Determination of nickel in standard rocks and glasses by photon activation analysis with 30-MeV bremsstrahlung

The determination of nickel in various silicate rocks and glasses by photon activation analysis with a linear electron accelerator is described. Simultaneous irradiation of the sample and comparative standards produces the ⁵⁸Ni(γ, n)⁵⁷Ni reaction, and a post-irradiation chemical separation is used in conjunction with Ge(Li) γ-spectrometry. Nickel abundances for ten standard silicate rocks and two elementally doped glasses are presented and compared with the data previously published. The method is quite simple and gives good reproducible results for nickel down to sub-p.p.m. levels.     

Synthesis of bis(alk-3-en-1-ynyl)benzene with either E- or Z-configuration via a one-pot three-component coupling reaction and its optical properties

A convenient, efficient and stereoselective synthesis of a range of bis(alk-3-en-1-ynyl)benzenes with E- and Z-configuration is described. The protocol involves Cu-mediated cross-coupling reaction of (E)- and (Z)-alk-1-enyldisiamylboranes with (trimethylsilyl)ethynyl bromide and Pd/Cu-catalyzed cross-coupling reaction with diiodobenzene. The sequential cross-coupling reaction proceeds readily under extremely mild conditions in a one-pot manner to afford bis(alk-3-en-1-ynyl)benzenes in good to excellent yields. The optical properties of the products are also described.     

Cationic polymerization behavior of hydroxystyrenes

Solution polymerizations of o-, m- and p-hydroxystyrene with boron trifluoride etherate were investigated. The results of infrared and ultraviolet spectroscopic investigations of the polymers thus obtained indicate that p-hydroxystyrene polymer consisted mainly of the structure formed through the normal vinyl polymerization mechanism, whereas o- and m-hydroxystyrene polymers contained considerable portions of the structures due to the reaction of the vinyl group with the phenol nucleus. The rate of polymerization and the intrinsic viscosity of the polymer decreased in the order p-hydroxystyrene ? o-hydroxystyrene > m-hydroxystyrene. It was of interest that on the cationic polymerization only p-hydroxystyrene gave polymer of high molecular weight. Plausible polymerization mechanisms were considered. Solid-state polymerization of p-hydroxystyrene at solid carbon dioxide temperature with the use of boron trifluoride etherate was also investigated. Appreciable polymerization occurred only at fairly high catalyst concentrations.     

Dependence of phase behavior of some non-ionic surfactants at the air-water interface on micellization in the bulk

The temperature-dependent surface phase behavior of two sparingly soluble surfactants, namely, ethylene glycol n-dodecyl ether (EGDE) and ethylene glycol n-tetradecyl ether (EGTE), at the air-water interface was investigated by film balance and Brewster angle microscopy (BAM). A cusp point followed by a pronounced plateau region in the surface pressure-time (pi-t) adsorption isotherms of the amphiphiles measured by film balance indicates the first-order phase transition. Bright two-dimensional condensed phase domains in a dark background are observed by BAM just after the phase transition. In both cases the critical surface pressure necessary for the phase transition increases with increasing temperature. The domains are found to be circular up to 5 and 27 degrees C for EGDE and EGTE, respectively, above which they show a fingering pattern. Condensed domains are observed up to 23 and 37 degrees C for EGDE and EGTE, respectively. The surface properties of the amphiphiles are found to be markedly affected by their tendency to aggregate in the bulk as micelles. The CMC values of both the amphiphiles show a maximum at a definite temperature, T(max), that corresponds well to their respective maximum temperatures of domain formation. An increase in temperature beyond T(max) results in an increasing trend for the formation of micelles. Consequently the system suffers from a shortage of two-dimensional surface concentration of the molecules to attain the surface pressure necessary for phase transition. With increasing temperature, the enthalpy, DeltaH(m) degrees , and entropy, DeltaS(m) degrees , of micellization change from negative to positive in both cases. An enthalpy-entropy compensation effect is found to hold for both the amphiphiles over the entire temperature range. The thermodynamic quantities reveal that the increase in temperature is favorable for micellization when the temperature exceeds the corresponding T(max) of the amphiphiles.     

Highly chemo- and regioselective phosphitylation of unprotected 2′-deoxyribonucleosides

We have developed the chemo- and regioselective phosphitylation of unprotected 2′-deoxyribonucleosides by the use of di-tert-butyl N,N-diethylphosphoramidite, a sterically hindered phosphoramidite. Both N/O- and primary hydroxy group-selectivities were simultaneously achieved, and the selectivity for the 5′-hydroxy groups was up to 97% regardless of the base moiety of the 2′-deoxyribonucleosides. The 3′-O-isomers and the 5′-O-isomers were easily separated by silica gel column chromatography or crystallization to give the pure 2′-deoxyribonucleoside 5′-phosphites in moderate to good yields.     

The yields of photonuclear reactions for multielement photon-activation analysis

A comprehensive study on the yields of photonuclear reactions of various types has been performed, and sensitivities and the effects of interferences in multielement photon-activation analysis have been evaluated by bremsstrahlung activation of many elements with maximum energies ranging from 30 to 60 MeV. The applicability and reliability of the method were demonstrated by analyzing standard round-robin samples and then by presenting the elemental abundances in several geological, biological and environmental materials. The method was almost insensitive to matrix effects and was assessed to be promising for nondestructive multielement determination of the materials of wide variety, giving good reproducible results for 20 or more elements.     

The microwave spectrum of thioformaldehyde,CD2S,and CH2S: Average structure,dipole moments,and 33S quadrupole coupling

Microwave transitions up to J = 53 in the ground vibrational state of deuterothioformaldehyde, CD₂S, were studied between 8 and 40 GHz. A detailed centrifugal distortion analysis yields accurate constants for comparison with force field values. The isotopic species ¹³CH₂S, CH₂³⁴S, CH₂³³S, ¹³CD₂S, CD₂³⁴S, and CD₂³³S were studied in natural abundance. Accurate average zero-point structures were determined for both CD₂S and CH₂S:

$\text{CH}{}_2\text{S}\text{CS}\text{=1.6138(4)}\text{CH}\text{= 1.0962(6)}\text{A}\text{?}\text{∠}\text{HCH}\text{=116° 16(6)′,}\text{CD}{}_2\text{S}\text{CS}\text{=1.6136(4)}\text{CD}\text{= 1.0931(4)}\text{A}\text{?}\text{∠}\text{DCD}\text{=116° 25(5)′}$

Changes in the zero-point geometry for deuterium substitution were established. Quadrupole fine structure arising from the ³³S nucleus has been measured in CH₂³³S and CD₂³³S. Analysis gives the following coupling constants (for both molecules) as χ_aa = ?11.7 and χ_bb - χ_cc = 88.1 MHz. The dipole moment of CD₂S was measured to be 1.6588(8)D and an accurate comparison with CH₂S was made; the ratio of dipole moments $\text{CD}{}_2\text{S}\text{CH}{}_2\text{S}$ was found to be 1.0062(4). The spectroscopic and bonding properties of CH₂S will be compared with formaldehyde and other molecules.