Alveolar Air-Water Interface

Structural analogy between cubic liquid crystals and a hypothetical stalk model developed for understanding vesicle breakdown at the air-water interface. Separate radii used to describe the curvatures of vesicle lipids in multiple axes, shown here as R₁ and R₂ applied to both mono- and double-layers of lipids. 

Work done in collaboration with Professor Hall.  

Vesicular Breakdown at the Air-Water Interface

How does a lipid mono-layer at the Air-Water interface in Alveoli (lung cell) Form?

The mono-layer forms due to the negative curvature between the vesicle and the water-air interface. This essentially is stalk hypothesis of fusion acting in reverse. The surfactant proteins are necessary to form the negatively curved stalk intermediate which connects the outer monolayer of the vesicle to the air water interface.

Shown here are lipid molecule tails in contact with air from above, having their polar heads in contact with vesicular water at the opposite end of the molecular chain.  Also shown are lipid monolayers breaking from the double-layer.

X-Ray Instruments

The schematic here shows the x-ray source emitting energy from the right and entering the Optical chamber, known as the "Coffin" and comprised of a slit, mirror (R=0.9), and Silicon [1,1,1] monochromator (other properties: α= -7°, △λ \ λ = 2e-4, Focused Flux Φ ~ 1x10⁹ hν s^-1 mA^-1).  From the Optical chamber, monochromatic energy approaches the sample from another slit and thereafter reaches the detector (D=2.7m). The control panels for the instrument include detector temperature and ion chamber readout, motor position encoders, hutch stopper control, electronics control chassis, motor control chassis, beamline control computer, and sample temperature control (pictured on the bottom left).

X-Ray Instruments

Shown here is a home built Small Angle X-Ray Scattering (SAXS) XRD instrument, using a copper tube source, a sample to detector distance of 0.45m, and with a circular spot size of 0.5mm.

X-Ray Studies of Lung Surfactants

Effect of Surfactant Proteins on lipid X-ray Diffraction Lineshape

Shown is the intensity vs spacing plot for varying molar ratios (CLSE-N&PL mixtures at 25°C) of lung surfactant using Small Angle X-ray Spectroscopy (SAXS).  Line broadening and shift to lower q indicates that system approaches unbinding transition, at 1% protein content!

Work done in collaboration with Dr. Samares Biswas and Prof. Stephen Hall

 Phosphorus NMR of Lung Lipids

Nuclear Magnetic Resonance scan of lung lipids.

Shown is "Plot of Experimental Data and Powder Pattern Fit of Pure DOPC" with frequency on the x-axis and intensity on the y-axis.

The change in width of the ³¹P-NMR lineshape and Orientiational order parameter (S) is described as <P₂(cos(θ))> and 1/2<(3cos²(θ)-1)> where θ is equal to the angle between the molecular long axis and a normal to the bilayer.

An NMR Analysis

Evans' polymer brush model figures for NMR analysis. Shown here is the equation for elastic bending stiffness in terms of elastic area modulus and hydrocarbon thickness.  Chemical shift anisotropy is shown here to depend on polymer chain length in the lower plot and G in the upper plot.

Relevant equations:

K = (K_Az_h²)/24 = β△σ²       

△σ = √[(K_A/(24β))z_h]

Work done in collaboration with Hall group.