Nonpolar Form Research Articles

Molecular Forms of Coumarin-307 in Sol-Gel Glasses

Coumarin-307(C-307) impregnated sol-gel glass samples were prepared by two methods - (I) predoping using HNO3 as catalyst, and (II) postdoping using HNO3 as catalyst and formamide as drying control chemical additive (DCCA). The absorption/fluorescence properties including fluorescence lifetime of the dye in these sol-gel host matrices were studied and results were compared with dye in methanol (MeOH). In addition to usual non-polar form of C-307 that exists in MeOH, amino-protonated form and dimer of dye have also been found to co-exist in the dried state of samples prepared by predoping method. This behaviour of dye was uncommon to sol and gel states of materials. The fluorescence quantum yield (Qf) of C-307 doped solid was found to be 0.77 and it was almost constant in the concentration range 5 x 10(16) to 8.8 x 10(17) cm(-3). On the other hand, only non-polar form of C-307 has been observed in the samples prepared by postdoping method. The Qf value of dye was 0.96 in the postdoped samples. To explain such behaviour of C-307 in the two types of sol-gel matrices: dye concentration, role of HNO3, water, formamide and matrix effect have been taken into account.

Photophysical Effects between Spirobenzopyran−Methyl methacrylate-Functionalized Colloidal Particles

Colloidal particles were derivatized with end-grafted polymethylmethacrylate polymer brushes containing varying concentrations of spirobenzopyran photochromic molecules. The polymers were grown from initiator-functionalized silica particles by an atom-transfer radical polymerization (ATRP). These core-shell colloids formed stable suspensions in toluene with the spirobenzopyran in its closed, nonpolar form. However, UV-induced photoswitching of the photochrome to its open, polar merocyanine isomer caused rapid aggregation. The nature of this colloidal stability transition was examined with respect to the spirobenzopyran content in the polymeric brush and solvent polarity. Turbidimetry, wettability studies, UV-vis spectroscopy, suspension rheology, SEM, and visual inspection were utilized to characterize the system photoswitchability. It was found that the system exhibiting the greatest transition in toluene was the copolymer brush composed of 20% spirobenzopyran and 80% methyl methacrylate.

Photo-regenerable surface with potential for optical sensing

Photochromic spiropyran was covalently immobilized using alkyldiamine couplers with varying chain length (2, 4, 6, 8 methylene groups) onto an optically transparent polymeric surface. The relatively nonpolar and colourless spiropyran form can be reversibly switched to a charged, highly coloured, zwitterionic merocyanine isomer using UV and visible light, respectively. The merocyanine form complexes with metal ions, and this results in a shift in the absorbance spectrum, and a corresponding colour change is observed. Upon irradiation of the complex with visible light, the cation is released and the merocyanine (active) isomer reverts back to the spiropyran (passive) form. Optical switching and complexation behaviour of the polymer-bound spiropyran–merocyanine system is highly dependent on the tether length of the spiropyran from the polymeric surface. The effect is demonstrated using cobalt(II) chloride in solution.

Triacylglycerol Is Synthesized in a Specific Subclass of Caveolae in Primary Adipocytes

A principal metabolic function of adipocytes is to synthesize triacylglycerol (TG) from exogenous fatty acids. The level of fatty acids has to be tightly controlled in the adipocyte, as they can act as detergents that rapidly dissolve the plasma membrane, causing cell lysis if allowed to accumulate. Fatty acids therefore have to be efficiently converted to TG and stored in the central lipid droplet. We report that in intact primary adipocytes exogenous oleic acid was taken up and directly converted to TG in the plasma membrane, in a novel subclass of caveolae that specifically contains the protein perilipin. Isolated caveolae catalyzed de novo TG synthesis from oleic acid and glycerol 3-phosphate. Electron microscopy revealed the presence of caveolin and perilipin in caveolae and in lipid-laden bulbs in the plasma membrane, and fluorescence microscopy demonstrated colocalization of fatty acids/TG with caveolin and perilipin at the plasma membrane. A second caveolae fraction was isolated, which lacked perilipin and the triacylglycerol synthesizing enzymes. Both caveolae fractions contained caveolin-1 and the insulin receptor. The findings demonstrate that specific subclasses of caveolae carry out specific functions in cell metabolism. In particular, triacylglycerol is synthesized at the site of fatty acid entry in one of these caveolae classes.

Conductivity studies of LiCF3SO3-doped and DMF-plasticized PVDF-based solid polymer electrolytes

Room temperature ionic conductivity measurements show that the conductivity of polyvinylidene fluoride (PVDF)-based solid polymer electrolyte films depends on the concentration of the doping salt and the plasticizer. The highest conductivity for the doped PVDF system is 3.40 × 10–5 S cm–1 and for the plasticized system is 1.30 × 10–4 S cm–1. Conductivity–temperature dependence studies on the pure, doped and plasticized PVDF systems show that the sudden change in the slope of Arrhenius plots corresponds to the glass transition of PVDF as inferred from tan δ-temperature plots. The decrease in ionic conductivity in the high-temperature range can be attributed to the transformation of PVDF from the polar to nonpolar form as shown by X-ray diffraction studies. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectroscopy and Kinetics of a Molecular Memory with Nondestructive Readout for Use in 2D and 3D Storage Systems

A new molecule has been designed, synthesized, and utilized as molecular memory for optical storage capable of write, erase, and readout without simultaneously effacing the stored informtion. This molecule is composed of a photochromic fulgimide and a fluorescent dye bonded, chemically, together to form a single molecule. Experimental spectroscopic studies are performed for each individual component and the composite molecule. The kinetics of the photochromic transformation from the open, nonpolar form to the closed, polar form are discussed. It is also shown that the fluorescence intensity of the dye component is strongly dependent upon the polarity of the fulgimide component. The write/nondestructive readout and erase operations and prototype systems are presented, and a prototype optical disk is described.

Nonvolatile read-out molecular memory.

A versatile molecule is described that performs as a nondestructible read-out optical-storage molecular memory. This molecular memory is composed of two distinct molecules that are chemically bonded to each other to form a single molecule with unique properties. One component is a photochromic fulgimide, and the other is a strongly fluorescing oxazine dye. This composite molecule was specifically designed and synthesized to display, under specific conditions, both the photochromic functions of the first component and the fluorescence properties of the dye. To store information, the polar, closed form of the photochromic component is illuminated with 530-nm light, which converts it to the open, nonpolar form. The information is accessed by excitation at the 650-nm band of the oxazine dye component, causing the dye to fluoresce. However, the dye emits intense fluorescence under a nonpolar environment, which is attained only when the fulgimide component is in its open, nonpolar structure. The ultrafast kinetics, spectroscopy, and mechanism of the photoreaction of this molecule and its photoinduced intermediates have been measured, and fluorescence quantum yields and cross sections were determined.

Ferroelectricity and piezoelectricity of nylon 11 films with different draw ratios

The first studies by Shuford et al. (Polym Eng Sci 1976, 16, 25) of the effect of draw ratio on the piezoelectric properties of poled poly(vinylidene fluoride) films concluded that the effect of molecular orientation due to draw prior to film polarization was to increase greatly the piezoelectric response. In fact, unoriented films (being crystallized in the nonpolar crystal form, phase II) showed negligible piezoelectricity. It was clear that the effect of increased draw ratio prior to film polarization was to increase the measured piezoelectric coefficients, because draw gave rise to a phase transition to a polar crystal phase, phase I, and molecular chain orientation in the plane of the film, subject to high electric poling fields perpendicular to the plane of the film, resulted in a preferred dipole orientation perpendicular to the plane of the film by a rotation about molecular stems. A detailed study of nylon 11 films and other odd nylons has shown that these polymers also can exhibit ferroelectricity, piezoelectricity, and pyroelectricity of comparable or greater magnitude than that exhibited by poly(vinylidene fluoride) with a greater thermal stability. For these polymers, the effect of draw on piezoelectricity and ferroelectricity is not complicated by the effect of crystal phase transitions. For this reason, a study of the effect of draw ratio on the ferroelectric and piezoelectric properties of nylon 11 was initiated in order to provide some insight into the direct effect of molecular orientation (without accompanying phase changes) on piezoelectric and ferroelectric properties. Some melt-quenched nylon 11 films were uniaxially drawn to draw ratios, ranging from 1.5 : 1 to 3.5 : 1 in increments of 0.5, at room temperature. Both undrawn and drawn films were found to exhibit an electric displacement vs. electric field hysteresis loop, characteristic of ferroelectric materials. As the draw ratio increased from 1 : 1 to 3.5 : 1, the remanent polarization increased from 25 to 53 mC/m2 and the coercive field decreased from 73 to 63 MV/m. The piezoelectric response and electromechanical coupling constant were also measured at temperatures of 25°C and 120°C under dry conditions. As the draw ratio of the films increased from 1 : 1 to 3.5 : 1, the piezoelectric strain coefficient d′31 measured at 25°C remained unchanged at ∼ 1.1 pC/N but the piezoelectric stress coefficient e′31 increased from 2.1 to 4.9 mC/m2. At 120°C, d′31 increased from 3.8 to 20 pC/N and e′31 from 0.5 to 27 mC/m2. d′31 showed a linear relationship with the remanent polarization Pr at both 25°C and 120°C for all draw ratios but e′31 showed this relationship only at 25°C. The electromechanical coupling constant k′31 increased from 0.42% to 0.61% at 25°C and from 0.42% to 1.56% at 120°C as the draw ratio increased to 3 : 1. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2737–2746, 1999

Structural and Electronic Characterization of Epitaxially-Grown Ferroelectric Vinylidene Fluoride Oligomer Thin Films

AbstractThe structural and electric properties of newly synthesized vinylidene fluoride (VDF) oligomer thin films evaporated on various substrate were investigated. The structural behavior of the VDF oligomer thin films strongly depended on the kinds of substrate and substrate temperature during film preparation. In particular, the VDF oligomers epitaxially grew on KBr(001), aligned their molecular chain along the <110> direction of substrate surface, and were similar to polar Form Itype crystals of poly(VDF). While, the thin films evaporated on NaCl(001), SiO2/Si were non-polar Form II-type or mixture of both Form I- and Form II-type crystals with their molecular chain normal to the surface. These facts indicated that crystal field of substrate, based on van der Waals and electrostatic interactions, strongly influenced to ferroelectric phase transition of the VDF oligomer. In addition, we demonstrate the formation of the local polarized domains in the epitaxial crystals by applying electric pulses from a conducting AFM probe used as a positionable topelectrode, and confirm their piezoelectricity of the VDF oligomers for the first time.

Ab initio Hartree-Fock Investigation of π-Conjugated Compounds Presenting Large βv/βe Ratio: Merocyanines

CHF/6-311G* calculations of the first electronic and vibrational hyperpolarizabilities reveal that merocyanines present a substantial βv/βe ratio under their quinonoid nonpolar form. It originates from a large vibrational first hyperpolarizability whereas its electronic counterpart is small for this class of push-pull π-conjugated molecules. The transition from the quinonoid to the aromatic configuration is accompanied by an increase of βe and a decrease of the βv/βe ratio as well as by a ≈ 180° rotation in the plane of the molecule of βe and βv with respect to the molecular frame. Our results support the recent experimental discovery that antiparallel aggregation of aromatic and quinonoid forms of merocyanine is energetically favoured and that their first hyperpolarizabilities, which combine constructively, present both electronic and non purely electronic origins.

Effects of an electrostatic field on crystallization of poly(vinylidene fluoride)

AbstractMelt crystallization of poly(vinylidene fluoride) (PVF2) under a static electric field was studied by optical microscopy. For most crystallization temperatures a mixture of α and γ spherulites was obtained. The growth rate of the spherulites was measured in the plane perpendicular to the direction of the field. The effect of an electric field on the growth rate of the γ spherulites corresponds in a qualitative way with the dependence predicted theoretically for the primary nucleation of the nonpolar form. It is shown, that the growth rate of γ spherulites is always reduced by the electric field. This reduction was larger the lower the undercooling. In the case of γ spherulites the interpretation of the results is more complicated. Both the morphology and the growth rate of γ spherulites under an electric field depend on electrode configuration. An increase of the growth rate of γ spherulites in an electric field was detected only when the sample was in direct contact with both electrodes. Under these circumstances, γ spherulites nucleate and grow at the PVF2‐positive electrode interface; and the increase of the growth rate is higher the lower the undercooling, and is greater in comparison with the decrease found for the nonpolar α phase. The reason for the sensitivity of the morphology of the γ form to the electrode configuration is not completely clear. © 1994 John Wiley & Sons, Inc.

Combined effects of pH, cosolvent and penetration enhancers on the in vitro buccal absorption of propranolol through excised hamster cheek pouch

The combined effect of pH and vehicle composition on the buccal absorption of propranolol has been evaluated in vitro using hamster cheek pouch. Ethanol was used as cosolvent in various binary-water mixtures. Lauric acid, 1-menthol, sodium salicylate and phosphatidylcholine were evaluated as penetration enhancers. Isopropyl myristate was used as a model of the mucosal lipid phase in partitioning experiments. Permeation of propranolol increased in extent with increasing pH of the vehicle, as compared with the unionized lipophilic fraction of the drug. Permeation of propranolol was decreased at pH 9.4 and increased at pH 6.8 on the addition of ethanol. Ethanol increases the solubility of propranolol in the aqueous vehicle and reduces the oil/vehicle partitioning of the drug through a thermodynamic effect. In addition, at low concentration, ethanol is assumed to increase the permeability of the buccal mucosa to the polar ionized form of propranolol, while higher concentration is required to enhance the diffusivity of the nonpolar unionized form. Menthol and lauric acid were effective at promoting the buccal absorption of propranolol only when the drug was ionized. It was assumed that the mechanism of permeation enhancement was an interaction with the membrane components for 1-menthol, increasing the diffusibility of propranolol, whereas lauric acid may form a more partitionable complex with the drug without any action on membrane permeability.

Molecular structure and conformation of fluoromethyl-substituted cyclopropane and oxirane. MP4(SDQ)/6-3110 ∗∗ results

Fluoromethylcyclopropane and the oxirane analog epifluorohydrin have been studied by ab initio calculations on the MP4(SDQ)/6-311G ∗∗ level of theory. We predict fluoromethylcyclo-propane to exist as an equilibrium mixture of the cis and two equivalent gauche forms. These conformers have almost equal energies; our best calculations predict the gauche form to lie only 0.2 kcal mol −1 below the cis form. Epifluorohydrin exists as an equilibrium mixture of three conformers, one cis form and two distinct gauche forms. In disagreement with predictions based on vibrational spectroscopy, we predict the polar gauche form to be the conformer with highest energy. Our best calculations show that the non-polar gauche form and the cis rotamer have virtually equal energies about 0.9 kcal mol −1 below the high-energy polar gauche form. The high relative abundance of the cis form of epifluorohydrin compared to related molecules can be explained by steric effects and by stabilization of the cis form by intramolecular van der Waals interactions.

Serum of patients with prostatic cancer or benign prostatic hypertrophy contains nonpolar testosterone

We have previously described a nonpolar form of radioimmunoassayable serum testosterone (NPT) not measured by available antitestosterone antibodies. It is detected by mild alkaline hydrolysis of the petroleum ether extract of serum and subsequent radioimmunoassay. The properties of NPT are consistent with that of a fatty acid ester of testosterone or dihydrotestosterone. The serum of young males contains 1 to 3 ng/ml NPT, but it is not detected infemale serum. We measured serum testosterone and NPT levels in 36 men between 58 and 87 years of age. Seventeen subjects with advanced prostatic cancer (NPT 1.70 ± 1.44 ng/ml) were compared with a control group consisting of six patients with benign prostatic hypertrophy (BPH) and 13 patients with no prostatic disease (NPT 0.72 ± 0.46, P = 0.07). There was no significant difference between BPH patients and patients with no prostatic disease; the results were pooled. The concentration of NPT in prostatic cancer patients but not in controls was inversely correlated with that of testosterone. Immunoassayable testosterone was present in the serum of two orchiectomized patients and, therefore, cannot derive solely from the testes. (Steroids 55:491–494, 1990)

2,3,7,8-Tetrachlorodibenzo- p-dioxin pretreatment of female mice altered tissue distribution but not hepatic metabolism of a subsequent dose

Lipid partitioning of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) inadequately explains its tissue distribution since higher concentrations occur in liver than fat except at high doses. This study provides in vivo evidence that an inducible, saturable system plays a predominant role in disposition of [ 14C]TCDD in female mice at doses between 5 and 20 μg/kg. Female C57BL 6J mice were gavaged with 0, 5, or 15 μg TCDD/kg, received a subsequent gavage of 5 or 20 μg [ 14C]TCDD after 6 days, and were killed 1 day later. In mice pretreated with 5 and 15 μg TCDD/kg and subsequently dosed with 20 μg [ 14C]TCDD/kg, liver weight and [ 14C]TCDD concentration increased. Total liver [ 14C]TCDD burden increased about 50% in both pretreatment groups. Concentrations of [ 14C]TCDD in kidney, fat, heart, lung, gastrointestinal tract, but not plasma or splenic lymphocytes, decreased in a reciprocal manner. Alterations in absorption, concentrations of polar metabolites of [ 14C]TCDD in liver, and hepatic lipid content failed to explain these results. About 97% of hepatic 14C was hexane extractable. HPLC of this extract indicated [ 14C]TCDD was the only significant nonpolar form of radiolabel in liver. In mice pretreated with 5 μg TCDD/kg and subsequently dosed with 5 μg [ 14C]TCDD/kg, a more marked pretreatment disposition response was observed. These results are consistent with a predominant role for an inducible, high affinity, low capacity system in whole animal pharmacokinetics of TCDD.

2,3,7,8-Tetrachlorodibenzo-p-dioxin Pretreatment of Female Mice Altered Tissue Distribution but Not Hepatic Metabolism of a Subsequent Dose

2,3,7,8-Tetrachlorodibenzo-p-dioxin Pretreatment of Female Mice Altered Tissue Distribution but Not Hepatic Metabolism of a Subsequent Dose. CURTIS, L. R., JCERKVLIET, N. I., BAECHER-STEPPAN, L., AND CARPENTER, H. M. (1990). Fundam. Appl. Toxicol14, 523–531. Lipid partitioning of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inadequately explains its tissue distribution since higher concentrations occur in liver than fat except at high doses. This study provides In vivo evidence that an inducible, saturable system plays a predominant role in disposition of [14C]TCDD in female mice at doses between 5 and 20 Mg/kg. Female C57BL/6J mice were gavaged with 0, 5, or 15 μg, TCDD/kg, received a subsequent gavage of 5 or 20 11% [14C]TCDD after 6 days, and were killed 1 day later. In mice pretreated with 5 and 15MgTCDD/ kg and subsequently dosed with 20 μg [14C]TCDD/kg, liver weight and [14C]TCDD concentration increased. Total liver [14C]TCDD burden increased about 50% in both pretreatment groups. Concentrations of [14C]TCDD in kidney, fat, heart, lung, gastrointestinal tract, but not plasma or splenic lymphocytes, decreased in a reciprocal manner. Alterations in absorption, concentrations of polar metabolites of [14C]TCDD in liver, and hepatic lipid content failed to explain these results. About 97% of hepatic 14C was hexane extractable. HPLC of this extract indicated [14C]TCDD was the only significant nonpolar form of radiolabel in liver. In mice pretreated with 511% TCDD/kg and subsequently dosed with 5 μg [14C]TCDD/kg, a more marked pretreatment disposition response was observed. These results are consistent with a predominant role for an inducible, high affinity, low capacity system in whole animal pharmacokinetics of TCDD.

Pressure effect on phase transition in ferroelectic polymers

Abstract Pressure effects of phase transition behaviour in two kinds of ferroelectric polymers of poly(vinylidene fluoride), PVDF, and copolymers of vinylidene fluoride and trifluoroethylene, (VDF/TrFE), are discussed. In the case of PVDF, several high-pressure treatments including a high-pressure annealing and a uniaxial compression were shown to induce a crystal transformation from a non-polar Form II crystal to a polar Form I crystal, which has ferroelectric characteristics and high piezoelectric activity. In addition, substantial pressure effects on ferroelectric phase transition points as well as crystal structures were observed for (VDF/TrFE) copolymers with different VDF contents. The most significant pressure effects were observed for copolymer samples with unstable ferroelectric structures at atmospheric pressure. From high-pressure X-ray and Raman scattering studies, these pressure effects were suggested to originate from the pressure-induced conformational transition from gauche to trans in the...

A preliminary X-ray study on ferroelectric phase transition of poly(vinylidene ruoride) crystal form I

Ferroelectric phase transition of poly(vinylidene fluoride) crystal form I has been investigated by X-ray diffraction measurements. The X-ray reflections of form I decrease in intensity steeply in the vicinity of 172°C and new reflections of the high-temperature phase, the conformation of which is essentially equivalent to that of form III (T3GT3¯G), begin to appear, maximize in intensity at about 183°C, and disappear above 190°C. These phenomena are consistent with the previously reported infrared spectral data. The X-ray reflections observed for the high-temperature phase contain the (100), (120), etc. forbidden for polar form III, suggesting a possibility of another crystal structure of anti-polar or non-polar form III.

Field-induced phase transitions in phase-II poly(vinylidene fluoride)

A calculation of the free energy of both the polar and nonpolar forms of phase-II poly(vinylidene fluoride) has been performed by means of a generalized mean-field approximation. The results show the nonpolar form to be lower in free energy than the polar form, and provide a good estimate of the critical electric field necessary to cause the recently observed, nonpolar-polar phase transition in this material.

A study of structural and electrical properties of stretched polyvinylidene fluoride films

X-ray diffraction profiles and piezoelectric strain coefficient d 31 of 50μm thick polyvinylidene fluoride (PVF 2) films, originally containing non-polar Form 2 type crystallites, have been studied after (i) corona poling (ii) uniaxial stretching and (iii) uniaxial stretching and corona poling. The results suggest that piezoelectricity in this material is of dipolar origin. Furthermore a study of the changes in birefringence and small angle light scattering (SALS) patterns have also been made in the present work. The results indicate that the major contribution to the observed orientation on uniaxial stretching originates from the crystalline region of the polymer.