Synthesis and characterization of a new family of bi-, tri-, tetra-, and pentanuclear ferric complexes

Nine members of a new family of polynuclear ferric complexes have been synthesized and characterized. The reaction of Fe(O(2)CMe)(2) with polydentate Schiff base proligands (H(2)L) derived from salicylidene-2-ethanolamine, followed in some cases by reaction with carboxylic acids, has afforded new complexes of general formulas [Fe(2)(pic)(2)(L)(2)] (where pic(-) is the anion of 2-picolinic acid), [Fe(3)(O(2)CMe)(3)(L)(3)], [Fe(4)(OR)(2)(O(2)CMe)(2)(L)(4)], and [Fe(5)O(OH)(O(2)CR)(4)(L)(4)]. The tri-, tetra-, and pentanuclear complexes all possess unusual structures and novel core topologies. M?ssbauer spectroscopy confirms the presence of high-spin ferric centers in the tri- and pentanuclear complexes. Variable-temperature magnetic measurements suggest spin ground states of S = 0, 1/2, 0, and 5/2 for the bi-, tri-, tetra-, and pentanuclear complexes, respectively. Fits of the magnetic susceptibility data have provided the magnitude of the exclusively antiferromagnetic exchange interactions. In addition, an easy-axis-type magnetic anisotropy has been observed for the pentanuclear complexes, with D values of approximately -0.4 cm(-)(1) determined from modeling the low-temperature magnetization data. A low-temperature micro-SQUID study of one of the pentanuclear complexes reveals magnetization hysteresis at nonzero field. This is attributed to an anisotropy-induced energy barrier to magnetization reversal that is of molecular origin. Finally, an inelastic neutron scattering study of one of the trinuclear complexes has revealed that the magnetic behavior arises from two distinct species.     

Decoding interleaved Reed–Solomon codes beyond their joint error-correcting capability

A new probabilistic decoding algorithm for low-rate interleaved Reed–Solomon (IRS) codes is presented. This approach increases the error correcting capability of IRS codes compared to other known approaches (e.g. joint decoding) with high probability. It is a generalization of well-known decoding approaches and its complexity is quadratic with the length of the code. Asymptotic parameters of the new approach are calculated and simulation results are shown to illustrate its performance. Moreover, an upper bound on the failure probability is derived.     

Electrochemical Synthesis of Pyrazolines and Pyrazoles via [3+2] Dipolar Cycloaddition

Pyrazolines and pyrazoles are common and important motifs of pharmaceutical agents and agrochemicals. Herein, the first electrochemical approach for their direct synthesis from easily accessible hydrazones and dipolarophiles up to decagram scale is presented. The application of a biphasic system (aqueous/organic) even allows for the conversion of highly sensitive alkenes, wherein inexpensive sodium iodide is employed in a dual role as supporting electrolyte and mediator. In addition, mechanistic insight into the reaction is given by the isolation of key step intermediates. The relevance of the presented reaction is underlined by the synthesis of commercial herbicide safener mefenpyr-diethyl in good yields.     

Persicamidines—Unprecedented Sesquarterpenoids with Potent Antiviral Bioactivity against Coronaviruses

A new family of highly unusual sesquarterpenoids (persicamidines A–E) exhibiting significant antiviral activity was isolated from a newly discovered actinobacterial strain, Kibdelosporangium persicum sp. nov., collected from a hot desert in Iran. Extensive NMR analysis unraveled a hexacyclic terpenoid molecule with a modified sugar moiety on one side and a highly unusual isourea moiety fused to the terpenoid structure. The structures of the five analogues differed only in the aminoalkyl side chain attached to the isourea moiety. Persicamidines A–E showed potent activity against hCoV-229E and SARS-CoV-2 viruses in the nanomolar range together with very good selectivity indices, making persicamidines promising as starting points for drug development.     

Effects of classical nonlinear resonances in grazing diatom-surface collisions

Energy transfer between vibrational, rotational, and translational degrees of freedom of a molecule during a collision process is enhanced when the classical frequencies associated with the initial state are in the proximity of nonlinear resonance conditions. We present an analysis of the classical resonant effects in the collisions of light diatoms with periodic surfaces, and discuss the initial conditions in which these effects can be observed. In particular, we find that for grazing incidence and resonant initial values of the classical frequencies, corresponding to specific vibro-rotational molecular states and translational energies, an efficient energy transfer between the intramolecular vibro-rotational degrees of freedom and the translational degree of freedom along a symmetry direction on the surface can be found. This efficient energy transfer manifests itself in the emergence of specific peaks in the molecular diffraction patterns. The predictions of the resonance analysis are contrasted with the results of classical trajectory calculations obtained in a diatom-rigid surface collision model.     

Development and validation of an HPLC method for the determination of seven penicillin antibiotics in veterinary drugs and bovine blood plasma

Herein a quantitative method for the determination of seven penicillins in bovine plasma and veterinary drugs has been developed. Amoxicillin (AMO), ampicillin (AMP), penicillin G (PENG), penicillin V (PENV), oxacillin (OXA), cloxacillin (CLO) and dicloxacillin (DICLO) were separated on a Perfectsil ODS‐2 (250×4 mm, 5 μm) column, using gradient elution, with a mobile phase of 0.1% v/v TFA and ACN–methanol (90:10 v/v). PDA detection was used at 240 nm. Penicillins were isolated from bovine plasma by SPE on Lichrolut RP‐18 cartridges with mean recoveries from 85.7 to 113.5%. Colchicine (3 ng/μL) was used as an internal standard. The developed method was validated in terms of selectivity, linearity, accuracy, precision, stability and sensitivity. Repeatability (n = 5) and between‐day precision (n = 5) revealed RSD < 12%. The detection limits in the bovine plasma were estimated as 18 ng for AMO and AMP, 25 for PENG, PENV and OXA, 3 ng for CLO and 12 ng for DICLO. Spiked plasma samples were stable for 1 wk, except for AMP and CLO, which were stable for 3 wk and OXA for 4 wk. AMO, PENG and PENV were stable for two freeze–thaw cycles, OXA, CLO and DICLO for four, while AMP only for one.     

Study of the critical points in lobenzarit disodium hydrophilic matrices for controlled drug delivery

Percolation theory is a multidisciplinary theory that studies chaotic systems. It has been applied in the pharmaceutical field since 1987. The application of this theory to study the release and hydration rate of hydrophilic matrices allowed for first time to explain the changes in release and hydration kinetic of swellable matrices type controlled delivery systems. The objective of the present paper is to estimate the percolation threshold of HPMC K4M in matrices of lobenzarit disodium and to apply the obtained result to the design of hydrophilic matrices for the controlled delivery of this drug. The materials used to prepare the tablets were Lobenzarit disodium (LBD) and HPMC of viscosity grade K4M. The drug mean particle size was 42+/-0.61 mum and the polymer was sieved and 150-200 microm granulometric fraction was selected. The formulations studied were prepared with different excipient contents in the range of 10-80% w/w. Dissolution studies were carried out using the paddle method and the water uptake measurements were performed using a modified Enslin apparatus. In order to estimate the percolation threshold, the behaviour of the kinetic parameters with respect to the volumetric fraction of each component at time zero, was studied. According to percolation theory, the critical points observed in dissolution and water uptake studies are attributed to the existence of an excipient percolation threshold. This threshold was situated between (18.58 to 24.33% v/v of HPMC). Therefore, the LBD-HPMC K4M matrices with a relative HPMC particle size of should be formulated with an excipient content above 24.33% v/v of HPMC, to obtain a control of the drug release from these systems.     

A spectral chart method for estimating the mean turbulent kinetic energy dissipation rate

We present an empirical but simple and practical spectral chart method for determining the mean turbulent kinetic energy dissipation rate $ \left\langle \varepsilon \right\rangle $ in a variety of turbulent flows. The method relies on the validity of the first similarity hypothesis of Kolmogorov (C R (Doklady) Acad Sci R R SS, NS 30:301–305, 1941) (or K41) which implies that spectra of velocity fluctuations scale on the kinematic viscosity ν and $ \left\langle \varepsilon \right\rangle $ at large Reynolds numbers. However, the evidence, based on the DNS spectra, points to this scaling being also valid at small Reynolds numbers, provided effects due to inhomogeneities in the flow are negligible. The methods avoid the difficulty associated with estimating time or spatial derivatives of the velocity fluctuations. It also avoids using the second hypothesis of K41, which implies the existence of a ?5/3 inertial subrange only when the Taylor microscale Reynods number R _λ is sufficiently large. The method is in fact applied to the lower wavenumber end of the dissipative range thus avoiding most of the problems due to inadequate spatial resolution of the velocity sensors and noise associated with the higher wavenumber end of this range.The use of spectral data (30?≤?R _λ?≤?400) in both passive and active grid turbulence, a turbulent mixing layer and the turbulent wake of a circular cylinder indicates that the method is robust and should lead to reliable estimates of $ \left\langle \varepsilon \right\rangle $ in flows or flow regions where the first similarity hypothesis should hold; this would exclude, for example, the region near a wall.