New chromogenic substrates of human neutrophil cathepsin G containing non-natural aromatic amino acid residues in position P1 selected by combinatorial chemistry methods

Specificity of human cathepsin G was explored using combinatorial chemistry methods. Deconvolution of a tetrapeptide library, where 5-amino-2-nitrobenzoic acid served as a chromophore attached at the C-terminus, yielded the active sequence Phe-Val-Thr-Tyr-Anb^5,2-NH₂. This sequence was used for a second-generation library with the general formula Ac-Phe-Val-Thr-X-Anb^5,2-NH₂, where position X was replaced with several amino acids: l-pyridyl- alanine (Pal), 4-nitro-l-phenylalanine (Nif), 4-amino-l- phenylalanine (Amf), 4-carboxy-l-phenylalanine (Cbf), 4-guanidine-l-phenylalanine (Gnf), 4-methyloxycarbonyl- l-phenylalanine (Mcf), 4-cyano-l-phenylalanine (Cyf), Phe, Tyr, Arg and Lys. Specificity ligand parameters, k _cat and K _M, with human cathepsin G were determined for all chromogenic substrates synthesized. The highest value of the specificity constant (k _cat/K _M) was obtained for a substrate with the Gnf residue in position P₁. This peptide was 10 times more active than the second most active substrate which contained the Amf residue. The following order of potency was established: Gnf > > Amf > Tyr = Phe > Arg= Lys > Cyf. Substrate specificity for cathepsin G is greatly enhanced when an aromatic side chain and a strong positive charge are incorporated in residue P₁.     

Two-proton correlations in the decay of 45Fe

The decay of extremely neutron-deficient 45Fe has been studied in detail by means of a novel type of a gaseous detector employing digital imaging to record tracks of charged particles. The two-proton radioactivity channel was clearly identified. For the first time, the angular and energy correlations between two protons emitted from the nuclear ground state were determined, indicating the genuine three-body character of this decay. The half-life of 45Fe was found to be 2.6+/-0.2 ms and the observed 2p decay branching ratio is 70+/-4%.     

Practical method for the absolute configuration assignment of tert/tert 1,2-diols using their complexes with Mo2(OAc)4

We describe here an application of the practical, simple, and reliable approach for the determination of the absolute configuration of sterically demanding tert/tert vic-diols. According to this method, it is only necessary to mix dimolybdenum tetraacteate and a chiral diol in DMSO and record the CD spectra in the 250-650 nm spectral range. From the sign of the CD bands occurring at around 310, 350, and 400 nm, it is possible to establish the chirality of the diol unit expressed by the sign of the O-C-C-O torsion angle. Because the preferred conformation of the diol in the formed complex is known, we are able to determine the absolute configuration of the carbon atoms in the diol subunit even in flexible tert/tert vic-diols.     

Validation of the HS-GC-FID method for the determination of ethanol residue in tablets

This paper describes the validation of a HS-GC-FID method (based on the Pharmacopeia’s method) for the determination of ethanol content in tablets. A general view of the procedure development/optimization process is presented. The main point of this study is the calculation of validation parameters. Selectivity of the method was determined. Linearity (r > 0.997) was observed in the range from 9.0 to 3,040 μg of ethanol per sample (because the mass of the tablets used was around 200 mg, this corresponds to 45–15,200 μg g⁻¹). The method showed good recoveries (average 99.0%), and a relative standard deviation for repeatability and intermediate precision of 4.5% and 5.5% respectively. The limit of detection was calculated to be 3.0 μg of ethanol per sample (15 μg g⁻¹). The uncertainty budget was done according to the "Guide to the Expression of Uncertainty in Measurement" (GUM)[1], and a relative expanded uncertainty was estimated as 4.8%.     

Metal-coated fused silica fibers as a support for immobilized compounds yielding a volatile analyte (C<Subscript>2</Subscript>H<Subscript>4</Subscript>)

This paper presents the results of investigations of chemically modified fibers comprising an immobilized compound that yields ethene as the analyte in generated standard gaseous mixtures. Prior to chemical modification, the fibers were coated with a thin aluminum layer to improve their mechanical strength. Commercially available Al-coated fibers were used in this work. During thermal decomposition of the immobilized compound, reproducible quantities of the analyte per unit fiber length were obtained for all the investigated fibers (fiber diameter (μm)/outside diameter (μm) of the Al-coated fiber = 110/146, 220/300, and 660/830), amounting to 0.685 ± 0.032, 0.8300 ± 0.0081, and 1.092 ± 0.010 ng cm⁻¹, respectively. The proposed procedure can be used successfully for the generation of measured component of matrix-free reference materials.     

Shape and topology optimization of contact problems by level set methods

This paper deals with the numerical solution of a topology and shape optimization problems of an elastic body in unilateral contact with a rigid foundation. The contact problem with the prescribed friction is considered. The structural optimization problem consists in finding such shape of the boundary of the domain occupied by the body that the normal contact stress along the contact boundary of the body is minimized. In the paper shape as well as topological derivatives formulae of the cost functional are provided using material derivative and asymptotic expansion methods, respectively. These derivatives are employed to formulate necessary optimality condition for simultaneous shape and topology optimization. Level set based numerical algorithm for the solution of the shape optimization problem is proposed. Level set method is used to describe the position of the boundary of the body and its evolution on a fixed mesh. This evolution is governed by Hamilton – Jacobi equation. The speed vector field driving the propagation of the boundary of the body is given by the shape derivative of a cost functional with respect to the free boundary. Numerical examples are provided. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preliminary Studies Using Differential Scanning Calorimetry of Radiation-Induced Transformations in Starch and Flour

Differential scanning calorimetry was applied in studies of the effect of gamma irradiation on the potato starch and wheat flour. Essential differences were noticed between endothermal effects observed in concentrated suspensions of the initial and irradiated potato starch and wheat flour heated at a rate of 2.5°C min^-1, while only small differences were noticed between gelatinization thermal effects recorded for ca. 20% suspensions of the initial and irradiated potato starch samples heated at a rate 10°C min^-1. Moreover, in the case of wheat flour, a decrease of decomposition temperature of the amylose-lipid complex was concluded. This revised version was published online in August 2006 with corrections to the Cover Date.