A novel electrochemical method for efficient reduction of disulfide bonds in peptides and proteins prior to MS detection

A novel electrochemical (EC) method for fast and efficient reduction of the disulfide bonds in proteins and peptides is presented. The method does not use any chemical agents and is purely instrumental. To demonstrate the performance of the EC reactor cell online with electrospray mass spectrometry, insulin and somatostatin were used as model compounds. Efficient reduction is achieved in continuous infusion mode using an EC reactor cell with a titanium-based working electrode. Under optimized conditions, the presented method shows almost complete reduction of insulin and somatostatin. The method does not require any special sample preparation, and the EC reactor cell makes it suitable for automation. Online EC reduction followed by collision-induced dissociation fragmentation of somatostatin showed more backbone cleavages and improved sequence coverage. By adjusting the settings, the EC reaction efficiency was gradually changed from partial to full disulfide bonds reduction in α-lactalbumin, and the expected shift in charge state distribution has been demonstrated. The reduction can be controlled by adjusting the square-wave pulse, flow rate or mobile phase composition. We have shown the successful use of an EC reactor cell for fast and efficient reduction of disulfide bonds for online mass spectrometry of proteins and peptides. The possibility of online and gradual disulfide bond reduction adds a unique dimension to characterization of disulfide bonds in mid- and top-down proteomics applications.

Stopping Power of Charged Particles II

The stopping power and the stopping number, respectively, of charged particles are determined in the frame of the dielectric formalism in random phase approximation. The high and low velocity limits are disscussed. Numerical evalution is given for arbitrary masses of the projectile particle using a dielectric function ?(κ, ω) valid for all values of degeneracy. The connection with transport (e.g. electrical resistivity) is considered.     

The blocking number of an affine space

It is proved that the minimum cardinality of a subset of AG(k, q) which intersects all hyperplanes is k(q ? 1) + 1. In case k = 2 this settles a conjecture of J. Doyen.     

Infrared study of intercomponent interactions in a switchable hydrogen-bonded rotaxane

The macrocycle in rotaxane 1 is preferentially hydrogen bonded to the succinamide station in the neutral form, but can be moved to the naphthalimide station by one-electron reduction of the latter. The hydrogen bonding between the amide NH groups of the macrocycle and the C double bond O groups in the binding stations in the thread was studied with IR spectroscopy in different solvents in both states. In addition, the solvent effect on the vibrational frequencies was analyzed; a correlation with the solvent acceptor number (AN) was observed. The conformational switching upon reduction could be detected by monitoring the hydrogen-bond-induced shifts of the nu(CO) frequencies of the C double bond O groups of the succinamide and the reduced naphthalimide stations. The macrocycle was found to shield the encapsulated station from the solvent: wavenumbers of nu(CO) bands of the C double bond O groups residing inside the macrocycle cavity remain unaffected by the solvent polarity.     

NMR crystallography of p-tert-butylcalix[4]arene host-guest complexes using 1H complexation-induced chemical shifts

(1)H magic-angle spinning (MAS) NMR spectra of p-tert-butylcalix[4]arene inclusion compounds with toluene and pyridine show large complexation-induced shifts of the guest proton resonances arising from additional magnetic shielding caused by the aromatic rings of the cavities of the host calixarene lattice. In combination with ab initio calculations, these observations can be employed for NMR crystallography of host-guest complexes, providing important spatial information about the location of the guest molecules in the host cavities.     

Notes on simplicial rook graphs

The simplicial rook graph \(\mathrm{SR}(m,n)\) is the graph of which the vertices are the sequences of nonnegative integers of length m summing to n, where two such sequences are adjacent when they differ in precisely two places. We show that \(\mathrm{SR}(m,n)\) has integral eigenvalues, and smallest eigenvalue \(s = \max \left( -n, -{m \atopwithdelims ()2}\right) \), and that this graph has a large part of its spectrum in common with the Johnson graph \(J(m+n-1,n)\). We determine the automorphism group and several other properties.     

Fluorescent perylene diimide rotaxanes: spectroscopic signatures of wheel-chromophore interactions

[2]- and [3]-rotaxanes with a tetraphenoxy perylene diimide core were synthesized. Hydrogen bonding between the wheel and the imide changes the optical properties of the perylene chromophore: the absorption and fluorescence spectra are red-shifted. The decay times of the rotaxanes are shorter in comparison with that of the axle. Single molecule fluorescence measurements reveal relatively narrow distributions of emission maxima and decay times. The averages are in agreement with ensemble measurements. The observed red shifts make the perylene diimide a suitable chromophore for sensing the position of the wheel on the axle.     

Solvent tuning from normal to inverted marcus region of intramolecular electron transfer in ferrocene-based organic radicals

The solvent dependence of spectroscopic data of two neutral paramagnetic donor-acceptor dyads, based on a polychlorinated triphenylmethyl radical acceptor unit linked through a vinylene pi-bridge to a ferrocene (compound 1) or a nonamethylferrocene donor (compound 2) unit, is described. Both compounds exhibit broad absorptions in the near-IR region, with band maxima appearing around 1000 and 1500 nm for 1 and 2, respectively. These bands correspond to the excitation of a neutral DA ground state to the charge-separated D+A- state, indicative of an intramolecular electron-transfer process. Compounds 1 and 2 show two reversible one-electron redox processes associated with the oxidation of the ferrocene and the reduction of the polychlorotriphenylmethyl radical subunits. The solvent dependence of the redox potentials was also investigated, allowing the determination of the redox asymmetries DeltaG degrees of both dyads. The latter values, along with the experimental Eopt spectroscopic data, allow us to estimate, using the total energy balance Eopt = lambda + DeltaG degrees , the reorganization energy values, lambda, and their solvent polarity dependence. Since DeltaG degrees and lambda are of the same order of magnitude but exhibit opposite trends in their solvent polarity dependence, a unique shift from the normal to the inverted Marcus region with the change in solvent polarity is found. The kinetics of the charge recombination step of the excited charge-separated D+A- state was studied by picosecond transient absorption spectroscopy, which allows us to observe and monitor for the first time the charge-separated D+A- state, thereby confirming unambiguously the photoinduced electron-transfer phenomena.     

Direct demonstration of enhanced diffusion in mesoporous ZSM-5 zeolite obtained via controlled desilication

A 2 orders of magnitude gas transport improvement in a medium pore ZSM-5 zeolite has been achieved upon introduction of intracrystalline mesoporosity in gradient-free crystals by desilication post-treatment in alkaline medium.