Ferromagnetic resonance studies in some polycrystalline magnesium nickel ferrites

Ferromagnetic resonance measurements were carried out on various compositions of magnesium nickel ferrites prepared by various heat treatments. Corrections were applied for polycrystalline and size effects for calculating the g factor and linewidth. The variation of these parameters has been explained on the basis of the cation distribution in these compounds as obtained from magnetization data assuming a collinear model of spin distribution.     

Integrality gap of the hypergraphic relaxation of Steiner trees: A short proof of a 1.55 upper bound

Recently, Byrka, Grandoni, Rothvoß and Sanità gave a 1.39 approximation for the Steiner tree problem, using a hypergraph-based linear programming relaxation. They also upper-bounded its integrality gap by 1.55. We describe a shorter proof of the same integrality gap bound, by applying some of their techniques to a randomized loss-contracting algorithm.     

Structural Investigation of the Hormone Melatonin and Its Alkali and Alkaline Earth Metal Complexes in the Gas Phase

Gas phase infrared dissociation spectra of the radical cation, deprotonated and protonated forms of the hormone melatonin, and its complexes with alkali (Li⁺, Na⁺, and K⁺) and alkaline earth metal ions (Mg²⁺, Ca²⁺, and Sr²⁺) are measured in the spectral range 800–1800 cm^?1. Minimum energy geometries calculated at the B3LYP/LACVP++** level are used to assign structural motifs to absorption bands in the experimental spectra. The melatonin anion is deprotonated at the indole-N. The indole-C linking the amide chain is the most favored protonation site. Comparisons between the experimental and calculated spectra for alkali and alkaline earth metal ion complexes reveal that the metal ions interact similarly with the amide and methoxy oxygen atoms. The amide I band undergoes a red shift with increasing charge density of the metal ion and the amide II band shows a concomitant blue shift. Another binding motif in which the metal ions interact with the amide-O and the π-electron cloud of the aromatic group is identified but is higher in energy by at least 18 kJ/mol. Melatonin is deprotonated at the amide-N with Mg²⁺ and the metal ion coordinates to the amide-N and an indole-C or the methoxy-O. These results provide information about the intrinsic binding of metal ions to melatonin and combined with future studies on solvated melatonin-metal ion complexes may help elucidate the solvent effects on metal ion binding in solution and the biochemistry of melatonin. These results also serve as benchmarks for future theoretical studies on melatonin-metal ion interactions.

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An expedient, regioselective synthesis of novel 2-alkylamino- and 2-alkylthiothiazolo[5,4-e]- and -[4,5-g]indazoles and their anticancer potential

Several novel 2-alkylamino- and 2-alkylthiothiazolo[5,4-e]- and -[4,5-g]indazoles and their 6-alkyl and 8-alkyl derivatives have been synthesised in high overall yields starting from 5-nitro and 6-nitroindazoles in a three-step route involving the regioselective cyclisation of thioureidoindazoles and indazolyl dithiocarbamates as the key steps. Some assorted thiazoloindazoles have been screened for anticancer properties, which demonstrated the anticancer potential of at least one product, justifying its further follow-up.     

Crystal structure of manganese-rich variety of eudialyte from Suchina Hill,India, and manganese ordering in eudialyte-group minerals

The crystal structure of eudialyte of hydrothermal genesis from Sushina Hill, India, where it was found associated with potassium feldspathoid, albite, aegirine, and nepheline, has been solved by X-ray diffraction analysis. One specific feature of the chemical composition of this mineral is a low content of CaO (7–8.5 wt %) and an elevated manganese content (9–10.5 wt % MnO). When compared with eudialytes of magmatic genesis, this eudialyte is enriched in Nb, Sr, Y, and rare earth elements (REEs). It is described within the sp. gr. R3m, with the unit-cell parameters a = 14.2483(3) Å and b = 30.294(1) Å; R = 4.7%. The idealized formula (Z = 3) is (Na,□,Sr)₁₅(Ca,Mn)₆Mn₃(Si,Nb)₂Zr₃[Si₂₄O₇₂](OH,Cl,H₂O)_5.5. It is established that Mn atoms occupy three sites: two subsites in five-vertex polyhedra M2a and M2b, spaced by a distance of 0.87 Å and characterized by occupancies of 0.51 and 0.49, respectively, and the M1 site in the octahedron of six-membered ring, jointly with Ca and REE. With allowance for the established features of chemical composition and structure, the mineral under study can be considered as a strontium-rich variety of kentbrooksite.     

Influence of steric factors on exciplex energy and magnetic field effect

With the advent of spin chemistry, magnetic field effect (MFE) on exciplex luminescence has emerged as an important domain of research. MFE is a diffusion controlled phenomenon and hence is solvent dielectric (epsilon) dependent. It maximizes at a particular epsilon (epsilon(max)) for a specific exciplex system. Various attempts have been made to explain the variation of this epsilon(max) from one exciplex to another. In our present work we have succeeded for the first time to enmark the energy of exciplex (E(ex)) as the prime factor in determining the epsilon(max). We have indicated a definite inverse correlation (1:1) between epsilon(max) and E(ex). We have also tried to correlate some parameters that are important in exciplex formation, e.g. Charton's steric constant (nu(c)), repulsive energy (R(e)) and E(ex).     

Synthesis of lariat ether carboxylic acids based on dibenzo‐16‐crown‐5

Synthetic routes to forty‐seven dibenzo‐16‐crown‐5 compounds with pendant carboxylic acid groups are reported. When taken together with previously described lariat ether carboxylic acids, these new compounds provide several series with systematic structural variations including changes in the identity and attachment site(s) of one or more lipophilic groups and the length of the spacer that connects the carboxylic acid group to the polyether framework.     

Detecting hidden spatial and spatio-temporal structures in glasses and complex physical systems by multiresolution network clustering

We elaborate on a general method that we recently introduced for characterizing the “natural” structures in complex physical systems via multi-scale network analysis. The method is based on “community detection” wherein interacting particles are partitioned into an “ideal gas” of optimally decoupled groups of particles. Specifically, we construct a set of network representations (“replicas”) of the physical system based on interatomic potentials and apply a multiscale clustering (“multiresolution community detection”) analysis using information-based correlations among the replicas. Replicas may i) be different representations of an identical static system, ii) embody dynamics by considering replicas to be time separated snapshots of the system (with a tunable time separation), or iii) encode general correlations when different replicas correspond to different representations of the entire history of the system as it evolves in space-time. Inputs for our method are the inter-particle potentials or experimentally measured two (or higher order) particle correlations. We apply our method to computer simulations of a binary Kob-Andersen Lennard-Jones system in a mixture ratio of A₈₀B₂₀ , a ternary model system with components “A”, “B”, and “C” in ratios of A₈₈B₇C₅ (as in Al₈₈Y₇Fe₅ , and to atomic coordinates in a Zr₈₀Pt₂₀ system as gleaned by reverse Monte Carlo analysis of experimentally determined structure factors. We identify the dominant structures (disjoint or overlapping) and general length scales by analyzing extrema of the information theory measures. We speculate on possible links between i) physical transitions or crossovers and ii) changes in structures found by this method as well as phase transitions associated with the computational complexity of the community detection problem. We also briefly consider continuum approaches and discuss rigidity and the shear penetration depth in amorphous systems; this latter length scale increases as the system becomes progressively rigid.