Base-dependent electron photodetachment from negatively charged DNA strands upon 260-nm laser irradiation

DNA multiply charged anions stored in a quadrupole ion trap undergo one-photon electron ejection (oxidation) when subjected to laser irradiation at 260 nm (4.77 eV). Electron photodetachment is likely a fast process, given that photodetachment is able to compete with internal conversion or radiative relaxation to the ground state. The DNA [6-mer]3- ions studied here show a marked sequence dependence of electron photodetachment yield. Remarkably, the photodetachment yield (dG6 > dA6 > dC6 > dT6) is inversely correlated with the base ionization potentials (G < A < C < T). Sequences with guanine runs show increased photodetachment yield as the number of guanine increases, in line with the fact that positive holes are the most stable in guanine runs. This correlation between photodetachment yield and the stability of the base radical may be explained by tunneling of the electron through the repulsive Coulomb barrier. Theoretical calculations on dinucleotide monophosphates show that the HOMO and HOMO-1 orbitals are localized on the bases. The wavelength dependence of electron detachment yield was studied for dG63-. Maximum electron photodetachment is observed in the wavelength range corresponding to base absorption (260-270 nm). This demonstrates the feasibility of gas-phase UV spectroscopy on large DNA anions. The calculations and the wavelength dependence suggest that the electron photodetachment is initiated at the bases and not at the phosphates. This also indicates that, although direct photodetachment could also occur, autodetachment from excited states, presumably corresponding to base excitation, is the dominant process at 260 nm. Excited-state dynamics of large DNA strands still remains largely unexplored, and photo-oxidation studies on trapped DNA multiply charged anions can help in bridging the gap between gas-phase studies on isolated bases or base pairs and solution-phase studies on full DNA strands.     

Synthesis and characterization of cationic tungsten(V) methylidynes

Cationic tungsten(V) methylidynes [L4W(X)[triple bond]CH]+[B(C6F5)4]- [L = PMe3, 0.5dmpe (dmpe = Me2PCH2CH2PMe2), X = Cl, OSO2CF3] have been prepared in high yield by a one-electron oxidation of the neutral tungsten(IV) methylidynes L4W(X)[triple bond]CH with [Ph3C]+[B(C6F5)4]-. The ease and reversibility of the one-electron oxidation of L4W(X)[triple bond]CH were demonstrated by cyclic voltammetry in tetrahydrofuran (E1/2 is approximately -0.68 to -0.91 V vs Fc). The paramagnetic d1 (S = 1/2) complexes were characterized in solution by electron spin resonance (g = 2.023-2.048, quintets due to coupling to 31P) and NMR spectroscopy and Evans magnetic susceptibility measurements (mu = 2.0-2.1 muB). Single-crystal X-ray diffraction showed that the cationic methylidynes are structurally similar to the neutral precursor methylidynes. In addition, the neutral (PMe3)4W(Cl)[triple bond]CH was deprotonated with a strong base at the trimethylphosphine ligand to afford (PMe3)3(Me2PCH2)W[triple bond]CH, a tungsten(IV) methylidyne complex that features a (dimethylphosphino)methyl ligand.     

On unpredictable ship rolling in irregular seas

Indirectly excited large amplitude roll motions of container ships and roll-on/roll-off ferries represent a considerable threat to goods and life in modern navigation. Especially when ships are heading into rough seas, or sailing away from following seas, large roll responses have been reported to occur in an unpredictable, random way. We approach this topic from deterministic bifurcation theory and generalize the analysis by characterizing the seaway as narrow band stochastic processes. It is demonstrated how the intermittent behavior of zero and large amplitude motions in irregular seas is related to the deterministic bifurcation scenario. Further, we identify parameter regions of intermittent roll motions and show how the on-/off intermittency can be characterized by the probability density function of the response amplitude.     

Influences of Proline and Cysteine Residues on Fragment Yield in Matrix-Assisted Laser Desorption/Ionization In-Source Decay Mass Spectrometry

Matrix-assisted laser desorption/ionization in-source decay produces highly informative fragments for the sequencing of peptides/proteins. Among amino acids, cysteine and proline residues were found to specifically influence the fragment yield. As they are both frequently found in small peptide structures for which de novo sequencing is mandatory, the understanding of their specific behaviors would allow useful fragmentation rules to be established. In the case of cysteine, a c?/w fragment pair originating from Xxx–Cys is formed by side-chain loss from the cysteine residue. The presence of a proline residue contributes to an increased yield of ISD fragments originating from N–C_α bond cleavage at Xxx₁–Xxx₂Pro, which is attributable to the cyclic structure of the proline residue. Our results suggest that the aminoketyl radical formed by MALDI-ISD generally induces the homolytic N–C_α bond cleavage located on the C–terminal side of the radical site. In contrast, N–C_α bond cleavage at Xxx–Pro produces no fragments and the N–C_α bond at the Xxx₁–Xxx₂Pro bond is alternatively cleaved via a heterolytic cleavage pathway.      

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

The synthesis of bis(formazanate) zinc complexes is described. These complexes have well‐behaved redox‐chemistry, with the ligands functioning as a reversible electron reservoir. This allows the synthesis of bis(formazanate) zinc compounds in three redox states in which the formazanate ligands are reduced to “metallaverdazyl” radicals. The stability of these ligand‐based radicals is a result of the delocalization of the unpaired electron over four nitrogen atoms in the ligand backbone. The neutral, anionic, and dianionic compounds (L₂Zn^0/?1/?2) were fully characterized by single‐crystal X‐ray crystallography, spectroscopic methods, and DFT calculations. In these complexes, the structural features of the formazanate ligands are very similar to well‐known β‐diketiminates, but the nitrogen‐rich (NNCNN) backbone of formazanates opens the door to redox‐chemistry that is otherwise not easily accessible.     

Preparation of magnetic polymer colloids with Brownian magnetic relaxation

Magnetic polymer colloids (MPCs) consisting of CoFe₂O₄ nanoparticles (NPs) embedded in a poly(methyl methacrylate) (PMMA) matrix were synthesized by magnetic miniemulsion polymerization. CoFe₂O₄ NPs were modified with 3-trimethoxysilylpropylmethacrylate and directly emulsified with different concentrations of sodium dodecyl sulfate under ultrasonication for subsequent miniemulsion polymerization. The average diameter of the CoFe₂O₄/PMMA spheres (about 200 nm) was controlled by varying the amount of surfactant. Thermogravimetric analysis indicated that the magnetic content was in the range of 44 to 73 %. Magnetic properties of the dispersions were investigated by measuring equilibrium magnetization curves and the dynamic magnetic susceptibility as a function of frequency. The MPCs were found to follow the Debye model for the dynamic magnetic susceptibility, with a characteristic time given by the rotational hydrodynamic resistance and thermal energy through the Stokes-Einstein relation. This demonstrates that the MPCs respond to applied magnetic fields by rotating. Due to their uniform size and high magnetic loading, these colloids may be suitable in a variety of applications, including nanoscale mechanical probes and actuators in complex fluids and biological systems.     

Correlating the Morphological Properties and Structural Organization of Monodisperse Spherical Silica Nanoparticles Grown on a Commercial Silica Surface

A variety of nanosilicas have been widely used to fabricate rough surfaces with superhydrophobic and superhydrophilic properties. In this context, we prepared mixed silica and mixed nanosilica that were generated by the growth and self‐assembly of synthesized monodisperse silica nanospheres (11–30 nm, 363 m² g^?1) on the surface of Sylopol‐948 and Dispercoll S3030 by using a base‐catalyzed sol–gel route. Using this process, the interactions and hierarchical structure between the nano‐ and microsized synthesized silica particles were studied by changing the amount of tetraethoxysilane. The resulting materials were characterized by BET analysis, small‐angle X‐ray scattering (SAXS), dynamic light scattering, FTIR spectroscopy, and SEM. The mixed silica presented a higher specific surface area (326 m² g^?1), a six‐fold higher percentage of (SiO)₆ (44–68 %), and a higher amount of silanol groups (14.0–30.7 %) than Sylopol‐948 (271 m² g^?1, 42.6 %, and 12.5 %, respectively). The morphological and hierarchical structural differences in the silica nanoparticles synthesized on the surface of commercial silica (micrometric or nanometric) were identified by SAXS. Mixed micrometric silica exhibited a higher degree of structural organization between particles than mixed nanosilica.     

MISER chromatography (multiple injections in a single experimental run): the chromatogram is the graph

An experimental approach for rapid analysis and convenient interpretation of multiparallel experiments is described. Conventional approaches use a series of individual chromatographic runs to produce integrated peak area data, which are stored in individual data files, then transferred to a spreadsheet program and graphed to allow interpretation of experimental results. A simpler and more direct approach utilizes multiple injections within a single chromatographic run to produce a continuous trace of chromatograms, which can often provide a direct visual readout of experimental outcome without the need for peak integration, data transfer, or graphing. In this approach, the chromatogram itself serves as the graph whereby the outcome of the multiparallel experiment can be discerned. The utility of the technique is greatly enhanced by the use of compound-specific detection technologies such as mass spectrometry or chiroptical spectroscopy, and can benefit from experimental designs that facilitate the direct interpretation of results.