Effect Of Solvent Deuteration Research Articles

Electron Spin Relaxation of Photoexcited Porphyrin in Water-Glycerol Glass.

Recently, the photoexcited triplet state of porphyrin was proposed as a promising spin-label for pulsed dipolar electron paramagnetic resonance (EPR). Herein, we report the factors that determine the electron spin echo dephasing of the photoexcited porphyrin in a water–glycerol matrix. The electron spin relaxation of a water-soluble porphyrin was measured by Q-band EPR, and the temperature dependence and the effect of solvent deuteration on the relaxation times were studied. The phase memory relaxation rate (1/Tm) is noticeably affected by solvent nuclei and is substantially faster in protonated solvents than in deuterated solvents. The Tm is as large as 13–17 μs in deuterated solvent, potentially expanding the range of distances available for measurement by dipole spectroscopy with photoexcited porphyrin. The 1/Tm depends linearly on the degree of solvent deuteration and can be used to probe the environment of a porphyrin in or near a biopolymer, including the solvent accessibility of porphyrins used in photodynamic therapy. We characterized the noncovalent binding of porphyrin to human serum albumin (HSA) from 1/Tm and electron spin echo envelope modulation (ESEEM) and found that porphyrin is quite exposed to solvent on the surface of HSA. The 1/Tm and ESEEM are equally effective and provide complementary methods to determine the solvent accessibility of a porphyrin bound to protein or to determine the location of the porphyrin.

Mesoporous Silica Nanoparticles Loaded with Surfactant: Low Temperature Magic Angle Spinning 13C and 29Si NMR Enhanced by Dynamic Nuclear Polarization

We show that dynamic nuclear polarization (DNP) can be used to enhance NMR signals of 13C and 29Si nuclei located in mesoporous organic/inorganic hybrid materials, at several hundreds of nanometers from stable radicals (TOTAPOL) trapped in the surrounding frozen disordered water. The approach is demonstrated using mesoporous silica nanoparticles (MSN), functionalized with 3-(N-phenylureido)propyl (PUP) groups, filled with the surfactant cetyltrimethylammonium bromide (CTAB). The DNP-enhanced proton magnetization is transported into the mesopores via 1H–1H spin diffusion and transferred to rare spins by cross-polarization, yielding signal enhancements eon/off of around 8. When the CTAB molecules are extracted, so that the radicals can enter the mesopores, the enhancements increase to eon/off ≈ 30 for both nuclei. A quantitative analysis of the signal enhancements in MSN with and without surfactant is based on a one-dimensional proton spin diffusion model. The effect of solvent deuteration is also investigated.

High-resolution X-ray study of the effects of deuteration on crystal growth and the crystal structure of proteinase K.

Deuteration of macromolecules is an important technique in neutron protein crystallography. Solvent deuteration of protein crystals is carried out by replacing water (H(2)O) with heavy water (D(2)O) prior to neutron diffraction experiments in order to diminish background noise. The effects of solvent deuteration on the crystallization of proteinase K (PK) with polyethylene glycol as a precipitant were investigated using high-resolution X-ray crystallography. In previous studies, eight NO(3)(-) anions were included in the PK crystal unit cell grown in NaNO(3) solution. In this study, however, the PK crystal structure did not contain NO(3)(-) anions; consequently, distortions of amino acids arising from the presence of NO(3)(-) anions were avoided in the present crystal structures. High-resolution (1.1 Å) X-ray diffraction studies showed that the degradation of PK crystals induced by solvent deuteration was so small that this degradation would be negligible for the purpose of neutron protein crystallography experiments at medium resolution. Comparison of the nonhydrogen structures of nondeuterated and deuterated crystal structures demonstrated very small structural differences. Moreover, a positive correlation between the root-mean-squared differences and B factors indicated that no systematic difference existed.

Excitation of the uranyl ion in U(IV) oxidation with xenon difluoride in frozen aqueous sulfuric acid solutions: III. Effect of solvent deuteration

The effect of the solvent deuteration on the reaction of U(IV) with XeF2 in solutions of H2SO4 in H2O and D2SO4 in D2O, occurring in the course of heating these solutions after their quick cooling (10–15 K s−1) to 77 K, was examined. The effect is manifested in essentially different temperature dependences of the chemiluminescence accompanying the oxidation of U(IV) with XeF2. The results obtained are interpreted within the framework of the concept that the low-temperature reaction of U(IV) with XeF2 is catalyzed by the juvenile surface of crystal hydrates of sulfuric and deuterosulfuric acids, formed in the course of low-temperature phase transitions. The isotope effect is due to different kinetics of the phase transitions in solutions of H2SO4 in H2O and D2SO4 in D2O. In the course of crystallization of supercooled H2SO4 solutions, depending on the mode of temperature variation, either one or two eutectics appreciably differing in the physical properties are formed. In the course of crystallization of supercooled solutions of D2SO4 in D2O, one stable eutectic is formed in each sample, and its characteristics depend on the thermal history of the sample. The eutectics melt in the course of heating of the frozen solution at temperatures differing by only 3–4 K.

Photocleavage of plasmid DNA by dibenzothiophene S-oxide under anaerobic conditions

The ability of dibenzothiophene S-oxide (1) to photochemically induce strand breaks in plasmid DNA was studied under anaerobic conditions. DNA cleavage is monitored by the conversion of closed circular pUC19 DNA (form I) to the nicked (form II) and linear forms (form III) using densitometer digital imaging of ethidium stained gels. In buffered aqueous–acetonitrile (9:1) solutions the single-strand cleavage is efficient and does not require an alkaline reaction workup. Photodeoxygenation of 1 in buffered aqueous–acetonitrile (9{:}1) solutions containing benzene led to the production of phenol. The effect of solvent deuteration does not support the involvement of 1O2 from a sulfoxide dimerization reaction nor a sensitized photooxygenation reaction. The results are interpreted in terms of a sulfoxide photodeoxygenation via oxygen atoms [O(3P)] where oxidation of DNA can lead to single-strand breaks. Since the reaction of O(3P) atoms with water itself is endoergic, we propose that hydroxyl radicals do not intervene in the DNA cleaving reaction.

Sonoluminescence of terbium chloride in an H2O-D2O mixture

The effect of solvent deuteration on the multibubble sonoluminescence (SL) of an aqueous solution of terbium chloride was studied. The dependence of the intensity of the characteristic SL of the TbIII ion on the composition of an H2O-D2O mixture is similar to an analogous dependence of its photoluminescence (PL) but with a much smaller isotope effect. In pure D2O, the SL intensity increases by 4 times only compared to the SL in water, while the PL intensity increases by 10 times. The mechanism of inner-bubble excitation of lanthanide ions is considered. According to this mechanism, an additional “heterogeneous” channel of quenching of excited TbIII ions appears, which is absent for PL. The proposed model satisfactorily describes the experimental data on the effect of solvent deuteration on the SL intensity.

Temperature Quenching of Uranyl Ion Photoluminescence in Frozen Deuterated Aqueous Solutions of Sulfuric Acid

The effect of solvent deuteration revealed as a difference in the shape of temperature dependence curves for the lifetime of uranyl ion in the electronically excited state (τ) upon warming H2SO4 solutions in Н2О and D2SO4 solutions in D2O frozen at 77 K was detected. The value of τ in the case of D2SO4 was shown to be shorter in the glassy solution than in the polycrystalline sample, whereas the reverse was observed in frozen H2SO4 solutions. This effect was explained by dissimilar occurrence of phase transitions in H2SO4 and D2SO4 solutions, as well as by a decrease in the probability of nonradiative deactivation of *(UO2+2) adsorbed on the surface of the crystal hydrate D2SO4·4D2O as compared with that on the surface of the crystal hydrates H2SO4·4H2O and H2SO4·6.5H2O.

Influence of Temperature on the Lifetime of Electronically Excited Uranyl Ion: III. Effect of Solvent Deuteration

The shape of the temperature dependences of the lifetime (τ) of electronically excited uranyl ion (UO22+)*, measured on warming from 77 K of UO2SO4 solutions in H2SO4 + H2O, differs from that measured in D2SO4 + D2O. The lifetime in glassy D2SO4 is shorter than in the polycrystalline sample, whereas in frozen H2SO4 solutions the pattern is opposite. The isotope effect is due both to different course of phase transitions in H2SO4 and D2SO4 solutions and to the fact that the probability of nonradiating deactivation of (UO22+)* adsorbed on the surface of D2SO4·4H2O crystal hydrate is appreciably lower than that of (UO22+)* adsorbed on the surface of H2SO4·4H2O and H2SO4·6.5H2O crystal hydrates. We suggest that the increase in τ due to adsorption appreciably exceeds the concentration quenching of excited uranyl ions in the course of crystallization of deuterated sulfuric acid.

Effect of Solvent Deuteration in the Radiative Deactivation of Electronically Excited Uranyl Ion upon Phase Transitions in Aqueous Sulfuric Acid Solutions

Effect of Solvent Deuteration in the Radiative Deactivation of Electronically Excited Uranyl Ion upon Phase Transitions in Aqueous Sulfuric Acid Solutions

Luminescence from neodymium(III) in solution

The luminescence lifetime of neodymium(III) in aqueous and organic solutions has been measured for the first time, and the effects of solvent deuteration on the excited state decay kinetics investigated. We have shown that the emissive 4 F 3 2 state is very short lived in water, τ = 29 ± 3 ns, and the lifetimeincreases significantly upon changing to D 2O, τ = 152 ± 7 ns. Complexing to polydentate ligands such as EDTA increases the lifetime due to the reduced solvation of the ion by water. In organic solvents the lifetime of the excited state of the ion is affected by both the presence of CH and OH oscillators; the latter are much more efficient at deactivating the excited state.

The effect of solvent deuteration on the photophysics of sulphonated aluminium phthalocyanine

The photophysics of disulphonated aluminium phthalocyanine in protiated and deuterated aqueous phosphate-buffered saline solution are reported. In the deuterated solvent the rate coefficients of fluorescence and intersystem crossing are unaffected by the heavier isotope; however, the rate of internal conversion from S 1 to S 0 has been shown to be considerably reduced. This results in increased quantum yields of fluorescence and triplet-state formation and also increased triplet and singlet lifetimes in deuterium oxide (Φ f0.40±0.04, τ f5.1±0.1 ns and τ t600±30 μs in H 2O and Φ f0.52±0.06, τ f6.8±0.1 ns and τ t1590±100 μs in D 2O). The implications of this with respect to the determination of the quantum yields of singlet oxygen formation in D 2O are discussed.

Multi-frequency e.p.r. studies of a mercury-containing mixed-metal derivative of laccase.

Multi-frequency e.p.r. studies of a derivative of laccase containing one mercury atom and three of copper were carried out at -150 degrees C. The e.p.r. signal of the mercury derivative and fluoride-binding studies establish that a type-2-like copper centre is present. The signal suffers broadening, owing to g-strain, but at low frequencies (S-band) ligand hyperfine splitting can be resolved, and it can be explained in terms of coupling to three nitrogen atoms. The g values and the effect of solvent deuteration on the line width suggest that the fourth ligand in the equatorial plane is a water molecule. Simulations of the e.p.r. spectrum reveal that the site is slightly rhombic at -150 degrees C, a finding in accord with the proposed N3O donor set. Finally, it is emphasized that a structural reorganization of the type-2 copper site occurs with the binding of fluoride at low temperature. The reorganization may be linked to a conformational change which has previously been claimed to occur on cooling; however, this transition is not necessarily relevant to the temperature-dependence of fluoride binding.

Influence of solvent deuteration on the spectral-luminescent and generational properties of xanthene and oxazine dyes

Solving the problem of realizing the energetic potential of laser devices based on dye solutions involves making deliberate changes in such characteristics of the active medium as the magnitude of the induced pumping loss, the quantum yield of fluorescence, and the degree of photostability of the laser solutions. This approach presumes either the synthesis of new highly effective compounds or the improvement in the laser characteristics of already existing materials by the selection of the appropriate solvents or chemical additives [1-3]. In a series of works, an increase in the fluorescence quantum yield of certain dyes has been observed on passing from ordinary to deuterated solvents [4, 5]. Unfortunately, the literature includes no information on the attendant changes in laser characteristics of the active media, and also the question of the mechanisms suppressing the nonradiative transfer of the excitation energy in the isotropic substitution of deuterium for hydrogen ions in the solvent molecules remains quite unclear. In the present work, it is established that the use of deuterated ethyl and methyl alcohols leads to improvement in the laser efficiency of xanthene and oxazine dyes; especially favorable effects of solvent deuteration are seen in oxazine-9 (cresyl violet). It is shown that the change in spectroscopic constants controlling the processes of triplet-molecule formation and deactivation in the given materials is not much expressed, and the increase in generational characteristics of the dye solutions is due to slowing of the nonradiational internal-conversion processes S~ § So. Deuterated ethyl and methyl alcohols of analytical grade were used as the solvents; the hydrogen-containing alcohols were doubly distilled. The absorption and luminescence spectra of the dyes, preliminarily purified by the methods of recrystallizatio n and chromatography,

Deuterium effects on radiationless electronic transitions of xanthene dyes in aqueous and alcoholic solutions

Solvent deuteration effects on internal conversion (S 1 ∼→ S 0) and intersystem crossing (S 1 ∼→ T 1) in 6-hydroxy-9-phenylfluoron and fluorescein were determined from fluorescence and triplet quantum yield measurements in alkaline solutions of H 2O, D 2O, CH 3OH, CH 3OD, C 2H 5OH, and C 2D 5OD. Deuterium substitution of the oxygen-bonded hydrogens of these solvenis reduces both the internal conversion (by approximately 1.6) and the intersystem crossing (by approximately 1.2) rate constants; the additional deuteration of the alkyl groups of the alcohols does not produce any further effect. The effect of solvent deuteration was negligible for fluorescein. Deuteration of the xanthene groups of the dyes does not influence the radiationless transition probabilities to any significant extent.