Pseudomonasfluorescens HK44 is a lux-based bioluminescent bioreporter capable of selective luminescence in the presence of naphthalene and/or salicylic acid intermediate of its metabolism. We attempted to induce bioluminescence (BL) in this strain with 72 compounds, viz. substituted naphthalenes, naphthalene-like compounds (e.g., quinoline), substituted salicylic acids, salicylic acid-like compounds (e.g., 2-anthranilic acid), oligocyclic aromates, and intermediates of naphthalene metabolism to better discriminate response specificity. From them, 42 induced BL significantly lower as compared to naphthalene, three (viz. isoquinoline, o-cresol, and salicylamide) induced BL significantly greater than naphthalene, and 27 yielded no bioluminescent response whatsoever. Strain HK44 is therefore not prone to extensive false-positive signaling and can serve as a fairly specific indicator organism for naphthalene bioavailability. At elevated concentrations, 41 compounds inhibited BL. Thus, the inclusion of constitutive bioreporter controls as indicators of sample toxicity is vital to successful biosensing application.
Eleven p-substituted benzaldoximes (p-XC6H4CH=NOH, where X = H, CH3, CF3, F, Cl, Br, OCH3, N(CH3)2, COOCH3, CN, NO2) have been synthesized and their dissociation constants determined in 10% (v/v) aqueous dioxane at 35 °C. Under the same conditions, the pseudo-first order rate constants kobs of their reactions with p-nitrophenyl acetate (PNPA) were measured at pH values from 7.8 to 10.8 and at concentrations coxime ranging from 0 to 4.00 × 10-3 mol l-1. The kinetic model and mechanism of the said reaction was proposed by means of mathematical statistical modelling of the dependences of kobs on pH and coxime. The mechanism involves a pre-equilibrium (k-1/k1) in which PNPA forms a tetrahedral intermediate (THI) with the deprotonated form of oxime. In the given medium, THI is in equilibrium with the non-reactive conjugated acid THIH (dissociation constant Ka,THIH) which is stabilized by intramolecular hydrogen bond. Depending on pH, the rate-limiting step consists either in formation of THI from educts (pH < pKa,oxime) or in its spontaneous (k2) and oxime-catalyzed (k3, general acid catalysis) decomposition to products (pH > pKa,oxime). Evaluation of substituent effects on dissociation constants (Ka,oxime) of the oximes showed that there is no direct conjugation between the substituent and the reaction centre (the found reaction constant ρ(Ka,oxime) = 0.91). The transmission coefficient of the transfer of these effects through C=N-O grouping corresponds approximately to one bond. The reaction constants in the Hammett equation obtained from the regression model are: ρ(k-1Ka,THIH/k1) = 1.29, ρ(k2Ka,THIH) = 0.20 and ρ(k3Ka,THIH) = 0.67. These reaction constants have been discussed with the regard to the reaction mechanism suggested.
Acidities of 19 meta-and para-substituted ethynylbenzenes were calculated at the B3LYP/6-311þG(d,p) level and correlated within the framework of the Hammett equation with the calculated acidities of equally substituted benzoic acids. The substituent effects were decomposed in terms of isodesmic reactions into those operating in the anions and in the uncharged molecules. Characteristic deviations from the Hammett equation were found for para-substituents, both for acceptors and donors; the former can be interpreted by the resonance formula only with an electron sextet. With reference to the series of ionization reactions investigated previously, it was possible to reinvestigate the validity of the Hammett equation on the basis of calculated reaction energies using a more homogeneous data set than had been ever accessible from the experimental reactivities. The equation was fulfilled for all meta-substituents with a higher accuracy than commonly attainable with the experimental data. When para-substituents were included, deviations occurred according to the character of the functional group: When this group was an acceptor, the donor substituents showed deviations and vice versa. Another series of reactions proceeding between uncharged groups bonded directly on the benzene ring was investigated in the same way: The Hammett equation held with a similar precision, although its original range of validity was surpassed. The properties of a set of common substituents were investigated by principal component analysis and cluster analysis. There is a fundamental difference between uniform acceptors and more discriminated donors but clustering is not so strong to depreciate common statistical analysis.The Hammett equation has become popular, in spite of its restricted applicability, as the first attempt to predict reactivity by means of an empirical formula. For many years, it has remained the most general and simplest structure-property relationship.1,2 In energy terms, it is expressed by eqn (1).The symbol E(X) may mean the reaction energy or enthalpy but in most cases it stands for the Gibbs energy, or activation Gibbs energy, in a series of reactions of meta-or para-substituted benzene derivatives. The empirical parameter s m or s p characterizes the substituent X, the parameter r is pertinent to the given reaction, E(H) relates to the unsubstituted compound (X = H). In simple terms of organic chemistry, eqn (1) means that the variable substituents X raise changes of reactivity always in the same succession: for instance the substituent effect of 4-CO 2 CH 3 is always twice the effect of 4-Cl. Eqn (1) has the main importance in interpreting the values of the parameters 2 s and r; less in predicting the unknown values of E. Nevertheless, it serves still as reference when investigating reactivities or activities of benzene derivatives. 3The exact range of validity is of central importance for any empirical relationship 2 and numerous attempts were made to delimit it for eqn (1) with more precision. 2,4 In kinetics, the...
Seven hypotheses on relationships between the structure of naphthalene analogs and bioluminescence response of bioreporter Pseudomonas fluorescens were formulated using GUHA (General Unary Hypotheses Automaton) on a training set of 37 compounds. Prediction of bioluminescence response of 12 new naphthalene analogs was successful in 69 % cases and resulted in rejection of single hypothesis. The results demonstrate applicability of GUHA in structure-activity research, especially for qualitative data.
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