Study of thioflavin-T immobilized in porous silicon and the effect of different organic vapors on the fluorescence lifetime

Steady-state and time-resolved emission techniques have been employed to study the fluorescence properties of thioflavin-T (ThT) adsorbed on oxidized porous silicon (PSi) surfaces, with an average pore size of ～10 nm. We found that the average fluorescence decay time of ThT, when it is adsorbed on the PSi surface, is rather long, τ(av) = 1.3 ns. We attribute this relatively long emission lifetime to the effect of the immobilization of ThT on the PSi surface, which inhibit the rotation of the aniline with respect to the benzothiazole moieties of ThT. We also measured the fluorescence properties of ThT in PSi samples in equilibrium with vapors of several liquids, such as methanol, acetonitrile, and water. We found that the fluorescence intensity drops by a factor of 10, and the average decay time, measured by a time-correlated single-photon counting technique, decreases by a factor of 3. We explain these results in terms of liquid condensation of the vapors in the PSi pores, which leads to partial dissolution of the ThT molecules in the liquid pools.     

Pressure effect on adhesion

Zusammenfassung Unter der Voraussetzung von Verknüpfungen wird die Anfangsgeschwindigkeit der Adhäsion untersucht.Wenn Epoxyharz-Aminsysteme als Klebstoff gebraucht werden, ist die Beziehung zwischen Härtezeit und Anfangs-Bindefestigkeit theoretisch wie folgt gegeben:S(t)/S(t ₀ )=t+1. Dabei sindS(t) undS(t ₀) die Klebefestigkeit nach den Härtezeitent bzw.t ₀ ist ein Maß für das Ansteigen der Verknüpfungen, t=t–t₀.Die Beziehung zwischen Härtungsdruck und Verhältnis der Klebfestigkeiten lautet lnS(p)/S(p ₀ )=ln+·p. Wieder sind die Werte der FestigkeitenS aufp bzw.p ₀ auf die Drucke bezogen. und sind Konstanten.Die experimentellen Ergebnisse für das Kleben von Kupfer mit Epoxyharz-Aminsystemen bestätigen diese theoretischen Voraussagen.

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With 7 figures and 3 tables     

Temperature dependence of the fluorescence properties of thioflavin-T in propanol, a glass-forming liquid

Steady-state and time-resolved emission techniques were employed to study the nonradiative process of Thioflavin-T (ThT) in 1-propanol as a function of temperature. We found that the nonradiative rate, k(nr), decreased by about 3 orders of magnitude when the temperature was lowered to 88 K. We found remarkably good correspondence between the temperature dependence of k(nr) of ThT and the dielectric relaxation times of the 1-propanol solvent.     

Short polyglutamine peptide forms a high-affinity binding site for thioflavin-T at the N-terminus

Thioflavin-T is one of the most important amyloid specific dyes and has been used for more than 50 years; however, the molecular mechanism of staining is still not understood. Chemically synthesized short polyglutamine peptides (Q(n), n = 5-10) were subjected to the thioflavin-T (ThT) staining assay. It was found that the minimum Q(n) peptide that stained positive to ThT was Q(6). Two types of ThT-binding sites, a high-affinity site (k(d1) = 0.1-0.17 μM) and a low-affinity site (k(d2) = 5.7-7.4 μM), were observed in short polyQs (n = 6-9). (13)C{(2)H}REDOR NMR experiments were carried out to extract the local structure of ThT binding sites in Q(8) peptide aggregates by observing the intermolecular dipolar coupling between [3-Me-d(3)]ThT and natural abundance Q(8) or residue-specific [1,2-(13)C(2)] labeled Q(8)s. (13)C{(2)H}REDOR difference spectra of the [3-Me-d(3)]ThT/natural abundance Q(8) (1/9) complex indicated that all of the five carbons of the glutamine residue participated in the formation of ThT-binding sites. (13)C{(2)H}DQF-REDOR experiments of [3-Me-d(3)]ThT/residue-specific [1,2-(13)C(2)] labeled Q(8) (1/50) complexes demonstrated that the N-terminal glutamine residue had direct contact with the ThT molecule at the high-affinity ThT-binding sites.     

Effect of nickel complexing on the catalysis of nonradiative transitions in anthracene

By means of kinetic spectrophotometry we have studied the kinetics of the nonradiative deactivation of anthracene molecules in the triplet state in ethylene glycol at 25 C with nickel chloride and nickel ethylenediaminetetraacetate, cyclohexanediaminetetraacetate and diethylenetriaminepentaacetate complexes. Rate constants for the quenching of anthracene triplets by these compounds were determined. The ligands studied give the following series when ordered according to the strength of their quenching action: cyclohexanediaminetetraacetate相似文献   

Influence of the polar medium fluctuation on the nonradiative electron transfer in molecules

The influence of the classical polar medium fluctuation on the nonradiative transition rate in molecules is considered. Change of the vibrational frequencies under electron excitation is taken into account. In the Gauss–Markov approximation for the fluctuation and the linear model of the vibrational term of the final electronic state, the formula for the rate of the process at low temperature is obtained. The formula reveals the temperature dependence arising from the influence of the environment medium on the barrier of the reaction. The theory is applied to the explanation of the value and temperature dependence of the rate of the low‐potential cytochrome oxidation. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 74: 381–386, 1999     

Modeling the nonradiative decay rate of electronically excited thioflavin T

A computational model of nonradiative decay is developed and applied to explain the time-dependent emission spectrum of thioflavin T (ThT). The computational model is based on a previous model developed by Glasbeek and co-workers (van der Meer, M. J.; Zhang, H.; Glasbeek, M. J. Chem. Phys. 2000, 112, 2878) for auramine O, a molecule that, like ThT, exhibits a high nonradiative rate. The nonradiative rates of both auramine O and ThT are inversely proportional to the solvent viscosity. The Glasbeek model assumes that the excited state consists of an adiabatic potential surface constructed by adiabatic coupling of emissive and dark states. For ThT, the twist angle between the benzothiazole and the aniline is responsible for the extensive mixing of the two excited states. At a twist angle of 90°, the S(1) state assumes a charge-transfer-state character with very small oscillator strength, which causes the emission intensity to be very small as well. In the ground state, the twist angle of ThT is rather small. The photoexcitation leads first to a strongly emissive state (small twist angle). As time progresses, the twist angle increases and the oscillator strength decreases. The fit of the experimental results by the model calculations is good for times longer than 3 ps. When a two-coordinate model is invoked or a solvation spectral-shift component is added, the fit to the experimental results is good at all times.     

Gas composition effect on the Klauss process efficiency

The effect of the initial gas composition on the efficiency of the catalytic reaction of the hydrogen sulfide oxidation by sulfur dioxide was studied experimentally.     

The effect of the mixing process on reaction kinetics

If the chemical rate constants of the initial reaction steps are large, any observed value of these constants may be affected by the mixing process. To investigate the effect of mixing efficiency on reaction kinetics we use two previously analyzed reaction systems, namely the glutamic aspartic aminotransferase system and the hemoglobin/O₂ system. A time constant k_a for the mixing process is introduced and four values for this parameter are considered, with the fastest essentially corresponding to complete mixing before any reaction can take place. The remaining three values are associated with mixing instruments, since they may be attainable in the real world. To evaluate the mixing efficiency (and conversely determine underlying k_a values) from observed kinetics, mixing was combined with chemical relaxation by temperature jumps initiated at different points in time during the mixing process. Computer simulations permit the development of specific criteria to determine (in reverse) appropriate values of k_a. In this respect, the aminotransferase system proved to be more revealing than the hemoglobin system. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 484–496, 2003     

Pressure effect investigations on spin-crossover coordination compounds

The piezochromic properties of spin-crossover complexes have been recognized for a long time, with increasing pressure favouring the low spin state due to its smaller volume and therefore shifting the spin equilibrium towards higher temperatures and accelerating the relaxation at a given temperature. However, the interpretation and quantification of pressure-induced changes have been several times compromised by the relatively poor and incomplete spectral and structural information provided by the detection methods or due to the experimental difficulties related to the need for hydrostatic conditions at low temperatures. The present review is therefore primarily focused on these experimental aspects of high-pressure spin crossover research providing an overview of methods of pressure generation and associated detection methods as well as on selected recent results.     

Temperature dependence of the nonradiative decay of indoles in solution

The nonradiative decay rate k_nr. of some indole derivatives has been measured as a function of temperature in three solvents : n-heptane, methanol and water. A temperature-independent component (attributed to S₁ → T₁ intersystem crossing) and a temperature-dependent component (attributed to S₁ → S₀ internal conversion) are present in all case. In aqueous solutions, our results indicate the existence of a second temperature-dependent process which can be identified with photoionization.     

Pressure effect on the phase transitions in Ni-base multicomponent systems

Summary The phase transformations in the three Ni-base alloys at the temperature range up to 1500°C and at the pressure of 170 MPa were studied. Solidus, -phase dissolution/precipitation, carbides dissolution/precipitation and liquidus temperatures are established. Multiple exceeding of the Ni-base alloys characteristic temperatures pressure coefficients over metal components ones (up to 10 times) is observed both at the heating and cooling scans during the experiments on the differential barothermal analysis. On the DBA curves had been obtained at 170 MPa, there are from two to three peaks, which connected with the carbides dissolution/precipitation, while on the each conventional DTA curve there was merely one carbide thermal effect. The liquidus temperature pressure coefficients correlate with the Ni melting point pressure coefficient.     

Pressure effect on the nematic-isotropic transition in dilaterally substituted nematogens

The effect of pressure on the liquid crystal properties of two new dilaterally substituted nematogens has been studied. The method employed involves measurement of the thermal pressure variation of a sample under isochoric conditions. The pressure-temperature phase diagrams were determined. As for unsubstituted compounds, the nematic phase is stabilized upon application of pressure. The values of the (?T/?P)^NI slopes of the clearing lines for these nematogens are, however, significantly higher than those generally characterizing rod-shaped nematics. The entropy separation method was used to estimate the constant volume and the volume-dependent terms of the entropy changes at the nematic-isotropic transition. The values of these contributions were determined on the basis of thermobarometric data showing that the transition entropy is strongly volume-dependent. This suggests that the higher values of the (?T/?P)^NI slopes observed for these compounds can be related to the rearrangement of the lateral flexible chains in the nematic phase when the pressure increases, leading to a decrease of the excluded free volume caused by the bulky core of the molecules.     

Pressure effect on the structural and electronic properties of CuInS2

The pressure dependence of the bond length and energy gap in chalcopyrite CuInS₂ between 0 and 40 GPa has been investigated using pseudopotentials plane-wave method within the generalized gradient approximation for the exchange-correlation potential. We found that the bond length decreases as the pressure increases. Also, the energy gap of CuInS2 expands as the pressure increases with a rate of 10.693 meV/GPa. The linear pressure coefficient calculated is approximately half the reported experimental value of 23 meV/GPA. Our calculated bulk modulus of 68.7 GPa is in good agreement with the available experimental and theoretical values. The present calculations show that the d-electrons of Cu ions are one of the important factors that dominate the contributions to the I-VI bonds and the energy gap in CuInS₂.     

Substituent effect on the nonradiative decay rates from 3MLCT excited state of ruthenium(II) complexes: A quantum chemical treatment

The radiationless transition rates from metal-to-ligand charge-transfer excited states of [Ru(phen)₃]²⁺ (phen = 1,10-phnanthroline) and its analogues were investigated in terms of the Huang–Rhys factors (S) using luminescence measurements and quantum chemical calculations. From the luminescence spectral fitting, it was found that not only S_M for medium frequency mode but also S_L for low frequency mode was significant for the nonradiative process. Huang–Rhys factors predicted by the conventional quantum chemical method were in agreement with the experimental values, S_M and S_L.     

Pressure effect on positronium reactions in organic solutions

The reaction rate constants of positronium (Ps) atoms with a series of nitrobenzene derivatives and nitromethane in toluene solutions have been determined as a function of external pressure up to 1000 kg cm⁻² (about 1000 atm). The rate constants for relatively weak Ps acceptors such as p-nitroanisole, 1,3-dimethyl-2-nitrobenzene and nitromethane increased considerably with external pressure, while those for relatively strong Ps acceptors like p-dinitrobenzene or nitrobenzene either decreased or changed little with external pressure. Comparison of the experimental results on pressure effects with those on temperature effects revealed that the application of external pressure suppresses the thermal decomposition of Ps complexes which are unstable at room temperature. The effect on a solvent of the Ps reaction was also studied by determining the reactivities of Ps atoms with nitrobenzene in various solvents as a function of external pressure.     

Pressure effect on electron localization in solid lithium

External pressure applied to a solid material causes modifications of the bonding which can provide a chemical explanations of phase transitions. The behaviour of the Electron Localization Function (ELF) has been examined for the body-centred cubic, face-centred cubic and \(I\bar 43d-16\) phase of lithium for a series of cell volumes accounting for external hydrostatic pressures in the 0-60 GPa range. It is shown that the ELF signatures of electron localization increase with the pressure. Moreover, the number of basins per atom is the high-pressure phases is less than in the low-pressure ones and therefore the basin population are larger in high pressure modifications. These results complement the study of Marques et al. Phys Rev Lett 106:095502 (2011) carried out on the C2c b ? 40 and C m c a ? 24 phases stable above 85 GPa.     

Theoretical calculations on radiative and nonradiative processes of quartet states of HeH

MRD CI calculations have been carried out on the lowest four ⁴Σ⁺ and the lowest two ⁴Π states of HeH. Potential energy curves, rates of radiative transitions and also rates of predissociation by radial coupling have been obtained, in order to make predictions on the possibility of observing quartet spectra in HeH.     

On vibronic coupling in nonradiative transitions of polyatomic molecules

The vibronic coupling between quasidegenerate adiabatic Born—Oppenheimer states has been calculated by going beyond the Condon approximation. A simplified model in which accepting modes are distorted (non-totally symmetric) and of the same frequency, has been considered. The decay rate obtained with this approach is one order of magnitude larger than in the Condon scheme and seems to be practically independent of the symmetry of the accepting modes.