Christian Merten

University of Alberta, Edmonton, Alberta, Canada

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Publications (24)97.21 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: The synthesis of the first examples of tellurophenes exhibiting phosphorescence in the solid state and under ambient conditions (room temperature and in air) is reported. Each of these main-group-element-based emitters feature pinacolboronates (BPin) as ring-appended side groups. The nature of the luminescence observed was also investigated using computational methods.
    Angewandte Chemie International Edition 03/2014; · 13.73 Impact Factor
  • Christian Merten, Robert McDonald, Yunjie Xu
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    ABSTRACT: In the present study, we use vibrational circular dichroism (VCD) spectroscopy to investigate the metal-centered Δ and Λ chirality of a tris(diamine)nickel(II) complex. Chiral diphenylethylenediamine is chosen as the ligand, which puts the Δ and Λ isomers of the complex in a diastereomeric relationship. X-ray crystallography indicates an equal preference of both stereoisomers in the solid state. This equal preference is also supported by the related density functional theory calculations. A comparison between the experimental and calculated VCD spectra also proves the existence of both isomers in an acetonitrile solution. However, a significant shift of the equilibrium toward the Λ diastereomer is found for the complex in dimethyl sulfoxide. This solvent-induced preference for a particular absolute configuration is hypothesized to arise from a stronger and more effective solvation of the Λ isomer. The observation that the solvent can significantly influence and shift an equilibrium between two diastereomeric forms is expected to have important implications on structural analysis and on how reaction mechanisms are rationalized.
    Inorganic Chemistry 03/2014; · 4.59 Impact Factor
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    ABSTRACT: The three-dimensional structure of a peptide is strongly influenced by its solvent environment. In the present study, we study three cyclic tetrapeptides which serve as model peptides for β-turns. They are of the general structure cyclo(Boc-Cys-Pro-X-Cys-OMe) with the amino acid X being either glycine (), or l- or d-leucine ( or ). Using vibrational circular dichroism (VCD) spectroscopy, we confirm previous NMR results which showed that adopts predominantly a βII turn structure in apolar and polar solvents. Our results for indicate a preference for a βI structure over βII. With increasing solvent polarity, the preference for is shifted from βII towards βI. This conformational change goes along with the breaking of an intramolecular hydrogen bond which stabilizes the βII conformation. Instead, a hydrogen bond with a solvent molecule can stabilize the βI turn conformation.
    Physical Chemistry Chemical Physics 02/2014; · 3.83 Impact Factor
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    ABSTRACT: A series of Lewis base adducts of 9-bromo-9-borafluorene (BrBFl-LB, LB = IPr, IPrCH2, PPh3, and PCy3), parent borafluorenes (HBFl-IPr and HBFl-IPrCH2), and the bisadduct [(DMAP)2BFl]Br were prepared and structurally characterized (IPr = [(HCNDipp)2C:], IPrCH2 = [(HCNDipp)2C═CH2], Dipp = 2,6-i-Pr2C6H3, and DMAP = N,N-dimethylaminopyridine). The adducts BrBFl-IPr, BrBFl-PPh3, BrBFl-PCy3, [(DMAP)2BFl]Br, BrBFl-IPrCH2, and HBFl-IPrCH2 were found to exhibit bright blue luminescence with low to moderately high quantum efficiencies (19 to 63%). Selective irradiation at different excitation wavelengths revealed the presence of two distinct emission processes in the adducts BrBFl-LB, leading to a ligand-independent, presumably borafluorene-based, blue light emission at 435 nm and another less intense emission band in the ultraviolet region (315-324 nm); [(DMAP)2BFl]Br exhibits an emission profile that tails into the visible region. Time-dependent density functional theory studies are also included for representative borafluorene adducts. With a judicious choice of functional groups at boron, one can envisage the future generation of a whole library of 4-coordinate borafluorene-based luminogens that complement the efficient light-emitting behavior known for the widely studied boron-dipyrromethene analogues.
    Inorganic Chemistry 01/2014; · 4.59 Impact Factor
  • Journal of Physical Chemistry Letters 10/2013; · 6.59 Impact Factor
  • Christian Merten, Yunjie Xu
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    ABSTRACT: Vibrational circular dichroism (VCD) spectroscopy is a powerful tool to characterize absolute configurations and conformations of chiral organometallic systems. Such characterizations rely on the corresponding density functional theory (DFT) spectral simulations which may become very time consuming and sometimes even impossible for systems with increasing complexity. Systematic studies on small model compounds can lead to empirical structure-spectra relationships. The present work continues the systematic investigations of transition metal complexes of chiral trans-1,2-diamino-cyclohexane (chxn). VA and VCD spectra of the mixed-ligand complexes [Cu(chxn)2L](2+) with L being either ethylene diamine (en) or N,N'-dimethylethylene diamine (dmen) are measured. The comparison of the experimental spectra of the mixed-ligand complexes with those of the distorted octahedral complex [Cu(chxn)3](2+) reveals that the VA and VCD patterns below 1500 cm(-1) of the three complexes are not significantly affected by the nature of the third ligand, while the VCD pattern of the NH2-bending modes in the 1500 to 1800 cm(-1) region features some characteristic changes. Comparison with the corresponding DFT spectral calculations shows that these spectral differences are related to the relative abundance of the Δ- and Λ-configurations at the metal ion. In addition, the results of this study highlight that the VCD pattern of the NH2-bending modes is characteristic of the coordination number and the configuration of the metal center.
    Dalton Transactions 06/2013; · 3.81 Impact Factor
  • Christian Merten, Myung Ho Hyun, Yunjie Xu
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    ABSTRACT: In the present work, we report a comprehensive vibrational circular dichroism (VCD) spectroscopic study of a chiral crown ether which features an axial chiral 3.3'-diphenyl-1,1'-binaphthyl group as chiral moiety. By comparing the experimental and calculated VCD spectra, we show that the presumably very flexible crown ether preferably adopts only one ring conformation. Conformational flexibility is observed in the 2,4-dinitrophenyl-diazophenol group, which was previously introduced for colorimetric detection of primary amines and amino alcohols (Cho et al., Chirality 2011;23:349-353). The VCD spectra of the host-guest complexes with phenyl glycinol (PG) and phenyl alaninol have been studied as well. Based on the spectra calculated, it is shown that the diastereomeric complexes in general can be differentiated using VCD spectroscopy. Furthermore, the experimental VCD spectra of the complexes of the host molecule with PG support the above finding. Chirality 25:294-300, 2013. © 2013 Wiley Periodicals, Inc.
    Chirality 05/2013; 25(5):294-300. · 1.72 Impact Factor
  • Christian Merten, Yunjie Xu
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    ABSTRACT: Hand-me-down chirality: Chirality transfer from methyl lactate to ammonia has been investigated and the mirror-imaged vibrational circular dichroism (VCD) spectra of a pair of enantiomers of a flexible chiral molecular complex are presented. The distinct VCD spectral pattern provides decisive evidence for the existence of two dominant and subtly different conformers of the complex.
    Angewandte Chemie International Edition 01/2013; · 13.73 Impact Factor
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    ABSTRACT: The influence of adhesion on molecular conformations-besides solely molecule orientation-and vice versa was rarely considered in adhesion science due to the difficult analysis of conformational equilibria, in general, and the high number of possible conformations in classical polymers, in particular. Fortunately, some insight is available from the interphase chemistry of proteins due to the importance regarding their biological function in heterogeneous systems. Peptides and proteins are, thus, ideal model systems for the experimental and theoretical investigation of conformational changes in interphases. The conformational equilibrium of any kind of compound or, more specifically, a polymer interacting with a surface must differ in the interphase when compared with the bulk. This is also the case for common adhesives. Therefore, we define that the interphase of an adhesive bond is the area in which the chemical composition or the conformational equilibrium differs from that of the bulk phase
    Journal of Adhesion. 01/2013; 89(2):77-95.
  • Christian Merten, Yunjie Xu
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    ABSTRACT: Vibrational circular dichroism (VCD) spectroscopy has a unique specificity to chirality and is highly sensitive to the conformational equilibria of chiral molecules. On the other hand, the matrix-isolation (MI) technique allows substantial control over sample compositions, such as the sample(s)/matrix ratio and the ratio among different samples, and yields spectra with very narrow bandwidths. We combined VCD spectroscopy with the MI technique to record MI-VCD and MI-vibrational absorption spectra of 3-butyn-2-ol at different MI temperatures, which allowed us to investigate the conformational distributions of its monomeric and binary species. Good mirror-imaged MI-VCD spectra of opposite enantiomers were achieved. The related conformational searches were performed for the monomer and the binary aggregate and their vibrational absorption and VCD spectra were simulated. The well-resolved experimental MI-VCD bands provide the essential mean to assign the associated vibrational absorption spectral features correctly to a particular conformation in case of closely spaced bands. By varying the matrix temperature, we show that one can follow the self-aggregation process of 3-butyn-2-ol and confidently correlate the MI-VCD spectral features with those obtained for a 0.1 M CCl(4) solution and as a neat liquid at room temperature. Comparison of the aforementioned experimental VCD spectra shows conclusively that there is a substantial contribution from the 3-butyn-2-ol aggregate even at 0.1 M concentration. This spectroscopic combination will be powerful for studying self-aggregation of chiral molecules, and chirality transfer from a chiral molecule to an interacting achiral molecule and in electron donor-acceptor chiral complexes.
    ChemPhysChem 10/2012; · 3.35 Impact Factor
  • Christian Merten, Kaitlynd Hiller, Yunjie Xu
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    ABSTRACT: Transition metal complexes of ethylenediamine have attracted significant interest as prototype systems for a range of studies related to their chiroptical properties. In order to better elucidate the effects of different central metal ions and also different coordination numbers on the vibrational circular dichroism (VCD) spectra, trans-1,2-diamino cyclohexane (chxn) was chosen as the chiral ligands in the current report. In this case the conformation of the diamino ligand is predetermined by its absolute configuration and the transition from the λ- to the δ-form that can occur in the case of ethylenediamine is no longer possible. The fingerprint region of the vibrational absorption and VCD spectra of three transition metal complexes of chxn have been analysed in detail. For the tris chelate complexes Ni(chxn)(3)(2+) and Cu(chxn)(3)(2+), selective enhancement of some VCD bands in the otherwise almost identical spectra has been observed and explained in terms of a ring current mechanism and of a different number of unpaired electrons of the metal centers. The comparison of the VCD spectra of Cu(chxn)(3)(2+) and Cu(chxn)(2)(2+) reveals the effects of coordination number that manifest as an inversion of the strong bisignate VCD pattern of the NH(2) scissor vibrational modes. This leads to the conclusion that this region can be used to extract information about the ligand environment and the chirality of the metal center.
    Physical Chemistry Chemical Physics 08/2012; 14(37):12884-91. · 3.83 Impact Factor
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    ABSTRACT: BINAP (2,2'-diphenylphosphino-1,1'-binaphthyl) is a unique binaphthyl diphosphine ligand with axial chirality. The palladium complexes of BINAP and of its derivative TOLBINAP have found extensive applications in the field of asymmetric syntheses. The conformational changes in the BINAP and TOLBINAP ligands before and after coordination with palladium have been investigated using density functional theory, vibrational absorbance (VA) and vibrational circular dichroism (VCD) spectroscopy. VA and VCD spectra of these two chiral ligands and their corresponding palladium complexes have been recorded in CDCl(3) solution. Extensive conformational searches have been carried out for both the ligands and the associated palladium complexes. Coordination with palladium has been found to introduce structural rigidity to the ligands. The calculated VA and VCD spectra of the ligands and complexes in the gas phase show substantial differences to the experimental data. Incorporation of the implicit polarisable continuum solvation model has provided much better agreement between theory and experiment, especially for the complexes, allowing clear identification of the species and conformations. This and the high specificity of VCD spectral signatures to chirality and to conformations suggest the potential applications of VCD spectroscopy for following these important catalytic species in solution reactions directly.
    Dalton Transactions 08/2012; 41(35):10817-24. · 3.81 Impact Factor
  • Christian Merten, Honggang Li, Laurence A Nafie
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    ABSTRACT: In the present work, the first observation of strong resonance Raman optical activity (RROA) involving more that one resonant electronic state is reported. The chiral transition metal complex bis-(trifluoroacetylcamphorato) copper(II), abbreviated Cu(tfc)(2), exhibits both resonance Raman (RR) and RROA spectra with laser excitation at 532 nm. Vibrational assignments for this complex were carried out by comparing the non-RR spectra of Cu(tfc)(2) excited at 1024 nm to density functional theory (DFT) calculations. The theory of the single-electronic-state (SES) RROA is extended to the next simplest level of theory involving two resonant electronic states (TES) without interstate vibronic coupling as an aide to the interpretation of the observed TES-RROA spectra. Based on measured UV-vis electronic absorbance spectra and corresponding TD-DFT calculations, the most likely two states associated with the RROA spectra are identified.
    The Journal of Physical Chemistry A 06/2012; 116(27):7329-36. · 2.77 Impact Factor
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    ABSTRACT: Splitting it up: Excellent agreement between the experimental and the quantum-chemically simulated Raman optical activity (ROA) spectrum of (+)-poly(trityl methacrylate) shows that the polymer backbone adopts a left-handed helical conformation while the trityl side groups display a left-handed propeller conformation. Thus ROA can be used to determine the complete structure of synthetic chiral polymers in solution.
    Angewandte Chemie International Edition 09/2011; 50(42):9973-6. · 13.73 Impact Factor
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    ABSTRACT: The afterglow of an atmospheric pressure plasma has been used for the fast oxidative functionalization of multi-walled carbon nanotubes (MWCNTs). Scanning electron microscopy and Raman spectroscopy demonstrate that the MWCNT morphology is mostly preserved when the MWCNTs are dispersed in a solvent and injected as a spray into the plasma. Contact angle measurements show that this approach enhances the wettability of MWCNTs and reduces their sedimentation in an aqueous dispersion. X-ray photoelectron spectroscopy, IR spectroscopy, and electrokinetic measurements show that oxygen plasma incorporates about 6.6 at.% of oxygen and creates mainly hydroxyl and carboxyl functional groups on the MWCNT surface. The typical effective treatment time is estimated to be in the range of milliseconds. The approach is ideally suited for combination with the industrial gas phase CVD synthesis of MWCNTs.
    Journal of Colloid and Interface Science 07/2011; 359(1):311-7. · 3.17 Impact Factor
  • Christian Johannessen, Lutz Hecht, Christian Merten
    ChemPhysChem 04/2011; 12(8):1419-21. · 3.35 Impact Factor
  • Christian Merten, Marc Amkreutz, Andreas Hartwig
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    ABSTRACT: The present work provides a comprehensive theoretical and experimental study of the vibrational circular dichroism of (S)-α-phenylethyl isocyanide in chloroform. The structure in solution is investigated systematically by density functional theory calculations starting from the isolated molecule and then by considering solvent effects implicitly using the PCM and explicitly by taking into account molecular complexes of the isocyanide molecule and chloroform. Furthermore, the influence of dimerisation is evaluated, and it is finally found that the structure of (S)-α-phenylethyl isocyanide in chloroform is best described assuming a solvated dimer. These results are underlined by a quantitative correlation of the experimentally and theoretically obtained rotational strengths and a robust modes analysis.
    Physical Chemistry Chemical Physics 10/2010; 12(37):11635-41. · 3.83 Impact Factor
  • Christian Merten, Andreas Hartwig
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    ABSTRACT: The structures of the helical chiral polymer poly(trityl methacrylate), PTrMA, in solid state and in chloroform solution are compared by using vibrational circular dichroism spectroscopy. The differences between the spectra are discussed in detail based on band assignments and density functional theory calculations. Therefore, VA and VCD spectra of oligomers of PTrMA were calculated. It is shown that in solution as well as in solid state the helical structure is maintained. Furthermore, it was possible to determine the helical screw sense of the dextrorotary enantiomer (+)-PTrMA to be left-handed.
    Macromolecules. 09/2010; 43(20).
  • Christian Merten, Marc Amkreutz, Andreas Hartwig
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    ABSTRACT: Chiral alpha-methylbenzyl amine is a well known and often used chiral auxiliary, e.g., in the resolution of racemates or asymmetric catalysis. In this work, alpha-methylbenzyl amine and its derivatives N,alpha-dimethylbenzyl amine, N,N,alpha-trimethylbenzyl amine, and bis[alpha-methylbenzyl] amine were investigated by vibrational circular dichroism (VCD) spectroscopy and density functional theory (DFT). For all compounds, stable low energy conformers were obtained by the DFT calculations and based on those, the theoretical vibrational absorption (VA) and VCD spectra were calculated and compared with experimental spectra. Hence, the absolute configurations and conformational preferences were determined. A qualitative comparison of all the experimental VCD spectra of the investigated chiral molecules supported by the calculated ones is given which clearly shows similarities between the spectra of the different chiral amines. These can be assigned to vibrations of the unchanged chiral center.
    Chirality 02/2010; 22(8):754-61. · 1.72 Impact Factor
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    ABSTRACT: Vibrational circular dichroism (VCD) spectroscopy and density functional theory (DFT) calculations are used to investigate the keto-enol equilibrium of 3-(trifluoroacetyl)-camphor (TFC) and to study the interaction of TFC with chiral amines in deuterated Chloroform. It is shown that the VCD spectra of the enol- and keto forms of TFC can clearly be distinguished and that the enol form is favored. By deprotonation of the TFC enol with chiral amines, no indication of a mutual diasteriomeric influence on the VCD spectra induced by transfer of stereochemical information between the chiral ionic species is found, neither experimentally nor theoretically.
    Chirality 02/2010; 22(8):772-7. · 1.72 Impact Factor

Publication Stats

41 Citations
1 Download
982 Views
97.21 Total Impact Points

Institutions

  • 2011–2013
    • University of Alberta
      • Department of Chemistry
      Edmonton, Alberta, Canada
    • University of Glasgow
      • School of Chemistry
      Glasgow, SCT, United Kingdom
  • 2008–2010
    • Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM
      • Department of Adhesive Bonding Technology and Surfaces
      Bremen, Bremen, Germany