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.
Three new DEPMPO-based spin traps have been designed and synthesized for improved superoxide dete... more Three new DEPMPO-based spin traps have been designed and synthesized for improved superoxide detection, each carrying a cyclodextrin (CD) moiety but with a different alkyl chain on the phosphorus atom or with a long spacer arm. EPR spectroscopy allowed us to estimate the half-life of the superoxide spin adducts which is close to the value previously reported for CD-DEPMPO (t1/2 ≈ 50-55 min under the conditions investigated). The spectra are typical of superoxide adducts (almost no features of the HO˙ adduct that usually forms with time for other nitrone spin traps such as DMPO) and we show that at 250 μM, the new spin trap enables the reliable detection of superoxide by 1 scan at the position opposite to the corresponding spin trap without the CD moiety. The resistance of the spin adducts to a reduction process has been evaluated, and the superoxide spin adducts are sensitive to ascorbate and glutathione (GSH), but not to glutathione peroxidase/GSH, reflecting the exposed nature of the nitroxide moiety to the bulk solvent. To understand these results, 2D-ROESY NMR studies and molecular dynamics pointed to a shallow or surface self-inclusion of the nitrone spin traps and of nitroxide spin adducts presumably due to the high flexibility of the permethyl-β-CD rim.
Free energies G(X)n of 12 1,ω‐dihydrooligomers (X)n (n, number of the monomeric units) have been ... more Free energies G(X)n of 12 1,ω‐dihydrooligomers (X)n (n, number of the monomeric units) have been determined by quantum calculations. We note that these values are correlated by (a) an excellent linear relationship: G(X)n = An – 761.86 ± 10 (kcal mol–1) (TPSS‐TPSS/6.311 + + G(dp)); (b) for two oligomers (X)n and (Y)n, the difference of weighted free energies—G(X)n/n – G(Y)n/n—is a constant irrespective of n which results from the difference of free energies of the substituent. Consequently, from the Gn values of 1,ω‐dihydrooligoethenes (in fact n‐alkanes), a determination of the free energies of a 1,ω‐dihydrooligomers (X)n is obtained with a good accuracy by the calculation of the G value of its substituent; (c) the corresponding increments G(X)n/n – G(X)(n–1)/(n–1) are equaled and led to a single power law: [Gn/n – G(n–1)/(n–1) = 1282/n2.156 (kcal mol–1), R = 0.9992] or a linear relationship: [Gn/n – G(n–1)/(n–1) = 756.73/n(n–1) + 0.0211 (kcal mol–1), R = 1]. Syndiotactic and isotactic 1,ω‐dihydrooligomers (X) are illustrated in the Electronic Supporting Information.
The sensitivity of NMR spectroscopy is considerably enhanced by dynamic nuclear polarization (DNP... more The sensitivity of NMR spectroscopy is considerably enhanced by dynamic nuclear polarization (DNP). In DNP polarization is transferred from unpaired electrons of a polarizing agent to nearby proton spins. In solids, this transfer is followed by the transport of hyperpolarization to the bulk via 1H‐1H spin diffusion. The efficiency of these steps is critical to obtain high sensitivity gains, but the pathways for polarization transfer in the region near the unpaired electron spins are unclear. Here we report a series of seven deuterated and one fluorinated TEKPol biradicals to probe the effect of deprotonation on MAS DNP at 9.4 T. The experimental results are interpreted with numerical simulations, and our findings support that strong hyperfine couplings to nearby protons determine high transfer rates across the spin diffusion barrier to achieve short build‐up times and high enhancements. Specifically, 1H DNP build‐up times increase substantially with TEKPol isotopologues that have fewer hydrogen atoms in the phenyl rings, suggesting that these protons play a crucial role transferring the polarization to the bulk. Based on this new understanding, we have designed a new biradical, NaphPol, which yields significantly increased NMR sensitivity, making it the best performing DNP polarizing agent in organic solvents to date.
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.
Bulletin des Sociétés Chimiques Belges, Sep 1, 2010
With the help of molecular mechanics (program GenMol), suitable molecular geometries were obtaine... more With the help of molecular mechanics (program GenMol), suitable molecular geometries were obtained for photochromic spiropyrans and spirooxazines to evaluate substituent effects on the spectroscopic and physicochemical properties. The results were compared to X-ray structures and used to explain relevant 1H NMR data.
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.
Three new DEPMPO-based spin traps have been designed and synthesized for improved superoxide dete... more Three new DEPMPO-based spin traps have been designed and synthesized for improved superoxide detection, each carrying a cyclodextrin (CD) moiety but with a different alkyl chain on the phosphorus atom or with a long spacer arm. EPR spectroscopy allowed us to estimate the half-life of the superoxide spin adducts which is close to the value previously reported for CD-DEPMPO (t1/2 ≈ 50-55 min under the conditions investigated). The spectra are typical of superoxide adducts (almost no features of the HO˙ adduct that usually forms with time for other nitrone spin traps such as DMPO) and we show that at 250 μM, the new spin trap enables the reliable detection of superoxide by 1 scan at the position opposite to the corresponding spin trap without the CD moiety. The resistance of the spin adducts to a reduction process has been evaluated, and the superoxide spin adducts are sensitive to ascorbate and glutathione (GSH), but not to glutathione peroxidase/GSH, reflecting the exposed nature of the nitroxide moiety to the bulk solvent. To understand these results, 2D-ROESY NMR studies and molecular dynamics pointed to a shallow or surface self-inclusion of the nitrone spin traps and of nitroxide spin adducts presumably due to the high flexibility of the permethyl-β-CD rim.
Free energies G(X)n of 12 1,ω‐dihydrooligomers (X)n (n, number of the monomeric units) have been ... more Free energies G(X)n of 12 1,ω‐dihydrooligomers (X)n (n, number of the monomeric units) have been determined by quantum calculations. We note that these values are correlated by (a) an excellent linear relationship: G(X)n = An – 761.86 ± 10 (kcal mol–1) (TPSS‐TPSS/6.311 + + G(dp)); (b) for two oligomers (X)n and (Y)n, the difference of weighted free energies—G(X)n/n – G(Y)n/n—is a constant irrespective of n which results from the difference of free energies of the substituent. Consequently, from the Gn values of 1,ω‐dihydrooligoethenes (in fact n‐alkanes), a determination of the free energies of a 1,ω‐dihydrooligomers (X)n is obtained with a good accuracy by the calculation of the G value of its substituent; (c) the corresponding increments G(X)n/n – G(X)(n–1)/(n–1) are equaled and led to a single power law: [Gn/n – G(n–1)/(n–1) = 1282/n2.156 (kcal mol–1), R = 0.9992] or a linear relationship: [Gn/n – G(n–1)/(n–1) = 756.73/n(n–1) + 0.0211 (kcal mol–1), R = 1]. Syndiotactic and isotactic 1,ω‐dihydrooligomers (X) are illustrated in the Electronic Supporting Information.
The sensitivity of NMR spectroscopy is considerably enhanced by dynamic nuclear polarization (DNP... more The sensitivity of NMR spectroscopy is considerably enhanced by dynamic nuclear polarization (DNP). In DNP polarization is transferred from unpaired electrons of a polarizing agent to nearby proton spins. In solids, this transfer is followed by the transport of hyperpolarization to the bulk via 1H‐1H spin diffusion. The efficiency of these steps is critical to obtain high sensitivity gains, but the pathways for polarization transfer in the region near the unpaired electron spins are unclear. Here we report a series of seven deuterated and one fluorinated TEKPol biradicals to probe the effect of deprotonation on MAS DNP at 9.4 T. The experimental results are interpreted with numerical simulations, and our findings support that strong hyperfine couplings to nearby protons determine high transfer rates across the spin diffusion barrier to achieve short build‐up times and high enhancements. Specifically, 1H DNP build‐up times increase substantially with TEKPol isotopologues that have fewer hydrogen atoms in the phenyl rings, suggesting that these protons play a crucial role transferring the polarization to the bulk. Based on this new understanding, we have designed a new biradical, NaphPol, which yields significantly increased NMR sensitivity, making it the best performing DNP polarizing agent in organic solvents to date.
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.
Bulletin des Sociétés Chimiques Belges, Sep 1, 2010
With the help of molecular mechanics (program GenMol), suitable molecular geometries were obtaine... more With the help of molecular mechanics (program GenMol), suitable molecular geometries were obtained for photochromic spiropyrans and spirooxazines to evaluate substituent effects on the spectroscopic and physicochemical properties. The results were compared to X-ray structures and used to explain relevant 1H NMR data.
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.
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