Automatische Analyse und Simulation von NMR-Spektren

Analytical and Bioanalytical Chemistry -     

Accurate determination of low pK values by (1)H NMR titration

The NMR titration methodology to determine acid dissociation constants in aqueous solutions is extended for pK(a) values between 0 and 2, where potentiometric titrations are no longer applicable. (1)H NMR spectra are acquired for single samples of constant acid concentration (e.g. 0.02M), controlled ionic strength (I=1M with HNO(3)/NaNO(3)) and varying pH. To avoid biased pH readings due to the acid error of the glass electrode, true, concentration-based pH values are deduced by combination of the charge balance equation with information from (1)H NMR chemical shifts of the investigated acid. The method has been tested on histidine (pK(1)=1.83+/-0.02) and yielded the dissociation constant of dichloroacetic acid (pK=1.06+/-0.01) for the first time with good accuracy and precision. Dichloroacetic acid is recommended as an NMR spectroscopical "indicator molecule" for in situ monitoring the pH in strong acidic solutions of other equilibrium systems.     

Molecular structure of t-butyl-phenylphosphinic acid (−)-menthyl ester: a comparison of solid state and solution

The molecular structure of t-butyl-phenylphosphinic acid (?)-menthyl ester (1eS) has been determined by X-ray analysis and the results compared with the findings of a detailed NMR-study. 1eS crystallises in the monoclinic space group P2 ₁ with a = 9.304(2), b = 10.678(4), c = 12.681(4) Å, β = 124.91(1)°, Z = 2, D_x = 1.08 g cm^?3. The structure was refined to R = 0.035 for 1842 independent reflections. The absolute configuration was confirmed as S_(p). Both methyl functions of the menthyl-iso-propyl substituent take up positions close to the phenyl ring system.     

31P-NMR-Untersuchung an PhPH(CO)6Fe2(PPh)3Fe2(CO)6PPhH ? einem Vierkernkomplex mit einer ungewöhnlichen (PPh)3-Brücke

(CO)₆Fe₂(PhPH)₂ bildet mit PhPCl₂ den phosphidoverbrückten tetranuklearen Komplex [PhPHFe₂(CO)₆PPh]₂PPh. ³¹P{¹H}-NMR-Spektren der Titelverbindung werden als [AB]₂C-Systeme analysiert, Stereoisomere werden diskutiert. ³¹P-NMR Studies on PhPH(CO)₆Fe₂(PPh)₃Fe₂(CO)₆PPhH ? a Tetranuclear Complex with an Unusual (PPh)₃ Bridge (CO)₆Fe₂(PhPH)₂ and PhPCl₂ form [PhPHFe₂(CO)₆PPh]₂PPh, a tetranuclear complex with phosphido bridges. ³¹P{¹H}-NMR spectra are analysed as [AB]₂C systems, stereoisomers are discussed.     

The kinetics of muon-catalyzed dt fusion

A main source of information about the muon-catalyzed fusion cycle in D-T mixtures are the cycling rates _c, which are characteristic for the kinetic equilibrium of states attained rapidly in dense targets. The measurement, analysis and interpretation of these rates will be discussed, concentrating on the extensive set of rates observed at PSI over the last decade in gaseous, liquid and solid targets.Invited talk presented by Peter Kammel.     

Biorelevant Phosphonic Acids - Protonation and Complexformation Equilibria

Abstract

Various methods of NMR- and PC-controlled titrations were developed in our laboratories. In addition to the by now well-investigated ³¹P- we applied ¹³C-, ¹H-, ¹⁹F- and ¹¹³Cd-NMR controlled titrations. Here we report about the methodical progress and results obtained from acylphophonic acids and corresponding hydroxyimino derivatives - as shown below - which gained interests as potentially anti-viral agents:     

Widespread occurrence of polyhalogenated compounds in fat from kitchen hoods

Food and contaminated indoor environments are the most relevant sources of human exposure to polyhalogenated chemicals. This study analyzed for the first time fat residues in kitchen hoods for contaminations with polyhalogenated compounds. A wide range of contaminants was detected in all kitchen hoods (n?=?15) and most of them could be quantified. Between 0.2 and 18 μg polyhalogenated chemicals/g fat were detected, with chlorinated paraffins being the most relevant contaminant group. Aside from the chlorinated paraffins, each kitchen hood fat sample showed a distinct fingerprint. A wide range of old and current-use brominated flame retardants were also detected in the samples. In addition to these contaminants originating from their use in indoor equipment, residues of organochlorine pesticides and semi-volatile halogenated natural products verified that cooking of food, accompanied with the release of contaminants from the heated food, was another relevant source of contamination. Re-analyses of two samples after 3 months only resulted in small variations in contaminant pattern and concentrations. Therefore, fat from kitchen hoods is proposed as an easily accessible matrix to assess contamination of these hazardous polyhalogenated chemicals.

Silver as a capturing material for iodine released from lead–bismuth eutectic in various conditions

Journal of Radioanalytical and Nuclear Chemistry - The usage of silver as a filtering material for removal of iodine from the gas phase of a lead–bismuth eutectic based nuclear reactor was...