Ramaswami Sammynaiken

Crystal field, phonon coupling and emission shift of Mn2+ in ZnS:Mn nanoparticles

The Mn2+ emission wavelengths are at 591, 588, 581 and 570 nm, respectively, for the ∼10, ∼4.5, ∼3.5 nm sized nanoparticles and the ZnS:Mn nanoparticles formed in an ultrastable zeolite-Y. To reveal the cause for the shift, the crystal field and phonon coupling were investigated. The results show that the predominant factor for the shift is the phonon coupling, whose strength is size dependent and is determined by both the size confinement and the surface modification of the nanoparticles. Although the crystal field strength decreases with the decreasing of the particle size, its change has little contribution to the emission shift of Mn2+ in ZnS:Mn nanoparticles.

Photoluminescence and photostimulated luminescence of Tb3+ and Eu3+ in zeolite-Y

Tb3+ and Eu3+ were codoped in zeolite-Y. Their photoluminescence and photostimulated luminescence were investigated. Due to the dissipation of excitation energy by OH vibrations, the luminescence from the hydrated zeolite containing Tb3+ and Eu3+ prepared at room temperature is very weak. However, the luminescence is enhanced greatly when the sample was treated at 800 °C. Strong photostimulated luminescence of both Tb3+ and Eu3+ was detected in the sample prepared at 800 °C. The photostimulated luminescence of Tb3+ is due to the recombination of electrons with Tb4+ ions, while the photostimulated luminescence of Eu3+ is caused by energy transfer from Tb3+ to Eu3+. The existence of Tb4+ and Eu2+ ions is due to charge transfer from Eu3+ to Tb3+. The occurrence of photostimulated luminescence and discrete emission lines in blue (434 nm), green (543 nm), and red (611 nm) colors indicate that this material has potential applications in white light-emitting devices and erasable optical storage.

Targeted alterations in iron homeostasis underlie plant defense responses.

Iron (Fe) is a ubiquitous redox-active element essential for most life. The formation of localized cell wall appositions, the oxidative burst and the production of pathogenesis-related proteins are hallmarks of plant defense responses. Here, we report that iron is a central mediator linking these three phenomena. We show that in response to pathogen attack, reactive Fe3+, but not Fe2+, is deposited at cell wall appositions where it accumulates and mediates the oxidative burst. We provide evidence that the bulk secretion of Fe3+ provoked by pathogen attack leads to intracellular iron depletion, and that H2O2 itself induces ATP-dependent intracellular iron efflux. Finally, we demonstrate that this intracellular iron depletion promotes the transcription of pathogenesis-related genes in concert with H2O2. This work identifies iron as an underlying factor associated with the oxidative burst and regulating cereal defenses, and establishes links between disease-related iron homeostasis in plants and animals.

Luminescence enhancement of ZnS:Mn nanoclusters in zeolite

The luminescence intensity of Mn2+ in the ZnS:Mn nanoclusters formed in an ultrastable zeolite-Y is seven orders of magnitude stronger than that of other nanoparticles deposited out of solutions. This remarkable effect is attributed to a strong quantum size confinement, the location of Mn2+ ions at the near-surface sites, and good surface passivation. The lowering of the energy loss in the 4E(4D), or/and 4T2(4D) states during the energy transfer from the ZnS host to the emitting state 4T1(4G) of Mn2+ may also contribute to the observed fluorescence enhancement.

Barley Grain Constituents, Starch Composition, and Structure Affect Starch in Vitro Enzymatic Hydrolysis

The relationship between starch physical properties and enzymatic hydrolysis was determined using ten different hulless barley genotypes with variable carbohydrate composition. The ten barley genotypes included one normal starch (CDC McGwire), three increased amylose starches (SH99250, SH99073, and SB94893), and six waxy starches (CDC Alamo, CDC Fibar, CDC Candle, Waxy Betzes, CDC Rattan, and SB94912). Total starch concentration positively influenced thousand grain weight (TGW) (r(2) = 0.70, p < 0.05). Increase in grain protein concentration was not only related to total starch concentration (r(2) = -0.80, p < 0.01) but also affected enzymatic hydrolysis of pure starch (r(2) = -0.67, p < 0.01). However, an increase in amylopectin unit chain length between DP 12-18 (F-II) was detrimental to starch concentration (r(2) = 0.46, p < 0.01). Amylose concentration influenced granule size distribution with increased amylose genotypes showing highly reduced volume percentage of very small C-granules (<5 μm diameter) and significantly increased (r(2) = 0.83, p < 0.01) medium sized B granules (5-15 μm diameter). Amylose affected smaller (F-I) and larger (F-III) amylopectin chains in opposite ways. Increased amylose concentration positively influenced the F-III (DP 19-36) fraction of longer DP amylopectin chains (DP 19-36) which was associated with resistant starch (RS) in meal and pure starch samples. The rate of starch hydrolysis was high in pure starch samples as compared to meal samples. Enzymatic hydrolysis rate both in meal and pure starch samples followed the order waxy > normal > increased amylose. Rapidly digestible starch (RDS) increased with a decrease in amylose concentration. Atomic force microscopy (AFM) analysis revealed a higher polydispersity index of amylose in CDC McGwire and increased amylose genotypes which could contribute to their reduced enzymatic hydrolysis, compared to waxy starch genotypes. Increased β-glucan and dietary fiber concentration also reduced the enzymatic hydrolysis of meal samples. An average linkage cluster analysis dendrogram revealed that variation in amylose concentration significantly (p < 0.01) influenced resistant starch concentration in meal and pure starch samples. RS is also associated with B-type granules (5-15 μm) and the amylopectin F-III (19-36 DP) fraction. In conclusion, the results suggest that barley genotype SH99250 with less decrease in grain weight in comparison to that of other increased amylose genotypes (SH99073 and SH94893) could be a promising genotype to develop cultivars with increased amylose grain starch without compromising grain weight and yield.

Electronic structure of TiO2 nanotube arrays from X-ray absorption near edge structure studies

We report an X-ray absorption near edge structure (XANES) investigation of several TiO2nanotube arrays, including the as-prepared nanotube arrays from electrochemical anodic oxidation of Ti foil (as-prepared ATNTA), as-prepared nanotube arrays after annealing at 580 °C (annealed ATNTA) and annealed ATNTA after electrochemical intercalation with Li (Li-intercalated ATNTA). XANES at the O K-edge and Ti L3,2 and K edges shows distinctly different spectral features for the as-prepared and the annealed ATNTA, characteristic of amorphous and anatase structures, respectively. Intercalation of Li into annealed ATNTA induces a surprising, yet spectroscopically unmistakable, anatase to rutile transition. XANES at the Li K-edge clearly shows ionic features of Li in ATNTA. The charge relocation from Ti 3d to O 2p at the conduction band in TiO2 was also observed when Li ions were intercalated into annealed ATNTA albeit no noticeable reduction of Ti4+ to Ti 3+ was observed. The O K-edge shows a distinctly enhanced feature in the multiple scattering regime, indicating a close to linear O–Li–O arrangement in Li-intercalated ATNTA. These results show bonding changes between Ti and O resulting from the interaction of Li ions in the TiO2 lattices. Such bonding variation has also been supported by X-ray excited optical luminescence (XEOL), which suggests Li+-defect interactions. The implications of these results are discussed.

Nano-scale chemical imaging of a single sheet of reduced graphene oxide

Scanning transmission X-ray microscopy (STXM) has been used to chemically image single and multiple layers of a thermally reduced graphene oxide (r-GO) multi-layer sheet of the size of ∼1 μm and a thickness of ∼5 nm. The thickness of individual layers in the single sheet can be identified through quantitative analysis of STXM. The local electronic and chemical structure of interest (edge versus center) in different regions within the single r-GO sheet has been studied by C K-edge X-ray absorption near edge structure spectroscopy (XANES) with 30 nm spatial resolution. High and localized unoccupied densities of states (DOS) of carbon σ* character were observed in r-GO compared to graphite and were interpreted as the lack of strong layer to layer interaction in the former. The azimuthal dependence of C K-edge XANES in selected locations has also been obtained and was used to infer the preferred edge structure. The r-GO sample was also characterized by TEM, AFM and Raman spectroscopy; the findings are in good accord with the STXM results.

Ultrathin W-Al dual interlayer approach to depositing smooth and adherent nanocrystalline diamond films on stainless steel.

The adherence of diamond coated on steel is commonly low and needs to be strengthened with thick intermediate layers. In this paper, a nanoscale W-Al dual metal interlayer has been applied on SS304 substrates to facilitate deposition of continuous, adherent and smooth diamond thin films. During the microwave plasma-enhanced chemical vapor deposition process, the Al inner layer 30 nm thick diffuses into steel surface inhibiting carbon diffusion and graphitization. The W outer layer 20 nm thick is transformed into W carbides, both preventing carbon diffusion and enhancing diamond nucleation. The diamond films synthesized are of high purity and have smooth surfaces and dense structures. Indentation and shear deformation tests indicate high delaminating tolerance of the diamond films.

The Origin and Dynamics of Soft X-Ray-Excited Optical Luminescence of ZnO

The distinct optical emission from ZnO materials, nanoneedles and microcrystallites synthesized with different sizes and morphologies by a flow deposition technique, is investigated with X-ray excited optical luminescence (XEOL) and time-resolved X-ray excited optical luminescence (TR-XEOL) from a synchrotron light source at the O K and Zn L(3,2) edges. The innovative use of XEOL, allowing site-specific chemical information and luminescence information at the same time, is fundamental to provide direct evidence for the different behaviour and the crucial role of bulk and surface defects in the origin of ZnO optical emission, including dynamics. XEOL from highly crystalline ZnO nanoneedles is characterized by a sharp band-gap emission (~380 nm) and a broad red luminescence (~680 nm) related to surface defects. Luminescence from ZnO microcrystallites is mostly dominated by green emission (~510 nm) associated with defects in the core. TR-XEOL experiments show considerably faster decay dynamics in nanoneedles compared to microcrystallites for both band-gap emission and visible luminescence. Herein we make a fundamental step forward correlating for the first time the interplay of size, crystallinity, morphology and excitation energy with luminescence from ZnO materials.

Non-functionalized carbon nanotube binding with hemoglobin

Carbon nanotube has a high potential to be used as a biosensor and drug carrier. However, its binding behavior with proteins needs to be studied before the full potential of carbon nanotube in biological studies can be realized. Although many studies have been conducted to characterize the affinity of functionalized carbon nanotube to various types of proteins, our present study for the first time reported that hemoglobin can bind with non-functionalized carbon nanotube, and this binding can be identified by Raman spectrum. Further, this binding has not changed Raman luminescence with specific excitation and emission wavelengths. The immediate application of these findings is to use non-functionalized carbon nanotube as a biosensor to measure H(2)S in blood in which hemoglobin takes about 37% of the total blood volume. Other potential uses of non-functionalized carbon nanotube to bind selective groups of proteins are also hinted.