Dielectric relaxation behavior of aqueous solutions of carbobetaines with varying intercharge distances

The dielectric relaxation behavior of aqueous triethylammonioalkanoate (carbobetaine: Et(3)nCB) solutions was examined as a function of frequency from 1.00 x 10(6) to 2.00 x 10(10) Hz (6.28 x 10(6) to 1.26 x 10(11) rad s(-1) in angular frequency); number of intercharge methylene groups, n = 1, 3, 4, 5, and 10; and solute concentration, c. Two major relaxation modes, fast and slow, were found in all solutions examined. Et(3)nCB systems with n = 5 and 10 possessed another, medium, relaxation mode with relaxation time tau(Dh) at high c values (above the contact concentration of solutes) in addition to the fast and slow modes. The fast mode with a relaxation time, tau(w), of approximately 10 ps was attributed to the rotational motion of bulk water molecules. The slow mode with a relaxation time, tau, of 0.08-1 ns, depending on the n value, was attributed to the overall rotational motion of each carbobetaine in aqueous solution. The concentration normalized relaxation strength, Deltaepsilonc(-1), and tau value of the slow relaxation mode increased with increasing n. These findings were quantitatively explained on the basis of changes in the intercharge distance resulting in increased size and dipole moment of the carbobetaines. Above the contact concentration, collisions between solute molecules likely hindered their rotational motions, leading to an increase in tau. The middle relaxation mode found in longer Et(3)nCBs (n = 5 and 10) with a relaxation time, tau(Dh), of approximately 0.2 ns, more than 20 times as long as that of bulk water molecules, tau(w), was attributed to the dehydration of water molecules tightly bound to all Et(3)nCBs examined (including those with n < 5). This mode was not observed in the solutions of Et(3)nCBs with n < 5, since the tau values corresponding to overall rotation were close to or shorter than the tau(Dh) values.     

Photobleaching of melanosomes from retinal pigment epithelium: I. Effects on protein oxidation

Melanin in the long-lived melanosomes of the retinal pigment epithelium (RPE) may undergo photobleaching with aging, which appears to diminish the antioxidant function of melanin and could make photobleached melanosomes less efficient in protecting biomolecules from oxidative modification. Here we analyzed whether photobleaching of melanosomes affects their ability to modify the oxidation state of nearby protein. As conventional methods developed to study soluble antioxidants are not well suited for analysis of granules such as melanosomes, we developed a new analytic method to focus on particle surfaces that involves experimentally coating granules with the cytoskeletal protein beta-actin to serve as a reporter for local protein oxidation. Isolated porcine RPE melanosomes were photobleached with visible light to simulate aging, then photobleached melanosomes, untreated melanosomes and control particles (black latex beads) were actin coated and illuminated in a photosensitized cell free system. Protein was re-stripped from particles and analyzed for carbonylation by Western blotting. Quantitative densitometry showed no reproducible differences for protein associated with untreated melanosomes when compared with control particles. Melanin has both anti- and pro-oxidant functions when light irradiated, but neither of these functions predominated in the protein oxidation assay when untreated melanosomes were used. However, protein extracted from photobleached melanosomes showed markedly increased carbonylation, both of associated actin and of endogenous melanosomal protein(s), and the effect increased with extent of granule photobleaching. Photobleaching of RPE melanosomes therefore changes the oxidation state of protein endogenous to the organelle and reduces the ability of the granule to modify the oxidation of exogenous protein near the particle surface. The results support the growing body of evidence that photobleaching of RPE melanosomes, which is believed to occur with aging, changes the physicochemical properties of the organelle and reduces the likelihood that the granules perform an antioxidant function.     

Monoline argon laser (514 nm) treatment of benign pigmented lesions with long pulse lengths.

A dichroic filter was adjusted in order to make use of the green line of an argon laser for the treatment of pigmented lesions (actinic and senile lentigo, ephelis, café-au-lait marks and spilus nevus). Using a power of 1.5 W, a spot size of 0.5 mm and pulse lengths of 200 or 300 ms, satisfactory elimination of 620 pigmented cutaneous lesions was achieved. Although the pulse lengths used were much longer than the thermal relaxation time of the melanosomes, the histology after treatment showed little damage of adjacent structures. Good restoration of the epidermis and a return of normal pigmentation led to excellent cosmetic results, with few complications.     

Vibrational relaxation of methane by oxygen collisions: measurements of the near-resonant energy transfer between CH4 and O2 at low temperature

Vibrational relaxation in methane-oxygen mixtures has been investigated by means of a time-resolved pump-probe technique. Methane molecules are excited into selected rotational levels by tuning the pump laser to 2nu3 lines. The time evolution in population of various vibrational levels after the pumping pulse is monitored by probing, near 3000 cm-1, stretching transitions between various polyads like 2nu3(F2) - nu3, (nu3+2nu4) - 2nu4, and (nu3+nu4) - nu4 transitions. Measurements were performed from room temperature down to 190 K. A numerical kinetic model, taking into account the main collisional processes connecting energy levels up to 6000 cm(-1), has been developed to describe the vibrational relaxation. The model allows us to reproduce the observed signals and to determine rate coefficients of relaxation processes occurring upon CH4-O2 collisions. For the vibrational energy exchange, the rate coefficient of transfer from O2 (v = 1) to CH4 is found equal to (1.32 +/- 0.09) x 10(-12) cm3 molecule-1 s(-1) at 296 K and to (1.50 +/- 0.08) x 10(-12) cm3 molecule(-1) s(-1) at 193 K.     

Photophysics and charge dynamics of Q-PbS based mixed ZnS/PbS and PbS/ZnS semiconductor nanoparticles

The surface of ZnS and PbS has been modified by interfacing PbS on ZnS and ZnS on PbS nanoparticles. This produced core-shell nanocomposites ZnS/PbS and PbS/ZnS with tunable electronic properties. In both structures PbS particles are present in cubic form with an average diameter of about 6 nm. The addition of Pb2+ (3 x 10(-4) mol dm(-3)) to Q-ZnS (1.5 x 10(-4) mol dm(-3)) in the basic pH range produces size-quantized fluorescent PbS particles coated by metal hydroxides. In these particles the relaxation kinetics of charge carriers has been followed using a picosecond single-photon counting technique. At 1.5 x 10(-4) mol dm(-3) Pb2+ an interfacial relaxation of charge from ZnS to PbS phase could be observed in subnanosecond time domain. An increase in [Pb2+] from 2 x 10(-4) to 1 x 10(-3) mol dm(-3) enhanced the average emission lifetime from 9.4 to 19.4 ns. Composite PbS/ZnS particles are produced at high [ZnS] only. These particles had emission lifetime in mus time range. The extent of charge separation and the dynamics of charge carriers could be manipulated by the surface modification of these nanostructures.     

The phane properties of anti-[2.2](1,4)biphenylenophane

[structure: see text] Anti-[2.2](1,4)biphenylenophane (4) was synthesized from de Meijere's tetrabromo[2.2]paracyclophane (5) through a four-step reaction sequence. Although an average separation of 3.09 A between the inner ring of the biphenylene units is normal for [2.2]paracyclophanes, a bond distance of 1.54 Afor the ethano C-C bridge at room temperature is shorter than usual. In addition, trimethylsilyl-substituted anti-[2.2](1,4)biphenylenophane 8 sublimes at 220 degrees C under a pressure lower than 1 x10(-5) Torr without decomposition or thermal isomerization. The high thermal stability of 8 suggested that the ethano bridges of the biphenylenophanes are less strained than those of [2.2]paracyclophane. Bathochromic shifts are observed in their UV-vis absorption spectra. The phane state interactions of 4 and 8 were evidenced by the weak structureless fluorescent emission maximized at 537 and 550 nm in CH(2)Cl(2) along with longer relaxation lifetimes of 229 and 292 ps, respectively.     

Electron scattering cross section on the surface of thin ag and au films induced by atomic deuterium adsorption

The electron scattering cross section on the surface of thin silver and gold films induced by adsorption of atomic deuterium under conditions when a single adsorption state is formed was determined. Adsorption of atomic deuterium carried out at 78 K on sintered thin silver (gold) films deposited on Pyrex glass under ultrahigh vacuum conditions was studied measuring the resistance changes DeltaR "in situ". The adsorption runs performed at various exposures were followed by thermal desorption. This allowed establishment of a correlation between DeltaR and the uptake of the adsorbate. BET measurements were performed to determine the real area of the thin films and calculate the density of the adsorbate on their surface. It was found that in agreement with Wissmann's equation1 a linear dependence of DeltaR on the density of the adsorbate nads exists within a large interval of the population (nads < or = 1 x 10(15) D adatoms/cm2 on silver and 7 x 10(14) D adatoms/cm2 on gold) available under our experimental conditions. On the basis of this equation the electron scattering cross section Aads induced by adsorption of atomic deuterium on sintered thin silver and gold films was calculated as reaching 4.75 x 10(-16) and 4.46 x 10(-16) cm2, respectively. A small isotope effect in the electron scattering cross section for adsorption of hydrogen on silver was observed: Aads = 5.48 x 10(-16) cm2.     

Electron spin resonance investigations of human retinal pigment epithelium melanosomes from young and old donors

Electron spin resonance (ESR) examinations of human retinal pigment epithelium melanosomes isolated from eyes of young and old donors were carried out. The examined ESR signal was a single line, which is characteristic for free radicals of eumelanin o-semiquinones. The content of free radicals related to melanosomes dry weight for samples from older donors (ages over 45 years) were higher than for sample from younger donors (between 14 and 22 years). Simultaneously, the content of free radicals calculated for one melanosome is constant and does not depend on age. The homogeneous broadening of the recorded ESR lines shows that there are no isolated spin packets in all investigated melanin samples. Slow spin-lattice (T1 approximately 10(-5) s) and fast spin-spin (T2 approximately 10(-8) s) relaxation processes occur in these samples. Saturation of the ESR lines at low microwave power was measured. High concentration of free radicals in melanosome samples was responsible for the fast spin-spin relaxation process.     

Dynamics of circular hydrogen bond array in calix[4]arene in a nonpolar solvent: a nuclear magnetic resonance study

Hydroxyl groups on the lower rim of calix[4]arene form a circular array of four equivalent hydrogen bonds. The rate constants of reversal of the array in the temperature range of 221-304 K were determined by means of the NMR measurements of quaternary (13)C nuclear spin transverse relaxation dependence on the effective radio frequency field. The flip-flop rate constants are in the range of 1.4 x 10(2)-4.2 x 10(4) s(-1), the activation enthalpy is 36.8 kJ/mol, the activation entropy is -36 J mol(-1) K(-1). This process was found uncorrelated with conformational transition cone-inverted cone, which is about thousand times slower. Molecular tumbling of calix[4]arene measured using (13)C spin relaxation was found isotropic with correlation times lying in the range of 0.1-3 ns and with the activation energy of 21 kJ/mol. In order to assess relaxation of (13)C aromatic nuclei, their principal components of chemical shift tensor were calculated using the density functional theory approach.     

Thermal characterization in vitro of human nail: photoacoustic study of the aging process

In the present work, the rear photoacoustic signal technique is used to determine thermal properties of human nails. The aging process of the human nail is analyzed through its thermal diffusivity and specific heat and using these results, thermal conductivity and thermal effusivity is determined. The study in vitro of this natural polymer showed a minimum for thermal properties to age about 20 years and an increase and possible saturation of them for ages over 50 years. The minimum value found for thermal diffusivity was close to 10x10(-4) cm2 s(-1) with saturation near 18x10(-4) cm2 s(-1). Thermal conductivity and effusivity presents the same behavior.     

Melanosomal damage in normal human melanocytes induced by UVB and metal uptake--a basis for the pro-oxidant state of melanoma

Melanins are ubiquitous catecholic pigments, formed in organelles called melanosomes within melanocytes, the function of which is to protect skin against harmful effects of UV radiation. Melanosomes within melanoma cells are characteristically abnormal, with fragmented melanin and disrupted membranes. We hypothesize that the disruption of melanosomal melanin might be an early event in the etiology and progression of melanoma, leading to increased oxidative stress and mutation. In this report, we examine the effect of a combination of UV treatment and metal ion exposure on melanosomes within melanocytes, as well as their ability to act as pro-oxidants in ex situ experiments, and assay the effects of this treatment on viability and cell cycle progression. UVB exposure causes morphologic changes of the cells and bleaching of melanosomes in normal melanocytes, both significantly enhanced in Cu(II) and Cd(II)-treated cells, as observed by microscopy. The promoted bleaching by Cu(II) is due to its ability to redox cycle under oxidative conditions, generating reactive oxygen species; verified by the observed enhancement of hydroxyl radical generation when isolated melanosomes were treated with both Cu(II) ions and UVB, as assayed by DNA clipping. Single-dose UVB/Cu treatment does not greatly affect cell viability or cell cycle progression in heavily pigmented cells, but did so in an amelanotic early stage melanoma cell line.     

Interaction of hydronium ion with dibenzo-18-crown-6: NMR, IR, and theoretical study

Interaction of dibenzo-18-crown-6 (DBC) with H 3O (+) (HP) in nitrobenzene- d 5 and dichloromethane- d 2 was studied by using (1)H and (13)C NMR spectra and relaxations, FTIR spectra, and quantum chemical DFT calculations. NMR shows that the DBC*HP complex is in a dynamic equilibrium with the reactants, the equilibrium constant K being 0.66 x 10 (3), 1.16 x 10 (4), and 1.03 x 10 (4) L x mol (-1) in CD 2Cl 2, nitrobenzene, and acetonitrile, respectively. The complex appears to have a C 2 v symmetry in NMR, but FTIR combined with DFT normal mode calculations suggest that such high symmetry is only apparent and due to exchange averaging of the structure. FTIR spectra as well as energy-optimized DFT calculations show that the most stable state of the complex in solution is that with three linear hydrogen bonds of HP with one CH 2-O-CH 2 and two Ar-O-Ar oxygen atoms. The structure is similar to that found in solid state but adopts a somewhat different conformation in solution. The dynamics of exchange between bound and free DBC was studied by NMR transverse relaxation. It was found to be too fast to give reproducible results when measured with the ordinary CPMG sequence or its variant DIFTRE removing residual static dipolar interaction, but it could be established by rotating-frame measurements with high intensity of the spin-lock field. The correlation time of exchange was found to be 5.6 x 10 (-6) and 3.8 x 10 (-6) s in dichloromethane and nitrobenzene, respectively. Such fast exchange can be explained by cooperative assistance of present water molecules.     

Determination of inorganic impurities in vinyl chloride by activation analysis

Trace impurities in vinyl chloride have been determined by activation analysis in a reactor thermal neutron flux of 1.2 x 10(9)n mm (2)sec . Irradiations were carried out on liquid and solid samples at the same time as a standard. Gamma-spectrometry was used to reveal the presence of arsenic and bromine, the quantitative estimation being based on two calculus methods., The impurities determined were: arsenic 8.0 +/- 0.6 x 10(-4)%, bromine 3.07 +/- 0.2 x 10(-3)% and phosphorus 2.0 +/- 0.15 x 10(-2)%.     

Determination of copper with neocuproine by thermal-lens spectrometry

Conditions for the spectrophotometric determination of copper with 2,9-dimethyl-l,10-phenan-throline (neocuproine) in the presence of ascorbic acid in a water-ethanol solution (9 : 1) at pH 4.5–5.0 have been found. The detection limit is 3 x 10^-6 M. The concentration range is from 4.4 x 10^-6 to 3 x 10^-4 M. Conditions for the determination of copper(I) with neocuproine by thermal lens spectrometry have been proposed. The detection limit is 4 x 10^-7 M. The concentration range is from 7 x 10^-7 to 6 x 10^-5 M. Iron(II) at concentrations as high asn x 10^-4 M does not interfere with the determination of copper. Changes in the conditions for the photometric reaction associated with passing from spectrophotometric measurements to thermal lensing are discussed.     

Host-assisted intramolecular vibrational relaxation at low temperatures: OH in an argon cage

The vibrational relaxation of hydroxyl radicals in the A (2)Sigma(+) (v=1) state has been studied using the semiclassical perturbation treatment at cryogenic temperatures. The radical is considered to be trapped in a closest packed cage composed of the 12 nearest argon atoms and undergoes local translation and hindered rotation around the cage center. The primary relaxation pathway is towards local translation, followed by energy transfer to rotation through hindered-to-free rotational transitions. Free-to-free rotational transitions are found to be unimportant. All pathways are accompanied by the propagation of energy to argon phonon modes. The deexcitation probability of OH(v=1) is 1.3 x 10(-7) and the rate constant is 4.7 x 10(5) s(-1) between 4 and 10 K. The negligible temperature dependence is attributed to the presence of intermolecular attraction (>kT) in the guest-host encounter, which counteracts the T(2) dependence resulting from local translation. Calculated relaxation time scales are much shorter than those of homonuclear molecules, suggesting the importance of the hindered and free motions of OH and strong guest-host interactions.     

Reactive uptake of O3 by multicomponent and multiphase mixtures containing oleic acid

The heterogeneous reaction of O3 with lauric acid/oleic acid (LA/OA) mixtures and myristic acid/oleic acid (MA/OA) mixtures were studied as a function of composition, physical state, and microstructure at 298 K. Lauric acid and myristic acid are both alkanoic acids, whereas oleic acid is an alkenoic acid. Additionally, we investigated the uptake of O3 by multicomponent mixtures that closely represent the composition of meat-cooking aerosols. These measurements were performed with a rotating-wall flow-tube reactor coupled to a chemical ionization mass spectrometer. The reactive uptake coefficients (gamma) of O3 on liquid LA/OA and MA/OA solutions range from 4 x 10(-4) to 7.2 x 10(-4). The gamma values measured for solid-liquid LA/OA and MA/OA mixtures (which consist of solid LA or solid MA in equilibrium with a liquid) range from 2 x 10(-5) to 1.7 x 10(-4). These experiments show that only 7% solid by mass in the solid-liquid mixture can decrease gamma by an order of magnitude compared to the liquid mixtures. The gamma values for solid-liquid mixtures that closely represent the composition of meat-cooking aerosols range from 1.6 x 10(-5) to 6.9 x 10(-5). We found that gamma of solid-liquid mixtures depends on the microstructure of the mixtures, which in turn depends on the method of preparing the films. Furthermore, experiments employing solid-liquid mixtures show an increase in gamma with increasing film age. This can be explained either by the formation of a nonequilibrium phase followed by its relaxation to the stable phase or by Ostwald's ripening, which refers to a change in the solid microstructure due to a tendency to minimize the total surface free energy of the solid. We used the obtained gamma values to estimate OA lifetimes for polluted atmospheric conditions. For liquid solutions, the lifetimes were on the order of a few minutes. The lifetimes derived for solid-liquid mixtures are up to 75 min, significantly longer than for liquid solutions. Our study emphasizes the effect of the physical state and microstructure of multicomponent mixtures on the heterogeneous chemistry.     

Experimental evidence for the formation of doubly charged oxide and hydroxide ions in inductively coupled plasma mass spectrometry

The formation of doubly charged polyatomic ions in inductively coupled plasma mass spectrometers was investigated using commercially available instruments. The species observed were ThO2+ and ThOH2+, which were found in similar amounts with the different instruments used in this study, when operated under routine analytical conditions. The signal ratios for ThO2+ were between 1.8 x 10(-4) and 4.2 x 10(-4) relative to the singly charged elemental ion and between 1.4 x 10(-2) and 2.2 x 10(-2) relative to the doubly charged elemental ion. The formation of ThOH2+, was between 1.1 x 10(-4) and 2.8 x 10(-4) relative to the singly charged elemental ion and between 0.72 x 10(-2) and 1.3 x 10(-2) relative to the doubly charged elemental ion. A mechanism is proposed for the formation of the doubly charged oxide and hydroxide ions that is based on the condensation of the doubly charged elemental ion with water or oxygen molecules in the interface region of the mass spectrometer.     

Denaturation of jack-bean urease by sodium n-dodecyl sulphate: a kinetic study below the critical micelle concentration

Kinetics of urease denaturation by anionic surfactant (sodium n-dodecyl sulphate, SDS) at concentrations below the critical micelle concentration (CMC) is investigated spectrophotometrically at neutral pH and the corresponding two-phase kinetic parameters of the process are estimated from a three-state reversible process using a binomial exponential relation based on the relaxation time method as: Using a prepared computer program, the experimental data are properly fitted into a binomial exponential relation, considering a two-phase denaturation pathway including a kinetically stable folded intermediate formed at SDS concentration of 1.1 mM. Forward and backward rate constants are estimated as: k(1)=0.2141+/-4.5 x 10(-3), k(2)=5.173 x 10(-3)+/-8.3 x 10(-5), k(-1)=0.09432+/-3.6 x 10(-4) and k(-2)=2.079 x 10(-3)+/-5.6 x 10(-5)s(-1) for the proposed mechanism. The rate-limiting step as well as the reaction coordinates in the denaturation mechanism are established. The mechanism involves formation of a kinetically stable folded native like intermediate through the electrostatic interactions. The intermediate was found to be more stable even than the native form (by about 9 kJmol(-1)) and still hexamer, because no loss of amplitude was observed. Electrophoresis experiments on the native and surfactant/urease complexes indicated a higher mobility for the kinetically folded native like intermediate.     

Thermal and Light-Induced Spin Switching Dynamics in the 2D Coordination Network of {[Zn(1-x)Fe(x)(bbtr)(3)](ClO(4))(2)}(∞): The Role of Cooperative Effects

The thermal spin transition, the photoexcitation, and the subsequent spin relaxation in the mixed crystal series of the covalently linked two-dimensional network {[Zn(1-x)Fe(x)(bbtr)(3)](ClO(4))(2)}(∞) (x = 0.02-1, bbtr =1,4-di(1,2,3-triazol-1-yl)-butane) are discussed. In the neat compound, the thermal spin transition with a hysteresis of 13 K is accompanied by a crystallographic phase transition (Kusz, J.; Bronisz, R.; Zubko, M.; Bednarek, H. Chem. Eur. J.2011, 17, 6807). In contrast, the diluted crystals with x ≤ 0.1 stay essentially in the high-spin state down to low temperatures and show typical first order relaxation kinetics upon photoexcitation, and the structural phase transition is well separated from the spin transition. With increasing Fe(II) concentration, steeper thermal transitions and sigmoidal relaxation curves indicate increasingly important cooperative effects. Already at x = 0.38, the spin relaxation is governed by cooperative interactions between Fe(II) centers, and the crystallographic phase transition begins to influence the spin transition. The kinetic behavior of the thermal spin transition is reproduced within the framework of a dynamic mean-field model.