Acetyl-L-carnitine normalizes the impaired long-term potentiation and spine density in a rat model of global ischemia.

As a consequence of an ischemic episode, energy production is disturbed, leading to neuronal cell death. Despite intensive research, the quest for promising neuroprotective drugs has largely failed, not only because of ineffectiveness, but also because of serious side-effects and dosing difficulties. Acetyl-l-carnitine (ALC) is an essential nutrient which plays a key role in energy metabolism by transporting fatty acids into mitochondria for ß-oxidation. It is an endogenous compound and can be used at high dose without toxicity in research into ischemia. Its neuroprotective properties have been reported in many studies, but its potential action on long-term potentiation (LTP) and dendritic spine density has not been described to date. The aim of the present study was an evaluation of the possible protective effect of ALC after ischemic insults inflicted on hippocampal synaptic plasticity in a 2-vessel occlusion (2VO) model in rats. For electrophysiological measurements, LTP was tested on hippocampal slices. The Golgi-Cox staining technique was used to determine spine density. 2VO resulted in a decreased, unstable LTP and a significant loss of dendritic spines. ALC administered after 2VO was not protective, but as pretreatment prior to 2VO it restored LTP nearly to the control level. This finding paralleled the histological analysis: ALC pretreatment resulted in the reappearance of dendritic spines on the CA1 pyramidal cells. Our data demonstrate that ALC administration can restore hippocampal function and spine density. ALC probably acts by enhancing the aerobic metabolic pathway, which is inhibited during and following ischemic attacks.

Post-ischemic treatment with L-kynurenine sulfate exacerbates neuronal damage after transient middle cerebral artery occlusion.

Since brain ischemia is one of the leading causes of adult disability and death, neuroprotection of the ischemic brain is of particular importance. Acute neuroprotective strategies usually have the aim of suppressing glutamate excitotoxicity and an excessive N-methyl-d-aspartate (NMDA) receptor function. Clinically tolerated antagonists should antagonize an excessive NMDA receptor function without compromising the normal synaptic function. Kynurenic acid (KYNA) an endogenous metabolite of the tryptophan metabolism, may be an attractive neuroprotectant in this regard. The manipulation of brain KYNA levels was earlier found to effectively enhance the histopathological outcome of experimental ischemic/hypoxic states. The present investigation of the neuroprotective capacity of L-kynurenine sulfate (L-KYNs) administered systemically after reperfusion in a novel distal middle cerebral artery occlusion (dMCAO) model of focal ischemia/reperfusion revealed that in contrast with earlier results, treatment with L-KYNs worsened the histopathological outcome of dMCAO. This contradictory result indicates that post-ischemic treatment with L-KYNs may be harmful.

Fundamental interstrain differences in cortical activity between Wistar and Sprague-Dawley rats during global ischemia.

Four-vessel occlusion (4VO), a frequently used model of global cerebral ischemia in rats, results in a dysfunction in wide brain areas, including the cerebral cortex and hippocampus. However, there are pronounced differences in response to global ischemia between the laboratory rat strains used in these studies. In the present work, the immediate acute effects of 4VO-induced global ischemia on the spontaneous electrocorticogram (ECoG) signals were analyzed in Wistar and Sprague-Dawley rats. The ECoG was isoelectric during the 10 min of global cerebral ischemia in Wistar rats and the first burst (FB) was seen 10-13 min after the start of reperfusion. In Sprague-Dawley rats, the FB was detected immediately after the start of 4VO or a few seconds later. The burst suppression ratio (BSR) in Wistar rats decreased to 45% in 5 min after FB, and after 25 min it was approximately 40%. In Sprague-Dawley rats, the BSR was 55% immediately after the FB and it decreased steeply to reach 0% by 10 min. There was also a significant difference between the two strains in the frequency composition of the ECoG pattern. The power spectral densities of the two strains differed virtually throughout the post-ischemic state. The histological results (Evans Blue, Cresyl Violet and Fluoro Jade C stainings) supplemented the electrophysiological data: the neuronal damage in the CA1 pyramids in Wistar rats was severe, whereas in the Sprague-Dawley animals it was only partial. These observations clearly demonstrate that the use of different rat strains (e.g. Wistar vs. Sprague-Dawley) can be a source of considerable variability in the results of acute experiments on global ischemia and it is important that the laboratory rats used in such experiments should be carefully chosen.

Ab initio study of the structures and stabilities of the dimer of ethyl cation, (C(2)H(+)(5))(2) and related C(4)H(10)(2+) isomers.

Ab initio calculations at the MP4(SDTQ)/6-311G//MP2/6-31G level were performed to study the structures and stabilities of the dimer of ethyl cation, (C(2)H(+)(5))(2), and related C(4)H(10)(2+) isomers. Two doubly hydrogen bridged diborane type trans 1 and cis 2 isomers were located as minima. The trans isomer was found to be more favorable than cis isomer by only 0.6 kcal/mol. Several other minima for C(4)H(10)(2+) were also located. However, the global energy minimum corresponds to C-H (C(4) position) protonated 2-butyl cation 10. Structure 10 was computed to be substantially more stable than 1 by 31.7 kcal/mol. The structure 10 was found to be lower in energy than 2-butyl cation 13 by 34.4 kcal/mol.

Acid-catalyzed isomerization of pivalaldehyde to methyl isopropyl ketone via a reactive protosolvated carboxonium ion intermediate.

Quantitative rearrangement of pivalaldehyde to methyl isopropyl ketone is observed in acids such as trifluoromethanesulfonic acid, anhydrous HF, and trifluoroethyl alcohol-BF3 but not in trifluoroacetic acid. Studies in a mixture of trifluoroacetic acid and trifluoromethanesulfonic acid show that acids with H(o) < or = -11 are able to carry out complete isomerization. These results and density functional theory calculations at the B3LYP/6-31G level suggest that protonated pivalaldehyde undergoes further protosolvation at higher acidities to a reactive superelectrophilic species resulting in rearrangement. A mechanism for the pivalaldehyde rearrangement to methyl isopropyl ketone in strong protic acids involving a reactive protosolvated superelectrophilic intermediate is suggested. Aspects of the related mechanism of the reaction with isobutane with CO in HF/BF3 medium leading to methyl isopropyl ketone are also discussed.

Asymmetric synthesis of trifluoromethylated allylic amines using alpha,beta-unsaturated N-tert-butanesulfinimines.

[reaction: see text]. The trifluoromethide ion generated in situ from TMSCF(3) and TBAT (tetrabutylammonium triphenyldifluorosilicate), as well as TMAF (tetramethylammonium fluoride), adds to the alpha,beta-unsaturated N-tert-butanesulfinimines exclusively in a 1,2 fashion with high diastereoselectivities, affording the first examples of chiral trifluoromethylated allylic amines.

N6(2+) and N4(2+) dications and their n(12) and n(10) azido derivatives: DFT/GIAO-MP2 theoretical studies.

The structures and energies of N(6)(2+) and N(4)(2+) were calculated by using the density functional theory method at the B3LYP/cc-aug-pVTZ level. The C(2)(h)() symmetric form 1 and D(infinity)(h) form 5 were found to be the stable minima for N(6)(2+) and N(4)(2+), respectively. Dissociation of 1 into 5 and N(2) was computed to be endothermic by 25.1 kcal/mol. (15)N NMR chemical shifts and vibrational frequencies of 1 and 5 were also calculated. Interactions of 1 and 5 with azide ions were also probed representing N(12) and N(10).

Gitonic and distonic alkanonium dications (diprotonated alkane dications C(n)H(2n+4(2+)), n = 1-4)(1).

The structures and stabilities of gitonic and distonic alkanonium dications, i.e., diprotonated alkane dications C(n)H(2n+4)(2+) (n = 1-4), were investigated at the MP4(SDTQ)/6-311G**//MP2/6-31G** level. The global minimum energy structures (2, 4, 7, and 10) of the C(n)H(2n+4)(2+) dications are double C--H protonated alkanes to give structures with two two electron three-center (2e-3c) bonds. Two different dissociation pathways for the dications, viz deprotonation and demethylation, were also computed. Demethylation was found to be the favorable mode of dissociation.

Nafion-H catalysed sulfonylation of aromatics with arene/alkenesulfonic acids for the preparation of sulfones1a.

Synthesis of both symmetric and unsymmetric diaryl/aryl alkyl sulfones is easily achieved by Friedel-Crafts type sulfonylation of aromatics with suitable arene- or alkane-sulfonic acids in the presence of Nafion-H, a perfluorinated resinsulfonic acid catalyst.

Poly(p-hydroxystyrene) grafted polystyrene nanospheres: excellent hosts for silver and ruthenium nanoparticles.

A novel approach is described for the preparation of surface functionalized micro- and nanobeads using one pot synthesis by a core-shell method. Monodisperse poly(p-hydroxystyrene) is successfully prepared by grafting the p-acetoxystyrene monomer during the last 30 min of the fabrication of polystyrene bead core by emulsifier-free emulsion polymerization followed by hydrolysis of the acetoxy group by a base. The size of the resulting beads is dictated mostly by the size of the core. Hydroxyl derivatized polystyrene microspheres have been found useful as a high surface area and stable support for anchoring catalytically active silver and ruthenium nanoparticles. The bead formation, surface functionalization, and coating with metal nanoparticles have been studied using scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectrometry, Fourier transform infrared spectrometry, and Auger analysis.

A facile stereocontrolled synthesis of anti-alpha-(trifluoromethyl)-beta-amino alcohols.

A short stereocontrolled preparation of anti-alpha-(trifluoromethyl)-beta-amino alcohols is described, involving an initial CF(3) transfer to cinnamaldehyde and a one-step, three-component condensation of 3,3,3-trifluorolactic aldehyde, an alkenyl (aryl) boronic acid, and an amine. Applying this methodology to chiral 3,3,3-trifluorolactic aldehyde allowed us to generate an amino alcohol enantioselectively in 92% ee.

Protonated and methylated dimethyl sulfoxide cations and dications. DFT/GIAO-MP2 NMR studies and comparison with experimental data.

Energies, electronic structures, and thermodynamics of protonated and methylated dimethyl sulfoxide (DMSO) cations and dications were calculated using the density functional theory (DFT) method. The O-protonated structure 2 was found to be 37.0 kcal/mol more stable than the S-protonated 3. For diprotonated DMSO dication, the O, O-diprotonated form 6 was found to be the global minimum, more stable by 20.8 kcal/mol than O,S-diprotonated 7. Interestingly, for dimethylated DMSO dication, O,O-dimethylated 11 and O,S-dimethylated 12 are isoenergetic. (13)C, (17)O, and (33)S NMR chemical shifts of the cations and dications were calculated using the GIAO-MP2 method and compared with the available experimental data.

Mutagenicity studies of methyl-tert-butylether using the Ames tester strain TA102.

Methyl-tert-butylether (MTBE) is an oxygenate widely used in the United States as a motor vehicle fuel additive to reduce emissions and as an octane booster [National Research Council, Toxicological and Performance Aspects of Oxygenated Motor Vehicle Fules, National Academy Press, Washington, DC, 1996]. But it is the potential for MTBE to enter drinking water supplies that has become an area of public concern. MTBE has been shown to induce liver and kidney tumors in rodents but the biochemical process leading to carcinogenesis is unknown. MTBE was previously shown to be non-mutagenic in the standard Ames plate incorporation test with tester strains that detect frame shift (TA98) and point mutations (TA100) and in a suspension assay using TA104, a strain that detects oxidative damage, suggesting a non-genotoxic mechanism accounts for its carcinogenic potential. These strains are deficient in excision repair due to deletion of the uvrB gene. We hypothesized that the carcinogenic activity of MTBE may be dependent upon a functional excision repair system that attempts to remove alkyl adducts and/or oxidative base damage caused by direct interaction of MTBE with DNA or by its metabolites, formaldehyde and tert-butyl alcohol (TBA), established carcinogens that are mutagenic in some Ames strains. To test our hypothesis, the genotoxicity of MTBE-induced DNA alterations was assayed using the standard Ames test with TA102, a strain similar to TA104 in the damage it detects but uvrB + and, therefore, excision repair proficient. The assay was performed (1) with and without Aroclor-induced rat S-9, (2) with and without the addition of formaldehyde dehydrogenase (FDH), and (3) with human S-9 homogenate. MTBE was weakly mutagenic when tested directly and moderately mutagenic with S-9 activation producing between 80 and 200 TA102 revertants/mg of compound. Mutagenicity was inhibited 25%-30% by FDH. TA102 revertants were also induced by TBA and by MTBE when human S-9 was substituted for rat S-9. We conclude that MTBE and its metabolites induce a mutagenic pathway involving oxidation of DNA bases and an intact repair system. These data are significant in view of the controversy surrounding public safety and the environmental release of MTBE and similar fuel additives.

Electrochemical preparation of tris(tert-butyldimethylsilyl)cyclopropene and its hydride abstraction to tris(tert-butyldimethylsilyl)cyclopropenium tetrafluoroborate.

Electrochemical reductive tert-butyldimethylsilylation of tetrachlorocyclopropene to 1,2,3-tris(tert-butyldimethylsilyl)cyclopropene, a potential strained precursor for Diels-Alder and related cycloaddition reactions, is described. By hydride abstraction with nitrosonium tetrafluoroborate, 1,2,3-tris(tert-butyldimethylsilyl)cyclopropene is ionized quantitatively to Hückeloid 2pi aromatic tris(tert-butyldimethylsilyl)cyclopropenium tetrafluoroborate.

Helionitronium trication (NO2He3+) and helionitrosonium trication (HeNO3+).

The structures and stabilities of helionitronium trication NO2He3+ and helionitrosonium trication HeNO3+ were calculated at the ab initio MP2/6-31G** level. The Cs symmetry structure was found to be a minimum for the NO2He3+ trication, which is isoelectronic and isostructural with the previously studied NO2H2+. Dissociation of the Cs symmetry structure into NO+ and OHe2+ is thermodynamically preferred by 183.1 kcal/mol (1 cal = 4.18 J), although a kinetic barrier of 12.4 kcal/mol has to be overcome. The Cinfinityv symmetry structure was also found to be a minimum for the HeNO3+ trication.

Structural changes measured by X-ray scattering from human flap endonuclease-1 complexed with Mg2+ and flap DNA substrate.

Human flap endonuclease-1 (FEN-1) is a member of the structure-specific endonuclease family and is essential in DNA replication and repair. FEN-1 has specific endonuclease activity for repairing nicked double-stranded DNA substrates that have the 5'-end of the nick expanded into a single-stranded tail, and it is involved in processing Okazaki fragments during DNA replication. Magnesium is a cofactor required for nuclease activity. We used small-angle x-ray scattering to obtain global structural information pertinent to nuclease activity from FEN-1, the D181A mutant, the wild-type FEN-1. 34-mer DNA flap complex, and the D181A.34-mer DNA flap complex. The D181A mutant, which has Asp-181 replaced by Ala, selectively binds to the flap structure, but has lost its cleaving activity. Asp-181 is thought to be involved in Mg2+ binding at the active site (Shen, B., Nolan, J. P., Sklar, L. A., and Park, M. S. (1996) J. Biol. Chem. 271, 9173-9176). Our data indicate that FEN-1 and the D181A mutant each have a radius of gyration of approximately 26 A, and the effect of Mg2+ on the scattering from the proteins alone is insignificant. The 34-mer DNA fragment was constructed such that it readily forms a 5'-flap structure. The formation of the flap conformation of the DNA substrate was evident by both the extrapolated Io scattering and radius of gyration and was supported by NMR spectrum and nuclease assays. In the absence of magnesium, the FEN-1.34-mer DNA flap complex has an Rg value of approximately 34 A, whereas the D181A.34-mer DNA flap complex self-associates, suggesting that a significant protein conformational change occurs by addition of the flap DNA substrate and that Asp-181 is crucial for proper binding of the protein to the DNA substrate. A time course change in the scattering profiles arising from magnesium activation of the FEN-1.34-mer DNA flap complex is consistent with the protein completely releasing the DNA substrate after cleavage.