- Limitations of the "tethering" strategy for the detection of a weak noncovalent interaction
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The success of applying the tethering strategy in a synthetic molecular system strongly depends on the experimental conditions and is related to the strength of the noncovalent interaction and the competition between the 'captured' and unbound ligand for the recognition site. The Royal Society of Chemistry.
- Gasparini, Giulio,Martin, Marco,Prins, Leonard J.,Scrimin, Paolo
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Read Online
- Enhancing the kinetics of hydrazone exchange processes: An experimental and computational study
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The capacity of hydrazone bonds to readily undergo component exchange processes sees their extensive utilization in dynamic combinatorial chemistry. The kinetics of hydrazone exchange are optimal at pH ～4.5, which limits the use of hydrazone-based dynamic combinatorial libraries, particularly for biological targets which are only stable at near-neutral pH values. It would thus be advantageous if hydrazone exchange proceeded with faster rates at pH values closer to neutral. We experimentally and computationally evaluated the hypothesis that hydrazones possessing neighbouring acidic or basic functional groups within the carbonyl-derived moitety of the hydrazone would enhance exchange rates. Our work suggests that judiciously placed N- or O-hydrogen bond acceptors within the carbonyl-derived moiety of the hydrazone stabilize transition states via hydrogen bonding interactions, providing a valuable boost to exchange kinetics at near-neutral pH values. We anticipate these findings will be of interest in dynamic combinatorial chemistry, dynamic covalent polymers/materials, functionalized nanoparticles and interlocked molecules, all of which may benefit from hydrazone exchange processes able to operate at near-neutral pH values.
- Higgs, Patrick L.,Ruiz-Sanchez, Antonio J.,Dalmina, Milene,Horrocks, Benjamin R.,Leach, Andrew G.,Fulton, David A.
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supporting information
p. 3218 - 3224
(2019/03/26)
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- Controlled release of volatile aldehydes and ketones from dynamic mixtures generated by reversible hydrazone formation
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Delivery systems generated by reversible hydrazone formation from hydrazine derivatives (see Fig. 1) and carbonyl compounds in H2O efficiently increase the long-lastingness of volatile aldehydes and ketones (R 1R2C=O) in various perfumery applications. The hydrazones are usually obtained in an (E) configuration at the imine double bond (NHN=C) and, in the case of aliphatic acylhydrazones R′CO-NH-N=CR 1R2 (R′ = alkyl), as syn and anti conformers with respect to the amide bond (CO-NHN). An average free-energy barrier of ca. 78kJ/mol was determined for the amide-bond rotation by variable-temperature 1H-NMR measurements (Fig. 2). In the presence of H2O, the hydrazone formation is entirely reversible, reaching an equilibrium composed of the hydrazine derivative, the carbonyl compound, and the corresponding hydrazone. Kinetic measurements carried out by UV/VIS spectroscopy showed that the same equilibrium was reached for the formation and hydrolysis of the hydrazone. Rate constants are strongly pH-dependent and increase with decreasing pH (Table 1). The influence of the hydrazine structure on the rate constants is less pronounced than the pH effect, and the presence of surfactants reduces the rate of equilibration (Tables 1 and 3). The full reversibility of the hydrazone formation allows to prepare dynamic mixtures by simple addition of a hydrazine derivative to several carbonyl compounds. Dynamic headspace analysis on dry cotton showed that the presence of a hydrazine derivative significantly increased the headspace concentrations of the different carbonyl compounds as compared to the reference sample without hydrazine (Table 4). The release of the volatiles was found to be efficient for fragrances with high vapor pressures and low H2O solubility. Furthermore, a special long-lasting effect was obtained for the release of ketones. The simplicity of generating dynamic mixtures combined with the high efficiency for the release of volatiles makes these systems particularly interesting for practical applications and will certainly influence the development of delivery systems in other areas such as the pharmaceutical or agrochemical industry.
- Levrand, Barbara,Fieber, Wolfgang,Lehn, Jean-Marie,Herrmann, Andreas
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p. 2281 - 2314
(2008/03/29)
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- Controlled release of volatile aldehydes and ketones by reversible hydrazone formation - "Classical" profragrances are getting dynamic
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Dynamic mixtures obtained by reversible covalent acylhydrazone formation of fragrance aldehydes and/or ketones and a hydrazide in water were found to be efficient delivery systems for the controlled release of highly volatile organic molecules. The Royal Society of Chemistry 2006.
- Levrand, Barbara,Ruff, Yves,Lehn, Jean-Marie,Herrmann, Andreas
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p. 2965 - 2967
(2008/09/20)
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- USE OF DYNAMIC MIXTURES FOR A CONTROLLED RELEASE OF FRAGRANCES
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The present invention relates to a delivery system in the form of a dynamic mixture obtained by reacting together, in the presence of water, at least one hydrazine derivative with at least one perfuming, flavoring, insect repellent or attractant, bactericide and/or fungicide aldehyde or ketone. The invention's mixture is capable of releasing in a controlled and prolonged manner said aldehyde or ketone in the surrounding environment. Furthermore, the present invention concerns also the use of said dynamic mixtures as perfuming ingredients as well as the perfuming compositions or perfumed articles comprising the invention's mixtures.
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Page/Page column 32-38
(2008/06/13)
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- Kinetics and Mechanism of the Formation of Girard T Hydrazones from Naphthaldehydes
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In aqueous solution, Girard T hydrazone formation from naphthaldehydes does not proceed to completion under the conditions used.The corresponding equilibrium constants have been determined and employed to calculate the rate of the reaction at completion.For all the reactions studied, the pH-rate profiles, extrapolated to zero buffer concentration, show one break at pH 4-5, characteristic of a change in the rate-determining step from aminomethanol dehydration to aminomethanol formation on going from pH 7 to pH 1.The formation of the aminomethanol is subject to catalysis by hydronium ion and by carboxylic acids present in the buffers used to maintain pH.Brensted α values for this catalysis vary from 0.24 to 0.26.We suggest a stepwise preassociation mechanism for the reaction catalysed by carboxylic acids.
- Stachissini, Antonia Sonia,Amaral, Antonia T. do,Amaral, Luciano do
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p. 1929 - 1931
(2007/10/02)
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- Kinetics and Mechanism of Benzaldehyde Girard T Hydrazone Formation
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In aqueous solution, Girard T hydrazone formation from para-substituted benzaldehydes does not proceed to completion under the condition used.The corresponding equilibrium constants were determined and employed to calculate the rate of the reaction at completion.For all the reactions studied, the pH-rate profiles, extrapolated to zero buffer concentration, show one break at pH 4-5, characteristic of a change in the rate-determining step from carbinolamine dehydration to carbinolamine formation upon going from pH 7 to pH 1.The formation of the carbinolamine is subject to catalysis by hydronium ion and by carboxylic acids present in the buffers used to maintain pH.Broensted α values for this catalysis varied from 0.19 to 0.37.Rate constants for the cyanoacetic, chloroacetic, and formic acid catalyzed formation of carbinolamine from the para-substituted benzaldehydes correlate with ?+ substituent constants, giving a value of ρ+ equal to 0.70.Rate constants for the hydronium ion catalyzed formation of the carbinolamine from the same benzaldehydes are, however, insensitive to the substituent effect.These observations lead to the conclusion that the reactions occur by different routes as a function of the catalyst.We suggest a stepwise preassociation mechanism for the reaction catalyzed by carboxylic acids and a concerted preassociation mechanism for that catalyzed by hydronium ion.
- Stachissini, Antonia Sonia,Amaral, Luciano do
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p. 1419 - 1424
(2007/10/02)
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