Apparent molar heat capacities and volumes of silver nitrate and silver perchlorate in aqueous solution at 298 K

We have made calorimetric and density measurements leading to apparent molar heat capacities and volumes of dilute aqueous solutions of silver nitrate and silver perchlorate at 298 K. Resulting apparent molar properties at infinite dilution are the following: φ^o_c(AgNO₃) = ? 36.8 J K^?1 mol^?1, φ^o_v(AgNO₃) = 29.1 cm³ mol^?1, φ^o_c(AgClO₄) = 11.0 J K^?1 mol^?1, and φ^o_v(AgClO₄) = 43.5 cm³ mol^?1.     

Diastereoselective arylithium addition to an alpha-trifluoromethyl imine. Practical synthesis of a potent cathepsin K inhibitor

A practical, chromatography-free synthesis of potent cathepsin K inhibitor 1 is described. The addition of 4-bromophenyllithium to an alpha-trifluoromethylimine derived from commercially available (S)-leucinol was accomplished in a highly diastereoselective manner (97.6% de, 91% yield). Subsequent Suzuki cross-coupling afforded biaryl 7. Oxidation of the alcohol and sulfide functionalities led to the formation of carboxylic acid 8. Crystallization of 7 and acid 8 as its dicyclohexylamine salt gave excellent impurity rejection. The final amide coupling with commercially available aminoacetonitrile hydrochloride afforded 1 in excellent purity (99.6A% by HPLC, 100% de, <3 ppm Pd, W, Cr).     

Studies into the mechanism of CO-induced N2 cleavage promoted by an ansa-hafnocene complex and C-C bond formation from an observed intermediate

Carbonylation of the hafnocene dinitrogen complex, [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-(t)Bu)Hf](2)(μ(2), η(2), η(2)-N(2)), yields the corresponding hafnocene oxamidide compound, arising from N(2) cleavage with concomitant C-C and C-N bond formation. Monitoring the addition of 4 atm of CO by NMR spectroscopy allowed observation of an intermediate hafnocene complex with terminal and bridging isocyanates and a terminal carbonyl. (13)C labeling studies revealed that the carbonyl is the most substitutionally labile ligand in the intermediate and that N-C bond formation in the bridging isocyanate is reversible. No exchange was observed with the terminal isocyanate. Kinetic data established that the conversion of the intermediate to the hafnocene oxamidide was not appreciably inhibited by carbon monoxide and support a pathway involving rate-determining C-C coupling of the isocyanate ligands. Addition of methyl iodide to the intermediate hafnocene resulted in additional carbon-carbon bond formation arising from CO homologation following nitrogen methylation. Similar reactivity with (t)BuNCO was observed where C-C coupling occurred upon cycloaddition of the heterocumulene. By contrast, treatment of the intermediate hafnocene with CO(2) resulted in formation of a μ-oxo hafnocene with two terminal isocyanate ligands.     

A new route to nanorods of cadmium sulfide

We report a novel synthesis of luminescent CdS nanorods which, unusually, are predominantly of the cubic phase.     

A catenane host system containing integrated triazole C-H hydrogen bond donors for anion recognition

A 3,5-bis(triazole)-pyridinium motif is integrated into a catenane structural framework via chloride anion templation. The catenane host system displays a high degree of selectivity for halide anions over dihydrogen phosphate.     

Prediction of the potency of inhibitors of adenosine deaminase by QM/MM calculations

QM/MM calculations show that the potency of a range of inhibitors of adenosine deaminase correlates with the relative stability of the reaction intermediate at the active site, rather than with the inhibitor binding energy.     

Synthesis and structural properties of lanthanide complexes formed with tropolonate ligands

We have previously reported the unique luminescence properties of ML4 complexes formed between tropolonate ligands and a series of lanthanide cations, several of them emitting in the near-infrared domain. The synthesis and composition of ML4 lanthanide tropolonate complexes have been previously described in the literature, but no structural information has been available so far. In this work, the crystal structures of several lanthanide tropolonate complexes (Ln3+ = Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+) have been isolated and systematically analyzed by X-ray diffraction and compared by using different criteria including the Kepert formalism. Such comparative work is rare in lanthanide coordination chemistry. The analysis of the structures in the solid state reveals that although the packing of the ML4 complexes depends on the nature of the metal ion, the coordination geometries around the different lanthanides is virtually similar for all the cations that have been analyzed; an indication that lanthanide-centered f orbitals play a role in controlling this coordination geometry. Analysis of the solution's behavior by stability constant determination reveals the formation of complexes with similar ML4 stoichiometries as those observed in the solid state. Nevertheless, analysis of the luminescence lifetimes indicates that the coordination environment around the lanthanide cations are different in the solid state and in solution, with the presence of one molecule of water bound to the lanthanide cation in solution. The presence of such a water molecule is a significant source of nonradiative deactivation of the excited states of the lanthanide cations, an unfavorable condition that leads to significant loss in fluorescence intensity of these lanthanide complexes. This exemplifies that such comparative analysis between the solid state and solution is important for the rationalization of the luminescence properties of the complexes. This analysis will aid us in optimizing ligand design for improved photophysical properties of the complex.