Oxidatively generated damage to DNA frequently appears in the human genome as the effect of aerobic metabolism or as the result of exposure to exogenous oxidizing agents such as ionization radiation. In this paper, for the first time, the electronic properties of nucleoside pairs containing 5′,8-cyclo-2′-deoxyadenosine (cdA) in their 5′R and 5′S diastereomeric forms (cdA(R)::T and cdA(S)::T) as the simplest model of ds-DNA have been discussed. The following values of the selected electronic parameters, measured in eV, were found for cdA(R)::T, cdA(S)::T, and dA::T, respectively, adiabatic/vertical electron affinity: 0.39/0.24, 0.35/0.18, 0.33/0.21; and adiabatic/vertical ionization potential: 7.27/7.50, 7.7.25/7.49, 7.03/7.27. Moreover, based on the results of the relaxation energy, the presence of cdA(S)::T should provide the highest barrier for electron transfer in ds-DNA. Analyses of hydrogen bond length deviations reveal that the formation of cationic forms results in higher elongation than that of anionic forms. Moreover, during the electron attachment or detachment for the investigated cdA(R)::T, cdA(S)::T, and dA::T nucleoside pairs, the same scheme of changes in hydrogen bond length was noted. 相似文献
A method for the preparation of the first acetylenedicarboxamidinium salt from a bis‐orthoamide derivative of acetylenedicarboxyclic acid has been established. The salt reacted with cyclopentadiene and furan at room temperature to give bicyclic [4+2]‐cycloaddition products. The solid compounds were characterized by solution NMR spectroscopy and by single‐crystal X‐ray diffraction. Quantum‐chemical calculations of the isolated N,N,N′,N′,N′′,N′′,N′′′,N′′′‐octamethyl‐acetylene‐bis(carboxamidinium) ion showed very good agreement with the spectroscopic and diffraction data. 相似文献
Why Pentose-And Not Hexose-Nucleic Acids? Part III. Oligo(2′,3′-dideoxy-β-D -glucopyranosyl)nucleotides. (‘Homo-DNA’): Base-Pairing Properties
1 Summary in collaboration with Prof. Dr. C. E. Wintner, Haverford College, Haverford, PA 19041-1392.
The paper presents results of a comprehensive investigation on the pairing properties of homo-DNA oligonucleotides, the preparation of which has been described in Part II of this series [2]. The investigation was carried out by using established methods described in the literature for the characterization of oligonucleotides in the natural series, such as determination of melting temperatures of oligonucleotide duplexes by temperature-dependent of melting temperatures, determination of pairing stoichiometry by ratio-dependent UV spectroscopy of binary mixtures of pairing partners, temperature-dependent CD spectroscopy, gel electrophoresis under non-denaturing conditions, and – in selected cases – 1H – and31P-NMR spectroscopy. The systematic comparison of the paring properties of homo-DNA oligonucleotides with corresponding DNA nucleotides (up to dodecamers) indicates that homo-DNA is a highly efficient, autonomous, artificial pairing system with a pairing behavior that is in part similar to, but also, in part, strikingly different from, the pairing behavior of DNA. The pairing properties established so far are listed below in a manner that reflects the sequence of subtitles in Chapt.2 of the text; they were determined under the conditions: H2O, 0.15M NaCl, 0.01M Tris-HCl buffer, pH 7, oligonucleotide concentrations in the μM range, 1:1 ratio of single strands in the case of non-selfcompementary sequences. 相似文献
The nature of the S? H???S hydrogen‐bonding interaction in the H2S dimer and its structure has been the focus of several theoretical studies. This is partly due to its structural similarity and close relationship with the well‐studied water dimer and partly because it represents the simplest prototypical example of hydrogen bonding involving a sulfur atom. Although there is some IR data on the H2S dimer and higher homomers from cold matrix experiments, there are no IR spectroscopic reports on S? H???S hydrogen bonding in the gas phase to‐date. We present experimental evidence using VUV ionization‐detected IR‐predissociation spectroscopy (VUV‐ID‐IRPDS) for this weak hydrogen‐bonding interaction in the H2S dimer. The proton‐donating S? H bond is found to be red‐shifted by 31 cm?1. We were also able to observe and assign the symmetric (ν1) stretch of the acceptor and an unresolved feature owing to the free S? H of the donor and the antisymmetric (ν3) SH stretch of the acceptor. In addition we show that the heteromolecular H2S–MeOH complex, for which both S? H???O and O? H???S interactions are possible, is S‐H???O bound. 相似文献
The hydrolysis of PEtOx is studied to evaluate the potential toxicity of partially hydrolyzed polymers that might interfere with its increasing popularity for biomedical applications. The hydrolysis of PEtOx is studied in the presence of digestive enzymes (gastric and intestinal) and at 5.8 M hydrochloric acid as a function of temperature (57, 73, 90, and 100 °C). It is found that PEtOx undergoes negligible hydrolysis at 37 °C and that thermal and solution properties are not altered when up to 10% of the polymer backbone is hydrolyzed. Mucosal irritation and cytotoxicity is also absent up to 10% hydrolysis levels. In conclusion, PEtOx will not decompose at physiological conditions, and partial hydrolysis will not limit its biomedical applications.
Direct ruthenium‐catalyzed C C coupling of alkynes and vicinal diols to form β,γ‐unsaturated ketones occurs with complete levels of regioselectivity and good to complete control over the alkene geometry. Exposure of the reaction products to substoichiometric quantities of p‐toluenesulfonic acid induces cyclodehydration to form tetrasubstituted furans. These alkyne‐diol hydrohydroxyalkylations contribute to a growing body of merged redox‐construction events that bypass the use of premetalated reagents and, hence, stoichiometric quantities of metallic by‐products. 相似文献
N-tosyl-2- and N-tosyl-4-halogen-substituted derivatives of 2-(1-methylbut-2-en-1-yl)aniline were synthesized and their molecular iodine-mediated cyclization was investigated. The cyclization upon interaction of N-tosyl-6-methyl-2-(1-methylbut-2-en-1-yl)aniline with molecular iodine in methyl tert-butyl ether or acetonitrile was studied, as well as the interaction of this sulfonamide with N-bromosucinimide in dichloromethane. Synthesized (2R*,3R*)- and (2R*,3S*)-N-arylsulfonyl-2-(1-halogenoethyl)-3-methylindoline derivatives showed cytotoxic activity against HEK293 cells, SH-SY5Y, Jurkat, and HepG2 cell lines. The compounds (2R*,3S*)-N-arylsulfonyl-7-bromo-2-(1-halogenoethyl)-3-methylindoline cis- 4a , stereoisomeric (2R*,3R*)-trans- 4h and (2R*,3S*)-N-tosyl-7-chloro-2-(1-halogenoethyl)-3-methylindoline cis- 4h demonstrated selective toxicity against SH-SY5Y cell line (IC50 ≈ 3 ÷ 5 μM), and did not affect HEK293, Jurkat, and HepG2 cells. 相似文献
(R,S)-5-Ethyl-5-(2′-pentyl)barbituric acid (I)1,2 is metabolized invivo to give all four possible optical isomers of 5-ethyl-5-(3′-hydroxy-1′-methylbutyl)barbituric acid (II). 3,4 From metabolism studies of pure (1′S)- I and (1′3)-I, Palmer and co-workers4,5 were able to determine the relative amounts of each of the four isomers formed. These studies showed that (1′S)-I gave mainly one enantiomer of (1′S)-II, whereas (1′R)-I gave approximately equal amounts of both (1′R)-II enantiomers. 相似文献
Six new complexes, Mn(CO)(
5-C5H5){Ph2P(S)(CH2)nP(S)Ph2}] (1a–3a) [(1a), n=1; (2a), n=2; (3a), n=3] and [Mn2(CO)4(
5-C5H5)2(cis--Ph2P(S)(CH2)nP(S)Ph2)] (1b–3b) [(1b), n=1; (2b), n=2; (3b), n=3] have been synthesized by the photochemical reaction of [(
5-C5H5)Mn(CO)3] with Ph2P(S)(CH2)nP(S)Ph2 [n=1, dppm(S)2; 2, dppe(S)2; 3, dppp(S)2]. The complexes have been characterized by elemental analysis, mass spectroscopy, f.t.-i.r. and 31P–[1H]-n.m.r. spectroscopy. The spectroscopic studies reveal that coordination of the ligand iscis-chelate bidentate in [Mn(CO)(
5-C5H5){Ph2P(S)(CH2)nP(S)Ph2}] (1a–3a) and cis-bridging bidentate between two metals in [Mn2(CO)4(
5-C5H5)2(cis--Ph2P(S)(CH2)nP(S)Ph2)] (1b–3b). 相似文献
A remote 4J(F,H) coupling (F? C(α)? C(O)? N? H) of up to 4.2 Hz in α‐fluoro amides with antiperiplanar arrangement of the C? F and the C?O bonds (dihedral angle F? C? C?O ca. 180°) confirms that previous NMR determinations, using the XPLOR‐NIH procedure, of the secondary structures of β‐peptides containing β3hAla(αF) and β3hAla(αF2) residues were correct. In contrast, molecular‐dynamics (MD) simulations, using the GROMOS program with the 45A3 force field, led to an incorrect conclusion about the relative stability of secondary structures of these β‐peptides. The problems encountered in NMR analyses and computations of the structures of backbone‐F‐substituted peptides are briefly discussed. 相似文献