Crystallographic report: The [bis(η5‐methylcyclopentadienyl)titanium(IV)‐bis(N‐methylglycine)] dichloride

The crystal network of [Cp′₂Ti(N?CH₃? Gly)₂]²⁺[Cl^?]₂ (Cp′ = (CH₃)C₅H₄) complex, which crystallizes as a solvate with CH₃OH, is built up with discrete cationic units connected through intermolecular H· · ·Cl bonds. The α‐amino acid ligands are attached through an intramolecular H· · ·O bond within one cationic unit. Copyright © 2004 John Wiley & Sons, Ltd.     

Interactions of the “piano‐stool” [ruthenium(II)(η6‐arene)(quinolone)Cl]+ complexes with water; DFT computational study

Full optimizations of stationary points along the reaction coordinate for the hydration of several quinolone Ru(II) half‐sandwich complexes were performed in water environment using the B3PW91/6‐31+G(d)/PCM/UAKS method. The role of diffuse functions (especially on oxygen) was found crucial for correct geometries along the reaction coordinate. Single‐point (SP) calculations were performed at the B3LYP/6‐311++G(2df,2pd)/DPCM/saled‐UAKS level. In the first part, two possible reaction mechanisms—associative and dissociative were compared. It was found that the dissociative mechanism of the hydration process is kinetically slightly preferred. Another important conclusion concerns the reaction channels. It was found that substitution of chloride ligand (abbreviated in the text as dechlorination reaction) represents energetically and kinetically the most feasible pathway. In the second part the same hydration reaction was explored for reactivity comparison of the Ru(II)‐complexes with several derivatives of nalidixic acid: cinoxacin, ofloxacin, and (thio)nalidixic acid. The hydration process is about four orders of magnitude faster in a basic solution compared to neutral/acidic environment with cinoxacin and nalidixic acid as the most reactive complexes in the former and latter environments, respectively. The explored hydration reaction is in all cases endergonic; nevertheless the endergonicity is substantially lower (by ～6 kcal/mol) in basic environment. © 2016 Wiley Periodicals, Inc.     

Enantiomeric purity control of <Emphasis Type="Italic">R</Emphasis>-cinacalcet in pharmaceutical product by capillary electrophoresis

The capillary zone electrophoresis method was developed for the chiral separation of R,S-cinacalcet. Cyclodextrins with different substituents were tested in both acidic and alkaline background electrolytes. The non-ionic cyclodextrin, 2-hydroxypropyl-γ-cyclodextrin, was selected as the best chiral selector. The separation was performed using a positive voltage in a phosphate buffer at pH 2.5. The analytes studied were separated within 12 min. The proposed method was applied to the analysis of tablets containing R-cinalcalcet as the active substance. The enantiopurity of R-cinacalcet in the tablets studied was confirmed. Subsequently, the analysis of tablets spiked with S-cinacalcet (chiral impurity) was also performed. The method here presented makes possible the determination of 0.1 % of S-cinacalcet in tablets. The analytical characteristics of the method, such as linearity, recovery and RSD values of the peak area and the migration time, were evaluated. The inter-day RSD values of the peak area and the migration time were lower than 3.71 % and 1.3 %, respectively.     

Evaluation of differences between Chiralpak IA and Chiralpak AD‐RH amylose‐based chiral stationary phases in reversed‐phase high‐performance liquid chromatography

Polysaccharide‐based chiral stationary phases can be used for the enantioselective separation of a wide range of structurally different compounds. These phases are available with chiral selectors coated or immobilized on silica gel support. The means of attachment of the chiral selector to the carrier can influence the separation performance of these stationary phases. This paper deals with evaluation of differences in the separation abilities of coated Chiralpak AD‐RH versus immobilized Chiralpak IA amylose‐based stationary phases in the reversed–phase mode of high–performance liquid chromatography. A set of chiral analytes was separated under acidic and basic conditions. Differences were observed in the enantioseparation potential of the tested phases. The linear‐free energy relationship and additional evaluation of ionic interactions were used to ascertain whether the interactions that participate in retention and enantioseparation are affected by the means of preparation of these phases. All the interactions covered by the linear‐free energy relationship were significant for the studied phases and their absolute values were almost always higher for the coated phase. Ionic interactions were found to be more important on the immobilized stationary phase but did not contribute to any improvement in the enantioselective separation performance.     

Fuzzy Galois Connections

The concept of Galois connection between power sets is generalized from the point of view of fuzzy logic. Studied is the case where the structure of truth values forms a complete residuated lattice. It is proved that fuzzy Galois connections are in one-to-one correspondence with binary fuzzy relations. A representation of fuzzy Galois connections by (classical) Galois connections is provided.     

Thionin-sensitized intrazeolite photooxygenation of trisubstituted alkenes: substituent effects on the regioselectivity as probed through isotopic labeling

The regioselectivity for the intrazeolite photooxygenation of several trisubstituted alkenes with geminal dimethyl groups was examined. The length of the alkyl chain at the lone position was varied, and as end groups, the phenyl or the cyclohexyl functionalities were chosen. The general trend for all alkenes is a significant increase of the reactivity at the twin position compared to the photooxygenation in solution. For the cyclohexyl-substituted alkenes, it was found that the regioselectivity is nearly independent of the alkyl chain length. However, for the phenyl-substituted alkenes, the ene reactivity of the allylic methylene hydrogen atoms at the lone position and the twix/twin regioselectivity depend significantly on the distance of the phenyl group from the double bond. These trends are discussed in terms of cation-pi interactions and conformational effects. Intramolecular and intermolecular isotope effects in the intrazeolite photooxygenation of deuterium-labeled alkenes suggest that a perepoxide-type intermediate is formed in the rate-determining step. Type I photooxygenation that involves reaction of the radical cations of the alkenes with superoxide ion are unlikely.     

Selectivity of Chemical Conversions: Do Light‐Driven Photoelectrocatalytic Processes Hold Special Promise?

One of the great challenges in chemistry is the development of innovative catalytic processes. In this context, significant opportunities are currently opening up for technologies based on electrocatalysis and photoelectrocatalysis, as these can drive various valuable catalytic redox transformations under very mild conditions. However, many catalytic processes lead to various different products of different value, and the technological attractiveness of catalytic processes depends to a large extent on their selectivity towards a specific desired product. In this Viewpoint, I propose and explore the idea that, due to the distinct features of interfacial energetics at illuminated semiconductors, light‐driven photoelectrocatalytic processes at well‐designed semiconductors represent a particularly attractive platform for the development of highly efficient systems for selective catalytic conversions. The investigations of selectivity and synthetic aspects of photoelectrocatalysis should gain momentum, especially as they also promise commercially viable applications on a more immediate time scale as compared to, for example, the light‐driven production of hydrogen.     

Electrokinetic partial filling technique as a powerful tool for enantiomeric separation of DL-lactic acid by CE with contactless conductivity detection

A modified partial filling method for chiral separation of DL-lactic acid as the model chiral compound with vancomycin chloride as the chiral selector was developed by CE with contactless conductivity detection. Electrokinetic partial filling technique (EK-PFT) was used as an alternative method to the conventional hydrodynamic partial filling method. EK-PFT, in contrast to the hydrodynamic partial filling technique, allowed the removal of the chloride counterions from the chiral selector which otherwise led to poor sensitivity in conductivity detection. The baseline separation of DL-lactic acid as the model analyte was achieved in 5 min in a polyacrylamide-coated capillary. The best resolution was achieved by electrokinetic partial filling of vancomycin cations from the injection solution containing 5 mmol/L oxalate L-histidinium at pH 4.5 with 10 mmol/L vancomycin chloride. Computer simulation was used to explain the observed phenomena in the boundary between the inject vial and the capillary during the EK-PFT of vancomycin cations.     

Chiral separability of hydrophobic boron cluster anions with native cyclodextrins in water-methanol background electrolytes

Cluster anions of boron are built up on three-center two-electron bonds in contrast to naturally occurring compounds and their synthetic analogs. Methanol works as a solvent and as a competing agent, which advantageously adjusts reasonable strength of their interaction with native CDs in water-organic BGE. The highest methanol concentration preserving chiral discrimination of atropoisomers of individual anions is approximately 35, 55 and 75% v/v for alpha-, beta- and gamma-CD, respectively. alpha-CD separates anionic 7, 8-nido-dicarbaundecaborate clusters with small exo-skeletal substituents. beta-CD separates anions of all four tested structural types. The efficiency of separation of a compound with alpha- or beta-CD is always markedly lower than the separation efficiency at the absence of a CD in BGE. The efficiency of separation of a compound with beta-CD is always lower than the efficiency of separation of the compound with alpha-CD. gamma-CD was proved to be unsuitable as a chiral selector because in BGEs with gamma-CD, effective mobilities of analytes as well as their differences continuously decrease. The decrease was ascribed to the decomposition of the gamma-CD. The assessment of analytical prospect of alpha- and beta-CDs as chiral selectors for chiral separations of boron cluster anions requires knowledge of stability of individual CDs at the conditions of analyses and recognition of the chance to eliminate low separation efficiency.