Untersuchung der Kinetik der Sorption der Lösungsmitteldämpfe durch Ionomere auf der Basis des Copolymerisats von Styrol und Acrylsäure

Ohne Zusammenfassung     

The determination of lecithin and total choline-containing phospholipids in amniotic fluid employing enzymes as reagents

Two assays which employ enzymes as reagents have been described for the determination of lecithin and TCCP in amniotic fluid. Both of these assays are relatively quick, simple, inexpensive, precise, involve no extractions, and are amenable to automation.Hemoglobin, blood cell membranes, and bilirubin, common interferences in $\text{L}\text{S}$ ratio determinations, have been studied. Their effects on these two assays appear to be negligible.It can be inferred from preliminary studies that the described assays correlate well with each other, and with the clinical status of the fetus. The values obtained for lecithin and TCCP cmncentrations are in the same range as previous reports employing different procedures.     

Microdetermination of magnesium in biological fluids

A modified procedure for the spectrophotometric determination of serum magnesium is described in which a direct addition of serum is made to a two-piece color reagent system. One solution contains an optimized concentration of the color reagent Magon, 1-azo-2-hydroxy-3-2-(2,4-dimethylcarboxanilido)-naphthalene-1′-(2-hydroxybenzene-5-sulfonate) sodium salt, in a dimethyl sulfoxide medium for binding magnesium and also EGTA, ethylene-bis(oxyethylenenitrilo)-tetraacetic acid, for binding calcium. The other is an alkaline solution of dilute cyanide to bind copper and iron and provide the optimum reaction pH. By means of these ingredients the simple procedure involves a reaction with serum magnesium while masking the interference of calcium and trace metals and allowing the reaction to take place without either separation or deproteinization steps. Optimized characteristics are shown for a linear reaction involving a variable reaction blank in the procedure where calcium is measured against a blank that is constant in its makeup. The linearity of the procedural reagent blank, with respect to its own concentration, helps attain the required linear results for the overall system and this is described by spectral studies.     

Essential serum trace metals: II. Determination of copper and zinc

Several complexing ligands for copper and zinc were tested for their feasibility as analytical reagents. Of these, tetraethylthiuram disulfide and its analog, bis (1-piperi-dylthiocarbonyl) disulfide were selected for copper with some advantages determined to accrue to each. Two others, 1-(2-pyridylazo)-2-naphthol and 1-[(5-chloro-2-pyridyl) azo]-2-naphthol were selected for zinc with the preference given to the former for stability of color formed and accessibility of the reagent although the chloro analog is inherently the more sensitive of the two reagents. For those who do not have atomic absorption spectrophotometry at their disposal, the molecular absorption approach still appears to be an excellent one with good selectivity for the two metals described.     

Total synthesis of thiostrepton. Retrosynthetic analysis and construction of key building blocks

The first phase of the total synthesis of thiostrepton (1), a highly complex thiopeptide antibiotic, is described. After a brief introduction to the target molecule and its structural motifs, it is shown that retrosynthetic analysis of thiostrepton reveals compounds 23, 24, 26, 28, and 29 as potential key building blocks for the projected total synthesis. Concise and stereoselective constructions of all these intermediates are then described. The synthesis of the dehydropiperidine core 28 was based on a biosynthetically inspired aza-Diels-Alder dimerization of an appropriate azadiene system, an approach that was initially plagued with several problems which were, however, resolved satisfactorily by systematic investigations. The quinaldic acid fragment 24 and the thiazoline-thiazole segment 26 were synthesized by a series of reactions that included asymmetric and other stereoselective processes. The dehydroalanine tail precursor 23 and the alanine equivalent 29 were also prepared from the appropriate amino acids. Finally, a method was developed for the direct coupling of the labile dehydropiperidine key building block 28 to the more advanced and stable peptide intermediate 27 through capture with the highly reactive alanine equivalent 67 under conditions that avoided the initially encountered destructive ring contraction process.     

Spectrophotometric study on minimizing bilirubin interference in an enzyme reagent mediated cholesterol reaction

A spectrophotometric study was carried out which describes the effect of the inclusion of potassium ferrocyanide into an enzyme reagent system as a protective device against the competitive interaction of bilirubin in the indicator reaction. A previously described system for depicting how bilirubin interacts competitively in a modified 4-aminoantipyrene-phenolic peroxidase-peroxide coupled reaction was used as a template to judge the effectiveness of the protective action. The results obtained indicate that the protection is not total, but that the close approximation may make this a worthwhile modification in procedure to consider for the determination of total, free, and/or high density lipoprotein cholesterol. At the same time it might be inferred that the interference of bilirubin can be diminished chemically for other oxidase-peroxidase coupled systems. A search for even better solutions to this interference problem may be possible. For us, this lead has pointed the way in other similar directions.In addition, this study reports on a preliminary investigation as to the site of coupling of phenolic compounds with 4-aminoantipyrene.     

Spectrophotometric study of bilirubin and hemoglobin interactions in several hydrogen peroxide generating procedures

The interference effects of bilirubin and hemoglobin have been described for the peroxidase-hydrogen peroxide oxidation of a hydrogen donor and the catalase-hydrogen peroxide oxidation of methanol to formaldehyde. A competition between bilirubin and the intended hydrogen donor is shown for the substitute analyte, hydrogen peroxide, with a resultant diminution of color due to the loss of intended reaction. No inhibition of peroxidase action appears to take place; its action when complexed with hydrogen peroxide is directed toward the competing hydrogen donor, bilirubin. The final color measured appeared to be partially compensatory, that is the sum of intended color plus the color of residual bilirubin. The subtraction of a serum blank representing a static system will result in a lowered value and a larger error. Hemoglobin, with its strong Soret band can, if its concentration is excessive, cause a major interference in reactions such as the Hantzsch reaction which result in overlapping bands at the reaction wavelength. Samples which are both hemolyzed and jaundiced would present as formidable blanking problems. Further studies on bilirubin and its glucuronide and their individual effect on the peroxidase-peroxide reaction are presently in progress.     

(+)-(5R,6S)-2-(1′-Aminoalkyl)-6-(hydroxyalkyl)penem-3-carboxylic Acids

In continuation of our work on penem antibiotics, novel chiral (5R,6S)-2-(1′-aminoalkyl)-6-(hydroxyalkyl)-derivatives 1 have been synthesized by two essentially different strategies. Whereas the starting materials for 1a - f , azetidinones 2 and 5 , were obtained from chiral building blocks (6-aminopenicillanic acid and L-threonine, resp.), the one for 1g , azetidinone 9 , was derived from racemic 4-acetoxyazetidinone and, as chiral auxiliary, (2R)-2-mercaptopropan-1-ol. The 2-aminomethyl derivatives 1a (CGP 30 779) and 1f (CGP 31 608) proved the most potent compounds in the antibacterial tests in vitro and showed a well-balanced spectrum of activity by comparison with that of established β-lactams.