Controlling Surface Properties with Peptides: New Methods in Molecular Self-Assembly
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CONTROLLING SURFACE PROPERTIES WITH PEPTIDES: NEW METHODS IN MOLECULAR SELF-ASSEMBLY
2 1 Troy Wilson and Mark D. Bednarski *
Department of Chemistry University of California at Berkeley Berkeley, California 94720 and Center for Advanced Materials Materials Sciences Division Lawrence Berkeley Laboratory Berkeley, California 94720
As part of our investigation into the design and applications of proteolytic enzymes, we required a convenient method to attach peptides to the surface of a variety of materials. In this paper we report the synthesis and characterization of a class of peptide derivatized lipids (PDL's) that can be selfassembled into monomolecular films. 3.4 These films can be used to control interfacial properties such as wetting and adhesion and provide a simple 5 method to coat surfaces with amino acids. Scheme I NH2
at
0
0
/
Et 3 N, CH 2 CI 2 R =CH
HN
0
NHS, EDCI 1
NH2
H2N--I
2
R 3
Et3 N, CHCI2
R' = H (3a) CH3 (3b) 3
CH 2OH (3c) CH 2C6Hs (3d)
Compounds 3a-d was prepared from commercially available 10, 12pentacosadiynoic acid (PDA) 1 by the sequence depicted in Scheme I. PDA was (NHS) using 1-(3first treated with N-hydroxysuccinimide
Mat. Res. Soc. Symp. Proc. Vol. 218. 01991 Materials Research Society
166
dimethylaminopropyl)-3-ethylcarbodiimide (EDCI) as a coupling agent to form the activated ester 2 in approximately 90% yield. Compound 2 was subsequently reacted with glycinamide, alaninamide, phenylalaninamide and serinamide to afford the peptide derivatized lipids listed in Table 1 (compounds 3a-d). The yields of PDAaIaNH2 and PDAPh-2 were approximately 50% while the yields of PDAserNI 2 and PDA9'~YN2 were 60-80%.6 Self-assembled PDL films were formed using a modified LangmuirBlodgett procedure. 7,8 The lipids were spread from an organic solvent at a heated, air-water interface and then crystallized with a differential cooling gradient along the water surface. The crystalline monolayer film was polymerized with ultra-violet (UV) irradiation and transferred to other surfaces by simple contact between the two interfaces. A detailed procedure for the formation of a PDAa•aNH2 film is given below. The PDAa'•aN2 monomer was dissolved in dichloromethane:hexane (1:1) solution at a concentration of 1.8 mM as determined by 1H NMR spectroscopy using an internal standard. An aqueous subphase was prepared from distilled water passed through a millipore Q purification system until the resistivity was greater than 18Mg-cm. The aqueous layer (sub-phase) was heated to 50 ± 2°C and approximately 20 pl of the lipid solution was spread from a microliter syringe. The subphase was then slowly cooled to 15-18 ± 2°C to induce crystallization, and the resulting crystalline monolayer was polymerized with ultraviolet radation at 254 nm. The polymerized peptide film was then transferred to a glass slide that had been made hydrophobic by incubation with octadecyltrichlorosilane in hexadecane5 . We postulate that it is the van der Waals attraction between the two lipophilic surfaces that is responsible for f
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