Aggregate, Polymer and Cluster Formation from Metal-Imino Carboxylate Complexes

Reaction of tris-(2-aminoethyl)amine (tren) andthe sodium salt of an -ketocarboxylic acid, typically sodium pyruvate, affordsin the presence of a lanthanide ion aseries of complexes and aggregates includingmononuclear, cyclic tetranuclear and polymerspecies of [L¹]^3- ([L¹]^3-=N[CH₂CH₂N=C(CH₃)COO^-]³).The aggregation of these and related d-block elementcomplexes with Na⁺ ions leadsto the formation of polymeric materials, and thefactors influencing the formation and controlof these various aggregation states are discussed.Metal cations also template the aggregationof the fragment [Ni(L²)] ([L²]^2- =CH₂[CH₂N = C(CH₃)COO^-]₂)to give, in high yield, the polynuclearaggregates {[Ni(L²)]₆M}^x+(M = Nd, Pr, Ce, La, x = 3; M = Sr, Ba, x = 2). The structures of{[Ni(L²)]₆M}^x+ show aninterstitial twelve co-ordinate, icosahedralcation M^x+ encapsulated by six [Ni(L²)]fragments. In the presence ofNa⁺, aggregation of [Ni(L²)] fragments affords {[Ni(L²)]₉Na₄(H₂O)(MeOH)(ClO₄)}³⁺ thestructure of whichshows four Na⁺ ions templating the formation ofa distorted tricapped trigonal prismatic[Ni(L²)]₉ cage. Thus, control overconstruction of various polynuclear cages viaself-assembly at octahedral junctions can beachieved using main group, transition metaland lanthanide ion templates.     

Termolecular ion-molecule reactions in Titan’s atmosphere. II: The structure of the association adducts of HCNH+ with C2H2 and C2H4

The ion-molecule reactivity of the products formed in the association reactions of HCNH+ with C2H2 (C3H4N+) and C2H4 (C3H6N+) has been investigated to provide information on the structures of the adducts thus formed. The C3H4N+ and C3H6N+ adducts were formed in the reaction flow tube of a flowing afterglow sourced-selected ion flow tube (FA-SIFT) and their reactivity with a neutral molecular "probe" examined. The reactivity of possible known structural isomers for the C3H4N+ and C3H6N+ ions was investigated in both the FA-SIFT and an ion cyclotron resonance spectrometer (ICR). Ab initio investigations of the potential energy surfaces for both structures at the G2(MP2) level have also been performed and structures corresponding to local minima on both surfaces have been identified and evaluated. The results of these experimental and theoretical studies show that at room temperature, the C3H4N+ adduct ion contains two isomers; a less reactive one that is likely to be a four-membered cyclic covalent isomer (approximately 70%) and a faster reacting component that is probably an electrostatic complex (approximately 30%). The C3H6N+ adduct ion formed from HCNH+ + C2H4 at room temperature is a single isomer that is likely to be the four-membered covalently bound cyclic CH2CH2CHNH+ species.     

SPECTRAL PERTURBATIONS OF THE AEQUOREA GREEN-FLUORESCENT PROTEIN

Abstract— In the jellyfish Aequorea, the green-fluorescent protein (GFP) functions as the in vivo bio-luminescence emitter via energy transfer from the photoprotein aequorin. Accumulated evidence has indicated that the Aequorea GFP is a relatively inflexible protein. Present evidence, however, indicates that the chromophore environment is readily accessible to a variety of external perturbants. Native Aequorea GFP has an absorbance maximum at 395 nm and a shoulder at 470 nm. In low ionic strength buffer at neutral pH and room temperature the 395/470 nm absorbance ratio is about 2.0. We show that this ratio is highly variable depending upon temperature, ionic strength, protein concentration, and pH. A maximum ratio of 6.5 (at a protein concentration of 18.6 mg/m/) and minimum of 0.42 (at a pH of 12.2) have been measured. In the latter case, the resulting absorption and excitation spectra resemble those of Renilla GFP in spectral shape (but not wavelength maximum). In all cases as the perturbant is varied the resulting spectra pass through a sharp isosbestic point, suggesting a relatively simple two-state mechanism. These spectral perturbations are fully reversible. On the basis of these results, we suggest that the chromophore binding site is conformationally flexible. pH-Dependent changes in the near-UV and visible circular dichroism spectra plus spectrophotometric titration of tyrosine residues lend additional support to this hypothesis.     

Fluorinations with complex metal fluorides. Part 6 [1] fluorination of yridine and related compounds with caesium tetrafluorocobaltate(III) [2]

Pyridine has been fluorinated over caesium tetrafluorocobaltate(III) (CsCo^IIIF₄) at 300–400°C to give a mixture of undecafluoro-N-methylpyrrolidine, bis(trifluoromethyl)amine, pentafluoropyridine and several polyfluoropyridines; the product composition depended to some extent on the geometry of the reactor. The fluorinations of pentafluoropyridine, piperidine and undecafluoropiperidine were also investigated.     

Fluorinations with potassium tetrafluorocobaltate(III) Part VII. Further investigations on the fluorination of pyridine

The product from the fluorination of pyridine by KCoF₄ at ca. 220° contains eleven fluoropyridines, two fluoro-2-azahex-enes, three azahexa- dienes, and two fluoro-N-methylpyrrolidines, besides an azacyclohexa-1,3- diene. Four products were isolated from a fluorination of pyridine by CoF₃ at ca. 150°, a 2-azahexene, two N-methylpyrrolidines, and 4H-nona- fluoropiperidine.     

Selectivity differences between sol-gel coated and immobilized liquid film open-tubular columns for gas chromatography

The solvation parameter model is used to determine the system constants for two sol-gel coated open-tubular columns at five equally spaced temperatures in the range 60-140 degrees C. Differences in the system constants as a function of temperature are used to determine the affect of sol-gel structure on the selectivity of SolGel-l and SolGel-Wax columns compared with conventionally coated and immobilized poly(dimethylsiloxane) and poly(ethylene glycol) stationary phases. The sol-gel columns should be suitable for similar separations to those presently performed on conventional immobilized liquid film columns of the same type but selectivity differences for polar compounds, which depend on temperature, should be anticipated.     

A novel piezo-optical styrene sensor incorporating polymer-supported tribromide ion

Encapsulation of Amberlyst A-26 supported tribromide in a 10,000 MW polyethylene glycol matrix gives a robust colour-sensitive reagent matrix which can be deposited on indium-tin oxide coated polyvinylidene fluoride (PVDF) piezoelectric film for the detection of styrene (and other alkene) vapours.     

Clinical investigations of catecholaminergic systems using liquid chromatography with electrochemical detection

Catecholamine levels in body fluids are reliable biochemical markers of several types of tumors, cardiovascular diseases and hereditary and metabolic disorders. Reversed-phase liquid chromatography with electrochemical detection (RPLC-EC) is now the method of choice for catecholamine analysis.