Mg-Al layered double hydroxide intercalated with porphyrin anions: molecular simulations and experiments.

Molecular modeling in combination with powder X-ray diffraction (XRD) provided new information on the organization of the interlayer space of Mg-Al layered double hydroxide (LDH) containing intercalated porphyrin anions [5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS)]. Anion-exchange and rehydration procedures were used for the preparation of TPPS-containing LDH with an Mg/Al molar ratio of 2. Molecular modeling was carried out in the Cerius(2) and Materials Studio modeling environment. Three types of models were created in order to simulate the experimental XRD patterns of LDH intercalates with a TPPS loading of 70-80% with respect to the theoretical anion exchange capacity (AEC). The models represent single-phase systems with a 100% TPPS loading in the interlayer space (Type 1) and models represent the coexistence of two phases corresponding to the total exchange from 75 to 92% (Type 2). To cover other possible arrangements, models with the coexistence of both TPPS and NO(3)(-) anions in the same interlayer space were calculated (Type 3). The models are described and compared with experimental data. In all cases, guest TPPS anions are tilted with respect to the hydroxide layers, and are horizontally shifted to each other by up to one-half of the TPPS diameter. According to the energy characteristics and simulated XRD, the most probable arrangement is of Type 2, where some layers are saturated with TPPS anions and others are filled with original NO(3)(-) anions.

The evaluation of nociceptive intensity by using free radicals direct measurement by EPR method in the tail of anaesthetized rats.

OBJECTIVES: The aim of the study was to demonstrate the ability to measure free radicals and singlet oxygen, using EPR methods, in the tail of anaesthetized rats. The advantage of this method lies in the potential for continuous evaluation of free radicals and singlet oxygen during nociceptive processes. METHODS: Electron paramagnetic (spin) resonance (EPR/ESR) was used. DMPO and PBN as spin traps and thermal mechanical pulp (TMP) as a spin detector of singlet oxygen were used. Thirty-one adult male (Wistar) rats were used for the experiments. They were housed according to principles of good laboratory practice. The animals were stimulated for 10 minutes on 5 consecutive days by using clamps on the hind limbs. During the EPR measurement they were anaesthetized with a mixture of ketamine and xylazine. Hydroxyl and nitroxide free radicals, as well as singlet oxygen were measured. RESULTS: After nociceptive stimulation, free hydroxyl radicals were increased as well as free nitroxide radicals. Singlet oxygen was also increased after nociceptive stimulation. Antioxidants significantly decreased the increase in hydroxyl radicals after nociceptive stimulation. CONCLUSIONS: Our results confirmed an increase in free radicals and singlet oxygen after nociceptive stimulation and a reduced increase after application of antioxidants. Direct EPR methods were first used in the tail of anaesthetized rats and represent an extremely useful tool for the evaluation of pain intensity in living animals.