Cis-trans isomeric and polymorphic effects on the magnetic properties of water-bridged copper coordination chains

The synthesis and magnetic characterization of vanillin-based Cu(II) mononuclear complexes of formula [Cu(van)(2)(H(2)O)(2)](H(2)O)(x) (van = vanillinate; x = 0, compound 1; x = 2, compounds 2 and 3) were performed. Despite the presence of very similar [Cu(van)(2)(H(2)O)(2)] moieties, the crystal structures exhibit distinct Cu···Cu contacts and display three different through-H-bond exchange-coupling pathways. As a result of the relative positions of the water molecules, the experimental (MAGSUS) exchange-coupling constants are dissimilar, i.e., J(1) = -3.0 cm(-1) (the data have been fitted to the Bleaney-Bowers equation considering a dimer; 2J = -6.0 cm(-1)), J(2) = -4.0 cm(-1) (the data have been fitted to the Bonner-Fischer equation for a chain of monomeric copper(II) units), whereas compound 3 is paramagnetic. Subsequently, the theoretical density functional theory (DFT) and wave function theory-based (DDCI) calculations were carried out to better understand the role of the water molecule as a mediator of the magnetic coupling. The use of localized orbitals allows one to elucidate the role of the H-bonds in generating exchange interactions. Since the exchange-coupling constants are strongly dependent on the mechanisms selectively introduced, the role of the H-bond is demonstrated.     

On the specificity of cyclodextrin complexes detected by electrospray mass spectrometry

Alpha-cyclodextrin complexes with linear alpha,omega-dicarboxylic acids were investigated by electrospray mass spectrometry. These hydrophobic complexes are known to have an equilibrium binding constant that increases with the diacid chain length. However, the electrospray mass spectrometry (ES-MS) spectra showed that the relative intensity of the complex did not vary significantly with chain length. This contradiction is caused by a contribution of nonspecific adducts to the signal of the complex in ES-MS. In order to estimate the contribution of nonspecific adducts to the total intensity of the complexes with alpha-cyclodextrin, the comparison was made between alpha-cyclodextrin and maltohexaose, the latter being incapable of making inclusion complexes in solution. The signal observed for complexes between diacids and maltohexaose can only result from nonspecific electrostatic aggregation, and is found to be more favorable with the shorter diacids. This is also supported by MS/MS experiments. A procedure is described which allows estimation of the contribution of the nonspecific complex in the spectra of the complexes with alpha-cyclodextrin by using the relative intensity of the complex with maltohexaose. The contribution of the specific complex to the total signal intensity is found to increase with the diacid chain length, which is in agreement with solution behavior.     

Electrochemical/chemical synthesis of hydroxyapatite on glassy carbon electrode for electroanalytical determination of cysteine

Journal of Solid State Electrochemistry - Hydroxyapatite (HAp)-modified glassy carbon (HAp/GC) electrode was prepared through a two-step chemical reaction process: Hydrogenphosphate, firstly formed...     

Copper(II) coordination compounds with ferulic acid

The first two molecular structures of the ferulic acid (3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid, C₁₀H₁₀O₄) coordination compounds are presented, namely, [Cu₂(C₁₀H₉O₄)₄(CH₃CN)₂] 1 and [Cu₂(C₁₀H₉O₄)₄(C₆H₆N₂O)₂]·4CH₃CN (C₆H₆N₂O = nicotinamide) 2. Both compounds were synthesised from the starting mixture of Cu₂O and CuCl upon copper oxidation in the acetonitrile solution. The single-crystal X-ray diffraction analysis of 1 and 2 reveals the binuclear structure of the ‘paddle–wheel’ type for both complexes. 1 and 2 are unstable outside mother liquid due to loosely bound acetonitrile molecules. The final products of decomposition are [Cu₂(C₁₀H₉O₄)₄] 1a and [Cu₂(C₁₀H₉O₄)₄(C₆H₆N₂O)₂] 2a, which were characterized by several physico-chemical methods. The triplet X-band EPR spectra of 1a and 2a, showing signals B_Z1  15 mT, B₂  460 mT and B_Z2  580 mT, are in agreement with the expected data for the binuclear tetracarboxylate units, found in the structures of the parent complexes 1 and 2. Together with the room temperature magnetic susceptibility data, μ_eff/B.M. 1.40 (1a), 1.48 (2a), the EPR spectra analysis confirm the antiferromagnetic interaction in 1a and 2a. This is suggesting preservation and stability of the paddle–wheel structures in 1a and 2a.     

Micro-HPLC–UV analysis of cocaine and its adulterants in illicit cocaine samples seized by Austrian police from 2012 to 2017

The worldwide consumption of illicit drugs presents a big problem in terms of health care and prosecution. In the recent years, hundreds of novel psychoactive substances came up and were traded through the Internet, but there is still a big demand for classic illicit drugs such as cocaine, heroin, cannabis, and ecstasy. Among these, cocaine particularly is frequently altered not only with excipients but also with other physiologically active substances. The purpose of this work was to estimate the trend of cocaine purity and abundance of its adulterants in samples seized by Austrian police from 2012 to 2017. A micro-HPLC method for quantification of cocaine and its most common adulterants was developed and validated using gradient elution and UV detection at four wavelengths. A total of 110 cocaine samples were analyzed. In all the samples, cocaine was present as hydrochloric salt. Caffeine, procaine, levamisole, phenacetin, lidocaine, and benzocaine were the most abundant adulterants.     

Soil respiration rates and δ13C(CO2) in natural beech forest (Fagus sylvatica L.) in relation to stand structure

Soil respiration rates were studied as a function of soil type, texture and light intensity at five selected natural beech forest stands with contrasting geology: stands on silicate bedrock at Kladje and Bricka in Pohorje, a stand on quartz sandstone at Vrhovo and two stands on a carbonate bedrock in the Karstic-Dinaric area in Kocevski Rog, Snezna jama and Rajhenav, Slovenia, during the growing season in 2005-2006. Soil respiration exhibited pronounced seasonal and spatial variations in the studied forest ecosystem plots. The CO(2) flux rates ranged from minimum averages of 2.3?μmol CO(2) m(-2) s(-1) (winter) to maximum averages of about 7?μmol CO(2) m(-2) s(-1) (summer) at all the investigated locations. An empirical model describing the relationship between soil respiration and soil temperature predicted seasonal variations in soil respiration reasonably well during 2006. Nevertheless, there were also some indications that soil moisture in relation to soil texture could influence the soil CO(2) efflux rates in both sampling seasons. It was shown that spatial variability of mean soil respiration at the investigated sites was high and strongly related to root biomass. Based on the [image omitted] data, it was shown that new photoassimilates could account for a major part of the total soil respiration under canopy conditions in forest ecosystems where no carbonate rocks are present, indicating that microbial respiration could not always dominate bulk soil CO(2) fluxes. At Snezna jama and Rajhenav, the abiotic CO(2) derived from carbonate dissolution had a pronounced influence on CO(2) efflux accounting, on average, to ～17%. Further spatial heterogeneity of soil respiration was clearly affected by management practice. Higher respiration rates as well as higher variability in respiration rates were observed in the virgin forest (Rajhenav) than in the management forest (Snezna jama) and could be related to a higher amount of detritus and consequently to less pronounced influence of inorganic pool to CO(2) efflux, lower mixing with atmospheric CO(2) and higher sensitivity to environmental changes. Major differences in soil carbon dynamics among these five forest ecosystems can be explained by the influence of bedrock geology (particularly, the presence or absence of carbonate minerals) and soil texture (affecting gas exchange with overlying air and soil moisture).     

Kinematic Model for Determination of Human Arm Reachable Workspace

In physiotherapy, a standard method to determine the movability and functionality of the human arm is to measure the ranges of motion in joints in sagittal, horizontal and frontal plane. It is clear, however, that these angles can hardly interpret the characteristics of the arm. The main idea in the article is to combine these angles with an adequate kinematic model in order to compute and graphically represent the reachable workspace of the arm, which then serves as an advanced criterion for a more objective evaluation. In this article, we report an improved kinematic model of the human arm which is appropriate for computing and visualizing the human arm reachable workspace. Optical measurements were performed to define the structure and parameters of the model and to develop the mathematical relations between the joint angles. The kinematic model was implemented in a computer programme which is now being introduced in practice and can be used in rehabilitation, ergonomics and sports.     

Carbon isotope fractionation in the decarboxylation of phenylpropiolic acid in hydrogen donating media

13C kinetic isotope effect (KIE) in the decarboxylation of phenylpropiolic acid (PPA) in tetralin medium (Tn) has been determined at 409-432 K and found to be of magnitude similar to the 13C KIE observed in the decarboxylation of malonic acid where the rupture of the C-C bond is the rate determining step. 13C KIE equals 1.0318/at 136 degrees C in the decarboxylation of PPA in Tn medium. Intramolecular 13C KIE in the decarboxylation of malonic acid equals 1.0316 at this temperature. Thus it has been shown that the nearly "full" 13C KIE can be achieved by providing the excess hydrogen to Calpha of PPA (or to triple acetylene bond) using not only strong mineral acids as the source of protons but also by carrying out the decarboxylation in organic medium like tetralin. A mechanism of decarboxylation of PPA in Tn is suggested.