On ion-pair photoseparation and recombination in micellar aggregates

Perylene (Pe) and tetramethylbenzidine (TMB) have been photoionized under continuous or laser pulse excitation in cationic (Mi⁺), neutral (Mi⁰) or anionic micelles (Mi^-). In the latter case, Mi^- composed of sodium dodecyl sulfate (SDS) surfactant molecules have been swollen upon the addition of various hydrocarbons and the interfacial electric potential ΔΨ modified by electrolyte addition.From previous and present data, the following conclusions can be drawn:

• •(a) Intramicellar ultrafast geminate recombinations are promoted by increasing the micellar volume but counteracted when high electron mobility values characterize the swelling agent;
• •(b) Recombinations involving the hydrated electron ρ^-_aq appear to be suppressed in negatively as well as in positively charged Mi and to occur in Mi⁰ to an extent depending upon the chromophore cation;
• •(c) The overall photoionization yield ø_ion of Pe or TMB is found to increase linearly as ΔΨ becomes more negative; such ΔΨ variation is shown to affect ø_ion through the primary electron ejection stage though the ionization threshold energy does not seem to be appreciably modified;
• •(d) For Mi^- aggregates, the photoionization efficiency curves ø_ion=f(λ) show a linear dependence on the photon excess energy in the threshold region; within such an energy range, the ø_ion(λ) curves would thus approximate the variation with λ of a primary ionization yield of the solute;
• •(e) As a corollary, it may be suggested that the shape of the ø_ion(λ) curves relative to homogeneous liquid solutions would be essentially governed by solute cation-ρ^-_solv recombination reactions.

     

Methylglyoxal in the Brain: From Glycolytic Metabolite to Signalling Molecule

Highlights

• ●MGO may be essential for glycometabolism and bioenergetics in homeostasis and neural development;
• ●MGO may be an essential molecule in the regulation of neural homeostasis (redox homeostasis, lipid metabolism homeostasis, energy homeostasis, protein steady-state, epigenetic mechanisms, and neurotransmitters);
• ●Glycolysis is a source of protein homeostasis destruction. MGO formation as a by-product of glycolysis drives damage to the proteome.

AbstractAdvances in molecular biology technology have piqued tremendous interest in glycometabolism and bioenergetics in homeostasis and neural development linked to ageing and age-related diseases. Methylglyoxal (MGO) is a by-product of glycolysis, and it can covalently modify proteins, nucleic acids, and lipids, leading to cell growth inhibition and, eventually, cell death. MGO can alter intracellular calcium homeostasis, which is a major cell-permeant precursor to advanced glycation end-products (AGEs). As side-products or signalling molecules, MGO is involved in several pathologies, including neurodevelopmental disorders, ageing, and neurodegenerative diseases. In this review, we demonstrate that MGO (the metabolic side-product of glycolysis), the GLO system, and their analogous relationship with behavioural phenotypes, epigenetics, ageing, pain, and CNS degeneration. Furthermore, we summarise several therapeutic approaches that target MGO and the glyoxalase (GLO) system in neurodegenerative diseases.     

Organically-Modified Silica Xerogels for Adsorption of CH4 at 298 K

Organic tethers have been incorporated into acid- and base-catalysed silica sol–gels. The surface area is modified by this insertion suggesting an interaction at a molecular level. The HCl-catalysed SiO₂ sol–gel had its relative extent of adsorption at 298 K of CH₄ relative to H₂O:

1. depressed by the addition of 5% bis(triethoxysilyl)methane
2. increased by the addition of 5% bis(trimethoxysilyl)hexane

which attributed the tether hydrophilic-lipophilic balance (HLB). The reasons for this unexpected physical adsorption of CH₄ at a temperature far above its boiling point are now being explored, along with the potential of these materials for selective hydrocarbon sensors and separators.     

Penetration von Polyethylenglycoldodecylethern in gespreitete Methylstearatmonoschichten

1. The penetration isotherms of octaethyleneglycoldodecyl ether and tetraethyleneglycoldodecyl ether in methyl stearate monolayers at different film areas A_M were measured at T=295 K.
2. The penetration isotherms of the system methyl stearate/octaethyleneglycoldodecyl ether depended only weakly on the area of methyl stearate. Also, the relative shift of the penetration isotherms, related to the adsorption isotherm, was small.
3. The general penetration behaviour of both the systems methyl stearate/tetraethyleneglycoldodecyl ether and methyl stearate/octaethyleneglycoldodecyl ether was nearly identical.
4. The thermodynamical analysis of the system methyl stearate/octaethyleneglycoldodecyl ether indicated that the components are only partially miscible.

     

Hydrogen separation from gas mixtures using LaNi5 pellets

Porous pellets containing the hydride-former LaNi₅ for use in an absorption bed for extracting hydrogen from gas mixtures were prepared and tested. The unique aspect of these pellets is their incorporation of thermal ballast. By this means the thermal effects of hydriding and dehydriding are reduced to controlled temperature swings and adiabatic operation is possible. Pellet bonding has been accomplished by

• 1.(1) sintering of a nickel powder thermal ballast
• 2.(2) the addition of silicone rubber binder
• 3.(3) the addition of a Teflon-polyethylene binder.

A flow-through reactor was designed and employed to evaluate pellet behavior in non-dilute gas mixtures. A model for hydrogen absorption from gas mixtures was developed to resolve the absorption kinetics data into the following rate-limiting factors:

• 1.(1) intrinsic rate;
• 2.(2) intrinsic rate retardation;
• 3.(3) microflow (intrapellet gas transport);
• 4.(4) macroflow (interpellet gas transport).

Flow-through absorption kinetics data are presented for the pellets in H₂-NH₃ gas mixtures.     

Heats of chemisorption ofn-Aliphatic alcohols on α-Al2O3 at 25–200°C

A differential microcalorimeter (E. Calvet) was used to study the processes of adsorption of five aliphatic alcohols (C₁-C₅) on α-Al₂O₃ at 25, 50, 100, 150 and 200°C. In particular, the importance of the thermokinetic study of the chemisorption of such alcohols at different experimental temperatures was demonstrated, with regard to the variations in the thermokinetic parameters (t_max, t_1/2 and t₀) and the evolution of the alcohol vapor pressure on the adsorbent during the adsorption process. It was concluded that:

1. all the heat emission peaks of alcohol adsorption have the same rounded shape at 25°C;
2. on passing from methanol to 1-pentanol, the area of the adsorption peaks increases as the chain length or molecular weight increases;
3. on passing from 25 to 200°C, the shape of the adsorption peaks becomes more pointed.

     

Kompressionsverhalten und Gleichgewichtsspreitungsdrucke binärer monomolekularer Dipalmitoylkephalin/Dimyristoylkephalin-Mischungen

1. The concentration dependence of theF/A-isotherms (premixed spreading, separate spreading) and the equilibrium spreading pressuresF ^e of the system dipalmitoylcephaline/dimyristoyl-cephaline were studied atT=298 K. The results were analysed and compared by means of thermodynamics with respect to miscibility of the components.
2. The spreading technique (pre-mixed spreading, separate spreading (with and without barrier), does not essentially influence the run of theF/A-isotherm. Alone, the collaps pressuresF _K differ.
3. The concentration dependence of theF/A-isotherms of premixed spread monolayers is analysed in terms of theA-x ^σ-diagram. The additivity of molecular areas at all surface pressures are assumed to indicate complete miscibility of the cephalins.
4. The phase rule according to Crisp was applied to analyse the spreading diagram in connection with the phase diagram of the mixtures in bulk. The results show that the cephalins are completely miscible in the monolayer.
5. The experimental collaps pressuresF _K of pre-mixed spread monolayers are very much larger than the equilibrium collapse presuresF _K calculated according to Garrett. The difference indicate the strong supercompression of mixed film during the compression.

     

The mechanism of plasma-induced deposition of amorphous silicon from silane

Time-resolved mass spectrometric data show that the concentration of di- and trisilane, which are formed from monosilane under discharge conditions typical for the deposition of high electronic quality amorphous silicon, correlate with the measured deposition rate of a-Si. The data can be quantitatively and self-consistently described by a simple set of consecutive reactions:

1. SiH₄ →-SiH₂ + H₂
2. SiH₂ + SiH₄ → Si₂H₆
3. SiH₂ + Si₂H₆ → Si₃H₈
4. Si _n H_{2(n + 1)} →n ·a-Si:H+(n+1)H₂,n=2,3

The only fitting parameter necessary for an excellent fit of the measured data over a wide range of experimental parameters is the value of the reactive sticking coefficient .for the decomposition of di- and trisilane (reaction 3). The resultant value agrees well with the published data of other authors and with those calculated from the measured deposition rate and Si₂H₆, concentration. We did not find and physically meaningful way to lit the measured data with the various “SiH₃ models” proposed by other authors who assumed that the dominant species responsiblefor the deposition of a-Si: H is the SiH₃, radical. For this and some additional reasons mentioned in the present paper. the SiH₃ model is in disagreement with available experimental data.     

Thermisches Phasenverhalten homologer α- und β-methylverzweigtkettiger Lecithine im wassergesättigten Zweiphasengebiet

1. By means of differential scanning calorimetry the phase transition temperatures (T _u) and phase transition enthalpies (ΔH _u) ofα- andβ-branched lecithins were determined. The lecithin samples contained 50% water per weight.
2. The occurrence of the pre-transition was dependent on the position of the methyl group in the acid residue as well as on the length of the carbon chains. TheΔH _u values of the pre-transition were about 2.5 kJ·mol^?1.
3. The hydration number (HZ) (number of water molecules per lecithin headgroup) was independent on the position of the methyl group and the length of the acyl group. The average HZ-values for all the lecithins studied is about HZ=14+-1.
4. The influence of the chain length of theα- andβ- branched acyl groups affects the thermodynamical parameters of the main transitions (gel→L _α). TheΔH _m andT _m-values increased as the chain length increases.

     

Phasenumwandlungserscheinungen in Lecithin/Wasser-Systemen

1. By means of differential-scanning-calorimetry the phase transition temperatures and -enthalpies were determined and evaluated for the three following lecithin/water systems: 1,2-dimyristoyl-lecithin/water; 1,2-dipalmitoyl-lecithin/water; 1,2-distearoyllecithin/water.
2. The preparation of the lecithin/water mixtures was made by adsorption of water from the gaseous phase. The adsorption isotherms were evaluated by the BET equation.
3. Four phase transitions were found for the monohydrates of the lecithins. The parameters depend systematically on the length of the alkyl residues.
4. In the heterogeneous two phase region the main-transition and the pre-transition occurred. The thermodynamical parameters of both transitions depend on the alkyl chain length.
5. Whole the results refer to the conclusion that the lecithin head group hydration is a stepwise process. The hydration of the first shell is finished if 5 to 6 molecules water per molecule lecithin are present, while the second hydration shell is complete when about 13 water molecules are adsorbed

     

Charakterisierung der Mischbarkeitseigenschaften binärer Monoschichten durch Messung der Gleichgewichtsspreitungsdrucke

1. The equilibrium spreading pressures were studied as a function of composition of the following binary systems by use of the Wilhelmy-method atT=295 K on aqueous substrate:

octadecyldiethylphosphine oxide/1-hexadecanol (I)

octadecyldiethylphosphine oxide/1-eicosanol (II)

octadecyldiethylphosphine oxide/stearic acid (III)

1. The equilibrium spreading pressures of the pure components of the systems I und II, respectively, decrease due to addition of the corresponding components of mixture. A minimum occurs at the mole fractionx=0,50. The equilibrium spreading pressures of mixtures of system III rise with increasing mole fraction of octadecyldiethylphosphine oxide.
2. The three spreading diagrams are based on one general type. The phase rule is applied and shows that the components of the 3 systems must be immiscible in the monolayer but miscible in the bulk phase.

     

Einfluß der thermischen Vorgeschichte auf die Phasenumwandlungen von Dipalmitoyllecithin/Wasser-Mischungen

1. The influence of the thermal pretreatment (first and second heating run, annealing process) on the phase transition temperaturesT _m, enthalpiesΔ¯H _m and the specific heatc _sp of 1,2-dipalmitoyllecithin-water-mixtures was studied by differential scanning calonmetry.
2. The differences in theT _m- andΔ¯H _m-data of the main transition of the first and second heating run were found in the concentration rangex ^w<0,75. In the concentration rangex _W>0.75 these differences disappear.
3. The annealing process of a 1,2-dipalmitoyllecithin-water-mixturex _W=0,89 leads to a splitting of the main transition peak in two separate peaks with a different shape. This behaviour may imply that 1,2-dipalmitoyllecithin coexists in two different hydration states.

     

Einfluß des Wassers und der thermischen Vorgeschichte auf das Phasenverhalten homologer Kephalin/Wasser-Systeme

1. By means of differential scanning calorimetry the phase behaviour of the following cephaline/water systems was studied: 1,2-dilauroyl-cephaline/water; 1,2-dimyristoyl-cephaline/water; 1,2-dipalmitoyl-cephaline/water; 1,2-distearoyl-cephaline/water; 1,2-diarachinoyl-cephaline/water. The phase transition temperatures (T _u ), enthalpies (ΔH _u ) and specific heat capacities (c _sp ) were determined and compared as a function of the water content and the alkyl chain length of the cephalines.
2. TheΔH _u andT _u values of the monohydrates depend systematically on the chain length. Differences occurred for the first and the second heating run.
3. With increasing water content theT _u values decrease while theΔH _u values become larger if one system cephaline/water is considered.
4. In the heterogeneous two phase region the increase of the chain, length of the homologous cephalines leads to a systematical increase of theΔH _u as well as theT _u values.
5. Below the annealing temperature dehydration and recrystallization occur. The kinetics of the phase transitionL _α →C was studied in the heterogeneous two phase region.

     

446 — Electrochemical examination of nucleoside interaction: Adenosine-guanosine and cytidine-guanosine

The adsorption at the solution/mercury electrode interface of guanosine, adenosine and cytidine alone and in guanosine—adenosine and guanosine—cytidine mixtures was examined for pH 4.0 and 7.2 solutions at 25 and 40°C; the principal index used was the a.c. polarographic quadrature current component. All of the nucleosides are adsorbed at the 1.0 mM and lower concentrations examined. There is evidence at 25°C for:

• 1.the self-association of uncharged adsorbed guaosine;
• 2.formation at pH 4 of a 2 : 1 guanosine—adenosine complex, which is at least partially positively charged, is more stable than the self-associated guanosine and associates in the adsorbed state;
• 3.formation at pH 7.2 of a similar 2 : 1 but uncharged guanosine—adenosine complex;
• 4.formation of a probably positively charged 1 : 1 guanosine—cytidine complex, which
• 5.adsorbs and associates at pH 4 and of a similar neutral complex at pH 7.2.

Association of the adsorbed species is not seen at 40°C. The controlling factor in determining the differential capacitance at the interface is generally the presence of the most surface-active species, guanosine.     

Hippurathydrolase,ein neues Enzym aus Mikroorganismen, 2. Mitt.: Enzymeigenschaften

Characteristic properties of the new enzymehippurate hydrolase are reported:

1. The Michaelis constant for hippurate hydrolysis is 5.5·10^?4 mole/l at 5° and pH 7.5. The specific activity of the purified enzyme preparation is 7.5 μmole/minute · mg enzyme protein at 37° and pH 7.5. The pH optimum is 7.5.
2. The effects of temperature on the reaction rate and on the stability of the enzyme were determined.
3. The effects of various inhibitors (HgCl₂, pCMB, EDTA, 8-hydroxyquinoline) and cations were studied. Participation of metal ions in the catalytic function ofhippurate hydrolase was not detectable.

     

Microscopic solvation: spectroscopic results vs. Monte Carlo simulations

Van-der-Waals clusters of carbazole (representing the ‘solute’) with up to 40 nitrogen or methane solvent molecules were characterized using two-color resonant two-photon ionization spectroscopy. Features in these spectra (redshift, homogeneous and heterogeneous broadening, etc.) are interpreted as being caused by various static and dynamic effects of the solvent shell surrounding the aromatic substrate. For a better understanding of such effects, Monte Carlo simulations of the clusters were performed: Statics: Using a Monte Carlo simulated annealing minimization procedure, minimum energy structures (local, probably global) were found for the various cluster species. Using a simple empirical additivity rule, spectral shifts are rationalized from these structures.Dynamics: Starting from these minimum configurations, canonical ensemble simulations were carried out in a temperature range from 0 to 35 K. Severalorder-disorder transitions were identified including:

1. orientational isomerization or ‘melting’
2. surface isomerization or decoupling
3. rigid → fluxional transitions
4. full cluster ‘melting’

We present some of our experimental results on the systems carbazole · (N₂) _n and carbazole · (CH₄) _n together with the corresponding simulation data.