Self-assembly complexes

The charge on the surface of colloid particles is an important parameter, and DNA/cation self-assembled complexes are no exception. It can be measured experimentally as the -potential or electrokinetic potential (the potential at the surface of shear be-... 

Molecular imprinting can be accomplished in two ways (a), the self assembly approach and (b), the preorganisation approach3. The first involves host guest complexes produced from weak intermolecular interactions (such as ionic or hydrophobic interaction, hydrogen bonding) between the analyte molecule and the functional monomers. The self assembled complexes are spontaneously formed in the liquid phase and are sterically fixed by polymerisation. After extraction of the analyte, vacant recognition sites specific for the imprint are established. Monomers used for self assembly are methacrylic acid, vinylpyridine and dimethylamino methacrylate. 

Kukowska-Latallo, J. F., Bielinska, A. U., Chen, C., Rymaszewski, M., Tomalia, D. A. and Baker J. R. Jr. Gene transfer using starburst dendrimers , in Kabanov, A. V., Feigner, P. L. and Seymour, L. W. (eds) Self-Assembling Complexes for Gene Delivery, John Wiley Sons, New York, 1998, pp. 241-253. 

The respective association constants of the latter anion to free 376 is only 10 M 1 while for the self-assembled complex it is equal to 2.5 104 M 1 [39]. Kubik and Goddard obtained a cyclic pseudopeptide ditopic receptor 378 for the simultaneous complexation of cations and anions [40]. Simultaneous encapsulation of N03 and PF6 ions by a highly charged (+12) anion receptor 379 was achieved by Schnebeck and coworkers [41]. By coordinating of 2,4,6-tris[(4-pyridyl)methylsulfa nyl]-l,3,5-triazine 380 with Ag, Hong and coworkers obtained nanosized tubes (Fig.7.8.1) that could host solvent and anionic molecules [42]. 

Significant improvement in the catalytic activity of ALB was realized without any loss of enantioselectivity by using the second-generation ALB [27] generated by the self-assembled complex formation of ALB with alkali metal-malonate or alkoxide. This protocol allowed the catalyst loading to be reduced to 0.3 mol %, for example, the Michael addition of methyl malonate to cyclohexenone catalyzed by the self-assembled complex of (ff)-ALB (0.3 mol %) and KO Bu (0.27 mol %) in the presence of MS 4A gave the adduct in 94% yield and 99% ee [28]. This reaction has been successfully carried out on a 100-g scale wherein the product was purified by recrystallization. The kinetic studies of the reactions catalyzed by ALB and ALB/Na-malonate have revealed that the reactions are second-order to these catalysts (the rate constant ALB = 0.273 M 1h 1 ALB/Na-maionate = 1-66 M 1h 1) [27]. This reaction was used as the first key step for the catalytic asymmetric total synthesis of tubifolidine (Scheme 8D. 11) [28]. 

Fig. 1 General principle of molecular imprinting. A molecular template (T) is mixed with functional monomers (M) and a cross-linker (CL) resulting in the formation of a self-assembled complex (1). The polymerization of the resulting system produces a rigid structure bearing imprinted sites (2). Finally removal of the template liberates cavities that can specifically recognize and bind the target molecule (3). Adapted with permission from [3]. Copyright 2003 American Chemical Society...

Koltover, I., Salditt, T. and Safinya, C.R. (1999) Phase diagram, stability, and overcharging of lamellar cationic lipid-DNA self-assembled complexes. Biophys. J., 77, 915-924. 

Kabanov, A.V., Szoka, F.C. and Seymour, L.W. (1998b) Interpolyelectrolyte complexes for gene delivery polymer aspects of transfection activity. In A. V.Kabanov, P.L.Felgner and L.W.Seymour (eds) Self-assembling Complexes for Gene Delivery. From Laboratory to Clinical Trial. Chichester, UK John Wiley Sons. pp. 197-218. 

Pozharski EV, MacDonald RC (2007) Single lipoplex study of cationic lipoid-DNA, self-assembled complexes. Mol Pharm 4 962-974... 

Figure 9.25 Progression from 0D discrete self-assembled complexes to ID, 2D and 3D architectures as the degree of protection around the metal centre from spectator ligands is decreased, as exemplified by 4,4 -bipyridyl complexes (a) [(Pd(en) (u-bpy) 4]8+,22 (b) [Zn(acac)2(u-bpy)]n,23 (c) [Co(bpy)2(CF3C02)2]n,24 and (d) the pyrazene complex [Ag(pyrazene)3] (SbF6) n.25...

The lower limit of e for which self-assembly may be realistically studied is e 4, since at this efficiency the self-assembled complex constitutes more than 90 % of the species present over a concentration range of only 102 mol dm-3. Even then, it is in equilibrium with significant amounts of oligomers. This may be readily appreciated from the speciation diagram for the tetramer 10.8 (Figure 10.14). 

Stang et al. [94JA4981, 9403776, 95JA1667, 95JA6273] described the self assembly of a series of unique cationic, tetranuclear, Pd(II)- and Pt(II)-based macrocyclic squares (e.g., 25), utilizing different bidentates as the sides of these structures. The similar self-assembly complexation of dipyridyl porphyrins by cis- and tran.v-substituted Pd(II) or Pt(II) ions possessing square planar coordination afforded multiporphyrin arrays with a square... 

An interesting dimension of metal-coordinated self-assembly that is often ignored, or at least not exploited to its fullest extent, occurs when the resulting coordination complex is a charged species and, as such, in need of a counterion. This counterion itself presents yet another subtle instance of ionic self-assembly, which often is overshadowed by its partner, the coordination complex. The second multi-functional side-chain supramolecular polymer system is based on this simple but important concept [14, 106-111]. In 2003, Ikkala and coworkers reported a study in which they exploited (1) a side-chain functionalized polymer, poly(vinyl-pyridine), (2) metal-coordination self-assembly via a tridentate Zn2+ complex and (3) ionic self-assembly through functionalized counterions, i.e. dodecylbenzene-sulfonate ions, to form multiple self-assembled complexes which adopted a cylindrical morphology (Fig. 7.23) [112]. 

Kabanov AV, Feigner PL, Seymour LW (1998) Self-assembling Complexes for Gene Delivery. Wiley... 

Successful synthetic transmembrane channels must have three characteristics if they are to replicate the behaviour of natural systems. They must span the cell membrane, implying a single molecule or stable self-assembled complex over 4 nm in length. Ideally they should also be able to discriminate in favour of one chemical species, if they are to mimic the highly selective channels, and transport that species at rates in the region of 104 to 108 ions per second to match the efficacy of natural channels. 

Kabonov, A.V., Feigner, P.L. and Seymour, L.W. (1998) Self-Assembling Complexes for Gene Therapy From Laboratory to Clinical Trials. John Wiley Sons. 

Kabanov, A. V. Feigner, P. L. Seymour, L. W. (eds) Self-assembling complexes for gene delivery. Wiley, Chichester, UK, 1998. 

The folds provide the cell with 1000 self-assembling, complex, diverse atomic architectures that are all compacted into a single polymer class. Each exhibits an exquisite balance of robustness and marginal stability, which makes them eminently adaptable and evolvable and allows allosteric control and a suite of intricate properties ideally suited to the vast range of structural and functional biological roles they... 

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