Table 1.
Comparison of strength and range of the non-covalent interactions.
| Interaction | Strength | Description | Example | References |
|---|---|---|---|---|
| Hydrogen bond | weak (mostly about 20 kJ/mol) |
interaction between hydrogen atom (e.g., -OH, -NH2) and electronegative atom (e.g., N, O, F) | proteins, nucleic acids, polysaccharides, PVA, PVP, PAAm, UPy | [10,11,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33] |
| Hydrophobic interactions | medium–strong (stronger than hydrogen bonds and Van der Waals) | interaction between nonpolar moieties of amphiphilic molecules | proteins, PNIPAAm, PEO-PPO-PEO (Pluronic), copolymers PEG-PLA, PEG-PLGA, PEG-DFA, CMC-NIPAAm | [11,34,35,36,37,38,39,40,41,42] |
| Ionic interactions | relatively strong | based on electrostatic attraction of oppositely charged ions or dipoles | sodium alginate and Ca2+; chitosan and phosphate salts/carboxylate salts/polysaccharides; sodium alginate and chitosan | [1,36,43,44,45,46,47,48,49] |
| Metal–ligand coordination | strong (comparable to the strength of a covalent bond) | interaction between central metal atom or ion and electron donor group(s) (ligands) | ferric ions and catechol ligands; zinc ions and histidine ligands; calcium ions and bisphophonates | [50,51,52,53,54,55,56,57] |
| Host–guest interaction | wide range of strength | complex hydrogen bonds, Van der Waals, hydrophobic, electrostatic interactions, coordination bonds | cyclodextrins, cucrbiturils, crown ethers, calixarenes, pillarenes | [11,13,36,58,59,60,61,62,63,64,65] |