Probing complex heterostructures using hard X-ray photoelectron spectroscopy (HAXPES)

X-ray Photoelectron Spectroscopy (XPS) plays a central role in the investigation of electronic properties as well as compositional analysis of almost every conceivable material. However, a very short inelastic mean free path (IMFP) and the limited photon flux in standard laboratory conditions render this technique very much surface sensitive. Thus, the electronic structure buried below several layers of a heterogeneous sample is not accessible with usual photoemission techniques. An obvious way to overcome this limitation is to use a considerably higher energy photon source, as this increases the IMFP of the photo-ejected electron, thereby making the technique more depth and bulk sensitive. Due to this obvious advantage, Hard X-ray Photo Electron Spectroscopy (HAXPES) is rapidly becoming an extremely powerful tool for chemical, elemental, compositional and electronic characterization of bulk systems, more so with reference to systems characterized by the presence of buried interfaces and other types of chemical heterogeneity. The relevance of such an investigative tool becomes evident when we specifically note the ever-increasing importance of heterostructures and interfaces in the context of a wide range of device applications, spanning electronic, magnetic, optical and energy applications. The interest in this nondestructive, element specific HAXPES technique has grown rapidly in the past few years; we discuss critically its extensive use in the study of depth resolved electronic properties of nanocrystals, multilayer superlattices and buried interfaces, revealing their internal structures. We specifically present a comparative discussion, with examples, on two most commonly used methods to determine internal structures of heterostructured systems using XPS. (C) 2015 Elsevier B.V. All rights reserved.

Estimation of Power Input to Complex Dielectric Barrier Discharge Reactor Geometries used in NOx Cleaning

Studies were carried out to estimate the power input to Dielectric Barrier Discharge (DBD) reactors powered by AC high voltage in the context of their application in non-thermal plasma cleaning of exhaust gases. Power input to the reactors was determined both theoretically and experimentally. Four different reactor geometries energized with 50 Hz and 1.5 kHz AC excitation were considered for the study. The theoretically estimated power using Manley's equation was found to agree with the experimental results. Results show that the analytically computed capacitance, without including the electrode edge effects, gives sufficiently good results that are matching with the measured values. For complex geometries where analytical calculation of capacitance is often difficult, a novel method of estimating the reactor capacitance, and hence the power input to the reactor, was introduced in this paper. The predicted results were validated with experiments.

Visible light-induced cytotoxicity of a dinuclear iron(III) complex of curcumin with low-micromolar IC50 value in cancer cells

Photoactive metal complexes have emerged as potential candidates in the photodynamic therapy (PDT) of cancer. We present here the synthesis, characterization and visible light-triggered anticancer activity of two novel mixed-ligand oxo-bridged iron(III) complexes, viz., {Fe(L)(acac)}(2)(mu-O)](ClO4)(2) (1) and {Fe (L)(cur)}(2)(mu-O)](ClO4)(2) (2) where L is bis-(2-pyridylmethyl)-benzylamine, acac is acetylacetonate and cur is the monoanion of curcumin (bis(4-hydroxy-3-methoxyphenyl)-1,6-diene-3,5-dione). The crystal structure of complex 1 (as PF6 salt, 1a) shows distorted octahedral geometry of each iron(III) centre formed by the FeN3O3 core. The 1: 2 electrolytic complexes are stable in solution and retain their oxo-bridged identity in aqueous medium. Complex 2 has a strong absorption band in the visible region and shows promising photocytotoxicity in HeLa and MCF-7 cancer cells in visible light giving respective IC50 values of 3.1 +/- 0.4 lM and 4.9 +/- 0.5 lM while remains non-toxic in the dark (IC50 > 50 lM). The control complex 1 is inactive both in the light and dark. Complex 2 accumulates in cytoplasm of HeLa and MCF-7 cells as evidenced from fluorescence microscopy and triggers apoptotic cell death via light-assisted generation of reactive oxygen species (ROS). Taken together, complex 2 with its promising photocytotoxicity but negligible dark toxicity in cancer cells has significant photochemotherapeutic potential for applications in PDT. (C) 2015 Elsevier B.V. All rights reserved.

The SPL7013 dendrimer destabilizes the HIV-1 gp120-CD4 complex

The poly (l-lysine)-based SPL7013 dendrimer with naphthalene disulphonate surface groups blocks the entry of HIV-1 into target cells and is in clinical trials for development as a topical microbicide. Its mechanism of action against R5 HIV-1, the HIV-1 variant implicated in transmission across individuals, remains poorly understood. Using docking and fully atomistic MD simulations, we find that SPL7013 binds tightly to R5 gp120 in the gp120-CD4 complex but weakly to gp120 alone. Further, the binding, although to multiple regions of gp120, does not occlude the CD4 binding site on gp120, suggesting that SPL7013 does not prevent the binding of R5 gp120 to CD4. Using MD simulations to compute binding energies of several docked structures, we find that SPL7013 binding to gp120 significantly weakens the gp120-CD4 complex. Finally, we use steered molecular dynamics (SMD) to study the kinetics of the dissociation of the gp120-CD4 complex in the absence of the dendrimer and with the dendrimer bound in each of the several stable configurations to gp120. We find that SPL7013 significantly lowers the force required to rupture the gp120-CD4 complex and accelerates its dissociation. Taken together, our findings suggest that SPL7013 compromises the stability of the R5 gp120-CD4 complex, potentially preventing the accrual of the requisite number of gp120-CD4 complexes across the virus-cell interface, thereby blocking virus entry.

Quick measurement of H-1-F-19 scalar couplings from the complex NMR spectra by real-time spin edition

Most often the measurement of VHF from the conventional 1D H-1 NMR spectrum is severely hindered consequent to similar magnitudes of JHF and JHH couplings and the spectral multiplicity pattern. The present study reports a new 1D NMR technique based on real time spin edition, which removes all JHF and JHH while retaining only VHF of a chosen fluorine. The obtained spectrum is significantly simplified and permits straightforward determination of all possible VHF values of a chosen fluorine. Due to one dimensional nature, the method is much faster compared to 2D GET-SERF by 1-2 orders of magnitude. (C) 2015 Elsevier B.V. All rights reserved.

The cis-Diammineplatinum(II) Complex of Curcumin: A Dual Action DNA Crosslinking and Photochemotherapeutic Agent

Pt(cur)(NH3)(2)](NO3) (1), a curcumin-bound cis-diammineplatinum(II) complex, nicknamed Platicur, as a novel photoactivated chemotherapeutic agent releases photoactive curcumin and an active platinum(II) species upon irradiation with visible light. The hydrolytic instability of free curcumin reduces upon binding to platinum(II). Interactions of 1 with 5'-GMP and ct-DNA indicated formation of platinum-bound DNA adducts upon exposure to visible light (lambda = 400-700 nm). It showed apoptotic photocytotoxicity in cancer cells (IC50 approximate to 15 mu M), thus forming (OH)-O-center dot, while remaining passive in the darkness (IC50 > 200 mu M). A comet assay and platinum estimation suggest Pt-DNA crosslink formation. The fluorescence microscopic images showed cytosolic localization of curcumin, thus implying possibility of dual action as a chemo-and phototherapeutic agent.

Complex patterns arise through spontaneous symmetry breaking in dense homogeneous networks of neural oscillators

There has been much interest in understanding collective dynamics in networks of brain regions due to their role in behavior and cognitive function. Here we show that a simple, homogeneous system of densely connected oscillators, representing the aggregate activity of local brain regions, can exhibit a rich variety of dynamical patterns emerging via spontaneous breaking of permutation or translational symmetries. Upon removing just a few connections, we observe a striking departure from the mean-field limit in terms of the collective dynamics, which implies that the sparsity of these networks may have very important consequences. Our results suggest that the origins of some of the complicated activity patterns seen in the brain may be understood even with simple connection topologies.

COMPLEX GEODESICS, THEIR BOUNDARY REGULARITY, AND A HARDY-LITTLEWOOD-TYPE LEMMA

We begin by giving an example of a smoothly bounded convex domain that has complex geodesics that do not extend continuously up to partial derivative D. This example suggests that continuity at the boundary of the complex geodesics of a convex domain Omega (sic) C-n, n >= 2, is affected by the extent to which partial derivative Omega curves or bends at each boundary point. We provide a sufficient condition to this effect (on C-1-smoothly bounded convex domains), which admits domains having boundary points at which the boundary is infinitely flat. Along the way, we establish a Hardy-Littlewood-type lemma that might be of independent interest.

Trans-dichlorooxovandium (IV) complex as a novel photoinducible DNA interstrand crosslinker for cancer therapy

Although DNA interstrand crosslinking (ICL) agents such as mitomycin C, cisplatin and psoralen serve as potent anticancer drugs, these agents are known to have dose-limiting toxic effects on normal cells. Moreover, tumor resistance to these agents has been reported. Here, we show that trans-dichlorooxovanadium (IV) complex of pyrenyl terpyridine (VDC) is a novel photoinducible DNA crosslinking agent. By a combination of in vitro and ex vivo experiments including plasmid-based assays, we find that VDC forms monoadducts on the DNA and can be activated by UV-A and visible light to generate DNA interstrand crosslinks. VDC efficiently activates Fanconi anemia (FA) pathway of DNA interstrand crosslink repair. Strikingly, photoinduction of VDC induces prolonged activation of cell cycle checkpoint and a high degree of cell death in homologous recombination (HR)/ICL repair defective cells. Moreover, VDC specifically targets cells that express pathological RAD51C mutants. These data imply that VDC can be potentially used for cancer therapy and suggest that tumors arising in patients with gene mutations in FA and HR repair pathway can be specifically targeted by a photoactivatable VDC.

Mitochondrial selectivity and remarkable photocytotoxicity of a ferrocenyl neodymium(III) complex of terpyridine and curcumin in cancer cells

A series of four novel neodymium(III) complexes of the formulation Nd(R-tpy)(O-O)(NO3)(2)] (1-4), where R-tpy is 4'-phenyl-2,2': 6', 2''-terpyridine (Ph-tpy; 1, 2) and 4'-ferrocenyl-2,2': 6', 2''-terpyridine (Fc-tpy; 3, 4); O-O is the conjugate base of acetylacetone (Hacac; 1, 3) or curcumin (Hcurc; 2, 4), are synthesized and characterized. The single crystal structure of 1 shows that the complex is a discrete mononuclear species with the Nd(III) centre in a nine coordinate environment provided by a set of O6N3 donor atoms. Complexes 1 and 3 having the simple acac ligand are prepared as control compounds. Complex 4, possessing an appended ferrocenyl (Fc) and the curcumin moiety, is remarkably photocytotoxic to HeLa and MCF-7 cancer cells in visible light giving respective IC50 values of 0.7 mu M and 2.1 mu M while being significantly less toxic to MCF-10A normal cells (IC50 = 34 mu M) and in the dark (IC50 > 50 mu M). The phenyl appended complex 2, lacking a ferrocenyl moiety, is significantly less toxic to both the cell lines when compared with 4. Complexes 1 and 3, lacking the photoactive curcumin moiety, do not show any apparent toxicity both in light and in the dark. The cell death is apoptotic in nature and is mediated by the light-induced formation of reactive oxygen species (ROS). Fluorescence imaging experiment with HeLa cells reveals mitochondrial accumulation of complex 4 within 4 h of incubation. The complexes bind to calf thymus (ct) DNA with moderate affinity giving K-b values in the range of 10(4)-10(5) M-1. The curcumin complexes 2 and 4 cleave plasmid supercoiled DNA to its nicked circular form in visible light via O-1(2) and (OH)-O-center dot pathways. The presence of the ferrocenyl moiety is likely to be responsible for the enhanced cellular uptake and photocytotoxicity of complex 4. Thus, the mitochondria targeting complex 4, being remarkably cytotoxic in light but non-toxic in the dark and to normal cells, is a potential candidate for photochemotherapeutic applications.