A quantum chemical investigation of pyrolysis reactions of glyoxylic acid ethylester

Two possible reaction paths for the pyrolysis of the ethylester of glyoxylic acid have been studied by ab initio molecular orbital calculations. The basis sets 3-21G and 6-31G * have been used, and electron correlation has been included by Møller–Plesset calculations up to fourth order. Our calculations indicate that the reaction leading to acid and ethylene through a 6-membered ring transition state is favored relative to a process involving a formyl hydrogen transfer via a 5-membered ring to the alkyl unit leading to ethane, CO, and CO₂. The predicted activation energies for these two reactions obtained at the highest level of calculation, MP 4(SDTQ )/6–31G *, are 50.4 and 71.7 kcal/mol, respectively. The transition states have RHF wave functions that are stable relative to UHF solutions using the 3–21G basis. The geometry of the transition states and IRC following indicate that both reactions are strongly asynchronous: The C? O bond rupture is virtually completed before hydrogen transfer occurs. For comparative purposes, analogous calculations have been performed for the ethylester of formic acid, where it is confirmed that a 6-membered ring transition state is preferred relative to a 4-membered one by around 42 kcal/mol at the highest level of calculation.     

Analysis of Phenolic Compounds in Lager Beers of Different Origin: A Contribution to Potential Determination of the Authenticity of Czech Beer

Beer contains a wide range of polyphenolic compounds originating mainly from malt and hops. In this work newly modified on-line coupled HPLC–photodiode-array (PDA)–MS methods were used for analysis of characteristic phenolic compounds in several Czech lager beers, in comparison with some foreign lager beers. After optimization of column type, elution mode, and gradient steepness, chromatography was performed with a Restek Ultra Aqueous, C₁₈ (5 μm, 250 mm × 4.6 mm) column at 30 °C and gradient elution using an optimized linear gradient of aqueous acetonitrile acidified with 1% acetic acid, at a flow rate 0.4 mL min^?1. In total, 49 compounds were identified. Eleven individual compounds, predominantly malt phenolics (gallic acid, (?)-catechin, epicatechin, ferulic acid, chlorogenic acid, morin, rutin, quercetin, caempherol, naringenin, and luteolin) were quantified by use of two detection techniques: MS with electrospray ionization and UV detection. Compared with foreign beers, Czech beers contained higher levels of most of the phenolic compounds; specific distributions of individual compounds were also observed. Experimental PDA results for individual polyphenols were evaluated statistically by modified cluster analysis. Because of very tight covariance of the data a new procedure was devised for correlation analysis. The set of beers analyzed can be divided into four clusters closely related to the origin of the and the technology used. It seems that some of the flavonoids have potential use in beer authenticity analysis.     

A rapid method of synthesizing the layered titanosilicate JDF-L1

A rapid procedure for synthesis of highly crystalline and pure samples of JDF-L1 without using organics are reactants or templates is described and indexation of the powder X-ray diffraction pattern of this phase is presented.     

Synthesis and photochemistry of Ru(II) complexes containing phenanthroline-based ligands with fused pyrrole rings

Hydrolysis of 1,10-phenanthrolinopyrrole ethyl ester leads to the acid derivative which is unstable at room-temperature releasing CO(2) and forming 1,10-phenanthrolinopyrrole (php). The ligand reacts with ruthenium(II) to form a series of complexes of the general formula [Ru(php)(n)(bpy)(3-n)](2+), where bpy = 2,2'-bipyridine and n = 1-3. The photochemical properties reveal that the complexes have longer-lived excited states than the standard complex, [Ru(bpy)(3)](2+). Their emission lifetimes range from 9.04 micros (n = 1) to 35.5 micros (n = 3) at 77 K compared to 7.57 micros for the standard. Similarly, at room-temperature, emission lifetimes range from 1.20 micros (n = 1) to 1.70 micros (n = 3) relative to the standard (0.56 micros). The emission quantum yields also have higher values than the standard [Ru(bpy)(3)](2+) under similar conditions. The temperature-dependent studies for the complexes establish the distribution among the radiative, nonradiative, and (3)MLCT to (3)d-d decay channels and are in agreement with the energy gap law.     

Synthesis of photochromic 1,2-dihetarylethene using regioselective acylation of thienopyrroles

[formula: see text] The influence of catalysts, acid chlorides, and solvents in the acylation of methyl 2-methyl-4H-thieno[3,2-b]pyrrole-5-carboxylate was studied. Conditions for the regioselective acylation processes were found. Thienopyrrole-based photochrome was synthesized for the first time.     

Antioxidative properties of <Emphasis Type="Italic">Sambucus nigra</Emphasis> extracts

Potential protective effects of elderberry (Sambucus nigra) extracts against oxidative degradation of hyaluronan (HA) were detected in vitro. To induce free-radical-mediated HA degradation, Weissberger’s biogenic oxidative system, which mimics the situation of acute inflammation, was applied. Time- and dose-dependent changes of dynamic viscosity of the HA solutions in the presence and absence of two elderberry extracts produced in 2006 and 2012 were recorded by rotational viscometry (RV). Radical scavenging capacity of both extracts was investigated by the spectrocolorimetric ABTS [2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt] assay and the “inverted” ABTS assay. Oxygen consumption of the system oxidizing HA either in the absence or presence of the elderberry extracts was determined. The results of RV revealed that an addition of the newer extract (2012) promoted the inhibition of HA degradation more markedly compared to the older extract (2006). The same effect of both extracts on ABTS^·+ scavenging was observed. Inverted ABTS assay demonstrated that colorful substances were not responsible for the radical-scavenging activity. Results of oximetry demonstrated that the effect of the extract from 2006 was more significant than that of the extract from 2012.     

Immobilization of porphyrins in poly(hydroxymethylsiloxane)

Three tetracationic porphyrins differing in the position of charged nitrogen atoms on the peripheral substituents — 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP4), 5,10,15,20-tetrakis(N-methylpyridinium-2-yl)porphyrin (TMPyP2), 5,10,15,20-tetrakis(4-trimethylammoniophenyl) porphyrin (TMAPP), and hydrophobic 5,10,15,20-tetraphenylporphyrin (TPP), were immobilized by adsorption and encapsulation in poly(hydroxymethylsiloxane) (PHOMS). The so prepared porphyrin-PHOMS composites were characterized by porosimetry, scanning electron microscopy, fluorescence and diffuse reflectance UV-VIS spectroscopy. It was found that porphyrins are immobilized in the PHOMS matrix in the free base monomer form Their irradiation produced singlet oxygen O₂(¹Δ_g) with the lifetime of 10–30 μs.