The dynamic structure of <Emphasis Type="Italic">cis</Emphasis> and <Emphasis Type="Italic">trans</Emphasis> conformers of substituted phosphinous acids

The potential energy surfaces of bis-(trifluoromethyl)-phosphinous (III), diemthylphosphinous (IV), and bis-(pentafluorophenyl)-phosphinous (V) acids, the geometric parameters of the cis and trans conformers of these acids, and their P-O and O-H stretching vibration frequencies were calculated by the density functional theory method (PBE, 4Z). The potential energy surface sections corresponding to internal rotations about the P-O bonds were constructed, and dynamic problems for such a motion of the proton in a cyclic potential were solved by the Ritz method using a basis set of 100 trigonometric functions. According to calculations, the energy differences between the cis and trans conformers of acids III–V were of 4–7 kJ/mol, and the heights of potential barriers separating these conformers were of from 11 to 16 kJ/mol. In acids III and V, the cis, and, in IV, the trans conformer was stabler. At 298 K, only the ground vibrational states were populated for both rotamers of IV and V and the cis conformer of III. The special features of the potential of III were such that, at 298 K, the first excited vibrational level of its trans conformer was also noticeably populated.     

Role of critical fluctuations in the formation of a skyrmion lattice in MnSi

The region in the H–T phase diagram near the critical temperature (T _c ) of the cubic helicoidal MnSi magnet is comprehensively studied by small-angle neutron diffraction. Magnetic field H is applied along the [111] axis. The experimental geometry is chosen to simultaneously observe the following three different magnetic states of the system: (a) critical fluctuations of a spin spiral with randomly orientated wavevector k _f , (b) conical structure with k _c ∥ H, and (c) hexagonal skyrmion lattice with k_sk ⊥ H. Both states (conical structure, and skyrmion lattice) are shown to exist above critical temperature T _c = 29 K against the background of the critical fluctuations of a spin spiral. The conical lattice is present up to the temperatures where fluctuation correlation length ξ becomes comparable with pitch of spiral d _s . The skyrmion lattice is localized near T _c and is related to the fluctuations of a spiral with correlation length ξ ≈ 2d _s , and the propagation vector is normal to the field (k_sk ⊥ H). These spiral fluctuations are assumed to be the defects that stabilize the skyrmion lattice and promote its formation.     

Synthesis,structural, and spectroscopic (FT-IR,NMR, and UV) Characterization of 1-(Cyclohexylmethyl)-2-(pyridin-2-yl)-1<Emphasis Type="Italic">H</Emphasis>-benzo[<Emphasis Type="Italic">d</Emphasis>]imidazole by experimental techniques and quantum chemical calculations

The title compound (II), 1-(cyclohexylmethyl)-2-(pyridin-2-yl)-1H-benzo[d]imidazole (C₁₉H₂₁N₃), was synthesized via N-alkylation of 2-(pyridin-2-yl)-1H-benzo[d]imidazole (I). Both compounds I and II were characterized by IR, NMR and UV-vis spectroscopy. Solid-state structure of compound II was determined by single-crystal X-ray diffraction technique. Furthermore, quantum chemical calculations employing density functional theory (DFT/B3LYP) method with the 6–311++G(d, p) basis set were performed for the theoretical characterization of the molecular and spectroscopic features of the compounds. Using the TD-DFT method, electronic absorption spectra of the compounds have been predicted at same level. When the obtained results were compared with the experimental findings, it is seen that theoretical results support the experimental data and a good agreement exists between them.     

Substituent Dependent Optical Properties of <Emphasis Type="Italic">p</Emphasis>-phenyl Substituted ethenyl-<Emphasis Type="Italic">E</Emphasis>-thiophenes

Various electron donor and acceptor substituted (NO₂, CN, Cl, H, OCH₃, NH₂) p-phenyl ethenyl-E- thiophenes (1–6) were synthesized and substituent dependent optical properties (dipole moment, transition dipole moment, oscillator strength, optical band gap, hyperpolarizability) were studied using Solvatochromism and Density functional theory. It is shown that thiophene acts as a weak electron donor in presence of an electron withdrawing p-phenyl substituent (NO₂, CN, Cl), whereas thiophene acts as a weak electron acceptor in presence of an electron donating p-phenyl substituent (OCH₃, NH₂). In comparison to ethenyl thiophene 4, the HOMO-LUMO energy band gap is decreased upon increasing the electron donating or electron withdrawing capacity of p-phenyl substituent. From the excited state dipole moment calculation, it is shown that the excited state is highly dipolar for nitro and amino compounds 1 and 6, whereas compounds 2–5 show a non-polar excited state. As compared to the ethenyl thiophene 4, the first hyperpolarizability (β) increases upon substitution either with a strong electron withdrawing or strong electron donating p-phenyl substituent. A large β value is found for p-nitro phenyl ethenyl-E-thiophene and p-amino phenyl ethenyl-E- thiophene. Overall, these studies provide useful information in understanding the optical properties of phenyl and heterocyclic based ethenyl systems.     

Identification of a novel putative inhibitor of the <Emphasis Type="BoldItalic">Plasmodium falciparum</Emphasis> purine nucleoside phosphorylase: exploring the purine salvage pathway to design new antimalarial drugs

Malaria, a tropical parasitic disease caused by Plasmodium spp., continues to place a heavy social burden, with almost 200 million cases and more than 580,000 deaths per year. Plasmodium falciparum purine nucleoside phosphorylase (PfPNP) can be targeted for antimalarial drug design since its inhibition kills malaria parasites both in vitro and in vivo. Although the currently known inhibitors of PfPNP, immucillins, are orally available and of low toxicity to animals and humans, to the best of our knowledge, none of these compounds has entered clinical trials for the treatment of malaria. Using a pharmacophore-based virtual screening coupled to a consensual molecular docking approach, we identified 59 potential PfPNP inhibitors that are predicted to be orally absorbed in a Caco-2 cell model. Although most of these compounds are predicted to have high plasma protein binding levels, poor water solubility (except for compound 25) and CYP3A4 metabolic stability (except for 4, 7 and 8), four structures (4, 7, 8 and 25) remain as potential leads because of their plausible interaction with a specific hydrophobic pocket of PfPNP, which would confer them higher selectivity for PfPNP over human PNP. Additionally, both predicted Gibbs free energies for binding and molecular dynamics suggest that compound 4 may form a more stable complex with PfPNP than 5\(^{\prime }\)-methylthio-immucillin-H, a potent and selective inhibitor of PfPNP.     

Excitons in monoclinic zinc diphosphide: The <Emphasis Type="Italic">A</Emphasis>-exciton series and Fano effect

The A-exciton series in the absorption spectra of β-ZnP₂ monoclinic zinc diphosphide samples is investigated at different directions of the wave vector and different polarization states of radiation. It is shown that the oscillator strengths determined for the observed transitions are adequately described by the relationship F _n ∝n^?3 characteristic of S-type exciton states. The assumption is made that the A-exciton series is associated with the partially allowed dipole transitions to nS states of the orthoexciton with Γ ₂ ^? (x) symmetry at m _s =0. These states are mixed, to a first approximation, with nS states of the Γ ₂ ^? (z) singlet exciton due to the spin-orbit 2 interaction and are split off by the long-range (nonanalytical) part of the exchange interaction. The Fano antiresonances arise in the absorption spectra at resonances of the A-exciton series when the radiation vector E (or the induction vector D) has a component along the crystallographic axis c. These antiresonances are induced by the configurational interaction of discrete exciton states of the A series with the continuum of the exciton-phonon spectrum due to indirect transitions to the 1S band of the singlet exciton with phonon emission.     

Microwave-assisted Synthesis and antifungal activity of coumarin[8,7-<Emphasis Type="BoldItalic">e</Emphasis>][1,3]oxazine derivatives

The synthesis of novel coumarin[8,7-e][1,3]oxazine derivatives through a microwave-assisted three-component one-pot Mannich reaction is described in this study. All the target compounds were evaluated in vitro for their antifungal activity against Botrytis cinerea, Colletotrichum capsici, Alternaria solani, Gibberella zeae, Rhizoctonia solani, and Alternaria mali. The preliminary bioassays showed that 5e, 5m, and 5s exhibited good antifungal activity and the most active compound was 5m with an \(\hbox {EC}_{50}\) value as low as 2.1 nM against Botrytis cinerea.     

Spin-frustrated antiferromagnets based on <Emphasis Type="Italic">BEDT-TTF</Emphasis> and manganese dicyanamide complexes

The magnetic properties of new radical cation salts (BEDT-TTF)₂[CuMn(dca)₄] (I) and (BEDT-TTF)₂[Mn(dca)₃] (II) [where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene and dca = N(CN₂)] are investigated using superconducting quantum interference device (SQUID) magnetometry and electron paramagnetic resonance (EPR) spectroscopy. It is established that, at temperatures below 25 K, both salts are characterized by antiferromagnetic deviations from the paramagnetic behavior. The Weiss constants for compounds I and II are determined to be ?5 and ?10 K, respectively. The corresponding correlations in the structure of compound I are short-range correlations and do not lead to a change in the effective spin equal to 5/2. It is found that the widths of the EPR lines attributed to the BEDT-TTF conducting sublattice correlate with the widths of the EPR lines associated with the magnetic sublattice of the Mn(dca) ₃ ^? counterion in the structure of salt II. This correlation suggests that the antiferromagnetic ordering in the magnetic sublattice of compound II affects the spin-lattice relaxation in the BEDT-TTF sublattice. The dependence of the magnetic moment on the magnetic field for compound II at a temperature of 2 K is typical of weakly frustrated uniaxial antiferromagnets and exhibits a kink in a magnetic field of 20 kOe, which corresponds to spin-flop transitions.     

An efficient and facile synthesis of new tetracyclic fused pyrazolo[4,3-<Emphasis Type="Italic">c</Emphasis>][1,2,4]triazino[4,5-<Emphasis Type="Italic">a</Emphasis>]quinolin-4(5<Emphasis Type="Italic">H</Emphasis>)-ones

Reaction of amidrazones 1a–1i with (1,5-dihydro-3-methyl-5-oxo-1-phenyl-4H-pyrazol-4-ylidene)propanedinitrile (2) in ethyl acetate solution in one-step reaction led to the formation of unprecedented pyrazolo[4,3-c][1,2,4]triazino[4,5-a]quinolin-4(5H)-ones 3a–3g along with pyrazolo[4,3-c][1,2,4]triazino[4,5-a]quinolin-12b-oles 3h–3m in moderate to excellent yields. These novel heterocycles were formed via a Michael addition reaction followed by intramolecular cyclization via a dearomatization process.     

Radiation of electromagnetic waves by a dipole in an external uniform electrostatic field

Exact solution for the electromagnetic field densities E and H of a dipole of uniformly accelerated point-charges with identical masses is discussed. It is shown that, for any fixed time t and a large distance R between the center of the dipole and the fieldpoint, |E| ~ R ^?4, |H| ~ R ^?5, while for large c|t| ~ R, |E| ~ |H| ~1/R as in spherical electromagnetic waves. Nevertheless, any irreversible radiation of electromagnetic waves is absent since the wave zone does not exist.     

Some exact solutions of the local induction equation for the motion of a vortex in a Bose–Einstein condensate with a Gaussian density profile

The dynamics of a vortex filament in a Bose–Einstein condensate whose equilibrium density in the reference frame rotating at the angular velocity Ω is Gaussian with the quadratic form r·D?r has been considered. It has been shown that the equation of motion of the filament in the local-induction approximation permits a class of exact solutions in the form R(β, t) = βM(t) + N(t) of a straight vortex, where β is the longitudinal parameter and is the time. The vortex slips over the surface of an ellipsoid, which follows from the conservation laws N · D?N=C ₁ and M · D?N=C ₀=0. The equation of the evolution of the tangential vector M(t) appears to be closed and has integrals of motion M ·D?M=C ₂ and (|M| ? M· G?Ω) = C, with the matrix G? = 2(I?TrD? ? D?)^?1. Crossing of the respective isosurfaces specifies trajectories in the phase space.     

First- and second-order Raman scattering from MoTe<Subscript>2</Subscript> single crystal

We report on Raman experiments performed on a MoTe₂ single crystal. The system belongs to the wide family of transition metal dichalcogenides which includes several of the most interesting two-dimensional materials for both basic and applied physics. Measurements were performed in the standard basal plane configuration, by placing the ab plane of the crystal perpendicular to the wave vector k _i of the incident beam to explore the in-plane vibrational modes, and in the edge plane configuration with k _i perpendicular to the crystal c axis, thus mainly exciting out-of-plane modes. For both configurations we performed a polarization-dependent study of the first-order Raman components and detailed computation of the corresponding selection rules. We were thus able to provide a complete assignment of the observed first-order Raman peaks, in agreement with previous literature results. A thorough analysis of the second-order Raman bands, as observed in both basal and edge plane configurations, provides new information and allows a precise assignment of these spectral structures. In particular, we have observed and assigned Raman active modes of the M point of the Brillouin zone previously predicted by ab initio calculations but never previously measured.     

Field Confinement Energy at a Nonlinear Interface between Nonlinear Defocusing Media

The dependences of the resistance of the layered quasi-one-dimensional semiconductor TiS₃ on the direction and magnitude of the magnetic field B have been measured. The anisotropy and angular dependences of the magnetoresistance indicate the two-dimensional character of the conductivity at T < 100 K. Below T₀ ≈ 50 K, the magnetoresistance for the directions of the field in the plane of the layers (ab plane) increases sharply, whereas the transverse magnetoresistance (B ∥ c) becomes negative. The results confirm the possibility of an electron phase transition to a collective state at T₀. The negative magnetoresistance (at B ∥ c) below T₀ is explained by the magnetic-field-induced suppression of two-dimensional weak localization. The positive magnetoresistance (at B ∥ ab) is explained by the effect of the magnetic field on the spectrum of electronic states.     

Synthesis and antibacterial evaluation of new N- and S-glycosides analogues with dinitrophenyl-substituted heterocyclic bases

Four N- and S-glycosides 13–16 having nucleobases 7–12 binding to sugar molecules from one side and to 3,5-dinitrophenyl moieties from another side were synthesized from 3,5-dinitrobenzoic acid 2. The synthetic intermediates, hydrazide 5 and thiosemicarbazide 6 regarded as important key compounds for the synthesis of nucleobases 7–12, each was obtained by two approaches. Structures of synthesized compounds were determined spectroscopically. Antibacterial activities for synthetic intermediates and glycosides were assessed using the paper disk diffusion method against Gram-negative bacteria: Pseudomonas aeruginosa, Pseudomonas fluorescens, and Escherichia coli and Gram-positive bacteria: Bacillus cereus and Staphylococcus aureus. Some of the synthetic compounds showed variant activity against some of the microorganisms tested. Nucleobases 8–10 and 12 showed moderate to slight activity against microorganisms under test at relatively high concentration, while the N-glycosides 14 and 15 exhibited persistent effect even at lower concentrations. Commercially available antibiotics polymyxine and oxytetracycline were used as positive controls.     

Influence of the ground state of the Pr<Superscript>3+</Superscript> ion on magnetic and magnetoelectric properties of the PrFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> multiferroic

The magnetic, magnetoelectric, and magnetoelastic properties of a PrFe₃(BO₃)₄ single crystal and the phase transitions induced in this crystal by the magnetic field are studied both experimentally and theoretically. Unlike the previously investigated ferroborates, this material is characterized by a singlet ground state of the rare-earth ion. It is found that, below T _N = 32 K, the magnetic structure of the crystal in the absence of the magnetic field is uniaxial (l ∥ c), while, in a strong magnetic field H ∥ c (H _cr ～ 43 kOe at T = 4.2 K), a Fe³⁺ spin reorientation to the basal plane takes place. The reorientation is accompanied by anomalies in magnetization, magnetostriction, and electric polarization. The threshold field values determined in the temperature interval 2–32 K are used to plot an H-T phase diagram. The contribution of the Pr³⁺ ion ground state to the parameters under study is revealed, and the influence of the praseodymium ion on the magnetic and magnetoelectric properties of praseodymium ferroborate is analyzed.     

Bond-breaking excitations with diverging coupling matrix of response density functional theory from highest-level functionals

Bond-breaking excitations ω _α are the problematic case of adiabatic time-dependent density functional theory (TDDFT). The calculated ω _α erroneously vanishes with the bond elongation, since the Hartree-exchange-correlation kernel and the corresponding response coupling matrix K of standard approximations lack the characteristic divergence in the dissociation limit. In this paper an approximation for K is proposed constructed from the highest-level functionals, in which both occupied and virtual Kohn-Sham orbitals participate with the weights w _p . The latter provide the correct divergence of K in the limit of dissociating two-electron bond. The present K brings a decisive contribution to the energy of the ¹Σ _u ⁺ in the prototype H₂ molecule calculated for various H-H separations. At shorter separations it improves ω _α compared to the zero-order TDDFT estimate, while at the largest separation it reproduces near-saturation of the reference excitation energy.     

Optical 4<Emphasis Type="Italic">f</Emphasis>-4<Emphasis Type="Italic">f</Emphasis> transitions in multiferroic HoMnO<Subscript>3</Subscript>

In the absorption spectra of the hexagonal single-crystal manganite HoMnO₃ in the paramagnetic ferroelectric state, lines near 1.1 and 2.0 μm were observed associated with the transitions ⁵ I ₈ → ⁵ I ₆ and ⁵ I ₈ → ⁵ I ₇, respectively, within the 4f ¹⁰ configuration of the Ho³⁺ ion. At T = 80 K, to the ⁵ I ₈ → ⁵ I ₇ transition corresponds one band at 1.9 μm for both polarizations E ∥ c and E ⊥ c. As the temperature increases from 80 to 293 K, a low-energy band with a peak at 2.04 μm for E ⊥ c and a peak at 2.07 μm for E ∥ c arises associated with transitions from an excited Stark level of the ground ⁵ I ₈ multiplet to the Stark levels of the ⁵ I ₇ multiplet and with an increase in the population of the initial Stark level, the energy of which is ～100 K.     

Exchange and correlation in finite-temperature TDDFT

We discuss the finite-temperature generalization of time-dependent density functional theory (TDDFT). The theory is directly analogous to that at temperature T = 0. For example, the finite-T TDDFT exchange-correlation kernel f_xc(T, n) in the local density approximation can again be expressed as a density derivative of the exchange correlation potential f_xc(T, n) = [?v_xc(T, n)∕?n]δ(r ? r′), where n = N∕V is the electron number density. An approximation for the kernel f_xc(T, n) is obtained from the finite-T generalization of the retarded cumulant expansion applied to the homogeneous electron gas. Results for f_xc and the loss function are presented for a wide range of temperatures and densities including the warm dense matter regime, where T ≈ T_F, the electron degeneracy temperature. The theory also permits a physical interpretation of the exchange and correlation contributions to the theory.     

Galvanomagnetic properties of atomically disordered Sr<Subscript>2</Subscript>RuO<Subscript>4</Subscript> single crystals

The effect of neutron-bombardment-induced atomic disorder on the galvanomagnetic properties of Sr₂RuO₄ single crystals has been experimentally studied in a broad range of temperatures (1.7–380 K) and magnetic fields (up to 13.6 T). The disorder leads to the appearance of negative temperature coefficients for both the in-plane electric resistivity (ρ_a) and that along the c axis (ρ_c), as well as the negative magnetoresistance Δρ, which is strongly anisotropic to the magnetic field orientation (H ∥ a and H ∥ c), with the easy magnetization direction along the c axis and a weak dependence on the probing current direction in the low-temperature region. The experimental ρ_a(T) and ρ_c(T) curves obtained for the initial and radiation-disordered samples can be described within the framework of a theoretical model with two conductivity channels. The first channel corresponds to the charge carriers with increased effective masses (～10m _e , where m _e is the electron mass) and predominantly electron-electron scattering, which leads to the quadratic temperature dependences of ρ_a and ρ_c. The second channel corresponds to the charge carriers with lower effective masses exhibiting magnetic scattering at low temperatures, which leads to the temperature dependence of the ρ_{a, c}(T) ∝ 1/T type.     

Dependence of the upper critical field on the defect concentration in MgB<Subscript>2</Subscript> and the electronic structure parameters

The upper critical field H _c 2 (H ‖ c) of the two-band superconductor MgB₂ is studied as a function of the residual resistivity ρ_n. It is found that the superconductor follows the standard trend: the slope-dH_c2/dT of the temperature dependence of H_c2(T) increases with the number of defects. The upper critical field in the clean limit is found, and direct estimations of the parameters of carriers in the 2D σ band (including the Fermi velocity and the coherence length) are made. The contribution of the electron scattering to the magnitude of H_c2 is determined, and the mean free path of electrons in samples with various defect concentrations is estimated. The density of states of σ electrons at the Fermi level is calculated using the dependence of the slope-dH_c2/dT on ρ_n and a band structure model. It is impossible to estimate this density of states directly, because the upper critical field is determined by the carriers of one band, whereas the resistivity depends on the carriers in both bands.