Traveling-wave ion mobility mass spectrometry analysis of isomeric modified peptides arising from chemical cross-linking

Traveling-wave ion mobility (TWIM) coupled to mass spectrometry (MS) has emerged as a powerful tool for structural and conformational analysis of proteins and peptides, allowing the analysis of isomeric peptides (or proteins) with the same sequence but modified at different residues. This work demonstrates the use of the novel TWIM-MS technique to separate isomeric peptide ions derived from chemical cross-linking experiments, which enables the acquisition of distinct product ion spectra for each isomer, clearly indicating modification on different sites. Experiments were performed with four synthetic peptides, for which variable degrees of mobility separation were achieved. In cases of partially overlapping mobility arrival time distributions (ATDs), extracting the ATDs of fragment ions belonging to each individual isomer allowed their separation into two distinct ATDs. Accumulation over regions from the specific ATDs generates the product ion spectrum of each isomer, or a spectrum highly enriched in their fragments. The population of both modified peptide isomers was correlated with the intrinsic reactivities of different Lys residues from reactions conducted at different pH conditions.     

Surface-enhanced Raman scattering on silver nanostructured films prepared by spray-deposition

Silver nanostructured films were directly prepared by spray deposition of preformed polyol-based Ag-PVP nanoparticles. These homogeneous films of high optical quality were tested as SERS-active substrates. Laser excitation at 514.5 nm within the red part of the plasmon band leads to intense and reproducible SERS spectra of acridine, used as the probe molecule. From SERS measurements at different pH values, it was possible to determine the apparent pK(a) of acridine and to obtain specific surface properties of the film. Finally, these SERS titrations along with enhancement factor estimates allowed us to further depict the nature of the films.     

Assessment of surfactant adsorption in oil-based magnetic colloids

We describe in this paper different and complementary experimental methods for assessing the adsorption of surfactants on metal particles in oil-based suspensions. Two different kinds of particles are dispersed in mineral oil: iron microparticles and CoNi nanoparticles. The adsorption of oleic acid in the Fe/oil interface in diluted suspensions can be determined by obtaining the adsorption isotherm. In addition, we present a method based on the time evolution of the optical absorbance of suspensions, from which the existence of adsorption can be inferred. For concentrated suspensions, the used of optical methods is not recommended, since they are affected by a significant inaccuracy. We present here a useful alternative based on electromagnetic induction phenomena. The results obtained allow a more comprehensive knowledge of the aggregation process in concentrated suspensions. With the same purpose, a third group of experiments, based on rheological techniques, is carried out in Fe/oil and CoNi/oil concentrated suspensions. In these series of experiments, the effect of three surfactants (oleic acid, aluminum stearate and lecithin) is tested by measuring either the viscosity, or the magnetic field-induced yield stress of the suspensions. The combination of these series of experiments gives us valuable information about the most appropriate surfactant/carrier combination capable of imparting a high stability and a strong magnetorheological response in magnetic colloids.     

Copointed Hopf algebras over S4

We study the realizations of certain braided vector spaces of rack type as Yetter–Drinfeld modules over a cosemisimple Hopf algebra H. We apply the strategy developed in [1] to compute their liftings and use these results to obtain the classification of finite-dimensional copointed Hopf algebras over ${\mathbb{S}}_4$.     

Iodine(III)-Promoted Intermolecular Diamination of Alkenes

A rapid and productive vicinal diamination of alkenes takes place in the presence of a hypervalent iodine(III) reagent and bissulfonimides as nitrogen sources. A total of more than 60 examples are presented. The reaction is characterized by its robustness and its wide substrate scope: it proceeds selectively with both terminal and internal alkenes and tolerates a range of functional groups.     

Approaching the Kinetic Inertness of Macrocyclic Gadolinium(III)‐Based MRI Contrast Agents with Highly Rigid Open‐Chain Derivatives

A highly rigid open‐chain octadentate ligand (H₄cddadpa) containing a diaminocylohexane unit to replace the ethylenediamine bridge of 6,6′‐[(ethane‐1,2 diylbis{(carboxymethyl)azanediyl})bis(methylene)]dipicolinic acid (H₄octapa) was synthesized. This structural modification improves the thermodynamic stability of the Gd³⁺ complex slightly (log K_GdL=20.68 vs. 20.23 for [Gd(octapa)]^?) while other MRI‐relevant parameters remain unaffected (one coordinated water molecule; relaxivity r₁=5.73 mm ^?1 s^?1 at 20 MHz and 295 K). Kinetic inertness is improved by the rigidifying effect of the diaminocylohexane unit in the ligand skeleton (half‐life of dissociation for physiological conditions is 6 orders of magnitude higher for [Gd(cddadpa)]^? (t_1/2=1.49×10⁵ h) than for [Gd(octapa)]^?. The kinetic inertness of this novel chelate is superior by 2–3 orders of magnitude compared to non‐macrocyclic MRI contrast agents approved for clinical use.