Formation of [M − nH + mNa](m−n)+ and [M − nH + mK](m−n)+ ions in electrospray mass spectrometry of peptides and proteins

The [M - nH + mNa](m-n)+ and [M - nH + mK](m-n)+ ions are common in the electrospray mass spectra of proteins and peptides. The feasibility of forming these ions in the gas phase via collision activation and/or ion-molecule reaction is investigated. Sodium and potassium affinities of the N-methylacetamide anion, the acetate anion, and the 1-propanamide anion have been calculated using density functional theory at the B3LYP/6-311+ +G(d,p) level of theory. These anions were chosen as models for the functional groups on a protein or peptide. These affinity values are then used to calculate reaction enthalpies of alkali hydroxides, chlorides, and hydrates with N-methylacetamide, acetic acid, the acetate anion, and 1-propanamine, model reactions that may lead to formation of the [M - nH + mNa](m-n) and [M - nH + mK](m-n)+ ions. It is found that a number of these reactions are exothermic or slightly endothermic (deltaH(o) < + 20 kcal/mol) and are accessible after collision activation in the lens region. The potential energy hypersurfaces of model reactions between NaOH and formamide as well as NaCl and formamide show relatively flat surfaces devoid of significant barriers.     

Theoretical Study of Electronic Structure and Stability of Mixed AlmBn−mH n 2− and CmBn−mH n 2−m (n = 6, 10, 12 and m = 1, 2) Clusters

Density functional theory (DFT) method with B3LYP functional and 6-311++G(d,p) basis set has been used to predict the geometries, relative stabilities, electronic structures and bonding analysis of Mixed Al_mB_n?mH _n ^2? and C_mB_n?mH _n ^2?m (n = 6, 10, 12 and m = 1, 2) clusters; being compared to the B_nH _n ^2? ones. Therefore, the DFT results suggest that the replacing of boron by aluminium or carbon is governed by Natural net charges following Gimar’s and Williams’s rules. The Al_mB_n?mH _n ^2? structures are relatively distorted compared to those of B_nH _n ^2? and C_mB_n?mH _n ^2?m . In Al_mB_n?mH _n ^2? structures Al atoms prefer the adjacent sites, however for the C₂B_n?2H_n cluster cages, the carbon atoms are positioned at diametrically opposed sites. The large HOMO–LUMO gaps show that the predicted clusters have chemical stabilities, principally, those of Al_mB_n?mH _n ^2? ones, which are not experimentally isolated. The optimized geometries obtained through boron substitution by Al and C lead to compactness and to contracted structures, respectively, where B–B bonds are the shortest in mono- and di-carbaboranes.     

Theoretical study of stepwise hydrogenated closo-alane clusters Al13H m − (m = 1–12)

The structure, energy, and vibrational characteristics of different stepwise-hydrogenated closo-alane clusters Al₁₃H _m ^? (m = 1–12) were calculated within the B3LYP approximation of the density functional theory using 6-31G* and 6-311+G* basis sets. For each of the m values, there is a set of several low-lying, closely spaced (within ～0.1–0.3 eV) isomers. In the first half of the series, inner isomers (with the centered cage Al@Al₁₂) are preferable; and in the second half, outer isomers (with the thirteenth Al atom located on the outside of the empty Al₁₂ icosahedron and coordinated to its face) are more favorable. In some of the outer isomers, the aluminum cage is severely distorted and loses its closo form. When a hydrogen atom is attached to paramagnetic radical anions (with odd m values), the most favorable site for attack is the Al* atom located opposite the Al^t-H bond and carrying most of the unpaired electron density. The resulting diamagnetic anions contain a maximum number of linear (or quasi-linear) HAl_H-Al_c-Al_HH or HAl_H…Al_HH fragments in the inner and outer isomers, respectively (the trans addition rule). The energy D _m (H) of successive addition of an H atom to the centered icosahedron Al ₁₃ ^? depends on m in a zigzag manner: the even bonds are always ～1 eV stronger than the odd bonds. This trend is interpreted in the framework of the molecular model of the valence states of the [Al₁₃] “superatom” with a variable valence increasing from 1 to 12 due to the unpairing of one to six electron pairs of the cage when the first, third, etc. odd H atoms are attached to it.     

Untersuchungen in den Systemen: V−B,Nb−B,V−B−Si und Ta−B−Si

Zusammenfassung Mit Hilfe röntgenographischer Messungen werden die Boride von Vanadin und Niob untersucht, wobei eine neue Phase der ungefähren Zusammensetzung V₂B identifiziert wird, welche mit der entsprechenden Nb-Borid-Phase isotyp ist. Dieselbe Kristallart tritt auch im System: Ta–B auf. Die in der Literatur angegebene -Phase im Zweistoff: Nb–B erweist sich als NbO.Im System: V–B–Si wird wie im analogen Mo-System die Existenz einer ternärenT 2-Phase Me₅(Si_1/3, B_2/3)₃ nach-gewiesen¹; ihre Gitterkonstanten werden ermittelt.Im Schnitt Ta₂Si–Ta₂B besteht ein geringes Lösungs-vermögen der beiden Phasen ineinander. Durch Zusatz von 20 Mol-% Ta₂Si zu Ta₂B erhält man die oben erwähnte neue Kristallart.Bei den Borid-Siliziden der Metalle aus der 4a-, 5a- und 6a-Gruppe werden die Stabilitätsbereiche derT 1-,T 2- undD 8₈-Phasen miteinander verglichen.     

Untersuchungen in den Dreistoffen: Cr−W−Si und Mo−W−Si

Zusammenfassung Der Schnitt: Me₃Si (Me=Cr, W bzw. Mo, W) wird an Hand heißgepreßter und in Argon homogenisierter Legierungen untersucht; es läßt sich weder das metastabile W₃Si, noch eine W-reiche Mischphase von diesem Typ beobachten. Cr₃Si nimmt bei 1500°C etwa 20 Mol%, W₃Si auf, während Mo₃Si selbst bei 1900°C praktisch kein W₃Si löst (ev. wenige Mol%). Dagegen bestehen lückenlose Mischreihen zwischen den Me₅Si₃-Phasen mit W₅Si₃-Typ. Die grundsätzliche Aufteilung der Phasenfelder ist damit möglich.Mit 2 Abbildungen     

Magnetische Messungen an den Teilsystemen TiC−ZrC,TiC−HfC,ZrC−HfC,TiC−VC,TiC−NbC,TiC−TaC und NbC−TaC

Ohne ZusammenfassungMit 3 Abbildungen     

Estimating of surface activity of Cl− and Br− ions in the (In-Ga)/[N-methylformamide + mc KCl + (1 − m)c KClO4] and (In-Ga)/[N-methylformamide + mc KBr + (1 − m)c KClO4] systems by different methods

Differential capacitance curves in the (In-Ga)/[N-methylformamide + mc KCl + (1 ? m)c KClO₄] and (In-Ga)/[N-methylformamide + mc KBr + (1 ? m)c KClO₄] systems are measured using an ac bridge for the following molar portions m of the surface-active anion: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. The Cl^? and Br^? anions specific adsorption in the systems can be described quantitatively by the Frumkin isotherm. The principal parameters of Cl^? and Br^? anions adsorption at the (In-Ga)/N-methylformamide interface are determined by different methods. Unlike Ga/N-methylformamide interface, where the adsorption energy increased in the sequence I^? ≈ Br^? < Cl^?, at the (In-Ga)/N-methylformamide interface it increased in the reverse sequence: Cl^? < Br^? < I^?. The adsorption parameters at the charge density q = 0, obtained by three different methods, are close to each other. However, the parameters α₁ and α₂, which characterize the charge effect on the adsorption energy, when determined by the analyzing of dependences of adsorption potential drop E _ads on ln(mc), differ from those determined by two other methods. The error may be caused by the assuming that the adsorption potential drop is proportional to the coverage of dense layer with the specifically adsorbed ions.     

Magnetische Kernresonanzuntersuchungen an Ti−C−H-Legierungen

Ohne ZusammenfassungMit 4 Abbildungen     

Transition Metal-Free Aromatic C−H,C−N,C−S and C−O Borylation

Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required.     

Photoelectron spectroscopy of (CO2)n(H2O) m − clusters

Photoelectron spectra of (CO₂)_nH₂O^? (2≤n≤8) and (CO₂)_n(H₂O) ₂ ^? (1≤n≤2) were measured at the photon energy of 3.49 eV. The spectra show unresolved broad features, which are approximated by Gaussians. The vertical detachment energies (VDEs) were determined as a function of the cluster size. For (CO₂)_nH₂O^?, the VDE-n plots exhibit a sharp discontinuity between n=3 and 4; the VDE value is ≈3.5 eV at n=3, while it drops down abruptly to 2.59 eV at n=4. This discontinuity in VDE is ascribed to "core switching" at n=4; a C₂O ₄ ^? dimer anion forms the core of (CO₂)_nH₂O^? for n≤3, while a monomer CO ₂ ^? is the core for n≥4. The (CO₂)₂(H₂O) ₂ ^? ion has a VDE of 2.33 eV, indicating the presence of a CO ₂ ^? monomer core in the binary clusters containing two H₂O molecules.     

Chromatography of Anions on Alumina Thin Layers: Effect of Transition Metals on CI−-Br−-I− and No− 2-NO− 3 Separations

Abstract

Chromatographic behaviour of eighteen anions on thin layers of alumina and alumina mixed with silica gel (1:1, 1:2 and 2:1) has been studied using mixed acidic organic solvent systems containing formic acid. Though the addition of silica gel to alumina enhances the mobility and clarity of detection of anions, but it causes the increased tailing for Fe(CN)^3- ₆, Cr0₄ ^2- and Cr₂O₄ ^2-. Formic acid is responsible for the differential migration of anions. All the anions remained at the starting line (R_F = 0) in pure organic solvents. Formic acid-Ketone systems gave better results compared to formic acid-alcohol systems. Development time increases with the increase of viscosity/mol. wt. of organic solvents. The mutual separation of C1, Br^?, Br^?, I^? and NO^? ₂ and NO^? ₃ were achieved on pure alumina using formic acid-acetone solvent systems. The effect of transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) on C1^?-Br^?-I^? and NO^? ₂-NO^? ₃ separations has been studied.     

Untersuchungen im Dreistoff: Mn−Al−Si

Zusammenfassung Mn–Al–Si-Legierungen werden aus den Komponenten hergestellt und röntgenographisch untersucht. Es werden vier neue Verbindungen festgestellt und zwei davon kristallchemisch charakterisiert.MnAl_0,75Si_1,25 kristallisiert im CrSi₂-Typ:a=4,47₅ Å,c=6,42₇ Å,c/a=1,43₆; MnAl_1,3Si_0,7 im TiSi₂-Typ:a=7,88₉ Å,b=4,57₀ Å,c=8,50₆ Å.Mit 2 Abbildungen     

F− Preference of Polyamide Cryptand to Cl−

The variations in geometry structure, IR spectra, as well as the molecular orbitals upon anion recognition for polyamide cryptand are explored with the hybrid density functional theory. The cavity generated by six amide NH groups shrinks upon F ^? recognition because of the strong hydrogen bonds between the amide protons and F ^? , while the cavity expands upon Cl ^? binding because of the strong electron repulsion between the p electron of Cl ^? and the lone pair electrons of the nitrogen atom of the pyridine moieties. The “electropositive field space” …Cl ^? coupling exists when Cl ^? is recognized. The strong anion binding energy with F ^? indicates that the polyamide cryptand prefers F ^? to Cl ^? .     

Zur Kenntnis der Salpetersäure. X Methoden zur Gasanalyse im System N2−NO−NO2−N2O4−N2O3−HNO2−HNO3

Zusammenfassung Es werden vier Methoden zur Analyse einer Gasmischung N₂–NO–NO₂–N₂O₄–N₂O₃–HNO₂ besprochen und ihre Bedeutung für die Bestimmung der einzelnen Molekelarten kritisch auseinandergesetzt. Nach keiner der Methoden kann man den Gehalt an Salpetriger Säure und Salpetersäure neben den Oxyden des Stickstoffes auffinden. Aus diesem Grunde ist die Analyse der genannten Gasmischung nach den vier Methoden allgemein nicht genau durchführbar.Mit 1 Abbildung.Herrn Prof. Dr.A. Skrabal zum 75. Geburtstag gewidmet.     

Kristallchemische Untersuchungen in den Systemen Mn−As,V−Sb,Ti−Sb

Zusammenfassung Im System Mn–As wurde die Struktur der Phase Mn₃As bestimmt. Sie kristallisiert in einem eigenen Typ, der eng in Beziehung zum Gitter von Mn₂As steht. Die Elementarzelle von Mn₃As ist pseudotetragonal orthorhombisch mit den Achsen:a=b=3,780 undc=16,2₆ k X·E. Im charakteristischen Raumsystem D_2h ¹³ werden die Parameter ermittelt. Auf die strukturellen Zusammenhänge zwischen der Zelle von -Mn, Mn₃As und Mn₂As wird hingewiesen; die Bauprinzipien bei solehen Gittern werden erörtert.Im System V–Sb wurde die zu TiSb₂ isotype Verbindung VSb₂ mit C 16-Struktur gefunden. Überraschend ist die hohe Dichte dieser Kristallarten. Die Achsen der Elementarzelle sind:a=6,54₂ undc=5,62₄ k X·E. Der Bereich der C 16-Strukturen erfährt damit bezüglich desB_Partners eine Erweiterung. Die sich daraus ergebenden Folgerungen werden besprochen.Im System Ti–Sb wird das Bestehen der Phase Ti₄Sb nachgewiesen, die gemäß einer Formulierung Ti₃(Ti_0,2Sb_0,8) im DO₁₉-Typ kristallisiert.Mit 2 Abbildungen     

Zur Kenntnis des m,m′-Divinylazobenzols und des m,m′-Divinylazoxybenzols

Ohne Zusammenfassung     

Determination of biogenic halogenated methyl-phenyl ethers (halogenated anisoles) in the picogram m−3 range in air

Halogenated anisoles (methyl-phenyl ethers) appear to be ubiquitous organic trace compounds in the environment. An analytical method is presented for analyzing the altogether 134 congeners of chloro-, bromo- and mixed bromochloro-anisoles on an isomer-specific basis in air. High volume sampling (20 m(3) per hour) is carried out by adsorption, using a mixture of silica gel 60 and ENVI-Carb. The preseparation of the anisoles is achieved by NP-LC on Florisil (a magnesium silicate). The interference by volatile n-alkyl nitrates in the electron-capture detection can be avoided by a LC-preseparation on a carboneous phase. The isomer-specific separation and detection is performed by HRGC-ECD and HRGC-MS-SIM. A structure-specific systematic numbering of the 134 congeners of the chloro-, bromo- and bromochloro-anisoles is suggested. The retention data are given of 16 chloroanisoles, 10 bromoanisoles and 27 bromo-chloroanisoles on three stationary phases with different polarity.