Intermolecular interaction energies in molecular crystals: comparison and agreement of localized Møller-Plesset 2, dispersion-corrected density functional, and classical empirical two-body calculations

A comparative analysis of the intermolecular energy for a data set including 60 molecular crystals with a large variety of functional groups has been carried out using three different computational approaches: (i) a method based on a physically meaningful empirical partition of the interaction energy (PIXEL), (ii) density functional methods with a posteriori empirical correction for the dispersion interactions (DFT-D), and (iii) a full periodic ab initio quantum mechanical method based on M?ller-Plesset perturbation theory for the electron correlation using localized crystal orbitals (LMP2). Due to the large computational cost, LMP2 calculations have been restricted to a subset of seven molecular crystal comprising benzene, formic acid, formamide, succinic anhydride, urea, oxalic acid, and nitroguanidine, and the results compared with PIXEL and DFT-D data as well as with the experimental data show excellent agreement among all adopted methods. This shows that both DFT-D and PIXEL approaches are robust predictive tools for studying molecular crystals. A detailed analysis shows a very similar dispersion contribution of the two methods across the 60 considered molecular crystals. The study also confirms that pure DFT shows serious deficiencies in properly handling molecular crystals in which the dispersive contribution is large. Due to the negligible requested computational resources, PIXEL is the method of choice in screening of a large number of molecular crystals, an essential step to predict crystal polymorphism or to study crystal growth processes. DFT-D can then be used to refine the ranking emerged from PIXEL calculations due to its general applicability and robustness in properly handling short-range interactions.     

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.     

Accelerated oxidative ageing of polypropylene fibers in aqueous medium under high oxygen pressure as studied by thermal analysis

Stabilised polypropylene fibres of 28 μm diameter have been exposed at 80 °C under 5 MPa oxygen pressure, in dry conditions, in pure water and in alkaline medium. Their residual stability is determined from the temperature T_ox of the onset of the oxidation exotherm, measured by differential scanning calorimetry at 10 K min⁻¹ scanning rate. The time t_ex to reach the characteristics of unstabilised samples (T_ox=175 °C) is of the order of 220 (dry conditions), 160 h (water) and 80 h (alkaline medium), whereas it is of the order of 750 h at 110 °C in classical tests made at atmospheric pressure. This increase of ageing rate is discussed in terms of kinetic effect of O₂ pressure and efficiency of the liquid medium to extract stabilisers.     

Kinetics of Stem Elongation in Light-Grown Tomato Plants. Responses to Different Photosynthetically Active Radiation Levels by Wild-Type and aurea Mutant Plants

Abstract— In this research, we measured the short- and long-term, stem elongation responses of wild-type and aurea(au) mutant tomato plants to different photosynthetically active radiation (PAR) levels by using linear voltage transducers. Stem elongation was continuously measured in green tomato plants over 2.75 days, under 12 h light/12 h dark photoperiods or in darkness after a 6 h irradiation period. There is no significant difference in stem elongation between wild-type plants pregrown at either LOO or 400 μmol m^?2 s^?1 and then exposed to 12 h photoperiods. However, in the au mutant there is a very large difference between plants pregrown under 100 or 400 umol m ^?2 s^?1 and then exposed either to 12 h photoperiods or to continuous darkness. Total stem elongation of the wild type appears to be maximal at 100 umol m^?2 s^?1, while that of the au mutant appears to be maximal with PAR 400 umol m^?2 s^?1. Wild-type plants displayed PAR-dependent (in the range 100-800 umol m^?2 s^?1) inhibition of growth both during the day and during the night. In contrast, the au mutant showed a fluence-rate-dependent promotion of growth during the dark periods in the range of 10-400 umol m^?2 s^?1. Large, fast and opposite changes in stem elongation rate at the light/dark and dark/light transitions were present in both genotypes. Internode elongation rate in the first half of the night was always modest in wild-type tomato, whereas it increased rapidly in the au mutant. Stem elongation rate of wild type starts to increase after about 6 h in darkness, showing the typical time course of escape from Pfr-mediated inhibition of elongation by an end-of-day response. The role of phytochrome level and type in sensing light quantity is discussed.