It is now well known that peripheral nerves are a target for the action of neuroactive steroids. This review summarizes observations obtained so far, indicating that through the interaction with classical and nonclassical steroid receptors, neuroactive steroids (e.g., progesterone, testosterone and their derivatives, estrogens, etc.) are able to influence several parameters of the peripheral nervous system, particularly its glial compartment (i.e., Schwann cells). Interestingly, some of these neuroactive steroids might be considered as promising neuroprotective agents. They are able to counteract neurodegenerative events of rat peripheral nerves occurring after experimental physical trauma, during the aging process, or in hereditary demyelinating diseases. On this basis, the hypothesis that neuroactive steroids might represent a new therapeutic strategy for peripheral neuropathy is proposed.

Neuroactive steroids: A therapeutic approach to maintain peripheral nerve integrity during neurodegenerative events.

Shiverer (shi/shi) is an autosomal recessive mouse mutation that produces a shivering phenotype in affected mice. A shivering gait can be seen from a few weeks after birth until their early death, which occurs between 50 and 100 days. The central nervous system of the mutant mouse is hypomyelinated but the peripheral nervous system appears normal. The myelin of the CNS, wherever present, is not well compacted and lacks the major dense line. Myelin basic protein (MBP), which is associated with the major dense line, is absent, and this is due to a deletion of the major part of the gene encoding MBP. Transgenic shiverer mice that have integrated and express the wild-type mouse MBP transgene no longer shiver and have normal life spans. Conversely, normal mice that have integrated an antisense MBP transgene, shiver. Myelin deficient shimld/shimld is allelic to shiverer (shi/shi) but the mutant mouse is less severely affected. Although MBP is present in the CNS, it is low in quantity and is not developmentally regulated. The gene encoding MBP has been both duplicated and inverted. Transgenic shimld/shimld mice with the wild-type MBP transgene have normal phenotypes.

The dysmyelinating mouse mutations shiverer (shi) and myelin deficient (shimld).

Two unimolecular dissociation reactions of formic acid have been investigated theoretically. The decarboxylation reaction yields molecular hydrogen and carbon dioxide, while the dehydration reaction produces water and carbon monoxide. The 1,2‐hydrogen shift rearrangement from formic acid to dihydroxymethylene has also been considered. Methods ranged from double zeta plus polarization self‐consistent field to triple zeta plus double polarization coupled cluster singles and doubles. For certain key structures, the coupled cluster method including single, double, and linearized triple excitations (CCSDT‐1) was applied as well with the double zeta plus polarization basis set. A barrier height of ∼71 kcal mol−1 with zero point vibrational energy correction is predicted for the dissociation to molecular hydrogen and carbon dioxide. A rather comparable value of ∼68 kcal mol−1 is predicted for the barrier to the dehydration reaction. The 1,2‐hydrogen shift transition state is somewhat higher in energy at ∼79 kcal...

The decarboxylation and dehydration reactions of monomeric formic acid

The initial steps involved in the thermal decomposition of formic acid in the temperature range of 1370–2000 K have been investigated by monitoring the IR emission intensities at 3.4 and 4.6 μm, corresponding to the reactant and carbon monoxide, respectively, behind reflected shock waves in mixtures diluted in Ar (0.1–1.5 mol%, total densities 5.3×10−6–3.2×10−5 mol cm−3). It was found that the decomposition proceeded via channel (1) HCOOH+Ar→CO+H2O+Ar dominantly and the contribution of channel (2) HCOOH+Ar→CO2+H2+Ar was very small. An Arrhenius expression of the second order rate constant was obtained as k1,0 =1014.32  exp(−40.4 kcal mol−1/RT) cm3 mol−1 s−1. Ab initio calculations were performed for probable transition states (TS) of channels (1) and (2). The results showed that the potential energy for a TS of channel (1) was lower than that of channel (2) by 20–30 kcal mol−1. On the basis of a RRKM weak collision, k2,0 values were estimated which was smaller than k1,0 by about two orders, being consistent with the experimental results.

Thermal unimolecular decomposition of formic acid

Primary dissociation pathways have been investigated for formic acid by ab initio molecular orbital methods. Reactant, transition state, and products were fully optimized with unrestricted Hartree–Fock and unrestricted second‐order Mo/ller–Plesset wave functions. The activation energy for decarboxylation of formic acid (CO2+H2) is 65.2 kcal mol−1, while that for the dehydration process (CO+H2O) is 63.0 kcal mol−1. These theoretical results suggest that the decarboxylation and dehydration processes are competitive. The activation energy barrier for isomerization of formic acid to yield dihydroxymethylene is 73.7 kcal mol−1 and may be a competitive process. Free radical initiation processes are predicted to be minor.

http://wwwuser.gwdg.de/~ggroenh/assignments/JChemPhys_96_1167.pdf

A comprehensive theoretical examination of primary dissociation pathways of formic acid

We report the isotopically selective decomposition of chlorodifluoromethane. Chlorodifluoromethane is used industrially in high volume for the production of tetrafluoroethylene and its polymers; thereby it is an attractive working substrate for a medium scale isotope separation process, both in terms of its price and availability. We have studied the infrared multiphoton decomposition of carbon-13 substituted chlorodifluoromethane molecules present at their natural abundance (1.11%). A well defined CO2 laser pulse (80 ns FWHM) was used and both the yield of carbon-13 enriched product and the net absorption of laser radiation were measured. These measurements were made as a function of substrate pressure (10-800 Torr), CO2 laser line (9P 12–9P 32) and fluence (2–8 J cm−2) and were used to determine the energy expenditure per carbon atom produced (e) at specified product carbon-13 content in the range 30%–96%. The results of these parametric studies were interpreted in terms of the kinetics of multiphoton absorption and dissociation, and allowed an initial optimization of the experimental conditions to minimize e. Optimum results were obtained at 1046.9 cm−1, 69 cm−1 to the red of the12CHClF2
v
9 band center. Irradiation of 100 Torr of chlorodifluoromethane at 3.5 J cm−2 gave tetrafluoroethylene containing 50% carbon-13 for an absorption of 140 photons (0.017 keV) per carbon atom produced. This efficiency compares favourably with existing carbon-13 enrichment technologies and would require an absorption pathlength of only 2 m to absorb half the incident photons.

Efficient production of 13 C 2 F 4 in the infrared laser photolysis of CHClF 2

Enrichment of carbon-13 in the products of the multiphoton dissociation of cf3x compounds

Isotopically selective multiphoton decomposition of CF3Br and CF3I: separation of selective and non-selective product sources☆

The yield and isotopic selectivity of the infrared multiphoton induced decomposition of hexafluoroacetone have been studied in both parallel and focused beam geometries as a function of temperature, pressure, fluence, and photolysing wavelength. At low conversions, the chemical stoichiometry of the decomposition process is simple, CF3COCF3    nhν    CO + 2CF3. Several potential interferences are discussed but it is concluded that the yield of CO directly reflects the yield of the primary dissociation event. Pressure effects are complex and not amenable to quantitative description, however, varying parameters such as fluence and photolysing wavelength lead to predictions which give a clear qualitative picture. In particular, it is possible to distinguish parametric variations due to spontaneous dissociation and dissociation dependent upon energy pooling. Isotopic selectivity provides a powerful insight in this area. Preliminary data on the effect of temperature have been obtained at constant incident fluen...

Multiphoton decomposition of hexafluoroacetone: Effects of pressure, fluence, wavelength, and temperature on the decomposition yield and C‐13 and O‐18 isotopic selectivity

C. Willis

Papers

Efficient production of 13 C 2 F 4 in the infrared laser photolysis of CHClF 2

Enrichment of carbon-13 in the products of the multiphoton dissociation of cf3x compounds

Isotopically selective multiphoton decomposition of CF3Br and CF3I: separation of selective and non-selective product sources☆

Multiphoton decomposition of hexafluoroacetone: Effects of pressure, fluence, wavelength, and temperature on the decomposition yield and C‐13 and O‐18 isotopic selectivity

The decomposition of formic acid vapor by infrared radiation from a pulsed HF-laser