Extended ab initio calculations on cyclopropane,cyclopropene and cyclopropenone

The three-membered ring systems, cyclopropane, cyclopropene and cyclopropenone, have been investigated using a (9,5,1 ) Gaussian basis set. A detailed study of the chemical binding in these systems has been of particular interest. Results for the molecular ground states have been compared with predictions made previously using smaller basis sets and also with pertinent experimental findings.     

Sleep disturbances in highly stress reactive mice: Modeling endophenotypes of major depression

Background  

Neuronal mechanisms underlying affective disorders such as major depression (MD) are still poorly understood. By selectively breeding mice for high (HR), intermediate (IR), or low (LR) reactivity of the hypothalamic-pituitary-adrenocortical (HPA) axis, we recently established a new genetic animal model of extremes in stress reactivity (SR). Studies characterizing this SR mouse model on the behavioral, endocrine, and neurobiological levels revealed several similarities with key endophenotypes observed in MD patients. HR mice were shown to have changes in rhythmicity and sleep measures such as rapid eye movement sleep (REMS) and non-REM sleep (NREMS) as well as in slow wave activity, indicative of reduced sleep efficacy and increased REMS. In the present study we were interested in how far a detailed spectral analysis of several electroencephalogram (EEG) parameters, including relevant frequency bands, could reveal further alterations of sleep architecture in this animal model. Eight adult males of each of the three breeding lines were equipped with epidural EEG and intramuscular electromyogram (EMG) electrodes. After recovery, EEG and EMG recordings were performed for two days.     

Ab initio calculations of the electronic structures of Dimethylnitrosamine (DMN) and its Metabolite Hydroxydimethylnitrosamine (HDMN): A possible intermediate in carcinogenesis by DMN

The structure of N,N'-dimethylnitrosamine (DMN) and its α-hydroxy derivative have been computed using the ab initio force method with a 4-21 basis set. The results are compared with experiment for DMN.     

Effects of lipopolysaccharide-induced inflammation on expression of growth-associated genes by corticospinal neurons

Background  

Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation.     

On the electronic and molecular structures of some fluoro-substituted cyclopropane derivatives

Ab initio calculations of double zeta quality have been carried out on cyclopropyl fluoride and 1,1-difluorocyclopropane. A partial geometry optimization has been carried out, and results have been compared to cyclopropane. An attempt is made to explain the differences in structure between cyclopropane and the fluorine derivatives.     

Ab initio calculations find 2,2-disilylcyclopentane-1,3-diyl is a singlet diradical with a high barrier to ring closure

Ab initio calculations on the lowest singlet and triplet states of 2,2-disilylcyclopentane-1,3-diyl find that the singlet lies well below the triplet. The C ₂ singlet diradical is calculated to be a minimum on the potential energy surface with an enthalpic barrier to ring closure of ΔH ^‡ ₂₉₈ = 13.5 kcal/mol at the CASPT2/6-31G* level of theory. The energy of the 1,3-divinyl-substituted singlet diradical is calculated to be only 0.8 kcal/mol higher than that of 5,5-disilyl-1,3-divinylbicyclo[2.1.0]pentane at this level of theory, but the transition state for their equilibration is computed to be 12.8 kcal/mol above the diradical in energy. Received: 2 July 1998 / Accepted: 4 August 1998 / Published online: 16 November 1998     

On the electronic and molecular structures of methyl chloride,cyclopropyl chloride and 1,1-dichlorocyclopropane

Ab initio SCF—MO calculations have been carried out on cyclopropyl chloride and 1,1-dichlorocyclopropane, to illuminate the effect of the substituent upon the cyclopropane ring. For cyclopropyl chloride, reasonable agreement is found with experimental findings. For 1,1-dichlorocyclopropane, excellent agreement is found with the results from a recent NMR study. As a means of studying the effect of a change in basis set, calculations are also carried out on methyl chloride.     

Contributions of resonance,hybridization, and nonbonded interactions to the structure of butadiene

The fully optimized geometries of four rotational conformers of butadiene have been calculated ab initio in order to investigate the relative importance of resonance, hydridization and nonbonded interactions. The results indicate that the short central CC bond is primarily due to hybridization, although resonance makes a minor contribution. The resonance stabilization of the planar conformers is responsible for the relatively large barrier to internal rotation, whereas the nonbonded interactions are only important in destabilizing the sterically crowded cis conformer.     

Vibrational force fields for strained hydrocarbons involving exo-double bonds. An ab initio study

Ab initio calculations of stretching force constants for the carbon-carbon double bond in a series of molecules characterized by different amounts of strain in the neighbourhood of the double bond were performed. The stretching force constants for bonds adjacent to the double bond have also been calculated as well as all relevant coupling terms. The variation in the force constant for the double bond is in agreement with the variations in bond distance predicted previously. Furthermore, it appears that the stretching force constants are linearly related to the product of s-character of the hybrids forming the bond in question, if other effects remain roughly constant. This seems to be the case in a series of studied molecules. It turns out that the strength of an exo-double bond is proportional to the amount of the angular strain inherent in the ring fragments attached to the double bond.     

Ab inttio structural analysis of some saturated 3- and 4-membered rings

Complete geometry optimizations of the ground states of ten 3- and 4-membered ring compounds have been carried out by ab initio SCF calculations using the gradient method at the 4–21 level. For sulfur, an optimized 3-3-21 basis has been constructed, and the importance of including d-functions is demonstrated. The main purpose of the study was to determine local orientations and geometries of the molecular CH₂-groups, information that is very difficult to obtain from experiment. A simple interaction model seems to account for the CH₂-group distortions in the 3-membered rings considered here, and also for similar structural deformations previously reported in a series of cyclopropyl derivatives.