Host-guest chemistry of tolbutamide

The molecular recognition features of tolbutamide with four synthetic hosts have been studied by means of NMR titrations, NOESY experiments and Monte Carlo (MC) conformational search. The interaction strength and the most probable structure reveal new insights on the recognition phenomena of this urea derivative in comparison with close related compounds.     

Host-guest chemistry at interface for photoswitchable bioelectrocatalysis

Photoswitchable bioelectrocatalysis of glucose with glucose oxidase in an "On-Off" state is fabricated from host-guest chemistry at an interface by using the photocontrolled reversible immobilization and detachment of ferrocene-labeled redox-polymer as mediator.     

Host-guest chemistry of copper(II)-histidine complexes encaged in zeolite Y

Structural analysis has been carried out on copper(II )–histidine (Cu²⁺/His) complexes after immobilization in the pore system of the zeolites NaY and de‐aluminated NaY (DAY). The aim of this study was to determine the geometrical structure of Cu²⁺/His complexes after encaging, to obtain insight into both the effect of the zeolite matrix on the molecular structure and redox properties of the immobilized complexes. In addition to N₂ physisorption and X‐ray fluorescence (XRF) analyses, a combination of UV/Vis/NIR, ESR, X‐ray absorption (EXAFS and XANES), IR, and Raman spectroscopy was used to obtain complementary information on both the first coordination shell of the copper ion and the orientation of the coordinating His ligands. It was demonstrated that two complexes ( A and B ) are formed, of which the absolute and relative abundance depends on the Cu²⁺/His concentration in the ion‐exchange solution and on the Si/Al ratio of the zeolite material. In complex A , one His ligand coordinates in a tridentate facial‐like manner through N_am, N_im, and O_c, a fourth position being occupied by an oxygen atom from a zeolite Brønsted site. In complex B , two His ligands coordinate as bidentate ligands; one histamine‐like (N_am, N_im) and the other one glycine‐like (N_am, O_c). In particular the geometrical structure of complex A differs from the preferred structure of Cu²⁺/His complexes in aqueous solutions; this fact implies that the zeolite host material actively participates in the coordination and orientation of the guest molecules. The tendency for complex A to undergo reduction in inert atmosphere to Cu¹⁺ (as revealed by dynamic XANES studies) suggests activation of complex A by the interaction with the zeolite material. EXAFS analysis confirms the formation of a distorted four coordinate geometry of complex A , suggesting that the combination of zeolite and one His ligand force the Cu²⁺ complex into an activated, entactic state.     

Cyclopeptide alkaloids: chemistry and biology

Recent progress in the synthesis and investigation of the biological activities of cyclopeptide alkaloids is reviewed. New strategies have been devised to overcome some of the synthetic challenges inherent in the formation of strained paracyclophanes. However, issues remain which offer opportunities for the application of catalytic enantioselective organometallic reactions. Members of this class of natural products have been isolated from various parts of a wide variety of plants and researchers will likely continue to show great interest in their formation and function. The biological properties of certain members of this class warrant further investigation. To gain additional insight into these areas, continuing development of synthetic methodology will be essential.     

The biology and chemistry of the zoanthamine alkaloids

Marine natural products have long played an important role in natural products chemistry and drug discovery. Mirroring the rich variety and complicated interactions of the marine environment, the substances isolated from sea creatures tend to be incredibly diverse in both molecular structure and biological activity. The natural products isolated from the polyps of marine zoanthids are no exception. The zoanthamine alkaloids, the first of which were isolated over 20 years ago, are of particular interest to the synthetic community because they feature a novel structural framework and exhibit a broad range of biological activities. In this Review, we summarize the major contributions to understanding the zoanthamine natural products with regard to their isolation and structure determination, as well as studies on their biological activity and total synthesis.     

Host-guest supramolecular chemistry at solid-liquid interface: An important strategy for preparing two-dimensional functional nanostructures

Supramolecular self-assembly,an important strategy in nanotechnology,has been widely studied in the past two decades.In this review,we have introduced the recent progress on construction of two-dimensional(2D)nanostructures by host-guest supramolecular chemistry at solid-liquid interface,and the interactions between the host assembly and the guest molecules are the major concerns.At first,the hydrogen bonds connected hybrid structures are discussed.And then we have paid a close attention on the surface-confined condensation reactions that has flourished recently in direct preparing novel nanostructures with increasing structural complexity.In the end,the cavity confinement of the 2D supramolecular host-guest architectures has been studied.On the basis of the above-mentioned interactions,a group of functional hybrid structures have been prepared.Notably,scanning tunneling microscopy(STM),a unique technique to probe the surface morphology and information at the single molecule level,has been used to probe the formed structures on highly oriented pyrolytic graphite(HOPG)surface.     

Host-guest antenna materials

The focus of this review is on host-guest composites with photonic antenna properties. The material generally consists of cylindrical zeolite L crystals the channels of which are filled with dye molecules. The synthesis is based on the fact that molecules can diffuse into individual channels. This means that, under the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out by adding a closure molecule. Functionalization of the closure molecules allows tuning of, for example, wettability, refractive index, and chemical reactivity. The supramolecular organization of the dyes inside the channels is a first stage of organization. It allows light harvesting within a certain volume of a dye-loaded nanocrystalline zeolite and radiationless transport to both ends of the cylinder or from the ends to the center. The second stage of organization is the coupling to an external acceptor or donor stopcock fluorophore at the ends of the channels, which can trap or inject electronic excitation energy. The third stage of organization is the coupling to an external device through a stopcock molecule. The wide-ranging tunability of these highly organized materials offers fascinating new possibilities for exploring excitation-energy-transfer phenomena, and challenges for developing new photonic devices.     

The chemistry of recently isolated naturally occurring quinazolinone alkaloids

The present review portrays a concise account of the isolation, bioactivity, and synthesis of bioactive quinazolinone-based natural products for the period 1983-2005 and the recent developments in the area of complex quinazolinone natural products with a special emphasis on new synthetic routes and strategies.     

Host-guest chemistry in the gas phase: complex formation with 18-crown-6 enhances helicity of alanine-based peptides

The gas-phase helix propensities of alanine-based polypeptides are studied with different locations of a Lys residue and host-guest interactions with 18-Crown-6 (18C6). A series of model peptides Ac-Ala(9-n)-LysH(+)-Ala(n) (n = 0, 1, 3, 5, 7, and 9) is examined alone and with 18C6 using traveling wave ion mobility mass spectrometry combined with molecular dynamics (MD) simulations. The gas-phase helices are observed from the peptides whose Lys residue is located close to the C-terminus so that the Lys exerts its capping effect on the C-terminal carbonyl groups. The peptides, which interact with 18C6 in the gas phase, show enhanced helical propensities. The enhanced helicity of the peptide in the complex is attributed by isolation of the Lys butylammonium group from the helix backbone and the interaction of methylene groups of 18C6, which possess localized positive partial charges, with C-terminal carbonyl groups serving as a cap to stabilize the helix.     

Host-guest interactions in acid-porphyrin complexes

In this report we use the weak interactions of acid-porphyrin complexes to selectively bind competing acids to the faces of a rigid cyclic porphyrin dimer, and characterise the resulting interactions by NMR spectroscopy and nano-electrospray ionisation spectrometry.     

Host-guest interaction of L-tyrosine with beta-cyclodextrin

The inclusion complexes of beta-cyclodextrin (beta-CD) with l-tyrosine (l-TYN) were investigated by using spectrophotometers. The absorption and fluorescence enhancement occurs with beta-CD and l-TYN forms 1:1 inclusion complex. The unusual blue shift of hydroxyl ion in the beta-CD medium confirms OH groups present in the interior part of the beta-CD cavity and -COOH group present in the upper part of the beta-CD cavity. A mechanism is proposed to explain inclusion process. The inclusion interaction was examined and the thermodynamic parameters of inclusion process DeltaG, DeltaH and DeltaS were determined. The results indicated that the inclusion process was an exergonic and spontaneous process. Stable solid inclusion complexes were established and characterized by FT-IR, scanning electron microscope (SEM) methods.     

Synthesis of naturally occurring pyridine alkaloids via palladium-catalyzed coupling/migration chemistry

The palladium-catalyzed cross-coupling of 3-iodopyridine, long-chain terminal dienes, and benzylic amines or tosylamides provides a novel route to key intermediates for the synthesis of the naturally occurring, biologically active pyridine alkaloids theonelladins C and D, niphatesine C, and xestamine D. This process involves (1) oxidative addition of the heterocyclic iodide to Pd(0), (2) carbopalladation of the least hindered carbon-carbon double bond of the diene, (3) palladium migration, and (4) pi-allylpalladium displacement by the nitrogen nucleophile with simultaneous regeneration of the Pd catalyst. Subsequent hydrogenation and deprotection affords good yields of the natural products. The Pd-catalyzed coupling of 3-iodopyridine and 2-methyl-11-dodecen-1-ol provides a convenient synthesis of a long-chain aldehyde by an analogous palladium migration process, which is easily converted to the pyridine alkaloid ikimine A.