Study of structural and optical properties of iron doped ZnO thin films prepared by sol-gel

Fe doped ZnO thin films with various levels of iron doping concentration (0, 1, 2, 3 at.%) content were produced by sol-gel dip coating method. The influence of Fe doping on the structural, morphological and optical properties of ZnO thin films was investigated. X-ray diffraction has shown that the films are polycrystalline and textured with the hexagonal structure. Scanning electron microscope has indicated that crystallites dispersion in the films is generally homogeneous and the particle morphology changes with increase in the doping concentration. FTIR measurements show that the intensity of Zn-O band increases with increasing doping concentration and the UV-visible transmittance results show a high transparency in the visible range. The room temperature photoluminescence (PL) spectra of Fe doped ZnO indicate that the green-orange emission decrease with increasing Fe doping

Effect of tris buffer in the intensity of the multipoint covalent immobilization of enzymes in glyoxyl-agarose beads

Tris is an extensively used buffer that presents a primary amine group on its structure. In the present work trypsin, chymotrypsin and penicillin G acylase (PGA) were immobilized/stabilized on glyoxyl agarose in presence of different concentrations of Tris (from 0 to 20 mM). The effects of the presence of Tris during immobilization were studied analyzing the thermal stability of the obtained immobilized biocatalysts. The results indicate a reduction of the enzyme stability when immobilized in the presence of Tris. This effect can be observed in inactivations carried out at pH 5, 7, and 9 with all the enzymes assayed. The reduction of enzyme stability increased with the Tris concentration. Another interesting result is that the stability reduction was more noticeable for immobilized PGA than in the other immobilized enzymes, the biocatalysts prepared in presence of 20 mM Tris lost totally the activity at pH 7 just after 1 h of inactivation, while the reference at this time still kept around 61 % of the residual activity. These differences are most likely due to the homogeneous distribution of the Lys groups in PGA compared to trypsin and chymotrypsin (where almost 50% of Lys group are in a small percentage of the protein surface). The results suggest that Tris could be affecting the multipoint covalent immobilization in two different ways, on one hand, reducing the number of available glyoxyl groups of the support during immobilization, and on the other hand, generating some steric hindrances that difficult the formation of covalent bonds

Effect of amine length in the interference of the multipoint covalent immobilization of enzymes on glyoxyl agarose beads

1 Tabla.-- 17 FigurasTrypsin, chymotrypsin, penicillin G acylase and ficin extract have been stabilized by immobilization on glyoxyl agarose, adding different aliphatic compounds bearing a primary amine group during the immobilization: ethyl amine, butyl amine, hexyl amine (at concentrations ranging from 0 to 20 mM) and octyl amine (from 0 to 10 mM) to analyze their effects on the immobilized enzyme stability. As expected, the presence of amines reduced the intensity of the enzyme-support multipoint covalent attachment, and therefore the enzyme stability. However, it is clear that this effect is higher using octyl amine for all enzymes (in some cases the enzyme immobilized in the presence of 10 mM octyl amine was almost inactivated while the reference kept over 50 % of the initial activity). This way, it seems that the most important effect of the presence of aminated compounds came from the generation of steric hindrances to the enzyme/support multi-reaction promoted by the ammines that are interacting with the aldehyde groups. In some instances, just 1 mM of aminated compounds is enough to greatly decrease enzyme stability. The results suggested that, if the composition of the enzyme extract is unknown, to eliminate small aminated compounds may be necessary to maximize the enzyme-support reaction.We gratefully recognize the financial support from Ministerio de Ciencia e Innovación-Spanish Government (project number CTQ2017-86170-R). RMS thank to Ministerio de Educacion -Spanish Government for a FPU fellowship, SAB and EHS thank Algerian Ministry of higher education and scientific research for their fellowships. The help and suggestions from Dr. Ángel Berenguer (Departamento de Química Inorgánica, Universidad de Alicante) are gratefully recognized.Peer reviewe