Mass spectrometric and charge density studies of organometallic clusters photoionized by gigawatt laser pulses.

Clusters on exposure to nanosecond laser pulses of gigawatt intensity exhibit a variety of photo-chemical processes such as fragmentation, intracluster reaction, ionization, Coulomb explosion, etc. Present article summarizes the experimental results obtained in our laboratory utilizing time-of-flight mass spectrometer which deal with one such aspect of cluster photochemistry related to generation of multiply charged atomic ions upon excessive ionization of cluster constituents (Coulomb explosion) at low intensity laser field (∼109 W/cm2 ). To understand the mechanism of laser-cluster interaction, laser as well as cluster parameters were varied. Mass spectrometric studies were carried out at different laser wavelength as well as varying the nature of cluster constituents, backup pressure, nozzle diameter, etc. In addition, charge density measurements were also preformed to get information about the total number of ions generated upon laser-cluster interaction as a function of laser wavelength. In case of pure molecular clusters, the charge state of atomic ions as well as charge density was observed to enhance with increasing laser wavelength, signifying efficient coupling of the cluster medium with nanosecond laser pulse at longer wavelength. While in case of clusters doped with species having comparatively lower ionization energy, the efficiency of laser-cluster interaction was less, in contrast to studies carried out using femtosecond lasers. Results obtained in the present work have been rationalized on the basis of proposed three-stage cluster ionization mechanism, that is, multiphoton ionization ignited-inverse Bremsstrahlung heating and electron ionization. © 2015 Wiley Periodicals, Inc. Mass Spec Rev. 36:188-212, 2017.

Magnetic nanoparticle-mediated hyperthermia therapy induces tumour growth inhibition by apoptosis and Hsp90/AKT modulation.

PURPOSE: We have evaluated the hyperthermia efficacy of oleic acid-functionalised Fe(3)O(4) magnetic nanoparticles (MN-OA) under in vivo conditions and elucidated the underlying mechanism of tumour growth inhibition. MATERIALS AND METHODS: The efficacy and mechanism of tumour growth inhibition by MN-OA-mediated magnetic hyperthermia therapy (MHT) was evaluated in a murine fibrosarcoma tumour model (WEHI-164) using techniques such as TUNEL assay, Western blotting (WB), immunofluorescence (IF) staining and histopathological examination. In addition, bio-distribution of MN-OA in tumour/other target organs and its effect on normal organ function were studied by Prussian blue staining and serum biochemical analysis, respectively. RESULTS: MN-OA-induced MHT resulted in significant inhibition of tumour growth as determined by measurement of tumour volume, as well as by in vivo imaging of tumour derived from luciferase-transfected WEHI-164 cells. Histopathology analysis showed presence of severe apoptosis and reduced tumour cells proliferation, which was further confirmed by TUNEL assay, reduced expression of Ki-67 and enhanced level of cleaved caspase-3, in tumours treated with MHT. Moreover, expression of heat stress marker, Hsp90 and its client protein, AKT/PKB was reduced by ∼50 and 80%, respectively, in tumours treated with MHT as studied by WB and IF staining. Serum analysis suggested insignificant toxicity of MN-OA (in terms of liver and kidney function), which was further correlated with minimal accumulation of MN-OA in target organs. CONCLUSIONS: These results suggest the involvement of apoptosis and Hsp90/AKT modulation in MN-OA-mediated MHT-induced tumour growth inhibition.

Differential distribution of pigment-protein complexes in the Thylakoid membranes of Synechocystis 6803.

Thylakoids in Synechocystis 6803, though apparently uniform in appearance in ultrastructure, were found to consist of segments which were functionally dissimilar and had distinct proteomes. These thylakoid segments can be isolated from Synechocystis 6803 by successive ultracentrifugation of cell free extracts at 40,000×g (40 k segments), 90,000×g (90 k segments) and 150,000×g (150 k segments). Electron microscopy showed differences in their appearance. 40 k segments looked feathery and fluffy, whereas the 90 k and 150 k thylakoid membrane segments appeared tiny and less fluffy. The absorption spectra showed heterogeneous distribution of pigment-protein complexes in the three types of segments. The photochemical activities of Photosystem I (PSI) and Photosystem II (PSII) showed unequal distributions in 40 k, 90 k and 150 k segments which were substantiated with low temperature fluorescence measurements. The ratio of PSII/PSI fluorescence emission at 77 K (λ(ex) = 435 nm) was highest in 150 k segments indicating higher PSII per unit PSI in these segments. The chlorophyll fluorescence lifetimes in the membranes, determined with a time-correlated single-photon counting technique, could be resolved in three components: τ(1) (=) <40 ps, τ(2) (=) 425-900 ps and τ(3) (=) 2.4-3.2 ns. The percentage contribution of the fastest component (τ(1)) decreased in the order 40 k > 90 k > 150 k segments whereas that of the other two components showed a reversed trend. These studies indicated differential distribution of pigment-protein complexes in the three membrane segments suggesting heterogeneity in the thylakoids of Synechocystis 6803.

Lanthanide-ion-assisted structural collapse of layered GaOOH lattice.

GaOOH nanorods were prepared by hydrolysis of Ga(NO(3))(3)·xH(2)O by urea at ~100 °C in the presence of different amounts of lanthanide ions like Eu(3+), Tb(3+), and Dy(3+). On the basis of X-ray diffraction and vibrational studies, it is confirmed that layered structure of GaOOH collapses even when very small amounts of lanthanide ions (1 atom % and more) are present in the reaction medium during the synthesis of GaOOH nanorods. The incorporation of lanthanide ions at the interlayer spacing of the GaOOH lattice, followed by its reaction with OH groups that connect the layers containing edge-shared GaO(6) in GaOOH, is the reason for the collapse of the layered structure and associated amorphization. This leads to the formation of finely mixed hydroxides of lanthanide and gallium ions. These results are further confirmed by steady-state luminescence and excited-state lifetime measurements carried out on the samples. The morphology of the nanorods is maintained upon heat treatment at high temperatures like 500 and 900 °C, and during this process, the finely mixed lanthanide and gallium hydroxides facilitate diffusion of lanthanide ions into the Ga(2)O(3) lattice, as revealed by the existence of strong energy transfer with an efficiency of more than 90% between the host and lanthanide ions.

Investigations of Ce3+ co-doped SbPO4:Tb3+ nano-ribbons and nanoparticles by vibrational and photoluminescence spectroscopy.

Nano-ribbons and very small nanoparticles (size 2-5 nm) of SbPO4 doped with lanthanide ions (Ce3+ and Tb3+) are prepared at a relatively low temperature of 120 degrees C based on a solution method. Detailed vibrational and luminescence studies on these samples establish that these lanthanide ions are incorporated at Sb3+ site of the SbPO4 lattice. The excitation spectrum corresponding to the Tb3+ emission and the excited state lifetime of the 5D4 level of Tb3+ ions in the sample confirm the energy transfer from Ce3+ to Tb3+ ions in the SbPO4 host. The extent of energy transfer from Ce3+ to Tb3+ in these samples is found to be around 60%. Dispersion of these nanomaterials in silica matrix effectively shields the lanthanide ions at the surface of the nano-ribbons/nanoparticles from the stabilizing ligands resulting in the reduction in the vibronic quenching of the excited state. Our results show significant reduction in the surface contribution in the decay curve corresponding to the 5D4 level of the Tb3+ ions after incorporating the nano-ribbons/nanoparticles in silica. These nanomaterials incorporated in silica matrix can have potential applications in bio-assays and bio-imaging.

Luminescence studies on SbPO4:Ln3+ (Ln = Eu, Ce, Tb) nanoparticles and nanoribbons.

Nanoparticles and nanoribbons of SbPO4 and lanthanide ions (Eu3+, Ce3+ and Tb3+) doped SbPO4 were prepared at a low temperature of 120 degrees C by co-precipitation method in solvents like ethylene glycol and glycerol. By varying the relative ratios of the two solvents, average crystallite size of SbPO4 has been varied over a range of 12 to 46 nm. Based on steady state luminescence studies, existence of energy transfer between host SbPO4 and lanthanide ions has been confirmed. Co-doping SbPO4:Tb3+ nanoparticles/nanoribbons with Ce3+, resulted in improved luminescence due to energy transfer from Ce3+ to Tb3+ ions. Further, these nanomaterials can be incorporated in sol-gel derived silica glass without any deterioration of their luminescence properties. Present study offers a viable method for preparing composite luminescent materials based on nanoparticles/ nanoribbons and glasses.

Room temperature exciton formation in SnO2 nanocrystals in SiO2:Eu matrix: quantum dot system, heat-treatment effect.

SnO2 nanocrystals in SiO2:Eu matrix have been prepared at a relatively low temperature of 170 degrees C for 4 h. Selective transition probability of Eu3+ emission could be done after a suitable excitation wavelength. The room temperature exciton formation at 285 nm for as-prepared nanoparticles is observed and this gives the Bohr's radius of 1.4 nm. Exciton formation disappears for the nanoparticles heated at 500 and 900 degrees C. This is related to the increase in particle size with heat-treatment. A wide-band-gap (4.35 eV) quantum dots is obtained and will be important in photonics and UV-lasing application.

Eu3+ and Dy3+ doped YPO4 nanoparticles: low temperature synthesis and luminescence studies.

Eu3+ and Dy3+ doped YPO4 nanoparticles dispersible in methanol/water were prepared by the reaction of Y3+ and Eu3+/Dy3+ ions with ammonium dihydrogen phosphate in ethylene glycol medium at 160 degrees C. Nature and extent of strain associated with lattice has been found to change with incorporation of Eu3+/Dy3+ ion in the nanoparticles as well as the heat treatment temperature. Based on the TEM studies, it has been established that particles are highly crystalline with an average particle size of around 5 nm. Co-doping YPO4:Eu nanoparticles with Dy3+ ions followed by annealing them at high temperature (900 degrees C) lead to reduction in both Eu3+ and Dy3+ luminescence intensities from the sample and this has been attributed to the clustering effect of the lanthanide ions.

Radiolanthanide-loaded agglomerated Fe3O4 nanoparticles for possible use in the treatment of arthritis: formulation, characterization and evaluation in rats.

This investigation reports the preparation of agglomerated Fe3O4 nanoparticles and evaluation of its utility as a viable carrier in the preparation of radiolanthanides as potential therapeutic agents for the treatment of arthritis. The material was synthesized by a chemical route and characterized by XRD, FT-IR, SEM, EDX and TEM analysis. The surface of agglomerated particle possessed ion pairs (-O-:Na+) after dispersing particles in a NaHCO3 solution at pH = 7 which is conducive for radiolanthanide (*Ln = 90Y, 153Sm, 166Ho, 169Er, 177Lu) loading by replacement of Na+ ions with tripositive radiolanthanide ions. Radiolanthanide-loaded particulates exhibited excellent in vitro stability up to ∼3 half-lives of the respective lanthanide radionuclides when stored in normal saline at 37 °C. The radiochemical purities of the loaded particulates were found to be retained to the extent of >70% after 48 h of storage when challenged by a strong chelator DTPA present at a concentration as high as 5 mM, indicating fairly strong chemical association of lanthanides with agglomerated Fe3O4 nanoparticles. Biodistribution studies of 90Y and 166Ho-loaded particulates carried out after intra-articular injection into one of the knee joints of a normal Wistar rat revealed near-complete retention of the radioactive preparations (>98% of the administered radioactivity) within the joint cavity even after 72 h post injection. This was further confirmed by sequential whole-body radio-luminescence imaging. These experimental results are indicative of the potential use of radiolanthanide-loaded agglomerated Fe3O4 nanoparticles for the treatment of arthritis.

Enhanced specific absorption rate in silanol functionalized Fe3O4 core-shell nanoparticles: study of Fe leaching in Fe3O4 and hyperthermia in L929 and HeLa cells.

Core-shell Fe3O4-SiO2 magnetic nanoparticles (MNPs) have been synthesized using a simple synthesis procedure at different temperatures. These MNPs are used to investigate the effect of surface coating on specific absorption rate (SAR) under alternating magnetic field. The temperature achieved by silica coated Fe3O4 is higher than that by uncoated MNPs (Fe3O4). This can be attributed to extent of increase in Brownian motion for silica coated MNPs. The sample prepared at optimized temperature of 80°C shows the highest SAR value of 111W/g. It is found that SAR value decreases with increase in shell thickness. The chemical stability of these samples is analyzed by leaching experiments at pH 2-7. The silica coated samples are stable up to 7 days even at pH 2. Biocompatibility of the MNPs is evaluated in vitro by assessing their cytotoxicity on L929 and human cervical cancer cells (HeLa cells) using sulforhodamine-B assay. Their hyperthermic killing ability is also evaluated in HeLa cells using the same method. Cells treated with MNPs along with induction heating show decrease in viability as compared to that without induction heating. Further, cell death is found to be ∼55% more in cells treated with silica coated MNPs under induction heating as compared to untreated control. These results establish the efficacy of Fe3O4-SiO2 prepared at 80°C in killing of tumor cells by cellular hyperthermia.

BiPO4: a better host for doping lanthanide ions.

In the present manuscript it is demonstrated that BiPO(4) is a better alternative to lanthanide phosphate host for making lanthanide ion-based luminescent materials. Hexagonal and monoclinic forms of BiPO(4) phase were prepared based on the reaction of Bi(3+) and PO(4)(3-) ions in ethylene glycol medium at 100 and 185 °C, respectively. From the differential thermal analysis (DTA) studies it is confirmed that the difference in the nucleation mechanism rather than the phase transition is responsible for the monoclinic phase formation at low temperatures (125 °C). Monoclinic BiPO(4) is quite stable and forms random solid solutions with lanthanide phosphates having both monoclinic (monazite) and tetragonal (xenotime) structures, as confirmed by XRD, FTIR and (31)P solid state nuclear magnetic resonance studies. On excitation corresponding to the (1)S(0)→(3)P(1) transition of Bi(3+) in BiPO(4):Ln samples, energy transfer from host to lanthanide ions takes place. The studies are quite relevant as there is a growing interest all over the world in replacing lanthanide based host used for different applications with easily available, easily purifiable and cheap main group elements (like Sb, Bi etc.) based hosts.

Luminescence properties of Eu3+ doped CaMoO4 nanoparticles.

When Eu(3+) ions occupy Ca(2+) sites of CaMoO(4), which has a body centered tetragonal structure with inversion symmetry, only the magnetic dipole transition ((5)D(0)→(7)F(1)) should be allowed according to Judd-Ofelt theory. Even if there are a few distortions in the Eu(3+) environment, its intensity should be more than that of the electric dipole transition ((5)D(0)→(7)F(2)). We report here the opposite effect experimentally and ascribe this to the polarizability effect of the MoO(4) tetrahedron, which is neighboring to EuO(8) (symmetric environment). The contribution of the energy transfer process from the Mo-O charge transfer band to Eu(3+) and the role of Eu(3+) over the surface of the particle could be distinguished when luminescence decay processes were measured at two different excitations (250 and 398 nm). Further, the luminescence intensities and lifetimes increase significantly with increasing heat-treatment temperature of the doped samples. This is attributed to the reduction of H(2)O from the surface of the particles and a non-radiative process after heat treatment.

Nucleation sequence on the cation exchange process between Y0.95Eu0.05PO4 and CePO4 nanorods.

Nanorods of Y0.95Eu0.05PO4@CePO4 (Y0.95Eu0.05PO4 phase was nucleated first and then a CePO4 phase was nucleated) and CePO4@Y0.95Eu0.05PO4 (CePO4 phase was nucleated first and then Y0.95Eu0.05PO4 phase was nucleated) were prepared at a relatively low temperature of 140 °C in ethylene glycol medium. Based on XRD, TEM and Raman studies it has been inferred that Y0.95Eu0.05PO4@CePO4 sample consists of a mixture of bigger (length around 800-1000 nm and width around of 80-100 nm) and smaller (length around 70-100 nm and width around 10-20 nm) nanorods, having monoclinic CePO4 and tetragonal YPO4 structure, whereas CePO4@Y0.95Eu0.05PO4 sample consists of mainly small nanorods having a single phase CePO4 structure. From the detailed luminescence studies it has been established that there exists significant incorporation of Y3+/Eu3+ ions in the CePO4 phase in CePO4@Y0.95Eu0.5PO4 sample. This has been attributed to the cation exchange taking place between Ce3+ ions in CePO4 host and Eu3+ and Y3+ ions in solution during the synthesis stage. Unlike this, such an exchange is not possible for Y0.95Eu0.05PO4@CePO4 sample synthesized under identical conditions due to the higher solubility product (Ksp) value of YPO4 compared to CePO4. Incorporation of Eu3+ in the CePO4 lattice of CePO4@Y0.95Eu0.5PO4 sample is confirmed by the significant reduction in the lifetime of 5D0 level of Eu3+ and the luminescence intensity from Eu3+, arising due to the electron transfer between the Ce3+/Ce4+ and Eu3+/Eu2+ species. These results are further supported by the non-radiative decay rates and quantum yields calculated from the emission spectrum.