Recognition features

The electrostatic motif represents an important recognition feature and also plays a part in determining the structure of biomacromolecules. 

The substrate in most reactions of this type is an alcohol, which becomes oxidized to an aldehyde or ketone, e.g. ethanol is oxidized to acetaldehyde. Some reactions employ the alternative phosphorylated cofactor NADP+ the phosphate does not function in the oxidation step, but is merely a recognition feature helping to bind the compound to the enzyme. The full structures of NAD+ and NADP+ are shown in Box 11.1. 

Wu, N. Kudo, F. Cane, D.E. Khosla, C. (2000) Analysis of the molecular recognition features of individual modules daived from the aythromycin polykaide synthase. J. Am. Chem. Soc., 122,4847-52. 

The electrochemical properties of the two types of iron-cluster-derivatized AuNPs resemble that of the monomeric tetrairon cluster, except that they additionally show adsorption due to their large size, and evidence that all the Fe4 clusters are active at about the same potential, thereby indicating that they are sufficiently remote from one another to behave independently. The changes in the cyclic voltammetric pattern caused by the addition of H2P04 and ATP2- oxoanions evidence recognition features that are very different from those obtained with dendritic ferrocene exoreceptors. In particular, the results show that with these iron-cluster-derivatized AuNPs... 

The substrate carries information defined by its molecular recognition features and constitutes a signal that may be modulated by the switching process. The stimulus to which the switch responds and the substrate on which it operates may both be either of photonic, electronic, ionic, magnetic, thermal or mechanical nature. Thus, a whole set of switches based on (substrate-stimulus) pairs, is defined by the combination of the various types opto-photo, opto-electro, electro-photo, etc. 

MIPs can be stored in the dry state at ambient temperature for several years without losing their recognition features. 

To put the above discussion into other words, the molecular components of a supramolecular system contain information in the form of specific molecular recognition features. The object of the exercise is to ensure that these molecular recognition features are mutually complementary. 

The last of the important concepts that we will consider is self-assembly. Most chemists have, at some time in their careers, wondered why molecules cannot just make themselves. The process by which molecules build themselves is termed self-assembly and is a feature of many supramolecular systems. If the molecular components possess the correct complementary molecular recognition features and their interaction is thermodynamically favourable then simply mixing them could result in the specific and spontaneous self-assembly of the desired aggregate. This assumes that there is no significant kinetic barrier to the assembly process. The recognition features within the components may be any of the intermolecular bonding processes mentioned above, but we will be concerned with interactions between transition metal ions and polydentate ligands. 

Fig. 7.6 Hypl IL8 chain B recognition. Feature weights are reported in parentheses, hydrogen atoms have been hidden for clarity.

The evolution of protein structures shows conservation in recognition features for common binding sites. For example, the adenosine triphosphate (ATP)/ guanosine triphosphate (GTP) binding site contains an amino acid motif A (P-... 

RJX Zawada, C Khosla. Domain analysis of the molecular recognition features of an aromatic polyketide synthase. J Biol Chem 272 16184-16188, 1997. 

The use of DNA molecules as wires in electronic systems may open a new opportunity in nanoelectronics. DNA has the appropriate molecular recognition features and well-characterized self-assembly. There is evidence to suggest that DNA is only a marginally better electron conductor than proteins [116-118], As a result, many studies have focused on various methods of DNA modification leading to improvement in its conductive properties. It is possible to enhance the conductivity of DNA by coating it with a thin film of metal atoms, but the molecular recognition properties of the DNA are then destroyed. An effective approach to this problem is the incorporation of metal ions into the DNA double helix [118-121], Preliminary results suggest that a metal ion-DNA complex may be a much better conductor than B-DNA, because the former shows a metallic conduction whereas the latter behaves like a wide-band gap semiconductor [118]. 

In a recent study from the same laboratory [26b] the same complementary pair was employed and the consequence of the recognition features on aggregation, adhesion and fusion were investigated, identifying the physicochemical pa-... 

However, crystal engineering did not become synonymous with supramolecular synthesis until die 1990s. As noted by J. S. Maddox in 19883 and more recendy by Gavezzotd17 and Ball,18 crystal structure prediction remains in its infancy. However, prediction is fundamentally very different from engineering and design. Predicting a crystal structure requires an analysis of the recognition features present in the molecular component in such... 

Self-assembly of a single molecular component or molecular tectonics. 27 In such a situation, all the molecular recognition features that lead to supra-molecular synthons15d are present in a single molecule. 

Self-assembly of two or more complementary components, a node and spacer, or modular self-assembly . The molecular recognition features are present in two or more complementary molecules (e.g. cocrystals) or ions (e.g. salts or metal-organic polymers). 

Wuest has demonstrated that the pyridone moiety also generates a hydrogen-bonded supramolecular synthon that is suitable for building extended arrays.67 Remarkably, methanetetra(6-phenylethynyl-2-pyridone) exhibits a diamondoid network, sevenfold interpenetration and cavities large enough to enclathrate butyric or valeric acid.27 Wuest introduced the concept of tectons to describe molecules that inherently possess the molecular structure and intermolecular recognition features to predictably self-assemble into crystalline networks. He followed this study with several other examples of diamondoid networks sustained by the pyridone moiety 27c d... 

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