Micropores in the vitteline layer of the eggs of the dragonfly Oligoaeshna pryeri: a preliminary observation from the viewpoint of oxygen uptake.

In dragonfly eggs, oxygen diffusing in, and carbon dioxide diffusing out, encounter barriers in the shell.According to Tullett and Board, in avian eggs the most important of these barriers results from the geometry of the pores through the shells. As in birds, dragonfly egg shells consist of three layers: the exochorion, endochorion and the innermost vitelline membrane. Trueman has described pores and fine anchorlike structures in the endochorion but the vitelline membrane does not seem to have been studied. In the present work we have used scanning electron microscopy to examine the vitelline membrane in hatching eggs of Oligoaeschna pryeri. We have assumed that the numerous openings seen on the micrographs are pores through the membrane.Results are expressed as means ± SD. The pore diameter, pore area and number per µm2 of the vitelline membrane were 74.7 ± 61.3 nm, 4380 ± 3555 nm2 and 4.16 ±1.3 pores/µm2 (4.16 x108 pores/cm2), respectively. The total pore area was calculated to be 18,222 nm2/ µm(2). In avian egg shells pore density depends on the weight of the egg. Results given by Tullett and Board suggest that an egg weighing 1 g may have a pore density of 300 pores/cm2, which is much lower than the present result for dragonflies. It seems likely that the difference reflects the fact that in Oligoaeshna pryeri the eggs are immersed in water.

True density analysis of a freeze-dried amorphous sugar matrix.

True density of an amorphous matrix represents the state of molecular packing in the matrix, which is closely related to the physical/chemical properties of the material. Dry gas pycnometry is one possible technique for measuring the true density of an amorphous sugar matrix prepared by freeze-drying. We herein report on the influence of conditions used for pycnometry on the measured density value and propose a protocol for obtaining the true density. The technique is sufficiently accurate to permit values for matrices comprised of different types of sugar to be compared. Using the protocol, the true densities of several amorphous sugar samples containing different types of sugar, freeze-drying conditions (temperature and sugar concentration at the time of freezing of an aqueous sugar solution), pretreatment (compaction and grind) were determined and the results were compared. A model for simulating an amorphous matrix of sugar (trehalose) was constructed using molecular dynamics/mechanics calculations, and the true density of the simulated sugar matrix was found to agree with the value experimentally determined using the proposed protocol. The relationship among the true density, the states of intermolecular interactions, and strain of sugar molecules in the matrix are discussed using the simulated amorphous sugar matrix.

Characteristics of hydrogen bond formation between sugar and polymer in freeze-dried mixtures under different rehumidification conditions and its impact on the glass transition temperature.

The characteristics of hydrogen bond formation between trehalose and polyvinylpyrrolidone (PVP) in amorphous mixtures at different hydration states were quantitatively investigated. Amorphous trehalose-PVP mixtures were prepared by freeze-drying and equilibrated at different relative humidities (RH). Infrared (IR) spectra of the trehalose-PVP mixtures were obtained by Fourier transform IR spectroscopy,(FTIR) and the IR band corresponding to C=O groups of PVP was deconvolved into the component bands responsible for C=O groups that were free and restricted by hydrogen bonds, to estimate the degree of the trehalose-PVP interactions. The FTIR analysis indicated that approximately 80% of the C=O groups of PVP formed hydrogen bonds with trehalose in the presence of more than 3 g of trehalose per gramme of PVP, independent of the RH. IR analysis of the O--H stretching vibration of the sugar demonstrated that the presence of PVP lead to an increase in the free hydroxyl groups of trehalose that did not form hydrogen bonds at RH 0%. On the other hand, the water sorption behavior of the trehalose-PVP mixtures suggested that rehumidification diminished the effect of PVP on increasing the free OH groups. Thus a peculiar relationship may exist between Tg, RH and the composition of the mixture: The presence of PVP increased Tg at RHs 0 and above 23% but decreased Tg at 11%.