Cluster chemistry: XXXIII. Reactions of [{Au(PPh3)}3O]+ with [Ru3(μ3-C2But)(CO)9]−: X-ray structure of [Ru3Au2(μ3-CCHBut)(CO)9(PPh3)2], containing a t-butylvinylidene ligand attached to a trigonal-bipyramidal Ru3Au2 core

Deprotonation (K[HBBu₃^s]) of HRu₃(μ₃-C₂Bu^t)(CO)₉, followed by reaction of the anion with [O{Au(PPh₃)}₃][BF₄], afforded the known complex Ru₃Au(μ₃-C₂Bu^t)(CO)₉ (9%), the vinylidene cluster Ru₃Au₂(μ₃-CCHBu^t)(CO)₉(PPh₃)₂ (16%) and the hexanuclear Ru₃Au₃(C₂Bu^t)(CO)₈(PPh₃)₃ (3%). The X-ray structure of the pentanuclear complex shows an asymmetric trigonal-bipyramidal Ru₃Au₂ core (Ru, Au at the apices) with the Ru₃ face bridged by a t-butylvinylidene ligand, being σ-bonded to Ru(1) and Ru(3), and η²-coordinated to Ru(2). Crystals are monoclinic, space group P2₁/n with a 19.121(3), b 13.109(3), c 23.649(4) Å, β 106.76(2)° and Z = 4. The structure was solved using 4405 observed diffractometer data, and refined to R 0.044, R_w 0.047.     

Cluster chemistry: XXIX. Preparation of cluster complexes containing aryldiazo ligands: Crystal structure of [HRu3(μ-N2C6H4)(μ3-PhAsCH2AsPh2)(CO)8]

Hydrogenation of [Ru₃(CO)₁₀(L₂)] (L₂ = dppm or dpam) affords [HRu₃(μ₃-PhECH₂EPh₂)(CO)₉] (E = P or As), which is deprotonated by K[HBBu₃^s] . Reactions of the anions with [PhN₂] [PF₆] give [Ru₃(μ-N₂Ph)(μ₃-PhECH₂EPh₂)(CO)₉], which undergo facile cyclometallation reactions when heated, as revealed by an X-ray structure of the title complex.     

Stir-bar sorptive extraction and thermal desorption-ion mobility spectrometry for the determination of trinitrotoluene and l,3,5-trinitro-l,3,5-triazine in water samples

Stir-bar sorptive extraction (SBSE) is interfaced to ion mobility spectrometry (IMS) for the rapid detection of trace analytes, with the explosives, trinitrotoluene (TNT) and l,3,5-trinitro-l,3,5-triazine (RDX) shown as examples. SBSE retains its inherent advantages as a sensitive, straightforward, solventless, and inexpensive method. Additionally, the new SBSE-IMS technique exhibits excellent sensitivity, has onsite field analysis capabilities and provides the potential to detect and quantitate analytes that are difficult to accomplish using gas chromatography (GC) or high-performance liquid chromatography (HPLC). The SBSE-IMS technique is shown to be an effective method for the low-level detection of TNT and RDX from water with method standard deviation of 8.6% for TNT and 6.6% for RDX. The short desorption time of 60 s and analysis time of less than 20 ms along with limits of detection of 0.1 ng/mL for TNT and 1.5 ng/mL for RDX and render the method potentially useful for trace analysis. Desorption profiles showing the kinetics of analyte transfer from the stir-bar into the IMS are shown and discussed; the SBSE-IMS configuration shows very rapid desorption from the stir-bar, with the analytes completely transferred in most cases, in under 1 min.     

Direct calculation of the binding free energies of FKBP ligands

Direct calculations of the absolute free energies of binding for eight ligands to FKBP protein were performed using the Fujitsu BioServer massively parallel computer. Using the latest version of the general assisted model building with energy refinement (AMBER) force field for ligand model parameters and the Bennett acceptance ratio for computing free-energy differences, we obtained an excellent linear fit between the calculated and experimental binding free energies. The rms error from a linear fit is 0.4 kcal/mol for eight ligand complexes. In comparison with a previous study of the binding energies of these same eight ligand complexes, these results suggest that the use of improved model parameters can lead to more predictive binding estimates, and that these estimates can be obtained with significantly less computer time than previously thought. These findings make such direct methods more attractive for use in rational drug design.     

Heat capacity,third-law entropy,and low-temperature physical behavior of bulk hematite (α-Fe2O3)

The constant pressure heat capacity of a bulk hematite powder was measured using a Quantum Design physical properties measurement system (PPMS). The results of two series showed good precision and agreed well with measurements reported by Westrum and Grønvold. The standard molar entropy at T = 298.15 K was calculated to be (87.32 ± 2) J · mol^?1 · K^?1 for Series 1 and (87.27 ± 2) J · mol^?1 · K^?1 for Series 2, which are in good agreement with the value of (87.40 ± 0.2) J · mol^?1 · K^?1 (originally 20.889 cal · deg^?1 · mole^?1) calculated by Westrum and Grønvold. No anomaly was observed for the Morin transition, and theoretical fits below T = 15 K required a ferromagnetic T^3/2 term.