Interaction of the human prion PrP(106-126) sequence with copper(II), manganese(II), and zinc(II): NMR and EPR studies

The synthetic peptide encompassing residues 106-126 (PrP106-126, KTNMKHMAGAAAAGAVVGGLG) of the human prion protein was considered for its binding properties toward copper(II), manganese(II) and zinc(II) at pH 5.7. 1H and 13C 1D spectra, 1H spin-lattice relaxation rates, and 1H-15N and 1H-13C HSQC 2D experiments were obtained in the absence and in the presence of metal ions. While Zn(II) was found to yield negligible effects upon any NMR parameter, metal-peptide association was demonstrated by the paramagnetic effects of Cu(II) and Mn(II) upon 1D and 2D spectra. Delineation of structures of metal complexes was sought by interpreting the paramagnetic effect on 1H spin-lattice relaxation rates. Exchange of peptide molecules from the metal coordination sphere was shown to provide sizable contribution to the observed relaxation rates. Such contribution was calculated in the case of Cu(II); whereas the faster paramagnetic rates of peptide molecules bound to Mn(II) were determining spin-lattice relaxation rates almost exclusively dominated by exchange. Proton-metal distances were therefore evaluated in the case of the Cu(II) complex only and used as restraints in molecular dynamics calculations where from the structure of the complex was obtained. The peptide was shown to bind copper through the imidazole nitrogen and the ionized amide nitrogen of His-111 and the amino-terminal group with the terminal carboxyl stabilizing the coordination sphere through ionic interactions. The data were interpreted as to demonstrate that the hydrophobic C-terminal region was not affecting the copper-binding properties of the peptide and that this hydrophobic tail is left free to interact with other target molecules. As for the complex with Mn(II), qualitative information was obtained on carbonyl oxygens of Gly-124 and Leu-125, beyond the terminal Gly-126 carboxyl, being at close distance from the metal ion, that also interacts, most likely, through a hydrogen bond of metal-bound water, with the imidazole ring of His-111.     

Determination of total carbon and total organic carbon from volatile air pollutants. Part II

Summary The possibility of specific removal of carbon monoxide from a stream of air in the presence of vapours of volatile organic compounds was investigated. Weighed samples of oxalic acid were pyrolyzed to obtain standard mixtures of CO with air. Carbon monoxide present in the stream of air (at the flow rate of 700 cm³/ min) is quantitatively oxidized to CO₂ by a layer of the Körbl catalyst (diameter=12 mm, length=35 mm) heated to 90° C. The CO₂ formed can be specifically bound by a heated layer of ascarite⁴⁶. On the basis of model experiments it was concluded that under the conditions described in the paper the degree of oxidation of 16 various organic compounds ranged from 0.7 to 8.7%. Thus, the developed method can be applied as a mean of practically specific removal of CO from a stream of analyzed air in the course of determination of total organic carbon (TOC).

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Zusammenfassung Die Möglichkeit einer spezifischen Entfernung von Kohlenoxid neben Dämpfen flüchtiger, organischer Verbindungen aus dem Luftstrom wurde untersucht. Zur Herstellung von CO-Luftstandardgemischen dienten gewogene Mengen Oxalsäure, die thermisch zersetzt wurden. Das im Luftstrom (700 cm³/Minute) anwesende CO wird an einer auf 90° C erhitzten Körblkatalysatorschicht von 35 mm Länge und 12 mm Durchmesser quantitativ zu Kohlendioxid oxydiert, das dann an einer erhitzten Ascariteschicht⁴⁶ spezifisch gebunden wird. Bei Modellversuchen mit 16 verschiedenen organischen Verbindungen wurde festgestellt, daß der Oxydationsgrad unter den angegebenen Bedingungen 0,7–8,7% beträgt. Das entwickelte Verfahren kann somit zur praktisch spezifischen Entfernung von Kohlenoxid aus dem analysierten Luftstrom bei der Bestimmung des TOC-Gehaltes aus flüchtigen, organischen Verunreinigungen nach ihrer Oxydation Anwendung finden.

     

Competitive transport of toxic metal ions by polymer inclusion membranes

The paper gives a short overview of application of polymer inclusion membranes (PIMs) for separation and removal of metal ions. Investigation of the selective removal of toxic metal ions, i.e. Cr(VI), Cd(II), Zn(II) from acidic chloride aqueous solutions, as well as trace radionuclides, i.e., ¹³⁷Cs, ⁹⁰Sr and ⁶⁰Co from wastewaters using transport across polymer inclusion membranes was studied. The carriers, i.e., tri-n-octylamine for anionic metal species, as well as dibenzo-21-crown-7, tertbutyl-dibenzo-21-crown-7, and dinonylnaphtalenesulfonic acid for metal cations were incorporated into polymer inclusion membranes composed of cellulose triacetate as a support and o-nitrophenyl pentyl ether as a plasticizer. Selective transport of chromium(VI) over zinc(II) and cadmium(II) chloride complexes through PIMs was observed. Competitive transport of trace radionuclide ions, i.e., ¹³⁷Cs, ⁹⁰Sr, and ⁶⁰Co from NaNO₃ aqueous solutions across polymer inclusion membranes containing a mixture of dinonylnaphtalenesulfonic acid, and dibenzo-21-crown-7 as the carrier provide the selectivity order Cs(I)>Sr(II)>Co(II).     

Catalysis of the Michael addition reaction by late transition metal complexes of BINOL-derived salens

Salen metal complexes incorporating two chiral BINOL moieties have been synthesized and characterized by X-ray crystallography. The X-ray structures show that this new class of Ni-BINOL-salen catalysts contains an unoccupied apical site for potential coordination of an electrophile and naphthoxides that are independent from the Lewis acid center. These characteristics allow independent alteration of the Lewis acidic and Br?nsted basic sites. These unique complexes have been shown to catalyze the Michael reaction of dibenzyl malonate and cyclohexenone with good selectivity (up to 90% ee) and moderate yield (up to 79% yield). These catalysts are also effective in the Michael reaction between other enones and malonates. Kinetic data show that the reaction is first order in the Ni*Cs-BINOL-salen catalyst. Further experiments probed the reactivity of the individual Lewis acid and Br?nsted base components of the catalyst and established that both moieties are essential for asymmetric catalysis. All told, the data support a bifunctional activation pathway in which the apical Ni site of the Ni*Cs-BINOL-salen activates the enone and the naphthoxide base activates the malonate.     

BINOL-salen metal catalysts incorporating a bifunctional design

Salen metal complexes incorporating two chiral BINOL moieties have been synthesized and characterized crystallographically. The corresponding bisnaphthoxide complexes have been found to catalyze the asymmetric addition of benzyl malonate to cyclohexenone in up to 90% ee. With these modular catalysts, the Lewis acid and Bronsted base portions can be independently altered.     

Determination of total carbon and total organic carbon from volatile air pollutants. Part III

Summary The possibility of selective oxidation of volatile organic compounds in the presence of methane was investigated. Thermal decomposition of a mixture of CH₃COONa and NaOH was used as the source of methane introduced into a stream of purified air. Oxidation of the methane present in a stream of air on a layer of the Körbl catalyst is only slight and does not exceed 10%, even in the case of simultaneous presence of acetic acid, which is completely oxidized under identical conditions. Other volatile organic compounds also undergo complete oxidation. It was found that the degree of oxidation of 16 organic compounds is 97.5%. The detection limit of the developed method depends primarily on the effective removal of the so-called carbon background of the air sample, resulting from the presence of CO₂, CO and CH₄. The developed method of selective oxidation can be used for specific elimination of the effect of methane on the results of determinations of TOC in volatile air pollutants.

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Zusammenfassung Die Möglichkeit einer selektiven Oxydation flüchtiger organischer Verbindungen neben Methan wurde untersucht. Methan wurde im gereinigten Luftstrom durch thermische Zersetzung eines Gemisches von CH₃COONa und NaOH hergestellt. Die Oxydation des Methans im Luftstrom an einer Körbl-Katalysatorschicht ist gering und überschreitet nicht 10%, sogar bei gleichzeitiger Anwesenheit von Essigsäure, welche unter diesen Bedingungen — wie andere flüchtige, organische Verbindungen — vollständig oxydiert wird. An 16 organischen Verbindungen wurde festgestellt, daß der Oxydationsgrad97,5% beträgt. Die Erfassungsgrenze der entwickelten Methode zur TOC-Bestimmung ist vor allem von einer effektiven Beseitigung des sogenannten Kohlenstoffblindwertes abhängig, der durch Anwesenheit von CO₂, CO und CH₄ in der Luftprobe verursacht wird. Das entwickelte, selektive Oxydationsverfahren kann somit zur spezifischen Eliminierung des Einflusses von Methan auf die Bestimmungsresultate des TOC-Gehaltes aus flüchtigen Luftverunreinigungen Anwendung finden.

     

Structural factors determining DNA length limitations in conformation-sensitive mutation detection methods

Numerous mutations and polymorphisms in human genes remain to be identified using reliable methods. Of the available mutation scanning methods those dependent on structural change-induced mobility shifts are highly effective. Their efficiency is, however, DNA length-sensitive and the reasons for that are poorly understood. In this study, we explain why scanning genes for mutations is less effective in longer DNA fragments, and reveal the factors which are behind this effect. We have performed a systematic analysis of the same sequence variants of exon 11 of the BRCA1 gene in DNA fragments of three different lengths using the combined single-strand conformation polymorphism (SSCP) and heteroduplex analysis (DA) by capillary electrophoresis (CE). There are two major structural factors responsible for the reduced mutation detection rate in long amplicons. The first is increased contribution from other secondary structure modules and domains in longer fragments, which mask the structural change induced by the mutation. The second is higher frequency of single-nucleotide polymorphisms (SNPs) including common polymorphisms in longer fragments. This makes it necessary to distinguish the structural effect of the mutation from that of each polymorphic variant, which is often difficult to achieve. Taking these factors into account, an efficient scanning of genes for sequence variants by conformation-sensitive methods may be performed.     

Capillary gas chromatographic analysis of highly brominated fire retardant compounds

We report the development of a capillary gas chromatographic method, superior to existing packed column methods, for the analysis of highly brominated additive fire-retardants, including decabromodiphenyl ether (1) and decabromodiphenoxyethane (II). Neither compound has been analyzed previously by capillary GC, and there are no published methods for (II). For (I), the new method is 5–10 times faster than an analogous packed column method, and it has 100 times lower detection limits and twice the precision of a gas chromatographic/mass spectrometric method. For (II), the capillary method is 30–50% faster than an unpublished liquid chromatographic method. The greater efficiency of the capillary method makes possible the complete resolution (R ≥ 1.25) of structurally very similar compounds (e.g. compound (II) and its Br₉Cl₁ and Br₈Cl₂ analogues). With the new method, commercial preparations of (I) and (II) can be rapidly analyzed, and samples from combustion and pyrolysis experiments can be evaluated for compositional changes.     

Refinable maps on ANR's

The map F:X→Y is refinable if for each >0 there is an -map f from X onto Y that is -close to F. The closed set A in X is N-elementary if each neighborhood U of A contains a neighborhood V such that the natural homomorphism ^N(U) → ^N(V) has finitely generated image. If X is a compact ANR, then every closed subset is N-elementary for every N.Suppose F:X → Y is a refinable map between compacta. Then:If B is a compactum in Y such that F^-1B is N-elementary in X then F induces an isomorphism from ^N(B) to ^N(F^-1B). In particular, if X is an ANR, then F induces isomorphisms ^N(B) ^N (F^-1B) and _N(F^-1B) _N(B).If X=S³ and Y=S³/A, then A is cellular.If X is a finite-dimensional ANR, then Y is an ANR if one of the following is true: (1) Y is LC¹, (2) F^-1(y) is locally connected for each y Y, (3) F^-1(y) is approximately 1-connected for each y Y or (4) for each >0 the f in the above definition can be chosen to be monotone.Applications are also made to generalized manifolds and ANR's in 2-dimensional manifolds.