8. For protein adsorption to the types of material surfaces designated below, indicate whetherthe adsorption process is primarily mediated by either enthalpic or entropic effects. Brieflyjustify your answers for each case.(A)A material surface functionalized with nonpolar groups (i.e., hydrophobic).(B)A material surface functionalized with polar groups (i.e., neutral hydrophilic).(C)A material surface functionalized with charged groups (i.e., +/-).

Since water is the most abundant molecule within living organisms and thereby almost all biomolecules are almost surrounded by water, the nature of interaction between these biomolecules and water plays central role in basic biochemistry. The binding between surfaces are favored or inhibited by 2 effects, the enthalpic effect and entropic effect. If the 2 binding surfaces are alike; i.e. if both are hydrophobic or if both are hydrophilic , then the formation of a bond between these like surfaces results in the release of heat (energy). Hence change in enthalpy during the interaction becomes negative. This a favorable change in enthalpy and also Gibbs free energy. . This is the enthalpy effect. When 2 unlike surfaces interact (i.e. a hydrophobic and a hydrophilic surface), then the formation of bond would require energy and hence change in enthalpy is not favored. The interaction between these unlike molecules will end up restraining (caging ) each other and would thereby cause an unfavorable decrease in entropy. To prevent this the hydrophobic molecules starts to aggregate with each other, to reduce the net surface area and so does hydrophilic molecules. Decreased surface area means less number of unfavorable interactions and so the entropy increase slightly favorable than before . Since it was this situation of unfavorable entropy that lead to their accumulation, this is called the entropy effectLets assume the protein of interest is a globular protein. Globular proteins have hydrophilic surface and hydrophobic core. (A) Here the interaction is between the hydrophilic surface of the protein and the hydrophobic surface of the material i.e. unlike surfaces. As explained above, both enthalpy and entropy is unfavorable in the case of unlike surface interactions. But the important point is, enthalpy does not initiate any driving force to the interactions or phenomenon (aggregation) that further takes place. The driving force to the process of aggregation that occurs when unlike surface interact is initiated by 'entropy'. If the protein molecules stay individually, all their surfaces are exposed to the material. This leads to caging and a very high unfavorable decrease in entropy, so the protein molecules start to aggregate. Some of the surfaces of some protein molecules gets gets hidden inside the agglomerate and hence, the total surface area decreases and so entropy slightly increases that before. So answer is entropic effect. Note that once entropy pushes like molecules towards each other, them clustering together by forming bonds with each other is enthalpy driven. But the primary effect is by entropy. (B)Here both the surfaces are polar. Like surfaces forming bonds is driven by enthalpy as this bond formation results in the release of heat. Change in enthalpy and Gibbs free energy becomes negative and thereby the interaction is spontaneous. So the answer is enthalpy effect. (C) Like in case 'B', here too both the surface are polar (charged species are hydrophilic) and alike. Only exception is that, not all points on the surface of protein and material can interact favorably now . Only oppositely charged surfaces interact favorably i.e. like between a positively charged amino acid on protein surface and a negative charge on the material. This bond formation is also exothermic and thereby release heat. So the primary effect is the enthalpy effect. Electromagnetic force also helps to drive and orient these opposite charges favorably.