3‐Formyl­phenyl­boronic acid

The mol­ecule of the title compound, C₇H₇BO₃, is planar, and the bond lengths and angles are typical. The formyl group is essentially coplanar with the benzene ring but does not influence significantly the distortion of the ring, although the formyl group does have a strong influence on the crystal packing. The geometry of the boronic acid group is typical. In the crystal structure, the mol­ecules are linked by O—H⋯O hydrogen bonds.     

Estimation of antioxidant capacity against peroxynitrite and hypochlorite with fluorescein

Peroxynitrite and hypochlorite are oxidants relevant in many pathological situations. We propose a simple spectrofluorometric assay to determine antioxidant capacity against hypochlorite and peroxynitrite based on protection against fluorescein bleaching. The assay can be performed on a microplate and requires minute amounts of material. Standard antioxidants show different reactivities for both oxidants. Antioxidant capacity of fruit bodies of edible mushrooms, tea, coffee and wine estimated as exemplary biological material point to considerable differences in the scavenging capacity of various biological material against hypochlorite, peroxynitrite and peroxyl radicals.     

Helix‐coil and beta sheet‐coil transitions in a simplified,yet realistic protein model

A reduced model of polypeptide chains and protein stochastic dynamics is employed in Monte Carlo studies of the coil‐globule transition. The model assumes a high‐resolution lattice representation of protein conformational space. The interaction scheme is derived from a statistical analysis of structural regularities seen in known three‐dimensional protein structures. It is shown that model polypeptides containing residues that have strong propensities towards locally expanded conformations collapse to β‐like globular conformations, while polypeptides containing residues with helical propensities form globules of closely packed helices. A more cooperative transition is observed for β‐type systems. It is also demonstrated that hydrogen bonding is an important factor for protein cooperativity, although, for systems with suppressed hydrogen bond interactions, a higher cooperativity of β‐type proteins is also observed.     

Propagation of Oscillating Chemical Signals through Reaction Networks

Akin to electronic systems that can tune to and process signals of select frequencies, systems/networks of chemical reactions also “propagate” time‐varying concentration inputs in a frequency‐dependent manner. Whereas signals of low frequencies are transmitted, higher frequency inputs are dampened and converted into steady‐concentration outputs. Such behavior is observed in both idealized reaction chains as well as realistic signaling cascades, in the latter case explaining the experimentally observed responses of such cascades to input calcium oscillations. These and other results are supported by numerical simulations within the freely available Kinetix web application we developed to study chemical systems of arbitrary architectures, reaction kinetics, and boundary conditions.     

Chiral Recognition of Amino Acid Esters in Organic Solvents Using a Glucose-Based Receptor

Due to the chemical and biological relevance of amino acids, efficient methods for the recognition and separation of their enantiomers are highly sought after. Chiral receptors based on extended molecular scaffolds are typically employed for this purpose. These receptors are often effective only in specific environments and towards a narrow scope of amino acid guests. Recently we reported a simple, glucose-based macrocycle capable of enantioselective binding of a broad range of amino acid methyl esters in water. Herein we demonstrate that the same receptor can be used for chiral recognition of amino acid esters in organic solvents. We show that the binding affinity and selectivity of the receptor are highly dependent on the coordinating strength of the solvent. An in-depth analysis of the receptor’s conformation and its interactions with amino acid methyl esters allowed us to propose a binding mode of amino acids to the receptor in CDCl₃. The binding modes in CDCl₃ and D₂O were then compared, highlighting the main interactions responsible for binding affinity and selectivity in each solvent. We envision that the insight provided by this study will facilitate the development of further amino acid receptors based on monosaccharides with improved binding affinities and both enantio- as well as chemoselectivities.     

Iron oxide thin film growth on Al2O3/NiAl(1 1 0)

The electronic structure and the growth morphology of iron oxide thin films were studied by means of Synchrotron Radiation Photoelectron Spectroscopy (SRPES) and Low Energy Electron Diffraction (LEED). A thin well-ordered alumina film on a NiAl(1 1 0) single crystal surface as a template for iron oxide growth was employed. Two different methods of iron oxide film preparation were applied. In the first attempt, iron deposited at room temperature was subsequently annealed in oxygen. Even though a whole layer of iron was oxidized, an expected long-range order was not achieved. The second attempt was to perform reactive deposition. For this reason iron was evaporated in oxygen ambient at elevated substrate temperature. This method turned out to be more efficient. Diffused but clear LEED patterns of six-fold symmetry indicating hexagonal surface atoms arrangement were observed. From the PES measurements, binding energies for Fe2p for grown iron oxide film were established as well as energy distribution curves for the valence band. Growth curves based on Fe3p core-level peak intensities for iron and iron oxide were plotted identifying type of film growth for both deposition methods. Based upon these results we have found evidence for interdiffusion in the interface between alumina and iron oxide at the early stages of growth. Further deposition led to formation of Fe₃O₄(1 1 1) (magnetite) overlayer. Moreover, the quality of the film could also be improved by long-time annealing at temperatures not exceeding 575 K. Higher annealing temperature caused disappearance of LEED pattern indicating loss of long-range ordering.     

Mechanical and electrical properties of nanostructured ‘plastic metals’

Deformable, supraspherical (SS) aggregates of metal nanoparticles (NPs) connected by long-chain dithiol ligands self-assemble into nanostructured materials of macroscopic dimensions. These materials are both malleable/moldable at room temperature as well as electrically conductive. Upon gentle heating, they harden into polycrystalline metals. The paper discusses qualitative models that rationalize the mechanical and electrical properties of these unusual ‘plastic metals’.     

Electro-optic polymer frequency shifter activated by input optical pulses

We demonstrate electro-optic frequency shifting of 1.55-microm optical pulses by as much as 86 GHz in a polymer traveling-wave phase modulator. The optical pulses were modulated with the linear region of quasi-sinusoidal microwave pulses. In the implemented configuration the electro-optic frequency shifter does not require synchronization with the source of the optical pulses, making it transparent to the optical-pulse repetition rate and increasing its utility. Electro-optic frequency conversion has a number of advantages compared with other methods of all-optical frequency conversion, including no need for a second optical source, high conversion efficiency, and simple control of the output frequency.     

Hypochlorous acid-induced oxidative damage of human red blood cells: effects of tert-butyl hydroperoxide and nitrite on the HOCl reaction with erythrocytes

Hypochlorous acid, one of the most powerful biological oxidants, is believed to be important in the pathogenesis of some diseases. The purpose of this study was to further characterise the membrane and intracellular events which resulted in HOCl-induced oxidative impairments and haemolysis of human erythrocytes and interaction of different oxidative agents, which accumulated during respiratory burst, in the process of RBS oxidation. The sequence of cellular events after red blood cell exposure to HOCl: cell morphological transformations, oxidation of cellular constituents, enzyme modifications, and haemolysis have been evaluated. It was shown that HOCl-treated cells underwent colloid-osmotic haemolysis, preceded by rapid morphological transformations and membrane structural transitions. The activation energy of the process of haemolysis (after removal of the excess of oxidative agent) was estimated to be 146+/-22 kJ/mol at temperatures above the break point of Arrhenius plot (31-32 degrees C). This value corresponds to the activation energy of the process of protein denaturation. Modification of erythrocytes by HOCl inhibited membrane acetylcholinesterase (uncompetitive type of inhibition), depleted intracellular glutathione, activated intracellular glutathione peroxidase, but did not induce membrane lipid peroxidation. The presence of other oxidants, nitrite or tert-butyl hydroperoxide (t-BHP), promoted the oxidative damage induced by HOCl and led to new oxidative reactions.