Synthesis, complete characterization, and enantioselective electrokinetic separation of functionalized ruthenium complex enantiomers

Electrokinetic chromatography was employed to separate the enantiomers of two novel functionalized ruthenium(II) complexes with different polypyridyl coordination spheres. The use of anionic carboxymethyl-beta-cyclodextrin as chiral mobile phase additive resulted in maximum efficiency and resolution for the enantiomer separation of both transition metal complexes. The syntheses of the [4-(3-hydroxypropyl)-4'-methyl-2,2'-bipyridine]-bis(2,2'-bipyridine)rethenium(II)-bis(tetrafluoroborate) and [4-(3-hydroxypropyl)-4'-methyl-2,2'-bipyridine]-bis(4,4'-dimethyl-2,2'-bypyridine)ruthenium(II)-bis(tetrafluoroborate) complexes and their complete characterization by means of two-dimensional (1)H and (13)C[(1)H] NMR techniques ((1)H-(1)H COSY and (1)H-(13)C HMQC) as well as elemental analyses and MALDI-TOFMS are described in detail. The functionalized complexes can be used as building blocks for further reactions with polymers, biopolymers, surfaces and nanoparticles.     

Comparison of the chiral separation of amino-acid derivatives by a teicoplanin and RN-beta-CD CSPs using waterless mobile phases: Factors that enhance resolution

A variety of compounds containing amines (i.e., amino acids, amino alcohols, etc.) were chemically derivatized with a variety of electrophilic tagging reagents to elucidate the chiral recognition sites on a teicoplanin-bonded chiral stationary phase (CSP) and on R-naphthylethylcarbamate-beta-cyclodextrin (RN-beta-CD)-bonded CSP. Solutes were separated under optimum chromatographic conditions on teicoplanin and RN-beta-CD CSPs for comparison using an acetonitrile-based mobile phase. It was noted that the size of the analyte or tagging reagent exerted a greater influence on compounds separated on teicoplanin than on RN-beta-CD when using the polar organic mode. This suggests that chiral recognition on teicoplanin CSP is more sensitive to size and indicates that the hydrophobic pocket of teicoplanin plays a significant role in chiral recognition in this mode. However, the type of functional groups had a greater impact than the size of analyte on separations obtained from RN-beta-CD phase in the polar-organic mode. Specifically, the pi-pi interaction was enhanced by derivatizing the aromatic ring of the tagging reagent with electron-withdrawing groups and thus altered the resolution substantially. For both phases, chiral recognition is most pronounced when the stereogenic center of the analyte is near the tagging moiety and surrounded by functional groups (e.g., carboxylic, etc.) which are favorable for hydrogen bonding.     

Chiral asymmetry in spiral galaxies?

Spiral galaxies are chiral entities when coupled with the direction of their recession velocity. As viewed from the Earth, the S‐shaped and Z‐shaped spiral galaxies are two chiral forms. What is the nature of chiral symmetry in spiral galaxies? In the Carnegie Atlas of Galaxies that lists photographs of a total of 1,168 galaxies, we found 540 galaxies, classified as normal or barred spirals, that are clearly identifiable as S‐ or Z‐ type. The recession velocities for 538 of these galaxies could be obtained from this atlas and other sources. A statistical analysis of this sample reveals no overall asymmetry but there is a significant asymmetry in certain subclasses: dominance of S‐type galaxies in the Sb class of normal spiral galaxies and a dominance of Z‐type in the SBb class of barred spiral galaxies. Both S‐ and Z‐type galaxies seem to have similar velocity distribution, indicating no spatial segregation of the two chiral forms. Chirality 13:351–356, 2001. © 2001 Wiley‐Liss, Inc.     

Optimization of the chiral separation of some 2-arylpropionic acids on an avidin column by modeling a combined response

The enantiomeric separation of some nonsteroidal antiinflammatory drugs was investigated on an avidin column. An experimental design approach (central composite design) was used to evaluate the effects of three method parameters (pH, concentration of organic modifier, and buffer concentration) on the analysis time and the resolution, as well as to model these responses. This revealed that the organic modifier concentration and sometimes the pH are significant parameters to control because of their influence on both analysis time and resolution. Furthermore, the central composite design results were combined in a multicriteria decision-making approach in order to obtain a set of optimal experimental conditions leading to the most desirable compromise between resolution and analysis time.     

Relationship between enantioselectivity of alternative molecularly imprinted polymeric membranes and species of amino acid residues composing chiral recognition sites

Molecularly imprinted polymeric membranes with tetrapeptide residue H-Asp(OcHex)-Asp(OcHex)-Asp(OcHex)-Asp(OcHex)-CH₂- (DDDD) or H-Glu(OBzl)-Glu(OBzl)-Glu(OBzl)-Glu(OBzl)-C H₂- (EEEE) were prepared during membrane preparation (casting) processing in the presence of print molecules. The Boc-L-Trp imprinted polymeric membranes thus obtained showed adsorption selectivity toward Ac-L-Trp from its racemic mixtures. From adsorption isotherms of Ac-Trp, the chiral recognition site, that had been formed by the presence of print molecules in the membrane preparation process, exclusively recognized Ac-L-Trp that possessed the same configuration of the print molecule. The affinity constants between chiral recognition sites in the membrane and Ac-L-Trp was determined to be 1.00 × 10⁴ mol^–1 dm³ and 1.08 × 10⁴ mol^–1 dm³ for the DDDD and EEEE membranes, respectively. Enantioselective electrodialysis could be attained by applying an optimum potential difference to give permselectivity, with a value close to its adsorption selectivity.     

Substrate inhibition mode of omega-transaminase from Vibrio fluvialis JS17 is dependent on the chirality of substrate

Substrate inhibition is a common phenomenon in enzyme chemistry, which is observed only with a fast-reacting substrate enantiomer. We report here for the first time substrate inhibition of an enantioselective enzyme by both substrate enantiomers. The enantioselective substrate inhibition, i.e., different mode of inhibition by each substrate enantiomer, of (S)-specific omega-transaminase was found with various chiral amines. A kinetic model based on ping-pong bi-bi mechanism has been developed and kinetic parameters were measured. The kinetic model reveals that the inhibition by (R)-amine results from formation of Michaelis complex with enzyme-pyridoxal 5'-phosphate, whereas the inhibition by (S)-amine results from the formation of the complex with enzyme-pyridoxamine 5'-phosphate. Substrate inhibition constants (K(SI)) of each (S)-enantiomer of four chiral amines showed a linear correlation with those of cognate (R)-amines. Such a correlation was also found between the K(SI) values and Michaelis constants of (S)-amines. These correlations indicate that recognition mechanisms and active site structures of both enzyme-pyridoxal 5'-phosphate, enzyme-pyridoxamine 5'-phosphate are similar. Taken together with the results, high propensity for non-productive substrate binding strongly suggests that binding pockets of the omega-transaminase is loosely defined, which accounts for the enantioselective substrate inhibition.     

Impact of endogenous nitric oxide on microglial cell energy metabolism and labile iron pool

Microglial activation is common in several neurodegenerative disorders. In the present study, we used the murine BV-2 microglial cell line stimulated with gamma-interferon and lipopolysaccharide to gain new insights into the effects of endogenously produced NO on mitochondrial respiratory capacity, iron regulatory protein activity, and redox-active iron level. Using polarographic measurement of respiration of both intact and digitonin-permeabilized cells, and spectrophotometric determination of individual respiratory chain complex activity, we showed that in addition to the reversible inhibition of cytochrome-c oxidase, long-term endogenous NO production reduced complex-I and complex-II activities in an irreversible manner. As a consequence, the cellular ATP level was decreased in NO-producing cells, whereas ATPase activity was unaffected. We show that NO up-regulates RNA-binding of iron regulatory protein 1 in microglial cells, and strongly reduces the labile iron pool. Together these results point to a contribution of NO derived from inflammatory microglia to the misregulation of energy-producing reactions and iron metabolism, often associated with the pathogenesis of neurodegenerative disorders.     

Release of salbutamol sulphate and ketoprofen enantiomers from matrices containing HPMC and cellulose derivatives

We studied the release of salbutamol and ketoprofen enantiomers from HPMC K100M matrices containing two types of cellulose derivatives: cellulose tris (3,5-dimethylphenylcarbamate) and cellulose tris (2,3-dichlorophenylcarbamate), chiral excipients used as stationary phases for liquid chromatography. These matrices provided an extended release of both drugs. Ketoprofen release from formulations elaborated with cellulose tris (2,3-dichlorophenylcarbamate) was by anomalous transport, because the value of n (release exponent of the diffusion equation) ranged between 0.60-0.68, whereas for all other formulations the value of exponent n ranged from 0.50-0.54. The drug thus diffuses through the matrix and is released following a quasi-Fickian diffusion mechanism (stereoselective process). The matrices preferentially retained R-salbutamol and S-ketoprofen and cellulose tris (3,5-dimethylphenylcarbamate) showed more capacity of chiral discrimination for both drugs than cellulose tris (2,3-dichlorophenylcarbamate). Moreover, we observed that stereoselectivity is dependent on the amount of chiral excipient in the formulation. Diffusion tests confirmed the chiral interaction between drugs and cellulose derivatives observed in the dissolution assays except for matrices elaborated with ketoprofen and cellulose tris (2,3-dichlorophenylcarbamate), where the low stereoselectivity observed with the matrices is due to the presence of HPMC K100M. We conclude that the inclusion of these cellulose derivatives in HPMC matrices does not result in a relevant stereoselectivity with respect to the two drugs studied.     

Enantioselective chromatography of alkyl derivatives of 5-ethyl-5-phenyl-2-thiobarbituric acid studied by semiempirical AM1 method

Complexation of alkyl derivatives of 5-ethyl-5-phenyl-2-thiobarbituric acid (2-thiophenobarbital) enantiomers by beta-cyclodextrin was investigated by the AM1 method. The inclusion complexes of beta-cyclodextrin with neutral and anionic forms of these enantiomers have been modeled and energetically optimized. The chiral discrimination of enantiomers was analyzed in terms of differences in the interaction energies. The calculated interaction energies between each enantiomer of the investigated 2-thiobarbiturates and beta-cyclodextrin confirm the ability of beta-cyclodextrin to act as a mobile phase additive in reversed-phase HPLC to separate enantiomers by liquid chromatography and rationalize their order of elution.     

Axially dissymmetric (R)-(+)-5,5',6,6',7,7',8,8' octahydro-[1,1']binaphthyldiimine chiral salen type-ligands for copper-catalyzed asymmetric aziridination

Axially dissymmetric chiral diimine ligand 2 was prepared from the reaction of (R)-(+)-5,5',6,6',7,7',8,8'-octahydro-[1,1']binaphthyl-2,2'-diamine 1 with 2,6-dichlorobenzaldehyde. The catalytic asymmetric aziridination of alkenes was examined using this novel chiral ligand. Excellent enantioselective aziridination of cinnamates was achieved using C(2)-symmetric chiral ligand 2.