Homolytic reactions of polyfluoroaromatic compounds. X. Biphenylyl radicals in the thermolysis of aroyl peroxides in polyfluoroaromatic solvents

The thermolyses of a number of aroyl peroxides in hexafluorobenzene, and of benzoyl peroxide in octafluorotoluene, gave the corresponding biaryls which were isolated by steam distillation. Mass spectrometry of the residues showed evidence of biphenylyl radicals arising from the arylation of the peroxides themselves or, possibly, of the derived aroic acids. Terphenyls, and the corresponding σ-intermediate radicals, could be found, and the relative molecular masses of the latter components showed that subsequent arylation of the main binuclear products was not the main source of terphenyls.     

A dimerization "switch" in the internalization mechanism of a cell-penetrating peptide

The internalization mechanism of a cell-penetrating peptide has been explored through combinatorial selection of a phage-displayed peptide dimer library, chemical synthesis, and biophysical characterization. Both energy-dependent and energy-independent modes for peptide uptake by the target mammalian cells were observed, suggesting a role for higher-order structure in modulating the action of this novel cell-penetrating peptide.     

Unprecedented chemistry of an aryloxychlorodiazirine: generation of a dihalodiazirine and diazirinone

The reaction of p-nitrophenoxychlorodiazirine with tetrabutylammonium fluoride follows three channels: (1) approximately 17% of p-nitrophenoxide/fluoride exchange to chlorofluorodiazirine and p-nitrophenol, (2) approximately 28% of Cl/F exchange to p-nitrophenoxyfluorodiazirine, and (3) approximately 55% of ipso fluoride attack, affording p-nitrofluorobenzene and the previously unknown diazirinone (diazacyclopropenone).     

Theoretical analysis of the 13C NMR of iodoalkynes upon complexation with Lewis bases

Recent experiments have demonstrated that the (13)C NMR spectra of iodoalkynes exhibit a strong solvent effect because of complexation with Lewis-basic solvents. This paper describes DFT NMR calculations (B3LYP-GIAO with LanL2DZ or Sadlej pVTZ basis set) of iodoalkynes and their Lewis acid-base complexes, interpreted by using Natural Chemical Shift (NCS) analysis within the framework of the Ramsey formalism for chemical shift. In particular, the paper presents calculations on diiodoethyne and its complexes with one and two ammonia molecules. Examination of the orbital changes upon forming the mono- and bisammonia complexes indicates that mixing of the nitrogen lone pair with the C-I antibonding orbital increases the paramagnetic deshielding at C1. Further increases can be attributed to increased polarization of the iodine lone-pair orbitals onto C1. The haloiodoalkyne series XCCI (X = F, Cl, Br, I) offers additional support for this model of the solvent effect.