The complexation behaviour of Cu(II) with di- and tripeptides containing the aromatic amino acids phenylalanine or typtophan has been investigated at different pH-values and compared with results obtained with di- and triglycine. The results obtained by means of ESR and optical absorption spectroscopy show an influence of the two different aromatic entities on the magnetic and optical parameters. A significant decrease of the g11-value and, concomittantly, an increase of the energy of the d-d transition was measured when an aromatic entity is present in the peptide. A possible explanation for this observation is given.

Copper↗

PubMedDate not supplied

1H-NMR investigations on the hydrogen bond formation between the tranquilizers diazepam and nitrazepam and some nucleobases.

The formation of hydrogen bonds between the minor tranquilizers diazepam and nitrazepam and a few nucleobases was studied in deuterochloroform solution by means of proton magnetic resonance spectroscopy. The thermodynamic and spectroscopic data of the associations were evaluated on the basis of a dimer model, using the concentration dependent shifts of the protons involved in hydrogen bonds. The interactions of nitrazepam (deltaH0=-10 to -21 kJ/mol; deltaG025 -0.2 to -7.4 kJ/mol) were found to be stronger than those of diazepam (deltaH0=-10 to -13 kJ/mol; deltaG025=6.0 to 6.4 kJ/mol). The various binding sites of the benzodiazepines for hydrogen bonds are discussed.

Adenine↗

PubMedDate not supplied

ESR investigations on blood treated intravenously with ascorbic acid.

The effect of 1 g of ascorbic acid, administered intravenously to healthy male and female volunteers, on blood and its constituents was investigated by means of electron spin resonance (ESR) spectroscopy and by differential hematologic examinations. The native blood ESR spectrum exhibits 2 min injection of vitamin C a considerable increase in spin concentration and a new signal at about g = 2.005 which we previously had found to correlate to the semidehydroascorbate radical. This spectrum is identical to that obtained in acute lymphatic leukemia. While it prevails in untreated leukemic patients, spin concentration and shape of the spectrum obtained return to normal within several hours to one day in healthy individuals. Since neither in erythrocytes nor in plasma modifications could be observed, the ESR changes detected must have their origin in the leukocytes. Hematologic studies of the peripheral blood show that the number of granulocytes, lymphocytes, and thrombocytes was not drastically affected by the vitamin C injection.

Adult↗

PubMedDate not supplied

Paramagnetic changes in pulmonary tumors.

Electron spin resonance studies on healthy and tumorous human lung samples have been conducted in order to determine possible differences in free radical concentration and shaped of the spectra between the different sections of the lung. It could be shown that in healthy lung tissue the signal caused by the semidehydroascorbate (SDA) radical is not prominent because of the prevailing high partial oxygen pressure. On formation of a tumor, the spin concentration increases, possibly due to the higher metabolic rate; here, the SDA peak is also more pronounced which indicates alterations in the interaction between cell constituents and ascorbic acid. Within the tumor, the spin concentration is considerably reduced which is probably caused by a still higher concentration of ascorbic acid. Addition of ascorbic acid to the different lung specimens enhanced the just described effect while oxidizing substances, such as H2O2, reversed it.

Dehydroascorbic Acid↗

PubMedDate not supplied

On a possible mechanism of action of interferon.

The effect of interferon on the ESR spectra of erythrocytes treated with ascorbic acid has been investigated. This model system has been chosen since it represents identically the spectra obtained in cases with acute lymphatic leukemia. The data obtained show that small interferon concentrations increase, while larger concentrations decrease the effect produced by ascorbic acid resulting, finally, in the original erythrocyte ESR spectrum. Atomic absorption studies reveal that presence of copper which might be part of the active principle.

Ascorbic Acid↗

PubMedDate not supplied

On the origin of the non-haemic iron transferrin ESR signal: ESR investigations on histidine-iron-ascorbic acid systems.

The nature of the ferric high spin iron complex located at g = 4.3 has been investigated by means of electron spin resonance spectroscopy. It could be shown that the iron is bound to two histidines, three ascorbic acids, and one bicarbonate. This agrees well with previous findings according to which the ligand field of iron is composed mainly of oxygen and nitrogen atoms. Another low-field signal located at g = 9.5 appears always concomitantly with the g = 4.3 signal. It should be due, therefore, to a transition between the two sublevels of the low-lying Kramers doublet in one principal direction.

Ascorbic Acid↗

PubMedDate not supplied

Structure of ascorbic acid and its biological function: V. Transport of ascorbate and isoascorbate across artificial membranes as studied by the spin label technique.

It could be shown by the reduction of the spin label (1,14) located within DPPC vesicles, that Na-ascorbate and K-isoascorbate can permeate membranes. At physiologic pH value, these two compounds exist as electroneutral radicals with a cyclic side chain structure. Ascorbic acid and isoascorbic acid, on the contrary, can hardly permeate such an artificial membrane. Since the radical will cause lipid peroxidation, it must be modified prior to permeation. This can be done by GSH which changes the radical state but maintains the electroneutral bicyclic configuration.

Ascorbic Acid↗

PubMedDate not supplied

On the origin of the non-haemic iron transferrin ESR signal: ESR investigations on histidine-iron-citric acid systems.

The nature of the high spin ferric iron complex located at g = 4.3 has been investigated by means of electron spin resonance spectroscopy and polarography. It could be shown that two complexes each exist in the acid and alkaline pH region, and that the iron is bound to two histidines, three citric acids, and probably to one bicarbonate. These results agree well with previous findings according to which the ligand field of iron should be composed mainly of oxygen and nitrogen atoms. Another low-field signal located at g = 3.6 appears in the pH range from 2 to 7 only and exhibits its maximum where the g = 4.3 signal has its minimum. Its exact nature is still unknown but it seems to represent some intermediate state of the ternary Fe3+-histidine-citric acid complex. When citric acid is used, the spin concentration seems to be always larger than in the case of ascorbic acid. Since the effect obtained with ascorbic acid and citric acid seems to be similar, it may be concluded that the biological function of both of the acids might be somehow related to each other.

Ascorbic Acid↗

PubMedDate not supplied

ESR investigations on the modification of the ascorbic acid-erythrocyte interaction by ferrous ions.

An ascorbic acid-erythrocyte interaction results in the formation of the semidehydroascorbate (SDA) radical and an increase in spin concentration. Addition of a more than ten-fold concentration of Fe2+ (as FeSO4) to such a system compensates the effect produced by ascorbic acid, that is the electron spin resonance spectrum obtained resembles very closely that of erythrocytes only. With the disappearance of the SDA radical a high spin ferric ion signal appears concomitantly at g = 4.3.

Ascorbic Acid↗

PubMedDate not supplied

The effect of alcohol oxidase on the ascorbic acid-erythrocyte interaction: ESR investigations.

Addition of alcohol oxidase to erythrocytes treated with ascorbic acid reverses the vitamin C effect, as expressed by the appearance of the semidehydroascorbate signal, and the increase in spin concentration. The original erythrocyte electron spin resonance (ESR) signal is, however, never restored completely, as it is in the case if ascorbate oxidase is used. Additional interaction between the enzyme alcohol oxidase and haemoglobin iron must occur, since both of the iron ESR signals at g = 4.3 and g = 6 disappear and the erythrocyte ESR spectrum at g approximately equal to 2 is changed characteristically. The spin concentration of the latter spectrum increases again above a certain concentration of alcohol oxidase.

Alcohol Oxidoreductases↗

PubMedDate not supplied

The influence of amino acid ligands and vitamin C on the reduction potential of Fe (III): polarographic and electron spin resonance investigations.

The pH dependence of Fe(III)-amino acid complexes has been studied polarographically and by means of ESR spectroscopy. It could be shown that, at least, two complexes exist: one with a low molecular weight, ESR detectable at acid pH, and one with a high molecular weight at alkaline pH, ESR non detectable. The half wave potential of Fe(III) is lowered by amino acid ligands. The redox interaction of the Fe(III)-amino acid complexes with vitamin C results in a decrease of the ascorbyl radical concentration. Ascorbic acid also forms a complex with Fe(III) as indicated by a polarographic half wave potential near -0.55 V vs. S.C.E. at pH 7.

Alanine↗