Slow-motion Component Research Articles

Investigation on chain segment motions of various starch molecules under different glycerol-water system

The molecular motion of starch at different glycerol concentrations (0, 20, 50, and 80 %) was investigated using Electron Paramagnetic Resonance (EPR) spectroscopy. Fourier-transform infrared (FTIR) spectroscopy and 1H nuclear magnetic resonance (1H NMR) spectroscopy confirmed that hydroxyl groups at the C2 and C3 positions of glucose units in corn starch (CS), waxy corn starch (WCS), and high amylose corn starch (HCS) were labeled with 4-amino-TEMPO. The crystallinities of CS, WCS, and HCS after spin-labeling decreased from 30.68 % to 3.21 %, 39.36 % to 1.65 %, and 28.54 % to 8.08 %, respectively. The pseudoplastic fluid properties of the spin-labeled starch remained shear-thin at different glycerol concentrations. EPR revealed the fast- and slow-motion components of the spin-labeled starch molecules dispersed in water. At a glycerol concentration of 20 %, the slow-motion component disappeared, indicating a faster rotational motion of the starch chain segments. As the glycerol concentration increased to 50 and 80 %, the rotational motion slowed because of high viscosity. In particular, the mobility of the spin-labeled WCS chains increased owing to easier access of glycerol and water to the branched structure. This study directly observed the dynamics of the molecular behavior of starch in glycerol-water systems.

Study on the synthesis of spin labeled poly(styrene-co-maleic acid)s and their segmental motion

Study of the segmental mobility of polymer chains is important when the polymer is used as drag reduction agents of crude oil. Electron spin resonance (ESR) spectroscopy can provide important information about segmental dynamics of polymer chains, which is related to their microenvironment. In this article, we employed an amphiphilic polymer to study the effect of hydrophilic/hydrophobic balance of the polymers on the segmental motion of polymer chains. Poly(styrene-co-maleic acid) (PSMA) was spin labeled with 4-amino TEMPO radicals by increasing the concentration of radical moiety on the polymer chains. The PSMA and spin labeled-PSMAs (SL-PSMAs) were characterized by nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, Cyclic voltammetry (CV) and ESR techniques. Inter-polymer complexes (IPCs) of SL-PSMA-2 were prepared by employing polyethylene glycols (PEGs) of varying molecular weights. The results showed that the increased hydrophobic interactions of nitroxide radicals on the SL-PSMAs’ chains reduced the rotational mobility of spin labels and the random coil-to-globular transition of polymer chains occurred at higher pH value for SL-PSMAs, which showed a slow motion component in the ESR spectra of SL-PSMAs. Further, by increasing the molecular weight of PEGs in IPCs the complexation was increased, which also reduced the rotational motion of spin labels due to interpolymer hydrogen bonding causing a slow motion component in the ESR spectra.

Synthesis of poly(diethylaminoethyl methacrylate-co-2,2,6,6-tetramethyl-4-piperidyl methacrylate)s and their segmental motion study

Poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) is a pH-sensitive polymer, while a few recent studies have shown it to possess temperature responsiveness as well. In this article, poly(2-(diethylamino)ethyl methacrylate-co-2,2,6,6-tetramethyl-4-piperidyl methacrylate)s, DEA-TMPMs, were synthesized. The TMPM moieties in DEA-TMPMs were subsequently oxidized with hydrogen peroxide to obtain poly(2-(diethylamino)ethyl methacrylate-co-2,2,6,6-tetramethylpiperidine-1-oxyl methacrylate), DEA-TMPs, having nitroxide radicals on the polymer chains. DEA-TMPMs were characterized by nuclear magnetic resonance spectroscopy, gel permeation chromatography, differential scanning calorimetry and thermogravimetry techniques, whereas DEA-TMPs were analyzed by Fourier transform infrared spectroscopy, cyclic voltammetry, and electron paramagnetic resonance (EPR) spectroscopy. The results showed that at low pH, the rotational mobility of nitroxide radicals was reduced as EPR spectra mostly consisted of slow-motion component. This slow-motion component in the EPR spectra remained unchanged below neutral pH. These results indicated a sort of interaction among nitroxide radicals and protonated amine groups of DEAEMA monomers.

Molecular order and T1-relaxation, cross-relaxation in nitroxide spin labels

Interpretation of saturation-recovery EPR experiments on nitroxide spin labels whose angular rotation is restricted by the orienting potential of the environment (e.g., membranes) currently concentrates on the influence of rotational rates and not of molecular order. Here, I consider the dependence on molecular ordering of contributions to the rates of electron spin-lattice relaxation and cross relaxation from modulation of N-hyperfine and Zeeman anisotropies. These are determined by the averages 〈cos2θ〉 and 〈cos4θ〉, where θ is the angle between the nitroxide z-axis and the static magnetic field, which in turn depends on the angles that these two directions make with the director of uniaxial ordering. For saturation-recovery EPR at 9 GHz, the recovery rate constant is predicted to decrease with increasing order for the magnetic field oriented parallel to the director, and to increase slightly for the perpendicular field orientation. The latter situation corresponds to the usual experimental protocol and is consistent with the dependence on chain-labelling position in lipid bilayer membranes. An altered dependence on order parameter is predicted for saturation-recovery EPR at high field (94 GHz) that is not entirely consistent with observation. Comparisons with experiment are complicated by contributions from slow-motional components, and an unexplained background recovery rate that most probably is independent of order parameter. In general, this analysis supports the interpretation that recovery rates are determined principally by rotational diffusion rates, but experiments at other spectral positions/field orientations could increase the sensitivity to order parameter.

Electron Paramagnetic Resonance (EPR) Study of Spin-Labeled Camptothecin Derivatives: A Different Look of the Ternary Complex

Camptothecin (CPT) derivatives are clinically effective poisons of DNA topoisomerase I (Top1) able to form a ternary complex with the Top1-DNA complex. The aim of this investigation was to examine the dynamic aspects of the ternary complex formation by means of site-directed spin labeling electron paramagnetic resonance (SDSL-EPR). Two semisynthetic CPT derivatives bearing the paramagnetic moiety were synthesized, and their biological activity was tested. A 22-mer DNA oligonucleotide sequence with high affinity cleavage site for Top1 was also synthesized. EPR experiments were carried out on modified CPT in the presence of DNA, of Top1, or of both. In the last case, a slow motion component in the EPR signal appeared, indicating the formation of the ternary complex. Deconvolution of the EPR spectrum allowed to obtain the relative drug amounts in the complex. It was also possible to demonstrate that the residence time of CPT "trapped" in the ternary complex is longer than hundreds of microseconds.

The study of the miscibility and morphology of poly(styrene‐co‐4‐vinylphenol)/poly(propylene carbonate) blends

AbstractBlends of poly(propylene carbonate) (PPC) with copolymer poly(styrene‐co‐4‐vinyl phenol) (STVPh) have been studied by electron spin resonance (ESR) spin probe method and Raman spectroscopy. The ESR results indicated that the nitroxide radical existed in a PPC‐rich and an STVPh‐rich micro domain in the blends, corresponding to the fast‐motion and slow‐motion component in the ESR spectra, respectively. And in the temperature dependence composite spectra, the fast‐motion fraction increased with increasing the hydroxyl group content in copolymer STVPh. Moreover, the ESR parameter T5mT, rotational correlation times (τc) and activation energies (Ea) showed similar dependence on the hydroxyl group content as the fast‐motion fraction. It resulted from the enhancement of the hydrogen‐bonding interaction between the hydroxyl groups in STVPh and the carboxyl groups and ether oxygen in PPC. However, the distinct band shift and intensity change among the Raman spectra of pure polymer components and those of the blends were observed. In the carboxyl‐stretching region, the band shifted to lower frequency with increasing the hydroxyl groups. Furthermore, the phase morphologies of the blends were obtained by optical microscopy. All could be concluded that the hydrogen‐bonding interaction between the two components was progressively favorable to the mixing process and was the driving force for the miscibility enhancement in the blends. Copyright © 2004 John Wiley & Sons, Ltd.

EPR spin labelling studies of molecular dynamics in elastomer-silica composites

Novel methods of nitroxyl spin labelling suitable for molecular dynamics studies within the interface regions of SBR elastomer/silica composites have been developed and used together with the nitroxyl spin probe technique. Fast and slow motional components have been identified within the interface regions and the corresponding rotational diffusion tensors have been measured as a function of the temperature and the SiO2 concentration. The fast rotational frequency is found to be orders of magnitude slower than that measured in the absence of SiO2. This difference is suggested to arise from a closer packing of the macromolecules near the silica surface caused by the van der Waals bonding interactions. Increase of the SiO2 concentration results in a decrease of the molecular mobility. This effect has been imputed to the overlapping of the bonding interaction regions. Spin probe measurements in the SBR-SiO2 matrices using TEMPO, strongly suggest that the hindrance to chain segmental motion induced by the SiO2-SBR interactions propagates beyond the interface regions thus involving the bulk polymer matrix. It is suggested that the information on the segmental chain dynamics obtained through the spin labelling and spin probe measurements can be developed as a method for investigating the polymer/filler interactions within the reinforcing mechanism by the filler.

Spin-label studies of blends of immiscible polymers: 6. Phase morphology in blends of poly(methyl methacrylate) and poly(2-ethyl hexyl methacrylate)

The correlation times, τ R, for rotation in the slow-motion regime of nitroxide free radicals sited at chain-end positions on poly(methyl methacrylate) (PMMA) in the pure, unblended state and in a 1:1 ( w w ) freeze-dried blend with unlabelled poly(2-ethyl hexyl methacrylate) (PEHMA) were determined by computer simulation of the slow-motion component of the composite electron spin resonance (e.s.r.) spectrum. Comparison of τ R values indicates that the rubbery PEHMA apparently plasticizes the rotation of nitroxide-labelled PMMA chain ends which are expected to be located in the pure glassy PMMA phase. Although the spin-label studies seem to suggest that PMMA and PEHMA are partially miscible, dynamic mechanical thermal analysis (d.m.t.a.) and phase-contrast microscopy prove that PMMA-PEHMA blends comprise two separate phases which are essentially immiscible. The conclusions from the e.s.r., d.m.t.a. and phase-contrast microscopy experiments can be reconciled in terms of a wide-diffuse interphase between the bulk PMMA and PEHMA phases.

Lipid chain dynamics in diacylglycerol-phosphatidylcholine mixtures studied by slow-motional simulations of spin label ESR spectra

Simulation of the ESR spectra from spin-labelled phosphatidylcholine and from spin-labelled diacylglycerol has been used to study the lipid chain dynamics in mixtures of dimyristoyl glycerol with dimyristoyl phosphatidylcholine, as a function of temperature and composition. Successful simulation of the ESR spectra required taking into account slow motional components which was done by using the very anisotropic reorientation model. Chain rotational rates varied with temperature, but not greatly with composition and chain position, which primarily affected chain order. The latter decreased progressively with increasing diacylglycerol content from the lamellar, to inverted hexagonal, to isotropic phase and was consistently lower for the diacylglycerol component than for the phosphatidylcholine component. The order profile of the spin-labelled chains was obtained for both the phosphatidylcholine and diacylglycerol components in a 58:42 mol/mol mixture in the fluid lamellar phase.

Spin-label study of immiscible polymers: 5. Blends of labelled poly(2-ethyl hexyl methacrylate) with poly(methyl methacrylate) and polystyrene

The electron spin resonance (e.s.r.) spectra of poly(2-ethyl hexyl methacrylate) (PEHMA) spin-labelled with nitroxide end groups were recorded over a temperature range for both the pure, bulk polymer and for 1 : 1 (w/w) immiscible blends with poly(methyl methacrylate) (PMMA) and polystyrene (PS). Both PMMA and PS have significantly higher glass transition temperatures than PEHMA, with which they are immiscible. Nevertheless, the glassy component of these blends exerts a retarding effect on the motion of a portion of the spin labels on the PEHMA, as evidenced by the presence of a persistent slow-motion component in the e.s.r. spectra of the blends. These experiments complement our earlier work in which the spin label was attached to the chain ends of the glassy component in a binary blend. The results support our previous conclusion that in a blend of two immiscible polymers, chain ends tend to congregate in the interphase where they experience the combined influences of accumulated free volume and the presence of the other polymer.

The effect of polymers on the crystallisation of n‐alkanes from solution, part 1. Preparation and investigation of spin‐labelled fumarate–vinyl acetate copolymers

AbstractSpin‐labelled fumarate‐vinyl acetate (FVA) copolymers with octyl (C8) and octadecyl (C18) ester groups were prepared and characterised. An interaction between the C18FVA and the developing crystals of n‐dotriacontane growing from dodecane solution was observed as a slow‐motion component in the electron spin resonace (ESR) spectrum of the system. The C8FVA showed no such behaviour, the spectrum being entirely of the motionally narrowed type through out the crystallisation process. Above the cloud point of the system, no interaction between the polymer and alkane could be detected either in the ESR spectra or from measurements of the rotational correlation times of the spinlabel nitroxide.

The effect of polymers on the crystallisation of n‐alkanes from solution, part 2. Mode of action of fumarate–vinyl acetate copolymers

AbstractThe amount of octadecyl fumarate‐vinyl acetate (C18FVA) copolymer which co‐crystallised with dotriacontane from dodecane solution was measured by infrared and electron spin resonance (ESR) spectroscopy. It was found that the magnitude of the slow‐motion component in the composite ESR spectra of the system below its cloud point did not accurately reflect the amount of polymer which had co‐crystallised with the dotriacontane. ESR studies of isolated samples of the co‐crystallate showed the C18FVA to be less tightly bound than in the bulk polymer, suggesting that the polymer molecules are adsorbed on to the surface of the dotriacontane crystals.

Binding of two spin-labelled derivatives of chlorpromazine to human erythrocytes

The binding to human intact erythrocytes of two different spin-labelled derivatives of chlorpromazine has been studied. The influence of the positively charged side chain of the drug has been the focus of our attention. The positively charged amphiphilic compound (spin derivative I) is water-soluble up to 80 microM at pH values below 5.9. The apolar analogue (spin derivative II) aggregates in aqueous buffer from the lowest concentration tested. Both spin derivatives undergo a slow reduction inside the erythrocyte. The reduced nitroxides are readily reoxidized by adding a low, non-quenching, concentration of potassium ferricyanide to the intact erythrocytes. The fractions of spin label I and II bound to the erythrocyte membrane or to the erythrocyte-extracted lipids remain constant as a function of the temperature (3-42 degrees C) and as a function of the concentration of the spin label up to 150 microM. E.s.r. spectra of both spin labels show a two-component lineshape when they are bound to intact erythrocytes. Below 35 degrees C for the positively charged spin probe, and below 32 degrees C for the apolar spin probe, the simulation of the lineshape shows that more than 50% of the spectrum originates from a slow-motion component. This slow-motion component is also found in erythrocyte-extracted lipids probed by the positively charged spin label below 25 degrees C. In contrast, no slow-motion component is detected in the range 4-40 degrees C for the apolar spin label in erythrocyte-extracted lipids. In this environment the apolar probe experiences a single fast anisotropic motion with an exponential dependence on 1/temperature. Detailed lineshape simulations take into account the exchange frequency between binding sites where the probe experiences a fast motion and binding sites where it experiences a slow motion. The exchange frequency is strongly temperature-dependent. Characterization of the different motions experienced inside the different locations has been achieved and compared for whole erythrocytes and for the extracted lipids. The biochemical nature of the binding sites (membrane protein/acidic phospholipid) giving rise to the slow-motion component is discussed as a function of the polarity of the spin-labelled drug and as a function of the temperature controlling the fluidity of the lipid bulk and influencing the distribution of the drug inside the membrane.

NMR Relaxation Times of Blood

The variation with field strength or interecho interval of the T1 and T2 relaxation times of oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), and methemoglobin (MHb) in either intact or lysed red blood cells was studied with a variable field (0.19-1.4 T) nuclear magnetic resonance spectroscopy unit. The T2 relaxation time of intracellular HbO2 decreased slightly with increasing field strength and interecho interval. The T2 relaxation times of intracellular Hb and MHb decreased markedly with increasing field strength and interecho interval. This T2 proton relaxation enhancement increased as the square of the applied field strength and was 1.6 times stronger for intracellular MHb than for intracellular Hb. The T2 relaxation enhancement is secondary to the loss of transverse phase coherence of water protons that diffuse across cellular magnetic field gradients. These field gradients occur when an external field is applied to a region with gradients of magnetic susceptibility. The heterogeneity of magnetic susceptibility is caused by the heterogeneous distribution (only intracellular) of the paramagnetic molecules (Hb or MHb). The T2 relaxation times of red cell lysates (homogeneous magnetic susceptibility) were independent of field strength or interecho interval. There was a decrease in the T1 relaxation times when the red cells were lysed. This may be due to an increase in the slow motional components of water molecules, because of the decrease in the average distance between water and hemoglobin molecules in the lysate. The T1 relaxation times of all the MHb samples were shortened because of proton-electron dipolar-dipolar relaxation enhancement. All the T1 relaxation times increased with increasing field strength.

Electron spin resonance study of phospholipid membranes employing a comprehensive line-shape model.

The electron spin resonance spectra of the 1-myristoyl-2-[6-(4,4-dimethyloxazolidine-N-oxyl)myristoyl]-sn-glycero- 3-phosphocholine spin-label in highly oriented, fully hydrated bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine have been studied as a function of temperature and magnetic field orientation. The oriented spectra show clear indications of slow motional components (rotational correlation times greater than 3 ns) even in the fluid phase (T greater than 23 degrees C), indicating that motional narrowing theory is not applicable to the spectral analysis. The spectra have been simulated by a comprehensive line-shape model that incorporates trans-gauche isomerization in addition to restricted anisotropic motion of the lipid long molecular axis and that is valid in all motional regimes. In the gel (L beta') phase the spin-label chains are found to be tilted at 28 degrees with respect to the normal of the orienting plane. In the intermediate (P beta') phase there is a continuous distribution of tilt angles between 0 degrees and 25 degrees. In fluid (L alpha) phase there is no net tilt of the lipid chains. The chains rotate at an intermediate rate about their long axis in the fluid phase (tau R,parallel = 1.4-6.6 ns for T = 50-25 degrees C), but the reorientation of the chain axis is much slower (tau R, perpendicular= 13-61 ns for T = 50-25 degrees C), whereas trans-gauche isomerization (at the C-6 position) is rapid (tau J less than or equal to 0.2 ns). Below the chain melting transition both chain reorientation and chain rotation are at the ESR rigid limit (tau R greater than or equal to 100 ns), and trans-gauche isomerization is in the slow-motion regime (tau J = 3.7-9.5 ns for T = 22-2 degrees C). The chain order parameter increases continuously with decreasing temperature in the fluid phase (SZZ = 0.47-0.61 for T = 50-25 degrees C), increases abruptly on going below the chain melting transition, and then increases continuously in the intermediate phase (SZZ = 0.79-0.85 for T = 22-14 degrees C) to an approximately constant value in the gel phase (SZZ congruent to 0.86 for T = 10-2 degrees C).(ABSTRACT TRUNCATED AT 400 WORDS)