20 research outputs found
Solvatochromism, aggregation and photochemical properties of Fullerenes, C<SUB>60</SUB> and C<SUB>70</SUB>, in solution
Fullerenes, C60 and C70, display interesting physicochemical properties in solutions, especially due to their unique chemical structures and their good electron accepting abilities. Solubility of fullerenes in different organic solvents and their unusual solvatochromic behavior, the ability of the fullerenes to form aggregates in solutions, and their electron transfer and charge transfer interactions with variety of electron donors, are the subjects of extensive research activities for more than one decade. Many research groups including ours have contributed substantially in the understanding of the solvatochromism, aggregation behavior, and the photoinduced electron transfer and charge transfer chemistry of fullerenes, in condensed phase. Present article is aimed to summarize the important results reported on the above aspects of fullerenes, subsequent to the earlier report from our group. (D.K. Palit and J.P. Mittal, Full. Sci. & Tech. 3, 1995, 643-659)
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Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021
BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation
Pulse radiolytic one-electron reduction of 2-hydroxy- and 2,6-dihydroxy-9,10-anthraquinones
The semiquinone free radicals produced by one-electron reduction of 2-hydroxy-9,10-anthraquinone (2HAQ) and 2,6-dihydroxy-9,10-anthraquinone (26DHAQ) in aqueous formate solution, water-isopropyl alcohol-acetone mixed solvent and isopropyl alcohol have been studied using the pulse radiolysis technique. The absorption characteristics, kinetic parameters of formation and decay, acid-base behaviour and redox characteristics of the semiquinones have been investigated and compared with the corresponding characteristics of a few intramolecularly hydrogen-bonded anthrasemiquinone derivatives. The non-hydrogen-bonded semiquinones show two pKa values (4.7 and 10.7 for 2HAQ and 5.4 and 8.7 for 26DHAQ, respectively) within the pH range 1-14, whereas other intramolecularly hydrogen-bonded semiquinones show only one pKa. The one-electron reduction potential (E'7) values for 2HAQ (-440 mV) and 26DHAQ (-400 mV) are more negative than those of the intramolecularly hydrogen-bonded systems
Single-molecule detection in exploring nanoenvironments: an overview
In the last one decade or so, a variety of optical experiments have been designed and performed that are capable of exploring down to the regime of single-molecule detection and measurements in all different environments, including solids, surfaces, and liquids. Single-molecule detection in condensed phases has many important chemical and biological applications. A few to list are: rapid DNA sequencing, DNA fragment sizing, medical diagnosis, forensic analysis, understanding of chemical dynamics and mechanisms, etc. Single-molecule spectroscopy allows us to observe the individual molecules hidden in a condensed phase sample, by using a tunable laser light. This technique has the ability to detect and monitor systems with an ultimate sensitivity level of ~1.66 × 10-24 moles (1/N0). Measurement at the single-molecule level can completely remove the complicacy associated with ensemble-averaged macroscopic measurements. It allows us to construct a frequency histogram of the distribution of values for a parameter of interest following a large number of measurements on many individual molecules. Such a distribution carries much more information than the average value of the parameter obtained from a macroscopic measurement. As there is no ensemble averaging involved, only measurements at the single-molecule level can give an appropriate test for microscopic dynamical theories. Using single-molecule spectroscopy one can, in principle, follow the temporal evolution of any complex reaction path. As the field is still emerging, with newer methodologies of detecting single molecules with improved signal-to-noise ratios, it is expected that many new physical and chemical phenomena will certainly be explored using this technique. In the present article, our endeavor is to give an overview of the different aspects of single-molecule detection, along with some of its important applications in the areas of bioscience and chemical physics
The fluorescence lifetimes of isomeric tyrosines
Fluorescence characteristics of isomeric ortho-, meta- and para-tyrosine have been determined. Differences in fluorescence lifetimes, especially at pH 1, provide a possible method for detection of ortho-tyrosine. A modified mathematical expression provides a photophysical method of detecting and estimating ortho-tyrosine in a mixture with para-tyrosine and phenylalanine. A possible application of this method is discussed
Nanosecond laser flash photolysis of 5-hydroxy-1,4-naphthoquinone (Juglone)
The triplet properties of juglone, a monohydroxyquinone, were thoroughly investigated in cyclohexane, acetonitrile, methanol and isopropanol, by the technique of nanosecond laser flash photolysis. While the triplets absorb at about 285, 325 and 370 nm, the decay product, which absorbs at about 370 nm, is shown to be a neutral semiquinone free radical of juglone. The extinction coefficient for T-T absorption and the quantum yields of both triplet formation and semiquinone formation are estimated, and all the kinetic parameters associated with the triplet decay are evaluated. The effect of juglone concentration, laser intensity and the presence of triplet scavengers on the triplet properties were studied
T-T absorption and semiquinone formation in solutions of 5,8-dihydroxy-1,4-naphthoquinone (naphthazarin): a nanosecond laser flash photolysis study
The triplet properties of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) have been investigated in cyclohexane, methanol and isopropanol solutions using the technique of nanosecond laser flash photolysis. The T-T absorption maxima are at around 280, 335, 377, 410 and 440 nm, while the transients formed after the disappearance of the triplets in alcohols absorb at around 265, 365, 395 and 440 nm. The second transient has been shown to be a semiquinone free radical of naphthazarin, produced by abstraction of a hydrogen atom from the alcohols. The extinction coefficient at many wavelengths and the quantum yields of both triplet and semiquinone formation have been estimated. Kinetic parameters associated with the decay of both the triplet and the semiquinone have been evaluated. The effect of laser intensity and the presence of triplet scavengers on the triplet properties have been studied. A comparison has been made with the corresponding transients produced from juglone (5-hydroxy-1,4-naphthoquinone)
Pulse radiolytic one-electron oxidation of some dihydroxy-substituted anthraquinones
The spectroscopic characteristics and the kinetic parameters associated with the transients formed on one-electron oxidation of quinizarin (1,4-dihydroxy-9, 10-anthraquinone), quinizarin 2- and 6-sulfonates, 1,5-dihydroxy-9, 10-anthraquinone and 1,8-dihydroxy-9, 10-anthraquinone have been studied by pulse radiolysis and kinetic spectrophotometric techniques, using OH•, O•-, N3•, Br and •CH2CHO as the oxidising radicals. The pKa and the disproportionation equilibria of the semi-oxidised quinones have been studied for the water-soluble sulfonates. In contrast to the complex decay of the semi-oxidised naphthazarin (5,8-dihydroxy-1,4-naphtho-quinone), the semi-oxidised anthraquinone derivatives decay by simple second-order kinetics. The pKa values of the latter are also much higher (ca. 8) compared to the former (ca. <4). The differences observed are attributed to the loss in symmetry in the free radical structures of the semi-oxidised anthraquinone derivatives
Interaction of the excited singlet state of disubstituted anthraquinones with aromatic hydrocarbons: a fluorescence-quenching study
The dynamic nature of the quenching of the fluorescence of 1,4-amino- and hydroxy-substituted 9,10-anthraquinone, with benzene, alkylbenzenes and other aryl hydrocarbons as quenchers, indicates formation of exciplexes, where charge transfer (CT) occurs from the S0 (quencher) to the S1 (fluorophore), as kq decreases with increasing ionisation potential of the quenchers, Exciplex emission spectra and kinetics have been established
One-electron reactions of 1,5- and 1,8-dihydroxy-9, 10-anthraquinones. A pulse radiolysis study
Absorption characteristics of the semiquinone free radicals formed by the one-electron reduction (using e-aq, CO•-2 and CH3OHCH3 as the reductant) as well as the oxidation (using OH•, O•- and N•3 as the oxidants) of 1,5-dihydroxy-9, 10-anthraquinone (1,5-DHAQ) and 1,8-dihydroxy-9, 10-anthraquinone (1,8-DHAQ) have been studied by pulse radiolysis in pure isopropyl alcohol and in aqueous solutions containing various appropriate additives. The first acid dissociation constants for the reduced semiquinones were measured as pKa= 3.65 and 3.95 for 1,5-DHAQ and 1,8-DHAQ, respectively. Second-order rate constants for various formation and decay reactions have been determined. The one-electron reduction potentials (vs. NHE) were determined at pH 11, as E111=-350 mV (for 1,5-DHAQ) and E111=-377 mV (for 1,8-DHAQ), respectively. Differences with 1,4-dihydroxy-9, 10-anthraquinone (quinizarin) are discussed