Examining water status in membranes by near infrared spectroscopy (NIR)

WENZ J.J.

San Miguel de tucumán

Congreso; XLV Reunión Anual de la Sociedad Argentina de Biofísica; 2016

SAB (Sociedad Argentina de Biofísica)

Near infrared spectroscopy (NIR) informsabout the covalent O-H bonds and H bonds in water systems, being sensitive to perturbationscaused by solutes. The absorption band centeredat 1450/55 nm is considered the first overtone of water representing signals ofdifferent overlapping water and O-H stretching bands. The less the number and/or thestrength of H-bonds the more the strength of the O-H bonds. Thus, they vibrateand absorb radiation at higher frequencies and this shift is employed here toevaluate the water status in different lipid membranes. Multilamellar vesiclesof DMPA or DMPC were prepared at 250 y 500 μM in MQ water and heated at 10 temperatures in the range 13-58 °C. Absorbance were registered every 1 nm inthe 1100-2300 nm interval with a path length of 1 mm.As NIR spectra have not astraightforward interpretation, spectroscopic data were subjected to PrincipalComponent Analysis. From the score plot of the first two PCs, significantdifferences were found in the water status depending on both the type andconcentration of phospholipids. Careful examination of the loading plots revealsthat both phospholipids increase the absorbance at shorter wavelengths anddecrease it at longer wavelengths of the water main band. The shift to higherfrequencies (i.e. higher energy) in the O-H vibration band implies disrupting/ weakeningeffects on the H-bonds, particularly for DMPC and for the highestconcentration. Increasing temperature dramatically debilitates H bonds, morethan any of the two phospholipid and/or concentration.