Pathologic Finding of Thymic Carcinoma Accompanied by Myasthenia Gravis.

BACKGROUND AND PURPOSE: The World Health Organization (WHO) has classified thymic carcinoma and other thymomas (types A, AB, and B) as different neoplasms. Myasthenia gravis (MG) is an early sign of thymoma and theoretically does not accompany thymic carcinoma; however, cases of thymic carcinoma with MG have been reported. Whether thymic carcinoma can accompany MG has yet to be established. METHODS: The medical records of patients who underwent thymectomy for MG between 1990 and 2011 in a single hospital were reviewed. All cases with the diagnostic code of "thymic carcinoma" or "thymoma type C" (old terminology) were selected. A pathologist re-reviewed the pathologic specimens using the new WHO criteria. The rate of thymic carcinoma among these MG patients was then calculated. RESULTS: A total of 81 patients with MG had thymic tumors, 10 of whom had thymic carcinomas or thymoma type C. Seven cases of well-differentiated thymic carcinomas (type B3) were excluded, leaving three (3.7%) cases of thymic carcinoma with MG. All three of these cases were type B3 thymoma with a focal squamous cell carcinoma component that was very small and well demarcated. In addition, two out of the three tumors were found to be at an early clinical stage. All of the cases survived without recurrence over follow-up periods of at least 5 years. CONCLUSIONS: Thymic carcinoma transformation from thymoma can occur during the early stages of thymoma. The association of this condition with MG is not as rare as was previously thought. Thymic carcinomas accompanying MG had a predominant B3 thymoma component with a focal thymic carcinoma area (squamous cell carcinoma).

SN2 fluorination reactions in ionic liquids: a mechanistic study towards solvent engineering.

In the catalysis of S(N)2 fluorination reactions, the ionic liquid anion plays a key role as a Lewis base by binding to the counterion Cs(+) and thereby reducing the retarding Coulombic influence of Cs(+) on the nucleophile F(-). The reaction rates also depend critically on the structures of ionic liquid cation, for example, n-butyl imidazolium gives no S(N)2 products, whereas n-butylmethyl imidazolium works well. The origin of the observed phenomenal synergetic effects by the ionic liquid [mim-(t)OH][OMs], in which t-butanol is bonded covalently to the cation [mim], is that the t-butanol moiety binds to the leaving group of the substrate, moderating the retarding interactions between the acidic hydrogen and F(-). This work is a significant step toward designing and engineering solvents for promoting specific chemical reactions.

Ab initio and DFT studies of the thermal rearrangement of trimethylsilyl(methyl)silylene: remarkable rearrangements of silicon intermediates.

A reaction scheme for the rearrangement of trimethylsilyl(methyl)silylene (Me3Si-Si-Me) discovered in a pioneering work of organosilicon chemistry (Wulff et al., J Am Chem Soc 1978, 100, 6236) was studied by the MP2 and DFT methods. We report a thermal reaction scheme for the rearrangement of Me3Si-Si-Me with the structures and energies of various silicon species along the isomerization paths, that can account for the experimentally found product ratio. The experimental product ratio is in good agreement with the theoretical one derived from the Gibbs free energy changes calculated in the present study.

A mechanistic study of S(N)2 reaction in a diol solvent.

We present calculations for the mechanism of S(N)2 reactions in ethylene glycol, focusing on the role of two protic functional groups (-OH) in the solvent molecule. We find that some hydroxyl groups act as Lewis base to interact with the cation, whereas others affect the reaction as Lewis acid to the nucleophile. We predict that the nucleophile (F-) reacts as an ion pair rather than as a solvent-separated ion when metal cation (Cs+) is used as a counterion. The overall influence of ethylene glycol manifests itself as the reaction barrier (E(double dagger) = 20.0, G(353K)(double dagger) = 21.5 kcal/mol) that is a bit smaller than that in tert-butyl alcohol, which proved to be a very efficient solvent for S(N)2 reactions [Kim, D. W., et al. J. Am. Chem. Soc. 2006, 128, 16394]. We therefore show that a small protic solvent such as ethylene glycol may be as efficient as a bulky alcohol for S(N)2 reactions.

Arginine zwitterion is more stable than the canonical form when solvated by a water molecule.

We present calculations for the Arg-H2O system and predict that the zwitterionic Arg is thermodynamically more stable than the canonical form in the gas phase under the influence of a single water molecule because of the strongly basic guanidine side chain. Canonical conformers of Arg-H2O are found to isomerize to the zwitterionic forms via a small barrier (approximately 6 kcal/mol).

Fluoroquinolone resistance and gyrA and parC mutations of Escherichia coli isolated from chicken.

Escherichia coli is a common inhabitant of the intestinal tracts of animals and humans. The intestines of animals also represent an ideal environment for the selection and transfer of antimicrobial resistance genes. The aim of this study was to investigate the resistance of E. coli isolated from chicken fecal samples to fluoroquinolones and to analyze the characterization of mutations in its gyrA and parC gene related resistance. One hundred and twenty-eight E. coil isolates showed a high resistance to ciprofloxacin (CIP; 60.2%), enrofloxacin (ENO; 73.4%) and norfloxacin (NOR; 60.2%). Missense mutation in gyrA was only found in the amino acid codons of Ser-83 or Asp-87. A high percentage of isolates (60.2%) showed mutations at both amino acid codons. Missense mutation in parC was found in the amino acid codon of Ser-80 or Glu-84, and seven isolates showed mutations at both amino acid codons. Isolates with a single mutation in gyrA showed minimal inhibitory concentrations (MIC) for CIP (