Azide trapping shows that the 4'-substituted-4-biphenylyloxenium ions 1b-d are generated during hydrolysis of 4-aryl-4-acetoxy-2,5-cyclohexadienones, 2c and 2d, and O-(4-aryl)phenyl-N-methanesulfonylhydroxylamines, 3b and 3c. In addition, the 4'-bromo-substituted ester, 2d, undergoes a kinetically second-order reaction with N3- that accounts for a fraction of the azide adduct, 5d. Since both first-order and second-order azide trapping occurs simultaneously in 2d, the second-order reaction is not enforced by the short lifetime of 1d, which has similar azide/solvent selectivity to the unsubstituted ion, 1a. In contrast the 4'-CN and 4'-NO2 ions 1e and 1f cannot be detected by azide trapping during the hydrolysis of the dichloroacetic acid esters 2e' and 2f' even though 18O labeling experiments show that a fraction of the hydrolysis of both esters occurs through C(alkyl)-O bond cleavage. These esters exhibit only second-order trapping by azide. Correlations of the azide/solvent selectivities of 1a-d with the calculated relative driving force for hydration of the ions (DeltaE of eq 4) determined at the pBP/DN//HF/6-31G and BP/6-31G//HF/6-31G levels of theory suggest that 1e and 1f have lifetimes in the 1-100 ps range. Ions with these short lifetimes are not in diffusional equilibrium with nonsolvent nucleophiles, and must be trapped by such nucleophiles via a preassociation mechanism. The second-order trapping that is observed in these two cases is enforced by the short lifetime of the cations, and may occur by a concerted S(N)2' mechanism or by internal azide trapping of an ion sandwich produced by azide-assisted ionization. Comparison of azide/solvent selectivities of the oxenium ions 1a-c with the corresponding biphenylylnitrenium ions 8a-c shows that 4'-substituent effects on reactivity in both sets of ions are similar in magnitude, although the nitrenium ions are ca. 30-fold more stable in an aqueous environment than the corresponding oxenium ions. The magnitude of the 4'-substituent effects for electron-donating substituents suggest that both sets of ions are more accurately described as 4-aryl-1-imino-2,5-cyclohexadienyl or 4-aryl-1-oxo-2,5-cyclohexadienyl carbocations. Calculated structures of the oxenium ions are also consistent with this interpretation.

Various surgical techniques and pharmaceutical treatments have been developed to improve the current technologies of treating brain diseases. Focused ultrasound (FUS) is a new brain stimulation modality that can exert a therapeutic effect on diseased brain cells, with this effect ranging from permanent ablation of the pathological neural circuit to transient excitatory/inhibitory modulation of the neural activity depending on the acoustic energy of choice. With the development of intraoperative imaging technology, FUS has become a clinically available noninvasive neurosurgical option with visual feedback. Over the past 10 years, FUS has shown enormous potential. It can deliver acoustic energy through the physical barrier of the brain and eliminate abnormal brain cells to treat patients with Parkinson's disease and essential tremor. In addition, FUS can help introduce potentially beneficial therapeutics at the exact brain region where they need to be, bypassing the brain's function barrier, which can be applied for a wide range of central nervous system disorders. In this review, we introduce the current FDA-approved clinical applications of FUS, ranging from thermal ablation to blood barrier opening, as well as the emerging applications of FUS in the context of pain control, epilepsy, and neuromodulation. We also discuss the expansion of future applications and challenges. Broadening FUS technologies requires a deep understanding of the effect of ultrasound when targeting various brain structures in diverse disease conditions in the context of skull interface, anatomical structure inside the brain, and pathology.

Pancreatic surgeons will see an increasing number of patients with Roux-en-Y anatomy who will require evaluation and resection for periampullary diseases. For PD after RYGB, we recommend remnant gastrectomy with reconstruction using the BP limb.

Objective: Describe magnetic resonance imaging (MRI) susceptibility changes in progressive multifocal leukoencephalopathy (PML) and identify neuropathological correlates. Methods: PML cases and matched controls with primary central nervous system lymphoma (PCNSL) were retrospectively identified. MRI brain at 3 T and 7 T were reviewed. MRI-pathology correlations in fixed brain autopsy tissue were conducted in three subjects with confirmed PML. Results: With PML ( n = 26 total, n = 5 multiple sclerosis natalizumab-associated), juxtacortical changes on susceptibility-weighted imaging (SWI) or gradient echo (GRE) sequences were noted in 3/3 cases on 7 T MRI and 14/22 cases (63.6%) on 1.5 T or 8/22 (36.4%) 3 T MRI. Similar findings were only noted in 3/25 (12.0%) of PCNSL patients (odds ratio (OR) 12.83, 95% confidence interval (CI), 2.9–56.7, p < 0.001) on 1.5 or 3 T MRI. On susceptibility sequences available prior to diagnosis of PML, 7 (87.5%) had changes present on average 2.7 ± 1.8 months (mean ± SD) prior to diagnosis. Postmortem 7 T MRI showed SWI changes corresponded to areas of increased iron density along the gray–white matter (GM-WM) junction predominantly in macrophages. Conclusion: Susceptibility changes in PML along the GM-WM junction can precede noticeable fluid-attenuated inversion recovery (FLAIR) changes and correlates with iron accumulation in macrophages.