Search results for "CEM"
showing 10 items of 3487 documents
Polycyclic aromatic hydrocarbons (PAHs) in indoor emission from decorative candles
2011
Abstract This study investigates PAHs indoor emissions from burning decorative candle in an indoor environment because emissions from burning wax in home have rarely been addressed. A total of 12 air samples were collected during the entire burning period of the decorative candles. Particulate and gaseous PAHs emissions were simultaneously measured by passing effluent through a filter (to collect particulate-phase PAHs), a cold trap and ORBO 43 tubes (to capture gaseous-phase PAHs). Analysis involved ultrasound extraction, followed by gas chromatography–mass spectrometry (GC–MS). The measured total PAHs concentration (particulate + aqueous phase + gas phases) for the candles, reported as ma…
Monitoring of Enzyme Substitution Using the Cholesteryl Octanoate Breath Test
1991
The efficiency of enzyme replacement therapy in pancreatic insufficiency is usually judged on the grounds of clinical improvement and the effect on steatorrhea: treatment is thought to be successful if steatorrhea is abolished or, at least, reduced. In the majority of patients, the amount of enzyme necessary to alleviate steatorrhea can be reduced if lipase is protected against acidic inactivation either by blocking H2 secretion of the stomach or by protecting enzymes by pH-sensitive enteric coating. However, steatorrhea is frequently not abolished and a differential treatment may be necessary in each patient.
Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)
2012
Chirality can have a decisive influence on the molecular structure formation upon self-assembly on surfaces. In this paper, we study the structures formed by enantiopure (M)-heptahelicene-2-carboxylic acid ((M)-[7]HCA) on the calcite (10 (1) over bar4) cleavage plane under ultrahigh vacuum conditions. Previous noncontact atomic force microscopy studies have revealed that the racemic mixture of (M)-[7]HCA and (P)-[7]FICA (1:1) self-assembles into well-defined molecular double rows that are oriented along the calcite [01 (1) over bar0] direction. Here, we investigate the enantiopure (M)[7]HCA compound, resulting in distinctly different molecular structures upon deposition onto calcite (10 (1)…
Antidiabetic Behavior of Biguanides
1983
The existence of active electron pairs on some nitrogen atoms in phenformin hydrochloride is inferred from the presence of a hydrogen catalytic polarographic wave. This finding emphasizes the ability of biguanides to form hydrogen bridges with other molecular species such as amino acids and proteins, as well as to form coordination complexes with zinc and other metallic cations by means of these electron pairs. The antidiabetic action of phenformin and other related biguanides can be explained in terms of competition between these molecules and insulin to coordinate cationic oligoelements together with their ability to form hydrogen bonds between the biguanide moiety and insulin itself.
Organo-phosphorus compounds—LXVI
1970
Abstract The recemization kinetics of (+)-methyl-n-propylphenylphosphine were studied in several solvents of widely varying polarity. The recemization followed first order kinetics in every solvent with approximately equal activation energies of 30 ±3 kcal/mole. The rate of racemization showed no dependence on solvent polarity and could not be correlated with any known solvent parameters. The unusually slow racemization in caproic acid and in tributyl borate were attributed to partial salt and adduct formation respectively.
Detection of poly(methylmethacrylate) wear particles in capsule tissue surrounding endoprotheses by pyrolysis gas chromatography
1982
Pyrolysis gas chromatography (PGC) is used to detect polymer wear particles in capsule tissue surrounding endoprotheses implanted with poly(methylmethacrylate) as bone cement. The method allows the detection of the polymer incorporated in tissue even in the range of 1 weight%.
Das System 2‐Halogenethylester/Cholinester als Zweistufen‐Schutzgruppe für die Carboxylfunktion von Aminosäuren und Peptiden
1979
Das System 2-Chlorethyl- und 2-Bromethylester/Cholinester wird als Carbonsaure-Schutzfunktion beschrieben. Die 2-Chlorethyl-(OEt(Cl))- und die 2-Bromethylester (OEt(Br)) der Aminosauren (4) lassen sich einfach herstellen und mit Z- und Boc-Aminosauren zu Z- und Boc-Dipeptidestern 5 und 6 verknupfen. Die Esterfunktionen sind gegen nicht zu stark saure und basische Einflusse bestandig. Sie konnen mit Natriumiodid in DMF in 2-Iodethylester 8 ubergefuhrt werden, welche mit Zink in einer Eintopfreaktion spaltbar sind. Durch Umsetzung mit Trimethylamin gehen die hydrophoben 2-Halogenethylester in die hydrophilen Cholinester 10 und 11 uber. Diese sind sehr stabil gegen Sauren. Sie konnen in wasrig…
On the regioselectivity of the Friedländer reaction leading to huprines: stereospecific acid-promoted isomerization of syn-huprines to their anti-reg…
2001
Abstract Racemic 12-amino-6,7,8,11-tetrahydro-7,11-methanocycloocta[ b ]quinoline derivatives ( syn -huprines) substituted at the 9-position with a methyl or ethyl group, and both enantioenriched forms of the 9-ethyl derivative, obtained by chiral MPLC resolution of the racemic mixture, were readily converted to the corresponding anti -isomers (huprines) by stereospecific acid-promoted (AlCl 3 or triflic acid) isomerization of the endocyclic CC double bond from the 9(10)- to the 8(9)-position. These results support the hypothesis that the hitherto unseen syn -huprines are also formed under the usual acidic Friedlander reaction conditions used to prepare the known huprines, but rearrange in…
5-Substituted 4,5-Dihydro-1,2,4-triazin-3(2H)-ones from the Unprecedented Reaction between α-N-Protected Amino Acid Hydrazides and NaBH4
2006
α-N-Protected amino acid hydrazides (1) readily reacted with NaBH4 to afford 5-substituted 4,5-dihydro-1,2,4-triazin-3(2H)-one derivatives 2 in good yields. Unfortunately, the reaction caused partial racemization at the α-amino acidic carbon atom of the starting hydrazide. A mechanism, supported by experimental evidence, has been proposed in an attempt to explain this to date unprecedented reaction. The structure of compounds 2 was confirmed by X-ray structural analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
The protein dynamical transition does not require the protein polypeptide chain
2011
We give experimental evidence that the main features of protein dynamics revealed by neutron scattering, i.e., the “protein dynamical transition” and the “boson peak”, do not need the protein polypeptide chain. We show that a rapid increase of hydrogen atoms fluctuations at about 220 K, analogous to the one observed in hydrated myoglobin powders, is also observed in a hydrated amino acids mixture with the chemical composition of myoglobin but lacking the polypeptide chain; in agreement with the protein behavior, the transition is abolished in the dry mixture. Further, an excess of low-frequency vibrational modes around 3 meV, typically observed in protein powders, is also observed in our mi…