Simultaneous measurement of proline and related compounds in oak leaves by high-performance ligand-exchange chromatography and electrospray ionization mass spectrometry for environmental stress studies

A mass spectrometer was coupled to high-performance ligand-exchange liquid chromatography (HPLEC) for simultaneous analysis of stress associated solutes such as proline, hydroxyproline, methylproline, glycine betaine and trigonelline extracted from leaves of drought stressed oaks and an internal standard namely N-acetylproline. Methanol/chloroform/water extracts were analyzed using an Aminex HPX-87C column and specifically quantified by the positive ion mode of an electrospray ionisation-mass spectrometry (ESI-MS) in single ion monitoring (SIM) mode. The recovery of N-acetyl proline added to oak leaf extracts ranged from 85.2 to 122.1% for an intra-day study. Standard calibration curves showed good linearity in the measured range from 0.3125 to 10 μmol L⁻¹ with the lowest correlation coefficient of 0.99961 for trigonelline. The advantages of this alternative procedure, compared to previously published methods using fluorescence or amperometric detections, are the simultaneous and direct detection of osmoprotectants in a single chromatographic run, a minimal sample preparation, a good specificity and reduced limits of quantification, ranging from 0.1 to 0.6 μmol L⁻¹. Fifty-six days of water deficit exposure resulted in increased foliar free proline levels (2.4-fold, P < 0.001, 155 μmol g⁻¹ FW) and glycine betaine contents (2.5-fold, P < 0.05, 175 μmol g⁻¹ FW) of drought stressed oak compared to control.     

The fully deprotonated anion of 1,3,5-benzene-triphosphonic acid: 1H, 31P,and 13C{1H} NMR and some comments on corresponding [AX]3 and AXX′2 spin systems and spectra

Abstract

The fully deprotonated anion of 1,3,5-benzene-triphosphonic acid 1,3,5-C₆H₃[PO₃^2?]₃ gives rise to deceptively simple ¹H and ³¹P NMR spectra due to a corresponding [AX]₃ spin system. The ¹³C{¹H} NMR spectrum reveals two ¹³C isotopomers which are identified via AXX′₂ systems. Results from analysis and iteration are described.     

Kinetics of the reaction of aqueous iron(vi) (FeVIO42-) with ethylenediaminetetraacetic acid

The reaction of aqueous iron(vi) (FeVIO42-, Fe(vi)) with ethylenediaminetetraacetic acid (EDTA) was studied kinetically as a function of pH (1.98-12.40) and temperature (15-45 degrees C) using a stopped flow kinetic technique. The rate law for the reaction of Fe(vi) with EDTA was found to be first-order with respect to each reactant over the entire studied pH range. The observed rate constants, k, decrease with an increase in pH, varying from 4.19 x 10(4) to 8.60 x 10(-2) M(-1) s(-1) over the pH range. The speciation of Fevi (H3FeO4+, H2FeO4, HFeO4-, and FeO42-) and EDTA (H4Y, H3Y-, H2Y2-, HY3-, and Y4-, Y = EDTA) species was used to explain the pH dependence of the k values. From the temperature effect on k at pH 5.4, 7.1, and 9.2, activation parameters, DeltaS(double dagger) and DeltaH(double dagger), were obtained for the reactions of Fe(VI) with EDTA. The values of DeltaS(double dagger) for the reactions were found to be negative, implying a highly ordered transition state in the reaction. The DeltaH(double dagger) for the reaction at pH 7.1 and 9.2 showed similar values within experimental error. Using the observed enthalpy parameters and the enthalpy of deprotonation of HFeO4- and EDTA species (HEDTA3- and H2EDTA2-), the enthalpy of deprotonation of H2FeO4 (DeltaH0H2FeO4) was determined as 5.7 +/- 3.0 kJ mol(-1). The reactivity of Fe(VI) with aminopolycarboxylates (APCs) was also studied in alkaline medium. The order of reactivity was determined as primary > secondary > tertiary, which suggests that FeVIO42- attacks at the nitrogen atom sites of APCs.     

Influence of polymeric additives on biomimetic silica deposition on patterned microstructures

Microstructured polymer films prepared by photochemical grafting of different polymers were used as restricted reaction areas in silica deposition experiments. Linear and branched poly(alkyleneimines) and poly(allylamine hydrochloride) in pure aqueous or phosphate-containing solutions were used as additives to silica precursor solutions. The silica deposits obtained by spin-coating these solutions onto microstructured polymer films were investigated by scanning electron microscopy and atomic force microscopy. Experiments with poly(alkylene imines) in the silica precursor solution show the deposition of smooth and granular silica structures that closely mimic the natural patterns. The structure formation can be explained by physicochemical processes. Hypotheses that have been made for the natural silification processes can be evaluated on this basis.     

Protein immobilization on epoxy-activated thin polymer films: effect of surface wettability and enzyme loading

A series of epoxy-activated polymer films composed of poly(glycidyl methacrylate/butyl methacrylate/hydroxyethyl methacrylate) were prepared. Variation in comonomer composition allowed exploration of relationships between surface wettability and Candida antartica lipase B (CALB) binding to surfaces. By changing solvents and polymer concentrations, suitable conditions were developed for preparation by spin-coating of uniform thin films. Film roughness determined by AFM after incubation in PBS buffer for 2 days was less than 1 nm. The occurrence of single CALB molecules and CALB aggregates at surfaces was determined by AFM imaging and measurements of volume. Absolute numbers of protein monomers and multimers at surfaces were used to determine values of CALB specific activity. Increased film wettability, as the water contact angle of films increased from 420 to 550, resulted in a decreased total number of immobilized CALB molecules. With further increases in the water contact angle of films from 55 degrees to 63 degrees, there was an increased tendency of CALB molecules to form aggregates on surfaces. On all flat surfaces, two height populations, differing by more than 30%, were observed from height distribution curves. They are attributed to changes in protein conformation and/or orientation caused by protein-surface and protein-protein interactions. The fraction of molecules in these populations changed as a function of film water contact angle. The enzyme activity of immobilized films was determined by measuring CALB-catalyzed hydrolysis of p-nitrophenyl butyrate. Total enzyme specific activity decreased by decreasing film hydrophobicity.     

Safety and Quality Aspects of Acrylic Monomers

Summary : Acrylic monomers are important intermediates for the chemical industry. Especially acrylic acid (AA) is the basis for various reactions, such as polymerizations and esterifications and is, therefore, responsible for high product diversity. Spontaneous polymerization is a safety problem during the transportation and storage of acrylic monomers. In the production process, polymerization leads to blockages in the apparatus. For the prevention of these issues, special stabilizer systems are used such as hydroquinone monomethyl ether (MeHQ)/oxygen and phenothiazine (PTZ). The reactions of these stabilizer systems are not well understood at the moment. Therefore a lot of expertise and experience are necessary to guarantee safe handling. In this paper some methods for the investigation of stability related reaction kinetics are presented. A better comprehension of the mechanism of the polymerization inhibition is generated by the kinetic simulation with these data.     

Substitution effect on the regioselective halogen/metal exchange of 3-substituted 1,2,5-tribromobenzenes

Regioselective halogen/metal exchange reactions using isopropylmagnesium chloride were studied on 3-substituted 1,2,5-tribromoarenes. Seven examples are given.     

Enantioseparation of underivatised amino acids by ligand exchange capillary electrophoresis in a counter-electroosmotic mode

Enantiomer separations of underivatised amino acids were carried out by using ligand exchange capillary electrophoresis (LECE). Chiral discrimination is based on the formation of ternary complexes between copper(II), a chiral selector (L-proline or trans-4-hydroxy-L-proline) and an amino acid. All amino acids containing aromatic moieties or not were detected at 214 nm because of their interactions with copper(II). In order to reduce copper(II) adsorption onto capillary walls, we used hexadimethrine bromide to reverse the electroosmotic flow. Using this original strategy, the studied enantiomers migrated in the opposite direction of the anodic electroosmosis. After optimising the analytical conditions taking into account the chiral resolution and the detection sensitivity, we performed very satisfactory enantioseparations not only of aromatic amino acids (tryptophan, tyrosine, phenylalanine and histidine) but also of aliphatic amino acids (threonine, serine, isoleucine and valine). These enantioseparations were performed in a short analysis time at 35 °C. In order to rationalise the obtained results, we evaluated the complexation constants corresponding to the formed ternary complexes by capillary electrophoresis and we used molecular mechanics modelling.     

Synthesis and immobilization of molecular switches onto titaniumdioxide nanowires

The precursor [Fe^III(L)Cl (L = N,N′-bis(2′-hydroxy-3′-methyl-benzyliden)-1,7-diamino-4-azaheptane) is combined with [Mo(CN)₈]^4? yields a star shaped nona-nuclear cluster, [Mo^IV{(CN)Fe^III(L)}₈]Cl₄. This Fe₈Mo molecule is a high-spin system at room temperature. On cooling to 20 K some of the iron(III) centres in the molybdenum(IV)-star switch to the low-spin state as proven by Mössbauer spectroscopy. This molecule was deposited on TiO₂ nanowires by electrostatic interactions between the cluster cations and the surface functionalized titanium oxide nanowire. The synthesis and surface binding of the multistable molecular switch was demonstrated using IR and UV–Vis spectroscopy (high-resolution) transmission electron microscopy ((HR)TEM) and Mössbauer spectroscopy. High- and low-temperature Mössbauer spectra indicate that the spin state transition of the free cluster molecules is preserved after surface binding. The above results emphasize the possibility of fabricating molecule-based low-dimensional structures by using traditional bottom-up approaches based on the electrostatic interaction between the cluster cations and polymer functionalized nanowires. These results can be generalized for the application to both charged and non-charged molecules.