Computational Description of a Huisgen Cycloaddition Inside a Self-Assembled Nanocapsule

Modeling Amine Methylation in Methyl Ester Cavitand

Methylation of amines inside an introverted resorcinarene-based deep methyl ester cavitand is investigated by means of molecular dynamics simulations and quantum chemical calculations. Experimentally, the cavitand has been shown to bind a number of amines and accelerate the methylation reaction by more than four orders of magnitude for some of them. Eight different amines are considered in the present study, and the geometries and energies of their binding to the cavitand are first characterized and analyzed. Next, the methyl transfer reactions are investigated and the calculated barriers are found to be in generally good agreement with experimental results. In particular, the experimentally-observed rate acceleration in the cavitand as compared to the solution reaction is well reproduced by the calculations. The origins of this rate acceleration are analyzed by computational modifications made to the structure of the cavitand, and the role of the solvent is discussed.

Further Improvement Based on Traditional Nanocapsule Preparation Methods: A Review

Nanocapsule preparation technology, as an emerging technology with great development prospects, has uniqueness and superiority in various industries. In this paper, the preparation technology of nanocapsules was systematically divided into three categories: physical methods, chemical methods, and physicochemical methods. The technological innovation of different methods in recent years was reviewed, and the mechanisms of nanocapsules prepared via emulsion polymerization, interface polymerization, layer-by-layer self-assembly technology, nanoprecipitation, supercritical fluid, and nano spray drying was summarized in detail. Different from previous reviews, the renewal iteration of core-shell structural materials was highlighted, and relevant illustrations of their representative and latest research results were reviewed. With the continuous progress of nanocapsule technology, especially the continuous development of new wall materials and catalysts, new preparation technology, and new production equipment, nanocapsule technology will be used more widely in medicine, food, cosmetics, pesticides, petroleum products, and many other fields.

Origin of the Rate Acceleration in the C-C Reductive Elimination from Pt(IV)-complex in a [Ga4 L6 ]12- Supramolecular Metallocage

The reductive elimination on [(Me3 P)2 Pt(MeOH)(CH3 )3 ]+ , 2P, complex performed in MeOH solution and inside a [Ga4 L6 ]12- metallocage are computationally analysed by mean of QM and MD simulations and compared with the mechanism of gold parent systems previously reported [Et3 PAu(MeOH)(CH3 )2 ]+ , 2Au. The comparative analysis between the encapsulated Au(III) and Pt(IV)-counterparts shows that there are no additional solvent MeOH molecules inside the cavity of the metallocage for both systems. The Gibbs energy barriers for the 2P reductive elimination calculated at DFT level are in good agreement with the experimental values for both environments. The effect of microsolvation and encapsulation on the rate acceleration are evaluated and shows that the latter is far more relevant, conversely to 2Au. Energy decomposition analysis indicates that the encapsulation is the main responsible for most of the energy barrier reduction. Microsolvation and encapsulation effects are not equally contributing for both metal systems and consequently, the reasons of the rate acceleration are not the same for both metallic systems despite the similarity between them.

Comprehensive Characterization of the Self-Folding Cavitand Dynamics

The conformational equilibria and guest exchange process of a resorcin[4]arene derived self-folding cavitand receptor have been characterized in detail by molecular dynamics simulations (MD) and ¹ H EXSY NMR experiments. A multi-timescale strategy for exploring the fluxional behaviour of this system has been constructed, exploiting conventional MD and accelerated MD (aMD) techniques. The use of aMD allows the reconstruction of the folding/unfolding process of the receptor by sampling high-energy barrier processes unattainable by conventional MD simulations. We obtained MD trajectories sampling events occurring at different timescales from ns to s: 1) rearrangement of the directional hydrogen bond seam stabilizing the receptor, 2) folding/unfolding of the structure transiting partially open intermediates, and 3) guest departure from different folding stages. Most remarkably, reweighing of the biased aMD simulations provided kinetic barriers that are in very good agreement with those determined experimentally by ¹ H NMR. These results constitute the first comprehensive characterization of the complex dynamic features of cavitand receptors. Our approach emerges as a valuable rational design tool for synthetic host-guest systems.

Modeling the Reaction of Carboxylic Acids and Isonitriles in a Self-Assembled Capsule

Quantum chemical calculations were used to study the reaction of carboxylic acids with isonitriles inside a resorcinarene-based self-assembled capsule. Experimentally, it has been shown that the reactions between p-tolylacetic acid and n-butyl isonitrile or isopropyl isonitrile behave differently in the presence of the capsule compared both with each other and also with their solution counterparts. Herein, the reasons for these divergent behaviors are addressed by comparing the detailed energy profiles for the reactions of the two isonitriles inside and outside the capsule. An energy decomposition analysis was conducted to quantify the different factors affecting the reactivity. The calculations reproduce the experimental findings very well. Thus, encapsulation leads to lowering of the energy barrier for the first step of the reaction, the concerted α-addition and proton transfer, which in solution is rate-determining, and this explains the rate acceleration observed in the presence of the capsule. The barrier for the final step of the reaction, the 1,3 O→N acyl transfer, is calculated to be higher with the isopropyl substituent inside the capsule compared with n-butyl. With the isopropyl substituent, the transition state and the product of this step are significantly shorter than the preceding intermediate, and this results in energetically unfavorable empty spaces inside the capsule, which cause a higher barrier. With the n-butyl substituent, on the other hand, the carbon chain can untwine and hence uphold an appropriate guest length.

Microsolvation and Encapsulation Effects on Supramolecular Catalysis: C-C Reductive Elimination inside [Ga4L6]12- Metallocage

The host effect of the supramolecular [Ga₄L₆]^12- tetrahedral metallocage on reductive elimination of substrate by encapsulated Au(III) complexes is investigated by means of computational methods. The behavior of the reactants in solution and within the metallocage is initially evaluated by means of classical molecular dynamics simulations. These results guided the selection of proper computational models to describe the reaction in solution and inside the metallocage at the DFT level. The calculated Gibbs energy barriers are in very good agreement with experiment both in solution and inside the metallocage. The analysis in solution revealed that microsolvation around the Au(III) complex increases the Gibbs energy barrier. The analysis within the metallocage shows that its encapsulation favors the reaction. The process can be formally described as removing explicit microsolvation around the gold complex and encapsulating the metal complex inside the metallocage. Both processes are important for the reaction, but the removal of the solvent molecules surrounding the Au(III) metal complex is fundamental for the reduction of the reaction barrier. The energy decomposition analysis of the barrier among strain, interaction, and thermal terms shows that strain term is very low whereas the contribution of thermal (entropic) effects is moderate. Interestingly, the key term responsible for reducing the Gibbs energy barrier is the interaction. This term can be mainly associated with electrostatic interactions in agreement with previous examples in the literature.

Modeling Decomposition of N-Nitrosoamides in a Self-Assembled Capsule

Density functional theory calculations are employed to investigate the mechanism and energies of the decomposition of N-nitrosoamides in the presence of a resorcinarene-based self-assembled nanocapsule. From experiments, it is known that confinement in the capsule inhibits the thermal decomposition of these compounds. N-Nitrosoamides with both aromatic and aliphatic substituents are considered here and the calculations show that, for both kinds, binding to the capsule leads to a significant increase in the energy barrier of the rate-determining step, the 1,3 N→O acyl transfer reaction. A distortion-interaction analysis is conducted to probe the reasons behind the inhibition of the reaction. In addition, we characterized hypothetical intermediates that might be involved in the formation of the decomposition products inside the capsule. Interestingly, it is found that the capsule stabilizes ion-pair species that are unstable in mesitylene solution. Finally, a possible explanation is proposed for the observed encapsulation of the decomposition product of only one of the substrates.

Mixed Explicit-Implicit Solvation Approach for Modeling of Alkane Complexation in Water-Soluble Self-Assembled Capsules

The host-guest binding properties of a water-soluble resorcinarene-based cavitand are examined using density functional theory methodology. Experimentally, the cavitand has been observed to self-assemble in aqueous solution into both 1:1 and 2:1 host/guest complexes with hydrophobic guests such as n-alkanes. For n-decane, equilibrium was observed between the 1:1 and 2:1 complexes, while 1:1 complexes are formed with shorter n-alkanes and 2:1 complexes are formed with longer ones. These findings are used to assess the standard quantum chemical methodology. It is first shown that a rather advanced computational protocol (B3LYP-D3(BJ)/6-311+G(2d,2p) with COSMO-RS and quasi-rigid-rotor-harmonic-oscillator) gives very large errors. Systematic examination of the various elements of the methodology shows that the error stems from the implicit solvation model. A mixed explicit-implicit solvation protocol is developed that involves a parametrization of the hydration free energy of water such that water cluster formation in water is predicted to be thermoneutral. This new approach is demonstrated to lead to a major improvement in the calculated binding free energies of n-alkanes, reproducing very well the 1:1 versus 2:1 host/guest binding trends.