Synthesis and Mesomorphic Properties of 2,6-Disubstituted Tetralins

Synthesis and mesomorphic behavior of nine members of each of the two classes of 6-phenyl- and 2-phenyltetralins and five members of the 2-trans-cyclohexyltetralins are reported. The synthesis of one member of each class is described in detail. Besides the target compounds, more than twenty intermediates showed liquid crystalline properties; their transition temperatures are recorded (see Tables 1-6).     

Sulle « catene » di numeri primi consecutivi a differenza limitata

Sunto Si considerano certi aggregati di numeri primi consecutivi, le cui differenze soddisfano a particolari disuguaglianze; aggregati a cui si attribuisce il nome di ? catene ?. Fra i vari tipi di catene (caratterizzate dalle disuguaglianze a cui soddisfano i numeri primi in esse contenuti) se ne studiano in particolare alcuni per i quali si giunge a fissare qualche limitazione relativa all'ampiezza massima della catena, oppure al numero delle catene presenti in un certo intervallo.     

Signs of heteronuclear spin–spin coupling constants in 15N-acetamide

By using digital deconvolution to improve spectral resolution, earlier NMR studies on ¹⁵N-enriched acetamide have been revised and extended to determine the signs of the heteronuclear spin-spin coupling constants. ¹J(¹³CO¹⁵N), ²J(¹³CH₃¹⁵N) and ³J(C¹H₃¹⁵N) are negative while ³J(¹H¹³CH₃)>0. The results, interpreted on the basis of the ‘selective decoupling’ formalism, were confirmed by computer simulation of the double resonance spectra. It is shown that ²J(¹H-α¹³CO) is significantly larger than ²J(¹H^{N 13}CO). Thus, jointly with {¹H-β}-¹³C′ double resonance experiments, {¹H-α}-¹³C′ experiments ought to be most helpful when assigning peptide group carbonyl resonances. The study provides valuable information for the interpretation of heteronuclear coupling constants in polypeptides.     

Diffusion coefficient of ionic solvation shell molecules

It is shown that, for a tightly bound ion-solvation shell complex, the mean square displacement for solvation molecules is characterized by a long lasting transitory. This initial portion is related to the rotational relaxation of the complex and can reach up to several hundred picoseconds for a representative example such as the Mg(2+) ion in water. As the diffusion coefficient is usually fitted using much shorter time spans, unnoticed overestimations are possible. It is argued that, instead of computing the aforementioned diffusion coefficient from the mean square displacement, it should be defined taking as a basic guideline the ratio between the rotational relaxation time of the complex and the lifetime within the first solvation shell.     

Analysis of sample-solvent induced modifier-solute peak interactions in biochromatography using equilibrium theory and detailed simulations

Batch liquid chromatographic columns are often equilibrated with an eluent stream being a mixture of inert compounds and so-called modifiers. The sample injected into the eluent stream usually consists of the solutes to be separated and of a mixture of the same solvents as in the eluent but in general with different concentration values. This results in two groups of peaks moving along the column: the solute peaks and the modifier pertubations. If the adsorptivity of the solute depends strongly on the modifier, as it is often the case in biochromatography, the interference between the two groups of peaks leads to peculiar phenomena like double peaks, split peaks, distorted peaks with anti-Langmurian shape, etc. In this work, these phenomena are analyzed based on an analytical solution of the equilibrium theory model and the results are compared with detailed simulations and experimental data. It is shown that the qualitative behavior is well predicted in the frame of equilibrium theory and general guidelines how to avoid these kinds of interactions are developed.