Search results for "SUBSTANCES"

Chitin: A Structural Biopolysaccharide with Multiple Applications

2014

Chitin is a naturally occurring fibre-forming polymer that plays a protective role in many lower eukaryotes similar to that of cellulose in plants. Chemically it is a long-chain unbranched polysaccharide made of N-acetylglucosamine residues linked through β-1,4 covalent bonds; it is the second most abundant organic compound in nature, after cellulose. Taking into account the role played by chitin in different biological structures (i.e. fungal cell walls, insect peritrophic matrix, insect and crustacean cuticles, eggshells from nematodes, cyst wall of protozoa), its metabolism (biosynthesis and degradation) is essential for different morphogenetic events. Absent in vertebrates and plants, c…

Molecular characterization of the phenolic acid metabolism in the lactic acid bacteria Lactobacillus plantarum

2001

The lactic acid bacteria Lactobacillus plantarumdisplays substrate-inducible decar- boxylase activities on p-coumaric, caffeic and ferulic acids. Purification of the p-coumaric acid decarboxylase (PDC) was performed. Sequence of the N-terminal part of the PDC led to the cloning of the corresponding pdc gene. Expression of this gene in Escherichia colirevealed that PDC displayed a weak activity on ferulic acid, detectable in vitro in the presence of ammonium sulfate. Transcrip- tional studies of this gene in L. plantarum demonstrated that the pdc transcription is phenolic acid- dependent. A mutant deficient in the PDC activity, designated LPD1, was constructed to study phe- nolic acid altern…

1981

Elution curves on spherosil gels in pure and mixed eluents of poly(dimethylsiloxane), PDMS, and poly(methyl methacrylate), PMMA, as well as those of polystyrene, PS, just for comparison, have been determined. In a general way, PDMS elution volumers fit to those of PS, whereas PMMA elution curves shift to higher retention volumes. The differences in retention volumes between the different polymeric solutes have been interpreted in terms of differences in polymer-gel and polymer-solvent interactions. Hydrogen-bonding seems to be the main contribution to solute-substrate interactions.

Characterization of Humic Acids from Raised Bog Peat

2014

Abstract Humic substances form most of the organic component of soil, peat and natural waters, but their structure and properties are very much dependent on the source. The aim of this study was to characterize humic acids from raised bog peat to evaluate the homogeneity of humic acids isolated from the bog bodies and to study peat humification impact on the properties of humic acids. Peat humic acids (HA) have an intermediate position between the living organic matter and coal organic matter, with their structure formed in a process where the relatively labile moieties (carbohydrates, amino acids, etc.) are destroyed, and thermodynamically more stable aromatic and polycyclic structures eme…

Methyl-Substituted α-Cyclodextrin as Affinity Material for Storage, Separation, and Detection of Trichlorofluoromethane

2018

Abstract The severely ozone‐depleting trichlorofluoromethane is still appearing in several recycling processes or industrial applications. A simple and selective supramolecular complex formation of per‐methylated α‐cyclodextrin (1) with the highly volatile trichlorofluoromethane (2) is reported. This interaction moreover leads to thermally stable crystals. Per‐methylated α‐cyclodextrin is successfully exploited as a reversible and selective adsorption material for liquid and airborne trichlorofluoromethane as well as an affinity material for the chemical sensing and detection of this particular volatile organic component.

Polymerization of methyl and phenyl oxazoline initiated with alkyl chloroformates

2010

It has been shown that alkyl chloroformates are capable of initiating the polymerization of oxazolines. Esters itself initiate rather slowly and the polymerization proceeds via covalent growing species. Exchange of counter ions with triflate or iodide anions leads to faster initiation and higher reaction rates. The polymerization is of living character.

Binding and Fluorescent Sensing of Dicarboxylates by a Bis(calix[4]pyrrole)-Substituted BODIPY Dye

2013

A bis(calix[4]pyrrole)-substituted BODIPY ditopic receptor 1 has been synthesised and characterised. The binding and sensing properties of 1 towards several aliphatic and aromatic dicarboxylates have been evaluated by using UV/Vis fluorescence and 1H NMR spectroscopy. The receptor strongly binds linear α,ω-dicarboxylates of appropriate lengths (C9 and C10) by acting as a cleft. For all dicarboxylates, the binding event is detected by a bathochromic shift in the UV/Vis spectra of the receptor and by strong quenching of its fluorescence.

Pharmakologisch aktive polymere, 5. Modellreaktionen zur umsetzung von pharmaka und enzymen mit monomeren und polymeren reaktiven estern

1973

Die Darstellung reaktiver Ester der Acryl-, Methacryl- und N-Vinylcarbaminsaure wird beschrieben. Die Verbindungen sind im Gegensatz zu anderen reaktiven Saurederivaten wie Saurechloriden, -anhydriden und Isocyanaten kristalline Monomere, die gut zu handhaben sind. Sie lassen sich leicht zu unvernetzten, loslichen Polymeren homo- und copolymerisieren. Die Copolymerisationsparameter wurden bestimmt. Entsprechend wie die aus der Peptidchemie bekannten reaktiven Ester reagieren sie in monomerer wie in polymerer Form bei niedriger Temperatur selektiv und schonend mit Nucleophilen in guten Ausbeuten, z. B. mit Aminen in wasriger Losung. Dies eroffnet die Moglichkeit zur nebenreaktionsfreien Bind…

Macromolecules with groups of high reactivity

1960

Reactions on the reactive groups of macromolecular substances (e.g., cellulose) have long been known, even since before the structures of macromolecules were understood. H. Staudinger carried out numerous reactions with macromolecules, maintaining the degree of polymerization constant, in order to substantiate the macromolecular structure of the substances investigated (polymeric-analogous reactions). During the last fifteen years reactions with macromolecules have been investigated because it was desirable to compare the chemical diversity of low molecular weight compounds with the corresponding chemical diversity of macromolecular compounds. These endeavors bring forth materials which sup…

Light Regulation of the Thylakoid LHCII Protein Phosphorylation at the Substrate Level

1998

The distribution of light energy between the two photosystems as well as the light-induced turnover of PSII proteins are regulated by the reversible phosphorylation of LHCII and the PSII-core proteins. The thylakoid protein kinase(s) is activated by a signal transduction system involving the interaction of reduced plastoquinone with the quinol oxidation site of the cytochrome bf complex [1]. Phosphorylation of the mobile pool of LHCII induces dissociation of this antenna from PSII and allows its interaction with the PSI in the stroma exposed membranes (state transition)[21. Dephosphorylation of LHCII by a membrane -bound phosphatase appears to be regulated by a cyclophilinlike protein locat…