Interaction of crosslinked polyvinylpyrrolidone with a homologous series of methyl orange derivatives in aqueous and nonaqueous solutions: Thermodynamics of the binding equilibria

The extent of binding of methvI orange, ethyl orange, propyl orange, and butyl orange by crosslinked polyvinylpyrrolidone was measured in all aqueous Solution. The first binding constants and the thermodynamic parameters accompanying the binding were evaluated. These values were compared with those of water-soluble polyvinylpyrrolidone. The first binding constant, the absolute magnitude of ΔF°, and the value of ΔS° of the crosslinked polyvinylpyrrolidone are substantially larger than those of the water-soluble product for any particular dye. These behaviors can be accounted for in terms of increased hydrophobic domains in the former and enhanced hydrophobic contribution in the binding process. Also the binding of the dye by the crosslinked polymer in a nonaqueous solvent, ethylene glycol, was measured to assess the contribution of hydrophobic interaction to the dye-polymer complex formation in aqueous medium. It was found that the binding of butyl orange by the crosslinked polymer is suppressed in ethylene glycol and the contribution of entropy term to the free energy change in the aqueous environment is large compared with that in ethylene glycol. The significance of the hydrophobic of the hydrophobic interaction in the dye-polymer association process is described.     

Visible fluorescence spectrometry using second harmonic emission self-induced in semiconductor laser as a light source

Second harmonic emission (416 or 453 nm) self-induced in a nearinfrared semiconductor laser (832 or 906 nm) is used as a light source for excitation of the fluorescent molecules which have absorption bands in the visible region. The conversion efficiency from fundamental to second harmonic emission is 1.7 × 10^–11 (0.5 pW) for a continuous wave (CW) laser, when it is operated at 30 mW. This value is further improved for a pulsed laser operated at a peak power of 10 W. Perylene is used as a standard sample for construction of an analytical curve. The detection limit is 10^–6 M for CW laser excitation. The present fluorimetric system is used for measurements of pH dependence of the fluorescence intensity for 8-hydroxy-1,3,6-pyrenetrisulfonic acid (HPTS). Neutralization titration is demonstrated by using HPTS as a pH indicator.     

Evaluation of selectivity-determining factors for membrane electrodes based on naphtho-15-crown-5 by liquid-liquid extraction

Liquid-liquid extractions of sodium and potassium picrates with naphtho-15-crown-5 (N15C5) into 1,2-dichloroethane are studied, in order to clarify the factors governing the high potassium ion selectivity of the N15C5-based membrane electrode. The distribution coefficient of N15C5 between water and 1,2-dichloroethane was 1800 at 15°C. The formation constants of the complexes of N15C5 with the sodium ion and the potassium ion in the aqueous phase were less than unity and there was no remarkable difference between their values. Potassium picrate was mainly extracted into 1,2-dichloroethane by forming the 2:1 N15C5-potassium complex, while sodium picrate was extracted by forming the 1:1 complex. The extraction constants for sodium picrate and potassium picrate were 10^3.86 and 10^7.61, respectively, The high potassium selectivity is concluded to be due to the high extractability of the 2:1 potassium complex.     

Synthesis of poly(epsilon-lysine)-grafted dextrans and their pH- and thermosensitive hydrogelation with cyclodextrins.

To give pH sensitivity to a thermoreversible supramolecular-structured hydrogel system, poly(epsilon-lysine) (PL), as a cationic polymer, was grafted to dextran and used for inclusion complexation with alpha-cyclodextrins (alpha-CDs). The synthesized graft copolymer was characterized by 1H NMR spectroscopy, and the hydrogel formation was confirmed by X-ray diffraction and solid-state 13C NMR analysis. The hydrogelation was induced from a phase-separated structure of hydrated dextrans and hydrophobically aggregated inclusion complexes in buffer solution at pH 10.0. The prepared hydrogels showed thermoreversible gel-sol transitions as well as pH-sensitive phase transitions, which were recorded by the changes in UV/Vis transmittance. A rapid phase transition from gel to sol was observed upon decreasing the pH value to 4.0, which resulted from the dissociation process between the protonated guest polymer and alpha-CDs. The stimuli-responsive physical properties of the hydrogels were improved by modulating the degree of substitution of the grafted PL and the combination with alpha-CDs.     

Interaction between poly[(R)-3-hydroxybutyrate] depolymerase and biodegradable polyesters evaluated by atomic force microscopy

Adsorption of PHB depolymerase from Ralstonia pickettii T1 to biodegradable polyesters such as poly[(R)-3-hydroxybutyrate] (PHB) and poly(l-lactic acid) (PLLA) was investigated by atomic force microscopy (AFM). The substrate-binding domain (SBD) with histidines within the N-terminus was prepared and immobilized on the AFM tip surface via a self-assembled monolayer with a nitrilotriacetic acid group. Using the functionalized AFM tips, the force-distance measurements for polyesters were carried out at room temperature in a buffer solution. In the case of AFM tips with immobilized SBD and their interaction with polyesters, multiple pull-off events were frequently recognized in the retraction curves. The single rupture force was estimated at approximately 100 pN for both PLLA and PHB. The multiple pull-off events were recognized even in the presence of a surfactant, which will prevent nonspecific interactions, but reduced when using polyethylene instead of polyesters as a substrate. The present results provide that the PHB depolymerase adsorbs specifically to the surfaces of polyesters and that the single unbinding event evaluated here is mainly associated with the interaction between one molecule of SBD and the polymer surface.     

Simultaneous determination of tungsten and molybdenum in sea water by catalytic current polarography after preconcentration on a resin column

The simultaneous determination of tungsten and molybdenum in sea water is based on preconcentration by column extraction with 7-(1-vinyl-3,3,5,5-tetramethylhexyl)-8-quinolinol (Kelex- 100) resin, and measurement of the polarographic catalytic currents obtained in a solution of chlorate, benzilic acid and 2-methyl-8-quinolinol. When the concentration factor is 50, the detection limits are 2.4 pM for tungsten and 17 pM for molybdenum (for a signal-to-noise ratio of 3). The precision of the determination is ca. 10% for 67 pM tungsten and ca. 5% for 106 nM molybdenum in sea water (n=4). Results for sea water and other natural waters are presented.     

Fiber-optic sensor for carbon dioxide with a ph indicator dispersed in a poly(ethylene glycol) membrane

A fiber-optic sensor for carbon dioxide gas is constructed, without an inner buffer solution, by using a dispersion of fluorescein in poly(ethylene glycol) deposited on the distal end of an optical fiber. Evaporation of the solvent is thus negligible. The response range is 0–28% (v/v) for carbon dioxide, with a detection limit of 0.1%. The response time achieved is 10 s. The membrane (ca. 10 μm thick) is composed of poly(ethylene glycol)s with molecular weights of 200 and 1540 dalton in a 20:80% (w/w) ratio. The best concentration of fluorescein is 5 × 10^?7 mol g^?1 of poly(ethylene glycol). The response mechanism of the sensor is discussed.     

Alkyl chain conformation and the electronic structure of octyl heavy chalcogenolate monolayers adsorbed on Au(111)

Adsorption states of dioctyl dichalcogenides (dioctyl disulfide, dioctyl diselenide, and dioctyl ditelluride) arranged on Au(111) have been studied by X-ray photoelectron spectroscopy (XPS), infrared-visible sum-frequency generation (SFG), and ultraviolet photoelectron spectroscopy (UPS). XPS measurements suggest that dioctyl dichalcogenides dissociatively adsorbed on Au(111) surfaces to form the corresponding monolayers having chalcogen-gold covalent bonds. The elemental compositions of octanechalcogenolates on Au(111) indicate that the saturation coverages of the octyl heavy chalcogenolate (OcSe, OcTe) monolayers are lower than that of the octanethiolate (OcS) self-assembled monolayers (SAMs). The SFG observations of the CH(2) vibrational bands for the heavy chalcogenolate monolayers strongly suggest that a discernible amount of gauche conformation exists in the monolayers, while OcS SAMs adopt highly ordered all-trans conformation. The intensity ratio of the symmetric and asymmetric CH(3) stretching vibration modes measured by SFG shows that the average tilt angle of the methyl group of the OcSe monolayers is greater than that of the OcS SAMs. The larger tilt angle of the methyl group and the existence of a discernible amount of gauche conformation in the OcSe monolayers are due to the lower surface coverage of the OcSe monolayers compared with the OcS SAMs. The smaller polarization dependence in the angle-resolved UPS (ARUPS) spectra of the OcSe monolayers than that of the OcS SAMs is caused by the more disordered structures of the alkyl chain in the former. XPS, SFG, and ARUPS measurements indicate a similar tendency for the OcTe monolayers. The density of states (DOS) observed by UPS at around 1.3 eV for OcS adsorbed on Au(111) is considered to be the antibonding state of the Au-sulfur bond. Similar DOS is also observed by UPS at around 1.0 eV for the OcSe monolayers and at approximately 1.6 eV for the OcTe monolayers on Au(111).     

Interaction of polyvinylpyrrolidone with methyl orange and its homologs in aqueous solution: Thermodynamics of the binding equilibria and their temperature dependences

The interaction of polyvinylpyrrolidone with methyl orange, ethyl orange, propyl orange, and butyl orange has been studied by an equilibrium dialysis method at 5, 15, 25, and 35°C. The first binding constants and the thermodynamic parameters in the course of the binding have been calculated. It was found that the free energy and the enthalpy changes are all negative and the entropy change is largely positive. The longer the alkyl chain of the dyes, the more positive is the enthalpy change (though it is always in the negative direction) and hence the larger is the entropy change. The favorable free energy of the binding of butyl orange observed for the formation of the dye–polymer complex seems to be a result of a favorable entropy change rather than any favorable enthalpy change. Temperature dependences of the thermodynamic functions were apparently observed. That is, ΔF and ΔH become larger in absolute magnitude as the temperature increases. The positive quantity of ΔS tends to decrease with increasing temperture. All these facts obtained can be interpreted satisfactorily by the hydrophobic interaction between hydrocarbon portions of the dyes and nonpolar parts of the macromolecule.