Antimalarial secondary metabolites from Morinda lucida

Antimalarial activities of secondary metabolites from Morinda lucida (Rubiaceae), were investigated. Even though M. lucida is traditionally used to treat malaria, diabetes, jaundice, hypertension, dysentery and many other diseases, the compounds in this plant have not yet been fully investigated and characterised. Most of the studies that have been done on this plant focused on the medicinal properties of the crude extracts but have not gone further to isolate and characterise the compounds. In this study, the methanol - dichloromethane crude extract from the bark of M. lucida was fractionated into fractions 1-8. Fractions 2-5 were purified in order to isolate active secondary metabolites. The isolated pure compounds were characterised and identified. An in vitro antimalarial assay was carried out on the crude extract, fractions, pure compounds and solutions made from different combinations of pure compounds using the parasite lactate dehydrogenase (pLDH) assay. An IC50 done on the methanolic crude extract gave a value of 25 µg/mL. The % cell viability for the crude extract in cell toxicity assay remained at 100%. Each of the pure compounds tested had very little activity. Their activities were increased when samples from the different compounds were mixed. One of these mixtures reduced malaria viability to about 22 % at 20 µM and gave an IC50 value of 17 µM. Antibacterial assays were also carried out on the crude extract and fractions. Fractions 2 and 3 were relatively active (MIC values ranging between 125-1000 µg/mL) against M. cattarhalis and E. faecalis. Fraction 2 was also the most active on S. typhimurium and S. aureus (MIC value of 1000 µg/mL) compared with the other fractions. This same fraction also showed some activity against M. tuberculosis with MIC90 and MIC99 values of 40.9 and 46.3 µg/mL respectively in an anti-tuberculosis assay.The following compounds, comprising of iridoids (asperuloside and asperulosidic acid), terpenoids (stigmasterol, P-sitosterol, campesterol, lanosterol and cycloartenol) and anthraquinones [5,15-O-dimethylmorindol, 1,7-dihydroxy-2-methoxy-5-(methoxymethyl) anthraquinone and 1,6-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone], were isolated. All these compounds have been isolated from different plants before with the exception of 1,7-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone and 1,6-dihydroxy-2-methoxy-5-(methoxymethyl)anthraquinone which were tentatively assigned the structures due to insufficient data. To the best of our knowledge, this is the first report on the identification of all of the mentioned compounds, with the exception of ß-sitosterol and stigmasterol, from M. lucida. Molecular docking was performed on one of the isolated anthraquinones (5,15-O- dimethylmorindol) to check if it can bind to cytochrome bci, a known target for atovaquone. This compound interacted with the same amino acids that atovaquone, a well known antimalarial agent, interacted with on cytochrome bc1 indicating a possible similar mode of action

On the correlation between annealing and variabilities in pulsed-luminescence from quartz

Properties of luminescence lifetimes in quartz related to annealing between 500 and 900ºC have been investigated. The luminescence was pulse-stimulated at 470 nm from sets of granular quartz annealed at 500, 600, 700, 800, and 900ºC. The lifetimes decrease with annealing temperature from about 42 to 33 µѕ when the annealing temperature is increased from 500 to 900ºC. Luminescence lifetimes are most sensitive to duration of annealing at 600ºC, decreasing from 40.2 ± 0.7 µѕ by as much as 7 µѕ when the duration of annealing is changed from 10 to 60 min. However, at 800–900ºC lifetimes are essentially independent of annealing temperature at about 33 µѕ. Increasing the exciting beta dose causes an increase in the lifetimes of the stimulated luminescence in the sample annealed at 800ºC but not in those annealed at either 500 or 600ºC. The temperature-resolved distribution of luminescence lifetimes is affected by thermal quenching of luminescence. These features may be accounted for with reference to two principal luminescence centres involved in the luminescence emission process

Insights into mouse models of human Down syndrome

Down syndrome, also referred to as trisomy 21, is a chromosomal abnormality in which the 21st human chromosome is partially or entirely duplicated. It is associated with a myriad of characteristics, including distinct facial deformities, intellectual disability, a heart defect, low muscle tone, and development of Alzheimer's disease symptoms with aging. This duplication is associated with increased levels of gene expression relative to what is present in euploid cells and disrupts the structure of some gene products. This study examines current mouse models of trisomy 21, describes a bioinformatics approach to evaluate relationships between genes on chromosome 21, and to determine the role they may play in Down syndrome associated intellectual disability. The Ts1Rhr, Tc1, and Ts65Dn mouse models are compared and contrasted to human trisomy 21. Representation of intellectual disability is determined by how the mice in each model perform on learning and memory tasks. Each model is examined for duplication of Down syndrome associated genes as well as for body weight, cerebral size, cerebellar size, balance, motor coordination, learning and memory, attention, activity, presence or absence of a heart defect, and presence or absence of a craniofacial defect. Next, a bioinformatics approach is proposed as tool with the capacity to examine the individual genes on chromosome 21, the relationships between the genes, group genes together by functional similarity and biological implication, and then establish which of these groups are enriched. The combined evaluation of mouse models and bioinformatics can be used as an innovative way to study the involvement in the intellectual disability associated with Down syndrome. Through the review of current mouse models and the evaluation of individual chromosome 21 genes using bioinformatics resources, the study seeks to determine what insights on intellectually disability can be gained

Corporate Voluntary Greenhouse Gas Emission Reporting in United Kingdom: Insights from Institutional and Upper Echelons Theories

This paper reports the results of an investigation into the extent to which various stakeholder pressures influence voluntary disclosure of greenhouse-gas (GHG) emissions in the United Kingdom (UK). The study, which is grounded on institutional theory, also borrows from the insights of upper echelons theory and examines whether specific managerial (chief executive officer) characteristics explain and moderates various stakeholder pressures in explaining GHG voluntary disclosure. Data were obtained from the 2011 annual and sustainability reports of a sample of 216 UK companies on the FTSE350 index listed on the London Stock Exchange. Generally the results suggest that there is no substantial shareholder and employee pressure on a firm to disclose GHG information but there is significant positive pressure from the market status of a firm with those firms with more market share disclosing more GHG information. Consistent with the predictions of institutional theory, we found evidence that coercive pressure i.e. regulatory pressure and mimetic pressures emanating in some industries notably industrials and consumer services have a significant positive influence on firms' GHG disclosure decisions. Besides, creditor pressure also had a significant negative relationship with GHG disclosure. While CEO age had a direct negative effect on GHG voluntary disclosure, its moderation effect on stakeholder pressure influence on GHG disclosure was only significant on regulatory pressure. The results have important implications for both policy makers and company boards strategizing to reign in their GHG emissions

Corporate Voluntary Greenhouse Gas Emission Reporting in United Kingdom: Insights from Institutional and Upper Echelons Theories

This paper reports the results of an investigation into the extent to which various stakeholder pressures influence voluntary disclosure of greenhouse-gas (GHG) emissions in the United Kingdom (UK). The study, which is grounded on institutional theory, also borrows from the insights of upper echelons theory and examines whether specific managerial (chief executive officer) characteristics explain and moderates various stakeholder pressures in explaining GHG voluntary disclosure. Data were obtained from the 2011 annual and sustainability reports of a sample of 216 UK companies on the FTSE350 index listed on the London Stock Exchange. Generally the results suggest that there is no substantial shareholder and employee pressure on a firm to disclose GHG information but there is significant positive pressure from the market status of a firm with those firms with more market share disclosing more GHG information. Consistent with the predictions of institutional theory, we found evidence that coercive pressure i.e. regulatory pressure and mimetic pressures emanating in some industries notably industrials and consumer services have a significant positive influence on firms' GHG disclosure decisions. Besides, creditor pressure also had a significant negative relationship with GHG disclosure. While CEO age had a direct negative effect on GHG voluntary disclosure, its moderation effect on stakeholder pressure influence on GHG disclosure was only significant on regulatory pressure. The results have important implications for both policy makers and company boards strategizing to reign in their GHG emissions

Concerning secondary thermoluminescence peaks in α-Al_2_O_3_:C

Thermoluminescence characteristics of two subsidiary glow peaks, one below 100°C and the other above 300°C, have been studied for measurements between 30°C and 500°C in α-Al_2_O_3_:C. The thermoluminescence intensity of the lower temperature peak decreased with storage with a half-life of about 150 s. In contrast, the intensity of the higher temperature peak increased with storage towards some maximum. The peak-temperature of each of the secondary glow peaks was essentially constant with dose, whereas that of the main peak decreased with irradiation. The dose response for the three peaks was similar except for sublinear growth in the higher temperature peak at low dose values. These effects are discussed in terms of changes in the concentration of F+ luminescence precursors brought about by competitive electron retrapping at deep electron-traps or hole-traps. This work refines the physics and application of α-Al_2_O_3_:C luminescence in radiation dosimetry

The Extent and determinants of greenhouse gas reporting in the United Kingdom.

The study investigates the extent and determinants of greenhouse gas voluntary disclosures by FTSE350 United Kingdom (UK) listed companies from both theory and practitioners’ views. In accomplishing the aim, the study has the following objectives: (1) to analyse the extent of voluntary disclosure of GHG information in annual and sustainability reports of FTSE350 companies over a four year period i.e. 2008-2011; (2) to establish whether voluntary GHG disclosures are influenced by corporate governance characteristics (board size, non-executive directors, environmental committee, audit committee, ownership concentration and director ownership) and firm characteristics (company size, profitability, gearing, liquidity and industry); and (3) To investigate whether practitioners consider the determinants (as in objective two above) motivates the extent of voluntary GHG disclosures. To accomplish the objectives, the study uses a mixed-method approach on data derived from a sample of 215 FTSE 350 companies listed on London Stock Exchange. Firstly, an econometric model was developed based on a set of explanatory factors i.e. the governance and company characteristics and a dependent variable of disclosure index drawn from a multiple GHG voluntary reporting frameworks. Panel regression was then employed to examine the relationship between the explanatory factors and the actual disclosures. Secondly, through survey questionnaire, company executives were asked to rate their perception of the extent to which a list of determinants derived from largely secondary data literature influenced voluntary GHG disclosure. The results indicate an increasing trend in GHG disclosures from 2008 to 2011 perhaps suggesting positive impact of the government initiatives on GHG disclosures in the UK. Overall there is more disclosure of qualitative information in particular information on company action on GHG and climate change rather than actual emission disclosures. Companies have also not been proactive in disclosing quantified estimates of all forms of risks emanating from climate change. Results of the econometric model show that there is no support for the influence of traditional board characteristics such as Non-executive Directors, board size, and audit committee whereas both forms of ownership had a significant negative influence. The presence of an environmental committee was only significant in enhancing qualitative information and not quantitative information. In addition, as in other voluntary disclosures, size plays a vital role in determining the extent of the disclosures and that highly geared companies disclose less GHG information than less geared firms. Liquidity and profitability have no significant influence. The survey results suggest that according to the practitioners, board environmental committee and firm size are the only determining factors to have received wide support by the respondents while all other factors were firmly rejected. The findings that other determinants do not influence disclosure of GHG from a practitioner point of view suggests the need for an in-depth investigation into the determinants of voluntary disclosures beyond the evidence as derived from secondary data based studies. The study contributes knowledge to the voluntary disclosure studies in a number of ways. First, through mixed data approach, it has brought additional insights into the determinants of GHG disclosures. For example, through the primary survey data approach, evidence is documented that confirm and also contradict the secondary data approach findings in respect of both some governance and company variables. This suggests the need for more research using the mixed-method approach in an attempt to reveal why the results contradict. Secondly the results enrich voluntary disclosure literature by bringing disclosure determinants evidence through longitudinal data. Insights obtained from both the data triangulation and longitudinal study setting will help inform existing debate on policy options with regard to GHG emission disclosure. Finally the study contributes to the GHG disclosure literature by developing a comprehensive GHG voluntary disclosure index drawn from a various reporting guidelines. Such a comprehensive index will help ensure that adequacy of company GHG disclosures is assessed based on robust instrument

Luminescence lifetime components in quartz: influence of irradiation and annealing

Pulsed optically stimulated luminescence measured from quartz under certain combinations of annealing and measurement temperature can be resolved into multiple lifetime components. We have studied the influence on these lifetime components of annealing temperature up to 900 °C, beta irradiation dose as high as 1700 Gy, and temperature of stimulation up to 200 °C. Although the time-resolved spectra from which the lifetimes are determined may be measured without heating between irradiation and measurement, a necessary protocol in steady-state optical stimulation applications, studies reported in this paper have been augmented with investigations on the effect of temperature and duration of preheating on the principal and secondary lifetimes. Luminescence spectra for measurements up to 200 Gy consist of a single lifetime but two components occur thereafter, both are independent of radiation dose. The principal lifetime of 35 μs is not affected by temperature of anneal whereas the secondary lifetime increases from 9 to 18 μs when the annealing temperature is changed from 600 to 900 °C. The dependence of both the principal and secondary luminescence lifetimes on measurement temperature can be explained by thermal quenching of the associated luminescence. However, the influence of irradiation, preheating, and annealing on the lifetimes can be explained with reference to an energy band scheme in which the primary mechanism in the processes leading up to luminescence emission is the change in concentration of holes at various luminescence centres caused by annealing

Time-resolved optically stimulated luminescence and spectral emission features of α-Al2O3:C

The authors acknowledge financial support from Rhodes University and the National Research Foundation of South Africa (Grant UID 87358).Abstract This report is concerned with the influence of measurement temperature on luminescence lifetime and on the spectral emission features of luminescence from α-Al2O3:C. The lifetimes were determined from time-resolved luminescence spectra. Spectral measurements were done using thermoluminescence and X-ray excited optical luminescence. The emission spectra of α-Al2O3:C studied in this work shows prominent bands at 330, 380 and 420 nm associated with vacancies in the oxygen sub-lattice in α-Al2O3:C and an additional band at 695 nm due to Cr substitution for Al. Emission bands below 500 nm are independent of temperature below 125 °C but widen with temperature. Direct evidence of thermal quenching of the 420 nm emission band is provided. Beyond 200 °C, the 380 and 420 nm bands merge and widen, with the 420 nm emission dominant. Before the onset of thermal quenching, luminescence lifetimes are affected by retrapping both in the shallow- and in the main electron trap. This was deduced from features of time-resolved luminescence spectra measured from samples with and without the shallow trap. Additional measurements with temperature decreasing from 160 to 20 °C, after phototransfer as well as after a considerable delay between irradiation and measurement, suggest that the change in lifetimes could also be related to other factors including slight shifts in emission wavelength for the 380 and 420 nm emissions.PostprintPeer reviewe