Metal binding to ligand-containing peptide nucleic acids

The substitution of nucleobases in nucleic acid duplexes with ligands that have high affinity for transition metal ions creates metal-binding sites at specific locations within the duplexes. Several studies on the incorporation of metal ions into DNA and peptide nucleic acid (PNA) duplexes have suggested that the stability constant of the metal complex formed within the duplexes is a primary determinant of the thermal stability of the duplexes. To understand this relationship, we have synthesized two PNA monomers that carry the same ligand, namely 8-hydroxyquinoline, but have this ligand attached differently to the PNA backbone. The PNA monomers have been incorporated into PNA duplexes. UV and CD spectroscopy and calorimetric studies of the 8-hydroxyquinoline-PNA duplexes showed that the effect of the stability of the metal complex on the PNA duplexes was significantly modulated by the steric relationship between the complex and the duplex. This information is useful for the construction of hybrid inorganic-nucleic acid nanostructures.     

Synthesis of trialkyl vanadates and trialkyl antimonites

Summary A method is proposed for the synthesis of trialkyl vanadates and trialkyl antimonites by reaction of VOCl₃ and SbCl₃, respectively, with alcohols in presence of ammonia.     

Copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with <Emphasis Type="Italic">N</Emphasis>-(2-carboxyethyl)anthranilic acid H<Subscript>2</Subscript>CEAnt. Synthesis and crystal structure of [Cu(CEAnt)(H<Subscript>2</Subscript>O)] ⋅ H<Subscript>2</Subscript>O

Protolytic equilibria and complexation of N-(2-carboxyethyl)anthranilic acid (H₂CEAnt) with copper(II) ions in aqueous solutions were studied by UV spectroscopy and pH potentiometry. The H₂CEAnt compound has no zwitterionic structure, and the protons are localized on the carboxy groups. The acid ionization constants of H₃CEAnt⁺ (T = 25 °C, I = 0.1 M KNO₃) are pK ₀ = 1.3±0.2 (=NH₂ ⁺), pK ₁ = 3.88±0.02 (Alk-COOH), and pK ₂ = 5.28±0.02 (Ar-COOH). The model of complexation of H₂CEAnt with copper(II) ions involves two deprotonated complexes [Cu(CEAnt)] and [Cu(CEAnt)₂]²⁻ (logβ = 6.31±0.04 and 8.0±0.2, respectively). The [Cu(CEAnt)(H₂O)]⋅H₂O complex was synthesized by the reaction of H₂CEAnt with (CuOH)₂CO₃, and its structure was established by X-ray diffraction. The coordination polyhedron of Cu is intermediate between the tetragonal pyramid and trigonal bipyramid. The CEAnt²⁻ ligand serves as a tetradentate chelating bridging ligand (Cu-O, 1.944(3) and 1.950(3) Å; Cu-O', 2.195(4) Å; Cu-N, 2.016(5) Å), and the fifth position of the polyhedron is occupied by a water molecule (Cu-O_w, 1.976(4) Å). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1518–1523, July, 2005.     

Synthesis, XRD structure and properties of diaqua(p-toluidine-N,N-di-3-propionato)copper(II) dihydrate [Cu(p-Tdp)(H2O)2]·2H2O

The copper(II) complex [Cu(p-Tdp)(H₂O)₂]·2H₂O, where p-Tdp is the anion of p-toluidine-N,N-di-3-propionic acid (or N,N-di(2-carboxyethyl)-p-toluidine), has been synthesized and characterized by X-ray diffraction. Three crystallographically independent [Cu(p-Tdp)(H₂O)₂] molecules have a similar structure. The Cu atoms have a square pyramidal environment (4+1) with a small trigonal bipyramidal distortion. The ortho-H atom of the benzene ring blocks up the sixth coordination position of the Cu polyhedron. The basal plane is formed by the donor atoms of the tridentate ligand and by the water molecule (average bond length Cu---N 2.03, Cu---O 1.93, Cu---O_w 2.00 Å), the apex is occupied by another water molecule (Cu---O_w 2.27 Å). The Cu atoms are located 0.20–0.30 Å out of the mean planes of the four basal atoms towards the apical O_w atom. The IR and electronic absorption spectra of p-Tdp and the title compound have been described. UV–Vis reflectance spectra shows that the complex has the same square pyramidal geometry in the crystal state and in solution. The protonation constants of the ligand log K₁=6.87(2), log K₂=3.75(2), log K₃=2.57(2) and stability constants log K_CuH(p-Tdp)=2.13(5), log K_Cu(p-Tdp)=6.38(3) were determined by pH-titration at 25.0 °C and I=0.1 M KNO₃.     

Chitosan conjugates with biologically active compounds: design strategies, properties, and targeted drug delivery

This review summarizes the current research on the development of biologically active polymer compounds based on chitosan and its derivatives; it systematizes approaches taken for the design of conjugates based on a given polymer, and it covers the latest trends in the development of targeted drug delivery systems. An analysis of published data shows that the conjugation of biologically active substances with chitosan and its derivatives results in promising materials for use as drug delivery systems and for the control of the properties of the biologically active substances.     

Self-similar potentials and theq-oscillator algebra at roots of unity

Properties of the simplest class of self-similar potentials are analyzed. Wave functions of the corresponding Schrödinger equation provide bases of representations of theq-deformed Heisenberg-Weyl algebra. When the parameterq is a root of unity, the functional form of the potentials can be found explicitly. The generalq ³ = 1 and the particularq ⁴ = 1 potentials are given by the equi-anharmonic and (pseudo) lemniscatic Weierstrass functions, respectively.