Additional Oxygen Atoms Research Articles

Structural and Biochemical Characterization of the Cytochrome P450 CypX (CYP134A1) from Bacillus subtilis: A Cyclo-l-leucyl-l-leucyl Dipeptide Oxidase

Cytochrome P450 CypX (CYP134A1), isolated from Bacillus subtilis, has previously been implicated in the three-step oxidative transformation of the diketopiperazine cyclo-l-leucyl-l-leucyl into pulcherriminic acid, a precursor of the extracellular iron chelate pulcherrimin. In this study, we present the first experimental data relating to CYP134A1, where we show that CYP134A1 binds cyclo-l-leucyl-l-leucyl with an affinity of 24.5 +/- 0.5 muM. Structurally related diketopiperazines sharing similar alkyl side chains to cyclo-l-leucyl-l-leucyl also bind to CYP134A1 with comparable affinity. CYP134A1 is capable of catalyzing the in vitro oxidation of diketopiperazine substrates when supported with several alternate electron transfer partner systems. Products containing one additional oxygen atom and which are intermediate products of the expected pulcherriminic acid were identified by GCMS. The oxidation of related diketopiperazines reveals that different oxidative pathways exist for CYP134A1-catalyzed diketopiperazine oxidation. The crystal structure of CYP134A1 has been determined to 2.7 A resolution in the absence of substrate and in the presence of bound phenylimidazole ligands to 3.1 and 3.2 A resolution. The active site is dominated by hydrophobic residues and contains an unusual proline residue in place of the normally conserved alcohol residue that typically plays an important role in oxygen activation. The B-B(2) substrate recognition loop, which forms part of the active site, shows considerable flexibility and was found in both open and closed conformations in different structures. These results represent the first insights into the structural and biochemical basis underlying the multistep oxidation catalyzed by CYP134A1.

Structural Characterisation of Degradation Products Formed upon Di-n-Butyl Phthalate Radiolysis by High-Performance Liquid Chromatography Electrospray Tandem Mass Spectrometry

Structural characterisation of 15 degradation products, formed upon di-n-butyl phthalate (DBP) radiolysis, has been achieved using a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) coupling. The dissociation behaviour of protonated DBP was first established to be further used to characterise structural deviation in the degradation products. Based on accurate mass measurements, compounds shown by HPLC-MS analysis were all found to be DBP oxidation products, amongst which various sets of isomers could be distinguished. Collision-induced dissociation experiments performed on each electrosprayed molecule first allowed unambiguous definition of the location of the additional oxygen atoms; that is, in the alkyl branch or on the aromatic ring. Although location of the oxygen atom in the alkyl branches could not always be precisely determined, relative abundances of some product ions allowed oxygenated functions to be identified.

Unravelling the atomic structure of cross-linked (1 × 2) TiO2(110)

The cross-linked (1 × 2) reconstruction of TiO(2)(110) is a frequently observed phase reflecting the surface structure of titania in a significantly reduced state. Here we resolve the atomic scale structure of the cross-linked (1 × 2) phase with dynamic scanning force microscopy operated in the non-contact mode (NC-AFM). From an analysis of the atomic-scale contrast patterns of the titanium and oxygen sub-structures obtained by imaging the surface with AFM tips having different tip apex termination, we infer the hitherto most accurate model of the atomic structure of the cross-linked (1 × 2) phase. Our findings suggest that the reconstruction is based on added rows in [001] direction built up of Ti(3)O(6) units with an uninterrupted central string of oxygen atoms accompanied by a regular sequence of cross-links consisting of linear triples of additional oxygen atoms in between the rows. The new insight obtained from NC-AFM solves previous controversy about the cross-linked TiO(2)(110) surface structure, since previously proposed models based on cross-links with a lower O content do not appear to be consistent with the atom-resolved data presented here. Instead, our measurements strongly support the Ti(3)O(6) motif to be the structural base of the cross-linked (1 × 2) reconstruction of TiO(2)(110).

Human IgG1 Hinge Fragmentation as the Result of H2O2-mediated Radical Cleavage

Hinge cleavage of a recombinant human IgG1 antibody, generated during production in a Chinese hamster ovary cell culture, was observed in the purified material. The cleavage products could be reproduced by incubation of the antibody with H(2)O(2) and featured complementary ladders of the C- and N-terminal residues (Asp(226)-Lys(227)-Thr(228)-His(229)-Thr(230)) in the heavy chain of the Fab domain and the upper hinge of one of the Fc domains, respectively. Two adducts of +45 and +71 Da were also observed at the N-terminal residues of some Fc fragments and were identified as isocyanate and alpha-ketoacyl derivatives generated by radical cleavage at the alpha-carbon position through the diamide and alpha-amidation pathways. We determined that the hinge cleavage was initiated by radical-induced breakage of the disulfide bond between the two hinge cysteines at position 231 (Cys(231)-Pro-Pro-Cys-Pro), followed by the formation of a thiyl radical (Cys(231)-S(*)) on one cysteine and sulfenic acid (Cys(231)-SOH) on the other. The location of the initial radical attack and the critical role of Cys(231) were demonstrated by the observation that 5,5-dimethyl-1-pyrroline N-oxide only reacted with the Cys(231) radical and completely blocked hinge cleavage, suggesting the necessity of an electron/radical transfer from the Cys(231) radical to the hinge residues where cleavage was observed. As a precursor of hydroxyl radicals, H(2)O(2) is widely produced in healthy cells and tissues and therefore could be the source for the radical-induced fragmentation of human IgG1 antibodies in vivo.

Mechanistic Studies and Improvement of Coinage Metal-Catalyzed Transformation of Alkynyloxiranes to Furans: An Alcohol Addition−Cyclization−Elimination Cascade

In the presence of alcohol Ag or Au salts or complexes catalyze the conversion of alkynyloxiranes to substituted furans. Both catalysts are effective, and a large furan diversity can be obtained in high yield with one or the other catalyst. Mechanistic studies revealed that a cascade pathway and not the sometimes reported direct intramolecular nucleophilic addition of oxirane oxygen atom to intermediate acetylene-metal pi-complex occurs. Under the defined conditions, the intermediate formation of epoxide opening products has been identified. Depending on the catalyst, one or both of the latter cyclized to dihydrofurans, and further elimination of the alcohol led to the corresponding furans. These results highlight the duality between oxophilicity and alkynophilicity of Ag or Au salts.

(Ni2), (Ni3), and (Ni2+ Ni3): A Unique Example of Isolated and Cocrystallized Ni2and Ni3Complexes

Structural and magnetic characterization of compound {[Ni(2)(L)(2)(OAc)(2)][Ni(3)(L)(2)(OAc)(4)]}.2CH(3)CN (3) (HL = the tridentate Schiff base ligand, 2-[(3-methylamino-propylimino)-methyl]-phenol) shows that it is a rare example of a crystal incorporating a dinuclear Ni(II) compound, [Ni(2)(L)(2)(OAc)(2)], and a trinuclear one, [Ni(3)(L)(2)(OAc)(4)]. Even more unusual is the fact that both Ni(II) complexes, [Ni(2)(L)(2)(OAc)(2)] (1) and [Ni(3)(L)(2)(OAc)(4)(H(2)O)(2)].CH(2)Cl(2).2CH(3)OH (2), have also been isolated and structurally and magnetically characterized. The structural analysis reveals that the dimeric complexes [Ni(2)(L)(2)(OAc)(2)] in cocrystal 3 and in compound 1 are almost identical-in both complexes, the Ni(II) ions possess a distorted octahedral geometry formed by the chelating tridentate ligand (L), a chelating acetate ion, and a bridging phenoxo group with very similar bond angles and distances. On the other hand, compound 2 and the trinuclear complex in the cocrystal 3 show a similar linear centrosymmetric structure with the tridentate ligand coordinated to the terminal Ni(II) and linked to the central Ni(II) by phenoxo and carboxylate bridges. The only difference is that a water molecule found in 2 is not present in the trinuclear unit of complex 3; instead, the coordination sphere is completed by an additional bridging oxygen atom from an acetate ligand. Variable-temperature (2-300 K) magnetic susceptibility measurements show that the dinuclear unit is antiferromagnetically coupled in both compounds (2J = -36.18 and -29.5 cm(-1) in 1 and 3, respectively), whereas the trinuclear unit shows a very weak ferromagnetic coupling in compound 3 (2J = 0.23 cm(-1)) and a weak antiferromagnetic coupling in 2 (2J = -8.7(2) cm(-1)) due to the minor changes in the coordination sphere.

Photoionization efficiency spectroscopy and density functional theory investigations of RhHo2On (n=–2) clusters

The experimental and theoretical adiabatic ionization energies (IEs) of the rhodium-holmium bimetallic clusters RhHo(2)O(n) (n=0-2) have been determined using photoionization efficiency spectroscopy and density functional theory (DFT) calculations. Both sets of data show the IE of RhHo(2)O to be significantly lower than the values for RhHo(2) and RhHo(2)O(2), which are found to be similar. This indicates that there are significant changes in electronic properties upon sequential addition of oxygen atoms to RhHo(2). The DFT investigations show that the lowest energy neutral structures are a C(2v) triangle for RhHo(2), a C(2v) planar structure for RhHo(2)O where the O atom is doubly bridged to the Ho-Ho bond, and a C(2v) nonplanar structure for RhHo(2)O(2), where the O(2) is dissociative and each O atom is doubly bridged to the Ho-Ho bond in the cluster above and below the RhHo(2) trimer plane. Good correlation between the experimental and computational IE data imply that the lowest energy neutral structures calculated are the most likely isomers ionized in the molecular beam. In particular, the theoretical adiabatic IE for the dissociative RhHo(2)O(2) structure is found to compare better with the experimentally determined value than the corresponding lowest energy O(2) associative structure.

Stability of Polynitrogen Compounds: The Importance of Separating the σ and π Electron Systems

Planar N(x) systems such as cyclo-N(5)(-) and N(5)(+) tend to be more stable than nonplanar systems such as the neutral cyclo-N(6). It is proposed that the key to stabilization is the separation of the sigma and pi electron systems. In both cyclo-N(5)(-) and N(5)(+), a six-pi-electron system is created upon either adding to or removing from the cyclo-N(5) radical one electron. Judicious addition of oxygen atoms to polynitrogen ring compounds such as cyclo-N(4) and cyclo-N(6) can increase their thermodynamic and kinetic stabilities, accompanied by only a small reduction in their efficiency as high energy density materials (HEDMs). The properties of some of these compounds are calculated and compared with the parent all-nitrogen compounds. Coordination of one or more oxygen atoms to the ring leads to effective separation of the sigma and pi electron systems helping to stabilize the systems. Natural bond analysis indicates that the exocyclic NO bonds can assume a single or double bond character, depending on the ring system.

Density functional theory study of the initial oxidation of the Pt(111) surface

We used density functional theory calculations to examine the initial stages of oxidation of the Pt(111) surface. Consistent with prior studies, our calculations predict that oxygen atoms adsorb on fcc sites and form $p(2\ifmmode\times\else\texttimes\fi{}2)$ and $p(2\ifmmode\times\else\texttimes\fi{}1)$ structures at coverages of 0.25 and 0.50 ML, respectively. In addition to various surface configurations of oxygen on fcc sites, we examined subsurface oxygen and clustering of oxygen atoms on the surface. We find that subsurface oxygen is not the precursor to the oxidation of the Pt(111) surface. Instead, we predict a strong preference for the formation and growth of one-dimensional Pt oxide chains within the $p(2\ifmmode\times\else\texttimes\fi{}1)$ structure. In particular, at coverages above 0.50 ML, additional oxygen atoms prefer to aggregate between the close-packed oxygen rows formed by the $p(2\ifmmode\times\else\texttimes\fi{}1)$ structure and induce large buckling $(\ensuremath{\sim}1.8\text{ }\text{\AA{}})$ and modification of the charge of the surface Pt atoms. The result is an oxide compound with threefold and fourfold Pt-O coordination that grows as a one-dimensional chain running parallel to the oxygen rows of the $p(2\ifmmode\times\else\texttimes\fi{}1)$ structure. Furthermore, half of the oxygen atoms in the Pt oxide chains reside near hcp sites, contrary to some reports that oxygen atoms reside only on the fcc sites on Pt(111). Our results agree well with a recent scanning tunneling microscopy study and suggest a precursor mechanism to the oxidation of metal surfaces involving Pt oxide chain formation and growth on terraces at moderate oxygen coverages. Our results should have important implications to current models of NO and CO oxidation on Pt(111) and potentially on studies of the initial oxidation of other transition-metal and bimetallic surfaces.

Variant c-type cytochromes as probes of the substrate specificity of the E. coli cytochrome c maturation (Ccm) apparatus

c-type cytochromes are normally characterized by covalent attachment of the iron cofactor haem to protein through two thioether bonds between the vinyl groups of the haem and the thiol groups of a CXXCH (Cys-Xaa-Xaa-Cys-His) motif. In cells, the haem attachment is an enzyme-catalysed post-translational modification. We have previously shown that co-expression of a variant of Escherichia coli cytochrome b(562) containing a CXXCH haem-binding motif with the E. coli Ccm (cytochrome c maturation) proteins resulted in homogeneous maturation of a correctly formed c-type cytochrome. In contrast, in the absence of the Ccm apparatus, the product holocytochrome was heterogeneous, the main species having haem inverted and attached through only one thioether bond. In the present study we use further variants of cytochrome b(562) to investigate the substrate specificity of the E. coli Ccm apparatus. The system can mature c-type cytochromes with CCXXCH, CCXCH, CXCCH and CXXCHC motifs, even though these are not found naturally and the extra cysteine residue might, in principle, disrupt the biogenesis proteins which must interact intricately with disulfide-bond oxidizing and reducing proteins in the E. coli periplasm. The Ccm proteins can also attach haem to motifs of the type CX(n)CH where n ranges from 2 to 6. For n=3 and 4, the haem attachment was correct and homogeneous, but for higher values of n the holocytochromes displayed oxidative addition of sulfur and/or oxygen atoms associated with the covalent haem-attachment process. The implications of our observations for the haem-attachment reaction, for genome analyses and for the substrate specificity of the Ccm system, are discussed.

Study of interstitial oxygen mobility in RuSr 2GdCu 2O 8 by internal friction

The discovery of the spatial uniform coexistence of superconductivity and ferromagnetism in ruthenocuprates, RuSr 2GdCu 2O 8 (Ru-1212), has spurred an extraordinary development in the study of the competition between magnetism and superconductivity. However, several points of their preparation process and characterization that determine their superconductive behaviour are still obscure. The improvement of sample preparation conditions involves some thermal treatments in inert atmosphere. Anelastic spectroscopy measurements were made using an inverted torsion pendulum, operating with an oscillation frequency of 38 Hz, temperature in the 90 and 310 K range, heating rate of 1 K/min, and vacuum better than 10 −3 Pa. The results show anelastic relaxation peaks at 210 K related to the presence of interstitial oxygen atoms. The peaks decrease significantly with the oxygen loss caused by the heat treatments in vacuum, appearing again after the annealing of the sample in an oxygen atmosphere. These observed peaks are clearly related to the additional oxygen atoms, with activation energy 0.13 and 0.36 eV, and can be explained in terms by diffusional jumps of interstitial oxygen in the RuO 2 planes.

Crystal and molecular structures of three 2-sulphur-substituted cyclohexanones studied by X-ray crystallography and by ab initio molecular orbital calculations

The conformational features of three 2-sulphur-substituted cyclohexanone derivatives, which differ in the number of sulphur-bound oxygen atoms, i.e. zero (I), one (II) and two (III), were investigated by single crystal X-ray crystallography and geometry optimized structures determined using Hartree-Fock method. In each of (I)–(III) an intramolecular S … Ocarbonyl interaction is found with the magnitude correlated with the oxidation state of the sulphur atom, i.e. 2.838(3) Å in (I) to 2.924(2) Å in (II) to 3.0973(18) Å in (III). There is an inverse relationship between the strength of this interaction and the magnitude of the carbonyl bond. The supramolecular aggregation patterns are primarily determined by C–H … O contacts and are similarly influenced by the number of oxygen atoms in the molecular structures. Thus, a supramolecular chain is found in the crystal structure of (I). With an additional oxygen atom available to participate in C–H … O interactions, as in (II), a two-dimensional array is found. Finally, a three-dimensional network is found for (III). Despite there being differences in conformations between the experimental structures and those calculated in the gas-phase, the S … O interactions persist. The presence of intermolecular C–H … O interactions involving the cyclohexanone-carbonyl group in the solid-state, disrupts the stabilising intramolecular C–H … O interaction in the energetically-favoured conformation. (I): C12H13NO3S, triclinic space group P-1 with a = 5.392(3) Å, b = 10.731(6) Å, c = 11.075(6) Å, α = 113.424(4)°, β = 94.167(9)°, γ = 98.444(6)°, V = 575.5(6) Å3, Z = 2, R1 = 0.052; (II): C12H13NO4S, monoclinic P21/n, a = 7.3506(15) Å, b = 6.7814(14) Å, c = 23.479(5) Å, β = 92.94(3)°, V = 1168.8(4) Å3, Z = 4, R1 = 0.046; (III): C12H13NO5S, monoclinic P21/c, a = 5.5491(11) Å, b = 24.146(3) Å, c = 11.124(3) Å, β = 114.590(10)°, V = 1355.3(5) Å3, Z = 4, R1 = 0.051.

Redox transformations in desorption electrospray ionization

Redox changes occur in some circumstances when organic compounds are analyzed by desorption electrospray ionization mass spectrometry (DESI-MS). However, these processes are limited in scope and the data presented here suggest that there are only limited analogies between the redox behavior in DESI and the well-known solution-phase electrochemical processes in standard electrospray ionization (ESI). Positive and negative ion modes were both investigated and there is a striking asymmetry between the incidence of oxidation and of reduction. Although in negative ion mode DESI experiments, some aromatic compounds were ionized as odd-electron anion radicals, examples of full reduction were not found. By contrast, oxidation in the form of oxygen atom addition (or multiple oxygen atom additions) was observed for several different analytes. These oxidation reactions point to chemically rather than electrochemically controlled processes. Data is presented which suggests that oxidation is predominantly caused by reaction with discharge-created gas-phase radicals. The fact that common reducing agents and known antioxidants such as ascorbic acid are not modified, while a saturated organic acid like stearic acid is oxidized in DESI, indicates that the usual electrochemical redox reactions are not significant but that redox chemistry can be induced under special experimental conditions.

Structure of TeO2·B2O3 glasses inferred from infrared spectroscopy and DFT calculations

Glasses in the system (1 − x )TeO 2 · x B 2 O 3 glasses (with x = 0.3 and 0.4) have been prepared from melt quenching method. The structural changes were studied by FTIR spectroscopy and DFT calculations. From the analysis of the FTIR spectra it is reasonable to assume that when increasing boron ions content the tetrahedral [BO 4 ] units are gradually replaced by trigonal [BO 3 ] units. The increase in the number of non-bridging oxygen atoms would decrease the connectivity of the glass network, would depolymerize of borate chains and would necessite quite a radical rearrangement of the network formed by the [TeO 6 ] octahedral. This is possible considering that tellurium dioxide brings stoichiometrically two oxygen atoms in [TeO 4 ] and needs an additional oxygen atom for the formation of [TeO 6 ] octahedra. This additional oxygen atom is evidently taken off from the boron co-ordination and thus boron atoms transfer their [BO 4 ] co-ordination into [BO 3 ] co-ordination. We used the FTIR spectroscopic data in order to compute two possible models of the glasses matrix. We propose two possible structural models of building blocks for the formation of continuous random network glasses used by density functional theory (DFT) calculations.

Hypochlorous acid oxidizes methionine and tryptophan residues in myoglobin

After acute myocardial infarction (AMI), infiltrating proinflammatory cells generate two-electron oxidants such as hypochlorous acid (HOCl). Myoglobin (Mb) is present at ∼ 0.3 mM in cardiomyocytes and, therefore, represents a significant target for oxidation. Exposure of horse Mb (50 μM) to reagent HOCl (0–500 μM) or activated human neutrophils (4–40 × 10 6 cells/ml) yielded oxidized Mb (Mb ox) as judged by amino acid analysis and peptide mass mapping. HOCl/Mb ratios of 1–5 mol/mol gave Mb ox with up to four additional oxygen atoms. Hydrolysis of Mb ox followed by amino acid analysis indicated that methionine (Met) and tryptophan (Trp) residues were modified by HOCl. Peptide mass mapping revealed that Met55 was oxidized at a lower HOCl/Mb ratio than Met131 and this preceded Trp7/14 modification (susceptibility Met55 > Met131 > Trp7 > Trp14). Incubation of Mb with activated neutrophils and physiological chloride anion yielded Mb ox with a composition similar to that determined with HOCl/Mb ratios < 2 mol/mol, with oxidation of Met, but not Trp, detected. These data indicate that Mb undergoes site-specific oxidation depending on the HOCl/protein ratio. As Mb is released from necrotic cardiomyocytes into the vasculature after AMI, HOCl-modified Mb may be a useful surrogate marker to gauge the extent of myocardial inflammation.

Solvent−Solute Interactions in Hydrofluoroalkane Propellants

Understanding solvation in hydrofluoroalkane (HFA) propellants is of great importance for the development of novel pressurized metered-dose inhaler (pMDI) formulations. HFA-based pMDIs are not only the most widely used inhalation therapy devices for delivering small drug molecules to the respiratory tract, but they also hold promise as vehicles for the delivery of therapeutic biomolecules to and through the lungs. In this work we use binding energy calculations to determine the degree of interaction between HFA propellants and candidate HFA-philes, including a methyl-based tail (isohexane, ISO), and fragments of poly(ethylene oxide) (EO), poly(propylene oxide) (PO), and poly(lactide) (LA). The distinct nature of solvation forces of the two HFA propellants approved by the FDA for use in pMDIs, 1,1,1,2-tetrafluoroethane (HFA134a) and 1,1,1,2,3,3,3-heptafluoropropane (HFA227), is also studied. Binding energy (Ebst) calculations demonstrated that an increase in tail polarity through the addition of oxygen atoms in the fragment backbone provides for sites capable of interacting with the HFA propellant molecules, thus enhancing the stabilization energy of the complexes. The interaction energy between HFA227 and LA (EbHFA227-LA = -24.7 kJ.mol(-1)) is significantly more favorable than that between HFA227 and its hydrocarbon analog (EbHFA227-ISO = -10.0 kJ.mol(-1)). However, it was shown that not only the fragment polarity is of relevance in stabilizing the complexes. The accessibility of the oxygen atoms in the fragments of interest is also relevant. Cluster studies indicate that although both oxygen atoms in the LA fragment are available to form H-bonds with the propellant molecules, the ether oxygen in PO is accessible to only one propellant molecule, thus decreasing significantly the stabilization energy of the cluster. The results shown here serve as a guide for the design of novel HFA-philes for HFA-based pMDIs.

Zinc(II) Phosphonate Cage Compounds Derived from Zn6(Zn)L6 Centered Octahedral Cores

Three zinc(II) phosphonate cluster compounds have been hydrothermally synthesized and structurally characterized. Compound 1 consists of a centered {Zn6(Zn)L6}4− core and two {Zn(Phen)2(H2O)2}2+ countercations (L = N-(phosphonomethyl)pipecolinic acid, O3PCH2−NC5H9−CO2). The {Zn6(Zn)L6}4− core in compound 2 or 3 is covalently bonded to two Zn(H2O)42+ or {Zn(2,2′-bipy)(H2O)3}2+ cations through the coordination of two additional carboxylate oxygen atoms to form a nonanuclear cluster.

Effect of prior structural defects in quartz fiber lightguides on defect formation by γ radiation

The absorption spectra of unirradiated and irradiated (to fast neutron fluence 1012 and1014 cm−2 in VVR-SM) quartz-quartz fibers after additional irradiation with 60Co γ rays to 108 rad are investigated. It is shown that neutrons transform E′ centers into ≡Si-Si≡ centers. The kinetics of accumulation of bridge oxygen atoms under the action of γ radiation exhibits two stages. The first stage is due to neutron irradiation and the manifestation of preliminary potential centers of nonbridge oxygen atoms. The second stage is associated with the creation of additional nonbridge oxygen atoms under the action of γ radiation. The γ-ray dose for the onset of the second stage decreases as the fluence of the preliminary neutron irradiation increases.

Positive Identification of the Principal Component of a White Powder as Scopolamine by Quantitative One‐Dimensional and Two‐Dimensional NMR Techniques

An unidentified white powder collected as evidence in an intelligence investigation was characterized exclusively by nuclear magnetic resonance (NMR) analysis. A small fraction of the powder dissolved in D2O was subjected to a series of one- and two-dimensional techniques which were used to elucidate the molecular structure of the powder's major component and positively identify it as the scopolamine biotoxin. Quantitative one-dimensional experiments identified individual proton and carbon atom sites, and conventional 14N spectroscopy detected a single nitrogen atom site. Heteronuclear single quantum coherence data correlated all protons to their directly bonded carbon atom, and together with the quantitative spectra, were used to determine the number of protons directly bonded to each carbon atom. The presence of a methyl, carboxyl, and a benzyl group was also identified from these data. Correlation spectroscopy detected a three proton and a nine proton JH,H network, representing a CH2CH moiety and seven carbon atom ring, respectively. These five elements were assembled into an almost complete molecular structure by using long-range, J-coupled, 1H-13C pairs detected by heteronuclear multiple bond correlation (HMBC) spectroscopy and 1H-1H dipolar-coupled pairs found from nuclear Overhauser effect spectroscopy (NOESY) data. Additional oxygen atom sites were inferred from 1H-13C correlation intensities in the HMBC spectra along with 1H and 13C chemical shift values, or directly from NOESY correlations. Only a single oxygen atom site could not be inferred from NMR data, but its presence was inferred from comparisons to target analyte structures to complete the structure of the scopolamine molecule. To confirm these results, an ethanol/H2O solution of the powder was analyzed by direct infusion into an ion trap mass spectrometer. A prominent base signal was observed at m/z 304.1 amu, corresponding to the protonated molecular ion of scopolamine. Subsequently, the ion was selected and subjected to collision-induced dissociation, producing characteristic major MS/MS fragments at m/z 138.1 and 156.1. Comparisons of 1H and 13C chemical shift values and JH,H values measured from our NMR data were found to agree very favorably with previously reported values for scopolamine in D2O.

Coordination behavior of benzimidazole, 2-substituted benzimidazoles and benzothiazoles, towards transition metal ions

Coordination chemistry of benzimidazole and 2-substituted benzimidazole derivatives towards transition metal ions is reviewed. Benzimidazole complexes containing halides or carboxylates derivatives are discussed, as well as the coordination chemistry of 2-substituted benzimidazoles bearing additional nitrogen, oxygen or sulfur atoms as potential binding sites, which may form chelates. The latter ligands give place to a variety of metal-ligand coordination modes. In some cases, these bidentate ligands favour the formation of a six membered ring, by inclusion of a metal ion in a planar delocalized system. Some of the studied 2-substituded benzimidazoles include 2-uroyl, 2-carbamate, 2-benzothiazole, 2-(2-benzothiazolylamino)benzothiazole, 2-(2- aminobenzothiazolyl-amino) benzoxazole, 2-(4'-thiazolyl)benzimidazole, 2-((5-methylpyrazol-3- yl)methyl)benzimidazole, 2-guanidinobenzimidazole, 2-aminomethylbenzimidazole, 1- (benzimidazol-2-yl)phenolato, 2-(2-benzimidazol-2-yl)pyridine-N-oxide-N,O and N- (benzothiazol-2-yl)-dithiocarbamic methyl ester. It is important to mention that benzimidazole and its derivatives promote intra and inter-molecular interactions, such as hydrogen bonding and π- stacking, giving place to the formation of molecular aggregates.