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Oxford Centre for Tropical Medicine and Global Health
Submicroscopic malaria in pregnancy and associated adverse pregnancy events: A case-cohort study of 4,352 women on the Thailand–Myanmar border
Background Malaria in pregnancy detected by microscopy is associated with maternal anaemia, reduced fetal growth, and preterm birth, but the effects of lower density (i.e., submicroscopic) malaria infections are poorly characterised. This analysis was undertaken to investigate associations between submicroscopic malaria at the first antenatal care (ANC) visit and these adverse pregnancy events on the Thailand–Myanmar border. Methods Blood samples taken from refugee and migrant pregnant women presenting for their first ANC visit were analysed retrospectively for malaria using ultrasensitive PCR (uPCR, limit of detection 22 parasites/mL). The relationships between submicroscopic malaria and subsequent microscopically detectable malaria, anaemia, birth weight, and preterm birth were evaluated using inverse probability weighting for stratified random sampling. Results First ANC visit samples from 4,352 asymptomatic women (median gestational age 16.5 weeks) attending between October 1st 2012 and December 31st 2015 were analysed. The weighted proportion of women with submicroscopic malaria infection was 4.6% (95% CI 3.9–5.6), comprising 59.8% (49.5–69.4) Plasmodium vivax, 6.5% (4.0–10.5) Plasmodium falciparum, 1.8% (0.9–3.6) mixed, and 31.9% (22.2–43.5) infections which could not be speciated. Submicroscopic parasitaemia at first ANC visit was associated with subsequent microscopically detected malaria (adjusted hazard ratio [HR] 12.9, 95% CI 8.8–18.8, p < 0.001) and lower birth weight (adjusted predicted mean difference −275 g, 95% CI −510 to −40, p = 0.022). There was no association with preterm birth. Submicroscopic P. falciparum mono-infection (adjusted HR 2.8, 95% CI 1.2–6.6, p = 0.023) and coinfection with P. falciparum and P. vivax (adjusted HR 10.3, 95% CI 2.6–40.4, p = 0.001) was associated with increased risk of maternal anaemia, but submicroscopic P. vivax mono-infection was not. That uPCR was conducted for only a part of the cohort due to cost constraints is a limitation. Conclusions In low transmission settings, uPCR identifies substantially more malaria infections at antenatal screening than conventional diagnostic methods. On the Thailand–Myanmar border, submicroscopic malaria at first antenatal consultation was associated with higher risks of microscopically diagnosed malaria later in pregnancy, anaemia, and reduced birth weight.
clonality V.0.4: a randomization-based program to test for heterozygosity-genet size relationships in clonal organisms.
clonality V.0.4 is a program for testing heterozygosity-genet size relationships in clonal organisms using a randomization procedure. The software has been developed under the Borland Delphi developing environment and a Windows-executable version is freely downloadable from http://gemi.mpl.ird.fr/SiteSGASS/Prugnolle/ClonalityPage.html. The program compares the observed F(IS) of the population with the F(IS) expected if genets (multilocus genotypes present in multiple copies within the population) were chosen randomly from the set of different multilocus genotypes. The randomization procedure is performed with the same number of genets and the same number of repetitions per genet as what is observed in the original data set.
Trends of the Dengue Serotype-4 Circulation with Epidemiological, Phylogenetic, and Entomological Insights in Lao PDR between 2015 and 2019.
Dengue outbreaks have regularly been recorded in Lao People's Democratic Republic (PDR) since the first detection of the disease in 1979. In 2012, an integrated arbovirus surveillance network was set up in Lao PDR and an entomological surveillance has been implemented since 2016 in Vientiane Capital. Here, we report a study combining epidemiological, phylogenetic, and entomological analyzes during the largest DENV-4 epidemic ever recorded in Lao PDR (2015-2019). Strikingly, from 2015 to 2019, we reported the DENV-4 emergence and spread at the country level after two large epidemics predominated by DENV-3 and DENV-1, respectively, in 2012-2013 and 2015. Our data revealed a significant difference in the median age of the patient infected by DENV-4 compared to the other serotypes. Phylogenetic analysis demonstrated the circulation of DENV-4 Genotype I at the country level since at least 2013. The entomological surveillance showed a predominance of Aedesaegypti compared to Aedesalbopictus and high abundance of these vectors in dry and rainy seasons between 2016 and 2019, in Vientiane Capital. Overall, these results emphasized the importance of an integrated approach to evaluate factors, which could impact the circulation and the epidemiological profile of dengue viruses, especially in endemic countries like Lao PDR.
The costs of delivering human papillomavirus vaccination to Grade 4 learners in KwaZulu-Natal, South Africa.
BackgroundThe national human papillomavirus (HPV) vaccination roll-out in South Africa provides two doses of Cervarix to all female Grade 4 learners in state schools. This study estimated the costs of vaccinating all learners in KwaZulu-Natal Province (females or males and females) using either the two- or three-dose strategies for both the bivalent and quadrivalent vaccines.ObjectiveTo determine costs of the HPV vaccination programme in KwaZulu-Natal.MethodsCosts were determined adapting World Health Organization vaccination costing guidelines.ResultsThe 2014 current cost of delivering three doses of Gardasil was ZAR510 per learner. The projected cost of delivering Cervarix to female learners at two or three doses over the period 2014 - 2018, adjusted for inflation, was ZAR172 717 342 and ZAR250 048 426, respectively. Similarly, the cost for Gardasil at these doses was ZAR197 482 200 and ZAR287 194 361, respectively. For male and female learners the cost for Cervarix over this period at two or three doses was ZAR337 101 132 and ZAR540 150 713, respectively. Similarly, the cost for Gardasil at these doses was ZAR426 597 971 and ZAR620 392 784, respectively. Accounting for population variation for females over 5 years, the cost of two doses of Cervarix ranged from ZAR168 888 677 to ZAR 176 545 977 at the lower and upper 95% confidence intervals (CIs), respectively. For three doses the cost ranged from ZAR244 505 544 to ZAR255 591 263 at the lower and upper 95% CIs, respectively. Similarly, the cost for two doses of Gardasil ranged from ZAR193 104 566 to ZAR201 859 798. For three doses the cost ranged from ZAR280 828 057 to ZAR293 560 614.ConclusionThis study gives decision makers a basis for structured planning and cost apportionment to ensure effective roll-out of the HPV vaccination programme.
Emerging variants develop total escape from potent monoclonal antibodies induced by BA.4/5 infection.
The rapid evolution of SARS-CoV-2 is driven in part by a need to evade the antibody response in the face of high levels of immunity. Here, we isolate spike (S) binding monoclonal antibodies (mAbs) from vaccinees who suffered vaccine break-through infections with Omicron sub lineages BA.4 or BA.5. Twenty eight potent antibodies are isolated and characterised functionally, and in some cases structurally. Since the emergence of BA.4/5, SARS-CoV-2 has continued to accrue mutations in the S protein, to understand this we characterize neutralization of a large panel of variants and demonstrate a steady attrition of neutralization by the panel of BA.4/5 mAbs culminating in total loss of function with recent XBB.1.5.70 variants containing the so-called 'FLip' mutations at positions 455 and 456. Interestingly, activity of some mAbs is regained on the recently reported variant BA.2.86.
An open randomised study of autoinflation in 4- to 11-year-old school children with otitis media with effusion in primary care
BackgroundOtitis media with effusion (OME) is a very common problem in primary care, but one that lacks an evidence-based non-surgical treatment.ObjectiveTo determine the clinical effectiveness of nasal balloon autoinflation for the treatment of OME in children.DesignA pragmatic, two-arm, open randomised controlled trial.SettingForty-three general practices from 17 UK primary care trusts recruited between January 2012 and February 2013.ParticipantsSchool children aged 4–11 years with a history of OME symptoms or related concerns in the previous 3 months, and a type B tympanogram, diagnostic of a middle ear effusion, in one or both ears.InterventionThree hundred and twenty children were randomised, 160 to each group, using independent web-based computer-generated randomisation (with minimisation based on age, sex and baseline severity of OME) to either nasal balloon autoinflation performed three times per day for 1–3 months plus usual care, or usual care alone.Main outcome measuresThe proportion of children demonstrating clearance of middle ear fluid in at least one ear (with normal tympanograms) at 1 and 3 months, assessed blind to treatment. An ear-related measure of quality of life (QoL) [a 14-point questionnaire on the impact of OME (OMQ-14)], weekly diary recorded symptoms, compliance and adverse events were all secondary outcomes.ResultsAt 1 month, the proportion of children with normal tympanograms was 47.3% (62/131) in those allocated to autoinflation and 35.6% (47/132) in those receiving usual care [adjusted relative risk (RR) 1.36, 95% confidence interval (CI) 0.99 to 1.88]. At 3 months, the proportions were 49.6% (62/125) and 38.3% (46/120), respectively (adjusted RR 1.37, 95% CI 1.03 to 1.83; number needed to treat = 9). The change in OMQ-14 also favoured the intervention arm (adjusted global score difference –0.42;p = 0.001). Reported compliance was good: 89% in the first month and 80% in months 2 and 3. Adverse events included otalgia in 4% of treated children compared with 1% in the control group. Minor nosebleeds (14% vs. 15%) and respiratory tract infections (18% vs. 13%) were noted.ConclusionWe found the use of autoinflation in young children with OME to be feasible in primary care and effective in both clearing effusions and improving child and parent ear-related QoL and symptoms. This method has scope to be used more widely. Further research is needed for very young children, and to inform prudent use in different health settings.Trial registrationCurrent Controlled Trials ISRCTN55208702.FundingThis project was funded by the National institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full inHealth Technology Assessment, Vol. 19, No. 72. See the NIHR Journals Library website for further project information.
In Vitro Activities of 2,4-Diaminoquinazoline and 2,4-Diaminopteridine Derivatives against Plasmodium falciparum
<jats:title>ABSTRACT</jats:title> <jats:p>The activities of 28 6-substituted 2,4-diaminoquinazolines, 2,4-diamino-5,6,7,8-tetrahydroquinazolines, and 2,4-diaminopteridines against <jats:italic>Plasmodium falciparum</jats:italic> were tested. The 50% inhibitory concentrations (IC<jats:sub>50</jats:sub>s) of six compounds were <50 nM, and the most potent compound was 2,4-diamino-5-chloro-6-[<jats:italic>N</jats:italic>-(2,5-dimethoxybenzyl)amino]quinazoline (compound 1), with an IC<jats:sub>50</jats:sub> of 9 nM. The activity of compound 1 was potentiated by the dihydropteroate synthase inhibitor dapsone, an indication that these compounds are inhibitors of dihydrofolate reductase. Further studies are warranted to assess the therapeutic potential of this combination in vivo.</jats:p>
Conformation of the sesquiterpenoid zerumbone: X-ray crystallographic analysis of zerumbone 2,4-dinitrophenylhydrazone
The molecular geometry of the title compound, C15H22O, has been determined by X-ray diffraction. The double bonds in the 2,6,9,9-tetramethylcycloundeca-2,6,10-trienone ring have trans-stereochemistry. The conformation of the macrocycle differs from that found in several derivatives of humulene, C15H24, and is related to one of the low-energy conformations of cycloundecane. Force-field calculations indicate that this zerumbone conformation is of lower energy than the alternative humulene-like conformation. Crystallographic data are a = 12.619(2), b = 7.290(3), c = 23.422(3) Å, β = 98.06(1)°, 2 = 4, space group P21/c. Diffractometer intensity measurements were made with Cu-Kαradiation and least-squares adjustment of the atomic parameters converged at R 0.046 for 3 222 |F0| values.
X-ray study of the molecular structure of 4-demethylhasubanonine p-bromobenzenesulphonate
Elucidation of the crystal structure of the title ester has established the parent alkaloid to be 4-demethylhasubanonine. In the alkaloid molecule, the five-membered ring containing the nitrogen atom has an envelope conformation with C(14) out-of-plane. The S-OC bond of the p-bromobenzenesulphonyl group is steeply inclined to the bromobenzene plane, and the conformation about the S-OC bond is gauche. The crystals are orthorhombic, space group P212121, Z = 4 in a cell of dimensions a = 8.52, b = 24.23, c = 12.60 Å. The structure was solved by Patterson and Fourier methods from photographic data and refined by least-squares techniques to R 11.3% for 1783 independent reflections.
Are better existing WASH practices in urban slums associated with a lower long-term risk of severe cholera? A prospective cohort study with 4 years of follow-up in Mirpur, Bangladesh
ObjectiveTo investigate the association between existing household water quality, sanitation and hygiene (WASH) practices and severe cholera risk in a dense urban slum where cholera is highly endemic.Design, setting and participantsWe assembled a large prospective cohort within a cluster randomised trial evaluating the effectiveness of oral cholera vaccine. Our dynamic cohort population (n=193 576) comprised individuals living in the ‘non-intervention’ clusters of the trial, and were followed over 4 years. This study was conducted in a dense urban slum community of Dhaka, Bangladesh and cholera surveillance was undertaken in 12 hospitals serving the study area.Primary outcome measureFirst severe cholera episode detected during follow-up period.MethodsWe applied a machine learning algorithm on a training subpopulation (n=96 943) to develop a binary (‘better’, ‘not better’) composite WASH variable predictive of severe cholera. The WASH rule was evaluated for performance in a separate validation subpopulation (n=96 633). Afterwards, we used Cox regression models to evaluate the association between ‘better’ WASH households and severe cholera risk over 4 years in the entire study population.ResultsThe ‘better’ WASH rule found that water quality and access were the most significant factors associated with severe cholera risk. Members of ‘better’ WASH households, constituting one-third of the population, had a 47% reduced risk of severe cholera (95% CI: 29 to 69; p<0.001), after adjusting for covariates. The protective association between living in a ‘better’ WASH household and severe cholera persisted in all age groups.ConclusionsSalutary existing household WASH practices were associated with a significantly reduced long-term risk of severe cholera in an urban slum of Dhaka. These findings suggest that WASH adaptations already practised in the community may be important for developing and implementing effective and sustainable cholera control programmes in similar settings.Trial registration numberThis article is a re-analysis of data from a cluster randomized trial; can be found on ClinicalTrials.govNCT01339845
Favorable Preclinical Pharmacological Profile of a Novel Antimalarial Pyrrolizidinylmethyl Derivative of 4-amino-7-chloroquinoline with Potent In Vitro and In Vivo Activities.
The 4-aminoquinoline drugs, such as chloroquine (CQ), amodiaquine or piperaquine, are still commonly used for malaria treatment, either alone (CQ) or in combination with artemisinin derivatives. We previously described the excellent in vitro activity of a novel pyrrolizidinylmethyl derivative of 4-amino-7-chloroquinoline, named MG3, against P. falciparum drug-resistant parasites. Here, we report the optimized and safer synthesis of MG3, now suitable for a scale-up, and its additional in vitro and in vivo characterization. MG3 is active against a panel of P. vivax and P. falciparum field isolates, either alone or in combination with artemisinin derivatives. In vivo MG3 is orally active in the P. berghei, P. chabaudi, and P. yoelii models of rodent malaria with efficacy comparable, or better, than that of CQ and of other quinolines under development. The in vivo and in vitro ADME-Tox studies indicate that MG3 possesses a very good pre-clinical developability profile associated with an excellent oral bioavailability, and low toxicity in non-formal preclinical studies on rats, dogs, and non-human primates (NHP). In conclusion, the pharmacological profile of MG3 is in line with those obtained with CQ or the other quinolines in use and seems to possess all the requirements for a developmental candidate.
Trends, determinants and inequities of 4+ ANC utilisation in Bangladesh.
BackgroundThe objectives of this study are to document the trend on utilisation of four or more (4+) antenatal care (ANC) over the last 22 years period and to explore the determinants and inequity of 4+ ANC utilisation as reported by the last two Bangladesh Demographic and Health surveys (BDHS) (2011 and 2014).MethodsThe data related to ANC have been extracted from the BDHS data set which is available online as an open source. STATA 13 software was used for organising and analysing the data. The outcome variable considered for this study was utilisation of 4+ ANC. Trends of 4+ ANC were measured in percentage and predictors for 4+ ANC were measured through bivariate and multivariable analysis. The concentration index was estimated for assessing inequity in 4+ ANC utilisation.ResultsUtilisation of 4+ ANC has increased by about 26% between the year 1994 and 2014. Higher level of education, residing in urban region and richest wealth quintile were found to be significant predictors. The utilisation of 4+ ANC has decreased with increasing parity and maternal age. The inequity indices showed consistent inequities in 4+ ANC utilisation, and such inequities were increased between 2011 and 2014.ConclusionsIn Bangladesh, the utilisation of any ANC rose steadily between 1994 and 2014, but progress in terms of 4+ ANC utilisation was much slower as the expectation was to achieve the national set target (50%: 4+ ANC utilisation) by 2016. Socio-economic inequities were observed in groups that failed to attend a 4+ ANC visit. Policymakers should pay special attention to increase the 4+ ANC coverage where this study can facilitate to identify the target groups whom need to be intervened on priority basis.
In vitro activities of 2,4-diaminoquinazoline and 2,4-diaminopteridine derivatives against Plasmodium falciparum.
The activities of 28 6-substituted 2,4-diaminoquinazolines, 2,4-diamino-5,6,7,8-tetrahydroquinazolines, and 2,4-diaminopteridines against Plasmodium falciparum were tested. The 50% inhibitory concentrations (IC(50)s) of six compounds were <50 nM, and the most potent compound was 2,4-diamino-5-chloro-6-[N-(2,5-dimethoxybenzyl)amino]quinazoline (compound 1), with an IC(50) of 9 nM. The activity of compound 1 was potentiated by the dihydropteroate synthase inhibitor dapsone, an indication that these compounds are inhibitors of dihydrofolate reductase. Further studies are warranted to assess the therapeutic potential of this combination in vivo.
2,4-Diaminopteridine-Based Compounds as Precursors for De Novo Synthesis of Antifolates: a Novel Class of Antimalarials
<jats:title>ABSTRACT</jats:title> <jats:p>We have tested the hypothesis that 2,4-diamino-6-hydroxymethyl-pteridine (DAP), 2,4-diaminopteroic acid (DAPA), and 2,4 diamino-N10-methyl-pteroic acid (DAMPA) could be converted into aminopterin (from DAP and DAPA) and methotrexate (from DAMPA), both of which are potent inhibitors of dihydrofolate reductase, a proven drug target for <jats:italic>Plasmodium falciparum</jats:italic>. DAP, DAPA, and DAMPA inhibited parasite growth in the micromolar range; DAMPA was the most active, with 50% inhibitory concentrations in vitro of 446 ng/ml against the antifolate-sensitive strain and 812 ng/ml against the highly resistant strain under physiological folate conditions. DAMPA potentiates the activity of the sulfone dapsone, an inhibitor of dihydropteroate synthase, but not that of chlorcycloguanil, a known inhibitor of dihydrofolate reductase (DHFR). Experiments with a <jats:italic>Saccharomyces cerevisiae</jats:italic> strain dependent upon the <jats:italic>P. falciparum</jats:italic> DHFR enzyme showed that DHFR is a target of DAMPA in that system. We hypothesize that DAMPA is converted to methotrexate by the parasite dihydrofolate synthase, which explains the synergy of DAMPA with dapsone but not with chlorcycloguanil. This de novo synthesis will not occur in the host, since it lacks the complete folate pathway. If this hypothesis holds true, the de novo synthesis of the toxic compounds could be used as a framework for the search for novel potent antimalarial antifolates.</jats:p>
Probing intraligand and charge transfer excited states of fac-[Re(R)(CO)(3)(CO(2)Et-dppz)](+) (R = py, 4-Me(2)N-py; CO(2)Et-dppz = dipyrido[3,2a:2',3'c]phenazine-11-carboxylic ethyl ester) using time-resolved infrared spectroscopy.
The photophysics of fac-[Re(R)(CO)(3)(CO(2)Et-dppz)](+) (R = py (), 4-Me(2)N-py (); CO(2)Et-dppz = dipyrido[3,2a:2',3'c]phenazine-11-carboxylic ethyl ester) was studied with luminescence spectroscopy and time-resolved infrared (TRIR) spectroscopy in the metal carbonyl (2,100-1,800 cm(-1)) and organic ester (1,800-1,600 cm(-1)) regions. For 1, the picosecond TRIR spectra in the metal carbonyl region provided evidence for the formation of an intra-ligand IL (pi-pi) excited state, which partially decays to an equilibrium with the metal-to-ligand charge transfer (MLCT) excited state. For 2 it is evident that both IL (pi-pi) and MLCT excited states are formed within 2 ps of excitation. The magnitude of the nu(CO) shift in the metal carbonyl region following excitation allows the MLCT excited states to be described more precisely as a dpi(Re) -->pi (phenazine) (3)MLCT state for 1 and as a dpi(Re) -->pi (phenanthroline) (3)MLCT state for 2.
Unraveling the photochemistry of Fe(CO)5 in solution: observation of Fe(CO)3 and the conversion between 3Fe(CO)4 and 1Fe(CO)4(Solvent).
The photochemistry of Fe(CO)5 (5) has been studied in heptane, supercritical (sc) Ar, scXe, and scCH4 using time-resolved infrared spectroscopy (TRIR). 3Fe(CO)4 ((3)4) and Fe(CO)3(solvent) (3) are formed as primary photoproducts within the first few picoseconds. Complex 3 is formed via a single-photon process. In heptane, scCH4, and scXe, (3)4 decays to form (1)4 x L (L = heptane, CH4, or Xe) as well as reacting with 5 to form Fe2(CO)9. In heptane, 3 reacts with CO to form (1)4 x L. The conversion of (3)4 to (1)4 x L has been monitored directly for the first time (L = heptane, kobs = 7.8(+/- 0.3) x 10(7) s(-1); scCH4, 5(+/- 1) x 10(6) s(-1); scXe, 2.1(+/- 0.1) x 10(7) s(-1)). In scAr, (3)4 and 3 react with CO to form 5 and (3)4, respectively. We have determined the rate constant (kCO = 1.2 x 10(7) dm3 mol(-1) s(-1)) for the reaction of (3)4 with CO in scAr, and this is very similar to the value obtained previously in the gas phase. Doping the scAr with either Xe or CH4 resulted in (3)4 reacting with Xe or CH4 to form (1)4 x Xe or (1)4 x CH4. The relative yield, [(3)4]:[3] decreases in the order heptane > scXe > scCH4 >> scAr, and pressure-dependent measurements in scAr and scCH4 indicate an influence of the solvent density on this ratio.
Excited-state dynamics of fac-[ReI(L)(CO)3(phen)]+ and fac-[ReI(L)(CO)3(5-NO2-phen)]+ (L = imidazole, 4-ethylpyridine; phen = 1,10-phenanthroline) complexes.
The nature and dynamics of the lowest excited states of fac-[Re(I)(L)(CO)(3)(phen)](+) and fac-[Re(I)(L)(CO)(3)(5-NO(2)-phen)](+) [L = Cl(-), 4-ethyl-pyridine (4-Etpy), imidazole (imH); phen = 1,10-phenanthroline] have been investigated by picosecond visible and IR transient absorption spectroscopy in aqueous (L = imH), acetonitrile (L = 4-Etpy, imH), and MeOH (L = imH) solutions. The phen complexes have long-lived Re(I) --> phen (3)MLCT excited states, characterized by CO stretching frequencies that are upshifted relative to their ground-state values and by widely split IR bands due to the out-of-phase A'(2) and A"nu(CO) vibrations. The lowest excited states of the 5-NO(2)-phen complexes also have (3)MLCT character; the larger upward nu(CO) shifts accord with much more extensive charge transfer from the Re(I)(CO)(3) unit to 5-NO(2)-phen in these states. Transient visible absorption spectra indicate that the excited electron is delocalized over the 5-NO(2)-phen ligand, which acquires radical anionic character. Similarly, involvement of the -NO(2) group in the Franck-Condon MLCT transition is manifested by the presence of an enhanced nu(NO(2)) band in the preresonance Raman spectrum of [Re(I)(4-Etpy)(CO)(3)(5-NO(2)-phen)](+). The Re(I) --> 5-NO(2)-phen (3)MLCT excited states are very short-lived: 7.6, 170, and 43 ps for L = Cl(-), 4-Etpy, and imH, respectively, in CH(3)CN solutions. The (3)MLCT excited state of [Re(I)(imH)(CO)(3)(5-NO(2)-phen)](+) is even shorter-lived in MeOH (15 ps) and H(2)O (1.3 ps). In addition to (3)MLCT, excitation of [Re(I)(imH)(CO)(3)(5-NO(2)-phen)](+) populates a (3)LLCT (imH --> 5-NO(2)-phen) excited state. Most of the (3)LLCT population decays to the ground state (time constants of 19 (H(2)O), 50 (MeOH), and 72 ps (CH(3)CN)); in a small fraction, however, deprotonation of the imH.+ ligand occurs, producing a long-lived species, [Re(I)(im.)(CO)(3)(5-NO(2)-phen).-]+.
Direct observation of competitive ultrafast CO dissociation and relaxation of an MLCT excited state: picosecond time-resolved infrared spectroscopic study of [Cr(CO)(4)(2,2'-bipyridine)].
Early excited-state dynamics of [Cr(CO)(4)(bpy)] were studied in a CH(2)Cl(2) solution by picosecond time-resolved IR spectroscopy, which made it possible to characterize structurally the individual species involved and to follow separately the temporal evolution of the IR bands due to the bleached ground-state absorption, the fac-[Cr(CO)(3)(Sol)(bpy)] photoproduct, and two (3)MLCT states. It was found that the fac-[Cr(CO)(3)(Sol)(bpy)] photoproduct is formed alongside population of two (3)MLCT states during the first picosecond after excitation at 400 or 500 nm by a branched evolution of the optically populated excited state. Vibrationally relaxed (3)MLCT excited states are unreactive, decaying directly to the ground state on a picosecond time scale. The photoproduct is long-lived, persistent into the nanosecond time domain. Changing the excitation wavelength from 400 to 500 nm strongly increases the extent of the bleach recovery and decreases the yield of the photoproduct formation relative to the initial yield of the population of the unreactive (3)MLCT states. The photochemical quantum yield of CO dissociation also decreases with increasing excitation wavelength (Víchová, J.; Hartl, F.; Vlcek, A., Jr. J. Am. Chem. Soc. 1992, 114, 10903). These observations demonstrate the relationship between the early dynamics of optically populated excited states and the overall outcome of a photochemical reaction and identify the limiting role of the branching of the initial excited-state evolution between reactive and relaxation pathways as a more general principle of organometallic photochemistry.
Ligand-to-diimine/metal-to-diimine charge-transfer excited states of [Re(NCS)(CO)3(alpha-diimine)] (alpha-diimine = 2,2'-bipyridine, di-iPr-N,N-1,4-diazabutadiene). A spectroscopic and computational study.
Two new complexes fac-[Re(NCS)(CO)3(N,N)] (N,N = 2,2'-bipyridine (bpy), di-iPr-N,N-1,4-diazabutadiene (iPr-DAB)) were synthesized and their molecular structures determined by X-ray diffraction. UV-vis absorption, resonance Raman, emission, and picosecond time-resolved IR spectra were measured experimentally and calculated with TD-DFT. A good agreement between experimental and calculated ground- and excited-state spectra is obtained, but only if the solvent (MeCN) is included into calculations and excited state structures are fully optimized at the TD-DFT level. The lowest excited states of the bpy and iPr-DAB complexes are assigned by TD-DFT as 3aA' by comparison of calculated and experimental IR spectra. Excited-state lifetimes of 23 ns and ca. 625 ps were determined for the bpy and DAB complex, respectively, in a fluid solution at room temperature. Biexponential emission decay (1.3, 2.7 micros) observed for [Re(NCS)(CO)3(bpy)] in a 77 K glass indicates the presence of two unequilibrated emissive states. Low-lying electronic transitions and excited states of both complexes have a mixed NCS --> N,N ligand-to-ligand and Re --> N,N metal-to-ligand charge-transfer character (LLCT/MLCT). It originates in mixing between Re d(pi) and NCS pi characters in high-lying occupied MOs. Experimentally, the LLCT/MLCT mixing in the lowest excited state is manifested by shifting the nu(CO) and nu(NC) IR bands to higher and lower wavenumbers, respectively, upon excitation. Resonant enhancement of both nu(CO) and nu(NC) Raman bands indicates that the same LLCT/MLCT character mixing occurs in the lowest allowed electronic transition.
Ultrafast excited-state dynamics preceding a ligand trans-cis isomerization of fac-[Re(Cl)(CO)3(t-4-styrylpyridine)2] and fac-[Re(t-4-styrylpyridine)(CO)3(2,2'-bipyridine)]+.
UV-vis absorption and resonance Raman spectra of the complexes fac-[Re(Cl)(CO)3(stpy)2] and fac-[Re(stpy)(CO)3(bpy)]+ (stpy = t-4-styrylpyridine, bpy = 2,2'-bipyridine) show that their lowest absorption bands are dominated by stpy-localized intraligand (IL) pi pi* transitions. For the latter complex a Re --> bpy transition contributes to the low-energy part of the absorption band. Optical population of the 1IL excited state of fac-[Re(Cl)(CO)3(stpy)2] is followed by an intersystem crossing (< or =0.9 ps) to an 3IL state with the original planar trans geometry of the stpy ligand. This state undergoes a approximately 90 degrees rotation around the stpy C=C bond with a 11 ps time constant. An electronically excited species with an approximately perpendicular orientation of the phenyl and pyridine rings of the stpy ligand is formed. Conversion to the ground state and isomerization occurs in the nanosecond range. Intraligand excited states of fac-[Re(stpy)(CO)3(bpy)]+ show the same behavior. Moreover, it was found that the planar reactive 3IL excited state is rapidly and efficiently populated after optical excitation into the Re --> bpy 1MLCT excited state. A 1MLCT --> 3MLCT intersystem crossing takes place first with a time constant of 0.23 ps followed by an intramolecular energy transfer from the ReI(CO)3(bpy) chromophore to a stpy-localized 3IL state with a 3.5 ps time constant. The fast rate ensures complete conversion. Coordination of the stpy ligand to the ReI center thus switches the ligand trans-cis isomerization mechanism from singlet to triplet (intramolecular sensitization) and, in the case of fac-[Re(stpy)(CO)3(bpy)]+, opens an indirect pathway for population of the reactive 3IL excited state via MLCT states.