the molecular motion of bovine serum albumin under physiological conditions is ion specific

Specific ion effects on the Brownian motion of BSA protein under physiological conditions give new useful insights into the electrolyte–protein interactions and the molecular mechanisms involved in the Hofmeister effect

A bienzymatic biocatalyst constituted by glucose oxidase and Horseradish peroxidase immobilized on ordered mesoporous silica

It is presently extremely challenging to realize an active immobilized multi-enzyme biocatalyst which allows to run in vitro multi-step cascade reactions. This work deals with the obtainment of a bienzymatic immobilized biocatalyst constituted by Glucose Oxidase (GOx) and Horseradish Peroxidase (HRP) immobilized onto SBA-15 mesoporous silica. The effect of co-immobilization (GOx/HRP@SBA-15) versus the separated immobilization (GOx@SBA-15/HRP@SBA-15), and the effect of covalent versus physical immobilization, on protein loading and enzymatic activity were investigated. Regardless the different immobilization strategy used, it was found that the catalytic activity could be retained only if the immobilized bienzymatic biocatalyst was kept wet. The obtained wet GOx/HRP@SBA-15 biocatalyst could be recycled 14 times keeping a good activity. Finally, the bienzymatic biocatalyst was tested for the oxidation of two model phenolic (caffeic acid and ferulic acid) pollutants of agricultural wastewaters, as olive mill wastewaters (OMWs). The biocatalyst was able to reach a 70% conversion within 15 min

Hofmeister Effects in Enzymatic Activity: Weak and Strong Electrolyte Influences on the Activity of Candida rugosa Lipase

The effects of weak and strong electrolytes on the enzymatic activity of Candida rugosa lipase are explored. Weak electrolytes, used as buffers, set the pH, while strong electrolytes regulate the ionic strength. The interplay between pH and ionic strength has been assumed to be the determinant of enzymatic activity. In experiments that probe activities by varying these parameters, there has been little attention focused on the role of specific electrolyte effects. Here we show that both buffers and the choice of background electrolyte ion strongly affect the enzymatic activity of Candida rugosa lipase. The effects here shown are dramatic at high salt concentration; indeed, a 2 M concentration of NaSCN is able to fully inactivate the lipase. By contrast, Na2-SO4 acts generally as an activator, whereas NaCl shows a quasi-neutral behavior. Such specific ion effects are well-known and are classified among the "Hofmeister effects". However, there has been little awareness of them, or of their potential for optimization of activities in the enzyme community. Rather than the effects per se, the focus here is on their origin. New insights into mechanism are proposed

Adsorption and release of ampicillin antibiotic from ordered mesoporous silica

In this work the adsorption and the release of ampicillin - a β-lactam penicillin-like antibiotic - from MCM-41, SBA-15, and (amino functionalized) SBA-15-NH2 ordered mesoporous silica (OMS) materials were investigated. The silica matrices differ for their pore size (SBA-15 vs. MCM-41) mainly, and also for surface charge (SBA-15 and MCM-41, vs. SBA-15-NH2). OMS samples were characterized through small-angle X-rays scattering (SAXS), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and potentiometric titrations. The quantification of immobilized and released ampicillin was monitored by mean of UV–Vis spectroscopy. Experimental adsorption isotherms evidenced that ampicillin's loading is not related to the pore size (dBJH) of the adsorbent. Indeed the maximal loadings were 237 mg/g for SBA-15 (dBJH = 6.5 nm), 278 mg/g for MCM-41 (dBJH = 2.2 nm), and 333 mg/g for SBA-15-NH2 (dBJH = 5.6 nm). Loading seems, instead, to be related to the surface charge density (σ) of the sorbent surface. Indeed, at pH 7.4 ampicillin drug is negatively charged and likely prefers to interact with SBA-15-NH2 (σSBA-15-NH2 = +0.223 C m−2) rather than the slightly negatively charged silicas (σSBA-15 = −0.044 C m−2 and σMCM-41 = −0.033 C m−2). Similarly, ampicillin release is affected by interfacial interactions. Indeed, we found a burst release from pure silica samples (SBA-15 and MCM-41), whereas a sustained one from SBA-15-NH2 sample. We explain this behavior as a result of an attractive interaction between the protonated amino group of SBA-15-NH2 and the negatively charged carboxylate group of ampicillin. In summary, in order to obtain a sustained drug release, the chemical nature of the matrix's surface plays a role which is more important than its textural features. SBA-15-NH2 matrix is hence a suitable candidate for local sustained release of antibiotic drugs

Adsorption and release of sulfamethizole from mesoporous silica nanoparticles functionalised with triethylenetetramine

Mesoporous silica nanoparticles (MSN) were synthesised and functionalised with tri-ethylenetetramine (MSN-TETA). The samples were fully characterised (transmission electron mi-croscopy, small angle X-ray scattering, Fourier transform infrared spectroscopy, thermogravimetric analysis, zeta potential and nitrogen adsorption/desorption isotherms) and used as carriers for the adsorption of the antimicrobial drug sulphamethizole (SMZ). SMZ loading, quantified by UV–Vis spectroscopy, was higher on MSN-TETA (345.8 mg g−1) compared with bare MSN (215.4 mg g−1) even in the presence of a lower surface area (671 vs. 942 m2 g−1). The kinetics of SMZ adsorption on MSN and MSN-TETA followed a pseudo-second-order model. The adsorption isotherm is described better by a Langmuir model rather than a Temkin or Freundlich model. Release kinetics showed a burst release of SMZ from bare MSN samples (k1 = 136 h−1) in contrast to a slower release found with MSN-TETA (k1 = 3.04 h−1), suggesting attractive intermolecular interactions slow down SMZ release from MSN-TETA. In summary, the MSN surface area did not influence SMZ adsorption and release. On the contrary, the design of an effective drug delivery system must consider the intermolecular interactions between the adsorbent and the adsorbate

BSA Fragmentation Specifically Induced by Added Electrolytes: an Electrospray Ionization Mass Spectrometry Investigation

Biointerfaces are significantly affected by electrolytes according to the Hofmeister series. This work reports a systematic investigation on the effect of different metal chlorides, sodium and potassium bromides, iodides and thiocyanates, on the ESI/MS spectra of bovine serum albumin (BSA) in aqueous solution at pH = 2.7. The concentration of each salt was varied to maximize the quality of the ESI/MS spectrum, in terms of peak intensity and bell-shaped profile. The ESI/MS spectra of BSA in the absence and in the presence of salts showed a main protein pattern characterized by the expected mass of 66.5 kDa, except the case of BSA/RbCl (mass 65,3 kDa). In all systems we observed an additional pattern, characterized by at least three peaks with low intensity, whose deconvolution led to suggest the formation of a BSA fragment with a mass of 19.2 kDa. Only NaCl increased the intensity of the peaks of the main BSA pattern, while minimizing that of the fragment. NaCl addition seems to play a crucial role in stabilizing BSA ionized interface against hydrolysis of peptide bonds, through different synergistic mechanisms. To quantify the observed specific electrolyte effects, two “Hofmeister” parameters (Hs and Ps) are proposed. They are obtained using the ratio of (BSA-Salt)/BSA peak intensities for both the BSA main pattern and for its fragment