Photoinitiated Single-Crystal to Single-Crystal Redox Transformations of Titanium-Oxo Clusters.

Titanium-oxo clusters can undergo photochemical reactions under UV light, resulting in the reduction of the titanium-oxo core and oxidation of surface ligands. This is an important step in photocatalytic processes in light-absorbing Ti/O-based clusters, metal-organic frameworks, and (nano)material surfaces; however, studying the direct outcome of this photochemical process is challenging due to the fragility of the immediate photoproducts. In this report, titanium-oxo clusters [TiO(OiPr)(L)]n (n = 4, L = O2PPh2, or n = 6, L = O2CCH2tBu) undergo a two-electron photoredox reaction in the single-crystal state via an irreversible single-crystal to single-crystal (SC-SC) transformation initiated by a UV laser. The process is monitored by single crystal X-ray diffraction revealing the photoreduction of the cluster with coproduction of an (oxidized) acetone ligand, which is retained in the structure as a ligand to Ti(3+). The results demonstrate that photochemistry of inorganic molecules can be studied in the single crystal phase, allowing characterization of photoproducts which are unstable in the solution phase.

Photoactivation of titanium-oxo cluster [Ti6O6(OR)6(O2C t Bu)6]: mechanism, photoactivated structures, and onward reactivity with O2 to a peroxide complex.

The molecular titanium-oxo cluster [Ti6O6(OiPr)6(O2C t Bu)6] (1) can be photoactivated by UV light, resulting in a deeply coloured mixed valent (photoreduced) Ti (iii/iv) cluster, alongside alcohol and ketone (photooxidised) organic products. Mechanistic studies indicate that a two-electron (not free-radical) mechanism occurs in this process, which utilises the cluster structure to facilitate multielectron reactions. The photoreduced products [Ti6O6(OiPr)4(O2C t Bu)6(sol)2], sol = iPrOH (2) or pyridine (3), can be isolated in good yield and are structurally characterized, each with two, uniquely arranged, antiferromagnetically coupled d-electrons. 2 and 3 undergo onward oxidation under air, with 3 cleanly transforming into peroxide complex, [Ti6O6(OiPr)4(O2C t Bu)6(py)(O2)] (5). 5 reacts with isopropanol to regenerate the initial cluster (1) completing a closed cycle, and suggesting opportunities for the deployment of these easily made and tuneable clusters for sustainable photocatalytic processes using air and light. The redox reactivity described here is only possible in a cluster with multiple Ti sites, which can perform multi-electron processes and can adjust its shape to accommodate changes in electron density.

A retrospective case series of adaptive servoventilation for complex sleep apnea.

STUDY OBJECTIVES: Central sleep apnea can be refractory to traditional positive airway pressure (PAP) therapy (CPAP or bilevel PAP), whether appearing first as a feature of baseline polysomnography or only later once PAP is applied in what is termed "complex sleep apnea" (CompSA). This retrospective study examined the efficacy of adaptive servoventilation (ASV) in 25 consecutive patients with PAP-refractory central sleep apnea, most exhibiting predominantly obstructive apnea during baseline polysomnography. METHODS: Patient characteristics were: age = 59.8 ± 16.5 yr; BMI = 30.4 ± 6.1 kg/m(2); apnea/hypopnea index (AHI) = 48.5 ± 30.2/h; and central apnea index (CAI) = 10.8 ± 16.0/h. Following unsuccessful PAP titrations, patients underwent ASV titration. Eighteen met established criteria for CompSA. RESULTS: On traditional PAP, AHI did not improve significantly compared to baseline, whether based on the entire titration (38.5 ± 23.4/h, p = 0.10) or the final PAP pressure(s) (44.4 ± 25.9/h, p = 0.54); CAI tripled across the titration (27.4 ± 23.5/h, p = 0.001) and at the final pressure(s) (34.8 ± 24.2/h, p < 0.001). On ASV, AHI fell to 11.4 ± 8.2/h across the titration (p < 0.001) and decreased further to 3.6 ± 4.2/h at the optimal end expiratory pressure (p < 0.001). AHI was ≤ 5/h in 80% of patients and < 10/h in 92%. ASV virtually eliminated central apneas at optimal end expiratory pressure (0.7 ± 2.2/h, p < 0.001). Respiratory arousals showed parallel improvements on ASV but not PAP. CONCLUSIONS: ASV proved superior to traditional PAP in reducing the AHI, CAI, and respiratory arousals in a heterogeneous patient group with sleep disordered breathing in whom central apneas emerged or persisted on PAP.