Bimolecular sinks of Criegee intermediates derived from hydrofluoroolefins:a computational analysis

A novel range of stabilised Criegee intermediate (sCI) species with halogenated substituent groups have been identified as products to the reaction between with gaseous ozone and hydrofluoroolefins (HFOs), a series of recently-developed and increasingly prevalent haloalkene refrigerants. The bimolecular chemistry of this group of hydrofluoroolefin-derived sCIs (HFO-sCIs) has yet to be explored in any significant detail so this work evaluates the reaction chemistry of common tropospheric gaseous species with the following group of HFO-sCIs: syn- & anti-CF3CHOO & syn- & anti-CF3CFOO. Using high-level theoretical calculations (DF-HF/DF-LCCSD(T)-F12a//B3LYP/aug-cc-pVTZ), this study demonstrates that HFO-sCIs will deplete many pollutants (e.g. HCHO, SO2 & H2S) but also act as a source of other atmospheric contaminants (e.g. SO3 & TFA). The bimolecular reactivity of the HFO-sCIs were compared against CH2OO, the most frequently studied sCI, for which the general reactivity trend has been identified: kTHEO (syn-CF3CHOO) < kTHEO (anti-CF3CHOO) ≈ kTHEO (CH2OO) ≪ kTHEO (anti-CF3CFOO) < kTHEO (syn-CF3CFOO). In general syn & anti-CF3 substituents reduce overall sCI reactivity compared to similar non-halogenated sCI species, whereas both syn & anti-F substituents significantly increase HFO-sCI reactivity. While HFO-sCI reactivity is largely dictated by the identity and location of the sCI substituent groups, there are co-reactants that alter these observed trends in reactivity, for example HCl reacts more rapidly with CH2OO than it does with syn- & anti-CF3CFOO

Polycationic Ru(II) luminophores: syntheses, photophysics, and application in electrostatically driven sensitization of lanthanide luminescence

A series of photoluminescent Ru(II) polypyridine complexes have been synthesized in a manner that varies the extent of the cationic charge. Two ligand systems (L1 and L2), based upon 2,2′-bipyridine (bipy) mono- or difunctionalized at the 5- or 5,5′-positions using N-methylimidazolium groups, were utilized. The resulting Ru(II) species therefore carried +3, +4, +6, and +8 complex moieties based on a [Ru(bipy)3]2+ core. Tetra-cationic [Ru(bipy)2(L2)][PF6]4 was characterized using XRD, revealing H-bonding interactions between two of the counteranions and the cationic unit. The ground-state features of the complexes were found to closely resemble those of the parent unfunctionalized [Ru(bipy)3]2+ complex. In contrast, the excited state properties produce a variation in emission maxima, including a bathochromic 44 nm shift of the 3MLCT band for the tetra-cationic complex; interestingly, further increases in overall charge to +6 and +8 produced a hypsochromic shift in the 3MLCT band. Supporting DFT calculations suggest that the trend in emission behavior may, in part, be due to the precise nature of the LUMO and its localization. The utility of a photoactive polycationic Ru(II) complex was then demonstrated through the sensitization of a polyanionic Yb(III) complex in free solution. The study shows that electrostatically driven ion pairing is sufficient to facilitate energy transfer between the 3MLCT donor state of the Ru(II) complex and the accepting 2F5/2 excited state of Yb(III)

An extended computational study of Criegee intermediate - alcohol reactions

High level ab initio calculations (DF-LCCSD(T)-F12a//B3LYP/aug-cc-pVTZ) are performed on a range of stabilized Criegee intermediate (sCI) – alcohol reactions, computing reaction coordinate energies, leading to the formation of α-alkyoxyl-alkyl-hydroperoxides (AAAHs). These potential energy surfaces are used to model bimolecular reaction kinetics over a range of temperatures. The calculations performed in this work reproduce the complicated temperature dependent reaction rates of CH2OO and (CH3)2COO with methanol, which have previously been experimentally determined. This methodology is then extended to compute reaction rates of 22 different Criegee intermediates with methanol, including several intermediates derived from isoprene ozonolysis. In some cases, sCI-alcohol reaction rates approach those of sCI-(H2O)2. This suggests that in regions with elevated alcohol concentrations, such as urban Brazil, these reactions may generate significant quantities of AAAHs, and may begin to compete with sCI reactions with other trace tropospheric pollutants such as SO2. This work also demonstrates the ability of alcohols to catalyse the 1,4-H transfer unimolecular decomposition of α-methyl substituted sCIs

Dual visible/NIR emission from organometallic iridium(III) complexes

A series of four substituted benzo[g]quinoxaline species have been synthesised and utilised as cyclometalating ligands for iridium(III). The ligands (L1-L4) were synthesised and isolated in good yield following the condensation of 2,3-diaminonaphthalene with benzil and three of its derivatives. The substituent modulated electronic properties of L1-L4 were dominated by intraligand π−π* transitions, with the fluorescence profile demonstrating vibronic features attributed to the highly conjugated nature of the chromophore. Iridium(III) complexes of the form [Ir(L)2(bipy)]PF6 were synthesised from L1-L4 in two steps. The electronic properties of the complexes reveal absorption in the UV-vis. region with spin forbidden metal-to-ligand charge transfer (MLCT) transitions possibly contributing at longer wavelengths to ca. 600 nm. Steady state luminescence (aerated, room temperature) on solutions of the complexes showed dual emissive properties in the visible and near-infra red (NIR) regions. Firstly, a vibronically structured emission in the visible region (ca. 525 nm) was attributed to ligand centred fluorescence (lifetime < 10 ns). Secondly, a broad emission peak in the NIR (ca. 950 nm) which extended to around 1200 nm was observed with corresponding lifetimes of 116–162 ns, indicative of triplet excited state emission

Ligand tuneable, red-emitting iridium(III) complexes for efficient triplet-triplet annihilation upconversion performance

A series of substituted 2‐phenylquinoxaline ligands have been explored to finely tune the visible emission properties of a corresponding set of cationic, cyclometalated iridium(III) complexes. The electronic and redox properties of the complexes were investigated using experimental (including time‐resolved luminescence and transient absorption spectroscopy) and theoretical methods. The complexes display absorption and phosphorescent emission in the visible region attributed to MLCT transitions. The different substitution patterns of the ligands induce variations in these parameters. TD‐DFT studies support these assignments and show that there is likely to be a strong spin‐forbidden contribution to the visible absorption bands at 500‐600 nm. Calculation also reliably predict the magnitude and trends in triplet emitting wavelengths for the series of complexes. The complexes were assessed as potential sensitizers in triplet‐triplet annihilation upconversion experiments using 9,10‐diphenylanthracene as the acceptor, with the methylated variants performing especially well with impressive upconversion quantum yields up to 39.3 %

A multicentre, randomised controlled trial to compare the clinical and cost-effectiveness of Lee Silverman Voice Treatment versus standard NHS Speech and Language Therapy versus control in Parkinson’s disease: a study protocol for a randomised controlled trial

Abstract: Background: Parkinson’s disease (PD) affects approximately 145,519 people in the UK. Speech impairments are common with a reported prevalence of 68%, which increase physical and mental demands during conversation, reliance on family and/or carers, and the likelihood of social withdrawal reducing quality of life. In the UK, two approaches to Speech and Language Therapy (SLT) intervention are commonly available: National Health Service (NHS) SLT or Lee Silverman Voice Treatment (LSVT LOUD®). NHS SLT is tailored to the individuals’ needs per local practice typically consisting of six to eight weekly sessions; LSVT LOUD® comprises 16 sessions of individual treatment with home-based practice over 4 weeks. The evidence-base for their effectiveness is inconclusive. Methods/design: PD COMM is a phase III, multicentre, three-arm, unblinded, randomised controlled trial. Five hundred and forty-six people with idiopathic PD, reporting speech or voice problems will be enrolled. We will exclude those with a diagnosis of dementia, laryngeal pathology or those who have received SLT for speech problems in the previous 2 years. Following informed consent and completion of baseline assessments, participants will be randomised in a 1:1:1 ratio to no-intervention control, NHS SLT or LSVT LOUD® via a central computer-generated programme, using a minimisation procedure with a random element, to ensure allocation concealment. Participants randomised to the intervention groups will start treatment within 4 (NHS SLT) or 7 (LSVT LOUD®) weeks of randomisation. Primary outcome: Voice Handicap Index (VHI) total score at 3 months. Secondary outcomes include: VHI subscales, Parkinson’s Disease Questionnaire-39; Questionnaire on Acquired Speech Disorders; EuroQol-5D-5 L; ICECAP-O; resource utilisation; adverse events and carer quality of life. Mixed-methods process and health economic evaluations will take place alongside the trial. Assessments will be completed before randomisation and at 3, 6 and 12 months after randomisation. The trial started in December 2015 and will run for 77 months. Recruitment will take place in approximately 42 sites around the UK. Discussion: The trial will test the hypothesis that SLT is effective for the treatment of speech or voice problems in people with PD compared to no SLT. It will further test whether NHS SLT or LSVT LOUD® provide greater benefit and determine the cost-effectiveness of both interventions. Trial registration: International Standard Randomised Controlled Trials Number (ISRCTN) Registry, ID: 12421382. Registered on 18 April 2016

A multicentre, randomised controlled trial to compare the clinical and cost-effectiveness of Lee Silverman Voice Treatment versus standard NHS Speech and Language Therapy versus control in Parkinson’s disease: a study protocol for a randomised controlled trial

Abstract: Background: Parkinson’s disease (PD) affects approximately 145,519 people in the UK. Speech impairments are common with a reported prevalence of 68%, which increase physical and mental demands during conversation, reliance on family and/or carers, and the likelihood of social withdrawal reducing quality of life. In the UK, two approaches to Speech and Language Therapy (SLT) intervention are commonly available: National Health Service (NHS) SLT or Lee Silverman Voice Treatment (LSVT LOUD®). NHS SLT is tailored to the individuals’ needs per local practice typically consisting of six to eight weekly sessions; LSVT LOUD® comprises 16 sessions of individual treatment with home-based practice over 4 weeks. The evidence-base for their effectiveness is inconclusive. Methods/design: PD COMM is a phase III, multicentre, three-arm, unblinded, randomised controlled trial. Five hundred and forty-six people with idiopathic PD, reporting speech or voice problems will be enrolled. We will exclude those with a diagnosis of dementia, laryngeal pathology or those who have received SLT for speech problems in the previous 2 years. Following informed consent and completion of baseline assessments, participants will be randomised in a 1:1:1 ratio to no-intervention control, NHS SLT or LSVT LOUD® via a central computer-generated programme, using a minimisation procedure with a random element, to ensure allocation concealment. Participants randomised to the intervention groups will start treatment within 4 (NHS SLT) or 7 (LSVT LOUD®) weeks of randomisation. Primary outcome: Voice Handicap Index (VHI) total score at 3 months. Secondary outcomes include: VHI subscales, Parkinson’s Disease Questionnaire-39; Questionnaire on Acquired Speech Disorders; EuroQol-5D-5 L; ICECAP-O; resource utilisation; adverse events and carer quality of life. Mixed-methods process and health economic evaluations will take place alongside the trial. Assessments will be completed before randomisation and at 3, 6 and 12 months after randomisation. The trial started in December 2015 and will run for 77 months. Recruitment will take place in approximately 42 sites around the UK. Discussion: The trial will test the hypothesis that SLT is effective for the treatment of speech or voice problems in people with PD compared to no SLT. It will further test whether NHS SLT or LSVT LOUD® provide greater benefit and determine the cost-effectiveness of both interventions. Trial registration: International Standard Randomised Controlled Trials Number (ISRCTN) Registry, ID: 12421382. Registered on 18 April 2016

Jet cooled spectroscopy of porphyrins and their sub-units

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Direct production of OH radicals upon CH overtone activation of (CH3)2COO Criegee intermediates

Ozonolysis of alkenes, a principle non-photolytic source of atmospheric OH radicals, proceeds through unimolecular decay of energized carbonyl oxide intermediates, known as Criegee intermediates. In this work, cold dimethyl-substituted Criegee intermediates are vibrationally activated in the CH stretch overtone region to drive the 1,4 hydrogen transfer reaction that leads to OH radical products. IR excitation of (CH3)2COO reveals the vibrational states with sufficient oscillator strength, coupling to the reaction coordinate, and energy to surmount the effective barrier (≤ 16.0 kcal mol−1) to reaction. Insight on the dissociation dynamics is gleaned from homogeneous broadening of the spectral features, indicative of rapid intramolecular vibrational energy redistribution and/or reaction, as well as the quantum state distribution of the OH X2Π (v = 0) products. The experimental results are compared with complementary electronic structure calculations, which provide the IR absorption spectrum and geometric changes along the intrinsic reaction coordinate. Additional theoretical analysis reveals the vibrational modes and couplings that permit (CH3)2COO to access to the transition state region for reaction. The experimental and theoretical results are compared with an analogous recent study of the IR activation of syn-CH3CHOO and its unimolecular decay to OH product