Nader de Sousa Amadeu - Academia.edu (original) (raw)
Papers by Nader de Sousa Amadeu
Journal of the Chemical Society, Perkin Transactions 2, 2002
Theoretical calculations plus the solvent dependence of the 1 H, 13 C NMR and IR spectra were use... more Theoretical calculations plus the solvent dependence of the 1 H, 13 C NMR and IR spectra were used to determine the conformational equilibrium in N-methyl-2-fluoroacetamide (NMFA) and N-methyl-2-fluoropropionamide (NMFP). Ab initio calculations were used to identify the stable rotamers and obtain their geometries and the application of solvation theory on the 1 J CF coupling constant gave the conformer populations in the solvents studied. In NMFA ab initio calculations at the CBS-Q level yielded only two stable rotamers, the cis and trans, with ∆E(cis-trans) = 19.7 kJ mol Ϫ1. The presence of two conformers was confirmed by the FTIR spectra. Assuming these forms, the observed couplings when analysed by solvation theory gave ∆E = 21.3 kJ mol Ϫ1 in the vapour phase, decreasing to 8.9 kJ mol Ϫ1 in CDCl 3 and to 0.8 kJ mol Ϫ1 in DMSO. For NMFP the B3LYP calculations at the 6-311ϩϩg(2df,2p) level gave only the trans rotamer as stable, while the gauche form was a plateau in the potential energy surface. However the FTIR spectra clearly showed the presence of two conformers. A minimum for the gauche rotamer was only found when the SCRF (self consistent reaction field) routine was included in the theoretical calculations. The equilibrium in NMFP was therefore analysed by solvation theory in terms of the trans and gauche rotamers to give ∆E(gauche-trans) = 15.9 kJ mol Ϫ1 in the vapour phase, decreasing to 10.8 kJ mol Ϫ1 in CCl 4 and to 0.5 kJ mol Ϫ1 in DMSO.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The 2H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT)2 (1a), Tp*RuD(D2)(TH... more The 2H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT)2 (1a), Tp*RuD(D2)(THT) (1b), Tp*RuD(D2)2 (1c), Cp*RuD3(PPh3) (2) and RuD2(η-D2)2(PCy3)2 (3) have been measured in a wide temperature range. These compounds were chosen as potential model systems for hydrogen surface species in Ru-nanoparticles. The deuterium quadrupolar coupling constants Qcc and asymmetry parameters were extracted by 2H NMR line-shape analysis. The Qcc values of the deuterons bound to the metal vary between 13 kHz and 76 kHz. In addition all spectra show that some of the deuterium is incorporated into carbon positions exhibiting quadrupolar coupling constants in the range of 134 kHz to 192 kHz. The room temperature spectra contain an additional weak very narrow line which was assigned to deuterons exhibiting a high mobility. These deuterons are attributed to crystallographic impurity and partially to D2 molecules which lost by the complexes. The temperature where their motion is quenched a...
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs... more By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO4 3 ), namely helicate, mesocate, and mono-bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordinationbased structures as in transition-metal complexes.
![Research paper thumbnail of Symmetric geminal bisphosphinic acids RR´C[P(CH3)(O)OH]2- NMR and analytical studies](https://attachments.academia-assets.com/87795385/thumbnails/1.jpg)
](Phosphorus, Sulfur, and Silicon and the Related Elements, 2020
Four bisphosphinic acids RR´C[P(CH 3)(O)OH] 2 are characterized by 1 H, 13 Cf 1 Hg, and 31 Pf 1 H... more Four bisphosphinic acids RR´C[P(CH 3)(O)OH] 2 are characterized by 1 H, 13 Cf 1 Hg, and 31 Pf 1 Hg NMR data. H 3 C-P-C-P-CH 3 skeletons give rise to [A 3 X] 2 spin systems. Some algebraic equations are derived for manual analysis of [A 3 X] 2 spectra. HR NMR data for heteroaromatic substituents R in RC(H)[P(CH 3)(O)OH] 2 are reported. Dissociation constants and ion-specific chemical shifts d P of CH 3 C(OH)[P(CH 3)(O)OH] 2 are determined by 31 Pf 1 Hg NMR controlled titrations of 2a.
![Research paper thumbnail of NMR and symmetry in bisphosphonates R1R2N-CH[P(O)(OMe)2]2](https://attachments.academia-assets.com/87795392/thumbnails/1.jpg)
](Phosphorus, Sulfur, and Silicon and the Related Elements, 2017
Amino-methylene)bisphosphonates R 1 R 2 N-CH[P(O)(OMe) 2 ] 2 bearing achiral and chiral substitue... more Amino-methylene)bisphosphonates R 1 R 2 N-CH[P(O)(OMe) 2 ] 2 bearing achiral and chiral substituents (R 1 = Ph, R 2 = H, Me; and R 1 = PhCH(Me), R 2 = Me, Bn) were synthesized and characterized in CDCl 3 by 1 H, 1 H{ 31 P}, 13 C{ 1 H}, 31 P{ 1 H}, and 31 P NMR spectra. [P(O)(OMe) 2 ] 2 fragments from achiral compounds give rise to complex 1 H NMR spectra characteristic for the [A 3 M 3 X] 2 1 H NMR spectra while chiral compounds yield A 3 G 3 M 3 T 3 XY type spectra. Aspects of molecular symmetry governing the multiplet patterns are discussed and precise spectral parameters are calculated by line-shape iterations.
ChemistrySelect, 2018
Here we report, room temperature heterogeneous catalysis of the Suzuki-Miyaura cross-coupling rea... more Here we report, room temperature heterogeneous catalysis of the Suzuki-Miyaura cross-coupling reaction by a Pd 0 nanoparticle-immobilized porous organic polymer (TPU-Pd), providing excellent yields (up to 99%) using low catalyst loading. High nitrogen-and oxygen-donor content of triazine-based porous polyurethane (TPU) makes it an efficient porous polymer for Pd-immobilization and subsequent heterogeneous catalysis of CC cross-coupling reactions. X-ray photoelectron spectroscopy of TPU-Pd showed characteristic binding energy peaks of Pd 0. Atomic absorption spectroscopy revealed 10.4 wt% of Pd 0 in TPU-Pd, and transmission electron microscopy images showed well-dispersed and facetted Pd 0 nanoparticles of size 5-20 nm. Catalysis of Suzuki-Miyaura reaction was observed to be completed in 3 h at 25 8C for a wide range of aryl halide substrates with phenylboronic acid, whereas increasing the reaction temperature to 80 8C largely allows decreasing the reaction time to 0.5-1 h. The porosity and surface area of the catalyst was not affected after catalysis, and the catalyst has been reused for five consecutive runs.
Chemistry - A European Journal, 2017
α-Peptoids, or N-substituted glycine oligomers, are an important class of peptidomimetic foldamer... more α-Peptoids, or N-substituted glycine oligomers, are an important class of peptidomimetic foldamers with proteolytic stability. Nevertheless, the presence of cis-/trans-amide bond conformers, which contribute to the high flexibility of α-peptoids, is considered as a major drawback. A modified peptoid backbone with an improved control of the amide bond geometry could therefore help to overcome this limitation. Here we have performed the first thorough analysis of the folding propensities of α-aminoxy peptoids (or N-substituted 2-aminoxyacetic acid oligomers). To this end, the amide bond geometry and conformational properties of a series of model α-aminoxy peptoids were investigated using 1D and 2D NMR experiments, X-ray crystallography, NBO analysis, CD spectroscopy, and MD simulations revealing a unique preference for cis-amide bonds even in the absence of cis-directing side chains. The conformational analysis based on the MD simulations revealed that α-aminoxy peptoids can adopt helical conformations that can mimic the spatial arrangement of peptide side chains in a canonical α-helix. Given their ease of synthesis and conformational properties, α-aminoxy peptoids represent a new member of the peptoid family capable of controlling the amide isomerism while maintaining the potential for side-chain diversity.
Chemistry - A European Journal, 2017
Investigation of guest diffusion in porous metal-organic frameworks (MOFs) is of major importance... more Investigation of guest diffusion in porous metal-organic frameworks (MOFs) is of major importance since many porosityrelated properties of MOFs are influenced by diffusion effects. The diffusion of dimethylsulfoxide (DMSO) in the metal-organic framework (MOF) MIL-53-NH2(Al) was investigated through pulsedfield-gradient (PFG) NMR spectroscopy. The microporous material was synthesized in small crystallites (under 500 nm), which agglomerated in a large range of particle sizes (from hundreds of nanometers to tens of micrometers), giving a morphologically very heterogeneous sample. No special agglomeration pattern could be observed, which makes a PFG-NMR investigation very challenging, yet it represents a realistic situation for the diffusion of guest molecules in porous materials. We were able to distinguish between two diffusion regimes existing in parallel with each other over the total range from 15 ms up to 200 ms of observation times as accessible in the experiments: In the large crystal agglomerates (diameters above 20 µm) guest movement was found to be subdiffusive, with a time exponent = 0.8 (rather than 1 as for normal diffusion). Guest diffusion in the remaining, smaller host particles followed the pattern of normal diffusion within a bed of spheres of impenetrable external surfaces, with a size distribution in good agreement with that of the material under study. Diffusion in a rather complex system could thus be referred to a two-region model with novel potentials for application to systems of intricate topology.
Chemical Communications, 2016
For the first time, a microporous polyurethane (MPU) is prepared – it acts as an organocatalyst f... more For the first time, a microporous polyurethane (MPU) is prepared – it acts as an organocatalyst for aldol-type C–C bond forming reactions with high yields and under mild conditions.
Angewandte Chemie (International ed. in English), Jan 5, 2015
Caged supramolecular systems are promising hosts for guest inclusion, separation, and stabilizati... more Caged supramolecular systems are promising hosts for guest inclusion, separation, and stabilization. Well-studied examples are mainly metal-coordination-based or covalent architectures. An anion-coordination-based cage that is capable of encapsulating halocarbon guests is reported for the first time. This A4 L4 -type (A=anion) tetrahedral cage, [(PO4 )4 L4 ](12-) , assembled from a C3 -symmetric tris(bisurea) ligand (L) and phosphate ion (PO4 (3-) ), readily accommodates a series of quasi-tetrahedral halocarbons, such as the Freon components CFCl3 , CF2 Cl2 , CHFCl2 , and C(CH3 )F3 , and chlorocarbons CH2 Cl2 , CHCl3 , CCl4 , C(CH3 )Cl3 , C(CH3 )2 Cl2 , and C(CH3 )3 Cl. The guest encapsulation in the solid state is confirmed by crystal structures, while the host-guest interactions in solution were demonstrated by NMR techniques.
Chemistry - A European Journal, 2014
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs... more By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A 2 L 3 complexes (A represents anion, here orthophosphate PO 4 3À), namely helicate, mesocate, and mono-bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordinationbased structures as in transition-metal complexes. Scheme 1. Various structural motifs (helicate, mono-bridged, and mesocate) of the [A 2 L 3 ] anion complexes with bis(biurea) ligands bearing different spacers (L 1-L 4).
Journal of the American Chemical Society, 2008
The 2 H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT) 2 (1a), Tp*RuD(D 2)... more The 2 H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT) 2 (1a), Tp*RuD(D 2)(THT) (1b), Tp*RuD(D 2) 2 (1c), Cp*RuD 3 (PPh 3) (2) and RuD 2 (η 2-D 2) 2 (PCy 3) 2 (3) have been measured in a wide temperature range. These compounds were chosen as potential model systems for hydrogen surface species in Ru-nanoparticles. The deuterium quadrupolar coupling constants Q cc and asymmetry parameters were extracted by 2 H NMR line-shape analysis. The Q cc values of the deuterons bound to the metal vary between 13 kHz and 76 kHz. In addition all spectra show that some of the deuterium is incorporated into carbon positions exhibiting quadrupolar coupling constants in the range of 134 kHz to 192 kHz. The room temperature spectra contain an additional weak very narrow line which was assigned to deuterons exhibiting a high mobility. These deuterons are attributed to crystallographic impurity and partially to D 2 molecules which lost by the complexes. The temperature where their motion is quenched and the types of these motions depend on the chemical structure. We propose to use the values of the quadrupolar coupling constants measured in order to characterize different hydrogen species on the surface of Ru-nanoparticles.
Zeitschrift für Physikalische Chemie, 2008
In this paper a possible explanation for an unexpected ortho/para-water ratio in the gas clouds o... more In this paper a possible explanation for an unexpected ortho/para-water ratio in the gas clouds of comets is given. The description is based on the quantum-mechanical density matrix formalism and the spin temperature concept. Only the nuclear spin system is treated quantum-mechanically. Employing the model of a four spin system, created by two nearest neighbour water molecules, spin eigenstates and their dynamics under the influence of their mutual dipolar interactions are studied. It is shown that a fast conversion between ortho- and para-states occurs on a msec time scale, caused by the intermolecular homonuclear magnetic dipolar interaction. Moreover the spin eigenstates of water in an ice crystal are determined by magnetic dipolar interactions and are not given by normal ortho- and para-H2O states of gaseous water. As a result of this the spin temperature of gaseous water evaporated from ice depends strongly on its evaporation history and the ortho/para-ratio of water molecules ...
Angewandte Chemie International Edition, 2013
Zeitschrift für Physikalische Chemie, 2012
The 2H-NMR solid echo spectra of biphenyl molecules as guests in the mesopores of neat and silyla... more The 2H-NMR solid echo spectra of biphenyl molecules as guests in the mesopores of neat and silylated SBA-15 have been measured as a function of temperature. At low temperatures typical 2H-Pake patterns with parameters of (Q zz =132 kHz, corresponding to Q cc =176 kHz) and (η=0.04) are observed. All samples exhibit a strong reduction of the melting point from the bulk value of 342.4 K to values between 222 K and 229 K, depending on both the pore diameter and the surface state and a glass like behavior of the biphenyl molecules in the melting regime. Employing the Roessler two-phase model of the modeling of glass-transitions by 2H-solid state NMR the distribution of activation energies for the rotational motions has been determined. At temperatures closely below the glass-transition temperature deviations from a static Pake pattern of an aromatic deuteron are observed, which indicate a pre-melting motion of biphenyl, which could be caused by C2-ring flips of the phenyl rings.
Journal of the Chemical Society, Perkin Transactions 2, 2002
Theoretical calculations plus the solvent dependence of the 1 H, 13 C NMR and IR spectra were use... more Theoretical calculations plus the solvent dependence of the 1 H, 13 C NMR and IR spectra were used to determine the conformational equilibrium in N-methyl-2-fluoroacetamide (NMFA) and N-methyl-2-fluoropropionamide (NMFP). Ab initio calculations were used to identify the stable rotamers and obtain their geometries and the application of solvation theory on the 1 J CF coupling constant gave the conformer populations in the solvents studied. In NMFA ab initio calculations at the CBS-Q level yielded only two stable rotamers, the cis and trans, with ∆E(cis-trans) = 19.7 kJ mol Ϫ1. The presence of two conformers was confirmed by the FTIR spectra. Assuming these forms, the observed couplings when analysed by solvation theory gave ∆E = 21.3 kJ mol Ϫ1 in the vapour phase, decreasing to 8.9 kJ mol Ϫ1 in CDCl 3 and to 0.8 kJ mol Ϫ1 in DMSO. For NMFP the B3LYP calculations at the 6-311ϩϩg(2df,2p) level gave only the trans rotamer as stable, while the gauche form was a plateau in the potential energy surface. However the FTIR spectra clearly showed the presence of two conformers. A minimum for the gauche rotamer was only found when the SCRF (self consistent reaction field) routine was included in the theoretical calculations. The equilibrium in NMFP was therefore analysed by solvation theory in terms of the trans and gauche rotamers to give ∆E(gauche-trans) = 15.9 kJ mol Ϫ1 in the vapour phase, decreasing to 10.8 kJ mol Ϫ1 in CCl 4 and to 0.5 kJ mol Ϫ1 in DMSO.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
The 2H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT)2 (1a), Tp*RuD(D2)(TH... more The 2H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT)2 (1a), Tp*RuD(D2)(THT) (1b), Tp*RuD(D2)2 (1c), Cp*RuD3(PPh3) (2) and RuD2(η-D2)2(PCy3)2 (3) have been measured in a wide temperature range. These compounds were chosen as potential model systems for hydrogen surface species in Ru-nanoparticles. The deuterium quadrupolar coupling constants Qcc and asymmetry parameters were extracted by 2H NMR line-shape analysis. The Qcc values of the deuterons bound to the metal vary between 13 kHz and 76 kHz. In addition all spectra show that some of the deuterium is incorporated into carbon positions exhibiting quadrupolar coupling constants in the range of 134 kHz to 192 kHz. The room temperature spectra contain an additional weak very narrow line which was assigned to deuterons exhibiting a high mobility. These deuterons are attributed to crystallographic impurity and partially to D2 molecules which lost by the complexes. The temperature where their motion is quenched a...
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs... more By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO4 3 ), namely helicate, mesocate, and mono-bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordinationbased structures as in transition-metal complexes.
Phosphorus, Sulfur, and Silicon and the Related Elements, 2020
Four bisphosphinic acids RR´C[P(CH 3)(O)OH] 2 are characterized by 1 H, 13 Cf 1 Hg, and 31 Pf 1 H... more Four bisphosphinic acids RR´C[P(CH 3)(O)OH] 2 are characterized by 1 H, 13 Cf 1 Hg, and 31 Pf 1 Hg NMR data. H 3 C-P-C-P-CH 3 skeletons give rise to [A 3 X] 2 spin systems. Some algebraic equations are derived for manual analysis of [A 3 X] 2 spectra. HR NMR data for heteroaromatic substituents R in RC(H)[P(CH 3)(O)OH] 2 are reported. Dissociation constants and ion-specific chemical shifts d P of CH 3 C(OH)[P(CH 3)(O)OH] 2 are determined by 31 Pf 1 Hg NMR controlled titrations of 2a.
Phosphorus, Sulfur, and Silicon and the Related Elements, 2017
Amino-methylene)bisphosphonates R 1 R 2 N-CH[P(O)(OMe) 2 ] 2 bearing achiral and chiral substitue... more Amino-methylene)bisphosphonates R 1 R 2 N-CH[P(O)(OMe) 2 ] 2 bearing achiral and chiral substituents (R 1 = Ph, R 2 = H, Me; and R 1 = PhCH(Me), R 2 = Me, Bn) were synthesized and characterized in CDCl 3 by 1 H, 1 H{ 31 P}, 13 C{ 1 H}, 31 P{ 1 H}, and 31 P NMR spectra. [P(O)(OMe) 2 ] 2 fragments from achiral compounds give rise to complex 1 H NMR spectra characteristic for the [A 3 M 3 X] 2 1 H NMR spectra while chiral compounds yield A 3 G 3 M 3 T 3 XY type spectra. Aspects of molecular symmetry governing the multiplet patterns are discussed and precise spectral parameters are calculated by line-shape iterations.
ChemistrySelect, 2018
Here we report, room temperature heterogeneous catalysis of the Suzuki-Miyaura cross-coupling rea... more Here we report, room temperature heterogeneous catalysis of the Suzuki-Miyaura cross-coupling reaction by a Pd 0 nanoparticle-immobilized porous organic polymer (TPU-Pd), providing excellent yields (up to 99%) using low catalyst loading. High nitrogen-and oxygen-donor content of triazine-based porous polyurethane (TPU) makes it an efficient porous polymer for Pd-immobilization and subsequent heterogeneous catalysis of CC cross-coupling reactions. X-ray photoelectron spectroscopy of TPU-Pd showed characteristic binding energy peaks of Pd 0. Atomic absorption spectroscopy revealed 10.4 wt% of Pd 0 in TPU-Pd, and transmission electron microscopy images showed well-dispersed and facetted Pd 0 nanoparticles of size 5-20 nm. Catalysis of Suzuki-Miyaura reaction was observed to be completed in 3 h at 25 8C for a wide range of aryl halide substrates with phenylboronic acid, whereas increasing the reaction temperature to 80 8C largely allows decreasing the reaction time to 0.5-1 h. The porosity and surface area of the catalyst was not affected after catalysis, and the catalyst has been reused for five consecutive runs.
Chemistry - A European Journal, 2017
α-Peptoids, or N-substituted glycine oligomers, are an important class of peptidomimetic foldamer... more α-Peptoids, or N-substituted glycine oligomers, are an important class of peptidomimetic foldamers with proteolytic stability. Nevertheless, the presence of cis-/trans-amide bond conformers, which contribute to the high flexibility of α-peptoids, is considered as a major drawback. A modified peptoid backbone with an improved control of the amide bond geometry could therefore help to overcome this limitation. Here we have performed the first thorough analysis of the folding propensities of α-aminoxy peptoids (or N-substituted 2-aminoxyacetic acid oligomers). To this end, the amide bond geometry and conformational properties of a series of model α-aminoxy peptoids were investigated using 1D and 2D NMR experiments, X-ray crystallography, NBO analysis, CD spectroscopy, and MD simulations revealing a unique preference for cis-amide bonds even in the absence of cis-directing side chains. The conformational analysis based on the MD simulations revealed that α-aminoxy peptoids can adopt helical conformations that can mimic the spatial arrangement of peptide side chains in a canonical α-helix. Given their ease of synthesis and conformational properties, α-aminoxy peptoids represent a new member of the peptoid family capable of controlling the amide isomerism while maintaining the potential for side-chain diversity.
Chemistry - A European Journal, 2017
Investigation of guest diffusion in porous metal-organic frameworks (MOFs) is of major importance... more Investigation of guest diffusion in porous metal-organic frameworks (MOFs) is of major importance since many porosityrelated properties of MOFs are influenced by diffusion effects. The diffusion of dimethylsulfoxide (DMSO) in the metal-organic framework (MOF) MIL-53-NH2(Al) was investigated through pulsedfield-gradient (PFG) NMR spectroscopy. The microporous material was synthesized in small crystallites (under 500 nm), which agglomerated in a large range of particle sizes (from hundreds of nanometers to tens of micrometers), giving a morphologically very heterogeneous sample. No special agglomeration pattern could be observed, which makes a PFG-NMR investigation very challenging, yet it represents a realistic situation for the diffusion of guest molecules in porous materials. We were able to distinguish between two diffusion regimes existing in parallel with each other over the total range from 15 ms up to 200 ms of observation times as accessible in the experiments: In the large crystal agglomerates (diameters above 20 µm) guest movement was found to be subdiffusive, with a time exponent = 0.8 (rather than 1 as for normal diffusion). Guest diffusion in the remaining, smaller host particles followed the pattern of normal diffusion within a bed of spheres of impenetrable external surfaces, with a size distribution in good agreement with that of the material under study. Diffusion in a rather complex system could thus be referred to a two-region model with novel potentials for application to systems of intricate topology.
Chemical Communications, 2016
For the first time, a microporous polyurethane (MPU) is prepared – it acts as an organocatalyst f... more For the first time, a microporous polyurethane (MPU) is prepared – it acts as an organocatalyst for aldol-type C–C bond forming reactions with high yields and under mild conditions.
Angewandte Chemie (International ed. in English), Jan 5, 2015
Caged supramolecular systems are promising hosts for guest inclusion, separation, and stabilizati... more Caged supramolecular systems are promising hosts for guest inclusion, separation, and stabilization. Well-studied examples are mainly metal-coordination-based or covalent architectures. An anion-coordination-based cage that is capable of encapsulating halocarbon guests is reported for the first time. This A4 L4 -type (A=anion) tetrahedral cage, [(PO4 )4 L4 ](12-) , assembled from a C3 -symmetric tris(bisurea) ligand (L) and phosphate ion (PO4 (3-) ), readily accommodates a series of quasi-tetrahedral halocarbons, such as the Freon components CFCl3 , CF2 Cl2 , CHFCl2 , and C(CH3 )F3 , and chlorocarbons CH2 Cl2 , CHCl3 , CCl4 , C(CH3 )Cl3 , C(CH3 )2 Cl2 , and C(CH3 )3 Cl. The guest encapsulation in the solid state is confirmed by crystal structures, while the host-guest interactions in solution were demonstrated by NMR techniques.
Chemistry - A European Journal, 2014
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs... more By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A 2 L 3 complexes (A represents anion, here orthophosphate PO 4 3À), namely helicate, mesocate, and mono-bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordinationbased structures as in transition-metal complexes. Scheme 1. Various structural motifs (helicate, mono-bridged, and mesocate) of the [A 2 L 3 ] anion complexes with bis(biurea) ligands bearing different spacers (L 1-L 4).
Journal of the American Chemical Society, 2008
The 2 H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT) 2 (1a), Tp*RuD(D 2)... more The 2 H solid-state NMR spectra of the transition metal complexes Tp*RuD(THT) 2 (1a), Tp*RuD(D 2)(THT) (1b), Tp*RuD(D 2) 2 (1c), Cp*RuD 3 (PPh 3) (2) and RuD 2 (η 2-D 2) 2 (PCy 3) 2 (3) have been measured in a wide temperature range. These compounds were chosen as potential model systems for hydrogen surface species in Ru-nanoparticles. The deuterium quadrupolar coupling constants Q cc and asymmetry parameters were extracted by 2 H NMR line-shape analysis. The Q cc values of the deuterons bound to the metal vary between 13 kHz and 76 kHz. In addition all spectra show that some of the deuterium is incorporated into carbon positions exhibiting quadrupolar coupling constants in the range of 134 kHz to 192 kHz. The room temperature spectra contain an additional weak very narrow line which was assigned to deuterons exhibiting a high mobility. These deuterons are attributed to crystallographic impurity and partially to D 2 molecules which lost by the complexes. The temperature where their motion is quenched and the types of these motions depend on the chemical structure. We propose to use the values of the quadrupolar coupling constants measured in order to characterize different hydrogen species on the surface of Ru-nanoparticles.
Zeitschrift für Physikalische Chemie, 2008
In this paper a possible explanation for an unexpected ortho/para-water ratio in the gas clouds o... more In this paper a possible explanation for an unexpected ortho/para-water ratio in the gas clouds of comets is given. The description is based on the quantum-mechanical density matrix formalism and the spin temperature concept. Only the nuclear spin system is treated quantum-mechanically. Employing the model of a four spin system, created by two nearest neighbour water molecules, spin eigenstates and their dynamics under the influence of their mutual dipolar interactions are studied. It is shown that a fast conversion between ortho- and para-states occurs on a msec time scale, caused by the intermolecular homonuclear magnetic dipolar interaction. Moreover the spin eigenstates of water in an ice crystal are determined by magnetic dipolar interactions and are not given by normal ortho- and para-H2O states of gaseous water. As a result of this the spin temperature of gaseous water evaporated from ice depends strongly on its evaporation history and the ortho/para-ratio of water molecules ...
Angewandte Chemie International Edition, 2013
Zeitschrift für Physikalische Chemie, 2012
The 2H-NMR solid echo spectra of biphenyl molecules as guests in the mesopores of neat and silyla... more The 2H-NMR solid echo spectra of biphenyl molecules as guests in the mesopores of neat and silylated SBA-15 have been measured as a function of temperature. At low temperatures typical 2H-Pake patterns with parameters of (Q zz =132 kHz, corresponding to Q cc =176 kHz) and (η=0.04) are observed. All samples exhibit a strong reduction of the melting point from the bulk value of 342.4 K to values between 222 K and 229 K, depending on both the pore diameter and the surface state and a glass like behavior of the biphenyl molecules in the melting regime. Employing the Roessler two-phase model of the modeling of glass-transitions by 2H-solid state NMR the distribution of activation energies for the rotational motions has been determined. At temperatures closely below the glass-transition temperature deviations from a static Pake pattern of an aromatic deuteron are observed, which indicate a pre-melting motion of biphenyl, which could be caused by C2-ring flips of the phenyl rings.