Joshua Kibet

Molecular Products and Radicals from Pyrolysis of Lignin

Thermal degradation of lignin under two reaction regimes (pyrolysis in N(2) and oxidative pyrolysis in 4% O(2) in N(2)) has been investigated in a tubular, isothermal, flow-reactor over the temperature range 200-900 °C at a residence time of 0.2 s. Two experimental protocols were adopted: (1) Partial pyrolysis in which the same lignin sample was continuously pyrolyzed at each temperature and (2) conventional pyrolysis, in which new lignin samples were pyrolyzed at each pyrolysis temperature. The results identified common relationships between the two modes of experiments, as well as some differences. The majority of products from partial pyrolysis peaked between 300 and 500 °C, whereas for conventional pyrolysis reaction products peaked between 400 and 500 °C. The principal products were syringol (2,6-dimethoxy phenol), guaiacol (2-methoxy phenol), phenol, and catechol. Of the classes of compounds analyzed, the phenolic compounds were the most abundant, contributing over 40% of the total compounds detected. Benzene, styrene, and p-xylene were formed in significant amounts throughout the entire temperature range. Interestingly, six ringed polycyclic aromatic hydrocarbons were formed during partial pyrolysis. Oxidative pyrolysis did not result in large differences from pyrolysis; the main products still were syringol, guaiacol, phenol, the only significant difference being the product distribution peaked between 200 and 400 °C. For the first time, low temperature matrix isolation electron paramagnetic resonance was successfully interfaced with the pyrolysis reactor to elucidate the structures of the labile reaction intermediates. The EPR results suggested the presence of methoxyl, phenoxy, and substituted phenoxy radicals as precursors for formation of major products; syringol, guaiacol, phenols, and substituted phenols.

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 modeling of major tobacco alkaloids in mainstream cigarette smoke

BackgroundConsensus of opinion in literature regarding tobacco research has shown that cigarette smoke can cause irreparable damage to the genetic material, cell injury, and general respiratory landscape. The alkaloid family of tobacco has been implicated is a series of ailments including addiction, mental illnesses, psychological disorders, and cancer. Accordingly, this contribution describes the mechanistic degradation of major tobacco alkaloids including the widely studied nicotine and two other alkaloids which have received little attention in literature. The principal focus is to understand their energetics, their environmental fate, and the formation of intermediates considered harmful to tobacco consumers.MethodThe intermediate components believed to originate from tobacco alkaloids in mainstream cigarette smoke were determined using as gas-chromatography hyphenated to a mass spectrometer fitted with a mass selective detector (MSD) while the energetics of intermediates were conducted using the density functional theory framework (DFT/B3LYP) using the 6-31G basis set.ResultsThe density functional theory calculations conducted using B3LYP correlation function established that the scission of the phenyl C–C bond in nicotine and β-nicotyrine, and C–N phenyl bond in 3,5-dimethyl-1-phenylpyrazole were respectively 87.40, 118.24 and 121.38 kcal/mol. The major by-products from the thermal degradation of nicotine, β-nicotyrine and 3,5-dimethyl-1-phenylpyrazole during cigarette smoking are predicted theoretically to be pyridine, 3-methylpyridine, toluene, and benzene. This was found to be consistent with experimental data presented in this work.ConclusionClearly, the value of the bond dissociation energy was found to be dependent on the π–π interactions which plays a primary role in stabilizing the phenyl C–C in nicotine and β-nicotyrine and the phenyl C–N linkages in 3,5-dimethyl-1-phenylpyrazole. This investigation has elucidated the energetics for the formation of free radicals and intermediates considered detrimental to human health in cigarette smoking.Graphical abstractSome molecular alkaloids of tobacco the plant

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.

Characterization of cyanobacterial toxins in Lake Naivasha, Kenya

Microcystins are a class of cyanobacterial toxins largely found in water and are often responsible for poisoning animals as well as humans. A more recent scenario is the poisoning of domestic water supply system in Toledo (Ohio), USA. Consequently, water supply to the city had to be suspended for weeks in order for authorities to ascertain the commoditys safety before restoring supply. In Kenya, there have been very few studies on cyanotoxins and their adverse health effects in spite of the fact that cyanobacteria have been implicated in several poisoning episodes of humans and animals worldwide, occasioned by drinking of microcystin contaminated water. This paper therefore, reports data on the first identification and characterization of hepatotoxic microcystins in water samples of Lake Naivasha. Samples from the lake were investigated over a modest period of three months. The phytoplankton community was mainly dominated by the cyanobacterium Microcystisaeruginosa. The colour of the water samples was found to be 520 ± 91 ptco, while the conductivity was 234 ± 0.8 μs/cm and the total dissolved solids was 1035 ± 12 mg/L. Due to the high turbidity (59.0 ± 24 ntu), phytoplankton biomass was low, ranging between 1.5 and 8.2 mg L−1. Using UV-Vis and HPLC techniques, the microcystin-LR and-RR were detected in all the water samples collected from the lake. HyperChem computational package was used to estimate the toxicity index of microcystin-RR based on the octanol-water partition coefficient and found to be 230 times more soluble in water than in octanol. Thus, microcyctin-RR is highly soluble in polar biological tissues which may result in cell injury, oxidative stress, and ultimately cancer. To the best of our knowledge, this is the first evidence of microcystins in Lake Naivasha.

The Speciation of Selected Trace Metals in Nairobi River Water, Kenya

Metal ions form complexes with naturally occurring ligands released from industrial effluent. The complexes are transported and enter the environment and biological system leading to environmental degradation and health problems. This contribution investigates the speciation of trace metals in water samples collected from Nairobi River. Heavy metals (Pb, Mn, Cu, Fe, Cr and Zn) were determined using spectroscopic techniques whereas sulfaver 4 method, diazotization, and titration methods were used to determine the concentration of SO42+, NO2-, Fand Clrespectively. It was found that ~ 69.8% of total iron was in oxidation state III; the dominant species being Fe2+, Fe(OH)SO4, [FeF4]-, FeSO4, Fe2+ and [Fe(OH)2]+ during both the dry and wet seasons. Manganese was found exclusively in oxidation state II (100%) in which some of its major chemical forms were Mn2+ and [MnF6]4-. Copper was present mostly in oxidation state II (Cu2+) while lead and zinc existed chiefly as ([Zn(SO4)4]6and [Pb(SO4)3]4-) complexes. Chromium was trivalent with its main complexes being [Cr4(OH)6]6+ and Cr(OH)(SO4)). Traces of free metal ions (Cu, Fe and Mn) were found in Lenana section of Nairobi River. Traces of free metal ions are the most aggressive water toxicants due to their high solubility in biological systems.

MOESM1 of Kinetic modeling of nicotine in mainstream cigarette smoking

Additional file 1. This has beeb corrected accordingly under the section GC-MS determination of nicotine and pyridine in ES1 and SM1 tobacco.

Determination of major tobacco alkaloids in mainstream cigarette smoking

The popularity of tobacco use worldwide has kicked off one of the greatest clinical debates on human toxicology and public health in general. Accordingly, this study investigates some of the alkaloids in tobacco believed not only to be addictive and carcinogenic but also as precursors for other related medical problems. The characteristic behaviour, identification and product evolution of β-nicotyrine and 3, 5-dimethyl-1-phenylpyrazole in tobacco is reported extensively in this study for the first time. Two commercial cigarette brands coded SM1 and ES1 were explored for evolution of major alkaloids over a modest temperature range of 200–700° C for a total pyrolysis time of 3 minutes using a tubular quartz reactor, typically in increments of 100°C using nitrogen as the pyrolysis gas at a residence time of 2.0 seconds under 1 atmosphere pressure. The heating rate of the heater was ∼ 20°C s−1. The pyrolysate was passed over 10 mL analytical grade methanol and analyzed using a Gas-Chromatography hyphenated to a mass spectrometer (GC-MS) with a mass selective detector (MSD). GC-MS results showed that nicotine was the major alkaloid in both cigarettes reaching a maximum at ∼ 400°C (8.0 x 108 GC-Area counts) for ES1 cigarette and 500°C (∼2.7 x 108 GC-Area counts for SM1 cigarette. Clearly, the ratio of nicotine for ES1 to SM1 is approximately 3 indicating that ES1 cigarette is rich in nicotine. Based on this data alone, ES1 cigarette was found to be more addictive.

Kinetic and Molecular Modeling of Selected Bio-hazardous By-products from High Temperature Cooking of Goat Meat

The environmental fate of thermally released organic toxins including radical formation from high temperature cooking has received mounting global concern due to the potential health impacts associated with them. Therefore, this contribution investigates the thermal degradation kinetics of pyrolysis products of red meat under conditions representative of high temperature cooking. Evolution of selected molecular toxins was monitored using an in-line Gas Chromatography hyphenated to a mass spectrometer (GC-MS) in the temperature range 500–525°C. The primary focus is to propose a kinetic model for the thermal destruction of bio-hazardous byproducts; 2-(ethylthio)phenol, indole and 2, 3-dimethylhydroquinone within a temperature region 723 and 798 K using pseudo-first order rate law. A reaction time of 2.0 s was employed in line with the average residence time in combustion systems. Nonetheless, for the formation kinetics of 2-(ethylthio)phenol), various cooking times were chosen. Kinetic results showed that the destruction rate constants for indole, 2, 3-dimethylhydroquinone, and 2-(ethylthio)phenol at 798 K were 1.19, 1.42, and 1.35 s−1 respectively. GC-MS results revealed the amount of 2-(ethylthio)phenol evolved decreased with increase in the cooking time. The scission of the phenyl-sulphur linkage in 2-(ethylthio)phenol was determined using the density functional theory (DFT) and found to proceed with an energy barrier of 319.31 kJmol−1. The band-gap energy for 2-(ethylthio)phenol was calculated using Chemissian and found to be 5.298 eV. The kinetic behavior of combustion by-products from red meat is important in understanding the formation of environmentally toxic free radicals from high temperature cooking considered harmful to human health and natural ecosystems.