Partition coefficient of small spin probes: An improved ESR determination method

We report on the improved determination of the partition coefficient,P _e, of the small hydrophobic spin probe di-tert-butyl nitroxide (DTBN) between the aqueous and the fluid hydrophobic phase of dipalmitoylphosphatidyl choline (DPPC) multilayers, made in terms of the second integral evaluation of the isotropic ESR resonance lines. The calculation of the second integral was carried out taking into account both the width and amplitude of the resonance lines and a shape factor related to the degree of inhomogeneous line broadening. The expression ofP _c obtained in this way has been tested by computer simulation using Voightian lineshapes for the ESR absorption resonance lines. The method has been applied to the determination of the degree of cooperativity of the gel → liquid-crystal phase transition of DPPC multilamellae, and the results were compared with those obtained using the traditional expression ofP _e. Finally, the calculation of the cooperativity parameter of the main phase transition of DPPC multilayers results improved of about 70% by using the new expression ofP _c.     

Synthesis and characterization of wire-like and near-spherical Eu2O3-doped Y2O3 phosphors by solvothermal reaction

Eu₂O₃-doped yttrium oxide (3 mol%) [Y₂O₃:Eu(3 mol%)] with wire-like and near-spherical morphologies were prepared by a solvothermal treatment using water, ethanol, ethylene glycol and glycerol as reaction media followed by calcination. The powders prepared in water and ethanol possessed wire structure, where the powder treated in water showed high aspect ratio and that in ethanol showed low aspect ratio. The powders prepared in ethylene glycol and glycerol possessed well-dispersed near-spherical powders, which showed almost the same level of photoluminescence emission intensity as that of submicron particles prepared without solvothermal treatment.     

Procain interaction with DPPC multilayers: an ESR spin label investigation

A spin label electron spin resonance (ESR) study has been carried out on the interaction between the local anesthetic procaine (PRC) and multilamellar dispersions of di-palmitoylphosphatidylcholine (DPPC). The investigation has been performed either in the gel or in the liquid crystal phase of DPPC varying the anesthetic/DPPC molar ratio as well as the pH of the dispersion medium and using spin labeled DPPC molecules (5- and 16-PCSL) and the di-tert-butyl nitroxide (DTBN) spin probe. On increasing the anesthetic concentration in the dispersion medium up to PRC/DPPC molar ratio of 33 mol.%, a lyotropic transition of the bilayer from the lamellar gel phase L_β, to the interdigitated L_βi one is observed either at pH 5.0 or at pH 10.0. At intermediate pH values, about pH 7.0, such a PRC concentration dependent transition is absent. A decrease of the partition of the DTBN molecules between the dispersion medium and the fluid hydrophobic phase of DPPC multilayers is observed at pH 5.0 with anesthetic concentration, while an opposite behaviour is evidenced at pH 10.0. The pre- and main-phase transition temperatures of the DPPC multilayers are also affected although to different extent. These results are interpreted in terms of adsorption of the PRC molecules at the surface of the model membrane at the extreme pH values investigated, while at about neutral pH values they intercalate among the DPPC molecules. The protonation state of procaine plays an important role as it determines the way of surface adsorption of the PRC molecules in the neutral form at the high pH value and in the charged cationic form at pH 5.0.     

Poly(ethylene glycol) and phospholipid packing in the structure of reverse micelles

The influence of water substitution by a substance with a different polarity on the structure of phospholipid monolayer interface in water-in-oil microemulsion has been studied by the Fourier-transform pulsed-gradient spin-echo (FT PGSE)¹H nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spin-label methods. For this purpose the soybean phosphatidylcholine-based microemulsion and water soluble poly(ethylene glycol) with molecular weight 400 (PEG400) were used. Self-diffusion coefficients of all microemulsion components obtained by the FT PGSE NMR technique provided information about both the size of reverse micelles and distribution of components between different microemulsion compartments. The maximum hyperfine splitting, 2A _max, in the ESR spectra was used to characterize the degree of the phospholipid hydrocarbon chain mobility. It was shown that PEG400 alters significantly the size of the reverse micelles and the motion of the labeled segments of the lipid tails. A mechanism of PEG400 acting in solution of the phospholipid-based reverse micelles on the basis of the rough decrease of the micelle core polarity was suggested.     

An electron spin resonance study of the soy bean phosphatidylcholine-based reversed micelles

The ESR spectra of l-palmitoyl-2-stearoyl-(n-doxyl)-glycero-3-phosphocholine spin label positional isomers (n = 5, 7, 10, 12 and 16) have been studied in soy bean phosphatidylcholine (SPC)-based microemulsions with various volume fractions of disperse phase over the wide temperature range. The maximum hyperfine splitting 2A _max and the order parametersS were taken as indices of the rotational mobility and the motion spatial restrictions of the labeled lipid chain segments. It is found that the temperaturesT _tr at which sharp enhancements of2A _max andS occur depend on concentration and size of the reversed micelles in solutions. To explain this, a plausible model, taking into account capability of the SPC molecule hydrocarbon chains to change a tilt angle with respect to the surface of a polar head group as temperature varies, is proposed. The estimations of the correlation times τ_sl obtained from the lineshape characteristics of the ESR spectra provided the possibility to suggest that these correlation times characterize the reorientations of the SPC chain axis about the normal to the surface of a polar head group of a reversed micelle.     

Time-resolved emission spectra and anisotropy profiles for symmetric diacyl- and dietherphosphatidylcholines

The solvent relaxation behavior of Patman (6-palmitoyl-2-[[2-(trimethylammonium) ethyl]methylamino]naphthalene chloride) was investigated in small unilamellar vesicles composed of symmetric diacyl( 1,2-dipalmitoylphosphatidylcholine; DPPC) and diether lipids (l,2-dihexadecylphosphatidylcholine; DHPC), calculating time-resolved emission spectra (TRES) and correlation functions. Both the steady-state spectra as a function of temperature and excitation wavelength and the TRES of Patman in DPPC are blue-shifted compared to those in DHPC. The solvent relaxation at three temperatures above and below the phase transition is considerably faster in DHPC than in DPPC. As the steady-state anisotropies of Patman and TMA-DPH [l-(4-trimethylammoniumphenyl)-6-phenyl-l,3,5-hexatriene] are similar in both lipids as a function of both temperature and emission wavelength, we conclude that the introduction of ether linkages allows more efficient water penetration in the glycerol region, leading to a more polar environment and therefore faster solvent relaxation of the incorporated dyes. Using a series ofn-(9-anthroyloxy) fatty acids (n = 2, 3, 6, 9, 12; 16-AP), we show that anisotropy profiles can be used to distinguish between noninterdigitated (DPPC) and fully interdigitated (DHPC) gel-phase structures. 16-(9Antroyloxy) palmitic acid (16-AP) is an especially useful probe exhibiting pronounced differences in the steady-state anisotropies in non- and fully interdigitated gel phases.     

Mitogens-DPPC-vesicles interaction: A spin label ESR study

Summary The electron spin resonance spectroscopy with the spin labelling technique has been used to investigate the interaction of sonicated di-palmitoyl-phosphatidylcholine (DPPC) small unilamellar vesicles with concanavalin A (Con A), phytohemagglutinin (PHA) and staphylococcal enterotoxin B (SEB) in the temperature range 0–50°C. Conventional ESR measurements show that the addition of mitogens to the vesicles suspensions up to the number of mitogens/number of vesicles ratio of 60 increases the orientational degree of order of the lipid molecules in the gel phase and the gel→liquid-crystalline phase transition temperature. No effects on the liquid-crystalline phase have been observed, also no matter for the mitogen used. The effectiveness results in the order: ConA>SEB>PHA. Saturation transfer-ESR measurements evidence more restricted rotation of the DPPC molecules in the gel phase in the presence of Con A and SEB than in the presence of PHA if compared to pure DPPC-vesicles. The effective rotational correlation time, σ_c, of the spin label 5-SASL results about one order of magnitude higher in the presence of 60 mitogen molecules/vesicle. The ESR findings suggest a mitogen-induced increase in the packing density of lipid bilayers which is attributed to a morphological change from sonicated vesicles, with a small radius of curvature, to a more planar mesophase. Con A is more effective than SEB and PHA in inducing this process. The authors of this paper have agreed to not receive the proofs for correction.     

Ionic conductivity of polymer electrolytes based on phosphate and polyether copolymers

Linear polyphosphate random copolymers (LPC) composed of phosphate as a linking agent with poly(ethylene glycol) (PEG) and/or poly(tetramethylene glycol) (PTMG) were synthesized to increase local segmental motion for improved ion transport. Ionic conductivity and thermal behavior of LPC series–LiCF₃SO₃ complexes were investigated with various compositions, salt concentrations and temperatures. The PEG(70)/PTMG(30)/LiCF₃SO₃ electrolyte exhibited ionic conductivity of 8.04×10⁻⁵ S/cm at 25°C. Salt concentration with the highest ionic conductivity was considerably dependent on EO/TMO compositions in LPC series–salt systems. Relationship between solvating ability and chain flexibility with various compositions and salt concentrations was investigated through theoretical aspects of the Adam–Gibbs configurational entropy model. Temperature dependence on the ionic conductivity in LPC6 series–salt systems suggested the ion conduction follows the Williams–Landel–Ferry (WLF) mechanism, which is confirmed by Vogel–Tamman–Fulcher (VTF) plots. The ionic conductivity was affected by segmental motion of the polymer matrix. VTF parameters and apparent activation energy were evaluated by a non-linear least square minimization method. These results suggested that the solvating ability of the host polymer might be a dominant factor to improve the ionic conductivity rather than chain mobility.     

Study of EVOH based single ion polymer electrolyte: Composition and microstructure effects on the proton conductivity

A comb-like EVOH based single ion polymer electrolyte (EVOH-g-SPEG) was synthesized by sulfonification of EVOH grafts 2-(2-chloroethoxy) ethanol (C₄H₉O₂Cl)/2-[2-(2-chloroethxy) ethoxy] ethanol (C₆H₁₃O₃Cl) with 1, 3-propane sultone. The main chain of the comb-like polymer is hydrophobic polyethylene segments; the side chain is hydrophilic poly (ethylene glycol) (PEG) segment, which can solubilize large amounts of inorganic salts. The sulfonic acid group was introduced onto the end of the PEG side chain. The acid form of SPE was successfully obtained by being dialyzed from the products with acid solution. The saturation water sorption of EVOH-g-SPEG membrane increased with the side chain length and the immersion time. The XRD results indicate that the water in SPE membrane region can destroy the membrane crystalline structure and the water absorption membranes are nearly amorphous. AFM phase images of the hydration membranes clearly show the hydrophilic domains, with sizes increasing from 10 to 35 nm as a function of the side chain length. A phase inversion could be observed when n ≥ 5, which was consistent with a rapid increase in water absorption. And the ion conductivity is also measured by AC impedance. The conductivity is greatly influenced by ion exchange capacity and water sorption. The comb-like EVOH-g-SPEG polymer electrolyte grafts with 2 PEG side chain provides the highest ionic conductivity (1.65 × 10^− 3 S cm^− 1). The comb-like polymer could be a candidate as new polymeric electrolyte material for fuel cells and other electrochemical devices.     

Conductivity studies on PEO:NaClO3 electrolyte system with different plasticizers

A new ion conducting solid polymer electrolyte thin film based on Polyethylene oxide (PEO) with NaClO₃ salt is prepared by solution-casting method. The solvation of salt with PEO has been confirmed by X-ray diffraction and IR spectral studies. Plasticizer effects were studied in PEO:NaClO₃ system by using low molecular weight polyethylene glycol (PEG), dimethyl formamide (DMF) and propylene carbonate(PC). AC conductivity in the temperature range (308–378 K) was measured to evaluate the conductivity of the polymer electrolytes. From the conductivity data, it was found that the conductivity value of pure PEO increases 10²–10⁴ order of magnitude with the addition of salts as well as plasticizers. From the transference number experiments, it was confirmed that the charge transport in these electrolyte is mainly due to the ions (t_ion≈0.94). Finally, the conductivity value of all PEO: NaClO₃ systems were compared.     

二氧化碳在电解质溶液中的盐溶盐析机制

The solvation of carbon dioxide in sea water plays an important role in the carbon circle and the world climate. The salting-out/salting-in mechanism of CO₂ in electrolyte solutions still remains elusive at molecule level. The ability of ion salting-out/salting-in CO₂ in electrolyte solution follows Hofmeister Series and the change of water mobility induced by salts can be predicted by the viscosity B-coefficients. In this work, the chemical potential of carbon dioxide and the dynamic properties of water in aqueous NaCl, KF and NaClO₄ solutions are calculated and analyzed. According to the viscosity B-coefficients, NaClO₄ (0.012) should salt out the carbon dioxide relative to in pure water, but the opposite effect is observed for it. Our simulation results suggest that the salting-in effect of NaClO₄ is due to the strongly direct anion-CO₂ interaction. The inconsistency between Hofmeister Series and the viscosity B-coefficient suggests that it is not always right to indicate whether a salt belongs to salting-in or salting-out just from these properties of the salt solution in the absence of solute.     

Anti-stokes Raman scattering from DODCI solutions

A clearly resolved anti-Stokes peak was observed in the Raman scattering of He-Ne laser radiation from room temperature solutions of DODCI in ethanol and ethylene glycol, but not from solutions of DODCI in glycerol. A slight red-shift and broadening of the Raman-active vibrational mode was noted in ethylene glycol compared to ethanol. Evidence is presented that solutions of DODCI in glycerol have photochemical instabilities.     

Analysis of anisotropic spin-label motion in saturation-transfer ESR spectra of spin-labeled cowpea chlorotic mottle virus

A saturation-transfer ESR study is carried out on maleimide spin-labeled cowpea chlorotic mottle virus dissolved in various glycerol-water systems. The saturation-transfer ESR spectra were analyzed by comparing them with reference spectra of isotropically reorienting spin labels. The results are interpreted in terms of the overall motion of the virus particle, described by an isotropic rotational correlation time τ_R, and a local anisotropic spin-label motion with rotational correlation times τ_| and τ_⊥.     

Poly(ethylene glycol)/poly(2-acrylamido-2-methyl-1-propane sulfonic acid) gel electrolytes: a detailed investigation of their conductivity and characterization

Poly(ethylene glycol)/poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PEG/PAMPS) with a transparent appearance were prepared in the presence of ammonium persulfate (APS) as an initiator at 70 °C for 24 h. PEG/PAMPS-based polymer gel electrolytes in a motionless and uniform state were obtained by adding the required amount of liquid electrolytes to a dry PEG/PAMPS polymer. Liquid electrolytes include organic solvents with high boiling points (-1-methyl-2-pyrrolidone (NMP) and γ-butyrolactone (GBL)) and a redox couple (alkali metal iodide salt/iodine). The optimized conditions for PEG/PAMPS-based gel electrolytes based on the salt type, the concentration of alkali metal iodide salt/iodine, and solvent volume ratio were determined to be NaI, 0.4 M NaI/0.04 M I₂, and NMP:GBL (7:3, v/v), respectively. The highest ionic conductivity and the liquid electrolyte absorbency were 2.58 mS cm^?1 and 3.6 g g^?1 at 25 °C, respectively. The ion transport mechanism in both the polymer gel electrolytes and liquid electrolytes is investigated extensively, and their best fits with respect to the temperature dependence of the ionic conductivity are determined with the Arrhenius equation.     

Phase transition and triplet exciton mobility in anthracene—tetracyanobenzene charge-transfer single crystals

Triplet-Excitons in a mixed 1 : 1 anthracene—tetracyanobenzene single crystal are established by ESR-spectrocopy. These excitons (lifetime 0.5 msec) are characterized by a hopping frequency of v = 1.3 × 10⁶ K at 300K. The temperature dependence of the ESR line shape indicates a phase transition of the crystal at T_t = 205K. Above and below the phase transition the exciton mobility is nearly temperature independent.     

Lyotropic model membrane structures of hydrated DPPC: DSC and small-angle X-ray scattering studies of phase transitions in the presence of membranotropic agents

Multibilayer structures of hydrated phospholipids, often considered as model biological membranes, are, from the physical viewpoint, lyotropic liquid crystalline systems undergoing temperature-induced mesomorphic phase transitions. Effects of silver nitrate and urocanic acid on lyotropic phase states of hydrated L-α-dipalmitoylphosphatidylcholine (DPPC) have been studied by small-angle X-ray scattering and differential scanning calorimetry (DSC). Both methods show increase of the main phase-transition temperature (T_m) of hydrated DPPC upon introduction of AgNO₃ or urocanic acid, decrease of pre-transition temperature (T_p) in the presence of urocanic acid and its increase in the presence of AgNO₃. Thus, urocanic acid widened the ripple-phase temperature region. Silver nitrate caused the appearance of an additional high-temperature peak on DSC thermograms, evidencing phase separation in the system. Both agents caused minor effects on DPPC lipid bilayer repeat distance (D) in gel phase, but resulted in noticeable increase of D in the liquid crystal phase with temperature as compared to undoped DPPC structures.     

Resolving domains of interdigitated phospholipid membranes with 95 GHz spin labeling EPR

High-field W-band (95 GHz) electron paramagnetic resonance (EPR) study of partitioning of a small nitroxide TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) in multilamellar liposomes composed from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) is described. The high-resolution spectra with a high signal-to-noise ratio were combined with automated least-squares simulation analysis to derive accurate partitioning coefficients of TEMPO in the membrane lipid phase and to follow the membrane phase transitions. The isotropic magnetic parameters, g_iso and A_iso were used to characterize the average polarity the spin label is experiencing in the membrane. We also report an empirical correlation between g_iso and A_iso for a set of protic and aprotic solvents and use this correlation to assign domains formed by interdigitation of DPPC bilayer under a high ethanol concentration of 1.2 M.     

Synthesis and characterization of novel urethane cross-linked ormolytes for solid-state lithium batteries

A novel family of Li⁺-based organic/inorganic materials obtained by the sol–gel process is proposed. The compounds, named urethanesils, are obtained as thin, transparent, elastomeric and amorphous monolithic films. They incorporate solvating pendant methyl end-capped short poly(oxyethylene) chains which are covalently bonded to the silica backbone by means of urethane cross-links. The urethane linkages are formed by reacting 3-isocyanatepropyltriethoxysilane with hepta(ethylene glycol) methyl ether (HEGME). Li⁺ has been introduced in the urethanesils as lithium triflate (LiCF₃SO₃). Two compositions of salt have been considered: n=100 and 8, where n represents the molar ratio of (OCH₂CH₂) units per lithium ion. Infrared spectroscopy provides conclusive evidence that, although the oligopolyether chains of HEGME become less disordered upon formation of the inorganic network, the addition of salt induces disorder. The FTIR spectrum of the most concentrated urethanesil strongly suggests that the triflate ions are essentially coordinated in the material. The thermal and mechanical properties of the undoped and doped urethanesils have been investigated by DSC and DMTA. At 90°C, the highest ionic conductivity (approximately 10⁻⁶ Ω⁻¹ cm⁻¹) is observed for composition n=8. The electrochemical stability domain of the least concentrated urethanesil spans 5 V.     

Poly-acrylonitrile-based gel-polymer electrolytes for sodium-ion batteries

Research and development activities on sodium-ion batteries are becoming prominent in the past few years. Compared to lithium-based batteries, the sodium-based batteries will be cheaper because of the abundancy of sodium raw materials in the earth’s crust and also in seawater. In the current study, we synthesized and characterized poly-acrylonitrile (PAN)-based gel-polymer electrolytes formed with NaClO₄ and dissolved in ethylene carbonate (EC) and propylene carbonate (PC). By systematically varying the weight ratios of polymer, salt, and the solvents, we obtained an optimum room temperature ionic conductivity of 4.5 mS cm⁻¹ for the composition 11PAN-12NaClO₄-40EC-37PC (wt.%), which is reasonably good for practical applications. This value of conductivity is comparable to a few other Na⁺ ion conducting gel-polymer electrolyte systems studied in the recent past. Variation of ionic conductivity with inverse temperature showed Arrhenius behavior. Activation energies estimated for all the samples showed only a slight variation suggesting that a single activation process which depends on the EC/PC co-solvent governs the ionic mobility in these gel-polymer electrolytes. Thermo-gravimetric analysis (TGA) revealed that there is no noticeable weight loss of these electrolytes up to 100 °C and hence the electrolytes are thermally stable for operating temperatures up to 100 °C.

     

Effects of solvent composition on the electrochemical performance of Li2FeSiO4/C cathode materials synthesized via tartaric-acid-assisted sol–gel method

Li₂FeSiO₄/C composites were synthesized via a tartaric-acid-assisted sol–gel method with ethanol and ethylene glycol (EG) as mixed solvents. Effects of solvent composition on the physical properties and electrochemical performances of Li₂FeSiO₄/C were studied. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical performances of Li₂FeSiO₄/C were evaluated by galvanostatic charge–discharge and electrochemical impedance spectra (EIS) measurements. The results show that the addition of EG to ethanol solvent during preparation has a positive effect on the electrochemical performance of Li₂FeSiO₄/C. The sample synthesized using EG–ethanol with the volume ratio of 2:7 has the best electrochemical performance. It delivers an initial discharge capacity of 105 mAh g^?1 at C/16. AC impendence investigation shows that Li₂FeSiO₄/C synthesized using the optimal EG/ethanol volume ratio has lower resistance of electrode/electrolyte interface and higher lithium-ion diffusion coefficient than that synthesized using ethanol as solvent.