Reversible Phase Transitions in the Phospholipid Monolayer

The polymorphism of phospholipid monolayers has been extensively studied because of its importance in surface thermodynamics, soft matter physics, and biomembranes. To date, the phase behavior of phospholipid monolayers has been nearly exclusively studied with the classical Langmuir-type film balance. However, because of experimental artifacts caused by film leakage, the Langmuir balance fails to study the reversibility of two-dimensional surface phase transitions. We have developed a novel experimental methodology called the constrained drop surfactometry capable of providing a leakage-proof environment, thus allowing reversibility studies of two-dimensional surface phase transitions. Using dipalmitoylphosphatidylcholine (DPPC) as a model system, we have studied the reversibility of isothermal and isobaric phase transitions in the monolayer. It is found that not only the compression and expansion isotherms but also the heating and cooling isobars, completely superimpose with each other without hysteresis. Microscopic lateral structures of the DPPC monolayer also show reversibility not only during the isothermal compression and expansion processes but also during the isobaric heating and cooling processes. It is concluded that the two-dimensional surface phase transitions in phospholipid monolayers are reversible, which is consistent with the reversibility of phase transitions in bulk pure substances. Our results provide a better understanding of surface thermodynamics, phase change materials, and biophysical studies of membranes and pulmonary surfactants

Analysis of semi-quantitative RT-PCR data and comparison of the expression levels of 176 detoxification genes between selected resistant strain JH-del at G30 and the susceptible JHS at G30.

<p>The band intensities were quantified using densitometry and normalized toβ-actin. Pair-wise comparisons were performed between susceptible JHS and selected resistant strain JH-del. Scatter plots showed the expression ratio (x-axis) and the statistical significance, expressed as the negative log scale of the p -value of the t -test of the fold change between JH-del and JHS (y -axis). Significantly overexpressed genes (≥2-fold) in JH-del are indicated by open circles. A, B, C and D showed the expression ratio of 71 P450, 56 CE, 63 PE and 12 GST genes respectively. The values were presented as mean±SE based on three replicates.</p

Expression levels of six up-regulated detoxification genes verified by quantitative real-time RT-PCR.

<p>Each bar represented the mean of three biological replicates, each performed in triplicate. Error bars indicated the standard errors from the mean. Data were normalized to the expression of β-actin and GADPH. Different letter indicated significant difference (P≤0.05) in the expression levels between strains based on a two-sample <i>t</i>-test. </p

The dynamics of deltamethrin resistance in <i>Laodelphax striatellus</i> during susceptibility recovery and resistance selection.

<p>Error bars represent standard errors of the means of three independent replicates.</p

Analysis of semi-quantitative RT-PCR data and comparison of the expression levels of 176 detoxification genes between selected resistant strain JH-del at G4 and the susceptible JHS at G30.

<p>The band intensities were quantified using densitometry and normalized toβ-actin. Pair-wise comparisons were performed between susceptible JHS and selected resistant strain JH-del-G4. Scatter plots showed the expression ratio (x-axis) and the statistical significance, expressed as the negative log scale of the <i>p</i> -value of the <i>t</i> -test of the fold change between JH-del-G4 and JHS (y -axis). Significantly overexpressed genes (≥2-fold) in JH-del-G4 are indicated by open circles. A, B, C and D showed the expression ratio of 71 P450, 56 CE, 63 PE and 12 GST genes respectively. The values were presented as mean±SE based on three replicates.</p

Graph Theoretical Representation of Atomic Asymmetry and Molecular Chirality of Benzenoids in Two-Dimensional Space

<div><p>In order to explore atomic asymmetry and molecular chirality in 2D space, benzenoids composed of 3 to 11 hexagons in 2D space were enumerated in our laboratory. These benzenoids are regarded as planar connected polyhexes and have no internal holes; that is, their internal regions are filled with hexagons. The produced dataset was composed of 357,968 benzenoids, including more than 14 million atoms. Rather than simply labeling the huge number of atoms as being either symmetric or asymmetric, this investigation aims at exploring a quantitative graph theoretical descriptor of atomic asymmetry. Based on the particular characteristics in the 2D plane, we suggested the weighted atomic sum as the descriptor of atomic asymmetry. This descriptor is measured by circulating around the molecule going in opposite directions. The investigation demonstrates that the weighted atomic sums are superior to the previously reported quantitative descriptor, atomic sums. The investigation of quantitative descriptors also reveals that the most asymmetric atom is in a structure with a spiral ring with the convex shape going in clockwise direction and concave shape going in anticlockwise direction from the atom. Based on weighted atomic sums, a weighted F index is introduced to quantitatively represent molecular chirality in the plane, rather than merely regarding benzenoids as being either chiral or achiral. By validating with enumerated benzenoids, the results indicate that the weighted F indexes were in accordance with their chiral classification (achiral or chiral) over the whole benzenoids dataset. Furthermore, weighted F indexes were superior to previously available descriptors. Benzenoids possess a variety of shapes and can be extended to practically represent any shape in 2D space—our proposed descriptor has thus the potential to be a general method to represent 2D molecular chirality based on the difference between clockwise and anticlockwise sums around a molecule.</p></div

Comparison of sections having the same atomic sums for four benzenoids.

<p>Comparison of sections having the same atomic sums for four benzenoids.</p

The numbers of the achiral benzenoids and all the benzenoids in 2D space, and the number of benzenoids in 3D space.

<p>The numbers of the achiral benzenoids and all the benzenoids in 2D space, and the number of benzenoids in 3D space.</p

An illustration of two benzenoids possessing the same F indexes vector.

<p>An illustration of two benzenoids possessing the same F indexes vector.</p

The atoms possessing the largest weighted atomic sums for the benzenoids of sizes 3∼11, separately.

<p>The size of a benzenoid is the number of hexagonal rings contained in a benzenoid.</p