Whole Range Of Salt Concentration Research Articles

On the thermodynamic properties of hydrolysed urine: Experimental data, predictive and correlative models for the design of concentrative urine treatment technologies

Source-separated urine contains the potential for water, nutrient and energy recovery. During the recovery of such resources, urine treatment technologies undergo temporal changes in the thermodynamic properties of urine. To inform the design of thermal, membrane and electrochemical urine treatment processes, this study experimentally measured and modelled the thermophysical properties of synthetic hydrolysed urine (vapour pressure, osmotic pressure, density, and electrical conductivity) across temperature and concentration profiles using two approaches: predictive thermodynamic equations based on an ionic speciation model and correlative modelling. The vapour pressure and osmotic pressure were accurately predicted to 14 wt% for the predictive model, within an error of 0.30% and 0.46%, respectively, while the correlative model based on the experimental data from this study demonstrated an error of <1% for both parameters across the whole range of salt concentrations and temperatures (4.5 to 32.2 wt%; 333 to 373 K). The predictive and correlative models for density and electrical conductivity showed adequate agreement with the experimental data, where error did not exceed 2.12% and 1.2%, respectively, across the entire range of concentrations and temperatures.The value of the models for the development of sustainable urine treatment technologies was demonstrated by their application to determine the optimum heating surface area of a urine evaporator and the energy requirements of a reverse osmosis process.

DNA terminal base pairs have weaker hydrogen bonds especially for AT under low salt concentration.

DNA base pairs are known to open more easily at the helix terminal, a process usually called end fraying, the details of which are still poorly understood. Here, we present a mesoscopic model calculation based on available experimental data where we consider separately the terminal base pairs of a DNA duplex. Our results show an important reduction of hydrogen bond strength for terminal cytosine-guanine (CG) base pairs which is uniform over the whole range of salt concentrations, while for AT base pairs, we obtain a nearly 1/3 reduction but only at low salt concentrations. At higher salt concentrations, terminal adenine-thymine (AT) pair has almost the same hydrogen bond strength than interior bases. The calculated terminal stacking interaction parameters display some peculiarly contrasting behavior. While there is mostly no perceptible difference to internal stacking, for some cases, we observe an unusually strong dependence with salt concentration which does not appear follow any pattern or trend.

Complex formation between ovalbumin and strong polyanion PSSNa: Study of structure and properties

The mixture system of long-chain polyelectrolyte complexed with a globular protein was investigated based on dynamic light scattering and turbidimetric measurements. We have discussed at different pH values the influence of high salt concentration and mass ratio (protein:PSSNa) on the behavior of the mixture. In dilute concentration regime, the PSSNa chain contracts at pHc by patch binding. We found two critical values of mass ratio: The first corresponds to the maximum shrinking of PSSNa. The second indicates the system that became more stable where the number of proteins attached to the PSSNa chain was constant. The screen of electrostatic interaction shows a high contribution of hydrophobic interaction at large salt concentration to form the coacervates. By building phase diagram, the continuity of pHφ1 in over whole range of salt concentrations and the widening of pH window (pHφ1–pHφ2) were observed. At certain salt concentrations, we can obtain the coexistence of two types of complex particles formed by electrostatic and hydrophobic interactions.

Hydrothermal synthesis of CSH-phases (tobermorite) under influence of Ca-formate

The influence of Ca-formate (C2H2CaO4) on the crystallization of the CSH-phase 11Å tobermorite was investigated under hydrothermal conditions at 200°C in a wide CaO/SiO2 range of 0.67–1.24. Besides clarifying questions on acceleration or retarding of CSH formation at high Ca-formate contents even a study on the effect of this salt addition on the crystal morphology was a main objective of the present work. All experiments were performed using fine grained SiO2 powder (P) or coarse grained quartz sand (S) as silicate source. The reactions were followed by XRD, SEM/EDX and FTIR. Except the reaction at lowest amount of formate (0.43g), where only a very small effect on the crystallization rate was observed, higher salt concentrations were found to retard the reaction clearly. Here the reduction of the CSH-crystallization velocity and formation of tobermorite with a distinct character of the pre-phase CSH-I could be stated in each case. Its amount and crystal quality was not rigorously dependant on the inserted mass of Ca-formate in the 0.67–1.34g range investigated here.A strong influence on the morphology of the CSH-crystals was further detected already in the whole range of salt concentration, i.e. even at the low value of 0.43g, examined in our experiments. Instead of the typical rod-like morphology of tobermorite formed without Ca-formate, a disturbed bent-needle-like morphology occurred at elevated formate concentrations. In contrast small compact crystals were observed at low amounts of Ca-formate.Syntheses with quartz powder and quartz sand in principle yielded to comparable results concerning the retarding effect and the change of crystal morphology. As expected, the reaction rate of experiments with quartz sand was diminished in general, according to the lower specific surface of the sand grains, compared with the powder.A change of the pH-value with marked influence on the solubility rate of the educts and the further course of reaction can be excluded as cause for the observed behavior. Further reasons, based on crystal growth under influence of adsorption of formate ions at specific crystal faces were discussed.The improvement of knowledge on effects of additives on CSH crystallization will be of importance for future modifications of reaction processes of cement and concrete as well as steam hardened construction materials, where 11Å tobermorite acts as the main binding agent.

SALT INDUCIBLE-PROTEINS AND CONJUGAL GENE TRANSFER OF HALOTOLERANT Staphylococcus ISOLATED FROM SALINITY SOIL

Halotolerent bacteria are those that can tolerate a broad range of NaCl concentrations (0-32% w/v) (Hezayen et al., 2010). So, there are different categories of halotolerant microbes: not tolerate, those which tolerate only a small concentrations of salt about 1%, slightly tolerant (6-8%), moderately tolerant (18-22%) and extremely tolerant, those microbes that grow over the whole range of salt concentrations (0-32%) (Larsen, 1986). Recently, Parthiban et al. (2010) classified halophilic bacteria according to their salt requirement and growth pattern to slight halophiles which growth at 2-5% NaCl, moderate halophiles which growth at 5-20% NaCl and extreme halophiles which growth at 20-30% NaCl. Extreme halophiles are microorganisms that grow under hostile to most organisms. Some of them, such as bacteria which thrive in hypersaline environments have been recognized for their use in biotechnological remediation applications. The applied of halophilic bacteria include recovery of saline soil by directly supporting of growth of vegetation thus indirectly increasing crop yields in saline soil. The other application of halophilic bacteria was in food and pharmaceutical industries, production of enzymes, polymers and various cosmetic products. The possibility of application of halophilic bacteria in soil is recovery and the importance of microbial diversity in soil (Kannika, 2003). Haophilic microorganisms respond to high salt external environment by accumulating osmotic in their cytosol, which protects them from cytoplasmic dehydration. Osmophily refers to the osmotic aspects of life at high salt concentrations, especially turgor pressure, cellular dehydration and desiccation. Halophily refers to the ionic requirements for life at high salt concentrations. Halophilic microorganisms usually adopt either at the two strategies of survival in saline environments: compatible solute strategy and salt-in strategy. Compatible solute strategy is employed by the majority of moderately halophlic and halotolerant bacteria, some yeasts, algae and fungi. In this strategy, cell maintains low concentrations of salt in their cytoplasm by balancing osmotic potential through the synthesis or uptake of organic compatible solutes. Hence these microorganisms are able to adapt to a wide range of salt concentrations. The compatible solutes include polyols such as glycerol, sugars and their derivatives, amino acids and their derivatives as well as quaternary amines such as glycine betaine and ectoines. Compatible solutes display a general stabilizing effect by preventing the unfolding and denaturation of proteins caused by heating, freezing and drying (Ventosa et al., 1998). The salt-in strategy is employed by true halophilies, including halophilic archaea and extremely halophilic bacteria. These microorganisms are adapted to high salt concentrations and cannot survive when the salinity of the medium is lowered. They generally do not synthesize organic solutes to maintain the osmotic equilibrium. This adaptation involves the selective influx of K+ ions into the cytoplasm. All enzymes and structural cell components must to be adapted to high salt concentrations for proper cell function (Shivanand and Mugeraya, 2011). Extreme environments such as acidic, thermophilic, hypersaline, and arid regions, are important ‘hot spots’ of microbial ‘megadiversity’. These are habitats of microorganisms which have the genetic and physiological capacity to survive and grow under these harsh or extreme conditions (Woese, 1987; Olsen et al., 1994). Extensive studies have been made in recent years into hyper saline environments resulting in a large number of new halophilic species being isolated e.g. Oceanobacillus aswanensis, it was isolated from salted fish sauce in Aswan city, Egypt (Hezayen et al., 2010), Paenibacillus chungwensis which isolated from Marakanam salterns in India (Parthiban et al., 2010). Gram-negative halophilic (Vibrio, Alteromonas, Acinetobacter, Marinomonas and Pseudomonas) (Prado et al., 1991) and Gram positive halophilic (Staphylococcus, Marinococcus, Sporosarcina Salinococcus and Bacillus) have been recovered from saline soils, salterns and activated sludge (Farrow et al., 1992; Ajibola et al., 2005; Olukanni et al., 2006; Elisangela et al., 2009). Staphylococcus spp., Micrococcus spp. and Bacillus spp. have been isolated from sea water and tropical marine fish but little information has been reported on the species level identities or specific sources of these bacteria (Surendran et al., 1989; Uddin et al., 2001; Rao and Surendran, 2003; Swaminathan et al., 2007; Jeyasekaran et al., 2008). The main objective of this study was to (1) isolation and characterization of some salt tolerant bacteria from salinity soil in Sharkia Governorate, (2) determine the protein pattern in halophilic bacteria and (3) studying the ability of salt tolerant gene(s) to transfer by natural gene transfer mechanisms.

Electrokinetics of a Poly(N-isopropylacrylamid-co-carboxyacrylamid) Soft Thin Film: Evidence of Diffuse Segment Distribution in the Swollen State

Streaming current measurements were performed on poly(N-isopropylacrylamid-co-carboxyacrylamid) (PNiPAAM-co-carboxyAAM) soft thin films over a broad range of pH and salt concentration (pH 2.5-10, 0.1-10 mM KCl) at a constant temperature of 22 °C. The films are negatively charged because of the ionization of the carboxylic acid groups in the repeat unit of the copolymer. For a given salt concentration, the absolute value of the streaming current exhibits an unconventional, nonmonotonous dependence on pH with the presence of a maximum at pH ∼6.4. This maximum is most pronounced at low electrolyte concentration and gradually disappears with increasing salinity. Complementary ellipsometry data further reveal that the average film thickness increases by a factor of ∼2.2 with increasing pH over the whole range of salt concentration examined. The larger the solution salt concentration, the lower the pH value where expansion of the hydrogel layer starts to take place. The dependence of film thickness on pH and electrolyte concentration remarkably follows that obtained for surface conductivity. The streaming current and surface conductivity results could be consistently interpreted on a quantitative basis using the theory we previously derived for the electrokinetics of charged diffuse (heterogeneous) soft thin films complemented here by the derivation of a general expression for the surface conductivity of such systems. In particular, the maximum in streaming current versus pH is unambiguously attributed to the presence of an interphasial gradient in polymer segment density following the heterogeneous expansion of the chains within the film upon swelling with increasing pH. A quantitative inspection of the data further suggests that pK values of ionogenic groups in the film as derived from the streaming current and surface conductivity data differ by ∼0.9 pH unit. Such a difference is attributed to the impact of position-dependent hydrophobicity across the film on the degree of ionization of carboxylic sites.

Cationic and anionic environments in LiTFSI-doped di-ureasils with application in solid-state electrochromic devices

Fourier Transform mid-infrared and Raman spectroscopies were used to investigate the cation/polymer, cation/urea bridge, cation/anion and hydrogen bonding interactions in poly(oxyethylene) (POE)/siloxane di-ureasil networks prepared by the sol–gel route and doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Materials with compositions 200 ⩾ n ⩾ 5 (where n expresses the molar ratio OCH 2CH 2/Li +) were studied. The Li + ions coordinate to the urea carbonyl oxygen atoms over the whole range of salt concentration considered. Bonding to the ether oxygen atoms of the POE chains occurs at n ⩽ 40, although a significant fraction of the POE chains remain non-coordinated. In these high salt content samples, the cations interact with the anions forming contact ion pairs. “Free” ions are probably the main charge carriers at the room temperature conductivity maximum of these ormolytes.

Vibrational spectra and microstructure of poly( ε-caprolactone)/siloxane biohybrids doped with lithium triflate

Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies and Scanning Electron Microscopy (SEM) were used to investigate ionic association, hydrogen bonding and morphology in a family of sol–gel derived lithium triflate (LiCF 3SO 3)-doped di-urethane cross-linked poly( ε-caprolactone) (PCL(530))/siloxane hybrid electrolytes. The materials studied, with compositions ∞ > n ⩾ 0.5 (where n – composition – expresses the molar ratio of PCL(530) ester repeat units per Li + ion), are non-porous and homogeneous. The Li + ions interact with the urethane and ester carbonyl oxygen atoms within the whole range of salt concentration analyzed, promoting the formation of hydrogen-bonded aggregates. The composition dependence of the relative concentration of “free” anions and coordinated anions (weakly coordinated anions, Li + CF 3 SO 3 - ion pairs or [Li(CF 3SO 3) 2] − triplets, aggregates I ([Li 2(CF 3SO 3)] +) and aggregates II ([Li 3(CF 3SO 3)] 2+) in all the samples is in perfect agreement with the values of the room temperature ionic conductivity reported previously.

Extension of the electrolyte NRTL and Wilson models for correlation of viscosity of strong electrolyte solutions at different temperatures

The electrolyte NRTL model [C.C. Chen, L.B. Evans, AIChE J. 32 (1986) 444–454] and electrolyte Wilson model [E. Zhao, M. Yu, R.E. Sauvé, M. Khoshkbarchi, Fluid Phase Equilibr. 173 (2000) 161–175] have been extended for the representation of the dynamic viscosity of strong electrolyte solutions. The models are based on Eyring's absolute rate theory and the electrolyte NRTL and Wilson models for calculating the excess Gibbs energy of activation of the viscous flow. The utility of the models is demonstrated with a successful representation of the viscosity of several electrolyte solutions at different temperatures. The results show that, the model is valid for the whole range of salt concentration and it is reliable for correlation of the viscosity of electrolyte solutions at different temperatures by only four adjustable parameters per binary system.

Cation coordination and hydrogen bonding in potassium and magnesium based-di-amidosil hybrids

Fourier transform mid-infrared and Raman spectroscopies were employed to elucidate the cation/alkylene chains, cation/cross-link, cation/anion interactions and hydrogen bonding occurring in amorphous di-amide cross-linked alkylene/siloxane hybrid materials (di-amidosils) doped with potassium and magnesium triflates (KCF 3SO 3 and Mg(CF 3SO 3) 2, respectively). Materials with compositions ∞ > n ⩾ 5 (where n expresses the molar ratio of carbonyl oxygen atoms per guest cation) were investigated. The conformations ( gauche) of the alkylene chains of the host di-amidosil matrix are not affected by the presence of the guest salt in both doped di-amidosil families. The K + and Mg 2+ ions coordinate to the carbonyl oxygen atoms of the amide cross-links within the whole range of salt concentration considered, leading to the saturation of the cross-linkages, to a redistribution of the amide–amide hydrogen-bonded aggregates of the host matrix and, in the case of the K +-doped sample with n = 10, to the formation of a new type of aggregate, stronger and more ordered than those detected at lower salt content. In both di-amidosil systems guest salt addition leads to the increase of ionic associated species and to a concomitant decrease of the concentration of “free” anions.

A Simple Phenomenological Fix for the Dielectric Constant within the Reference Interaction Site Model Approach

The effective interactions among ions immersed in water are studied by means of the effective pair potentials (EPPs) [J. Chem. Phys. 2002, 117, 6133] obtained after contracting (integrating out) the degrees of freedom of the solvent molecules. The dressed interaction site theory (DIST) leads to a simple way of adjusting the effective dielectric constant of the model solvent to its experimental value at standard conditions. The molecular structure of the solvent is mirrored in the structure of the short-ranged component of the induced EPPs, with noticeable differences between the cases with trivial (ideal gas) and nontrivial (experimental) values of the dielectric constant. The shape of these EPPs remains almost invariant over the whole range of salt concentrations considered here. The asymptotic behavior of the EPP between two macroions obtained after contracting the supporting electrolyte (water molecules plus small ions) is also briefly discussed.

Optically Functional Di-Urethanesil Nanohybrids Containing Eu3+ Ions

Sol−gel derived poly(oxyethylene)/siloxane hybrids (di-urethanesils) doped with europium triflate, Eu(CF3SO3)3, were examined by XRD, 13C and 29Si MAS NMR and FT-IR, FT-Raman, and photoluminescence spectroscopies. The host framework of these materials consists of a siliceous network grafted through urethane linkages to both ends of polymer chains with 6 oxyethylene repeat units. Xerogels with ∞ ≥ n ≥ 1 (where n is the molar ratio (OCH2CH2)/Eu3+) were analyzed. The compounds with n ≥ 10 are amorphous. In samples with n ≤ 5 crystalline Eu(CF3SO3)3 was detected. In the di-urethanesils with n ≥ 10 the cations interact with the urethane carbonyl oxygen atoms. The complexation of the polyether chains to the cations is initiated at approximately n = 10. At n ≤ 10 both types of cation bonding situations occur. “Free” and weakly coordinated CF3SO3- ions exist in the whole range of salt concentrations analyzed. Ionic aggregates are formed in samples with n = 5 and 1. For 200 ≥ n ≥ 20 the emission quantum yields range from 0.7 to 8.1%. The decrease in the quantum yield with the increase of the Eu3+ concentration markedly depends on the activation of the energy transfer between the hybrid host's emitting centers and the cations, permitting, therefore, a fine-tuning of the emission chromaticity across the CIE (Commission Internationale d'Éclairage) diagram (e.g., (x, y) color coordinates from (0.19, 0.18) to (0.50, 0.49), for n = 200 and 5, respectively).

Urethane cross-linked poly(oxyethylene)/siliceous nanohybrids doped with Eu3+ions : Part 2. Ionic association

Fourier transform mid-IR and Raman spectroscopies were employed to investigate the anionic local surrounding in sol-gel derived organic/inorganic materials-monourethanesils-incorporating europium triflate, Eu(CF 3 SO 3 ) 3 . The hybrid framework of these xerogels contains short methyl end capped polyether segments grafted to a siliceous network through urethane cross-links. Samples with compositions ∞ > n ≥ 10 (where n indicates the ratio of (OCH 2 CH 2 ) moieties per lanthanide ion) were examined. The spectral data obtained provide conclusive evidence of the presence of free and weakly coordinated CF 3 SO 3 - ions located in two distinct sites in the whole range of salt concentration analyzed. At n = 30 and 10, along with these species, two new anionic configurations, assigned to contact ion pairs and cross-link separated ions pairs, emerge. Two-dimensional correlation spectroscopic analysis allowed to clarify the number of components present in two critical bands containing strongly overlapped spectral profiles. The number of anionic environments found in the m-Ut(750) n Eu(CF 3 SO 3 ) 3 family confirms the rich coordinating possibilities offered by polymer systems incorporating trivalent triflate salts.

Cationic and anionic environments in mono-urethanesil hybrids doped with magnesium triflate

Sol–gel derived poly(oxyethylene), POE/siloxane hybrids (mono-urethanesils) with a wide range of magnesium triflate (Mg(CF 3SO 3) 2) concentrations were analyzed by infrared and Raman spectroscopies with the goal of examining the cation/polymer, cation/cross-link, hydrogen bonding and cation/anion interactions. In the host matrix of these xerogels short CH 3-terminated POE segments are covalently bonded to the siliceous backbone through urethane linkages. Samples with ∞> n≥6 (where n is the molar ratio of (OCH 2CH 2) moieties per Mg 2+ ion) were synthesized. The spectral data obtained provided conclusive evidence that the ether oxygen atoms of the polymer chains of the host structure complex the alkaline-earth ions in materials with n≤60. “Free” triflate ions and weakly coordinated anions were detected over the whole range of salt concentration examined. The coordinated triflate species are formed in two different bonding environments. Contact ion pairs appear in materials with n≤60. This work confirms previous studies that suggested that the nature of the cations added to the mono-urethanesil-type framework plays a key-role in the properties of these composites.

Precision measurement of ternary diffusion coefficients and implications for protein crystal growth: lysozyme chloride in aqueous ammonium chloride at 25°C

Isothermal ternary diffusion coefficients for the system lysozyme chloride (1)+NH 4Cl (2)+H 2O at 25°C and pH 4.5 have been measured interferometrically for five mean NH 4Cl concentrations, C 2=0.25, 0.5, 0.9, 1.2 and 1.5 M, with C 1=0.6 mM. The main-term diffusion coefficient ( D 11) v varies slowly with C 2. The main-term ( D 22) v increases with increasing NH 4Cl concentration, as does the binary D v in aqueous NH 4Cl, but the ( D 22) v values are lower in the ternary system. The cross-term ( D 21) v, which relates the coupled flow of NH 4Cl to the protein concentration gradient, increases sharply with increasing salt concentration, and is 19 times larger than ( D 22) v at the highest concentration. The values of ( D 12) v are smaller than the corresponding values previously obtained for the lysozyme chloride+NaCl+H 2O system over the whole range of salt concentration studied. Using equations based on the Onsager Reciprocal Relations, we have calculated the derivative of the chemical potential of lysozyme chloride with respect to the NH 4Cl concentration, and have estimated the protein cation charge. Integration with respect to the NH 4Cl concentration gives the dependence of the chemical potential of lysozyme chloride on NH 4Cl concentration, providing information about the driving force for nucleation and crystal growth of lysozyme chloride.

Study on ionic conductive property of polyurethane/oligo-ether sulfate complex

A new oligo-ether sulfate (SPEG) and linear polyether urethane (PU) have been synthesized successfully, and a series of novel solid polymer electrolytes based on PU/oligo-ether sulfate complexes were prepared. Effects of temperature, salt concentration (O:Na +, the molar ratio of ether unit to sodium cation), content of SPEG and polydioxolane (PDXL) on morphological structure and ionic conductive property were investigated in detail. It was found that oligo-ether sulfate had great effect on morphological structure of samples. Results showed that ionic conductivity of this system could reach 10 −5 S cm −1 at medium temperature (60°C) and temperature dependence of ionic conductivity was not an Arrhenius-type one. The ionic conductivity increased with increase of SPEG content over whole range of salt concentration studied and ionic conductivity of SPU-600 was higher than that of SPU-400 at the same O:Na +. In addition, plasticizer PDXL and its content significantly influenced the ionic conductive properties of the samples.

REAPPRAISAL OF PHYSIOLOGICAL ATTRIBUTES OF NINE STRAINS OF DUNALIELLA (CHLOROPHYCEAE): GROWTH AND PIGMENT CONTENT ACROSS A SALINITY GRADIENT

Among the few taxonomic characters used to circumscribe sections within the subgenus Dunaliella are the physiological response to changes in salt concentration, which define a specific range for optimal growth, and the carotenogenic ability of the vegetative cells, responsible for the change in cell color from green to orange or red, under suboptimal culture conditions. Previous work based on molecular data from seven taxa of different sections of the subgenus showed no correlation between the genetic relationship inferred from the internal transcribed spacer RFLP data and the morphophysiological attributes in use in taxonomy. The present work was performed to experimentally reevaluate the physiological attributes in the same seven previous taxa (D. tertiolecta Butcher UTEX 999 and CCMP 1320, D. parva Lerche UTEX 1983 and CCMP 362, D. salina Teodoresco UTEX 200, D. viridis Teodoresco CONC 002, and D. peircei Nicolai et Baas Becking UTEX 2192) adding D. parva CCAP 19/9 and D. pseudosalina Massyuk et Radchenko CONC 010. Growth responses and pigment content in a wide range of NaCl concentrations were assessed. The results revealed that two strains of D. parva, two strains of D. tertiolecta, and one strain of D. peircei showed similarity in their growth responses to the whole range of salt concentrations. Dunaliella parva UTEX 1983, on the other hand, showed a growth rate pattern very different from those of their conspecifics and similar to those of D. viridis CONC 002 and D. salina UTEX 200. In relation to the pigment content, none of the strains turned orange or red in color under the whole range of salt concentrations assayed, and the total carotenoids to chlorophyll ratios were always lower or equal to 1.0. These results reaffirm the validity of the physiological attributes used to discriminate sections within the subgenus Dunaliella and show correlation with the previous molecular data, but stress the need for relocating some strains into different sections.

Effect of Calcium Chloride on the Isobaric Vapor−Liquid Equilibrium of 1-Propanol + Water

The effect of calcium chloride at salt mole fractions from 0.02 to saturation on the vapor−liquid equilibrium (VLE) of 1-propanol + water has been studied at 101.32 kPa using a modified Othmer equilibrium still. The salt exhibited a salting-out effect of the alcohol over the whole range of liquid composition, the azeotrope being eliminated at salt mole fractions greater than 0.080. A liquid phase splitting into two immiscible liquid phases on the whole range of salt concentration and over a liquid range of about 0.01−0.54 1-propanol mole fraction (salt-free basis) was observed. The results were compared with the values predicted from the extended UNIQUAC models of Sander et al. and Macedo et al. and the modified UNIFAC group-contribution model of Kikic et al.

The hydrophobic behaviour of Orange IV in water and in aqueous electrolyte solutions

Unlike the stepwise manner of self-aggregation shown by homologues of the surface-active azo dye Methyl Orange in aqueous solution, cooperative self-aggregation is shown in electrolyte solutions of Orange IV (C6H5—NH—[graphic omitted]—NN—[graphic omitted] SO–3Na+). Evidence of a critical micellar concentration (c.m.c.) appears from the breaks in the plots of absorbance and surface tension values against the dye concentration.The quantitative treatment of the effects of NaCl and SrCl2 reveals that the equation log (c.m.c.)=–KCsalt+constant, derived for zwitterionics by Mukerjee (J. Phys. Chem., 1965, 69, 4038) on the basis of the salting-out of their hydrocarbon groups, is only obeyed at lower salt concentrations. An equation log (c.m.c.)=–K log Csalt+constant fits our experimental results over the whole range of salt concentrations considered and remains valid when 1.0 mol dm–3 urea, a well known disturber of hydrophobic bonds, is introduced.

Study of salt effects on adenosine–polyuridylic acid interaction

AbstractComplex formation between poly(U) and adenosine in solutions of salts that stabilize (Na2SO4), destabilize (NaClO4), or have little effect on the water structure (NaCl), as well as the poly(U)·poly(A) interaction in NaClO4, was studied by equilibrium dialysis and uv spectroscopy. At 3°C and neutral pH, Ado·2 poly(U) is formed in 1M NaCl and 0.33M Na2SO4. In NaClO4 solutions under the same conditions, an Ado·poly(U) was found over the whole range of salt concentration investigated (10 mM−1M), which has not been previously observed under any conditions. The Ado‐poly(U) was also found in a NaCl/NaClO4 mixture, the transition from the triple‐ to the double‐helical complex occurring within a narrow range of concentration of added NaClO4. In the presence of 1M NaCl this transition is observed on adding as little as 10 mM NaClO4, i.e., at a [ClO]/[Cl−] ratio of about 1:100. However, when NaClO4 is added to a 1M solution of the stabilizing salt Na2SO4, no transition occurs even at a [ClO]/[SO] ratio of 1:4. Investigation of melting curves and uv spectra has shown that in an equimolar mixture of the polynucleotides, only a double‐helical poly(U)·poly(A) exists in 1M NaClO4 at low temperatures; this also holds for 1M NaCl. This changes to a triple‐helical 2 poly(U)·poly(A) and then dissociates as the temperature increases. At low temperatures and the poly(U)/poly(A) concentration ratio of 2:1, a mixture of 2 poly(U)·poly(A) and poly(U)·poly(A) was observed in 1M NaClO4, in contrast to the case of 1M NaCl. Thus, sodium perchlorate, a strong destabilizer of water structure, promotes formation of double‐helical complexes both in the polynucleotide–monomer and the polynucleotide–polynucleotide systems.Beginning with a sufficiently high ionic strength (μ ≃ 0.9), a further increase in the salt molarity results in an increase of the poly(U)·adenosine melting temperature in both stabilizing and neutral salts and a decrease in the destabilizing salt. In Na2SO4 concentrations higher than 1.2M Ado·2 poly(U) precipitates at room temperature. Analysis of the binding isotherms and melting profiles of the complexes between poly(U) and adenosine according to Hill's model shows that the cooperativity of binding, due to adenosine stacking on poly(U), increases in the order NaClO4 &lt; NaCl &lt; Na2SO4. The free energy of adenosine stacking on the template is similar to that of hydrogen bonding between adenosine and poly(U) and ranges from −1 to −2 kcal/mol. The values of ΔHt [the effective enthalpy of adenosine binding to poly(U) next to an occupied site, obtained from the relationship between complex melting temperature and free monomer concentration at the midpoint of the transition] are −14.2, −18.3, and −16.8 kcal/mol for 1M solutions of NaClO4, NaCl, and Na2SO4, respectively. The results indicate that the effects of anions of the salts studied are related to water structure alterations rather than to their direct interaction with the complexes between poly(U) and adenosine.