Thiol Dative Bonds

Thiol-containing molecules can interact with metal ions and metal surfaces to form dative bonds. Dative bonds also are known as coordinate covalent bonds. They differ from normal 

2-Mercapto- Cystamine Lipoic acid Dihydrolipoic DSP Thioacetic 

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Figure 2.2 A number of small thiol-containing molecules have proven useful for modification of gold or metallic surfaces. The dithiol derivatives provide better dative bond stability and can t be displaced easily by competing thiols or oxidation. Most thiol-containing compounds used for surface modification also contain terminal functional groups or reactive groups for coupling affinity ligands.

Figure 9.60 Many different thiol-containing linkers can be used to prepare water-soluble QDs. The monothiol compounds suffer from the deficiency of being easily oxidized or displaced off the surface, thus creating holes for potential nonspecific binding. The dithiol linkers are superior in this regard, as they form highly stable dative bonds with the semiconductor metal surface that do not get displaced. The PEG-based linkers are especially effective at creating a biocompatible surface for conjugation with biomolecules.

Direct attachment of proteins and peptides to the Qdot surface is based on two types of Qdot surface protein interactions dative thiol-bonding between Qdot surface sulfur atoms and cysteine residues and metal-affinity coordination of histidine (HIS) residues to the Qdot surface Zn atoms (Fig. 17.3(c)). The Weiss group demonstrated the former by using phytochelatin-related peptides to cap CdSe/ZnS (core/shell) Qdots, providing not only surface passivation and water solubility, but also a point of biochemical modification. Using peptides for both dispersion and biofunctionalization represents a new class of rationally designed multifunctional biological cap. ... 

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