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Data useful for a characterization of the thermodynamic behaviour of a few nonionic aminoacid anhydrides (diketopiperazines) in water are reported. In particular, results of heat of dilution, heat of solution and osmotic coefficient measurements (the latter two only for sarcosine anhydride) are illustrated. As an interesting extension of our study, the likelihood that the compounds considered might exhibit a denaturant action on globular proteins has been tested using ribonuclease. Our results clearly point out that the diketopiperazines are strong denaturants indeed. A few results of spectral measurements of the monomer-dimer equilibrium of acridine orange in aqueous diketopiperazines solutions are also reported, as they appear to pertain to the mechanism of ribonuclease unfolding promoted by the diketopiperazines.

In prosecution of earlier studies from this laboratory, a detailed investigation on the potentialities of differential enthalpic analysis (DEA) in the evaluation of enthalpies of thermal denaturation as welt as of activation energies for the denaturation processes of three different proteins in concentrated aqueous solutions has been carried out. Our results suggest that DEA may indeed be an useful tool for the evaluation of such thermal and kinetic parameters despite some difficulties encountered in quantitation mainly because of the high biopolymer concentrations necessary with the DEA apparatuses available.

A study by differential scanning calorimetry (DSC) of ribonuclease thermal denaturation in water, 1.5, 2.5, and 4M aqueous urea, and in 1M and 2M aqueous hexame-thylenetetramine has been carried out. Application of the DSC technique to this type of investigation appears a useful one, in our experience. Our results indicate that whereas urea only slightly changes enthalpy variation accompanying denaturation but lowers the melting temperature of ribonuclease, hexamethylenetetramine does not effect either factor. According to these results, which are beyond experimental errors, the ability of hexamethylenetetramine in influencing hydrophobic-forces-driven phenomena (Barone, Crescenzi & Quadrifoglio 1967) has thus apparently no counterpart in any important action of this compound on the stability of a partially hydrophobic protein in aqueous solution.

A calorimetric investigation of the heat of dissociation of a maleic acid-butyl vinyl ether copolymer sample in aqueous solution has been carried out. Measurements were performed using dilute copolymer solutions (ca. 10−2 equiv/liter) in water, 0.04M NaCl, and 0.20M NaCl, respectively, at 25°C. Heat of dissociation data for the copolymer in water at 45°C are also reported. The calorimetric data allow evaluation in each case, (except for the solutions in 0.2M NaCl) of the enthalpy for the conformational transition which the maleic acid-copolymer undergoes upon ionization. With the aid of potentiometric data the associated entropy changes are finally estimated. Our data point out the notable influences of temperature and of added simple salts on the energetics of the conformational transition.

Atactic and syndiotactic 1,2-polybutadiene, atactic 3,4-polyisoprene and poly(4-methyl-1,3-pentadiene)1,2 syndiotactic, having respectively vinyl, methylvinyl and dimethylvinyl pendant groups have been ozonized. The reaction products and the reaction speed toward ozone attack in solution have been studied by FT-IR spectroscopy. The tacticity seems to have no influence on either the reaction products or the reaction speed with ozone. The main product formed by ozonization of syndiotactic 1,2-polybutadiene and of poly(4-methyl-1,3-pentadiene)1,2 syndiotactic is a poly(acrolein) or poly(propenal). Thus each vinyl or dimethylvinyl monomer unit can be mainly converted into an aldehyde pendant group. In the case of atactic 3,4-polyisoprene, ozonization allows changing the methylvinyl group into a methylketone pendant group. Ozonization of atactic 3,4-polyisoprene and also poly(4-methyl-1,3-pentadiene)1,2 syndiotactic, introduces some epoxy groups into the vinyl double bonds as a secondary reaction. The reaction speed with ozone was found to be faster with the most alkyl-substituted double bond in agreement with a general rule. Thus the reaction speed is from the fastest to the slowest as follows: [poly(4-methyl-1,3-pentadiene)1,2 syndiotactic]>[3,4-polyisoprene]>[1,2-polybutadiene]. Ozonization of vinyl polymers could be a way for introducing oxygenated functional groups which can then be used as sites for crosslinking these polymers to prepare new polymer networks.

The interactions of high molecular weight hyaluronan (HA) with di-palmitoyl phosphatidylcholine (DPPC) liposomes in aqueous buffer have been investigated. The superstructures resulting from co-incubation in vitro were observed by means of negative staining and rotary shadowing electron microscopy and were also characterized by rheometric techniques. The existence of a supramolecular complex between the two partners is clearly demonstrated; this complex would exist in vivo in the synovial fluid (whose major components are, in fact, HA and DPPC) and should be responsible for the unique physiological properties of the latter.

Attention has been focused on two uronans, namely, mannuronan and galactose-depleted C-6 oxidized guar, the former of microbial origin and the latter of artificial nature, to provide original data on the extent of epimerization they can undergo in dilute aqueous solution using two C-5 mannuronic acid epimerizing enzymes, that is, AlgE-4 and AlgE-6, alone or in admixture. Original circular dichroism data coupled with 1H NMR spectra clearly point out that both uronans can be epimerized, depending on the enzyme or enzyme mixture used, to high levels yielding guluronic-rich alginate samples and guluronic-rich heteropolysaccharides, respectively. Mannuronan and its epimerization products can easily form clear, firm aqueous gels when an excess of HCl is added or when mixed with aqueous CaCl2, respectively. Depleted-guarox does not gel upon addition of excess HCl, while the heterouronan derived from it having a percent of epimerization nearly identical to that of epimerized mannuronan, that is, ca. 70%, can form gel in the presence of Ca(II) only at higher polymer and Ca(II) concentrations. With the latter, heterouronan alpha-D-galacturonic side groups exert hindrance to "junction zone" formation.

Original data are provided demonstrating that the title condensations are simple and versatile methods for the synthesis of hydrogels based on a variety of carboxylated polysaccharides. In this work, the biopolymers considered are sodium hyaluronate and sodium alginate. Nonnatural carboxylated polysaccharides were commercial (carboxymethyl)cellulose or were obtained by carboxymethylation or selective oxidation of primary alcohol groups of scleroglucan and dextran. Hydrogels prepared via the Passerini reaction were transparent, alkali labile materials whereas the transparency of the Ugi gels depended on the polysaccharide, the cross-linker, and the degree of cross-linking. The Ugi gels were stable for several months at a pH ranging from 1.3 to 11 and up to temperatures over 90 degreesC. The structure of the networks was studied by means of C-13 CP-MAS and N-15 CP-MAS NMR spectroscopy. A quantitative NMR analysis and elemental analysis of the dry gels allowed us to estimate the efficiency of the reactions, i.e., the actual degree of cross-linking, which appeared to be about 80% of theoretical. The influence of added salt and pH on the swelling of several Ugi gels with different degrees of cross-linking was studied in a qualitative manner.

The study of the proton dissociation process of weak polyacids (eg a carboxylic poly(monoprotic)acid) is based on the knowledge of the change in electrostatic free energy, G(el), as a function of the variation of the number of charges on the polymer chain. The original treatment proposed by Manning can be used to describe the proton dissociation process of weak poly(monoprotic)acids, in the absence of pH-induced conformational transitions. In order to describe the alpha dependence of pKa of weak co-poly(monoprotic)acids containing two different acidic groups in different amounts along the polymer chain, a simple modification of the model is proposed.

The behavior of a high molecular weight sodium poly[bis(carboxylatophenoxy)phosphazene] (NaPCPP) polyelectrolyte sample in aqueous solution has been investigated by means of viscosity, conductivity, sodium counterion potentiometric ''activity coefficient'' (gamma(+)) measurements, and Na-23-NMR experiments. The set of data clearly and consistently points out the peculiar polyelectrolytic behavior of NaPCPP in water. In our opinion, this is essentially due to the pal tial hydrophobic character of flexible NaPCPP chains which would easily ''entangle'' even at low concentrations in water and, in addition, would give rise to ''entanglement collapse'' with increasing solution temperature.

The sequence encoding the endopolygalacturonase (PG) of Fusarium moniliforme was cloned into the E. coli/yeast shuttle vector Yepsec1 for secretion in yeast. The recombinant plasmid (pCC6) was used to transform Saccharomyces cerevisiae strain S150-2B; transformed yeast cells were able to secrete PG activity into the culture medium. The enzyme (wtY-PG) was purified, characterized, and shown to possess biochemical properties similar to those of the PG purified from F. moniliforme. The wtY-PG was able to macerate potato medullary tissue disks and was inhibited by the polygalacturonase-inhibiting protein (PGIP) purified from Phaseolus vulgaris. The sequence encoding PG in pCC6 was subjected to site-directed mutagenesis. Three residues in a region highly conserved in all the sequences known to encode PGs were separately mutated: His 234 was mutated into Lys (H 234-->K), and Ser 237 and Ser 240 into Gly (S 237-->G and S 240-->G). Each of the mutated sequences was used to transform S. cerevisiae and the mutated enzymes were purified and characterized. Replacement of His 234 with Lys abolished the enzymatic activity, confirming the biochemical evidence that a His residue is critical for enzyme activity. Replacement of either Ser 237 or Ser 240 with Gly reduced the enzymatic activity to 48% and 6%, respectively, of the wtY-PG. When applied to potato medullary tissue, F. moniliforme PG and wtY-PG caused comparable maceration, while the variant PGs exhibited a limited (S 234-->G and S 240-->G) or null (H 234-->K) macerating activity. The interaction between the variant enzymes and the P. vulgaris PGIP was investigated using a biosensor based on surface plasmon resonance (BIAlite). The three variant enzymes were still able to interact and bind to PGIP with association constants comparable to that of the wild type enzyme.

The interaction between endo polygalacturonase from Fusarium moniliforme and PGIP, from Phaseolus vulgaris L. was investigated using a biosensor technique based on surface plasmon resonance (BIAlite). This new analytical system provides information on the strength and the kinetics of biomolecular interactions. PGIP (the ligand) was covalently attached to the dextran matrix of a sensor chip while endo polygalacturonase (the analyte) was introduced in a flow passing over the surface. Results from real-time BIA are presented as a sensorgram, which is a plot of changes in the resonance signal as a function of time. The experimental data were evaluated with an appropriate software to derive the values of kinetic rate constants and to compare the affinities of PGIP for several variant endo polygalacturonases obtained by site-directed mutagenesis of the Fusarium moniliforme enzyme.

(1995). Analysis of the Interaction between Phaseolus PGIP and fungal Endopolygalacturonases Using Biosensor Technology. Giornale botanico italiano: Vol. 129, No. 4, pp. 1118-1119.

Results are reported for spectroscopic and calorimetric studies of ethidium bromide (EBr) in water and in aqueous solutions of three alternating maleic acid copolymers. The dimerization constant, dimerization enthalpy and the dimer spectrum of EBr are derived. The interaction of EBr with the polycarboxylates is characterized on the basis of spectral and microcalorimetric data according to two limiting mechanisms: at low dye-to-polymer concentration ratios, EBr would be bound essentially in monomeric form with small exothermic effects: at high concentration ratios, the observed comparatively large exothermic heat is attributed to bound dye stacking.

The luminescence properties of a series of lanthanide-substituted ionic polysaccharides have been examined in an attempt to learn about the nature of interactions between the metalions and the polymers. Emission and excitation spectra were obtained for Tb(III) complexes with carboxymethyl cellulose, Sclerox S-1.0, alginate, polygalacturonic acid, amylose sulfate, dextran sulfate, and i-carrageenan. Studies of the chirality associated with the metal-ion binding sites were performed through the use of circularly polarized luminescence spectroscopy. It was learned that the lanthanide ions could form complexes with polysaccharides in the electrostatic manner of polyelectrolytes, and that specific ligating groups could further influence the metal-ion binding characteristics.

The results of thermal denaturation, fluorescence, calorimetric and viscosimetric studies on the interaction of adriamycin and its beta anomer with DNA are reported. Whereas all equilibrium, hydrodynamic and thermodynamic measurements are consistent with the proposed intercalative binding model for the adriamycin-DNA complex, the binding mechanism for the reaction of the beta anomer with DNA remains uncertaian. All DNA binding properties of this stereoisomer are substantially different from those of the parent compound. The results suggest that the amino sugar residue of the natural antibiotic may interact stero-specifically with the DNA helix, thus dictating the orientation of the tetracvclic chromophore within the intercalation site. The alteration in the DNA binding capacity and the changes in interactions with DNA following in inversion of configuration at C-1', parallel a lack of biological activity observed for the beta anomer.

The “strong” binding of two antibiotics, actinomycin D and daunomycin, to native DNA (calf-thymus) in dilute aqueous solution has been studied by means of calorimetric and spectroscopic measurements. In essence our results show: (1) Daunomycin interaction with DNA is an exothermic process, all features of which depend in a discontinuous way on the fraction of DNA binding sites engaged by the drug. Fluorescence data indicate that such a discontinuous trend should be independent of the GC content of DNA. (2) Actinomycin binding to DNA is, on the contrary, characterized by a positive enthalpy. For such binding, no discontinuity appears discernible with increasing the molar ratio of drug to DNA (phosphorous) on the basis of calorimetric and fluorescence data. (3) Both antibiotics can be bound simultaneously to DNA: our results would suggest that their binding sites on the biopolymer are independent. Discussion is focussed on the possible information derivable from our data on whether or not intercalation may indeed be the main process through which each antibiotic considered “strongly” interacts with DNA.

The results of an investigation on the interaction of proflavine and of ethidium bromide with DNA (calf thymus) in dilute aqueous solution are reported. The binding of the two dyes by DNA has been studied by means of microcalorimetric and of equilibrium dialysis measurements. Data on the thermodynamics of dimerization of both proflavine and ethidium bromide in aqueous solution obtained on the basis of spectroscopic and/or calorimetric experiments are also reported. The enthalpy data show that dye-dimerization and dye “strong” interaction with DNA are energetically favourable and quite similar while only in the latter case the phenomenon is also entropy driven. This is taken as further evidence in support of the concept that “strong” interaction-of both proflavine and ethidium bromide with DNA means dye molecules intercalation into the native, double helical structure of the biopolymer.

A soil bacterium grown on propan-2-yl sulphate as sole source of carbon and sulphur yielded extracts containing an enzyme capable of liberating sulphate from racemic lactate-2-sulphate. The enzyme was purified to homogeneity by a combination of streptomycin sulphate precipitation of nucleic acids, batch treatment with DEAE-cellulose, and chromatography on columns of DEAE-cellulose, Sephacryl S-300 and butyl-agarose. The protein was monomeric with an Mr of 55 000-60 000. The enzyme activity was specific for D-lactate-2-sulphate (Km 6.6 nM; maximal specific activity 14.3 mumol/min per mg of protein) and showed no activity towards the L-isomer. The products of the enzyme's action were inorganic sulphate and D-lactate which were released in equimolar amounts and stoicheiometrically with the amount of ester hydrolysed. No L-lactate was formed. Retention of configuration implied cleavage of the O-S bond of the C-O-S ester link and this was confirmed by 18O-incorporation experiments in which 18O from 18O-enriched water in the incubation medium was incorporated exclusively and quantitatively into inorganic sulphate. Only two other esters (serine-O-sulphate and p-nitrophenyl sulphate) of a total of 29 compounds tested were substrates for the enzyme. D-Lactate, L-lactate-2-sulphate and the substrate analogues glycollate-2-sulphate and butyrate-2-sulphate were significantly inhibitory.

Potentiometric, calorimetric, and dilatometric data on the ionization of several saturated dicarboxylic acids in water at 25°C are reported. A correlation is attempted between structure and thermodynamic evidences for the two dissociation stages of the diacids considered, in particular in terms of the propensity toward intramolecular hydrogen bond formation of some singly ionized species.

SUMMARY: A strain of Pseudomonas syringae was isolated from garden soil for its ability to utilize propan-2-yl sulphate as sole source of carbon and energy. Growth was accompanied by disappearance of the ester from culture fluids and formation of stoicheiometric amounts of inorganic sulphate. However, enzyme activity capable of desulphating propan-2-yl sulphate was not detected under a wide range of assay conditions, either intracellular or extracellular, or at different phases of batch culture. No organic radioactive metabolites were detected during growth on propan-2-yl [35S]sulphate or [1,3-14C]propan-2-yl sulphate alone, but when the latter compound was supplemented with unlabelled lactate, small amounts of 14C-labelled lactate were detected. This and the induction by propan-2-yl sulphate of a specific d-lactate-2-sulphatase led to a proposed pathway in which propan-2-yl sulphate undergoes a stereospecific oxidation to d-lactate-2-sulphate before rapid desulphation to d-lactate and inorganic sulphate.

Thermodynamic data relative to the reversible interaction between human or bovine serum albumin and some organic ligands (S-and R-warfarin, d-and l-oxazepam hemisuccinate, phenyl-butazone, fluorescein) in dilute aqueous solution were determined by means of gel permeation chromatography and microcalorimetric measurements. From an analysis of these data and on the basis of fluorescence titrations the identity of the “primary” binding site on the proteins for some ligands was evidenced, while in other cases a cooperative binding of two different ligands to different binding sites could be discerned.

The binding affinity of fluorescein and of phenylbutazone to human serum albumin (HSA) and to bovine serum albumin (BSA), respectively, as well as of the two drugs together to each protein in dilute aqueous solution has been studied by means of gel permeation chromatography, circular dichroism, U.V. absorption and fluorescence spectroscopy. Identity of and/or interdependence between primary binding sites for the two ligands considered on HSA and BSA are evidenced and correlated with a simple theoretical approach to mixed drugs binding.

The thermal behaviour of isotactic poly[(S)-4-methyl-1-hexene], (P(S)4 MH), isotactic poly[(R)-4-methyl-1-hexene], (P(R)4 MH), of their equimolar mixture (r-P4MH) and of poly[(R)(S)-4-methyl-1-hexene], (P4MH), was investigated. The DSC curves obtained by melting P(S)4MH and P(R)4MH showed two endothermic peaks, while only one peak was found in the DSC curves obtained by melting r-P4MH or P4MH. For the optically active polymers the formation of a mesophase is proposed and the results are discussed on the basis of the conformation of these polymers in the crystalline and in the liquid state. Das thermische Verhalten von isotaktischem Poly[(S)-4-methyl-1-hexen], (P(S)4MH), Poly[(R)-4-methyl-1-hexen], (P(R)4MH), ihrer aquimolaren Mischung (r-P4MH) und von Poly[(R)(S)-4-methyl-1-hexen] (P4MH) wurde untersucht. Die DSC-Kurven von P(S)4MH und P(R)4MH ergaben beim Schmelzen zwei endotherme Peaks, wahrend nur ein Peak in den DSC-Kurven von r-P4MH und P4MH gefunden wurde. Fur die optisch aktiven Polymeren wird die Bildung einer Mesophase vorgeschlagen und die experimentellen Ergebnisse werden auf der Basis der Konformation dieser Polymeren im kristallinen und flussigen Zustand besprochen.

The changes in enthalpy, entropy and volume upon melting have been determined by dilatometric and differential scanning calorimetry measurements for four polyesteramides of the type: -[- COφCONH(CH 2 ) n  NHCOφCOO(CH 2 ) m  O -]- x with the following values for n and m; 6-6, 12-2, 12-6 and 12-12. The changes in each state function vary quite regularly with the number of CH2 groups/repeating unit. A comparison is made between experimental data on the entropy of fusion and theoretical predictions. There is emphasis on the influence on the thermodynamics of melting of the rigidity of the -OCO-φ-CONH- residues and, in particular, of the persistence in the molten state of many interchain hydrogen bonds.

The optical and rotatory properties of poly-L-tyrosine (PLT) dissolved in trimethyl phosphate and in water have been measured. The results, however, cannot be explained in terms of one conformation or another, since the side-chains chromophores interact with the peptide groups or among themselves, thus giving rise to complex circular dichroic spectra. IR measurements carried out on films of PLT cast from trimethylphosphate (TMP) or directly on solutions of the polymer in TMP strongly suggest that the polypeptide assumes an α-helical conformation. The sense of spiralization of the helix cannot be obtained with such measurements. Es wurden die optischen und polarimetrischen Eigenschaften von Poly-L-tyrosin (PLT) in Trimethylphosphat und Wasser als Losungsmittel untersucht. Die Ergebnisse konnen jedoch nicht durch das Vorliegen einer bestimmten Konformation gedeutet werden, da Wechselwirkungen der Seitenketten-Chromophore mit sich selbst oder mit Peptidgruppen zu komplexen CD-Spektren fuhren. IR-Messungen an Filmen von PLT, die aus Trimethylphosphat (TMP) gegossen waren, oder direkt an Losungen des Polymeren in TMP machen wahrscheinlich, das das Polypeptid eine α-helikale Konformation ausbildet. Der Helixsinn kann aus solchen Messungen jedoch nicht bestimmt werden.

Solution properties of two polyesters, poly(β-propiolactone) and poly(ϵ-caprolactone) in dioxane have been studied. Data reported are: polymer densities, thermal expansion coefficients, thermal pressure coefficients, solution densities (volume changes on mixing: (ΔVM) and heats of dilution (ΔH1). It is found that the solution properties of the two polyesters in dioxane differ; e.g. poly(β-propiolactone): ΔVM 0; poly(ϵ-caprolactone): ΔVu > 0; ΔH1 < 0. Flory's theory is used to interpret these results. The theory contains one adjustable parameter (X12) which is fixed by fitting the theory to the heat of dilution data. Sign and order of magnitude of the volume changes on mixing are then correctly predicted.

The results obtained in a study of the heat and entropy of fusion, and a few data on the crystallization kinetics, of poly-β-propiolactone and poly-ϵ-caprolactone are reported. Attention is focused on the entropy data for the two polymers. A comparative, theoretical analysis of the constantvolume entropy of melting of the polylactones and of three aliphatic polyesters is made. The remainder of the entropy of melting of the polymers considered is qualitatively correlated with chemical constitution and crystal structures.

The rate of electron transfer in the system (+)-tris-(o-phenanthroline)cobalt(III)–tris-(o-phenanthroline)cobalt(II) has been determined in dilute aqueous solutions of sodium poly(styrenesulphonate), sodium poly (vinylsulphonate), and sodium poly(phosphate). Electron exchange was followed by studying the change in optical rotation of the cobalt(III) complex. Powerful catalytic action on the exchange is exhibited by the polyelectrolytes, particularly sodium poly(vinylsulphonate), under appropriate experimental conditions. Further the rate of electron transfer between the two complex ions is, at a given concentration of the reactants, influenced in a marked and specific manner by varying polyion concentrations. An explanation of the correlation of the rate data with binding data is not feasible. The influence of forces other than coulombic ones in the interaction between macroions and counterions is, in fact, certainly very important in determining the behaviour of the system considered, notably in dilute solutions of sodium poly(styrenesulphonate).

A detailed uv spectral investigation of the interaction of methyl orange (and other similar anionic azo-dyes) with four different synthetic cationic polyelectrolytes, with colloidal electrolytes, as well as with two proteins in dilute aqueous solutions, has been carried out. Under appropriate conditions, binding of methyl orange, ethyl orange, and butyl orange to poly( l -ornithine, poly- l -lysine), poly ( N -methylvinyl pyridinium chloride), and trimethyldodecylammonium chloride, gives rise to marked changes in the spectrum of each of the three dyes (but not of other dyes examined). These spectral changes are quite different from those which result from the binding of the azo-dyes on to the strongly ionized poly(vinylbenzyltrimethyl ammonium chloride) chains. The effects observed with the four synthetic polyelectrolytes mentioned above and with the colloidal electrolytes, are postulated to be connected with a conformational change of bound dye molecules. Interaction of methyl orange with bovine serum albumin and with lysozyme would mainly result in a partial solubilization of the dye in the hydrophobic regions of the proteins.

Calculations of the unperturbed dimensions of Na-polyacrylate have been carried out, for various concentrations of meso and racemic diads, allowing for coulombic interactions both between side charges within the chain and between side charges and the counter-ions. Contrary to previous calculations where the counter-ion was neglected, the present approach can explain the rather high experimental value of the characteristic ratio. Both the Monte Carlo method and the method suggested by one of the authors, based on the hypothesis of a conditional stereo chemical equilibrium within the chain, are employed; the results are in substantial agreement.

The effect of several polyelectrolytes on the absorption spectrum of crystal violet (CV) has been studied over a wide range of pH. The following polymers were used: isotactic poly(methacrylic acid), PMAi; conventional poly(methacrylic acid), PMAc; a methacrylic acid (80%)-styrene (20%) copolymer, PMAS; and poly(styrene sulfonic acid), PSSA. Distinctly different effects were observed in the four cases. This has been interpreted in terms of a dependence of the degree and mode of binding of cationic dye molecules onto the polyacids on the hydrophobicity of the macroions.

The synthesis and characterization of new polymers is reported. These polymers were prepared by reaction of 3.6-bifunctional 2.5-diketopiperazines with aliphatic and aromatic diisocyanates. Using D-3.6-bis(aminoxymethyl)-2.5-diketopiperazine optically active polymers have been obtained. Es wird uber die Synthese und Charakterisierung von neuen Polymeren berichtet. Die Polymeren wurden durch Umsetzung von 3.6-bifunktionellen 2.5-Diketopiperazinen mit aliphatischen und aromatischen Diisocyanaten dargestellt. Ausgehend vom D-3.6-Bis(aminoxymethyl)-2.5-diketopiperazin, wurden optisch aktive Polymere erhalten.

The helix coil transition of poly(L-tyrosine) in dimethylsulfoxide/trimethylphosphate and in dimethylsulfoxide/dimethylformamide solution, induced by either changing the solvent composition (at 25°C) or by changing the temperature was studied calorimetrically (heat of dilution experiments) and by means of optical activity measurements, respectively. The calorimetric enthalpy of transition, in particular, and the VAN'T HOFF heat of transition of poly(L-tyrosine) at 25°C resulted, dependent upon the mixed solvent considered. As a consequence, the σ parameter of the theory of ZIMM and BRAGG appeared solvent dependent in the case studied by us. Der Helix Knauel-Ubergang von Poly(L-tyrosin) in Dimethylsulfoxid/Trimethylphosphat- und in Dimethylsulfoxid/Dimethylformamid-Losung, hervorgerufen durch Anderung der Solvens-Zusammensetzung (bei 25°C) oder der Temperatur, wurde kalorimetrisch (Untersuchung der Verdunnungswarmen) und mit Hilfe optischer Aktivitatsmessungen untersucht. In Abhangigkeit vom untersuchten Solvens-Gemisch resultierten die kalorimetrische Enthalpie und die VAN'T HOFFsche Warme des Uberganges von Poly(L-tyrosin) bei 25°C. Aus den untersuchten Fallen ergab sich die Folgerung, das die σ-Parameter der Theorie von ZIMM und BRAGG vom Losungsmittel abhangig sind.

The activity coefficient γ, of sodium ion, in aqueous solutions of both isotactic and conventional poly(methacrylic acid) (PMA) has been studies throughout the whole range of degree of neutralization α with a Beckman Na electrode and membrane electrodes. The results show that the fraction of sodium ions bound to isotactic PMA is higher than that bound to conventional (or syndiotactic) PMA over the entire range of α. The binding of divalent counterions (Mg+2, Cu+2, Co+2, and Ni+2) by the two forms of PMA (at α = 0.95) has been evaluated from the release of Na+ ions with the Beckman Na electrode. Turbidimetric determinations of the critical amount of various divalent cation chlorides necessary to bring about precipitation of both isotactic and conventional PMA (at α = 0.95) have also been carried out.

The conformational state of poly-L-glutamic acid (PLGA) in the mixed solvent pyridine/water has been studied by means of different techniques (ORD, IR, PMR, and viscosity). It has been found that at low water contents PLGA forms aggregates the stability of which depends in a sensitive manner on temperature and solvent composition. At higher water content PLGA undergoes a helix–coil transition. Die Konformation von Poly-L-glutaminsaure (PLGA) in Pyridin/Wasser-Gemischen wurde mit Hilfe verschiedener Techniken untersucht (ORD, IR, NMR und Viskosimetrie). Es wurde gefunden, das bei niedrigen Wassergehalten PLGA Aggregate bildet, deren Stabilitat sehr empfindlich von der Temperatur und der Zusammensetzung des Losungsmittelgemisches abhangt. Bei hoherem Wassergehalt des Mediums findet eine Helix–Knauel-Umwandlung statt.

The unperturbed dimensions of poly-ϵ-caprolactone (PϵL), poly-β-propiolactone (PβL) and polypivalolactone (PPL) have been evaluated theoretically. We find that the values of the characteristic ratio, C∞, are 6 · 66 (PϵL), 3 · 98 (PβL) and 8 · 10 (PPL). The calculations are based, as usual, on the isomeric rotational state model. Statistical weights are assigned to allowed rotational states around the different bonds along polylactone chains on the basis of indications derived from conformational van der Waals energy maps and by analogy with the cases of other similar chains studied by other authors. Dipolar interactions were not explicitly taken into account. Theoretical evaluations of the mean square dipole moments of PϵL, PβL and PPL chains are also made. Correlation of theory and experiment must await more detailed investigations, as experimental data are limited to the PϵL case for which there is apparently a disagreement between our C∞ value and that extrapolated from intrinsic viscosity data (in good solvents). Theoretical C∞ values, however, depend critically on the choice of the values of one or two statistical weights: theory is thus flexible enough to lead to ready agreement with information from future and reliable experimental data.

An investigation has been carried out of the interaction of optically active tris(ethylenediamine)–Co(III) and of tris(o-phenanthroline)–Ni(II) complex ions with different polyelectrolytes in dilute aqueous solution. Optical rotatory dispersion measurements reveal that binding of the Co(III) complex ions occurs with a noticeable degree of specificity which in addition to depending on the nature of the fixed charges is also affected by the chemical constitution of the polyelectrolytes chain backbones. The dependence of tris(ethylenediamine)–Co(III) optical activity on polyelectrolyte concentration also exhibits interesting features. Polarimetric measurements of the rate of racemization of tris(o-phenanthroline)–Ni(II) ions in the presence of different polyelectrolytes lead to similar conclusions. Sodium dextran sulfate is shown to interact selectively with one of the antipodes of tris(phenanthroline)–Ni(II) complex.

A molecular model has been built to explain complex formation between DNA and spermine or spermidine. This model has been derived on the basis of the results obtained from the X-ray analysis of the crystal structure of spermine hydrochloride. It has made it possible to predict strong interactions between DNA and protonated polyamines. Determinations of the degree of binding of the polyamines to DNA deduced from measurements of activity coefficients and electrophoretic mobilities have in fact shown that a fraction of the protonated polyamine close to unity is strongly associated to the macro-ion. These results and the stabilization toward thermal denaturation of DNA brought about by the polyamine lead to the conclusion that a complex is formed in solution characterized by a very regular conformation with the elimination of defects, which in aqueous solutions are very likely to be concentrated within regions rich in the more solvated A-T pairs.