Spectroscopic study and antioxidant properties of the inclusion complexes of rosmarinic acid with natural and derivative cyclodextrins

Measurement of total antioxidant activity/capacity of polyphenols in various solvent media necessitates the use of cyclodextrins to solubilize lipophilic antioxidants of poor aqueous solubility. The inclusion complexes of the slightly water soluble antioxidant, rosmarinic acid (RA), with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), 2-hydroxyethyl-β-cyclodextrin (HE-β-CD), and methyl-β-cyclodextrin (M-β-CD) were investigated for the first time. The effect of cyclodextrins (CDs) on the spectral features of RA was measured in aqueous medium using UV-vis and steady-state fluorescence techniques by varying the concentrations of CDs. The molar stoichiometry of RA-CD inclusion complexes was verified as 1:1, and the formation constants of the complexes were determined from Benesi-Hildebrand equation using fluorescence spectroscopic data. Among the CDs, maximum inclusion ability was measured in the case of M-β-CD followed by HP-β-CD, HE-β-CD, β-CD and α-CD. Solid inclusion complexes were prepared by freeze drying, and their functional groups were analyzed by IR spectroscopy. Antioxidant capacity of CD-complexed rosmarinic acid was measured to be higher than that of the lone hydroxycinnamic acid by the CUPric Reducing Antioxidant Capacity (CUPRAC) method. The mechanism of the TAC increase was interpreted as the stabilization of the 1-e oxidized o-catechol moiety of RA by enhanced intramolecular H-bonding in a hydrophobic environment provided by CDs, mostly by M-β-CD.     

2,2′,3,4-Tetrahydroxy-3′-sulpho-5′-nitroazobenzene for spectrophotometric determination of aluminium in pharmaceutical suspensions and granite

A selective and sensitive new spectrophotometric method has been developed for the determination of aluminium. 2,2′,3,4-Tetrahydroxy-3′-sulpho-5′-nitroazobenzene (tetrahydroxyazon SN) formed an orange chelate with aluminium at pH 4. Molar absorptivity of the complex in 1:2 is 5.46 × 10⁴ l mol⁻¹ cm⁻¹ at 479 nm. The method obeys Beer's law in the range of 0.005-1.079 μg ml⁻¹. The determination of aluminium is not interfered with by earth alkaline, alkaline elements, rare earth elements, halides, phosphates, sulphates, urea, ascorbic acid, Sn²⁺, Sr²⁺, Cr³⁺, Cd²⁺, Hg²⁺, or Mn²⁺. The proposed method is rapid and simple, and it has been successfully applied to the determination of aluminium in certified pharmaceutical suspension and granite.     

An EPR and optical absorption study of VO2+ ions in di-ammonium hydrogen citrate [(NH4)2C6H6O7] single crystals

Single crystal and powder EPR studies of VO2+ doped di-ammonium hydrogen citrate [(NH4)2C6H6O7] are carried out at room temperature. The angular variation of the EPR spectra show three different VO2+ complexes that are located in different chemical environment, and each environment contains two magnetically inequivalent VO2+ sites in distinct orientations occupying substitutional positions in the lattice. Crystalline field around the VO2+ ion is nearly axial. The optical absorption spectrum shows two bands centred at 16,949 and 12,345cm(-1). Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and optical data, and results are discussed.     

Effects of MA-g-PP and lignocellulosic filler addition on several properties of poly(L-lactic acid)/polypropylene composites

The aim of this study was to investigate the effects of maleic anhydride-graft-polypropylene (MA-g-PP) as a compatibilizer and wood fiber as a lignocellulosic filler on technical properties of poly(l-lactic acid) (PLLA)/polypropylene composites. The obtained composites were characterized through mechanical tests, thermogravimetric analysis, differential scanning analyzer, and chemical analysis via Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The obtained results showed that the mechanical properties of the composites containing MA-g-PP were higher than those of the composites without MA-g-PP. SEM images revealed that the morphological properties of the composites including PP and PLLA were improved. The chemical interactions between PP and PLLA were demonstrated through FTIR results of composites with MA-g-PP.