Immobilized macrocycles

Run/Nin heteronuclear complexes such as (653), in which a photosensitizer [Ru(bpy)3]2+ or [Ru(phen)3]2+ is covalently attached to the Ni1 cyclam complex, have been synthesized in order to improve the efficiency of electron transfer from the photoexcited photosensitizer to the catalytic site.1 44-1646 However, these complexes did not perform particularly well, either due to unfavorable configuration of the Nin-cyclam subunit and the resulting steric hindrance or due to short lifetime of the excited states of the Ru photosensitizer moieties. A stable catalytic system has been prepared by immobilizing macrocyclic Ni11 complexes and [Ru(bipy)3]2+ in a nafion membrane.164... 

AnaLig sorbents, with predetermined molecular recognition chemistry for specific ions, using immobilized macrocycles Pb from fresh and seawater, Cu, Ni from drug extract, Fe, NI from petroleum, Hg from water 111... 

Iminobispropylamine, 94 Immobilization of toxic heavy metals, 18 Immobilized macrocycles, 20, 21,756, 757 Immunotherapy, 798 Indicators for metal ions, 9 Indium(III) delivery to tumors, 553, 554 Insulin, 74... 

Sulfur-containing macrocycles bound to silica gel are highly selective concentration and purification ligands for Pd", Hg" and Ag. These immobilized macrocycles efficiently removed Au " and Pd" from solutions of HCl and FeCls. Similarly, Ag+, Au" and Pd" were separated by these columns and selectively eluted from the columns with purities of 99.9%. It was also shown that Pd" can be removed from industrial silver electrolyte solutions with 99.9% purity in one pass through these columns <91ANC1014>. 

Self-assembled monolayers (SAMs) of alkylthio-, arylthio-, and thiol-derivatized MN4 macrocyclic compounds have also been employed [71-83], providing a convenient way of directly immobilizing macrocyclic complexes onto electrode surfaces, without requiring highly complex matrices. The binding of thiol-derivatized MN4 macrocyclic compounds to a gold substrate by means of their thiol arms results in the formation of reproducible and stable films [84, 85]. 

Catalysts can also be immobilized through nonphosphine ligands. A new type of immobilized Pd° complex with a macrocyclic triolefin ligand (L30) has been successfully used for simple crosscoupling reactions of aryl iodides and allyl bromide with arylboronic acids, in both aqueous and anhydrous media.498... 

Typical systems. A considerable number of immobilized polyether systems have been synthesized both for phase transfer catalysis as just discussed and for use in a number of analytical applications. Such immobilized systems are generally synthesized by either copolymerization of suitably functionalized macrocycles in the presence of cross-linking agents or by appending functionalized macrocycles to existing polymeric substrates. Structures (184)-(186) give examples of different... 

Synthetic Strategies for the Immobilization of Macrocyclic Antibiotics Surface Coverage Data... 

Scheme 2.1 General synthetic schemes for the immobilization of macrocyclic antibiotics. (a) (i) 1,6-Diisocyanatohexane (ii) glycopeptide (TE, TAG, and A-40,926). (b) (i) Glycopeptide (eremomycin, ristocetin A, vancomycin), (c) (i) NaI04 (ii) glycopeptide (vancomycin, ristocetin A, MDL 63,246). (d) (i) 3-Isocyanatopropyl-silyl derivative of macrocyclic antibiotic (TE, rifamycin B, vancomycin, DMP-vancomycin, NVC).

In this synthetic strategy, the macrocyclic antibiotic is covalently bonded to the silica matrix in two steps (1) chemical modification of the selector via reaction between suitable groups of the antibiotic and proper groups of the spacer, reacting also as a di- or trialkoxysilane (2) immobilization of the functionalized selector on unmodified silica particles. 

In a typical reaction, the macrocycle is treated with a 2-3 M excess of (3-isocyanatopropyl)triethoxysilane in dry DMF. The derivative is then added to a dry DMF slurry of silica gel ( 2 g of functionalized selector to 4 g of silica gel). The solution is stirred, allowed to react for 20 h at 107°C, and then cooled, filtered, and washed with methanol, 50% aqueous methanol, and methanol again, and finally dried. Surface coverage data are reported only in the case of the commercially available vancomycin CSP (see Table 2.2), immobilized by joining on average three linkers per vancomycin molecule, probably via a 3-isocyanatopropyl-silane [48]. 

Another factor that remarkably affects the enantioresolution of given enantiomeric pairs has been shown to be the binding chemistry used for the silica immobilization of glycopeptides (see Section 2.2). This was illustrated in the case of ristocetin A, which was covalently bonded to silica microparticles by immobilization onto epoxy-activated silica under mild conditions [22], and compared with the corresponding commercially available CSP, where the macrocycle was immobilized as previously reported for vancomycin, rifamycin B, thiostrepton [7], and teicoplanin [30]. The comparison proved that immobilization of ristocetin A onto epoxy-activated silica could significantly improve the enantioselectivity and the resolution of the corresponding CSP in the separation of a-amino acids under RP conditions [22]. 

Brush-type, proteins, CDs, natural molecular imprint-based polymers (MIP), and macrocyclic antibiotics have been immobilized as chiral selectors on packed-CEC columns. Zheng and Shamsi demonstrated the possibility of using chiral CEC—ESI/MS with a commercially packed column for the determination of warfarin enantiomers in human plasma using coumachlor as an internal standard (IS). Robustness of this chiral CEC capillary was recently improved by a novel procedure and applied for the simultaneous enantiosepara-tion of height /1-blockers with multimodal CSP using different combinations of vancomycin and teicoplanin, as presented in Figure 5. ... 

Polyaza macrocycle derivatives have been employed in a number of analytical applications." " For example, polymer-immobilized cyclam has been employed for the preconcentration of manganese in seawater prior to analysis." ... 

An interesting example of a system whose components become mechanically bound upon surface immobilization is rotaxane trans-21 (Fig. 13.24), consisting of a ferrocene-functionalized /3-cyclodextrin (fi-CD) macrocycle threaded on a molecule containing a photoisomerizable azobenzene unity and a long alkyl chain.33 A monolayer of trans-21 was self-assembled on a gold electrode. Therefore, the ring... 

To date, reverse cyclative cleavage with C-C bond formation has relied on ylid chemistry. A single example was reported54 of the intramolecular Wittig condensation of an immobilized amide to give a two-substituted indole (Fig. 18). Macrocyclization through an immobilized... 

Dudler, V., Lindoy, L. F., Sallin, D., and Schlaepfer, C. W. (1987) An oxygen-nitrogen donor macrocycle immobilized on silica gel. A reagent showing high selectivity for copper(II) in the presence of cobalt(II), nickel(II), zinc(II) or cadmium(II), Aust. J. Chem. 40(9), 1557-1563. 

Photochemical host-guest systems on the basis of photoswitchable macrocycles have also been investigated most recently in a number of publications. Schafer et al.23 and Anselmetti et al.24 modified a bifunctional resorcin[4]arene with two anthracene units and proved its switching function in photochemical induction and heating cycles. Moreover, they modified the lower rim of the resorcin[4]arene with four 10-(decylthio)decyl linkers for an oriented surface immobilization on gold via molecular self-assembly (Fig. 15.7). The affinity modulation of this optical switch was... 

The self-assembly of threaded supramolecular complexes on solid surfaces can be obtained in systems in which either the acyclic or the macrocyclic component of a pseudorotaxane is immobilized on an appropriate surface.86... 

---