Water-macromolecule assemblies

Water can be regarded as the most important substance for life oti Earth. It is the most widely used solvent of biomolecules. However, it is also a very complicated solvent. With H-bonding donor and acceptor sites, this polar solvent strongly influences the properties of solutes. It is interesting that water forms supramolecular structures with many kinds of macromolecules, including DNA, proteins, and many synthetic polymers [26, 29, 32, 41, 57, 58]. Several typical water-macromolecule assemblies have been investigated by SMFS. 

As noted above, the nucleophilicity of water allows it to enter into reactions that cause the degradation of biological macromolecules, including DNA and proteins. Analogous problems are associated with the assembly of biopolymers. In water, the assembly of nucleosides from component sugars and nucleobases, the assembly of nucleotides from nucleosides and phosphate, and the assembly of oligonucleotides from nucleotides are all thermodynamically uphill in water. 

Rangelov S, Almgren M, Tsvetanov Ch, Edwards K (2002) Shear-induced rearrangement of self-assembled PEG-lipid structures in water. Macromolecules 35 7074-7081... 

Ranganathan K, DengR, Kainthan RIC, Wu C, Brooks DE, KizhakkedathuJN Synthesis of thermoresponsive mixed arm star polymers by combination of RAFT and ATRP from a multifunctional core and its self-assembly in water. Macromolecules 41 4226-4234, 2008. 

The advantage of the LB technique is that it allows systematic studies of 2-D organization, both before and after transfer from the air—water interface onto a soHd substrate. However, the coupling of 3-D self-organization of macromolecules in solution with organization at a soHd surface may best be achieved using the self-assembly technique. 

Most of the molecules introduced in this chapter are hydrophobic. Even those molecules that have been functionalized to improve water-solubility (for example, CCVJ and CCVJ triethyleneglycol ester 43, Fig. 14) contain large hydrophobic structures. In aqueous solutions that contain proteins or other macromolecules with hydrophobic regions, molecular rotors are attracted to these pockets and bind to the proteins. Noncovalent attraction to hydrophobic pockets is associated with restricted intramolecular rotation and consequently increased quantum yield. In this respect, molecular rotors are superior protein probes, because they do not only indicate the presence of proteins (similar to antibody-conjugated fluorescent markers), but they also report a constricted environment and can therefore be used to probe protein structure and assembly. 

The structural state of dendritic macromolecules at air-water (Langmuir mono-layers) and air-solid (adsorbed monolayers, self-assembled films and cast films) interfaces have been reviewed by Tsukruk [17]. Although this work summarizes various characterization techniques for dendritic films by AFM techniques, in this chapter, we will present recent progress on the characterization of the dendritic film surface morphologies. 

Some the structural state of dendritic macromolecules at air - water (Langmuir monolayers) and air - solid (adsorbed monolayers, self - assembled films, and cast films) interfaces has been discussed by V. V. Tsukruk [106] and Frechet [107],... 

Fig. 4.13 General scheme of dendritic macromolecules within molecular layers at interfaces (a) compressed Langmuir bilayer at air-water interface (b) adsorbed and self-assembled monolayers of neutral dendrimers (left) and dendrimers with sticky surface groups (right) (c) multilayer self-assembled films obtained by layer-by-layer deposition of dendrimers low molar mass ions (left) and two adjacent dendrimer generations (right). (From ref. [106])...

In previous sections of this chapter, as well as in chapter 6, we have discussed several reasons why liquid water is so critical for life. To briefly review the salient points (1) Water is essential for driving the formation of the three-dimensional structures of macromolecules. These structures, on which macromolecular function depends, are encoded in a latent form in the linear primary structures of proteins and nucleic acids, but can be manifested only when liquid water is present to foster hydrophobic interactions. (2) The assembly of bilayer membranes from lipids and proteins likewise is driven in large measure by hydrophobic effects. (3) Water in the liquid state is a requirement for most types of transport of materials between organism and environment and between compartments within the organism. (4) Lastly, the... 

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