Number Of Polar Groups Research Articles

Modeling the flavor thresholds of organic acids in beer as a function of their molecular properties

A mathematical model of the flavor thresholds of organic acids in beer as a function of their physical and chemical properties was constructed. Principal components analysis (PCA) was applied to 11 properties for 17 acids; this resulted in four significant principal components (PCs), which accounted for 93% of the variance in the property data. The PCs were dominated by the number of polar groups, the number of double bonds, molecular size, and solubility in non-polar solvents, respectively. PC scores indicating each acid's location along each of four scales were obtained. Literature data for acid flavor thresholds in beer were modeled as a function of the principal components using multiple linear regression and partial least squares (PLS) regression. The best-fit and best prediction equations were identical, with an R 2 of 0·905. ©

Electron transfer induces side-chain conformational changes of glutamate-286 from cytochrome bo3.

Heme-copper oxidases have two putative proton channels, the so-called K-channel and the membrane-spanning D-channel. The latter contains a number of polar groups with glutamate-286 located in its center, which could-together with bound water-contribute to a transmembrane hydrogen-bonded network. Protonation states of carboxyl groups from cytochrome bo3 of Escherichia coli were studied by redox Fourier transform infrared (FTIR) difference spectroscopy. A net absorbance increase in the carboxyl region was observed upon reduction. The band signature typically found in heme-copper oxidases comprises an absorbance decrease (reduced-minus-oxidized difference spectra) at 1745 cm-1 and increase at 1735 cm-1. No significant changes in the carboxyl region were found in the site-specific mutants D135E and D407N. The difference bands were lacking in redox spectra of mutants at position 286; they could clearly be related to Glu-286. In wild-type oxidase, the pK of Glu-286 appears to be higher than 9.8. Upon solvent isotope exchange from H2O to D2O, the band at 1745 cm-1 shifts more readily than the one at 1735 cm-1, indicating dissimilar accessibility of the carboxyl side chain to the hydrogen-bonded network in both redox states. The data are consistent with a redox-triggered conformational change of Glu-286, which attributes to the carboxyl group an orientation toward the interior of the D-channel for the oxidized form. The change of Glu-286 is retained in cyanide complexes of cytochrome bo3 and of cytochrome c oxidase; therefore it should be related to oxidoreduction of the heme b and/or CuB metal centers.

The relationship between peptide structure and transport across epithelial cell monolayers

The successful development of orally bioavailable peptides and peptide-like substances as therapeutic agents will require an understanding of how structure influences absorption across the intestinal mucosa. In an attempt to define such relationships, homologous series of peptides were prepared which varied in lipophilicity, chain length and number of polar functionalities, and permeability studies conducted across Caco-2 cell monolayers as a model of the intestinal mucosa. The results suggested that the number of polar groups in the peptide, which presumably require desolvation before transfer of the peptide into the cell membrane, was a principal determinant of transport. Consistent with this hypothesis, two experimental methods of determining desolvation potential were found to correlate well with the observed permeability results for the peptides. The insights gained from these studies were used in an attempt to rationally modify a renin inhibitory peptide, in order to improve its permeability across the intestinal mucosa. Based on the results of this work, it is argued that a peptide must possess a delicate balance of affinity for the aqueous-membrane interface and a reasonably low desolvation energy in order for it to efficiently cross an epithelial cell membrane.

Network Formation by Association of Polar Groups in Elastomers

Abstract If an elastomer containing polar groups forms interchain associations, can we observe them independently from the effect of chain entanglement? Polyethylacrylate and polyepichlorohydrin are polar elastomers. Our previous deformational study indicated that these elastomers contain interchain associations, which are stronger than the physical entanglements. The conclusion was based on the results of large, unidirectional extension and small simple shear measurements. On the other hand, butadiene—acrylonitrile copolymer (NBR) containing 33% acrylonitrile did not indicate a presence of such a strong interchain association. In this work, we examined NBRs containing 40% acrylonitrile. The polar association, though weak, was detected with these elastomers. This indicates that the effective association involves a number of polar groups closely placed along the polymer chain. Also, in this work, nonpolar elastomers, SBRs, were chemically crosslinked and used as models. The polar association turned out to be not as strong as the chemical crosslinks. This indicates that the polar association disengage and reengage during the deformation.

Fragmentation of the unsubstituted carbohydrate units of cardenolide monosides

In the mass spectra of unsubstituted monosides of cardenolide nature are observed the M+ peaks, and also, in each case, three characteristic processes of the fragmentation of the carbohydrate unit. The formation of the ions AglOCH=OH+ is the most universal property of these compounds. The stability of ions of the type under consideration depends on the nature and position of attachment of the sugar residue and on the number of polar groups in the aglycone. The laws of the fragmentation of the carbohydrate unit are extended to the spectra of glycosides of other classes.

The effect of chemical structure of derivatives of 1,1‐bis(4‐hydroxyphenyl)‐2,2‐propane on the antiplasticization of polycarbonate

AbstractThe antiplasticizing effect of ester derivatives of bisphenol A: 1,1‐bis(4‐hydroxyphenyl)‐2,2‐propane diacetate (DAPP), 1,1‐bis(4‐hydroxy‐3,5‐dichlorophenyl)‐2,2‐propane diacetate (DACPP), 1,1‐bis(4‐hydroxy‐3,5‐dibromophenyl)‐2,2‐propane diacetate (DABPP), 1,1‐bis(4‐hydroxy‐3,5‐dichlorophenyl)‐2,2‐propane dibenzoate (DBCPP), 1,1‐bis(4‐hydroxy‐3,5‐dichlorophenyl)‐2,2‐propane di‐2,4‐dichlorobenzoate (DCBCPP) on polycarbonate was investigated. Obtained results indicate that antiplasticizing abilities of these compounds depend on the number of polar groups in the molecule, as well as on the possibility of tight filling the free volume by the molecules in polymer–antiplasticizer system.

The effect of polar groups on the dielectric loss of polyethylene

AbstractThe dielectric loss tangent for polyethylene with low dielectric loss was approximated by tan δ = Cf Σ(nμ2), where n and μ are the number and dipole moment of polar groups, respectively, and Cf is a parameter. The type and number of polar groups in the polyethylenes were mainly determined from infrared spectra obtained with a Fourier transform spectrometer. It was found that the contribution of hydroxyl and carbonyl groups to tan δ was significantly large, but the contribution of double bond groups was less significant. The tan δ was observed to decrease with a decrease of methyl group density although the overall contribution of methyl groups to tan δ was small. This suggests that tan δ is closely related to the secondary structure of polyethylenes, thus indicating the methyl groups seem to play an important role in the secondary structure.

The Effect of Poly(oxyethylene) Alkyl Ethers, Alkanediols, and Alkanols on the Critical Micelle Concentration of Sodium Dodecyl Sulfate

Abstract The effect of the addition of the homologues of poly(oxyethylene) alkyl ethers (CmH2m+1(OCH2CH2)nOH: m=3–6, n=1–4), α,ω-alkanediols (m=4–6,8), and 1-alkanols (m=2–7) on the critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS) was examined. The homologous additives are appropriate for studying the effect of polar groups as well as an alkyl group. The CMC decreases with an increase in the concentration of additive. The rate of CMC-decrease estimated at the infinite dilution of the additive increases with the length of alkyl chain in each homologue. The dependence of the rate on the alkyl chain length is the same for all the homologues with longer chain (m≥4 for ethers and alkanols, and m>6 for alkanediols). This is ascribed to the complete transfer of the long alkyl chain into the interior of micelles. The dependence of rate on the number of polar groups (OH, OCH2CH2) is as follows. The rate for alkanediol is lower than that for alkanol with a given alkyl chain. The rate for ethers increases asymptotically with the length of oxyethylene chain. The result for alkanediol is ascribed to the pronounced hydrophilic nature, and that for ethers to the reduction of electrostatic repulsive force between ionic head groups of the surfactant in micelles.

The Dependence of Dielectric Properties on Crosslink Density of Rubbers

Abstract The dielectric properties of natural rubber, synthetic polyisoprene, andpolybutadiene samples crosslinked with sulfur and of natural rubber samplescrosslinked simultaneously with sulfur and dicumyl peroxide were studied. Inthe investigated systems, the number of polar groups in unit volume and thecrosslink density may be changed independently over relatively wide ranges.The measurements were performed in the frequency range from 101 to 105 Hzat various temperatures, and macroscopic parameters describing the dielectricproperties of the samples were evaluated. The position and intensity of thedielectric dispersion peak in the main transition zone is only slightly dependenton the crosslink density of the samples. These two values are mainly influencedby the amount of combined sulfur, or more generally, by the number and thedipole moments of polar groups in the sample. The influence of crosslink densityon the width of the absorption curve is very strong; the width increases withincreasing crosslink density. The possibility of explaining this effect in termsof the dependence of the free volume distribution function on crosslink densityis discussed.

Grafting on polyester fibers

Acrylic acid (AA) and acrylonitrile (AN) were used to carry out grafting on polyester (PE) fibers using the techniques of initiation by γ-radiation as well as benzoyl peroxide. The nature of the grafted fiber substance was found to be the same, irrespective of the grafting technique. Extent of grafting depended upon the time, concentration of the initiator, and the monomer as well as on the irradiation dose. The increase in the moisture regain was directly proportional to the amount of graft in the fiber. AA grafted fibers were rendered more hydrophilic than AN grafted fibers for equivalent amount of grafts. Considerable improvement in dyeability of the PE fibers was possible through grafting. About 50% to 100% improvement with disperse dyes was observed in case of PE fibers containing 22.4% and 9.0% graft of AA and AN, respectively. Intense fast dyeing with direct and basic (cationic) dyes was also possible, and the dye content was proportional to the extent of graft introduced in the fiber. The CN groups were reduced to NH2 groups in the AN graft on the fiber. In this way, deep, fast, and bright dyeing was obtained with reactive dyes. Electrokinetic studies were carried out on the grafted fibers. With the increased amount of AA graft, the maxima in the zeta potential curve shifted toward higher acidic pH as greater amounts of alkali was utilized by the COOH groups in the graft. In this respect, CN groups were less sensitive due to their lesser polarity as compared to the carboxylic groups. It was observed from surface charge density (S.C.D.) studies that the effective surface area of the fiber decreased with the increase in the amount of graft, particularly in case of AN graft. Surface conductivity (S.C.) studies revealed that with increase in the number of polar groups (COOH) on the surface of the fiber, the S.C. increased with the increase in the amount of AA graft. In case of AN grafts, the reduction in effective surface area of the fiber played a more important role than the contribution by the CN groups to surface conductivity.

The dependence of dielectric properties on crosslinking density of rubbers

AbstractThe dielectric properties of natural rubber, synthetic polyisoprene, and polybutadiene samples crosslinked with sulfur and of natural rubber samples crosslinked simultaneously with sulfur and dicumyl peroxide were studied. In the investigated systems, the number of polar groups in unit volume and the crosslinking density may be changed independently in relatively wide ranges. The measurements were performed in the frequency range from 101 to 105 Hz at various temperatures, and macroscopic parameters describing the dielectric properties of the samples were evaluated. The position and intensity of the dielectric dispersion peak in the main transition zone is only slightly dependent on the crosslinking density of the samples. These two values are mainly influenced by the amount of combined sulfur, or more generally, by the number and the dipole moments of polar groups in the sample. The influence of crosslinking density on the width of the absorption curve is very strong; the width increases with increasing crosslinking density. The possibility of explaining this effect in terms of the dependence of the free volume distribution function on crosslinking density is discussed.

Steroid-protein XIX. Complex formation between α1-acid steroid hormones

Interaction of cortexone, corticosterone, cortisol, testosterone and estradiol with α 1-acid glycoprotein (orosomucoid) was investigated at 4° and 37°. The binding affinity of these steroids to α 1-acid glycoprotein was found to follow the polarity rule in that the steroid with the least number of polar groups was bound most firmly. In analogy to previous results with progesterone, cortexone, corticosterone, cortisol and testosterone associated with α 1-acid glycoprotein at a single primary binding site. The apparent association constants were determined. Estradiol interacted at several binding sites; as many as 7 and 3 were observed at 4° and 37°, respectively. The low solubility of the steroids studied did not permit a general analysis of secondary binding sites although their presence was suggested by the experimental data. In the case of the more soluble cortisol at 37°, approx. 30 secondary binding sites were indicated, with an apparent association constant several hundred times smaller than that of the primary binding site. The changes of free energy, ΔF°, and of enthalpy, ΔH°, for all complexes were found to be negative. The entropy changes, ΔS°, were positive in every case. Corticosterone and testosterone competed with progesterone for the single binding site, whereas estradiol did not show competition. This finding is in agreement with the assumption that the Δ 4-3-keto grouping is involved in the interaction with α 1-acid glycoprotein.

SOME PROPERTIES OF TASTE RECEPTORS IN FRESHWATER FISH: RESPONSES TO WEAK SOLUTIONS.

1. Gustatory stimulatory characteristics of various salts and several nonelectrolytes were studied in the carp by recording integrated electrical responses from the whole palatine nerve supplying the taste receptors on the palatal organ.2. In low concentration, the chemoreceptors do not display a sensitivity which shifts progressively with progressive variation in salt concentration. The same is true of the response to most non-electrolytes. Salt solutions in medium concentration were found to depress rather than to stimulate chemoreceptor activity. The degree of depression varied according to the kind of salt. The inhibitory phenomenon of chemoreceptor activity was noted with. non-electrolytes as well. For salts, the greatest stimulating effectiveness was at concentrations specific to a given salt.3. Comparison of the response-concentration curves for various salts revealed that the difference in stimulating effectiveness of a salt over wide concentration range probably depends on the anion rathr than the cation.4. Stimulatory characteristics of several non-electrolytes containing different numbers of polar groups in their molecules were compared.5. Application of distilled water following previous adaptation to the salt solution at the concentration where chemoreceptor activity was depressed elicited a remarkable stimulatory response (“distilled water effect”). No such effect was observed as long as the receptors were responsive to the salt solution previously applied. A similar effect was observed with non-electrolytes. The mechanism involved in the distilled water effect is discussed.

Sulfhydryls—a new factor in frost resistance. I. Changes in SH content during frost hardening

It has been known for some time (6), that there are at least two distinct factors in frost hardinessA: cell sap concentration or sugar content, and B: physicochemical properties of protoplasm. The first must be in some way associated with enzyme activity, since it results from either a starch-sugar conversion or an accumulation of photosynthate in the form of sugar. The second seems to be dependent on protein hydration. Enzyme activation is in many cases associated with SH, and protein hydration depends on the number of polar groups and therefore perhaps on SH. These facts led to the hypothesis that SH might be quantitatively related to frost hardiness, and to the following investigation of that hypothesis. Although there is no record in the literature of an investigation of the relation of SH to frost hardiness there is one report of a relation to drought resistance (4). Since frost hardiness is usually correlated witlh drought hardiness (6), this might be considered as evidence in favor of a relationship between SH and frost hardiness. Unfortunately, no attempt was inade to measure the drought resistance of the several strains of loblolly pine used other than to accept the order well established by field experiment. The only attempt to measure desiccation resistance in the laboratory failed to yield any relationship to the field determined resistance. This agrees with Parker (7), who could not detect any better ability of the more drought resistance coniferous species to recover from a low leaf moisture than in the case of the less drought resistant species. There was, however, a greater ability to retain a high moisture content. In other words, the available evidence indicates that the drought resistance involved in the above investigation was avoidance rather than tolerance and therefore unrelated to frost resistance.

Adhesion Phenomena in the Bonding of Rubber to Metal by Means of Lei˘konat Bonding Agent. 2. Unfilled Vulcanized Rubber

Abstract 1. The bond strength of vulcanized rubber to metal brought about by means of a bonding agent film is regulated by the ratio of the intensities of interaction of the bonding agent film with the contacting surfaces at the bonding agent- rubber and bonding agent-metal interfaces. Where these are approximately equal the bond strength is greatest. Where they differ sharply the bond strength decreases. 2. One of the factors influencing the intensity of interaction of a bonding agent film with vulcanized rubber is a reduction in the thickness of the bonding agent film ; with reduction in the thickness of the bonding agent film the intensity of interaction of the bonding agent with the vulcanized rubber falls; this is expressed in varying ways in the bond strength to metal of vulcanizates of various rubbers, causing a fall-off in some cases, and in some other cases a certain increase in the bond strength of the vulcanized rubber to the metal. 3. By means of the Lei˘konat bonding agent it is possible to bond unfilled vulcanizates based on the majority of existing polymers, whether polar or non-polar, to metal sufficiently strongly. 4. It is established that on increasing the number of polar groups in the polymer there is an increase in the intensity of interaction of the bonding agent film with the vulcanizate containing that rubber.