Zwei neue pentacyclische dimere des cycloheptatriens

Titanium - catalyzed dimerization of cycloheptatriene affords pentacyclo[7.5.0.0^2,8.0^5,14.0^7,11]tetradeca-3,12-diene, $\text{3}$, and pentacyclo[8.4.0.0^3,7.0^4,14.0^6,11]tetradeca-8,12-diene, $\text{4}$. By heating, $\text{3}$ is converted quantitatively into $\text{4}$.     

Modeling deoxyribose radicals by neutralization-reionization mass spectrometry. Part 1. Preparation,dissociations, and energetics of 2-hydroxyoxolan-2-yl radical,neutral isomers,and cations

Collisional neutralization of several isomeric C(4)H(7)O(2) cations is used to generate radicals that share some structural features with transient species that are thought to be produced by radiolysis of 2-deoxyribose. The title 2-hydroxyoxolan-2-yl radical (1) undergoes nearly complete dissociation when produced by femtosecond electron transfer from thermal organic electron donors dimethyl disulfide and N,N-dimethylaniline in the gas phase. Product analysis, isotope labeling ((2)H and (18)O), and potential energy surface mapping by ab initio calculations at the G2(MP2) and B3-PMP2 levels of theory and in combination with Rice-Ramsperger-Kassel-Marcus (RRKM) kinetic calculations are used to assign the major and some minor pathways for 1 dissociations. The major (approximately 90%) pathway is initiated by cleavage of the ring C-5[bond]O bond in 1 and proceeds to form ethylene and *CH(2)COOH as main products, whereas loss of a hydrogen atom forms 4-hexenoic acid as a minor product. Loss of the OH hydrogen atom forming butyrolactone (2, approximately 9%) and cleavage of the C-3[bond]C-4 bonds (<1%) in 1 are other minor pathways. The major source of excitation in 1 is by Franck-Condon effects that cause substantial differences between the adiabatic and vertical ionization of 1 (5.40 and 6.89 eV, respectively) and vertical recombination in the precursor ion 1(+) (4.46 eV). (+)NR(+) mass spectra distinguish radical 1 from isomeric radicals 2-oxo-(1H)oxolanium (3), 1,3-dioxan-2-yl (9), and 1,3-dioxan-4-yl (10) that were generated separately from their corresponding ion precursors.     

Phase-fixed double-group 3-Γ symbols. IV. Real 3-Γ symbols and coupling coefficients for the group hierarchies T* ⊃ C 3 * and T* ⊃ C 2 *

We present sets of real 3- symbols which correspond to explicitly given irreducible matrix representations for the two double group hierarchies T* C ₃ ^* and T* C ₂ ^* . They fit into the formalism exposed in a previous paper [1] on the general theory of 3- symbols and coupling coefficients and illustrate much of the discussion in a subsequent one [2] treating the particular properties of the double groups.     

Hydrogen bonding in transient bifunctional hypervalent radicals by neutralization-reionization mass spectrometry

Neutralization—reionization mass spectrometry is used to generate hypervalent 9-N-4 (ammonium) and 9-O-3 (oxonium) radicals derived from protonated α,ω-bis-(dimethylamino)alkanes and α,ω-dimethoxyalkanes, which exist as cyclic hydrogen-bonded structures in the gas phase. Collisional neutralization with dimethyl disulfide, trimethylamine, and xenon of the hydrogen-bonded onium cations followed by reionization with oxygen results in complete dissociation. Bond cleavages at the hypervalent nitrogen atoms are found to follow the order CH₂-N>CH₃-N>N-H, which differs from that in the monofunctional hydrogen-n-heptyldimethylammonium radical, which gives CH₂-N>N-H>CH₃-N. No overall stabilization through hydrogen bonding of the bifunctional hypervalent ammonium and oxonium radicals is observed. Subtle effects of ring size are found that tend to stabilize large ring structures and are attributed to intramolecular hydrogen bonding.     

Reactions of cyclochlorotriphosphazatriene with 2-mercaptoethanol. Calorimetric and spectroscopic investigations of the derived products

Abstract

The reactions of hexachlorocyclotriphosphazatriene, N₃P₃Cl₆ (1) with 2-mercaptoethanol, 2-HS-CH₂-CH₂-OH (2), in (1:1, 1:2 and 1:3) mole ratios, in excess of NaH, in THF and diethylether solutions yield a total of 6 novel products: one mono spiro, N₃P₃Cl₄[O-CH₂-CH₂-S] (3); one mono-substituted open chain, N₃P₃Cl₅[S-CH₂-CH₂-OH] (4); one dispiro, N₃P₃Cl₂[O-CH₂-CH₂-S]₂ (5); one tri-substituted open chain, N₃P₃Cl₃[S-CH₂-CH₂-OH]₃ (6); one tris-spiro, N₃P₃[O-CH₂-CH₂-S]₃ (7) and one disubstituted open chain, N₃P₃Cl₄[S-CH₂-CH₂-OH]₂ (8) derivatives. The spiro products (3, 5 and 7) are formed as the major products in this system and all of the synthesized compounds are found to be stable at room temperature. The structures of the derived compounds were elucidated by elemental analysis, TLC-MS, ³¹P and ¹H NMR spectral data. For evaluation of melting behavior of derivatives (6) and (7), thermal transition peaks and their corresponding enthalpies were determined via DSC technique.     

Charge-Tagged DNA Radicals in the Gas Phase Characterized by UV/Vis Photodissociation Action Spectroscopy

Adenosine radicals tagged with a fixed-charge group were generated in the gas phase and structurally characterized by tandem mass spectrometry, deuterium labeling, and UV/Vis action spectroscopy. Experimental results in combination with Born–Oppenheimer molecular dynamics, ab initio, and excited-state calculations led to unambiguous assignment of adenosine radicals as N-7 hydrogen atom adducts. The charge-tagged radicals were found to be electronically equivalent to natural DNA nucleoside radicals.     

Modeling deoxyribose radicals by neutralization-reionization mass spectrometry. Part 2. Preparation,dissociations, and energetics of 3-hydroxyoxolan-3-yl radical and cation

The title radical (1) is generated in the gas-phase by collisional neutralization of carbonyl-protonated oxolan-3-one. A 1.5% fraction of 1 does not dissociate and is detected following reionization as survivor ions. The major dissociation of 1 (approximately 56%) occurs as loss of the hydroxyl H atom forming oxolan-3-one (2). The competing ring cleavages by O[bond]C-2 and C-4[bond]C-5 bond dissociations combined account for approximately 42% of dissociation and result in the formation of formaldehyde and 2-hydroxyallyl radical. Additional ring-cleavage dissociations of 1 resulting in the formation of C(2)H(3)O and C(2)H(4)O cannot be explained as occurring competitively on the doublet ground (X) electronic state of 1, but are energetically accessible from the A and higher electronic states accessed by vertical electron transfer. Exothermic protonation of 2 also produces 3-oxo-(1H)-oxolanium cation (3(+)) which upon collisional neutralization gives hypervalent 3-oxo-(1H)-oxolanium radical (3). The latter dissociates spontaneously by ring opening and expulsion of hydroxy radical. Experiment and calculations suggest that carbohydrate radicals incorporating the 3-hydroxyoxolan-3-yl motif will prefer ring-cleavage dissociations at low internal energies or upon photoexcitation by absorbing light at approximately 590 and approximately 400 nm.     

Dipole-Guided Electron Capture Causes Abnormal Dissociations of Phosphorylated Pentapeptides

Electron transfer and capture mass spectra of a series of doubly charged ions that were phosphorylated pentapeptides of a tryptic type (pS,A,A,A,R) showed conspicuous differences in dissociations of charge-reduced ions. Electron transfer from both gaseous cesium atoms at 100 keV kinetic energies and fluoranthene anion radicals in an ion trap resulted in the loss of a hydrogen atom, ammonia, and backbone cleavages forming complete series of sequence z ions. Elimination of phosphoric acid was negligible. In contrast, capture of low-energy electrons by doubly charged ions in a Penning ion trap induced loss of a hydrogen atom followed by elimination of phosphoric acid as the dominant dissociation channel. Backbone dissociations of charge-reduced ions also occurred but were accompanied by extensive fragmentation of the primary products. z-Ions that were terminated with a deaminated phosphoserine radical competitively eliminated phosphoric acid and H₂PO₄ radicals. A mechanism is proposed for this novel dissociation on the basis of a computational analysis of reaction pathways and transition states. Electronic structure theory calculations in combination with extensive molecular dynamics mapping of the potential energy surface provided structures for the precursor phosphopeptide dications. Electron attachment produces a multitude of low lying electronic states in charge-reduced ions that determine their reactivity in backbone dissociations and H- atom loss. The predominant loss of H atoms in ECD is explained by a distortion of the Rydberg orbital space by the strong dipolar field of the peptide dication framework. The dipolar field steers the incoming electron to preferentially attach to the positively charged arginine side chain to form guanidinium radicals and trigger their dissociations.     

Protonation sites and dissociation mechanisms of t-butylcarbamates in tandem mass spectrometric assays for newborn screening

Structures of tert-butylcarbamate ions in the gas-phase and methanol solution were studied for simple secondary and tertiary carbamates as well as for carbamate-containing products and internal standards for lysosomal enzyme assays used in newborn screening of a α-galactosidase A deficiency (Fabry disease), mucopolysaccharidosis I (Hurler disease), and mucopolysaccharidosis II (Hunter disease). The protonation of simple t-butylcarbamates can occur at the carbonyl group, which is the preferred site in the gas phase. Protonation in methanol solution is more favorable if occurring at the carbamate nitrogen atom. The protonation of more complex t-butylcarbamates occurs at amide and carbamate carbonyl groups, and the ions are stabilized by intramolecular hydrogen bonding, which is affected by solvation. Tertiary carbamates containing aminophenol amide groups were calculated to have substantially greater gas-phase basicities than secondary carbamates containing coumarin amide groups. The main diagnostically important ion dissociation by elimination of 2-methylpropene (isobutylene, i-C(4)H(8)) and carbon dioxide is shown by experiment and theory to proceed in two steps. Energy-resolved collision-induced dissociation of the Hurler's disease enzymatic product ion, which is a coumarin-diamine linker-t-butylcarbamate conjugate (3a(+)), indicated separate energy thresholds for the loss of i-C(4)H(8) and CO(2). Computational investigation of the potential energy surface along two presumed reaction pathways indicated kinetic preference for the migration of a t-butyl hydrogen atom to the carbamate carbonyl resulting in the isobutylene loss. The consequent loss of CO(2) required further proton migrations that had to overcome energy barriers.     

Enzymatic degradation of model cellulose films

Enzymatic degradation of model cellulose films prepared by a spin-coating technique was investigated by ellipsometry. The cellulose films were prior to degradation characterized by ellipsometry, contact angle measurements, ESCA (electron spectroscopy for chemical analysis) and AFM (atomic force microscopy). At enzyme addition to preformed cellulose films an initial adsorption was observed, which was followed by a total interfacial mass decrease due to enzymatic degradation of the cellulose films. The degradation rate was found to be constant during an extended time of hours, whereafter the degradation leveled off. In parallel to the decreased interfacial mass, the cellulose degradation resulted in a thinner and more dilute interfacial film. At long degradation times, however, there was an expansion of the cellulose film. The enzyme concentration affected the degradation rate significantly, with a faster degradation at a higher enzyme concentration. The effects of pH, temperature, ionic strength and stirring rate in the cuvette were also investigated.