Comments on "Speech Understanding and Aging"

The hypothesis advanced by the CHABA Working Group on Speech Understanding and Aging [J. Acoust. Soc. Am. 83, 859-895 (1986)] that the systematic decline in speech understanding with age might be explained by concomitant decline in extra-auditory cognitive factors was tested by examining speech audiometric findings in patients with dementia. The fact that performance was consistent with normal central auditory function in 12 of 23 such patients, in spite of deficits in immediate memory for spoken material, tolerance of distraction, mental tracking and sequencing, cognitive flexibility, and set shifting argues against the hypothesis that speech understanding deficits in the elderly can be explained as the simple consequence of cognitive decline.     

EPR on tetrabutylammonium tetraiodo-nitrosyltechnetate(II), (Bu4N)[Tc(NO)I4]

An EPR study on tetrabutylammonium tetraiodo-nitrosyltechnetate(II), (Bu₄N)[Tc(NO)I₄], is reported. The frozen solution EPR spectrum is described by an axially symmetric spin Hamiltonian. The ⁹⁹Tc hyperfine interaction is used to estimate the spin density distribution in the MO of the unpaired electron which is of “in-plane-π-type”.     

Endor and triple resonance on covalent copper(II) complexes,comparison of experimental results with semi-empirical quantum-chemical calculations

Results of ENDOR and TRIPLE resonance investigations on covalent copper(II) complexes are interpreted by means of semi-empirical EHMO, INDO and NDDO calculations. The spin-unrestricted INDO and NDDO calculations show that spin polarization mainly determines the large ligand hyperfine coupling constants observed for the “next neighbours” in the chelate rings of the investigated compounds.     

Redoxreaktionen an nickelorganokomplexen durch nitrosoverbindungen und aliphatische aldehyde: Möglichkeiten des einsatzes der spintrapmethode

ESR investigations of the reaction between (bipy)Ni(C₂H₅)₂ and aromatic nitroso compounds (RNO) show the formation of paramagnetic, unstable complexes containing the radical RNO^. which is followed by elimination of nitroxide radicals C₂H₅(R)NO^..(bipy)Ni(COD) is oxidized by RNO to give nickel(I) species and several trapped radicals derived from COD. In the presence of aldehydes no paramagnetic nickel species, but ethyl radicals and spin adducts of the aldehydes can be observed. The mechanism of the reaction is discussed.     

Ultrastructural examination of dentin using focused ion-beam cross-sectioning and transmission electron microscopy

Focused ion-beam (FIB) milling is a commonly used technique for transmission electron microscopy (TEM) sample preparation of inorganic materials. In this study, we seek to evaluate the FIB as a TEM preparation tool for human dentin. Two particular problems involving dentin, a structural analog of bone that makes up the bulk of the human tooth, are examined. Firstly, the process of aging is studied through an investigation of the mineralization in ‘transparent’ dentin, which is formed naturally due to the filling up of dentinal tubules with large mineral crystals. Next, the process of fracture is examined to evaluate incipient events that occur at the collagen fiber level. For both these cases, FIB-milling was able to generate high-quality specimens that could be used for subsequent TEM examination. The changes in the mineralization suggested a simple mechanism of mineral ‘dissolution and reprecipitation’, while examination of the collagen revealed incipient damage in the form of voids within the collagen fibers. These studies help shed light on the process of aging and fracture of mineralized tissues and are useful steps in developing a framework for understanding such processes.     

Synthese von 2-Hydeoxy-3-methyl-2-hexen-4-olid

Synthesis of 2-Hydroxy-3-methyl-2-hexen-4-olid The title compound 13a, a substance used in food-flavoring, was synthesized in 89% overall yield, starting from methyl 2-hydeoxy-3-butenoate (3_a). The key step in this transformation is the isomerization of the C?C bond in 3_a which yielded methyl 2-oxobutanoate as an intermediate. The latter underwent a self-condensation yielding 2-hydroxy-4-(methoxycarbonyl)-3-methyl-2-hexen-4-olid ( 11 _a), which, after hydrolysis and decarboxylation, gave 13 _a. In addition, the syntheses of five other compounds related to 13 _a are reported.     

Wechselwirkungen von Hetero-π-Systemen mit Zentralmetallatomen in niedrigen Oxydationsstufen. ESR-Untersuchungen zur Struktur und Bindung an Niedrig-spin-d5-(S = 1/2)-Tris(benzil-bis-N-phenylimin)vanadium(0) und Bis(benzil-bis-N-phenylimin)cobalt(0)

Interaction of Hetero-π-Systems with Central Metal Atoms in Low Oxidation States. ESR Investigations on Structure and Bonding in Low Spin d⁵-(S = 1/2)-Tris(benzil-bis-N-phenylimine)vanadium(0) and Bis(benzil-bis-N-phenylimine)cobalt(0) ESR investigations on V(N??N)₃ and Co(N??N)₂(N??N: Benzil-bis-N-phenylimine) are reported. The ESR parameters — g, A^V — indicate trigonal coordination geometry (D₃) for V(N??N)₃ disturbed by a small lower-symmetric ligand-field component. Interpretation of these parameters in terms of a ligand-field model for a low-spin d⁵ electronic configuration shows the electronic ground state to be ²A₁ and yields a large value for the trigonal field splitting parameter K. The ESR spectrum of Co(N??N)₂ could be obtained at 4.2 K only. Its rhombic symmetry and the absence of hyperfine interactions with the nuclei ⁵⁹Co and ¹⁴N is consistent with a rhombically distorted, compressed tetrahedral symmetry (D₂) for Co(N??N)₂. The spin-Hamiltonian parameters are discussed in terms of the metal-ligand bond character and the electronic spectrum.     

Darstellung und Charakterisierung von [N-(2-Mercaptoacetyl)-N′ -4-(penten-3on-2)ethylen-1,2-diaminato]oxorhenium(V), ReO(MRP 40)

Synthesis and Characterization of [N-(2-Mercaptoacetyl)-N′ -4-(penten-3on-2)ethylen-1,2-diaminato]oxorhenium(V), ReO(MRP 40) The title complex is obtained in good yields from the reaction of the triphenylmethyl-protected ligand with (Bu₄N)ReOBr₄ or ReOCl₃(Ph₃P)₂. The structure of the compound as neutral oxorhenium(V) complex is confirmed by analytical, ¹H-, ¹³C-NMR, IR, UV/Vis as well as mass spectrometric studies.     

Die massenspektrometrische Fragmentierung von NiII-Chelaten mit O-, N-, S-, Se-Donoratomen

Mass Spectrometric Fragmentation of Ni^II Chelates with O-, N-, S-, Se-Donor Atoms The mass spectra of 6Ni^II chelates having the same substituents but different donor atoms (sequence of ligand atoms ? C(X)? NH? C(Y)? ; X, Y = O, S, Se, NH; see formula (1)) are discussed. The fragmentation pattern of the (thio)benzoyl(thio, seleno)ureas are characterized by the abstraction of S or Se atoms. The appearence of small neutral molecules seems to be typical for the fragmentation of all complexes. The mass spectrum of the Ni^II chelate having a NiS₂Se₂ coordination sphere shows no molecular ion peak. The contents of molecular ions in the total ion stream correlates with the stability of the complexes.