Conformational Transition Of Poly Research Articles

Application of temperature modulation to FTIR spectroscopy: an analysis of equilibrium and non-equilibrium conformational transitions of poly(ethylene terephthalate) in glassy and liquid states

In this paper, the application of a temperature modulation to the temperature-resolved FTIR analysis is reported. The advantage offered by the spectroscopic investigation, able to follow the micro-structural and conformational sample modification involved in sample thermal transformation, was merged to that of temperature modulation, related to the possibility to separate the reversing (in-equilibrium within the experimental condition) to the non-reversing (non-equilibrium) processes. The potentiality of the technique (modulated temperature FTIR, MTFTIR) is highlighted through the study of the thermal transitions of amorphous poly(ethylene terephthalate) from 50 °C to the cold-crystallization. After the presentation of the theoretical framework and the experimental conditions, a step-by-step description of acquired data elaboration is given. The total variation of a selected band intensity as function of mean temperature as well as its reversing and non-reversing components are obtained. The evolution of the bands at 1340 and 971 cm−1, assigned to the trans conformation of the ethylenic unit and to the all-trans conformation of the repeating unit, respectively, are investigated. As expected, the glass transition is observed in the reversing components meanwhile the recovery of the glass relaxation and cold crystallization in non-reversing ones. Particularly interesting resulted the behaviour of the sample in the supercooled liquid state, between the glass transition and the cold-crystallization onset, in which the results show that the ethylenic conformers are in-equilibrium while the all-trans sequences are not. MTFTIR is confirmed to be a technique particularly suitable for the characterization of non-equilibrium conformational states of polymers.

How does the addition of shape distinct gold nanoparticles influence on the conformational transition of poly(N-isopropylacrylamide)?

HypothesisThe subject of nanomaterials has created immense interest and expectations in the field of science and nanotechnology. Plentiful aspects proposed by gold nanoparticles (AuNPs) and their capability to affect macromolecular transition is the main driving force to execute the current study. A thermo-responsive polymer poly(N-isopropylacrylamide) (pNIPAM) is studied in presence of nanoparticles, particularly gold nanorods and nanospheres to elucidate completely the effect of their shape, surface area and structural morphology on the conformation of pNIPAM. ExperimentsIn this respect, several biophysical techniques such as fluorescence spectroscopy, dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) are utilized to examine the interaction of Au nanospheres/nanorods with pNIPAM. For a better understanding of Au nanoparticles morphology, transmission electron microscopy (TEM) is also employed. FindingsIntroducing gold nanoparticles with the polymeric solution promotes the polymer to stay in the coil conformation at a higher temperature than the LCST of aqueous pNIPAM. A shift of 2 and 25.5 °C in the LCST of pNIPAM is observed along with Au nanospheres and nanorods, respectively. The current study provides a better impact in the field of biomedical science specifically drug delivery and tissue engineering as the LCST approaches human body temperature.

Molecular dynamics study of the intercalation and conformational transition of poly (N-vinyl caprolactam), a thermosensitive polymer in hydrated Na-montmorillonite

In this study, we performed molecular dynamics (MD) simulations of the intercalation of poly (N-vinyl caprolactam) (PNVCL) into Na-montmorillonite (Na–Mt) to evaluate the solvation dynamics, the ordering of H2O molecules and the effect of interlayer attractive forces in inducing conformational transitions in PNVCL from 275 to 335 K. Conformational transformation of PNVCL into Na–Mt and in bulk water were compared and contrasted to understand the effects of interlayer attractive forces on PNVCL. The results showed that the coil-to-globule transition of PNVCL appeared at 305 K when in bulk water and not into Na–Mt due to the reduction of the hydrophobic interaction between PNVCL residues by the electrostatic forces in the interlayer. H2O molecules formed H-bonded cage-like structure around PNVCL, and the amount of these H-bonds and H2O molecules decreased with the thermal perturbation. Our investigations suggest that the solubility, solvation dynamics and the conformation transformation of PNVCL into Na–Mt are determined by the electrostatics forces existing in the interlayer and the structure of proximal H2O molecules when the temperature increased. PNVCL exhibited good inhibition effect on Na–Mt by reducing its interlayer particles mobility. The radial distribution function curves and the solvent accessibility surface area indicated that PNVCL was more exposed to H2O molecules into Na–Mt than in bulk water due to their proximity with the large hydration shells formed around Na cations and the strong H-bonds formed between clay mineral surface and H2O molecules. H-bonds analysis into Na–Mt showed that clay mineral surface was more likely to form H-bond with H2O molecules than PNVCL because of their hydrophilic properties. These results highlight the conformational transition of PNVCL into hydrated Na–Mt and predict its stability against environmental condition changes.

Conformational transitions of poly(ethylene oxide) in supersonic jets of supercritical CO2

The supersonic gas jets are proposed as a tool for researching conformational transitions of polymer chain molecules in untraditional (supercritical) fluids. The working fluid of the jet and the solvent for polymers in this case are supercritical fluids. This method is used for the microencapsulation of TiO2 nanoparticles in poly(ethylene oxide) (Mv = 8,000,000). The suspension of TiO2 nanoparticles in the polymer solution in supercritical carbon dioxide is expanded into vacuum or background gas. The substrate of the jet resulting from rapid expansion was investigated by SEM. Along the axis of the jet, zones of coil-globule-coil transitions were found. The position and extent of these zones can be controlled by varying the conditions in the reactor (pressure, temperature, co-solvent concentration) and background gas pressure in the nozzle chamber.

Strain-Induced Crystallization and Conformational Transition of Poly(trimethylene terephthalate) Films during Uniaxial Deformation Probed by Polarized Infrared Spectroscopy

The structure development during the drawing of PTT films immediately above the glass transition temperature at two different strain rates (8.33 × 10–3 and 8.33 × 10–4 s–1) has been investigated using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. It was found that both the melting temperature and the crystallinity development are dependent on the strain rate. The cold crystallization peak decreases with increasing draw ratio and disappears completely beyond a draw ratio of 2.5. DSC results showed that the decreasing strain rate delays crystallization and reduces the rate of crystallization. The bands at 1358 and 976 cm–1 were chosen to determine the gauche and trans conformations of methylene segments in PTT as a function of the draw ratios and strain rates. It was found that the crystalline gauche conformation increases at the expense of the amorphous trans conformation during the strain-induced crystallization of PTT. The conversion of the amorphous trans conformation into the crystalline gauche conformation is also delayed at lower strain rate, which is consistent with our DSC observation. Polarized IR spectroscopy was used to measure the crystalline and the amorphous orientation functions separately with draw ratios and strain rates, and it was demonstrated that the crystalline orientation develops rapidly with strain-induced crystallization and that the amorphous orientation stays constant up to draw ratio of 2.5 and increases slowly above a draw ratio of 2.5, which is typical behavior for flexible chain polymers.

Conformational Transitions of Poly(l-proline) in Copolypeptides with Poly(γ-benzyl-l-glutamate) Induced by Packing

The hierarchical self-assembly and dynamics of poly(γ-benzyl-l-glutamate)-b-poly(l-proline) (PBLG-b-PLP) polypeptides are investigated with X-rays and solid state NMR. Both blocks possess helices stabilized solely either by hydrogen bonds (PBLG) or by steric hindrance (PLP) and are further packed in two different hexagonal cells. We report a trans/cis conformational change of PLP upon confinement that mimics the isomerization of isolated proline residues in proteins. These cis PLP conformations reside primarily at the PLP/PBLG interface, alleviate the packing frustration, and permit PBLG and PLP helices to pack with their bulk properties.

Dynamic light scattering in semi-interpenetrating polymer networks based on polyacrylamide and poly(N-vinylcaprolactam)

Semi-interpenetrating networks based on polyacrylamide gel and linear thermosensitive poly(N-vinylcaprolactam) are obtained for the first time and studied via the method of dynamic light scattering. Contributions associated with dynamic fluctuations and frozen inhomogeneities to scattering are determined. It is shown that the ensemble-average scattering intensity strongly depends on the quantity and dimensions of frozen inhomogeneities. As temperature increases, scattering due to both dynamic fluctuations and spatial inhomogeneities tends to increase. At the temperature of the conformational transition of poly(N-vinylcaprolactam), the intensity of scattering increases abruptly, whereas the correlation function assumes the shape of a strongly stretched exponent that corresponds to high relaxation times (∼1 s). It is found that the relaxation-time distribution restored with the use of the inverse Laplace transform contains several modes. For all the studied networks, the correlation length of the mode of cooperative motion (the fast mode) is independent of the concentration of poly(N-vinylcaprolactam) and coincides with the correlation length of the mode of collective motion for the polyacrylamide gel.

Conformational transition of Poly (vinylbenzyltrimethylammonium chloride) (PVBTMAC) brush in the presence of Hofmeister anions

This study pertains to the conformational changes of Poly (vinylbenzyltrimethylammonium chloride) (PVBTMAC) brush onto SiO2-coated resonator; which was further incorporated by using quartz crystal microbalance with dissipation (QCM-D) in the presence of Hofmeister series of anions as a function of ionic strength. Gradual shrinkage of highly extended PVBTMAC followed by loose inhomogeneous layer was on account of change in frequency (∆f) and dissipation (ΔD) at low ionic strength. On the contrary, the increase in ionic strength collapses chains and dense homogenous layer is formed. The chaotropic anions comparativley bring drastic change in frequency unlike kosmotropic anions. This is because weakly hydrated chaotropic anions form strong ion pair with weakly hydrated trimethyl ammonium group on the PVBTMAC brush and as a result strong counter ion condensation was observed on polymer chain. Thus, the apparent mass associated with PVBTMAC chains increases that accounts for large change in ∆f.

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

AbstractA 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.

Thermodynamics in Conformational Transition of Poly(β-benzyl l-aspartate) As Studied by High-Resolution Solid-State 13C NMR Spectroscopy

The thermodynamic characteristics associated with conformational change of poly(β-benzyl l-aspartate) (PBLA) in the solid state are studied by using 13C high-resolution solid-state NMR. PBLA was chosen because four different conformations, i.e., the right-handed (αR-) and left-handed α-helices (αL-helix), left-handed ω-helix (ωL-helix), and antiparallel β-sheet (β-sheet), can be prepared separately, and the thermally induced transition occurs among them. In this work, we analyze spectral changes due to conformational transformation of PBLA and determine the enthalpic and entropic changes associated with the transformation of αR-helix to other conformations; the enthalpic change ΔH per residue becomes ca. 1.4 kJ mol−1, and the entropic change ΔS per residue becomes ca. 3.5 J K−1 mol−1. With using these ΔH and ΔS values, we show that the observed transition curve can be reproduced by a simple statistical model.

Polymerization and Conformational Transition of Poly(methacrylic Acid) Probed by Electronic Spectroscopy of Aminoacridines

9-Aminoacridinium vinyl monomers with intramolecular charge transfer (ICT) state were studied as molecular probes for copolymerization with methacrylic acid. The fading of the dye color after its addition to the poly(methacrylic acid) (PMA) chain leads to sweeping spectral changes from a broad absorption band in the red region before the polymerization to structured absorption and emission bands in the blue region after labeling. Also, the dyes bound lost their multiexponential decay behavior due to the ICT process and have only a single lifetime of the locally excited state of the aminoacridinium fluorophore. The conformational transition of PMA is sharply determined at pH = 5.2 by time-resolved fluorescence anisotropy. This probe technique also indicates strong polymer segments interactions prior to the critical transition of the chain opening with increases of the pH of the aqueous PMA solution.

Two-dimensional Raman and Raman optical activity correlation analysis of the α-helix-to-disordered transition in poly(l-glutamic acid)

Rich and complex Raman scattering and Raman optical activity (ROA) spectra have been measured monitoring the pH induced alpha-helix-to-disordered conformational transition in poly(L-glutamic acid). Two-dimensional (2D) correlation techniques have been applied to facilitate a comprehensive analysis of these two complementary spectral sets. Synchronous contour plots have identified band assignments of alpha-helical and disordered conformations, and have revealed bands characteristic of changes in the protonation state of the polypeptide. Asynchronous plots, on the other hand, have probed the relative sequential orders of intensity changes indicating a decrease in intensity of alpha-helical bands in the backbone skeletal stretch region, followed by a subsequent decrease in intensity in the extended amide III and amide I regions, underlying the appearance of disordered structure, including poly(L-proline) II (PPII) helix. The application of a 2D correlation 'moving' window has also disclosed two distinct phases during helix unfolding in the alpha-helix-to-disordered transition, occurring at approximately pH 4.9 and approximately pH 5.2, possibly a result of the difference in helical stability between the end and central regions of the alpha-helix. This paper demonstrates the potential value of combining 2D Raman, 2D ROA and moving window correlation techniques for the detailed investigation of complex and subtle changes of secondary structure during the unfolding mechanisms of polypeptides and proteins.

On the Nature of Conformational Transition in Poly(ethylene glycol) Chains Grafted onto Phospholipid Monolayers

This study was aimed at understanding the nature of conformational transition(s) that occur in poly(ethylene glycol) chains with molecular weight 5000 (PEG5000) grafted onto phospholipid monolayers. The study was performed with monolayers of PEG−phospholipid, DSPE−PEG5000, at the air/water interface and on solid substrates. Surface pressure and surface potential measurements together with ellipsometry and Brewster angle and atomic force microscopy were used to assess changes in the conformation and hydration of PEG5000 chains with increasing PEG grafting density. A comparative analysis of our experimental data suggests that neither the concept of the first-order pancake-to-brush conformational transition nor the model considering two subsequent transitions, namely, pancake-to-mushroom and mushroom-to-brush transitions, are adequate in describing conformational changes in the DSPE−PEG5000 monolayer at the air/water interface. At low grafting densities, PEG5000 chains did behave as grafted polymeric chains ...

A linear lattice model for polyglutamine in CAG-expansion diseases.

Huntington's disease and several other neurological diseases are caused by expanded polyglutamine [poly(Gln)] tracts in different proteins. Mechanisms for expanded (>36 Gln residues) poly(Gln) toxicity include the formation of aggregates that recruit and sequester essential cellular proteins [Preisinger, E., Jordan, B. M., Kazantsev, A. & Housman, D. (1999) Phil. Trans. R. Soc. London B 354, 1029-1034; Chen, S., Berthelier, V., Yang, W. & Wetzel, R. (2001) J. Mol. Biol. 311, 173-182] and functional alterations, such as improper interactions with other proteins [Cummings, C. J. & Zoghbi, H. Y. (2000) Hum. Mol. Genet. 9, 909-916]. Expansion above the "pathologic threshold" ( approximately 36 Gln) has been proposed to induce a conformational transition in poly(Gln) tracts, which has been suggested as a target for therapeutic intervention. Here we show that structural analyses of soluble huntingtin exon 1 fusion proteins with 16 to 46 glutamine residues reveal extended structures with random coil characteristics and no evidence for a global conformational change above 36 glutamines. An antibody (MW1) Fab fragment, which recognizes full-length huntingtin in mouse brain sections, binds specifically to exon 1 constructs containing normal and expanded poly(Gln) tracts, with affinity and stoichiometry that increase with poly(Gln) length. These data support a "linear lattice" model for poly(Gln), in which expanded poly(Gln) tracts have an increased number of ligand-binding sites as compared with normal poly(Gln). The linear lattice model provides a rationale for pathogenicity of expanded poly(Gln) tracts and a structural framework for drug design.

Conformational transition of poly[2-methoxy-5-(2′-ethylhexoxy)- p-phenylene vinylene] in solutions: solvent-induced emitter change

The spectroscopy and fluorescence lifetime of poly[2-methoxy-5-(2′-ethylhexoxy)- p-phenylene vinylene] (MEH-PPV) in mixtures of a poor solvent (cyclohexane or methanol) and a good solvent (chloroform) have been studied. With an increasing proportion of the poor solvent, the absorption, excitation and emission spectra change significantly when the poor solvent proportion is above a critical value. A new component is formed with spectra (absorption, excitation and fluorescence) at longer wavelength (lower energy). Fluorescence decay in different solvents has been measured and the new component has a longer lifetime compared with that in chloroform. All the results illustrate that a new emission center (emitter) is formed when the mixed solvent of MEH-PPV contains a higher proportion of the poor solvent.

Europium(III) Fluorescence Lifetime in Poly(methacrylic acid) Related to Its Conformational Transition

Abstract The number of water molecules (NH2O) in the inner-sphere of Eu(III) complexed with poly(methacrylic acid) and poly(acrylic acid) was reported at various temperatures and α (degree of ionization) of these polyelectrolytes using laser-induced fluorescence spectroscopy. It is suggested that the conformational transition of poly(methacrylic acid) is reflected in the α dependence of NH2O.

Конформационные переходы поли (С) и поли(сІС): исследование методом протонной буферной емкости

Конформационные переходы поли (С) и поли(сІС): исследование методом протонной буферной емкости

Conformational transitions of alternating purine-pyrimidine DNAs in perchlorate ethanol solutions

Conformational transitions of poly(dA-dC).poly(dG-dT), poly(dA-dT).poly(dA-dT), and other alternating purine-pyrimidine DNAs were studied in aqueous ethanol solutions containing molar concentrations of sodium perchlorate, which is a novel solvent stabilizing non-B duplexes of DNA. Using CD and UV absorption spectroscopies, we show that this solvent unstacks bases and unwinds the B-forms of the DNAs to transform them into the A-form or Z-form. In the absence of divalent cations poly(dA-dC).poly(dG-dT) can adopt both of these conformations. Its transition into the Z-form is induced at higher salt and lower ethanol concentrations, and at higher temperatures than the transition into the A-form. Submillimolar concentrations of NiCl2 induce a highly cooperative and slow A-Z transition or Z-Z' transition, which is fast and displays low cooperativity. Poly(dA-dT).poly(dA-dT) easily isomerizes into the A-form in perchlorate-ethanol solutions, whereas high perchlorate concentrations denature the polynucleotide, which then cannot adopt the Z-form. At low temperatures, however, NiCl2 also cooperatively induces the Z'-form in poly(dA-dT).poly(dA-dT). Poly(dI-dC).poly(dI-dC) is known to adopt an unusual B-form in low-salt aqueous solution, which is transformed into a standard B-form by the combination of perchlorate and ethanol. NiCl2 then transforms poly(dI-dC).poly(dI-dC) into the Z'-form, which is also adopted by poly(dI-br5dC).poly(dI-br5dC).

Conformational transition of poly(methacrylic acid- co-styrenesulfonic acid) in aqueous solution

The conformational transition of poly(methacrylic acid- co-styrenesulfonic acid) (PMAS) in aqueous solution was investigated by the luminescence probe method using Ru(bpy) 3 2+ and viscometry. PMAS-8 (8 mol% styrenesulfonic acid (SS) residue) and PMAS-16 (16 mol% SS residue) revealed a unique conformational transition with changing negative charge on a polymer chain that had at least four conformations in aqueous solution. The luminescence behaviour of Ru(bpy) 3 2+ and the viscosity characteristics of PMAS solution indicated that the conformational transition was brought about by changing the negative charge of the polymer chain.

AZ conformational transition in poly(rArU) and structure marker bands in UV resonance Raman spectroscopy

Abstract Ultraviolet resonance Raman (RR) spectra of poly(rArU), poly(dAdU) and poly(rA)·poly(rU) in aqueous solutions, excited at 257 and 281 nm wavelengths, have been reported in the spectral region between 400 and 1800 cm −1 . In comparing the RR data of these various AU duplexes, conformational marker bands of the right-handed A structure have been determined. In addition, a conformational transition of poly(rArU) has been monitored in the presence of a high concentration of NH 4 F in aqueous solution. This transition has also been observed by CD spectroscopy (M. Vorlickova, J. Kypr and T.M. Jovin, Biopolymers, 27 (1988) 351) without any clearcut conclusion as to the final structure adopted by the polymer. The present RR data, compared with previous RR results obtained from other alternating purine—pyrimidine duplexes (polyribo- and polydeoxyribonucleotides), show that the final structure of the polyribonucleotide in highly concentrated NH 4 F solution is a left-handed Z helix. Moreover, the current study allowed RR structure marker bands of Z form duplexes to be determined in a general manner.