Determination of 4-nonylphenol in water samples using 4-(2,6-dimethylhept-3-yl)phenol as new internal standard

A new method for determining the endocrine disrupting substance 4-nonylphenol (technical grade = mixture of isomers, 4-NP) from water samples has been developed by using 4-(2,6-dimethylhept-3-yl)phenol (4-sec-NP) as model compound. This branched monoalkylphenol is shown to serve as internal standard (IS) for the determination of technical 4-nonylphenol. To the best of our knowledge, 4-(2,6-dimethylhept-3-yl)phenol (racemic mixture) is a newly synthesized 4-nonylphenol isomer and has not been described elsewhere. Recoveries have been determined by analyzing spiked water samples from distilled water, river water and wastewater. Following acetylation, the compounds were enriched via solid phase extraction (SPE). Analyses of the compounds were performed by capillary column gas chromatography/mass spectrometry (GC/MS), operating in selected ion-monitoring (SIM) mode. The recovery of technical 4-NP using either the newly prepared 4-sec-NP or 4-n-nonylphenol (4-n-NP) as IS have been compared. 4-sec-NP showed slightly better results. However, in the first series of experiments using wastewater, the yields for the derivatization of the two standard compounds were remarkably different. The yield for derivatization of 4-n-NP was approximately 20%, probably due to the difficult matrix of the wastewater. In contrast, the yield for the derivatization of 4-sec-NP was considerably higher (approximately 63%). This problem can be solved by increasing the concentration of the reagent used for derivatization. For better control of the clean-up process, we recommend application of 4-sec-NP as internal standard, at least in water samples with complex matrices (e.g., high content of hydroxylated compounds).     

Zur Bestimmung- von Benzinen und Petroleum

Ohne Zusammenfassung     

Displacement of Activated Amino Groups. C,N- vs. N,S-Bond Cleavage in the Reaction of N-Alkyl-disulfonamides with Nucleophiles

Sodiumthiophenoxide and sodiumphenylselenide react with N-benzyl- and N-hexyl-di-p-toluenesulfonamides ( 1 and 2 ) via displacement at the C-atom to afford the corresponding organosulfides and selenides in yields of 68–96%. In contrast, sodium cyanide converts disulfonamides to monosulfonamides by attack on the S-atom. The different selectivities of phenylsulfide and selenide as compared to cyanide anions with respect to attack on the C- and S-atoms are rationalized on the grounds of the HSAB (hard and soft acids and bases) principle of Pearson.     

Quantum chemical study of hydrogen abstraction reactions of the ethynyl radical with hydrogen compounds (C2H+HX)

We have theoretically investigated the hydrogen abstraction reactions of ethynyl radical with simple hydrogen compounds, C₂H+HX, using quantum chemical computations. Computations have been performed using the density functional theory with the recently proposed MPW1K functional and the 6-311++G(3df,2p) basis set. An analysis of the resulting energy barriers for hydrogen abstraction reactions has been carried out using the bond dissociation energy of the breaking X–H bond and DFT-based reactivity parameters to rationalize the reaction behavior.     

Simulations of photomodulated solute transport in doubly illuminated liquid membranes containing photoactive carriers

A steady-state model describing photofacilitated transport in liquid membranes under double illumination is presented. The model allows for the exploration of the effects of a wide range of thermodynamic and kinetic carrier properties on the control of photoinduced transport rates of solutes, called photomodulation. Most previous experimental and theoretical studies have explored the illumination of only the feed or sweep side of the membrane, while this study examines the effects of illuminating both sides simultaneously. Under double illumination, solute transport rates can be as much as five times greater than those measured in the dark and 2.5 times greater than rates obtained under single illumination. Carriers that are predominantly in the weakly binding form in the dark generally provide slightly better performance at lower light intensities than do carriers that are predominantly in the strongly binding form in the dark. The greatest enhancement in solute transport under double illumination is seen for carriers with very slow interconversion rate constants between the strongly and weakly binding forms. These results provide guidelines to help those studying photofacilitated membranes select or design photoactive molecules that will act as optimal carriers in liquid membranes under double illumination.     

Electronic structure of 1,3,5-triaminobenzene trication and related triradicals: doublet versus quartet ground state

Quantum chemical calculations have been carried out to determine the electronic ground state of the parent 1,3,5-triaminobenzene trication triradical (TAB3+,C6H9N3 3+) containing a six-membered benzene ring coupled with three exocyclic amino NH(*+)2 groups, each containing an unpaired electron, as the simplest model for high-spin polyarylamine polycations. Related triradicals, including the 1,3,5-trimethylenebenzene (TMB, C9H9) and its nitrogen derivatives such as the monocation C8H9N+, the dication C7H9N2 2+, and the neutral C8H8N, C7H7N2, and C6H6N3 systems containing NH groups, have also been considered. Results obtained using the CASSCF [multiconfigurational complete active space (SCF--self-consistent field)] method, with active spaces ranging from (9e/9o) to (15e/12o), followed by second-order perturbation theory [CASPT2 and MS-CASPT2 (MS--multistate)] with polarized 6-311G(d,p) and natural orbital (ANO-L) basis sets reveal the following: (i) both TAB3+ and TMB (D3h) have a quartet 4A"1 ground state with doublet-quartet 2B1-4A"1 energy gaps of 8.0+/-2.0 and 12.4+/-2.0 kcal/mol, respectively; (ii) in the neutral N series, the quartet state remains the electronic ground state, irrespective of the number of N atoms, but each with slightly reduced gap, 11 kcal/mol for C8H8N (4A"), 10 kcal/mol for C7H7N2 (4A2), and 9 kcal/mol for C6H6N3 (4A2); and (iii) the ground state of monoamino cation and diamino dication is a low-spin doublet state (2B1 for C8H9N+ and 2A2 for C7H9N2 2+) and lying well below the corresponding quartet state by 10 and 12 kcal/mol, respectively. In the monocationic and dicationic amino systems, a slight preference is found for the low-spin state, apparently violating Hund's rule. This effect is due to the splitting of the orbital energies and the presence of the positive charge whose delocalization strongly modifies the electronic distribution and some structural features. In the latter cations, the positive charge basically pushes unpaired electrons onto the ring forming a kind of distonic radical cations and thus gives a preference for a low-spin state.     

A Unified Monotonic Approach to Generalized Linear Fractional Programming

We present an efficient unified method for solving a wide class of generalized linear fractional programming problems. This class includes such problems as: optimizing (minimizing or maximizing) a pointwise maximum or pointwise minimum of a finite number of ratios of linear functions, optimizing a sum or product of such ratios, etc. – over a polytope. Our approach is based on the recently developed theory of monotonic optimization.     

New cytotoxic cucurbitacins from the pericarps of Trichosanthes tricuspidata fruits

An extract of the fruits of Trichosanthes tricuspidata collected in North Vietnam was found cytotoxic in KB cells. A bioassay-guided fractionation led to the isolation of a series of cucurbitacins of which two are new: tricuspidatin and 2-O-glucocucurbitacin J. Their isolation and structure determination are described.