Statistical techniques in activation analysis

Technical methods involved in activation analysis have received widespread publicity during recent years. Even more recently, various statistical techniques have been employed in conjunction with such technical methods in order to provide a better means of estimating the amounts of various pure chemical elements contained in an unknown mixture. In particular, the method of “least squares” has been employed extensively. However, for the most part, usual least squares applications in activation analysis have utilized the ordinary matrix model Y = Xβ +ρ, under the “error” assumptions (a) zero means, (b) variances proportional to Y and (c) zero covariances. In addition to the fact that assumptions (b) and (c) may lead to erroneous results, previous applications allow only point estimation, with no provision for confidence intervals and tests for model goodness of fit. The present paper is concerned with a feasible iterative estimation procedure which eliminates the necessity for assumptions (b) and (c), and which allows construction of confidence intervals and a test for model goodness of fit. A numerical example of the application of the technique is included. Further, an indication is given of how the technique can be extended to apply in the case of “restricted” least squares (quadratic programming).     

EVALUATION OF NEW BENZOPORPHYRIN DERIVATIVES WITH ENHANCED PDT EFFICACY*

Abstract— A first report on the biological evaluation of a series of isomerically pure benzoporphyrin derivatives ( cis- and frarcs-isomers) as methyl esters is described. In preliminary in vivo studies, the n- bexyl ether analogues of both cis- and trans -isomers of benzoporphyrin derivatives were found to be more active than the industrially prepared benzoporphyrin derivative, a mixture of monocarboxylic acids (BPDMA, Quadralogic Technologies, Vancouver). Further studies with 4-de-vinyl-4-(I-hexyloxyethyl) benzoporphyrin derivative showed that, like BPDMA, it had reduced residual skin phototoxicity compared in mice with Photofrin®. The uptake and clearance characteristics of BPDMA were also compared with the 4-(1-hexyloxyethyl)-derivative by in vivo reflection spectroscopy.     

Far-infrared laser magnetic resonance spectrum of NHD

Far-infrared laser magnetic resonance spectra of NHD (X ²A′') (0,0,0) have been observed. Data are presented for the rotational transitions 3₁₃ ← 2₀₂ and 4₁₃ ← 3₂₂ observed at wavelengths of 211.3 and 374.1 μm respectively. Theoretical values of the transition magnetic field strengths have been calculated using the best available molecular constants. The agreement between theory and experiment confirms our spectroscopic assignments, but indicates that with further experimental data, considerable refinement of the molecular constants will be obtained.     

Formation of dinuclear,macrocyclic, and chain structures from HgI(2) and a semirigid benzimidazole-based bridging ligand: an example of ring-opening supramolecular isomerism

The reactions of HgI(2) with the semirigid ditopic ligand 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (bbimms) afforded three new complexes, [Hg(2)(mu-I)(2)I(2)(bbimms)] (1), [Hg(2)I(4)(bbimms)(2)] (2), and catena-poly[HgI(2)(bbimms)] (3). The ligand and all complexes have been structurally characterized by single-crystal X-ray diffraction. 1 is a triply bridged dinuclear complex comprised of two Hg(II) ions, one bridging ligand, two bridging I(-) anions, and two terminal I(-) anions. 2 is a dinuclear metallamacrocycle comprised of two Hg(II) ions, two bridging ligands, and four terminal I(-) anions, while 3 is a helical chain with the repeating unit of HgI(2)(bbimms). 2 and 3 can be classified as supramolecular isomers, and both are related to the triply bridged precursor 1 via the addition of one more ligand in a ring-opening process.     

Factors affecting the endo : exo ratio in diels-alder reactions of cyclopentadiene

The ratio of endo-CHO:exo-CHO in the Diels-Alder addition of a trans-αβ-unsaturated aldehyde to cyclopentadiene can be changed from 1:2 to 8:1, depending on temperature and BF₃-catalysis.     

A new synthesis of platinum—carbon bonds

Syntheses of cis-[PtCl(CH₂COCH₃)(PEt₃)₂], cis-[PtCl(CH₂NO₂) (PEt₃)₂], and trans-[Pt(CCPh)₂ (PEt₃)₂] are described. The procedure involves reaction of cis-[PtCl₂(PEt₃)₂] with Ag₂O and acidic CH bonds to precipitate AgC1 and generate a PtC bond. The method may represent a new general route to platinum—carbon bonds.     

Organometallic reagents in organic synthesis—V: An organocuprate conjugate addition—Aldol condensation synthetic procedure for sequential formation of two carbon-carbon bonds

The enolates produced from the conjugate addition reaction of lithium dialkylcuprates with α,β- unsaturated ketones react with aldehydes in the presence of zinc chloride to give overall β-alkyl α-hydroxyalkyl addition to the original alkene. Reaction of these enolates with carbon dioxide and ethyl formate is also reported.     

Resonance type dielectric behavior in solids

Experimental evidence now indicates that the microwave dielectric properties of solids are strongly influenced by the infrared active phonon modes. The “real dielectric constant”, ε′, of polar materials, i. e. those in which ?′ is noticeably greater than the square of the optical index of refraction, exhibits a temperature dependence dominated by the change of integrated infrared absorption. The microwave dielectric loss, ?″, is influenced by the low frequency “tail” of the infrared resonance type absorption, as may be inferred from the monotonic increase with temperature and proportionality to frequency. It is suggested that the one dimensional coupling of the electric field to the acoustic modes of a dielectric solid would lead to additional low frequency “background” dielectric losses which are essentially frequency independent, in agreement with experimental observations.     

Isotope fractionation of water during evaporation without condensation

The microscopic events engendering liquid water evaporation have received much attention over the last century, but remain incompletely understood. We present measurements of isotope fractionation occurring during free molecular evaporation from liquid microjets and show that the isotope ratios of evaporating molecules exhibit dramatic differences from equilibrium vapor values, strong variations with the solution deuterium mole fraction, and a clear temperature dependence. These results indicate the existence of an energetic barrier to evaporation and that the evaporation coefficient of water is less than unity. These new insights into water evaporation promise to advance our understanding of the processes that control the formation and lifetime of clouds in the atmosphere.     

Plutonium(IV) mononitrate and dinitrate complex formation in acid solutions as a function of ionic strength

Titrations of Pu(IV) with HNO₃ in a series of aqueous HClO₄ solutions ranging in ionic strength from 2 to 19 molal were followed using visible and near-infrared absorption spectrophotometry. The Pu 5f-5f spectra in the visible and near IR range change with complex formation. At each ionic strength, a series of spectra were obtained by varying nitrate concentration. Each series was deconvoluted into spectra of Pu⁴⁺ (aq), Pu(NO₃)³⁻ and Pu(NO₃)₂ ²⁺ complexes, and simultaneously their formation constants were determined. When corrected for the incomplete dissociation of nitric acid, the ionic strength dependence of each formation constant can be described by two parameters, β⁰ and Δε using the formulae of specific ion interaction theory.