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The dynamic features of Noyori’s mechanism for the dimethylaminoisoborneol (DAIB) catalyzed alkylzinc addition to benzaldehyde have been investigated using the whole set of differential equations that describe the evolution of 19 species (starting products, intermediates, final compounds) involved in 36 coupled reversible or non-reversible processes. Using all the data available in the literature regarding the kinetic and thermodynamic parameters, the modeling confirms that the non-linear correlation between the enantiomeric excess of the chiral auxiliary (ee aux ) and that of the product (ee prod ) originates from the accumulation of the heterochiral alkylzinc amino alkoxide dimer (a reservoir effect). The variations of the enantiomeric excess of the product versus the benzaldehyde conversion are shown. Inhibition by the product can be understood by considering a reversible interaction between the alkoxide produced and the monomeric alkylzinc amino alkoxide catalyst. The effect of the order of the reactant addition on the ee prod and the rate of reaction as observed with 1-piperidino-3,3-dimethyl-2-butanol (PDB) instead of DAIB can be simulated without changing the relative thermodynamic stabilities of the homo- and heterochiral dimers although at the expense of a slowing-down of their equilibration rates.

Several biphasic systems giving rise to periodical Marangoni instability have been analyzed from the point of view of the physicochemical properties of the involved compounds. In each case, the compound at the origin of the oscillatory behavior has been identified: the reactant cetyltrimethylammonium bromide (CTAB) for the CTAB/picric acid (PH) system and the product of reaction dodecyl sulfate tetraalkylammonium (TAADS) for the sodium dodecyl sulfate/tetraalkylammonium bromide (SDS/TAAB) system. The properties of the latter system have been varied progressively by increasing the chain length of the tetraalkylammonium ion. Oscillations were observed whichever the direction of transfer (from water to dichloromethane and from dichloromethane to water). The comparison of the dynamic interfacial tension, recorded during transfer, to equilibrium measurements shows that the instability is favored when partition is highly in favor of the organic phase. The main criteria for the appearance of the instability are a high surface activity and a low interfacial adsorption.

Numerical kinetic simulations have been employed to understand the origin of enantioselectivity reversal of chiral beta-amino alcohol catalysts occurring in the presence of their achiral analogs in the autocatalytic addition of diisopropylzinc to pyrimidine carbaldehydes (Soai reaction). In a preceding work (Rivera Islas, J.; Lavabre, D.; Grevy, J. M.; HernAndez Lamoneda, R.; Rojas Cabrera, H.; Micheau, J. C.; Buhse, T. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 13743-13748), we provided a possible explanation for the phenomenon of spontaneous mirror-symmetry breaking observed in this reaction. The effect of enantioselectivity reversal, giving rise to steep and abrupt transitions between opposed optically active states, has been identified by our current approach as another manifestation of such mirror-symmetry breaking capability. In the present case, we considered the involvement of the chiral catalyst and its achiral analog in the reaction network. Our modeling indicates that the enantioselectivity reversal can be either caused (i) by an interaction between the chiral and achiral additives or (ii) by an interaction of the customary products of the Soai reaction with the additives. The second option, which stands for the reversible inhibition of the chirally selective autocatalysts by the additives, could also explain a number of further additive effects in the Soai reaction reflecting the extraordinary sensitivity of this system toward the initial addition of almost any, even catalytically inactive, chiral substance.

The partition at equilibrium, in a two-phase liquid system, of a compound dissociated in one phase, or both, is expressed in terms of general equations and analyzed. Dissociation in the second phase, even weak, has a non-negligible influence. The distribution ratio depends strongly on the concentration and can even be reversed in certain cases. All the partition and dissociation constants in each phase can be obtained from the concentrations at equilibrium measured under some given conditions. In less favorable cases, an apparent partition constant can still be estimated. This is illustrated by an experimental study, in the water/dichloromethane system, involving the partition of picric acid and cetyltrimethylammonium bromide (CTAB) followed by UV-Visible spectroscopy, and of a series of tetraalkylammonium bromides (ethyl, propyl, and butyl) assayed by mass spectroscopy. Copyright © 2006 John Wiley & Sons, Ltd.

Association constants and adsorption parameters of tetraalkylammoniumdodecyl sulfate (TAADS) ion pairs in water were determined. We have analyzed water/air surface tension measurements obtained for mixtures of sodium dodecyl sulfate (SDS) and tetraalkylammonium bromide of increasing chain lengths (TMAB, TEAB, TPAB, and TBAB). To reproduce the experimental isotherms, we coupled the association equilibrium of the ion pairs to the equations proposed by Fainerman and co-workers to model the adsorption of binary mixtures of surfactants (SDS and TAADS) with different molar areas at a nonideal surface layer. The parameters found showed that the model is not convenient to describe the effect of the addition of TMAB but a clear coherency was obtained for the three longer compounds. Ranging from TEADS to TBADS increasing hydrophobic interactions give rise to a higher associability but to a lower surface activity. Self-interactions coefficients extracted by the fitting procedure confirmed the importance of attractive interactions between the ion pairs. The calculated surface coverage showed that in every case the compound mainly adsorbed at the interface was the ion pair. For TBADS strong attractive interactions result in a phase transition at very low concentration.

The first X-ray characterization of an azacrown ferrocenyl chalcone [(C5H5)Fe(C5H4COCH=CHC6H4-p-aza-15-crown-5)] (2) is reported. Its cation electrochemical detection capabilities have been evaluated and its behaviour towards protonation and calcium addition has been thoroughly examined. The uncommon ligand–Ca2+ interaction process involves three species of different stoichiometry in equilibrium in solution. Their association constants have been calculated. These species are formed by interaction of calcium with both the azacrown and CO functions of compound 2, as evidenced by NMR and IR spectroscopy. The theoretical MESP analysis also suggests that, contrary to its N-ethyl-substituted homologue [(C5H5)Fe(C5H4COCH=CHC6H4NEt2)] (1a), both coordination sites of 2 are involved in this interaction process. The study highlights that the CO group of 2 improves the selectivity of the cation electrochemical detection whencompared to the known compound [(C5H5)Fe(C5H4CH=CHC6H4-p-aza-15-crown-5)]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Oscillations of the electric potential and of the interfacial tension were simultaneously recorded in a water−oil−water system (cetyltrimethylammonium bromide (CTAB) in water/picric acid in dichloromethane/water). Both types of oscillations were perfectly correlated in time and shape. In each oscillatory cycle, the fast jumps in the electric potential are related to a rapid adsorption of the surfactant at the interface while the slow motion relaxations correspond to the liberation of the interface from the surfactant by the formation of hydrophobic cetyltrimethylammonium picrate ion pairs that diffuse into the CH2Cl2 phase. The fast inflow of CTAB to the interface is probably caused by periodically occurring convective Marangoni instabilities. The transitions to the convective regime are assumed to be controlled by the fractional surfactant coverage of the interface.

International audience; The fluorescence quenching of 1,5-bis[4-(diethylamino)phenyl]penta-1,4-dien-3-one (1), 1-[4-(diethylamino)phenyl]-5-phenylpenta-1,4-dien-3-one (2) and chalcone 3 (1-[4-(diethylamino)phenyl]but-1-en-3-one) was studied in acetonitrile using ferrocene and three commercially available derivatives, 1,1′-diacetylferrocene, acetylferrocene and 1,1′-dimethylferrocene. The spectroscopic and electrochemical characteristics of all the compounds were investigated. The feasibility of the quenching process was calculated, showing in particular that electron transfer was thermodynamically possible in every case. The steady-state fluorescence of the three organic dyes was then measured in the presence and in the absence of the ferrocenyl derivatives and the data were corrected for inner-filter effects. 1,1′-Diacetylferrocene and acetylferrocene proved to be the most efficient quenchers, and among the three dyes investigated, chalcone 3 was the most sensitive to the presence of the ferrocenyl derivatives. However, the fluorescence decay times of the ketocyanines were not affected by the presence of the ferrocene derivatives, indicating that quenching was not diffusion-controlled but rather the consequence of the formation of a ground state complex.

The autocatalytic biphasic alkaline hydrolysis of C-4 to C-8 ethyl alkanoates was studied in a CSTR. In our experimental conditions, the two shorter esters (C-4 and C-5) showed monostable behavior ...

Autocatalytic kinetics are observed during the biphasic alkaline hydrolysis of C-4, C-6 and C-8 (butanoate, hexanoate and octanaoate) ethyl esters. Ethanol and alkanoate anions are the products of the reaction. A kinetic model including spontaneous dissolution of the organic phase into the aqueous phase, aqueous hydrolysis of the ester, formation of ester containing aggregates and micellisation has been proposed. For C-4, taking into account salting-in and solvent effects is sufficient to reproduce the autocatalytic behaviour. For C-8, the major autocatalytic process is an ester containing aggregates (ECA) mediated phase transfer. For C-6, it appears that the role of ECA is double. Small sized ECA which are formed at the beginning of the reaction do not perform rapid phase transfer and trap surfactant molecules. Larger ECA which appear at the end of the reaction are the main phase transfer agent. Using an empirical formula to describe the size of the interface, the model is able to reproduce the effect of a variation of the volumic ratio of the two phases as well as the effect of stirring rate and non-emulsified experiments.

The photochromism of the 1,3,3-trimethylspiro[indoline-naphthoxazine] A has been studied under continuous monochromatic irradiation (313 and 365 nm) in liquid toluene solution at 278 K. The values of the main photochromic parameters (quantum yields and absorption coefficients) have been determined by kinetic modelling of absorbance (Abs) versus time curves recorded under continuous irradiation. We showed that the quantum yields of both photocoloration and reversible photochemical bleaching were wavelength-dependent. Under 365 nm irradiation, photodegradation processes that are not sensitive to the presence of oxygen were observed. The degradation occurs either from the direct irradiation of the closed spiro form A or from the thermal decomposition of the open photomerocyanine form B. Under our experimental conditions, photochemical decomposition of the open photomerocyanine form B was negligible.

The alkaline hydrolysis of C-4 to C-8 (butanoate to octanoate) ethyl esters shows autocatalytic kinetics when performed under two-phase conditions without any mixing solvent. Alkanoate anions and ethanol are the products of the reaction. A dynamic model is proposed that describes quantitatively this kinetic behavior. The model includes the main processes occurring in the biphasic medium and the corresponding thermodynamic calculations of the average size and stoichiometry of the molecular aggregates. Modeling indicates that salting-in and solvent effects caused by the alkanoate anions and ethanol determine the autocatalytic kinetics in the hydrolysis of C-4 ethyl ester where no aggregation occurs. In the C-5 to C-8 experiments, ester-containing micelles (ECM) are mainly formed by cooperative aggregation of alkanoate anions with ester molecules. ECM is formed only after a threshold concentration of the alkanoate anion has been reached. In a phase-transfer-like process, ECM carries ester molecules into the ...

The biphasic alkaline hydrolysis of ethyl caprylate (EC) exhibits highly nonlinear kinetics that has been attributed in the literature to “micellar autocatalysis” (Bachmann, P. A. et al. Nature 1992, 357, 57). New experimental results enable us to establish a macroscopic kinetic model quantitatively accounting for the dynamics of this reaction. According to the model, EC is carried from the organic to the aqueous phase by a transient micelle−EC complex (MEC). Curve fitting of the experimental kinetic data by inverse treatment shows that the formation of MEC is more favorable than that of the pure caprylate micelles (M) and occurs at a critical concentration that is smaller than the cmc associated with the formation of M. We demonstrate, in contrast to previous claims, that classical micellar catalysis is not involved in the overall reaction process, but the observed nonlinear kinetics is a consequence of the dynamics of the MEC-mediated phase-transfer reaction.

International audience; A reaction mechanism for the photooxidation of dimethyldisulfide (DMDS) in aqueous acetonitrile has been established by kinetic modeling the UV absorbance vs. time curves under continuous irradiation. The model, built according to the known solution reactivity of oxysulfur radicals [1], consists of 22 steps involving 6 radical and 10 nonradical species. The first steps of the mechanism are the homolytic cleavage of the DMDS S - S bond with formation of methanethiyl radicals (CH3S) followed by addition of these radicals to molecular oxygen. There are photoequilibria between thiyl (CH3S), sulfinyl (CH3S), and sulfonyl (CH3SO2) radicals and the corresponding molecular species (methyl methanethiosulfinate CH3S(O)SCH3 or MMTSI, methyl methanethiosulfonate CH3S(O)2SCH3 or MMTS and methanesulfinic acid CH3S(O)OH or MSIA) which appear as long lived intermediates. Reactions of sulfonyl radicals with oxygen lead to methanesulfonic acid (CH3S(O)2OH) or MSA. Cleavage of sulfonyl radicals gives SO2 and CH3, the parent compounds of sulfuric (H2SO4) and methanoic (HCOOH) acids. The predictive power of the model was tested at higher initial concentration of DMDS in anhydrous and aqueous acetonitrile. In these conditions, the proposed mechanism gives a semiquantitative description of the course of the reaction and reproduces the kinetic behavior of the long lived intermediates. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet:.

In photochemistry, under continuous irradiation, kinetic non-linearity results from Beer-Lambert's law. In monophotonic or photoequilibrated systems, non-linearity is too weak in order to exhibit dynamic instabilities. On the other hand, when there is a biphotonic process, as in the so-called ABC system or a process of auto-inhibition, as in the self-quenching model, screen effects (internal filter) are sufficient to give rise to kinetic instabilities such as bistability or oscillations. Starting from a simple bistable photochemical system, the kinetic scheme of a sustained photochemical oscillator operating in an isothermal reactor closed to flux of matter is designed. From the experimental point of view, the photochemistry of the triphenylimidazyl dimer (TPID) in chloroform is described as an example of a photochemical bistable system in a CSTR. The mechanism is interpreted quantitatively by application of the laws and concepts of photochemical dynamics. A series of experimental systems are reviewed and discussed in order to highlight the non-linear nature of their kinetics. Our objective is to pave the way for further experimental demonstrations of bistable or oscillating systems in photochemistry.

The autoxidation of tetralin is treated as a model reaction system to define the applicability of stereospecific autocatalysis. This concept, predicting a spontaneous amplification of enantiomeric excess generated by an autocatalytic chemical reaction, is used in several theoretical models as an explanation for the origin of natural optical activity. The reaction system investigated obeys the basic criteria of these models: a chiral intermediate (tetralin hydroperoxide) is produced from an achiral substrate (tetralin) via an autocatalytic pathway where the feedback mechanism is expected to generate a state of broken chiral symmetry. In order to test the amplification capacity of this reaction a computer analysis of the kinetic scheme is performed. This simulation is derived from the known kinetic scheme of autoxidation and is validated by fitting the experimentally observed data of hydroperoxide evolution. Calculations show that this model allows powerful amplification of enantiomeric excess and a transient amplification of the optical rotation. It is also demonstrated that the model system exhibits pronounced sensitivity toward any loss of absolute configuration of the involved chiral species. Since an amplification effect results exclusively at a high degree of stereoselectivity, it is concluded that stereospecific autocatalysis is possible in systems which show template reactions, crystallization, or colloidal effects. © 1993 Wiley-Liss, Inc.

The rate law of an elementary photochemical reaction: A → B ( hv ), contains 4 independent factors: the quantum yield, the photon flux, the concentration of the photosensitive substrate and the photokinetic factor. This type of reaction will always slow down. However, by increasing one of these 4 factors artificially, the reaction can be made to speed up. Using kinetic models comprising one or more photochemical reactions, we show that appropriate coupling between two or more elementary processes gives rise to a cooperative effect. This effect increases one or more of these 4 factors, and makes the coupled photochemical model bistable in a CSTR. The values of the parameters for which one observes bistability are experimentally realistic. One of these models provides a simplified simulation of the stages underlying the bistable photochemical behavior of the TPID/CHCl 3 , system.

Investigation of the photochromic system TPID/CHCl3 (TPID = triphenylimidazolyl dimer) in a CSTR provided the first example of isothermal photochemical bistability. The reaction mechanism was established and the relevant kinetic and spectroscopic parameters were estimated experimentally. In order to predict the quantitative dynamic behavior of the TPID/CHCl3 system these parameters were refined numerically using batch reactor data. The adjusted model simulates very accurately bistability either as a function of residence time τ, or as a function of incident photon flux I0.

International audience; The optical study of ferrocenyl ligands 1–2 is presented, and reveals several interesting points. Contrary to their monosubstituted counterparts, these ligands exhibit fluorescence properties in acetonitrile. They can detect calcium, and also barium, by four different techniques: NMR, electrochemistry, UV–Vis absorption spectroscopy and fluorimetry in the same solvent. Each ligand detects both salts in the same manner by UV–Vis absorption and by fluorimetry. The response depends on the nature of the N terminal groups of the ligand. In each case, the ligand–calcium interaction is complex and involves 3–5 species in equilibrium in solution. Their association constants have been determined by fitting the UV–Vis data. Remarkably, for 2 and the calcium salts, nearly the same set of association constants can be used to fit not only the UV–Vis data obtained with calcium triflate (in a restricted range of concentration) or with calcium perchlorate, but also the NMR data obtained with calcium triflate. Interestingly, these results strengthen the fact that, in this family of compounds, the azacrown derivatives are less sensitive to high calcium triflate concentrations than their simple N-alkyl homologues. It is noteworthy that the complex non-monotonous fluorescence behaviour of compounds 1 and 2 upon Ca2+ or Ba2+ addition is quite original for ferrocenyl chalcones. These ligands constitute scarce examples of multi-signalling fluorescent ferrocenyl chemosensors for Ca2+ and Ba2+ cations in CH3CN.

The addition of diisopropylzinc to prochiral pyrimidine carbaldehydes (Soai reaction) is the onlyknown example of spontaneous asymmetric synthesis in organic chemistry. It serves as a model systemfor the spontaneous occurrence of chiral asymmetry from achiral initial conditions. This review describesthe possible kinetic origin of specific experimental features of this reaction. It is shown that generickinetic models, including enantioselective autocatalysis and mutual inhibition between the enantiomers,are adequate to describe a variety of the astonishing properties of the Soai reaction. Namely, theseare the unprecedented strong chiral amplification, extreme sensitivity to the presence of very small amountsof chiral initiator, mirror-symmetry breaking when starting from achiral conditions, and the reversal ofenantioselectivity of chiral catalysts by addition of achiral additives. The described kinetic approachallows a closer insight into the nonlinear dynamics of the Soai reaction. It also reveals that a numberof open questions concerning the detailed reaction mechanism are still to be solved and that further experimentalstudies are required.

We show here that the disubstituted ferrocenyl chalcones 1 and 2 are good electrochemical sensors for calcium and barium in CH 3 CN. However, these two triflate salts are detected in a different way by both ligands. To clarify this point, a thorough and informative NMR study of the ligand–salt interactions is presented. The unusual shapes of the titration curves obtained depend on both the ligand and cation used. For example, they illustrate that ligand 1 mainly interacts with the metal by its CO functions, while ligand 2 also interacts by its azacrown groups. These curves also reflect complex equilibriums in solution involving several ligand–salt adducts detected by mass spectrometry. To evaluate the strength of these interactions, the association constants of all the species formed have been determined by fitting the NMR data. It is noteworthy that changing the diethylamino groups in molecule 1 by the azacrown residue enhances the selectivity for the calcium salt, as pointed out by the value of the association constant of the 2 Ca 2+ species. The synthesis of the protonated counterparts 3 and 4 was useful to clarify the electrochemical behaviour of 1 and 2 . Although the two ligand–salt interactions present several common points, the whole results obtained allow us to propose an original explanation for the difference observed between the Ca 2+ and Ba 2+ electrochemical sensing.

Periodic Marangoni convective instability has been observed in a biphasic system during the mass transfer of cetyltrimethylammonium bromide (CTAB) from an aqueous to a dichloromethane organic phase. Visualization of the convective fluxes was possible thanks to the CTAB crystals that are formed in the aqueous phase at a temperature below the Krafft point. Surface tension and electrical potential oscillations have been shown to be correlated with the fluid motion. Surface tension measurements, representative of the adsorption state, showed fast adsorption during the convective stage, followed by a slower desorption process in the quiet stage. To account for the electrical potential data, two components need to be taken into account. In the quiet stage, the signal was comparable to surface tension, and the main contribution would result from the electrical double layer formed at the interface by charged surfactants. In the convective stage, the electrical potential was furthermore related to the velocity of the fluid in the aqueous layer. Perturbations of the charge distribution in the Gouy-Chapman layer due to tangential flows could be at the origin of the phenomenon.

International audience; We have synthesized a novel disubstituted ferrocenyl compound [Fe(C5H4CO(CHCH)2C6H4NEt2)2] (3) that displays a remarkable fluorescence quantum yield (1.1 × 10-1) in acetonitrile, and we have studied its capacity for calcium detection in depth using both electrochemical and optical techniques in this medium. The results of our NMR analysis reveal that the ligand−calcium interaction is CO-centered and that an uncommon equilibrium occurs between 3 and calcium triflate, involving five species of different stoichiometries. In contrast, our analysis of the UV−vis absorption data indicates that only three species of different stoichiometries are formed when calcium perchlorate is used with 3. Mass spectrometry measurements provide strong support for the formation of all these different species in solution. In addition, the electrochemical detection of calcium triflate by 3 leads to an irreversible FeII/FeIII oxidation process with an unusual negative shift (−60 mV) caused by the nBu4NBF4 salt effect on the Ca2+−3 interaction process. Compound 3 can also be an original optical probe to detect calcium perchlorate over a wide range of salt concentration by UV−vis absorption spectroscopy. The most original and intriguing property of compound 3 is that it exhibits an unprecedented “multistep” fluorescence behavior upon addition of this salt.

We show how structural changes in the basic framework of ferrocenyl chalcone [(C 5 H 5 )Fe(C 5 H 4 COCH CHC 6 H 4 NEt 2 )] ( 1 ) induce different capabilities of detecting calcium by UV/vis absorption spectroscopy. In particular, compound 1 , and its derivatives ( 2 ) and ( 3 ) incorporating a supplementary ethylenic unit into the conjugated link, allow a specific detection of calcium triflate with regard to calcium perchlorate. Investigations related to the unprecedented behaviour of these chalcone-like derivatives are presented. This study confirms that while the interaction of ligands 1 – 3 with calcium is centred on the CO group, the interaction of ligand 4 with calcium is aza-centered. The strength of these interactions was examined by processing the UV/vis absorption data with a curve fitting model. Remarkably, in the case of compound 4 , the set of association constants issued from processing the absorption data was successfully used to fit the NMR data. In addition, mass spectrometry experiments provided strong support for the formation of the different species involved in the interaction of compounds 1 – 4 with calcium. This work underlines the importance of considering the nature of the salt used as well as the experimental conditions in cation detection processes.

The biphasic alkaline hydrolysis of ethyl caprylate, which has attracted attention as a prototype reaction for the so-called self-reproduction of micelles (Bachmann, P. A.; et al. Nature 1992, 357, 57), was shown to give rise to kinetic bistability in a continuous flow stirred tank reactor. At higher flow rates, the stationary state composition was characterized by a turbid two-phase oil/water mixture, while at lower flow rates a single transparent aqueous phase was obtained. For intermediate residence times, either situation may be attained depending on the initial conditions in the reactor. Near the hysteresis limits, the characteristic increase in relaxation times was observed. A macroscopic model, which accounts for the nonlinear behavior in terms of micelle-mediated phase transfer, predicts the bistability, and the observed transient kinetics are in good agreement with the experimental results.

Kinetic modeling using nonlinear differential equations is proposed to analyze the spontaneous generation of enantiomeric excess in the autocatalytic addition of diisopropylzinc to prochiral pyrimidine carbaldehydes (Soai reaction). Our approach reproduces experimentally observed giant chiral amplification from an initial enantiomeric excess of –6% to >60%, high sensitivity and positive response to the presence of minute amounts of chiral initiator at concentrations –14M, and spontaneous absolute asymmetric synthesis from achiral starting conditions. From our numerical simulations using kinetic schemes derived from the Frank model, including stereospecific autocatalysis and mutual inhibition, we have shown that it is possible to reproduce the mirror-symmetry-breaking behavior of the Soai reaction under batch conditions leading to a bimodal enantiomeric product distribution. Mirror-symmetry breaking was found to be resistant to a loss of stereoselectivity up to 30%. While the mutual inhibition between enantiomers seems to originate from the presence of dimerization equilibria, the exact nature of the autocatalytic stereoselective process still remains to be revealed. From the kinetic viewpoint, simple autocatalysis involving monomers as the catalytic species is consistent with all reported experimental effects of the Soai reaction.

A new UV filter, the 1-(4-tert-butylphenyl)-2-decanyl-3-(4'-methoxyphenyl)-propane-1,3-dione, called C10-DBM, was prepared by grafting a 10-carbon aliphatic chain to the alpha-carbonyl position of 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM), a well-known and often used UV filter. The UV-A absorption efficiency of organic solutions containing the new filter was tested and compared with identical solutions containing BM-DBM with or without irradiation (xenon lamp). The originality of this new filter is that its UV-A absorbance appeared during irradiation of the molecule. Although the molar absorption coefficient of C10-DBM in the UV-A domain was lower than that of BM-DBM, the solutions absorption exhibited a much more photostable behavior under irradiation. In this study, we first demonstrated that C10-DBM was a precursor of BM-DBM (enol isomer) by means of high-performance liquid chromatography followed by mass spectrometry. Indeed, we showed that the UV-A absorption of C10-DBM solutions appearing during the irradiation of the molecule was due to a Norrish-II reaction (beta-cleavage), which induced the release of the BM-DBM enol form and 1-decene. Then, we established a kinetic model for the photochemistry of C10-DBM and fitted the variation of UV absorption spectra to confirm the proposed mechanism.

[(C(5)H(5))Fe(C(5)H(4)COCH=CHC(6)H(4)NEt(2))] (1) has been electrochemically evaluated toward different cations in solution. Calcium sensing by this compound and its two new derivatives [(C(5)H(5))Fe(C(5)H(4)CO(CH=CH)(2)C(6)H(4)NMe(2))] (2) and [(C(5)H(5))Fe(C(5)H(4)CH=CHCOCH=CHC(6)H(4)NEt(2))] (3) that exhibit a conjugated link between the ferrocene unit and the nitrogen atom has been thoroughly examined. Compounds 2 and 3 have been structurally characterized by single-crystal X-ray diffraction studies. The three related protonated species [1H][BF(4)] (4), [2H][BF(4)] (5), and [3H][BF(4)] (6) have been isolated in a good yield. NMR experiments clearly established that calcium interaction occurs in the vicinity of the carbonyl group, and mass spectrometry studies confirmed that this interaction, which involves several ligand-Ca(2+) adducts, is complex. A combination of electrochemical and NMR experiments highlighted an original salt influence on the electrochemical calcium sensing result.

Microcrystals of an organic fluorescent dye, 4-n-octylamino-7-nitrobenz-2-oxa-1,3-diazole (NBD-C8), were prepared by reprecipitation in water. The crystallization kinetics was monitored by UV/vis absorption spectroscopy, and a model was proposed. The size and shape of the microcrystals were analyzed by laser light scattering, fluorescence microscopy, and scanning electron microscopy. In the presence of PAMAM dendrimers of generation 2.5, 3.5, and 4.5, the crystallization process was drastically accelerated. The crystals obtained were smaller and more regular than those formed in pure water and were not agglomerated. There are probably two levels of interaction of NBD-C8 with the dendrimers, which act as both templates and colloid stabilizers.

The excited-state properties of a calcium dicomplex (AM2) of 2,5-[bis-[4N-(aza-15-crown-5)phenyl]methylene]cyclopentanone (A) in acetonitrile are investigated by ultrafast absorption spectroscopy. Spectroscopic evidence of an ultrafast cation decoordination following subpicosecond excitation of the chromophore is given. A global analysis of the time-resolved data is performed, and a kinetic scheme is tentatively proposed, which quantitatively describes the dynamics of the deactivation pathway of the AM2 dicomplex. A first step would involve the disruption of one of the two nitrogen−calcium bonds at a rate constant of 4 × 1011 s-1, followed by the diffusion of the cation out of the crown at a rate of 5.8 × 1010 s-1. The resulting AM complex would then relax both to its ground state (5.4 × 108 s-1) and to its triplet state (2.8 × 108 s-1).

International audience; A new ferrocene receptor binds a calcium guest via complex processes involving the whole unsaturated core of the ligand. Complexation induces significant changes in the ligand properties, as evidenced by the unprecedented cation sensing observed both by electrochemistry and fluorescence spectroscopy.

A new fluoroionophore bearing two crown ethers on the conjugated system, 1,5-bis[4N-(aza-15-crown-5)phenyl]-1,4-pentadien-3-one (II), was synthesized together with model compound I where the crown ethers are replaced by diethylamino groups. The behavior of molecules I and II in the presence of alkali and alkaline-earth perchlorates was investigated in acetonitrile solution by absorption and emission spectroscopy (including picosecond techniques), mass spectrometry, and NMR spectroscopy. Two types of interaction must be distinguished: on the one hand, the expected complexation of the crown ether moieties, which generated strong spectroscopic effects with Na+, Li+, Ba2+, and Ca2+ ions, and on the other hand, an interaction between the unsaturated ligand core and the cation, particularly noticeable with magnesium. The absorption data were correctly fitted by taking into account three different stoichiometries and the corresponding association constants were calculated. The emissive properties of the species...

Fluorescence quantum yields are used to quantify the efficiency of the emission process. In spite of the importance of these data, experimental directions for their acquisition are rarely given. A general procedure for determining the relative fluorescence quantum yield of solutions is described here, drawing attention to the many pitfalls that students may encounter. Starting materials are common yellow and pink highlighter pens.

The absorption spectrum of 4-hydroxy-7-nitrobenzofurazan (NBDOH) and its conjugate anion has been recorded in 23 solvents. The data has been analysed according to the Taft and Kamlet treatment and compared with that of some parent compounds: 4-methoxy-, 4-propylamino- and 4-diethylamine-7-nitrobenzofurazan. The phenolate anion NBDO– has been shown to exhibit the solvatochromic behaviour characteristic of this NBD series in aprotic media, although in protic media hydrogen bonding had a drastic effect on the UV–VIS spectrum. Such a sensitivity to erotogenic solvents was not encountered for other phenoxide anions such as picrate. This difference of behaviour is discussed on the basis of electrostatic potentials obtained by MNDO calculations. Evidence is given of strong negative charges located on the C(5) and C(7) atoms of NBDO–, indicating that strong hydrogen bonding may take place with solvent molecules. However, this stabilization of the anion by hydrogen bonding does not seem to influence the dissociation equilibrium, the acidity of NBDOH being perfectly in line with that of other nitrophenols whatever the solvent.

The authors describe a new and simple method for accurate determination of the first-order rate constant.

Resume L'adsorption des chlorures d'ethyl-4 pyridine ( 1 ) et de decyl-4 pyridine ( 2 ) a l'interface mercure/eau a ete etudiee par electrocapillarite. Les exces de surface et taux de recouvrement ont pu etre determines. L'aire occupee par une molecule adsorbee en a ete deduite. II a pu ainsi etre montre que 2 s'adsorbe perpendiculairement a la surface alors que pour 1 le cycle pyridinique est parallele a la surface. Ces resultats sont en bon accord avec le comportement inhibiteur de corrosion de 1 et 2 .

Much of the experimental work in chemical dynamics has been based on inorganic oxidation-reduction reactions in aqueous ionic solution (1). In general, these are special cases in which the oxidants are oxygenated or oxyhalogenated ions, and the reducers inorganic ions or simple organic substrates serving as electron donors (2). Such reactions have been shown to have non-linear properties (oscillations, multiple stationary states, etc.) involving numerous intermediate species, usually in complex reaction mechanisms.

Thermochromic reactions are of particular interest not only from the practical (1) and pedagogic (2) points of view, but also from a more fundamental standpoint (3). A number of studies drawn from a wide variety of domains have been devoted to their behavior (4–6).

Dihydroindolizines (DHI) are photochromic compounds, which on irradiation with long wavelength UV or visible light afford a colored open photoisomer, the betdine. Light induces breaking of the azacyclopentene ring. In the dark, there is only one thermal back reaction (ring closure) The determination of photochromic parameters of these systems such as the quantum yields and the UV/visible spectra of the unstable photoisomers is not a trivial problem and requires appropriated methods. In this paper, we show that kinetic modelling and inverse treatment of experimental (Abs vs t) plots recorded under continuous irradiation can help to solve this problem (dynamic method).

This study was designed to evaluate two main factors: 1) the influence of temperature change on equilibria and 2) the structural changes of the complexes interpreted in terms of ligand field theory.