Cerebral Angiography Can Demonstrate Changes in Collateral Flow During Induced Hypertension

AbstractA 52-year-old woman with a large left-hemispheric stroke was transferred to our hospital for possible endovascular treatment. The patient underwent a cerebral angiogram at 7 hours after symptom onset with intent to treat and was found to have occlusion of the proximal M1-segment of the left middle cerebral artery (MCA). At that time it was felt that this was a high-risk patient for mechanical clot retrieval and it was decided to treat her with induced hypertension. The diagnostic catheter was left in place in the left internal carotid artery (ICA) and hypertension was induced in the angiography suite by means of an infusion of neosynephrine. Ten minutes after the goal blood pressure levels had been reached, a repeat left ICA injection was performed, which demonstrated more extensive collateralization of the MCA territory from anterior cerebral artery branches. Mean transit times (MTT) for the left ICA circulation improved from 9.5 seconds prior to induced hypertension to 6.0 seconds. The neosynephrine infusion was continued for a total of 24 hours and the patient showed neurological improvement. We suggest that induced hypertension led to the improved collateralization to the left MCA as evidenced by the improved MTT and augmentation of leptomeningeal collaterals, which in turn led to the patient's clinical improvement

Tuning Catalytic Selectivity: Zeolite- and Magnesium Oxide-Supported Molecular Rhodium Catalysts for Hydrogenation of 1,3-Butadiene

[EN] Regulation of the catalytic selectivity of rhodium for the industrially important hydrogenation of 1,3-butadiene to n-butenes has been achieved by controlling the structure of essentially molecular rhodium species bound to supports. The selectivity for n-butene formation increases as the nuclearity of the metal species decreases from several Rh atoms to one, but these catalysts form the undesired product n-butane, even at low diene conversions. The n-butene selectivity increases when the rhodium is selectively poisoned with CO ligands, and it is highest when the support is the electron-donor MgO and the rhodium is in the form of clusters that are well approximated as dimers. The electron-donor support is crucial for stabilization of the rhodium carbonyl dimer sites, as it limits the oxidative fragmentation of the clusters which is facilitated when the support is HY zeolite (a poor electron donor) that leads to decreased catalytic activity and selectivity. The selective MgO-supported rhodium carbonyl dimers suppress the catalytic routes that yield butane, limiting the activity for H-2 dissociation to avoid butane formation via primary reactions and also favoring the bonding of I,3-butadiene over butenes to limit secondary reactions giving butane. With this catalyst, selectivities to n-butene of >99% were achieved at 1,3-butadiene conversions as high as 97%. This selectivity matches that of any reported for this reaction, and the catalyst works under milder conditions (313 K and I bar) than others that are selective for this reaction.We thank the DOE Division of Materials Sciences for its role in the operation and development of beamline 4-1 at the Stanford Synchrotron Radiation Lightsource. We thank the beamline staff for valuable support. The research was supported by the European Union Seventh Framework Programme (FP7/2007- 2013) under grant agreement PIOF-GA-2009-253129 (P.S.) and by DOE Basic Energy Sciences (Contract No. FG02- 04ER15513) (D.Y.).Yardimce, D.; Serna Merino, PM.; Gates, BC. (2012). Tuning Catalytic Selectivity: Zeolite- and Magnesium Oxide-Supported Molecular Rhodium Catalysts for Hydrogenation of 1,3-Butadiene. ACS Catalysis. 2:2100-2113. https://doi.org/10.1021/cs300475cS21002113