Conformational Changes Of Poly Research Articles

Conformational changes of poly(ethylene oxide) during association with sodium dodecylsulfate

Conformational changes of poly(ethylene oxide) during association with sodium dodecylsulfate

Fluorescence studies of the conformational changes of poly(methacrylic acid) with pH

Influence du pH sur la duree de vie de la fluorescence du pyrene piege dans l'acide polymethacrylique

Conformational change of poly(l-lysine) induced by lipid vesicles of dilauroylphosphatidic acid

The effect of negatively charged dilauroylphosphatidic acid (DLPA) vesicles on the conformation of poly(L-lysine) was investigated by circular dichroism measurements. DLPA vesicles induced a conformational change of poly(L-lysine) from the random coil to beta-structure in 5 mM Tes, pH 7.0. The fraction of induced beta-structure (F beta) was determined via a procedure of curve fitting of the observed spectra to the reference spectra. F beta increased linearly with the molar ratio, r, of DLPA to lysine residues up to r congruent to 0.7, and reached a saturation value of 1 at r greater than 1. Within the range 0.7 less than or equal to r less than or equal to 1, precipitation occurred. The effect of dilution of the negative charge on vesicle membranes was examined by mixing DLPA with dilauroylphosphatidylcholine (DLPC). Although the beta-structure of poly(L-lysine) was also induced by mixed vesicles, the saturation value of F beta decreased with decreasing DLPA content in mixed vesicles. The variation in saturation value of F beta with the composition of mixed vesicles was interpreted in terms of the change in average distance between DLPA head groups in mixed vesicles.

Anomalous temperature and concentration dependence of poly(methyl methacrylate) and polystyrene adsorption on Aerosil

The effect of conformational changes of poly(methyl methacrylate) and polystyrene on their adsorption from solutions on Aerosil has been studied. The adsorbed amount is governed not by polymer conformation but by energy effects, in particular by the interplay of interaction energies polymer-solvent, polymer-polymer, and polymer-adsorbent.

Light-induced reversible conformational changes in poly(L-lysine) with photochromic side chains

Light-induced reversible conformational changes in poly(L-lysine) with photochromic side chains

A polycationic amine that induces unique conformational changes in poly(dA-dT) in low salt.

Circular dichroism was used to examine alterations in the secondary structure of poly(dA-dT) X poly(dA-dT) upon binding polymer X, a polycationic CD probe for aspects of DNA structure. Stable complex formation is evidenced by increasing Tm and the appearance of large extrinsic bands in the greater than 300 nm, region which increase proportionally with r (ratio of polymer charge to DNa phosphate), in the range 0.0 to 0.32. At relatively low values of r (less than .32), CD spectra of the poly(dA-dT) X poly(dA-dT)-polymer X complex show a gradual non-cooperative inversion in the long wavelength portion (275 nm) of the intrinsic band in low salt solutions suggesting structural and conformational flexibility in poly(dA-dT) X poly(dA-dT) and further implicating polymer X as a potential probe for variations in DNA secondary structure. The dinucleotide repeat configuration of poly(dA-dT) X poly(dA-dT) is presumed to play a role in the observed intrinsic CD changes. NMR data support an "alternating B" conformation for the complex.

Some solution properties of poly(ethyl methacrylate)

AbstractThe viscosity of dilute solutions of poly(ethyl methacrylate) in each of methyl acetate, ethyl acetate and isobutyl acetate was studied over the temperature range of 20–65°C. The intrinsic viscosity either remained approximately constant or slightly decreased over the temperature range because of conformational changes. The temperature ranges of conformational change were 40–50°C, 40–50°C, and 35–55°C for the polymer in methyl acetate, ethyl acetate, and isobutyl acetate, respectively. The Huggins constant was also influenced by the type of solvent and by temperature changes, especially over the temperature range in which conformational changes took place. Conformational changes of poly(ethyl methacrylate) in aliphatic organic esters as solvents are believed to be due to changes in the interaction between the polymer segments and the solvent.

Kinetic Study on Conformational Changes of Poly(l-lysine) in Sodium Alkyl Sulfate Solutions. Effects of Surfactant Chain Length and Added NaCl

Abstract The conformational changes of poly(l-lysine) (PLL) were observed in alkyl sulfate solutions by a circular dichroic method. PLL forms a β-structure in sodium dodecyl sulfate solution with an apparent first-order rate constant of 3.0×10−2 s−1 (20 °C). In sodium octyl sulfate (SOS) solution, PLL assumes the α-helix within a certain concentration range of the surfactant, above which the β-structure is favored. The rate of coil to β-structure transition slows down with increase in hydrophobic interaction between surfactants and PLL. The presence of sodium ions decreases the rate of coil to α-helix transition by about two orders of magnitude (2.0×10−1 s−1 salt free to 3.0×10−3 s−1 in the presence of 2.0×10−2 mol/dm3 NaCl at 20 °C). These phenomena are explained in terms of a rearrangement process of bound surfactants adjusting for a free energy minimum; a stronger binding force brings about a slower rearrangement rate.

Poly(dA-dT) complexes with histone H1 and pancreatic ribonuclease: specific base recognition evidenced by ultraviolet resonance raman spectroscopy.

AbstractThe conformational changes of poly(dA‐dT) from random coil to ordered structure with stacked bases produce important changes in the Raman line intensities (hypochromism) when the polymer is excited under the preresonance Raman conditions (λ excitation = 300 nm). Poly(dA‐dT)–RNase and poly(dA‐dT)–histone H1 interactions have been studied as models of mechanisms of destabilization and stabilization by proteins of the DNA secondary structure, respectively, following this intense preresonance Raman hypochromism. In addition, the specific variation of the intensity of the 1582‐cm−1 line of adenine is interpreted in terms of the interaction of the amino group with the RNase (thus involving the large groove). In the poly(dA‐dT)–H1 complex, the intensity of the 1665‐cm−1 line of thymine increases. This increase appears to involve the C2O group of thymine, located in the narrow groove.

Conformational Change of Poly(l-lysine) by Sodium Octyl Sulfate as Studied by Stopped-flow Circular Dichroism Method

Abstract Circular dichroism (CD) studies were made on the conformational changes of poly(l-lysine) (PLL) induced by sodium octyl sulfate (SOS). The conformation of PLL has a negative double maximum characterizing the α-helix in 4.0–6.0×10−3 mol/dm3 SOS solutions. At a higher concentration of SOS, PLL takes the β-structure, the random coil remaining below it. These conformational changes were followed by measuring ellipticities at 192, 207, and 221 nm according to a CD stopped-flow method. The rate constant was ca. 2.7×10−1 s−1 for the coil-helix transition, the transition rate from coil to β-structure being high depending on SOS concentration. The β-structure was attained by adding a small amount of 1-octanol to the α-helical PLL in 5.0×10−3 mol/dm3 SOS. The effect of the surfactant on the triphasic conformation changes is discussed in terms of hydrophobic environment.

Conformational change of poly(L‐lysine) by formation of complexes with poly(styrene sulfonate)

AbstractCircular dichroic studies were made on the conformational change of poly(L‐lysine) (PLL) by complex formation with sulfonated polystyrenes (PSS) as functions of pH, temperature and polymer compositions in comparison with the complexes of PLL with sulfated poly(vinyl alcohol) (PVS). The coil‐to‐helix transition of PLL by complex formation at neutral and acidic pHs, which took place in the PLL/PVS (with high degrees of sulfation) complexes, was prevented in the PLL/PSS complexes due to the less chain flexibility of PSS than PVS. Above pH 11, the α‐helix of PLL was partially broken into random coil by complex formation with PSS. The drastic decrease in the solution viscosity by the complex formation revealed a large contraction of PSS chain and subsequently a large strain of the α‐helical PLL chain so as to give the breakdown of the α‐helix. This is denoted a strain‐induced conformational change of PLL. It was found that the α‐helix of PLL was thermally stabilized by the complex formation with PSS as in the case of PLL/PVS complexes. A β‐to‐α transition of PLL by the complex formation with PSS was also found, while the β‐form was maintained in the PLL/PVS (with high degrees of sulfation) complexes.

Interaction between Poly(L-ornithine) and Sulfated Poly(vinyl alcohol)

Studies were made on the conformational changes of poly(L-ornithine) (PLO) by interaction with sulfated poly(vinyl alcohol)s (PVS) as functions of pH, temperature, the degree of sulfation and the composition of the polymeric moieties. Polymer–polymer interaction took place below ca. pH 10.6, while no interaction of PLO with PVS was found at ca. pH 12.0. PLO took on a random coil conformation through complex formations with PVS-25 and PVS-30 (the number indicates the degree of sulfation in mol %) at low pHs. In these complexes with PVS-46 and PVS-95, the α-helix and the β2-form of PLO were formed at 1.5°C in the acidic pH region and in the pH region from ca. 8.8 to ca. 10.5, respectively. The conformation of PLO in the complexes is also discussed in terms of the free-energy change resulting from the conformational change from random coil to the α-helix.

Salt-induced conformational changes of poly(dA-dT)

Conformational changes of poly(dA-dT) . poly(dA-dT) induced by increasing ionic strength were studied using CD spectroscopy. It was found that a pronounced noncooperative inversion of the long-wavelength part of the CD spectrum of poly(dA-dT) . poly(dA-dT) occurred at high concentrations of CsF in solution. It was suggested that a great difference between the geometries of the purine and pyrimidine residues in the helix was characteristic of the structure of poly(dA-dT) . poly(dA-dT) in concentrated CsF solutions.

Conformational changes of poly(L‐histidyl‐L‐alanyl‐α‐L‐glutamic acid) in solution. Transition pathways and conformational intermediates

AbstractThe conformation and conformational transitions of poly(His‐Ala‐Glu) have been investigated by ir, nmr, and CD measurements. The results obtained—as well as the results of our previous investigations by potentiometric titration and hydrodynamic techniques [Goren et al., Biopolymers (1977) 16, 1541–1555]—indicate that when dissolved in water, the co‐polymer assumes a disordered conformation. On changing the pH of the solution, the states of ionization of the side‐chain imidazole and carboxyl groups change in the same manner as in low‐molecular‐weight model compounds. Concomitantly, the overall shape of the macromolecule is altered, while the conformation of the polypeptide backbone changes from one disordered state to another but never assumes a regular form. In water/methanol and water/trifluoroethanol mixtures, transitions from a disordered state to the α‐helix conformation were observed on increasing the alcohol content of the system. The conformational transitions followed pathways which differ from one another according to the experimental conditions employed. Conformational landmarks (intermediates) have been identified along these pathways.

Comparison of the helix–coil conformational changes of poly(deoxyadenylate‐deoxytymidylate) and poly(deoxyadenylate‐deoxythymidylate) induced by variations of hydrogen‐ion concentration

AbstractDouble‐helical poly(dG‐dC) and poly(dA‐dT) are DNA analogs in which the interactions between the two strands of the helix are, respectively, either the stronger G/C type or the weaker A/T type along the entire length of macromolecules. Thus, these synthetic polynucleotides can be considered as representatives of the most stable and the least stable DNA. In the investigations presented here, potentiometric titrations and stopped‐flow kinetic experiments were carried out in order to compare the pH‐induced helix–coil conformations (10°C and 150mM [Na+]) the pH of the helix–coil transition (pHm) is 12.81 for poly(dG‐dC) and 11.76 for poly(dA‐dT). The unwinding of double‐helical poly(dG‐dC) initiated by a sudden change in pH was found to be a simple exponential process with rate constants in the range of 200–600 sec−1, depending on the final value of the pH jump. The intramolecular double‐helix formation of poly(dG‐dC) was studied by lowering the pH of the solutions from a value above pHm to that below pHm in dilute solutions (15.5 ug/ml [polymer]). Under these conditions, the observed rewinding reactions displayed a major and two exponential phases, all of which were independent of polymer concentration. From the comparison of the results of poly(dA‐dT) and poly(dG‐dT) would unwind faster than poly(dG‐dC). However, if the pH jumps are such that they present the same perturbation of these polymers relative to their pHm values, no significant differences exist between the rates of helix–coil conformation changes of poly(dA‐dT) and poly(dG‐dC).

Laser‐excited raman spectroscopy of biomolecules. XII. Thermally induced conformational changes in poly(L‐glutamic acid)

AbstractThe α‐helical from of poly(L‐glutamic acid) [α‐poly(Glu)] gives rise to the same amide I and III lines as α‐poly(γ‐benzyl‐L‐glutamate) at 1652 and 1296 cm−1, respectively. The latter is a superposition of the amide III line near 1290 cm−1 and a line deu to vibrational made of CH2 groups of the side chain near 1300 cm−1. A line at 924 cm−1 is tentatively identified as characteristics of α‐poly(Glu). Both the β1‐ and β2‐ forms of poly(Glu) give rise to characteristic of β‐amide. III frequencies that are similar because of their similar backbone structures. Differences in the conformations of their side chains and in the environments of the backbone are reflected in the region 800–1200 cm−1 and in the amide I. A line at 1042 cm−1 and a pair at 1021 and 1059 cm−1 are tentatively assigned as characteristic of β1‐poly(Glu) and β2‐poly(Glu), respectively. The α‐β2 transition in poly(L‐Glu78L‐Val22) is shown by the appearance of all the β2‐characteristic lines in the thermally transformed sample. The same features observed in poly(L‐Glu95L‐Val5) also indicate that the α‐β2 transition of poly(Glu) is facilitated by the presence of L‐valine and that the content of L‐valine is not critical for this purpose. Investigation of the Raman spectra of the calcium, strontium, barium and sodium slats of poly(Glu) shows that these salts, under the conditions of preparation used, all the have random‐coil conformations.

Conformational changes of poly(oxymethylene) induced by pressure and mechanical treatment

AbstractIR spectra of hexagonal poly(oxymethylene) samples prepared by various polymerization procedures have been studied. The samples were further modified by pressure and by milling in liquid nitrogen. It was found that the considerable differences observed in IR spectra in the range 900–1250 cm−1 are caused by irregularities of the G conformation of the polymer chain. The regularity of the G conformational structure increases by pressing and milling.

Thermally induced conformational changes in poly(vinyl chloride)

AbstractFourier transform infrared spectroscopy has been used for the detection of thermally induced conformational changes in atactic poly(vinyl chloride) (PVC). Difference spectra emphasize changes in the distribution of gauche defects in the chains as functions of temperature and annealing. Specific bands in the ν(CCl) and δ(CH2) regions varied with inverse temperature, allowing a calculation of the activation energies of the rotamer species. Conformational changes were also detected in quenched PVC films as a result of annealing below the glass transition temperature, Tg.

A study of stepwise conformational changes in poly(beta-benzyl-L-aspartate) with the helix-coil transition by means of proton and carbon-13 NMR.

AbstractThe helix–coil transition for poly(β‐benzyl‐L‐aspartate) [poly(Asp[OBzl])] in solvent mixtures of trifluoroacetic acid/deuterated chloroform (F3AcOH/CDCl3) was studied by means of proton and carbon‐13 nmr. Conformational fixation of the side chain occurs before the coil–helix transition of the backbone, when neighboring phenyl rings face each other. Another type of conformational fixation occurs in the side chain after the coil–helix transition of the backbone. These conformational changes of the side chain are due to the changes of the strength of the interaction between the side‐chain ester group and the F3AcOH molecule. In the absence of F3AcOH (coil‐forming solvent), the polymer has a rather rigid structure in which the side chain may wrap around the backbone. These conformational changes of the polymer are closely related to the changes of the interaction between the polymer and F3AcOH molecules.

Nature of conformational changes in poly[d(A-T)-d(A-T)] in the premelting region.

The conformation of the synthetic DNA, poly-[d(A-T)-d(A-T)], has been investigated both in the solid state and in dilute aqueous solutions at different temperatures below its melting point. The change of the circular dichroism (CD) spectra of poly[d(A-T)-d(A-T)] solutions with decreasing temperatures from just below the melting point to 0 degrees involves a specific decrease of the intensity of the 262 nm CD band. This conformational change has been assigned to a gradual and partial transition from the B to C form, on the basis of the following results: (i) By the use of infrared dichroism measurements on oriented films we have defined humidity and salt conditions under which B and C forms of poly[d(A-T)-d(A-T](Li+) are stable. In addition, we find that ammonium salts induce the C form of poly[d(A-T)-d(A-T)] even at high relative humidity. (ii) CD studies of the films of the lithium salt of poly[d(A-T)-d(A-T)] under the same conditions have given CD spectra corresponding to the B and C forms of this polynucleotide. In addition, the CD spectrum of the ammonium salt of poly[d(A-T)-d(A-T)] in solution approaches that of the C form in films. (iii) The conformational change of poly[d(A-T)-d(A-T)] as a function of temperature can be entirely explained on the basis of changes in the double-stranded base-paired structure. Our data rule out hydrogen bond breaking and unstacking or "breathing" as an explanation of the premelting changes. Curves of the continuous variation of CD(epsilon at 262 nm) as a function of temperature (from 0 degrees to the melting zone) show similar slopes in the presence of different agents stabilizing the double-stranded structure, such as Mg++, or at different salt concentration (KCl), indicating that the nature of the process is independent of ionic strength. Some specific effects were observed in the influence of certain neutral salts; ammonium induces the C form whereas magnesium favors the B form. CD data give direct evidence that a DNA like poly[d(A-T)-d(A-T)] need not change conformation upon transition from a dilute aqueous solution to a highly hydrated (film/gel) solid state. The change of conformation begins only at a defined partial dehydration.