Complexation electron paramagnetic resonance

The [Fe =0(TMP+ )]+ complex exhibited a characteristic bright green color and corresponding visible absorbance in its UV-vis spectrum. In its NMR spectrum, the meta-proton doublet of the porphyrin mesityl groups were shifted more than 70 ppm downfield from tetramethylsilane (TMS) because they were in the presence of the cation radical, while the methyl protons shift between 10 and 20ppm downfield. In Mossbauer spectroscopy, the isomer shift, 5 of 0.06 mm/s, and A q value of 1.62mm/s were similar to those for other known Fe(IV) complexes. Electron paramagnetic resonance (EPR), resonance Raman (RR), and EXAFS spectroscopies provided additional indications of an Fe =0 n-cation radical intermediate. For instance,... 

Electron paramagnetic resonance spectroscopy (HER), also called electron spin resonance spectroscopy (ESR), may be used for direct detection and conformational and structural characterization of paramagnetic species. Good introductions to F.PR have been provided by Fischer8 and I.effler9 and most books on radical chemistry have a section on EPR. EPR detection limits arc dependent on radical structure and the signal complexity. However, with modern instrumentation, radical concentrations > 1 O 9 M can be detected and concentrations > I0"7 M can be reliably quantified. 

The X-ray structure of zinc naphthalocyanate has been determined with Zn—N bond lengths of 1.983(4) A.829 Pentanuclear complexes with a zinc phthalocyanine core and four ruthenium subunits linked via a terpyridyl ligand demonstrate interaction between the photoactive and the redox active components of the molecule. The absorbance and fluorescence spectra showed considerable variation with the ruthenium subunits in place.830 Tetra-t-butylphthalocyaninato zinc coordinated by nitroxide radicals form excited-state phthalocyanine complexes and have been studied by time-resolved electron paramagnetic resonance.831... 

D. Collison, M. Helliwell, V.M. Jones, F.E. Mabbs, E.J.L. Mclnnes, P.C. Riedi, G.M. Smith, R.G. Pritchard and W.I. Cross, Single and double quantum transitions in the multi-frequency continuous wave electron paramagnetic resonance (cwEPR) of three six-co-ordinate nickel(II) complexes ... 

Various other techniques have been used to determine molybdenum, including adsorption voltammetry [510], electron-paramagnetic resonance spectrometry [512], and neutron activation analysis [513,514]. EPR spectrometry is carried out on the isoamyl alcohol soluble Mo(SCN)s complex and is capable of detecting 0.46 mg/1 molybdenum in seawater. Neutron activation is carried out on the /J-naphlhoin oxime [514] complex and the pyrrolidone dithiocar-bamate and diethyldithiocarbamate complex [513]. The neutron activation analysis method [514] was capable of determining down to 0.32 xg/l of molybdenum in seawater. 

Besides the electrically active complexes discussed above, there is indirect evidence for the existence of neutral complexes. In close analogy to the observations in silicon and several III-V materials it appears that hydrogen passivates deep and shallow acceptors. Because of the small concentrations of these neutral centers, all attempts to detect them directly with local vibrational mode (LVM) spectroscopy or electron paramagnetic resonance (EPR) have been unsuccessful. 

Complex-symmetric matrices might arise in some problems in chemical physics. Examples include the electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) line shape problems.207 Another... 

Most stable ground-state molecules contain closed-shell electron configurations with a completely filled valence shell in which all molecular orbitals are doubly occupied or empty. Radicals, on the other hand, have an odd number of electrons and are therefore paramagnetic species. Electron paramagnetic resonance (EPR), sometimes called electron spin resonance (ESR), is a spectroscopic technique used to study species with one or more unpaired electrons, such as those found in free radicals, triplets (in the solid phase) and some inorganic complexes of transition-metal ions. 

Electron paramagnetic resonance (continued) cobalt-thermolysin complex, 28 334, 335 exchange reactions, 31 106-107 glutamine synthetase, 28 358-364 invisible oxygen species, 31 94-95 metalloenzymes, 28 324, 326 metal particle size distribution, 36 99-100, 104... 

Based on our current understanding of ribosomal protein synthesis, several strategies have been developed to incorporate amino acids other than the 20 standard proteinogenic amino acids into a peptide using the ribosomal machinery . This allows for the design of peptides with novel properties. On the one hand, such a system can be used to synthesize nonstandard peptides that are important pharmaceuticals. In nature, such peptides are produced by nonribosomal peptide synthetases, which operate in complex pathways. On the other hand, non-natural residues are a useful tool in biochemistry and biophysics to study proteins. For example, incorporation of non-natural residues by the ribosome allows for site-specific labeling of proteins with spin labels for electron paramagnetic resonance spectroscopy, with... 

One of the earliest reports of LO inhibition concerned the effects of ortho-dihydroxybenzene (catechol) derivatives on soybean 15-LO [58]. Lipophilic catechols, notably nordihydroguaiaretic acid (NDGA) (19), were more potent (10 /zM) than pyrocatechol itself. The inactivation was, under some conditions, irreversible, and was accompanied by oxidation of the phenolic compound. The orfAo-dihydroxyphenyl moiety was required for the best potency, and potency also correlated with overall lipophilicity of the inhibitor [61]. NDGA and other phenolic compounds have been shown by electron paramagnetic resonance spectroscopy to reduce the active-site iron from Fe(III) to Fe(II) [62] one-electron oxidation of the phenols occurs to yield detectable free radicals [63]. Electron-poor, less easily oxidized catechols form stable complexes with the active-site iron atom [64]. 

Amine-terminated, full-generation PAMAM and PPI dendrimers, as well as carboxylate-terminated half-generation PAMAM dendrimers, can directly bind metal ions to their surfaces via coordination to the amine or acid functionality. A partial hst of metal ions that have been bound to these dendrimers in this way includes Na+, K+, Cs+, Rb+, Fe +, Fe +, Gd +, Cu+, Cu +, Ag+, Mn +, Pd, Zn, Co, Rh+,Ru +,andPt + [18,19,27,36,54,82-96]. Tuxro et al.have also shown that the metal ion complexes, such as tris(2,2 -bipyridine)ruthenium (Rulbpylj), can be attached to PAMAM dendrimer surfaces by electrostatic attraction [97]. A wide variety of other famihes of dendrimers have also been prepared that bind metal ions to their periphery. These have recently been reviewed [3]. Such surface-bound metal ions can be used to probe dendrimer structure using optical spectroscopy, mass spectrometry, and electron paramagnetic resonance (EPR) [86-88,90,97-99]. 

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