Sulphited tannins for exterior wood adhesives

Summary Condensed tannins such as wattle (Mimosa) extract can be partially modified, through hydrolysis of a benzyl ether link and consequent opening of the flavonoid heterocyclic ring, through sulphitation. The introduction of a sulphonic group in the flavonoid structure and the heterocyclic ring opening produces tannin solutions of lower viscosity. While the sulphonic group introduced is deleterious to the strength and water resistance of simple tannin-formaldehyde adhesives, a moderate degree of sulphitation is inconsequential on the strength and water resistance of tannin-formaldehyde adhesives fortified with small amounts of simple phenolic resins used to enhance cross-linking in such a network. Their low viscosity renders these sulphited tannin adhesives particularly useful in applications, like particleboard manufacture, where this is needed.

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Zusammenfassung Kondensierte Tannine, wie z. B. Wattle (Mimosa) Extrakte, können, durch Hydrolyse einer Benzyläther-Bindung und nachfolgende Öffnung des flavonoid heterozyklischen Ringes, durch Sulphitation teilweise modifiziert werden. Die Einfuhrung einer Sulphongruppe in die Flavonoidstruktur und die Öff-nung des heterozyklischen Ringes. ergeben Tannin-Lösungen von niedriger Viskositat. Die Stärke und Wasserfestheit einfacher Tannin-Formaldehyd-Klebstoffe werden durch die eingeführte Sulfongruppe nachteilig beinflußt. Dieselben Eigenschaften von Tannin-Formaldehyd-Klebstoffen, die mit kleinen Mengen phenolischer Harze zur Verbesserung der Querverbindung behandelt sind, bleiben jedoch unbeeinflußt nach mäßiger Sulfitation. Zufolge der niedrigen Viskosität dieser sulfitierten Tannin-Klebstoffe sind selbige besonders geeignet zur Herstellung von Preßspanholz, bei der diese Klebstoff eigenschaft wichtig ist.

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With 2 tables

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Now at the National Timber Research Institute, CSIR, Pretoria, R.S.A.     

Development of a tandem thin-layer chromatography-high-performance liquid chromatography method for the identification and determination of corticosteroids in cosmetic products

A solid-phase extraction clean-up and and a liquid chromatographic method with ultraviolet detection were developed for the analysis of 51 corticosteroids in cosmetic samples in order to screen commercial samples for the presence of undeclared synthetic corticosteroids. A thin-layer chromatographic analysis was carried out on silica gel plates, using different eluants and detection reagents. When such a preliminary chromatographic separation gave some indications about the presence of steroid compounds, the methanol extracts from real samples were applied to a solid-phase extraction C₁₈ cartridge, and the analytes eluted with ethyl ether. The high-performance liquid chromatographic separation was then carried out for the identification and determination of the analytes using a Purospher RP-18 column, an isocratic or a gradient elution with a mixture acetonitrile-water and a photodiode-array detector. The accuracy of the method was determined by spiking experiments on home-made cosmetic samples. The analytical recoveries were satisfactory.     

Evaluation of enzymatic kinetic parameters by thin-layer chromatography with radiometric detection

A radiochromatographic method is described for evaluating K_m and v_max based on a simple modification of the integrated Michaelis-Menten equation. Experimental points are ritted directly to this equation be an iterative technique, the validity of which is tested on simulated experimental data. Results for lysine, ornithine, and glutamic acid decarboxylases are reported.     

Chemistry of μ-hydridobis[pentacarbonylchromium(0)] species. Part III. Redox reactions with mercury(II) compounds and iodine

Summary [Cr₂(CO)₁₀(-H)]^– undergoes ready hydride substitution on reaction with HgX₂ (X = Cl, Br, I or SCN) or with iodine in acetone, yielding [Cr₂(CO)₁₀(-X)]^– complex species which can be converted quantitatively into [Cr(CO)₅X]^– anions by reactions conducted in the presence of an excess of X^–.LCr(CO)₅ and (L-L)Cr(CO)₄ complexes (L = pyridine; L-L = 1,10-phenanthroline or 2,2-bipyridine) are easily prepared by reactions performed in the presence of the L or L-L ligand, respectively.     

Halogenation of the N-Terminus Tyrosine 10 Promotes Supramolecular Stabilization of the Amyloid-β Sequence 7–12

Here, we demonstrate that introduction of halogen atoms at the tyrosine 10 phenol ring of the DSGYEV sequence derived from the flexible amyloid-β N-terminus, promotes its self-assembly in the solid state. In particular, we report the crystal structures of two halogen-modified sequences, which we found to be stabilized in the solid state by halogen-mediated interactions. The structural study is corroborated by Non-Covalent Interaction (NCI) analysis. Our results prove that selective halogenation of an amino acid enhances the supramolecular organization of otherwise unstructured biologically-relevant sequences. This method may develop as a general strategy for stabilizing highly polymorphic peptide regions.     

A Universal Formulation for Tannin Adhesives for Exterior Particleboard

A tannin-based adhesive formulation for particleboard based on the simultaneous reactions of small amounts of diisocyanates and formaldehyde with tannin extracts of the flavonoid type and useful to prepare good exterior grade particleboard is presented and discussed. The adhesive performs well when using any kind of flavonoid-type tannin extract.     

Physicochemical characterisation of sugar cane bagasse lignin oxidized by hydrogen peroxide

The oxidation of soda lignin extracted from sugar cane bagasse was studied in acid medium. Soda lignin was precipitated from black liquor by adding (36N) sulphuric acid until the pH of the resultant solution was close to 2. The resultant, dried, material was oxidized using hydrogen peroxide. Soda lignin oxidized at different times was investigated by CHNS and EDX chemical analysis, GPC, FTIR and solid state CP-MAS ¹³C NMR spectroscopy. Oxidation increased the amount of carboxylic groups, while that of associated carbohydrates decreased. In addition, self-condensation with increase of molecular weight was observed.     

Aristotle’s Cubes and Consequential Implication

It is shown that the properties of so-called consequential implication allow to construct more than one aristotelian square relating implicative sentences of the consequential kind. As a result, if an aristotelian cube is an object consisting of two distinct aristotelian squares and four distinct “semiaristotelian” squares sharing corner edges, it is shown that there is a plurality of such cubes, which may also result from the composition of cubes of lower complexity.      

Development of an HPLC method for the identification and dosage of non-allowed substances in cosmetic products. Part I: local anaesthetics and antihistaminics

An HPLC method with ultraviolet detection coupled with a solid-phase extraction sample clean up was developed for the analysis of five local anaesthetics and four antihistaminics in cosmetic products. The presence of these compounds in commercial cosmetic samples is fordbidden. Extracts from real samples were applied to a solid-phase extraction C₁₈ cartridge, and the analytes were eluted with 8:2 (v/v) acetonitrile/water containing 1 trifluoroacetic acid. HPLC separation was then performed for the identification and determination of the analytes using a Purospher RP-18 column, two gradient eluting systems and a photodiode-array detector. The accuracy of the method was verified by spiking experiments on home-made cosmetic samples. The analytical recoveries were satisfactory.     

Reactions of Ru3(CO)12 with Ene-yne and Alkoxy-silyl Functionalized Compounds. The Crystal Structure of (μ-H)Ru3(CO)9[μ3-η2-HC=N(CH2)3Si(OEt)3]

Ru₃(CO)₁₂ has been reacted with the compounds hex-1-en-3-yne [EtC≡CCH=CH₂], 2-methyl-hex-1-en-3-yne [EtC≡CC(=CH₂)CH₃] and with 3(ethoxy-silyl)propyl isocyanate [(EtO)₃Si(CH₂)₃NCO] and the compound tb [(EtO)₃Si(CH₂)₃NHC(=O)OCH₂C≡CCH₂OC(=O)NH(CH₂)₃Si(OEt)₃] in hydrocarbon solution. Some reactions in CH₃OH/KOH solution (followed by acidification) have also been performed. The main products of the reactions with ene-ynes are the clusters Ru₃(CO)₆(μ-CO)₂L₂ (L = C₆H₈, C₇H₁₀) and their demolition products, the “ferrole” Ru₂(CO)₆L₂ complexes. One of the isomers of Ru₃(CO)₆(μ-CO)₂L₂, and Ru₂(CO)₆L₂ (L = C₇H₁₀) have been reacted with vinyl-triethoxysilane [(EtO)₃SiCH=CH₂]: these reactions did not afford complexes containing new carbon–carbon bonds or triethoxy-silyl groups. Only polymerization of vinyl-triethoxysilane occurred. The reactions of Ru₃(CO)₁₂ with triethoxysilyl-propyl-isocyanate and tb (in the presence of Me₃NO) lead to the same products, that is the isomeric complexes (μ-H)Ru₃(CO)₉[C=N(H)(CH₂)₃Si(OEt)₃] with a “perpendicular” ligand (complex 3, as proposed on the basis of spectroscopic results) and (μ-H)Ru₃(CO)₉[HC=N(CH₂)₃Si(OEt)₃] with a “parallel” ligand (complex 4, as confirmed by a X-ray analysis). The reaction pathways leading to these products are discussed. Complex 4 has been reacted with tetraethyl orthosilicate and the resulting material has been characterized. These reactions are part of a study on the synthesis of inorganic-organometallic materials through sol–gel techniques. This paper is dedicated to Prof. Gunther Schmid in the occasion of his 70th birthday.