Structure of a trinuclear dizirconium-aluminum (Zr_2Al) µ-ketone complex with a bridging trigonal-bipyramidal methyl group

The reaction of a zirconocene acyl chloride with 0.5 equiv of trimethylaluminum results in the formation of the trinuclear Zr_2Al complex [Cp_2Zr(η^2(C, O)-OC-(CH_3)_2]_2(µ-AIMe_2Χ-µMe), which contains a trigonal-bipyramidal bridging methyl group. The complex crystallizes in the monoclinic system, in space group P2_1ln (C^5_(2h) No. 14), with a = 10.574 (1) Å, b = 16.456 (2) Å, c =16.763 (2) Å, β = 103.71 (1)°, V = 2833.6 (9) Å^3, and Z = 4. This is one of the few structures that contains a bridging methyl group with a near-trigonal-bipyramidal structure in which the metals occupy the axial positions and the three hydrogen atoms are in the equatorial plane

Nuclear Magnetic Resonance and Hyperfine Structure

Contains reports on four research projects

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

Experimental and Computational Studies on the Mechanism of Zwitterionic Ring-Opening Polymerization of δ‑Valerolactone with N‑Heterocyclic Carbenes

Experimental and computational investigations of the zwitterionic ring-opening polymerization (ZROP) of δ-valerolactone (VL) catalyzed by the N-heterocyclic carbenes (NHC) 1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene (<b>1</b>) and 1,3,4,5-tetramethyl-imidazol-2-ylidene (<b>2</b>) were carried out. The ZROP of δ-valerolactone generates cyclic poly­(valerolactone)­s whose molecular weights are higher than predicted from [VL]₀/[NHC]_0. Kinetic studies reveal the rate of polymerization is first order in [VL] and first order in [NHC]. Density functional theory (DFT) calculations were carried out to elucidate the key steps involved in the ring-opening of δ-valerolactone and its subsequent oligomerization. These studies have established that the initial steps of the mechanism involve nucleophilic attack of the NHC on δ-valerolactone to form a zwitterionic tetrahedral intermediate. DFT calculations indicate that the highest activation barrier of the entire mechanism is associated with the ring-opening of the tetrahedral intermediate formed from the NHC and δ-valerolactone, a result consistent with inefficient initiation to generate reactive zwitterions. The large barrier in this step is due to the fact that ring-opening requires a partial positive charge to develop next to the directly attached NHC moiety which already bears a delocalized positive charge