Thin-Layer Chromatographic Quantifcation of trans-Resveratrol in Cosmetic Raw Materials of Botanic Origin

JPC – Journal of Planar Chromatography – Modern TLC - Recently, a growing interest has been observed in preventive and “anti-ageing” medicine, accompanied by a dynamic...     

Bases,solvates and salts: new benzimidazole‐ and pyridine‐scaffolded ligands

The intermolecular interactions in the structures of a series of Schiff base ligands have been thoroughly studied. These ligands can be obtained in different forms, namely, as the free base 2‐[(2E)‐2‐(1H‐imidazol‐4‐ylmethylidene)‐1‐methylhydrazinyl]pyridine, C₁₀H₁₁N₅, 1 , the hydrates 2‐[(2E)‐2‐(1H‐imidazol‐2‐ylmethylidene)‐1‐methylhydrazinyl]‐1H‐benzimidazole monohydrate, C₁₂H₁₂N₆·H₂O, 2 , and 2‐{(2E)‐1‐methyl‐2‐[(1‐methyl‐1H‐imidazol‐2‐yl)methylidene]hydrazinyl}‐1H‐benzimidazole 1.25‐hydrate, C₁₃H₁₄N₆·1.25H₂O, 3 , the monocationic hydrate 5‐{(1E)‐[2‐(1H‐1,3‐benzodiazol‐2‐yl)‐2‐methylhydrazinylidene]methyl}‐1H‐imidazol‐3‐ium trifluoromethanesulfonate monohydrate, C₁₂H₁₃N₆⁺·CF₃O₃S^?·H₂O, 5 , and the dicationic 2‐{(2E)‐1‐methyl‐2‐[(1H‐imidazol‐3‐ium‐2‐yl)methylidene]hydrazinyl}pyridinium bis(trifluoromethanesulfonate), C₁₀H₁₃N₅²⁺·2CF₃O₃S^?, 6 . The connection between the forms and the preferred intermolecular interactions is described and further studied by means of the calculation of the interaction energies between the neutral and charged components of the crystal structures. These studies show that, in general, the most important contribution to the stabilization energy of the crystal is provided by π–π interactions, especially between charged ligands, while the details of the crystal architecture are influenced by directional interactions, especially relatively strong hydrogen bonds. In one of the structures, a very interesting example of the nontypical F…O interaction was found and its length, 2.859 (2) Å, is one of the shortest ever reported.     

Synthesis of Amino Acid Derivatives of Neamine and 2-Deoxystreptamine to be used as Mutasynthons

ABSTRACT

6′-N derivatives of neamine with alanine, phenylalanine and lysine were synthesized either using an active esters method in one step under controlled conditions, or using a mixed anhydride method after blocking every functional group of neamine and leaving the 6′-amino group free to react. Similarly N,N′-diamino acid and monoamino acid derivatives of 2-deoxystreptamine were synthesized.     

N‐{3‐[(2‐Ammonioethyl)amino]propyl}ethane‐1,2‐diaminium tris(trifluoromethanesulfonate): a salt of a folded triply protonated tetramine

The structure of a trifluoromethanesulfonate salt of a nontypical triply protonated linear tetramine, C₇H₂₃N₄³⁺·3CF₃SO₃⁻, with a layered crystal structure is presented. One N atom remains unprotonated. The conformation of the cation is enforced by intra‐ and intermolecular hydrogen bonds. The crystal structure is built of ca 10 Å deep layers, within which cations and anions are hydrogen bonded. Each layer is only weakly bound to its neighbours. This study shows a rare example of an unsymmetrically protonated polyamine and the relation between the lack of protonation, intramolecular hydrogen bonding and the conformation of the cation.     

Mg2+-free Bacillus stearothermophilus tryptophanyl-tRNA synthetase retains a major fraction of the overall rate enhancement for tryptophan activation

Few experimental data are available for rates of enzymatic phosphoryl-transfer reactions in the absence of the divalent metal ions associated with such reactions. Such data are of interest for amino acid activation by class Ic aminoacyl-tRNA synthetases, for which there is substantial evidence that binding energy of ATP may account for a major fraction of the overall rate enhancement, and it is crucial to know if these effects themselves depend on the divalent metal ion. We describe a nested, nonlinear model for the sum of metal-free and metal-catalyzed activities and its use in determining metal-free enzyme activity jointly with transition-state metal binding affinity, by fitting observed values obtained from Mg2+-depleted assays with increasing [EDTA] at known [Mg2+]total. Tryptophan activation by Bacillus stearothermophilus tryptophanyl-tRNA synthetase falls asymptotically to a plateau value 5 orders of magnitude below that observed for the Mg2+-supplemented enzyme at EDTA concentrations that reduce the free metal concentration to <1 pmolar. The fitted regression model parameters yield a relative rate acceleration of 9.3 x 10(4) attributable to the catalytic effect of Mg2+ and an enhanced (K(E)(double dagger) = 1.15 x 10(-7) M) transition-state binding of Mg2+. Factorial analysis indicates that 80% of the reduction in free energy of activation effected by TrpRS arises from protein-ligand interactions.     

On isomorphisms of some Köthe function <Emphasis Type="Italic">F</Emphasis>-spaces

We prove that if Köthe F-spaces X and Y on finite atomless measure spaces (Ω _X ; Σ _X , µ _X ) and (Ω _Y ; Σ _Y ; µ _Y ), respectively, with absolute continuous norms are isomorphic and have the property

$\mathop {\lim }\limits_{\mu (A) \to 0} \left\| {\mu (A)^{ - 1} 1_A } \right\| = 0$

(for µ = µ _X and µ = µ _Y , respectively) then the measure spaces (Ω _X ; Σ _X ; µ _X ) and (Ω _Y ; Σ _Y ; µ _Y ) are isomorphic, up to some positive multiples. This theorem extends a result of A. Plichko and M. Popov concerning isomorphic classification of L _p (µ)-spaces for 0 < p < 1. We also provide a new class of F-spaces having no nonzero separable quotient space.

     

The synthesis of new potential photosensitizers. 1. Mono-carboxylic acid derivatives of tetraphenylporphyrin

Abstract  

A series of mono-alkylcarboxylic acid derivatives of tetraphenylporphyrin have been prepared. All the porphyrins were completely characterized by use of mass, ¹H NMR, UV–visible, and fluorescence spectroscopy. Experimental log P were determined by use of reversed-phase thin-layer chromatography with use of log P _Rekker. These porphyrins are potential photosensitizers in photodynamic therapy.