Substrate-free copper nanoclusters exhibit super diamagnetism and surface based soft ferromagnetism.

Pure metallic copper nanoparticles free of any substrate were synthesized by the thermo-chemical reduction of copper acetate using triethanolamine as a reducing-cum-protection agent. The structure and physical and magnetic properties of the Cu NPs were analysed physicochemically. Microscopic analysis reveals the formation of particles of size of 3-5 nm as seen by TEM but present as a large agglomeration as identified by SEM. A structure of Cu9 is predicted for the Cu NPs on the basis of investigations using XPS, MALDI, EPR, and magnetic measurements and supported by the prediction of DFT calculation from an earlier work. The most important findings come from magnetization studies which prove the existence of giant diamagnetism from the nanomer clusters of copper as well as the formation of two different ferromagnetic transitions at ∼40 K and ∼100 K, the latter two arising from the surface properties possibly due to thin films of CuO and/or the presence of TEOA giving rise to temperature dependent coercivity revealing them to be soft room temperature ferromagnets. The clusters of Cu NPs with the identified structure show temperature and field dependent giant diamagnetism which is about 29-39 times larger than the diamagnetism calculated from known and established atomic values. Though such enhanced diamagnetism has been predicted for noble metal clusters, experimental observation so far has been restricted to Au and Pt and this is probably the first report on substrate-free metallic copper clusters.

Zinc Oxide-Supported Copper Clusters with High Biocidal Efficacy for Escherichia coli and Bacillus cereus.

Cu clusters on ZnO have been prepared by a simple low-temperature solid-state reaction from their respective acetate precursors. The formation of metallic Cu along with a small quantity of CuO was influenced by the presence of the zinc acetate precursor. Although there is a lack of formation of any metallic Cu in the absence of zinc acetate, increase in the heating duration helps in the formation of increased metallic Cu. A mechanism for formation of the Cu@ZnO nanocomposite has been suggested. The prepared Cu@ZnO nanocomposite, with metallic Cu, was identified by X-ray diffraction studies followed by confirmation of clusters of the kind Cu9 and Cu18 by transmission electron microscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The photoelectron spectroscopy is able to clearly distinguish the Cu from CuO, which is very well complimented by electron spin resonance analysis. The morphological feature of ZnO changes from flakes to rods on increasing the duration of heating, as shown by scanning electron microscopy (SEM) analysis. The observed Cu plasmonic band in UV-vis diffuse reflectance gets blue-shifted to 463 nm from its normally observed position of 550-580 nm possibly due to cluster formation and interaction with ZnO, the band gap of the latter getting red-shifted to 3.2-3.0 eV. The antibacterial activity of the synthesized Cu cluster-ZnO nanocomposites was investigated against Escherichia coli ATCC-25922 for Gram-negative and Bacillus cereus ATCC-10876 for Gram-positive bacteria. Tests were performed on a nutrient agar medium and liquid broth supplemented with different concentrations of nanoparticles. SEM analysis of the native and treated Gram-positive and Gram-negative bacteria established a high efficacy of biocide activity in 24 h, with 200 µg/mL of Cu@ZnO nanocomposites.

Oxygen vacancies and intense luminescence in manganese loaded Zno microflowers for visible light water splitting.

ZnO nanorods and Mn/ZnO microflowers with nano-sized petals exhibit singly ionized oxygen vacancies, V. This is strongly supported by a green photoluminescence emission at 2.22 eV and an EPR g value of 1.953, both of which are suppressed greatly after annealing in an oxygen atmosphere. A strong red emission observed during exposure to X-rays reveals the presence of F(+) centres as a consequence of the V. Mn/ZnO displayed enhanced H2 generation with visible light exposure, when compared to pure ZnO and annealed Mn/ZnO in the visible region, which directly correlated with the oxygen vacancy concentration. There is an interesting correlation between the intensities of the EPR lines at the g-value of 1.953 due to the oxygen vacancies, the intensity of light emitted from the exposure to X-rays, the intensity of the photoluminescence due to oxygen vacancies and the quantity of H2 produced by the photocatalytic effect when comparing the three different nanomaterials, viz. pure ZnO, Mn/ZnO before and after annealing, all having been made exactly by the same methodologies.

Fuel mediated solution combustion synthesis of ZnO supported gold clusters and nanoparticles and their catalytic activity and in vitro cytotoxicity.

Nanocomposites of gold nanoparticles and semiconductor ZnO with wurtzite structure, made by solution combustion synthesis (SCS), as a function of the Zn/fuel ratio with polyethylene glycol (PEG) as fuel exhibit the presence of both nanoparticles and clusters. Atomic gold clusters present on the surface of ZnO nanorods which can be identified by XPS and SEM are easily monitored and characterized by positive ion MALDI experiments as mostly odd numbered clusters, Au3 to Au11 in decreasing amounts. Low concentrations of the fuel produce AuClO and nanoparticles (NPs), with no clusters. Au-ZnO nanocomposites at all [Au] exhibit single blue shifted plasmon absorption and corresponding photoluminescence (PL). Increasing particle size prefers surface plasmon resonance (SPR) scattering of metal that could lead to PL enhancement; however, available ZnO surface in the Au-ZnO composite becomes more important than the particle size of the composite with higher [Au]. The catalytic activity of these Au-ZnO nanocomposites tested on 4-nitrophenol clearly revealed the presence of an intermediate with both NPs and clusters playing different roles. An in vitro study of cytotoxicity on MCF-7 cell lines revealed that these gold nanostructures have turned out to be powerful nanoagents for destruction of cancer cells even with small amounts of gold particles/clusters. The nanorods of ZnO, known to be nontoxic to normal cells, play a lesser role in the anticancer activity of these Au-ZnO nanocomposites.

Spectroscopic dimensions of silver nanoparticles and clusters in ZnO matrix and their role in bioinspired antifouling and photocatalysis.

Silver doped zinc oxide nanoparticles are synthesized by a solution combustion method. The samples characterized by a variety of spectroscopic and other techniques clearly reveal the presence of silver nanoparticles as well as silver clusters. The silver in the two forms was identified by careful deconvolution of X-ray photoelectron spectral results. Their formation was also confirmed by the presence of plasmons, the concentration and energy of which increase on increasing silver input, indicating the presence of perpendicular excitons since aggregates of clusters are known to shift the plasmon resonances depending on their topologies. Further confirmation of clusters came from EPR (electron paramagnetic resonance), HRSEM (high resolution scanning electron microscopy) and HRTEM (high resolution transmission electron microscopy); direct proof for clusters came from matrix assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectral measurements. The antimicrobial activity of the silver doped zinc oxide polymer nanocomposites as biomedical devices are measured by zone of inhibition. Also, samples coated on paper disk with acacia binder are evaluated by a disk diffusion method. While pure zinc oxide does not show any antimicrobial property, the activity of silver-doped zinc oxide is comparable to that of commercial antibiotics and found to be related to nanoparticulate silver. Similarly, the microbial adherence to the surface of polymer nanocomposite which mimics a biomedical device also was influenced by nanoparticles of silver. The photocatalytic water treatment was carried out using silver carrying nanoparticles with Rhodamine-B and 4-chlorophenol as model pollutants. The increased photocatalytic activity of silver containing zinc oxide as compared to pure zinc oxide nanoparticles is attributed to the synergistic display of the properties of silver nanoparticles and clusters in zinc oxide. This activity depends upon the dispersion of silver nanoparticles over the zinc oxide lattice where charge separation plays a dominant role. The mechanisms for both photocatalysis and antimicrobial activity are discussed.

Internal Spin Trapping of Thiyl Radical during the Complexation and Reduction of Cobalamin with Glutathione and Dithiothrietol.

The activation of cobalamin requires the reduction of Cbl(III) to Cbl(II). The reduction by glutathione and dithiothreitol was followed using visible spectroscopy and electron paramagnetic resonance. In addition the oxidation of glutathione was monitored. Glutathione first reacts with oxidized Cbl(III). The binding of a second glutathione required for the reduction to Cbl(II) is presumably located in the dimethyl benzimidazole ribonucleotide ligand cavity. The reduction of Cbl(III) by dithiothreitol, which contains two thiols, is much faster even though no stable Cbl(III) complex is formed. The reduction, by both thiol reagents, results in the formation of thiyl radicals, some of which are released to form oxidized thiol products and some of which remain associated with the reduced cobalamin. In the reduced state the intrinsic lower affinity for the benzimidazole base, coupled with a trans effect from the initial GSH bound to the ß-axial site and a possible lowering of the pH results in an equilibrium between base-on and base-off complexes. The dissociation of the base facilitates a closer approach of the thiyl radical to the Co(II) α-axial site resulting in a complex with ferromagnetic exchange coupling between the metal ion and the thiyl radical. This is a unique example of 'internal spin trapping' of a thiyl radical formed during reduction. The finding that the reduction involves a peripheral site and that thiyl radicals produced during the reduction remain associated with the reduced cobalamin provide important new insights into our understanding of the formation and function of cobalamin enzymes.

A new paramagnetic intermediate formed during the reaction of nitrite with deoxyhemoglobin.

The reduction of nitrite by deoxygenated hemoglobin chains has been implicated in red cell-induced vasodilation, although the mechanism for this process has not been established. We have previously demonstrated that the reaction of nitrite with deoxyhemoglobin produces a hybrid intermediate with properties of Hb(II)NO(+) and Hb(III)NO that builds up during the reaction retaining potential NO bioactivity. To explain the unexpected stability of this intermediate, which prevents NO release from the Hb(III)NO component, we had implicated the transfer of an electron from the ß-93 thiol to NO(+) producing ·SHb(II)NO. To determine if this species is formed and to characterize its properties, we have investigated the electron paramagnetic resonance (EPR) changes taking place during the nitrite reaction. The EPR effects of blocking the thiol group with N-ethyl-maleimide and using carboxypeptidase-A to stabilize the R-quaternary conformation have demonstrated that ·SHb(II)NO is formed and that it has the EPR spectrum expected for NO bound to the heme in the ß-chain plus that of a thiyl radical. This new NO-related paramagnetic species is in equilibrium with the hybrid intermediate "Hb(II)NO(+) ↔ Hb(III)NO", thereby further inhibiting the release of NO from Hb(III)NO. The formation of an NO-related paramagnetic species other than the tightly bound NO in Hb(II)NO was also confirmed by a decrease in the EPR signal by -20 °C incubation, which shifts the equilibrium back to the "Hb(II)NO(+) ↔ Hb(III)NO" intermediate. This previously unrecognized NO hemoglobin species explains the stability of the intermediates and the buildup of a pool of potentially bioactive NO during nitrite reduction. It also provides a pathway for the formation of ß-93 cysteine S-nitrosylated hemoglobin [SNOHb:S-nitrosohemoglobin], which has been shown to induce vasodilation, by a rapid radical-radical reaction of any free NO with the thiyl radical of this new paramagnetic intermediate.

Molecular packing and magnetic properties of lithium naphthalocyanine crystals: hollow channels enabling permeability and paramagnetic sensitivity to molecular oxygen.

The synthesis, structural framework, magnetic and oxygen-sensing properties of a lithium naphthalocyanine (LiNc) radical probe are presented. LiNc was synthesized in the form of a microcrystalline powder using a chemical method and characterized by electron paramagnetic resonance (EPR) spectroscopy, magnetic susceptibility, powder X-ray diffraction analysis, and mass spectrometry. X-Ray powder diffraction studies revealed a structural framework that possesses long, hollow channels running parallel to the packing direction. The channels measured approximately 5.0 × 5.4 Å(2) in the two-dimensional plane perpendicular to the length of the channel, enabling diffusion of oxygen molecules (2.9 × 3.9 Å(2)) through the channel. The powdered LiNc exhibited a single, sharp EPR line under anoxic conditions, with a peak-to-peak linewidth of 630 mG at room temperature. The linewidth was sensitive to surrounding molecular oxygen, showing a linear increase in pO(2) with an oxygen sensitivity of 31.2 mG per mmHg. The LiNc microcrystals can be further prepared as nano-sized crystals without the loss of its high oxygen-sensing properties. The thermal variation of the magnetic properties of LiNc, such as the EPR linewidth, EPR intensity and magnetic susceptibility revealed the existence of two different temperature regimes of magnetic coupling and hence differing columnar packing, both being one-dimensional antiferromagnetic chains but with differing magnitudes of exchange coupling constants. At a temperature of ∼50 K, LiNc crystals undergo a reversible phase transition. The high degree of oxygen-sensitivity of micro- and nano-sized crystals of LiNc, combined with excellent stability, should enable precise and accurate measurements of oxygen concentration in biological systems using EPR spectroscopy.

Responses of the photosynthetic machinery of Spirulina maxima to induced reactive oxygen species.

The photosynthetic machinery of Spirulina maxima was studied when subjected to induced reactive oxygen species (ROS) to examine the organism's responses to stress. Significant decreases in both photosynthetic efficiency and growth rate were observed. Exposure to 0.01 mmol H(2)O(2)/(g cell), which induced the lowest specific intracellular ROS level (siROS) led to a 15% decrease in specific growth rate; an increase in siROS by 70-fold led to a 25% decrease in specific growth rate. Similarly, siROS induced by 0.01 mmol H(2)O(2)/(g cell) led to 15% inhibition in photosynthetic efficiency, while an increase in siROS by 40- or 70-fold led to about 60% inhibition in photosynthetic efficiency. To further understand the effects of induced ROS on photosynthetic machinery, we performed a detailed pigmentation analysis as well as analyzed Phycobilisomes (PBS), Photosystem II (PSII), and Photosystem I (PSI), the three important components of cyanobacterial photosynthetic apparatus. We found carotenoids (beta-carotene and lutein) to be most sensitive to siROS. Also, specific levels of phycocyanin and allophycocyanin, which are important PBS pigments, decreased significantly in response to H(2)O(2). Further, electron transport assays revealed that ROS cause damage primarily to PSII, whereas they do not significantly affect PSI in comparison; siROS induced by 0.01 mmol H(2)O(2)/(g cell) led to a 15% inhibition of PSII, and increase in siROS by 9-, 40-, and 70-fold led to 22%, 36%, and 46% inhibition, respectively.

Effect of nitrogen dioxide on the EPR property of lithium octa-n-butoxy 2,3-naphthalocyanine (LiNc-BuO) microcrystals.

Lithium octa-n-butoxy-naphthalocyanine (LiNc-BuO) is a stable free radical that can be detected by electron paramagnetic resonance (EPR) spectroscopy. Previously we have reported that microcrystals of LiNc-BuO exhibit a single sharp EPR peak, whose width varies linearly with the partial pressure of paramagnetic molecules such as oxygen and nitric oxide. In this report, we present the effect of nitrogen dioxide (NO2), which is also a paramagnetic molecule, on the EPR properties of LiNc-BuO. The gas-sensing property of LiNc-BuO is attributed to the open molecular framework of the crystal structure which is arranged with wide channels capable of accommodating large molecules such as NO2. The EPR linewidth of LiNc-BuO was highly sensitive to the partial pressure of NO2 in the gas mixture. The line-broadening was quick and reversible in the short-term for low concentration of NO2. However, the EPR signal intensity decreased with time of exposure, apparently due to a reaction of NO2 with LiNc-BuO crystals to give diamagnetic products. The results suggested that LiNc-BuO may be a useful probe for the determination of trace amounts of NO2 using EPR spectroscopy.

Photoexcitation and relaxation properties of a spin-crossover solid in the case of a stable high-spin state.

The molecular solid [Fe(II)L(2)](ClO(4))(2).CH(3)CN where L is 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine provides a stable high-spin (HS) state at low temperature. Photoexcitation and subsequent relaxation have been studied using light-induced excited state spin trapping [LIESST(H --> L)] in the 700-850 nm range, determination of T(LIESST), relaxation curves at different temperatures, and temperature dependence of the light-induced spin equilibrium under constant irradiation. The measured photoinduced population of the metastable low-spin (LS) state (<30%) was drastically limited by the concomitant L --> H photoprocess. The absence of static light-induced thermal hysteresis and the stretched exponential shape of the relaxation curves respectively revealed the absence of sizable interactions and a large spreading of the activation energies attributed to the ligand flexibility. The whole data set has been simulated using a linear rate equation, with a simplified correction for the bulk extinction of light in the powder sample.

Studies on nitrosyl hemes in Ni(II)-Fe(II) hybrid hemoglobins.

Subunit heterogeneity within a particular subunit in hemoglobin A have been explored with electron paramagnetic resonance spectroscopy using the nitrosyl hemes in Ni-Fe hybrid Hb under various solution conditions. Our previous studies on the crystal structure of NiHb demonstrated the presence of subunit heterogeneity within alpha-subunit. To further cross check this hypothesis, we made a hybrid Hb in which either the alpha- or beta-subunit contains iron, which alone can bind to NO. By this way dynamic exchange between penta- and hexa-coordinated forms within a subunit was confirmed. Upon the addition of inositol hexa phosphate (IHP) to these hybrids, R to T state transition is observed for [alpha(2)(Fe-NO)beta(2)(Ni)] but such a direct transformation is less marked in [alpha(2)(Ni)beta(2)(Fe-NO)]. Hence the bond between N(epsilon) and Fe is fundamental to the structure-function relation in Hb, as the motion of this nitrogen triggers the vast transformation, which occurs in the whole molecule on attachment of NO.

Iron chelation abrogates excessive formation of hydroxyl radicals and lipid peroxidation products in monocytes of patients with Eales' disease: direct evidence using electron spin resonance spectroscopy.

PURPOSE: Eales' disease (ED) is an idiopathic retinal vasculitis condition, which affects the retina of young adult males. Retinal changes include perivasculitis, non-perfusion and neovascularization. Disruption of blood-retinal barrier (BRB) is the common feature in intra-ocular inflammatory diseases. Disruption of BRB results in vascular hyper permeability and infiltration of circulating leukocytes into the retinal parenchyma. Monocyte (MC) activation results in oxidant thrust and subsequent tissue damage. This has been reported in various intra-ocular inflammatory diseases such as uveitis and Behcet's disease. However, there are no such reports available in ED. Hence in the present study we have investigated the role of MC activation and hydroxyl radicals (OH) production and its possible involvement in promoting the development of retinal vasculitis in patients with ED. METHODS: Twelve patients with ED and twelve healthy volunteers were recruited for the study. MC was separated from their peripheral blood. MC from patients with ED and control subjects was stimulated with phorbol-12-myristate-acetate (PMA) and OH generated was analyzed using an electron spin resonance spectrometer (ESR). Superoxide dismutase (SOD), thiobarbituric acid reactive substances (TBARS), and iron content was determined in MC to assess the oxidant thrust and antioxidant defense. RESULTS: OH generation was elevated in MC from patients with ED, which coincided with diminished SOD activity and elevated levels of iron and TBARS, when compared with healthy control subjects. OH generation was abrogated when MC from ED were co-incubated with PMA and iron chelators such as diethylenetriaminepentacetic acid (DTPA) and desferrioxamine. Iron chelation also inhibited TBARS accumulation restored SOD activity in MC of patients with ED. CONCLUSIONS: For the first time we have demonstrated the production of OH generation in MC of patients with ED using ESR. Further we have shown the beneficial effect of iron chelation in mitigating free radical mediated changes in cellular metabolism. Based on our findings, we provide further evidence for the role of oxidant thrust in promoting retinal tissue damage in patients with ED.

Synthesis, Structure, Magnetic Properties, and (1)H NMR Studies of a Moderately Antiferromagnetically Coupled Binuclear Copper(II) Complex.

A binuclear Cu(II) complex of [(Cu(2)(HAP)(2)IPA)(OH)(H(2)O)](ClO(4))(2).H(2)O (HAP = 3-amino-1-propanol; IPA = 2-hydroxy-5-methylisophthalaldehyde) has been synthesized and characterized by X-ray crystallography, by solid state magnetic susceptibility, and in solution by (1)H NMR studies. The binuclear copper(II) complex crystallizes in the orthorhombic system, space group Pbcn, a = 27.9972(9) Å, b = 8.8713(3) Å, c = 19.5939(6) Å, and Z = 8. The two copper(II) atoms in this binuclear Cu(II) complex are bridged by the oxygen atoms of the phenolate and hydroxy groups. The axial position at one Cu atom is occupied by a water molecule while another Cu has weak interaction with a perchlorate group. The coordination geometries around the two Cu atoms are distorted square pyramid and square planar. The solid state magnetic susceptibility measurement reveals a moderate antiferromagnetic exchange interaction between the two Cu atoms with a -2J value of 113 +/- 9 cm(-)(1). The variable-temperature (1)H NMR studies in CD(3)CN solution show that the observed relatively sharp hyperfine shifted signals follow a Curie behavior. The exchange coupling constant (-2J) obtained in solution by using chemical shift as a function of temperature also reveals a moderate antiferromagnetic exchange interaction between two Cu(II) ions. An analysis of the relaxation data shows that the reorientational correlation time (tau(c)) is dominated probably by a combination of electronic relaxation time tau(s) and rotational correlation time (tau(r)) due to an exchange-modulated dipolar mechanism for this moderately antiferromagnetically coupled binuclear copper(II) system.