Determination of Dialkyltin Compounds in Poly(Vinyl Chloride) by High-Performance Liquid Chromatography

A high-performance liquid chromatography (HPLC) method has been developed for the analysis of dialkyltin compounds in polyvinyl chloride (PVC) materials. The PVC sample was first dissolved in tetrahydrofuran. Concentrated hydrochloric acid was then added to convert the dissolved dialkyltin stabilizers into the chloride forms, followed by extraction with hexane. The extracted dialkyltin chlorides were preconcentrated and were finally separated by HPLC. Separation was performed using a C₁₈ column and an eluent of aqueous methanol containing 8-hydroxyquinoline (oxine) as the completing agent. Photometric detection of the dialkyltin-oxine complexes was carried out at 380 mm. Under optimum experimental conditions, the detection limits for dimethyltin, dibutyltin and dioctyltin are 1.7 ng, 2.1 ng and 2.9 ng (all as tin), respectively. Residual dialkyltin stabilizers in several commercially available PVC products were successfully analyzed via this method.     

Spectroscopic Study of the Na2 2Σg State by cw Perturbation-Facilitated Optical-Optical Double-Resonance Spectroscopy

The Na₂(3sσ_g)(4sσ_g) 2³Σ⁺_g state of Na₂ has been observed and studied by cw perturbation-facilitated optical-optical double-resonance (PFOODR) spectroscopy for the first time. A single-mode dye laser and a Ti-sapphire laser served as the pump and the probe lasers, respectively. A total of 543 PFOODR excitation signals have been assigned to the 2³Σ⁺_g ← b³Π_1u transitions. Absolute vibrational numbering was determined by counting nodes in the 2³Σ⁺_g → a³Σ⁺_u bound-free spectra. Spectroscopic constants and the corresponding RKR potential energy curve are presented in this vsork. The values of T_e, R_e, and D_e, are found to be 25 551.237(49) cm⁻¹, 3.53463(35) Å, and 6211.5(1) cm⁻¹ respectively.     

Stimuli‐Responsive Reversible Fluorescence Switching in a Crystalline Donor–Acceptor Mixture Film: Mixed Stack Charge‐Transfer Emission versus Segregated Stack Monomer Emission

We report on a molecularly tailored 1:1 donor–acceptor (D‐A) charge‐transfer (CT) cocrystal that manifests strongly red‐shifted CT luminescence characteristics, as well as noteworthy reconfigurable self‐assembling behaviors. A loosely packed molecular organization is obtained as a consequence of the noncentrosymmetric chemical structure of molecule A1 , which gives rise to considerable free volume and weak intermolecular interactions. The stacking features of the CT complex result in an external stimuli‐responsive molecular stacking reorganization between the mixed and demixed phases of the D‐A pair. Accordingly, high‐contrast fluorescence switching (red?blue) is realized on the basis of the strong alternation of the electronic properties between the mixed and demixed phases. A combination of structural, spectroscopic, and computational studies reveal the underlying mechanism of this stimuli‐responsive behavior.     

Kinetics and mechanism of the aminolysis of aryl ethyl chloro and chlorothio phosphates with anilines

The reactions of ethyl Y-phenyl chloro (1) and chlorothio (2) phosphates with X-anilines in acetonitrile at 55.0 degrees C are studied kinetically and theoretically. Kinetic results yield the primary kinetic isotope effects (k(H)/k(D) = 1.07-1.80 and 1.06-1.27 for 1 and 2, respectively) with deuterated aniline (XC(6)H(4)ND(2)) nucleophiles, and the cross-interaction constants rho(XY) = -0.60 and -0.28 for and , respectively. A concerted mechanism involving a partial frontside attack through a hydrogen-bonded, four-center-type transition state is proposed. The large rho(X) (rho(nuc) = -3.1 to -3.4) and beta(X) (beta(nuc) = 1.1-1.2) values seem to be characteristic of the anilinolysis of phosphates and thiophosphates with the Cl leaving group. Because of the relatively large size of the aniline nucleophile, the degree of steric hindrance could be the decisive factor that determines the direction of the nucleophilic attack to the phosphate and thiophosphate substrates with the relatively small-sized Cl leaving group.     

Determination of Butyltins in Sea Water by Gas Chromatography with Flame Photometric Detection

Use of a gas chromatograph with a flame-photometric detector (GC-FPD) is described to determine butyltin compounds in sea water. The butyltins in an acidified water sample (pH 3.0) are first complexed with tropolone, followed by solid-phase extraction (SPE) with a tropolone-treated C₁₈ cartridge. HCI at a small concentration is then added to the concentrated SPE eluate before GC analysis. This procedure is simple and off-column derivatization of analytes is not required. The organotins, viz. mono-, di- and tributyltin, are separated as their respective chlorides on a capillary column (HP-1) and are detected with a flame-photometric detector and an interference filter at 610 nm. Recoveries of the three butyltin species are quantitative (> 90%). Based on a sea water sample 200-mL, the detection limits for mono-, di- and tributyltin are 6,4 and 3 ng tin L^?1, respectively. This method is applied to analysis of trace butyltins in various samples of sea water.     

Nucleophilic substitution reactions of aryl dithioacetates with pyridines in acetonitrile

Kinetic studies of the pyridinolysis (XC(5)H(4)N) of aryl dithioacetates (CH(3)C(=S)SC(6)H(4)Z) are carried out in acetonitrile at 60.0 degrees C. A biphasic Br?nsted plot is obtained with a change in slope from a large value (beta(X) congruent with 0.9) to a small value (beta(X) congruent with 0.4) at pK(a) degrees = 5.2, which is attributed to a change in the rate-limiting step from breakdown to formation of a zwitterionic tetrahedral intermediate, T(+/-), in the reaction path as the basicity of the pyridine nucleophile increases. A clear-cut change in the cross-interaction constants rho(XZ) from a large positive value (rho(XZ) = +1.34) to a small negative value (rho(XZ) = -0.15) supports the mechanistic change proposed.     

Transition metal ion directed supramolecular assembly of one- and two-dimensional polyrotaxanes incorporating cucurbituril

This paper reports a synthetic strategy to construct one- and two-dimensional (1D and 2D) polyrotaxanes, in which a number of rings are threaded onto a coordination polymer, by the combination of self-assembly and coordination chemistry. Our approach to construct polyrotaxanes with high structural regularity involves threading a cucurbituril (CB) "bead" with a short "string" to form a stable pseudorotaxane, followed by linking the pseudorotaxanes with metal ions as "linkers" to organize into a 1D or 2D polyrotaxane. A 4- or 3-pyridylmethyl group is attached to each end of 1,4-diaminobutane or 1,5-diaminopentane to produce the short "strings", which then react with the cucurbituril "bead" to form stable pseudorotaxanes. The reaction of the pseudorotaxanes with various transition metal ions including CuII, CoII, NiII, AgI, and CdII produces 1D or 2D polyrotaxanes, in which many molecular "beads" are threaded onto 1D or 2D coordination polymers as confirmed by X-ray crystallography. The overall structure of a polyrotaxane is the result of interplay among various factors that include the coordination preferences of the metal ion, spatial disposition of the donor atoms with respect to the CB beads in the pseudorotaxane, and the size and coordination ability of the counteranion.     

High uniform illumination of light-emitting diodes lighting with applying the multiple-curvature lens

Light-emitting-diode (LED) sources will play a very important role in the future. Nowadays, there are many traditional light sources gradually being replaced by LED sources. From the viewpoint of illumination, different environments have the same requirement uniformity of illumination. The basic reason for this is to insure human comfort. Therefore, the promotion of illumination uniformity is an especially important key issue. In this article, we propose one effective design to improve the uniformity of illumination of LEDs with Lambertian radiation profiles by inserting into the lighting system, multiple-curvature lens. The enhanced illumination uniformity of LEDs, in this system, is due to energy redistribution by controlling the direction of incident light, using geometrical optics theory. Ray tracing was applied for the simulations required. Finally, the uniformity of illumination is 76.17% in LEDs using multiple-curvature lens, which is twice the uniformity of conventional LEDs. Furthermore, the phenomenon of overload in the multiple-curvature lens is reduced by increasing the numbers of rings on the lens. The overload is less than 0.02 lm in the case of lens designed with 23 rings.     

Fabrication and characterization of poly(methyl methacrylate) photopolymer doped with 9,10-phenanthrenequinone (PQ) based derivatives for volume holographic data storage

We present our studies on the photopolymer of poly(methyl methacrylate) (PMMA) doped with 9,10-phenanthrenequinone based derivatives for volume holographic storage. By introducing different functional groups on the side-chain of 9,10-phenanthrenequinone molecule, the holographic characteristics of the material can be modified. The photoreaction involved with the holographic recording in the samples was investigated by measuring UV-Vis absorption spectrum and mass spectrum. The experimental results show that the similar behaviors were exhibited in these photopolymers. It is found that phase hologram recording in our PQ derivatives doped PMMA photopolymer involves a structure change of the quinone based molecule, which induces a strong change of the refractive index. Experimental characterizations on holographic data storage, including material sensitivity, dynamic range (M#) and bit-error-rate have been performed. We found that, by selecting appropriate functional groups, an improvement in sensitivity and M# for holographic data storage can be achieved.     

Interface study of ion irradiated Cu/Ni/Cu(0 0 2)/Si magnetic thin film by X-ray reflectivity

The irradiation effect of 1 MeV C⁺ on the interface and magnetic anisotropy of epitaxial Cu/Ni system with a perpendicular magnetic anisotropy was investigated by using magneto-optical Kerr effects, grazing incident diffraction and X-ray reflectivity. The magnetic easy-axis was altered from the direction along the surface normal to in-plane and the strain in the Ni layer was relaxed after ion irradiation. Though the interface between the top Cu layer and the Ni layer becomes rough, the contrast of electron densities of Cu and Ni layer increases and the grain-growth occurs during ion irradiation. These phenomena arise from thermo-chemical driving force, i.e. heat of formation, which may be a crucial factor in determining the interface shape in the case of indirect energy transfer mechanism. Therefore, the change of the magnetic anisotropy of the Ni/Cu system after ion irradiation is not due to the formation of the intermixed layer at the interface. The ion irradiation effects on the grain-growth and enhancement of the electronic contrast between Ni and Cu are explained by the interfacial atomic movement caused by thermo-chemical driving force.