An exploration of benchtop X-ray emission spectroscopy for precise characterization of the sulfur redox state in cementitious materials

The evolution of sulfur chemistry in cements is best known in the bailiwick of failure mechanisms via sulfate attack, but is equally important for its contributions to the reduction capacity of cementitious materials often used for immobilizing nuclear waste streams destined for long-term storage, for example, cementitious waste forms (CWF). The total reduction capacity of CWFs, encompassing contributions from both S and Fe reductants, and its implications toward radionuclide immobilization is most often studied by destructive wet chemistry methods requiring acid digestion in the presence of Ce(IV) and subsequent titration and colorimetric interpretation. Here, we investigate a similarly analytical but nondestructive alternative, benchtop high resolution wavelength-dispersive X-ray fluorescence spectroscopy, most commonly known as X-ray emission spectroscopy (XES), for probing the bulk sulfur oxidation state distribution. We present here an initial investigation of S XES, including an improved experimental protocol for lab XES of inhomogeneous samples, both as a complement to the Ce(IV) test and for new scientific opportunities that it enables for observing changes in sulfur chemistry. We discuss future improvements and opportunities, including: (1) the practical challenges associated with coordinating XES and Ce(IV) liquid extraction for a more comprehensive perspective on reduction capacity and for a high-precision evaluation of uncertainties in the Ce(IV) test; and (2) new opportunities, due to the nondestructive nature of XES, for controlled evolution studies aimed at elucidating specific chemical responses of CWFs exposed to invasive gas or liquid species or to accelerated aging by radiative dose or thermal treatment.     

On a Particular Construction of Skew-Selfadjoint Operator Matrices

We consider a particular construction for skew-selfadjoint operator matrices, which are of central importance in initial boundary value problems of mathematical physics. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gasentwickelungs-Apparat

Ohne Zusammenfassung     

Errata to ``Totally positive Toeplitz matrices and quantum cohomology of partial flag varieties'

We make a correction to Remark 4.3 and the proof of Theorem 4.2 (Peterson's Theorem) which identifies with the coordinate ring of a certain affine stratum of the Peterson variety . Explicitly, we introduce additional coordinates to obtain a complete coordinate system on and then show that they lie in the defining ideal of the Peterson variety , hence play no role in the presentation of .

     

The local electronic structure of alpha-Li3N

New theoretical and experimental investigations of the occupied and unoccupied local electronic densities of states (DOS) are reported for alpha-Li(3)N. Band-structure and density-functional theory calculations confirm the absence of covalent bonding character. However, real-space full-multiple-scattering (RSFMS) calculations of the occupied local DOS find less extreme nominal valences than have previously been proposed. Nonresonant inelastic x-ray scattering, RSFMS calculations, and calculations based on the Bethe-Salpeter equation are used to characterize the unoccupied electronic final states local to both the Li and N sites. There is a good agreement between experiment and theory. Throughout the Li 1s near-edge region, both experiment and theory find strong similarities in the s-and p-type components of the unoccupied local final DOS projected onto an orbital angular momentum basis (l-DOS). An unexpected, significant correspondence exists between the near-edge spectra for the Li 1s and N 1s initial states. We argue that both spectra are sampling essentially the same final DOS due to the combination of long core-hole lifetimes, long photoelectron lifetimes, and the fact that orbital angular momentum is the same for all relevant initial states. Such considerations may be generally applicable for low atomic number compounds.     

Palladium-catalyzed total synthesis of euchrestifoline using a one-pot Wacker oxidation and double aromatic C-H bond activation

We describe the total synthesis of euchrestifoline featuring an unprecedented one-pot Wacker oxidation and double aromatic C-H bond activation.     

Structural and mechanistic information on c<Subscript>1</Subscript> ion formation in collision-induced fragmentation of peptides

The formation of c₁ ions during collision-induced fragmentation of peptides with asparagine, ornithine, or glutamine at the N-terminal position 2 has been studied. For this purpose, the corresponding fragment ion spectra of a large set of synthetic peptides were investigated. It is demonstrated that the c₁ ion intensity depends on the nature of the second residue in the N-terminal dipeptide motif as well as on the peptide length. It is shown that the formation of c₁ ions proceeds by two competing mechanisms. One mechanism is the secondary fragmentation of the b₂ ion, the efficiency of which shows only a minor dependency on the complete peptide sequence. The other mechanism is the direct formation from the molecular ion, which is identified to be connected with sequence-specific c₁ ion intensities. A model for this latter mechanism is proposed based on the analysis of the formation and secondary fragmentation of the z_max-1 ion, which is the complementary ion to the c₁ ion. Additional evidence is obtained by investigation of peptides with ornithine in N-terminal position 2, which in general exhibit c₁ ion intensities intermediate between the asparagine- and glutamine-containing species. The data presented support the reliable assignment of N-terminal dipeptide motifs using collision-induced dissociation.     

Analysis of autophosphorylation sites in the recombinant catalytic subunit alpha of cAMP-dependent kinase by nano-UPLC–ESI–MS/MS

The catalytic subunit of recombinant wild-type cyclic adenosine monophosphate-dependent protein kinase A (PKA) has been analyzed by a combination of 1D gel electrophoresis, in-gel digestion by trypsin, chymotrypsin, or endoproteinase AspN, and nano-ultraperformance liquid chromatography–MS/MS. The MS/MS spectra were annotated by MASCOT and the annotations were manually controlled. Using Ga(III)-immobilized metal ion affinity chromatography (IMAC), in addition to the four established autophosphorylation sites of the catalytic subunit of recombinant PKA, pSer10, pSer139, pThr197, and pSer338, six new phosphorylated residues have been characterized–pSer14, pThr48, pSer53, pSer212, pSer259, and pSer325. The established phosphorylation sites all are part of a PKA consensus motif and were found to be almost completely modified. In contrast, the newly detected sites were only partially phosphorylated. For estimation of their degree of phosphorylation, a method based on signal intensity measurements was used. For this purpose, signal intensities of all phospho- and non-phosphopeptides containing a particular site were added for estimation of site-specific phosphorylation degrees. This addition was performed over all peptides observed in the different digestion experiments, including their different charge states. pThr48 and pSer259 are located within PKA consensus motifs and were observed to be phosphorylated at 20% and 24%, respectively. pSer14 and pSer53 are located within inverted PKA consensus motifs and were found to be phosphorylated around 10% and 15%, respectively. The sequence environments of pSer212 and pSer325 have no similarity to the PKA consensus motif at all and were observed to be phosphorylated at about 5% or lower. All newly observed phosphorylation sites are located at the surface of the native protein structure of the PKA catalytic subunit. The results add new information on the theme of site-specific (auto)phosphorylation by PKA.