Azamacrocyclic systems

AZAMACROCYCLIC SYSTEMS WITH DIFFERENT SUPRAMOLECULAR FUNCTIONS... 

The discussed examples clearly demonstrate the importance of azamacrocycles as structural element to create supramolecular function. Their rigid structure, the basicity and transition metal-ion coordinating ability make them suitable as scaffolds and binding sites. Lanthanide chemosensors containing azamacrocyclic ligands have already reached applications in medical diagnostics. Other applications of azamacrocyclic systems with supramolecular functions, particularly in biochemistry, will follow. 

Metal ions with closed electron shells, such as s p, d or d s, serve mainly to obtain crown ethers - with the exception of small ions of comparatively high charge, such as Be +, Mg, Zn +, Cd, Al + and Sc. To assemble poly-azamacrocyclic systems, 3d cations with either filled or incomplete electron shells are suitable. 

In this chapter, we also evaluate the application polyalkyne and enediyne azamacrocyclic systems [177,182,183]. Since the macrocyclic systems include a nitrogen atom between multiple bonds, their [2-1-2- -2] cycloaddition reactions represent a route to the structures with the polycyclic aza-heterocycles. 

Imine metathesis has continued to be a popular exchange reaction for DCLs. Various groups have found novel systems in which the reaction can be applied, as well as interesting ways to halt the equilibration. For example, Wessjohann and coworkers have demonstrated that Ugi reactions can efficiently halt equilibration of an imine DCL, combining an irreversible diversification process with areversible library selection [24]. Xu and Giusep-pone have integrated reversible imine formation with a self-duplication process [25], and Ziach and Jurczak have examined the ability of ions to template the synthesis of complex azamacrocycles [26]. The mechanistically related reactions of hydrazone [27] and oxime [28] exchange have also been explored as suitable foundations for DCL experiments. 

Konig, B., Pelka, M., Reichenbach-Klinke, R., Schelter, J., Daub, J. A model system for flavoenzyme activity - binding of flavin and modulation of its redox potentials through coordination to a Lewis-acidic azamacrocyclic zinc(II) complex, Eur. J. Org. Chem. (2001), 2297-2303. 

Several rather basic azamacrocycles act as receptor components within lumo/fluorophore-spacer-receptor systems (29) [82], (30) [83] and (31) [84], which are at least structurally related to PET sensors. However, the lack of any substantial luminescence/fluorescence quenching in the cation-free state suggests that the thermodynamic criteria for PET (Eq. (1)) are not met in some of these cases. The low luminescence quantum yields seen in some variants of (31) [84] are due to the intrusion of metal centered lowest excited states. Related cases, with or without macrocyclic units, (32) [85] and (33) [86] carry the... 

This chapter has been organized by considering several aspects. An introduction concerning the relevance of the electronic properties and applications of the azamacrocycles related to surface phenomena as well as the general aspects and characteristics of the vibrational techniques, instruments and surfaces normally used in the study of the adsorbate-surface interaction. The vibrational enhanced Raman and infrared surface spectroscopies, along with the reflection-absorption infrared spectroscopy to the study of the interaction of several azamacrocycles with different metal surfaces are discussed. The analysis of the most recent publications concerning data on bands assignment, normal coordinate analysis, surface-enhanced Raman and infrared spectroscopies, reflection-absorption infrared spectra and theoretical calculations on models of the adsorbate-substrate interaction is performed. Finally, new trends about modified metal surfaces for surface-enhanced vibrational studies of new macrocycles and different molecular systems are commented. 

Inspired by these natural complexes, chemists were interested, since the early 1960s, in obtaining synthetic azamacrocycles that could be employed as model systems for understanding their particular properties, and later to... 

Azamacrocyclic ligands with pendant arms have recently attracted considerable attention mainly due to their analytical, biological and catalytic applications [l]. Compounds of this class combine the properties of a rigid macrocyclic structural unit with those of a flexible side-chain to which the functional group can be bound. Such systems are especially interesting for studying the influence of axial coordination on the properties of the coordinated metal ion. 

Veiga et al. (2013) developed a rapid method for efiScient palladium catalyzed N-arylation of polynitrogenated macrocycles. Its applicability for functionalization of protected azamacrocycles of various sizes with substituted aryl bromides of optional electronic properties has been established. The compatibility of the protocol with common N-protecting schemes as well as the impact of electronic versus steric factors was also discussed. This method provides moderate to excellent yields of N-arylated azamacrocycles (45-96%) using a commercially available catalytic system and easily available alkoxide or phenoxide base. 

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