563 research outputs found
Optical and magnetic resonance studies of the interaction of metallo tetraphenylporphyrins with nitrobenzofuroxan
Metallo tetraphenylporphyrins form 1:1 molecular complexes with 4,6-dinitrobenzofuroxan. The molecular association is described in terms of π-π interaction with porphyrins functioning as donors. The association constants and thermodynamic parameters have been evaluated using optical absorption and 1H nmr spectral methods. Based on the binding constants, the donor ability of various metalloporphyrins can be arranged in the following order: Pd(II) > Co(II) > Cu(II) > Ni(II) ˜ VO(IV) ˜ 2H > Zn(II). Electron paramagnetic resonance studies of the complexes reveal that the π-complexation results in changes in the electronic structure of the central metal ions which are reflected in the changes in the M-N σ bonding. The dipolar contribution to the acceptor proton chemical shifts in the CoTPP complex has been partitioned from ring current contributions using the shifts observed in the ZnTPP complex. The shifts, along with the line broadening ratios observed for the CoTPP complex, are used to arrive at the possible solution structures of the complexes
Decoherence on a two-dimensional quantum walk using four- and two-state particle
We study the decoherence effects originating from state flipping and
depolarization for two-dimensional discrete-time quantum walks using four-state
and two-state particles. By quantifying the quantum correlations between the
particle and position degree of freedom and between the two spatial ()
degrees of freedom using measurement induced disturbance (MID), we show that
the two schemes using a two-state particle are more robust against decoherence
than the Grover walk, which uses a four-state particle. We also show that the
symmetries which hold for two-state quantum walks breakdown for the Grover
walk, adding to the various other advantages of using two-state particles over
four-state particles.Comment: 12 pages, 16 figures, In Press, J. Phys. A: Math. Theor. (2013
Inverted porphyrins and expanded porphyrins: an overview
Porphyrins and metallopophyrins have attracted the attention of chemists for the past 100 years or more owing to their widespread involvement in biology. More recently, synthetic porphyrins and porphyrin-like macrocycles have attracted the attention of researchers due to their diverse applications as sensitizers for photodynamic therapy, MRI contrasting agents, and complexing agents for larger metal ions and also for their anion binding abilities. The number of π-electrons in the porphyrin ring can be increased either by increasing the numberof conjugated double bonds between the pyrrole rings or by increasing the number of heterocyclic rings. Thus, 22π sapphyrins, 26π rubyrins, 30π heptaphyrins, 34π octaphyrins and higher cyclic polypyrrole analogues containing 40π, 48π, 64π, 80π and 96π systems have recently been reported in the literature. These macrocycles show rich structural diversity where normal and different kinds of inverted structures have been identified. In this review, an attempt has been made to collect the literature of the inverted porphyrins and expanded porphyrins reported until December 2001. Since themeso aryl expanded porphyrins have tendency to form both inverted and non-inverted structures more emphasis has been given to meso aryl expanded porphyrins
Quantum walk on distinguishable non-interacting many-particles and indistinguishable two-particle
We present an investigation of many-particle quantum walks in systems of
non-interacting distinguishable particles. Along with a redistribution of the
many-particle density profile we show that the collective evolution of the
many-particle system resembles the single-particle quantum walk evolution when
the number of steps is greater than the number of particles in the system. For
non-uniform initial states we show that the quantum walks can be effectively
used to separate the basis states of the particle in position space and
grouping like state together. We also discuss a two-particle quantum walk on a
two- dimensional lattice and demonstrate an evolution leading to the
localization of both particles at the center of the lattice. Finally we discuss
the outcome of a quantum walk of two indistinguishable particles interacting at
some point during the evolution.Comment: 8 pages, 7 figures, To appear in special issue: "quantum walks" to be
published in Quantum Information Processin
Spectroscopic studies on monomers and dimers of thiaporphyrins
Synthesis and spectroscopic properties of porphyrin macrocycles with sulphur as the heteroatom in the porphyrin core have been studied. Electronic absorption spectra of these macrocycles show porphyrin-like behaviour with a strong Soret band and weakQ-bands. Substitution of the -NH groups of tetraphenylporphyrin (TPPH2) by sulphur causes a red shift of all the absorption bands and the magnitude of the red shift depends on the number of sulphur atoms substituted. Both the mono and dications of dithiaporphyrins (S2TPP) show larger bathochromic shifts ofQ-bands relative to TPPH2 indicating a stronger resonance interaction with the phenyl groups. A positive shift for both oxidation and reduction potentials is observed upon substitution of sulphur atoms. 1H NMR spectra of symmetrically substituted dithiaporphyrins show two sharp singlets for pyrrole protons and thiophene protons confirming the presence of a two-fold axis of symmetry. Only monothia derivatives (STPPH) form metal complexes [Ni(II), Cu(II)] and these metal complexes are five-coordinate with an apical chloride ligand. The water-soluble S2TPPS, prepared from sulphonating the para positions of phenyl rings shows extensive aggregation at high concentrations (> 10-4M). At low concentrations (≈ 10-610-7M), dimerisation can be induced by the addition of cations (K+, NH4+ ) and cation-crown ether complex. The induced red shifts upon dimerisation parallel findings reported for a variety of cofacial covalently linked porphyrin dimers
A class of energy based ensembles in Tsallis statistics
A comprehensive investigation is carried out on the class of energy based
ensembles. The eight ensembles are divided into two main classes. In the
isothermal class of ensembles the individual members are at the same
temperature. A unified framework is evolved to describe the four isothermal
ensembles. Such a description is provided both in the second and the third
constraint formalisms. The isothermal- isobaric, grandcanonical and the
generalized ensembles are illustrated through a study of the classical
nonrelativistic and the extreme relativistic ideal gas models. In the adiabatic
class of ensembles the individual members of the ensemble have the same value
of the heat function and a unified formulation to described all the four
ensembles is given. The nonrelativistic and the extreme relativistic ideal
gases are studied in the isoenthalpic-isobaric ensemble, the adiabatic ensemble
with number fluctuations, and, the adiabatic ensemble with number and particle
fluctuations
Quantum walks: a comprehensive review
Quantum walks, the quantum mechanical counterpart of classical random walks,
is an advanced tool for building quantum algorithms that has been recently
shown to constitute a universal model of quantum computation. Quantum walks is
now a solid field of research of quantum computation full of exciting open
problems for physicists, computer scientists, mathematicians and engineers.
In this paper we review theoretical advances on the foundations of both
discrete- and continuous-time quantum walks, together with the role that
randomness plays in quantum walks, the connections between the mathematical
models of coined discrete quantum walks and continuous quantum walks, the
quantumness of quantum walks, a summary of papers published on discrete quantum
walks and entanglement as well as a succinct review of experimental proposals
and realizations of discrete-time quantum walks. Furthermore, we have reviewed
several algorithms based on both discrete- and continuous-time quantum walks as
well as a most important result: the computational universality of both
continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing
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