OD Oscillators Research Articles

Arresting "Loose Bolt" Internal Conversion from -B(OH)2 Groups is the Mechanism for Emission Turn-On in ortho-Aminomethylphenylboronic Acid-Based Saccharide Sensors.

Different mechanisms for the emission turn-on of ortho-aminomethylphenylboronic acids with appended fluorophores in response to saccharide binding in aqueous media have been postulated, such as photoinduced electron transfer (PET), "pKa switch", and disaggregation. However, none of the hypotheses is consistent with all the data for boronic acid-based sensors. To create a unifying theory that can explain the data, we performed a series of experiments to explore the origin of the emission turn-on with several boronic-acid based sensors upon binding fructose. First, we showed that the receptors and their complexes with fructose are solvent-inserted, with no B-N interactions. Second, we verified that the sensors are not aggregated. Third, in pure methanol, that exchanges -B(OH)2 to -B(OMe)2 groups, we found no fluorescence response upon binding fructose. We propose this occurs via lessening of internal conversion mechanisms. To investigate this proposal further, we performed a solvent isotope effect study. The fluorescence of the probes in D2O (-B(OH)2 → -B(OD)2) does not change upon fructose binding. It is well accepted that -OD oscillators are less efficient energy acceptors due to their lower frequency vibrational modes. Thus, our studies reveal that modulating the -B(OH)2-induced internal conversion (an example of a "loose bolt effect") explains how potentially all ortho-aminomethylphenylboronic acid-based fluorescence sensors signal the presence of sugars.

Contrasting the experimental properties of hydrogen in SnO2, In2O3, and TiO2

IR spectroscopy has been used to investigate the properties of H and D in single crystals of the transparent conducting oxides, SnO2, and In2O3. H introduces several O-H stretching lines and also the broad absorption arising from free carriers. IR spectroscopy has been used to identify the sources of n-type conductivity, its thermal stability, and the reactions of H-containing defects. The properties of OH and OD centers in TiO2, while studied for decades, reveal new surprises and properties that are in sharp contrast to the shallow, H-related donors seen in SnO2 and In2O3. Recent theory and EPR experiments find that electrons in TiO2 become self-trapped at Ti sites to form small polarons. The OD center in TiO2 shows a multiline vibrational spectrum with an unusual temperature dependence that can be explained by a small polaron model with the donor electron self-trapped at different Ti sites near the OD oscillator.

Water inertial reorientation: hydrogen bond strength and the angular potential.

The short-time orientational relaxation of water is studied by ultrafast infrared pump-probe spectroscopy of the hydroxyl stretching mode (OD of dilute HOD in H(2)O). The anisotropy decay displays a sharp drop at very short times caused by inertial orientational motion, followed by a much slower decay that fully randomizes the orientation. Investigation of temperatures from 1 degrees C to 65 degrees C shows that the amplitude of the inertial component (extent of inertial angular displacement) depends strongly on the stretching frequency of the OD oscillator at higher temperatures, although the slow component is frequency-independent. The inertial component becomes frequency-independent at low temperatures. At high temperatures there is a correlation between the amplitude of the inertial decay and the strength of the O-D O hydrogen bond, but at low temperatures the correlation disappears, showing that a single hydrogen bond (OD O) is no longer a significant determinant of the inertial angular motion. It is suggested that the loss of correlation at lower temperatures is caused by the increased importance of collective effects of the extended hydrogen bonding network. By using a new harmonic cone model, the experimentally measured amplitudes of the inertial decays yield estimates of the characteristic frequencies of the intermolecular angular potential for various strengths of hydrogen bonds. The frequencies are in the range of approximately 400 cm(-1). A comparison with recent molecular dynamics simulations employing the simple point charge-extended water model at room temperature shows that the simulations qualitatively reflect the correlation between the inertial decay and the OD stretching frequency.

Anharmonicity of water stretching vibrations in series of isomorphous crystalline hydrates: Copper and manganese saccharinates hexahydrates

On the basis of the experimentally obtained frequencies of isotopically isolated OH and OD species, the anharmonicity constants, as well as the harmonic eigenvalues of the OH and OD stretching vibrations for two members of the isomorphous series of metal(II) saccharinates hexahydrates (those of Mn and Cu) were calculated using several theoretical models [B. Berglund, J. Lindgren, J. Tegenfeldt, J. Mol. Struct. 43 (1978) 169, M.G. Sceats, S.A. Rice, J. Chem. Phys. 71 (1979) 973, H. Engstrom, J.B. Bates, L.A. Boatner, J. Chem. Phys. 73 (1980) 1073]. The anharmonicity constants and the ν(OH)/ ν(OD) isotopic ratios correlate well with the stretching frequencies of the isotopically isolated OH and OD oscillators. Both anharmonicity constants and isotopic ratios as criteria for the anharmonicity of the OH (OD) vibrations show that, with a very few exceptions, it increases with the increase in the hydrogen bond strength. The exceptions from the trend are explained in terms of local electrostatic field differences and force constant changes due to the coordination to the metal ion. The obtained regression equations were used to predict the anharmonicity constants of the ν(OD) modes in other members of the series. Within the three-particle model of the hydrogen bonded complex, the parameters characterising the coupling of the ν(OH)/ ν(OD)/modes with the low-frequency ν(O⋯O) ones were estimated. The positions of the overtones of OH and OD stretching vibrations in the compounds of copper and manganese were estimated using the calculated anharmonicity parameters. The predicted values for the OD oscillators were compared with the experimentally obtained data. Model calculations of the described type are shown to be valuable in the assignment of the second-order transitions, especially in complex systems.

Infrared induced isomerizations of water polymers trapped in nitrogen matrix

In a first step mid-infrared spectra of water (H 2O and D 2O) doped rare gas (Ne, Ar) or nitrogen matrices have been reexamined with the purpose of analyzing the aggregation processes occurring on annealing. In rare gases there is a smooth evolution, the concentration in polymers increasing steadily whatever their size; in nitrogen dimers and probably trimers nearly totally vanish so that the spectra of large aggregates in the absorption domains of these small polymers are better observed. In a second step selective irradiation has been performed at absorption frequencies of free and bonded OH or OD oscillators. Significant spectral changes have been observed only in nitrogen matrices for the partially deuterated dimer and for polymers larger than the heptamer. For H/D mixed dimers, two isomerization processes are identified: a donor/acceptor exchange between the two partners and, for HDO acting as donor, a proton donor/deuteron donor exchange between the OH and OD bonds. For larger polymers of natural water an isomerization process is observed for one species characterized by absorptions at 3185 and 3133 cm −1 which is converted into several metastable species distinguishable by their behaviour upon temperature increase or large band infrared irradiation. For H/D mixed polymers proton donor/deuteron donor exchanges for the HDO partners are clearly identified after irradiation in the free OH and OD and in the bonded OH regions, leading to complicated coupling/decoupling effects within aggregates involving several equivalent OH(D) oscillators.

Anharmonicity of water stretching vibrations in series of isomorphous crystalline hydrates. II. Metal(II) saccharinates hexahydrates (metal(II)∈{Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd})

Using three theoretical models, the anharmonicity constants and the harmonic eigenvalues of the O–H and O–D stretching vibrations were calculated for several members of the isomorphous series of metal(II) saccharinates hexahydrates (those of Cr, Mn, Fe, Co, Ni, Cu, Zn and Cd), on the basis of the experimentally obtained (by FTIR spectroscopy) frequencies of isotopically isolated OH and OD species. With a very few exceptions, the anharmonicity of the νOH(OD) vibrations increases with the increase in the hydrogen bond strength. A good correlation was found to exist between the anharmonicity constants and the νOH(OD) frequencies. The positions of the νOH(OD) overtones were estimated using the calculated anharmonicity parameters and the predicted values for the OD oscillators were compared with the experimentally obtained data.

Higher vibrational states of OH/OD in the bulk of congruent LiNbO3 and in proton/deuteron exchanged layers at the surface of LiNbO3

The fundamental vibrational transition nu 01 of the higher vibrational transitions nu 02, nu 03 and nu 04 and the OH and the OD oscillator in the bulk of congruent LiNbO3 and in proton/deuteron exchanged LiNbO3:PE/DE surface layers are investigated with respect to their spectroscopic properties and their temperature dependence. All observed vibrational transitions are completely polarized perpendicular with respect to the ferroelectric z direction. The spectral positions of the vibrational transitions follow closely a Morse type potential with De=4.75 eV and a=22.23 nm-1 ( omega e,OH=3684 cm-1 and Omega exe,OH=88.5 cm-1 for LiNbO3:PE). No hint of possible hydrogen bonding was found. The integrated absorption intensity ratios of the higher vibrational transitions exhibit the existence of an electrical anharmonicity, i.e. a non-linearity of the dipole moment versus O-H separation. The electrical anharmonicity reveals a noticeable temperature dependence whereas the vibrational transition energies and therefore the mechanical anharmonicity shows no temperature dependence in the range from room temperature to liquid helium temperature.

Crystallization kinetics of water below 150 K

Metastable liquid water, obtained by heating its hyperquenched glassy state above its glass→liquid transition temperature, crystallizes to cubic ice. Kinetics of this crystallization has been studied by Fourier transform infrared spectroscopy by determining the change in the spectra of stretching vibrations of the decoupled OD oscillator in 3.6 mole % HOD in H2O. The crystallization kinetics follows the equation x=[1−exp(−ktn)] and is diffusion controlled. Annealing at a temperature below its glass→liquid transition temperature alters this kinetics as the grain–growth process begins to control the early stages of crystallization.

Raman spectroscopic study of dilute HOD in liquid H2O in the temperature range − 31.5 to 160 °C

We present Raman data for the OD stretch mode of 10 mol % HOD in H2O for the liquid phase from −31.5 to 160 °C. We find that an exact isosbestic does not hold, but rather the crossing of isotherms slowly but uniformly changes with temperature. We present an analysis based on Boltzmann statistics which gives evidence for a distribution of deuterium hydrogen bond strengths with minimum energy near the frequency (2440 cm−1) also found in the solid ice and amorphous solid phases. This analysis also gives evidence for a band of frequencies above 2630 cm−1 due to OD oscillators all at essentially the same high energy relative to the strongest hydrogen bonds, and we interpret this band as due to broken hydrogen bonds. This allows us to calculate hydrogen bond probabilities, and we find this probability increases with decreasing temperature and approaches a value equal to the four bonded percolation threshold near the singular temperature Ts ≂−45 °C for the anomalies of supercooled water. Peak frequency and full width at half-maximum of the OD stretch band are found to drop precipitously to the amorphous solid values as T→Ts implying the ultimate state of supercooled water is similar to the amorphous solid.

Determination of the intrinsic network defect density in liquid water

Collective OH stretching motions in liquid water are shown to be disrupted by network defects in the form of weak hydrogen bonds and mass defects in the form of introduced OD oscillators. The equivalence of these defects is demonstrated, and the network defect density deduced as a function of temperature at 1 atm.

Intermolecular coupling in HOD solutions

Intermolecular coupling of OD oscillators from HOD in H2O has been investigated by Raman spectroscopy. The data indicate that at concentrations of HOD greater than 10 mol % the effects of intermolecular coupling of OD ⋅⋅⋅ OD pairs become noticeable. Difference spectra show a characteristic derivativelike feature with an increase of intensity around 2400 cm−1 as intermolecular coupling increases. The peak frequency of the OD stretching vibration in HOD decreases from 2525 cm−1 at infinite dilution to 2500 cm−1 in 50 mol % HOD, while the width of the OD stretching band increases from 150 cm−1 (infinite dilution) to 178 cm−1 (50 mol % HOD). Depolarization measurement indicates that the band at ∼2500 cm−1 is polarized. By comparing these difference spectra with the spectrum of OD oscillators from D2O we suggest that the major features of the D2O spectrum in the liquid state can be obtained by considering intermolecular coupling of OD oscillators.

Intermolecular coupling in liquid water

Changes in the Raman spectra of H2O from addition of OD oscillators indicate that there is significant intermolecular coupling of OH stretching vibrations in H2O at temperatures from −10 to 70°C. Measurements on solutions of KI in H2O indicate that the primary effect of salt addition on the spectrum of H2O is to diminish intermolecular coupling of OH oscillators. The disruption of intermolecular coupling by addition of a K+ and I− ion is about nine times more effective than addition of a single OD oscillator.

Raman intensities of the uncoupled OD oscillators in liquid water

Raman data were obtained for both polarizations of the OD stretching vibration of HDO in solutions containing different amounts of D2O(1–10 mole%) in H2O in order to assess the extent to which interand intramolecular couplings might perturb the OD stretching vibrations of HDO. The results were extrapolated to infinite dilution and the extrapolations are presented as the relative molar intensities for the uncoupled OD vibrations in liquid water. As the amount of D2O in each solution was increased noticeable, regular shifts in the frequency of the peak intensities and the bandwidths of the OD spectral band were observed. Although these shifts are small, apparently the presence of D2O and the effects due to coupled OD oscillators still make measurable perturbations to the OD vibrations for solutions containing as little as 1 mole% D2O. Consistent depolarization ratios were also obtained which clearly demonstrate that the value of this ratio is not constant across the OD stretching region. In addition functional fits to the spectral band data were made and their results are presented.

Line Shape of the OD Absorption in the Infrared Spectrum of Partially Deuterated Water

SHARP OH bands have recently been reported in partially deuterated solid alcohols which have been attributed to the absence of intermolecular coupling1. We wish to call attention to the remarkable change in band shape for the uncoupled OD oscillator of HDO in H2O on freezing. We have measured the infrared absorption of the OD band near 2,500 cm−1 in dilute solutions of D2O in H2O in conditions where the wings of the band can be observed for at least 250 cm−1 on either side of the absorption maximum. The spectra were digitally recorded and band shapes subjected to numerical analysis. The OD band of ice is sharp (31 cm−1 wide at half-peak height) and Lorentzian for at least twelve half-widths and exhibits no asymmetry in this range. With melting, the band broadens (half-width of 150 cm−1) and is Gaussian in shape for two half-widths. At 4° C no asymmetry is seen; however, at higher temperatures asymmetry appears on the low frequency side of the band. Our high temperature data appear to be in good agreement with those of Falk and Ford2.