The effect of benzene moiety fused with macrocyclic ring on the proton affinity of crown ethers studied in MS/MS experiment

In this paper we address the question how the presence of an aromatic moiety affects the proton affinity of crown ethers. In order to compare the proton affinities of crown ethers studied (M), we compared the abundances of protonated crown ethers ([M + H]+ ions) with the abundance of the ion [NH2-B15C5 + H]+ (formally also protonated crown ether). Both [M + H]+ and [NH2-B15C5 + H]+ were formed as a result of decomposition of [NH2-B15C5 + H + M]+. The presence of a benzene moiety fused with a macrocyclic ring strongly decreases the ratio [M + H]+/[NH2-B15C5 + H]+. Thus, the higher ring strain caused by the benzene moiety leads to a substantial lowering of the proton affinity of crown ethers. It is also suggested that for protonated benzocrown ethers the ring strain is partly compensated by the proton-đ interaction. The presence of an NO2 group decreases the electron density on the aromatic ring and, consequently, the proton-đ interaction is suppressed. As expected, the proton affinity of benzo-crown ethers increases with increasing size of their cavity since the ring strain is lower for larger molecules. An unexpectedly high proton affinity of dicyclohexano-18-crown-6 (DC18C6) has been observed

Improved sensitivity of HPLC-ESI/MS analysis of the of biodegradation products of alkyl ethoxylates and alkylphenol ethoxylates by post-column lithium addition

Biodegradation of nonylphenol ethoxylates and dodecyl ethoxylates (C9H19-C6H4- -(OCH2CH2)n-OH and C12H25-(OCH2CH2)n-OH respectively) in river water in a static die-away test was performed. By using high performance liquid chromatography with electrospray ionization mass spectrometric detection (HPLC-ESI/MS), surfactants containing 2-4 ethoxylene units were detected as biodegradation products. Post-column addition of a number of metal cation was tested in order to improve the sensitivity of HPLC-ESI/MS analysis. Among the metal cations taken into account, the use of a lithium cation gave the best results provided that the cone voltage was increased to 40-50 V

Biodegradation of alkyl ethoxylates and alkylphenol ethoxylates in river water in a static die-away test as studied by HPLC-ESI/MS

Biodegradation of nonylphenol ethoxylates and dodecyl ethoxylates (C9H19-C6H4- (OCH2CH2)n-OH and C12H25-(OCH2CH2)n-OH, respectively) in river water in a static die-away test was analyzed by using high performance liquid chromatography with mass spectrometric detection using the Applied Biosystems quadrupole-linear ion trap mass spectrometer Model 4000 QTrap. Surfactants containing 2-4 ethoxylene units may be regarded as persistent metabolites of longer surfactants. Homologues C9H19-C6H4- (OCH2CH2)5-OH and C12H25-(OCH2CH2)5-OH underwent substantial biodegradation till the 9th day of the test, their further biodegradation proceeded very slowly. The longer homologues (n > 5) were fully biodegraded during the test. Although the biodegradation of the surfactants studied consisted in shortening the ethoxylene chain (hydrophilic part), it was found that the hydrophobic part also affected their biodegradation