Revealing carbocations in highly asynchronous concerted reactions: The ene-type reaction between dithiocarboxylic acids and alkenes

The ene-type reaction between (dithio)carboxylic acids and alkenes has been studied computationally by DFT and topological (analysis of the electron localization function, ELF) methods. The reaction proceeds under kinetic control and the observed differences in regioselectivity are well-explained by the relative stability of the different transition structures. In agreement with experimental observations, electron-rich alkenes lead to Markownikoff adducts while electron-poor alkenes lead to Michael adducts. In all cases the reaction proceeds through an only transition structure (one kinetic step) although a different synchronicity was observed depending on the alkene electronics. The ELF analysis of the reactions corroborates the existence of a transient carbocation (hidden intermediate) in the reactions with electron-rich alkenes. On the other hand, electron-poor alkenes proceed through a more synchronous concerted mechanism. It can be predicted that with electron-rich alkenes bearing highly donating the transient carbocations might be captured by a nucleophile.     

Variable Markovnikov orientation and "cis effect" in ene reactions of nitrosocarbonyl intermediates

Nitrosocarbonyl intermediates, generated at room temperature by the mild oxidation of nitrile oxides, undergo clean ene reactions with trisubstituted olefins. Allylic hydrogens on the more congested side of the alkene are exclusively abstracted (the "cis effect"), thus resembling singlet oxygen behavior. Nitrosocarbonyl benzene follows a Markovnikov orientation and abstracts preferentially the twix hydrogens over the lone ones. With the more sterically demanding nitrosocarbonyl mesitylene, the Markovnikov directing effect is relieved, and comparable twix and lone abstraction are observed.     

Interaction of thorium(IV) with nitrate in aqueous solution: medium effect or weak complexation?

Microcalorimetric titrations were performed to study the Th(IV)/nitrate interaction in aqueous solution. The results show the formation of a weak mononuclear complex of Th(IV) with nitrate and allow the determination of the complexation thermodynamic parameters at 298 K and ionic strength 1.0 mol dm(-3). The reaction is endothermic and entropy driven. Data and comparison with similar actinide(IV) complexes allow to confirm the inner-sphere nature of the Th(NO(3))(3+) complex.     

Determination of nitrogen trichloride (NCl3) levels in the air of indoor chlorinated swimming pools: an impinger method proposal

The quality of the environmental air from indoor swimming pools has been associated with various health risks. Particular attention has focused on the effects of chronic lung exposure to chlorine and its by-products, especially in young children. We developed a simple, non-toxic approach to detect and monitor nitrogen trichloride air levels in the indoor swimming pool environment. The proposed Impinger Method (IM) was used to measure the environmental levels of nitrogen trichloride (NCl₃) in 17 indoor swimming pools located in Northern Italy. This new analytical protocol is based on a colorimetric reaction commonly employed to detect the total and free chlorine levels in water. Specifically, IM allows the entrapment of NCl₃ into a water solution containing diethyl-p-phenylenediamine (DPD 1) and Potassium Iodide (DPD 3). NCl₃ from the air environment reacts with DPD 3 releasing iodine, which reacts with DPD 1 and produces a coloration proportional to the amount of NCl₃ from the sampled indoor swimming pool air. Our sampling of the monitored swimming pool environments evidenced a mean NCl₃ level (637?±?220?µg/m³) higher than the recommended WHO value (500?µg/m³). The IM was validated in terms of linearity (R ^2?=?0.996), limit of detection (3.6?µg/m³) and repeatability (CV?=?1.7%), demonstrating easy-to-use characteristics, good efficiency and low cost.     

Effects of low-dose dexamethasone and prednisolone long term administration in beef calf: chemical and morphological investigation

An analytical, pharmacokinetic and histopathologic investigation was conducted by two experimental trials on beef cattle in order to determine fate and effects of dexamethasone and prednisolone, administered to distinct cattle groups at low dosage for long periods of time. In trial 1, eighteen Charolaise beef cattle, male, 17-22-months-old, were divided in three groups: to group A (n=6) dexamethasone-21-sodium-phosphate 0.7 mg day(-1) per os for 40 days was administered; group B (n=6) was orally treated with prednisolone 15 mg day(-1) for 30 days, while group C (n=6) served as negative control. Urine was collected at days 0, 7, 15, 25 and 47 from groups A and C, and at days 0, 8, 18 and 42 from group B. In trial 2, sixteen Friesian cattle, male, 10-17-months-old, were randomly divided into two groups: group D (n=8) was administered prednisolone 30 mg day(-1) per os for 35 days, while group K (n=8) served as control. In both trials, the animals were slaughtered after a 6-days drug withdrawal and thymus and livers were collected and properly stored until the analysis was performed. Quantitative determinations of dexamethasone, prednisolone and its main metabolite, prednisone, in urine and liver samples were conducted by HPLC-MS/MS, after the analytical procedure was optimized and fully validated. The method validation included the assessment of specificity, linearity, precision, trueness, robustness, CC(α) and CC(β) values. By a morphological point of view, severe atrophy of thymus parenchyma was observed in group A, together with a significant (P<0.005) reduction of the mean thymus weight (217±94 g), while group B (646±215 g) presented normal thymus features and weights (group C, 415±116 g). Accordingly, no differences were found in trial 2 for groups D (727±275g) and K (642±173 g). Average dexamethasone concentrations in group A urine samples ranged from 1.4 to 3.0 μg L(-1) during the treatment, while no residue was detected in the urine samples collected 6-7 days after the end of the treatment. Low amounts of dexamethasone (<1 μg L(-1)) were detected in liver samples of group A. All average prednisolone concentrations in group B urine samples (sum of conjugate and free form) turned out to be below 1.0 μg L(-1) during the treatment, despite the much higher concentration administered (15-30 mg day(-1)) with respect to dexamethasone in group A (0.7 mg day(-1)). No prednisolone residues were found in the urine and liver samples taken at the slaughterhouse. The absence of any prednisolone residue in the urine samples of control group animals supports the theory that the origin of this molecule is fundamentally exogenous, at least for this cattle category maintained under unstressing conditions. Remarkable findings are represented by the absence of thymus atrophy in the prednisolone treated animals and the extremely low residue concentrations found in urine during the treatment. Both findings reveal that the detection of illegal growth-promoting treatments with this drug is difficult.     

On the performance of cooperative systems with distributed linear block coding

Small-scale fading is one of the main problems in wireless communication systems. Multiple transmit/receive antennas, providing spatial diversity, are a common solution to combat fading, but practical constraints at the user location may limit their use. User cooperation is an efficient technique to introduce spatial diversity when multiple antennas are not suitable. In this paper we study the physical-layer performance of a cooperative system based on distributed linear block coding. Analytical results in terms of bit error rate and outage probability are presented when perfect decoding at the user location is assumed. Simulation results in terms of bit error rate are shown, taking into account the impact of errors on decoding and channel estimation at both the user location and the receiver location. Two scenarios are considered, representing uplink communications from static users to a static or mobile base station.     

Gas-Free Amino- and Alkoxycarbonylation of Aryl Iodides in a Bioinspired Deep Eutectic Solvent with Mo(CO)6 as a Safe CO Source

The Pd-catalyzed amino- and alkoxycarbonylation of aryl iodides has been exploited, for the first time, in a bioinspired Deep Eutectic Solvent and under gas-free conditions, by using Mo(CO)₆ as the CO source. The method allows for the preparation of carboxylic amides and esters in high yields (up to 99 %), short reaction time (2 h) and under mild reaction conditions (80 °C), with a low catalyst loading (2.5 mol %). Noteworthy, in the case of N-hexylbenzamide, it has been demonstrated that both the catalyst and DES can be used for four consecutive runs, with a moderate decrease of catalytic efficiency. The methodology has been also applied to the preparation of an Active Pharmaceutical Ingredient used for the treatment of human scabies and lice.