Electrochemical impedance spectroscopy reveals a new mechanism based on competitive binding between Tris and protein on a conductive biomimetic polydopamine surface.

A novel mechanism was developed to study the interaction of mussel inspired polydopamine surfaces with bovine serum albumin using cyclic voltammetry and electrochemical impedance spectroscopy supplemented with XPS, IR spectroscopy, UV spectroscopy and atomic force microscopy. The polydopamine surfaces reveal different mechanisms that give a new insight into understanding the interaction with BSA under the variable conditions used for PDA preparation and BSA adsorption. The study provides an in-depth analysis of the orientations and interactions of BSA with polydopamine surfaces. The protein interaction behavior changed significantly in different environments including different pH values and concentrations of buffer and it revealed a competitive binding mechanism of protein binding. The study provides an outlook for studying the interaction of protein foulants with PDA, which should be carried out in nucleophilic buffers, while the covalent binding or immobilization of biomolecules to PDA surfaces should be carried out in non-nucleophilic buffer for higher efficiency.

Application of a Biodegradable Polyesteramide Derived from L-Alanine as Novel Excipient for Controlled Release Matrix Tablets.

This pre-formulation study assays the capacity of the polyesteramide PADAS, poly (L-alanine-dodecanediol-L-alanine-sebacic), as an insoluble tablet excipient matrix for prolonged drug release. The flow properties of PADAS were suitable for tableting, and the compressibility of tablets containing exclusively PADAS was evaluated by ESEM observation of the microstructure. The tablets were resistant to crushing and non-friable and they did not undergo disintegration (typical features of an inert matrix). Tablets containing 33.33% sodium diclofenac (DF), ketoprofen (K) or dexketoprofen trometamol (DK-T) as a model drug, in addition with 66.67% of polymer, were formulated, and the absence of interactions between the components was confirmed by differential scanning calorimetry. Dissolution tests showed that PADAS retained DF and K and prolonged drug release, following a Higuchi kinetic. The tablets containing DK-T did not retain the drug sufficiently for prolonged release to be established. Tablets containing DK-T and 66.67, 83.33 or 91.67% PADAS, compressed at 44.48 or 88.96 kN, were elaborated to determine the influence of the polymer amount and of the compression force on DK-T release. Both parameters significantly delayed drug release, except when the proportion of polymer was 91.67%.

Enhanced transfection efficiency of poly(N,N-dimethylaminoethyl methacrylate)-based deposition transfection by combination with tris(hydroxymethyl)aminomethane.

We have developed a substrate-mediated transfection method called "deposition transfection technology" using a poly(N,N-dimethylaminoethylmethacrylate) (PDMAEMA) homopolymer with both thermoresponsive and cationic characteristics. In this study, we enhanced deposition transfection efficiency by using tris(hydroxymethyl)aminomethane (Tris buffer) as a pH adjuster for transfection solution composed of PDMAEMA and plasmid DNA (pDNA). PDMAEMA with a molecular weight of 9.7 × 10(4) g mol(-1) was synthesized by photoinduced radical polymerization. The pH of PDMAEMA solution was increased gradually in the range from 8 to 11 by the addition of Tris, and then the solubility of PDMAEMA was significantly decreased and the dissolution time was extended from 15 to 40 min at Tris/PDMAEMA ratio of 1 and higher. On the other hand, while the polyion complexes (polyplexes) were formed by mixing PDMAEMA with luciferase-encoding plasmid DNA even under an excess amount of Tris at Tris/PDMAEMA ratio of 8, the binding affinity between PDMAEMA and pDNA was decreased with increasing Tris at Tris/PDMAEMA ratio of 2 and higher. When HeLa cells, smooth muscle cells, and cardiac fibroblasts were transfected by the deposition method using polyplex solution containing various amounts of Tris, the transgene expression dramatically increased at a Tris/PDMAEMA ratio of 2 in all cell types, which were more than 150-fold in HeLa cells, 40-fold in smooth muscle cells, and 30-fold in cardiac fibroblasts compared to those in the Tris-free condition. In addition, the enhanced transgene expression by Tris was sustained for over 10 days post-transfection as well as that observed in Tris-free condition. Thus, deposition transfection efficiency can be dramatically enhanced by using Tris buffer as a pH adjuster for polyplex solution.

Effect of extraction and assay media on analysis of airborne endotoxin.

The measurement of airborne endotoxins is thus far not standardized. Earlier studies reported higher endotoxin yields when Tween 20 was added to the media used for filter extraction and in the Limulus amebocyte lysate (LAL) assay. This study compared four common media and assessed the effects of Tween during extraction and analysis separately. Parallel airborne dust samples from five work environments (n = 250) were used to compare the four media (pyrogen-free water [PFW], PFW-Tween 20, PFW-Tris, and PFW-triethylamine-phosphate [TAP]) and an extraction time of 10 or 60 min. A subset of the extracts in PFW or PFW-Tween (n = 40) were analyzed in parallel LAL assays with PFW or PFW-Tween as the assay medium. The results produced by a shorter extraction time or the presence of Tris were similar to the results for the reference procedure (PFW and 60 min of shaking). The use of PFW-TAP showed overall lower yields and a deviant calibration curve. The presence of Tween in the extraction medium resulted in significantly (P < 0.05) higher endotoxin yields from all dust types, independent of the effect of Tween in the assay. Tween in the LAL assay, however, also strongly inhibited the reactivity of the lipopolysaccharide (LPS) standard, thus shifting the calibration curve to higher values. The inhibition of LPS in test samples was less pronounced and varied between dust sources, resulting in enhanced calculated concentrations. This assay effect could be circumvented by diluting extracts at least 50-fold before the LAL assay. In conclusion, of the media tested, only Tween enhances the efficiency of endotoxin extraction from airborne dust samples in a consistent manner. We recommend extraction in PFW-Tween combined with dilution and LAL analysis in PFW.

Structure of the two-subsite beta-d-xylosidase from Selenomonas ruminantium in complex with 1,3-bis[tris(hydroxymethyl)methylamino]propane.

The three-dimensional structure of the catalytically efficient beta-xylosidase from Selenomonas ruminantium in complex with competitive inhibitor 1,3-bis[tris(hydroxymethyl)methylamino]propane (BTP) was determined by using X-ray crystallography (1.3A resolution). Most H bonds between inhibitor and protein occur within subsite -1, including one between the carboxyl group of E186 and an N group of BTP. The other N of BTP occupies subsite +1 near K99. E186 (pK(a) 7.2) serves as catalytic acid. The pH (6-10) profile for 1/K(i)((BTP)) is bell-shaped with pK(a)'s 6.8 and 7.8 on the acidic limb assigned to E186 and inhibitor groups and 9.9 on the basic limb assigned to inhibitor. Mutation K99A eliminates pK(a) 7.8, strongly suggesting that the BTP monocation binds to the dianionic enzyme D14(-)E186(-). A sedimentation equilibrium experiment estimates a K(d) ([dimer](2)/[tetramer]) of 7 x 10(-9)M. Similar k(cat) and k(cat)/K(m) values were determined when the tetramer/dimer ratio changes from 0.0028 to 26 suggesting that dimers and tetramers are equally active forms.