Influences of temperature,pressure and eluent composition on the behavior of binary eluents at sub- and supercritical conditions. Pentane and diethyleneglycol dimethyl ether

Summary In supercritical fluid chromatography (SFC), studies on binary eluents composed of pentane and diethyleneglycol dimethylether were performed in the concentration rage of 5 to 15% of the ether compound and at pressures of 20 to 50 bar. Influences of temperature, pressure and eluent composition on the behavior of the mobile phase were found to closely resemble those for pentane-dioxane mixtures. Resolution depended on variations in capacity ratios, selectivities, and plate numbers. The critical data for diethyleneglycol dimethylether were estimated by means of different group contribution methods.     

All-valence-electron CI study of the ground and lowest excited states of the hydroperoxyl radical

Ab initio calculations using a double-zeta plus polarization AO basis are used to study the lowest-lying (²A′ ← ²A″) transition of the HO₂ radical. A large-scale CI treatment is found to result in a transition energy for this system which agrees to within less than 0.1 eV with its experimental value. The life-time of the process is predicted to be in the order of 3 × 10^?3 s using the dipole length formula for this quantity, while the generally less reliable dipole velocity result is found to be several orders of magnitude larger.     

Time-series analysis in analytical process control

Analysis of time series tries to extract tendencies from measured values dependent on time. For this purpose the cusum technique has proved to be a very sensitive tool for the evaluation of both current and completed time series. Even very weak tendencies can be detected at a high level of noise. Time-series analysis further tries to predict values to come from hitherto performed measurements. As a very flexible model exponential smoothing could be successfully used. Even for processes with a high extent of non-stationarity this model allowed a good prediction owing to the dynamics of the process. Three types of time-series analysis, i.e., evaluation of current measurements, retrospective evaluation and prediction of data (also known as “in vivo”, “post mortem” and “in futurum” time-series analysis) are demonstrated for problems stemming from analytical process control.     

Bending potentials for H2O in the ground and the first six singlet excited states

MRD CI calculations are presented for the bending potentials of H₂O in the ground and first six singlet excited states. The results are discussed with reference to the H(²S) + OH(A ²Σ⁺) dissociation path of H₂O.     

Study of enzyme kinetics of phenol sulfotransferase by electrophoretically mediated microanalysis

Electrophoretically mediated microanalysis (EMMA) was applied for the study of the kinetic parameters of the enzymatic reaction of phenol sulfotransferase SULT1A1 isoenzyme with 4-nitrophenol as a substrate. The SULT1A1 activity was determined by the quantitation of the product, 4-nitrophenyl sulfate, at 274 nm by using different injection and separation steps. This new approach solved the problem of the presence of the very strong inhibitor, adenosine 3',5'-bisphosphate (PAP), in the co-substrate solution (adenosine 3'-phosphate 5'-phosphosulfate, PAPS) which is unstable at room temperature. The inhibitor PAP was electrophoretically separated from the co-substrate PAPS before the injection of enzyme and substrate inside the capillary (and thus before their in-capillary encountering). With the developed in-capillary SULT1A1 activity assay an average Michaelis constant (Km) for 4-nitrophenol was calculated to be 0.84 microM, a value which is consistent with a previously reported value. Strong substrate inhibition (above a 4-nitrophenol concentration of 2.5 microM) was observed, and this is also in accordance with literature values.     

New Types of Very Efficient Photolabile Protecting Groups Based upon the [2‐(2‐Nitrophenyl)propoxy]carbonyl (NPPOC) Moiety

Based upon the photolabile [2‐(2‐nitrophenyl)propoxy]carbonyl group (NPPOC), a large number of modified 2‐(2‐nitrophenyl)propanol derivatives substituted at the phenyl ring (see 23 – 34 and 57 – 76 ) as well as at the side‐chain (see 85 – 92 and 95 – 98 ) were synthesized to improve the photoreactivity of this new type of photolabile entity. The phenyl moiety was also exchanged by the naphthalenyl group (see 102, 103, 105, 108, 110, 113 , and 114 ), the thienyl substituent (see 115, 117, 118 , and 120 ), and the benzothienyl substituent (see 121 ). The 2‐(2‐nitroaryl‐ and heteroaryl)propanols were converted with diphosgene into the corresponding carbonochloridates, which reacted subsequently with thymidine to the thymidine 5′‐(protected carbonates) 123 – 178 as the main reaction products. In several cases, the corresponding 3′‐carbonates and 3′,5′‐dicarbonates 179 – 212 were also isolated and characterized. Photolysis studies under standardized conditions (see Table) indicated that the rate of photocleavage varies in a broad range depending on the substituents. So far, the thymidine 5′‐[2‐(5‐halo‐2‐nitrophenyl)propyl carbonates] 127 – 129 , 5′‐[2‐(nitro[1,1′‐biphenyl]3‐yl)propyl carbonates] 136 – 139 , 5′‐{2‐[2‐nitro‐5‐(thianthren‐1‐yl)phenyl]propyl carbonate} ( 140 ), 5′‐[2‐(5‐naphthalenyl‐2‐nitrophenyl)propyl carbonates] 141 and 142 , and 5′‐[2‐(2‐nitro‐5‐thienylphenyl)propyl carbonates] 143 and 144 showed the best properties regarding fast and uniform deprotection. Since the nucleobases of 213 – 215 do not influence the photocleavage features, in general, the new type of photolabile building blocks allows in form of their 3′‐phosphoramidites the photolithographic formation of high‐quality biochips.     

Individualized configuration selection in CI calculations with subsequent energy extrapolation

A configuration selection method for CI calculations is discussed and applied in which the energy lowering produced in a secular equation by the addition of a given test species to a series of dominant configurations is used as an ordering parameter. Configurations with energy lowerings below a given energy cut-off value are not included in the final secular equations but instead a method of estimating the combined effect of the neglected species on the corresponding non-selected CI results is developed. The influence of the choice of main configurations used in the selection process is given close examination as well as the importance of the MO basis employed in the treatment as a whole; in the latter case a non-iterative procedure for obtaining approximate natural orbitals for such calculations is suggested. The resulting configuration selection procedure is equally applicable to all types of electronic states in any nuclear geometry and the results of the associated CI calculations are seen to be essentially equivalent to a complete treatment in which all single- and double-excitation species with respect to aseries of dominant configurations in a given state are included. Senior U.S. Scientist Awardee of the Alexander von Humboldt Foundation, on leave from the Department of Chemistry, University of Nebraska.     

Investigation of electron correlation on the theoretical prediction of zero-field splittings of 2Π molecular states

First-order ²Π zero-field splittings are computed for the H₂S⁺, BO, NO, CH, CO⁺ and OH ground electronic states by employing ab initio multi-configuration wavefunctions and by including all one-and two-electron spin-orbit interactions in a gaussian AO basis explicitly in the theoretical treatment.     

8-Aza-2′-deoxyguanosine and Related 1,2,3-Triazolo[4,5-d]pyrimidine 2′-Deoxyribofuranosides

The synthesis of 8-azaguanine N⁹-, N⁸-, and N⁷-(2′-deoxyribonucleosides) 1–3 , related to 2′-deoxyguanosine ( 4 ), is described. Glycosylation of the anion of 5-amino-7-methoxy-3H-1,2,3-triazolo[4,5-d]pyrimidine ( 5 ) with 2-deoxy-3,5-di-O-(4-toluoyl)-α-D -erythro-pentofuranosyl chloride ( 6 ) afforded the regioisomeric glycosylation products 7a/7b, 8a/8b , and 9 (Scheme 1) which were detoluoylated to give 10a, 10b, 11a, 11b , and 12a . The anomeric configuration as well as the position of glycosylation were determined by combination of UV, ¹³C-NMR, and ¹H-NMR NOE-difference spectroscopy. The 2-amino-8-aza-2′-deoxyadenosine ( 13 ), obtained from 7a , was deaminated by adenosine deaminase to yield 8-aza-2′-deoxyguanosine ( 1 ), whereas the N⁷- and N⁸-regioisomers were no substrates of the enzyme. The N-glycosylic bond of compound 1 (0.1 N HCl) is ca. 10 times more stable than that of 2′-deoxyguanosine ( 4 ).