Effect Of Carbon Chain Length Research Articles

Toward better halon substitutes: Effects of carbon chain length on pyrolytic and fire-suppressing mechanisms of perfluoroalkanes

The use of halon fire extinguishants has led to the depletion of the ozone layer, prompting numerous international organizations to invest significant efforts in finding suitable halon alternatives. Among the counterparts, perfluorinated compounds stand out due to their environmental friendliness, specifically, CF3CF3, CF3CF2CF3 and CF3CF2CF2CF3 have been identified by NASA as the most promising candidates within this chemical family. This study digs into the impact of carbon chain length on thermal decomposition and fire suppression mechanisms of perfluoroalkanes with the three agents as model substances, employing experimental and theoretical analyses. Thermal decomposition products within the temperature range of 600 °C - 900 °C and fire suppression performances, including fire-extinguishing concentrations (9.38 vol.%, 7.81 vol.%, and 6.87 vol.%, respectively), variation of the flame morphology and temperature, are intensively analyzed and compared for the three perfluoroalkanes. Theoretical calculations indicate a decrease in carbon chain stability with the increasing chain length, and CF3CF2CF2CF3 manifests the most diversified self-decomposition paths at low energy barriers. Moreover, a wider spectrum of free radicals can be generated from the longer carbon chain via the CC cleavage, which can efficiently react with and continuously consume flame radicals (H• and OH•) to interrupt the combustion chain reaction. These findings enrich the structure-performance relationship of perfluoroalkanes, highlight the potential of specific perfluorinated compounds as viable halon alternatives and offer theoretical guidance for the selection and design of environmentally benign and efficient halon substitutes.

The effect of carbon chain length of cross-linking agent on the functionality of carrier- free immobilized Thermomyces lanuginosa lipase particles

The cross-linked enzyme (CLEs) of Thermomyces lanuginosa lipase (TLL) was prepared in an isocyanide-based multi-component reactions (ICMRs) platform by applying three di-acidic cross-linkers to unveil more factors contributing to the functional properties of CLEs. The linkers were 1,11-undecanedicarboxylic acid, azelaic acid, and adipic acid with 11, 7, and 4 carbon lengths, respectively, providing a proper tool to investigate the effect of linker length on the activity, stability, and selectivity of the resulting CLEs. The immobilization yields of 60–90 % and the specific activities of 168, 88.4 and 49 U/mg were obtained for the CLEs of 1,11-undecanedicarboxylic acid, azelaic acid, adipic acid, respectively. The lower activity of azelaic and adipic acid-mediated CLEs compared to the soluble TLL (110 U/mg) was explained by in silico calculations. The results revealed that as opposed to 1,11-undecanedicarboxylic acid, both linkers tended to penetrate the enzyme active site, thus resulting in a major inhibitory effect on the enzyme functionality. The thermal and co-solvent stability of the immobilized derivatives improved compared to those of free TLL. The selectivity of CLEs was also examined by catalytic release of main omega-3 fatty acids from fish oil, presenting the highest selectivity of 22 for the CLEs of azelaic acid.

Experimental and theoretical investigation of amine-modified biomass-derived activated carbon for CO2 capture: The effects of carbon chain length and types of amine

Sustainable feedstocks and low-cost precursors are crucial for the development of adsorbents for CO2 capture. In this study, three different amine-modified adsorbents were synthesized using sustainable green feedstock, coconut shells, and physical impregnation of DETA, TETA, and TEPA at different loadings (30%, 30%, and 10%, respectively). Their potential as alternative adsorbents for CO2 capture was investigated. Compared to the original activated carbon, all three amine-modified adsorbents showed improved CO2 uptake, with the DETA-modified adsorbent showing the highest CO2 adsorption capacity. The influence of carbon chain length and amine types on CO2 capture was studied in detail. Density functional theory (DFT) calculations were performed to study the CO2 adsorption on the bare activated carbon and the amine-modified adsorbents. The results showed that shorter carbon chains and primary amines could improve the CO2 adsorption performance of the adsorbents regardless of whether the organic amines were dehydrogenated.

Electrochemical oxidation degradation of xanthate and its mechanism: Effects of carbon chain length and electrolyte type

There are a lot of residual flotation reagents such as xanthate remaining in the mineral processing wastewater, which must be deeply removed for recycling or discharge. However, there are few studies using electrochemical oxidation to remove xanthate. This article employs the electrochemical oxidation method to treat simulated xanthate-containing wastewater, which investigates the mechanisms involved in removing four xanthate homologues under different electrolyte conditions. Results show that under 1 g/L of Na2SO4, current density of 40 mA/cm2, initial pH of 7.0, and initial concentration of xanthates 1 mM, four alkyl xanthates can be completely removed within 60 min. The COD removal and TOC removal can reach 71.42%–88.61% and 54.23%–81.50%, respectively. By contrast, NaCl electrolyte is more favorable for xanthate degradation. The generated SO42− concentration can reach 145.4 mg/L at 60min, resulting in the sulfur mineralization ratio (ηs) of 75.72%. Regardless of the electrolyte type, as the carbon chain length increases, the xanthate degradation rate accelerates, accompanied by higher COD and TOC removal. The results of UV–vis spectra and LC–MS indicate that intermediate substances such as xanthate peroxides and alcohols are first formed in the process, ultimately leading to the complete mineralization of small molecule substances such as SO42−, CO2, and H2O. The fate of S and Cl elements confirms it. EPR and probe fluorescence spectroscopy results indicate that in Na2SO4 electrolyte, the main active substances are ·OH and a small amount of SO4∙–. Additionally, the production of ·OH increases as the electrolysis time is prolonged. In NaCl electrolyte, ·OH undergoes a series of reactions with Cl− to convert into Cl∙ and active chlorine, which constitute the primary reactive oxygen species.

Effect of spacer length between N atoms of linear alkyl triamines on adsorption of anionic platinum(IV) ions

In this study, the effect of carbon chain length between N atoms in linear alkyl triamines on the adsorption of anionic platinum ions was studied. For this purpose, bis(3-aminopropyl)amine (BAPA-SG) and diethylenetriamine (DETA-SG) groups were covalently bonded to the silica gel surface. The modified silica gels were characterized through C, H, N elemental analyses and FTIR spectroscopy before being utilized for adsorption and preconcentration Pt(IV) ions from aqueous solutions. Various factors influencing the batch adsorption of Pt(IV) ions with BAPA-SG and DETA-SG, such as nitric acid, chloride, initial Pt(IV) concentration, and contact time, were investigated. The adsorption of Pt(IV) ions was most efficient in the solutions containing 0.1 M hydronium and 0.1 M chloride ions. The adsorbed amount of Pt(IV) increased with an increase in the initial concentration of Pt(IV). The adsorption of Pt(IV) ions with BAPA-SG and DETA-SG reached equilibrium in 2 and 4 h, respectively. The kinetics of Pt(IV) adsorption on both modified silica gels were found to be compatible with the Pseudo-second-order kinetic model. Langmuir isotherm accurately described the adsorption Pt(IV) ions with BAPA-SG and DETA-SG, with maximum monolayer adsorption capacities of 158.7 and 227.3 mg/g, respectively. In the column solid phase extraction studies, Pt(IV) ions could be quantitatively recovered from 500 mL sample solutions using both modified silica gels by eluting with acidic thiourea solutions. The recovery of Pt(IV) by DETA-SG from chloride-containing solutions was more effective than with BAPA-SG. As a result, it was concluded that diethylenetriamine-bonded silica gel could adsorb Pt(IV) ions more effectively than bis(3-aminopropyl)amine bonded silica gel.

Effects of carbon chain length of acrylate monomer on sizing properties of sesbania gum-g-polyacrylate

A series of acrylate monomers with different carbon chain lengths including methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA) and 2-ethylhexyl acrylate (EHA) has been grafted onto molecular chains of native sesbania gum (SG) to obtain SG-g-polyacrylate with similar grafting ratios through Fenton’s initiator respectively. Effects of carbon chain length of the series of acrylates on sizing properties of the grafted SG on polyester yarn have been studied. It is found that, by grafting acrylates onto the molecular chains of SG, its sizing properties are improved markedly. Under the condition of similar grafting ratios, SG-g-PMA shows the highest apparent viscosity, tenacity of sizing film, wettability and adhesion strength to polyester fibre in all the grafted SG prepared. SG-g-PEA and SG-g-PEHA show the highest wear resistance and elongation of sizing film respectively. The polyester/cotton (65/35) warp yarns sized by SG-g-PMA, SG-g-PEHA and SG-g-PEA possess the highest tensile strength, tensile elongation and abrasion resistance respectively, in all the sized conditions. The SG grafted with acrylate monomers with different carbon chain lengths can meet various requirements in sizing polyester yarn.

Effects of Carbon Chain Length on N-Alkane Counterflow Cool Flames: A Kinetic Analysis

An in-depth understanding of the low-temperature reactivity of hydrocarbon fuels is of practical relevance to developing advanced low-temperature combustion techniques. The present study aims to study the low-temperature chemistry of several large n-alkanes with different carbon chain lengths in counterflow cool diffusion flames by kinetic analysis. The large n-alkanes that were chosen are n-heptane (NC7H16), n-decane (NC10H22) and n-dodecane (NC12H26), which are important components of practical fuels. Firstly, the thermochemical structure of a typical cool diffusion flame is understood through its comparison with that of a hot diffusion flame. The boundary conditions, including the ozone concentration, fuel concentration and flow velocity—where cool flames can be established—are identified with a detailed chemical mechanism that evaluates the low-temperature reactivity of the investigated n-alkanes. The results show that the n-alkane with a longer carbon chain length is more reactive than the smaller one, thereby indicating the order of NC12H26 > NC10H22 > NC7H16. This trend is qualitatively similar to the findings from non-flame reactors. The reaction pathway and sensitivity analysis are performed to understand the effects of carbon chain length on the low-temperature reactivity. The contribution of an n-alkane with a longer carbon chain to the dehydrogenation reaction, oxidation reaction and isomerization reaction is greater than that of a smaller n-alkane, and abundant O and OH radicals are generated to promote the fuel low-temperature oxidation process, thereby resulting in an enhanced low-temperature reactivity. The effects of ozone addition on the low-temperature reactivity of n-alkanes are also highlighted. It is found that the addition of ozone could provide a large number of active O radicals, which dehydrogenate with the fuels to generate OH radicals and then promote fuel low-temperature oxidation. The present results are expected to enrich the understanding of the low-temperature characteristics of large n-alkanes.

Hydrophobic Ionic Liquids for Efficient Extraction of Oil from Produced Water

Produced water contaminated with oil has adverse effects on human health and aquatic life. Providing an efficient method for the removal of oil from produced water is a challenging task. In this study, the effects of carbon chain length and the cation nature of ionic liquids (ILs) on the removal efficiency of oil from produced water were investigated. For this purpose, seven ILs containing the bis (trifluoromethylsulfonyl) imide (NTf2) anion, and various cations such as imidazolium, pyridinium, phosphonium, and ammonium, were employed for the removal of oil from produced water via liquid–liquid extraction. The effects of process parameters such as the initial concentration of oil in produced water, contact time, pH, salinity, phase ratio, and temperature on the removal efficiency of oil were studied and optimized. 1-Decyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ([C10mim][NTf2]) (IL4) was found to give the highest oil extraction efficiency of 92.8% under optimum conditions. The extraction efficiency was found to increase with increasing cation alkyl chain length from C2 to C10. The extraction efficiency of ILs based on cations follows the order imidazolium > ammonium > phosphonium > anpyridinium. Fourier Transform infrared spectroscopy (FTIR) was used to explore the ILs interaction with oil using [C10mim][NTf2] as a model. In addition, 1H and 13C NMR spectra were recorded to obtain a better understanding of the molecular structure of IL and to investigate the peak shifts in H and C atoms. Moreover, the cell viability of the most efficient IL, [C10mim][NTf2], in human cells was investigated. It has been concluded that this IL exhibited minimal cytotoxic effects at lower concentrations against human cell lines and is effective for the extraction of oil from aqueous media.

Characteristics and Mechanism of the Adsorption of Imidazole Ionic Liquids in Wastewater by Montmorillonite: Effect of Carbon Chain Length and Dosage of Ionic Liquids

This paper studied the adsorption characteristics and mechanism of four kinds of ionic liquids (ILs) with different carbon chain lengths in montmorillonite (Mt). The results of isothermal adsorption at 25 °C show that the adsorption of four kinds of IL in Mt conforms to the Modified-Langmuir model, and the adsorbance of IL in Mt is positively correlated with the dosage and the carbon chain length of IL. The dynamics research results show that the adsorption of IL in Mt fits well with the quasi-second-order dynamics equation. The reaction constant k is negatively correlated with the dosage of IL but positively correlated with the carbon chain length. The thermodynamics results show that the adsorption of IL in Mt is exothermic. The carbon chain length and the dosage of IL have a cross effect on the adsorption capacity of Mt for IL and the structure of the adsorption products. The adsorption capacity of Mt increases first and then decreases with the increase of dosage, and it increases with the increase of carbon chain length. The dosage of IL has little effect on the d(001) of IL/Mt with the short carbon chain, but the d(001) of IL/Mt with the long carbon chain increases with the increase of the dosage of IL. The carbon chain length has little effect on the d(001) of IL/Mt with a low dosage of IL, however, when the dosage of IL is high, the d(001) of IL/Mt increases with the increase of carbon chain length. The specific surface area, pore volume and the most probable radius of IL/Mt decrease with the increase of the dosage and carbon chain length, but excessive amounts of IL will still increase the most probable radius. Molecular dynamics simulation results show that when the dosage of IL is 0.3CEC, four ILs with different carbon chain lengths are arranged in a monolayer between Mt layers, N (N in IL) coordinates with Ot (O on the tetrahedral surface) at a distance of 3.0 Å, and the coordination strength increases with the increase of the carbon chain length of IL.

Effects of Carbon Chain Length of Acrylate Monomer on Sizing Properties of Locust Bean Gum-g-P (AA-co-Acrylate)

In order to impart good application properties to locust bean gum size for all-polyester yarn, a series of acrylate monomers including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and common hydrophilic monomer–acrylic acid were grafted onto molecular chains of native locust bean gum to obtain locust bean gum- g-P(AA-co-acrylate) products with similar grafting ratios through Fenton’s reagent, respectively. The effects of carbon chain length of the series of acrylates on sizing properties of the grafted locust bean gum for polyester warp were studied. It was found that by grafting acrylates onto the molecular chains of locust bean gum the sizing properties of the locust bean gum were improved markedly. Under the condition of similar grafting ratios, locust bean gum- g-poly(AA-co-methyl acrylate) showed the highest apparent viscosity, water solubility, film strength, wettability, and adhesion to polyester fiber in all the grafted locust bean gum prepared. Meanwhile, locust bean gum- g-poly(AA-co-butyl acrylate) and locust bean gum- g-poly(AA-co-2-ethylhexyl acrylate) had the highest wear resistance and elongation of sizing film, respectively. The modified locust bean gum grafted with acrylate monomers with different carbon chain lengths was able to meet various requirements in the sizing process for polyester yarn.

Performance of Carboxyl Groups in Chemical Mechanical Polishing of GCr15 Bearing Steel: Effects of Carbon Chain Length and pH

Performance of Carboxyl Groups in Chemical Mechanical Polishing of GCr15 Bearing Steel: Effects of Carbon Chain Length and pH

Effect of carbon chain length of chlorinated carboxylic acids on morphology of the carbon films electrodeposited from aqueous solutions

Diamond-like carbon films can be electrodeposited from organic acids in aqueous solutions. Chlorinated carboxylic acids with different chain lengths, ie. chloroacetic acid, 3-chloropropionic acid, 4-chlorobutyric acid and 5-chlorovaleric acid, were used as the carbon sources in the electrolytes. It showed an interesting even-odd effect of carbon chain length on the surface morphology of the electrodeposited carbon films. The odd carbon-numbered chlorinated carboxylic acids lead to smooth carbon films whose morphologies were insensitive to the deposition parameters. On the contrary, the morphologies of the films obtained from the even carbon-numbered chlorinated carboxylic acids were island-like and dependent on the film thickness. Fourier transform infrared and Raman analysis indicated that the electrodeposited diamond-like carbon films were hydrogenated and contaminated by oxygen.

Exploring the solvation behavior of guanidinium based carboxylate ionic liquids in DMSO and DMF through apparent molar properties

The solvation behavior of 1,1,3,3 tetramethylguanidinium [TMG] ionic liquids (ILs) containing different carboxylate anions, octanoate (C8H15O2)-, decanoate (C10H19O2)- and laurate (C12H23O2)-, in dimethylsulfoxide (DMSO) and dimethylformamide (DMF) are examined through apparent molar properties. In this work, three ILs were chosen as they are protic and interact with polar solvents, affecting the thermophysical properties. We have measured the thermophysical properties to study the interactions between ion-ion and ion–solvent and analyzed the influence of IL anion and temperature through the experimental measurements of density and speed of sound. The measurement was carried out as a function of molality (0.05–1.0 mol∙kg−1) and temperature from 293.15 to 328.15 K under atmospheric pressure. The binary systems contained the ILs [TMGH]+[C8H15O2]-, [TMGH]+[C10H19O2]- and [TMGH]+[C12H23O2]-. The apparent molar volume (Vϕ) and the apparent molar isentropic compressibility (Ks,∅)were calculated using the experimental data and a Redlich-Mayer type equation was fitted to calculate the limiting parameters (V∅∞ and Ks,∅∞)to understand the vital empirical parameters of the studied ILs. The effect of carbon chain length on apparent molar volume (Vϕ) and the apparent molar isentropic compressibility (Ks,∅) with concentration and temperature range was studied.

Mechanistic insights into the effect of structural factors on film formation and tribological performance of organic friction modifiers

The influence of molecular structure of organic friction modifiers (OFMs) on their adsorption behaviour on iron oxide surface immersed in PAO oil was investigated using neutron reflectometry (NR). The effects of carbon chain length and levels of unsaturation on film formation was studied using a series of fatty acids with 18–20 carbon atoms in the temperature range between 25 and 100 °C. The results revealed that saturated OFM molecules generate thicker films compared to its unsaturated counterparts. Further, a decrease in film thickness was observed with the degree of unsaturation with the exception of linolenic acid. The film thickness and grafting density of the OFM increased with temperature. A decreased film thickness for the binary additive system comprising GMO and saturated molecules suggested that the adsorption of OFMs on the surface is hindered in the presence of glycerol mono oleate (GMO). A lower boundary friction coefficient and wear exhibited by OFMs with longer chain and linear structure suggest that their tribofilms are more effective in withstanding shear. The tribofilm thickness measured using optical interferometry showed no correlation with the adsorbed layer thickness determined from NR data; this lack of correspondence is attributed to the load and shearing forces experienced by the OFM molecules at the contact surfaces during friction measurements.

Effect of Carbon Chain Length, Ionic Strength, and pH on the In Vitro Release Kinetics of Cationic Drugs from Fatty-Acid-Loaded Contact Lenses.

This paper explores the use of fatty acids in silicone hydrogel contact lenses for extending the release duration of cationic drugs. Drug release kinetics was dependent on the carbon chain length of the fatty acid loaded in the lens, with 12-, 14- and 18-carbon chain length fatty acids increasing the uptake and the release duration of ketotifen fumarate (KTF) and tetracaine hydrochloride (THCL). Drug release kinetics from oleic acid-loaded lenses was evaluated in phosphate buffer saline (PBS) at different ionic strengths (I = 167, 500, 1665 mM); the release duration of KTF and THCL was decreased with increasing ionic strength of the release medium. Furthermore, the release of KTF and THCL in deionized water did not show a burst and was significantly slower compared to that in PBS. The release kinetics of KTF and THCL was significantly faster when the pH of the release medium was decreased from 7.4 towards 5.5 because of the decrease in the relative amounts of oleate anions in the lens mostly populated at the polymer–pore interfaces. The use of boundary charges at the polymer–pore interfaces of a contact lens to enhance drug partition and extend its release is further confirmed by loading cationic phytosphingosine in contact lenses to attract an anionic drug.

Ionic liquid-biosurfactant blends as effective dispersants for oil spills: Effect of carbon chain length and degree of saturation

The well-known toxicity of conventional chemical oil spill dispersants demands the development of alternative and environmentally friendly dispersant formulations. Therefore, in the present study we have developed a pair of less toxic and green dispersants by combining lactonic sophorolipid (LS) biosurfactant individually with choline myristate and choline oleate ionic liquid surfactants. The aggregation behavior of resulted surfactant blends and their dispersion effectiveness was investigated using the baffled flask test. The introduction of long hydrophobic alkyl chain with unsaturation (attached to choline cation) provided synergistic interactions between the binary surfactant mixtures. The maximum dispersion effectiveness was found to be 78.23% for 80:20 (w/w) lactonic sophorolipid-choline myristate blends, and 81.15% for 70:30 (w/w) lactonic sophorolipid-choline oleate blends at the dispersant-to-oil ratio of 1:25 (v/v). The high dispersion effectiveness of lactonic sophorolipid-choline oleate between two developed blends is attributed to the stronger synergistic interactions between surfactants and slower desorption rate of blend from oil-water interface. The distribution of dispersed oil droplets at several DOR were evaluated and it was observed that oil droplets become smaller with increasing DOR. In addition, the acute toxicity analysis of developed formulations against zebra fish (Danio rerio) confirmed their non-toxic behavior with LC50 values higher than 400 ppm after 96 h. Overall, the proposed new blends/formulations could effectively substitute the toxic and unsafe chemical dispersants.

Experimental investigation on the effect of carbon chain length to the droplet combustion characteristic of fatty acid methyl ester

Biodiesel which produces from vegetable oil consists of various fatty acids as fatty acid methyl ester constituent. Each fatty acid has a specific combustion characteristic due to the difference in physicochemical characteristics. This study was done with a single fatty acid methyl ester from various saturated fatty acids to analyze the effects of carbon chain length on the droplet combustion during the evaporation and combustion stages in ambient temperature and atmospheric pressure. Results show that the ignition delay time increase with the longer carbon chain due to the higher viscosity and boiling point. The higher oxygen content in the fatty acid methyl ester molecule promotes the faster combustion, gives a higher burning rate, and cause the flame dimension shorter. Furthermore, oxygen content results in higher radiation caused a brighter flame. The high droplet temperature occurs in the long carbon chain due to the higher of combustible matter gives an increase to the heating value. Low radiation heat loss in a long carbon chain which indicates by the flameless bright also causes the droplet temperature higher. The higher droplet temperature gives the lower gas density which causes the flame dimension higher due to the natural convection.

Effect of carbon chain length on the hydrolysis and transport characteristics of alkyl gallates in rat intestine.

Phenolipids such as alkyl gallates (A-GAs) have been approved by food industry as non-toxic antioxidant additives. However, their digestion and absorption mechanisms in the intestine have not yet been clarified. In this research, the hydrolysis and transport characteristics of A-GAs with fatty alcohols of various chain lengths (C1:0, C2:0, C3:0, C4:0, C8:0, C12:0 and C16:0) were estimated by the everted-rat-gut-sac model (ERGSM) for the first time. High-performance liquid chromatography measurements proved that measurable peaks corresponding to methyl gallate (G-C1:0), ethyl gallate (G-C2:0), propyl gallate (G-C3:0) and butyl gallate (G-C4:0) were discovered in the serosal fluids, which showed the short-chain alkyl gallates can cross the membrane in the form of esters. Besides, all A-GAs were hydrolyzed to GA in the mucosal solution, which contributed evidently to the transport of GA across the membrane of the small intestine. Meanwhile, the hydrolysis rate of A-GAs and transport rate of GA initially increased and then decreased with the chain length, exhibiting a maximum for octyl gallate (G-C8:0). In general, all A-GAs have the behavior of sustained-release. In consequence, the production of A-GAs should be an effective method to extend action time and further increases biological activities of GA.

A hierarchical single-pulse shock tube pyrolysis study of C2–C6 1-alkenes

A single-pulse shock tube study of the pyrolysis of 2% C2–C6 1-alkenes is presented at 2 bar in the temperature range 900–1800 K in the current study. Reactant, intermediate and product species are obtained and quantified using gas chromatography-mass spectrometry (GC–MS) analysis. MS is used for species identification and a flame ionization detector is used for quantification. The experiments show the effect of carbon chain length on the production of smaller C1–C3 fragments. A new detailed kinetic mechanism, NUIGMech1.0, is used to simulate the data and the predictions for the major species are satisfactory. The improvement in predictions of the current mechanism, which includes C6 and C7 species, is substantial compared to AramcoMech3.0. Kinetic analyses are conducted with the current mechanism to identify the formation and consumption pathways of the quantified species. The experimental data are expected to contribute to a database for the validation of mechanisms at pyrolytic conditions. Additionally, the mechanism aims to provide a fundamental understanding of the pyrolytic chemistry of olefins.

Lumichrome tautomerism in alcohol-water mixtures: Effect of carbon chain length and mole fraction of alcohols

Alcohol-water mixtures are important solvent systems, widely used in many applications. In this study, the intriguing water induced tautomerism of the fluorescent chromophore, Lumichrome (LC), has been explored to reveal interesting changes in the solvent environments of alcohol-water mixtures of methanol (MeOH), ethanol (EtOH), n-propanol (PrOH) and tert-butanol (t-BuOH), as a function of the carbon chain length/alkyl group size and concentrations of the alcohols. Since LC remains in the alloxazine form in pure aqueous medium, the appearance of emission from the isoalloxazine tautomer in alcohol-water mixtures provides compelling evidence that addition of alcohol disrupts the H-bonded network structure of bulk water to facilitate the availability of isolated water molecules in the solvent medium, which can form the required LC-water precursor complex for conversion of the alloxazine form to isoalloxazine form. Interestingly, two estimated parameters for LC tautomerism, namely, Rlong, which is the relative emission contribution of the isoalloxazine form in the fluorescence decay traces of LC (and hence a measure of the population of isoalloxazine form in the solution), and τlag, which is the lagtime involved in the evolution of the isoalloxazine emission band in the time-resolved area normalized emission spectra of LC (and hence a measure of the ease with which the LC-water precursor complex is formed), show a non-monotonic dependence on the mole fraction of alcohols (χalcohol) in the mixed solvent systems. The unique variation of Rlong and τlag with χalcohol, indicates the occurrence of three composition zones in the alcohol-water mixtures, which we correlate with characteristic transformations in the microscopic structures of the solvent mixtures. Our results reveal that the ability of the alcohols to disrupt the H-bonded network structure of bulk water increases with increasing size of their hydrophobic alkyl groups, following the trend, t-BuOH > PrOH > EtOH > MeOH.