Study of the formation of copper phthalocyanine by EPR spectroscopy

The mechanism of the formation of copper phthalocyanine in the phthalic anhydride/urea process was elucidated by employing ¹⁴N, ¹⁵N or mixed nitrogen donors and enriched ⁶³Cu for the synthesis of the pigment. Both EPR spectroscopy of the magnetically dilute complex and IR spectroscopy of oxidative fission products provide information about the isotopic composition of the inner chelate sphere. The range of superhyperfine interaction detectable by the EPR method was analysed by means of copper phthalocyanine labelled with ¹³C at positions 1, 4, 6, 9, 11, 14, 16 and 19. The results confirm a reaction mechanism which includes the formation of phthalonitrile as an intermediate product.     

Eine Variante des Fano-Axioms fü angeordnete Ebenen

An ordered plane is an incidence structure ( ) with an order function , which satisfies the axioms (G), (V) and (S), but no continuation--axiom is required. Points a, b E are said to be in distinct sides of a line iff and in the same side if , respectively. For any lines , and we prove that if b,c are in the same side of line A and a,c are in the same side of B , then a and b are in distinct sides of C. As conclusions we deduce that is harmonic and that in each complete quadrangle the intersection points of the diagonals are never collinear, which is known as the axiom of Fano. So the Fano-axiom holds in each ordered plane, and also in those with boundary points.     

Über N1- und N2-substituierte 2-Amino-5,6-dihydro-4(1H)-pyrimidinone

The reactions of the monosubstituted guanidines2 b-h with methyl acrylate in dimethylformamide or ethanol as solvent preferentially afford 1-substituted 2-amino-5,6-dihydro-4(1H)-pyrimidinones6 b-h. The structures of 1-hexyl- and 1-benzyl-4-pyrimidinones6 c, e and of the picrate of 1-phenylpyrimidinone6 g were proved by comparison with authentic samples, which were prepared from N-substituted ethyl 3-amino-propionates14 c, e andg and cyanamide. Accordingly,6 g is not identical with authentic 2-phenylaminopyrimidinone7 g (prepared from 2-methylthio-4-pyrimidinone10 and 2-thioxo-4-pyrimidinone12 respectively, compare¹⁰).N,N-Disubstituted guanidines2 i-m react with methyl acrylate in dimethylformamide as solvent to afford N²,N²-disubstituted 2-amino-5,6-dihydro-4-(1H)-pyrimidinones7 i-m. Action of morpholine-4-carboxamidine (21) on methyl acrylate in ethanol yields 2-morpholinopyrimidinone71 as byproduct and 3-ethoxy-N-[morpholino(amino)methylene]propionamide (91) as mainproduct.

Herrn Prof. Dr.Robert Ott mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Thermal inactivation of immobilized enzymes: A kinetic study

The thermal inactivation kinetics of chymotrypsin, trypsin, and—-amylase bound to silica, polyacrylamide, and polystyrene were studied at different temperatures. The inactivation curves were analyzed by a kinetic model, assuming a first-order reaction of differently stable enzyme fractions on the matrix. In all cases the assumption of two enzyme fractions with distinctly different inactivation constants was sufficient for describing the inactivation progress (standard deviations between experimental and calculated inactivation curves, 1-4%). Both the inactivation constants as well as the relative concentrations of the enzyme fractions were found to change in dependence on temperature.     

A practical synthesis of betulinic acid

A new synthetic route for the synthesis of betulinic acid from betulin has been developed. The main step of this procedure is the selective oxidation of the primary alcohol function of betulin without affecting the secondary hydroxyl group. Applying shorter reaction times and lower temperatures results in the exclusive formation of the corresponding aldehyde, betulinal.     

The melting behaviour of poly(3-hydroxybutyrate) by DSC. Reproducibility study

This work is concerned with the melting behaviour and accuracy of differential scanning calorimeter (DSC) analyses of poly(3-hydroxybutyrate) (PHB), a semi-crystalline thermoplastic polymer completely biodegradable and biocompatible, and obtained from renewable resources. Melting parameters of PHB were determined for the first fusion event applying standard experimental procedures for thermal analysis, using heating rates ranging between 1 °C/min and 20 °C/min. The analyses of DSC energy flow scans showed a complex melting peak that may be resolved into three elementary peaks having different intensities at different melting temperatures. Peak temperatures depend on heating rate, while the total crystallinity detected was independent of the rate. A study of 24 DSC runs showed good temperature reproducibility (±0.5 °C), but poor reproducibility of mass crystallinity (±10%).     

The first N‐terminal unprotected (Gly‐Aib)n peptide: H‐Gly‐Aib‐Gly‐Aib‐OtBu

Glycine (Gly) is incorporated in roughly half of all known peptaibiotic (nonribosomally biosynthesized antibiotic peptides of fungal origin) sequences and is the residue with the greatest conformational flexibility. The conformational space of Aib (α‐aminoisobutyric acid) is severely restricted by the second methyl group attached to the C_α atom. Most of the crystal structures containing Aib are N‐terminal protected. Deprotection of the N‐ or C‐terminus of peptides may alter the hydrogen‐bonding scheme and/or the structure and may facilitate crystallization. The structure reported here for glycyl‐α‐aminoisobutyrylglycyl‐α‐aminoisobutyric acid tert‐butyl ester, C₁₆H₃₀N₄O₅, describes the first N‐terminal‐unprotected (Gly‐Aib)_n peptide. The achiral peptide could form an intramolecular hydrogen bond between the C=O group of Gly1 and the N—H group of Aib4. This hydrogen bond is found in all tetrapeptides and N‐terminal‐protected tripeptides containing Aib, apart from one exception. In the present work, this hydrogen bond is not observed (N...O = 5.88 Å). Instead, every molecule is hydrogen bonded to six other symmetry‐related molecules with a total of eight hydrogen bonds per molecule. The backbone conformation starts in the right‐handed helical region (and the left‐handed helical region for the inverted molecule) and reverses the screw sense in the last two residues.     

Modulating surface rheology by electrostatic protein/polysaccharide interactions

There is a large interest in mixed protein/polysaccharide layers at air-water and oil-water interfaces because of their ability to stabilize foams and emulsions. Mixed protein/polysaccharide adsorbed layers at air-water interfaces can be prepared either by adsorption of soluble protein/polysaccharide complexes or by sequential adsorption of complexes or polysaccharides to a previously formed protein layer. Even though the final protein and polysaccharide bulk concentrations are the same, the behavior of the adsorbed layers can be very different, depending on the method of preparation. The surface shear modulus of a sequentially formed beta-lactoglobulin/pectin layer can be up to a factor of 6 higher than that of a layer made by simultaneous adsorption. Furthermore, the surface dilatational modulus and surface shear modulus strongly (up to factors of 2 and 7, respectively) depend on the bulk -lactoglobulin/pectin mixing ratio. On the basis of the surface rheological behavior, a mechanistic understanding of how the structure of the adsorbed layers depends on the protein/polysaccharide interaction in bulk solution, mixing ratio, ionic strength, and order of adsorption to the interface (simultaneous or sequential) is derived. Insight into the effect of protein/polysaccharide interactions on the properties of adsorbed layers provides a solid basis to modulate surface rheological behavior.     

Isotachophoretic analysis of pharmaceutic formulations with different matrices: Determination of nicotinic acid in capsules,tablets, dragees,ointments and tinctures

The selectivity of isotachophoresis is investigated concerning the quantitative determination of an anionic agent in a variety of pharmaceutic application forms with different matrices. As a result, no interferences caused by matrix components were observed in any case. Therefore sample pretreatment can be neglected. The simultaneous quantitation of other anionic constituents, present in the formulations, is possible. The method is evaluated by other analytical characteristics besides selectivity, like precision, accuracy and time of analysis. The contributions of aliquotation and isotachophoretic measurement to the total error were determined by analysis of variance. Systematic errors, due to adsorption of the analyte on solid matrix material were examined by standard addition. The results of the analytical characteristics indicate the excellent applicability of isotachophoresis for the routine analysis of anionic analytes in pharmaceutic preparations