Sorption of molybdate anions by a quasi-liquid film on the surface of dispersed ice

Molybdate anion sorption on the surface of dispersed ice in the presence of KCl as a background electrolyte is studied depending on the pH and temperature. The revealed dependences are interpreted in terms of the properties of a liquid-like film present on the surface of the ice.     

Spectroscopic and computational evidence for SO2 ionization on 128 K ice surface

The experimental part of this study focuses on FTIR spectroscopy of SO(2) adsorbate on the surface of ice nanoparticles at 128 K, in the 0.5-1 monolayer coverage range. In addition to the infrared spectroscopic features due to molecular SO(2), a structured band is observed at approximately 1030 cm(-1). A similar band was observed in past spectroscopic studies of SO(2) aqueous solutions, and assigned to anionic products of SO(2) ionization. Ab initio normal mode analysis of HSO(3)(-) yielded intense SO stretch bands in the vicinity of the observed "ionic" feature. The relative intensities of the molecular and the anionic bands indicate that 0.3 approximately 0.5 of the adsorbate is ionized. These results are consistent with the previously published data on isotopic exchange in SO(2)-covered ice nanoparticles (Devlin and Buch, J. Chem. Phys., 2007, 127, 091101) which pointed towards substantial SO(2) ionization at low temperatures. Density functional theory modeling of molecular and ionized adsorbate on a crystal ice slab suggests that anion solvation by molecular SO(2) adsorbate facilitates the SO(2) ionization process at the ice surface.     

Spectroscopic analysis of the tribological behavior of a model boundary layer lubricant

Highly ordered alkanethiol self-assembled monolayers (SAMs) on gold substrates are suitable models of boundary layer lubricants and may be used in actual nanoscale device applications. Here, such monolayers were studied by spectroscopic methods as a function of tribological wear (rubbing) using a pin-on-disk microtribometer. The coefficient of friction (COF) (ratio of the frictional force to the load) was measured with the tribometer, and reflectance infrared spectra and X-ray photoelectron spectra were obtained as the monolayer film failed and the COF changed. The results show that it is possible to correlate disorder in the monolayer film with tribological failure of the film, and that continued rubbing produces a chemical change in the monolayer film. Disorder in the monolayer is distinct from the influence of wear in the underlying gold substrate. Aged SAMs, having sulfonate rather than thiol headgroups and initially less well ordered, behave differently to the well-ordered freshly prepared SAMs. Interestingly, they show a lower COF over many more cycles of exposure to the rubbing pin. The impact of the mechanism of film failure in boundary layer lubrication is discussed.     

Spectroscopic study of harmane in micelles at 77 K using fluorescent probes

Steady-state and time-resolved emission for spectroscopic techniques at 77 K, and molecular orbital calculations using PM3-MOPAC/93 and HAM/3-CI have been used to study the two forms of harmane, the neutral (HN) and the monoprotonated (HH), in different environments. In hydrophobic media, for (HN), four species were determined and in hydrophilic medium, for (HH), we found just one species. The photophysical properties of all these species were determined, and we verified that each one of them displays distinct photophysical properties from one to another. For example, for monomer of (HN), the lowest electronic singlet state S₁ is (π,π^*) and the lowest electronic triplet state T₁ is (π,π^*), due to the phosphorescence lifetime it is t=0.8 s. For the (HH) monomer, the S₁ is (π,π^*) and T₁ is (π,π^*) and the spin–orbital coupling is inefficient. These determinations were used to characterise and to identify the harmane species that is solubilised into the interior of neutral (triton X-100), anionic (dodecyl lithium sulphate) and cationic (hexadecyltrimethyl ammonium bromide) micelles, all of them were prepared under physiological conditions. The results indicated that active species in the interior of the micelles is a hydrogen bond complex between (HN) and micellar environments that is anchored in the aqueous region of micelles.     

Spectroscopic evidence for hydrogen diffusion through a several-nanometers-thick titanium carbonitride layer on silicon

Multiple internal reflection Fourier transform infrared spectroscopy, together with other analytical techniques, was used to follow the diffusion of atomic hydrogen through a 10-nm-thick titanium carbonitride layer deposited onto a Si(100)-2x1 surface from tetrakis(dimethylamino)titanium as a chemical vapor deposition precursor. The recombinative desorption of hydrogen from the TiCN/Si interface was shown to coincide with the temperature range where most Ti-based diffusion barriers break down.     

The thickness of a liquid layer on the free surface of ice as obtained from computer simulation

Molecular dynamic simulations were performed for ice I(h) with a free surface by using four water models, SPC/E, TIP4P, TIP4P/Ice, and TIP4P/2005. The behavior of the basal plane, the primary prismatic plane, and of the secondary prismatic plane when exposed to vacuum was analyzed. We observe the formation of a thin liquid layer at the ice surface at temperatures below the melting point for all models and the three planes considered. For a given plane it was found that the thickness of a liquid layer was similar for different water models, when the comparison is made at the same undercooling with respect to the melting point of the model. The liquid layer thickness is found to increase with temperature. For a fixed temperature it was found that the thickness of the liquid layer decreases in the following order: the basal plane, the primary prismatic plane, and the secondary prismatic plane. For the TIP4P/Ice model, a model reproducing the experimental value of the melting temperature of ice, the first clear indication of the formation of a liquid layer, appears at about -100 degrees C for the basal plane, at about -80 degrees C for the primary prismatic plane, and at about -70 degrees C for the secondary prismatic plane.     

Spectroscopic evaluation of painted layer structural changes induced by gamma radiation in experimental models

The degradation of cultural heritage objects by insects and microorganisms is an important issue for conservators, art specialists and humankind in general. Gamma irradiation is an efficient method of polychrome wooden artifacts disinfestation. Color changes and other modifications in the physical chemical properties of materials induced by gamma irradiation are feared by cultural heritage responsible committees and they have to be evaluated objectively and precisely. In this paper FTIR and FT-Raman spectroscopy methods were used to investigate the structural changes in some experimental models of tempera paint layers on wood following 11 kGy gamma irradiation at two dose rates. Radiation chemistry depends on the particular pigment, matrix formed by protein, resin (in case of varnished samples) and water presence. For the majority of painted layer in experimental models very small spectral variations were observed. Small changes in the FTIR spectra were observed for the raw sienna experimental model: for the higher dose rate the egg yolk protein oxidation peaks and the CH stretching bands due to lipids degradation products increased.     

脱辅基神经红蛋白热稳定性的光谱法研究

采用酸丙酮法制备了脱辅基神经红蛋白(apo-Ngb)。利用紫外-可见吸收光谱和圆二色光谱(CD)对apo-Ngb的热稳定性进行了研究。结果表明,在高温下apo-Ngb发生了变性,其二级结构遭到破坏,α-螺旋的含量减少。计算得到了apo-Ngb热变性的中点温度(61.8℃)和热力学参数(ΔH=93.1 kJ·mol-1,ΔS=277.8J·mol-1·K-1)。与Ngb相比,由于血红素辅基的去除,apo-Ngb蛋白肽链结构变得疏松无序,从而使apo-Ngb的热稳定性有所降低。     

Molecular dynamics study of the interactions of ice inhibitors on the ice {001} surface

The interactions of antifreeze protein (AFP) type I, antifreeze glycoproteins, polyvinyl pyrrolidone (PVP), and various amino acids with ice are investigated using Cerius2, a molecular modelling tool. Binding energies of these additives to a major ice crystal face {001} are computed. Binding energy comparison of threonine molecules (by themselves) and as threonine residues within AFP type I demonstrate their role in improving AFP's binding ability to the ice crystal face. The shifts in onset points of ice crystallization with AFP type I, PVP, and amino acids are measured using differential scanning calorimetry. These values when correlated with their respective binding energies reveal a direct proportionality and demonstrate AFP's effectiveness in inhibiting growth and nucleation of ice, over amino acids.     

Spectroscopic probes for real-time monitoring of polymer modification and degradation reactions

The processing of polymers may be accompanied by oxidation and elimination reactions that affect the quality of the final product. In reactive processing, polymerisation occurs in the extruder or autoclave and the extent of reaction becomes an important process variable. The monitoring of these chemical changes in real-time so that processing may be optimised requires the use of analytical methods such as fibre-optic Near Infrared (NIR) spectroscopy. In this paper the requirements and limitations for this and related spectroscopic probes are described and novel approaches based on infrared emission and transient infrared transmission spectroscopy (TIRTS) are discussed. To cite this article: G. George et al., C. R. Chimie 9 (2006).     

Spectroscopic inference on the structure of liquid ammonia

IR and Raman spectral data of liquid NH₃ and ND₂H are analysed. Spectroscopic evidence is in favour of extensive hydrogen bonding in the liquid. The number, frequencies and intensities of the transitions in the 3200–3500 cm^?1 region can be explained if cyclic dimers are the major species present in liquid NH₃. This hypothesis is compatible with the low viscosity and low boiling point of liquid NH₃.     

Spectroscopic studies on the oligomers of bromotrifluoro ethylene

The photo-initiated oligomerization of bromotrifluoroethylene in chlorotrifluoromethane medium was found to yield a complex mixture of products. ¹⁹F-nmr, infrared and GC-MS spectra revealed the presence of -CF₂Br and —CF = CF₂ and the absence of —CF Br₂ and —CF₃ end groups in the products. Oligomers up to pentamers were identified and their structures elucidated by GC-MS. A plausible mechanism for their formation is suggested.     

Spectroscopic studies on the protonation of Schiff bases

This short review concerns the protonation of Schiff bases by halogenic or carboxylic acids with a bias toward the chromophore of visual and bacterial rhodopsins. It is pointed out that the weak acids available in these pigments could not protonate the retinyl Schiff base 100% and that a supporting mechanism is needed to achieve full protonation. Our Fourier transform infrared studies both at room and low temperatures relating to this problem are summarized, and the propable role of water is emphasized.     

Spectroscopic Studies on the Simple Rcooh System

The carbonyl stretching vibration of monocarboxylic acid in CCl₄ solution has been investigated. We introduce a new “m-factor” to study the polymerization of this simple RCOOH system. The value of “m-factor” was evaluated and tested in different concentrations and temperatures. Three classes of acid polymers were found as followings: linear dimer in class I (m?2); linear and cyclic dimers in class II (m?4); linear, cyclic dimers, and linear trimer in class III (m?8). A linear relationship between log K₁ and (??1)/(2?+1) was found.     

Eu2+ and V2+ as electrode kinetic probes of the structure of the diffuse layer in dilute electrolytes

The structure of the diffuse double layer at positive electrode charges in dilute perchlorate, chloride and bromide electrolytes is inferred from the kinetics of oxidation of the Eu²⁺ and V²⁺ cations. Diffuse layer potentials calculated from the measured kinetics disagree, both in magnitude and (in some cases) in sign with potentials calculated from electrocapillary data and Gouy-Chapman-Stern theory. The possible origin of the discrepancies and their consequences in attempts to apply Frumkin double layer corrections or to detect discreteness-of-charge effects are discussed.     

Spectroscopic studies on modified wood

The FTIR spectra of solid resin-free samples of chemically modified Norway spruce wood were recorded. Correlations were noted between spectral and hydrogen bond structure, chemical modification, fibre crystallinity and macroscopic softening point.     

乙嘧酚磺酸酯波谱表征研究

利用红外光谱（IR）、核磁共振（NMR）、有机质谱（MS）、紫外光谱（UV）对乙嘧酚磺酸酯进行了波谱表征,对其化学结构中官能团特征红外吸收、核磁共振1H的化学位移、质谱准分子离子、紫外吸收进行解析,并获得了相关波谱图,为乙嘧酚磺酸酯的合成及其产品质量控制提供参考。     

Investigating the effects of solid surfaces on ice nucleation

Understanding the role played by solid surfaces in ice nucleation is a significant step toward designing anti-icing surfaces. However, the uncontrollable impurities in water and surface heterogeneities remain a great challenge for elucidating the effects of surfaces on ice nucleation. Via a designed process of evaporation, condensation, and subsequent ice formation in a closed cell, we investigate the ice nucleation of ensembles of condensed water microdroplets on flat, solid surfaces with completely different wettabilities. The water microdroplets formed on flat, solid surfaces by an evaporation and condensation process exclude the uncontrollable impurities in water, and the effects of surface heterogeneities can be minimized through studying the freezing of ensembles of separate and independent water microdroplets. It is found that the normalized surface ice nucleation rate on a hydrophilic surface is about 1 order of magnitude lower than that on a hydrophobic surface. This is ascribed to the difference in the viscosity of interfacial water and the surface roughness.