630 research outputs found
Towards Understanding the Structure, Dynamics and Bio-activity of Diabetic Drug Metformin
Small molecules are often found to exhibit extraordinarily diverse biological
activities. Metformin is one of them. It is widely used as anti-diabetic drug
for type-two diabetes. In addition to that, metformin hydrochloride shows
anti-tumour activities and increases the survival rate of patients suffering
from certain types of cancer namely colorectal, breast, pancreas and prostate
cancer. However, theoretical studies of structure and dynamics of metformin
have not yet been fully explored. In this work, we investigate the
characteristic structural and dynamical features of three mono-protonated forms
of metformin hydrochloride with the help of experiments, quantum chemical
calculations and atomistic molecular dynamics simulations. We validate our
force field by comparing simulation results to that of the experimental
findings. Nevertheless, we discover that the non-planar tautomeric form is the
most stable. Metformin forms strong hydrogen bonds with surrounding water
molecules and its solvation dynamics show unique features. Because of an
extended positive charge distribution, metformin possesses features of being a
permanent cationic partner toward several targets. We study its interaction and
binding ability with DNA using UV spectroscopy, circular dichroism, fluorimetry
and metadynamics simulation. We find a non-intercalating mode of interaction.
Metformin feasibly forms a minor/major groove-bound state within a few tens of
nanoseconds, preferably with AT rich domains. A significant decrease in the
free-energy of binding is observed when it binds to a minor groove of DNA.Comment: 60 pages, 24 figure
An alternate model for magnetization plateaus in the molecular magnet V_15
Starting from an antiferromagnetic Heisenberg Hamiltonian for the fifteen
spin-1/2 ions in V_15, we construct an effective spin Hamiltonian involving
eight low-lying states (spin-1/2 and spin-3/2) coupled to a phonon bath. We
numerically solve the time-dependent Schrodinger equation of this system, and
obtain the magnetization as a function of temperature in a time-dependent
magnetic field. The magnetization exhibits unusual patterns of hysteresis and
plateaus as the field sweep rate and temperature are varied. The observed
plateaus are not due to quantum tunneling but are a result of thermal
averaging. Our results are in good agreement with recent experimental
observations.Comment: Revtex, 4 pages, 5 eps figure
On-shell Supersymmetry and higher-spin amplitudes
We use on-shell Supersymmetry to constrain the three-point function of two
massless particles and one massive particle in 3+1 dimensions. We use this
information to write down the tree-level four-point function of massless
particles for , and theories. In particular, we derive
the expressions for four-photon/gluon amplitudes with massive higher spin
exchange in theories with Supersymmetry in 3+1 dimensions.Comment: 39 pages+ 4 appendice
Properties of a mixed-valent iron compound with the kagomélattice
An organically templated iron sulfate of the formula [HN(CH2)6NH][FeIIIFe2IIF6(SO4)2]·[H3O] possessing the kagomé lattice has been prepared and characterized by single-crystal crystallography and other techniques. This mixed-valent iron compound shows complex magnetic properties including spin-glass behavior and magnetic hysteresis. The low-temperature specific heat data show deviation from the T2 behavior found in two-dimensional frustrated systems. Simple calculations have been carried out to understand the properties of this kagomé compound
Interacting Generalised Cosmic Chaplygin gas in Loop quantum cosmology: A singularity free universe
In this work we investigate the background dynamics when dark energy is
coupled to dark matter with a suitable interaction in the universe described by
Loop quantum cosmology. Dark energy in the form of Generalised Cosmic Chaplygin
gas is considered. A suitable interaction between dark energy and dark matter
is taken into account in order to at least alleviate (if not solve) the cosmic
coincidence problem. The dynamical system of equations is solved numerically
and a stable scaling solution is obtained. A significant attempt towards the
solution of the cosmic coincidence problem is taken. The statefinder parameters
are also calculated to classify the dark energy model. Graphs and phase
diagrams are drawn to study the variations of these parameters. It is seen that
the background dynamics of Generalised Cosmic Chaplygin gas is completely
consistent with the notion of an accelerated expansion in the late universe.
From the graphs, generalised cosmic Chaplygin gas is identified as a dark fluid
with a lesser negative pressure compared to Modified Chaplygin gas, thus
supporting a 'No Big Rip' cosmology. It has also been shown that in this model
the universe follows the power law form of expansion around the critical point,
which is consistent with the known results. Future singularities that may be
formed in this model as an ultimate fate of the universe has been studied in
detail. It was found that the model is completely free from any types of future
singularities.Comment: 10 pages, 10 figures. arXiv admin note: text overlap with
arXiv:1109.1481, arXiv:1102.275
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