Human respiration relies on the function of pulmonary surfactants, surface-active complexes produced by alveolar cells. An investigation of the thermodynamics of the interactions between carbohydrates and lipids was conducted in order to determine the properties of potential artificial surfactants. The effects of various carbohydrates on the phase-transition properties of an aqueous dispersion of 1,2-dipalmitoyl phosphatidylcholine (DPPC, Figure 1), the major phospholipoprotein component of human pulmonary surfactant, were studied. Infantile Respiratory Distress Syndrome (IRDS), a common condition among premature infants, is characterized by insufficient production of DPPC, increased respiratory effort (a measure of the work required to inflate the lungs), and progressive respiratory failure.Figure 1 1,2-dipalmitoyl phosphatidylcholineAqueous dispersions of DPPC have well-defined values of ΔH and ΔS for the endothermic phase transition from an amorphous gel to a liquid-crystalline state. The free energy change associated with this transition may be written according to Equation 1, where Glc and Gg are the Gibbs free energies of aqueous dispersions of DPPC in liquid-crystalline and gel phases, respectively. The values of ΔS and ΔH (at the specified T) for this transition in solutions containing various carbohydrates tested are given in Table 1. ΔG = Glc – GgEquation 1The free-energy pairwise-interaction coefficient {AA}g is a measure of self-interaction of a solute in aqueous solution. The value of {AA}g is inversely related to the solute molecules’ tendency for pairwise interaction and the strength of the hydrophobic interactions between them.Table 1 Entropies and Enthalpies of Formation for the Transition of DPPC-carbohydrate SolutionsQuestion 2Underproduction of pulmonary surfactant in IRDS leads to decreased compliance of alveolar tissue. Based upon this information, which of the following must be true regarding pulmonary surfactant? A.Its adsorption to the water-alveolar interface increases surface tension, preventing alveolar collapse due to intra-thoracic pressure.B.Its absence decreases the minimum radial size of alveoli able to avoid collapse at a given pressure of inspired air.C.Its adsorption to the water-alveolar interface decreases surface tension, decreasing the pressure difference required to inflate the airway.D.Its presence increases the efficiency of gas exchange across the alveolar membrane by decreasing the surface area of the alveolus at a given pressure of inspired air.