(S)-(−)-1-Phenyl­ethanaminium 4-(4,4-di­fluoro-1,3,5,7-tetra­methyl-3a,4a-diaza-4-borata-s-indacen-8-yl)benzoate

The title compound, C8H12N+·C20H18BF2N2O2 −, crystallizes with a significant amount of void space [4.0 (5)%] in the unit cell. The structure displays N—H⋯O hydrogen bonding between the components. The plane formed by the benzoic acid moiety of the BODIPY-CO2 − is twisted by 80.71 (6)° relative to the plane formed by the ring C and N atoms of the tetramethyldipyrrin portion of the molecule

The Gramicidin Dimer Shows Both EX1 and EX2 Mechanisms of H/D Exchange

We describe the use of H/D amide exchange and electrospray ionization mass spectrometry to study, in organic solvents, the pentadecapeptide gramicidin as a model for protein self association. In methanol-OD, all active H's in the peptide exchange for D within 5 min, indicating a monomer/dimer equilibrium that is shifted towards the fast-exchanging monomer. H/D exchange in n-propanol-OD, however, showed a partially protected gramicidin that slowly converts to a second species that exchanges nearly all the active hydrogens, indicating EX1 kinetics for the H/D exchange. We propose that this behavior is the result of the slower rate of unfolding in n-propanol compared with that in methanol. The rate constant for the unfolding of the dimer is the rate of disappearance of the partially protected species, and it agrees within a factor of two with a value reported in literature. The rate constant of dimer refolding can be determined from the ratio of the rate constant for unfolding and the affinity constant for the dimer, which we determined in an earlier study. The unfolding activation energy is 20 kcal mol−1, determined by performing the exchange experiments as a function of temperature. To study gramicidin in an even more hydrophobic medium than n-propanol, we measured its H/D exchange kinetics in a phospholipids vesicle and found a different H/D amide exchange behavior. Gramicidin is an unusual peptide dimer that can exhibit both EX1 and EX2 mechanisms for its H/D exchange, depending on the solvent

Self-reporting molecularly imprinted polymer with the covalently immobilized ferrocene redox probe for selective electrochemical sensing of p-synephrine

Article simultaneously imprinting the p-synephrine 1 template and covalently immobilizing a a ferrocene redox probe in a (bis-bithiophene)-based polymer. The resulting molecularly imprinted polymer (MIP) was deposited on the Pt electrode as a thin film to form a redox self-reporting MIP film-based chemosensor

Electrospray Ionization-Mass Spectrometry and Tandem Mass Spectrometry Reveal Self-Association and Metal-Ion Binding of Hydrophobic Peptides: A Study of the Gramicidin Dimer

Gramicidin is a membrane pentadecapeptide that acts as a channel, allowing the passage of monovalent metal ions and assisting in bacterial cell death. The active form is a noncovalently bound dimer. One means to study the self-assembly of this peptide has been to compare the state of the peptide in various solvents ranging from hydrophilic (e.g., trifluoroethanol) to hydrophobic (e.g., n-propanol). In this article, we report the use of electrospray mass spectrometry to study the self-association of gramicidin in various organic and mixed solvents that are introduced directly into the mass spectrometer. The dimer (both homo and hetero) can survive the introduction into the gas phase, and the amount in the gas phase increases with the decreasing dielectric constant of the solvent, reflecting solution-phase behavior. Tandem mass spectrometry data reveal that the stability of dimer in the gas phase decreases with increasing metal ion size, strongly suggesting that the metal ion binds inside the dimer between the monomers

A Molecular Light-Driven Water Oxidation Catalyst

Two mononuclear Ru­(II) complexes, [Ru­(ttbt)­(pynap)­(I)]­I and [Ru­(tpy)­(Mepy)₂(I)]I (tpy = 2,2′;6,2″-terpyridine; ttbt = 4,4′,4″-tri-<i>tert</i>-butyltpy; pynap = 2-(pyrid-2′-yl)-1,8-naphthyridine; and Mepy = 4-methylpyridine), are effective catalysts for the oxidation of water. This oxidation can be driven by a blue (λ_max = 472 nm) LED light source using [Ru­(bpy)₃]­Cl₂ (bpy = 2,2′-bipyridine) as the photosensitizer. Sodium persulfate acts as a sacrificial electron acceptor to oxidize the photosensitizer that in turn drives the catalysis. The presence of all four components, light, photosensitizer, sodium persulfate, and catalyst, are required for water oxidation. A dyad assembly has been prepared using a pyrazine-based linker to join a photosensitizer and catalyst moiety. Irradiation of this intramolecular system with blue light produces oxygen with a higher turnover number than the analogous intermolecular component system under the same conditions