Effect of cyclodextrins on pH-induced conformational transition of poly(methacrylic acid)

A pH-induced conformational transition of atactic poly(2-methylprop-2-enoic acid) (poly(methacrylic acid), PMMA) from the contracted to expanded conformation was investigated by viscometry, potentiometric titration, and anthracene solubilisation in the presence of low-molecular-mass non-ionogenic co-solutes-glucose, α-cyclodextrin (αCD), and γ-cyclodextrin (γCD), respectively. No effect of glucose and αCD on the conformational transition was observed with either of the methods used. On the other hand, the characteristic features of the conformational transition were absent in the presence of γCD. The different effects of the co-solutes indicate that the interaction between PMAA and γCD corresponds to the partial inclusion of the PMAA chain into the γCD cavity. The viscometry and anthracene solubilisation imply that γCD promotes the expanded conformation of PMAA at low pH. The potentiometric titration does not support this conclusion. Even though there is no break on the Henderson-Hasselbalch plot, a characteristic of the conformational transition, the potentiometric behaviour corresponds to that of the contracted PMMA conformation. Thus the results suggest the hierarchical picture of the PMAA conformation at low pH in which the local arrangement of the PMAA chain is a prerequisite for clustering on a larger scale.     

Cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures: Synthesis and gradient stimuli‐responsive properties

We report the synthesis and gradient stimuli‐responsive properties of cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures. A ionic hyperbranched poly(β‐cyclodextrin) (β‐CD) core was firstly synthesized via a convenient “A₂+B₃” approach. Double‐layered shell architectures, composed of poly(N‐isopropyl acrylamide) (PNIPAm) and poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) miktoarms as the outermost shell linked to poly(N,N‐diethylaminoethyl methacrylate) (PDEAEMA) homoarms which form the inner shell, were obtained by a sequential atom transfer radical polymerization (ATRP) and parallel click chemistry from the modified hyperbranched poly(β‐CD) macroinitiator. The combined characterization by ¹H NMR, ¹³C NMR, ¹H‐²⁹Si heteronuclear multiple‐bond correlation (HMBC), FTIR and size exclusion chromatography/multiangle laser light scattering (SEC/MALLS) confirms the remarkable hyperbranched poly(β‐CD) core and double‐shell miktoarm architectures. The gradient triple‐stimuli‐responsive properties of hyperbranched core‐double‐shell miktoarm architectures and the corresponding mechanisms were investigated by UV–vis spectrophotometer and dynamic light scattering (DLS). Results show that this polymer possesses three‐stage phase transition behaviors. The first‐stage phase transition comes from the deprotonation of PDEAEMA segments at pH 9–10 aqueous solution under room temperature. The confined coil‐globule conformation transition of PNIPAm and PDMAEMA arms gives rise to the second‐stage hysteretic cophase transition between 38 and 44 °C at pH 10. The third‐stage phase transition occurs above 44 °C at pH = 10 attributed to the confined secondary conformation transition of partial PDMAEMA segments. This cyclodextrin‐overhanging hyperbranched core‐double‐shell miktoarm architectures are expected to solve the problems of inadequate functionalities from core layer and lacking multiresponsiveness for shell layers existing in the dendritic core‐multishell architectures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Low temperature splinting activity and catalytic behavior of nano Ag doped sulphamicacid bridged diblock copolymer

A novel silver nanoparticle doped diblock copolymer was synthesized by a 3‐step process via bulk polymerization process under nitrogen atmosphere. The above prepared polymer is characterized by FTIR spectroscopy, fluorescence emission spectroscopy, circular dichroism (CD), HRTEM, and FESEM. The sulphamicacid end capped poly(ε‐caprolactone) (P1) system exhibited higher tensile strength than the sulphamicacid bridged diblock copolymer (P2) and nano Ag doped sulphamicacid bridged diblock copolymer (P3) systems. The splinting activity of the diblock copolymers was tested and confirmed the low temperature splinting activity of the diblock copolymer. The Ag nanoparticle catalyzed catalytic reduction of p‐nitrophenol (NiP) was tested, and the apparent rate constant (k_app) was determined as 7.36 × 10⁻³ sec⁻¹. The thermal studies were carried out by DSC and TGA methods. The TGA study declared that the P1 system has higher degradation temperature than the P2 and P3 systems. The P1 system has higher melting temperature (T_m) (75.5°C) than the P2 and P3 systems. The CD study indicated that the conformation of sulphamicacid was not changed even after the formation of nano Ag doped sulphamicacid bridged diblock copolymer.     

Anomalous change of viscosity and conductivity in blood plasma lipoproteins in the physiological temperature range

Study on temperature dependencies of viscosity (η) and conductivity (σ) of blood lipoproteins [high‐density lipoprotein (HDL), low‐density lipoprotein (LDL), and very low density lipoprotein (VLDL)] and A‐I apolipoprotein (human and rats) has revealed the presence of the anomalous region at temperature 35–38±0.5°C (T_c). Transition width is 2°C. Viscous flow enthalpy, activation energy (ΔH), and transition enthalpy (ΔH_trans.) as well as thermal coefficients Δη/ΔT and Δσ/ΔT on either side of T_c have been calculated. Transition heat is very low in human HDL, VLDL and apoA‐I, and in LDL it is higher by a factor of 4–5. Some mechanisms of the cortisol interaction with HDL and apoA‐I have been studied by infrared (IR) spectroscopy and conductometry. The hormone has been found to strengthen the tangle → α‐helixes and tangle → β‐structures transitions and increase the ordering of lipids. Therewith, ΔH_trans. rises markedly (13 and more times), and at the same time the anomalous region is shifted by 1–2°C in apoA‐I. The anomalous change of viscosity and conductivity in the physiological temperature range for all lipoprotein fractions and apoA‐I seems to be due to the structural phase transition in both proteins and lipids. In view of the heat capacity jump and a low value of ΔH_trans. in human HDL, one may assume the phospholipids of these particles to exhibit the orientation transition of smectic A↔C type, which is assigned to the second type of phase transition. The structural transition into apoA‐I is likely to contain the elements of phase transition of the first and second types. In human and rat VLDL, the smectic → cholesteric phase transition seems to occur. Enthalpy of viscous flow and structural transition in VLDL is higher for rats than for human. The pH shift of the medium to the neutral region (pH 6.1) results in shifting the anomalous region by 1–2°C. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 348–369, 2001     

A Dinuclear Mercury(II)‐Mediated Base Pair in DNA

The first dinuclear metal‐mediated base pair containing divalent metal ions has been prepared. A combination of the neutral bis(monodentate) purine derivative 1,N⁶‐ethenoadenine (ϵA), which preferentially binds two metal ions with a parallel alignment of the N−M bonds, and the canonical nucleobase thymine (T), which readily deprotonates in the presence of Hg^II and thereby partially compensates the charge accumulation due to the two closely spaced divalent metal ions, yields the dinuclear T‐Hg^II₂‐ϵA base pair. This metal‐mediated base pair stabilizes the DNA oligonucleotide duplex as shown by an increase of 8 °C in its melting temperature. Formation of the base pair was demonstrated by temperature‐dependent UV spectroscopy as well as by titration experiments monitored by UV and CD spectroscopy.     

Aqueous solution behavior of thermosensitive (N-isopropylacrylamide-acrylic acid-ethyl methacrylate) terpolymers

A series of N-isopropylacrylamide (NIPAM)-acrylic acid–ethyl methacrylate terpolymers with varied monomer compositions was prepared by radical polymerization. The solution behavior of these polymers was studied in dilute aqueous solution using spectrophotometry, fluorescence spectroscopy and high-sensitivity differential scanning calorimetry. The results obtained revealed that the lower critical solution temperatures depend strongly on the copolymer composition, solution pH and ionic strength. At a high pH, the ionization of acrylic acid (AA) units leads to an increase in solution cloud points (T_c). Solutions of polymers containing 10% or less of AA display a constant T_c for pH above 5.5, with 15% there is a continuous increase in T_c with pH and, for higher AA contents, no clouding was observed within the studied temperature range. Fluorescence probe studies were conducted by following the I ₁/I ₃ ratio of pyrene vibronic bands and the emission of anilinonaphtalene sulfonic acid, sodium salt (ANS), both approaches revealing the existence of hydrophobic domains for polymers with higher ethyl methacrylate content at temperatures lower than T_c, suggesting some extent of aggregation and/or a coil-to-globule transition. Scanning calorimetry measurements showed an endothermic transition at temperatures agreeing with the previously detected cloud points. Moreover, the transition curves became broader and with a smaller transition enthalpy, as both the AA content and the solution pH were increased. These broader transitions were interpreted to be the result of a wider molecular distribution upon polymer ionization, hence, displaying varied solution properties. The decrease in transition enthalpy was rationalized as a consequence of reminiscent hydration of NIPAM units, even after phase separation, owing to the presence of electric charges along the polymer chain.     

A Gadolinium‐Binding Cyclodecapeptide with a Large High‐Field Relaxivity Involving Second‐Sphere Water

A new cyclodecapeptide incorporating two prolylglycine sequences as β‐turn inducers and bearing four side chains with acidic carboxyl groups for cation complexation has been prepared. Structural analysis in water by ¹H NMR spectroscopy and CD shows that this template adopts a conformation suitable for the complexation of lanthanide ions Ln³⁺, with its carboxyl groups oriented on the same face of the peptide scaffold. Luminescence titrations show that mononuclear Ln–PA complexes are formed with apparent stability constants of log β₁₁₀≈6.5 (pH 7). The high‐field water relaxivity values arising from the Gd–PA complex at 200–500 MHz have been interpreted with molecular parameters determined independently. The experimentally determined water relaxivities are undoubtedly 30 % higher than the expected values for this complex with two inner‐sphere (IS) water molecules and a medium‐range rotational correlation time (τ_R=386 ps (±10 %)). This led us to propose the existence of a large second‐sphere (2S) contribution to the relaxivity caused by the interaction of water molecules with the hydrophilic peptide ligand by hydrogen‐bonding.     

Investigation and characterization of PVA-g-AAc/Zol membranes for possible practical use in separation processes

Poly(vinyl alcohol) films were grafted with two monomers (acrylic acid and N-vinyl imidazole) using the gamma irradiation technique. The melting temperature (T_m) and glass transition temperature (T_g) of the grafted membranes were determined with respect to the grafting yield. The ability of these membranes to separate cobalt from nickel has been investigated. The diffusion of cobalt and nickel ions from the feed compartment to the receiver compartment depends on the grafting yield and the pH of the feed solution. Cobalt ions do not diffuse through the membrane when the pH of the feed solution is >4.5. Thus, the prepared membranes could be considered for the separation of cobalt ions from nickel ions. The temperature of thermal decomposition of pure PVA-g-AAc/Zol membrane, PVA-g-AAc/Zol membranes containing cobalt ions, and PVA-g-AAc/Zol membranes containing nickel ions are determined using TGA analyzer; it was shown that the presence of cobalt and nickel increases the decomposition temperature. Also the membranes bonded with cobalt ions are more stable than the membranes containing nickel ions.     

Three‐Component Supramolecular System with Multistimuli‐Responsive Properties in Water

Hyperbranched polyethylenimine terminated with isobutyramide groups (HPEI‐IBAm), 4‐(phenylazo)benzoic acid (PABA), and α‐cyclodextrin (α‐CD) were assembled together at pH≈7 to form the three‐component supramolecular complexes that were verified by ¹H and 2D ROESY ¹H NMR spectroscopy. UV/Vis spectrometric titration experiments showed that the content of α‐CD in the three‐component complexes was less than the feed amount and it was difficult for all the PABA units in the complexes to further form complexes with α‐CD. The obtained three‐component supramolecular complexes exhibited thermoresponsive properties in water. Increasing the α‐CD concentration led to a sharp increase in the cloud point temperature (T_cp) at the beginning, but after the [α‐CD]/[PABA] ratio was in the region of 1.3–1.6, the T_cp increased gradually When the concentration of α‐CD was low, a higher concentration of PABA led to a lower T_cp, however, the opposite was observed when the concentration of α‐CD was high. For the three‐component complex, increasing the α‐CD concentration at pH≈7 or at pH≈9 led to different T_cp temperatures. In the low α‐CD concentration range, adjusting the pH from ≈7–≈9 resulted in an increase in the T_cp, similar but not so pronounced as that of the two‐component system of HPEI‐IBAm/[PABA]. When the concentration of α‐CD was high, adjusting the pH from ≈7–≈9 decreased the T_cp; this observation is different to that of the two‐component system of HPEI‐IBAm/[PABA]. Reversible trans‐to‐cis photoisomerization of azobenzene units in the complexes occurred, following irradiation with UV or visible light. Trans‐to‐cis isomerization of azobenzene units decreased the T_cp. However, this result differed to that of the two‐component system of HPEI‐IBAm/PABA.     

Harnessing the Flexibility of Peptidic Scaffolds to Control their Copper(II)‐Coordination Properties: A Potentiometric and Spectroscopic Study

Designing small peptides that are capable of binding Cu²⁺ ions mainly through the side‐chain functionalities is a hard task because the amide nitrogen atoms strongly compete for Cu²⁺ ion coordination. However, the design of such peptides is important for obtaining biomimetic small systems of metalloenyzmes as well as for the development of artificial systems. With this in mind, a cyclic decapeptide, C‐Asp, which contained three His residues and one Asp residue, and its linear derivative, O‐Asp, were synthesized. The C‐Asp peptide has two Pro? Gly β‐turn‐inducer units and, as a result of cyclization, and as shown by CD spectroscopy, its backbone is constrained into a more defined conformation than O‐Asp, which is linear and contains a single Pro? Gly unit. A detailed potentiometric, mass spectrometric, and spectroscopic study (UV/Vis, CD, and EPR spectroscopy) showed that at a 1:1 Cu²⁺/peptide ratio, both peptides formed a major [CuHL]²⁺ species in the pH range 5.0–7.5 (C‐Asp) and 5.5–7.0 (O‐Asp). The corrected stability constants of the protonated species (log K*_CuH(O?Asp)=9.28 and log K*_CuH(C?Asp)=10.79) indicate that the cyclic peptide binds Cu²⁺ ions with higher affinity. In addition, the calculated value of K_eff shows that this higher affinity for Cu²⁺ ions prevails at all pH values, not only for a 1:1 ratio but even for a 2:1 ratio. The spectroscopic data of both [CuHL]²⁺ species are consistent with the exclusive coordination of Cu²⁺ ions by the side‐chain functionalities of the three His residues and the Asp residue in a square‐planar or square‐pyramidal geometry. Nonetheless, although these data show that, upon metal coordination, both peptides adopt a similar fold, the larger conformational constraints that are present in the cyclic scaffold results in different behaviour for both [CuHL]²⁺ species. CD and NMR analysis revealed the formation of a more rigid structure and a slower Cu²⁺‐exchange rate for [CuH(C‐Asp)]²⁺ compared to [CuH(O‐Asp]²⁺. This detailed comparative study shows that cyclization has a remarkable effect on the Cu²⁺‐coordination properties of the C‐Asp peptide, which binds Cu²⁺ ions with higher affinity at all pH values, stabilizes the [CuHL]²⁺ species in a wider pH range, and has a slower Cu²⁺‐exchange rate compared to O‐Asp.     

NMR study on trapping techniques to deduce the conformations of 1-alkyl-3- hydroxypiperidines

The conformational equilibrium of 1-alkyl-3-hydroxypiperidines in n-heptane and aqueous solution is investigated. Several methods, e.g. IR and NMR spectroscopy, are discussed. The conformation trapping in D₂SO₄-D₂O mixtures, and subsequent analysis of the ¹H and ¹³C NMR spectra, is proven to be the most reliable method. In an apolar solvent the conformation with an axial hydroxyl group is always dominant (69%). In aqueous solution the same conformation predominates in the protonated form (56%, pH<5), while only 43% of this conformation is present in the free base (pH～11). A detailed ¹³C NMR study is described of 1-isopropyl-3-hydroxypiperidine in aqueous solution at pH between 2 and 11.     

Correlation between Luminescence and EPR Spectroscopy as Evidence of Ytterbium Pair Formation in Li6Ln(BO3)3:Yb3+ (Ln=Gd,Y) Borate Single Crystals

Synthesized powders and grown single crystals of nominal compositions Li₆Ln(BO₃)₃:Yb³⁺ (Ln=Y, Gd) were investigated by means of powder and single‐crystal X‐ray diffraction (XRD), as well as optical near‐IR spectroscopy in conjunction with electron paramagnetic resonance (EPR) spectroscopy. The appearance of two distinct zero‐phonon lines suggests the existence of two kinds of Yb³⁺ ions in the single crystals. The XRD results exclude the possibility of a phase transition occurring between room and low temperatures. EPR spectra of single crystals show the presence of both isolated ions and pairs of ytterbium ions substituted for Y³⁺. A strong temperature dependence of the intensity of Yb–Yb pairs resonance lines coincides with temperature dependence of emission peak at 978 nm, confirming a common origin of the defect giving rise to these spectra. Calculated from EPR spectra, the distance between pairs of Yb³⁺ is in good agreement with crystallographic ones: R=3.856 Å, R_cryst=3.849 Å.     

Poly(N‐phenylmaleimide‐co‐acrylic acid)–copper(II) and poly(N‐phenylmaleimide‐co‐acrylic acid)–cobalt(II) complexes: Synthesis,characterization, and thermal behavior

The free‐radical copolymerization of N‐phenylmaleimide (N‐PhMI) with acrylic acid was studied in the range of 25–75 mol % in the feed. The interactions of these copolymers with Cu(II) and Co(II) ions were investigated as a function of the pH and copolymer composition by the use of the ultrafiltration technique. The maximum retention capacity of the copolymers for Co(II) and Cu(II) ions varied from 200 to 250 mg/g and from 210 to 300 mg/g, respectively. The copolymers and polymer–metal complexes of divalent transition‐metal ions were characterized by elemental analysis, Fourier transform infrared, ¹H NMR spectroscopy, and cyclic voltammetry. The thermal behavior was investigated with differential scanning calorimetry (DSC) and thermogravimetry (TG). The TG and DSC measurements showed an increase in the glass‐transition temperature (T_g) and the thermal stability with an increase in the N‐PhMI concentration in the copolymers. T_g of poly(N‐PhMI‐co‐AA) with copolymer composition 46.5:53.5 mol % was found at 251 °C, and it decreased when the complexes of Co(II) and Cu(II) at pHs 3–7 were formed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4933–4941, 2005     

GPC,CD and sedimentation analysis of poly-Lys and branched chain poly-Lys-poly-DL-Ala polypeptides

Three different poly-L-lysine (pLys) samples and a branched polypeptide poly-[L-Lys-(DL-Ala)_m] (poly-L-Lys-poly-DL-Ala, AK) were synthetized. Relative molar mass distribution, its average and the degree of polymerisation were determined by sedimentation analysis and gel permeation chromatography (GPC). The conformation of the polymers in solution was studied by circular dichroism (CD) spectroscopy at various pH values and ionic strengths. The data obtained by different methods were compared.A preliminary account of this work was read at the 4^th Conference on Colloid Chemistry, Eger, 1983.     

Investigation on Electronic Property of Passive Film on Nickel in Bicarbonate/Carbonate Buffer Solution

The electronic properties of passive film formed on nickel in bicarbonate/carbonate buffer solution were studied by electrochemical impedance spectra (EIS) and Mott‐Schottky plot. The film composition was analyzed by X‐ray photoelectron spectroscopy (XPS). The results showed that passive film exhibited p‐type semi‐conductive character, and the acceptor density (N_A) decreased with increasing potential, prolonging time, decreasing temperature, increasing pH value and decreasing chloride/sulfur ions concentration. The transfer resistance and film resistance increased with the above factors changing. XPS results showed that passive film was composed of NiO and a little amount of Ni₂O₃.     

Confromational Studies on Peptides Containing Enantiometric α-Methyl α-Amino Acids. Part I. Differential conformational properties of (R)- and (S)-2-methylaspartic acid

The conformational properties of four model peptides of the general formula Ac-Tyr-Xaa-Yaa-Zaa-Ala-Lys-Glu-ala-Ala-Glu-Lys-Ala-Zaa-Yaa-Xaa-Lys-NH₂ (Xaa-Yaa-Zaa = Ala-Ala-(R)-Asp(2-Me), 1 ; Ala-Ala-(S)-Asp(2-Me), 2 ; Ala-Aib-Asp, 3 ; Ala-Ala-Asp, 4 ; Asp(2-Me) = 2-methylaspartic acid; Aib = 2-aminoisobutyric acid) were studied by CD spectroscopy in solution, to evaluate the helix-inducing potential of enantiomerically pure 2-methylaspartic acid as a function of its chirality at C(2). At neutral pH and 1°, all peptides exhibit significant helix formation in aqueous solution, the degree of helicity increasing in the order 4 3 ≈ 1 . Lowering the pH to 2 results in a dramatic increase in helicity for peptide 1 , while the diastereoisomeric peptide 2 now exists in a predominantly unordered conformation. Helix induction by protonated (R)-Asp(2-Me) exceeds Aib-induced helix formation in peptide 3 , and the helix content of 1 in aqueous solution at pH 2 is comparable to the degree of helicity in the strongly helix-inducing solvent 2,2,2-trifluoroethanol.     

The Impact of pH on Catalytically Critical Protein Conformational Changes: The Case of the Urease,a Nickel Enzyme

Urease uses a cluster of two Ni^II ions to activate a water molecule for urea hydrolysis. The key to this unsurpassed enzyme is a change in the conformation of a flexible structural motif, the mobile flap, which must be able to move from an open to a closed conformation to stabilize the chelating interaction of urea with the Ni^II cluster. This conformational change brings the imidazole side chain functionality of a critical histidine residue, αHis323, in close proximity to the site that holds the transition state structure of the reaction, facilitating its evolution to the products. Herein, we describe the influence of the solution pH in modulating the conformation of the mobile flap. High-resolution crystal structures of urease inhibited in the presence of N-(n-butyl)phosphoric triamide (NBPTO) at pH 6.5 and pH 7.5 are described and compared to the analogous structure obtained at pH 7.0. The kinetics of urease in the absence and presence of NBPTO are investigated by a calorimetric assay in the pH 6.0–8.0 range. The results indicate that pH modulates the protonation state of αHis323, which was revealed to have pK_a=6.6, and consequently the conformation of the mobile flap. Two additional residues (αAsp224 and αArg339) are shown to be key factors for the conformational change. The role of pH in modulating the catalysis of urea hydrolysis is clarified through the molecular and structural details of the interplay between protein conformation and solution acidity in the paradigmatic case of a metalloenzyme.     

Poly(β-Amino acids). V. Synthesis and conformation of oligomeric α-isobutyl-L-aspartate

α-Isobutyl-L -aspartate oligomers, Z-(α-i-Bu-Asp)_2n–OEt (n = 1–5), where Z = benzyloxycarbonyl and OEt = ethyl ester, were prepared stepwise, and their conformation in solution was investigated by optical rotation, circular dichroism (CD), and NMR spectroscopy. The oligomers up to hexamer existed only in a disordered form. An ordered structure began to appear at octamer and decamer in chloroform and 2,2,2-trifluoroethanol. The ordered structure was more favorable for N-unprotected oligomers, H-(α-i-Bu-Asp)_2n–OEt, in comparison with the corresponding Z-(α-i-Bu-Asp)_2n–OEt. The effects of oligomer concentration and temperature on the structure were slightly observed. The most likely ordered structure was a β form caused by intramolecular association.     

Two phases of bis­(tetraethyl­ammonium) di‐μ‐chloro‐bis­[di­chloro­palladium(II)]

A phase transition was found to occur at ∼153 K in the title compound, (C₈H₂₀N)₂[PdCl₆]. The structures of the two phases are reported at 292 and 130 K. The low‐temperature phase is twinned. The phase transition is accompanied by a minor displacement of the ions. There are C—H⋯Cl interactions as short as ∼2.80 Å, indicating the existence of hydrogen bonds, and this was confirmed by vibrational spectroscopy. The [Pd₂Cl₆]²⁻ anion occupies sites of mmm and 2/m symmetry in the room‐temperature and low‐temperature phases, respectively.     

Effects of acrylic acid incorporation on the pressure–temperature behavior and the calorimetric properties of poly(N-isopropylacrylamide) in aqueous solutions

 We studied the effects of pH on the pressure–temperature dependence of coil–collapse transition for aqueous solutions of copolymers of N-isopropylacrylamide and acrylic acid (Ac). At low pressures, the transition temperature (T _tr) increased with pressure, but T _tr decrease with increasing pressure at pressures higher than 50–100 MPa. By increasing the pH, the transition contour shifted to a higher temperature. When the Ac content was increased, the effects of pH became more evident. From a calorimetric study at atmospheric pressure, ΔH _tr was found to become smaller by increasing the portion of the ionized residues in the copolymer. The ratio to the van't Hoff enthalpy changes became larger with an increase in pH, which indicated that the production of charge decreased the cooperative domain size. Received: 19 July 1999 /Accepted in revised form: 7 September 1999