有机试剂结构与性质的研究——Ⅳ.金莲橙000的酸碱平衡、互变异构平衡及存在形式的研究

应用分光光度法及量子化学方法研究金莲橙000的酸碱平衡及其存在的形式,表面活性剂存在下,吸收光谱变化的机理。实验证明加入有机溶剂,平衡向生成偶氮型方向移动。     

Spontaneous emission of an atom placed near a prolate nanospheroid

The frequency shift and linewidth variation of an atomic oscillator placed next to a prolate dielectric or metal spheroid are found within the framework of the classical approach. Both the frequency shift and linewidth are shown to be substantially dependent on the location of the atom and the form of the nanospheroid and capable of reaching very high values near the surface of the nanospheroid under plasmon (polariton) resonance conditions. The predictions are compared with those found for spherical and cylindrical geometries. The prolate spheroid is treated as a model of a needle tip in apertureless optical scanning microscopy. Effects of sharpness of interaction between the nanospheroid tip and atoms are considered. Received 2 January 2002 and Received in final form 3 April 2002 Published online 28 June 2002     

Effect of sample preparation conditions and degree of neutralization on the dynamic mechanical properties of poly(styrene-co-sodium methacrylate) ionomers

A study was undertaken of the effect of sample preparation conditions, especially moisture content, annealing conditions, and degree of neutralization, on the dynamic mechanical properties of poly(styrene-co-sodium methacrylate) ionomers. Water plasticizes the ionic cores; however, very small amounts of water do not affect the cluster glass transition mechanism. The study of the annealing effect showed that the morphology of ionomers is fixed during sample molding. No clustering was observed in samples below a degree of neutralization of 50%, possibly due to a decrease in the lifetime of the multiplets. The 50 and 75% neutralized samples showed weak clustering, with the cluster tan δ peaks shifting to higher temperatures with increasing degree of neutralization. The addition of neutralizing agents causes an increase in the size of multiplets; as a result, the strength of the electrostatic interaction between ion pairs increases. The 100–150% neutralized samples showed identical tan δ peaks and also very similar SAXS peaks. Therefore, it is speculated that excess NaOH resides in or near the multiplets and does not affect the electrostatic interaction between ion pairs. The 200–300% neutralized samples showed increased flow above the cluster T_g, as well as a strong small-angle upturn in the SAXS profile. In agreement with previous results, it appears that in these materials, the excess NaOH resides in the hydrocarbon phase in the form of NaOH crystals, which can act as sites on which the carboxylate ion pairs can reside temporarily; the binding, however, is believed to weaken at high temperatures, which allows flow to occur. The 200% overneutralized Ba²⁺ sample showed the cluster T_g at much higher temperatures than the 100% neutralized sample, which implies that, for this sample, the stability of the multiplets is higher. © 1995 John Wiley & Sons, Inc.     

Dynamic mechanical properties of sulfonated polystyrene/alumina composites

Amino units were grafted onto the surface of small particle size alumina by reaction with 3-aminopropyltriethoxysilane. Atactic polystyrene (PS) was sulfonated (1-14 mol% sulfonation) and mixed with both modified and unmodified alumina at filler loadings varying from 30 to 80 wt %. The resulting composites were characterized by differential scanning calorimetry, Fourier transform infra-red spectroscopy, and dynamic mechanical spectroscopy in the glass transition region at a frequency of 1 Hz. Whereas mixtures of unsulfonated PS with either filler showed essentially no change in T_g with filler content, sulfonated PS saw its T_g increase as a function of filler loading at a rate which was greater following modification of the alumina. At a fixed filler loading of 30 wt%, the composite rubbery plateau modulus was found to increase with copolymer sulfonic acid content, while the loss tangent maximum corresponding to the glass transition broadened and decreased. These observations were interpreted as a manifestation of the decrease in polymer mobility brought upon by the formation of noncovalent crosslinks resulting from the proton transfer from the sulfonic acid units on the polymer to hydroxyl and/or amino units at the surface of the filler. © 1994 John Wiley & Sons, Inc.     

Facile synthesis and characterization of acid-base bifunctionalized mesoporous silica

A simple acid-base bifunctionalized approach has been developed through grinding the precursors, magnesium and aluminium nitrates, with the as-prepared SBA-15, and then the generation of acid-base active sites and removal of host template were combined into a single step in the subsequent calcination procedure. A series of acid-base bifunctional mesoporous materials MgO-Al₂O₃-SBA-15 (MA-SBA-15) have been successfully synthesized by means of this approach. X-ray diffraction (XRD), high-resolution transmission electron microscopes (HRTEMs), N₂ adsorption, FT-IR spectra, ²⁷Al and ²⁹Si magic-angle-spinning (MAS) NMR, NH₃- and CO₂-temperature programmed desorption (TPD), pyridine adsorption were employed to characterize the resultant mesoporous materials. The results indicate that the guests can be well dispersed in the channel of SBA-15, and the resultant materials exhibit excellent acid-basic properties with well mesoporous backbone, which make it possessing high activity for the synthesis of ethyl methyl carbonate, an important asymmetric carbonate ester compound.     

Time-varying migration process of moving neutralization boundary on the immobilized pH gradient strip in the weak-base rehydration buffer

This paper quantificationally probes into time-varying migration processes of moving neutralization boundary (MNB) on immobilized pH gradient (IPG) strip in ammonia-rehydration buffers. The time-varying migration processes are determined by both time-varying dissociation equilibria of ammonia and position-varying pH environments formed by immobilized carrier ampholytes (CAs) on the IPG strip. Thus, the local dissociation equilibria of ammonia and the position-varying pH are introduced into the recursion equation of position of MNB migrations. The theoretical position-time curves and the velocity-time curves of MNB migrations obtained by the recursion approach were satisfactorily validated by a series of images of boundary migrations from the IPG-MNB experiments by using rehydration buffers with different ammonia concentrations on pH 3-6 IPG strips. The results achieved herein have significant evidence to a quantificational understanding of the mechanism of MNB and IEF.     

Hybridization of layered niobates with cationic dyes

The hybridization of two different types of organic polycations, 1,1’-dimethyl-4,4’-bipyridinium dications (methyl viologen, MV²⁺) and 5,10,15,20-tetrakis(N-methyl-pyridinium-4-yl)-21H,23H-porphine tetracations (TMPyP⁴⁺), into layered niobates was investigated to construct an efficient dye-modified semiconductor for solar conversion and storage. Two different methods were employed for the direct intercalation of the cationic species, i.e., conventional ion-exchange with K₄Nb₆O₁₇ · 3H₂O as the starting host and a novel acid-base neutralization method with H₄Nb₆O₁₇ as the starting host. These two methods showed totally different behavior and the characteristic features of both will be discussed in relation to the structure of the hybrid formed, the amount of absorption observed for the guest molecules and the intercalation rates. An analysis of the photo-induced electron-transfer reactions will also be discussed to show how control of the intercalation of guest molecules affects the photofunctionality of these unique hybrids.     

Surface neutralization/surface reionization (Ping–Pong) mass spectrometry

Experiments are reported that utilize surface neutralization of hyperthermal organic ions to obtain hyperthermal neutral species that are reionized on oxygen-activated rhenium surface and detected by mass spectrometry. A special Ping–Pong mass spectrometer was designed and coupled to a double-focusing mass spectrometer to allow energy and angle-resolved measurements. Neutralization of pyridine and benzene ions on gold, copper, and aluminum surfaces generated substantial ion currents into the collecting plate. The ion currents obtained on gold surfaces were found to depend on the recombination energy of the ion projectile. Hyperthermal neutrals coming off the first surface were found to mainly originate from hydrocarbon adsorbates.     

The Limit of Detection of a Weak Acid,in the Presence of Another,by Potentiometric Acid-Base Titrimetry and Deviation-Pattern Recognition

Abstract

When a solution containing a single monobasic weak acid is titrated potentiometrically with a strong base, non-linear regression analysis of the data yields a random scatter of the residuals around the best fit to the appropriate equation. If the same equation is used when a second weak acid is also present, systematic errors arise and yield a deviation plot having a characteristic shape. If the amplitude of that plot is substantially larger than the random error of measurement, the presence of the second acid can be detected, and its concentration can then be evaluated by non-linear regression onto the equation that takes its presence into account. The amplitude increases as the relative concentration of the second acid increases, and as the difference between the values of pK_a for the two acids increases. Examination of these dependences shows, for example, that it should be possible to detect 1 per cent of an impurity for which pK_a differs by 0.57 unit from that of the major component.