Hydrolysis of the Peptide Bond in N-Acetylated L-Methionylglycine Catalyzed by Various Palladium(II) Complexes: Dependence of the Hydrolytic Reactions on the Nature of the Chelate Ligand in cis-[Pd( L)(H 2O) 2] 21 Complexes

Summary. Hydrolytic reactions between various palladium(II) complexes of the type cis-[Pd(L)(H₂O)₂]²⁺ in which L is ethylenediamine (en), 1,2-propylenediamine (1,2-pn), isobutylenediamine (ibn), 1,2-diaminocyclohexane (1,2-dach), N-methylethylenediamine (Meen), N,N,N,N-tetramethylethylenediamine (Me₄en), S-methyl L-cysteine (MeS-L-HCys), L-methionine (L-HMet), and 2,5-dithiahexane (dth) and dipeptide N-acetylated L-methionylglycine (MeCOMet-Gly) were studied by ¹H NMR spectroscopy. The reactions were carried out in the pH range 2.0–2.5 and at 50°C. In all these reactions, palladium(II) complex bound to a methionine residue effects the regioselective cleavage of the amide bond involving the carboxylic group of methionine. We found that the rate of hydrolysis and mechanism of this reaction are strongly dependent from the nature of the chelate ligand L in palladium(II) complexes of the type cis-[Pd(L)(H₂O)₂]²⁺.     

Asymmetric synthesis of [7]helicene-like molecules

[reaction: see text] A new approach to nonracemic [7]helicene-like molecules has been developed. Stereoselective Co(I)-mediated [2 + 2 + 2] cycloisomerization of aromatic triynes containing an asymmetric carbon atom produces [7]helicene-like scaffolds in diastereomeric ratios up to 100:0. This central-to-helical chirality transfer can be controlled by the absolute configuration at the asymmetric center and by the presence of carbon substituents.     

Organopolysiloxanes as Chemically Sensitive Coatings for Optical Fibers

Various types of UV-curable organically modified siloxanes have been synthesized by the sol-gel method with the aim of fabricating chemically sensitive coatings for silica optical fibers. The refractive index of the coating material can be tailored in the range from 1.46 to 1.56 and sensitivity towards CO2 is achieved by incorporation of amino groups. The interaction of the cured layers with CO2 or with hydrocarbons has been studied in immersion experiments. Both the reaction of CO2 with incorporated amino groups and the penetration of hydrocarbons into the layer induce changes of the light absorption coefficient and the refractive index of the coating which are detected by measuring the output light intensity from the fiber.     

Some useful data of continuous variation method

Summary Conditions for the correct application of continuous variation are presented. The data (parameterR _mn , effective stability constant and total concentration) that enable a safe determination of the molar ratio metalligand (m/n) in the complex are computed. The possibility of the determination of true valuesm andn and effective stability constant from one continuous variation curve are discussed and demonstrated on the example of the iron(III)-chrome azurol S complex.

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Einige nützliche Daten zur Methode der kontinuierlichen Variation

Zusammenfassung Bedingungen für die korrekte Anwendung der Methode der kontinuierlichen Variation werden gegeben. Die Daten (ParameterR _mn effektive Stabilitätskonstante und Gesamtkonzentration), die eine zuverlässige Bestimmung des molaren Verhältnisses MetallLigand (m/n) im Komplex ermöglichen, werden berechnet. Die Möglichkeit zur Bestimmung der wahren Werte fürm undn sowie der effektiven Stabilitätskonstanten aus einer Kurve der kontinuierlichen Variation werden erörtert und am Beispiel des Eisen(III)-Chromazurol S-Komplexes demonstriert.

     

Enhanced post-source decay and cross-ring fragmentation of oligosaccharides facilitated by conversion to amino derivatives

Post-source decay (PSD) fragmentation of chemically or enzymatically produced aminoglycans has been evaluated through matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Conversion of native glycans to their respective aminoglycan derivatives improved detection sensitivity of the usual fragments and promoted cross-ring fragmentation of linear oligosaccharides, facilitating linkage recognition. The cross-ring fragmentations for both dextrin and dextran oligosaccharides were not limited to the reducing-end glucose moiety, as they were extended throughout the entire molecule. When the amino group was generated for N-glycans derived from three different glycoproteins, an enhancement of PSD was observed, without a significant extent of cross-ring fragmentation.     

Dynamic mechanism of photochemical induction of turing superlattices in the chlorine dioxide-iodine-malonic acid reaction-diffusion system

We study the mechanism of development of superlattice Turing structures from photochemically generated hexagonal patterns of spots with wavelengths several times larger than the characteristic wavelength of the Turing patterns that spontaneously develop in the nonilluminated system. Comparison of the experiment with numerical simulations shows that interaction of the photochemical periodic forcing with the Turing instability results in generation of multiple resonant triplets of wave vectors, which are harmonics of the external forcing. Some of these harmonics are situated within the Turing instability band and are therefore able to maintain their amplitude as the system evolves and after illumination ceases, while photochemically generated harmonics outside the Turing band tend to decay.     

Analytical characterization of a facile porous polymer monolithic trypsin microreactor enabling peptide mass mapping using mass spectrometry

A simple and rapid single-step method is presented to fabricate an enzyme reactor using trypsin immobilized on a macroporous polymer monolith. A reactor produced in a capillary format is ready to use within 1 h of preparation. The monomers making up the monolith, including N-acryloxysuccinimide for covalent immobilization of the enzyme, are mixed with trypsin and introduced into the column by capillary force for polymerization/immobilization. The enzyme activity from column-to-column is reproducible below 5% relative standard deviation (RSD), while the reactor is durable for at least 20 weeks when stored at room temperature. The apparent kinetic constants V(max) and K(m) are of value similar to those obtained by free trypsin in solution. Enzymatic digestion of proteins was shown to be feasible on a time-scale of seconds and submicromolar concentrations enabling peptide mass mapping by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.     

Photometric determination of calcium with antipyrylazo III

Antipyrylazo III or diantipyrylazo (3,6-bis(4-antipyrylazo)-4,5-dihydroxy-2, 7-napthalenedisulfonic acid) forms at PH 12.7 a complex Ca₂HL with calcium. The logarithmic overall stability constant, 10g β₂₁₁, is 23.99 ±0.03 (0.1 MNaClO₄,25°C).The effective molar absorptivity is 21,500 ±100 l mole^-1 cm^-1 at 605 nm. The complex can be used for a selective photometric determination of calcium(0.25–3.50μmole) if tri-and tetravalent ions are removed by extraction with cupferron (into chloroform) and transition divalent ions are masked with sodium cyanide. Only strontium (0.5 μmole) and EDTA (0.1 μmole) interfere seriously.     

Arsenic colorimetry with silver diethyldithiocarbamate

The effect of 22 interferences had been studied. Sulfur(II) must be oxidized by nitric acid; germanium, nitric acid, and perchloric acid must be removed by repeated evaporation with hydrochloric acid. Antimony, phosphate, selenium, tellurium, iron, tin, copper, nickel, and many other elements are eliminated by extraction of arsenic(III) chloride in concentrated hydrochloric acid with p-xylene or benzene. Metal ions forming complex or insoluble iodide can be blocked with an excess of potassium iodide. The method enables the determination of 2–30 μg of arsenic with a relative error <10%. It was tested with the materials of copper production.     

Chemical Composition,Antitumor Potential,and Impact on Redox Homeostasis of the Essential Oils of Orlaya grandiflora from Two Climate Localities

It is well known that abiotic components can affect biosynthetic pathways in the production of certain volatile compounds. The aim of this study was to compare the chemical composition of essential oils obtained from Orlaya grandiflora (L.) Hoffm. collected from two localities in Serbia (continental climate, OG1) and Montenegro (Mediterranean climate, OG2) and to assess their antitumor potential on the human colon cancer HCT-116 and breast cancer MDA-MB-231 cell lines. EOs obtained by hydrodistillation were analyzed using GC-MS and GC-FID methods. The results indicate considerable differences in the chemical compositions of the two samples. Although in both samples the main class of volatiles observed was sesquiterpenes (47.5% for OG1 and 70.1% for OG2), the OG1 sample was characterized by a high amount of monoterpene hydrocarbons (29.3%), and sesquiterpene germacrene D (29.5%) as the most abundant compound. On the other hand, the OG2 sample contained a high quantity of oxygenated sesquiterpenes (20.6%), and β-elemene (22.7%) was the major constituent. The possible antitumor mechanisms of these EOs in the HCT-116 and MDA-MB-231 cell lines were examined by means of cell viability, apoptosis, redox potential, and migratory capacity. The antiviability potential appeared to be dose dependent, since the results showed that both EOs decreased the viability of the tested cells. Stronger antitumor effects were shown in MDA-MB-231 cells after short-term treatment, especially at the highest applied concentration, where the percentage of viability was reduced by over 40%. All tested concentrations of EOs exhibited proapoptotic activity and elevated activity of caspase-3 in a dose- and time-dependent manner. The results also showed decreased concentrations of superoxide anion radical in the treated cells, which indicates their significant antioxidative role. Long-term treatments showed mild recovery effects on cell viability in both cell lines, probably caused by the balancing of redox homeostasis. Elevated levels of nitrites indicate high levels of nitric oxide (NO) production and suggest its higher bioavailability due to the antioxidative environment. The tested EOs also induced a drop in migratory capacity, especially after short-time treatments. Taken together, these results suggest considerable antitumor activity of both EOs, which could have potential therapeutic applications.