Q-band ESR

Electron and Hole Transfer from the Hydration Layer to DNA. - Debije et al. investigated the transfer of X-radiation-induced electrons and holes (H20 +) from the hydration layer of crystalline oligonucleotides into the oligo itself.57 Results from these Q-band ESR experiments at 4 K suggest that ionization of hydration water results in both electron and hole transfer to the DNA model structures. The proton transfer reaction from H20 + to form the hydroxyl radical occurs on the timescale of a few molecular vibrations, thus it limits hole transfer distance from a water hole to DNA. 

X- and Q-band ESR experiments have been carried out on both the normal and the superconducting states of YBa2Cu307 5. Both above and below Tc, a resonance... 

The local structure of iron sites in Fe-mazzite and Fe-ZSM-5, in which iron was incorporated during zeolite synthesis, was studied by X- and Q-band ESR, electron spin echo detected ESR (ED-ESR), electron spin echo envelope modulation (ESEEM), and diffuse reflectance UV-vis [94G1]. The X-band ESR spectra of Fe-MAZ (100 Fe/(Fe + A1 + Si) = 1.20) render three signals at g = 4.3, g = 2.3, and g = 2.0 - Table 14a. The Q-band spectra testifies only the signal atg = 2.0. The linewidths of the g = 2.0 signals are smaller in the Q-band spectra - Table 14. This narrowing indicates that the linewidth is at least partially due to the second-order broadening of the -l/2> l/2> transition. The X-band spectrum of Fe-MAZ with 100 Fe/(Fe + A1 + Si) = 0.07 exhibits the... 

More recently, this problem was faced by Goldfarb et al. who performed the characterization of several Fe-containing molecular sieves (SOD, LTL, MFI, M AZ, FAU) by X-band and Q-band ESR, Pulsed ESR and UV-Visible spectroscopy... 

For routine studies with the ESR spectrometer, it is most convenient to work at X-band frequencies ( 9.5 MHz or 3 cm). The sample is usually contained in a 4 or 5 mm diameter quartz tube having a sensitive region about 2 cm in length. An alternative frequency is at Q-band ( 35,000 MHz or 1 cm). Here, the cavity dimensions are much smaller and the diameter of the sample tube is less than 2 mm. This creates some problems in handling and degassing powder samples. By varying the frequency it is possible to determine which features in a spectrum are due to Zeeman interactions... 

In many systems ESR line widths of Cu(ll) depend on the microwave frequency. It was shown in some early papers that lines are broader at Q-band (35 GHz)" and narrower at S-band" 7 compared with those at X-band. This was our initial motivation for... 

The ESR spectra of some copper complexes of benzotriazole, benzotriazolate, A-methyl-benzotriazole, and 5-nitrobenzotriazole have been described. They show either isotropic g values or indications of axial or rhombic splittings. In no cases are copper hyperfine splittings observed. This indicates that the copper ions in the solid compounds are exchange coupled. The fact that the g values observed at X-band frequency differ from those obtained at Q-band frequency also indicates... 

DTA studies were done with a DTA apparatus (Netzsch-Geratebau, GmbH, Selb) in an argon atmosphere with heating at 10°/min. ESR signals were taken in the X-band with an ER 9 spectrometer (VEB Carl Zeiss Jena) and in the Q-band with a 35-GHz ESR-XQ spectrometer (Akademie der Wissenschaften der DDR, Berlin). 

Figure 5. ESR spectrum (low field components) of CuNaY zeolite (a = 29%) in the Q-band taken al room temperature as a function of dehydration temperature (numbers on the right are pretreatment temperatures)...

Most ESR instruments use the fixed frequency of 9500 MHz (X-band frequency),886 but a number of ESR spectra are measured at 3500 MHz (Q-band frequency),892 which, in the case of misaligned concentrated copper(II) complexes, can resolve the local molecular g values of... 

The ESR spectrum of a copper(H) complex measured at (a) X-band and (b) Q-band frequency, showing the resolution of the g values of the local molecular Cu chromophore in (b) and (c) in solution29 ... 

Frozen-solution ESR spectra of Tc2G in mixed aqueous hydrochloric acid and ethanol provided data consistent with equal coupling of the unpaired electron to both technetium nuclei (101). IsotopicaUy pure "Tc (/ = 9/2) in 99Tc2Cl leads to a large number of lines in the X-band spectrum owing to second-order effects, in addition to the hyperfine lines presence for this dimeric axially symmetric system. The Q-band spectrum obtained at 77°K with a microwave frequency of 35.56 GHz exhibited fewer lines, and computer-simulated spectra were generated to correspond to the experimental spectrum withgit = 1.912, gi = 2.096, An = 166 x 10 4 cm"1, IAL = 67.2 x 10 4 cm 1, and gav = 2.035. 

For Re2(02CC Hs)4Cl2 the first reduction wave near —0.3 V is quasi-reversible. The product of this one-electron oxidation was not isolated as a solid, but ESR spectra were obtained on frozen dichloromethane solutions at 77°K at both X- and Q-band frequencies. Both naturally occurring rhenium isotopes have a nuclear spin of 5/2 with slightly different nuclear magnetic moments. For dimeric rhenium species there are three distinct isotopic isomers and each generates a unique ESR spectrum as a result of differing hyperfine interactions. The observed ESR spectrum is a superposition of these lines with the intensity... 

Large line-widths, sometimes in conjunction with insufficiently resolved hyperfine structure, can preclude the determination of individual g factor components close to g = 2 under conventional ESR conditions (X band, 9.5 GHz, 330 mT). As in NMR spectroscopy, an increase in the field and frequency is then appropriate via the Q band (35 GHz) to the W band (95 GHz) or even higher frequencies and magnetic fields [48]. An application of such high-field ESR for the inorganic radical 10 with sizeable metal participation has been reported [49a]. 

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