Infrared and NMR study of some 2-styrylindolium dyes

A series of 18 molecules of the 2-styrylindolium dyes group is examined by means of infrared and ¹H NMR spectroscopy. The effect of electron-withdrawing and electron-releasing substituents on the spectral behavior of the compounds is assessed and the most appropriate structure for these molecules is suggested.     

On the Mixed Crystals Formation in the Fe(Zn) (HCOO)2–Cd(HCOO)2–H2O System

The solubility in the Fe(HCOO)₂–Cd(HCOO)₂–H₂O and Zn(HCOO)₂–Cd(HCOO)₂–H₂O systems have been studied by the method of physico-chemical analysis at 25 °C and mixed crystals of the type Fe_1-xCd_x(HCOO)₂.2 H₂O and Zn_1-xCd_x (HCOO)₂. 2 H₂O have been obtained. The lattice parameters of the mixed crystals have been calculated. It has been established that the isostructural Fe(HCOO)₂. 2 H₂O and Cd(HCOO)₂. 2 H₂O form isomorphous mixed crystals, whereas the isostructural Zn(HCOO)₂. 2 H₂O and Cd(HCOO)₂. 2 H₂O yield isodimorphous mixed crystals. The difference in the behaviour of the two pairs of formate salts has been attributed to the difference in the Me–O_m, bond lengths in the coordination octahedra, forming the crystal structures.     

Polymer-Modified Single-Walled Carbon Nanotubes Affect Photosystem II Photochemistry,Intersystem Electron Transport Carriers and Photosystem I End Acceptors in Pea Plants

Single-walled carbon nanotubes (SWCNT) have recently been attracting the attention of plant biologists as a prospective tool for modulation of photosynthesis in higher plants. However, the exact mode of action of SWCNT on the photosynthetic electron transport chain remains unknown. In this work, we examined the effect of foliar application of polymer-grafted SWCNT on the donor side of photosystem II, the intersystem electron transfer chain and the acceptor side of photosystem I. Analysis of the induction curves of chlorophyll fluorescence via JIP test and construction of differential curves revealed that SWCNT concentrations up to 100 mg/L did not affect the photosynthetic electron transport chain. SWCNT concentration of 300 mg/L had no effect on the photosystem II donor side but provoked inactivation of photosystem II reaction centres and slowed down the reduction of the plastoquinone pool and the photosystem I end acceptors. Changes in the modulated reflection at 820 nm, too, indicated slower re-reduction of photosystem I reaction centres in SWCNT-treated leaves. We conclude that SWCNT are likely to be able to divert electrons from the photosynthetic electron transport chain at the level of photosystem I end acceptors and plastoquinone pool in vivo. Further research is needed to unequivocally prove if the observed effects are due to specific interaction between SWCNT and the photosynthetic apparatus.     

DTA,DSC, and X-ray Powder Diffraction Studies on Some Zinc Selenate Hydrates

The thermal dehydration of ZnSeO₄ · 6 H₂O, ZnSeO₄ · 5 H₂O, and ZnSeO₄ · 3 H₂O has been studied by TG, DTA, and DSC-analyses. It has been established that the dehydration of ZnSeO₄ · 6 H₂O occurs stepwise and as intermidiate hydrates ZnSeO₄ · 5 H₂O, ZnSeO₄ · 3 H₂O and ZnSeO₄ · H₂O are produced. The enthalpy of dehydration of the observed phase transitions has been determined. The enthalpy of formation of ZnSeO₄ · 6 H₂O, ZnSeO₄ · 5 H₂O, ZnSeO₄ · 3 H₂O, and ZnSeO₄ · H₂O has been calculated on the basis of the DSC-data. ZnSeO₄ · 5 H₂O and ZnSeO₄ · 3 H₂O have been studied rentgenographically: ZnSeO₄ · 5 H₂O crystallizes in triclinic system with lattice parameters: a = 6.387(2) Å; b = 10.706(3) Å; c = 6.167(3) Å; α = 98.66(2)°; β = 109.32(3)° γ = 75.52(3)° V = 384.3(2) ų; SG P1 . ZnSeO₄ · 3 H₂O forms orthorhombic crystals with lattice constants: a = 8.165(4)Å; b = 11.314(5) Å; c = 12.465(7) Å; V = 1151.5(7) ų; SG Pbca.     

Transition metal complexes with thiosemicarbazide-based ligand – Part LV: Synthesis and X-ray structural study of novel Ni(II) complexes with pyridoxal semicarbazone and pyridoxal thiosemicarbazone

Reaction of aqueous solutions of Ni(NO₃)₂ and pyridoxal semicarbazone (PLSC) in the presence of NaN₃ afforded two complexes, viz. green, paramagnetic binuclear octahedral [Ni₂(PLSC)₂(μ_1,1-N₃)₂(N₃)₂] · 2H₂O (1) and, as admixture, red, octahedral [Ni(PLSC–H)₂] · 2H₂O (2) complex. Under the same reaction conditions, pyridoxal thiosemicarbazone (PLTSC) gave only one diamagnetic square-planar, red complex [Ni(PLTSC–H)N₃] · H₂O (3). In the absence of NaN₃, the reaction of PLTSC and Ni(NO₃)₂ yielded brown paramagnetic octahedral complex [Ni(PLTSC)₂](NO₃)₂ · H₂O (4).     

Antimicrobial Triterpenoids and Ingol Diterpenes from Propolis of Semi-Arid Region of Morocco

The chemical composition and antimicrobial activity of propolis from a semi-arid region of Morocco were investigated. Fifteen compounds, including triterpenoids (1, 2, 7–12), macrocyclic diterpenes of ingol type (3–6) and aromatic derivatives (13–15), were isolated by various chromatographic methods. Their structures were elucidated by a combination of spectroscopic and chiroptical methods. Compounds 1 and 3 are new natural compounds, and 2, 4–6, and 9–11 are newly isolated from propolis. Moreover, the full nuclear magnetic resonance (NMR) assignments of three of the known compounds (2, 4 and 5) were reported for the first time. Most of the compounds tested, especially the diterpenes 3, 4, and 6, exhibited very good activity against different strains of bacteria and fungi. Compound 3 showed the strongest activity with minimum inhibitory concentrations (MICs) in the range of 4–64 µg/mL. The combination of isolated triterpenoids and ingol diterpenes was found to be characteristic for Euphorbia spp., and Euphorbia officinarum subsp. echinus could be suggested as a probable and new plant source of propolis.     

Spectral analysis and crystal structure of a new mononuclear copper(II) complex of 3-aminopyridine

A new Cu(II)-complex of 3-aminopyridine, [CuCl(3-AP)₄][Cu(3-AP)₄(H₂O)]Cl₃ · 2H₂O (1), containing two contrasting complex cations has been synthesized and structurally characterized by single crystal X-ray diffraction and solid-state linear-dichroic infrared (IR-LD) spectral analysis. In both cations four 3-AP molecules coordinate the Cu(II) atom in a monodentate fashion through their endocyclic (N_py) nitrogens, thereby generating a square-planar coordination geometry for the CuN₄ chromophor. Perpendicular to the N₄ plane, the metal ion is coordinated by a chloride anion in the first cation and a water ligand in the second cation. One of three additional water molecules of crystallization occupies the vacant octahedral site of the second cation and participates in a weak Cu···OH₂ interaction. An IR-LD spectral analysis of the samples, oriented as a suspension in a nematic liquid crystal confirmed the crystallographic data and the retention of the pyridine ring aromatic character after coordination. The presented results are additionally supported by UV, ¹H-NMR, EPR and MS analysis and by thermogravimetric and calorimetric data.     

Special manifolds and shape fibrator properties

Our main interest in this paper is further investigation of the concept of (PL) fibrators (introduced by Daverman [R.J. Daverman, PL maps with manifold fibers, J. London Math. Soc. (2) 45 (1992) 180-192]), in a slightly different PL setting. Namely, we are interested in manifolds that can detect approximate fibrations in the new setting. The main results state that every orientable, special (a new class of manifolds that we introduce) PL n-manifold with non-trivial first homology group is a fibrator in the new category, if it is a codimension-2 fibrator (Theorem 8.2) or has a non-cyclic fundamental group (Theorem 8.4). We show that all closed, orientable surface S with χ(S)<0 are fibrators in the new category.     

Bifocal-polarization holographic lens

We present a holographic lens with novel features recorded in an azopolymer film. Two holographic modulations, bulk birefringence and surface relief, are induced in the medium at the same time. The resultant holographic element has two focal planes, and the polarization of light in the focal points depends on the polarization of the incident light. Applications of this device for writing-reading information in two planes simultaneously or separately are described.     

Thermal behavior of some aromatic copolyethers containing a propylenic spacer

The main objective of this paper is to study the thermal stability of some aromatic copolyethers containing a propylenic spacer. Some of the investigated copolyethers displayed a liquid crystalline (LC) behavior, with the presence of the mesogenic groups in the main chain, inducing high values of the thermal transition temperatures. As a consequence, a thermal stability study was necessary to establish the maximum temperature value for the LC behavior characterization. A thermal degradation mechanism is proposed, taking into consideration the azobenzenic unit as the weakest link in the polymer chain and thus, the starting point of the thermal degradation process. The degradation mechanisms were correlated with the chemical structure and the polarity and conformation of the chains. Conformational analysis was performed using molecular simulations. Freeman-Caroll and Coats-Redfern methods were used to calculate some kinetic characteristics.