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Sophisticated and Spontaneous Template-Free Organization of Silica Nanoparticles During Storage
Nina Bogdanchikova,Oxana Martynyuk,Roberto L. Vazquez-Gomez,Francisco Ruiz,Alejandro Huerta-Saquero,Trino A. Zepeda,Alexey Pestryakov,Josue D. Mota-Morales 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.4
Hierarchical self-assembling of materials represents one of the most appealing subjects in nanoscience, since bottom-up strategies allow for tailor-made synthesis of functional structures in commodities as well as in living systems. Herein we show that nanorings of ca. 10 nm silica nanoparticles without any inorganic metal oxide or organic participant are able to spontaneously self-assemble presenting sophisticated forms and hierarchy. It was observed that after synthesis, silica nanoparticles are chaotically distributed but during storage at ambient conditions they spontaneously form self-assembled aggregates with multiplicity of morphologies when a small amount of water is added in the environment. Detailed description of the morphology of such structures by high resolution transmission electron microscope (HRTEM) is presented together with a discussion about the role of water during their spontaneous formation.
( Moreno Enriquez Angelica ),( Zahaed Evangelista Martinez ),( Edith G. Gonzalez-mondragon ),( Arturo Calderon Flores ),( Roberto Arreguin ),( Ernesto Perez Rueda ),( Alejandro Huerta Saquero ) 한국미생물 · 생명공학회 2012 Journal of microbiology and biotechnology Vol.22 No.3
We report the expression, purification, and characterization of L-asparaginase (AnsA) from Rhizobium etli. The enzyme was purified to homogeneity in a single-step procedure involving affinity chromatography, and the kinetic parameters Km, Vmax, and kcat for L-asparagine were determined. The enzymatic activity in the presence of a number of substrates and metal ions was investigated. The molecular mass of the enzyme was 47 kDa by SDS-PAGE. The enzyme showed a maximal activity at 50oC, but the optimal temperature of activity was 37oC. It also showed maximal and optimal activities at pH 9.0. The values of Km, Vmax, kcat, and kcat/Km were 8.9±0.967×10-3 M, 128±2.8 U/mg protein, 106±2 s-1, and 1.2±0.105×104M-1s-1, respectively. The L-asparaginase activity was reduced in the presence of Mn2+, Zn2+, Ca2+, and Mg2+ metal ions for about 52% to 31%. In addition, we found that NH4 +, L-Asp, D-Asn, and β-aspartyl-hydroxamate in the reaction buffer reduced the activity of the enzyme, whereas L-Gln did not modify its enzymatic activity. This is the first report on the expression and characterization of the L-asparaginase (AnsA) from R. etli. Phylogenetic analysis of asparaginases reveals an increasing group of known sequences of the Rhizobialtype asparaginase II family.