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41.
Xeroderma pigmentosum (XP) is a rare, recessively transmitted genetic disease characterized by increasingly marked dyspigmentation and xerosis (dryness) of sun‐exposed tissues, especially skin. Skin cancers characteristically develop in sun‐exposed sites at very much earlier ages than in the general population; these are often multiple and hundreds or even thousands may develop. Eight complementation groups have been identified. Seven groups, XP‐A…G, are associated with defective genes encoding proteins involved in the nucleotide excision DNA repair (NER) pathway that recognizes and excises mutagenic changes induced in DNA by sunlight; the eighth group, XP‐V, is associated with defective translesion synthesis (TLS) bypassing such alterations. The dyspigmentation, xerosis and eventually carcinogenesis in XP patients appear to be due to their cells’ failure to respond properly to these mutagenic DNA alterations, leading to mutations in skin cells. A subset of cases, especially those in some complementation groups, may develop neurological degeneration, which may be severe. However, in most XP patients, in the past the multiple skin cancers have led to death at an early age due to either metastases or sepsis. Using either topical 5‐fluorouracil or imiquimod, we have developed a protocol that effectively prevents most skin cancer development in XP patients. 相似文献
42.
Seguin J Moutiez M Li Y Belin P Lecoq A Fonvielle M Charbonnier JB Pernodet JL Gondry M 《Chemistry & biology》2011,18(11):1362-1368
Cyclodipeptide synthases (CDPSs) are small enzymes structurally related to class-I aminoacyl-tRNA synthetases (aaRSs). They divert aminoacylated tRNAs from their canonical role in ribosomal protein synthesis, for cyclodipeptide formation. All the CDPSs experimentally characterized to date are?bacterial. We show here that a predicted CDPS from the sea anemone Nematostella vectensis is an active CDPS catalyzing the formation of various cyclodipeptides, preferentially containing tryptophan. Our findings demonstrate that eukaryotes encode active CDPSs and suggest that all CDPSs have?a similar aminoacyl-tRNA synthetase-like architecture and ping-pong mechanism. They also raise questions about the biological roles of the cyclodipeptides produced in bacteria and eukaryotes. 相似文献
43.
Aubert V Ordronneau L Escadeillas M Williams JA Boucekkine A Coulaud E Dragonetti C Righetto S Roberto D Ugo R Valore A Singh A Zyss J Ledoux-Rak I Le Bozec H Guerchais V 《Inorganic chemistry》2011,50(11):5027-5038
A series of cationic Ir(III) substituted bipyridyl ()(N(∧)N (N(∧)N-bpy) complexes incorporating electron-donor and -acceptor substituents, [Ir(C(∧)N-ppy-R')(2)(N(∧)N-bpy-CH═CH-C(6)H(4)-R)][X] (X(-) = PF(6)(-) or C(12)H(25)SO(3)(-)), 2 (a, R = NEt(2) and R' = Me; b, R = O-Oct and R' = Me; c, R = NO(2) and R' = C(6)H(13); C(∧)N-ppy = cyclometalated 2-phenylpyridine, [Ir(C(∧)N-ppy-Me)(2)(N(∧)N-bpy-CH═CH-thienyl-Me)][PF(6)], 2d, and the dithienylethene (DTE)-containing complex 2e have been synthesized and characterized, and their absorption, luminescence, and quadratic nonlinear optical (NLO) properties are reported. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations on the complexes facilitate a detailed assignment of the excited states involved in the absorption and emission processes. All five complexes are luminescent in a rigid glass at 77 K, displaying vibronically structured spectra with long lifetimes (14-90 μs), attributed to triplet states localized on the styryl-appended bipyridines. The second-order NLO properties of 2a-d and related complexes 1a-d with 1,10-phenanthrolines have been investigated by both electric field induced second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques. They are characterized by high negative EFISH μβ values which decrease when the ion pair strength between the cation and the counterion (PF(6)(-), C(12)H(25)SO(3)(-)) increases. The EFISH response is mainly controlled by metal-to-ligand charge-transfer/ligand-to-ligand charge-transfer (MLCT/L'LCT) processes. A combination of HLS and EFISH techniques is used to evaluate both the dipolar and octupolar contributions to the total quadratic hyperpolarizability, demonstrating that the major contribution is controlled by the octupolar part. The incorporation of a photochromic DTE unit into the N(∧)N-bpy ligand (complex 2e) allows the luminescence to be switched ON or OFF. The photocyclisation of the DTE unit can be triggered by using either UV (365 nm) or visible light (430 nm), leading to an efficient quenching of the ligand-based 77 K luminescence, which can be restored upon irradiation of the closed form at 715 nm. In contrast, no significant modification of the EFISH μβ value is observed upon photocyclization, suggesting that the quadratic NLO response is dominated by the MLCT/L'LCT processes, rather than by the intraligand excited states localized on the substituted bipyridine ligand. 相似文献
44.
45.
Florine Cavelier Sylvie Gomez Robert Jacquier Muriel Llinares Jean-Luc Mercadier Clment Petrus Jean Verducci 《Tetrahedron: Asymmetry》1993,4(12)
This work describes a convenient and accurate method for optical purity determination of α-hydroxy acids. Their derivatization with commercially available valine methyl ester affords diastereoisomers easily separable by HPLC using achiral C18 columns. 相似文献
46.
Patrick Rozier Laure Vendier Jean Galy 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):i111-i113
A single crystal of KVTeO5, potassium vanadium tellurite, has been grown. The present structure determination has been conducted together with the refinement of the NaVTeO5 homologue, sodium vanadium tellurite, for the sake of precise comparison. The network consists of [VTeO5]n ribbons built up by VO4 tetrahedra linking centrosymmetric Te2O6 groups and stacked along the [010] direction; the alkali cations are intercalated in between. The TeIV atom exhibits a typical one‐sided coordination number (CN) of 4, completed by a lone pair, which forms a distorted triangular bipyramid with the four O atoms. 相似文献
47.
R. Faure J. P. Galy G. Giusti E. J. Vincent J. Elguero 《Magnetic resonance in chemistry : MRC》1974,6(9):485-486
Azido-tetrazole equilibrium is observed in the case of a solution of tetrazolo [5,1-b] benzothiazole in CDCl3, using proton magnetic resonance at 250 MHz. Analysis of the spectra obtained yields the chemical shifts and the coupling constants of the two tautomeric forms. 相似文献
48.
W. J. Firth C. T. Seaton E. M. Wright S. D. Smith M. E. Prise G. Litfin J. Mlynek F. Mitschke R. Deserno W. Lange H. J. Eichler F. Maßmann C. Zaki J. Heritage F. V. Karpushko G. V. Simitsyn J. A. Martin-Pereda M. A. Muriel P. W. Smith W. J. Tomlinson Ch. Harder K. Y. Lau A. Yariv J. C. Khoo S. Shepard S. Nahar S. L. Zhuang 《Applied physics. B, Lasers and optics》1982,28(2-3):131-141
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50.
An electrochemical sensor with two soluble enzymes allows assay of 0.1–10 mM, l- carnitine with an accuracy of 2%. The assay takes about 2 min. The first enzyme, carnitine dehydrogenase, catalyzes the oxidation of l-carnitine by NAD+. The NADH formed is oxidized by hexacyanoferrate(III) in a reaction catalyzed by diaphorase, and the hexacyanoferrate(II) produced is oxidized by electrolysis at 0.3 V. The sensor can be used for several days. 相似文献