Ditopic Ligands. The Synthesis of a Series of Phosphine-Functionalised Macrocycles

The synthesis of a series of phosphine-functionalised macrocycles, 1–6 , is described. The combination of N-and O-sites with P- and S-sites provides ligands which may bind transition or non-transition metal ions; as a consequence, they give access to dinuclear complexes containing both a Lewis acid and a redox metallic site. Compounds 1,2 and 6 are heterodinucleating ligands capable of binding two dissimilar metals in proximity. Macrocycles 3–5 are homotopic ligands which may form homodinuclear complexes of transition metals.     

Superacid-Catalyzed Oxygenation of Alkanes. [New synthetic methods (26)]

Owing to the ready availability of the starting materials, the functionalization of saturated hydrocarbons for preparing chemical intermediates and products represents an attractive goal. The possibility of converting alkane in a controlled way into alcohols, ketones etc., i.e. to oxyfunctionalize them, is particularly challenging. After a short account of previous methods used for the oxidation of alkanes, particular emphasis will be given to recently developed reactions of alkanes with oxygenating agents in superacidic media.     

Phthalocyanine polymers. V. Novel type of thermally stable polyimides derived from metal phthalocyanine tetraamines and pyromellitic dianhydride

New poly(metal phthalocyanine) pyromellitimides of copper, cobalt, nickel, and zinc were synthesized and elemental, IR, TGA, and inherent viscosity measurement studies were done to characterize these polymers. They showed exceptional thermal and thermo-oxidative stability with char yields at 800°C ranging from 75 to 87% in a nitrogen atmosphere. The ratio of the polymer decomposition temperatures in air and nitrogen (PDT) (air)/PDT (N₂) varied from 0.91 to 0.97, which indicated that the onset of degradation of these polymers is greatly affected by the presence of an oxidizing atmosphere. Isothermal studies were done to evaluate the long-term thermal stability of these polymers.     

A validated LC-MSMS method for the simultaneous quantification of meropenem and vaborbactam in human plasma and renal replacement therapy effluent and its application to a pharmacokinetic study

A simple method for the simultaneous quantification of meropenem and the recently approved β-lactamase inhibitor, vaborbactam, in human plasma and renal replacement therapy effluent (RRTE) was developed and validated. This antibiotic combination protects a primary β-lactam, meropenem, with a new β-lactamase inhibitor, and expands the limited options for treatment of multidrug-resistant Gram-negative infections. Meropenem, vaborbactam, and the internal standards [²H₆]-meropenem and sulbactam in plasma and RRTE were processed using acetonitrile followed by a chromatographic separation on a Poroshell HPH-C18 column with a gradient elution of the mobile phases and monitored using mass spectrometry detection. The calibration range was 0.05 to 100 μg mL⁻¹ for both meropenem and vaborbactam. The intra-day and inter-day precision and accuracy were less than 15% for both meropenem and vaborbactam and the recovery from plasma was 96% for both meropenem and vaborbactam and the recovery from RRTE was 93% and 103% for meropenem and vaborbactam, respectively. This methodology was successfully applied to an ex vivo characterisation study of the effects of renal replacement therapy modalities on the pharmacokinetics of meropenem and vaborbactam (Antimicrob Agents Chemother 62(10), 2018).

Graphical abstract

     

Isotope effects on the picosecond time-resolved emission spectroscopy of tris(2,2'-bipyridine)ruthenium (II)

The excited-state properties of the transition metal complexes tris(2,2'-bipyridine) ruthenium(II) and tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) are examined using picosecond time-resolved luminescence spectroscopy. For both complexes, direct observation of a short-lived high-energy emission with a lifetime of less than 4 ps is reported. Upon deuteriation of the complexes the lifetime of the high-energy emission shows a marked increase with a biexponential decay (20 and approximately 300 ps components). Examination by time-resolved excited-state resonance Raman shows that for the perprotio complexes features attributable to the 3MLCT excited state are formed within 4 ps, while for the perdeuterio a rise time of approximately 20 ps is observed in the 3MLCT features. The results indicate that the emission in both cases may be 1MLCT in origin and are discussed with respect to heterogeneous electron transfer.     

Hydride-exchange reactions between NADH and NAD+ model compounds under non-steady-state conditions. Apparent and real kinetic isotope effects

The kinetics of the hydride exchange reaction between NADH model compound 10-methyl-9,10-dihydroacridine (MAH) and 1-benzyl-3-cyanoquinolinium (BQCN+) ion in acetonitrile were studied at temperatures ranging from 291 to 325 K. The extent of reaction-time profiles during the first half-lives are compared with theoretical data for the simple single-step mechanism and a 2-step mechanism involving initial donor/acceptor complex formation followed by unimolecular hydride transfer. The profiles for the reactions of MAH deviate significantly from those expected for the simple single-step mechanism with the deviation increasing with increasing temperature. The deviation from simple mechanism behavior is much less pronounced for the reactions of 10-methyl-9,10-dihydroacridine-10,10-d2 (MAD) which gives rise to extent of reaction dependent apparent kinetic isotope effects (KIEapp). Excellent fits of the experimental extent of reaction-time profiles with theoretical data for the 2-step mechanism, in the pre-steady-state time period, were observed in all cases. Resolution of the kinetics of the hydride exchange reaction into the microscopic rate constants over the entire temperature range resulted in real kinetic isotope effects for the hydride transfer step ranging from 40 (291 K) to 8.2 (325 K). That the reaction involves significant hydride tunnelling was verified by the magnitudes of the Arrhenius parameters; Ea D - EaH = 8.7 kcal mol-1 and AD/AH = 8 x 10(4). An electron donor acceptor complex (lambda max = 526 nm) was observed to be a reaction intermediate. Theoretical extent of reaction-time profile data are discussed for the case where a reaction intermediate is formed in a non-productive side equilibrium as compared to the case where it is a real intermediate on the reaction coordinate between reactants and products. The common assumption that the two cases are kinetically indistinguishable is shown to be incorrect.     

The structure of alkali silicate glasses

Pulsed neutron diffraction has been used to study the structure of three alkali silicate glasses of nominal composition SiO₂ · (M₂O)_0.5, with M = K, K_0.46Li_0.54 and Li. The data are quantitatively consistent with the modified random network model. Lithium is coordinated by two oxygen atoms with an interatomic distance of 1.97 Å. The potassium-oxygen distance is similar to the tetrahedral oxygen-oxygen distance, 2.66 Å, with potassium being coordinated by approximately four oxygen atoms.     

The space of geodesics

Let M be a manifold with linear connection . The space G(M) of all geodesics of M may be given a topological structure and may be realized as a quotient space of the reduced tangent bundle of M. The space G(M) is a T ₁ space iff the image of each geodesic is a closed subset of M. It is Hausdorff iff each tangentially convergent sequence of geodesics converges in the Hausdorff limit sense to the limit geodesic. If M has no conjugate points and G(M) is Hausdorff, then M is geodesically connected.Supported in part by NSF grant DMS-8803511.