Influence of Eu, Dy co-doped strontium aluminate composition on mechanoluminescence intensity

We have investigated the mechanoluminescence (ML) of Eu,Dy co-doped strontium aluminates. The SrAl₂O₄ and Sr₃Al₂O₆ indicate high ML intensity, which is clearly visible to the naked eye in the air. SrAl₂O₄:Eu,Dy shows the highest ML intensity and has many filled traps, high quantum efficiency and moderate stiffness. On the other hand, Sr₃Al₂O₆:Eu,Dy does not have many filled traps and high relative quantum efficiency, but Sr₃Al₂O₆:Eu,Dy shows relatively high ML intensity. Sr₃Al₂O₆:Eu,Dy indicates low stiffness. SrAl₄O₇:Eu,Dy has many filled traps and high relative quantum efficiency, but SrAl₄O₇:Eu,Dy shows very small ml intensity. SrAl₄O₇:Eu,Dy indicates high stiffness. This suggests that the stiffness is an important factor for the ML intensity of the Eu,Dy co-doped strontium aluminate system.     

The kinetic study of thermal dehydration stages of SrCl2 · 2H2O and its deuterium analog

The kinetic deuterium isotope effect in the thermal dehydration stages of powdered SrCl₂ · 2H₂O was examined by means of both isothermal and dynamic gravimetries. These dehydration processes proved to be controlled by a random nucleation and its subsequent growth mechanism. No significant kinetic isotope effect was seen in these dehydration stages. It seems that there exists a kinetic compensation effect between the hydrate and its deuterium analog, if any isotopic differences in activation energy and frequency factor could exist.     

Deuterium isotope effects in the thermal dehydration of K2Mg(SO4)2 · 6H2O

Deuterium isotope effects in the thermal stability, enthalpy change, and kinetic parameters were examined by means of TG-DSC recorded simultaneously for the dehydration stages of

The thermal stability and enthalpy change for the hydrate were smaller than those for its deuterium analog in stage (1). In addition, the rate constant for the hydrate was larger than that for the deuterate in this stage. As for stages (2) and (3), any isotope effect in these parameters was not recognized in practice. The correlation of these isotope effects observed in stage (1) is briefly discussed     

Synthesis of phosphate-type fluorocarbon-hydrocarbon hybrid surfactants and their adsorption onto calcium hydroxyapatite

Five novel phosphate-type hybrid surfactants, C_mF_2m+1C₆H₄CH[OPO₂(OC₆H₅)Na]C_nH_2n+1 (FmPHnPPhNa: m = 4, 6, 8; n = 3, 5), have been synthesized. When compared with sulfate-type hybrid surfactants, C_mF_2m+1C₆H₄CH(OSO₃Na)C_nH_2n+1 (C₆H₄ = p-phenylene), the new hybrid surfactants were found to have comparable abilities to lower the surface tension of water. The critical micelle concentrations of FmPHnPPhNa followed Klevens’ rule and their occupied areas per molecule increased with increasing m and n. Calcium hydroxyapatite (CaHAp) pellets modified with FmPH3PPhNa gave high hydro and lipophobic surfaces. The hybrid surfactants are expected to be useful as new dental reagents for oral hygiene.     

Chloride ion catalyzed conformational inversion of carbocation intermediates in the hydrolysis of a benzo[a]pyrene 7,8-diol 9,10-epoxide

A highly efficient procedure for converting 7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (1) to its trans-9,10-chlorohydrin (5) with excellent yield and purity by the reaction of anhydrous HCl in THF has been developed. The rate of reaction of 5 has been determined as a function of sodium chloride concentration in 1:1 dioxane-water solutions. A large common ion rate depression for the reaction of the chlorohydrin was observed, and the rate data are fit to a mechanism in which all of the tetrol products are formed by the reaction of water with the C-10 carbocation intermediate. Yet, the cis/trans ratio of tetrols from the reaction of the carbocation intermediate from the hydrolysis of chlorohydrin 5 is different than the cis/trans tetrol ratio from the acid-catalyzed hydrolysis of diol epoxide 1, which hydrolyzes via a carbocation with the same connectivity as that formed in the hydrolysis of 5. To rationalize these results, it is proposed that the S(N)1 reaction of chlorohydrin 5 yields a different distribution of carbocation conformations than that formed from the reaction of 1 with H(+). The energy barrier for the inversion of these carbocation conformations must be large relative to the energy barriers for the reaction of each carbocation conformation with water. In solutions containing sufficient concentrations of chloride ion, however, a lower energy pathway via a halohydrin exists for the interconversion of the carbocation conformations. Thus, chloride ion catalyzes the interconversion of these two carbocation conformations.     

Theory of the high-frequency limiting viscosity of a dilute polymer solution,part 2

Summary High-frequency limiting viscosities of dilute polymer solutions are calculated on the basis of our previous theory [Colloid and Polymer Sci.,253, 905 (1975) for (i) necklace model of a chain with constant bond length and bond angle under a hindering rotational potential, and (ii) broken rod model consisting ofN rods with equal length connected by universal joints. Exact treatment is possible for a once-broken rod model, but the Monte Carlo method is utilized in the other calculations.

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Zusammenfassung Es werden die hochfrequenten Grenzviskositäten von verdünnten Lösungen auf Grundlagen unserer voran publizierten Theorie (Colloid and Polymer Sci. 253, 905 (1975)) für ein Perlschnur-Kettenmodell für mit konstanter Bindungslänge und Bindungswinkel unter einem Rotationsbehinderungspotential berechnet. Dasselbe wird für ein gebrochenes Stäbchenmodell getan, das aus N-Stäbchen mit gleicher Länge durch frei drehbare Gelenke aufgebaut ist. Eine exakte Behandlung ist möglich für ein einmal gebrochenes Stäbchenmodell, jedoch wird die Monte Carlo-Methode für die anderen Berechnungen verwendet.

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With 2 figures     

Electronic transition moment of the AΠr-XΣ system of TiN

The A²Π_r-X²Σ⁺ transition of TiN was observed by the dispersed laser induced fluorescence (DLIF) spectroscopy. The relative intensities of the DLIF spectra were analyzed to determine the dependence of the electronic transition moment, R_e(r), on the internuclear distance, r, as R_e(r)∝{1−0.281(26)r} (1.380 Å≤r≤1.823 Å). This r-dependence was analyzed simultaneously with the reported values of the spin-orbit constants for A²Π_r and the hyperfine-coupling constants for X²Σ⁺ to evaluate the ionic character of the TiN bond, the 4s atomic character in the 9σ orbital of X²Σ⁺, and the 4p atomic character in the 4π orbital of A²Π_r. These characters were confirmed to be in accordance with the reported theoretical prediction. A strong r-dependence was indicated for the 3d-4p mixing in the A²Π_r state due to the configuration mixing of the Ti(3d⁴) and Ti(3d³4p) states at a large internuclear distance.     

RA‐dimer B,a New Dimeric RA‐series Cyclopeptide Incorporating Two Different Types of Cycloisodityrosine Units,from Rubia cordifolia L.

RA‐dimer B, a new cytotoxic RA‐series peptide, was isolated from the roots of Rubia cordifolia L. Its structure was elucidated on the basis of spectroscopic analysis to be a dimeric cyclopeptide composed of deoxybouvardin and allo‐RA‐V. Those two cyclopeptide units are connected by an ether linkage between the phenolic oxygen atom of deoxybouvardin and the ?a carbon atom of Tyr‐6 of allo‐RA‐V. RA‐dimer B was synthesized by the coupling reaction of deoxybouvardin with the boronic acid derivative of allo‐RA‐V, and subsequent deprotection, confirming the relative stereochemistry and establishing the absolute configuration of this peptide. RA‐dimer B showed cytotoxic activity against human promyelocytic leukaemia HL‐60, human colonic carcinoma HCT‐116, and human renal cell carcinoma ACHN cells with IC₅₀ values of 0.59, 0.54, and 0.74 μm , respectively.     

Stereocontrolled synthesis of the A/B-ring fragment of gambieric acid B: reassignment of the absolute configuration of the polycyclic ether region

Stereocontrolled synthesis of the A/B-ring fragment of the originally assigned structure of gambieric acid B and its possible diastereomers has been accomplished. Detailed comparison of their 1H and 13C NMR data with those of the corresponding moiety of the natural product culminated in a stereochemical reassignment of the absolute configuration of the polycyclic ether region of gambieric acid B.