Sorption of components from a mixture of odorants by polysaccharides of starch, chitosan, and carrageenan

Sorption of components from a mixture of odorants in aqueous suspensions of native cornstarch, chitosan, and carrageenan was studied by the method of capillary gas-liquid chromatography. Binding was primarily effected via hydrophobic cooperative interactions. The amount of sorbed odorants depended linearly on their initial concentration in the suspension. The differences in sorption characteristics of starch and chitosan were related to the presence of amino groups in the latter polysaccharide, which contributed to an increased binding of aldehydes via polar interactions. Sorption of odorants by the sulfated polysaccharide carrageenan largely depended on the structure of odorants and properties of their functional groups. Carrageenan was potent in binding aldehydes, ketones, and esters. Alcohols were less strongly bound to this polysaccharide. Sorption of lactones and guaiacol by carrageenan was the least significant.     

Binding of aliphatic aldehydes by cornstarch polysaccharides

Binding by cryotextured cornstarch of individual aliphatic aldehydes (C6-C10; saturated or unsaturated) and their mixtures from aqueous solutions has been studied using capillary gas chromatography. The amount of compounds absorbed by the cryotextures depended linearly on the concentration of aldehydes in the original gel. The majority of the compounds under study were bound irreversibly. Aldehydes with low molecular weight were better absorbed by the cryotextures than by granules of intact cornstarch. Data of IR spectrocopy demonstrated that binding to cornstarch polysaccharides decreased the conformational mobility of odorants. The appearance of binding isotherms depended of the extent of aldehyde sorption, suggesting the involvement of multiple mechanisms of binding. The formation of supramolecular complexes through cooperative hydrophobic interactions between aldehydes and cornstarch polysaccharides was the preferential mechanism of the sorption.     

Binding of Aliphatic Aldehydes by Cornstarch Polysaccharides

Binding by cryotextured cornstarch of individual aliphatic aldehydes (C₆–C₁₀; saturated or unsaturated) and their mixtures from aqueous solutions has been studied using capillary gas chromatography. The amount of compounds sorbed by the cryotextures depended linearly on the concentration of aldehydes in the original gel. The majority of the compounds under study were bound irreversibly. Aldehydes with low molecular weight were better sorbed by the cryotextures than by granules of native cornstarch. Data of IR spectroscopy demonstrated that binding to cornstarch polysaccharides decreased the conformational mobility of odorants. The appearance of binding isotherms depended on the extent of sorption, suggesting the involvement of complex mechanisms of binding. The formation of supramolecular complexes through cooperative hydrophobic interactions between aldehydes and cornstarch polysaccharides was the preferential mechanism of the sorption.     

Binding of aromatic compounds to cornstarch polysaccharides

Sorption of aromatic compounds from aqueous solutions by cryotextures and suspensions of native cornstarches was studied by capillary gas chromatography. Acetophenone and benzyl alcohol were not sorbed by cryotropic-cornstarch gel and native-cornstarch suspension. A linear concentration dependence was found for aldehydes. Phenylethyl alcohol was characterized by a nonlinear concentration dependence. The presence of a benzene ring contributed to decreased binding (relative to the level characteristic of aliphatic compounds). The degree of binding depended considerably on the type of functional group in the aromatic compounds. Cryotextures were more potent than granules of native cornstarch in binding aromatic compounds.     

Binding of aromatic compounds to cornstarch polysaccharides

Sorption of aromatic compounds from aqueous solutions by cryotextures and suspensions of native cornstarches was studied by capillary gas chromatography. Acetophenone and benzyl alcohol were not sorbed by cryotropic-cornstarch gel and native-cornstarch suspension. A linear concentration dependence was found for aldehydes. Phenylethyl alcohol was characterized by a nonlinear concentration dependence. The presence of a benzene ring contributed to decreased binding (relative to the level characteristic of aliphatic compounds). The degree of binding depended considerably on the type of functional group in the aromatic compounds. Cryotextures were more potent than granules of native cornstarch in binding aromatic compounds.     

Sorption of components from a mixture of essential oils by cryotextured cornstarches

Sorption by cryotextured cornstarches of components of the aqueous phase of a mixture of essential oils was studied by capillary gas chromatography. The amount of cryotexture-sorbed substances depended linearly on their concentration in the initial gel. The sorption of components from the mixture by starch polysaccharides was mainly associated with hydrophobic cooperative interactions, which resulted in the formation of supramolecular structures and inclusion complexes. The structure of the compounds was a major factor determining the degree of sorption. Sorption of monoterpene carbohydrates was the most pronounced. We revealed a synergistic increase in the degree of sorption from the mixture as compared to binding of individual compounds.     

Inhibitory receptor binding events among the components of complex mixtures contribute to mixture suppression in responses of olfactory receptor neurons of spiny lobsters

Responses of olfactory receptor neurons of spiny lobsters Panulirus argus to two-component mixtures can be shaped by inhibitory events such as odor-activated hyperpolarizations and inhibition of odor-receptor binding (Daniel et al. 1996). In the current study, we extend this analysis to complex mixtures by examining responses of spiny lobster olfactory receptor neurons to mixtures containing up to seven odorants, consisting of adenosine-5′-monophosphate, ammonium, betaine, l-cysteine, l-glutamate, dl-succinate, and taurine. The response to a mixture was often less than the response to its most excitatory component. The effect of adding an excitatory odorant to a mixture depended on olfactory receptor neuron type, composition of the mixture, and which compound was added. In some cases the added excitatory compound had no effect or even decreased the mixture's response intensity, thus demonstrating nonlinear contributions of the components. Response intensities predicted by a noncompetitive model, which is most representative of these olfactory receptor neurons, were improved when the model included a term for empirical measurements of inhibitory binding interactions, suggesting that inhibitory binding interactions are one mechanism contributing to mixture suppression. This model's predictions were accurate for binary mixtures but not for larger mixtures, suggesting that additional inhibitory mechanisms are needed to account for mixture interactions in complex mixtures. Accepted: 24 July 1998     

Sorption of Components from a Mixture of Essential Oils by Cryotextured Cornstarches

Sorption by cryotextured cornstarches of components of the aqueous phase of a mixture of essential oils was studied by capillary gas chromatography. The amount of cryotexture-sorbed substances depended linearly on their concentration in the initial gel. The sorption of components from the mixture by starch polysaccharides was mainly associated with hydrophobic cooperative interactions, which resulted in the formation of supramolecular structures and inclusion complexes. The structure of the compounds was a major factor determining the degree of sorption. Sorption of monoterpene hydrocarbons was the most pronounced. We revealed a synergistic increase in the degree of sorption from the mixture as compared to binding of individual compounds.__________Translated from Prikladnaya Biokhimiya i Mikrobiologiya, Vol. 41, No. 4, 2005, pp. 463–469.Original Russian Text Copyright © 2005 by Terenina, Misharina.     

Preparation of N-vanillyl chitosan and 4-hydroxybenzyl chitosan and their physico-mechanical, optical, barrier, and antimicrobial properties

Chitosan derivatives such as N-vanillyl chitosan and 4-hydroxybenzyl chitosan were prepared by reacting chitosan with 4-hydroxy-3-methoxybenzaldehyde (vanillin) and 4-hydroxybenzaldehyde. Amino groups on chitosan reacts with these aldehydes to form a Schiff base intermediate, which is later on converted into N-alkyl chitosans by reduction with sodium cyanoborohydride. The chemical reaction was monitored by ¹H NMR spectroscopy and the absence of aldehydic proton at 9.83 ppm in NMR spectra was observed for both the modified chitosan derivatives confirming the reaction. Modified chitosan films were later prepared by solution casting method and their physico-mechanical, barrier, optical and thermal properties were studied. The results clearly indicated significant change in tensile strength, water vapour transmission rate, and haze properties of modified chitosans. Modified chitosan films were also studied for their antimicrobial activity against Aspergillus flavus. The results showed a marked reduction of aflatoxins produced by the fungus in the presence of the N-vanillyl chitosan and 4-hydroxybenzyl chitosan film discs to 98.9% and non-detectable levels, respectively.     

Molecular cloning,expression profile,odorant affinity,and stability of two odorant‐binding proteins in Macrocentrus cingulum Brischke (Hymenoptera: Braconidae)

The polyembryonic endoparasitoid wasp Macrocentrus cingulum Brischke (Hymenoptera: Braconidae) is deployed successfully as a biocontrol agent for corn pest insects from the Lepidopteran genus Ostrinia in Europe and throughout Asia, including Japan, Korea, and China. The odorants are recognized, bound, and solubilized by odorant‐binding protein (OBP) in the initial biochemical recognition steps in olfaction that transport them across the sensillum lymph to initiate behavioral response. In the present study, we examine the odorant‐binding effects on thermal stability of McinOBP2, McinOBP3, and their mutant form that lacks the third disulfide bonds. Real‐time PCR experiments indicate that these two are expressed mainly in adult antennae, with expression levels differing by sex. Odorant‐binding affinities of aldehydes, terpenoids, and aliphatic alcohols were measured with circular dichroism spectroscopy based on changes in the thermal stability of the proteins upon their affinities to odorants. The obtained results reveal higher affinity of trans‐caryophelle, farnesene, and cis‐3‐Hexen‐1‐ol exhibits to both wild and mutant McinOBP2 and McinOBP3. Although conformational flexibility of the mutants and shape of binding cavity make differences in odorant affinity between the wild‐type and mutant, it suggested that lacking the third disulfide bond in mutant proteins may have chance to incorrect folded structures that reduced the affinity to these odorants. In addition, CD spectra clearly indicate proteins enriched with α‐helical content.     

Quaternization of N-aryl chitosan derivatives: synthesis, characterization, and antibacterial activity

Chemical modification of chitosan by introducing quaternary ammonium moieties into the polymer backbone renders excellent antimicrobial activity to the adducts. In the present study, we have synthesized 17 derivatives of chitosan consisting of a variety of N-aryl substituents bearing either electron-donating or electron-withdrawing groups. Selective N-arylation of chitosan was performed via Schiff bases formed by the reaction between the 2-amino groups of the glucosamine residue of chitosan with aromatic aldehydes under acidic conditions, followed by reduction of the Schiff base intermediates with sodium cyanoborohydride. Each of the derivatives was further quaternized using N-(3-chloro-2-hydroxypropyl)trimethylammonium chloride (Quat-188) as the quaternizing agent that reacted with either the primary amino or hydroxyl groups of the glucosamine residue of chitosan. The resulting quaternized materials were water soluble at neutral pH. Minimum inhibitory concentration (MIC) antimicrobial studies of these materials were carried out on Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria in order to explore the impact of the extent of N-substitution (ES) on their biological activities. At ES less than 10%, the presence of the hydrophobic substituent, such as benzyl and thiophenylmethyl, yielded derivatives with lower MIC values than chitosan Quat-188. Derivatives with higher ES exhibited reduced antibacterial activity due to low quaternary ammonium moiety content. At the same degree of quaternization, all quaternized N-aryl chitosan derivatives bearing either electron-donating or electron-withdrawing substituents did not contribute antibacterial activity relative to chitosan Quat-188. Neither the functional group nor its orientation impacted the MIC values significantly.     

Three Amino Acid Residues Bind Corn Odorants to McinOBP1 in the Polyembryonic Endoparasitoid of Macrocentrus cingulum Brischke

Odorant binding proteins (OBPs) play a central role in transporting odorant molecules from the sensillum lymph to olfactory receptors to initiate behavioral responses. In this study, the OBP of Macrocentrus cingulum McinOBP1 was expressed in Escherichia coli and purified by Ni ion affinity chromatography. Real-time PCR experiments indicate that the McinOBP1 is expressed mainly in adult antennae, with expression levels differing by sex. Ligand-binding experiments using N-phenyl-naphthylamine (1-NPN) as a fluorescent probe demonstrated that the McinOBP1 can bind green-leaf volatiles, including aldehydes and terpenoids, but also can bind aliphatic alcohols with good affinity, in the order trans-2-nonenal>cis-3-hexen-1-ol>trans-caryophelle, suggesting a role of McinOBP1 in general odorant chemoreception. We chose those three odorants for further homology modeling and ligand docking based on their binding affinity. The Val58, Leu62 and Glu130 are the key amino acids in the binding pockets that bind with these three odorants. The three mutants, Val58, Leu62 and Glu130, where the valine, leucine and glutamic residues were replaced by alanine, proline and alanine, respectively; showed reduced affinity to these odorants. This information suggests, Val58, Leu62 and Glu130 are involved in the binding of these compounds, possibly through the specific recognition of ligands that forms hydrogen bonds with the ligands functional groups.     

Complex binding interactions between multicomponent mixtures and odorant receptors in the olfactory organ of the Caribbean spiny lobster Panulirus argus

Our study was designed to examine how components of complex mixtures can inhibit the binding of other components to receptor sites in the olfactory system of the spiny lobster Panulirus argus. Biochemical binding assays were used to study how two- to six-component mixtures inhibit binding of the radiolabeled odorants taurine, L-glutamate and adenosine-5'-monophosphate to a tissue fraction rich in dendritic membrane of olfactory receptor neurons. Our results indicate that binding inhibition by mixtures can be large and is dependent on the nature of the odorant ligand and on the concentration and composition of the mixture. The binding inhibition by mixtures of structurally related components was generally predicted using a competitive binding model and binding inhibition data for the individual components. This was not the case for binding inhibition by most mixtures of structurally unrelated odorants. The binding inhibition for these mixtures was generally smaller than that for one or more of their components, indicating that complex binding interactions between components can reduce their ability to inhibit binding. The magnitude of binding inhibition was influenced more by the mixture's precise composition than by the number of components in it, since mixtures with few components were sometimes more inhibitory than mixtures with more components. These findings raise the possibility that complex binding interactions between components of a mixture and their receptors may shape the output of olfactory receptor neurons to complex mixtures.      

Human olfactory receptor families and their odorants

The human nose detects volatile chemical stimuli by at least three different receptor families: odorant receptors, trace amine-associated receptors, and vomeronasal type-1 receptors. As G protein-coupled receptors, all of the few functionally characterized olfactory receptors share major functional features: when expressed in heterologous cell systems, they 1) respond to odorants of certain chemical groups, e.g., amines, aliphatic carboxylic acids or aldehydes, floral or fruity odorants, including certain key-food odorants, and putative pheromones, and 2) transduce their signals to intracellular cAMP signaling. However, little is known yet about specific differences in the functional designation of the three olfactory receptor families. Recently, two heterologous cell systems expressing olfactory signaling molecules have been developed. Different screening strategies will shed light on the yet sparsely available odorant specificity profiles and structure-function relationships of olfactory receptors, as well as the structure-activity relationships of their odorants.     

Specialized receptor neurons for pheromones and host plant odors in the boll weevil, Anthonomus grandis Boh. (Coleoptera: Curculionidae)

Antennal olfactory receptor neurons in the boll weevil, Anthonomusgrandis, were investigated through single neuron recordings.Receptor neurons for both pheromone components and host plantodors were associated with type I sensilla within the sensoryband regions. Nine types of receptor neurons were identified,based on their responsiveness to the four aggregation pheromonecomponents and selected host plant odors. Three receptor neurontypes responded to either compound I, II or IV of the aggregationpheromone. Dose—response curves were similar for eachof these receptor neuron types, which differed only in theirkey compound. In each instance, I neurons responded primarilyto (+)-I, the optical isomer produced by the boll weevil whichwas found to be active in field tests. Receptor neurons forII also responded to a lesser degree to III, its aldehydic analog,at the same stimulus load. Six additional receptor neuron typesresponded to selected host plant odors: ß-caryophyllene,trans-2-hexen-l-o1 and other six carbon alcohols and aldehydes,trans-ß-ocimene, benzaldehyde, linalool, and B-bisabolol.These neurons were as responsive as, or in some cases more responsiveat the same stimulus load as receptor neurons for pheromonecomponents. Receptor neurons responsive to six-carbon alcoholsand aldehydes were generally most responsive to trans-2-hexen-l-ol.Receptor neurons for other plant odors responded principallyto only one compound among the odorants tested. However, responsesof these neurons were not uniform, suggesting possible specializationfor other unidentified key odorants. Comparisons were also madebetween single neuron and electroantennogram responses. Theresults indicate that the boll weevil, a narrowly oligaphagousinsect, detects its host plant at some distance, and utilizesinformation about a wide range of chemical structures in itsolfactory-mediated behavior.     

Sorption of tartrate, citrate, and EDTA onto chitosan and its regeneration applying electrolysis

The equilibrium isotherm data obtained by the sorption of tartrate, citrate, and EDTA onto chitosan were analyzed using Langmuir and Freundlich equations. The process fits best the Langmuir equation. Kinetic investigations showed that the sorption process obeys the pseudo-second-order kinetic equation. Sorption and desorption peculiarities, FTIR investigations, and measurements of molecular weight enable one to hypothesize that sorption proceeds along with the electrostatic interaction between the positively charged -NH3+ groups of chitosan and the negatively charged -COO(-) of carboxylic acids in the formation of amide bonds between the -NH(2) groups of chitosan and the -COOH groups of the carboxylic acid. Electrolysis under galvanostatic conditions in a mixture of chitosan with a 0.1 mol L(-1) Na(2)SO(4) solution enables one to destroy the amide bonds in the cathode compartment of the electrochemical cell and to anodize organics in the anodic compartment. The choosing of relevant conditions of electrolysis enables one to obtain chitosan with properties (deacetylation degree, molecular weight, and sorption ability) similar to those of initial chitosan. After electrolysis the regenerated chitosan possesses the same or even higher ability for sorption of the carboxylic acids as the initial chitosan.     

Encapsulation of tannase for the hydrolysis of tea tannins

Tannase was encapsulated in alginate, chitosan, carrageenan or pectin gel matrices, and in the case of alginate, coated with high or low molecular weight chitosan to reduce enzyme release. Cross-linking with glutaraldehyde also improved enzyme retention. Active enzyme preparations were obtained, although carrageenan gels were unstable in tea. Tannase activity was evaluated by reduction in centrifugable (flocculated) tea solids, and a reduction in tea cream measured turbidimetrically after removal of flocculated solids. Tannin interactions with the polysaccharide gels increased the level of centrifugable solids (flocculent) in the tea. An optimum bead formulation consisted of an alginate core, coated with chitosan and cross-linked with glutaraldehyde. Both core and coating materials contained active enzyme. Beads were prepared in a single step procedure involving extrusion of alginate/tannase solution into a hardening bath containing tannase-loaded, chitosan solution. Tannase retained hydrolytic activity through three successive batch cycles, for a total period of 39h processing, and tea cream was visibly removed by treatment with the immobilized tannase. Activity remained stable during 1-month bead storage under refrigeration.     

Chitosan-Based Mucoadhesive Systems for the Inclusion of the Echinochrome Active Substance

Polyelectrolyte complexes (PECs) of chitosan (CH) with kappa/beta carrageenan (κ/β-K), a polysaccharide of red algae, were obtained in a soluble form and as films. Using porcine intestinal mucosa as a model, it was shown that single-layer films obtained from polysaccharides and a three-layer film containing their polyelectrolyte complex exhibited mucoadhesive properties. The mucoadhesive ability of the films depended on the polysaccharide type and changed after PEC formation. Comparative analysis of the ζ-potential values determined for the soluble form of polyelectrolyte complexes in an aqueous solution and in a mucin-containing solution confirmed the mucoadhesive properties of the PECs. It was found that the complexes retained their mucoadhesive properties upon the inclusion of echinochrome A in their soluble form. This made it possible to consider them noninvasive forms of drug delivery.     

Synthesis and characterization of N-aryl chitosan derivatives

Selective N-arylation of chitosan was performed via a Schiff bases formed by the reaction between the 2-amino group of glucosamine residue of chitosan with an aromatic aldehyde under acidic condition followed by reduction of the Schiff base intermediate with sodium cyanoborohydride (Borch reduction). Aromatic aldehydes bearing either an electron donating or electron withdrawing substituent were used. The chemical structures and thermal properties of the N-aryl chitosans were characterized by FT-IR, (1)H NMR, (13)C NMR, TGA, and DSC. The extent of N-substitution (ES) was influenced by the molar ratio of the aldehyde to the glucosamine residue of chitosan, the reaction time and the substituent on the aromatic ring. Lower ESs resulted from N-arylation using an aldehyde with an electron donating substituent. A linear relationship between the targeted ES and the ES obtained was observed when aldehydes bearing electron withdrawing substituents were employed.     

Insights into structural features determining odorant affinities to honey bee odorant binding protein 14

Molecular interactions between odorants and odorant binding proteins (OBPs) are of major importance for understanding the principles of selectivity of OBPs towards the wide range of semiochemicals. It is largely unknown on a structural basis, how an OBP binds and discriminates between odorant molecules. Here we examine this aspect in greater detail by comparing the C-minus OBP14 of the honey bee (Apis mellifera L.) to a mutant form of the protein that comprises the third disulfide bond lacking in C-minus OBPs. Affinities of structurally analogous odorants featuring an aromatic phenol group with different side chains were assessed based on changes of the thermal stability of the protein upon odorant binding monitored by circular dichroism spectroscopy. Our results indicate a tendency that odorants show higher affinity to the wild-type OBP suggesting that the introduced rigidity in the mutant protein has a negative effect on odorant binding. Furthermore, we show that OBP14 stability is very sensitive to the position and type of functional groups in the odorant.