Hydrogen bonding versus ion pairing in polyelectrolyte multilayers with homopolynucleotides

Area of Science:

• Materials Science
• Biochemistry
• Polymer Chemistry

Background:

• Layer-by-layer assembly is a common technique for creating thin films.
• Polyelectrolytes like poly(ethylenimine) (PEI) and nucleic acids like poly(adenylic acid) (poly(A)) and poly(uridylic acid) (poly(U)) are building blocks for such films.
• Understanding the forces driving film formation is crucial for controlling film properties.

Purpose of the Study:

• To investigate the assembly of thin films using homopolynucleotides (poly(A), poly(U)) and a polyelectrolyte (PEI).
• To differentiate the roles of electrostatic and hydrogen bonding in multilayer film formation.
• To explore how film morphology and thickness are affected by assembly conditions and salt concentration.

Main Methods:

• Layer-by-layer assembly of poly(A), poly(U), and PEI.
• Varying the sequence and combination of deposition steps.
• Annealing films with salt.
• Optical waveguide light-mode spectroscopy (OWLS) to monitor adsorption.
• Surface morphology analysis.

Main Results:

• Alternating assembly of poly(A) and poly(U) failed due to strong complementary strand interactions.
• Film morphology was influenced by deposition order and salt annealing.
• Smooth films were achieved using preformed poly(A)/poly(U) duplexes.
• OWLS confirmed that only complementary polynucleotides adsorb via hydrogen bonding.
• Film thickness decreased with increasing salt concentration, contrary to typical polyelectrolyte behavior.

Conclusions:

• The assembly of polynucleotide/PEI multilayers is governed by a complex interplay of electrostatic and hydrogen bonding.
• Complementary polynucleotide interactions can inhibit film growth.
• Salt concentration significantly impacts film thickness and assembly behavior.
• This study provides insights into designing functional thin films using nucleic acids and polyelectrolytes.