Hydrogen bonding, hydrophilic amino

Figure 6. Schematic representation of glucose in the pore of the facilitative glucose transporter. The amphipathic a-helices of the membrane spanning domains are thought to form a hydrophilic pore through which glucose moves via hydrogen bonding to amino acids. The importance of the hydrogen bonds at positions 1,3, and 6 of the glucose molecule for efficient transport (see text) is shown.

Helices that form pores will be amphiphilic because it is more favorable to have situated in the inner side of the pore hydrophilic amino acid side chains, while the outer side of the pore represents a more favorable environment for hydrophobic amino acid side chains since these are in contact with lipids. Some authors point to the possibility that such a structure contains hydrogen bonds between amino acid residues and the main chain in order to compensate opposite charges and oppositely oriented dipoles. A comparison between the strength of different interactions in the structure of soluble and membrane proteins leads to the conclusion that because of the decreased strength of hydrophobic interactions and increased strength of electrostatic interactions (because of the reduced dielectric constant), the electrostatic interactions play the main role in stabilizing the structure of membrane proteins. ... 

Among the common amino acids, eleven have side chains that contain polar functional groups that can form hydrogen bonds, such as —OH, —NH2, and — CO2 H. These hydrophilic amino acids are commonly found on the outside of a protein, where their interactions with water molecules increase the solubility of the protein. The other nine amino acids have nonpolar hydrophobic side chains containing mostly carbon and hydrogen atoms. These amino acids are often tucked into the inside of a protein, away from the aqueous environment of the cell. 

Noncovalent interactions play a key role in biodisciplines. A celebrated example is the secondary structure of proteins. The 20 natural amino acids are each characterized by different structures with more or less acidic or basic, hydrophilic or hydrophobic functionalities and thus capable of different intermolecular interactions. Due to the formation of hydrogen bonds between nearby C=0 and N-H groups, protein polypeptide backbones can be twisted into a-helixes, even in the gas phase in the absence of any solvent." A protein function is determined more directly by its three-dimensional structure and dynamics than by its sequence of amino acids. Three-dimensional structures are strongly influenced by weak non-covalent interactions between side functionalities, but the central importance of these weak interactions is by no means limited to structural effects. Life relies on biological specificity, which arises from the fact that individual biomolecules communicate through non-covalent interactions." " Molecular and chiral recognition rely on... 

In summary, the structural characteristics of peptides with high antioxidant activity are as follows a hydrogen bonding and hydrophilic amino acid residue in the position next to the C-terminus, a hydrophobic amino acid residue at the N-terminus, and an electronic amino acid residue at the C-terminus. 

The NIPA gel has a molecular structure which contains not only hydrophilic (NH, C=0) but also hydrophobic (isopropyl) groups. Recently, Hirotsu [8] investigated the phase transition behavior of NIPA gel/water/alcohol systems and explained the thermoshrinking by the destruction of hydrogen bonds between water molecules and amino or carbonyl groups. However, Ulbrich and Kopecek [9] pointed out the importance of hydrophobic interactions in then-study on the mechanical properties of N-substituted acrylamide gels. 

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