THE VAPOUR PRESSURES OF AQUEOUS SOLUTIONS WITH SPECIAL REFERENCE TO THE PROBLEM OF THE STATE OF WATER IN BIOLOGICAL FLUIDS

Data for the depression of vapour pressure are presented for the following aqueous solutions: NaCl (0.03 to 0.1 molar), KCl (0.03 to 0.1 molar), urea (0.05 to 0.5 molar), sucrose (0.05 to 0.10 molar), lactic and succinic acids, creatine, CaCl₂ (0.05 molar), and mixtures of these substances with one another and with certain other solutions (gelatin, gum acacia, sea water, LiCl, etc.). The relation of the depression of vapour pressure of a mixed solution to that of solutions of the individual constituents was investigated in order to ascertain to what extent such studies may be used for the determination of the degree of hydration, or of the state of water, in solutions. Organic substances (urea, sucrose, etc.) showed anomalous results which were markedly affected and unpredictable in mixed solutions. They are, therefore, unsuited for the study of water binding. In the case of solutions of inorganic substances—LiCl and CaCl₂—the principle of the additive nature of colligative properties is also only approximately true—except perhaps in very dilute solutions. The limitations of the colligative method for determining the degree of hydration have been defined in accord with the above findings. Studies of the vapour pressures of mixtures of gelatin or gum acacia with NaCl or KCl demonstrated that hydration in gelatin is relatively small at pH = 7 and undetectable in gum acacia solutions. The view, therefore, that hydrophilic colloids are strongly hydrated has not been substantiated. The passage from the sol to the gel state also was not accompanied in gelatin or in blood by any appreciable change in the degree of hydration of the hydrophilic colloids present in these substances.     

Characterization and application of a new aqueous two phase system based on gum acacia (ex.Acacia senegal), a naturally occuring polysaccharide,and polyethylene glycol

Summary Gum acacia has been used with polyethylene glycol to form a two phase aqueous polymeric system. The system followed Newtonian fluid behaviour and the acacia rich phase supported a high concentration of protein (>1.3 mg/ml) in solution. The data on partitioning of various proteins in this system indicates that it can be used for selective separation of a particular protein from a protein mixture.     

Factors Affecting the Activity of Phenolic Disinfectants

Low challenge phenol coefficient and high challenge use-dilution tests were made on a neutral cocoanut oil soap emulsion of o-phenylphenol and aqueous solutions of sodium o-phenylphenate prepared in the laboratory from the phenol using a stoichiometric amount of NaOH as well as with increasing amounts of excess NaOH. The phenol had considerably greater activity in both test methods when emulsified with the neutral soap than when converted to the phenate and dissolved in water. Use dilution test results against Salmonella choleraesuis with both the phenol and the phenate were within the range which would have been predicted from the Salmonella typhosa coefficient results employing the conventional conversion multiple of 20 to determine the maximal number of parts of water to which one part of germicide could be added. With the emulsified phenol this was also true where Staphylococcus aureus was employed in both procedures. With the aqueous solution of the phenate the maximal safe use-dilution by the phenol coefficient found for S. aureus and the same conventional conversion procedure was roughly five times higher than the maximal safe use-dilution found by the use-dilution method. Results with aqueous solutions of the phenate to which increasing amounts of excess NaOH were added showed no significant differences in the phenol coefficient method with either S. typhosa or S. aureus. In the use-dilution method, significant decreases in activity were found as the excess NaOH was increased to 4% with both S. choleraesuis and S. aureus. Although the pH values of aqueous solutions of the phenate were raised as the amount of free NaOH was increased, the decreases in pH observed as the dilution with water was increased were such that only small differences existed at the high critical killing dilutions found in the low challenge phenol coefficient method, whereas rather large differences existed at the lower critical killing dilutions in the high challenge use-dilution method.     

In situ measurement of plant water potentials by equilibration with microdroplets of polyethylene glycol 8000

Microdroplets (3-5 nanoliters) of polyethylene glycol 8000 solution were allowed to equilibrate with plant water potential by placing the microdroplet on an abraded surface and covering it with mineral oil to prevent evaporation. Osmolality was followed by cryoscopic measurements, accurate to about ±0.1 bar, on subnanoliter samples.

Under constant environmental conditions, apparent equilibrium between microdroplet and plant water potentials was attained in about 1 to 2 hours. Microdroplet osmolality responded promptly to treatments (illumination, excision, osmotica) which changed plant water status. The values obtained for plant water potentials appeared to be physiologically reasonable. However, comparison with values obtained by other means (dewpoint hygrometry, treatment of tissue with polyethylene glycol solutions, calculation from turgor and osmotic pressures) suggest that they might be somewhat more negative than the actual tissue water potential.

Aside from the advantage of providing in situ measurements of plant water status, the method is not temperature sensitive and requires only about 10 square millimeters of surface area, which allows its use on even small structures with little interference by shading or with gas exchange.

     

A Physiological Approach to Perfusion-Flxation of Tissues with Formalin

A method of perfusion-fixation with formalin is here presented which is based upon well established physiological principles. It represents an attempt to preserve more accurately the structure and relationships of nervous tissue found in the living state. The essential points include the following: (1) Perfusion at an hydrostatic pressure equivalent to the mean arterial pressure of the animal to be fixed to maintain the normal patency of the vascular bed. For the guinea pig, it is approximately 70 mm. Hg; for the cat and monkey, it is approximately 120 mm. Hg. (2) The addition of a colloid to the perfusion fluid which will exert an osmotic pressure equal to the hydrostatic pressure in the capillaries and thus prevent edema. Gum acacia is used in this method. Its concentration depends upon the hydrostatic pressure to be used: for 70 mm. Hg, in the guinea pig it is 2.4%; for 122 mm. Hg, in the cat and the monkey, it is 5.6% gum acacia. (3) The addition of an electrolyte to the perfusion fluid to make it isotonic to the tissue fluid and thus prevent a disturbance in the distribution of water in the animal with resultant tissue distortion. NaCl (0.9%) is used in this method. (4) For further fixation or for preservation of the tissues, they are placed in a solution of 10% formalin which contains 0.9% NaCl to minimize swelling.     

Physical Properties and Chemical Composition of β-Glucans from Fleshy Fungi

Physical properties and chemical structure of two related polysaccharides produced fermentatively by Plectania occidentalis NRRL 3137 and by Helotium sp. NRRL 3129 were studied. Both polymers were readily recovered as amorphous gels by precipitation from culture liquors with two parts of ethyl alcohol or methanol. Dried polymeric material was redissolved in water with agitation to give uniform aqueous solutions up to about 1.5% by weight. The polymers were similar in physical properties but possessed different chemical structures. The viscosity of aqueous solutions of each polymer varied from about 50 centipoises at 0.1% to approximately 2,200 centipoises at 1.4% concentrations by weight. Highly viscous solutions at concentrations of 1% or greater behaved like thixotropic gels. Mono-, di-, and trivalent salts, except borate, did not affect viscosity of either polymer. The viscosities were slightly increased by the addition of borate. Autoclaving did not alter the physical properties of neutral polymer solutions. The polymers were stable in acid or alkaline solutions at moderate temperatures but degraded under extremes of pH at 70 C or above. Each polymer had a specific rotation of +20° in aqueous dimethylformamide (1:1). The results of acid hydrolysis and periodate oxidation, in conjunction with paper and gas chromatography, indicate that both polymers are branched glucans containing appreciable amounts of β-1,3 linkages.     

Ethephon-Induced Gummosis in Sour Cherry (Prunus cerasus L.) : I. Effect on Xylem Function and Shoot Water Status

Ethephon, (2-chloroethyl)phosphonic acid, was sprayed at concentrations up to 69.2 millimolar to enhance gum formation in 1-year-old shoots of mature Prunus cerasus L. cv Montmorency trees. Gum accumulation caused rupturing of the shoot periderm, followed by gum extrusion. Lower ethephon concentrations were required to induce gum formation in spring and early summer (1.7-3.5 millimolar) then in late summer and fall (13.8-69.2 millimolar). The number of functional vessels, shoot hydraulic conductance, and water potential of both leaf and internode tissue decreased as gum content of shoots increased. Nontreated control shoots also contained small quantities of gum. There was no difference in neutral sugar composition of gum exuded by the tree, obtained from aqueous shoot extracts, or flushed from the vessels of shoots, whether induced by ethephon or not. Severe decrease in shoot and leaf water potential was associated with shoot die-back. Recovery of xylem function may occur where gummosis is less severe. Discrepancy between measured and predicted hydraulic conductance increased as shoot gum content increased, suggesting that decrease in number of functional vessels alone was not sufficient to explain the effects of gum on loss of shoot hydraulic conductance. Increased gum content in those vessels remaining functional would increase vessel sap viscosity and further reduce hydraulic conductance. The viscosities necessary to account for discrepancy between measured and predicted hydraulic conductance were calculated. Gum concentration less than 1.0% (w/v) would produce these viscosities.     

Dielectric studies on water in solutions of purified lecithin vesicles

The complex permittivity of sonicated aqueous solutions of purified dimyristoylphosphatidylcholine has been measured as a function of frequency between 3 kHz and 40 GHz. The dielectric spectrum of the samples shows two dispersion/absorption regions, one centered at about 80 MHz the other at about 20.GHz (30°C). Otherwise than in previous studies no additional dispersion/absorption process has been found at frequencies below 10 MHz.The complex dielectric spectrum of the samples is discussed with respect to the dynamical state of solvent water in solutions of single-bilayer vesicles. The main relaxation time of the solvent water, τ₁ ((2πτ₁)^?1 ≈ 20 GHz), is smaller than that of pure water, τ_W, at the same temperature. This effect results from the action of internal depolarizing fields which obviously overcompensate and enhancement of τ₁ due to specific solute/solvent interactions (hydration) as had been previously found with micellar solutions of lysolecithins.It cannot be excluded, that some solvent water shows unusual dynamical behaviour. If there exists a substantial amount of such motionally perturbed water, however, it must be characterized by a relaxation time close to that of the phosphorylcholine zwitterions, τ₂ ((2πτ₂)^?1 ≈ 80 MHz).     

Flow injection analysis-based methodology for automatic on-line monitoring and quality control for biodiesel production

An automated on-line approach based on determination of free and bound glycerol was here proposed to monitor biodiesel production. The method was based on liquid-liquid extraction of glycerol from the biodiesel to an aqueous ethanolic phase in which glycerol is oxidized to formaldehyde with meta periodate with subsequent reaction with acetylacetone. The reaction product was photometrically measured at 410 nm. Free and bound glycerol were differentiated by glycerides hydrolysis with potassium ethylate. The experimental set-up consisted of a flow-injection manifold for liquid-liquid extraction without phase separation and iterative change of the flow direction that enabled: (a) filling the flow manifold with a meta periodate-acetylacetone acceptor phase; (b) sampling of small amounts (microl) from the reactor; (c) determination of free glycerol by extraction from biodiesel to the aqueous phase with simultaneous oxidation-reaction with acetylacetone in the acceptor phase; (d) continuous monitoring of the aqueous phase by passage through a photometric detector; (e) filling the flow manifold with a potassium ethylate-meta periodate-acetylacetone new acceptor phase; (d) repetition of steps b-to-d to determine total glycerol after saponification of the bound glycerol by potassium ethylate; and (f) determination of bound glycerol by difference between the second and first analyses. The results showed that the proposed automated on-line method is a suitable option in routine analysis during biodiesel production.     

THE INFLUENCE OF ALCOHOL UPON THE GROWTH OF SEEDLINGS

In this paper it is shown that if the dry seeds of the cantaloupe (Cucumis melo) are soaked for 3 hours in solutions of ethyl alcohol of concentration ranging from 2 to 16 per cent by volume, and then germinated and grown in distilled water in the dark, the total growth attained is greater by amounts ranging from 9 to 35 per cent than is that made by seeds treated in every way identically except that they are initially soaked in distilled water instead of alcohol. It is shown that this result is not due simply to differences in osmotic pressure in the different alcohol solutions. It is probably due to a simple selective action of the alcohol which eliminates the constitutionally weak and defective seeds.     

DNA binding studies of PdCl<Subscript>2</Subscript>(LL)(LL = chelating diamine ligand: N,N-dimethyltrimethylenediamine) complex

The interaction of native calf thymus DNA with the Pd(II) complex, PdCl2(LL) (LL = chelating diamine ligand: N,N-dimethyltrimethylenediamine), in 10 mM Hepes aqueous solutions at neutral pH has been monitored as a function of metal complex/DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD), viscosimetry, and fluorescence spectroscopy. The results support two modes of interaction. In particular, this complex showed absorption hypochromism and then hyperchromism, increase in melting temperature, and some structural changes in specific viscosity when bound to calf thymus DNA. The binding constant determined using absorption measurement is 2.69.10(3) M(-1). As evidenced by the increasing fluorescence of methylene blue-DNA solutions in the presence of increasing amounts of metal complex, PdCl(2)(LL) is able to displace the methylene blue intercalated into DNA, but not so completely, as indicated by partial intercalation. CD spectral changes in two steps and viscosity decrease confirm our conclusions.     

INFLUENCE OF A SLIGHT MODIFICATION OF THE COLLODION MEMBRANE ON THE SIGN OF THE ELECTRIFICATION OF WATER

1. It is shown that collodion membranes which have received one treatment with a 1 per cent gelatin solution show for a long time (if not permanently) afterwards a different osmotic behavior from collodion membranes not treated with gelatin. This difference shows itself only towards solutions of those electrolytes which have a tendency to induce a negative electrification of the water particles diffusing through the membrane, namely solutions of acids, acid salts, and of salts with trivalent and tetravalent cations; while the osmotic behavior of the two types of membranes towards solutions of salts and alkalies, which induce a positive electrification of the water particles diffusing through the membrane, is the same. 2. When we separate solutions of salts with trivalent cation, e.g. LaCl₃ or AlCl₃, from pure water by a collodion membrane treated with gelatin, water diffuses rapidly into the solution; while no water diffuses into the solution when the collodion membrane has received no gelatin treatment. 3. When we separate solutions of acid from pure water by a membrane previously treated with gelatin, negative osmosis occurs; i.e., practically no water can diffuse into the solution, while the molecules of solution and some water diffuse out. When we separate solutions of acid from pure water by collodion membranes not treated with gelatin, positive osmosis will occur; i.e., water will diffuse rapidly into the solution and the more rapidly the higher the valency of the anion. 4. These differences occur only in that range of concentrations of electrolytes inside of which the forces determining the rate of diffusion of water through the membrane are predominantly electrical; i.e., in concentrations from 0 to about M/16. For higher concentrations of the same electrolytes, where the forces determining the rate of diffusion are molecular, the osmotic behavior of the two types of membranes is essentially the same. 5. The differences in the osmotic behavior of the two types of membranes are not due to differences in the permeability of the membranes for solutes since it is shown that acids diffuse with the same rate through both kinds of membranes. 6. It is shown that the differences in the osmotic behavior of the two types of collodion membranes towards solutions of acids and of salts with trivalent cation are due to the fact that in the presence of these electrolytes water diffuses in the form of negatively charged particles through the membranes previously treated with gelatin, and in the form of positively charged particles through collodion membranes not treated with gelatin. 7. A treatment of the collodion membranes with casein, egg albumin, blood albumin, or edestin affects the behavior of the membrane towards salts with trivalent or tetravalent cations and towards acids in the same way as does a treatment with gelatin; while a treatment of the membranes with peptone prepared from egg albumin, with alanine, or with starch has no such effect.     

The Importance of Acacia Trees for Insectivorous Bats and Arthropods in the Arava Desert

Anthropogenic habitat modification often has a profound negative impact on the flora and fauna of an ecosystem. In parts of the Middle East, ephemeral rivers (wadis) are characterised by stands of acacia trees. Green, flourishing assemblages of these trees are in decline in several countries, most likely due to human-induced water stress and habitat changes. We examined the importance of healthy acacia stands for bats and their arthropod prey in comparison to other natural and artificial habitats available in the Arava desert of Israel. We assessed bat activity and species richness through acoustic monitoring for entire nights and concurrently collected arthropods using light and pit traps. Dense green stands of acacia trees were the most important natural desert habitat for insectivorous bats. Irrigated gardens and parks in villages and fields of date palms had high arthropod levels but only village sites rivalled acacia trees in bat activity level. We confirmed up to 13 bat species around a single patch of acacia trees; one of the richest sites in any natural desert habitat in Israel. Some bat species utilised artificial sites; others were found almost exclusively in natural habitats. Two rare species (Barbastella leucomelas and Nycteris thebaica) were identified solely around acacia trees. We provide strong evidence that acacia trees are of unique importance to the community of insectivorous desert-dwelling bats, and that the health of the trees is crucial to their value as a foraging resource. Consequently, conservation efforts for acacia habitats, and in particular for the green more densely packed stands of trees, need to increase to protect this vital habitat for an entire community of protected bats.     

THE PHAGOCYTOSIS OF SOLID PARTICLES : IV. CARBON AND QUARTZ IN SOLUTIONS OF VARYING ACIDITY.

1. Leucocytes ingest quartz particles more readily than carbon in acid solutions, and carbon more readily than quartz in alkaline solutions. 2. In the presence of acacia carbon is always preferred to quartz even in acid solutions. 3. Manganese dioxide particles are ingested by leucocytes with extraordinary rapidity as compared with manganese silicate or quartz. 4. Leucocytes are not attracted toward carbon or quartz particles but manganese dioxide exerts a distinct attraction for them. 5. Spores of Penicillium are ingested more readily than quartz. 6. Very small quartz particles, 1 micron in diameter, are not ingested as readily as larger particles of the same material. This result being contrary to the predictions of surface tension indicates that some other factor is involved in the ingestion of these small particles. 7. Measurements of the carbon electrode potentials and the cataphoretic charges on the particles have failed to supply an explanation for the varying relative rates of ingestion of carbon and quartz with varying hydrogen ion concentration.     

Membrane proteins in reverse micelles: myelin basic protein in a membrane-mimetic environment

The solubility, reactivity, and conformational dynamics of myelin basic protein (MBP) from bovine brain were studied in reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-isooctane and water. Such a membrane-mimetic system resembles the aqueous spaces of native myelin sheath in terms of physicochemical properties as reflected in the high affinity of MBP for interfacial bound water. This is marked by the unusual profile of the solubility curve of the protein in reverse micelles, which shows optimal solubility at a much lower molar ratio of water to surfactant ([ H2O]/[AOT] = w0) than that reported for other water-soluble proteins. The role of counterions and/or charged polar head groups in the solubilization process is revealed by comparison of the solubility of MBP in nonionic surfactant micellar solutions. Whereas MBP is unfolded in aqueous solutions, insertion into reverse micelles generates a more folded structure, characterized by the presence of 20% alpha-helix. This conformation is unaffected by variations in the water content of the system (in the 2.0-22.4 w0 range). The reactivity of epsilon-amino groups of lysine residues with aqueous solutions of o-phthalaldehyde demonstrates that segments of the peptide chain are accessible to water. Similar results were obtained with the sequence involved in heme binding. In contrast, the sole tryptophan residue, Trp-117, is shielded from the aqueous solvent, as indicated by lack of reaction with N-bromosuccinimide. The invariance of the wavelength maximum emission in the fluorescence spectra as a function of w0 is consistent with this result.(ABSTRACT TRUNCATED AT 250 WORDS)     

Water binding by glycogen molecules

Low temperature NMR spectra have been obtained of the water bound to glycogen. These data have allowed the evaluation of the amount of water bound and the energy and entropy associated with this bonding. High molecular weight glycogen (approx. 1·10⁹) exhibits water binding properties analogous to those previously found for other glycoproteins. Low molecular weight glycogen (approx. 1 · 10⁷), however, shows anomalous binding characteistics, with large amounts of associated “non-freezing” water. These findings are discussed in terms of previously proposed molecular architecture.     

EPR-Spin Trapping and Flow Cytometric Studies of Free Radicals Generated Using Cold Atmospheric Argon Plasma and X-Ray Irradiation in Aqueous Solutions and Intracellular Milieu

Electron paramagnetic resonance (EPR)-spin trapping and flow cytometry were used to identify free radicals generated using argon-cold atmospheric plasma (Ar-CAP) in aqueous solutions and intracellularly in comparison with those generated by X-irradiation. Ar-CAP was generated using a high-voltage power supply unit with low-frequency excitation. The characteristics of Ar-CAP were estimated by vacuum UV absorption and emission spectra measurements. Hydroxyl (·OH) radicals and hydrogen (H) atoms in aqueous solutions were identified with the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M₄PO), and phenyl N-t-butylnitrone (PBN). The occurrence of Ar-CAP-induced pyrolysis was evaluated using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) in aqueous solutions of DNA constituents, sodium acetate, and L-alanine. Human lymphoma U937 cells were used to study intracellular oxidative stress using five fluorescent probes with different affinities to a number of reactive species. The analysis and quantification of EPR spectra revealed the formation of enormous amounts of ·OH radicals using Ar-CAP compared with that by X-irradiation. Very small amounts of H atoms were detected whereas nitric oxide was not found. The formation of ·OH radicals depended on the type of rare gas used and the yield correlated inversely with ionization energy in the order of krypton > argon = neon > helium. No pyrolysis radicals were detected in aqueous solutions exposed to Ar-CAP. Intracellularly, ·OH, H₂O₂, which is the recombination product of ·OH, and OCl^- were the most likely formed reactive oxygen species after exposure to Ar-CAP. Intracellularly, there was no practical evidence for the formation of NO whereas very small amounts of superoxides were formed. Despite the superiority of Ar-CAP in forming ·OH radicals, the exposure to X-rays proved more lethal. The mechanism of free radical formation in aqueous solutions and an intracellular milieu is discussed.     

THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR : XI. THE PREPARATION AND PROPERTIES OF "MEGAPERMSELECTIVE" COLLODION MEMBRANES COMBINING EXTREME IONIC SELECTIVITY WITH HIGH PERMEABILITY

1. The electronegative membranes described in the literature which show a high degree of ionic selectivity (permitting cations to pass and restricting the anions) have serious shortcomings: their absolute permeability is extremely low, much too small for convenient experimentation; their ionic selectivity in most cases is not as perfect as would be desirable, and is moreover adversely affected by prolonged contact with electrolyte solutions. 2. A method has been worked out to prepare membranes substantially free from these defects. Porous collodion membranes were cast on the outside of rotating tubes and then oxidized with 1 M NaOH. By allowing the oxidized porous membranes to dry in air on the tubes membranes of desirable properties are obtained. These membranes are smooth, have a well defined shape, and allow considerable handling without breaking. 3. This new type membrane when tested for ionic selectivity by the measurement of the "characteristic concentration potential," consistently gives potentials of 54 to 55 mv., the maximum thermodynamically possible value (at 25°C.) being 55.1 mv. This high degree of ionic selectivity is not lost on prolonged contact with water, and is only very slowly affected by electrolyte solutions. 4. The absolute permeability of the new type membranes can be varied over a very wide range by changing the time of oxidation. Under optimum conditions membranes can be obtained with a resistance in 0.1 N KCl solution of only 0.5 ohms per 50 cm.² membrane area. The absolute rate of cation exchange through these membranes between solutions of different uni-univalent electrolytes is very high, in one case, e.g. 0.9 m.eq. cations per 4 hours, the anion leak being 0.02 m.eq. Thus, the absolute permeability of the new type membranes is two to four orders of magnitude greater than the permeability of the dried collodion membranes and the oxidized ("activated") dried collodion membranes used heretofore. Because of the characteristic properties of the new type membranes the term "megapermselective" (or "permselective") collodion membranes is proposed for them.     

THE RECIPROCAL RELATION BETWEEN THE OSMOTIC PRESSURE AND THE VISCOSITY OF GELATIN SOLUTIONS

1. These experiments confirm the conclusion that protein solutions are true solutions consisting of isolated ions and molecules, and that these solutions may or may not contain in addition solid submicroscopic particles capable of occluding water. 2. The typical influence of electrolytes on the osmotic pressure of protein solutions is due to the isolated protein ions since these alone are capable of causing a Donnan equilibrium across a membrane impermeable to the protein ions but permeable to most crystalloidal ions. 3. The similar influence of electrolytes on the viscosity of protein solutions is due to the submicroscopic solid protein particles capable of occluding water since the amount of water occluded by (or the amount of swelling of) these particles is regulated by the Donnan equilibrium. 4. These ideas are supported by the fact that the more the submicroscopic solid particles contained in a protein solution or suspension are transformed into isolated ions (e.g., by keeping gelatin solution for 1 hour or more at 45°C.) the more the viscosity of the solution is diminished while the osmotic pressure is increased, and vice versa.     

Transfer free energies of peptide backbone unit from water to aqueous electrolyte solutions at 298.15 K

Transfer free energies (ΔG_tr) of amino acids from water to aqueous electrolyte solutions have been determined from the solubility measurements, as a function of salt concentration at 298.15 K under atmospheric pressure. The investigated aqueous systems contain amino acids of zwitterionic glycine peptides: glycine (Gly), diglycine (Gly₂), triglycine (Gly₃), and tetraglycine (Gly₄) and cyclic glycylglycine (c(GG)) with an electrolyte compound of potassium chloride (KCl), potassium bromide (KBr) or potassium acetate (KAc). The solubilities of glycine and diglycine in aqueous solution decrease with increasing the concentration of salts (salting-out effect), whereas those of triglycine and tetraglycine increase with increasing the concentration of salts (salting-in effect). Furthermore, salting-in effect was found in aqueous c(GG)/KBr system, while salting-out effect was observed in aqueous c(GG)/KCl or c(GG)/KAc system. The experimental results were used to estimate the transfer free energies (Δg_tr) of the peptide backbone unit (–CH₂CONH–) from water to the aqueous electrolyte solutions. We developed a new trail to determine the activity coefficients (γ) for aqueous and aqueous electrolyte solutions using an activity coefficient model, with which the total contribution of transfer free energy between solute and the solvent was calculated. We compared the difference between neglecting and using the activity coefficients term in predicting ΔG_tr. Since the transfer free energy contribution is negative, interactions between the ionic salts and the peptide backbone unit of zwitterionic glycine peptides are favorable and thus the ionic salts destabilize these amino acids. It was also found that KBr stabilizes c(GG), whereas KCl and KAc destabilize c(GG). These results provide evidence for the existence of interactions between the amide unit and ionic salts, in aqueous solution, which may be of importance in maintaining protein structure as well as in protein–solute and protein–solvent interactions.