The reaction of PCl3 with SnCl2 in THF solution, followed by treatment with dpp-BIAN (dpp = 2,6-i-Pr2C6H3), affords the phosphenium complex [(dpp-BIAN)P][SnCl5.THF]. The 31P chemical shift (delta 232.5) and the metrical parameters from a single-crystal X-ray diffraction study indicate that the oxidation state of phosphorus in this compound is +3. A similar conclusion was reached regarding the phosphorus oxidation state in [(dpp-BIAN)P][I3], which was prepared via the reaction of dpp-BIAN with PI3 in CH2Cl2 solution. The arsenium salt [(dpp-BIAN)As][SnCl5.THF] was prepared by treatment of AsCl3 with SnCl2 in THF solution, followed by the addition of dpp-BIAN. The X-ray crystal structure of this salt was determined, and the pattern of bond distances and angles indicates that arsenic is present in the +3 oxidation state.

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New data indicate that the NMR data originally presented were not correctly interpreted because the critical samples were contaminated by an impurity. The TROSY NMR spectrum presented in the original Figure 1 exhibited over 250 peaks, which were interpreted as arising from the human vasopressin V2 receptor (V2R). We recently purified two other G proteincoupled receptors using the same expression/purification procedure originally used for V2R and observed the presence of a common set of peaks in the TROSY NMR spectra from both the new receptors and V2R. These peaks arise from one or more impurities that were present in the samples for all three receptors. As described in the new Supporting Information, we have reoptimized purification of V2R to yield protein of much higher purity ( Figure S2) and have re-acquired a TROSY spectrum ( Figure S3). About two-thirds of the peaks observed in the original Figure 1 are no longer observed. The number of bona fide V2R peaks is roughly 80, all of which were present in the original Figure 1, but are absent in the spectra (not shown) of the other receptors. The tentative NMR resonance assignments presented in the original Figure 2 were reasonable on the basis of peak connectivity patterns, chemical shifts, V2R sequence, and our assumption that they arose from pure protein, but they are now shown to be incorrect. The contaminant protein(s) present in the original samples failed to be observed in control samples prepared from cells in which a blank plasmid was used instead of a vector encoding V2R, most likely because this protein is expressed at NMR-detectable levels only in response to the stress induced by expressing the human receptors in Escherichia coli. We sincerely apologize for our errors in the interpretation of the original data. Supporting Information Available:Further details about the expression and purification of V2R. This information is available free of charge via the Internet at http://pubs.acs.org.

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