Non-exponential relaxation, fictive temperatures, and dispersive kinetics in the liquid-glass-liquid transition range of acetaminophen, sulfathiazole, and their mixtures

To investigate the effects of added molecular heterogeneity on the hysteretic features of liquid-glass-liquid transition, we studied acetaminophen, sulfathiazole, and three of their mixtures by calorimetry, and determined the T(g) and the fictive temperature, T(f), from changes in the enthalpy and entropy on the cooling and heating paths, as well as the non-exponential parameter, β(cal). We find that, (i) T(f) for cooling is within 1-3 K of T(f) for heating and both are close to T(g), (ii) the closed loop entropy change in the liquid-glass-liquid range is negligibly small, (iii) T(g) and T(f) increase on increasing sulfathiazole in the mixture, (iv) β(cal) first slightly increases when the second component is added and then decreases, and (v) ageing causes deviations from a non-exponential, nonlinear behavior of the glass. In terms of fluctuations in a potential energy landscape, adding a solute heterogeneity would shift the state point to another part of the landscape with a different distribution of barrier heights and a different number of minima accessible to the state point. Part of the change in β(cal) is attributed to hydrogen-bond formation between the two components. Ageing changes the relaxation times distribution, more at short relaxation times than at long relaxation times, and multiplicity of relaxation modes implied by β(cal) < 1 indicates that each mode contributing to the enthalpy has its own T(g) or T(f). β(cal) differs from β(age) determined from isothermal ageing, and the distribution parameter of α-relaxation times would differ from both β(cal) and β(age).

Effects of 2 nm size added heterogeneity on non-exponential dielectric response, and the dynamic heterogeneity view of molecular liquids

To investigate how non-exponential response could vary under different conditions, we studied the effects of adding 2 nm size polyhedral oligomeric silsesquioxane (POSS) to diglycidyl ether of bisphenol-A, whose molecules have the same terminal (epoxide) dipoles as the tentacle-like side chains attached to the silsesquioxane core of the POSS molecule. Dielectric relaxation spectra show that, on initial addition, the POSS nano-heterogeneity decreases the non-exponential response parameter β, which is consistent with the dynamic heterogeneity view, but it also decreases the relaxation time τ(m), which is inconsistent with that view. The variations in β and τ(m) with the composition have a thermal equivalence. Despite the lack of translational diffusion required for dynamic heterogeneity, plastic crystals show non-exponential response and non-Arrhenius dynamics. Measurements of β and τ(m) seem more appropriate than using probe molecules or modeling nonlinear response data as a sum of linear responses for testing the dynamic heterogeneity view. Data on molecular liquid mixtures is not generally consistent with this view, and adding a solute does not always decrease β. Studies of mixtures of different size rigid molecules with identical dipolar groups, including polymers, may be useful for comparing the relative effects of temperature and molecular size on β and τ(m).

[Early diagnosis and treatment of cytomegalovirus polyradiculoneuritis in a child infected by HIV]

BACKGROUND

Axonal polyradiculopathy due to cytomegalovirus (CMV) in AIDS has been reported in adults but it is not well documented in children.

OBJECTIVE

We describe the elements of diagnosis and the outcome after anti-CMV therapy in a pediatric case.

CASE REPORT

A 11-year-old boy with post-transfusional AIDS and low CD4 count (< 50/mm3) suffered from bilateral leg pain and weakness progressing within 15 days to paraplegia and cauda equina syndrome. Electromyography showed pure axonal neuropathy. Examination of the CSF showed increased proteins, low glucose concentration, neutrophilic pleiocytosis and positive detection of CMV by polymerase-chain reaction. The CMV viremia was positive. Treatment with ganciclovir and foscarnet allowed dramatical clinical improvement. Retinitis occurred during the maintenance therapy and was cured after reintroduction of the initial doses of ganciclovir and foscarnet. The child died five months later from a bacterial pneumopathy.

CONCLUSIONS

Children with advanced AIDS may benefit from early recognition and treatment of CMV polyradiculopathy. The interactions and cumulated toxicities between anti-CMV and anti-retroviral drugs must be considered. The prognosis remains poor for CMV neuropathy due to the severe immunodepression caused by the HIV infection.

Tetralogy of Fallot with pulmonary atresia in siblings

We present two sisters with tetralogy of Fallot and pulmonary valve atresia. Both had identical anatomical findings as seen at cardiac catheterization and angiography and verified operatively, with, in particular, identical bronchial circulation and pulmonary valve structure. The parents are first cousins and there is no history of other affected relatives. We suggest that this is a specific, recessively inherited type of tetralogy of Fallot.