The Influence of Two‐Dimensional Organization on Peptide Conformation

Molecular crowding plays a significant role in regulating molecular conformation in cellular environments. It is also likely to be important wherever high molecular densities are required, for example in surface‐phase studies, in which molecular densities generally far exceed those observed in solution. Using on‐surface circular dichroism (CD) spectroscopy, we have investigated the structure of a synthetic peptide assembled into a highly packed monolayer. The immobilized peptide undergoes a structural transition between α‐helical and random coil conformation upon changes in pH and ionic concentration, but critically the threshold for conformational change is altered dramatically by molecular crowding within the peptide monolayer. This study highlights the often overlooked role molecular crowding plays in regulating molecular structure and function in surface‐phase studies of biological molecules.     

A novel polynuclear donor complex based on helical peptides with aligned electroactive moieties

Two newly synthesised 21-amino acid peptides substituted with ferrocene groups preserve the helical structure of the peptide and behave as multi-centre donor systems with six electroactive reversible redox centres per molecule. The formal potential of the hexaferrocene compound is slightly less positive than that of its single centre analogue.     

Global attractor for heat convection problem in a micropolar fluid

The article is devoted to describe asymptotics in the heat convection problem for a micropolar fluid in two dimensions. We show the existence and the uniqueness of global in time solutions and then prove the existence of a global attractor for considered model. Next, the Hausdorff dimension of the global attractor is estimated. Copyright © 2006 John Wiley & Sons, Ltd.     

Two thia­zolino­[2,3-a]­iso­quinolinone S-oxides

The structures of two racemic thia­zolino­[2,3-a]­isoquinolinone S-oxides, i.e. 8,9-di­methoxy-2,3,5,6-tetra­hydro-10bH-thia­zolo­[2,3-a]­isoquinolin-3-one 1-oxide [C₁₃H₁₅NO₄S, (IIa)] and 8,9-di­methoxy-10b-methyl-2,3,5,6-tetra­hydro-10bH-thia­zolo­[2,3-a]­isoquinolin-3-one 1-oxide [C₁₄H₁₇NO₄S, (IIb)], are described. The thia­zolinone ring in (IIa) exists in an envelope conformation, while in (IIb), it assumes a half-chair conformation. In (IIa) and (IIb), the six-membered heterocyclic ring adopts an envelope conformation. The O atom at sulfur is oriented in a pseudo-axial position, whereas the H atom in (IIa) and the methyl group in (IIb), linked to the stereogenic C centre, occupy a bisectional position with respect to the partially saturated pyridine ring and a pseudo-axial position with respect to the thia­zolinone ring. In both structures, the S=O group and the substituent at the stereogenic C centre are trans with respect to one another. Intermolecular C—H⋯O hydrogen bonds are observed in the crystal lattice of (IIa) and (IIb).     

Polyketanils. Polymers protonated with Bronsted acid

New luminescent materials—aromatic polyketanils (PKs) containing p‐phenylene and biphenylene linkages in the backbone and electron‐donating, side‐group substitutions—were synthesized via melt polycondensation with the goal of studying the interactions between the polymer chains (PKs), primary dopant [1,2‐(di‐2‐ethylhexyl)ester of 4‐sulfophthalic acid (PSA)], and secondary dopant [m‐cresol (MC)] with ¹H NMR, ¹³C NMR, Fourier transform infrared (FTIR), ultraviolet–visible, and photoluminescence measurements. Spectral changes were observed for the PKs after primary and secondary doping, and they supported ionic‐ and hydrogen‐bond formation between the PKs and the PSA and MC, respectively. This specific interaction of the dopant with the host polymer influenced the PK properties, and the following observations were made: (1) HOMO/LUMO energy gap of the protonated PKs; (2) bathochromic/hypsochromic photoluminescence shifts observed after protonation with PSA; (3) a downfield chemical shift of the labile proton in the protonating agent OH group in the ¹H NMR spectra of the protonated polymers; (4) a protonation decrease in the intensity of the C?N stretching band in the FTIR spectrum; and (5) a spherulite‐like morphology, detected by atomic force microscopy and polarized optical microscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5645–5660, 2006     

Mass spectrometric and PM5 study of N-(2-pyridyl)-aminomethyldiphoshonic acids and their complexes with alkali cations

Four N-(2-pyridyl)aminomethyldiphoshonic acids have been synthesized and the formation of the complexes between them and alkali cations were studied by the electrospray ionization mass spectrometry (ESI MS). The ESI spectra have evidenced formation of various types of complexes of the acids and monovalent cations, directly related to the formation of respective mono- and disalts of the acids. The main fragmentation path of the acids and their complexes is realized by the elimination of H₂O or H₃PO₃ molecules. The structures of the acids and their complexes with monovalent cations have been calculated by the PM5 method. The structure and the stabilization role of the intramolecular hydrogen bonds for the complexes are discussed.     

Diverse reactivity of 2-formylphenylboronic acid with secondary amines: synthesis of 3-amino-substituted benzoxaboroles

In the reaction of 2-formylphenylboronic acid with secondary amines different products are formed depending on the structure of the amines. For aliphatic amines the reaction proceeds with the formation of 3-amino-substituted benzoxaboroles or with the formation of complexed boroxins. A crystal structure of the benzoxaborole with a thiomorpholinyl substituent was determined.