Edward Gelerinter

Mechanisms of formation and decomposition of hypervalent chromium metabolites in the glutathione-chromium (VI) reaction.

A long-lived chromium(IV) intermediate is generated during the reaction between Cr(VI) and glutathione in glycine below pH 3. The intermediate reacts with the tripeptide to produce Cr(III) and oxidized glutathione. A dynamic magnetic susceptibility measurement based on a nuclear magnetic resonance method yielded a 2.8 microB magnetic movement for the chromium(IV) species. The intermediate is formed by parallel third-order and second-order processes. The third-order process (k = 5.9 x 10(2) M-2 s-1) involves first-order participation by each of the oxidant, reductant, and hydrogen ions. A hydrogen ion independent pathway leads to a sluggish second-order process (k = 0.11 M-1 s-1) that is first order with respect to reduced glutathione [GSH] and [Cr(VI)]. Chromium(IV) species is reduced to Cr(III) by a second-order process (k = 0.13 M-1 s-1) that is first order in each of [Cr(IV)] and [GSH] and does not depend on [H+]. At pH 3.4, a chromium(V) species was detected as a minor intermediate as well. In the pH range 6.5-7.5, three dominant chromium(V) intermediates were detected. The existence of Cr(IV) in low pH offers an opportunity to examine the mechanism of DNA damage by this rare oxidation state.

An EPR spin label study of the glass forming liquid dibutyl phthalate

Spectra from a small nearly spherical probe and a large nearly cylindrical probe are studied as a function of temperature from 130–370 K. These spectra are used to calculate a rotational correlation time τ and the temperature dependence of τ is matched, at higher temperatures, to existing viscosity models such as the energy activation, Vogel–Fulcher, and Grest–Cohen models. The glass temperature is observed at ∼ 180 K and the data indicate a reduction in translational diffusion, but not rotational diffusion, as the glassy state is reached. We also observe that the spherical probe tumbles isotropically while the cylindrical probe tumbles anisotropically. In the latter case, the tumbling can be represented by an axially symmetric rotational diffusion tensor whose axis coincides with the long axis of the molecule. Finally, we present a phenomenological model for the temperature dependence of τ which fits the data well at all temperatures.

The spin 32 state (?) in six-coordinate iron (III). A Mössbauer and EPR investigation

Tris-(4-morpholinecarbodithioato-S,S′) iron (III) (FeM) and its dichloromethane solvate, (FeM·CH2Cl2), have been prepared and their temperature-dependent Mossbauer and EPR spectra have been determined at temperatures between liquid nitrogen and ambient. The Mossbauer spectra of FeM·CH2Cl2 differ considerably from that of FeM and is interpreted in terms of a four-line spectrum at 77 K. The EPR spectra of the two complexes indicate that the lower spin state of FeM·CH2Cl2 populates much more rapidly in the temperature range studied (100–300 K) than does FeM. These results support the postulation of an S = 52 ⇋ S = 12 spin-equilibrium for FeM and a corresponding S = 52 ⇋ S = 32 equilibrium for FeM·CH2Cl2.

Paramagnetic resonance studies of a possible spin crossover system

Abstract We present evidence for the existence of a spin equilibrium between the S = 5 2 and S = 1 2 states in tris (dicyclohexyldithiocarbamato) iron (III) (μ = 2.75BM at room temperature) by identifying paramagnetic resonance lines associated with these states. Studies of tris (di-n-butyldithiocarbamato) iron (III) (μ - 5.32 BM at room temperature) help to cofirm our intepretation.

Saturation Studies of N2− in Irradiated Sodium Azide

Saturation studies of N2− in sodium azide (NaN3) were performed at temperatures of 4.2° and 2°K and at a frequency of 9 GHz. The product T1T2 was found to be approximately 10−11 sec2. The assumption that the width of the partially resolved hyperfine structure is equal to the width of the homogeneously broadened packet allowed estimations of T2 as 10−8 sec and T1 as 10−3 sec. This assumption, justified in the text, also allowed one to calculate an upper limit on the ratio (a) of the homogeneous to inhomogeneous linewidths of 0.07. The saturation data yielded values of 0.4–0.8 for this ratio. The spin‐diffusion time, T21, was shown to be the order of 10−5 sec, so that spin diffusion was a dominant relaxation mechanism. This was used to explain apparent ambiguities in the values of a. The relaxation times were highly anisotropic when the dc magnetic field was nearly parallel to the crystalline c axis. Further experiments are needed before one can understand this variation.

Janusene and tetrafluorojanusene in superacid media ; radical cation formation and chemistry

Abstract Both janusene 1 and the facial tetrafluorojanusene undergo one electron oxidation in FSO 3 H.SbF 5 (1:1) ‘magic acid’/SO 2 ClF and in HF.SbF 5 (1:1)/SO 2 ClF at low temperature to give persistent radical cations. Rapid dimerization → polymerization follows. Stable σ-complexes of protonation were not observed at all. In the less oxidizing milder superacid FSO 3 H/SO 2 , neither 1 nor 2 are fully protonated or oxidized. Radical cation-mediated condensation of 1 is much more rapid than for the fluorinated analog. Two structurally different dimeric compounds could be isolated in quenching experiments. The extent of transannular donor-acceptor interactions in the facially fluorinated janusenes were compared with those for the tropylium-containing janusene, fluorinated [2.2] paracyclophane and its stable σ-complex.

A Spin Label Study of Nystatin and Amphotericin B Action on Lipid Planar Multibilayers

Abstract EPR spectra of a cholestane probe and a stearic acid probe dissolved in egg yolk lecithin and lecithin-cholesterol planar multibilayers were observed as a function of nystatin and amphotericin B dose. Spectral components characteristic of bilayer fragmentation (tilted domains) were most evident in cholesterol-containing samples and increased with drug dose. The spectra indicate that cholesterol-containing films decrease in microscopic order as drug dose is increased. This suggests that cholesterol is involved in the commonly accepted pore-formation model for nystatin and amphotericin, since removal of cholesterol from interaction with lecithin would account for the observed decrease in order. Spectra from the cholestane probe in liposomes (with and without the drugs) were also observed.

Concentration Dependent Relaxation Time Studies of N2− in X‐Irradiated Sodium Azide

The concentration dependence of the relaxation time of N2− in sodium azide was studied using paramagnetic resonance at 4.2°K. The relaxation rate was found to be independent of defect concentration within the experimental error of the saturation technique employed. The relaxation time product, T1T2, displayed the same strong anisotropy at K band (23 GHz) as was previously reported at X band. With the crystal platelet parallel to the static magnetic field, T1T2=0.5× 10−12sec2, and with the crystal platelet perpendicular to the static field, T1T2=1.6× 10−12sec2. The concentration was shown to be linear with irradiation time over the temporal range of interest by employing optical studies. These experiments indicate that the dominant relaxation mechanism is intramolecular in nature.

The anomalous EPR spectra of the iron(III) dichalcogenocarbamates

Abstract Recently, a new limiting resonance structure was proposed to more completely explain the bonding in the spincrossover tris(diorganodichalcogenocarbamato)iron(III) complexes, Fe(XYCNRR′)3 (where XY=SS, Sse or SeSe; R and R′ are organic substituents). This new limiting resonance structure involved a low-spin Fe(II) and an unpaired electron on the N of the radical ligand. This proposal was the result of the observation of structure in the narrow X-band EPR line at g ≈ 2 and a computer fit of this structured line which supported an assignment of electron density to an I=1 nucleus. The X-band EPR spectra (120 K) of 20 of these complexes have been re-examined, as pure powders and diluted in the corresponding Co(III) or In(III) complex matrix; 14 of these exhibit this structure in the region g≈2 which can be fit to an electron on an I=1 nucleus. An alternative explanation of the structured line resulting from an impurity of Fe(XYNCRR′)2NO is possible, but, if this is correct, the source of the NO is not ligand decomposition, since the X-band EPR spectrum (120 K) of Fe(S2CNEt2)3 prepared using 15N (I=1/2) is identical to the natural abundance complex. The EPR signal is believed to be of a common impurity in each of the Fe(XYCNRR′)3 complexes.

EPR studies of spin-crossover of the tris-(di-n-butyldithiocarbamato)Fe(III) chlorobenzene solvate

Abstract EPR studies of tris-(di-n-butyldithiocarbamato)Fe(III), with and without a chlorobenzene solvate, were performed from −160°C to room temperature. A line at an approximate g-value of 4.4 was assigned as a S = 5 2 line and its temperature dependent behavior was correlated with solid magnetic moment observations. An additional narrower line was noted in the spectrum of the solvated sample. We associate this line with a second possible high-energy site for the chlorobenzene solvate molecule. A solvate molecule in this site appears to “shut off” the spin-crossover.