Molecular Dynamics at the Interface between Ice and Poly(vinyl alcohol) and Ice Recrystallization Inhibition

Ice formation is a ubiquitous process that poses serious challenges for many areas. Nature has evolved a variety of different mechanisms to regulate ice formation. For example, many cold-adapted species produce antifreeze proteins (AFPs) and/or antifreeze glycoproteins (AFGPs) to inhibit ice recrystallization. Although several synthetic substitutes for AF­(G)­Ps have been developed, the fundamental principles of designing AF­(G)P mimics are still missing. In this study, we explored the molecular dynamics of ice recrystallization inhibition (IRI) by poly­(vinyl alcohol) (PVA), a well-recognized ice recrystallization inhibitor, to shed light on the otherwise hidden ice-binding mechanisms of chain polymers. Our molecular dynamics simulations revealed a stereoscopic, geometrical match between the hydroxyl groups of PVA and the water molecules of ice, and provided microscopic evidence of the adsorption of PVA to both the basal and prism faces of ice and the incorporation of short-chain PVA into the ice lattice. The length of PVA, i.e., the number of hydroxyl groups, seems to be a key factor dictating the performance of IRI, as the PVA molecule must be large enough to prevent the joining together of adjacent curvatures in the ice front. The findings in this study will help pave the path for addressing a pressing challenge in designing synthetic ice recrystallization inhibitors rationally, by enriching our mechanistic understanding of IRI process by macromolecules

Trellis graph of dotplots.

<p>Each row corresponds to a storage temperature and each column to a developmental transition. It shows the effect of storage time on the percent of arrested embryos conditioned on stage (developmental transition point) and temperature. The stages, across the columns of graphs, are: 3/4 cells, 3/4–5/8 cells, 5/8 cells – morula, morula – blastocysts. Percent arrested: percent of embryos that arrested at the next stage of development.</p

The distribution of embryos at various stages of development 5 days following ICSI using sperm dried with 100 mmol/L 3-OMG for 6 minutes and stored in LiCl jars for different time at 4°C and 22°C.

<p>Probability that the patterns of development are the same in all drying conditions: 4°C, P<10⁻⁵; 22°C, P<10⁻⁵ (Exact Jonckheere-Terpstra Test).</p

The estimated parameters and their confidence limits (P = 0.95) of the logistic regressions (b and a) fitted to the data from storage at 4 °C and ambient temperature.

<p>The table also includes the estimated parameters from a logistic regression fitted to the data from storage at 4°C reported in a previous paper <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099809#pone.0099809-Li1" target="_blank">[10]</a>.</p><p>*The regression coefficient was transformed to convert the independent variable from weeks to months.</p

Fertilization rate using sperm dried in the Na-EGTA solution with and without 100 mmol/L 3-OMG and stored in LiCl jars at 4°C for 1 and 3 months.

a<p>Percent of survived oocytes developed to two-cell embryos.</p><p>Probability that the fertilization rates are the same in all drying conditions = 0.0004 (Exact Fisher test).</p

Number of oocytes survived injection and number of survived oocytes developed to two-cell embryos following ICSI using sperm dried with 100 mmol/L 3-OMG for 6 minutes and stored in LiCl jars for 1 to 12 months at 4°C and 22°C.

a<p>Percent of survived oocytes developed to two-cell embryos.</p><p>Probability that the patterns of development are the same in all drying conditions: 4°C, P = 0.276; 22°C, P = 0.061 (Exact Fisher Test).</p

Mice produced by ICSI.

<p>Mice produced from sperm dried with 100 mmol/L 3-OMG for 6 minutes and stored in LiCl jars at 4°C for one year.</p

Regressions of the percent blastocyst on time of storage.

<p>Computed by transformation of the following logit responses on storage time to percentages, where p is the proportion of blastocysts: 4°C: logit(p) = −0.108 t+0.3338 22°C: logit(p) = −0.514 t−0.247.</p

The embryo transfer results for evaporatively dried sperm stored at ambient temperature for 12 to 24 months.

<p>The embryo transfer results for evaporatively dried sperm stored at ambient temperature for 12 to 24 months.</p

Moisture content and trehalose concentration.

<p>Moisture content of the samples was positively correlated with the concentration of trehalose. Error bars on Y axis indicate standard deviations.</p