Single-molecule orientations in dyed salt crystals

We present single-molecule confocal microscopy studies of orientational distributions for luminophores isolated in potassium hydrogen phthalate (KAP) crystals. The incorporation of dye molecules that bear no size or shape similarity to the host ions is observed, demonstrating that single-molecule studies on mixed crystals need not be restricted to isomorphous host/guest pairs. Violamine R is oriented and overgrown by the fast vicinal slopes of growth hillocks within the symmetry-related {010} growth sectors and DCM deposits in the {11} growth sectors of KAP. Both mixed crystals exhibit modest absorption dichroism relative to basic pyranine-doped K(2)SO(4). The latter was studied to ensure that a range of orientations was sampled in our experiments. Average orientations determined at the single-molecule level were in close agreement to ensemble-averaged measurements for all three systems, and the chromophore orientational distributions were broader than anticipated, indicating that the crystals incorporate guest molecules in a range of orientations outside the measured ensemble average.     

Photooxidation of dyed styrene-butadiene and natural rubbers

Dyed natural rubber (NR) and styrene-butadiene rubber (SBR) designed for outdoor applications were exposed to accelerated artificial aging in xenon light. The aging results in the deterioration of the properties of the exposed surface material. The ability of dyed polymers to withstand prolonged sunlight exposure without fading or undergoing any physical deterioration is largely determined not only by the photochemical characteristics of the absorbing dyestuff itself but also by the polymer structure and fillers. Results indicate that dyed filled NR and SBR samples behave differently during photooxidation. The photodegradation products were observed by Fourier transform infrared spectroscopy (FTIR) to characterize the changes occurring in the polymer matrix during UV aging. The fading of the dyed polymers was found to be promoted in the NR sample. Moreover, the effects of photooxidation on the dyed SBR and NR materials were assessed by the formation of cracks and the thickness of the degraded area. The degradation thickness is more important for the NR sample than for the SBR one according to environmental scanning electron microscopy (ESEM) observations. For the NR sample, cracks appear initially at the surface and then grow through the thickness of the specimen, while for the SBR sample cracks are small and discontinuous. Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 6, pp. 1081–1085. This article was submitted by the authors in English.     

Photoelectric effects in chlorophyll membranes

Photoinduced potentials and currents and photo-electroosmotic velocities were measured across cellulose acetate membranes impregnated with chlorophyll pigments. Chlorophyll was extracted by both solvent extraction, Chl^s, and column chromatography, Chl. Photoelectric effects in membranes prepared with the following pigments were investigated: (i) Chl^s-a + β-carotene, (ii) Chl^s-b + xanthophyll, (iii) Chl^s-a, (iv) Chl^s-b, (v) β-carotene, (vi) xanthophyll, (vii) Chl^s-a + anthraquinone, (viii) Chl^s-b + anthraquinone, (ix) Chl-a, (x) Chl-b, (xi) Chl-a + anthraquinone, (xii) Chl-b + anthraquinone, (xiii) Chl-a + benzoquinone, and (xiv) Chl-b + benzoquinone. β-Carotene, xanthophyll, Chl-a and Chl-b obrained by chromatographic separation do not show a photoinduced potential or current. However, these effects are observed when “pure” (doubly chromatographed) Chl-a or Chl-b are mixed with anthraquinone or benzoquinone. These effects are observed in systems (i), (ii), (iii), (iv), (vii) and (viii) involving Ch^s. Although photoinduced potentials and photoinduced currents are not observed in Chl-a or Chl-b membranes, photoelectroosmosis is still observed. p]Both photoinduced potentials and currents are found to depend on pH. When the pH is changed appropriately, Chl^s-a acts as photocathode while Chl^s-b becomes a photoanode. Photocurrents are considerably enhanced when the pH is lowered. The change of photopotential with temperature is found to be insignificant. Photoelectroosmosis is always found to be directed towards the dark side, regardless of the polarity of the electrodes. A model based on the role of plastiquinone has been proposed to explain these phenomena, which have excellent reproducibility. The model predicts that ΔpH = (pH)_d — (PH)₁ (where (pH)_d and (pH)₁ denote the pH on the dark and illuminated side of the membrane respectively) would be positive when the pH of the bathing solution is higher than approximately 7, while it would be negative for lower pH. This behaviour is observed in the case of mixture of pure Chl-a + anthraquinone and pure Chl-b + benzoquinone. The model also predicts photoelectroosmosis irrespective of the presence of plastiquinone, in agreement with experimental observation.     

聚萘的合成及其光电器件*

本文系统回顾和总结了化学方法制备聚萘的历史进程和研究成果, 包括上世纪六十年代的Lewis酸直接氧化萘单体缩聚法和最近的萘衍生物的Yamamoto法和Suzuki法。指出萘基格氏试剂中介法是高产率获得各种具有确定结构聚萘的有效方法;等离子体沉积法等可直接制备聚萘膜,从而避免了因聚萘的难溶、难熔而引起的加工成型问题;而Yamamoto法和Suzuki法则是合成可溶性聚萘衍生物的有效途径,且聚合物产物具有优异的荧光性能,荧光量子效率最高达0.96。对于萘在1,4- 和5,8-位同时链接形成的规整的一维石墨结构具有非常高的菲边缘碳和边缘碳密度,有望显示出比二维石墨材料更高的锂掺杂能力,另外其较强的蓝色荧光发射特性以及高温稳定性,聚萘在锂离子二次电池电极材料、聚合物发光二极管、耐高温材料等领域都将显示出诱人的应用前景。     

Laser addressed thermo-optic effect in a novel dyed liquid-crystalline polysiloxane

Initial experimental evaluation of a novel liquid-crystalline polysiloxane for thermo-optical recording is presented. A versatile system using a single laser source has been used to gather information on the dynamics of laser addressing. To ensure the most stable, highest-contrast pixel the polymer must be heated through its biphasic region and some way into the isotropic phase. It was found that at 60°C using laser pulses of 300μs or less, write-in and selective erasure times were on the submillisecond timescale, and that bulk erasure required 1-2 min. The use of the polymer in an analogue optical store has been demonstrated and an unoptimized sensitivity of 12nJ/μm² for 632°8 nm light was found at 24°C.     

Hydrogen exchange and hydration dynamics in gelatin gels

Gelatin, derived from the collagen triple helix, is the most widely used functional biopolymer and a prototype for studies of physical gels. Gelatin gels have also served as models for soft biological tissue in efforts to elucidate the molecular basis of the magnetic relaxation phenomena that govern magnetic resonance image contrast. Yet, the microstructure, hydration, and magnetic relaxation behavior of gelatin gels are not well understood. To address these issues, we report here the water 2H and 17O magnetic relaxation dispersion (MRD) profiles from gelatin gels over wide ranges of resonance frequency and pH. For the global analysis of this extensive data set, we use a generalized relaxation theory that remains valid for arbitrarily slow molecular dynamics. The strong pH dependence in the 2H profiles can be rationalized quantitatively as the result of exchange with bulk water of labile hydrogens in gelatin side chains. The global analysis of the MRD data yields hydrogen-exchange rate constants, acid dissociation constants, and orientational order parameters in agreement with independent structural, thermodynamic, and kinetic data. The MRD analysis reveals a highly mobile hydration layer at the surface of the gelatin triple helix and a small number of trapped water molecules with residence times on the order of 10(-8) s, presumably associated with structural defects and branch points in the gel. The MRD data also indicate that approximately 20% of the gelatin residues belong to flexible polypeptide chains, rather than to rigid triple-helical segments. By identifying the molecular species and motions responsible for the 2H and 17O dispersion profiles, this study takes a significant step toward a quantitative understanding of water relaxation in aqueous gels and biological tissue.     

Helix formation and formaldehyde crosslinking in gelatin solutions

Optical rotation measurements on 5% gelatin solutions containing 0, 2, and 5% formaldehyde (w/w gelatin) are carried out at a series of temperatures between 20°C and 50°C. The solutions without formaldehyde show a diminished growth in rotation with rising temperatures, but even at 50°C there is still a steady rise in rotation with time. The addition of formaldehyde diminishes the optical rotation growth, and at 40°C and above solutions with 5% formaldehyde show no change in rotation at all. The specific rotation and time figures are fitted to a series of third-degree polynomial equations. It is shown that the data do not conform to any pattern of simple reaction kinetics. The mechanism of the formaldehyde–gelatin interaction is discussed.     

Surfactant induced softening in gelatin hydrogels

Effect of binding of three surfactants, alpha olefin sulfonate (AOS, anionic), Triton-X100 (TX-100, non-ionic) and cetyl trimethyl ammonium bromide (CTAB, cationic) to the hydrogels of gelatin was studied at room temperature (25 °C) by dynamic light scattering and oscillatory rheology with surfactant concentrations (20-100 mM) much larger than the critical micellar concentrations (cmc) of these surfactants. The measured intensity auto-correlation function of light scattered from gels revealed the presence of finite heterodyne contribution ≈0.11 ± 0.01 that increased to ≈0.25 ± 0.02 after transition to the soft gel state indicating a softening process for surfactant concentrations exceeding 50 mM. The dynamic structure factor S(q, t) of micelle bound gelatin gels revealed two clearly identifiable relaxation modes namely; the fast mode, S(q, t) ∼ exp · (−D_fq²t) for t ? 1 ms and a stretched exponential mode, S(q, t) ∼ exp · −(t/τ_c)^β for 1 ms ? t ? 1 s. This behaviour was universal with β ≈ 0.85 ± 0.04 independent of the surfactant type. The low frequency (1.5 rad/s) storage modulus G′, loss modulus G″ and tan δ behaviour revealed a gradual softening of the gel independent of the surfactant type. The exponent (β) fast mode diffusivity (D_f) and stretched exponential mode relaxation time were found to be less sensitive to this softening transition.     

Crystallization and melting of aqueous gelatin

Gelation and melting of aqueous gelatin were investigated by differential scanning calorimetry. This phenomenon can be analyzed as a conventional crystallization process assuming predetermined primary nucleation and unidirectional growth. The results were interpreted in terms of the fringed micelle model. Calculated values of the diameter of the renatured collagen fibril were found in excellent agreement with those determined previously by electron microscopy.     

Nanocomposites based on gelatin and montmorillonite

Model gelatin/montmorillonite (Ge/MMt) composites were obtained for a variety of unmodified clay concentrations and in the absence of additives, with the main goal of evaluating the effect of the morphologies developed on the composites thermal stability. Morphologies turned form partially exfoliated to exfoliate/intercalated and eventually agglomerated with increasing clay loading, as was observed by atomic force microscopy. Formulations containing 3–10 mass% montmorillonite resulted in an enhancement of composites thermal stability due to stabilizing interactions between co-components, such as strong hydrogen-type bonds, in agreement with the partially exfoliated/intercalated morphologies. Higher clay concentrations showed lower stabilizing effect in agreement with the agglomerated structures developed and the less effective interactions between co-components.     

Phase transition of collagen and gelatin

Summary In order to investigate physical properties of semicrystalline high polymer, such as collagen or gelatin, over a wide temperature range, the phase change which might occur in this range is first of all required to elucidate. For this purpose, experiments seeking for the temperature dependence of linear thermal expansion, retractive stress, complex dynamic elasticity moduli, and equilibrium stress, the time rate of change of stress at constant temperatures, differential thermal analysis, and wide-angle X-ray diffraction analysis were performed on dried steer Achilles tendon fiber and gelatin film. The following conclusions were obtained. Tendon fiber consists of three regions of different structure: amorphous region having a second order phase transition point at 120 °C, less oriented unstable crystalline region having widely distributed melting temperatures over the range between 80–100° and 180 °C, and stable crystalline region having sharply distributed melting temperatures around 200 °C. Gelatin also consists of the same three regions, and the stable crystalline region is stabilized further by the higher degree of cross-linking having bonds of ionic nature and possesses its melting temperatures around 220 °C.

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Zusammenfassung Um physikalische Eigenschaften teilkristalliner Hochpolymerer wie Kollagen oder Gelatine zu untersuchen, wurde über einen weiten Temperaturbereich der Phasenwechsel, der in diesem Bereich eintritt, untersucht. Zu diesem Zweck wurde die Temperatur abh?ngigkeit der linearen thermischen Ausdehnung, die Zugkraft, der komplexe Elastizit?tsmodul, der Gleichgewichtszug, die Geschwindigkeit der ?nderung des Zugs bei konstanter Temperatur, ‘differential-thermoanalytische Daten und Weitwinkel-R?ntgenstreuung an getrockneter Stier-Achilles-Sehne und Gelatinefilm durchgeführt. Es ergaben sich folgende Schlüsse: Fasern der Sehnen bestehen aus drei Bereichen verschiedener Struktur: amorphen Bereichen, die einen Phasenübergang zweiter Ordnung bei 120 °C zeigen, weniger orientierten instabilen kristallinen Bereichen mit weit verteilten Schmelztemperaturen im Bereich zwischen 80–100 und 180 °C und stabilen kristallinen Bereichen mit scharf verteilten Schmelztemperaturen um 200° herum. Auch Gelatine besteht aus denselben drei Anteilen, und die stabilen kristallinen Bezirke sind au?erdem durch einen h?heren Grad von Vernetzung mit Bindungen ionischer Natur stabilisiert und besitzen Schmelztemperaturen um 220 °C.

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With 13 figures in 18 details and 1 table

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Dedicated to Prof. Dr. R. Hilsch for his 60th birthday.     

Dielectric relaxation of collagen and gelatin

Dielectric dispersions of reconstituted collagens and gelatin were measured from 0.1 to 10 kHz and ?160 to +160°C. At 0.1 kHz there is a γ transition at ?80°C which is attributed to the H₂O-coupled local modes. The process has an activation energy of 7.5 kcal. A devitrification process is observed at 10–20°C. Both of these processes have their counterparts in the dynamic mechanical measurements. The tan δ values are up to 3 times as great for the dynamic mechanical dispersions. There is an additional hightemperature dielectric loss transition which does not correspond to any seen with the mechanical experiments. A probable mechanism for this absorption is the Maxwell-Wagner-Sillars effect.     

Transport phenomena in membranes

The realization that many elementary biological processes occur at membrane-like structures has led to renewed interest in the theory of molecular transport through membranes. Coupling phenomena in membranes, some of which are very complex, can now be rationally described with the aid of the thermodynamics of irreversible processes. The investigation of theoretical membrane models has proved a valuable complement to the thermodynamic method.     

Electrolysis phenomena in electrophoresis

We present a new theoretical approach for calculating changes in the physico-chemical properties of BGEs for measurements by CZE due to the electrolysis in electrode vials (vessels). Electrolysis is an inevitable phenomenon in any measurement in CZE. Water electrolysis, which occurs in most measurements, can significantly alter the composition of the BGE in electrode vials and in the separation capillary and has a negative influence on the robustness and quality of separations. The ability to predict changes in the composition of the BGE is important for evaluation of the suitability of the BGEs for repeating electrophoretic runs. We compared theoretically calculated changes in the physico-chemical properties (pH, conductivity) with those measured using pH-microelectrode and contactless conductivity detection of the BGE after the electrophoretic run. We confirmed the validity of our theoretical approach with a common BGE composed of acid-base pair, where one constituent is fully dissociated while the second constituent is dissociated by only half, and with Good's buffer. As predicted by theoretical approach, the changes in the physico-chemical properties of the Good's buffer after the electrophoretic run were several times lower than in the case of a common BGE composed of a weak acid – strong base pair.     

Isomorphism in critical phenomena

A dielectric liquid in a low external field is considered from the point of view of the effect of hidden variables on critical thermodynamic functions. Isomorphism is satisfied within scaling theory.     

Structure induced by irradiation of femtosecond laser pulse in dyed polymeric materials

We investigated the structures induced by an irradiation of a near‐infrared (NIR) femtosecond laser pulse in dye‐doped polymeric materials {poly(methyl methacrylate) (PMMA), thermoplastic epoxy resin (Epoxy), and a block copolymer of methyl methacrylate and ethyl acrylate‐butyl acrylate [p(MMA/EA‐BA) block copolymer]}. Dyes used were classified into two types—type 1 with absorption at 400 nm and type 2 with no absorption at 400 nm. The 400‐nm wavelength corresponds to the two‐photon absorption region by the irradiated NIR laser pulse at 800 nm. Type 1 dye‐doped PMMA and p(MMA/EA‐BA) block copolymer showed a peculiar dye additive effect for the structures induced by the line irradiation of a NIR femtosecond laser pulse. On the contrary, dye‐doped Epoxy did not exhibit a dye additive effect. The different results among PMMA, p(MMA/EA‐BA) block copolymer, and Epoxy matrix polymers are supposed to be related to the difference of electron‐acceptor properties. The mechanism of this type 1 dye‐additive‐effect phenomenon for PMMA and p(MMA/EA‐BA) block copolymer is discussed on the basis of two‐photon absorption of type 1 dye at 400 nm by the irradiation of a femtosecond laser pulse with 800 nm wavelength and the dissipation of the absorbed energy to the polymer matrix among various transition processes. Dyes with a low‐fluorescence quantum yield favored the formation of thicker grating structures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2800–2806, 2002     

Overshoot and oscillation in surface tension of gelatin solutions

The experimental data of the surface tension of aqueous gelatin solution reported by Sato and Ueberreiter [H. Sato, K. Ueberreiter, Macromol. Chem. 180 (1979) 829; H. Sato, K. Ueberreiter, Macromol. Chem. 180 (1979) 1107; H. Sato, K. Ueberreiter, ACS Polym. Preprints 20 (1979) 907] were analyzed with a theory of adsorption kinetics with time delay. It is found that the observed overshoot and oscillation of the surface tension are well explained by the present theory. The delay time and the rate constants of adsorption and desorption of gelatin molecules onto the air/gelatin solution interface have been evaluated.     

Ultralow interfacial tensions in an aqueous phase-separated gelatin/dextran and gelatin/gum Arabic system: a comparison

Many protein/polysaccharide mixtures phase separate when the concentrations ofthese biopolymers are sufficiently high. One of the properties involved in this phenomenon is the interfacial tension. Here we present measurements of the interfacial tension of two different protein/polysaccharide mixtures. The protein gelatin was mixed with either dextran or gum arabic, all used in a variety of food products. The phase diagrams were constructed using optical rotation. Although both polysaccharides have the same molecular weight, the phase diagrams differed. The interfacial tension of samples, varying in the distance from the critical point, was determined using the spinning drop method. The interfacial tension was found to be in the range of 1-15 microN/m. For both systems, the scaling behavior of the interfacial tension was investigated. The investigated gelatin/dextran system gave critical exponents of 2.5+/-0.1 and 1.4+/-0.1, in reasonable agreement with the mean-field values 3 and 1.5, respectively. The gelatin/gum arabic system did not show critical behavior. For this system, the interfacial tension shows a logarithmic dependence on the distribution of the gelatin and the gum arabic molecules in the separated phases.     

Chemiluminescence of hemoglobin and identification of related compounds with the hemoglobin chemiluminescence in plasma

A low level of chemiluminescence by hemoglobin (Hb) was detected in the reaction with H2O2 and hydrogen donors such as gallic acid and catechins. The photon intensity was affected by the ferric state of Hb (methemoglobin > oxyhemoglobin), and was roughly correlated with the radical-scavenging potential of catechins. We hypothesized the reversible activation reaction of Hb as the chemiluminescence mechanism of the H2O2/gallic acid/Hb system. It is indicated that the oxidized-Hb (Hb-OOH) formation was a chemiluminescence-rate-determining step and one-electron reduction by a hydrogen donor of the compound-I-type intermediate ([.XFeIV] = O) proved a chemiluminescence-specificity-determining step. Spectral analysis showed that the photon emission from the H2O2/gallic acid/Hb system was produced without singlet oxygen generation. The concentration dependence of photon intensity suggests a high consumption ratio of H2O2 leading to protection from H2O2 toxicity. Albumin was defined as a hydrogen donor by the isolation of chemiluminescent substance in plasma using this chemiluminescence system.