Reversal of a single base pair step controls guanine photo-oxidation by an intercalating Ru(II) dipyridophenazine complex

Small changes in DNA sequence can often have major biological effects. Here the rates and yields of guanine photo-oxidation by Λ [Ru(TAP)2(dppz)]2+ have been compared in 5′-{CCGGATCCGG}2 and 5′-{CCGGTACCGG}2 using ps/ns transient visible and time-resolved IR (TRIR) spectroscopy. The inefficiency of electron transfer in the TA sequence is consistent with the 5′-TA-3′ vs. 5′-AT-3′ binding preference predicted by X-ray crystallography. The TRIR spectra also reveal the differences in binding sites in the two oligonucleotides

Enantiomeric conformation controls rate and yield of photoinduced electron transfer in DNA sensitized by Ru(II) Dipyridophenazine complexes

Photosensitized oxidation of guanine is an important route to DNA damage. Ruthenium polypyridyls are very useful photosensitizers as their reactivity and DNA-binding properties are readily tunable. Here we show a strong difference in the reactivity of the two enantiomers of [Ru(TAP)2(dppz)]2+, by using time-resolved visible and IR spectroscopy. This reveals that the photosensitized one-electron oxidation of guanine in three oligonucleotide sequences proceeds with similar rates and yields for bound delta-[Ru(TAP)2(dppz)]2+, whereas those for the lambda enantiomer are very sensitive to base sequence. It is proposed that these differences are due to preferences of each enantiomer for different binding sites in the duplex

Monitoring guanine photo-oxidation by enantiomerically resolved Ru(II) dipyridophenazine complexes using inosine-substituted oligonucleotides

The intercalating [Ru(TAP)2(dppz)]2+ complex can photo-oxidise guanine in DNA, although in mixed-sequence DNA it can be difficult to understand the precise mechanism due to uncertainties in where and how the complex is bound. Replacement of guanine with the less oxidisable inosine (I) base can be used to understand the mechanism of electron transfer (ET). Here the ET has been compared for both L- and D-enantiomers of [Ru(TAP)2(dppz)]2+ in a set of sequences where guanines in the readily oxidisable GG step in {TCGGCGCCGA}2 have been replaced with I. The ET has been monitored using picosecond and nanosecond transient absorption and ps-time-resolved IR spectroscopy. In both cases inosine replacement leads to a diminished yield, but the trends are strikingly different for L- and D-complexes

Inosine can increase DNA's susceptibility to photo-oxidation by a Ru(II) complex due to structural change in the minor groove

Key to the development of DNA-targeting phototherapeutic drugs is determining the interplay between the photoactivity of the drug and its binding preference for a target sequence. For the photo- oxidising lambda-[Ru(TAP)2(dppz)]2+ (Ʌ-1) complex bound to either d{T1C2G3G4C5G6C7C8G9A10}2 (G9) or d{TCGGCGCCIA}2 (I9), the X- ray crystal structures shows the dppz intercalated at the terminal T1C2;G9A10 step or T1C2;I9A10 step. Thus substitution of the G9 nucleobase by inosine does not affect intercalation in the solid state although with I9 the dppz is more deeply inserted. In solution it is found that the extent of guanine photo-oxidation, and the rate of back electron transfer, as determined by ps and ns time-resolved infrared and transient visible absorption spectroscopy, is enhanced in I9, despite it containing the less oxidisable inosine. This is attributed to the nature of the binding in the minor groove due to the absence of an NH2 group. Similar behaviour and the same binding site in the crystal.are found for d{TTGGCGCCAA}2 (A9), In solution we propose that intercalation occurs at the C2G3;C8I9 or T2G3;C8A9 steps, respectively, with G3 the likely target for photo-oxidation. This demonstrates how changes in the minor groove (in this case removal of an NH2 group) can facilitate binding of Ru(II)dppz complexes and hence influence any sensitised reactions occurring at these sites. No similar enhancement of photooxidation on binding to I9 is found for the delta enantiomer

Monitoring one-electron photo-oxidation of guanine in DNA crystals using ultrafast infrared spectroscopy

To understand the molecular origins of diseases caused by ultraviolet and visible light, and also to develop photodynamic therapy, it is important to resolve the mechanism of photoinduced DNA damage. Damage to DNA bound to a photosensitizer molecule frequently proceeds by one-electron photo-oxidation of guanine, but the precise dynamics of this process are sensitive to the location and the orientation of the photosensitizer, which are very difficult to define in solution. To overcome this, ultrafast time-resolved infrared (TRIR) spectroscopy was performed on photoexcited ruthenium polypyridyl–DNA crystals, the atomic structure of which was determined by X-ray crystallography. By combining the X-ray and TRIR data we are able to define both the geometry of the reaction site and the rates of individual steps in a reversible photoinduced electron-transfer process. This allows us to propose an individual guanine as the reaction site and, intriguingly, reveals that the dynamics in the crystal state are quite similar to those observed in the solvent medium

Chromium deposition and poisoning of La0.8Sr0.2MnO3 oxygen electrodes of solid oxide electrolysis cells

The effect of the presence of an Fe–Cr alloy metallic interconnect on the performance and stability of La0.8Sr0.2MnO3 (LSM) oxygen electrodes is studied for the first time under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The presence of the Fe–Cr interconnect accelerates the degradation and delamination processes of the LSM oxygen electrodes. The disintegration of LSM particles and the formation of nanoparticles at the electrode/electrolyte interface are much faster as compared to that in the absence of the interconnect. Cr deposition occurs in the bulk of the LSM oxygen electrode with a high intensity on the YSZ electrolyte surface and on the LSM electrode inner surface close to the electrode/electrolyte interface. SIMS, GI-XRD, EDS and XPS analyses clearly identify the deposition and formation of chromium oxides and strontium chromate on both the electrolyte surface and electrode inner surface. The anodic polarization promotes the surface segregation of SrO and depresses the generation of manganese species such as Mn2+. This is evidently supported by the observation of the deposition of SrCrO4, rather than (Cr,Mn)3O4 spinels as in the case under the operating conditions of solid oxide fuel cells. The present results demonstrate that the Cr deposition is essentially a chemical process, initiated by the nucleation and grain growth reaction between the gaseous Cr species and segregated SrO on LSM oxygen electrodes under SOEC operating conditions

Bio-impedance spectroscopy added to a fluid management protocol does not improve preservation of residual kidney function in incident hemodialysis patients in a randomized controlled trial

Avoiding excessive dialysis-associated volume depletion may help preserve residual kidney function (RKF). To establish whether knowledge of the estimated normally hydrated weight from bioimpedance measurements (BI-NHW) when setting the post-hemodialysis target weight (TW) might mitigate rate of loss of RKF, we undertook an open label, randomized controlled trial in incident patients receiving HD, with clinicians and patients blinded to bioimpedance readings in controls. A total of 439 patients with over 500 ml urine/day or residual GFR exceeding 3 ml/min/1.73m2 were recruited from 34 United Kingdom centers and randomized 1:1, stratified by center. Fluid assessments were made for up to 24 months using a standardized proforma in both groups, supplemented by availability of BI-NHW in the intervention group. Primary outcome was time to anuria, analyzed using competing-risk survival models adjusted for baseline characteristics, by intention to treat. Secondary outcomes included rate of RKF decline (mean urea and creatinine clearance), blood pressure and patient-reported outcomes. There were no group differences in cause-specific hazard rates of anuria (0.751; 95% confidence interval (0.459, 1.229)) or sub-distribution hazard rates (0.742 (0.453, 1.215)). RKF decline was markedly slower than anticipated, pooled linear rates in year 1: –0.178 (–0.196, –0.159)), year 2: –0.061 (–0.086, –0.036)) ml/min/1.73m2/month. Blood pressure and patient-reported outcomes did not differ by group. The mean difference agreement between TW and BI-NHW was similar for both groups, Bioimpedance: –0.04 kg; Control: –0.25 kg. Thus, use of a standardized clinical protocol for fluid assessment when setting TW is associated with excellent preservation of RKF. Hence, bioimpedance measurements are not necessary to achieve this

Time-resolved infra-red studies of photo-excited porphyrins in the presence of nucleic acids and in HeLa tumour cells: insights into binding site and electron transfer dynamics

Cationic porphyrins based on the 5,10,15,20-meso-(tetrakis-4-N-methylpyridyl) core (TMPyP4) have been studied extensively over many years due to their strong interactions with a variety of nucleic acid structures, and their potential use as photodynamic therapeutic agents and telomerase inhibitors. In this paper, the interactions of metal-free TMPyP4 and Pt(II)TMPyP4 with guanine-containing nucleic acids are studied for the first time using time-resolved infrared spectroscopy (TRIR). In D2O solution (where the metal-free form exists as D2TMPyP4) both compounds yielded similar TRIR spectra (between 1450–1750 cm−1) following pulsed laser excitation in their Soret B-absorption bands. Density functional theory calculations reveal that vibrations centred on the methylpyridinium groups are responsible for the dominant feature at ca. 1640 cm−1. TRIR spectra of D2TMPyP4 or PtTMPyP4 in the presence of guanosine 5'-monophosphate (GMP), double-stranded {d(GC)5}2 or {d(CGCAAATTTGCG)}2 contain negative-going signals, ‘bleaches’, indicative of binding close to guanine. TRIR signals for D2TMPyP4 or PtTMPyP bound to the quadruplex-forming cMYC sequence {d(TAGGGAGGG)}2T indicate that binding occurs on the stacked guanines. For D2TMPyP4 bound to guanine-containing systems, the TRIR signal at ca. 1640 cm−1 decays on the picosecond timescale, consistent with electron transfer from guanine to the singlet excited state of D2TMPyP4, although IR marker bands for the reduced porphyrin/oxidised guanine were not observed. When PtTMPyP is incorporated into HeLa tumour cells, TRIR studies show protein binding with time-dependent ps/ns changes in the amide absorptions demonstrating TRIR's potential for studying light-activated molecular processes not only with nucleic acids in solution but also in biological cells

Suitability of UK biobank retinal images for automatic analysis of morphometric properties of the vasculature

To assess the suitability of retinal images held in the UK Biobank--the largest retinal data repository in a prospective population-based cohort--for computer assisted vascular morphometry, generating measures that are commonly investigated as candidate biomarkers of systemic disease.Non-mydriatic fundus images from both eyes of 2,690 participants--people with a self-reported history of myocardial infarction (n=1,345) and a matched control group (n=1,345)--were analysed using VAMPIRE software. These images were drawn from those of 68,554 UK Biobank participants who underwent retinal imaging at recruitment. Four operators were trained in the use of the software to measure retinal vascular tortuosity and bifurcation geometry.Total operator time was approximately 360 hours (4 minutes per image). 2,252 (84%) of participants had at least one image of sufficient quality for the software to process, i.e. there was sufficient detection of retinal vessels in the image by the software to attempt the measurement of the target parameters. 1,604 (60%) of participants had an image of at least one eye that was adequately analysed by the software, i.e. the measurement protocol was successfully completed. Increasing age was associated with a reduced proportion of images that could be processed (p=0.0004) and analysed (p<0.0001). Cases exhibited more acute arteriolar branching angles (p=0.02) as well as lower arteriolar and venular tortuosity (p<0.0001).A proportion of the retinal images in UK Biobank are of insufficient quality for automated analysis. However, the large size of the UK Biobank means that tens of thousands of images are available and suitable for computational analysis. Parametric information measured from the retinas of participants with suspected cardiovascular disease was significantly different to that measured from a matched control group

Seventeen year mortality in a cohort of patients attending opioid agonist treatment in Ireland. Commentary on 'methadone-maintained patients in primary care have higher rates of chronic disease' (O'Toole et al., European Journal of General Practice 2014; 20:275-80)

OAT has substantially changed the course of the drug use epidemic. Although noted to reduce morbidity and mortality of patients attending specialised treatment clinics, limited longitudinal information is available on cohorts of such patients. To explore the mortality rates, we conducted a prospective observational study, through the Registrar of Births, Deaths and Marriages in Ireland and the Central Methadone Treatment List.European CommissionHealth Research BoardIrish Research CouncilUniversity College DublinMERIT grant: Medical Emergency Responders: Integration and Training from Department of HealthMarie Cure Action