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31.
W. Pilz und Ilse Johann 《Fresenius' Journal of Analytical Chemistry》1969,248(3-4):149-153
Zusammenfassung Eine Methode zur Bestimmung von Hexamethylendiisocyanat (Desmodur H) in Luft wurde ausgearbeitet. In Anlehnung an frühere Methoden wurde Hexamethylendiisocyanat sauer zu Hexamethylendiamin verseift, dieses mit 1-Fluor-2,4-dinitrobenzol an beiden Aminogruppen umgesetzt, das entstehende Reaktionsprodukt mit Chloroform aus der wäßrigen Phase extrahiert und gegen den entsprechenden Leerwert photometriert. Wesentliche Fehler früherer Methoden konnten vermieden werden. Es wurde gezeigt, daß sowohl das Lambertsche als auch das Lambert-Beersche Gesetz erfüllt sind, und daß die Umsetzung mit 1-Fluor-2,4-dinitrobenzol quantitativ an beiden Aminogruppen des Hexamethylendiamins erfolgt. Äquimolare Mengen von Hexamethylendiamin und Hexamethylendiisocyanat ergeben unter den beschriebenen Reaktions-bedingungen dieselbe Extinktion. Die Absorption verläuft quantitativ. Es können Mengen von 1–1000 g Hexamethylendiisocyanat erfaßt werden. Die Methode darf nicht auf Additionsprodukte auf der Basis von Hexamethylendiisocyanat angewendet werden.
II. Mitteilung: Pilz, W., u. Edith Stelzl: diese Z. 219, 416 (1966).
Heinrich Hörlein zum Gedenken. 相似文献
Special analytical methods for occupational medicine and industrial hygieneIII. Determination of minimum quantities of hexamethylene diisocyanate (Desmodur H) in air
With reference to earlier methods hexamethylene diisocyanate is saponified to hexamethylenediamine in acid solution, which is reacted with 1-fluoro-2,4-dinitrobenzene at both amino groups. The reaction product formed is extracted from the aqueous phase by chloroform and is photometrically measured against a corresponding blank value. Essential errors of earlier methods could be avoided. It is shown that Lambert's and Lambert-Beer's laws are obeyed and that the reaction with 1-fluoro-2,4-dinitrobenzene is quantitative at both amino groups of the diamine. Under the conditions described equimolecular amounts of hexamethylenediamine and hexamethylene diisocyanate yield the same absorbance. Absorption is quantitative. Amounts of 1–1000 g of hexamethylene diisocyanate can be determined. The method cannot be applied to addition products on the basis of hexamethylene diisocyanate.
II. Mitteilung: Pilz, W., u. Edith Stelzl: diese Z. 219, 416 (1966).
Heinrich Hörlein zum Gedenken. 相似文献
32.
Zusammenfassung Die durch Einwirkung von konz. Schwefelsäure auf Camphandion-(2.3) in der Kälte entstehenden Substanzen werden durch Derivate charakterisiert und ihre Entstehung diskutiert.Herrn Professor Dr.Friedrich Asinger zum 60. Geburtstag gewidmet.Verstorben am 12. Dezember 1966. 相似文献
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35.
Monti S Manet I Manoli F Marconi G 《Physical chemistry chemical physics : PCCP》2008,10(44):6597-6606
In the present contribution we address the study of the interaction of a flavonoid-derivative licochalcone A (LA) with human serum albumin (HSA). The application of circular dichroism, UV-Vis absorption, fluorescence and laser flash photolysis combined with molecular mechanics, molecular dynamics and quantum mechanical calculations of rotational strength afforded a clear picture of the modes of association of the LA neutral molecule to HSA, evidencing specific interactions with protein amino acids and their photophysical consequences. The drug is primarily associated in subdomain IIA where a strong interaction with Trp214 is established. At least two different positions of LA with respect to tryptophan are possible, one with the phenolic ring of the drug facing the aromatic ring of Trp214 and the other with the methoxyphenolic ring of LA in proximity to Trp214. In both cases LA is at ca. 4 angstroms from Trp214. This vicinity does not affect much the S1 singlet state deactivation of the bound drug, which exhibits a slightly higher fluorescence quantum yield and fluorescence lifetime on the order of that of the free molecule. The LA triplet lifetime appears to be somewhat shortened in this site. The secondary binding site is in subdomain IIIA. Here, the carbonyl group of LA experiences a strong H-bond with the OH-phenolic substituent of Tyr411. This interaction reduces substantially the LA molecular degrees of freedom, thereby determining a decrease of both radiative and nonradiative rate constants for decay of the singlet. The overall rigidity of the structure causes a lengthening of the triplet lifetime. 相似文献
36.
Gaining an insight into the photoreactivity of a drug in a protein environment: a case study on nalidixic acid and serum albumin 总被引:1,自引:0,他引:1
Monti S Manet I Manoli F Capobianco ML Marconi G 《The journal of physical chemistry. B》2008,112(18):5742-5754
The binding of nalidixic acid (NA) with human and bovine serum albumin (HSA and BSA) in buffer solution at pH 7.4 was investigated using circular dichroism (CD), UV absorption and fluorescence spectroscopy. Global analysis of multiwavelength spectroscopic data afforded the equilibrium constants of the most stable noncovalent drug/protein adducts of 1:1 and 2:1 stoichiometry and their individual CD, UV absorption, and fluorescence spectra. The primary binding site of the drug was located in subdomain IIIA (Sudlow Site II), whereas the secondary one was assigned to subdomain IIA. Conformational and CD calculations afforded the binding geometries. In the complexes, the fluorescence of the protein was strongly quenched by energy transfer and that of the drug was suppressed by electron transfer. Laser flash photolysis at 355 nm evidenced the formation of a radical pair consisting of a tyroxyl radical (lambdamax = 410 nm) and a reduced nalidixate anion radical NA(2-)* (lambdamax = 640 nm) with quantum yield of 0.4-0.5. Strong evidence was obtained that the process that involves Tyr411 in HSA (Tyr409 in BSA). A further transient with lambdamax approximately 780 nm observed in HSA was attributed to oxidation of the -(S200-S246)- bridge upon electron transfer to NA(-)*. Decay of the confined radical pairs occurred with rates approximately 10(7) s(-1). Formation of covalent drug-protein adducts in mixtures irradiated at lambdairr> 324 nm was proved using HPLC with fluorescence detection. 相似文献
37.
In recent papers (cf. [J.L. Arregui, O. Blasco, (p,q)-Summing sequences, J. Math. Anal. Appl. 274 (2002) 812-827; J.L. Arregui, O. Blasco, (p,q)-Summing sequences of operators, Quaest. Math. 26 (2003) 441-452; S. Aywa, J.H. Fourie, On summing multipliers and applications, J. Math. Anal. Appl. 253 (2001) 166-186; J.H. Fourie, I. Röntgen, Banach space sequences and projective tensor products, J. Math. Anal. Appl. 277 (2) (2003) 629-644]) the concept of (p,q)-summing multiplier was considered in both general and special context. It has been shown that some geometric properties of Banach spaces and some classical theorems can be described using spaces of (p,q)-summing multipliers. The present paper is a continuation of this study, whereby multiplier spaces for some classical Banach spaces are considered. The scope of this research is also broadened, by studying other classes of summing multipliers. Let E(X) and F(Y) be two Banach spaces whose elements are sequences of vectors in X and Y, respectively, and which contain the spaces c00(X) and c00(Y) of all X-valued and Y-valued sequences which are eventually zero, respectively. Generally spoken, a sequence of bounded linear operators (un)⊂L(X,Y) is called a multiplier sequence from E(X) to F(Y) if the linear operator from c00(X) into c00(Y) which maps (xi)∈c00(X) onto (unxn)∈c00(Y) is bounded with respect to the norms on E(X) and F(Y), respectively. Several cases where E(X) and F(Y) are different (classical) spaces of sequences, including, for instance, the spaces Rad(X) of almost unconditionally summable sequences in X, are considered. Several examples, properties and relations among spaces of summing multipliers are discussed. Important concepts like R-bounded, semi-R-bounded and weak-R-bounded from recent papers are also considered in this context. 相似文献
38.
Ilse Manet Luca Francini Stefano Masiero Silvia Pieraccini GianPiero Spada Giovanni Gottarelli 《Helvetica chimica acta》2001,84(7):2096-2107
The self‐assembly of guanosine (G) derivatives in the presence of alkali‐metal ions gives octameric or polymeric aggregates composed of stacked G quartets. This process is studied for some lipophilic G derivatives by means of ESI‐MS. The ESI‐MS results are discussed in the light of complementary information obtained from NMR and SANS (small‐angle neutron scattering) studies. ESI‐MS gives an excellent picture of the self‐assembly process and gives new information on the effect of different cations and anions on the dimensions of the assembled species, information that could not have been obtained with SANS and NMR alone. 相似文献
39.
Monti S Manet I Manoli F Morrone R Nicolosi G Sortino S 《Photochemistry and photobiology》2006,82(1):13-19
The photodegradation of the S(+)- and R(-)-ketoprofen (KP) enantiomers in the bovine serum albumin matrix was studied by steady-state photolysis with the use of lambda(irr) > 320 nm and transient absorption spectroscopy with lambda(exc) = 355 nm, at 1/1 and 2/1 KP/BSA molar ratios. R(-)-KP was found to be more labile than S(+). Triplet ketoprofen species were evidenced with lifetimes of 400 ns for S(+) and 600 ns for R(-)-KP. Further longer-lived transients with lifetimes of 2.6 and 6.0 mus for S(+) and R(-), respectively, were detected. On the basis of the binding constants of the drug enantiomers to the two main binding sites of the protein, obtained from circular dichroism experiments, the individual disappearance quantum yields of the 1:1 and 2:1 diastereomeric KP:BSA complexes could be estimated. The photoreactivity in the BSA matrix was rationalized on the basis of diastereoselective photodecarboxylation in the two main protein sites. 相似文献
40.
Bonesi SM Manet I Freccero M Fagnoni M Albini A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(18):4844-4857
The oxidation of diethyl and diphenyl sulfide photosensitized by dicyanoanthracene (DCA), N-methylquinolinium tetrafluoroborate (NMQ(+)), and triphenylpyrylium tetrafluoroborate (TPP(+)) has been explored by steady-state and laser flash photolysis studies in acetonitrile, methanol, and 1,2-dichloroethane. In the Et(2)S/DCA system sulfide-enhanced intersystem crossing leads to generation of (1)O(2), which eventually gives the sulfoxide via a persulfoxide; this mechanism plays no role with Ph(2)S, though enhanced formation of (3)DCA has been demonstrated. In all other cases an electron-transfer (ET) mechanism is involved. Electron-transfer sulfoxidation occurs with efficiency essentially independent of the sulfide structure, is subject to quenching by benzoquinone, and does not lead to Ph(2)SO cooxidation. Formation of the radical cations R(2)S(*+) has been assessed by flash photolysis (medium-dependent yield, dichloroethane>CH(3)CN>CH(3)OH) and confirmed by quenching with 1,4-dimethoxybenzene. Electron-transfer oxidations occur both when the superoxide anion is generated by the reduced sensitizer (DCA(*-), NMQ(*)) and when this is not the case (TPP(*)). Although it is possible that different mechanisms operate with different ET sensitizers, a plausible unitary mechanism can be proposed. This considers that reaction between R(2)S(*+) and O(2)(*-) mainly involves back electron transfer, whereas sulfoxidation results primarily from the reaction of the sulfide radical cation with molecular oxygen. Calculations indeed show that the initially formed fleeting complex RS(2)(+)...O-O(*) adds to a sulfide molecule and gives strongly stabilized R(2)S-O(*)-(+)O-SR(2) via an accessible transition state. This intermediate gives the sulfoxide, probably via a radical cation chain path. This mechanism explains the larger scope of ET sulfoxidation with respect to the singlet-oxygen process. 相似文献