Determination of calcium,phosphorus and fluorine in bone by instrumental fast neutron activation analysis

The determination of fluorine, calcium and phosphorus in bone by instrumental fast neutron activation analysis is described. Results for the IAEA standard material “Animal Bone” A3-74 re: Ca=313±10 mg/g, P=155±5 mg/g and F-613±20μg/g. The accuracy for all three elements is≤4%, precision being about 3%. The limit of determination for F is 120 μg, for Ca 30 mg and for P 1 mg in a sample of 500 mg.     

The determination of inorganic arsenic in water by thermal neutron activation analysis

A simple method is presented for the determination of inorganic arsenic in water samples. The lower limit of determination is 0.01 μg·1⁻¹. Penta-and trivalent arsenic ions as well as arsenic acid substituted with aromatic ligands are collected by coprecipitation with Fe(OH)₃. After irradiation the arsenic is separated from the iron by adsorption to Al₂O₃. The overall efficiency is (97∓1)%. The procedure takes one day per ∼20 samples. It has been checked by standard addition. Data for sea- and surface-water are given. As the concentration of aromatic arsenic-compounds is very small in comparison to that of the inorganic species, it does not affect the result of the determination.     

Exchange of mercury between mercuric ions and methylmercuric nitrate

The rate constant for the exchange between Hg²⁺ and CH₃Hg⁺ ions in a Cl-free 1NH₂SO₄ solution at 25°C was measured with²⁰³Hg as a radiotracer and separation of the two compounds by liquid extraction of the organic species into benzene from a NaCl- or NaI-solution.     

Isolement de l'acide 3-amino 12-methyl tetradecanoique et de l'acide 3-amino 12-methyl tridecanoique a partir de l'iturine,antibiotique de Bacillus subtilis

lturin, a peptide antibiotic from Bacillus subtilis, was separated into three iturins: A, B, C by thin-layer chromatography. Iturin A, which has an antifungal activity, contains Asp, Glu, Tyr, Ser, Pro in a molar ratio 3:1:1:1:1 and a lipid moiety AL. The latter was shown to be a mixture of C₁₄ (40%) and C₁₅, (60%) amino-acids. The structure of these was determined by combined gas chromatography-mass spectrometry of the N-acetylmethyl esters. Strong peaks at m/e = 144 and m/e = 102 indicate a β-amino group. Identification of acetone and methylethylketone after chromic acid oxidation indicates an iso and anteiso structure. After comparison of the natural amino-acids with synthetic 3-amino pentadecanoic acid it is concluded that the lipid AL is a mixture of 3-amino 12- methyltetradecanoic acid and 3-amino 12-methyltridecanoic acid.     

Determination of critical micelle concentration by hyper-rayleigh scattering

The critical micelle concentration (CMC) of several surfactants that contain an NLO chromophore, either at the hydrocarbon tail, or at the hydrophilic headgroup, or even as a counterion, was determined by hyper-Rayleigh scattering (HRS). In all cases, the HRS signal exhibited a similar variation with surfactant concentration, wherein the CMC is inferred from a rather unprecedented drop in the signal intensity. This drop is attributed to the formation of small pre-micellar aggregates, whose concentrations become negligible above CMC. In addition, a probe molecule, which upon protonation yielded a species with significantly enhanced HRS intensity, was developed and its utility for the determination of the CMC of simple fatty acids was demonstrated.     

Aromatic-aromatic interactions in crystal structures of helical peptide scaffolds containing projecting phenylalanine residues

Aromatic-aromatic interactions between phenylalanine side chains in peptides have been probed by the structure determination in crystals of three peptides: Boc-Val-Ala-Phe-Aib-Val-Ala-Phe-Aib-OMe, I; Boc-Val-Ala-Phe-Aib-Val-Ala-Phe-Aib-Val-Ala-Phe-Aib-OMe, II; Boc-Aib-Ala-Phe-Aib-Phe-Ala-Val-Aib-OMe, III. X-ray diffraction studies reveal that all three peptides adopt helical conformations in the solid state with the Phe side chains projecting outward. Interhelix association in the crystals is promoted by Phe-Phe interactions. A total of 15 unique aromatic pairs have been characterized in the three independent crystal structures. In peptides I and II, the aromatic side chains lie on the same face of the helix at i/i + 4 positions resulting in both intrahelix and interhelix aromatic interactions. In peptide III, the Phe side chains are placed on the opposite faces of the helix, resulting in exclusive intermolecular aromatic interactions. The distances between the centroids of aromatic pair ranges from 5.11 to 6.86 A, while the distance of closest approach of ring carbon atoms ranges from 3.27 to 4.59 A. Examples of T-shaped and parallel-displaced arrangements of aromatic pairs are observed, in addition to several examples of inclined arrangements. The results support the view that the interaction potential for a pair of aromatic rings is relatively broad and rugged with several minima of similar energies, separated by small activation barriers.     

Kinetics and mechanism of complex formation between O-bonded cis-(diglycinato)bis(ethylenediamine)cobalt(III) and α-cis-(diglycinato) (triethylenetetramine)cobalt(III) with nickel(II) in aqueous medium

Summary The kinetics of reversible complexation of Ni(OH₂) _inf6 ^sup2+ with oxygen-bonded glycinatocobalt(III) substrates N₄-Co(glyH)gly²⁺ [N₄ = (en)₂ or trien; glyH = H₃N⁺CH₂-COO^–] have been investigated by the stopped-flow technique in the 20–35° C range, at pH = 6.08–6.82 and I = 0.3 mol dm^–3. The formation of N₄Co(glyH)glyNi⁴⁺ occurred via the reaction of Ni(OH₂) _inf6 ^sup2+ with the deprotonated form of the cobalt(III) substrates, N₄Co-(glyH)gly²⁺. The rate and activation parameters for the formation and dissociation of the binuclear species are reported. The formation rate constants k _f (at 25° C), activation enthalpy and entropy H , S for N₄Co-(glyH)glyNi⁴⁺ are 320±49, 341 ± 52dm³mol^–1 s^–1, 78 ± 7, 79 ± 5 kJmol^–1 and 64 ± 24, 69 ± 18 JK^–1 mol^–1 for the ethylenediamine and triethylenetetraminecobalt(III) substrates, respectively. This result indicates that the rate and activation parameters are virtually independent of the nature of N₄ moities, which strongly suggests that the formation of mono-bonded species occurs via entry of one of the pendant NH₂ groups into the coordination sphere of nickel(II) via a rate-limiting Ni-OH₂ bond dissociation mechanism (I_d). The binuclear species exist in dynamic equilibrium between the monodentate and chelated forms, with the chelate form predominating. The low values of spontaneous dissociation rate constant for the binuclear species (k _r- 0.095^–1 at 25° C) in comparison with the high values of dissociation rate constants of monodentate nickel(II) complexes reported in the literature also support the chelate nature of the binuclear species.     

A LASER FLASH PHOTOLYSIS STUDY OF PYRENE-1-ALDEHYDE. INTERSYSTEM CROSSING EFFICIENCY, PHOTOREACTIVITY AND TRIPLET STATE PROPERTIES IN VARIOUS SOLVENTS

Abstract— Triplet-and singlet-related photoprocesses of pyrene-1-aldehyde (PA) in various solvents have been investigated in detail using 337.1 and 355 nm laser flash photolysis in conjunction with time-correlated determination of fluorescence lifetimes (τ_F) and steady-state photochemical and absorption-emission spectral measurements. In benzene, the lowest triplet of PA (43 < E_T < 46 kcal/mol) has a lifetime of about 50 µs (τ_T) and displays the absorption maximum at 443 nm with a maximum extinction coefficient (ε_max) of 21000 M ^-1cm^-1; the corresponding ketyl radical has a sharp absorption maximum at 428 nm (ε_max≥ 25000 M ^-1cm^-1). The quantum yields (φ_T) of lowest triplet occupation are high in nonprotic solvents (0.6–0.8), decrease in protic solvents (alcohols) as the polarity of the latter is increased, and maintain a complementary relationship with the quantum yields (φ_F) of fluorescence. Quantum yields (φ_PC) of loss of PA due to photoreactions in some solvents have also been determined under conditions of steady irradiation at 366 nm; φ_PC is in the range 0.1–0.2 in electron-rich olefinic solvents such as cyclohexene and tetramethylethylene. These results concerning τ_F, τ_T, φ_F. φ_T and φ_PC as well as the effects of 1,2,4-trimethoxybenzene and 2,5-dimethyl-2,4-hexadiene as quenchers for fluorescence, triplet yield, and photochemistry are discussed in the light of possible state orders for PA in polar and nonpolar environments.     

Coordination modes of 1-allyl benzotriazole: synthesis and characterization of cobalt(II), nickel(II), copper(II), copper(I) and silver(I) complexes

Summary The synthesis and coordination behaviour of 1-allylbenzotriazole (ABT), containing both -donating heterocyclic ring nitrogen(s) and a -bonding olefinic group, has been studied by complexation with Co^II, Ni^II, Cu^II, Cu^I and Ag^I salts. The solid complexes M(ABT)₂X₂ (M=Co, Ni or Cu and X=a counterion) and M(ABT)X (M=Cu or Ag and X=Br, I, or NO₃) have been characterised by¹H-n.m.r. (representative Cu^I species) and other physical data. Different modes coordination for the title ligand have been proposed based upon i.r. data which indicate the participation of a -donating ring nitrogen only in complexes with bivalent metal salts, and the involvement of both the ring nitrogen and the allylic olefinic component in bonding to a monovalent metal ion.¹H-n.m.r. data are qualitatively commensurate with participation of the allyl group in monovalent metal complexes.