Showing papers by "Claus J. Nielsen published in 2007"
TL;DR: The integrated UV absorption cross-sections of HCHO, HCDO, and DCDO are equal to within the experimental uncertainty.
Abstract: UV (240-370 nm) and IR (3200-1500 cm(-1)) absorption cross-sections of HCHO, HCDO, and DCDO in a bath gas of N(2) at atmospheric pressure and 296 K are reported from simultaneous measurements in the two spectral regions. Cross-sections were placed on an absolute scale through quantitative conversion of formaldehyde to CO and HCOOH by titration with Br atoms, also monitored by FTIR. The integrated UV absorption cross-sections of HCHO, HCDO, and DCDO are equal to within the experimental uncertainty.
48 citations
TL;DR: The solvation shell of aqueous formaldehyde has been studied by ab initio molecular dynamics using two different DFT approaches using BLYP and PBE functionals as discussed by the authors.
Abstract: The solvation shell of aqueous formaldehyde has been studied by ab initio molecular dynamics. Two different DFT approaches using BLYP and PBE functionals were explored. The results show only a slightly different mobility in the solvation shells and allow characterization of the hydrogen bonded structure with a H2C = O··HOH hydrogen bond lifetime of ca. 3 ps. Formaldehyde hydrolysis was studied by following the reverse process, methanediol decomposition, by Blue Moon constrained MD showing that four water molecules are directly involved in the reaction and assisted by the whole hydration shell. The total energy of the aqueous methanediol to formaldehyde inter-conversion process is calculated with a barrier height of ca. 95 kJ mol−1 while the corresponding free energy barrier is only ΔG‡ = 46 kJ mol−1 at 300 K.
38 citations
TL;DR: The atmospheric implications of the large isotope effect in the relative rate of photolysis and quantum yield of the formaldehyde isotopologues are discussed in relation to the global hydrogen budget.
Abstract: The relative photolysis rates of HCHO and HCDO have been studied in May 2004 at the European Photoreactor Facility (EUPHORE) in Valencia, Spain. The photolytic loss of HCDO was measured relative to HCHO by long path FT-IR and DOAS detection during the course of the experiment. The isotopic composition of the reaction product H2 was determined by isotope ratio mass spectrometry (IRMS) on air samples taken during the photolysis experiments. The relative photolysis rate obtained by FTIR is jHCHO/jHCDO ) 1.58 ( 0.03. The ratios of the photolysis rates for the molecular and the radical channels obtained from the IRMS data, in combination with the quantum yield of the molecular channel in the photolysis of HCHO, …HCHOfH2+CO (JPL Publication 06-2), are jHCHOfH2+CO/jHCDOfHD+CO ) 1.82 ( 0.07 and jHCHOfH+HCO/(jHCDOfH+DCO + jHCDOfD+HCO) ) 1.10 ( 0.06. The atmospheric implications of the large isotope effect in the relative rate of photolysis and quantum yield of the formaldehyde isotopologues are discussed in relation to the global hydrogen budget.
34 citations
TL;DR: In this paper, the FT infrared spectrum in the 4000-400 cm−1 range of SO3 vapors, matrix isolated in argon and in water doped argon solid layers, is reported.
29 citations
TL;DR: In this article, the vibrational properties of two fluorophenol derivatives, 2-fluorophenol (1 ) and 2,3,5,6-tetrafluorohydroquinone (2 ), have been studied by FT-IR and FT-Raman spectroscopy.
18 citations
TL;DR: In this paper, a series of new uracil non-nucleosides analogues of S-DABO's was synthesised by reaction of 5-alkyl-6-(p-chlorobenzy)-2-thiouracilswithchloroethyldialkylaminehydrochloride, N-(2-chloroethyl)-pyrrolidinehydro chloride, n-(2)-piperidine hydrochloride or appropriate haloethers.
Abstract: A series of new uracil non-nucleosides analogues of S-DABO's was synthesised by reaction of 5-alkyl-6-(p-chlorobenzy)-2-thiouracilswithchloroethyldialkylaminehydrochloride, N-(2-chloroethyl)-pyrrolidinehydrochloride, N-(2-chloroethyl)-piperidine hydrochloride or appropriate haloethers. Novel emivirine analogues were synthesised by silylation of 5-alkyl-6-(p-chlorobenzyl)uracils and treatment with bromomethyl methyl ether, chloromethyl ethyl ether or benzyl chloromethyl ether. Compounds 6-(p-chlorobenzyl)-5-ethyl-1-ethyloxymethyluracil (9e) and 1-benzyloxymethyl-6-(4-chlorobenzyl)-5-ethyluracil (9f) showed activity against wild-type HIV-1 strain III B in MT-4 cells.
17 citations
TL;DR: Raman spectra of the solutions reveal a strong iron(III)-sulfate inner-sphere interaction through the nu(1) sulfate band at 981 cm(-1) and its shoulder at 1005 cm-1, which may be facilitated by hydrogen bonds and monitored in the Raman spectra.
16 citations
TL;DR: In this paper, the authors present a set of table-based models for the problem of the same problem in terms of the number of tables and the number in the table: 000249470600009.
Abstract: 6 pages, 5 figures, 1 table.-- ISI Article Identifier: 000249470600009.-- Printed version published Sep 2007.
15 citations
TL;DR: Although HIV-1 has been introduced into Greenland at least nine times, only one introduction gave rise to an epidemic, and this effect is most likely due to a founder effect.
Abstract: Introduction of HIV-1 into a population may not always give rise to a subsequent epidemic. Greenland is an isolated and sparsely populated island in The Danish Kingdom. We aimed to estimate the number of introductions of HIV-1 into Greenland, the number of subsequent epidemics, and the countries from which the virus was introduced. Phylogenetic analyses were performed on three regions of HIV-1 (gag, pol, and env) in samples from 70 Greenlandic patients. Furthermore, we included gene sequences from contemporary Danish HIV-1-infected patients and sequences from the Los Alamos HIV Sequence Database. All Greenlandic sequences were subtype B except one sequence found to be a recombinant (probably CRF13). Sequence clusters in the phylogenetic trees indicated that there had been at least nine introductions of HIV-1 into Greenland. One cluster, supported by bootstrap values of 81, 76, and 96% for gag, pol, and env, corresponding to one introduction, contained 53 (76%) of the Greenland patients. The patients in the cluster differed from other Greenlandic patients in epidemiological parameters. Two distinct subgroups within the main cluster were concentrated around the two largest Greenlandic towns. Although HIV-1 has been introduced into Greenland at least nine times, only one introduction gave rise to an epidemic. The phylogeny did not indicate from where the main Greenland cluster had been introduced as no database sequence from outside Greenland was genetically close to this cluster. The large diversity between the main Greenland cluster and the rest of the sequences is most likely due to a founder effect.
13 citations
TL;DR: Raman spectra of 1,3-disilabutane (SiH3CH2SiH2CH3) as a liquid were recorded at 293 K and as a solid at 78 K as discussed by the authors.
Abstract: Raman spectra of 1,3-disilabutane (SiH3CH2SiH2CH3) as a liquid were recorded at 293 K and as a solid at 78 K In the Raman cryostat at 78 K an amorphous phase was first formed, giving a spectrum similar to that of the liquid After annealing to 120 K, the sample crystallized and large changes occurred in the spectra since more than 20 bands present in the amorphous solid phase vanished These spectral changes made it possible to assign Raman bands to the anti or gauche conformers with confidence Additional Raman spectra were recorded of the liquid at 14 temperatures between 293 and 137 K Some Raman bands changed their peak heights with temperature but were countered by changes in linewidths, and from three band pairs assigned to the anti and gauche conformers, the conformational enthalpy difference ΔconfH(gauche–anti) was found to be 0 ± 03 kJ mol−1 in the liquid Infrared spectra were obtained in the vapor and in the liquid phases at ambient temperature and in the solid phases at 78 K in the range 4000–400 cm−1 The sample crystallized immediately when deposited on the CsI window at 78 K, and many bands present in the vapor and liquid disappeared Additional infrared spectra in argon matrixes at 5 K were recorded before and after annealing to temperatures 20–34 K Quantum chemical calculations were carried out at the HF, MP2 and B3LYP levels with a variety of basis sets The HF and DFT calculations suggested the anti conformer as the more stable one by ca 1 kJ mol−1, while the MP2 results favored gauche by up to 04 kJ mol−1 The Complete Basis Set method CBS-QB3 gave an energy difference of 01 kJ mol−1, with anti as the more stable one Scaled force fields from B3LYP/cc-pVQZ calculations gave vibrational wavenumbers and band intensities for the two conformers Copyright © 2007 John Wiley & Sons, Ltd
9 citations
TL;DR: In this paper, the Mannich reaction was used to give 5,5-dimethylimidazolidine-2,4-dithione, which on treatment with (2,3,4,6-tetra-O-acetyl-α -D-glucopyranosyl)bromide (ABG) gave 5, 5-dimethyl-3(4-morpholinomethyl)-2-(2′,3′,4′,6′, 6-6′-Tetra O-acet
Abstract: 5,5-Dimethylimidazolidine-2,4-dithione ( 1 ) undergoes a Mannich reaction to give 5,5-dimethyl-3-(4-morpholinomethyl)imidazolidine-2,4-dithione ( 2 ), which on treatment with (2,3,4,6-tetra-O-acetyl-α -D-glucopyranosyl)bromide (ABG) afforded 5,5-dimethyl-3(4-morpholinomethyl)-2-(2′,3′,4′,6′-tetra-O-acetyl-β -D-thioglucopyranosyl)-4-thiohydantoin ( 3 ). Oxidation of 3 with KMnO4 furnished the corresponding sulfone 4 . Deblocking of 3 with sodium ethoxide afforded 1 . Reaction of 1 with ABG gave the N-glucoside 5 . Deblocking of 5 afforded 5,5-dimethyl-3-N-(3,4,5-trihydroxy-6-hydroxy-methyltetrahydropyran-2-yl)imidazolidine-2,4-dithione ( 6 ). Oxidation of 5 yielded 5,5-dimethyl-imidazolidine-3-N-(2′,3′,4′,6′-tetra-O-acetyl-β -D-glucopyranosyl)-2-oxo,4-thione ( 7 ). Reaction of 1 with phenacyl chloride afforded 8 , which on thiation with P4S10 gave 9 . 5-Benzylidene-2-thioxoimidazolidin-4-one ( 10 ) reacted with some halo compounds and afforded 11 and 12 . Treatment of 10 with 2,4-dinitro-1-chlorobenzene af...
TL;DR: In this paper, a 5-ethyl-2-thiouracil derivative with a 6-(tetrahydronaphthalen-1-yl)methyl substituent was synthesized by condensation of thiourea with an adequate β-ketoester.
Abstract: An 5-ethyl-2-thiouracil derivative with a 6-(tetrahydronaphthalen-1-yl)methyl substituent was synthesized by condensation of thiourea with an adequate β-ketoester which in turn was synthesized in a single step from (tetrahydronaphthalen-1-yl)acetonitrile. The latter starting material was also used to synthesize an analogously substituted tetrahydronaphthalen-1-yl substituted uracil with a locked conformation. Only the non-nucleoside derivatives prepared from the desulfurized substituted 2-thiouracil showed moderate activity against HIV whereas a corresponding non-nucleoside derivative was devoid of activity against HIV.
TL;DR: In this paper, the conformational enthalpy differences ΔH(gauche-anti) were found to be between 1.3 and 1.7 ǫ(kJ) using peak heights, and the more stable anti conformer was present in the crystal.
Abstract: Raman spectra of 1,3-disilabutane (SiH3CH2SiH2CH3) were recorded as a liquid at room temperature and at 14 temperatures between 293 and 137 K. Spectra of an amorphous and annealed solid were recorded at 78 K, and very distinct changes occurred on crystallization. In the variable temperature Raman spectra, some bands changed in intensity and were interpreted in terms of conformational equilibria between the two possible conformers. Complete assignments were made for all the bands of the most stable conformer, anti. From three band pairs assigned to the anti and gauche conformers, the conformational enthalpy differences ΔH(gauche-anti) were found to be between 1.3 kJ mol−1 and 1.7 kJ mol−1, using peak heights, and the more stable anti conformer was present in the crystal. A lower value of 0 ± 0.3 kJ mol−1 was obtained employing band areas. Ab initio calculations in the RHF and MP2 approximations and DFT calculations were carried out pointing to the anti conformer as the low energy form.