Explanation of Ionic Sequences in Various Phenomena. I. Salting-Out of Uncharged Molecules

Abstract

Theoretical models for hydrated ions and their calculated effective dielectric constants obtained previously were used to explain the salting-in or salting-out of nonionic molecules. Three types of salting-out sequences were obtained: nonpolar (Na⁺ > K⁺ > Li⁺ Rb⁺ > Cs⁺), basic (K⁺ > Na⁺ > Rb⁺ > Cs⁺ > Li⁺), and acidic (Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺). The nonpolar sequence is not influenced by the A region of a cation, and therefore the ability to salt-out is great if the effective dielectric constant of the ion is small. The A region on hydrated Li⁺ ions (the tightly bound water) salts-in basic compounds because of the interaction of its positively charged hydrogen atoms with the negative dipolar charge of the base. Conversely, the A region of a cation salts-out acidic compounds because the hydroxyl group on carboxylic acids behaves as a similar cationic A region. A sulfonic polymer will cause the salting-in of the base p-nitroaniline because the addition of salts to an aqueous solution of the base and polymer destroys hydrogen bonds in the polymer and in so doing releases hydronium ions from the polymer. This release of H⁺, in turn, produces a positive charge on part of the p-nitroaniline molecules, which produces a salting-in effect.     

Explanation of Ionic Sequences in Various Phenomena. II. Reversal of Colloid Charge and Ion Binding

Abstract

Previous proposed models for the structure of hydrated ions and the calculated values of the effective dielectric constant of such hydrated ions were used to explain the reversal of colloid charge and ion binding phenomena. In contrast to the conclusions made by Bungenberg de Jong, it is shown that the more soluble the counter -cation or counter-anion of a colloid charge, the greater is the ability of the counterion to reverse the electrical charge of the colloid. The reversal of charge phenomenon is therefore associated with the counterions's solubility, not its insolubility. The solubility sequence is determined by whether or not the carboxylate, sulfate, or phosphate ion is positively (A regions) or negatively hydrated. The phosphate group of DNA or RNA must be associated with a base by means of ion-ion bonds in order to produce the observed reversal of charge sequence. Just as in the reversal of charge phenomenon, the ion-binding phenomenon involves the electrostatic attraction of a counterion with the polyelectrolyte rather than a binding or insolubilization of the counterion. The reverse ion-binding sequence can be obtained if one dialyzes extensively in the presence of sufficient salt before physical measurements are made. This is because the solubility of a counterion determines the true electrostatic charge of the polymer. In other words, different concentrations of salt arise in the dialysis bag when different counter-ions are added because the activity coefficient of the counterion is determined by the solubility of the ion-ion complex between the counterion and the colloid′s charged group.     

Explanation of Ionic Sequences in Various Phenomena. VI. The Formation and Destruction of Helices in Bovine Plasma Albumin in Neutral and Acidic Solutions

Abstract

The structure of bovine plasma albumin (BPA) was examined by optical rotatory dispersion studies at both low (pH 1.5 and 2.0) and high (pH 9.0) pH values in various aqueous salt solutions. The resulting cationic sequences were compared to those observed by Pedersen for values of the sedimentation constant. At pH 9.0 the destruction of the “helix” produces an acidic sequence. The relative pH position of the “helix” transition, the fact that addition of salt increases the apparent helical content of BPA, and the observed acidic-type of sequence rule out the possibility of (1)ionic bonds between carboxylate and ?-amino groups, (2) hydrophobic bonds, or (3) hydrogen bonds between peptide linkages as major contributing forces in the formation of the helix. The stability of the “helix” in BPA between pH 3.0 and 9.0 must therefore be due to hydrogen bonds between carboxylate ions and hydroxyl groups such as those of serine, threonine, and tyrosine. Repulsive forces between the positively charged groups on BPA strengthen these bonds by preventing the expanded form of BPA from collapsing. At pH 2.0 two types of sequences were observed: The s⁰ _{20, w}, [α]_D and a₀ values gave an acidic-type cationic sequence. The b₀ (helix content), λ_c and [λ]₂₃₃ values gave essentially a nonpolar sequence. The nonpolar or hydrophobic salting-out sequences show that the formation of hydrophobic bonds at pH 2.0 hinders the formation of the helix or folded structure. The acidic sequences show that hydrogen bonds between carboxylic acid groups stabilize both the apparent helix or helices and the intermolecular aggregation of the BPA molecules. From a comparison of the S⁰ ₂₀,w values and the helical content of BPA at pH 9.0 it is also concluded that the formation of these apparent helices or folded structures expands or stiffens the BPA molecule.     

Salting-Out and Salting-in Effects in the Reversed-Phase Thin-Layer Chromatography of Dansylated Amino Acids. Effect of Acids

Abstract

The retention of 15 dansylated amino acid derivatives was determined in aqueous solutions of formic, acetic, propionic and perchloric acid in reversed-phase thin-layer chromatography. The acids increased the retention of each derivatives at the low concentration range. This effect has been tentatively explained by the suppression of dissociation of polar groups in the solute molecules resulting in increased apparent lipophilicity (salting-out phenomenon). The higher concentrations of acid solutions decreased the retention (salting-in effect), the undissociated acid molecules probably act as an organic mobile phase. Both salting-in and salting-out phenomena can be simultaneously described by bilinear function. The polarity parameters of the amino acids, their hydrophobicity and the strength of the acid in the eluent simultaneously influence the retention.     

Acids in dimethylformamide. III. Ionic equilibria of dicarboxylic acids

Dissociation and homoconjugation constants of succinic, malonic, and dimethylmalonic acids have been determined potentiometrically at 25°C. Conductometric studies on the tetraethylammonium salts of the acids permitted the evaluation of the corresponding dissociation constants, which allowed a better fit of calculated curves with experimental data. Homoconjugation of two monovalent anions with a divalent anion was pointed out in all cases. No appreciable homoconjugation of the monovalent anion with the diprotic acids was found. In order to standardize the glass electrode at high paH values, the dissociation constant of diethylbarbituric acid has also been determined.     

Explanation of Ionic Sequences in Various Phenomena. IV. General Method for Determination of the Type of Bonding in Polymers; Bonds in Ovalbumin,Ribonuclease, Collagen,Hemoglobin, and Starch Determined

Abstract

The salting-out or -in of hydrocarbons, uncharged nitrogen bases, and acids containing polarized hydroxyl groups give different cationic sequences. Also various ionic groups have different solubility sequences. Such neutral or electrostatically charged groups are attached to polymers and are involved as forces which hold together aggregates or helicies in inter- or intramolecular interactions. In aqueous solutions, the addition of various salts can destroy or produce these inter- or intramolecular interactions. Consequently, by applying the ionic solubility sequences, the observed salting-in and -out sequences of low molecular weight molecules, and other solubility criteria to the destruction or formation of such polymer interactions, it is possible to determine the major force or forces which are involved in holding the aggregate or helix together. Such forces involve hydrophobic bonds, hydrogen bonds between neutral bases, hydrogen bonds involving polarized hydroxyl groups, ionic bonds, and/or repulsive forces between electrostatically charged groups. The method is applied to the salting-out of ovalbumin, the destruction of the α-helix of ribonuclease, the collagen-gelatin transformation, the dissociation of hemoglobin, and the retrogradation and solubilization of starch. These five examples involve all the secondary forces considered. The method should find wide applicability because it can be applied to any method of physical measurement involving ionic solutions.     

Ionic Liquids in Polyethylene Glycol Aqueous Solutions: Salting-in and Salting-out Effects

Changes of the fluid phase behaviour of polyethylene glycol (PEG) aqueous solutions – viz. critical solution temperature shifts at atmospheric pressure – were produced by the addition of different ionic liquids, namely 1-ethyl-3-methylimidazolium ethyl sulfate and 1-alkyl-3-methylimidazolium chloride (alkyl = ethyl to decyl). The addition of ionic liquids with long alkyl chains improves the solubility of PEG in water (salting-in effect), whereas the impact of short-chain ionic liquids is usually the contrary (salting-out effect). The results are interpreted taking into account the kosmotropic (water-structuring) or chaotropic (water-structure-breaking) nature of ionic liquids, as compared to other inorganic salts.     

Ionic Liquids in Polyethylene Glycol Aqueous Solutions: Salting-in and Salting-out Effects

Summary. Changes of the fluid phase behaviour of polyethylene glycol (PEG) aqueous solutions – viz. critical solution temperature shifts at atmospheric pressure – were produced by the addition of different ionic liquids, namely 1-ethyl-3-methylimidazolium ethyl sulfate and 1-alkyl-3-methylimidazolium chloride (alkyl = ethyl to decyl). The addition of ionic liquids with long alkyl chains improves the solubility of PEG in water (salting-in effect), whereas the impact of short-chain ionic liquids is usually the contrary (salting-out effect). The results are interpreted taking into account the kosmotropic (water-structuring) or chaotropic (water-structure-breaking) nature of ionic liquids, as compared to other inorganic salts.     

Chiral Sensing of Various Amino Acids Using Induced Circularly Polarized Luminescence from Europium(III) Complexes of Phenanthroline Dicarboxylic Acid Derivatives

Circularly polarized luminescence (CPL) was observed from [Eu(dppda)₂]^? (dppda=4,7‐diphenyl‐1,10‐phenanthroline‐2,9‐dicarboxylic acid) and [Eu(pzpda)₂]^? (pzpda=pyrazino[2,3‐f][1,10]phenanthroline‐7,10‐dicarboxylic acid) in aqueous solutions containing various amino acids. The selectivity of these complexes towards amino acids enabled them to be used as chiral sensors and their behavior was compared with that of [Eu(pda)₂]^? (pda=1,10‐phenanthroline‐2,9‐dicarboxylic acid). As these Eu^III complexes have achiral D_2d structures under ordinary conditions, there were no CPL signals in the emission assigned to f–f transitions. However, when the solutions contained particular amino acids they exhibited detectable CPL signals with g_lum values of about 0.1 (g_lum=CPL/2 TL; TL=total luminescence). On examining 13 amino acids with these three Eu^III complexes, it was found that whether an amino acid induced a detectable CPL depended on the Eu^III complex ligands. For example, when ornithine was used as a chiral agent, only [Eu(dppda)₂]^? exhibited intense CPL in aqueous solutions of 10^?2 mol dm^?3. Steep amino acid concentration dependence suggested that CPL in [Eu(dppda)₂]^? and [Eu(pzpda)₂]^? was induced by the association of four or more amino acid molecules, whereas CPL in [Eu(pda)₂]^? was induced by association of two arginine molecules.     

Exotic Amino Acids. 8. Synthesis of Monomethyl Esters of N-Arylaminomethylenemalonic Acids

N-Arylaminomethyleneisopropylidenemalonates, obtained from ethoxymethyleneisopropylidenemalonate and aromatic amines, underwent methanolysis to form monomethyl esters of N-arylaminomethylenemalonic acids. The conditions of their formation and their yields depend on the nature and positions of the substituents in the aromatic ring of the initial amine.     

Correlations Between Amino Acids at Different Sites in Local Sequences of Protein Fragments with Given Structural Patterns

Ample evidence suggests that the local structures of peptide fragments in native proteins are to some extent encoded by their local sequences. Detecting such local correlations is important but it is still an open question what would be the most appropriate method. This is partly because conventional sequence analyses treat amino acid preferences at each site of a protein sequence independently, while it is often the inter-site interactions that bring about local sequence-structure correlations. Here a new scheme is introduced to capture the correlation between amino acid preferences at different sites for different local structure types. A library of nine-residue fragments is constructed, and the fragments are divided into clusters based on their local structures. For each local structure cluster or type, chi-square tests are used to identify correlated preferences of amino acid combinations at pairs of sites. A score function is constructed including both the single site amino acid preferences and the dual-site amino acid combination preferences, which can be used to identify whether a sequence fragment would have a strong tendency to form a particular local structure in native proteins. The results show that, given a local structure pattern, dual-site amino acid combinations contain different information from single site amino acid preferences. Representative examples show that many of the statistically identified correlations agree with previously-proposed heuristic rules about local sequence-structure correlations, or are consistent with physical-chemical interactions required to stabilize particular local structures. Results also show that such dual-site correlations in the score function significantly improves the Z-score matching a sequence fragment to its native local structure relative to nonnative local structures, and certain local structure types are highly predictable from the local sequence alone if inter-site correlations are considered.     

高效液相色谱法测定羊水中兴奋性氨基酸、抑制性氨基酸的含量

建立了反相高效液相色谱法测定羊水中兴奋性氨基酸天门冬氨酸、谷氨酸,抑制性氨基酸甘氨酸含量的方法,色谱柱为LUNAC18柱(4.6mm×250mm,5μm),流动相为乙腈水(V/V),按低压梯度洗脱,梯度系统0～4min,乙腈40%;4～20min,乙腈40%～52%;20～30min,乙腈52%～60%;30～40min,乙腈60%～40%。流速0.8mL/min,柱温40℃,紫外检测波长260nm;进样量10μL。结果显示,天门冬氨酸、谷氨酸和甘氨酸三者的线性范围均为2.5～85mg/L;标准加入的回收率为99.6%～102.6%。本方法灵敏度高、测定结果可靠。用本方法对201例不同孕期的羊水作兴奋性和抑制性氨基酸检测,发现羊水中3种氨基酸随妊娠进展而增加的趋势,胎儿畸形或宫内缺氧时羊水中这3种氨基酸水平明显升高。     

Microwave-Assisted Esterification of Diverse Carboxylic Acids and Chiral Amino Acids

A facile and efficient synthetic method of esters from their corresponding carboxylic acids and amino acids is described. The esterification reaction of carboxylic acids and amino acids could be greatly accelerated under microwave irradiation because the reactions described in this article took place in only 5 min with almost quantitative yields, and distinct acidity of catalytic acids was well tolerated. Unlike the racemation problem in microwave-assisted N-acylation reactions, the esters of chiral amino acids could be achieved with retention of configuration under this condition.     

Separation and Determination of Amino Acids by CE Using 1-Butyl-3-methylimidazolium-Based Ionic Liquid as Background Electrolyte

Capillary electrophoresis using 1-butyl-3-methylimidazolium tetrafluoroborate as background electrolyte for the separation and determination of 11 amino acids was studied. Several parameters, such as ionic liquid concentration, pH of background electrolyte and applied voltage, were optimized. Amino acids were derived with Sanger’s reagent (2,4-dinitrofluorobenzene) and the detection was performed by an ultraviolet absorption detector at 360 nm. Under selected conditions, 11 amino acids were completely separated within 16 min. The RSD values of integrated areas and migration times are <3.03 and <1.64%, respectively. The electroosmotic flow can be influenced by imidazolium cation, and the association between the imidazolium cation and the derived amino acids plays an important role in the separation mechanism. This method not only provides an approach for the separation and determination of amino acids, but is also an extension of the ionic liquid application to capillary electrophoresis.     

一些土壤和有机肥中氨基酸测定方法研究

一些土壤和有机肥中氨基酸测定方法研究袁吕江，熊凤麒，王正银（西南农业大学中心实验室重庆６３０７１６）（西南农业大学土化系重庆６３０７１６）关键词液相色谱法，氨基酸，土壤，有机肥１前言我国耕作土含氮量为０．４～３．８ｇ／ｋｇ［１］，其中９０％～９８％为...     

Pattern Recognition of Amino Acids in Wines

New synthesized fatty acid amides (N‐(2‐(piperidin‐1‐yl)ethyl)oleamide, and N‐(2‐(pyrrolidin‐1‐yl)ethyl)oleamide) were used for the design of stochastic sensors based on nanographene paste. The stochastic sensors were used for pattern recognition of four amino acids: L‐histidine, L‐tyrosine, L‐ornithine, and L‐lysine in wines. The pattern recognition was performed based on the signatures recorded for each of the amino acids. The limits of determination allow the assay of amino acids in wine at very low concentrations faster, reliable, and more cost effective than other methods proposed to date.     

Complexation of a Macrocycle Containing Thiopyrimidine and Uracil Moieties with Dicarboxylic and Amino Acids in Various Organic and Aqueous Organic Solutions

The complexation of a macrocycle containing thiopyrimidine and uracil moieties (M) with amino acids and some dicarboxylic acids was studied by pH-metric, UV-VIS, ¹H NMR spectroscopy methods in chloroform, methanol, aqueous 1,4-dioxane, and biphasic water–chloroform media. The complexation of M with acids is too weak to solubilize them from the solid state into chloroform solutions containing M. The ¹H NMR spectra and pH-metric data of aqueous 1,4-dioxane (80 vol.%) reveal the pH-dependent 1:1 binding between M and the acids studied. The protonation of M is not a prerequisite for binding of fumaric, succinic, o-phtalic acids and the series of amino acids, whereas binding of maleic acid requires the protonation of both thiopyrimidine moieties of M. Therefore,M·(H⁺)₂ exhibits strong selectivity towards maleic acid in aqueous 1,4-dioxane and in biphasic water–chloroform media.