Deuterated Solvents Research Articles

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.

Hydrogen isotope effects and mechanism of aqueous ozone and peroxone decompositions.

Hydrogen peroxide exalts the reactivity of aqueous ozone by reasons that remain obscure. Should H2O2 enhance free radical production, as it is generally believed, a chain mechanism propagated by (.OH/.O2-) species would account for O3 decomposition rates in neat H2O, HR-O3, and in peroxone (O3 + H2O2) solutions, HPR-O3. We found, however, that: (1) the radical mechanism correctly predicts HR-O3 but vastly overestimates HPR-O3, (2) solvent deuteration experiments preclude radical products from the (O3 + HO2-) reaction. The modest kinetic isotope effect (KIE) we measure in H2O/D2O: HR-O3/DR-O3 = 1.5 +/- 0.3, is compatible with a chain process driven by electron- and/or O-atom transfer processes. But the large KIE found in peroxone: HPR-O3/DPR-O3 = 19.6 +/- 4.0, is due to an elementary (O3 + HO2-) reaction involving H-O2- bond cleavage. Since the KIE for the hypothetical H-atom transfer: O3 + HO2- HO3. +.O2-, would emerge as a KIE1/2 factor in the rates of the ensuing radical chain, the magnitude of the observed KIE must be associated with the hydride transfer reaction that yields a diamagnetic species: O3 + HO2- HO3- + O2. HO3-/H2O3 may be the bactericidal trioxide recently identified in the antibody-catalyzed addition of O2(1Deltag) to H2O.

External double reference method to study concentration and temperature dependences of chemical shifts determined on a unified scale

Abstract We present the principle of an external reference method of NMR, named the external double reference method, to study concentration and temperature dependences of chemical shifts. By the method, we refer chemical shifts of various samples at different temperatures to the peak of a reference substance at a fixed referring temperature. Thus, we can determine the chemical shifts in a variety of sample conditions on a unified scale. Results of the application of the method to 1H- and 1 3C-chemical shifts of water and methanol are presented. We also report new data of volume magnetic susceptibilities for several deuterated solvents useful for the calibration in the method.

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

SANS from Poly(ethylene oxide)/Water Systems

The poly(ethylene oxide) (PEO)/water system is investigated using small-angle neutron scattering (SANS). This system associates to form hydrogen-bonded clusters at high enough concentrations. Two correlation lengths are observed: one long range representing cluster sizes and the other short range representing polymer chain correlations. Clusters are formed at a volume fraction of 4% hPEO in D2O. An LCST transition is obtained between a mixed phase (through hydrogen bonding) and a demixed two-phase region. Solvent deuteration is seen to enhance hydrogen bonding. Deuteration of the polymer backbone is seen to enhance hydrophobic interactions. The average polymer contrast match method fails due to the isotopic dependence of specific interactions. Pressure was seen to lower the LCST by breaking hydrogen bonds. At even higher temperature (beyond the boiling point of water) a UCST transition was observed.

Temperature dependence study on photophysics of RuL(CN) 4 2− complexes: effects of diimine ligand and solvent deuteration

Photophysics of [RuL(CN) 4] 2− complexes, where L=2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (dmb), 4,4′-diphenyl-2,2′-bypiridine (dpb), 1,10-phenantrolin (phen), has been investigated by luminescence spectroscopy and flash photolysis at various temperatures. Luminescence quantum yield and lifetime of the 3MLCT excited state have been measured in aqueous solutions and in D 2O. The rate of direct deactivations to the ground state via radiative and non-radiative decay and the parameters of the thermally activated deactivation pathway have been determined. The rate coefficients of the radiative decay are quite close to each other (4×10 4–7×10 4 s −1) and are not sensitive to the replacement of H to D in the solvent, while the rate of non-radiative decay strongly depends on the nature of the polypyridyl ligand and on solvent deuteration. The activation energy and the pre-exponential factor of the thermally activated deactivation also depend on the nature of the α,α′-diimine ligand. The value of the potential barrier and the pre-exponential coefficient vary between 1010–1400 cm −1 and 5.5×10 8–14×10 8 s −1, respectively. Analysis of the emission spectra and the decay kinetics has confirmed that the excited state distortion and the interaction between the excited species and the solvent molecule through H or D bond are the factors that count in determining the rate of non-radiative deactivation pathways.

New convulsive compounds, brasiliamides A and B, from Penicillium brasilianum batista JV-379.

New convulsive compounds, brasiliamides A (1) and B (2), were isolated by activity-guided fractionation from okara fermented with a soil isolate of Penicillium brasilianum Batista JV-379. Their structures were elucidated on the basis of spectral and chemical evidence and by X-ray crystallography of the hydrogenated product of 2. In the 1H- and 13C-NMR spectra of 2, the signals were complicated, all being doubled or broadened in several deuterated solvents at room temperature. The conformational change of 2 was clarified as the rotational isomerization of amide bonds in solution by NMR measurements at various temperatures. Four rotamers of 2 at two amide bonds were presented at -60 degrees C in CDCl3, whereas only two isomers were apparent at room temperature, owing to rapid rotation of one of the amide bonds. Brasiliamides A and B respectively showed convulsive activity against silkworms with ED50 values of 300 and 50 microg/g of diet.

Structure of polymer solutions containing fumed silica

Small angle neutron scattering is employed to estimate the interactions in complex multicomponent systems. The method is applied to describe a ternary system, poly(dimethyl siloxane) toluene with silica filler particles. Contrast variation by solvent deuteration is used to distinguish the three different partial structure factors of filled polymer samples, S(pp)(q), S(pf)(q), and S(ff)(q), where the subscripts p and f refer to polymer and filler. This procedure allows changes to be detected in the distribution of the polymer close to the solid surface. Independent dynamic light scattering measurements are used to validate the method. A comparison is made between the behavior of different filled poly(dimethyl siloxane) PDMS samples. It is found that the polymer distribution is perturbed in the vicinity of the solid surfaces. In the case of weak interactions, the solvent removes the polymer almost completely from the filler particles, while, when the interaction is strong, the surface remains covered.

Formation of Excited Uranyl in U(IV) Oxidation with Oxygen in Aqueous HClO4 Solutions: III. Effects of Deuteration of Solvents and Heterogeneous Decay of Radicals

The surface of the glass introduced in the form of spheres with R = 1 mm into Teflon reactor affects both the kinetics of the liquid-phase chemiluminescent chain-radical oxidation of U(IV) with oxygen and the efficiency of conversion of the chemical reaction energy into the light energy. In the case of deuterated solutions, the reaction deceleration and the decrease in the chemiluminescence efficiency in the presence of the glass were less pronounced. A mechanism of the chemiluminescent reaction was considered which assigns an important role to heterogeneous decay of OH and HO2 (OD and DO2) radicals.

Protein-Bound Water Molecule Counting by Resolution of 1H Spin-Lattice Relaxation Mechanisms

Water proton spin-lattice relaxation is studied in dilute solutions of bovine serum albumin as a function of magnetic field strength, oxygen concentration, and solvent deuteration. In contrast to previous studies conducted at high protein concentrations, the observed relaxation dispersion is accurately Lorentzian with an effective correlation time of 41 ± 3 ns when measured at low proton and low protein concentrations to minimize protein aggregation. Elimination of oxygen flattens the relaxation dispersion profile above the rotational inflection frequency, nearly eliminating the high field tail previously attributed to a distribution of exchange times for either whole water molecules or individual protons at the protein–water interface. The small high-field dispersion that remains is attributed to motion of the bound water molecules on the protein or to internal protein motions on a time scale of order one ns. Measurements as a function of isotope composition permit separation of intramolecular and intermolecular relaxation contributions. The magnitude of the intramolecular proton–proton relaxation rate constant is interpreted in terms of 25 ± 4 water molecules that are bound rigidly to the protein for a time long compared with the rotational correlation time of 42 ns. This number of bound water molecules neglects the possibility of local motions of the water in the binding site; inclusion of these effects may increase the number of bound water molecules by 50%.

(Liquid + liquid) equilibria of (polystyrene + nitroethane). Molecular weight, pressure, and isotope effects

We report experimental cloud-point and spinodal data on the solubility of (polystyrene + nitroethane) as a function of temperature (265 <T/K< 345), weight fraction of polystyrene (0 <wps< 0.30), pressure (0 <p/MPa< 6.5), polystyrene (PS) molecular weight (13 000 <Mw/a.m.u.< 130 000), and H/D isotope substitution on PS and/or nitroethane. A new high-precision apparatus based on a LASER light scattering technique was built and is described. Only phase transitions of the UCS type have been experimentally observed. Apparently, nitroethane degrades at high temperatures (T≈ 420 K). Results show that the effects of increasing pressure or increasing the degree of deuteration on the polymer increase miscibility. In contrast, solvent deuteration decreases miscibility. Nitroethane seems to be a theta -solvent for polystyrene and therefore does not present any hypercritical temperature within the range of conditions of the experimental measurements, which have included the study of solutions slightly under tension.

A Vibrational Structural Analysis of Benzotriazole Adsorption and Phase Film Formation on Copper Using Surface-Enhanced Raman Spectroscopy

The adsorption of benzotriazole (BTAH) on copper in aqueous electrolytes is examined by means of a vibrational analysis utilizing surface-enhanced Raman spectroscopy (SERS) as a function of solvent deuteration, pH, and electrode potential in order to examine adsorbate speciation, surface bonding, and the potential-dependent onset of CuIBTA phase film formation. In acidic media at pH > 1, the monoprotonated acid BTAH constitutes the predominant adsorbate, being replaced by the diprotonated BTAH2+ species by pH 0, and the basic BTA- form in alkaline electrolytes. The analysis of adsorbate speciation is facilitated by the presence of several coupled ring modes yielding vibrational bands in the 1050−1350 cm-1 region that are sensitive to deuteration of the triazole ring nitrogen(s). Insight into the adsorbate molecular geometry and mode of surface attachment is obtained by examining the adsorption-induced alterations in frequency, bandwidth, and relative intensity of the various benzotriazole ring modes. These changes are especially prevalent for triazole ring vibrations and some deuteration-sensitive modes, the latter apparently associated with Fermi resonance effects. The former torsional/bending ring vibrations also exhibit potential-dependent frequencies (i.e., an electrochemical Stark effect), reflecting copper−triazole electronic interactions. Taken together, the SER spectral features for BTAH and BTA- suggest surface attachment via a pair of triazole nitrogens with a tilted (or vertical) orientation; the single nitrogen binding site anticipated for BTAH2+ is consistent with the milder vibrational perturbations observed for this adsorbate. The transformation from adsorbed benzotriazole to a CuIBTA film at higher potentials is readily diagnosed from the SER spectra, including the observed lack of a D/H vibrational effect on the latter species. The structure of benzotriazole films in air is also examined; emersion of adsorbed BTAH from solution spontaneously yields a CuIBTA layer via a coupled O2-induced electrochemical pathway. The thermal stability of copper-benzotriazole films in ambient-pressure O2 and N2 from 25 to 300 °C was also probed with SERS.

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.

Nature of rate-limiting steps in the soybean lipoxygenase-1 reaction.

A series of kinetic isotope effect experiments were performed with the goal of understanding the nature of rate-limiting steps in the soybean lipoxygenase-1 (SBL-1) reaction. SBL-1 was reacted with linoleic acid (LA) and deuterated linoleic acid (D-LA) under a variety of experimental conditions involving changes in temperature, pH, viscosity, and replacement of H2O with D2O. The extrapolated intrinsic primary H/D isotope effect can be estimated to be possibly as large as 80. This value is probably the largest isotope effect published for an enzymatic reaction, and much larger than that predicted from semiclassical models. Due to this large primary isotope effect, the C-D bond cleavage fully limits the rate of reaction under all conditions tested. In the case of protonated linoleic acid, a number of steps are partially rate-limiting at room temperature; three distinct mechanistic steps which include substrate binding, an H2O/D2O sensitive step, and C-H bond cleavage have been characterized. Use of glucose as a solvent viscosogen demonstrates that substrate binding is approximately 48% rate-limiting for LA at 20 degrees C. SBL-1 is one of the few enzymes that fit the definition of a "perfect enzyme", in the sense that further optimization of any single step at room temperature will not significantly increase the overall rate. At lower temperatures, the step sensitive to solvent deuteration begins to dominate the reaction, whereas at higher temperatures, the hydrogen abstraction step is rate-limiting. The pH dependence of kcat/Km for SBL-1 can be explained as arising from two pKa's, one controlling substrate binding and the other substrate release. Below pH 7.8, the rate of substrate release increases, thus decreasing the commitment to catalysis and unmasking the large intrinsic isotope effect on the subsequent hydrogen abstraction. An abnormally high pKa, in the range of 7-8, has been determined for LA in the concentration range employed in these studies. We propose that the negatively charged form of LA, predominating above pH 7.8, is the preferred substrate with larger commitments to catalysis.

Temperature, Orientation, and Solvent Dependence of Electron Spin-Lattice Relaxation Rates for Nitroxyl Radicals in Glassy Solvents and Doped Solids

T 1 was measured by saturation recovery for nitroxyl radicals as a function of temperature, solvent, and position in the CW spectrum. Long saturating pulses were used such that contributions to the saturation recovery curve were dominated by T 1 rather than by the tumbling correlation time or the nitroxyl nitrogen nuclear spin relaxation time. Data between about 20 and 150 K were fitted to log (1/ T 1) = (2.34 ± 0.15) × log ( T) + (7.0 ± 0.3). This temperature dependence is consistent with a two-phonon Raman process, although the relevant vibrations are likely to be intramolecular rather than lattice modes. At higher temperatures and in solvents with weak solute-solvent and or solvent/solvent interactions, there is increasing mobility of the nitroxyl, which causes T 1 to be more strongly temperature dependent. T 1 values are orientation dependent: T 1 is longer when the external magnetic field is along the molecular z axis and shorter when the magnetic field is in the perpendicular plane. This orientation dependence is consistent with the orientation dependence of spin-orbit coupling and with symmetry arguments concerning the orientation dependence of vibrations. Deuteration of the nitroxyl, deuteration of solvent, or replacement of natural-abundance nitrogen by nitrogen-15 in the nitroxyl caused less than 10% change in T 1, which indicates that inter- or intramolecular electron-nuclear couplings are not the dominant factors in nitroxyl spin-lattice relaxation in the temperature regimes examined.

A molecular theory of relaxation and magnetization transfer: Application to cross‐linked BSA, a model for tissue

Homogeneous soft tissue, as regards its magnetic relaxation properties, is well-modeled by solutions of cross-linked protein (see Koenig and Brown, Prog. NMR Spectr. 22, 487 (1991)). Interactions at the solute-solvent interface alter the hydrodynamics of solvent water, and also couple the solute and solvent proton Zeeman energy reservoirs, giving hydrodynamic and cross-relaxation contributions to water proton relaxation that respond differently to deuteration of solvent. We report measurements of the magnetic field dependence of 1/T1 of water protons in cross-linked bovine serum albumin (BSA), for partially deuterated solvent and, in order to separate these two contributions, of 1/T1 of deuterons. The major experimental finding is that, in addition to recently identified water-binding sites on protein (covering approximately 0.2% of the surface) with water lifetimes of about 1 microsecond, there is another group of sites with lifetimes of about 23 ns, covering approximately 2% of the surface, which are evident in both proton and deuteron data. In addition, we have formulated a theory of interfacial proton-proton magnetic interactions which--with these four parameters, plus two that quantify the protein-water coupling at each site--can account for all the proton and deuteron data, in both native and cross-linked BSA.

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.

Factors affecting nonradiative decay: temperature dependence of the picosecond fluorescence lifetime of tetrakis(dihydrogen diphosphate)diplatinum(4-)

The lifetime of the picosecond fluorescence of Pt{sub 2}(pop = {mu}-P{sub 2}O{sub 5}H{sub 2}) has been observed to increase with decreasing temperature (e.g., from 40 ps at 290 K to 740 ps at 80 K in H{sub 2}O:glycerol (1:2)). The longer lifetimes at the lower temperatures are attributed to a decrease in the rate of the nonradiative decay of the short-lived emissive state, {sup 1A}{sub 2u}, to the long-lived emissive state, {sup 3}A{sub 2u}, of the complex. The variation of the lifetime of the {sup 1}A{sub 2u} state with temperature has been fit to two-channel expressions that include both a temperature-independent term and a term that is derived from a single-mode quantum treatment of nonradiative decay in either its normal or high-temperature limit. The temperature dependence of the lifetime in each solvent yields sufficient information to define only three parameters, while the two-channel, single-mode quantum term in the high-temperature limit is used ({kappa}{sub obs}= {kappa}{sub o} + (A/{radical}RT) exp(-E{sub a}/RT)), the three independent parameters can be well defined in each solvent. In nondeuterated solvents the decay of the {sup 1}A{sub 2u} state gives values of A that vary from 9.2 x 10{sup 12} to 6.0 x 10{sup 14} s{sup {minus}1},more » values of E{sub a} that vary from 890 to 1590 cm{sup {minus}1}, values of {kappa}{sub o} that are almost independent of solvent ((1.5 {plus_minus} 0.2) x 10{sup 9} s{sup {minus}1}), and low-temperature lifetimes that vary from 620 to 850 ps. Upon solvent deuteration, the low-temperature lifetime of the {sup 1}A{sub 2u} state increases to 2170 ps. The temperature-dependent component of the {sup 1}A{sub 2u} decay is attributed to a nonradiative pathway involving strong coupling between the {sup 1}A{sub 2u} and {sup 3}A{sub 2u} states in which the high-energy modes of the solvent are important accepting modes. 53 refs., 6 figs., 4 tab.« less

7-Azaindole in alcohols: solvation dynamics and proton transfer

The photoinduced excited-state double proton-transfer reaction of 7-azaindole has been examined in a variety of alcohol solvents. The influence of temperature and solvent deuteration has been investigated.

Solvent deuteration enhancement of hydrophobicity: DSC study of the inverse temperature transition of elastin-based polypeptides

As previously shown, the polypentapeptide of elastin, (Val{sup 1}-Pro{sup 2}-Gly{sup 3}-Val{sup 4}-Gly{sup 5}){sub n} or simply poly(VPGVG), undergoes an inverse temperature transition which is seen macroscopically as a phase separation with a dense viscoelastic phase of about 60% water, 40% peptide by weight and which is characterized molecularly by increase in intra- and intermolecular order as evidenced by formation of specific hydrophobic contacts. Furthermore, from an extensive study of polypentapeptides of the composition poly(f{sub x}(VPGXG), f{sub v}(VPGVG)), where f{sub x} + f{sub v} = 1 and X is any of the amino acid residues with apolar (hydrophobic) side chains, it has been shown that the temperature of the transition decreases and the heat of the transition increases with increased hydrophobicity. In the present paper differential scanning calorimetry has been utilized to determine the effect of D{sub 2}O on the temperature and heats of the inverse temperature transitions for poly(VPGVG), poly(IPGVG), poly(LPGVG), and poly(VPAVG) and in the latter case in the presence of 0.5 and 1.0 N NaCl and of 1,2, and 3 M urea. In all cases, the effect of D{sub 2}O as compared to H{sub 2}O is to lower the transition temperature about 2 C and to increase themore » heat of the transition about 10%, and this occurs also in the presence of NaCl, which itself lowers the temperature and increases the heat, and in the presence of urea, which itself raises the temperature and decreases the heat of the transition. It is concluded that the effect of replacement of H{sub 2}O by D{sub 2}O by D{sub 2}O in these polypeptides is to effect a small but consistent increase in the expression of hydrophobicity.« less