Lipoamide-PEGs Confer Extra Strong Binding

3.7 PEG-Thiols

3.7.1 Lipoamide-PEGs

Nanotechnology and nanobiotechnology using gold or silver particles, quantum dots or even magnetic particles are broadly diverse, rapidly expanding areas of study in medical diagnostics and therapeutics, sensoric and chemistry. Metal particles, however, are not water soluble without further modification. Thiols readily form dative bonds to gold and silver surfaces creating selfassembled monolayers (SAMs) which modify surfaces for coupling proteins and other molecules. Monothiols, however, can be readily removed by reducing agents such as DTT (Cleland’s Reagent). The disulfide lipoic acid (also known as thioctic acid) binds far stronger to metal surfaces and is much more resistant towards removal from the metal surface by DTT and similar reagents than monothiols. PEG linkers impart hydrophilicity, non-antigenicity and nonimmunogenicity to nanoparticles. With the methoxy-capped PEG linker a water shell can be created around the nanoparticle. Lipoamido-PEG-acids and lipoamido-PEG-alcohols can be used as intermediates for derivatizing the PEG linker after attaching to the surface. A co-coating with methoxy-PEG-lipoamides will specifically reduce the density of functional groups on the surface. This is essential if interaction with large molecules like proteins and antibodies is expected. Stench is often operative for thiols! Lipoic acid derivatives, however, have NO ODOR.

Protocol:

A variety of protocols exist in the literature and on various websites for reducing lipoic acid (LA) to dihydrolipoic acid (DHLA). Both Tris(2-carboxyethyl)phosphine (TCEP) and sodium borohydride (NaBH4) have been used successfully for reduction of LA to DHLA. For specific procedures, please consult literature. In general, TCEP reduction is carried out in water or aqueous buffer (excluding phosphate buffer, in which TCEP is unstable), in three times or greater molar excess to the lipoic acid derivative, using an incubation temperature of 25°C to 50°C, for about 1-2 hours. Each reduction procedure must be optimized for the particular lipoic acid derivative being reduced to the corresponding DHLA derivative.

References:

  • Bioconjugate Techniques; G. T. Hermanson; 2nd Edition; Elsevier 2008; 188-190, 485-497, 924-935; ISBN 978-0-12- 370501-3
  • Self-assembled organic monolayers: model systems for studying adsorption of proteins at surfaces; K. Prime and G. Whitesides; Science 1991; 252: 1164-1167. doi:10.1126/ science.252.5009.1164
  • Biosensing with Luminescent Semiconductor Quantum Dots; K. Sapsford, T. Pons, I. Medintz and H. Mattoussi; Sensors 2006; 6: 925-953.
  • Enhanced oligonucleotide–nanoparticle conjugate stability using thioctic acid modified oligonucleotides; J. A. Dougan, C. Karlsson, W. E. Smith and D. Graham; Nucleic Acids Res 2007; 35: 3668-3675. doi:10.1093/nar/gkm237
  • Design of biotin-functionalized luminescent quantum dots; K. Susumu, H. T. Uyeda, I. L. Medintz and H. Mattoussi; J Biomed Biotechnol 2007; 90651: 90651. doi:10.1155/2007/90651
  • Toward Reliable Gold Nanoparticle Patterning On Self- Assembled DNA Nanoscaffold; J. Sharma, R. Chhabra, C. S. Andersen, K. V. Gothelf, H. Yan and Y. Liu; J Am Chem Soc 2008; 130: 7820-7821. doi:10.1021/ja802853r
  • Simultaneous determination of α-lipoic acid and its reduced form by high-performance liquid chromatography with fluorescence detection; S. Satoh, T. Toyo’oka, T. Fukushima and S. Inagaki; Journal of Chromatography B 2007; 854: 109-115. doi:10.1016/j.jchromb.2007.04.003
  • Recent advances in separation and detection methods for thiol compounds in biological samples; T. Toyo’oka; Journal of Chromatography B 2009; 877: 3318-3330. doi:10.1016/j.jchromb.2009.03.034
  • Oriented Immobilization of Antibodies with GST-Fused Multiple Fc-Specific B-Domains on a Gold Surface; T. H. Ha, S. O. Jung, J. M. Lee, K. Y. Lee, Y. Lee, J. S. Park and B. H. Chung; Anal Chem 2007; 79: 546-556. doi:10.1021/ ac061639+
  • Polyethylene glycol-based bidentate ligands to enhance quantum dot and gold nanoparticle stability in biological media; B. C. Mei, K. Susumu, I. L. Medintz and H. Mattoussi; Nat. Protocols 2009; 4: 412-423. doi:10.1038/ nprot.2008.243
  • Influence of anchoring ligands and particle size on the colloidal stability and in vivo biodistribution of polyethylene glycol-coated gold nanoparticles in tumorxenografted mice; G. Zhang, Z. Yang, W. Lu, R. Zhang, Q. Huang, M. Tian, L. Li, D. Liang and C. Li; Biomaterials 2009; 30: 1928-1936. doi:10.1016/j.biomaterials.2008.12.038
  • Modular poly(ethylene glycol) ligands for biocompatible semiconductor and gold nanocrystals with extended pH and ionic stability; B. C. Mei, K. Susumu, I. L. Medintz, J. B. Delehanty, T. J. Mountziaris and H. Mattoussi; Journal of Materials Chemistry 2008; 18: 4949-4958. doi:10.1039/ b810488c

Categories: