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11.
12.
Ole Faurskov Nielsen 《Chemical physics letters》1979,60(3):515-517
The recently developed molecular form of the ground state inversion potential method (GIPM) is applied here to the calculation of the total subshell photoionization cross sections of the water molecule in the energy range from threshold to 50 eV. The results show that the ionization can be accurately represented as a superposition of atomic processes. 相似文献
13.
John T. W. Lai Frankie W. Lau Damon Robb Peter Westh Gerda Nielsen Christa Trandum Aase Hvidt Yoshikata Koga 《Journal of solution chemistry》1995,24(1):89-102
The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H2O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H2O. The values of the excess partial molar Gibbs energies for both DMSO and H2O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H2O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H2O molecules from exposure to the nonpolar alkyl groups of DMSO. 相似文献
14.
A cyclic dinucleotide with a butylene linker between the upper 2'-C position and the 3'-O-phosphate linkage was synthesised from simple nucleoside building blocks via a tandem ring-closing metathesis and hydrogenation procedure. The major of two phosphorus epimers was incorporated into an oligodeoxynucleotide, as well as into an LNA-DNA mixmer oligonucleotide. These were evaluated as parts in three different secondary structures, a duplex, a bulged duplex and a three-way junction, with both DNA and RNA complements. In the DNA:RNA hybrid molecule, the oligodeoxynucleotide containing this single 2'-C to 3'-O-phosphate butylene linkage was found to stabilise a three-way junction. 相似文献
15.
An optimized semi-automatic protocol for parallel synthesis of up to 96 peptide nucleic acids (PNA) or PNA-peptide conjugates using Boc-protection strategy has been developed using a robotic system. The approach is illustrated by synthesizing PNA and PNA-peptide libraries varying between 15 and 27 amino acid units. The peptides (NLS (nuclear localization signal) or Tat-peptide) were attached to N-terminus of the PNA. The method was found to be far superior to that based on the SPOT/Fmoc protocol by which PNA oligomers are synthesized on a modified cellulose membrane. On a 0.5 micromole scale the method typically yielded 2 mg product of 90% purity by HPLC/MALDI-TOF analysis. This approach is suitable for screening of a large number of PNA and/or peptide sequences for biochemical and biological studies. 相似文献
16.
Axel Ingendoh Jan Becher Helen Clausen Helle Chris Nielsen 《Tetrahedron letters》1985,26(9):1249-1252
The high reactivity of the -1-acyloxy-1,3-pentadiene-5-ols as dienes in intramolecular Diels-Alder reactions with maleic anhydride and fumaric acid ethylester monochloride is discussed. 相似文献
17.
Nasser R. El-Brollosy Claus Nielsen Erik B. Pedersen 《Monatshefte für Chemie / Chemical Monthly》2005,12(2):1247-1254
A series of Emivirine and GCA-186 analogues substituted at N-1 with indan-1-yloxymethyl (6a–6c) and indan-2-yloxymethyl (6d–6f) were synthesized by reaction of the corresponding bis(indanyloxy)methans with uracils having 5-ethyl or 5-isopropyl and 6-benzyl or 6-(3,5-dimethylbenzyl) substituents. A route to the corresponding N-1 substituted 4-hydroxybut-2-enyloxymethyl analogue was also devised. All newly synthesized compounds showed potent activity against wild-type HIV-1, the most active compound being 5-ethyl-1-(indan-1-yloxymethyl)-6-(3,5-dimethylbenzyl)uracil (6b), which was 50-fold more active than Emivirine. 相似文献
18.
DNA sequences have previously been reported to act as templates for the synthesis of PNA, and vice versa. A continuous evolutionary transition from an informational replicating system based on one polymer to a system based on the other would be facilitated if it were possible to form chimeras, that is molecules that contain monomers of both types. Here we show that ligation to form chimeras proceeds efficiently both on PNA and on DNA templates. The efficiency of ligation is primarily determined by the number of backbone bonds at the ligation site and the relative orientation of template and substrate strands. The most efficient reactions result in the formation of chimeras with ligation junctions resembling the structures of the backbones of PNA and DNA and with antiparallel alignment of both components of the chimera with the template, that is, ligations involving formation of 3'-phosphoramidate and 5'-ester bonds. However, double helices involving PNA are stable both with antiparallel and parallel orientation of the two strands. Ligation on PNA but not on DNA templates is, therefore, sometimes possible on templates with reversed orientation. The relevance of these findings to discussions of possible transitions between genetic systems is discussed. 相似文献
19.
Yasser M. Loksha Per T. Jrgensen Erik B. Pedersen Mahmoud A. El‐Badawi Ahmed A. El‐Barbary Claus Nielsen 《Journal of heterocyclic chemistry》2002,39(2):375-382
5‐Alkyl‐4‐benzyl‐1,3‐dihydroimidazol‐2‐ones ( 3a‐d ) and 5‐alkyl‐4‐benzyl‐1,3‐dihydroimidazole‐2‐thiones (7a‐d) were prepared via Dakin West reaction on DL‐phenylalanine with the appropriate aliphatic acid anhydrides followed by hydrolysis and reaction with potassium cyanate or potassium thiocyanate. Compounds 3a‐d were alkylated with ethoxymethyl chloride to give the alkylated imidazoles 5a‐d which were considered analogues of Emivirine with deletion of carbonyl group at the 4‐position. Alkylation of 7a‐d afforded the corresponding S‐alkylated derivatives 8a‐p which in a similar way were considered analogues of S‐DABO. However all the imidazole derivatives were devoid of activity against HIV. 相似文献
20.
A new protocol for the oxidative cleavage of terminal alkenes to give exclusively primary alcohols in high yields is introduced. The protocol is based on RuO4-mediated dihydroxylation, NaIO4-mediated diol cleavage, and NaBH4-mediated reduction, but the introduction of a reducing step before the diol cleavage removes the formation of byproducts and improves the yield significantly. The new protocol has been developed and used for the improved preparation of a [3.2.0]bicycloarabinonucleoside with important potential in antisense and antigene technology. 相似文献