Molecular Products from the Thermal Degradation of Selected Tobacco Components: Lignin, Tyrosine, Glutamic Acid, and Modeling of Lignin Pyrolysis using CHEMKIN Combustion Suite

This study explores the thermal decomposition behavior of selected tobacco components: lignin, tyrosine, and glutamic acid using the system for thermal diagnostic studies (STDS) in an in-line gas chromatography-mass spectrometer analytical technique. The pyrolysis conditions employed in this study were a flowing atmosphere of nitrogen and 4% O2 in nitrogen at a residence time of 0.2 seconds for a total pyrolysis time of 3 minutes. The results identified common relationships between the two modes of reaction atmospheres, as well as some differences. While some products were favored by an inert regime, some were favored under an oxidative regime. Oxidative pyrolysis of tyrosine for instance yielded compounds of interest, e.g., hydroquinone, p-benzoquinone, dibenzofuran, and dibenzo-p-dioxin, although no such products were observed under pyrolysis. A comprehensive product distribution at distinct pyrolysis and oxidative pyrolysis temperature of various compounds is presented. The mechanistic channels for the formation of compounds of biological concern such as phenols, and polycyclic aromatic hydrocarbons (PAHs) have also been discussed in detail. Of the classes of compounds analyzed from the thermal degradation of lignin, the phenolic compounds were the most abundant, accounting for over 60% of the total compounds detected. The principal products from pyrolysis of tyrosine were phenol, p-cresol, o-cresol, and benzaldoxime. For the oxidative pyrolysis, the main products were p-tyramine, phenol, p-cresol, and benzonitrile. The principal products from pyrolysis of glutamic acid in order of decreasing abundance were succinimide, pyrrole, 2-pyridone, and acetonitrile. On the other hand, succinimide, propiolactone, ethanol, and hydrogen cyanide were the key products under oxidative pyrolysis. CHEMKIN combustion Suite was used to model the pyrolysis of lignin and consequently, a 15 reaction model was developed to determine the kinetics as well as the thermodynamic parameters of reaction products. By use of pseudo first order rate law, the rate coefficients for various products were evaluated. Arrhenius equation was used to compute the pre-exponential factor A, as well as the activation energy Ea for numerous reaction products including phenol, syringol, 4-vinylguaiacol, furfural, toluene, and benzene. Experimental reaction conditions were used to constrain the model. Simulation data reproduced experimental results with reasonable accuracy

The Impact of Workers’ remittances On Economic Growth: Evidence from Kenya

For many years workers’ remittances have grown to become a significant source of foreign exchange in many developing countries, however, workers’ remittances has not been given a big recognition as a source of economic growth in developing countries especially when considering that  remittances in Kenya continued to show an upward trend in the past. An explanatory design was used.  Data was collected for the periods 1970 to 2010. This study relied purely on secondary annual time series data. The analysis of the data will be carried out by OLS (Ordinary Least Squares) method. Time series Regression was used to analyze the data. we found that there is positive and highly significant relationship between workers’ remittances and real GDP per capita, indicating that higher economic growth is related with higher remittances. Further, we paper found a positive impact of gross capital formation and change of exchange rate regime from fixed to floating on economic growth. The government can improve their economic growth performance by reaping the contributions of workers’ remittances by reducing the cost of transactions of sending and receiving money from abroad. Keywords;          Economic Growth, Workers’ Remittance

Genome sequence of the tsetse fly (Glossina morsitans):Vector of African trypanosomiasis

Tsetse flies are the sole vectors of human African trypanosomiasis throughout sub-Saharan Africa. Both sexes of adult tsetse feed exclusively on blood and contribute to disease transmission. Notable differences between tsetse and other disease vectors include obligate microbial symbioses, viviparous reproduction, and lactation. Here, we describe the sequence and annotation of the 366-megabase Glossina morsitans morsitans genome. Analysis of the genome and the 12,308 predicted protein-encoding genes led to multiple discoveries, including chromosomal integrations of bacterial (Wolbachia) genome sequences, a family of lactation-specific proteins, reduced complement of host pathogen recognition proteins, and reduced olfaction/chemosensory associated genes. These genome data provide a foundation for research into trypanosomiasis prevention and yield important insights with broad implications for multiple aspects of tsetse biology.IS

The analysis of the essential metal contents in khat (Catha edulis Forsk) from Meru County, Kenya

Background: Chemical composition of plants has attracted considerable interest in recent years with considerable research tailored into determining metal contents in food substances. Particularly, essential elements which are necessary for normal human body functioning and are strongly recommended in optimal proportions for better health. This study determined the levels of essential elements; calcium (Ca), magnesium (Mg), sodium (Na), potassium (K) and manganese (Mn) in eleven khat (Catha edulis Forsk) samples collected from Meru County. Methodology: 1.0 g of dry ground khat samples were wet-digested in a solvent mixture of 10 mL of HCl, HNO3 and 20 vol of H2O2 for 3 h at variable temperature of 50–90 °C and later reconstituted in 25 mL 0.05 molL−1 HCl before analysis. The samples were analyzed using inductively coupled plasma atomic emission spectrometry (ICP AES) after acid digestion whereas Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to investigate elemental characteristics and determine the sources of essential metals in khat. In addition, Pearson correlation coefficient (PCC) was used to evaluate the relationships between the essential metals. Results: Spinach leaves certified reference material (CRM 1750a) was analyzed and the percentage recoveries (%) of 98.4 and 101.7 determined showing that the digestion method employed in this work had adequate accuracy. The validated method was employed for the analysis of all the khat samples. The analyzed metal concentration ranges (mg100g−1) in fresh-weight basis per day of five metals were 160.9–267.3, 44.6–81.7, 2.0–3.0, 237.6–393.6, and 220.3 -349.0 for Ca, Mg, Mn, K, and Na, respectively. Both HCA and PCA results showed that these elements could be linked to natural soils and anthropogenic sources. PCC reported significant correlations between Na and K indicating they may have been derived from the same source. The daily metal intakes were below the World Health Organization (WHO) permissible limits implying no associated health risks for khat users. Conclusion: Based on the findings of this study, the consumption of khat from regions of Meru County may be a potential source for essential elements required for human biological processes

A Review of the Technological Advances in the Design of Highly Efficient Perovskite Solar Cells

The search for renewable and sustainable energy for energy security and better environmental protection against hazardous emissions from petro-based fuels has gained significant momentum in the last decade. Towards this end, energy from the sun has proven to be reliable and inexhaustible. Therefore, better light harvesting technologies have to be sought. Herein, the current trends in the development of perovskite solar cells with a focus on device engineering, band alignment, device fabrication with superior light harvesting properties, and numerical simulation of solar cell architectures are critically reviewed. This work will form the basis for future scientist to have a better scientific background on the design of highly efficient solar cell devices, which are cost-effective to fabricate, highly stable, and eco-friendly. This review presents thorough essential information on perovskite solar cell technology and tracks methodically their technological performance overtime. The photovoltaic (PV) technology can help to reduce pollution related to greenhouse gas emissions, criterion pollutant emissions, and emissions from heavy metals and radioactive species by nearly 90%. Following the introduction of highly efficient perovskite solar cell (PSC) technologies, the problems associated with stability, short life-time and lead-based perovskite solar cell configurations have significantly been minimized. The fabrication and simulation of perovskite solar cells has been made possible with advanced technologies and state-of-the-art computational codes. Furthermore, device simulation strategies have lately been used to understand, select appropriate materials, and gain insights into solar cell devices’ physical behavior in order to improve their performances. Numerical simulation softwares such as the 1-dimenional solar cell capacitance simulator (SCAPS-1D), Silvaco ATLAS, and wx-analysis of microelectronic and photonic structures (wxAMPS) used to understand the device engineering of solar cells are critically discussed. Because of the need to produce charge collection selectivity, hole transport materials (HTMs) as well as electron transport materials (ETMs) constitute essential PSC components. In this work, the synthesis of inorganic HTMs, as well as their characteristics and uses in various PSCs comprising mesoporous and planar designs, are explored in detail. It is anticipated that the performance of inorganic HTLs on PSCs would encourage further research which will have a significant influence on the future designs and fabrication of highly efficient solar cells

Phenols from pyrolysis and co-pyrolysis of tobacco biomass components

Phenol and its derivatives (phenol, o-, m-, p-cresols, catechol, hydroquinone, methoxy substituted phenols, etc. referred to as phenolic compounds or phenols) are well-known toxicants that exist in the environment and affect both human and natural ecosystems. This study explores quantitatively the yields of phenolic compounds from the thermal degradation (pyrolysis and oxidative pyrolysis) of common tobacco biomass components (lignin, tyrosine, ethyl cellulose, sodium alginate, and laminarin) as well as some mixtures (lignin/tyrosine, ethyl cellulose/tyrosine and sodium alginate/tyrosine) considered important in high temperature cooking, tobacco smoking, and forest fires. Special attention has been given to binary mixtures including those containing tyrosine-pyrolysis of binary mixtures of tyrosine with lignin and ethyl cellulose results in significant reductions in the yields of majority phenols relative to those from the thermal degradation of tyrosine. These results imply that the significant reductions of phenol yields in mixtures are not only dependent upon the mass fractions of the components but also the synergetic inhibition effect of biomass components on the thermal degradation of tyrosine. A mechanistic description of this phenomenon is suggested. The results may also be implied in tobacco industry that the cigarette paper (as ethyl cellulose derivative) may play a critical role in reducing the concentration of phenolic compounds released during tobacco burning

Molecular products from the pyrolysis and oxidative pyrolysis of tyrosine

The thermal degradation of tyrosine at a residence time of 0.2s was conducted in a tubular flow reactor in flowing N2 and 4% O2 in N2 for a total pyrolysis time of 3min. The fractional pyrolysis technique, in which the same sample was heated continuously at each pyrolysis temperature, was applied. Thermal decomposition of tyrosine between 350 and 550°C yielded predominantly phenolic compounds (phenol, p-cresol, and p-tyramine), while decomposition between 550 and 800°C yielded hydrocarbons such as benzene, toluene, and ethyl benzene as the major reaction products. For the first time, the identification of p-tyramine, a precursor for the on of formation of p-tyramine and its degradation to phenol and p-cresol, and toxicological discussion of some of the harmful reaction products is also presented

Molecular products from the thermal degradation of glutamic acid

The thermal behavior of glutamic acid was investigated in N2 and 4% O2 in N2 under flow reactor conditions at a constant residence time of 0.2 s, within a total pyrolysis time of 3 min at 1 atm. The identification of the main pyrolysis products has been reported. Accordingly, the principal products for pyrolysis in order of decreasing abundance were succinimide, pyrrole, acetonitrile, and 2-pyrrolidone. For oxidative pyrolysis, the main products were succinimide, propiolactone, ethanol, and hydrogen cyanide. Whereas benzene, toluene, and a few low molecular weight hydrocarbons (propene, propane, 1-butene, and 2-butene) were detected during pyrolysis, no polycyclic aromatic hydrocarbons (PAHs) were detected. Oxidative pyrolysis yielded low molecular weight hydrocarbon products in trace amounts. The mechanistic channels describing the formation of the major product succinimide have been explored. The detection of succinimide (major product) and maleimide (minor product) from the thermal decomposition of glutamic acid has been reported for the first time in this study. Toxicological implications of some reaction products (HCN, acetonitrile, and acyrolnitrile), which are believed to form during heat treatment of food, tobacco burning, and drug processing, have been discussed in relation to the thermal degradation of glutamic acid

Surface bound radicals, char yield and particulate size from the burning of tobacco cigarette

Abstract Background Tobacco smoke is a toxic gas-phase cocktail consisting of a broad range of organics, and free radical intermediates. The formation of smoke from a burning cigarette depends on a series of mechanisms, including generation of products by pyrolysis and combustion, aerosol formation, and physical mass transfer processes. Methods The current study simulates the deposition of particulate matter on the human lung surface by trapping the tobacco smoke particulates in situ on silica gel. To mimic this phenomenon, the cigarette was smoked directly on siliga gel. The surface morphology of smoke condensate trapped on silica gel, and pure silica gel (control) was investigated using a scanning electron microscope (SEM). Electron paramagnetic resonance (EPR) was used to explore the presence of free radicals on the particulate matter trapped on silica. Standard procedures for cigarette smoking (ISO 3402:1999) were adopted. The char yields of tobacco cigarette in the temperature range 200–700 °C was also investigated in an inert atmosphere using a quartz reactor. Results SEM images showed the surface morphology of pure silica gel was smooth while silica gel on which cigarette smoke was smoked on contained particulates of various sizes. Generally, the particulate size of cigarette smoke adsorbed on silica was found to be 2.47 ± 0.0043 µm (~PM2.5). Electron paramagnetic resonance (EPR) results showed a g-value of 2.0037 typically that of a carbon-centred radical. Conclusions It is therefore evident from this investigation that cigarette smoke contains surface bound radicals considered harmful to the health of cigarette smokers. The particulate size of tobacco smoke (PM2.5) can impact severely on the lives of the cigarette smoking community because of its near ultrafine nature. This significantly small particulate size in cigarette smoke can be inhaled deeper into the lungs thus causing serious cell injury and possible tumour growth in addition to other grave diseases. Graphical abstract Cigarette smoking and analytical techniques employed in this stud

INFORMATION DISCLOSURES AND IMPLEMENTATION OF WATER PROJECTS IN MACHAKOS COUNTY, KENYA

This study investigated the effects of information disclosure as part of engagement of stakeholders on implementation of water projects in Machakos County, Kenya. The paper is guided by stakeholder theory advanced by Freeman (1984). The study was guided by causal comparative research design. The study targeted 172 water projects being implemented in Machakos County from the year 2016-2018 with the respondents being seven members of project management committees. Simple random sampling technique was used in selecting 17 water projects that was involved in this study. Questionnaires were used to collect data for the research. The collected data was analysed using both descriptive and inferential statistics. Qualitative data from open-ended questions was analysed using thematic content analysis. It was found out that there was an above degree level of correlation (r=0.584) between information disclosure and implementation of water projects. The paper concludes that when all information pertaining project is disclosed to the respondents, implementation goals would be achieved. On recommendations, the research suggests that communication needs to be improved during implementation stages to ensure every information from the project is relayed to all stakeholders.  Article visualizations