ISSN:1061-0278    

DOI:10.1080/10610279508032515

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The use of molecular recognition to activate the occurrence of self-assembly has become an important principle in the template-directed syntheses of molecular assemblies and supramolecular arrays. In our early lock-and-key systems, we investigated, as the lock, crown ethers like bisparaphenylene-34-crown-10 and, as the key, the 4,4′-bipyridinium dication. Now, they have been transformed into ‘permanent’ inclusion complexes,viaa post-assembly modification pathway, leading to a range of mechanically-interlocked molecules in the shape of the catenanes and rotaxanes. The knowledge and experience gained by carrying out self-assembly on these relatively simple systems in solution go a long way toward establishing the fundamental rules for the elaboration of larger polymolecular assemblies. By modifying the nature of the components that make up the molecular assemblies, we have been able to gain a fundamentally better understanding of the limitations and the opportunities available for controlling self-assembly in a structural, geometric, and electronic sense during chemical synthesis. This account deals mainly with a carefully chosen selection of different molecular components in which the principle recognition sites have been varied to provide an opportunity for a predetermined bias in the translational isomerism of the [2]catenanes and [2]rotaxanes. These systems, which have been produced recently at Birmingham, are helping toward achieving an understanding of the processes of formation of, and the dynamics associated with, the mechanically-interlocked molecular compounds.

ISSN:1061-0278    

DOI:10.1080/10610279508032516

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

After a brief account on previous results obtained in this Laboratory in the field of layered and pillared α- and γ-zirconium phosphonates, the perspectives for a development of a “molecular recognition” in porous and in layered solids are examined. In particular, the preparation and the preliminary characterisation of some new zirconium phosphonates more specifically designed for a “molecular recognition”, such as: a) layered and pillared derivatives of γ-zirconium phosphate containing crown ethers in the interlayer region, b) α-layered zirconium phosphate containing chiral centres anchored to its surface and c) pillared derivatives of γ-zirconium phosphate containing non rigid pillars, are reported and discussed.

ISSN:1061-0278    

DOI:10.1080/10610279508032517

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In the final structure of an enzyme-substrate complex, or of a related molecular complex, the two components may fit together in a lock and key relationship, but flexibility is often needed in the binding process. Furthermore, flexibility is needed in enzyme-substrate complexes and their mimics to accommodate the geometric changes that the reaction causes. Examples of such situations from enzyme mimic studies are described.

ISSN:1061-0278    

DOI:10.1080/10610279508032518

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Adsorption of tetradentate Schiff base ligands on MnIINaY zeolites yields catalysts for selective oxidation of hydrocarbons with PhIO or tert-butylhydroperoxide (tBHP). The interaction between Mn and the ligands is proved by IR, diffuse reflectance and EPR spectroscopy. Olefin epoxidation with these catalysts suffers from formation of undesirable products when tBHP is used, but reasonable epoxide selectivities are obtained with PhIO. Very active catalysts for alkane oxidation with tBHP are produced by adsorption of the pyridine derived pyren and pyrpn ligands on MnIINaY (pyren = bis(2-pyridinecarboxaldehyde)ethylenediimine; pyrpn = bis(2-pyridinecarboxaldehyde)propylenediimine). With these catalysts, very high selectivities are obtained for formation of monoketones from alkanes. A relation is proposed between the appearance of low-field features in the Mn(II) EPR spectra and a high activity in hydrocarbon oxidation.

ISSN:1061-0278    

DOI:10.1080/10610279508032519

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

There are two aspects to this problem: stoichiometry determined by the framework structure and changes in composition of clathrate phase due to the possibility of the partial filling of the cavities in it. In the simplest case structural stoichiometry is defined as the ratio of the number of the host molecules to the number of cavities in a unit cell but more complicated cases are not difficult to understand either.

ISSN:1061-0278    

DOI:10.1080/10610279508032520

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A variety of synthetic compounds mediate ion transport across bilayer membranes. The majority of reported cases involve transport across vesicle membranes, with mechanism inferred by comparison with known transporters. Single channel conductance techniques provide more direct mechanistic information. Two examples are discussed. In the first, an active unimolecular transporter (G8TrgP)4Tet is shown to induce erratic formation of transient high conductivity pores. In the second, a linear pore-former A8TrgPA8TrgA is shown produce regular multi-level channels in diphytanoylPC membranes. The pore formed shows ion selectivity in the sequence Cs+> K+> Na+. A model consisting of an aggregate of a few A8TrgPA8TrgA molecules in the bilayer would be qualitatively consistent with the data.

ISSN:1061-0278    

DOI:10.1080/10610279508032521

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Several novel ferrocene derivatives have been prepared which possess functional groups on both cyclopentadienyl rings. The ability of these compounds to complex protons and other cations has been assessed by several methods and the results are reported. Evidence is presented for sidearm cooperativity in the complexation phenomenon.

ISSN:1061-0278    

DOI:10.1080/10610279508032522

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Two general methods of the synthesis of diazacoronands: the high-pressure approach and thatviabisamidation are presented. Several examples of the X-ray structure studies of the compounds obtained are given.

ISSN:1061-0278    

DOI:10.1080/10610279508032523

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have studied the DNA binding and DNA cleavage specificities of two novel classes of synthetic DNA breakage agents. One class comprises redox-activated metalloporphyrins, the other uses the photoactivablep-nitrobenzoyl group as the DNA breaking moiety linked covalently to a DNA recognizing entity such as an oligoN-methylpyrrolecarboxamide or oligothiazole group. Studies of DNA cleavage using end-labeled DNA restriction fragments and high resolution sequencing gel electrophoresis have allowed DNA break sites to be identified at the nucleotide level. This work in conjunction with induced CD spectroscopy has shown that these compounds, especially photoactive agents containing thiazole units, display high sequence specificity. The mechanism of sequence recognition appears to be quite different for the two series of compounds.

ISSN:1061-0278    

DOI:10.1080/10610279508032524

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor