Calculation of the surface tension of planar interfaces by molecular simulations: from Lennard-Jones fluids to binary mixtures

The relative longevity of the research in the field of the molecular simulations of the liquid–vapour interfaces of Lennard-Jones (LJ) particles can be explained by the dependence of the surface tension on many methodological factors. After a few illustrations on the parameters that can impact the results of surface tension on the LJ interfaces, we establish the ability of the current methodologies to quantitatively predict the surface tension of various liquid–vapour interfaces of pure components at different temperatures. We also show that the methods perform very well for the reproduction of the interfacial tension of binary mixtures in a wide range of pressures.     

Response of olfactory receptor neurons in honeybees to odorants and their binary mixtures

Recordings were made from single sensilla placodea of the worker honeybee (Apis mellifera). The sensilla were stimulated with one of two sets of four compounds and their binary mixtures, at two dosage levels. Aromatic compounds comprised one set, and saturated n-octane derivatives comprised the other set. Correlation, principal component, and cluster analyses indicate that responses to binary mixtures are not linear combinations of responses to the component compounds. The first principal component indicated that neuronal units had either more excitatory or more inhibitory responses to all odorants than would be expected from a model where inhibitory and excitatory responses are randomly distributed among the neuronal units. When compared to the responses to the component odorants, synergistic responses to binary odors occurred more often than would be expected by chance. Clear inhibitory responses to binary odors were less prevalent. This study agrees with an earlier study employing aromatic odorants in that most of the aromatic odorants each had groups of receptor neurons that were relatively selective for it, and each odorant had a distinctly different number of receptor neurons selective for it. Among the octane derivatives, receptor neurons were selective for the level of oxidation of the functional group or its site of attachment, rather than specific compounds.     

酿酒葡萄品质评价及其对气象条件的响应

根据2004～2005年我国北方6省酿酒葡萄主要产区葡萄取样和宁夏芦花台园艺场田间试验葡萄化验结果,运用层次分析方法（AHP）对酿酒葡萄主要品质因子总糖、糖酸比pH、单宁进行综合评价,运用主成分分析方法和因子分析法研究影响每个地区酿酒葡萄综合品质的主要气象因子和影响时段。结果表明：2004～2005年贺兰山东麓的御马、玉泉营、广夏三基地、贺东在庄园;河西走廊的高台、武威;新疆石河子酿酒葡萄品质优良,渤海湾的烟台、蓬莱、昌藜等地酿酒葡萄品质表现一般。酿酒葡萄综合品质主要受果实着色期、全生育期和7～8月的降水量和水热系数的影响,其中降水量起主导作用。果实着色期气温日较差和全生育期平均相对湿度对酿酒葡萄综合品质的形成也有重要影响,影响相对较小的是果实着色期的最低气温。采样地区的光照、温度等气象条件基本适宜酿酒葡萄品质形成,对优质酿酒葡萄形成没有大的限制作用。     

Lactic acid bacteria in the quality improvement and depreciation of wine

The winemaking process includes two main steps: lactic acid bacteria are responsible for the malolactic fermentation which follows the alcoholic fermentation by yeasts. Both types of microorganisms are present on grapes and on cellar equipment. Yeasts are better adapted to growth in grape must than lactic acid bacteria, so the alcoholic fermentation starts quickly. In must, up to ten lactic acid bacteria species can be identified. They belong to the Lactobacillus, Pediococcus, Leuconostoc and Oenococcus genera. Throughout alcoholic fermentation, a natural selection occurs and finally the dominant species is O. oeni, due to interactions between yeasts and bacteria and between bacteria themselves. After bacterial growth, when the population is over 10⁶CFU/ml, malolactic transformation is the obvious change in wine composition. However, many other substrates can be metabolized. Some like remaining sugars and citric acid are always assimilated by lactic acid bacteri a, thus providing them with energy and carbon. Other substrates such as some amino acids may be used following pathways restricted to strains carrying the adequate enzymes. Some strains can also produce exopolysaccharides. All these transformations greatly influence the sensory and hygienic quality of wine. Malic acid transformation is encouraged because it induces deacidification. Diacetyl produced from citric acid is also helpful to some extent. Sensory analyses show that many other reactions change the aromas and make malolactic fermentation beneficial, but they are as yet unknown. On the contrary, an excess of acetic acid, the synthesis of glucane, biogenic amines and precursors of ethylcarbamate are undesirable. Fortunately, lactic acid bacteria normally multiply in dry wines; moreover some of these activities are not widespread. Moreover, the most striking trait of wine lactic acid bacteria is their capacity to adapt to a hostile environment. The mechanisms for this are not yet c ompletely elucidated . Molecular biology has provided some explanations for the behaviour and the metabolism of bacteria in wine. New tools are now available to detect the presence of desirable and undesirable strains. Even if much remains unknown, winemakers and oenologists can nowadays better control the process. By acting upon the diverse microflora and grape musts, they are more able to produce healthy and pleasant wines.     

Miscibility of phosphatidylcholine binary mixtures in unilamellar vesicles: Phase equilibria

Summary Miscibility among phospholipids with different lipid chain-lengths or with different head groups has attracted a number of research efforts because of its significance in biological membrane structure and function. The general consensus about the miscibility of phosphatidylcholines with varying lipid chainlengths appears to be that binary mixtures of phospholipids with a difference of two carbon atoms in the lipid chain mix well at the main phase transition. Miscibility between phosphatidylcholines with differences of four carbon atoms appears to be inconclusive. Previous reports on the phase transition of binary phospholipid mixtures are concerned mainly with multilamellar vesicles and are mostly limited to the main transition. In the present study, unilamellar vesicles were used and miscibility in binary systems between dimyristoyl-, dipalmitoyl- and distearoyl-phosphatidylcholines at pretransition, as well as main transition temperatures was evaluated by constructing phase diagrams. Two methods were used to monitor the phase transitions: differential scanning microcalorimetry and optical absorbance methods. The optical method has the advantage that unilamellar vesicles of dilute phospholipid concentrations can be used. The liquidus and solidus phase boundaries were determined by the onset temperature of heating and cooling scans, respectively, because the completion temperature of a phase transition has no meaning in binary solutions. Dimyristoyl- and distearoyl-phosphatidylcholines. where the difference in the, lipid chain-length is four carbon atoms, mixed well even at pretransition temperature.     

Asymmetric suppression of components in binary aldehyde mixtures: behavioral studies in the laboratory rat

The aim of the present study was to assess component interaction in the perception of the 2 aldehydes butanal and heptanal when presented in binary mixtures to rats. A further aim was to develop a behavioral paradigm for testing suppression of components in mixtures using rodent subjects. Thirsty rats were initially trained to discriminate between the 2 aldehydes butanal and heptanal in an olfactometer using a go/no-go discrimination task. This involved rats learning to place their noses in a sniff port where odors were presented and to lick a tube for water reward when one of the aldehydes was presented (S+) while withholding licking at the tube to the other, unrewarded, aldehyde (S-). A mixture condition was then introduced into the task, whereby a proportion of trials involved presentation of a combination of the 2 aldehydes as an additional unrewarded condition. Rats readily learned to withhold licking on trials when the mixture was presented. The concentration of the nonrewarded (S-) aldehyde in the mixture was then systematically decreased, whereas the concentration of the S+ component was held constant. This eventually caused the S+ component in the mixture to suppress detection of the S-, as shown by an increasing number of lick responses (false alarms) on trials when the mixture was presented. These suppressing effects occurred well above the detection threshold for the S- aldehyde presented alone. Results showed asymmetric suppression in the mixture condition such that butanal suppressed detection of heptanal at much lower concentrations than vice versa. A second experiment showed that when both butanal and heptanal were present in a binary mixture at the same concentration (10(-6) volume %), then rats responded to the mixture as if only butanal was present. These findings are discussed in terms of butanal having higher mobility and being able to compete more effectively than heptanal for occupation of shared receptor sites.     

Harvest and nitrogen effects on bioenergy feedstock quality of grass-legume mixtures on Conservation Reserve Program grasslands

Perennial grass mixtures established on Conservation Reserve Program (CRP) lands can be an important source of feedstock for bioenergy production. This study aimed to evaluate management practices for optimizing the quality of bioenergy feedstock and stand persistence of grass-legume mixtures under diverse environments. A 5-year field study (2008–2012) was conducted to assess the effects of two harvest timings (at anthesis vs after complete senescence) and three nitrogen (N) rates (0, 56, 112 kg N ha⁻¹) on biomass chemical compositions (i.e., cell wall components, ash, volatiles, total carbon, and N contents) and the feedstock energy potential, examined by the theoretical ethanol yield (TEY) and the total TEY (i.e., the product of biomass yield and TEY, L ha⁻¹), of cool-season mixtures in Georgia and Missouri and a warm-season mixture in Kansas. The canonical correlation analysis (CCA) was used to investigate the effect of vegetative species transitions on feedstock quality. Although environmental variations (mainly precipitation) greatly influenced the management effect on chemical compositions, the delayed harvest after senescence generally improved feedstock quality. In particular, the overall cell wall concentrations and TEY of the warm-season mixtures increased by approximately 7%. Additional N supplies improved the total TEY of both mixtures by ~1.6–4.2 L ha⁻¹ per 1.0 kg N ha⁻¹ input but likely lowered the feedstock quality, particularly for the cool-season mixture. The cell wall concentrations of cool-season mixture reduced by approximately 3%–6%. The CCA results indicated that the increased legume compositions (under low N input) likely enhanced lignin but reduced ash concentrations. This field research demonstrated that with proper management, grass-legume mixtures on CRP lands can provide high-quality feedstock for bioenergy productions.     

Behavioral discrimination of binary mixtures and their components: effects of mixture interactions on coding of stimulus intensity and quality

There is mounting evidence that mixture interactions resultin a physiological response that is different from that predictedfrom observed responses to individual mixture components. Mixtureinteractions that act to alter the neural coding of mixtureintensity (intensity mixture interactions) or quality (patternmixture interactions) may ultimately lead to dramatic differencesbetween the perceived intensities and qualities of a mixtureand its components. These perceptions could be expressed andobserved at the behavioral level. Toward examining this question,we have tested the ability of the Florida spiny lobster (Panulirusargus) to behaviorally discriminate between three odorant compounds[adenosine 5'-monophosphate (AMP), L-glutamate (Glu), and taurine(Tau)] and their binary mixtures through the use of a differentialaversive associative conditioning paradigm. Six groups of lobsterswere used, each being conditioned to avoid one of the singlecompounds or binary mixtures. Behavioral expression of intensitymixture interactions was evident. Preconditioning response magnitudesto binary mixtures were either less than those to their components(e.g. AMP + Glu) or less than predicted from responses to theircomponents (e.g. AMP + Tau). Behavioral expression of patternmixture interactions was also observed. Relationships betweenthe quality of each binary mixture and the qualities of themixture's components were determined from the results of analysisof variance and multidimensional scaling analysis. Analysesincorporated observed responses to all stimuli and ‘predicted’responses to the binary mixtures. Lobsters easily discriminatedbetween the qualities of AMP, Glu and Tau. The quality of themixture of AMP + Glu was different from either component aswell as from the predicted value for this mixture. The mixtureof AMP + Tau was intermediate between both components and wassimilar to the predicted value. The mixture of Glu + Tau, whilemore similar to Glu than to Tau, was different from the predictedvalue, and there was some indication that the Glu was actingto suppress the response to Tau. Behavioral results for AMP+ Tau, which suggest no pattern mixture interactions betweenthese compounds, are in accordance with results of recentlyconducted binding assays which indicate independent receptorsfor these compounds (Olson et al., 1992). Results, especiallyfor AMP + Glu and Glu + Tau, are consistent with results ofour electrophysiological analysis of the effects of patternmixture interactions on coding of stimulus quality and intensityby olfactory receptor cells (Derby et al., 1991a,b). This providesfurther evidence for the effects of peripherally initiated mixtureinteractions on the coding and perception of the quality ofodorant mixtures. ¹Present address: Departments of Psychology and Biology, GeorgiaState University, University Plaza, Atlanta, Georgia 30303,USA     

美国酿酒葡萄品种在北京地区的生长和适应性表现

调查研究了首次引进的13个美国酿酒葡萄品种在北京地区栽培后的植物学性状、果实品质和抗寒及抗霜霉病能力,并与传统的欧亚种酿酒葡萄及砧木品种进行了比较与分析,总结了它们之间的植物学性状与抗逆性的差异。本试验选出了在抗寒及抗霜霉病方面表现优良的美国酿酒葡萄品种,为这些品种在我国的实际栽培推广提供科学依据。     

生境破碎化过程对流域生境质量的影响

近几十年来,随着工业化、城市化的加速推进,人类活动对自然生境的干扰越来越频繁,导致生境破碎化与生境质量下降。在流域尺度上科学模拟生境破碎化过程及其对生境质量的影响,对于提升生物多样性和生态系统功能具有重要意义。以鄱阳湖流域为研究区域,基于InVEST模型分析区域生境质量的演变特征;从生境面积、生境边缘和生境隔离三个特征维度模拟生境破碎化过程;采用广义加性模型和地理探测器探究不同生境破碎化过程对生境质量变化的影响与交互作用。研究结果表明:(1)鄱阳湖流域生境质量呈下降趋势,从2000年的0.7862下降到2010年的0.7807,再下降到2020年的0.7715,但总体生境质量较好。生境质量较优的区域主要分布在流域南部、东北部以及西部地区,生境质量较差的区域主要分布在各个子流域的交界处。(2)2000-2010年,鄱阳湖流域生境面积占比下降、生境边缘增加和生境隔离增加三个生境破碎化过程分别占总研究区网格数的34.70%、30.15%和4.50%;2010-2020年分别占总研究区网格数的34.80%、30.69%和4.40%;2000-2020年分别占总研究区网格数的40.82%、37.50%和5.46%。生境面积减少的网格主要集中在鄱阳湖流域的中北部地区;生境边缘增加的网格分布和生境面积减少的网格分布相似;相比之下,生境隔离增加的网格较少,主要分布在各城市的中心城区范围。(3)生境破碎化过程对生境质量具有显著影响,两者呈非线性负相关关系;三个生境破碎化过程两两之间交互作用对生境质量的影响呈现双因子增强趋势。研究结果可为鄱阳湖流域生态格局优化与生境质量提升提供科学参考。     

Activation, orientation and landing of female Culex quinquefasciatus in response to carbon dioxide and odour from human feet: 3-D flight analysis in a wind tunnel

This study investigated the interaction between carbon dioxide (CO(2) ) and human foot odour on activation, upwind orientation and landing of host-seeking female Culex quinquefasciatus (Say) (Diptera: Culicidae) in a wind tunnel. More mosquitoes landed on warmed glass beads coated with foot odour than on clean beads; adding a plume of 4% CO(2) did not influence the proportion of mosquitoes landing. A second experiment used 3-dimensional video tracking to assess flight performance. Activation was more rapid with CO(2) and with CO(2) + foot odour than with clean air or with foot odour alone. Upwind flights were fastest with CO(2) and with clean air, and slowest with foot odour; the CO(2) + foot odour treatment overlapped the previous three treatments in significance. Flight headings tended more towards due upwind with CO(2) and with clean air than with CO(2) + foot odour or with foot odour alone. In both experiments, many mosquitoes flew upwind in clean air. There was little evidence of females changing course upon entering or exiting the CO(2) plume or reacting to foot odour during flight.     

Marked recent increases of colonial scaled chrysophytes in boreal lakes: implications for the management of taste and odour events

1. Lake managers suspect that taste and odour‐causing algal blooms are increasing in frequency and intensity, although long‐term monitoring records are scarce, and a number of critical scientific and management questions remain unanswered. 2. In nutrient‐poor lakes and reservoirs, these events are caused primarily by sporadic outbreaks of some chrysophyte algae, which leave identifiable markers in lake sediments. We examine the siliceous remains of these organisms in more than fifty boreal lakes at broad temporal and spatial scales. 3. Colonial scaled chrysophytes, including the taste and odour‐causing Synura petersenii, have increased markedly in more that 90% of the lakes examined since pre‐industrial times. 4. Detailed stratigraphic analyses of two lakes show a rise in the abundance of colonial taxa in the 1930s to 1950s, with a sharp increase over the past two decades. 5. An examination of biogenic silica and biological ratios in Crosson Lake, Ontario, Canada, indicate that these changes represent true increases in the absolute abundance of colonial chrysophytes. 6. Rapid increases over the past two decades indicate that these trends are the result of one or more anthropogenic stressors that are operating at a broad, regional scale.     

Chemometrics and visible-near infrared spectroscopic monitoring of red wine fermentation in a pilot scale

The modern wine industry needs tools for process control and quality assessment in order to better manage fermentation or bottling processes. During wine fermentation it is important to measure both substrate and product concentrations (e.g. sugars, phenolic compounds), however, the analysis of these compounds by traditional means requires sample preparation and in some cases several steps of purification are needed. The combination of visible/near-infrared (Vis/NIR) spectroscopy and chemometrics potentially provides an ideal solution to accurately and rapidly monitor physical or chemical changes in wine during processing without the need for chemical analysis. The aim of this study was to assess the possibility of combining spectral and multivariate techniques, such as principal component analysis (PCA), discriminant partial least squares (DPLS), or linear discriminant analysis (LDA), to monitor time-related changes that occur during red wine fermentation. Samples (n = 652) were collected at various times from several pilot scale fermentations with grapes from either Cabernet Sauvignon or Shiraz varieties, over three vintages (2001-2003) and scanned using a monochromator instrument (Foss-NIRSystems 6500, Silver Spring, MD) in transmission mode (400-2,500 nm). PCA was used to demonstrate consistent progressive spectral changes that occur through the time course of the fermentation. LDA using PCA scores showed that regardless of variety or vintage, samples belonging to a particular time point in fermentation could be correctly classified. This study demonstrates the potential of Vis/NIR spectroscopy combined with chemometrics, as a tool for the rapid monitoring of red wine fermentation.     

Molecular simulation of the preferential adsorption of CH4 and CO2 in middle-rank coal

The adsorption of the CO₂/CH₄ mixture in coal affects the CO₂-enhanced coalbed methane recovery project. To gain a better understanding of CH₄ and CO₂ interaction with middle-rank coal, we developed a molecular concept with support for the sorption of CH₄ and CO₂ on Ximing-8 coal (XM-8) (1.8% vitrinite reflectance). A XM-8 coal model was built by using molecular dynamic (MD) simulations. The molecular simulations were established by the Grand Canonical Monte Carlo and MD methods to study the effects of the temperature, pressure, and species bulk mole fraction on the pure component adsorption isotherms, isosteric heat and adsorption selectivity. It turns out that the CO₂ selectivity decreases as the pressure and its own bulk mole fraction increases, but it increases as temperature increases, and the selectivity values are not always greater than 1. The interactions between the small molecules and XM-8 were determined by using density functional theory. It was found that the interactions between the CO₂ and XM-8 surface is greater, particularly for the heteroatoms than CH₄. The adsorption selectivity and interaction were simultaneously used to reveal that the advantageously substituted range is high temperature, low pressure and a high content of heteroatoms.     

Effect of media composition on yield values of bacteria growing on binary and ternary substrate mixtures in continuous culture.

Pseudomonas aeruginosa 142 and a presumed variant were grown axenically in chemostats on salicylate/benzoate or salicylate/glucose binary feeds. Each substrate was supplied at 2, 10, 50, 90, 98, or 100% of the total energy flux. Two experiments were also run with ternary mixtures using the same substrates. Aliquots were transferred to fed-batch reactors receiving the same substrates at the same specific rates as the chemostat, but with one substrate radiolabeled with 14C. Radiolabel incorporated into biomass, 14CO2, and soluble microbial products over a period of 8 minutes was used to establish the biomass yield, CO2 yield, and product yield, respectively, associated with a given substrate. The effect of the percent substrate in the feed on the yields depended on the pair of substrates supplied. When benzoate comprised 50% or more of the applied substrate in salicylate/benzoate feeds, the fraction of benzoate in the feed had a small effect on the yield values associated with benzoate. However, when benzoate constituted 2% or 10% of the feed, CO2 yields were lower, biomass yields were slightly lower, and product yields were higher. In contrast, the percent of salicylate in the feed had little effect on any of the salicylate yields for cells growing on the salicylate/benzoate feeds. When salicylate was mixed with glucose, the yields associated with salicylate behaved quite differently. Biomass and CO2 yields were lower and product yields higher when salicylate was 2% or 10% of the feed than when it was higher. In the same substrate mixtures, glucose-based biomass yields were higher and CO2 yields were lower when glucose constituted 2% or 10% of the feed but were constant for higher percentages. The results suggest that the fate of a substrate is relatively independent of the feed composition as long as the substrate in question constitutes a significant percentage of the mixture. Thus, in those situations the assumption of a constant biomass yield in multicomponent substrate modeling is justified. However, when a given substrate constitutes a small percentage of the feed, significant changes in yield may occur.     

Comparative dynamics of gestalt odour formation in two ant species Camponotus fellah and Aphaenogaster senilis (Hymenoptera: Formicidae)

Abstract. Ant colonies experience continuous shifts in worker populations, which may affect odour composition in the nest. A major question regarding the dynamics of gestalt formation is that of the speed at which the scent of a new individual will be incorporated into the gestalt. It is predicted from the gestalt model of colony odour that workers have to exchange recognition cues continuously to maintain themselves within the gestalt and become well integrated within their colony. Using radioactive tracers the rates of transfer were measured between a labelled donor ant and one or 10 recipient ants, as a close approximation to the within-nest situation. The labelled hydrocarbons were first transferred to a small number of individuals and progressively to all the individuals of the group so that the distribution of hydrocarbon transfer rate approached a normal distribution. Furthermore, in Camponotus fellah Dalla Torre, which performs trophallaxis, homogeneity was reached more rapidly than in Aphaenogaster senilis Mayr, which does not show this behaviour. In the latter species, the gestalt seems to be maintained mainly by allogrooming. These experiments were accompanied by behavioural observations to ascertain the respective importance of trophallaxis and allogrooming in the behavioural time-budget of the ants. In A. senilis , allogrooming was more frequent than in ants that trophallax, which corroborates the role of allogrooming in the establishment of the gestalt in this species.     

Phase behavior and dynamic heterogeneities in lipids: A coarse-grained simulation study of DPPC-DPPE mixtures

The coarse-grained Marrink-model for biomembrane simulation is used to study mixtures of dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE) at various concentrations and temperatures. At high temperatures close to ideal mixing is observed. In the low temperature ordered phase dynamic heterogeneities are identified under some conditions. These are correlated with heterogeneities in the local order and define local neighborhoods.     

A simulation study for the analysis of uncertain binary responses: Application to first insemination success in beef cattle

A simulation was carried out to investigate the methods of analyzing uncertain binary responses for success or failure at first insemination. A linear mixed model that included, herd, year, and month of mating as fixed effects; and unrelated service sire, sire and residual as random effects was used to generate binary data. Binary responses were assigned using the difference between days to calving and average gestation length. Females deviating from average gestation length lead to uncertain binary responses. Thus, the methods investigated were the following: (1) a threshold model fitted to certain (no uncertainty) binary data (M1); (2) a threshold model fitted to uncertain binary data ignoring uncertainty (M2); and (3) analysis of uncertain binary data, accounting for uncertainty from day 16 to 26 (M3) or from day 14 to 28 (M4) after introduction of the bull, using a threshold model with fuzzy logic classification. There was virtually no difference between point estimates obtained from M1, M3, and M4 with true values. When uncertain binary data were analyzed ignoring uncertainty (M2), sire variance and heritability were underestimated by 22 and 24%, respectively. Thus, for noisy binary data, a threshold model contemplating uncertainty is needed to avoid bias when estimating genetic parameters.     

Effect of viscosity and dielectric constant variation on fractional fluorescence quenching analysis of coumarin dye in binary solvent mixtures

Photo physical properties of fluorescent organic compounds give an immense improved knowledge on characteristics of excited state that is beneficial to devise innovate molecules and understand their performance in particular applications. Coumarin derivatives have been extensively investigated in this regard. This article narrates steady state fluorescence quenching measurements of a coumarin derivative namely 3‐hydroxy‐3‐[2‐oxo‐2‐(3‐oxo‐3H‐benzo[f]chromen‐2‐yl)‐ethyl]‐1,3‐dihydro‐indol‐2‐one (3HBCD) in a binary mixture of acetonitrile and 1,4‐dioxane. Aniline is used as quencher. Fluorescence intensity is large in acetonitrile and decreases as the percentage of 1,4‐dioxane in the solvent mixture increases. With modest quencher concentration a deviation towards the x axis is noticed in the Stern–Volmer (S–V) plots. This downward curvature is interpreted as due to the presence of 3HBCD in different conformers in the lowest energy level. Ground state intramolecular hydrogen bonding formation is observed due to the conformational changes in the solute. Figured estimations of various quenching parameters recommend that, while dynamic quenching prompts linearity in S–V plot at lower quencher concentration, increasing quenching efficiency with increasing medium viscosity suggests that reaction is not entirely controlled by material diffusion. Stern–Volmer constant increases with decreasing medium dielectric constant.     

Formation of binary complexes of Pb(II), Cd(II) and Hg(II) with maleic acid in CTAB-water mixtures

Abstract

Complexation of toxic metal ions with maleic acid in (0.0–2.5% w/v) cetyltrimethylammonium bromide (CTAB)–water mixtures has been studied pH-metrically at ambient conditions and an ionic strength of 0.16 mol L^-1. The existence of different binary species was established from modelling studies using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters such as the crystallographic R factor and sum of the squares of residuals in mass-balance equations. The models for binary complex systems contain the chemical species ML₂, ML₂H and ML₃ for Pb(II), Cd(II) and Hg(II) in CTAB–water mixtures. The trend in the variation of stability constants with change in the mole fraction of the medium was explained based on electrostatic and non-electrostatic forces. Distribution of the species with pH at different compositions of CTAB–water mixtures was also presented.