Showing papers by "Adelheid Godt published in 2017"
TL;DR: The results emphasize the importance of differentiating between framework damage caused through hydrolysis in water and through drying from a water-wetted state and reversible bending of the linkers contributes to the stability of the PEPEP-PIZOFs.
Abstract: A Zr-based MOF of the PIZOF type, which consists of two independent and mutually interpenetrating UiO-type frameworks with [Zr6O4(OH)4(O2C)12] nodes, does not only form with a PEPEP dicarboxylic acid (P = phenylene, E = ethynylene). Also dicarboxylic acids with the shorter PPPP and PEPP spacers were found to give PIZOFs, denoted PPPP-PIZOF and PEPP-PIZOF, respectively. Reducing the spacer length even further to a PEEP segment caused a switchover to the formation of a UiO framework. The hysteresis in the Ar sorption curve of PEPP-PIZOF-1 and the slightly too large amount of combustion residue from PPPP-PIZOF-1 suggest structural defects. These hint at a mismatch between the requirement of the optimal linker length for PIZOF formation and the lengths of the PEPP and PPPP dicarboxylates. Nevertheless, these dicarboxylates prefer the formation of a PIZOF over the formation of a UiO structure. PEPEP-PIZOF-2, PPPP-PIZOF-1, and PEPP-PIZOF-1 are stable in air up to 325, 350, and 300 °C, respectively, and have BET...
45 citations
TL;DR: An extensive optimization procedure was carried out on two model systems to evaluate the applicability of shaped pulses to Gd(III) complexes and nitroxides, which are two important classes of spin labels used in modern DEER/EPR experiments and found the choice of the best set of parameters depends on the D parameter of the Gd (III) complex.
44 citations
TL;DR: The calibration of the overtone coefficients for the RIDME kernel is described, the accuracy of distance distributions obtained with this approach is demonstrated, and it is shown that for the authors' series of Gd-rulers R IDME technique provides more accurate distance distributions than Gd(iii)-Gd(ii) double electron-electron resonance (DEER).
Abstract: Extraction of distance distributions between high-spin paramagnetic centers from relaxation induced dipolar modulation enhancement (RIDME) data is affected by the presence of overtones of dipolar frequencies. As previously proposed, we account for these overtones by using a modified kernel function in Tikhonov regularization analysis. This paper analyzes the performance of such an approach on a series of model compounds with the Gd(III)–PyMTA complex serving as paramagnetic high-spin label. We describe the calibration of the overtone coefficients for the RIDME kernel, demonstrate the accuracy of distance distributions obtained with this approach, and show that for our series of Gd-rulers RIDME technique provides more accurate distance distributions than Gd(III)–Gd(III) double electron–electron resonance (DEER). The analysis of RIDME data including harmonic overtones can be performed using the MATLAB-based program OvertoneAnalysis, which is available as open-source software from the web page of ETH Zurich. This approach opens a perspective for the routine use of the RIDME technique with high-spin labels in structural biology and structural studies of other soft matter.
37 citations
TL;DR: B bis(Gd-chelate)s which enable cross effect (CE) DNP owing to spatial confinement of two dipolar-coupled electron spins are presented and foster the understanding of the CE mechanism and the design of high-spin PAs for specific applications of DNP.
Abstract: High-spin complexes act as polarizing agents (PAs) for dynamic nuclear polarization (DNP) in solid-state NMR spectroscopy and feature promising aspects towards biomolecular DNP. We present a study on bis(Gd-chelate)s which enable cross effect (CE) DNP owing to spatial confinement of two dipolar-coupled electron spins. Their well-defined Gd⋅⋅⋅Gd distances in the range of 1.2-3.4 nm allowed us to elucidate the Gd⋅⋅⋅Gd distance dependence of the DNP mechanism and NMR signal enhancement. We found that Gd⋅⋅⋅Gd distances above 2.1 nm result in solid effect DNP while distances between 1.2 and 2.1 nm enable CE for 1 H, 13 C, and 15 N nuclear spins. We compare 263 GHz electron paramagnetic resonance (EPR) spectra with the obtained DNP field profiles and discuss possible CE matching conditions within the high-spin system and the influence of dipolar broadening of the EPR signal. Our findings foster the understanding of the CE mechanism and the design of high-spin PAs for specific applications of DNP.
20 citations
TL;DR: In this paper, the authors present CW EPR measurements at 240 GHz (86 Tesla) on a series of Gd-rulers of the type Gd PyMTA-spacer-Gd-PyMTA, with distances ranging from 12 nm to 43 nm.
Abstract: Electron paramagnetic resonance spectroscopy in combination with site-directed spin labeling is a very powerful tool for elucidating the structure and organization of biomolecules Gd3+ complexes have recently emerged as a new class of spin labels for distance determination by pulsed EPR spectroscopy at Q- and W-band We present CW EPR measurements at 240 GHz (86 Tesla) on a series of Gd-rulers of the type Gd-PyMTA-spacer-Gd-PyMTA, with Gd-Gd distances ranging from 12 nm to 43 nm CW EPR measurements of these Gd-rulers show that significant dipolar broadening of the central |-1/2〉 → |1/2〉 transition occurs at 30 K for Gd-Gd distances up to ∼34 nm with Gd-PyMTA as the spin label This represents a significant extension for distances accessible by CW EPR, as nitroxide-based spin labels at X-band frequencies can typically only access distances up to ∼2 nm We show that this broadening persists at biologically relevant temperatures above 200 K, and that this method is further extendable up to room temperature by immobilizing the sample in glassy trehalose We show that the peak-to-peak broadening of the central transition follows the expected 1/r3 dependence for the electron-electron dipolar interaction, from cryogenic temperatures up to room temperature A simple procedure for simulating the dependence of the lineshape on interspin distance is presented, in which the broadening of the central transition is modeled as an S = 1/2 spin whose CW EPR lineshape is broadened through electron-electron dipolar interactions with a neighboring S = 7/2 spin
20 citations
TL;DR: This triple electron resonance experiment (TRIER) is an extension the double electron-electron resonance (DEER) experiment, which is widely used for distance determination in the nanometer range, and can potentially provide the missing connection between distances as correlations between dipolar frequencies.
19 citations
TL;DR: In this article, the authors presented the design of three resonators for Q-band frequencies (33-36 GHz) with a larger bandwidth than what was reported so far, and the new resonators are of a loop-gap type with 4-6 loops and were designed for 16-mm sample tubes to achieve higher field homogeneity.
Abstract: The emerging technology of ultra-wide-band spectrometers in electron paramagnetic resonance—enabled by recent technological advances—provides the means for new experimental schemes, a broader range of samples, and huge gains in measurement time Broadband detection does, however, require that the resonator provides sufficient bandwidth and, despite resonator compensation schemes, excitation bandwidth is ultimately limited by resonator bandwidth Here, we present the design of three resonators for Q-band frequencies (33–36 GHz) with a larger bandwidth than what was reported so far The new resonators are of a loop-gap type with 4–6 loops and were designed for 16 mm sample tubes to achieve higher field homogeneity than in existing resonators for 3 mm samples, a feature that is beneficial for precise spin control The loop-gap design provides good separation of the B
1 and E field, enabling robust modes with powder samples as well as with frozen water samples as the resonant behavior is largely independent of the dielectric properties of the samples Experiments confirm the trends in bandwidth and field strength and the increased B
1 field homogeneity predicted by the simulations Variation of the position of the coupling rod allows the adjustment of the quality factor Q and thus the bandwidth over a broad range The increased bandwidth of the loop-gap resonators was exploited in double electron–electron resonance measurements of a Cu(II)-PyMTA ruler to yield significantly higher modulation depth and thus higher sensitivity
19 citations