Study Of Host-guest Interactions Research Articles

Endogenous metal-ion dynamic nuclear polarization for NMR signal enhancement in metal organic frameworks.

Rational design of metal-organic framework (MOF)-based materials for catalysis, gas capture and storage, requires deep understanding of the host-guest interactions between the MOF and the adsorbed molecules. Solid-State NMR spectroscopy is an established tool for obtaining such structural information, however its low sensitivity limits its application. This limitation can be overcome with dynamic nuclear polarization (DNP) which is based on polarization transfer from unpaired electrons to the nuclei of interest and, as a result, enhancement of the NMR signal. Typically, DNP is achieved by impregnating or wetting the MOF material with a solution of nitroxide biradicals, which prevents or interferes with the study of host-guest interactions. Here we demonstrate how Gd(iii) ions doped into the MOF structure, LaBTB (BTB = 4,4',4''-benzene-1,3,5-triyl-trisbenzoate), can be employed as an efficient polarization agent, yielding up to 30-fold 13C signal enhancement for the MOF linkers, while leaving the pores empty for potential guests. Furthermore, we demonstrate that ethylene glycol, loaded into the MOF as a guest, can also be polarized using our approach. We identify specific challenges in DNP studies of MOFs, associated with residual oxygen trapped within the MOF pores and the dynamics of the framework and its guests, even at cryogenic temperatures. To address these, we describe optimal conditions for carrying out and maximizing the enhancement achieved in DNP-NMR experiments. The approach presented here can be expanded to other porous materials which are currently the state-of-the-art in energy and sustainability research.

Phyto-liposomes as nanoshuttles for water-insoluble silybin-phospholipid complex.

Among various phospholipid-mediated drug delivery systems (DDS) suitable for topic and oral administration, phytosome technology represents an advanced innovation, widely used to incorporate standardized bioactive polyphenolic phytoconstituents into phospholipid molecular complexes. In order to extend their potential therapeutic efficiency also to other routes of administration, we proposed a novel phytosome carrier-mediated vesicular system (phyto-liposome) as DDS for the flavonolignan silybin (SIL), a natural compound with multiple biological activities related to its hepatoprotective, anticancer and antioxidant (radical scavenging) effects. We screened the optimum fraction of its phytosome, available in the market as Siliphos™, into liposomes prepared by extrusion, such that vesicle sizes and charges, monitored through dynamic light scattering and laser doppler velocimetry, satisfied several quality requirements. Special emphasis was placed on the study of host-guest interaction by performing UV-vis absorption, spectrofluorimetry and NMR experiments both in aqueous and non-polar solvents to probe the effect of the presence of phospholipids on the electronic properties of SIL and its propensity to engage H bonding with the lipid headpolar groups. Finally, fluorescence microscopy observations confirmed the ability of phyto-liposomes to be internalized in human hepatoma cells, which was promising for their potential application in the treatment of acute or chronic liver diseases.

Synthesis, Complexation and Pharmaceutical Applications of Tetra‐directional Cascade Dendrimers*

A synthetic strategy based on repetitive, divergent, stepwise growth has been used to prepare a tetra-directional cascade dendrimer with a modified peripheral layer. The study of host-guest interactions with this new type of container molecule indicated that complexation increased the solubility of different hydrophobic guests (benzoic acid, 1-naphthoic acid and 9-anthracenecarboxylic acid) which are sparingly soluble in water. Flow microcalorimetric analysis confirmed the effectiveness of suitable drug-dendrimer complexes. The size of the cavity within the dendrimer plays a vital role in the accommodation of the guest.

The Paternò-Büchi Reaction ofN-Acyl Enamines and Aldehydes - The Development of a New Synthetic Method and its Application to Total Synthesis and Molecular Recognition Studies

The Paterno-Buchi reaction of aldehydes and N-acyl or N-alkoxycarbonyl enamines represents a short and efficient method for the stereoselective synthesis of cis-3-aminooxetanes. Consecu- tive ring opening reactions facilitate the preparation of cyclic and acyclic 1,2-amino alcohols. The application of a photocycloaddi- tion/ring opening sequence to the synthesis of an enantiomerically pure pyrrolidinol alkaloid is discussed. The use of cyclic NH-acidic lactams as alkene components in the photocycloaddition allows the study of host-guest interactions. An achiral guest can be attached to a chiral host by two hydrogen bonds in such a way that a dis- crimination of enantiotopic faces is possible.

Vibrational spectroscopic and quantum theoretical study of host-guest interactions in clathrates: I. Hofmann type clathrates

Hofmann type clatharates are host-guest compounds with the general formula M(NH3)2M'(CN)4.2G, in which M(NH3)2M'(CN)4 is the host lattice and G is benzene, the guest molecule. In previous studies, host-guest interactions have been investigated by analyzing the RT and LNT vibrational (infrared, far infrared and Raman) spectra of these clathrates. All the observed changes in the vibrational spectra of these clathrates are referred to a host-guest interaction originating from weak hydrogen bonding between the ammonia hydrogen atoms from the host lattice and the p electron cloud of the guest (benzene) molecules. In order to obtain an insight into the relative importance of the local crystalline field vs. the anharmonicity effects on the spectroscopic properties of the guest species upon enclathration, as well as to explain the observed band shifts and splittings, several quantum theoretical approaches are proposed.

Host-guest chemistry in the gas phase and at the gas-solid interface: Fundamental aspects and practical applications

Abstract

ChemInform Abstract: Applications of Calorimetry (Macro and Micro) to the Study of Host‐ Guest Interactions in Solution

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

New Chiral Macrocyclic Compounds from D-Mannitol

Abstract We have recently reported the synthesis of new chiral macrocyclic polyhydroxyethers by reduction of cyclodextrins 1. These compounds display appreciable conformational freedom in solution as it occurs with the ionophores. Our chiral macrocycles may be considered as built by units of alditol (1 → 4) alditols. Such units, conveniently substituted, prepared by us by reduction of disaccharide derivatives2, are possible synthons for the synthesis of other macrocyclic polyhydroxyethers in which the nature and number of alditol (1 → n) alditol components can be varied at will. We are interested in the preparation and the structural studies of these type of receptors since the synthesis of new chiral macrocycles is a topic of interest and the building of chiral cavities may be of importance in the study of host-guest interactions. We now report on the preparation, from D-mannitol, a readily available starting material with C2symmetry, and tetraethylene glycol, of the chiral macrocycles 1, 2, and 3, as model compounds in exploring the synthesis of more complex macrocyclic polyhydroxyethers derived from alditol (1 → n) alditol. Other macrocyclic compounds from D mannitol have been previously synthesised.

Study of host-guest interaction in mixed molecular crystals

The measurement of the polarization ratio (PR) of guest transitions in mixed molecular crystals has been used as a tool to study the effect of host-guest interaction. Two mixed crystal systems, namely naphthacene in trans-stilbene and anthracene in carbazole, have been studied. In the former system, the lowest energy host and guest transitions are oppositely polarized. It has been observed that in this system the ( b:a) PR value for the guest absorption system decreases progressively for the higher members of the vibronic bands as their energy difference from the host excited state decreases. This result quite convincingly demonstrates the effect of the host on a guest transition. In the latter system, the lowest energy host and guest transitions are polarized in the same direction, and in this system the ( b:a) PR value has been found to be more or less constant over the entire guest absorption band system. The results of the polarization measurement in these two mixed crystals are in conformity with the theory of host-guest interaction developed by Craig and Thirunamachandran.