Vibrations Of H2O Research Articles

Improved photoluminescence of di, tri, and tetra-aminobenzene molecules hydrogen-bonded by polyethyleneimine and their application for metal ion sensing

Higher photoluminescence quantum yield (PLQY) is always a required property for fluorescent molecule dyes used as probes in aqueous environment because of non-radiative relaxation via O–H vibrations. 1,2,4-triaminobenzene (TriAB) dihydrochloride has been reported as a red-emitting fluorescent dye, although its photoluminescence (PL) intensity is very low. Here, a bright orange-emitting fluorophore was prepared by simply mixing TriAB and polyethyleneimine (PEI) in water at pH 7 and applied to metal ion sensing. The PLQY was increased from 3.1 % to 10.0 % by the addition of PEI into an aqueous TriAB solution. Our experiments by exchanging H2O for D2O and changing the pH from 7 to 1 revealed that the role of PEI in enhancing the PL intensity is attributed to the interaction between the amino groups of TriAB and PEI via hydrogen bonding, the prevention of contact between TriAB and water molecules, and thus the suppression of the non-radiative relaxation via O–H vibrations of H2O. We further demonstrated this role for 1,4-diaminobenzene and 1,2,4,5-tetraaminobenzene.

Vibrational Mode-Specific Dynamics of the OH + C2H6 Reaction.

We investigate the effects of the initial vibrational excitations on the dynamics of the OH + C2H6 → H2O + C2H5 reaction using the quasi-classical trajectory method and a full-dimensional analytical ab initio potential energy surface. Excitation of the initial CH, CC, and OH stretching modes enhances, slightly inhibits, and does not affect the reactivity, respectively. Translational energy activates the early-barrier title reaction more efficiently than OH and CC stretching excitations, in accord with the Polanyi rules whereas CH stretching modes have similar or higher efficacy than translation, showing that these rules are not always valid in polyatomic processes. Scattering angle, initial attack angle, and product translational energy distributions show the dominance of direct stripping with increasing collision energy, side-on OH and isotropic C2H6 attack preferences, and substantial reactant-product translational energy transfer without any significant mode specificity. The reactant vibrational excitation energy of OH and C2H6 flows into the H2O and C2H5 product vibrations, respectively, whereas product rotations are not affected. The computed mode-specific H2O vibrational distributions show that initial OH excitation appears in the asymmetric stretching vibration of the H2O product and allow comparison with experiments.

Regulation of O–H and O–O stimulated Raman scattering peaks in H2O–H2O2 solution by excess electrons

Stimulated Raman scattering (SRS) not only expands the spectral range of stimulated emission but also presents a way to delve into the intricate microscopic dynamics of matter. In this manuscript, SRS of O–O and O–H stretching vibrations in H2O–H2O2 solution is measured using 532 nm Nd:YAG laser. SRS peak intensities of O–O and O–H stretches are observed to engage in a competitive process, depending on the coupling direction of the excess electrons, which is determined by the recombination rate of H2O2 and H2O under laser-induced breakdown. Notably, a high-order (fifth order) SRS peak originating from H2O2 is detected, attributable to the Raman-active enhancement caused by surplus electrons and the amplification of vibration energy resulting from shockwaves. This experiment holds potential for advancing multi-wavelength selective regulation in terms of its contributions.

Thaumasite in calcic skarns from the Zvezdel-Pcheloyad Pb-Zn deposit, Eastern Rhodopes, Bulgaria

Thaumasite was found in zoned calcic skarns hosted by the monzonitic rocks of the Zvezdel pluton, Eastern Rhodopes. Associated minerals are wollastonite, clinopyroxene, grossular-andradite garnets, Ti-rich garnets, plagioclase, calcite, quartz, epidote, prehnite, and chlorite. Titanite, apatite and magnetite are present as accessories. The mineral has been characterized using optical microscopy, PXRD, SEM/EDS, EPMA, and FTIR. Thaumasite forms sheaf-like and fan-shaped aggregates, which consist of acicular crystals elongated along the c axis. The IR spectrum of thaumasite is in accordance with the chemical composition and contains absorption bands in the range 3500–3291 cm–1 (O–H stretching vibrations); 1683, 1650 cm–1 (bending vibrations of H2O); 1389 cm–1 (stretching vibrations of CO32–); 1100, 1069 cm–1 (asymmetric stretching vibrations of SO42–); 882 cm–1 (symmetric bending vibration of CO32–); 768, 742, 680 cm–1 (Si–O stretching vibrations of Si(OH)6 octahedra); 670 cm–1 (bending vibrations of SO42–).

Thermal behavior of natural stellerite: high-temperature X-ray powder diffraction and IR spectroscopy study.

The thermal behavior of stellerite from the Savinskoye deposit (Transbaikalia, Russia), Ca7.69Na0.25K0.06(Si56.24Al15.76)O144·53.39H2O, was investigated by in situ high-temperature X-ray powder diffraction (HTXRPD) and ex situ HT infrared (IR) spectroscopic analysis. Four different HTXRPD experimental procedures were used to study the thermal behavior of the powder samples: (1) RT-750°C, (2) RT-220°C -RT, (3) 200-350-RT °C, and (4) 350-700°C. Electron probe microanalysis and single-crystal X-ray diffraction were preliminary used to determine the chemical composition and crystal structure of stellerite. The A → B phase transition (Fmmm → Amma) starts at ∼110°C and is completed at about 140°C (in situ HTXRPD) and 200°C (ex situ HTIR) depending on the experimental conditions. It involves a cell volume decrease of 5.8% (Experiment 1). The thermal expansion of stellerite is more pronounced along the b and c axes, with αa: αb: αc (× 10-5) = 2.50:-25.52:-6.84 at 100°C, 0.44:-21.75:-25.64 at 150°C after the completion of the phase transition, and 3.06:-1.86:-16.94 at 500°C. The reverse B → A transition occurs at temperatures below 100°C during slow cooling (Experiment 2), however, it does not occur upon rapid cooling (Experiment 3). The B → D phase transition above 300°C is not observed (Experiment 4). The temperature barrier of phase transition in the ex situ HTIR spectroscopy experiment is shifted towards high temperatures. The heating above 200°C leads to an increase of 3430cm-1 and a decrease of 3600 and 3260cm-1 bands, which correspond to the stretching vibration of H2O. The heating above 400°C causes complete dehydration of the stellerite.

Isotope Effects in the Spectra of Hydrogen-Bonded Complexes. Calculation of the Structure and Vibrational Absorption Spectra of the H-=SUB=-2-=/SUB=-O...HF, H-=SUB=-2-=/SUB=-O...DF, D-=SUB=-2-=/SUB=-O...HF, and D-=SUB=-2-=/SUB=-O...DF Complexes

The frequencies and intensities of IR absorption bands of the H2O...HF, H2O...DF, D2O...HF, and D2O...DF hydrogen-bonded complexes are calculated using the second-order vibrational perturbation theory. The MP2/aug-cc-pVTZ method with the basis set superposition error taken into account is used to calculate the electronic wave functions in determining the equilibrium configuration, the potential energy and dipole moment surfaces of these complexes, as well as in calculating spectral parameters. It is shown that upon complexation the frequencies and intensities of the stretching vibration of HF (DF) molecules and the intensities of stretching vibrations of H2O (D2O) molecules change most significantly. A variational calculation of librational motion of the water molecule in the two-well potential explained the reason for the higher value of the fundamental transition frequency of the ν1(H-F) mode as compared to the frequency of this mode upon hot transition from the first excited librational state. The dependence of the intermode anharmonic interaction on isotope substitution was analyzed. Keywords: hydrogen bond, calculations of spectra of molecular complexes, anharmonic interactions, isotope effects.

Synergistic Coupling of CO2 and H2O during Expansion of Clays in Supercritical CO2-CH4 Fluid Mixtures.

We used IR and XRD, with supporting theoretical calculations, to investigate the swelling behavior of Na+-, NH4+-, and Cs+-montmorillonites (SWy-2) in supercritical fluid mixtures of H2O, CO2, and CH4. Building on our prior work with Na-clay that demonstrated that H2O facilitated CO2 intercalation at relatively low RH, here we show that increasing CO2/CH4 ratios promote H2O intercalation and swelling of the Na-clay at progressively lower RH. In contrast to the Na-clay, CO2 intercalated and expanded the Cs-clay even in the absence of H2O, while increasing fluid CO2/CH4 ratios inhibited H2O intercalation. The NH4-clay displayed intermediate behavior. By comparing changes in the HOH bending vibration of H2O intercalated in the Cs-, NH4-, and Na-clays, we posit that CO2 facilitated expansion of the Na-clay by participating in outer-sphere solvation of Na+ and by disrupting the H-bond network of intercalated H2O. In no case did the pure CH4 fluid induce expansion. Our experimental data can benchmark modeling studies aimed at predicting clay expansion in humidified fluids with varying ratios of CO2 and CH4 in real reservoir systems with implications for enhanced hydrocarbon recovery and CO2 storage in subsurface environments.

Influence of Hydrogen Bond and Sodium Alginate on Bovine Serum Albumin Adhesion on ZnSe Surface

Serum albumin is the most abundant protein in mammalian plasma and is often used as a model to understand the adhesion behavior of proteins on surfaces. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) is used to non-destructively and dynamically detect the chemical change information between the protein and the surface during the adhesion process, which is especially suitable for in-situ measurement of samples in water. Therefore, the adhesion of bovine serum albumin (BSA) on the surface in H2O and D2O is investigated by ATR-FTIR technology, which effectively avoids the interference of the characteristic peak of deformation vibration of liquid H2O (1645 cm−1) on the amide I band of BSA. Sodium alginate, a polysaccharide widely present in the ocean, is introduced into the BSA solution to explore the changes in the adhesion process of proteins on the surface of ZnSe, and polarized ATR-FTIR spectra are also collected to study the adhesion orientation of BSA. Sodium alginate presents a negative effect on the adhesion of BSA on the surface and there is no specific orientation of BSA on the surface.

Hydroxyplumbopyrochlore, (Pb1.5,□0.5)Nb2O6(OH), a new member of the pyrochlore group from Jabal Sayid, Saudi Arabia

ABSTRACTA new mineral species of the pyrochlore supergroup, hydroxyplumbopyrochlore (IMA2018-145), (Pb1.5,□0.5)Nb2O6(OH), has been discovered in the Jabal Sayid peralkaline granitic complex of the Arabian Shield, Saudi Arabia. It is associated with quartz, microcline, ‘biotite’, rutile, zircon, calcite, rhodochrosite, columbite-(Fe), goethite, thorite, bastnäsite-(Ce), xenotime-(Y), samarskite-(Y), euxenite-(Y), hydropyrochlore and fluornatropyrochlore. Hydroxyplumbopyrochlore usually shows euhedral octahedra, slightly rhombic dodecahedra and cubes or their combination (0.01–0.06 mm). The mineral is pale yellow to pale brown, transparent with white streak, and has adamantine to transparent lustre. It is brittle with conchoidal fracture. No cleavage or parting are observed. It is isotropic and non-fluorescent. The average microhardness is 463.4 kg mm–2. The calculated density is 6.474 g cm–3.Hydroxyplumbopyrochlore belongs to the cubic crystal system and exhibits the space group Fd$\bar{3}$m with unit-cell parameters a = 10.5456(6) Å, V = 1172.8(2) Å3 and Z = 8. Electron microprobe analysis gave (6-point average composition, wt.%): CaO 0.32, SrO 0.16, FeO 0.17, Ce2O3 0.07, Pr2O3 0.02, PbO 51.69, Nb2O5 40.06, SiO2 0.05, TiO2 1.68, Ta2O5 4.74, H2Ocalc 0.95, total 99.90, yielding the empirical formula (Pb1.34Ca0.03Fe0.01Sr0.01□0.61)Σ2(Nb1.75Ti0.12Ta0.12Si0.01)Σ2O6(OH0.53O0.08□0.39)Σ1, where □ = vacancy. The Raman spectrum of hydroxyplumbopyrochlore contains the characteristic bands of O–H vibrations and no bands for H2O vibrations.

Raman characteristics of Alpine–Himalayan serpentine polymorphs: A case study of Khankuie ultramafic complex, southeast of Iran

Chrysotile, antigorite, and lizardite were analyzed to determine their chemical and structural properties as a function of Raman spectral patterns. Serpentine polymorph discrimination is a challenging issue as each polymorph represents different crystal structure and different thermodynamic phase situation of formation. Microtextural investigation, SEM (Scanning Electron Microscope), XRD (X-Ray Diffraction), and EMPA (Electron Microprobe Analysis) illustrate that there are some chemical and structural variations between our studied serpentine polymorphs. In the case of the three strongest Raman peaks at around 230, 390 and 690 cm−1, we obtained that antigorite tends to lower Raman Stoke lines, lizardite to moderate wavenumbers and the highest Raman Stoke lines belong to chrysotile. These main bands with principal peaks were used to find special spectral peak patterns of each polymorph, along with some other ‘weak’ peaks (around 350, 520, and 620 cm−1) with different behaviours. When Raman Stoke line shifts were plotted against each other, we reached to 25 scatter plots with different classified validation. The best 2d scatter discrimination diagrams are those of 230–390 cm−1 and 350–390 cm−1 with the overall accuracy rate of 94% and 98%, respectively. Also, there are proportional relations between chemical band vibrations of SiO4, MgO, and H2O, and Raman Stoke lines of 390, 620 and 230 cm−1, respectively. This information increases our ability to predict polymorph types and geochemical trends of serpentine group minerals just using the Raman spectra.

Lanthanide-DNA probe for spectrofluorimetric determination of some 6-fluoroquinolones in eye-ear pharmaceutical preparations

A sensitive, accurate and precise spectrofluorimetric method was established for the quantification of ciprofloxacin HCl and norfloxacin drugs. The spectrofluorimetric method has involved the development of a ternary complex between the investigated drugs and Tb3+ in presence of Calf thymus DNA which was used as a fluorescence enhancing agent causing reduction in the non-radiative energy loss produced by OH vibration of H2O in the original Tb3+–drug complex. Thus, the fluorescence of the system (Tb3+–drug–DNA) at ʎem of 545 nm for ʎex of 272 nm was enhanced. Investigation of all the conditions that could affect the reaction as well as the formed complexes' spectral properties was performed. Upon utilization of the optimum reaction conditions; the spectrofluorimetric method was highly sensitive and showed linearity over the concentration range of 40–700 ng/mL for both ciprofloxacin and norfloxacin with a correlation coefficient of 0.9998 and 0.9997, respectively. The limit of detection was 12.56 ng/mL and 11.44 ng/mL, while the limit of quantification was 38.06 ng/mL and 34.66 ng/mL for ciprofloxacin and norfloxacin, respectively. The developed method was effectively utilized for the estimation of the studied drugs in eye-ear pharmaceutical dosage forms. The achieved results were compared statistically with those of the pharmacopoeial method where no significant difference was perceived concerning both accuracy and precision.

The universal characteristic water content of aqueous solutions**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474325, 11474335, and 51172272), the Fund from the Chinese Academy of Sciences (Grant No. 1731300500030), and the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB07030100).

Raman measurements at room temperature reveal a characteristic concentration for a series of aqueous solutions of electrolytes, through which O–H stretching vibration of H2O or dilute HDO obviously changes their concentration dependence. This characteristic concentration is very consistent with another, through which the solutions undergo an abrupt change in their glass-forming ability. Interestingly, the molar ratio of water to solute at these two consistent concentration points is almost solute-type independent and about twice the hydration number of solutes. We suggest that just when the concentration increases above this characteristic concentration, bulk-like free water disappears in aqueous solutions and all water molecules among closely-packed hydrated solutes exhibit the characteristics of confined water.

Hydroxynatropyrochlore, (Na,Сa,Ce)2Nb2O6(OH), a new member of the pyrochlore group from the Kovdor phoscorite–carbonatite pipe, Kola Peninsula, Russia

AbstractHydroxynatropyrochlore, (Na,Сa,Ce)2Nb2O6(OH), is a new Na–Nb–OH-dominant member of the pyrochlore supergroup from the Kovdor phoscorite–carbonatite pipe, Kola Peninsula, Russia. It is cubic, Fd$\bar{3}$m, a = 10.3211(3) Å, V = 1099.46(8) Å3 and Z = 8 (from powder diffraction data) or a = 10.3276(5) Å, V = 1101.5(2) Å3 and Z = 8 (from single-crystal diffraction data). Hydroxynatropyrochlore is a characteristic accessory mineral of the low-carbonate phoscorite in the contact zone of the phoscorite–carbonatite pipe with host foidolite as well as in the carbonate-rich phoscorite and carbonatite of the pipe axial zone. It usually forms zonal cubic or cubooctahedral crystals (up to 0.5 mm in diameter) with irregularly shaped relics of amorphous U–Ta-rich hydroxykenopyrochlore inside. Characteristic associated minerals include rock-forming calcite, dolomite, forsterite, hydroxylapatite, magnetite and phlogopite, accessory baddeleyite, baryte, barytocalcite, chalcopyrite, chamosite–clinochlore, galena, gladiusite, juonniite, ilmenite, magnesite, pyrite, pyrrhotite, quintinite, spinel, strontianite, valleriite and zirconolite. Hydroxynatropyrochlore is pale brown, with an adamantine to greasy lustre and a white streak. The cleavage is average on {111} and the fracture is conchoidal. Mohs hardness is ~5. In transmitted light, the mineral is light brown, isotropic and n = 2.10(5) (λ = 589 nm). The calculated and measured densities are 4.77 and 4.60(5) g cm−3, respectively. The mean chemical composition determined by electron microprobe is: F 0.05, Na2O 7.97, CaO 10.38, TiO2 4.71, FeO 0.42, Nb2O5 56.44, Ce2O3 3.56, Ta2O5 4.73, ThO2 5.73, UO2 3.66, total 97.65 wt.%. The empirical formula calculated on the basis of Nb + Ta + Ti = 2 apfu is (Na1.02Ca0.73Ce0.09Th0.09 U0.05${\rm Fe}_{{\rm 0}{\rm. 02}}^{2 +} $)Σ2.00(Nb1.68Ti0.23Ta0.09)Σ2.00O6.03(OH1.04F0.01)Σ1.05. The simplified formula is (Na,Ca,Ce)2Nb2O6(OH). The mineral dissolves slowly in hot HCl. The strongest X-ray powder-diffraction lines [listed as (d in Å)(I)(hkl)] are as follows: 5.96(47)(111), 3.110(30)(311), 2.580(100)(222), 2.368(19)(400), 1.9875(6)(333), 1.8257(25)(440) and 1.5561(14)(622). The crystal structure of hydroxynatropyrochlore was refined to R1 = 0.026 on the basis of 80 unique observed reflections. The mineral belongs to the pyrochlore structure type A2B2O6Y1 with octahedral framework of corner-sharing BO6 octahedra with A cations and OH groups in the interstices. The Raman spectrum of hydroxynatropyrochlore contains characteristic bands of the lattice, BO6, B–O and O–H vibrations and no characteristic bands of the H2O vibrations. Within the Kovdor phoscorite–carbonatite pipe, hydroxynatropyrochlore is the latest hydrothermal mineral of the pyrochlore supergroup, which forms external rims around grains of earlier U-rich hydroxykenopyrochlore and separated crystals in voids of dolomite carbonatite veins. The mineral is named in accordance with the pyrochlore supergroup nomenclature.

Delocalization and stretch-bend mixing of the HOH bend in liquid water.

Liquid water's rich sub-picosecond vibrational dynamics arise from the interplay of different high- and low-frequency modes evolving in a strong yet fluctuating hydrogen bond network. Recent studies of the OH stretching excitations of H2O indicate that they are delocalized over several molecules, raising questions about whether the bending vibrations are similarly delocalized. In this paper, we take advantage of an improved 50 fs time-resolution and broadband infrared (IR) spectroscopy to interrogate the 2D IR lineshape and spectral dynamics of the HOH bending vibration of liquid H2O. Indications of strong bend-stretch coupling are observed in early time 2D IR spectra through a broad excited state absorption that extends from 1500 cm-1 to beyond 1900 cm-1, which corresponds to transitions from the bend to the bend overtone and OH stretching band between 3150 and 3550 cm-1. Pump-probe measurements reveal a fast 180 fs vibrational relaxation time, which results in a hot-ground state spectrum that is the same as observed for water IR excitation at any other frequency. The fastest dynamical time scale is 80 fs for the polarization anisotropy decay, providing evidence for the delocalized or excitonic character of the bend. Normal mode analysis conducted on water clusters extracted from molecular dynamics simulations corroborate significant stretch-bend mixing and indicate delocalization of δHOH on 2-7 water molecules.

An Empirical Study on Raman Peak Fitting and Its Application to Raman Quantitative Research.

Fitting experimentally measured Raman bands with theoretical model profiles is the basic operation for numerical determination of Raman peak parameters. In order to investigate the effects of peak modeling using various algorithms on peak fitting results, the representative Raman bands of mineral crystals, glass, fluids as well as the emission lines from a fluorescent lamp, some of which were measured under ambient light whereas others under elevated pressure and temperature conditions, were fitted using Gaussian, Lorentzian, Gaussian-Lorentzian, Voigtian, Pearson type IV, and beta profiles. From the fitting results of the Raman bands investigated in this study, the fitted peak position, intensity, area and full width at half-maximum (FWHM) values of the measured Raman bands can vary significantly depending upon which peak profile function is used in the fitting, and the most appropriate fitting profile should be selected depending upon the nature of the Raman bands. Specifically, the symmetric Raman bands of mineral crystals and non-aqueous fluids are best fit using Gaussian-Lorentzian or Voigtian profiles, whereas the asymmetric Raman bands are best fit using Pearson type IV profiles. The asymmetric O-H stretching vibrations of H2O and the Raman bands of soda-lime glass are best fit using several Gaussian profiles, whereas the emission lines from a florescent light are best fit using beta profiles. Multiple peaks that are not clearly separated can be fit simultaneously, provided the residuals in the fitting of one peak will not affect the fitting of the remaining peaks to a significant degree. Once the resolution of the Raman spectrometer has been properly accounted for, our findings show that the precision in peak position and intensity can be improved significantly by fitting the measured Raman peaks with appropriate profiles. Nevertheless, significant errors in peak position and intensity were still observed in the results from fitting of weak and wide Raman bands having unnormalized intensity/FWHM ratios lower than 200 counts/cm-1.

Optical character enrichment of NdF3 – doped lithium fluoroborate glasses

Optical spectra in combination with Fourier transform infrared FTIR spectra of base undoped lithium fluoroborate glasses and samples that doped with NdF3 were measured before and after subjecting to (8Mrad) gamma irradiation. Base glass reveals strong absorption in the UV region attributed to unavoidable iron impurity (Fe3+ ions) while gamma irradiated sample shows extended additional peaks related to the photochemical reactions of some Fe2+ impurities transformed to Fe3+ ions by acquiescent positive holes while the induced visible band is related to (BOHC) boron oxygen hole center or (NBOHC) nonbridging oxygen hole center. The NdF3-doped samples display the same strong UV spectra as the undoped sample beside additional characteristic visible absorption peaks due to the presence of Nd3+ ions. UV–Vis. absorption spectra were applied to assess their optical properties, comprising indirect and direct optical energy band gaps taking into account the effect of gamma irradiation. Infrared absorption spectra of the undoped lithium fluoroborate glass reveal characteristic IR bands due to both BO3 and BO4 borate groups as usually observed in various alkali–oxide B2O3 glasses. Suggested BO3F tetrahedral units are advanced to interpret the close similarity of the IR spectra obtained from fluoroborate glass with alkali or alkaline earth oxide borate glasses. The increase of NdF3 content causes minor changes in the IR spectra that can be attributed to the non-conventional loose OH, H2O or similar vibrations while the structural building borate units remain unchanged as evidence from the deconvoluted FTIR data before and after the irradiation process.

Structural and optical characterization and efficacy of hydrothermal synthesized Cu and Ag doped zinc oxide nanoplate bactericides

This study reports on a novel synthesis of pure zinc oxide and both Cu and Ag doped ZnO nanoplates using a simple and low-cost hydrothermal method. The structural and optical properties of the nanoplates were quantified and the materials were tested for antibacterial activity. X-ray diffraction revealed the formation of the wurtzite phase of ZnO and scanning and transmission electron microscopy showed the formation of randomly oriented ZnO nanoplates, having a thickness less than 80 nm and diameter less than 350 nm. The elemental analyses of both the pure and doped samples were evaluated by energy dispersive X-ray spectrometry. The FTIR spectra of ZnO nanomaterials showed the predictable bands at 3385 cm−1 (OH stretching), 1637 cm−1 (stretching vibration of H2O), 400 cm−1–570 cm−1 (MO stretching). The as synthesized samples showed a strong absorption peak in the UV region (∼376 nm) and a near band edge emission at 392 nm with some defect peaks in the visible region. From the XPS spectra the oxidation states of Zn, Cu and Ag were found to be +2, +2 and 0 respectively. Escherichia coli, Staphylococcus aureus and Salmonella typhi bacteria were used to evaluate the antibacterial activity of undoped and doped ZnO. Ag doped ZnO exhibited low minimum inhibitory concentration (MIC) values as 40 μg/ml for E. coli and S. aureus and 20 μg/ml for S. typhi, which are comparable to commercial antibiotics without optimization. Further, these chemically modified nanoparticles will be applicable in the development of medicine to control the spread and infection of a variety of bacterial strains.

Anharmonic exciton dynamics and energy dissipation in liquid water from two-dimensional infrared spectroscopy.

Water's extended hydrogen-bond network results in rich and complex dynamics on the sub-picosecond time scale. In this paper, we present a comprehensive analysis of the two-dimensional infrared (2D IR) spectrum of O-H stretching vibrations in liquid H2O and their interactions with bending and intermolecular vibrations. By exploring the dependence of the spectrum on waiting time, temperature, and laser polarization, we refine our molecular picture of water's complex ultrafast dynamics. The spectral evolution following excitation of the O-H stretching resonance reveals vibrational dynamics on the 50-300 fs time scale that are dominated by intermolecular delocalization. These O-H stretch excitons are a result of the anharmonicity of the nuclear potential energy surface that arises from the hydrogen-bonding interaction. The extent of O-H stretching excitons is characterized through 2D depolarization measurements that show spectrally dependent delocalization in agreement with theoretical predictions. Furthermore, we show that these dynamics are insensitive to temperature, indicating that the exciton dynamics alone set the important time scales in the system. Finally, we study the evolution of the O-H stretching mode, which shows highly non-adiabatic dynamics suggestive of vibrational conical intersections. We argue that the so-called heating, commonly observed within ∼1 ps in nonlinear IR spectroscopy of water, is a nonequilibrium state better described by a kinetic temperature rather than a Boltzmann distribution. Our conclusions imply that the collective nature of water vibrations should be considered in describing aqueous solvation.

(Invited) First-Principles Simulations of Electrochemical Reactions and Properties at Water|Pt Interfaces

A first step for understanding the electrochemical reactions from fundamental point of view is ab-initio calculations to find the reaction path and the energy profile along the reaction cooprdinate. More reliable and more realistic way including solvent, temperature, electrolyte, electrode interface, etc., is to use first-principles molecular dynamics. A pioneer work in this direction is that by Ishiwaka and co-workers [1]. They used a cluster Pt with water molecules. They followed the first step of the hydrogen evolution, i.e. H adsorption on Pt. They controlled the electrode potential by changing the number of electrons in the system. We used the slab model under the periodic boundary conditions [2]. Electrode potential was controlled by using the effective screening medium (ESM) [3] separated from the water layer on Pt with a vacuum layer. Hydrogen adsorption from H3O+was observed with a charge transfer between Pt layer and the hydronium ion. Water structure on Pt is important properties to understand fuel cell reactions and H2/O2 evolution from water by electrochemical reactions [6-11]. H-down adsorption structure of water molecules with well-developed hydrogen network with H3O+ was observed on Pt(111) surface. O-H stretching vibrations of H2O on Pt was in a function of the electrode potential. Specific adsorption on Pt electrode is also an important factor in the electrochemical reaction on it. SO4 2– and HSO4 –adsorptions were observed on the potential controlled Pt [12,13]. Vibration properties of adsorbed (bi)sulfate on the Pt(111) surface were obtained by FPMD with the cluster and slab models. Our work shown here has been performed with collaboration among M. Otani (AIST), I. Hamada (NIMS), O. Sugino (Univ. Tokyo), Y. Morikawa (Osaka Univ.), Y. Okamoto (NEC), and Y. Qian (FC-Cubic). [1] Y. Ishikawa, J. J. Mateo, D. A. Tryk, and C. R. Cabrera: J. Electroanal. Chem. 607, 37 (2007). [2] J. A. Santana, J. J. Mateo, and Y. Ishikawa, J. Electroanal. Chem. 607, 37 (2007). [3] M. Otani and O. Sugino, Phys. Rev. B 73, 115407 (2006). [4] O. Sugino, I. Hamada, M. Otani, Y. Morikawa, T. Ikeshoji, and Y. Okamoto, Surf. Sci. 601, 5237 (2007). [5] M. Otani, I. Hamada, O. Sugino, Y. Morikawa, Y. Okamoto, and T. Ikeshoji, J. Phys. Soc. Jpn. 77, 024802 (2008). [6] Y. Ishikawa, J. J. Mateo, D. A. Tryk, and C. R. Cabrera, J. Phys. Chem. C 114, 4995–5002 (2010). [7] J. A. Santana, C. R. Cabrera, Y. Ishikawa, Phys. Chem. Chem. Phys. 12, 9526 – 9534 (2010). [8] M. Otani, I. Hamada, O. Sugino, Y. Morikawa, Y. Okamoto, and T. Ikeshoji Phys. Chem. Chem. Phys. 10, 3609- 3612 (2008). [9] T. Ikeshoji, M. Otani, I. Hamada, and Y. Okamoto, Phys. Chem. Chem. Phys., 13, 20223-20227 (2011). [10] T. Ikeshoji, M. Otani, I. Hamada, O. Sugino, Y. Morikawa, Y. Okamoto, Y. Qian, and I. Yagi, AIP Adv. 2, 032182 (2012). [11] Y. Qian, I. Hamada, M. Otani, and T. Ikeshoji, Catal. Today 202, 163-167 (2013). [12] J. A. Santana, C. R. Cabrera, Y. Ishikawa, Phys. Chem. Chem. Phys. 12, 9526 – 9534 (2010). [13] Y. Qian, T. Ikeshoji, Y. Zhao, and M. Otani, ChemElectroChem 1, 1632-1635 (2014).

Structure and Dynamics of Water—Smectite Interfaces: Hydrogen Bonding and the Origin of the Sharp O-Dw/O—Hw Infrared Band From Molecular Simulations

AbstractExperimental studies have shown that a sharp, high-frequency IR band at ~3615 cm-1 (in H2O form) and at ~2685 cm-1 (in D2O form) is a common feature for all smectites, and its position correlates with layer charge. In order to explain the molecular origin of this band in terms of total layer charge, charge localization, as well as nature of interlayer cations influencing the position and intensity of this peak, a series of classical molecular dynamics (MD) simulations was performed for several smectite models. The smectite layers were described using a modified CLAYFF force field, where the intramolecular vibrations of H2O were described more accurately by the Toukan-Rahman potential. The power spectra of molecular vibrations of hydrogens were calculated for selected sub-sets of interlayer H2O to analyze quantitatively their contribution to the observed spectral features. The statistics of hydrogen bonds in the smectite interlayers were also analyzed to support the spectral calculations.The simulation results demonstrated clearly that only the H2O molecules in close proximity to the smectite surface are responsible for the sharp vibrational band observed. Other hypotheses for the possible origins of this band were considered carefully and eventually rejected. Two orientations of H2O molecules donating one or two H bonds to the basal oxygens of the smectite surface (monodentate and bidentate orientations, respectively) were observed. In both orientations, these H bonds are quite weak, pointing to a generally hydrophobic character of the smectite surface. Both orientations contributed to the high-frequency band, but the monodentate orientation provided the predominant contribution because surface H2O molecules in this orientation were much more abundant. In good agreement with experiment, only a small difference in the peak position was observed between smectites with different charge localization. The effect of the total layer charge, i.e. the red-shift for higher-charge smectites, was also confirmed. This shift arose from the decrease in the H-bonding distances of H2O in monodentate and bidentate orientation.