Structural studies of metalloporphyrins. VI—13C relaxation time,T1, measurements and the nature of the axial N—metal bond in some macrocyclic complexes

Rotation barriers around the metal—pyridine bond of various macrocyclic complexes of cobalt(III), rhodium(III), zinc(II) and magnesium(II) have been studied using the ¹³C longitudinal relaxation times, T₁, of the carbon atoms of pyridine and the macrocycle. The data have been rationalized on the basis of steric and electronic factors. The influence of π back-donation on the rates of rotation around the axial Co? N and Rh? N bonds is discussed. The agreement found between the conclusions drawn from this study and X-ray data reported for complexes of identical or closely related structure demonstrates the validity of this method.     

High-Resolution Laser Photoacoustic Spectroscopy of HSiF(3): The 5nu(1) and 6nu(1) Overtone Bands

A spectrum of HSiF(3) has been recorded at room temperature with a gas pressure of 20-50 Torr in the near-infrared region. A laser photoacoustic spectrometer consisting of a longitudinal resonant cell coupled to a titanium:sapphire ring laser was employed. The 5nu(1) and 6nu(1) overtone bands of H(28)SiF(3) associated with the Si-H stretching have been observed at high resolution (3 x 10(-2) cm(-1)) in the regions 10 900-10 960 and 12 875-12 925 cm(-1), respectively. About 450 lines of the 5nu(1)-0 band have been assigned (J 相似文献   

Influence of the nature of the electrolyte on the chiral separation of basic compounds in nonaqueous capillary electrophoresis using heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin

The influence on the enantiomeric resolution of the nature of the cationic BGE component (sodium, ammonium or potassium) and that of the anionic component (chloride, formate, methanesulfonate or camphorsulfonate) as well as the concentration of heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-cyclodextrin (HDMS-beta-CD), the selected chiral selector, was studied in nonaqueous capillary electrophoresis (NACE). For this purpose, two D-optimal designs with 33 and 26 experimental points were applied. Three beta-blockers (atenolol, celiprolol and propranolol) and three local anesthetics (bupivacaine, mepivacaine and prilocaine) were selected as basic model compounds. Both cationic and anionic BGE components were found to have a deep impact on the enantiomeric resolution of the investigated analytes but it is the cationic component that has shown the strongest influence. Indeed, in some cases, the change of the latter led to a complete loss of enantioresolution. Based on the observed results, two NACE systems were recommended, namely ammonium formate and potassium camphorsulfonate in a methanolic solution containing HDMS-beta-CD and acidified with formic acid, in order to separate efficiently the enantiomers of basic drugs.     

13C relaxation times,T1, in six-coordinate cobalt(III) complexes: Study of the axial Co?N (heterocyclic) bond

Carbon-13 relaxation times, T₁, have been measured for ten cobalt(III)–cyclohexanedione dioxime complexes: CH₃CH₂? Co(Niox)₂-p-R-pyridine [R?H, N(CH₃)₂, CH₃, C₂H₅, C(CH₃)₃, Cl, Br, CN and COCH₃] and CH₃CH₂? Co(Niox)₂-3-N-methylimidazole. The values obtained have been rationalized by making assumptions on the length of the metal—hetrocyclic nitrogen bond. The internal rotation around the axial Co? N (heterocyclic) bond is faster for the 3-N-methylimidazole ligand than for the pyridine ligands. Correlations of the T₁ values with the σ-donor and π-acceptor character of the pyridine ligands were attempted. The interpretation of the results suggests the existence of π-back-bonding from the metal to the N-1 pyridine nitrogen atom, in agreement with the results of other workers. This conclusion, however, was not supported by the use of the para-C chemical shift as a criterion for back-bonding in pyridine–transition metal complexes.     

Saturated 5-membered ring conformations. 2—1H NMR study of protonated N-methylpyrrolidines

The ¹H NMR spectra of the protonated and unprotonated forms of cis- and trans-N-methylhexahydroisoindoline, of 1,3,3,4,4-pentamethylpyrrolidine and of 1,3,3-trimethylpyrrolidine were analyzed. The coupling constants between the NH⊕ and the CH protons α to the nitrogen allowed the study of the conformation of the cyclic systems in pseudorotation.     

Development of an ELISA screening test for nitroimidazoles in egg and chicken muscle

An antibody was generated that can bind metronidazole (MNZ), a nitroimidazole drug used in veterinary medicine to treat poultry for coccidiosis and histomoniasis. A direct competitive enzyme-linked immunosorbent assay (cELISA) is described. It was used to characterise binding of this antibody to a number of nitroimidazole drugs. It displayed cross-reactivity with dimetridazole (DMZ), ronidazole (RNZ), hydroxydimetridazole (DMZOH), and ipronidazole (IPZ).Egg and chicken muscle samples were extracted with acetonitrile and de-fatted by washing with hexane. Detection capabilities (CCβ) were determined: dimetridazole, <1 ppb (egg) and <2 ppb (muscle); metronidazole, <10 ppb; ronidazole and hydroxydimetridazole, <20 ppb; ipronidazole, <40 ppb.