A facile synthesis of Robinson’s NHC-stabilised diborane(4)

Reactions of bis(pinacolato)diboron (B2pin2) with [(IDip)AlH3] (IDip = (HCNDip)2C:, Dip = 2,6-iPr2C6H3) afforded both the new diborane [(IDip)BH2B(pin)] and the known compound [(IDip)BH2BH2(IDip)] in a facile one-pot procedure; the latter reaction is improved by the addition of free IDip. [(IDip)AlH3] transfers both IDip and hydride ligands to the diborane moiety in a halide-free approach. [(IDip)BH2B(pin)] was structurally and spectroscopically characterised and additional spectroscopic data for [(IDip)BH2BH2(IDip)] is reported.Publisher PDFPeer reviewe

Tuning the optical properties of silicon quantum dots via surface functionalization with conjugated aromatic fluorophores

The authors acknowledge Karen Nygard at UWO Biotron for assistance with confocal microscopy. This work was financially supported by NSERC Canada Discovery (Charpentier).Silicon Quantum Dots (SQDs) have recently attracted great interest due to their excellent optical properties, low cytotoxicity, and ease of surface modification. The size of SQDs and type of ligand on their surface has a great influence on their optical properties which is still poorly understood. Here we report the synthesis and spectroscopic studies of three families of unreported SQDs functionalized by covalently linking to the aromatic fluorophores, 9-vinylphenanthrene, 1-vinylpyrene, and 3-vinylperylene. The results showed that the prepared functionalized SQDs had a highly-controlled diameter by HR-TEM, ranging from 1.7–2.1 nm. The photophysical measurements of the assemblies provided clear evidence for efficient energy transfer from the fluorophore to the SQD core. Fӧrster energy transfer is the likely mechanism in these assemblies. As a result of the photogenerated energy transfer process, the emission color of the SQD core could be efficiently tuned and its emission quantum efficiency enhanced. To demonstrate the potential application of the synthesized SQDs for bioimaging of cancer cells, the water-soluble perylene- and pyrene-capped SQDs were examined for fluorescent imaging of HeLa cells. The SQDs were shown to be of low cytotoxicity.Publisher PDFPeer reviewe

The value of 2 J P–CO as a diagnostic parameter for the structure and thermal reactivity of carbonyl-stabilised phosphonium ylides

A survey of 20 carbonyl-stabilised phosphonium ylides with recently reported X-ray structures shows a strong correlation between the CP to CO torsion angle and the value of 2JP–CO, with high values being associated with an anti configuration and low with syn. Seven new X-ray structural determinations are reported, several for types of ylide not crystallographically characterised before, and these also conform to this pattern. The value of 2JP–CO is then correlated with whether or not thermal extrusion of Ph3PO occurs to give alkynes for over 200 ylides and an empirical rule developed that the extrusion never occurs for ylides where this value is > 11 Hz. This is used to rationalise the anomalous behaviour of some trioxo ylides and cyclic ylides, two of which afford cycloalkynes, isolated after rearrangement as the isomeric 1,3-dienes. The rule also holds for a family of novel highly fluorinated ylides which afford fluorinated alkynes in good yield upon flash vacuum pyrolysis.EPSRC (U.K.) for a DTA Studentship (Grant No. EP/P505712/1

Energy Expenditure in Kidney Failure: Implications for Management

Renal replacement therapy, in the form of dialysis or transplantation, is the cornerstone of management for end-stage renal disease. UK renal registry shows nearly half of those needing renal replacement therapy are treated by dialysis – predominantly by haemodialysis. Patients on renal replacement therapy have increased mortality risk compared to age matched general population. Moreover, some specific subgroups of patients on haemodialysis have increased risk of mortality than expected. The survival benefit seen in women in the general population is attenuated resulting in similar survival for men and women on haemodialysis therapy. In addition, obese individuals and those of non-Caucasian origin have better survival outcome. Though the underlying reason for these findings is not clear and is likely to be multi-factorial, it has been hypothesised that this paradox could be due to the current practice of normalising dialysis dose to total body water. A number of metabolic factors – body surface area, resting energy expenditure and total energy expenditure – have been proposed as alternative to total body water for scaling dialysis dose. There were two overarching aims of this work – one was to study the effect of declining renal function on resting and total energy expenditure and to study the influence of various energy expenditure measures on uraemic toxin generation. The second was to study the impact on survival outcome of using these alternate parameters for normalising dialysis dose and to derive dialysis dose adjustments based on these metabolic parameters. In order to study these aims, studies were designed to explore different aspects of energy expenditure measures along with a longitudinal study to examine the impact of these parameters on survival outcome. The relationship between energy metabolism, body composition and uraemic toxin generation was studied with a retrospective analysis of 166 haemodialysis patients in whom urea generation rate was used as surrogate marker of uraemic toxin generation. It was found that total energy expenditure and fat-free mass predicted uraemic toxin generation after adjustment for other relevant variables. This study provided the preliminary data which was useful in designing further studies for this work. The effect of renal function on resting and total energy expenditure was studied in 80 patients with varying stages of chronic kidney disease who were not on renal replacement therapy. Resting and total energy expenditures were measured directly using gold-standard methods. It was found that declining renal function did not have a significant influence on either of these measures. This supports the hypothesis that metabolic rate is the driving force for glomerular filtration rate and not vice-versa. The directly measured energy expenditure measures were also found to have a moderately strong relationship with urea generation rate in these patients not on renal replacement therapy. The impact of physical activity on uraemic toxin generation, and thereby dialysis requirement, was studied in a prospective cross-sectional study of 120 haemodialysis patients in whom the physical activity was measured by an accelerometer device. Results from the study showed physical activity level to be a significant predictor of uraemic toxin generation after adjustment for gender and body size differences. This study results stressed the importance of adjusting dialysis dose based on individual’s physical activity level. To study the impact of using metabolic factors as normalising parameter for scaling dialysis dose on survival outcome, a large-scale longitudinal study was conducted with 1500 maintenance haemodialysis patients recruited for the study. Dialysis dose-related parameters and survival outcomes were collected at baseline and at various time points during the follow-up period of 18 months. Study results were analysed in two parts - the theoretical basis for using these metabolic factors as scaling parameters was explored which showed that current minimum target dialysis dose risks under-dialysis in certain subgroups of patients and using these alternative parameters may provide a more equivalent dialysis dose across individuals of different body sizes and gender. With these results arguing for potential use of the alternative parameters, the impact on survival of using them were examined. It was found that all three parameters performed better than the current parameter (total body water) with regards to predicting mortality. Total energy expenditure was found to be the best parameter with the lowest hazard ratio for risk of death. The study data was also analysed to derive an algorithm for adjustment of minimum target dialysis dose based on body size and physical activity level. This newly derived minimum dose target was also shown to impact on survival with those underdialysed based on this criteria having poorer survival outcomes. To understand the impact of whole body protein turnover on resting energy expenditure and uraemic toxin generation, a cross-sectional study was conducted on 12 patients with advanced CKD – 6 each in pre-dialysis CKD and haemodialysis group. It was found that haemodialysis patients had higher rate of protein turnover compared to pre-dialysis patients. Whole body protein turnover was found to contribute significantly to resting energy expenditure and had a moderately strong relationship with urea generation rate. In the course of these studies, two questionnaire tools have been validated for use for clinical and research purposes – one is a self-report comorbidity questionnaire and the other, the Recent Physical Activity Questionnaire. The comorbidity questionnaire was developed as part of this work and was validated against Charlson Comorbidity Index. The Recent Physical Activity Questionnaire was validated for physical activity data collection and energy expenditure calculation against the gold-standard doubly labelled water method. In conclusion, it has been demonstrated that metabolic factors such as body surface area, resting energy expenditure and total energy expenditure are more closely related to uraemic toxin generation compared to total body water. It has also been demonstrated that physical activity contributes to metabolic waste production and may necessitate changes in dialysis requirement. It has been shown that these metabolic factors, when used as scaling parameter for dialysis dosing, may predict survival better than the current parameter in use. The algorithm for dialysis dose adjustment and the questionnaires validated in this work have provided novel tools for further research studies and clinical practice. The central hypothesis of this work is that some metabolic factors may be better markers of uraemic toxin generation compared to total body water. It is hypothesised that modifications in dialysis practice based on these factors may improve the quality of haemodialysis and favourably impact on survival outcome for patients with end-stage renal disease. The work presented here largely supports this hypothesis

Shape controlled assembly of carboxylic acids : formation of a binary monolayer by intercalation into molecular nanotunnels

Support by the Leverhulme Trust (RGP -2013-177) and EPSRC via doctoral training grants (R .O .d.l.M .,H.A.) and the EPSRC Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT) (PhD studentship to K.T.) is gratefully acknowledged. A. A. acknowledges the financial support by the DAAD-Aceh Scholarship of Excellence.Binary self-assembled monolayers (SAMs) combining a Y-shaped aromatic carboxylic acid (1,3,5-benzenetribenzoic acid, H3BTB) and a cage-type alicyclic carboxylic acid (adamantane carboxylic acid, AdCA) were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The SAMs, prepared by molecular adsorption from solution on Au substrates modified by underpotential deposition of Ag, exhibit a pronounced dependence of their structure on the assembly protocol. Exposing an H3BTB SAM to AdCA, the highly regular row structure of the native H3BTB layer persists and STM imaging does not show signs of AdCA adsorption. This is in striking contrast to the disordered arrangements of H3BTB and the presence of AdCA employing the inverted adsorption sequence or coadsorption of the two molecules. However, spectroscopic analysis of the H3BTB SAM exposed to AdCA reveals the presence also of the latter, suggesting that the AdCA molecules are hidden in the nanotunnels of the H3BTB monolayer. Direct evidence for the intercalation of AdCA is obtained by STM manipulation experiments which lay bare areas of AdCA molecules upon local removal of H3BTB. Surprisingly, these are densely packed and arranged into a highly ordered monolayer. Formation of such a compact AdCA layer is explained by expulsion of AdCA from the H3BTB nanotunnels of the surrounding intact mixed SAM, driven by release of stress in the nanotunnels built up when AdCA is intercalated.PostprintPeer reviewe

Electronic effects in mixed N-heterocyclic carbene/phosphite indenylidene ruthenium metathesis catalysts

The authors gratefully acknowledge the Royal Society (University Research Fellowship to CSJC), the EC (CP-FP 211468-2 EUMET and CIG09-GA-2011-293900) and the MICINN (PGC2018-097722-B-I00 to AP) for funding.Five new complexes [RuCl2(SIMes)(Ind)(O-pXC5H4)] bearing different para-substituted triphenylphosphites (X = H, OCH3, CF3, Cl, SF5 and CN) were synthesised and used to study the effect of the electronic properties of the phosphite on olefin metathesis activity. Investigations of the physical properties of the new ligands and complexes were performed using physicochemical and DFT calculations. The catalytic activity of the complexes was benchmarked in challenging ring closing metathesis transformations featuring the formation of tetra-substituted double bonds. Complex [RuCl2(SIMes)(Ind)P(O-pCF3C5H4)3] (3c) exhibited a particularly high catalytic activity, superior to state-of-the-art catalysts, and was further tested on a wide range of substrates.PostprintPeer reviewe

New iron tetrazolate frameworks : synthesis temperature effect, thermal behaviour, Mössbauer and magnetic studies

The exploration of the FeF3/FeF2-Hamtetraz-HF system in dimethylformamide by solvothermal synthesis evidences two isostructural 3D hybrid fluoroferrates. They are prepared from the same starting mixture at two different synthesis temperatures: 120 °C for [Hdma]·(Fe4IIFeIIIF8(H2O)2(amtetraz)4) (1) and 140 °C for [Hdma]1.5·(Fe4.5IIFe0.5IIIF7(H2O)(HCOO)(amtetraz)4) (2). Both compounds are characterized by single crystal X-ray diffraction, X-ray thermodiffraction, TGA analysis, Mössbauer spectrometry and SQUID magnetometry. They crystallize in the monoclinic system and are built from two distinct chains connected by aminotetrazolate anions. The first chain ∞(FeIIFN4) is common to 1 and 2 and can be found in numerous fluorides. In the second chain ∞(Fe3X12) (X = F, N, O), iron cations adopt both valence states Fe(II)/Fe(III). The hydrolysis of DMF implies the formation of a [Hdma]+ cation and a (HCOO)− anion. The presence of Fe3+ in both phases is evidenced by 57Fe Mössbauer spectrometry. The magnetic properties are studied and two transitions from a paramagnetic regime to a long range ordered state below 30 K and 5 K are identified.PostprintPeer reviewe

An inter-subunit protein-peptide interface that stabilizes the specific activity and oligomerization of the AAA+ chaperone Reptin

The work was supported by: the Czech Science Foundation 16-20860S (PM, LH) and 16-07321S (BV, TH), the project MEYS – NPS I – LO1413, and MH CZ - DRO (MMCI, 00209805); the BBSRC RASOR consortium (BB/C511599/1; United Kingdom); Cancer Research UK (C21383/A6950); The International Centre for Cancer Vaccine Science project carried out within the International Research Agendas programme of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund; A*STAR, Singapore and NSCC, Singapore.Reptin is a member of the AAA+ superfamily whose members can exist in equilibrium between monomeric apo forms and ligand bound hexamers. Inter-subunit protein-protein interfaces that stabilize Reptin in its oligomeric state are not well-defined. A self-peptide binding assay identified a protein-peptide interface mapping to an inter-subunit “rim” of the hexamer bridged by Tyrosine-340. A Y340A mutation reduced ADP-dependent oligomer formation using a gel filtration assay, suggesting that Y340 forms a dominant oligomer stabilizing side chain. The monomeric ReptinY340A mutant protein exhibited increased activity to its partner protein AGR2 in an ELISA assay, further suggesting that hexamer formation can preclude certain protein interactions. Hydrogen-deuterium exchange mass spectrometry (HDX-MS) demonstrated that the Y340A mutation attenuated deuterium suppression of Reptin in this motif in the presence of ligand. By contrast, the tyrosine motif of Reptin interacts with a shallower pocket in the hetero-oligomeric structure containing Pontin and HDX-MS revealed no obvious role of the Y340 side chain in stabilizing the Reptin-Pontin oligomer. Molecular dynamic simulations (MDS) rationalized how the Y340A mutation impacts upon a normally stabilizing inter-subunit amino acid contact. MDS also revealed how the D299N mutation can, by contrast, remove oligomer de-stabilizing contacts. These data suggest that the Reptin interactome can be regulated by a ligand dependent equilibrium between monomeric and hexameric forms through a hydrophobic inter-subunit protein-protein interaction motif bridged by Tyrosine-340. Significance Discovering dynamic protein-protein interactions is a fundamental aim of research in the life sciences. An emerging view of protein-protein interactions in higher eukaryotes is that they are driven by small linear polypeptide sequences; the linear motif. We report on the use of linear-peptide motif screens to discover a relatively high affinity peptide-protein interaction for the AAA+ and pro-oncogenic protein Reptin. This peptide interaction site was shown to form a ‘hot-spot’ protein-protein interaction site, and validated to be important for ligand-induced oligomerization of the Reptin protein. These biochemical data provide a foundation to understand how single point mutations in Reptin can impact on its oligomerization and protein-protein interaction landscape.PostprintPeer reviewe

Ligand electronic fine-tuning and its repercussion on the photocatalytic activity and mechanistic pathways of the copper-photocatalysed aza-Henry Reaction

C.Li thanks the Prof. & Mrs Purdie Bequests Scholarship and AstraZeneca PhD Studentship.A family of six structurally related heteroleptic copper(I) complexes of the form of [Cu(N^N)(P^P)]+ bearing a 2,9-dimethyl-1,10-phenanthroline diimine (N^N) ligand and a series of electronically tunable xantphos (P^P) ligands have been synthesized and their optoelectronic properties characterized. The reactivity of these complexes in the copper-photocatalyzed Aza-Henry reaction of N-Phenyltetrahydroisoquinoline was evaluated, while the related excited state kinetics were comprehensively studied. By subtlety changing the electron-donating properties of the P^P ligands with neglegible structural differences, we could tailor the photoredox properties and relate it to their reactivity. Moreover, depending on the exited-state redox potential of the catalysts, the preferred mechanism can shift between reductive quenching, energy transfer and oxidative quenching pathways. A combined study of structural modulation of copper(I) photocatalysts, optoelectronic properties and photocatalytic reactivity resulted in a clearer understanding of both the rational design of the photocatalyst and the complexity of competing photoinduced electron and energy transfer mechanisms.Publisher PDFPeer reviewe

Peri-substituted phosphorus-tellurium systems – an experimental and theoretical investigation of the P∙∙∙Te through-space interaction

The authors are thankful to the EPSRC, the EPSRC National Mass Spectrometry Service Centre (NMSSC) Swansea, the School of Chemistry St. Andrews, and EaStCHEM for support.A series of peri-substituted phosphorus-tellurium systems R’Te–Acenap–PR2 (R’ = Ph, p-An, Nap, Mes, Tip; R = iPr, Ph) exhibiting large “through space” spin-spin coupling constants and the “onset” of three-centre four-electron type interactions are presented. The influence of the substituents at the phosphorus and tellurium atoms as well as their behavior upon oxidation (with S, Se) or metal-coordination (Pt, Au) is discussed using NMR spectroscopy, single crystal X-ray diffraction, and advanced DFT studies including NBO, AIM and ELI-D analyses.PostprintPeer reviewe