 《Colloids and surfaces. B, Biointerfaces》2008,65(2):300-307
Penetration enhancing potential of tulsi and turpentine oil on transdermal delivery of flurbiprofen, a potent non-steroidal anti-inflammatory agent, was investigated. The transdermal permeation rate of flurbiprofen across the rat abdominal skin from binary solvent mixture composition of propylene glycol (PG):isopropyl alcohol (IPA) (30:70%, v/v) was 98.88 microg/cm(2)/h, significantly higher than other binary solvent mixtures. The corresponding steady state plasma concentration, 0.71 microg/ml, was much lower than required steady state plasma concentration of 3-5 microg/ml. Hence influence of tulsi and turpentine oil in the optimized binary solvent mixture along with the increased drug load on the flurbiprofen permeation was evaluated. The magnitude of the flux enhancement factor with turpentine oil and tulsi oil was 2.4 and 2.0 respectively at 5% (v/v) concentration beyond which there was no significant increase in the flux. Addition of 2% (w/v) hydroxypropyl methylcellulose (HPMC), as a thickening agent, resulted in desired consistency for the fabrication of patch with insignificant effect on permeation rate of flurbiprofen. The reservoir type of transdermal patch formulation, fabricated by encapsulating the flurbiprofen reservoir solution within a shallow compartment moulded from polyester backing film and microporous ethyl vinyl acetate membrane, did not modulate the skin permeation of flurbiprofen through rat skin in case of turpentine formulations whereas flux of formulations with tulsi oil was significantly altered. The influence of penetration enhancer and solvents on the anatomical structure of the rat skin was studied. Enhancement properties exhibited by turpentine oil and tulsi oil in optimized binary solvent mixture were superior as compared to solvent treated and normal control groups with negligible skin irritation. The fabricated transdermal patches were found to be stable. The bioavailability of flurbiprofen with reference to orally administered flurbiprofen in albino rats was found to increase by 2.97, 3.80 and 5.56 times with transdermal patch formulation without enhancer, tulsi and turpentine oil formulations, respectively. The results were confirmed by pharmacodynamic studies in rat edema inflammation model. 相似文献