Mass Spectroscopic Evidence Research Articles

Transition-Metal-Free Transfer Hydrogenative Cascade Reaction of Nitroarenes with Amines/Alcohols: Redox-Economical Access to Benzimidazoles.

This report describes an efficient transition-metal-free process toward the transfer hydrogenative cascade reaction between nitroarenes and amines or alcohols. The developed redox-economical approach was realized using a combination of KOtBu and Et3SiH as reagents, which allows the synthesis of benzimidazole derivatives via σ-bond metathesis. The reaction conditions hold well over a wide range of substrates embedded with diverse functional groups to deliver the desired products in good to excellent yields. The mechanistic proposal has been depicted on the basis of a series of control experiments, mass spectroscopic evidence which is well supported by density functional theory (DFT) calculations with a feasible energy profile.

In vitro metabolic profiles of adamantyl positional isomers of synthetic cannabinoids

Illegal use of synthetic cannabinoids (SCs) is a serious problem worldwide. Legal regulation of SCs requires fundamental analytical studies regarding the differentiation of potential structural isomers. Accumulation of SC metabolic profiles is also essential for forensic investigation because SCs are immediately metabolized after intake. Thus, we investigated the in vitro metabolism of N-adamantyl-1-(tetrahydropyran-4-ylmethyl)-1H-indazole-3-carboxamide isomers (ATHs) using human liver microsomes (HLMs). Moreover, we validated the applicability of the isomeric differentiation by investigation of N-adamantyl-1-(4-fluorobenzyl)-1H-indazole-3-carboxamide isomers (AFUs). Metabolites were collected at designated time points during the incubation period with HLMs for up to 180 min. The structures of the metabolites were annotated on the basis of mass spectroscopic evidence obtained by liquid chromatography–ion trap–time of flight mass spectrometry. The secondary stage mass (MS2) spectra obtained from the protonated molecules revealed a clear difference in both ATHs and their major metabolites because of the stability of the adamantyl (AD) cation. In HLMs, ATHs were quickly metabolized, and hydroxylation of the AD ring was deduced as the major metabolic pathway. The major metabolites of ATH 1 and ATH 2 after 180 min showed dihydroxylation and monohydroxylation of the AD ring. The AFUs showed analytical and metabolic profiles similar to those of the ATHs described above. We characterized the metabolism of ATHs for the first time and discriminated between the two isomers by mass spectrometric analysis of either the parent compounds or their major metabolites. Our investigation of AFUs also demonstrated a useful method for distinguishing between AD isomers.

ChemInform Abstract: Fullerenes C60 and C70 in Flames

THE fullerenes C60 and C70 were first identified1 in carbon vapour produced by laser irradiation of graphite, and have recently been produced in macroscopic quantities2–5 by vaporization of graphite with resistive heating. It has also been suggested6–9 that fullerenes might be formed in sooting flames, and indeed all-carbon ions with mass/charge ratios suggestive of fullerenes have been detected in flames10–12. These species were assumed to have the cage structures of fullerenes, but the mass spectroscopic evidence could not establish this conclusively. We have now collected samples of condensible compounds and soot from hydrocarbon combustion under a range of conditions, and analysed these using conventional techniques in an effort to detect fullerenes. Spectroscopic studies reveal the presence of C60 and C70 in yields and ratios that depend on temperature, pressure, carbon/oxygen ratio and residence time in the flame. Control of these conditions allows optimal yields of 3 g of fullerenes per kilogram of fuel carbon burned, and variation of the C70/C60 ratio over the range 0.26–5.7.

Spin-Trapping of the p-Benzyne Intermediates from Ten-Membered Enediyne Calicheamicin γ1I

In the presence of thiols, the ten-membered-ring enediyne calicheamicin gamma1I generates a p-benzyne biradical that initiates oxidative cleavage of double-stranded DNA. Application of spin-trapping has successfully provided ESR and mass spectroscopic evidence for the formation of the monoadducts with phenyl tert-butyl nitrone (PBN). [reaction: see text].

Homo- and heteropolynuclear helicates with a ‘2 + 3 + 2’-dentate compartmental ligand

An octadentate ligand L has been prepared which contains a sequence of bidentate (pyrazolyl-pyridine), terdentate [bis(pyrazolyl)pyridine] and bidentate (pyrazolyl-pyridine) binding sites separated by p-xylyl spacers. This forms a range of double helical complexes in which the two ligands define 4-, 6-, and 4-coordinate binding sites, and there is substantial π-stacking between overlapping parallel areas of the ligands. In [Cu3L2][PF6]4 the sequence of oxidation states for the copper ions is +1, +2, +1 with the Cu(I) ions being four-coordinate at the terminal sites and Cu(II) being in the central six-coordinate site. In [Cu3(OAc)2L2][PF6]4 all copper centres are in oxidation state +2, with the terminal ions having an additional monodentate acetate ligand giving them a five-coordinate geometry. The 4 + 6 + 4 arrangement of coordination numbers means that reaction of L with a mixture of Fe(II) and Ag(I) results in high yield formation of [Ag2FeL2][BF4]4 in which Ag(I) ions occupy the terminal 4-coordinate sites and Fe(II) occupies the central pseudo-octahedral site. Reaction of L with Ag(I) produced a mixture of [Ag3L2][BF4]3 (major product) and [Ag4L2][BF4]4 (minor product). In [Ag3L2][BF4]3 the central Ag(I) ion is, unusually, in a pseudo-octahedral coordination environment from the two meridional, terdentate bis(pyrazolyl)pyridine donors. In [Ag4L2][BF4]4 in contrast the central 6-coordinate cavity is occupied by two Ag(I) ions separated by 2.85 A. The terdentate chelating bis(pyrazolyl)pyridine units at the centre of the helicate are now substantially twisted such that each donates a bidentate pyrazolyl-pyridine to one Ag(I) centre and a monodentate pyrazole unit to the other. In solution, 1H NMR and mass spectroscopic evidence indicates that the fourth Ag(I) ion is lost and [Ag3L2][BF4]3 forms, unless a large excess of Ag(I) is present in which case traces of [Ag4L2][BF4]4 can be detected by mass spectrometry.

Covalent cross-linking of proteins without chemical reagents.

A facile method for the formation of zero-length covalent cross-links between protein molecules in the lyophilized state without the use of chemical reagents has been developed. The cross-linking process is performed by simply sealing lyophilized protein under vacuum in a glass vessel and heating at 85 degrees C for 24 h. Under these conditions, approximately one-third of the total protein present becomes cross-linked, and dimer is the major product. Chemical and mass spectroscopic evidence obtained shows that zero-length cross-links are formed as a result of the condensation of interacting ammonium and carboxylate groups to form amide bonds between adjacent molecules. For the protein examined in the most detail, RNase A, the cross-linked dimer has only one amide cross-link and retains the enzymatic activity of the monomer. The in vacuo cross-linking procedure appears to be general in its applicability because five different proteins tested gave substantial cross-linking, and co-lyophilization of lysozyme and RNase A also gave a heterogeneous covalently cross-linked dimer.

Dehydrogenation Reaction from a Dihydrogen Bonded Precursor Complex in the Gas Phase

In this paper, we present mass spectroscopic evidence for the dehydrogenation reaction from a dihydrogen bonded complex between phenol and borane-trimethylamine following resonance enhanced multiphoton ionization in the gas phase. The evidence presented herein is based on observed fragmentation pattern of the complex cation having high internal energy. To the best of our knowledge, it is the first report of such observation.

Non‐Ionic Template Synthesis of Amide‐Linked Rotaxanes: Olefinic and Aliphatic Axle Building Blocks

AbstractThe first synthesis of amide‐linked rotaxanes with non‐arene axle building blocks is reported. The threading synthesis of rotaxane 8 with olefinic fumaryl chloride proves that arene moieties are not necessary for non‐ionic template syntheses. Mass spectroscopic evidence of a rotaxane bearing an aliphatic axle, derived from succinic acid, revealed that hydrogen bonding, rather than π,π interactions, is the predominant template binding force. 1H‐NMR titration studies on the threading synthesis of these mechanically bonded molecules were carried out. The association constants measured suggest that the incorporation of the corresponding monoamide monochloride (cf. 7), rather than the incorporation of the diacid dichloride (cf. 5), plays the key role in these rotaxane syntheses. The X‐ray structural analysis of a semi axle (14) reveals hydrogen bonding patterns characteristic of diamides.

The 3Σu− ← X 3Σg− electronic absorption spectrum of linear C 4 in a neon matrix

The electronic absorption spectrum of linear C 4 in a neon matrix has been detected. This was achieved by codepositing mass selected C 4 − ions with an excess of neon and UV irradiation of the matrix during or after deposition. Mass selection, experimental and spectroscopic evidence, available ab initio calculations and comparison with the spectra of C 2 n ( n=3–7) chains lead to the conclusion that the observed band system with origin at ≈ 380 nm is due to the 3 Σ u −←X 3 Σ g − transition of linear C 4. Vibrational frequencies of C 4 in the excited electronic state have been inferred.

Isotopic Enrichment by Asymmetric Deuteriation. An Investigation of the Synthesis of Deuteriated (S)-(−)-Methylsuccinic Acids from Itaconic Acid

Two different asymmetric hydrogenation methodologies based on gaseous hydrogen at 1 atm pressure and transfer hydrogenation from the decomposition of formic acid, in the presence of a rhodium catalyst, have been used to prepare (S)-(−)-methylsuccinic acid enriched with the deuterium isotope. NMR and mass spectroscopic evidence indicates that complex labeling occurs. We interpret this labeling pattern as the result of an equilibrium which exists between the olefin and a catalyst-alkyl intermediate in a Wilkinson-type mechanism. This phenomenon has not been reported in similar experiments with (E)-phenylitaconic acid where the expected cis-addition of deuterium from either deuterium gas at 1 atm, or deuteriated formic acid under transfer hydrogenation conditions, was observed. In our studies reducing itaconic acid (methylenebutanedioic acid), there was no loss of asymmetric induction (above 90% ee), approximately 2.4 deuterons were incorporated into (S)-(−)-methylsuccinic acid, a ratio of 1.8:1 methyl:methine deuteriation was observed, and there was no evidence for olefin isomerization into conjugation with both carboxylic acid groups. Following these isotopic enrichment studies, we present the first evidence for reversible transfer addition of deuterium to methylsuccinic acid, either by gaseous or transfer hydrogenation at atmospheric pressure. Such a mechanism has recently been eliminated for reduction at elevated pressures. These results have general applicability to the synthesis of isotopically labeled homochiral substituted carboxylic acids and also in interpreting the 13C NMR data which are generated by the simultaneous presence of several deuterium containing isotopomers.

Electronic absorption spectra of linear carbon chains in neon matrices. I. C−6, C6, and C6H

Electronic absorption spectra of linear C−6, C6, and C6H have been identified in neon matrices at 5 K. The species were produced by codepositing mass selected cations and anions with neon. The ions were generated in a hot cathode discharge source using diacetylene. The spectra of C−6 and C6 could also be observed using a pure carbon anion source or laser vaporization of graphite. The assignment is based on the mass selection, experimental and spectroscopic evidence, leading to the location of the 000 transitions of C−6: 2Πg←X 2Πu, C6: 3Σ−u←X 3Σ−g, and C6H: 2Π←X 2Π at 16 458, 19 558, and 18 854 cm−1, respectively. The frequencies of the symmetric carbon stretching vibrations have been obtained for these species in their excited electronic states.

Nuclear magnetic resonance and mass spectra of organomercury hydrides and deuterides, part II

Further mass spectroscopic and NMR evidence is given for the existence of several organomercury hydrides and deuterides.

Mass spectroscopic nuclear magnetic resonance evidence confirming the existence of methyl mercury hydride

Mass spectroscopic and NMR evidence involving deuterium labelling is presented for the existence of CH 3HgH.

Mass spectroscopic evidence for the formation of mixed-metal octahedral clusters [Mo nW 6− nCl 14] 2−

Mixed-metal clusters containing molybdenum and tungsten have been prepared by reducing MoCl 5 and WCl 6 with aluminum in a NaClAlCl 3 melt. Liquid secondary ion mass spectra of the product indicates the presence of seven-metal clusters across the full range, n=0 to 6 for [Mo n W 6− n Cl 14] 2−. The distribution of molybdenum and tungsten in the clusters is dependent on the Mo/W ratio in the starting melt, and is biased in favor of molybdenum.

Electron paramagnetic resonance studies of lanthanum-containing C82

THE conjecture that atoms can be trapped inside closed carbon cages such as the fullerenes was first made by Kroto et al1. Mass spectroscopic evidence obtained soon after2 suggested that lanthanum atoms were encapsulated in fullerenes prepared by laser vaporization of a lanthanum-impregnated graphite disk, and these results were later corroborated3,4. Recently, helium atoms have been incorporated into fullerenes through collisions in the gas phase5, and evidence has been obtained for the formation of metal-containing fullerenes during arc burning of composite graphite rods6. All of these studies, however, have produced quantities too small for characterization using standard spectroscopic techniques. We report here the preparation of milligram quantities of lanthanum-containing C82, which can be solvent-extracted in yields of about 2% along with empty C60 and C70 cages. We have measured the electron paramagnetic resonance spectrum of this mixture, both in solution and in the solid state, which reveals that the lanthanum atom has a formal charge of 3+, and the C82a charge of 3-. This runs contrary to some expectations that the doubly charged f ulleride anions would be the most stable species6,7; it also reveals that the fullerene cages have the same formal charge as in the superconducting alkali-metal-doped phases8,9.

Fullerenes C60 and C70 in flames

The fullerenes C60 and C70 were first identified in carbon vapour produced by laser irradiation of graphite, and have recently been produced in macroscopic quantities by vaporization of graphite with resistive heating. It has also been suggested that fullerenes might be formed in sooting flames, and indeed all-carbon ions with mass/charge ratios suggestive of fullerenes have been detected in flames. These species were assumed to have the cage structures of fullerenes, but the mass spectroscopic evidence could not establish this conclusively. We have now collected samples of condensible compounds and soot from hydrocarbon combustion under a range of conditions, and analysed these using conventional techniques in an effort to detect fullerenes. Spectroscopic studies reveal the presence of C60 and C70 in yields and ratios that depend on temperature, pressure, carbon/oxygen ratio and residence time in the flame. Control of these conditions allows optimal yields of 3 g of fullerenes per kilogram of fuel carbon burned, and variation of the C70/C60 ratio over the range 0.26-5.7.

The spectrophotometric determination of indole-3-methanol in small samples with p-dimethylaminocinnamaldehyde on the basis of the formation of an azafulvenium salt

Indole-3-methanol is coupled, at acidic pH, with p-dimethylaminocinnamaldehyde to give a highly colored azafulvenium salt. IR, 1H NMR, and mass spectroscopic evidence indicates that this azafulvenium salt is the 2-[3′- ( p-dimethylaminophenyl) - 2′-propenyliden]-3 - hydroxymethyl-2 H-indolenine hydrochloride. This reaction led us to elaborate a rapid colorimetric assay for quantitative determination of indole-3-methanol formed by peroxidases as the product of oxidation of the plant growth regulator indole-3-acetic acid.

2,3-diaminophenazine is the product from the horseradish peroxidase-catalyzed oxidation of o-phenylenediamine

NMR and mass spectroscopic evidence has been obtained which indicates that the product of the oxidation of o-phenylenediamine by hydrogen peroxide, uncatalyzed or catalyzed by horseradish peroxidase, is 2,3-diaminophenazine. These results settle disparate literature descriptions. The process is most likely free radical in nature starting with the abstraction of a labile amino hydrogen atom.

Magic numbers for water–ammonia binary clusters: Enhanced stability of ion clathrate structures

The formation of water–ammonia binary clusters (H2O)n(NH3)mH+ (q≲40, q=n+m), have been investigated employing a neutral supersonic nozzle expansion of premixed water–ammonia gas with molecular-beam-mass spectrometry. The analysis of the mass spectra reveals that the number of water-rich clusters is greatly increased as the cluster size is increased. Mass spectroscopic evidence for the existence of enhanced structural stabilities (‘‘magic numbers’’) has been found at the protonated clusters (H2O)20(NH3)mH+ (m=1–6) and (H2O)27NH+4 . Considerations for the magic number stabilities are presented within the framework of ion clathrate (ion-centered cage) structures. Monte Carlo simulations are also presented for ionized (protonated) clusters around n=20 and n=27 with m=1. The clusters (H2O)20NH+4 and (H2O)27NH+4 have greater binding energies per molecule than their neighbors, in agreement with the mass spectroscopic observations. The calculated structure for (H2O)20NH+4 also indicates the stability of pentagonal rings of water molecules and deformed dodecahedral structure with an NH+4 ion trapped inside; the cluster is especially stable due not only to the strong Coulombic interaction (ionic hydrogen bonding) between the NH+4 ion and the surrounding 20 water molecules but to hydrogen bonding networks forming the cage structure. The proposed ion-centered cage model can also explain satisfactorily the well-known stability of the water cluster of (H2O)20H3O+.

Jeediflavanone—a biflavonoid from Semecarpus anacardium

A new biflavonoid, jeediflavanone, has been isolated recently from the alcoholic extract of the nut shells of Semecarpus anacardium. It was dehydrogenated with iodine and potassium acetate in acetic acid to the corresponding, relatively more stable biflavone SA5. The solvent induced methoxy shift studies of SA5 heptamethyl ether confirmed the interflavonoid linkage as well as the structure of jeediflavanone. Chemical, 1H NMR and mass spectroscopic evidence are presented in support of the structures of both jeediflavanone and SA5.