Asymptotic Behavior of Beta-Integers

Beta-integers (“β-integers”) are those numbers which are the counterparts of integers when real numbers are expressed in an irrational base β > 1. In quasicrystalline studies, β-integers supersede the “crystallographic” ordinary integers. When the number β is a Parry number, the corresponding β-integers realize only a finite number of distances between consecutive elements and are in this sense the most comparable to ordinary integers. In this paper, we point out the similarity of β-integers and ordinary integers in the asymptotic sense, in particular for a subclass of Parry numbers – Pisot numbers for which their Parry and minimal polynomial coincide.     

Sparsely intersecting perfect matchings in cubic graphs

In 1971, Fulkerson made a conjecture that every bridgeless cubic graph contains a family of six perfect matchings such that each edge belongs to exactly two of them; equivalently, such that no three of the matchings have an edge in common. In 1994, Fan and Raspaud proposed a weaker conjecture which requires only three perfect matchings with no edge in common. In this paper we discuss these and other related conjectures and make a step towards Fulkerson’s conjecture by proving the following result: Every bridgeless cubic graph which has a 2-factor with at most two odd circuits contains three perfect matchings with no edge in common.     

Three-branched dendritic dipolar nonlinear optical chromophores, more than three times a single-strand chromophore?

To elucidate the dependence of the nonlinear optical (NLO) response on the conformation of triply branched derivatives, a new series of D-pi-A dendrimers has been synthesized. A combined approach of experiments (UV-vis and EOA measurements) and computational predictions (semiempirical and ab initio) was applied both on the dendrimers and on the corresponding single-strand chromophores. It has been shown that depending on the surrounding media the NLO activity of a flexible dendrimer can be very different. Two limiting cases are proposed: (i) the dendrimer resembles a solution of the corresponding single-strand chromophores with about 3-fold concentration, where the hyperpolarizability is the sum of the effect of three noninteracting single-strand subunits ("independent chromophores" limit); (ii) the dendrimers show nearly parallel or helical alignments of the single-strand subunits. Because of this change of conformation the NLO activity can be enhanced up to nine times the value of the "independent chromophores" limit and, thus, are more than a single strand chromophore. Conformers of dendrimers with interacting single-strand chromophores have been identified experimentally in nonpolar solutions by the EOA spectroscopy and possible structures have been revealed by numerical calculations, which could moreover show the tendency of the effects on the hyperpolarizability due to structural changes of the flexible dendritic architecture. Implications for future research developments are given to implement the "more than three times" concept.     

Switching the Inhibitor-Enzyme Recognition Profile via Chimeric Carbonic Anhydrase XII

A key part of the optimization of small molecules in pharmaceutical inhibitor development is to vary the molecular design to enhance complementarity of chemical features of the compound with the positioning of amino acids in the active site of a target enzyme. Typically this involves iterations of synthesis, to modify the compound, and biophysical assay, to assess the outcomes. Selective targeting of the anti-cancer carbonic anhydrase isoform XII (CA XII), this process is challenging because the overall fold is very similar across the twelve CA isoforms. To enhance drug development for CA XII we used a reverse engineering approach where mutation of the key six amino acids in the active site of human CA XII into the CA II isoform was performed to provide a protein chimera (chCA XII) which is amenable to structure-based compound optimization. Through determination of structural detail and affinity measurement of the interaction with over 60 compounds we observed that the compounds that bound CA XII more strongly than CA II, switched their preference and bound more strongly to the engineered chimera, chCA XII, based on CA II, but containing the 6 key amino acids from CA XII, behaved as CA XII in its compound recognition profile. The structures of the compounds in the chimeric active site also resembled those determined for complexes with CA XII, hence validating this protein engineering approach in the development of new inhibitors.     

Volatiles of Helichrysum italicum (Roth) G. Don from Croatia

Helichrysum italicum (Roth) G. Don is a flowering plant of the family Asteraceae. It is rich in oil that is used for different medicinal purposes and in fragrance industry. Volatile profile of four populations of H. italicum, collected from natural habitat in Dalmatia (Croatia), was analysed by capillary GC–MS. Sample from Bra? Island had α-trans-bergamotene (10.2%) and β-acoradiene (10.1%) as the majors, whereas sample collected on Biokovo Mt. was rich in neryl acetate (8.1%). β-Acoradiene was also the main constituent of sample collected near Tijarica, whereas rosifoliol (8.5%) was the most abundant constituent in sample collected near Makarska. Presented results show the influence of environmental conditions on chemical differentiation of the volatiles of H. italicum from Croatia.     

Interaction of cellulose-based cationic polyelectrolytes with mucin

Mucoadhesivity of water-soluble polymers is an important factor, when testing their suitability for controlled drug delivery systems. For this purpose, the interaction of new cationic cellulose polyelectrolytes with lyophilized mucin was investigated by means of turbidimetric titration, microscopy and measurement of zeta potential and particle size changes in the system. Results show that the cellulose derivatives interact with mucin. This interaction became stronger if cellulose macromolecules contained positively charged groups and an electrostatic interaction with the negatively charged mucin particles occurred. Under certain conditions flocculation of mucin particles by the cellulose polyelectrolyte was observed.     

Comparison of Glassy Carbon and Copper Microparticles as a Renewable Working Electrode Material for Amperometric Determination of Amino Acids Using Flow Through Detector

Flow‐through detector with renewable working material based on glassy carbon or copper microparticles was used for flow injection determination of tyrosine by direct oxidation and phenylalanine via the complexation reaction with copper ions, respectively. Copper‐based detector allows the determination of electrochemically inactive amino acid, but the detection conditions are limited and fabrication and handling of the detector are more demanding. Low working potential, applied for the detection on copper microparticles, makes the determination very selective. Moreover, low baseline noise compensates lower sensitivity of copper‐based detector, enabling to reach quantification limit 4.7×10^?6 mol L^?1, in comparison with quantification limit 1.6×10^?6 mol L^?1 obtained for tyrosine on carbon‐based detector.     

Synthese der Clathratverbindungen des Typs Cd(en)Pd(CN)4·2G

In this paper three compounds with the same host molecule of Cd(en)Pd(CN)₄ type, but of different organic components such as thiophene, pyrrole and furan were described.     

In-Groove Carbon Nanotubes Device for SPME of Aromatic Hydrocarbons

A new solid phase microextraction (SPME) fibre using carbon nanotubes as fibre coating incorporated into a groove of a stainless steel rod is suggested. It is mechanically stable and exhibits relatively high thermal stability (up to 280 °C). The coating showed especially good extraction efficiency for aromatic hydrocarbons. The extraction properties of the fibre to benzene, toluene, ethylbenzene and o-xylene were examined using both direct and headspace SPME modes coupled to gas chromatography-flame ionization detection. The parameters affecting the extraction efficiency (extraction temperature and time, salt addition, desorption temperature and time) were investigated and quality parameters were measured under the optimized conditions. For both headspace and direct SPME the calibration graphs were linear up to 100 mg L⁻¹ (R ² > 0.996) and detection limits ranged from 0.09 to 0.39 μg L⁻¹. The repeatabilities were 5.9–13.3%. The proposed coating was applied for aromatic hydrocarbons determination in petrol station waste waters.