Electron spin resonance investigation of small spin probes in aqueous and vesicle phases of mixed membranes made from poly(oxyethylene) hydrogenated castor oil and hexadecane

Small spin probes in the vesicle and aqueous phases of mixed membranes made from poly(oxyethylene) hydrogenated castor oil (HCO) and hexadecane were investigated by ESR (electron spin resonance) spectroscopy. Partitioning (partition coefficients), rotational correlation times, and activation energies of the spin probes in the vesicle phase were determined. The quantitative results obtained by an ESR simulation indicated that the spin probe DTBN (di-tert-butyl nitroxide), in the vesicle of the mixed membrane, was partitioned similar to that of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) at 50 degrees C, and the partitioning for both probes showed no abrupt change across the temperatures examined. The results differed considerably from conventional analyses of the high-field signal intensities. Activation energies obtained by the simulation for DTBN and TEMPO were 21 and 20 kJ/mol, respectively. In addition, the hyperfine values of 15.8 (DTBN) and 16.1 G (TEMPO) in the vesicle phase were consistent with the activation energies and supported the probe environments in the membrane. Thus, the present ESR results provided detailed information regarding the probe behavior in the membrane.     

Spin-Probe Investigations of Head Group Behavior in Aqueous Dispersions of a Nonionic Amphiphilic Compound

Head group behavior of nonionic amphiphilic compound, (poly(oxyethylene) hydrogenated castor oil, HCO), in aqueous dispersions were investigated by EPR (electron paramagnetic resonance) in conjunction with a modern slow-tumbling simulation. The aliphatic spin probes, 5-doxylstearic acid (5-DSA) and 3β-doxyl-5α-cholestane (CHL), were used to obtain fluidity of the surface region of the membrane. The order parameter (S ₀) using the simulation for 5-DSA and CHL in the region were approximately 0.4 and 0.2, respectively. The ordering results suggest that the head group region of the membrane is somewhat fluid. The rotational diffusion coefficients (R _⊥ ≈ 1/(6τ_R)) for the probes were 3.4 × 10⁷ and 7.1 × 10⁷ s⁻¹, respectively. Activation energies, calculated using the temperature dependence of diffusion coefficients, were 18 and 17 kJ/mol for the probes. The EPR results imply that the CHL probe in the HCO membrane has quite different behavior in comparison with that of PC (phosphatidylcholine) from egg. Thus, the present EPR analyses have provided quantitative insight into the surface region of the amphiphilic membrane.     

Molecular Dynamics and Partitioning of Di-<Emphasis Type="Italic">tert</Emphasis>-butyl Nitroxide in Stratum Corneum Membranes: Effect of Terpenes

In this work, we have used electron paramagnetic resonance (EPR) spectroscopy of the small spin label di-tert-butyl nitroxide (DTBN), which partitions the aqueous and hydrocarbon phases, to study the interaction of the terpenes α-terpineol, 1,8-cineole, l(−)-carvone and (+)-limonene with the uppermost skin layer, the stratum corneum, and the membrane models of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The EPR spectra indicated that the terpenes increase both the partition coefficient and the rotational correlation time of the spin labels in the stratum corneum membranes, whereas similar effects were observed in the DMPC and DPPC bilayers only at temperatures below the liquid-crystalline phase. The EPR parameter associated to probe polarity inside the membranes showed thermotropically induced changes, suggesting relocations of spin probe, which were dependent on the membrane phases. While the DMPC and DPPC bilayers showed abrupt changes in the partitioning and rotational correlation time parameters in the phase transitions, the SC membranes were characterized by slight changes in the total range of measured temperatures, presenting the greatest changes or membranes reorganizations in the temperature range of ~50 to ~74 °C. The results suggest that terpenes act as spacers, weakening the hydrogen-bonded network at the polar interface and thus fluidizing the stratum corneum lipids.     

Distribution in correlation times for rotational diffusion of spin probes in polymers

Electron spin resonance spectra of poly(vinyl acetate) (PVAc) and plasticised PVAc doped with nitroxide spin probes show a double-peak feature at temperatures immediately below T_{50 G}. This can be explained on the basis that probe tumbling occurs with a distribution of correlation times τ_R arising from a distribution of free volume within the polymeric matrix. The two-component e.s.r. spectra arise because the distribution in τ_R of the probes straddles the value (c. 3 × 10^?9 s) which marks the change-over from fast- to slow-motion spectra. The implications of the existence of a distribution of τ_R values for calculations based on the assumption of a single value are examined. It is concluded that when probe tumbling is slow the error in τ_R could be significant, but for rapid tumbling (motionally narrowed spectra) the error is likely to be insignificant.     

Stratum Corneum Lipid Structure Investigated by EPR Spin-Probe Method: Application of Terpenes

Electron paramagnetic resonance (EPR) in conjunction with a slow-tumbling simulation was utilized for defining stratum corneum (SC) lipid structure. SC from the back of hairless mouse (HOS:HR-1) was stripped consecutively from one to three or four times using a glass plate coated with a cyanoacrylate resin. Aliphatic spin probes, 5-doxylstearic acid (5-DSA) and 3β-doxyl-5α-cholestane (CHL), were used to evaluate the SC ordering. EPR spectrum of 5-DSA incorporated in the SC demonstrated a characteristic peak for the first strip. A slow-tumbling simulation for 5-DSA showed clear differences in EPR intensities as well as ordering values (S ₀) of the SC for control and terpenes treated SC. The α-terpineol enhanced the permeation of the single chain 5-DSA about three times more than that of the control. However, EPR spectra of CHL in the SC did not show a clear difference for each strip, except for the signal intensity. The results imply that CHL permeates into SC lipid differently from 5-DSA. The enhancement of the 5-DSA is more significant than that of CHL. Therefore, the present results can be useful for various drug administrations via the skin.     

Effect of Sonication on the Thermotropic Behavior of DODAB Vesicles Studied by Fluorescence Probe Solubilization

The effect of sonication on fluorescence probe solubilization in cationic vesicles of dioctadecyldimethylammonium bromide (DODAB) was investigated by steady-state fluorescence of pyrene (Py), trans-diphenylpolyenes—diphenylbutadiene (DPB), diphenylhexatriene (DPH), and their corresponding 4,4′-dialkyl derivatives 4B4A and 4H4A fluorescence probes. The data indicate that sonication affects the bilayer polarity, the melting temperature (T _m), and the cooperativity of the melting process due to changes in vesicle morphology. The effect of temperature on the fluorescence intensity and yielding Φ_f and anisotropy <r> shows that the ionizable probes 4B4A and 4H4A are solubilized close to the vesicle interfaces, whereas the non-ionizable DPH and DPB are deeper in the bilayers. Py solubilization indicates that sonicated vesicles exhibit less densely packed bilayers.     

Initiation of combustion processes in a hydrogen-oxygen mixture under the action of a low-energy strong-current electron beam

The process of combustion initiation in a hydrogen-oxygen mixture by a beam of electrons with an energy of ≈10 keV and a mean cross-sectional size of ≈10 cm is considered theoretically and experimentally. The initial pressure in the mixture is 500 Pa. The reaction was visualized by recording the time evolution of fluorescence intensity in the lines of molecular (λ = 310 nm) and atomic hydrogen and sodium doublet (λ = 589 nm). The calculations are performed on the basis of a semi-empirical model developed in a three-temperature (T ₀, T _e , and T _v) approximation. The induction and burning times determined in experiments and calculations are in good agreement. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 10–17, March–April, 2007.     

Spin Probe Study of IPN-like Systems based on Polyethylene and Polymethacrylates

A system similar to an interpenetrating polymer network (IPN), based on polyethylene/poly(methylmethacrylate-co-dodecyl methacrylate), was studied by the spin probe method with a nitroxide spin probe, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). The influence of changes in the composition of the copolymer (methyl methacrylate-co-dodecyl methacrylate) on the molecular mobility and composition of the IPNs is characterized by changes of the empirical spectral parameters T_50G and τ_R. The molecular mobility was shown to diminish with rising content of methyl methacrylate in the copolymer. © of SCI.     

Isothermal physical aging of thin PMMA films near the glass transition temperature

Isothermal physical aging and the glass transition temperature (T _g) of PMMA thin films were investigated by means of differential scanning calorimetry (DSC). Freestanding thin films of different molecular weights (M _w = 120,000, 350,000, 996,000 g/mol) and film thicknesses (40–667 nm) were obtained by spin coating onto a silicon wafer substrate and then releasing the coated film using a water floating technique. The thin films were stacked in a DSC pan and isothermally aged for different aging times (t _a = 1 and 12 h) and aging temperatures (T _a = 105, 110, and 115 °C) below but near T _g. Enthalpy relaxation (ΔH _Relax), resulting from the isothermal physical aging, initially increased with increasing ΔT (T _g − T _a, driving force of aging), reached a maximum value, and then decreased with further increase in ΔT. Below ~100 nm film thickness, ΔH _Relax of samples aged near their T _g (i.e., T _a = 110 and 115 °C) decreased with decreasing film thickness, indicating the suppression of physical aging. Up to 9.9 °C depression in T _g was observed for thinner films (~40 nm), when compared to the thicker films (~660 nm) in this study. The decrease in ΔH _Relax with decreasing film thickness at a given T _a appears to be associated with the reduction in T _g.     

Determination of Hansen solubility parameters for cellulose acrylate by inverse gas chromatography

The solubility parameters of cellulose acrylate (CEA) were examined by inverse gas chromatography (IGC). The test probes were pentane, hexane, heptane, octane, nonane, ether, acetone, tetrahydrofuran, toluene, chloroform, isopropanol, and hexanol. The minimal test probe was injected into chromatographic column in order to achieve the infinite dilution conditions. The retention times of the test probes were determined and Flory–Huggins interaction parameters (χ) and solubility parameters (δ ₂) were calculated according to DiPaola-Baranyi and Guillet method from experimentally collected retention data for the series of carefully selected test probes. The Hansen’s three-dimensional solubility parameters concept is applied to determine the components (δ _d, δ _p, δ _h) of total solubility parameter (δ _T). The solubility parameter (δ _T) was increased with increasing temperature.     

EPR study of solid solutions La1 ? 0.33yBa0.33yMnyAl1 ? yO3 (y = 0.02, 0.04, 0.10)

Solid solutions La_{1 − 0.33y} Ba_0.33y Mn _y Al_{1 − y} O₃ (y = 0.02, 0.04, 0.10) prepared using the ceramic technique have been investigated by the EPR method at temperatures of 77 and 300 K. By comparing with the calculated spectra, the experimental spectra have been assigned to Mn²⁺ ions (g = 2.04 and line width ΔH _pp = 64 × 10⁻⁴ T at T = 77K) and Mn⁴⁺ ions (g = 1.97 and ΔH _pp = 76 × 10⁻⁴ T at T = 77 K) and the broad line (ΔH _pp = 500 × 10⁻⁴ T at T = 77 K) has been attributed to clusters. The dilution of manganese ions as a result of the dissolution of La_0.67Ba_0.33MnO₃ in LaAlO₃ has allowed one to trace the cluster formation and the spin dynamics of Mn ions. It has been established that, at room temperature, compared to the system in which the Sr²⁺ ion with a smaller ionic radius is the replacing element, the localized states are more stable at all three manganese concentrations (the EPR lines are more intense). The La_0.67Ba_0.33MnO₃ clusters dissolved in LaAlO₃ retain some properties of a concentrated compound even upon dilution to y = 0.02.     

Correlating viscosity with temperature and other properties

Simple viscosity equations based on linearities [1/η^e (or φ^e) vs. T; T/η^e vs. T and φ^e vs. P; (η, viscosity; φ, fluidity; T, temperature; and P, any property or property function linear with T, such as, density, refractivity, and surface tension)] are given for glycerol, triglycerides, glyceride oils, n-fatty acids, esters, an alcohol, and an amine.     

Hot Photoluminescence in γ-In2Se3 Nanorods

The energy relaxation of electrons in γ-In₂Se₃ nanorods was investigated by the excitation-dependent photoluminescence (PL). From the high-energy tail of PL, we determine the electron temperature (T _e) of the hot electrons. The T _e variation can be explained by a model in which the longitudinal optical (LO)-phonon emission is the dominant energy relaxation process. The high-quality γ-In₂Se₃ nanorods may be a promising material for the photovoltaic devices.     

Synthesis and characterization of the novel block copolymer poly(ε‐caprolactone)‐b‐poly(4‐vinyl pyridine) by the combination of coordination and controlled free‐radical polymerizations

A novel block copolymer, poly(ε‐caprolactone)‐b‐poly(4‐vinyl pyridine), was synthesized with a bifunctional initiator strategy. Poly(ε‐caprolactone) prepolymer with a 2,2,6,6‐tetramethylpiperidinyloxy (TEMPO) end group (PCL_T) was first obtained by coordination polymerization, which showed a controlled mechanism in the process. By means of ultraviolet spectroscopy and electron spin resonance spectroscopy, the TEMPO moiety was determined to be intact in the polymerization. The copolymers were then obtained by the controlled radical polymerization of 4‐vinyl pyridine in the presence of PCL_T. The desired block copolymers were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, and NMR spectroscopy in detail. Also, the effects of the molecular weight and concentration of PCL_T on the copolymerization were investigated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2280–2285, 2004     

E.s.r. and saturation transfer e.s.r. spectroscopy of spin-probed poly(vinyl acetate): A new spectral transition correlating with glass transition temperature

From the temperature dependence of the rotational frequency of a nitroxide spin probe dispersed in poly(vinyl acetate) the size of the polymer segment involved in the glass to rubber relaxation can be estimated. The calculation is based on a free volume model which relates f, the ratio of the volumes of the spin probe and the polymer segment, to the rotational frequency of the probe. An increase in f with increasing size of the probe is demonstrated. Saturation transfer electron spin resonance spectra of two nitroxide probes are shown to undergo a rapid change with temperature at a temperature T_R which is characteristic of both the probe and its environment. T_R corresponds to a pseudo-isofrequency point and is analogous to, though at a lower characteristic frequency than, the widely-used parameter T_50G. For the systems examined, T_R correlates with the glass to rubber relaxation.     

EPR study of compounds in the LaAlO<Subscript>3</Subscript>-La<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> system

The EPR spectra of compounds in the LaAlO₃-La_0.67Sr_0.33Mn _y O₃ system at a frequency of 9.4 GHz have been investigated at the temperatures T = 77 and 300 K as a function of the manganese concentration y (y = 0.015, 0.030, 0.080). It has been revealed that, in the paramagnetic state at y = 0.015, there exist isolated Mn²⁺ and Mn⁴⁺ ions, which has been confirmed by simulating the EPR spectra. The parameters of the EPR spectra have been determined. The effective magnetic moments μ_eff of the Mn²⁺ and Mn⁴⁺ ions have been calculated from the EPR spectra. It has been demonstrated that an increase in the Mn concentration leads to a decrease in the number of isolated ions and to the formation of new spin clusters. This manifests itself in the predominance of a broad line with weak traces of the hyperfine structure due to the isolated manganese ions.     

Study of rotational mobility of stable nitroxide radicals in solid polymers

The rotational mobility of stable nitroxide radicals in PS, PMMA, PVC, PP and PE has been studied over a wide temperature range by the e.s.r. method. At temperatures T lower than T_g, spin probes act as kinetically independent particles, the rotational frequency of which is deter mined mainly by the micropore dimensions of the polymer and depends indirectly on the mobility of segments or side groups.     

Permeable domains of segmented polyurethanes studied with paramagnetic spin probe

Studies on the permeable regions of the dense polyurethane-based membranes were performed by electron spin resonance spectroscopy (ESR) using TEMPO spin probe incorporated into the membrane via diffusion from the vapour phase. The ESR spectra were measured as a function of temperature and microwave power for polyurethanes (PU) varying in the molecular structure and morphology. It was found that the TEMPO spin probe exhibited anisotropic rotation whose anisotropy increased as temperature decreased and was more pronounced for PU with shorter soft segments. The simplified method was used to obtain apparent correlation time τ_c enabling the comparison of the polyurethanes studied. This approach was based on the Arrhenius relation of τ_c vs. 1/T determined from motionally narrowed ESR spectra and on the assumption that this behaviour prevails over a broader temperature range at temperatures generally greater than T_g of a given polymer.     

Segment size in synthetic polymers by the spin-probe method

Following the approach of Kusumoto an equation is derived which relates the correlation time for the tumbling of a nitroxide spin probe in a polymer matrix with the parameter f, the ratio of the volumes of the probe and the polymer segment undergoing motion at T>T_g. For poly(vinyl acetate) probed with a series of nitroxides the correlation between f and the molecular volumes of the probes is poor, possibly because of wide variations in probe flexibility and polarity. An approximate version of the equation also permits evaluation of f from the parameter T_50G. Values of f calculated in this manner for the probe 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl-benzoate in nine different polymers suggest that polymers with high glass transition temperatures have relatively bulky segments.     

Employment of Differential Scanning Calorimetry in Detecting Lard Adulteration in Virgin Coconut Oil

Lard (LD) has been commonly used as an adulterant in fats and oils. The similar physical characteristic of virgin coconut oil (VCO) to LD makes LD a desirable adulterant in VCO. Differential scanning calorimetry (DSC) provides unique thermal profiling for each oil and can be used to detect LD adulteration in VCO. In the heating thermogram of the mixture, there was one major endothermic peak (peak A) with a smaller shoulder peak embedded in the major peak that gradually smoothed out to the major peak as the LD% increased. In the cooling thermogram, there were one minor peak (peak B) and two major exothermic peaks, peak C which increased as LD% increased and peak D which decreased in size as the LD% increased. From Stepwise Multiple Linear regression (SMLR) analysis, two independent variables were found to be able to predict LD% adulteration in VCO with R ² (adjusted) of 95.82. The SMLR equation of LD% adulteration in VCO is 293.1 − 11.36 (T _e A) − 2.17 (T _r D); where T _e A is the endset of peak A and T _r D is the range of thermal transition for peak D. These parameters can serve as a good measurement index in detecting LD adulteration in VCO.