K. Spartalian

Mössbauer spectroscopic study of compound es of cytochrome c peroxidase

Mössbauer spectra of Compound ES of cytochrome c peroxidase have been observed over a range of temperature and applied magnetic field. These have been interpreted in terms of a crystal field model of the iron site in which the iron is assumed to be in the Fe(IV) state with unpaired spin S = 1. Detailed least-squares fitting of the spectra fitting of the spectra indicates that both the electric field gradient choice of a single parameter, the axial crystal field, the magnetic properties are well reproduced. The model also provides the observed positive sign for the electric field gradient interaction, but overestimates its magnitude. This apparent discrepnancy may be caused by the presence of significant electronic charge in filled bonding orbitals, a feature which is in keeping with expected covalent charge compensation of the extreme oxidation state. There is no evidence in the Mössbauer spectra of interaction between the iron and the ESR-visible free radical. This suggests they are well separated.

Low temperature photodissociation studies of ferrous hemoglobin and myoglobin complexes by Mössbauer spectroscopy.

57Fe-enriched complexes of hemoglobin and myoglobin with CO and O2 were photodissociated at 4.2 degrees K, and the resulting spectra were compared with those of the deoxy forms. Differences in both quadrupole splitting and isomer shift were noted for each protein, the photoproducts having smaller isomer shift and larger quadrupole splitting than the deoxy forms. The photoproducts of HbCO and HbO2 had narrow absorption lines, indicating a well-defined iron environment. The corresponding myoglobin species had broader absorption lines, as did both deoxy forms. The weak absorption lines of photodissociated NO complexes appeared to be wide, possibly indicating magnetic interaction with the unpaired electron of the nearby NO.

Mössbauer investigation of deoxymyoglobin in a high magnetic field. Orientation of the electric field gradient and magnetic tensors

We have examined the Mössbauer spectra of deosymyoglobin in a 6 T magnetic field in the temperature range 4.2-195 K. Spectra were fitted by the least-squares method using a phenomenological model in which the internal magnetic hyperfine field was assumed to be related to the applied field by a temperature dependent tensor õmega. The results indicate that õmega has axial symmetry and a principal axis system aligned with that of the electric field gradient (efg). The principal component of the latter is negative and lies on the symmetry axis of õmega. Our fits indicate that of efg asymmetry parameter is eta = 0.7, with no appreciable temperature dependence. Both axial and transverse components of õmega have the expected 1/T temperature dependence for T greater than 20 K. Our experimentally determined value of eta, combined with published single crystal zero-field measurements, constrains the efg-heme relative orientation to two possibilities. In neither of these is an efg principal axis near to the heme normal.

Interference effects produced by single photons

SummaryInterference patterns produced by low-intensity photon beams passing through a Fabry-Perot interferometer have been studied. Photons were detected by means of an image intensifier tube of high quantum detection efficiency. No change in the nature of the pattern was observed when the intensity of the beam was reduced from 5·104 to 15 photons per second in the entire pattern.RiassuntoSi sono studiate le figure d’interferenza prodotte dai fasci di fotoni di bassa intensità passanti attraverso un interferometro di Fabry-Perot. Si sono rivelati i fotoni tramite un tubo che intensifica l’immagine con alta efficienza nella rivelazione dei quanti. Non si è osservata alcuna variazione nella natura della figura una volta ridotta l’intensità del fascio da 5·104 a 15 fotoni per secondo nell’intera figura.РеэюмеБыли исследованы интерференционные диаграммы, обраэованные фотонными пучками с ниэкой интенсивностью, при прохождении череэ интерферометр Фабри-Перо. Фотоны детектировались посредством злектронно-опт ического усилителя иэображения с высокой зффективностью детектирования квантов. Не наблюдалось никакого иэменения природы диаграммы, когда интенсивность пучка уменьщалась от 5·104 до 15 фотонов в секунду.

Mössbauer effect studies in the fungus Phycomyces

Mossbauer spectra of 57- Fe have been observed from different parts (mycelia, spores, sporangiophores) of the fungus Phycomyces blakesleeanus grown in an agar medium isotopically enriched with 57- Fe. The spectra indicate that the iron within Phycomyces exists primarily in two chemical states: one which is the same as that of the iron in the growth medium and the other in the form of ferritin, an iron-storage protein. The amount of iron in the former state is observed to decrease relative to the amount of iron in the latter state in going from mycelia to the sporangiophores to the sporangia themselves. Thus, the conversion of iron from the chemical state of the nutrient to ferritin has been monitored for different parts of the phycomyces. In addition, our spectra indicate that at low temperatures the iron atoms clustered within a ferritin molecule are antiferromagnetically coupled. The size of these clusters is inferred from their superparamagnetic behavior at low tempertures and comparison with horse ferritin indicates that the phycomyces ferritin iron clusters are smaller by a factor of two.

Models for vanadium–tunichrome interactions

N,N′,N″-Tris(2,3,4- and 3,4,5-trihydroxybenzoyl)-1,5,10-triazadecanes have been synthesized as models for the tunichromes thought to be involved in vanadium metabolism of many tunicates.

Rectangles in Physics

In a recent article,1 Greenslade presents a nomograph from an old textbook describing a geometrical construction for the equivalent resistance of two resistors in parallel. Greenslades final remark is that the motivation for this construction “is obscure.” When I saw the article, I realized I could make an educated guess for the motivation. In this paper I will use the nomograph discovered by Greenslade as a springboard and present some of my thoughts on the geometrical presentation of physics in hopes to amuse the experts.

Superparamagnetism in the Fungus, Phycomyces

The iron storage protein, ferritin, in the single cell plant‐like fungus Phycomyces Blakesleeanus has been studied with the Mossbauer effect. Mossbauer spectra in different parts of the cells grown in a 57Fe rich medium have been observed. The spectra indicate that the iron forms superparamagnetic clusters within the ferritin molecules. The size of these clusters, smaller in phycomyces ferritin than in horse ferritin, was inferred by the superparamagnetic behavior which appears in the Mossbauer spectrum. Comparison with horse ferritin data leads to the conclusion that phycomyces ferritin is smaller by a factor of two. The iron in the spores at the top is nearly all in the chemical form of ferritin. The roots (mycelium) contain nearly equal amounts of iron in ferritin and in the form of the nutrient.