Peptides targeting biomolecules

Fig. 10. N4 ligand systems for conjugation 99mTc to biomolecules R = in vivo targeting biomolecules (e.g., biotin [100, 101], somatostatin receptor-avid peptide [103,104])...

Aptamers are oligonucleic acids or peptide molecules that bind to a specific target biomolecule (Fig. 2). A dye molecule can be noncovalently or covalently bound to an aptamer. 

The pharmacokinetics of a radiopharmaceutical can be systematically altered by chemical modification of the targeting biomolecule or metal chelate, and the use of a pharmacokinetic modifying Hnker. The chemical modification of a biomolecule can be achieved by introducing various hydrophiUc or Hpophilic groups onto the side-chains of the targeting biomolecule. Sometimes a peptide sequence, such as polyaspartic acid, can be used to improve the hydrophiUcity. The chemical modification of the metal chelate can be achieved using BFCs with different charge and hydrophiUcity. 

This mode of separation, as the name suggests, uses stationary phases with a special affinity for a specific analyte. The affinity ligand immobilized on the stationary phase varies dramatically from peptide, to protein, to oligonucleotide, to monoclonal antibody. In some cases the target molecule is labelled with an affinity tag to simplify the separation. This approach is common in the synthesis of recombinant proteins where the system can be engineered so that the target biomolecule expresses a tag such as polyhistidine. A stationary phase functionalized with aminodiacetic acid and nickel chelate is then used to fish out the required molecule by chelating with the polyhistidine tag. 

The use of MALDI to image biological materials is another interesting application [33,34], Indeed, as with LD and SIMS, MALDI has been used to map the distribution of targeted biomolecules in tissue. It allows for example the study of peptides, proteins and other biomolecules directly on tissue sections. 

Some of their derivatives have been used as antiviral drugs. Due to their flexible chemistry, they can be exploited to design drug delivery systems and in molecular nanotechnology. In such systems, they can act as a central lipophilic core and different parts like targeting segments, linkers, spacers, or therapeutic agents can be attached to the said central nucleus. Their central core can be functionalized by peptidic and nucleic acid sequences and also by numerous important biomolecules. 

Nanoparticle surface modification is of tremendous importance to prevent nanoparticle aggregation prior to injection, decrease the toxicity, and increase the solubility and the biocompatibility in a living system [20]. Imaging studies in mice clearly show that QD surface coatings alter the disposition and pharmacokinetic properties of the nanoparticles. The key factors in surface modifications include the use of proper solvents and chemicals or biomolecules used for the attachment of the drug, targeting ligands, proteins, peptides, nucleic acids etc. for their site-specific biomedical applications. The functionalized or capped nanoparticles should be preferably dispersible in aqueous media. 

Biomaterials such as proteins/enzymes or DNA display highly selective catalytic and recognition properties. Au nanoparticles or nanorods show electronic, photonic and catalytic properties. The convergence of both types of materials gives rise to Au NP-biomolecule hybrids that represent a very active research area. The combination of properties leads to the appearance of biosensors due to the optical or electrical transduction of biological phenomena. Moreover, multifunctional Au NP-peptide hybrids can be used for targeting nuclear cells where genetic information is stored and could be useful for biomedical applications [146]. 

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