On the Reaction of Glycerol Dehydratase with But‐3‐ene‐1,2‐diol

Intriguing inactivation : Calculations suggest that the ability of relatively high‐energy radical intermediates to inactivate glycerol dehydratase (GDH) may reflect a general and hitherto unidentified inactivation mechanism in the reaction of coenzyme B₁₂‐dependent enzymes and 3‐unsaturated 1,2‐diols (see scheme; AdoCbl: adenosylcobalamin or coenzyme B₁₂).

     

Syntheses of Novel Dipyrrylmethene-BF2 Dyes and Their Performance as Labels in Two-Photon Excited Fluoroimmunoassay

Two-photon excitation of fluorescence (TPE) has been found a powerful tool in the field of microscopy imaging and recently also in the field of bioanalytics. The recently introduced bioaffinity assay technology, ArcDia TPX, enables separation-free ultra-sensitive immunoassays from microvolumes. This assay technique is based on the use of microspheres as a solid reaction carriers and two-photon excited fluorescence detection. In the ArcDia TPX-technology, the individual microparticles are observed and the number of bound biomolecules on the microparticle surface is quantified by two-photon excited fluorescence. Here we present synthesis and use of a novel dipyrrylmethene-BF2 fluorophore that has been designed to be used as label in ArcDia TPX assay technique. The absorption and emission wavelengths of the label are tuned to allow excitation with a 1064 nm microchip laser. The label contains two-carboxylic residues, one of which is activated as N-hydroxysuccinimide ester to enable labeling of amino residues of biomolecules. The other carboxylic group is in free form to increase solubility in aqueous solutions. This new fluorescent label is tested in a separation-free immunoassay using ArcDia TPX assay technique. The performance of the new label is compared to that of one of the brightest fluorophores available, R-phycoerythrin (RPE). According to the results, the dipyrrylmethene-BF2 label provides significantly better signal-to-background ratio, leading to higher assay sensitivity and broader dynamic range compared to that of RPE. Good solubility to aqueous solutions and high fluorescence quantum efficiency, suggests the dipyrrylmethene-BF2 label is applicable also in other fluorescence-based applications.     

Dipyrrylmetheneboron Difluorides as Labels in Two-Photon Excited Fluorometry. Part I-Immunometric Assays

Seven different two-photon excitable dipyrrylmetheneboron difluoride labels (dipyrrylmethene-BF₂ labels) and a frequently used TAMRA label were conjugated to mouse IgG against α-fetoprotein in variable substitution degrees. Altogether 40 IgG conjugates were prepared, and studied with respect to one-photon absorption and emission properties, and two-photon fluorescence efficiency using 1064 nm laser as illumination source. Performance of the IgG conjugates as tracers in a separation-free immunometric assay of α-fetoprotein was evaluated using two-photon excitation assay technology, ArcDia^TM TPX. The results show that the dipyrrylmethene-BF₂ labels provide subpicomolar sensitivity, which is an order of magnitude better than that of TAMRA label. The effect of chromophore structure and substitution degree of IgG-label conjugates on the assay performance is discussed.     

Technetium removal from the aqueous solution using zeolites A and Y containing transition metal ions Co2+ and Zn2+

Journal of Radioanalytical and Nuclear Chemistry - The adsorption properties of two zeolite types, faujasite (NaY, ZnY, CoY) and LTA-4A zeolite (NaA, ZnA, CoA), towards technetium were studied in...     

High-temperature decomposition of amorphous and crystalline cellulose: reactive molecular simulations

We study the thermal decomposition of cellulose using molecular simulations based on the ReaxFF reactive force field. Our analysis focuses on the mechanism and kinetics of chain scission, and their sensitivity on the condensed phase environment. For this purpose, we simulate the thermal decomposition of amorphous and partially crystalline cellulose at various heating rates. We find that thermal degradation begins with depolymerization via glycosidic bond cleavage, and that the order of events corresponds to a randomly initiated chain reaction. Depolymerization is followed by ring fragmentation reactions that lead to the formation of a number of light oxygenates. Water is formed mainly in intermolecular dehydration reactions at a later stage. The reaction rate of glycosidic bond cleavage follows a sigmoidal reaction model, with an apparent activation energy of 166?±?4 kJ/mol. Neither the condensed phase environment nor the heating programme have appreciable effects on the reactions. We make several observations that are compatible with mechanisms proposed for cellulose fast pyrolysis. However, due to the absence of anhydrosugar forming reactions, the simulations offer limited insight for conditions of industrial interest. It remains unclear whether this is a natural consequence of the reaction conditions, or a shortcoming of the force field or its parameter set.

Graphic abstract

     

The origin of aromaticity: important role of the sigma framework in benzene.

The physical nature of aromaticity is addressed at a high ab initio level. It is conclusively shown that the extrinsic aromatic stabilization energy of benzene E(ease)B, estimated relative to its linear polyene counterpart(s), is very well-reproduced at the Hartree-Fock (HF) level. This is a consequence of the fact that the contributions arising from the zero-point vibrational energy (ZPVE) and electron correlation are rather small. More specifically, they yield together 2.0 kcalmol(-1) to the destabilization of benzene. A careful scrutiny of the HF energies by virial theorem shows further that the kinetic energies of the sigma and pi electrons E(T)HF(sigma) and E(T)HF(pi) are strictly additive in the gauge linear zig-zag polyenes, which also holds for their sum Et(T)HF This finding has the important corollary that E(ease)B is little dependent on the choice of the homodesmic reactions involving zig-zag polyenes. A detailed physical analysis of the sigma- and pi-electron contributions to extrinsic aromaticity requires explicit introduction of the potential energy terms Vne, Vee, and Vnn, which signify Coulomb interactions between the electrons and the nuclei. The Vee term involves repulsive interaction Vee(sigmapi) between the sigma and pi electrons, which cannot be unequivocally resolved into sigma and pi contributions. The same holds for the Vnn energy, which implicitly depends on the electron density distribution via the Born-Oppenheimer (BO) potential energy surface. Several possibilities for partitioning Vee(sigmapi) and Vnn terms into sigma and pi components are examined. It is argued that the stockholder principle is the most realistic, which strongly indicates that E(ease)B is a result of favorable sigma-framework interactions. In contrast, the pi-electron framework prefers the open-chain linear polyenes.     

The photoexcitation and photoluminescence of the crystalline tetrahedral complexes of manganese(II) chloride with hydrochloride of phenazone and aminophenazone

Summary The excitation and emission spectra of the complexes (PH)₂MnCl₄ and (APH)₂. MnCl₄ have been studied. All the bands characteristic of excitation transitions ofd ⁵ configuration — the manganese(II) ion being of tetrahedral symmetry — were identified. The spectrum was interpreted in terms of the Orgel's weak field matrix for quartet levelsd ⁵; and the Racah's parametersB andC, the secular determinants, the ground terms and the field strength of thsse complexes were calculated. The 10Dq value for either of the two compounds was found to be 400 cm^–1.The theories of a harmonic oscillator make possible the determination of characteristic parameters from the emission spectrum.The character and the arrangement of bands of excitation and emission spectra — green luminescence — of the crystals are indicative of tetrahedral structure of the complexes. The phenomenon of luminescence has been explained by the⁴ T ₁(G) ⁶ A ₁(S) transition.     

The excitation spectra of tetrahedral complex compounds of manganese(II) bromide with hydrobromides of some derivatives of pyridine and pyperidine

The excitation spectra of complex compounds of magnanese (II) bromide with hydrobromides of some derivatives of pyridine and pyperidine have been studied at temperatures of 77 and 298 K. The character and arrangement bands of the excitation spectra as well as the green luminescence observed are indicative of tetrahedral structure of these compounds. The mechanism of production of the spectra has been explained in terms of ligand field theory. The Racah parameters calculated and the value of 10Dq was estimated to be about 3100 cm^–1. In analyzing the excitation spectra an original method of computation was applied which gave very good results in resolving the bands.     

Deswelling of microfibril bundles in drying wood studied by small-angle neutron scattering and molecular dynamics

Cellulose - Structural changes of cellulose microfibrils and microfibril bundles in unmodified spruce cell wall due to drying in air were investigated using time-resolved small-angle neutron...     

Spectral properties of Eu(III) compound with antibacterial agent ciprofloxacin (cfqH). Crystal structure of [Eu(cfqH)(cfq)(H2O)4]Cl2 · 4.55H2O

A novel europium complex of fluoroquinolone ciprofloxacin (cfqH) with formula [Eu(cfqH)(cfq)(H₂O)₄]Cl₂ · 4.55H₂O (1) was synthesized and its crystal structure determined by X-ray crystallography. The coordination number of europium is eight and in this structure two bidentate, O,O-bonded quinolone molecules and four aqua ligands are coordinated to the metal. One molecule of quinolone is anionic whereas the other is zwitterionic. Additionally, two chloride ions are also present in the structure to compensate the charge of the europium(III) whilst disordered solvent water molecules too are present. The spectral properties (IR, Raman, luminescence) of compound 1 were studied. Analysis of the Stark structure of the luminescence spectra was carried out and the scheme of the electronically excited states and photophysical processes of compound 1 was arranged. The spectral properties show that europium–ciprofloxacin complexes could be suitable for various applications based on their solution-state stability as measured by ¹H and ¹⁹F NMR.