Investigations on the dynamic properties of 25,26,27,28-tetraalkoxycalix[4]arenes: para-substituent- and solvent-dependent properties of paco conformers and determination of thermodynamic parameters of the pinched cone/pinched cone conversion

Soi, Antonio; Bauer, Walter; Mauser, Harald; Moll, Claus; Hampel, Frank; Hirsch, Andreas

doi:10.1039/a708606g

Cited by 37 publications

(26 citation statements)

References 26 publications

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“…Compared to the wealth of experimental studies of calix[4]arenes, their computational study lagged behind due to the large system size of calixaromatics that limited the methods that could be used in their study. Since 1990, computational studies have focused on structural features34–36 and properties37, 38 initially using molecular mechanics and later semi‐empirical methods such as PM3 and AM1 39–45. However, most of these studies were not able to accurately describe the structures and the conformational equilibria and therefore only yielded a very qualitative understanding of the experimental results.…”

Section: Introductionmentioning

confidence: 99%

Semifield testing of a bioremediation tool for atrazine‐contaminated soils: Evaluating the efficacy on soil and aquatic compartments

Chelinho

Moreira‐Santos

Silva

et al. 2012

Enviro Toxic and Chemistry

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The present study evaluated the bioremediation efficacy of a cleanup tool for atrazine-contaminated soils (Pseudomonas sp. ADP plus citrate [P. ADP + CIT]) at a semifield scale, combining chemical and ecotoxicological information. Three experiments representing worst-case scenarios of atrazine contamination for soil, surface water (due to runoff), and groundwater (due to leaching) were performed in laboratory simulators (100 × 40 × 20 cm). For each experiment, three treatments were set up: bioremediated, nonbioremediated, and a control. In the first, the soil was sprayed with 10 times the recommended dose (RD) for corn of Atrazerba and with P. ADP + CIT at day 0 and a similar amount of P. ADP at day 2. The nonbioremediated treatment consisted of soil spraying with 10 times the RD of Atrazerba (day 0). After 7 d of treatment, samples of soil (and eluates), runoff, and leachate were collected for ecotoxicological tests with plants (Avena sativa and Brassica napus) and microalgae (Pseudokirchneriella subcapitata) species. In the nonbioremediated soils, atrazine was very toxic to both plants, with more pronounced effects on plant growth than on seed emergence. The bioremediation tool annulled atrazine toxicity to A. sativa (86 and 100% efficacy, respectively, for seed emergence and plant growth). For B. napus, results point to incomplete bioremediation. For the microalgae, eluate and runoff samples from the nonbioremediated soils were extremely toxic; a slight toxicity was registered for leachates. After only 7 d, the ecotoxicological risk for the aquatic compartments seemed to be diminished with the application of P. ADP + CIT. In aqueous samples obtained from the bioremediated soils, the microalgal growth was similar to the control for runoff samples and slightly lower than control (by 11%) for eluates.

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Section: Introductionmentioning

confidence: 99%

Semifield testing of a bioremediation tool for atrazine‐contaminated soils: Evaluating the efficacy on soil and aquatic compartments

Chelinho

Moreira‐Santos

Silva

et al. 2012

Enviro Toxic and Chemistry

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“…In contrast, calix[4]arenes bearing methyl groups are fully flexible and freely rotate between the four conformations with the equilibrium being solvent and p ‐substituent dependent (Figure ) . Both experimental NMR studies and MM3 calculations gave the relative stabilities for tert ‐butyl calix[4]arene as partial cone>cone>1,2‐alternate>1,3‐alternate at room temperature with the majority product at −30 °C being assignable to the partial cone…”

Section: Introductionmentioning

confidence: 99%

Fixing the Conformation of Calix[4]arenes: When Are Three Carbons Not Enough?

Matthews

Cecioni

O’Brien

et al. 2018

Chemistry A European J

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Calix[4]arenes are unique macrocycles that through judicious functionalisation at the lower rim can be either fixed in one of four conformations or remain conformationally flexible. Introduction of propynyl or propenyl groups unexpectedly provides a new possibility; a unidirectional conformational switch, with the 1,3-alternate and 1,2-alternate conformers switching to the partial cone conformation, whilst the cone conformation is unchanged, under standard experimental conditions. Using H NMR kinetic studies, rates of switching have been shown to be dependent on the starting conformation, upper-rim substituent, where reduction in bulk enables faster switching, solvent and temperature with 1,2-alternate conformations switching fastest. Ab initio calculations (DFT) confirmed the relative stabilities of the conformations and point towards the partial cone conformer being the most stable of the four. The potential impact on synthesis through the "click" reaction has been investigated and found not to be significant.

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“…When the substituents are small, e.g. a methoxy group, the tetrasubstituted CCA and TCA are in conformational equilibrium of these forms . However, in the particular case of all R=H, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…in the non substituted calix[4]arenes, four ОН groups form a very strong cooperative cyclic hydrogen bond (HB) which essentially stabilize the C 4 symmetrical cone conformation (Fig. a) . If these key stabilizing HBs are totally eliminated by the tetrasubstitution with some groups, the geometry of the cone conformation is changed dramatically.…”

Section: Introductionmentioning

confidence: 99%

“…Namely, according to the X‐ray single crystal diffraction and calculations, the cone conformation of tetra substituted CCA and TCA has actually only the C 2 symmetry and so‐called pinched cone ( PC ) conformation (Fig. b), while the cone structure with the C 4 symmetry is a saddle point. Moreover, due to a higher barrier of the interconversion between these two PC forms in TCA, it was easily observed experimentally also in solution .…”

Section: Introductionmentioning

confidence: 99%

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Conformational diversity and dynamics of distally disubstituted calix and thiacalix[4]arenes in solution

Latypov

Kharlamov

Muravev

et al. 2013

J. Phys. Org. Chem.

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According to the quantum chemical calculations and Dynamic NMR experiments in the distally disubstituted classical and thiacalix[4]arenes (CCA and TCA) in addition to the C 2v symmetrical pinched cone (PC) conformation, the distorted cone (DC) form with an approximate C s overall symmetry (with two OH groups bonded to one oxygen atom) also corresponds to the energy minimum. Moreover, in DC form, two different mutual orientations of O-R groups at a lower rim lead to two stable conformations: the first -with both these groups directed outward, the second -with both these groups pointing toward the same direction. In CCA, the PC is essentially favoured over the DC, while in TCA, energies of these forms are similar or the latter may be even preferable.

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Investigations on the dynamic properties of 25,26,27,28-tetraalkoxycalix[4]arenes: para-substituent- and solvent-dependent properties of paco conformers and determination of thermodynamic parameters of the pinched cone/pinched cone conversion

Cited by 37 publications

References 26 publications

Semifield testing of a bioremediation tool for atrazine‐contaminated soils: Evaluating the efficacy on soil and aquatic compartments

Semifield testing of a bioremediation tool for atrazine‐contaminated soils: Evaluating the efficacy on soil and aquatic compartments

Fixing the Conformation of Calix[4]arenes: When Are Three Carbons Not Enough?

Conformational diversity and dynamics of distally disubstituted calix and thiacalix[4]arenes in solution

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