Modeling of negative Poisson’s ratio (auxetic) crystalline cellulose Iβ

Energy minimizations for unstretched and stretched cellulose models using an all-atom empirical force field (Molecular Mechanics) have been performed to investigate the mechanism for auxetic (negative Poisson’s ratio) response in crystalline cellulose Iβ from kraft cooked Norway spruce. An initial investigation to identify an appropriate force field led to a study of the structure and elastic constants from models employing the CVFF force field. Negative values of on-axis Poisson’s ratios nu31 and nu13 in the x1-x3 plane containing the chain direction (x3) were realized in energy minimizations employing a stress perpendicular to the hydrogen-bonded cellobiose sheets to simulate swelling in this direction due to the kraft cooking process. Energy minimizations of structural evolution due to stretching along the x3 chain direction of the ‘swollen’ (kraft cooked) model identified chain rotation about the chain axis combined with inextensible secondary bonds as the most likely mechanism for auxetic response

UV-photoconversion of ethosuximide from a longevity-promoting compound to a potent toxin

The anticonvulsant ethosuximide has been previously shown to increase life span and promote healthspan in the nematode Caenorhabditis elegans at millimolar concentrations. Here we report that following exposure to ultraviolet irradiation at 254 nm, ethosuximide is converted into a compound that displays toxicity toward C. elegans. This effect is specific for ethosuximide, as the structurally related compounds trimethadione and succinimide do not show similar toxicities following UV exposure. Killing by UV-irradiated ethosuximide is not attenuated in chemosensory mutants that are resistant to toxicity associated with high doses of non-irradiated ethosuximide. Non-irradiated ethosuximide extends life span at 15°C or 20°C, but not at 25°C, while irradiated ethosuximide shows similar toxicity at all three temperatures. Dietary restriction by bacterial deprivation does not protect against toxicity from irradiated ethosuximide, while non-irradiated ethosuximide further extends the long life spans of restricted animals. These data support the model that ethosuximide extends life span by a mechanism that is, at least partially, distinct from dietary restriction by bacterial deprivation and demonstrates an unexpected photochemical conversion of ethosuximide into a toxic compound by UV light. © 2013 Choi et al

Practical Porous Matrix for Molecular Structure Determination of General Liquid Chemicals

A practical porous crystalline matrix for molecular structure determination of a wide range of liquid chemicals has been set up. We herein report proof-of-concept research on the temperature-dependent single-crystal-to-single-crystal (SCSC) guest exchange of the <i>P</i>- and <i>M</i>-helix-enantiomeric multilayered ensemble with flexible open-channels of the shortest diameter, 4.4 × 4.4 Ų. This landmark ensemble is, to the best of our knowledge, the most efficient, practical, tolerant, and reproducible porous matrix for single crystal structure determination of general liquid compounds via easy SCSC guest exchange without any desolvation process. The innovative channel behaves in a guest-dependent flexible response manner and enables scientists to solve structures of a wide range of liquid chemicals. This paper reports the molecular structures of 41 liquid chemicals including chiral and natural compounds via guest exchange at >75% success rate

Duration of UV treatment of ethosuximide affects toxicity, absorption spectrum, and longevity of <i>C. elegans</i>.

<p>(<b>A</b>) Ethosuximide was exposed to UV-light (254nm) for varying lengths of time. L4 worms were transferred to Amp/FUDR plates containing UV-treated ethosuximide added topically to a final concentration of 10 mM and were scored for life span. Increased length of UV-exposure, led to an increased toxicity, as measured by a shortened life span. (<b>B</b>) Ethosuximide was exposed to UV light for various lengths of time (shown in graph legend). An absorption spectrum over the ranges of 220nm to 400nm was collected for the untreated and UV-treated ethosuximide solutions. (<b>C</b>) Ethosuximide delays development in wild-type (N2) worms. Eggs were transferred to NGM plates with topical addition of water (control), 30 mM ethosuximide, or 30 mM UV-irradiated ethosuximide at 20°C. The developmental stage of each worm was determined after 1, 2, 4 and 6 days as L1/L2, L3 and L4 larvae and young adult/egg-laying adult nematodes. Data from two experiments (3 independent plates each experiment) were pooled.</p

Ethosuximide treatment without UV-exposure extends the adult life span in <i>C. elegans</i> in a temperature-dependent manner.

<p>NGM containing 10-type (N2) animals at (<b>A</b>) 15°C and (<b>B</b>) 20°C, but not at (<b>C</b>) 25°C. Irradiated ethosuximide showed similar toxicity at all three temperatures. (<b>D</b>) Dietary restriction further extended the life span of ethosuximide-treated worms, but failed to rescue the short life span of UV-ethosuximide treated worms.</p

Statistics for life span data presented in this study.

<p> The notation (UV) indicates that the ethosuximide was exposed to UV light and BD indicates that the animals were maintained in the absence of bacterial food during adulthood until death. Conc., concentration; Etho, Ethosuximide; N, number of worms in the experiment; BD, bacterial deprivation by removal of the bacterial food source during adulthood.</p><p>*p<0.05. p-values compare the experimental group with the control group of the upper row. Significant vales </p