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71.
Yong‐Min Lee Yoon‐Bo Shim Seung Jae Lee Sung Kwon Kang Sung‐Nak Choi 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(12):o733-o734
The structure of the title compound, C15H27N2+·ClO4?, consists of a monoprotonated sparteinium cation and a perchlorate anion. The two tertiary N atoms of the cation, one perchlorate O atom and a H atom form a bifurcated hydrogen bond, the four hydrogen‐bonding atoms being nearly in the same plane. 相似文献
72.
Abstract—
The relative biological importance of cis-syn cyclobutane dimer and pyrimidine(6–4)pyr-imidone photoadduct ([6–4] photoadduct) appears to be dependent on the biological species, dipyrimidine sites and the local conformational variation induced at the damaged sites. The single-stranded deoxyn-ucleotide 10-mers containing the site-specific (6–4) adduct or cis-syn cyclobutane dimer of thymidylyl (3'-5')-thymidine were generated by direct photolysis of d(CGCATTACGC) with UVC (220–260 nm) irradiation or UVB (260–320 nm) photosensitization. Three-dimensional structures of the duplex cis-syn and (6–4) decamers of d(CGCATTACGC)d(GCGTAATGCG) were determined by NMR spectroscopy and the relaxation matrix refinement method. The NMR data and structural calculations establish that Watson-Crick base pairing is still intact at the cis-syn dimer site while the hydrogen bonding is absent at the 3'-side of the (6–4) lesion where the T → C transition mutation is predominantly targeted. Overall conformation of the duplex cis-syn decamer was B-DNA and produced a 9° bending in the DNA helix, but a distinctive base orientation of the (6–4) lesion provided a structural basis leading to 44° helical bending. The observed local structure and conformational rigidity at the (6–4) adduct of the thymidylyl(3'-5')-thymidine (T-T [6–4]) lesion site suggest the potential absence of hydrogen bonding at the 3' sides of the (6–4) lesion with a substituted nucleotide during replication under SOS conditions. Contrasting structural distortions induced by the T-T (6–4) adduct with respect to the T-T cis-syn cyclobutane pyrimidine photodimer may explain the large differences in mutation spectrum and repair activities between them. 相似文献
The relative biological importance of cis-syn cyclobutane dimer and pyrimidine(6–4)pyr-imidone photoadduct ([6–4] photoadduct) appears to be dependent on the biological species, dipyrimidine sites and the local conformational variation induced at the damaged sites. The single-stranded deoxyn-ucleotide 10-mers containing the site-specific (6–4) adduct or cis-syn cyclobutane dimer of thymidylyl (3'-5')-thymidine were generated by direct photolysis of d(CGCATTACGC) with UVC (220–260 nm) irradiation or UVB (260–320 nm) photosensitization. Three-dimensional structures of the duplex cis-syn and (6–4) decamers of d(CGCATTACGC)d(GCGTAATGCG) were determined by NMR spectroscopy and the relaxation matrix refinement method. The NMR data and structural calculations establish that Watson-Crick base pairing is still intact at the cis-syn dimer site while the hydrogen bonding is absent at the 3'-side of the (6–4) lesion where the T → C transition mutation is predominantly targeted. Overall conformation of the duplex cis-syn decamer was B-DNA and produced a 9° bending in the DNA helix, but a distinctive base orientation of the (6–4) lesion provided a structural basis leading to 44° helical bending. The observed local structure and conformational rigidity at the (6–4) adduct of the thymidylyl(3'-5')-thymidine (T-T [6–4]) lesion site suggest the potential absence of hydrogen bonding at the 3' sides of the (6–4) lesion with a substituted nucleotide during replication under SOS conditions. Contrasting structural distortions induced by the T-T (6–4) adduct with respect to the T-T cis-syn cyclobutane pyrimidine photodimer may explain the large differences in mutation spectrum and repair activities between them. 相似文献
73.
Corn silk induces nitric oxide synthase in murine macrophages 总被引:1,自引:0,他引:1
Corn silk has been purified as an anticoagulant previously and the active component is a polysaccharide with a molecular mass of 135 kDa. It activates murine macrophages to induce nitric oxide synthase (NOS) and generate substantial amounts of NO in time and dose-dependent manners. It was detectable first at 15 h after stimulation by corn silk, peaked at 24 h, and undetectable by 48 h. Induction of NOS is inhibited by pyrolidine dithiocarbamate (PDTC) and genistein, an inhibitor of nuclear factor kappa B (NF-kappaB) and tyrosine kinase, respectively, indicating that iNOS stimulated by corn silk is associated with tyrosine kinase and NF-kappaB signaling pathways. IkappaB-alpha degradation was detectible at 10 min, and the level was restored at 120 min after treatment of corn silk. Corn silk induced nuclear translocation of NF-kappaB by phosphorylation and degradation of IkappaB-alpha. 相似文献
74.
Hwang JY Choi HS Seo JS La HJ Kim DS Jeon HS Jeon MK Lee DH Gong YD 《The Journal of organic chemistry》2005,70(24):10151-10154
[reaction: see text] A library containing 1200 analogues of 2,6-difunctionalized 2-methyl-2H-1-benzopyran was constructed by using a solid-phase synthesis protocol. Polymer-bound 6-amido-, 6-sulfonamido-, and 6-uredo-functionalized 2-hydroxymethyl-2-methylbenzopyrans 10 were prepared as part of a first-generation diversification step by employing reactions of respective acid halides, sulfonyl chlorides, and isocyanates with the amine precursor 7. Transformations of the resin-bound intermediates 10 by reactions with alkyl and acid halides were then used to produce a diverse series of 2,6-difunctionalized 2-methyl-2H-1-benzopyran analogues 12 and 14. 相似文献
75.
Kang EJ Cho EJ Ji MK Lee YE Shin DM Choi SY Chung YK Kim JS Kim HJ Lee SG Lah MS Lee E 《The Journal of organic chemistry》2005,70(16):6321-6329
(+)-SCH 351448 (Na+ salt A) was synthesized employing ring-closing olefin metathesis reaction of an open diene diester intermediate for construction of the 28-membered macrodiolide structure. The open diene diester was prepared from the monomeric hydroxy carboxylic acid and two different olefin fragments. The monomeric hydroxy acid was synthesized via Julia-Julia coupling reaction of intermediates derived from the same olefinic fragments. Oxane units in these fragments were prepared by radical cyclization reactions of beta-alkoxyacrylates. Analogous SCH 351448 salts incorporating other mono- and divalent cations may be prepared. Under acidic conditions, SCH 351448 (Na+ salt A) was the most stable complex, but SCH 351448 (Ca2+ salt) and (Na+ salt B) appear to be physiologically important species. 相似文献
76.
Lee KB Kim DJ Lee ZW Woo SI Choi IS 《Langmuir : the ACS journal of surfaces and colloids》2004,20(7):2531-2535
The micropatterns of biological ligands (biotin and RGD peptides) were generated on a flat surface of biodegradable polymer, poly(glycolic acid) (PGA). The immobilization of biological ligands onto the surface of biodegradable polymers (especially aliphatic polyesters) is usually hampered by the absence of functionalizable groups on the polymer backbone. We demonstrate herein that PGA polymer films were modified by surface hydrolysis to introduce carboxylic acid groups on the film surfaces, which were subsequently used for patterning amine-terminated ligands by microcontact printing. Fluorescence microscopy was used to verify the pattern of biotin on the surface of the PGA films after complexation with fluorescein-conjugated streptavidin. In addition, the cellular micropatterns were obtained from micropatterns of RGD peptides on the surface-hydrolyzed PGA films. 相似文献
77.
Chi YS Jung YH Choi IS Kim YG 《Langmuir : the ACS journal of surfaces and colloids》2005,21(10):4669-4673
In this paper, we report surface-initiated d(A-T) polymerization by Taq DNA polymerase as a method for constructing DNA-tethered surfaces using an enzyme. The enzymatic polymerization was conducted successfully via two steps: tethering of oligo d(A-T)s onto the surface presenting carboxylic acids by amide coupling and surface-initiated polymerization using Taq DNA polymerase. In this enzymatic polymerization process, the design and construction of carboxylic acid-presenting surfaces were found to be an important factor: DNA growth did not occur on the gold surface coated only with the self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid (MHDA), but effectively proceeded on the surfaces presenting mixed SAMs of MHDA and 1-pentadecanethiol. The coupling of oligo d(A-T)s and the subsequent DNA polymerization reaction were characterized by polarized infrared external reflectance spectroscopy, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy. 相似文献
78.
Hyun-Nam Cho Sam-Kwon Choi 《Journal of polymer science. Part A, Polymer chemistry》1985,23(5):1469-1475
The ring-opening polymerization of an unsaturated bicyclic lactam, 2-azabicyclo-[2,2,1]-hept-5-en-3-one (ABHEO), was carried out using metathesis catalysts under various reaction conditions. It is observed that the best results (34% conversion and ηinh: 0.18 dL/g) were obtained when the mole ratios of ABHEO to WCl6 as a catalyst and WCl6 to AlEt3 as a cocatalyst were 200 and 4, respectively. The infrared (IR) and nuclear magnetic resonance (1H- and 13C-NMR) spectra of the polymer obtained indicated that the ABHEO was transformed to the ring-opened polymer, poly(2-pyrrolidone-3,5-diylvinylene) [poly(ABHEO)]. The resulting polymer was amorphous as determined by DSC analysis, which showed only secondary transition at 100°C. 相似文献
79.
Yu-Ping Zhang Kwang-Pill Lee Hyun-Joo Noh Ali Md Showkat Seong-Ho Choi 《Microchemical Journal》2004,78(2):99-106
An appropriate optimization strategy should be used to find a desired resolution or selectivity with a minimum number of experiments in a limited time, which could assure the baseline separation of all target compounds. It was usually realized by means of a specialized computer program. In this paper, mapping optimization method and overlapping resolution mapping were compared for the optimization of a reversed-phase high-performance liquid chromatography (HPLC) isocratic separation of neutral compounds. The calculated resolutions and separation time of 7 to 10 experiments are fitted by different equations, which were used to build a contour plot with a minimum effective resolution and maximum retention time as a function of a mobile phase composition. The balance between resolution and analysis time could be easily realized by the overlapping of the final overlapping resolution mapping and analysis time mapping. The validity of the two methods was confirmed by some typical experiments. The models are simple, visual, and common without theoretical arithmetic. 相似文献
80.
Novel 5-5-6 tricyclic compounds containing cyclopentenone have been constructed by the dicobalt octacarbonyl catalyzed tandem [2 + 2 + 1] and [2 + 2 + 2] cycloaddition reaction between a diyne and two phenylacethylene under CO pressure. 相似文献