Icosahedron oligomerization and condensation in intermetallic compounds. Bonding and electronic requirements

Icosahedron-based clustering has been found to be very common in intermetallics, particularly for group 13 and early p-block icosogen elements. Linking of the icosahedral building blocks depends on the valence electron concentrations. Vertex-, edge-, or face-sharing icosahedra occur as the structure compensates for electron deficiency. Some examples of icosahedron-based clusters have been selected for an analysis of the relationships between the structural features (icosahedron oligomerization, atomic defects, etc.) and the bonding and electronic requirements. The extended Hückel method has been used with either a molecular approach or an electronic band structure calculation to rationalize bonding in the intermetallic framework.     

Computerized flow constant-current stripping analysis for some electroactive organic compounds: application to the determination of erythromycin in urine

The possibility of determining various electroactive organic compounds, e.g., erythromycin and riboflavin, by adsorptive preconcentration at constant potential on a mercury-coated carbon-fibre electrode in a flow system prior to stripping with a reductive constant current, is demonstrated. The advantages of measuring the electrode potential vs. time instead of current vs. electrode potential during stripping, the possibility of operating with non-deoxygenated solutions, the increased linear calibration range is in the multiple scanning mode, and the possibility of using the technique for detection in liquid chromatography, are discussed. An analytical procedure for the determination of erythromycin at the 10(-6)M level in urine after extraction with diethyl ether is described.     

Optical Properties of Model Compounds of Polyaniline

The UV and visible spectra of six model compounds were studied. These compounds can be considered as models of polyaniline in the reduced, cation radical, partially oxidized and oxidized forms. After treatment of a mixture of equal molar quantities of the reduced form (DPPD) and the oxidized form (QDIM) with acid, the following reaction was observed: DPPD(I)+QDIM(III)+2H⁺=2DPPD⁺(II) After similar treatment of the partially oxidized form (V) with acid, the radical cation salt formed. The UV and visible spectra of polyaniline in the reduced form, oxidized form and conductive form are similar to the spectra of DPPD, QDIM and DPPD⁺ or radical cation salt of V respectively. We propose that the polyaniline synthesized by chemical oxidation of aniline consists of oxidized and reduced repeat units. Upon protonation a redox reaction (or electron rearrangement) occurs and forms delocalized radical cations (polarons) in the polymer chain which are highly conductive.     

Trace rare earth element analysis of IAEA Hair (HH-1), Animal Bone (H-5) and other biological standards by radiochemical neutron activation

A radiochemical neutron activation analysis using a rare earth group separation scheme has been used to measure ultratrace levels of rare earth elements (REE) in IAEA Human Hair (HH-1), IAEA Animal Bone (H-5), NBS Bovine Liver (SRM 1577), and NBS Orchard Leaf (SRM 1571) standards. The REE concentrations in Human Hair and Animal Bone range from 10^–8 g/g to 10^–11 g/g and their chondritic normalized REE patterns show a negative Eu anomaly and follow as a smooth function of the REE ionic radii. The REE patterns for NBS Bovine Liver and Orchard Leaf are identical except that their concentrations are higher. The similarity among the REE patterns suggest that the REE do not appear to be fractionated during the intake of biological materials by animals or humans.     

An unusual synthetic way to 2-methyl-3-alkyl-6-ethoxy-heptan-2-ols from 2-ethoxy-5-alkyl-3,4-dihydro-2H-pyrans

A simple and swift preparation of 2-methyl-3-alkyl-6-ethoxyheptan-2-ols may be accomplished in two steps starting from 2-ethoxy-5-alkyl-3-,4-dihydro-2H-pyrans via chlorination of the heterocyclic compounds and subsequent reaction with MeMgBr.     

Synthesis of N-methyl-3-aza[10] paracyclophane: A rigid analog of phenethylamine

The synthesis of N-methyl-3-aza[10]paracyclophane is reported which represents the first example of this ring system being formed via an acyloin reaction. This 3-aza[10]paraeyclophane ring system behaves physiochemically inbetween the normal [9]- and [10]paracyclophane ring systems. Reductive desulfurization of N-methyl-3-aza[10]paracyclophane-6-ethylene thioketal in ethanol provides a small amount of the title compound and an unexpected, ring-opened product, N-ethyl-N-methyl-p-heptylphenethylamine. A possible mechanism for the ring-opening process is suggested.     

Pentalene complexes of group 7 metal carbonyls: an organometallic mixed-valence system with very large metal-metal electronic coupling

The bimetallic complexes [M(CO)(3)](2)(mu:eta(5):eta(5)-Pn) (Pn = pentalene, C(8)H(6); M = Mn, Re) have been synthesized and characterized crystallographically; the Mn compound was isolated as solely the anti-isomer, while the Re analogue was formed as a mixture of anti- and syn-isomers. [Mn(CO)(3)](2)(mu:eta(5):eta(5)-Pn) may be reduced chemically to its mono- and dianions; the mixed-valence Mn(I)/Mn(0) monoanion is shown by ESR, vibrational, and electronic spectroscopies to be a Robin-Day class III system with an exceptionally large electronic coupling between the metal centers.     

Optimization of performance and minimization of silicate interference in continuous flow phosphate analysis

Specific reaction conditions for automated continuous flow analysis of phosphate are optimized in regard to minimizing coating and silicate interference, while maintaining high sensitivity. Use of Sb in the reagent increases sensitivity and yields absorbances with little temperature dependence. Coating can be minimized by using a final solution at a pH>0.5. At final pH of 0.78 there is maximum interference from silicate in the sample. We recommend therefore as an optimal reaction condition with minimal silicate interference, the use of Sb, a final solution pH of 1.00, room temperature for the reaction and a [H(+)]/[Mo] ratio of 70. An equation is provided to correct silicate interference in high precision phosphate determination.     

A heterocyclic peptide nanotube

An open-ended hollow tubular structure is designed based on hydrogen-bond-directed self-assembly of a chimeric cyclic peptide subunit comprised of alternating alpha- and epsilon-amino acids. The design features a novel 1,4-disubstituted-1,2,3-triazole epsilon-amino acid and its utility as a peptide backbone substitute. The N-Fmoc-protected epsilon-amino acid was synthesized in high yield and optical purity in three steps from readily available starting materials and was employed in solid-phase peptide synthesis to afford the desired cyclic peptide structure. The cyclic peptide self-assembly has been studied in solution by (1)H NMR and mass spectrometry and the resulting tubular ensemble characterized in the solid state by X-ray crystallography.