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P. O. Fedichev

Publications and source records attributed to P. O. Fedichev.

At least 19 recordsLinked to original sources

Hybrid quantum-classical machine learning for generative chemistry and drug design

Deep generative chemistry models emerge as powerful tools to expedite drug discovery. However, the immense size and complexity of the structural space of all possible drug-like molecules pose significant obstacles, which could be overcome with hybrid architectures combining quantum computers with deep classical networks. As the first step toward this goal, we built a compact discrete variational autoencoder (DVAE) with a Restricted Boltzmann Machine (RBM) of reduced size in its latent layer. The size of the proposed model was small enough to fit on a state-of-the-art D-Wave quantum annealer and allowed training on a subset of the ChEMBL dataset of biologically active compounds. Finally, we generated 2331 novel chemical structures with medicinal chemistry and synthetic accessibility properties in the ranges typical for molecules from ChEMBL. The presented results demonstrate the feasibility of using already existing or soon-to-be-available quantum computing devices as testbeds for future drug discovery applications.

quant-ph

Critical dynamics of gene networks is a mechanism behind ageing and Gompertz law

Although accumulation of molecular damage is suggested to be an important molecular mechanism of aging, a quantitative link between the dynamics of damage accumulation and mortality of species has so far remained elusive. To address this question, we examine stability properties of a generic gene regulatory network (GRN) and demonstrate that many characteristics of aging and the associated population mortality rate emerge as inherent properties of the critical dynamics of gene regulation and metabolic levels. Based on the analysis of age-dependent changes in gene-expression and metabolic profiles in Drosophila melanogaster, we explicitly show that the underlying GRNs are nearly critical and inherently unstable. This instability manifests itself as aging in the form of distortion of gene expression and metabolic profiles with age, and causes the characteristic increase in mortality rate with age as described by a form of the Gompertz law. In addition, we explain late-life mortality deceleration observed at very late ages for large populations. We show that aging contains a stochastic component, related to accumulation of regulatory errors in transcription/translation/metabolic pathways due to imperfection of signaling cascades in the network and of responses to environmental factors. We also establish that there is a strong deterministic component, suggesting genetic control. Since mortality in humans, where it is characterized best, is strongly associated with the incidence of age-related diseases, our findings support the idea that aging is the driving force behind the development of chronic human diseases.

q-bio.MN

Universality of the Berezinskii-Kosterlitz-Thouless type of phase transition in the dipolar XY-model

We investigate the nature of the phase transition occurring in a planar XY-model spin system with dipole-dipole interactions. It is demonstrated that a Berezinskii-Kosterlitz-Thouless (BKT) type of phase transition always takes place at a finite temperature separating the ordered (ferro) and the disordered (para) phases. The low-temperature phase corresponds to an ordered state with thermal fluctuations, composed of a "gas" of bound vortex-antivortex pairs, which would, when considered isolated, be characterized by a constant vortex-antivortex attraction force which is due to the dipolar interaction term in the Hamiltonian. Using a topological charge model, we show that small bound pairs are easily polarized, and screen the vortex-antivortex interaction in sufficiently large pairs. Screening changes the linear attraction potential of vortices to a logarithmic one, and leads to the familiar pair dissociation mechanism of the BKT type phase transition. The topological charge model is confirmed by numerical simulations, in which we demonstrate that the transition temperature slightly increases when compared with the BKT result for short-range interactions.

cond-mat.stat-mech

Wetting regimes and interactions of parallel plane surfaces in a polar liquid

We apply a phenomenological theory of polar liquids to calculate the interaction energy between two plane surfaces at nm-distances. We show that depending on the properties of the surface-liquid interfaces, the interacting surfaces induce polarization of the liquid in different ways. We find, in full agreement with available experiments, that if the interfaces are mostly hydrophobic, then the interaction is attractive and relatively long-ranged (interaction decay length λ\sim1.2\, nm). The water molecules are net polarized parallel to the surfaces in this case. If the surfaces are mostly hydrophilic, then the molecules are polarized against the surfaces, and the interaction becomes repulsive, but at a short-range (λ\sim0.2\, nm). Finally, we predict there exists an intermediate regime, where the surfaces fail to order the water molecules, the interaction becomes much weaker, attractive and, at relatively small distances, decays with the inverse square of the distance between the surfaces.

cond-mat.soft

How does confinement in nano-scale pores change the thermodynamic properties and the nature of phase transitions of water?

We analyze thermodynamics of water samples confined in nanopores and prove that although the freezing temperature can be dramatically lower, the suppression of the ice nucleation leading to the freezing temperature depression is a truly macroscopic effect rather than a consequence of microscopic interactions. The freezing transition itself is a truly collective phenomenon described by a macroscopic order parameter (the nearly homogeneous density of the liquid within the pore away from the pores wall) exactly in the same way as in the bulk liquid. The thermodynamics properties of the confined and the bulk liquid can be described by macroscopic thermodynamics and be readily related to each other simply by proper inclusion of the additional Laplace pressure exerted by the solid-liquid boundary.

cond-mat.soft

Experimental evidence of the ferroelectric phase transition near the $λ-$point in liquid water

We studied dielectric properties of nano-sized liquid water samples confined in polymerized silicates MCM-41 characterized by the porous sizes \sim 3-10nm. We report the direct measurements of the dielectric constant by the dielectric spectroscopy method at frequencies 25Hz-1MHz and demonstrate clear signatures of the second-order phase transition of ferroelectric nature at temperatures next to the λ- point in the bulk supercooled water. The presented results support the previously developed polar liquid phenomenology and hence establish its applicability to model actual phenomena in liquid water.

cond-mat.soft

Ferro-electric phase transition in a polar liquid and the nature of λ-transition in supercooled water

We develop a series of approximations to calculate free energy of a polar liquid. We show that long range nature of dipole interactions between the molecules leads to para-electric state instability at low temperatures and to a second-order phase transition. We establish the transition temperature, T_{c}, both within mean field and ring diagrams approximation and show that the ferro-electric transition may play an important role explaining a number of peculiar properties of supercooled water, such as weak singularity of dielectric constant as well as to a large extent anomalous density behavior. Finally we discuss the role of fluctuations, shorter range forces and establish connections with phenomenological models of polar liquids.

cond-mat.stat-mech

Phospholipid membranes repulsion at nm-distances explained within a continuous water model

We apply recently developed phenomenological theory of polar liquids to calculate the repulsive pressure between two hydrophilic membranes at nm-distances. We find that the repulsion does show up in the model and the solution to the problem fits the published experimental data well both qualitatively and quantitatively. Moreover, we find that the repulsion is practically independent on temperature, and thus put some extra weight in favour of the so called hydration over entropic hypothesis for the membranes interactions explanation. The calculation is a good proof of concept example a continuous water model application to non-trivial interactions on -size bodies in water arising from long-range correlations between the water molecules.

cond-mat.soft

O(N) continuous electrostatics solvation energies calculation method for biomolecules simulations

We report a development of a new fast surface-based method for numerical calculations of solvation energy of biomolecules with a large number of charged groups. The procedure scales linearly with the system size both in time and memory requirements, is only a few percent wrong for any molecular configurations of arbitrary sizes, gives explicit value for the reaction field potential at any point, provides both the solvation energy and its derivatives suitable for Molecular Dynamics simulations. The method works well both for large and small molecules and thus gives stable energy differences for quantities such as solvation energies of molecular complex formation.

q-bio.QM

Fast Surface Based Electrostatics for biomolecules modeling

We analyze deficiencies of commonly used Coulomb approximations in Generalized Born solvation energy calculation models and report a development of a new fast surface-based method (FSBE) for numerical calculations of the solvation energy of biomolecules with charged groups. The procedure is only a few percents wrong for molecular configurations of arbitrary sizes, provides explicit values for the reaction field potential at any point of the molecular interior, water polarization at the surface of the molecule, both the solvation energy value and its derivatives suitable for Molecular Dynamics (MD) simulations. The method works well both for large and small molecules and thus gives stable energy differences for quantities such as solvation energies contributions to a molecular complex formation.

q-bio.QM

BKT phase transition in a 2d system with long range dipole-dipole interaction

We consider phase transitions in 2d XY-like systems with long range dipole-dipole interactions and demonstrate that BKT-type phase transition always occurs separating the ordered (ferroelectric) and the disordered (paraelectric) phases. The low-temperature phase corresponds to a thermal state with bound vortex-antivortex pairs characterized by linear attraction at large distances. We show that bound vortex pairs polarize and screen the vortex-antivortex interaction leaving only the logarithmic attraction at sufficiently large separations between the vortices. At higher temperatures the pairs dissociate and the phase transition similar to BKT occurs, though at a larger temperature than in a system without the dipole-dipole interaction.

cond-mat.mes-hall

From protein binding to pharmacokinetics: a novel approach to active drug absorption prediction

Due to inherent complexity active transport presents a landmark hurdle for oral absorption properties prediction. We present a novel approach carrier-mediated drug absorption parameters calculation based on entirely different paradigm than QSPR. We capitalize on recently emerged ideas that molecule activities against a large protein set can be used for prediction of biological effects and performed a large scale numerical docking of drug-like compounds to a large diversified set of proteins. As a result we identified for the first time a protein, binding to which correlates well with the intestinal permeability of many actively absorbed compounds. Although the protein is not a transporter, we speculate that it has the binding site force field similar to that of an important intestinal transporter. The observation helped us to improve the passive absorption model by adding non-liner flux associated with the transporting protein to obtain a quantitative model of active transport. This study demonstrates that binding data to a sufficiently representative set of proteins can serve as a basis for active absorption prediction for a given compound.

q-bio.QM

Long-Range Order and Interactions of Macroscopic Objects in Polar Liquids

We develop a phenomenological vector model of polar liquids capable to describe aqueous interactions of macroscopic bodies. It is shown that a strong, long-range and orientationally dependent interaction between macroscopic objects appears as a result of competition between short-range (hydrogen bonding) and the long-range dipole-dipole interactions of the solvent molecules. Spontaneous polarization of molecular dipoles next to a hydrophobic boundaries leads to formation of globally ordered network of hydrogen-bonded molecules with ferroelectric properties. The proposed vector model naturally describes topological excitations on the solute boundaries and can be used to explain the hydrogen bonds networks and order-disorder phase transitions in the hydration water layer.

cond-mat.soft

Atomic quantum dots coupled to BEC reservoirs

We study the dynamics of an atomic quantum dot, i.e. a single atom in a tight optical trap which is coupled to a superfluid reservoir via laser transitions. Quantum interference between the collisional interactions and the laser induced coupling to the phase fluctuations of the condensate results in a tunable coupling of the dot to a dissipative phonon bath, allowing an essentially complete decoupling from the environment. Quantum dots embedded in a 1D Luttinger liquid of cold bosonic atoms realize a spin-Boson model with ohmic coupling, which exhibits a dissipative phase transition and allows to directly measure atomic Luttinger parameters.

cond-mat.other

Single Atom Cooling by Superfluid Immersion: A Non-Destructive Method for Qubits

We present a scheme to cool the motional state of neutral atoms confined in sites of an optical lattice by immersing the system in a superfluid. The motion of the atoms is damped by the generation of excitations in the superfluid, and under appropriate conditions the internal state of the atom remains unchanged. This scheme can thus be used to cool atoms used to encode a series of entangled qubits non-destructively. Within realisable parameter ranges, the rate of cooling to the ground state is found to be sufficiently large to be useful in experiments.

quant-ph

Extended molecules and geometric scattering resonances in optical lattices

We develop a theory describing neutral atoms scattering at low energies in an optical lattice. We show that for a repulsive interaction, as the microscopic scattering length increases, the effective scattering amplitude approaches a limiting value which depends only on the lattice parameters. In the case of attractive interaction a geometric resonance occurs before reaching this limit. Close to the resonance, the effective interaction becomes repulsive and supports a weakly bound state, which can extend over several lattice sites.

cond-mat.soft

Defect-Suppressed Atomic Crystals in an Optical Lattice

We present a coherent filtering scheme which dramatically reduces the site occupation number defects for atoms in an optical lattice, by transferring a chosen number of atoms to a different internal state via adiabatic passage. With the addition of superlattices it is possible to engineer states with a specific number of atoms per site (atomic crystals), which are required for quantum computation and the realisation of models from condensed matter physics, including doping and spatial patterns. The same techniques can be used to measure two-body spatial correlation functions. We illustrate these ideas with a scheme to study the creation of a BCS state with a chosen filling factor from a degenerate Fermi gas in an optical lattice.

cond-mat.soft

Dissipative spin-boson model and Kondo effect in low dimensional quantum gases

We show that ultracold atoms confined in a quasi-1d trap can be used to study the dissipative spin-boson model with {\it tunable} tunneling splitting and strength of dissipation. It is shown that with realistic parameters this system allows to study the crossover from coherent Rabi dynamics to incoherent tunneling.

cond-mat