I. Electron spin relaxation studies of manganese(II) complexes in acetonitrile. II. Nuclear spin relaxation studies of bromine in tetrabromomanganese(II) in acetonitrile

Magnetic resonance techniques have given us a powerful means for investigating dynamical processes in gases, liquids and solids. Dynamical effects manifest themselves in both resonance line shifts and linewidths, and, accordingly, require detailed analyses to extract desired information. The success of a magnetic resonance experiment depends critically on relaxation mechanisms to maintain thermal equilibrium between spin states. Consequently, there must be an interaction between the excited spin states and their immediate molecular environment which promote changes in spin orientation while excess magnetic energy is coupled into other degrees of freedom by non-radiative processes. This is well known as spin-lattice relaxation. Certain dynamical processes cause fluctuations in the spin state energy levels leading to spin-spin relaxation and, here again, the environment at the molecular level plays a significant role in the magnitude of interaction. Relatively few electron spin relaxation studies of solutions have been conducted and the present work is addressed toward the extension of our knowledge in this area and the retrieval of dynamical information from line shape analyses on a time scale comparable to diffusion controlled phenomena.

Specifically, the electron spin relaxation of three Mn⁺²3d⁵ complexes, Mn(CH₃CN)₆⁺², MnCl₄^-2 in acetonitrile has been studied in considerable detail. The effective spin Hamiltonian constants were carefully evaluated under a wide range of experimental conditions. Resonance widths of these Mn⁺² complexes were studied in the presence of various excess ligand ions and as a function of concentration, viscosity, temperature and frequency (X-band, ~9.5 Ԍ Hz and K-band, ~35 Ԍ Hz).

A number of interesting conclusions were drawn from these studies. For the Et₄NCl-₄^-2 system several relaxation mechanisms leading to resonance broadening were observed. One source appears to arise through spin-orbit interactions caused by modulation of the ligand field resulting from transient distortions of the complex imparted by solvent fluctuations in the immediate surroundings of the paramagnetic ion. An additional spin relaxation was assigned to the formation of ion pairs [Et₄N⁺…MnCl₄^-2] and it was possible to estimate the dissociation constant for this specie in acetonitrile.

The Bu₄NBr-MnBr₄^-2 study was considerably more interesting. As in the former case, solvent fluctuations and ion-pairing of the paramagnetic complex [Bu₄N⁺…MnBr₄^-2] provide significant relaxation for the electronic spin system. Most interesting, without doubt, is the onset of a new relaxation mechanism leading to resonance broadening which is best interpreted as chemical exchange. Thus, assuming that resonance widths were simply governed by electron spin state lifetimes, we were able to extract dynamical information from an interaction in which the initial and final states are the same

MnBr₄^-2 + Br^- = MnBr₄^-2 + Br^-.

The bimolecular rate constants were obtained at six different temperatures and their magnitudes suggested that the exchange is probably diffusion controlled with essentially a zero energy of activation. The most important source of spin relaxation in this system stems directly from dipolar interactions between the manganese 3d⁵ electrons. Moreover, the dipolar broadening is strongly frequency dependent indicating a deviation between the transverse and longitudinal relaxation times. We are led to the conclusion that the 3d⁵ spin states of ion-paired MnBr₄^-2 are significantly correlated so that dynamical processes are also entering the picture. It was possible to estimate the correlation time, ^Td, characterizing this dynamical process.

In Part II we study nuclear magnetic relaxation of bromine ions in the MnBr4-2-Bu4NBr-acetonitrile system. Essentially we monitor the 79Br and 81Br linewidths in response to the [MnBr4-2]/[Br-] ratio with the express purpose of supporting our contention that exchange is occurring between "free" bromine ions in the solvent and bromine in the first coordination sphere of the paramagnetic anion. The complexity of the system elicited a two-part study: (1) the linewidth behavior of Bu4NBr in anhydrous CH3CN in the absence of MnBr4-2 and (2) in the presence of MnBr4-2. It was concluded in study (1) that dynamical association, Bu4NBr k1= Bu4N+ + Br-, was modulating field-gradient interactions at frequencies high enough to provide an estimation of the unimolecular rate constant, k1. A comparison of the two isotopic bromine linewidth-mole fraction results led to the conclusion that quadrupole interactions provided the dominant relaxation mechanism. In study (2) the "residual" bromine linewidths for both 79Br and 81Br are clearly controlled by quadrupole interactions which appear to be modulated by very rapid dynamical processes other than molecular reorientation. We conclude that the "residual" linewidth has its origin in chemical exchange and that bromine nuclei exchange rapidly between a "free" solvated ion and the paramagnetic complex, MnBr4-2.

Treading in Mortimer's footsteps: the geochemical cycling of iron and manganese in Esthwaite water

A study of the geochemical cycling of iron and manganese in a seasonally stratified lake, Esthwaite water is described. This work is based on speculative ideas on environmental redox chemistry of iron which were proposed by C.H. Mortimer in the 1940's. These observations have been verified and some speculations confirmed, along with a new understanding of the manganese cycle, and detailed information on the particulate forms of both iron and manganese. Details on the mechanisms and transformations of iron have also emerged.

I. Proton magnetic resonance of polynucleotides and transfer RNA. II. Electron spin relaxation studies of manganese (II) complexes in acetonitrile

Part I. Proton Magnetic Resonance of Polynucleotides and Transfer RNA.

Proton magnetic resonance was used to follow the temperature dependent intramolecular stacking of the bases in the polynucleotides of adenine and cytosine. Analysis of the results on the basis of a two state stacked-unstacked model yielded values of -4.5 kcal/mole and -9.5 kcal/mole for the enthalpies of stacking in polyadenylic and polycytidylic acid, respectively.

The interaction of purine with these molecules was also studied by pmr. Analysis of these results and the comparison of the thermal unstacking of polynucleotides and short chain nucleotides indicates that the bases contained in stacks within the long chain poly nucleotides are, on the average, closer together than the bases contained in stacks in the short chain nucleotides.

Temperature and purine studies were also carried out with an aqueous solution of formylmethionine transfer ribonucleic acid. Comparison of these results with the results of similar experiments with the homopolynucleotides of adenine, cytosine and uracil indicate that the purine is probably intercalating into loop regions of the molecule.

The solvent denaturation of phenylalanine transfer ribonucleic acid was followed by pmr. In a solvent mixture containing 83 volume per cent dimethylsulf oxide and 17 per cent deuterium oxide, the tRNA molecule is rendered quite flexible. It is possible to resolve resonances of protons on the common bases and on certain modified bases.

Part II. Electron Spin Relaxation Studies of Manganese (II) Complexes in Acetonitrile.

The electron paramagnetic resonance spectra of three Mn⁺² complexes, [Mn(CH₃CN)₆]⁺², [MnCl₄]^-2, and [MnBr₄]^-2, in acetonitrile were studied in detail. The objective of this study was to relate changes in the effective spin Hamiltonian parameters and the resonance line widths to the structure of these molecular complexes as well as to dynamical processes in solution.

Of the three systems studied, the results obtained from the [Mn(CH₃CN)₆]⁺² system were the most straight-forward to interpret. Resonance broadening attributable to manganese spin-spin dipolar interactions was observed as the manganese concentration was increased.

In the [MnCl₄]^-2 system, solvent fluctuations and dynamical ion-pairing appear to be significant in determining electron spin relaxation.

In the [MnBr₄]^-2 system, solvent fluctuations, ion-pairing, and Br- ligand exchange provide the principal means of electron spin relaxation. It was also found that the spin relaxation in this system is dependent upon the field strength and is directly related to the manganese concentration. A relaxation theory based on a two state collisional model was developed to account for the observed behavior.

Copper, zinc, iron and manganese in sediments and in the rock oyster Saccostrea cucullata in Mumbai coast

Sediment and oyster (Saccostrea cucullata) samples were collected at Dhanda, a fishing village in Mumbai, Maharashtra. The samples were analysed for copper, zinc, iron and manganese contents. Metal concentrations in the sediments and bioaccumulated levels in oysters were correlated. There is no positive correlation between the total sedimentary levels of metals analysed and the bioaccumulated levels of respective metals in oyster. A positive correlation between the bioavailable fractions of zinc, iron and manganese, and the bioaccumulated levels exists. Copper, however, shows a negative correlation with respect to the bioaccumulated levels.

Effect of zinc and manganese supplementation to tricalcium phosphate rich diet for tiger puffer (Takifugu rubripes)

Effects of zinc (Zn) and manganese (Mn) supplementation to a tricalcium phosphate (TCP) rich diet for tiger puffer have been investigated. A TCP supplement to the diet decreased the growth of fish compared to the control diet with a Ca supplementation from Ca-lactate. However, addition of either Zn or Mn to the TCP supplemented diet could not improve the growth of tiger puffer. Addition of both zinc and manganese to the TCP supplemented diet improved the growth of tiger puffer.

Copper and manganese forms in Lake Edku sediments, Alexandria, Egypt

Lake Edku is one of the Nile Delta lakes. It is subjected to contaminations by several anthropogenic materials such as trace elements and other wastes. The distribution of the different chemical forms of copper and manganese has been studied using sequential extraction techniques. Chemical analysis of the sediments shows that CaCO sub(3) ranged from 3.7% to 9.6% and organic matter from 3.06% to 8.11%. The results indicate that the distribution of manganese among the six chemical forms in the sediments of the lake obeys the following order: Mn-residual>Mn-carbonate>Mn-moderately reducible>Mn-organic form>Mn-exchangeable > Mn-easily reducible fraction. Also, the data revealed that more than 50% of the total manganese was found in the residual form, while the remainder was distributed among the other forms. In contrast, more than 70% of the total copper content was associated with the five chemical forms (exchangeable, carbonate, easily and moderately reducible and organic forms). Generally, the enrichment of manganese in the residual form revealed the important role in building up of clay minerals, while the distribution of copper among the different forms reflects an important role in biological and biochemical processes.

Effects of dietary manganese on growth and tissue manganese concentrations of juvenile gibel carp, Carassius auratus gibelio

A 68-day growth trial was conducted in a flow-through system to determine the effect of dietary manganese levels on growth and tissue manganese concentration of juvenile gibel carp (Carassius auratus gibelio). Seven purified diets containing 7.21, 8.46, 9.50, 10.50, 13.03, 19.72 and 22.17 mg manganese (as manganic sulfate) per kilogram diet were fed to triplicate groups of fish (initial weight 3.21 +/- 0.01 g). The results showed that dietary manganese levels did not significantly affect feed intake of the fish. Specific growth rate, feed efficiency, total hepatic superoxide dismutase activity, carcass and skeletal manganese concentration increased significantly with increased dietary manganese(P < 0.05) while condition factor decreased significantly(P < 0.05). It was concluded that dietary requirement of manganese was 13.77 mg Mn per kilogram diet. Carcass and skeletal manganese concentration could also be used to evaluate the manganese requirement. Total hepatic superoxide dismulase activity was not a sensitive indicator for dietary requirement.

Molecular cloning and characterization of the copper/zinc and manganese superoxide dismutase genes from the human parasite Clonorchis sinensis

A copper/zinc superoxide dismutase (Cu/ZnSOD) gene and a manganese superoxide dismutase (MnSOD) gene of the human parasite Clonorchis sinensis have been cloned and their gene products functionally characterized. Genes Cu/ZnSOD and MnSOD encode proteins of 16 kDa and 25.4 kDa, respectively. The deduced amino acid sequences of the two genes contained highly conserved residues required for activity and secondary structure formation of Cu/ZnSOD and MnSOD, respectively, and show up to 73.7% and 75.4% identities with their counterparts in other animals. The genomic DNA sequence analysis of Cu/ZnSOD gene revealed this as an intronless gene. Inhibitor studies with purified recombinant Cu/ ZnSOD and MnSOD, both of which were functionally expressed in Escherichia coli, confirmed that they are copper/zinc and manganese-containing SOD, respectively. Immunoblots showed that both C. sinensis Cu/ZnSOD and MnSOD should be antigenic for humans, and both, especially the C. sinensis MnSOD, exhibit extensive cross-reactions with sera of patients infected by other trematodes or cestodes. RT-PCR and SOD activity staining of parasite lysates indicate that there are no significant differences in mRNA level or SOD activity for both species of SOD, indicating cytosolic Cu/ZnSOD and MnSOD might play a comparatively important role in the C. sinensis antioxidant system.

Microcalorimetric investigation of the effect of manganese(II) on the growth of Tetrahymena shanghaiensis S(1)99

The heat output of and the effect of manganese (II) on Tetrahymena shanghaiensis S(1)99 growth metabolism has been determined by means of a LKB-2277 BioActivity monitor. Different concentrations of manganese(II) ions have different effects on the growth of T. shanghaiensis. At low concentrations (0-40 mug/mL) culture growth is promoted, whereas high concentrations (60-800 mug/mL) slow growth. Furthermore, concentrations of 1200 mug/mL or greater stop the growth of this protozooa completely.

Giant Zeeman splitting in manganese-doped ZnSe quantum spheres: Eight-band effective-mass calculations

We deduce the eight-band effective-mass Hamiltonian model for a manganese-doped ZnSe quantum sphere in the presence of the magnetic field, including the interaction between the conduction and valence bands, the spin-orbit coupling within the valence bands, the intrinsic spin Zeeman splitting, and the sp-d exchange interaction between the carriers and magnetic ion in the mean-field approximation. The size dependence of the electron and hole energy levels as well as the giant Zeeman splitting energies are studied theoretically. We find that the hole giant Zeeman splitting energies decrease with the increasing radius, smaller than that in the bulk material, and are different for different J(z) states, which are caused by the quantum confinement effect. Because the quantum sphere restrains the excited Landau states and exciton states, in the experiments we can observe directly the Zeeman splitting of basic states. At low magnetic field, the total Zeeman splitting energy increases linearly with the increasing magnetic field and saturates at modest field which is in agreement with recent experimental results. Comparing to the undoped case, the Zeeman splitting energy is 445 times larger which provides us with wide freedom to tailor the electronic structure of DMS nanocrystals for technological applications.

Magnetism and luminescence evolution due to nitrogen doping in manganese-gallium oxide nanowires

We report a new method for large-scale production of GaMnN nanowires, by annealing manganese-gallium oxide nanowires in flowing ammonia at high temperature. Microstructure analysis indicates that the GaMnN nanowires have wurtzite GaN structure without Mn precipitates or Mn-related second phases. Magnetism evolution due to nitrogen doping in manganese-gallium oxide nanowires was evaluated by magnetic measurements. Magnetic measurement reveals that the magnetization increases with the increase of nitrogen concentration. Ferromagnetic ordering exists in the GaMnN nanowires, whose Curie temperature is above room temperature. Luminescence evolution was investigated by the cathodoluminesence measurement for a single nanowire and photoluminescence measurement in a temperature range between 10 and 300 K. Experimental results indicate that optical properties can be modulated by nitrogen doping in manganese-gallium oxide nanowires. (c) 2005 Elsevier B.V. All rights reserved.

Magnetism and photoluminescence in manganese-gallium oxide nanowires with monoclinic and spinel structures

Manganese-gallium oxide nanowires were synthesized via in situ Mn doping during nanowire growth using a vapor phase evaporation method. The microstructure and composition of the products were characterized via transmission electron microscopy (TEM), field emission scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The field and temperature dependence of the magnetization reveal the obvious hysteresis loop and large magnitude of Curie-Weiss temperature. The photoluminescence of the manganese-gallium oxide nanowires were studied in a temperature range between 10 and 300 K. A broad green emission band was observed which is attributed to the T-4(1)-(6)A(1) transition in Mn2+ (3d(5)) ions. (c) 2005 Elsevier B.V. All rights reserved.