An alternative approach to the synthesis of [1,2,4]triazolo[1,5-a]pyridine-8-carbonitriles,their crystal structure,and DFT calculations

New representatives of [1,2,4]triazolo[1,5-a]pyridine-8-carbonitriles were synthesized via the condensation of β-diketones or β-dialdehydes and characterized using MS spectrometry, ¹H, ¹³C and, ¹⁹F NMR and IR spectroscopy. Crystal structures of two compounds were established using X-ray analysis and showed that title compounds are prone to the formation of planar molecules. The absence of band responsible for CN stretching vibration in trifluoromethyl-containing compounds was explained using the DFT calculations method, which also showed a significant influence of fluorines introducing on the energy gap between HOMO and LUMO.     

Multivalued evolution equations with nonlocal initial conditions in Banach spaces

We prove the existence of integral solutions to the nonlocal Cauchy problem in a Banach space X, where is m-accretive and such that –A generates a compact semigroup, has nonempty, closed and convex values, and is strongly-weakly upper semicontinuous with respect to its second variable, and . The case when A depends on time is also considered.      

An unprecedented co-crystal including a cis-high-spin and a trans-low-spin FeII complex molecule

Two structurally and magnetically nonequivalent isomeric molecules, a cis-high-spin and a trans-low-spin isomer constitute the unit cell of a new iron(II) complex {cis-[FeL(B5)(NCS)(2)].trans-[FeL(B5)(NCS)(2)]}.CH(3)OH, , (L(B5) = N,N'-bis((2-N-methylimidazol-1-yl)methylene))-2,2-dimethylpropane-1,3-diamine); the synthesis, X-ray structure, and magnetic and M?ssbauer study of this unique example of co-crystallised geometric, conformational and electronic isomers are reported.     

Interpretation of the photoelectron spectra of FeS(2)(-) by a multiconfiguration computational approach

The ground states of FeS(2) and FeS(2)(-), and several low-lying excited electronic states of FeS(2) that are responsible for the FeS(2)(-) photoelectron spectrum, are calculated. At the B3LYP level an open, quasi-linear [SFeS](-) conformation is found as the most stable structure, which is confirmed at the ab initio CASPT2 computational level. Both the neutral and the anionic unsaturated complexes possess high-spin electronic ground states. For the first time a complete assignment of the photoelectron spectrum of FeS(2)(-) is proposed. The lowest energy band in this spectrum is ascribed to an electron detachment from the two highest-lying 3dpi antibonding orbitals (with respect to the iron-sulfur bonding) of iron. The next-lowest experimental band corresponds to an electron removal from nonbonding, nearly pure sulfur orbitals. The two highest bands in the spectra are assigned as electron detachments from pi and sigma bonding mainly sulfur orbitals.     

Nonlinear Programming Problems Associated with Closed Range Operators

Necessary conditions for the optimality of a pair with respect to a locally Lipschitz cost functional L(y,u) , subject to Ay + F(y) = Cu + B(u) , are given in terms of generalized gradients. Here A and C are densely defined, closed, linear operators on some Banach spaces, while F and B are (Fréchet) differentiable maps, which are suitably related to A and C . Various examples and potential applications to nonlinear programming models and nonlinear optimal control of partial differential equations are also discussed. Accepted 18 March 1998     

Fe Spin crossover materials based on dissymmetrical N4 Schiff bases including 2-pyridyl and 2R-imidazol-4-yl rings: Synthesis,crystal structure and magnetic and Mössbauer properties

The synthesis and characterization of new symmetrical Fe^II complexes, [FeL^A(NCS)₂] (1), and [FeL^Bx(NCS)₂] (2–4), are reported (L^A is the tetradentate Schiff base N,N′-bis(1-pyridin-2-ylethylidene)-2,2-dimethylpropane-1,3-diamine, and L^Bx stands for the family of tetradentate Schiff bases N,N′-bis[(2-R-1H-imidazol-4-yl)methylene]-2,2-dimethylpropane-1,3-diamine, with: R = H for L^B1 in 2, R = Me for L^B2 in 3, and R = Ph for L^B3 in 4). Single-crystal X-ray structures have been determined for 1 (low-spin state at 293 K), 2 (high-spin (HS) state at 200 K), and 3 (HS state at 180 K). These complexes remain in the same spin-state over the whole temperature range [80–400 K]. The dissymmetrical tetradentate Schiff base ligands L^Cx, N-[(2-R₂-1H-imidazol-4-yl)methylene]-N′-(1-pyridin-2-ylethylidene)-2,2-R₁-propane-1,3-diamine (R₁ = H, Me; R₂ = H, Me, Ph), containing both pyridine and imidazole rings were obtained as their [FeL^Cx(NCS)₂] complexes, 5–10, through reaction of the isolated aminal type ligands 2-methyl-2-pyridin-2-ylhexahydropyrimidine (R₁ = H, 5–7) or 2,5,5-trimethyl-2-pyridin-2-ylhexahydropyrimidine (R₁ = Me, 8–10) with imidazole-4-carboxaldehyde (R₂ = H: 5, 8), 2-methylimidazole-4-carboxaldehyde (R₂ = Me: 6, 9), and 2-phenyl-imidazole-4-carboxaldehyde (R₂ = Ph: 7, 10) in the presence of iron(II) thiocyanate. Together with the single-crystal X-ray structures of 7 and 9, variable-temperature magnetic susceptibility and Mössbauer studies of 5–10 showed that it is possible to tune the spin crossover properties in the [FeL^Cx(NCS)₂] series by changing the 2-imidazole and/or C2-propylene susbtituent of L^Cx.     

Modular High-Intensity Monochromatic In Situ Illumination Set-Up for Investigating ESR Photoactive Centers in Semiconductors

A versatile, modular in situ high-intensity monochromatic illumination set-up installed on a standard Q-band ESR spectrometer equipped with a cryostat and probe head for measurements at cryogenic temperatures, which can be easily assembled from commercially available optical components is presented. Using as monochromatic light sources pig-tailed laser diodes (LDs) or fiber-coupled light-emitting diodes (LEDs), a high efficiency of the light transfer (more than 95%) through an optical guide inserted in the sample holder is achieved in the sample area of the microwave cavity. With various LEDs and LDs, one can perform ESR in situ illumination experiments from UV to far-IR, in both cw and pulse mode. Its operation is illustrated with an experiment revealing the presence of certain ESR silent defects in oxygen-doped floating-zone ultrapure Si samples irradiated at room temperature with high-energy–high-fluence electron beams and pulse annealed up to 300 °C. New information is obtained by comparing the ESR spectra recorded at T = 120 K, without and with 1.06 µm across-the-gap in situ illumination.     

Antibacterial and Antifungal Silver Nanoparticles with Tunable Size Embedded in Various Cellulose-Based Matrices

The aim of this study was to synthesize silver nanoparticles (AgNPs) using cellulose derivatives and to evaluate their antimicrobial potential. As effective reducing and stabilizing agents for AgNPs, cellulose derivatives, such as hydroxypropyl cellulose (HPC), methylcellulose (MC), ethylcellulose (EC), and cellulose acetate (CA), were used. Their ability to reduce silver ions as well as the size of the resulting AgNPs were compared. The formation and stability of the reduced AgNPs in the solution were monitored using UV-Vis analysis. The size, morphology, and charge of the AgNPs were evaluated. We found that, when using cellulosic derivatives, AgNPs with sizes ranging from 17 to 89 nm and different stabilities were obtained. The parameters, such as size and ζ potential indicate the stability of AgNPs, with AgNPs-CA and AgNPs-HPC being considered more stable than AgNPs-EC and AgNPs-MC since they show higher ζ potential values. In addition, the AgNPs showed antimicrobial activity against all reference strains and clinical isolates. MIC values between 0.0312 and 0.125 mM had a bactericidal effect on both Gram-positive and Gram-negative bacteria. The fungicidal effect was obtained at a MIC value of 0.125 mM. These results may provide rational support in the design of medical gauze products, including gauze pads, rolls, and sponges.