Solutions of alkali soaps and water in fatty acids VIII. Correlations of X-ray data with other experimental observations

In the system sodium octanoate-octanoic acid-water an obvious parallel exists between the low-angle X-ray observations in the isotropic liquidL ₂-phase and its composition, properties and structure. This parallel does not exist only with respect to the total content of acid sodium octanoates (with stoichiometric compositions 1NaC₈2HC₈x H₂O, and 1NaC₈3 HC₈x H₂O, where NaC₈=sodium octanoate and HC₈=octanoic acid) but also with respect to their amphiphilic composition and their water content (the value of x).In the region of 55–70% water, where the structure of the phase closely resembles, in many respects, that of the adjacent liquid crystalline lamellar D-phase, the dependence of of the quasi-Bragg values on concentration parallels that of the Bragg value in the mesophase, in spite of the disorder of aggregates in the isotropic phase. Furthermore, the numerical values of the quasi-Bragg spacings at given concentrations of the acid sodium octanoates are almost of the same sizes as those of the real Bragg spacings in the D-phase. In this region, the quasi-Bragg values give information of the same type about structure as do the real Bragg values in the D-phase; that is, information about the interplanar distances of adjacent double layers of acid soap, separated by intermediate layers of water.At low water contents (up to about 40%) where a direct comparison with a liquid crystalline phase is not possible, the quasi-Bragg values obviously increase in parallel with the molecular volume of the hydrated acid sodium actanoates and thus reflect one of the structural dimensions of these molecules. If one also considers those changes inside the molecules that, according to other observations, are caused by the incorporation of water, the mentioned parallel becomes still more obvious and it may be primarily the length of the hydrated acid soap molecules that is reflected in the quasi-Bragg values.At water contents above 40%, where increased amounts of unbound, bulk-water begin to appear in the phase, this parallel ceases. Above 55% water, where the phase obtains the character of an aqueous solution of hydrated acid sodium octanoates, the quasi-Bragg values are then shown to reflect the thickness of the aggregates of hydrated acid sodium octanoates (1 NaC₈2 HC₈x H₂O and 1NaC₈3 HC₈x H₂O) together with their intercalated layers of bulk-water.Based upon the comparison of X-ray phenomena with previously obtained experimental evidence, it is possible to draw some conclusions about the structure of theL ₂-phase. The most important is that the elongation of hydrated acid sodium actanoate molecules, caused by the incorporation of water up to about 40%, is strongly supported.     

Solutions of alkali soaps and water in fatty acids XIII. Circumstances that regulate the extension of theL 2-phase and the role of the acid-soaps rich in fatty acid for the occurrence of the phase

A basic requirement for that type ofL ₂-phase which exists in the system sodium octanoate-octanoic acid-water is the formation of acid-soaps. In order for the phase to be formed at all, the temperature must lie above the melting point of the fatty acid so that a reaction in non-aqueous milieu between neutral soap and fatty acid is possible. In order to obtain the characteristic shape and complete extension of the phase in direction of high water content the temperature must be so high that also the hydrated acid-soaps occur in fluid state. On the other hand the temperature cannot be so high that the acid-soaps become unstable.At temperatures at which the phase has obtained its full extension those circumstances differs which in different regions regulate the location of the phase borders; they depend on the composition of the acid soaps and on their amounts. In that part of the phase where the molar ratio between octanoic acid and sodium octanoate lies between 2 and 3 and where one has a continuous transition from reversed to normal structure only the two acid octanoates 1 NaC₈ 2 HC₈ x H₂O and 1 NaC₈ 3 HC₈ x H₂O occur and both are at 20 °C in fluid state.At water contents from about 22 % to 40 % the hydrate-water molecules belonging to the first mentioned soap are capable of contributing actively to the formation of large aggregates of acid-soap, a process which however is counteracted by the inmixing of the latter acid-soap. This mixture of the two acid-soaps decides in this region where the border of the phase will lie in direction towards an increased content of sodium octanoate; the result is that in spite of the fact that the hydration is increased, the border is only slowly displaced towards a higher content of fatty acid. As soon as the hydration of the acid octanoates has been completed and the additional water occurs as unbound bulkwater, the location of the phase boundary will no longer be influenced by the water content — now it will be the amphiphilic composition of the acid-soaps that determines the location of the border and it remains at the molar ratio 2.5 between octanoic acid and sodium octanoate at water contents from about 40% and up to 82%.In the direction of decreasing content of neutral sodium octanoate and increased content of water theL ₂-phase both at the highest content of fatty acid and the highest contents of water will be in equilibrium with the water-richL ₁-phase; in the first mentioned region with theL ₁-phase below the lac where at the border it is saturated with octanoic acid and in the latter region with theL ₁-phase just above the lac, where the dilute sodium octanoate solution contains dissolved 1 NaC₈ 1HC₈ x H₂O. In the large central part of theL ₂-phase, from about 20 % to about 86 % of water, the location of the border is dominated by the acid octanoate 1 NaC₈ 3 HC₈ x H₂O and that makes an equilibrium with theL ₁-phase impossible; instead one has an equilibrium via a two-phase zone between the amphiphile-rich region of theL ₂-phase and its water-rich region. In the first region the location of the border is regulated by the decreasing capability of the hydrated acid octanoate 1 NaC₈ 3 HC₈ x H₂O to dissolve octanoic acid; in the latter it is regulated by the fact that 1 NaC₈ 3 HC₈ x H₂O is the most fatty acid-rich acid-soap that is formed and that the octanoic acid is very little soluble in water and in the aqueous solution of this acidsoap.The middle part of theL ₂-phase, especially the region between about 55 % and 82 % of water, constitutes a direct continuation of the liquid crystalline lamellarD-phase. The liquid crystalline character of theD-phase is lost at the transition, but the lamellar organization is retained. That the molecules at least up to a water content of about 40 % are of the original reversed type and have an elongated shape with a central part of hydrated polar groups, from which core the hydrocarbon chains extend in two opposite directions, is the reason to that they, at crowding, form transient layer-like agglomerates of tightly packed more or less parallel molecules; this facilitates the transformation to coherent double amphiphilic layers, in which all molecules lie with the hydrated polar groups outwards toward coherent domains of bulk-water, without another liquid phase occurs.     

Solutions of alkali soaps and water in fatty acids XI. Correlation between the acid sodium octanoate in the most water-rich part of the L2-phase and the acid soaps in two adjacent phases

The special nature of the outer-most water-rich region of theL ₂-phase in the ternary system sodium octanoate-octanoic acid-water is evidenced by its somewhat turbid appearance and by the character of its equilibria with adjacent phases. The phase contains aggregated acid sodium octanoate which is dispersed in a very dilute aqueous solution of sodium octanoate. The acid octanoate has the composition 1 NaC₈2 HC₈x H₂O and is composed of closely packed amphiphilic units, all with the polar groups in the same direction. This acid soap obviously forms double-layered aggregates with the lipophilic hydrocarbon chains pointing inwards and the polar groups pointing outwards towards the surrounding bulk-water. The phase is formed when octanoic acid is added to theL ₁-phase of the system just above the l.a.c.; in this aqueous solution, the acid reacts with dissolved acid octanoate 1 NaC₈1 HC₈x H₂O and that results in the formation of the slightly soluble acid soap 1 NaC₈ 2 HC₈x H₂O that separates as a new phase, the turbidL ₂ phase. On further addition of octanoic acid, the content of the mentioned acid soap increases until the solution phase is transformed into a liquid crystalline lamellarD-phase with the same acid soap composition. This formation of acid soap 1 NaA2 HA on addition of fatty acid to the dilute soap solution just above the l.a.c., has been known for a long time to occur in various systems containing a long-chain sodium soap. However, at suitably low temperatures, the reaction in these systems does not result in separation of the acid soap in the liquid crystalline, but in the solid crystalline state.     

Solutions of alkali soaps and water in fatty acids X. The basic structure of the molecules and the size of the particles of acid octanoates in the L2-phase at water contents below 40%

The acid sodium octanoate molecules in the isotropic liquidL ₂-phase of the system sodium octanoate-octanoic acid-water have the same basic structure in the whole region, from non-aqueous melt up to a water content of 40 %. This molecular structure is characterized by amphiphilic units oriented with the polar groups directed inwards and bound to each other, forming a central core from which the hydrocarbon chains protrude in at least two opposite directions. The size of the molecules increases due to the incorporation of water, and their shape changes from spherical to elongated rods or ribbons. They occur as monomers or dimers; no aggregation to lasting large particles has been observed. However, transient agglomerates of the free molecules seem to occur.     

Solutions of alkali soaps and water in fatty acids IX. The location of theL 2-phase in three-component systems of sodium soap — fatty acid — water,in view of the occurrence of acid soaps

Previous studies of the occurrence of acid soaps in systems containing a longchain sodium soap and the corresponding fatty acid, and the study of phase equilibria in the system sodium octanoate — octanoic acid — water, performed by our group at the beginning of the 1960s, show that the isotropic liquidL ₂-phase of the last mentioned system in its whole region of existence is situated in that part in which acid soaps occur. This provides an explanation for the fact that theL ₂-phase itself contains acid sodium octanoates in all regions. TheL ₂-phase has its origin in the water-free melt of fatty acid and neutral soap in which these components react with each other under the formation of an acid soap. When water is added to the system, this water-free acid soap is transformed into different hydrated acid soaps. In a large region of concentration, there is an extremely close relation between theL ₂-phase and the liquid-crystalline lamellarD-phase, which itself consists of hydrated acid soaps. At its outermost water-rich tip, theL ₂-phase is in equilibrium with theL ₁-phase of the system, just above the+LAC, that is, with the most dilute aqueous soap solution in which acid soap still may be formed in aqueous environment. Formation of acid soap is a fundamental requirement for the existence of this isotropic liquidL ₂-phase.     

Phase diagrams and structures of lecithin/water systems with branched lecithin components

The influence of chain branching on the phase transition parameters and structures of the homologous series of 1-(x-methylpalmitoyl)-2-hexadecyllecithins in the water-saturated two-phase region (50 wt.% water) were studied by differentialscanning-calorimetry as a function of the position x of methyl branching. With increasing x a linear decrease in the enthalpies and alternating temperatures of main transition were observed. The phase diagram of the ternary system 1-(3-methyl-palmitoyl)-2-hexadecyllecithin/1,2-dipalmitoyllecithin/water (50 wt.% water) showed that both components are completely miscible within the high-temperature phase (L -phase). However, in the low-temperature phase (gel phase), the components are partially miscible only. It follows that gel phases with interdigitated chains and those with tilted chains are not completely miscible. The phase diagram of the ternary system 1,2-di-(8-methylpalmitoyl)-lecithin/1,2-dipalmitoyllecithin/water (50 wt.% water) showed that both components are completely miscible within the high-temperature phase and low-temperature phase. Within the concentration range between the mole fraction x=0.91 and x=0.97, a drop-like course in the phase diagram was obtained.     

Solutions of alkali soaps and water in fatty axids VII. X-ray scattering of the isotropic liquid L2-phase

The isotropic liquid pase,L ₂, in the system sodium octanoate/octanoic acid/ water (at 20 °C) exhibits low-angle X-ray scattering. The strength of the phenomenon and the position of the peak in the scattering curve vary with composition. This phenomenon is presented and described.     

Phase diagram of the system dihexadecylphosphatidylcholine/dihexadecyl-phosphatidic acid/water/NaOH at pH=14

Differential-scanning-calorimetry, freeze-fracture electron microscopy, and³¹P-NMR spectroscopy were used to study the lyotropic and thermotropic properties of the system dihexadecylphosphatidylcholine/dihexadecylphosphatidic acid/water/ NaOH in dispersion with excess water at pH=14. The phase diagram showed that both phospholipids are demixed nearly completely in the gel phase. The coexistence of theP and theB -phase in the mixtures was pointed out in the freeze-fracture electron micrographs by the ripple structure (P -phase) and by the lamellar structure (B -phase).     

Solutions of alkali soaps and water in fatty acid V. Measurements of water vapour pressure and electrical conductivity

Measurements of water pressure and electrical conductivity have contributed to show that the extended, isotropic liquid L₂-phase region in the system sodium octanoate/ octanoic acid/water may be divided into several subregions, inside which the character of the system is different. In the non-aqueous part of the phase and at low contents of water and more than about three moles of octanoic acid per mole of sodium octanoate the character is that of a solution of acid sodium octanoate in octanoic acid. At high water contents the L₂-phase has the character of a solution of acid sodium octanoate in water. Intermediately there is a large region where the character of the phase is reminiscent of a hydrated acid sodium octanoate in fluid state. In this region the content of octanoic acid is below three moles per mole of sodium octanoate and the maximal water content is about that bound to the polar groups.In the intermediate region the water vapour pressure is regulated mainly by the extent and type of the bonding of the water to the polar groups, and the electrical conductivity by the migration of free hydrated sodium ions in an environment of hydrated polar groups. In the part of the L₂-phase where the character of the phase is that of an aqueous solution the vapour pressure and conductivity are regulated by the concentration of molecularly dispersed acid sodium octanoate and its ions in water.     

Change of water structure by solvents and polymers Part 4: Albumin-water solutions with acetylsalicylic,hydrochloric and ascorbic acid,lysine- and ammonium chloride and with dextrane and sorbit

Viscosity measurements were made in the temperature range of 10 °–40 °C. The equation= _o exp(B/(T-T _o )) was used with the parameterT ₀ as structure indicator, which is called the limiting temperature. For instance, hydrocarbons, as liquids with quasifree molecules, haveT ₀=O; water as a highly structured liquid hasT ₀= 140–150 K.The polymer investigated was ovalbumin in aqueous solution in a concentration comparable to that of blood. Acetylsalicylic acid produces a protein conformation which breaks the water structure in solution at a pH of within the in vivo region.The question of whether only the acidity determines the water structure breaking properties of the protein is investigated by acidifying albumin-water solutions with hydrochloric acid, lysine chloride and ascorbic acid. All these acids exhibit similar effects. A stronger influence is observed for ammonium chloride. Its interaction with ovalbumin produces a strong structure-breaking effect. The most powerful water structure breaker in albumin-water solutions is dextrane. In a concentration of 10 % it changes the polymer conformation so that the water structure is broken to such an extent that the solution behaves as an almost quasifree liquid withT ₀=O.     

Water self-diffusion in micellar solutions and in lyotropic mesophases of the system water/Triton TX-100

Studies by Pulsed Field Gradient NMR (PFG-NMR) methods and other physico-chemical experiments have been used to clarify the processes connected with water self-diffusion in mixtures formed by water and Triton TX-100. In micellar solutions the solvent diffusive trend is related to micelle hydration and, to a much less extent, to micelle size and shape. Hydration numbers from PFG-NMR are close to those obtained by viscosity experiments. In solution phases of the reversed kind, water in oil, water self-diffusion data suggest that aqueous domains are large and bicontinuous. Water self-diffusion in the hexagonal lyotropic mesophase has been interpreted by introducing a geometrydependent contraint, , termed structural factor, which is related to the parameters of the phase.     

Dependence of the activity of a rhizopus lipase on microemulsion composition

Enzymatic hydrolysis of a model triglyceride, palm oil, was carried out with lipase fromRhizopus sp. in microemulsions with varying water content. The microemulsions were based on a nonionic surfactant, pentaethylene glycol monododecyl ether (C12 EO5), buffered water solution and an oil component consisting of isooctane and palm oil at a weight ratio of 20:1. The structure of the microemulsions was characterized using Fourier transform pulsed-gradient spin-echo¹H NMR. The rate of reaction decreased as the water content of the reaction medium was increased. The self-diffusion coefficient of water, D_w was found to be constant within the interval 1–20% water. The difference in reactivity is believed to be due to a difference in structure of the palisade layer between water and hydrocarbon microdomains. The nonionic surfactant was demonstrated to be unsuitable for enzymatic reactions since only partial hydrolysis was obtained in all experiments. The surfactant, however, did not cause enzyme deactivation, even at very high concentrations.     

Cubic phases in surfactant and surfactant-like lipid systems

Cubic liquid crystalline phases are common in surfactant and surfactant-like lipid systems at temperatures above the Krafft point. They are optically isotropic and very stiff. Therefore, they are often not recognized as independent phases and separated in pure state. The liquid crystalline nature is evidenced by a low-angle diffraction pattern with sharp reflections having Bragg-values above 20 Å coupled with a diffuse wide-angle reflection at 4.5 Å, proving that the hydrocarbon moiety is in a liquid state. The cubic phases occur in a variety of lipid/water systems (also with liquid organic solvents), such as simple soaps, amphiphilic lipids of biological origin, and extracts from membrane lipids. The location of the cubic phases in a phase diagram varies.The original concept of a cubic structure composed of closed globular aggregates, either of oil-in-water or water-in-oil type in face-centered array seems to be obsolete. The present structure concepts include closed anisotropic aggregates, short rod-like aggregates forming continuous networks or lamellar aggregates with zero curvature forming networks of Infinite Periodic Minimal Surfaces (IPMS). The structure is mostly primitive or body-centered cubic.     

Determination of the regime in the reverse wilson chamber at critical supersaturation measurements

The pressure in the Reverse Wilson Chamber (RWC) was directly measured at different rates of compression of the gas mixture. It was shown that at compression time in the range from 0.06 to 0.3 s an intermediate, between adiabatic and isothermal, process took place in the chamber. To obtain the relative pressure increase P _m /P _at from the values of the relative gas compression V/V, a calibration of the experimental set-up was carried out. The calibration showed that the values of critical supersaturationSc for water condensation on hexadecane, estimated for intermediate regime of the gas compression, were reduced with respect to the values calculated when the adiabatic regime was assumed. This fact confirmed the conclusions made earlier [1–3] that the classical theory was not applicable in this case of heterogeneous phase formation and that the line tension < 0 should be taken into account. Moreover, in an atmosphere of very pure argon (instead of room air [1–3]) the critical supersaturation turned out to be independent of the initial state of undersaturationS _o . The more accurate values obtained for condensation of water on hexadecane were: lnS _c =0.204 (instead of the maximum value obtained earlier: lnS _c =0.26) and=–1.9×10^–5 dyne (instead of=–1.5×10^–5 dyne).     

A two-ply artificial blood vessel of polyurethane and poly(L-lactide)

A biodegradable microporous small-caliber vascular prosthesis has been developed that consists of two layers. The inner layer has been made highly antithrombogenic by cross-linking of a mixture of linoleic acid and an aliphatic polyetherurethane with dicumylperoxide. Microporosity was introduced by adding sodiumfluoride crystals of about 5 m in diameter prior to cross-linking and leaching them out afterwards.The outer ply has been constructed by precipitating a (95/5) physical mixture of polyesterurethane and poly(L-lactide) from solution in the presence of sugar crystals with dimensions in the range 30–90 m which were removed by exposing the graft to water.The two-ply grafts were tested in vivo by replacing 1 cm of the abdominal aorta of rats. All the grafts remained patent at least up to 1 year and did not exhibit any aneurismal formation. The inner layer was covered with endothelial cells and several layers of smooth muscle cells.     

Phase behavior and dynamic properties in mixed systems of anionic and cationic surfactants: lithium perfluorooctanesulfonate/diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMAC) and lithium dodecyl sulfate/DEFUMAC aqueous mixtures

Two ternary phase diagrams of the cationic perfluorosurfactant diethanolheptadecafluoro-2-undecanolmethylammonium chloride (DEFUMAC) with an anionic perfluorosurfactant lithium perfluorooctanesulfonate (LiFOS) and an anionic hydrocarbon surfactant lithium dodecyl sulfate (LiDS) have been established at 25°C. The total surfactant concentration was less than 20wt%. In a wide mixing region of the LiFOS/DEFUMAC system, a lamellar-type phase,P , was identified by its texture under a polarization microscope and by its x-ray diffraction pattern. Dispersed fragments ofP -phase are present in the dilute solutions in which one surfactant was in excess. The anisotropy of electrical conductivity, flow birefringence, dynamic light scattering, and electric briefringence demonstrate that theP fragments are disk-like with a radius of 0.7 m. The disk-likeP particles are transformed by shear into a spherical aggregate ofL above a critical shear gradient. LiDS/DEFUMAC mixed solution forms dispersed and precipitatedL in the dominant region. Radius and micropolarity of the dispersedL aggregates are decreased as the ratio of LiDS:DEFUMAC approaches 1:1. On the basis of x-ray diffraction measurement the structure of precipitatedL -phase seems to consist of monolayers.     

Thermotropic gelation of ovalbumin 1. Viscoelastic properties of gels as a function of heating conditions and protein concentration at various pH values

A study has been undertaken of stress relaxation in ovalbumin thermotropic gels with a concentration of 8–20%, depending on time and temperature of heating (respectively, 20–60 min, 70°–110°C), at pH 2.5–10.0. In all instances, the dependence of the initial gel elasticity modulus on heating has a single maximum. Gelation conditions corresponding to this maximum are considered optimal. Optimal gelation time is 30 min, regardless of pH. On the other hand, the optimal heating temperature depends on pH. To the right and left of the isoelectric point of protein (2.5pH<4.0 and 5.5G) of gels on heating conditions, pH and protein concentration (X ₁,X ₂,X ₃,X ₄), as well as on time of relaxation (t) may be generally described asG(X ₁,X ₁,X ₁,X ₁,t)=G _e(X ₁,X ₂,X ₃,X ₄)f(t), whereG _e is the equilibrium value of the elasticity modulus, and f(t) the relaxation function. Thus, a change in the parameters only affects the value of the equilibrium elasticity modulus, and exerts no effect on the relaxation time spectrum. For this reason, all the relaxation curves obtained may be transformed into two normalized relaxation functions:f(t)=f(t)/f(1)=G(X ₁,X ₂,X ₃,X ₄,t)/G(X ₁,X ₂,X ₃,X ₄, 1)Each of these normalized functions corresponds to one of the homologous groups. Rheological similarity of gels in each homologous group evidently points to their structural similarity. Invariance of the gel relaxationproperties with regard to protein concentration, leads to a concentration dependence of the equilibrium modulus at various pH values. These dependences are curvilinear on a double logarithmic scale. The slope of the curve exceeds 2 in the entire concentration interval studied. In other words, the dependences obtained cannot be described by the usual law of squares. On the other hand, they adequately match Hermans theoretical relation for a network formed by random association of identical polyfunctional particles without cyclization. This simple model evidently gives a true picture of the major regularities of thermotropic gelation for ovalbumin. An agreement between this theory and experiment was achieved for a protein concentration ofC ^*=6.0±1.0% at the gel point regardless of pH. Invariance of gelpoint position with regards to pH demands further confirmation.List of symbols T _h,t _h heating temperature and time - T _h ^* ,t _h ^* optimal heating temperature and time - C protein concentration - C ^* protein concentration in gel-point - G relaxation modulus - G _e equilibrium modulus - f(t) relaxation function - t time of relaxation - f(t) normalized relaxation function - fT _A (t), f _B (t) normalized relaxation functions of groups A and B - G ₁ T _h,t _h-reduced modulus - G ₂ T _h,t _h, pH-reduced modulus - G ₃ C-reduced modulus - b ₁ T _h, t_h reduction parameter of modulus - b ₂ pH reduction parameter of modulus - b ₃ C reduction parameter of modulus - W_g gel-fraction     

Electrolytic conductivity of poly(1,3-propylene phosphate) solutions containing mono- and divalent-counterions

The results of conductivity measurements for aqueous solutions of poly(1,3-propylene phosphate) (PPP), which can be considered as a synthetic analogue of naturally occurring teichoic acids, are reported. Experiments were carried out with oligomeric fractions of a polymer in acidic, sodium, potassium, magnesium and calcium forms. The concentration and molecular weight dependence of the equivalent conductivity of PPP was analysed and the limiting equivalent conductivity determined. From the conductivity data, the polyion-counterion interaction parameter F and the equivalent conductivity of a polyion _p were calculated. It was shown that both F and _p depend on polyelectrolyte solution concentration and molecular weight of PPP. Conclusions concerning mono- and divalent metal ions binding to PPP are drawn.     

Association of poly-(L-lysine) homologues in sodium carbonate solution

The molecular weights of isopoly(L-Iysine), poly(L-ornithine), and poly(L-, -diaminobutylic acid), the homologues of poly (L-lysine), were determined by the sedimentation equilibrium method in aqueous solutions of 1.0 M NaCl or 0.1 M Na₂CO₃. In every sample the molecular weights in the presence of carbonate ions was twice that in NaCl solution. In a previous paper we reported that poly(L-lysine) behaved as a dimer at concentrations higher than 0.4 g/dl in the presence of carbonate ions and as a monomer in dilute solution, and these two forms were related by a monomer-dimer equilibrium. The homologues did not have a monomer-dimer equilibrium relationship under the conditions of the measurements that we carried out. The CD spectrum of isopoly(L-lysine) in water showed a uniform increase with a decrease in the wave length in the presence of carbonate ions. However, in the alkaline region in NaOH solution, the spectrum changed and a small minimum at 212 nm was found. When additional carbonate ions were added a large minimum at 205 nm was observed. This result can be explained by a change in the conformation from a random coil to a regular structure. We could not compare isopoly(L-lysine) with other polypeptides, because it does not have peptide bonds. The CD spectra of poly(L-ornithine) and poly(L-, -diaminobutylic acid) in NaOH or Na₂CO₃ solutions showed only slightly regular structures. It was also confirmed that the dimer-structures of the poly (L-lysine) homologues do not have regular structures.This paper was presented at the VI. Symposium on Analytical Ultracentrifugation, Marburg, FRG, February 16–17,1989.     

Hyaluronic acid-copper(II) complexes: Spectroscopic characterization

Hyaluronic acid-copper(II) complexes were studied by ultraviolet and electron spin resonance spectroscopy (ESR), as well as by rheological measurements. Spin-Hamiltonian parameters were obtained from experimental spectra measured at 200 K by non-linear optimization method. These showg _x g _y <g _z and indicate the ground electronic state of copper ion, which is characteristic for carboxylato-copper(II) complexes. The non-axial symmetry of theg-tensor suggest rhombic crystal field symmetry. Formation of HA-Cu(II) complex is realized through the interaction of copper ions with carboxyl groups of the HA macromolecule. This complex is characteristic of the network-like rheological properties of its aqueous solution.