The structure of fluid trifluoromethane and methylfluoride

We present hard X-ray and neutron diffraction measurements on the polar fluorocarbons HCF3 and H3CF under supercritical conditions and for a range of molecular densities spanning about a factor of ten. The Levesque-Weiss-Reatto inversion scheme has been used to deduce the site-site potentials underlying the measured partial pair distribution functions. The orientational correlations between adjacent fluorocarbon molecules -- which are characterized by quite large dipole moments but no tendency to form hydrogen bonds -- are small compared to a highly polar system like fluid hydrogen chloride. In fact, the orientational correlations in HCF3 and H3CF are found to be nearly as small as those of fluid CF4, a fluorocarbon with no dipole moment.Comment: 11 pages, 9 figure

Neonatal presentation of ventricular tachycardia and a Reye-like syndrome episode associated with disturbed mitochondrial energy metabolism

BACKGROUND: Hyperammonemia, hypoglycemia, hepatopathy, and ventricular tachycardia are common presenting features of carnitine-acylcarnitine translocase deficiency (Mendelian Inheritance in Man database: *212138), a mitochondrial fatty acid oxidation disorder with a lethal prognosis. These features have not been identified as the presenting features of mitochondrial cytopathy in the neonatal period. CASE PRESENTATION: We describe an atypical presentation of mitochondrial cytopathy in a 2 day-old neonate. She presented with a Reye-like syndrome episode, premature ventricular contractions and ventricular tachycardia. Initial laboratory evaluation exhibited a large amount of 3-methylglutaconic acid on urine organic acid analysis, mild orotic aciduria and a nonspecific abnormal acylcarnitine profile. The evaluation for carnitine-acylcarnitine translocase deficiency and other fatty acid oxidation disorders was negative. The patient later developed a hypertrophic cardiomyopathy and continued to be affected by recurrent Reye-like syndrome episodes triggered by infections. A muscle biopsy exhibited signs of a mitochondrial cytopathy. During the course of her disease, her Reye-like syndrome episodes have subsided; however, cardiomyopathy has persisted along with fatigue and exercise intolerance. CONCLUSIONS: This case illustrates that, in the neonatal period, hyperammonemia and ventricular tachycardia may be the presenting features of a lethal carnitine-acylcarnitine translocase deficiency or of a mitochondrial cytopathy, associated with a milder clinical course. This association broadens the spectrum of presenting phenotypes observed in patients with disturbed mitochondrial energy metabolism. Also, the presence of 3-methylglutaconic aciduria suggests mitochondrial dysfunction and mild orotic aciduria could potentially be used as a marker of mitochondrial disease

The 3-methylglutaconic acidurias: what’s new?

The heterogeneous group of 3-methylglutaconic aciduria (3-MGA-uria) syndromes includes several inborn errors of metabolism biochemically characterized by increased urinary excretion of 3-methylglutaconic acid. Five distinct types have been recognized: 3-methylglutaconic aciduria type I is an inborn error of leucine catabolism; the additional four types all affect mitochondrial function through different pathomechanisms. We provide an overview of the expanding clinical spectrum of the 3-MGA-uria types and provide the newest insights into the underlying pathomechanisms. A diagnostic approach to the patient with 3-MGA-uria is presented, and we search for the connection between urinary 3-MGA excretion and mitochondrial dysfunction

Effects of solidification of the oil phase on the structure of colloidal dispersions in cyclohexane

The liquid-to-solid transition of the alkane-continuous phase of a dilute surfactant-stabilized particle or droplet dispersion can be induced in a reversible manner without destabilizing the colloid by pressure and/or temperature changes. The structural changes have been studied by small-angle neutron scattering (SANS) over a range of pressure (1-600 bar) and temperatures (3-20-degrees-C). The SANS results indicate that there are different levels of structure in the solidified system in which a solid alkane coexists with fluid cluster domains. The clusters show large-scale structural correlations of order 5-50 mum; within these clusters the particles are in close contact, so that under certain conditions, e.g. high pressure, the stabilizing surfactant layers of adjacent particles are interdigitated. The distance between particle centers, and therefore the degree of surfactant interdigitation, can be readily varied by the application of pressure. An interpretation of the SANS results is given in terms of the effects of temperature and pressure upon the osmotic pressure of the concentrated solution of particles/droplets. The analysis provides an estimate of the interparticle pair potential energy between adjacent particles in a cluster as a function of separation

Measurement of inter-particle forces from the osmotic pressure of partially frozen dispersions

When an oil-continuous dispersion is frozen two microdomains are formed: one, the pure oil solvent which is selectively solidified (I), the other, a concentrated 'liquid' dispersion of particles in oil (II). These two domains are intimately mixed within the frozen colloid and exist in a state of equilibrium determined by the system pressure and temperature. The position of equilibrium controls the proportion of the solvent which is solidified, and thereby the concentration of particles within the fluid microdomains (II). Combined with SANS measurements, to determine the inter-particle separation in these microdomains, an analysis based on osmotic pressure provides a measure of the inter-particle repulsion forces presented by the surfactant layers