Inclusion supramolecular structures

Summary The analysis of supramolecular structures containing polymers, and the discussion about the effect of polymeric materials with different chemical structures that form inclusion complexes is extensively studied. The effect of the inclusion complexes at the air-water interface is discussed in terms on the nature of the interaction. The entropic or enthalpic nature of the interaction is analyzed. The description of these inclusion complexes with different cyclodextrines with several polymers is an interesting way to understand some non-covalent interaction in these systems. The discussion about the generation and effect of supramolecular structures on molecular assembly and auto-organization processes is also presented in a single form. The use of block copolymers and dendronized polymers at interfaces is a new aspect to be taken into account from both basic and technological interest. The effect of the chemical structure on the self-assembled systems is discussed. 

The generation of supramolecular structure of interest usually relies on molecular self-assembly and auto-organization processes. Much attention has been recently focused on the design of nanometer-scale (nanoscale) molecular devices. One approach to the molecular devices is the self - assembly of supramolecular structures such as the inclusion complexes [1,2,7,8],... 

In this report, we will describe some of our studies aimed at (i) obtaining new inorganic photosensitizers by second-sphere modification of known ones, and (ii) assembling photosensitizer units with other molecular components in discrete, covalently bound supramolecular structures. Studies of type (i), besides their intrinsic interest, have some relevance to the problem of how the properties of a photosensitizer are modified by inclusion in a supramolecular structure. Systems of type (ii) would be useful to study the basic processes of intramolecular electron and energy transfer involved in the performance of molecular photochemical devices. 

The advances in the studies on the inclusion complexes of CDs threading onto polymer chains have led to interesting development of supramolecular hydrogels with many different molecular and supramolecular structures. Both physical and chemical hydrogels of many different types were developed based on the CD-based polypseudorotaxanes and polyrotaxanes. 

A special situation is encountered with metal-porphyrin or metal-phthalo-cyanine molecules that can be either deposited by sublimation under UHV conditions or in solution environments. For these macrocyclic compounds, free-base species exist, i.e., the metal centers are not required per se as a construction unit. The building of supramolecular structures that incorporate porphyrin subunits is of great interest to many research groups. The rich photochemistry and redox properties (e.g., photoinduced electron transfer, luminescence, and light harvesting) of porphyrins have driven this interest. Porphyrins or phtalocyanines have a rich coordination chemistry that allows the inclusion of many different metal centers at their macrocycle. They serve in many respects as a model system since this constitutes a low-coordination complex. Recent STM studies report on the organization of metal-coordinated or free-base porphyrins as well as phthalocyanines on... 

D. Krois, U. H. Brinker, Induced circular dichroism and UV-vis absorption spectroscopy of cyclodextrin inclusion complexes structural elucidation of supramolecular aziadamantane (spiro[adamantane-2,3 -diazirine]), /. Am. Chem. Soc., 1998, 120, 11627-11632. 

In most supramolecular structures, the temperature dependence of the characteristic dielectric relaxation time follows the Arrhenius equation, r = Toexp(A dip/ T). where tq is the preexponential factor that is often of the magnitude of the vibrational time scale and A dip is the activation energy of the dipolar process.The dipolar process of the host lattice and the trapped molecules follows this behavior, but A trapped molecules is less than that for the host lattice molecules. In ice ciathrates, the dipolar processes of the water molecules that form the host lattice and the guest molecules inside the cages of this lattice occur at widely different time scales. This allows for a reliable attribution of the dielectric spectra features to water molecules and to the guest molecules. As an example of the magnitude of the dielectric properties of supiainolecular structures, the data on selected ice clathrates and other inclusion compounds are summarized in Tables 1 and 2. 

The diaza-15-crown-5 molecule adsorbed on Cu(lll) was studied by ECSTM. The molecule forms a well-ordered layer on the metal under a certain range of potentials. The molecular interaction with the substrate is thought to be responsible for the adlayer formation. Di-benzo-18-crown-6-ether and its inclusion compound with potassium were studied on Au(lH). The STM images obtained with submolecular resolution show that the species arrange in a two-dimensional (2D) supramolecular structure under potential control. 

Weak interactions which are characteristic for supramolecular chemistry have been found to also operate in baU-miUing conditions. It was demonstrated that supramolecular structures held by weak noncovalent interactions snch as co-crystals, cages, rotaxanes, open metal-organic frameworks, and noncovalent organic inclusion complexes could be built by self-assembly processes in the solid state [1],... 

Cyclodextrins, for example, form inclusion complexes with metallocenes such as ferrocene, cobaltocene and nickelocene to form crystalline compounds. The structures of the complexes are dependent on the size of the cyclodextrin. Although ferrocene and its derivatives are strongly bound in uncharged states, when they are oxidized, the complexes dissociate. Dendrimers containing ferrocene units at the ends of the molecule have been prepared. The dendrimers form large supramolecular structures that can be broken apart or assembled upon... 

The self-assembly of supramolecular structures such as host-guest inclusion complexes has r ently bem the focus of a number of research efforts. This approach allows the d ign and building of nanoscale molecular device. It constitutes a conveni t route to realizing the polymerization of hydrophobic molecules (guests) such as thiophene derivatives in aqueous soluticm by using CDs (hosts) and to customizing the polymer ardiitectures 9-11). 

A review has been published on cyclodextrins as building blocks for supramolecular structures and functional units. Included was a treatment of the the synthesis of cyclodextrins, their inclusion properties, catenanes derived from them and their use as catalysts. 

Various aspects of the physico chemical properties of organic inclusion compounds have been considered. Analysis of their thermal stability and kinetics of formation and decomposition yield a better understanding of their reactivity. Their mechanism of host selectivity is driven by the process of molecular recognition and can be elucidated by analyzing the secondary interactions responsible for their supramolecular structure. 

There is also a close relationship between the inclusion crystal structures of hydroquinone 49, Dianin s compound 8, and the alicyclic diol 103. This is revealed if the two motifs used by MacNicol in the hexa-host design, namely the aromatic ring and (0-H)6 cycle structures, are regarded as equivalent supramolecular nodal points. The network connectivity (see Network and Graph Set Analysis, Supramolecular Materials Chemistry) and familial relationship of these three lattices is then revealed. ... 

The diol derivatives of bicyclo[3.3.1]nonanes (Figure 9) are such systems, and the unique molecular shape of this building block has been used to form self-assembled supramolecular structures and inclusion complexes with various guest molecules. Some derivatives of this ring skeleton, the so-called tubuland diols, give controllable crystal structures with a variety of inclusion guests. 

The concept of cyclodextrin guest inclusion has been extended to the synthesis of a library of multicavity dimers and trimers of cyclodextrin that can bind specific guest molecules to mimic enzymes (Figure 6) Such supramolecular structures were tested with mono-, di-, and tri-substituted Gd + complexes bearing hydrophobic cyclohexyl moieties for interaction with the cyclodextrin cavities. The relaxivity enhancement increased with the number of cyclohexyl groups on the Gd + chelate. Further, the cyclodextrin trimer host-guest supramolecule with the tri-substituted Gd " " complex exhibited the greatest relaxivity... 

The 1 1 complex between the tetracationic cyclophane and tetrathiafulvene (TIT) forms continuous stacks with no hinderance of the central channel by either solvent molecules or the counterions Figure 4). The TTF molecules have their long axis almost perfectly aligned along this crystallographic direction with a separation of 4.9 A between the tertiary alkenic carbon atoms in adjacently located TTF molecules." This supramolecular structural arrangement also demonstrates the potential of the tetracationic cyclophane to form polyrotaxane-like assemblies with suitably linked n-donor compounds. Furthermore, its inclusion inside [BBIPYBIXYCY] illustrates its potential for the production of molecular "shuttles and "switches . 

Scheme 70 a Structural formula of the free-base porphyrin dimer and the porphyrin (Hj-CPDpy), and b a single crystal structure of its inclusion complex with Cgo, determined by X-ray crystallography (C6o H4-CPDpy). Reprinted from Nobukuni H, Shimazaki Y, Uno H, Naruta Y, Ohkubo K, Kojima T, Fukuzumi S, Seki S, Sakai H, Hasobe T, Tani F (2010) Supramolecular structures and photoelectronic properties of the inclusion complex of a cyclic free-base porphyrin dimer and Ceo- Chem Fur J 16(38) 11611-11623, Copyright (2010), with permission from Elsevier... 

Nobukuni H, Shimazaki Y, Uno H et al (2010) Supramolecular structures and photoelectronic properties of the inclusion complex of a cyclic free-base porphyrin dimer and Cfio. Chem Fur J 16(38) 11611-11623... 

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