Correlation between the shape of the ion mobility signals and the stepwise folding process of polylactide ions

In the field of polymer characterization, the use of ion mobility mass spectrometry (IMMS) remains mainly devoted to the temporal separation of cationized oligomers according to their charge states, molecular masses and macromolecular architectures in order to probe the presence of different structures. When analyzing multiply charged polymer ions by IMMS, the most striking feature is the observation of breaking points in the evolution of the average collision cross sections with the number of monomer units. Those breaking points are associated to the folding of the polymer chain around the cationizing agents. Here, we scrutinize the shape of the arrival time distribution (ATD) of polylactide ions and associate the broadening as well as the loss of symmetry of the ATD signals to the coexistence of different populations of ions attributed to the transition from opened to folded stable structures. The observation of distinct distributions reveals the absence of folded/extended structure interconversion on the ion mobility time scale (1-10 ms) and then on the lifetime of ions within the mass spectrometer at room temperature. In order to obtain information on the possible interconversion between the different observed populations upon ion activation, we performed IM-IM-MS experiments (tandem ion mobility measurements). To do so, mobility-selected ions were activated by collisions before a second mobility measurement. Interestingly, the conversion by collisional activation from a globular structure into a (partially) extended structure, i.e. the gas phase unfolding of the ions, was not observed in the energetic regime available with the used experimental setup. The absence of folded/extended interconversion, even upon collisional activation, points to the fact that the polylactide ions are 'frozen' in their specific 3D structure during the desolvation/ionization electrospray processes. Copyright © 2017 John Wiley & Sons, Ltd.

Unique alternating peptide–peptoid copolymers from dipeptides via a Ugi reaction in water

Unprecedented alternating poly(peptide-alt-peptoid) copolymers are prepared in a single step from dipeptides, aldehydes and isocyanidesviaa Ugi reaction in water.

The influence of the end-group on the chiral self-assembly of all-conjugated block copolymers

This research demonstrates the influence of the end-group on the self-assembly of conjugated polymers.

Two ruthenium complexes capable of storing multiple electrons on a single ligand – photophysical, photochemical and electrochemical properties of [Ru(phen)2(TAPHAT)]2+ and [Ru(phen)2(TAPHAT)Ru(phen)2]4+

The photophysical, photochemical and electrochemical properties of two newly synthesized ruthenium(ii) complexes are reported.

Letter: OCCO*+, NNCO*+ and NNNN*+ radical cations

Chemical ionization of a mixture of nitrogen and carbon monoxide produces three stable isobaric species at m/z 56: OCCO, OCNN and NNNN radical cations. Separated at increased resolution, these ions are readily identified by collisional activation. Neutralization-reionization experiments performed on two different mass spectrometers have not allowed the detection of any recovery signals for the corresponding neutrals.

New experiments on HNCSe and HCNSe radical cations

Dissociative ionization of the selenourea Se=C(NH(2))(2) (2) conveniently generates beams of pure isocyanoselenic acid radical cations. The HNCSe(.+) connectivity is established by collisional activation and by associative ion-molecule reactions with dimethyl sulfide or nitric oxide using a large-scale hybrid mass spectrometer.

High-energy collisional activation of the molecular ions of thiophene-2-one with different target gases

Collisional activation of keV thiophene-2-one radical cations 1(+*) with O(2) or NO(*) as the target gas leads to a desulfuration reaction. This peculiar reaction is insignificant or absent with other targets such as helium, argon, methane or nitrogen. The radical cations produced in this desulfuration reaction are most probably vinylketene ions, as indicated by a triple mass spectrometric (MS/MS/MS) experiment performed on a 'hybrid' tandem mass spectrometer of sector--quadrupole--sector configuration. Tentatively, it is proposed that population of an excited state accounts for the non-ergodic behavior of 1(+*) upon collision with oxygen or nitric oxide. Ab initio molecular orbital calculations using molecular orbital theory (UMP2, UCCSD(T)) and density functional theory (B3LYP) with 6--31G(d,p) and 6--311++G(d,p) basis sets were used to evaluate the relative energy of the excited quartet state of 1(+*) radical cations. This quartet state is calculated to lie about 3.6 eV above the (2)A(") ground state and 0.9 eV above the C(4)H(4)O(+*)+S dissociation products. It is proposed that the quartet ion serves as the precursor for the spontaneous desulfuration.

Mass spectrometric studies of elusive molecules that contain an N(+)-X- bond

This review will be concerned with the gas phase chemistry of 1,2- and 1,3-dipolar systems that contain a carbon-nitrogen bond. Although most of these compounds are stable molecules under normal conditions, certain congeners are reactive species that cannot be prepared using conventional procedures. The isolation and observation of these elusive compounds therefore require appropriate experimental conditions such as those provided by the gas phase of a mass spectrometer. In these experiments, the radical cations, corresponding to the molecule under study, must be prepared via indirect procedures, including dissociative electron ionization, on-line flash-vacuum pyrolysis-mass spectrometry, or ion-molecule reactions. Their characterization is mainly based on collisional activation and ion-molecule reactions. The formation of the corresponding highly reactive neutrals is attempted by neutralization-reionization mass spectrometry. This review presents more than one hundred different molecules together with their methods of preparation and the experiment used to identify them.

Characterization of ionized heterocyclic carbenes by ion-molecule reactions

1,2-Hydrogen shift isomers of ionized pyridine, thiazole and imidazole are readily characterized by the study of their associative ion-molecule reactions with dimethyl disulfide in the quadrupole collision cell of a new hybrid sector-quadrupole-sector mass spectrometer. Efficient trapping reactions of CH(3)S(.) radicals are indeed observed and the actual structure of the adduct [M + CH(3)S](+) ions is clearly indicated by their high-energy collisional activation mass spectra. These trapping reactions are not observed for the 'conventional' pyridine, thiazole and imidazole molecular ions, which only react by charge exchange producing m/z 94, [CH(3)SSCH(3)](*+), ions.