Effect of elevated temperature and UV radiation on molecular structure of linoleic acid by ATR-IR and two-dimensional correlation spectroscopy.

The effect of elevated temperature (44 °C) and ultraviolet (UV) radiation on molecular structure of linoleic acid (LA) was studied by Attenuated Total Reflection Infrared (ATR-IR) spectroscopy. To obtain more detailed information on molecular mechanism of these changes we applied moving-window analysis and two-dimensional correlation spectroscopy (2DCOS). Analysis of the time-dependent ATR-IR spectra of LA before and after UV irradiation revealed the structural changes in molecules of LA. The extent of these changes was significantly higher after an application of UV radiation. During 24 h experiment temperature was constant, therefore the spectral changes result from relatively slow processes (and requiring more energy), e.g. cis/trans isomerization, disruption of the C=C double bonds and partial breaking of hydrogen bonds in the cyclic dimers. As a side effect of these structural changes one can observe variations in the orientation of the chains. It is of note that the methyl and methylene groups reveal slightly different behaviour.

ATR-IR study of skin components: Lipids, proteins and water. Part II: Near infrared radiation effect.

Near infrared (NIR) radiation has been widely used in medicine and biomedical engineering. In spite of numerous studies the molecular mechanism of NIR radiation on biological systems has not been established as yet. The objective of this work was examination of the effect of NIR irradiation on the skin components. Modifications of lipid organization after NIR exposure vs. temperature (from 20 to 90 °C) have been investigated using Attenuated Total Reflectance Infrared (ATR-IR) spectroscopy. This work is a continuation of our previous studies on the temperature effect on skin components [1]. After NIR exposure a temperature shift of the phase transition from the orthorhombic to hexagonal packing (≈40 °C) has been observed. In contrast, the second phase transition temperature (≈70 °C) is almost invariable. The phase transitions in lipids were correlated with modifications of the structure of water and proteins. To our knowledge, for the first time the temperatures of the phase transitions after NIR exposure were investigated.

ATR-IR study of skin components: Lipids, proteins and water. Part I: Temperature effect.

In this work we report the studies of the effect of temperature on skin components, such as lipids, proteins and water. Modifications of lipids structure induced by increasing temperature (from 20 to 90°C) have been studied using ATR-IR (Attenuated Total Reflectance Infrared) spectroscopy, which is a powerful tool for characterization of the molecular structure and properties of tissues, such as skin. Due to the small depth of penetration (0.6-5.6µm), ATR-IR spectroscopy probes only the outermost layer of the skin, i.e. the stratum corneum (SC). The assignment of main spectral features of skin components allows for the determination of phase transitions from the temperature dependencies of band intensities [e.g. νas(CH2) and νs(CH2)]. The phase transitions were determined by using two methods: the first one was based on the first derivative of the Boltzmann function and the second one employed tangent lines of sigmoidal, aforementioned dependencies. The phase transitions in lipids were correlated with modifications of the structure of water and proteins.

Structural characterization of clear human lens lipid membranes by near-infrared Fourier transform Raman spectroscopy.

Regional differences in human lens membrane lipid composition have been documented and could be responsible for alterations in the function of lens membranes. The phospholipid composition of epithelial membranes of human lenses has been shown to be different from that of fiber membranes. To establish lipid composition-membrane structure relationships, we have examined spectroscopically the structure of lipid membranes from human lens epithelium, cortex and nucleus. Near-infrared Fourier transform Raman spectroscopy was used to obtain the lipid structure of membranes in which the lipid composition was determined previously by 31P-NMR. The disorder (fluidity measured structurally) of the epithelium was evaluated to be 80%, whereas that of the lipids from the cortical and nuclear regions was 55%. The large size of the band at 1650 cm-1 arising from sphingolipids supported the compositional studies which indicate that the major component of human lens membranes is a sphingolipid. Sphingolipids probably account for the high degree of lipid order found in lens membranes. Epithelial membranes were found to contain more glycerolipids and less sphingolipids than fiber cell membranes. This compositional difference would be expected to disorder the epithelial membrane.