Alcohols as Latent Hydrophobes: Entropically Driven Uptake of 1,2-Diol Functionalized Ligands by a Porous Capsule in Water

Chakraborty S, Grego AS, Garai S, Baranov M, Müller A, Weinstock IA. Alcohols as Latent Hydrophobes: Entropically Driven Uptake of 1,2-Diol Functionalized Ligands by a Porous Capsule in Water. Journal of the American Chemical Society. 2019;141(23):9170-9174.Alcohols, with hydroxyl groups compositionally identical to water itself, are consummate hydrophiles, whose high solubilities preclude spontaneous self-assembly in water. Nevertheless, the solute-solvent interactions associated with their highly favorable solvation enthalpies impose substantial entropic costs, similar in magnitude to those that drive the hydrophobic assembly of alkanes. We now show that under nanoconfined conditions this normally dormant "hydrophobicity" can emerge as the driving force for alcohol encapsulation. Using a porous molecular capsule, the displacement of endohedrally coordinated formate ligands (HCO2-) by 1,2-hydroxyl-functionalized L-glycerate (L-gly, L-HOCH2(HO)CHCO2-) was investigated by van't Hoff analysis of variable-temperature H-1 NMR in D2O. At pD 5.8, L-gly uptake is enthalpically inhibited. Upon attenuation of this unfavorable change in enthalpy by cosequestration of protons within the alcoholic environment provided by encapsulated diol-functionalized ligands, -T Delta S degrees dominates over Delta H degrees, spontaneously filling the capsule to its host capacity of 24 L-gly ligands via an entropically driven hydrophobic response

Flexible Pores of a Metal Oxide-Based Capsule Permit Entry of Comparatively Larger Organic Guests

Ziv A, Grego A, Kopilevich S, et al. Flexible Pores of a Metal Oxide-Based Capsule Permit Entry of Comparatively Larger Organic Guests. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. 2009;131(18):6380-6382.In zeolites and other rigid solid-state oxides, substrates whose sizes exceed the pore dimensions of the material are rigorously excluded. Now, using a porous 3 nm diameter capsule-like oxomolybdate complex [{(Mo6O21)-O-VI(H2O)(6)}(12){((Mo2O4)-O-V)(30)(OAc)(21)(H2O)(18})](33-) as a water-soluble analogue of solid-state oxides (e.g., as a soluble analogue of 3 A molecular sieves), we show that carboxylates (RCO2-) can negotiate passage through flexible Mo9O9 pores in the surface of the capsule and that the rates follow the general trend R = 1 degrees >> 2 degrees > 3 degrees >> phenyl (no reaction). Surprisingly, the branched alkanes (R = iso-Pr and tert-Bu) enter the capsule even though they are larger than the crystallographic dimensions of the Mo9O9, pores. Four independent lines of spectroscopic and kinetic evidence demonstrate that these organic guests enter the interior of the capsule through its Mo9O9 apertures and that no irreversible changes in the metal oxide framework are involved. This unexpected phenomenon likely reflects the greater flexibility of molecular versus solid-state structures and represents a sharp departure from traditional models for diffusion through porous solid-state (rigid) oxides

Guests on Different Internal Capsule Sites Exchange with Each Other and with the Outside

Petina O, Rehder D, Haupt ETK, et al. Guests on Different Internal Capsule Sites Exchange with Each Other and with the Outside. Angewandte Chemie. International Edition. 2011;50(2):410-414

Densely Packed Hydrophobic Clustering: Encapsulated Valerates Form a High-Temperature-Stable {Mo-132} Capsule System

Garai S, Bögge H, Merca A, et al. Densely Packed Hydrophobic Clustering: Encapsulated Valerates Form a High-Temperature-Stable {Mo-132} Capsule System. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION. 2016;55(23):6633-6636.Porous molecular nanocontainers of {Mo-132}-type Keplerates offer unique opportunities to study a wide variety of relevant phenomena. An impressive example is provided by the highly reactive {Mo-132-CO3} capsule, the reaction of which with valeric acid results in the very easy release of carbon dioxide and the uptake of 24 valerate ions/ligands that are integrated as a densely packed aggregate, thus indicating the unique possibility of hydrophobic clustering inside the cavity. Two-dimensional NMR techniques were used to demonstrate the presence of the 24 valerates and the stability of the capsule up to ca. 100 degrees C. Increasing the number of hydrophobic parts enhances the stability of the whole system. This situation also occurs in biological systems, such as globular proteins or protein pockets