9,11-DIcis-12-FLUORORHODOPSIN. CHROMOPHORE PROPERTIES FROM 19F-NMR STUDIES

From a 19F-NMR study of 9,11-dicis-12-fluororhodopsin and its photobleached product, we concluded that the initially formed chromophore retained its configuration and the photoproduct corresponded to the two-bond isomerized all-trans. Upon standing, it slowly isomerized to the 9-cis isomer. The method represents a direct, non-destructive procedure for determining configuration purity of the pigment formed. Its unique fluorine opsin shift value is consistent with the expected different orientation of the fluoro-substituent in a dicis pigment.     

Direct observation of cations and polynucleotides explains polyion adsorption to like-charged surfaces

We show an experimental approach for directly observing the condensation of polynucleotides and their electrolyte counterions at a liquid/solid interface. X-ray standing waves (XSW) generated by Bragg diffraction from a d = 20 nm Si/Mo multilayer substrate are used to measure the distinct distribution profiles of the polyanions and simple cations along the surface normal direction with subnanometer resolution. The 1D spatial sensitivity of this approach is enhanced by observing the XSW induced fluorescence modulations over multiple orders of Bragg peaks. We study the interesting divalent cation driven adsorption of anionic polynucleotides to anionic surfaces by exposing a hydroxyl-terminated silica surface to an aqueous solution with ZnCl2 and mercurated poly-uridylic acid (a synthetic RNA molecule). The in situ long-period XSW measurements are used to follow the evolution of both the Zn and Hg distribution profiles during the adsorption process. The conditions and physical mechanisms that govern the observed divalent cation adsorption and subsequent polynucleotide adsorption to an anionic surface are explained by a thermodynamic model that incorporates nonlinear electrostatic effects.     

Separation of proteins with a molecular mass difference of 2 kDa utilizing preparative double-inverted gradient polyacrylamide gel electrophoresis under nonreducing conditions: application to the isolation of 24 kDa human growth hormone

A method for separating proteins with a molecular mass difference of 2 kDa using SDS-PAGE under nonreducing conditions is presented. A sample mixture containing several human growth hormone (hGH) isoforms was initially separated on a weak anion-exchange column. Fractions rich in 24 kDa hGH as determined by analytical SDS-PAGE were pooled and further separated by cation-exchange chromatography. The fractions pooled from the cation-exchange chromatography contained two hGH isoforms with a 2 kDa molecular mass difference according to SDS-PAGE analysis, 22 and 24 kDa hGH. The 22 and 24 kDa hGH were separated using continuous-elution preparative double-inverted gradient PAGE (PDG-PAGE) under nonreducing conditions. The preparative electrophoresis gel was composed of three stacked tubular polyacrylamide matrices, a 4% stacking gel, a 13-18% linear gradient gel, and a 15-10% linear inverted gradient gel. Fractions containing purified 24 kDa hGH were pooled and Western blot analysis displayed immunoreactivity to antihGH antibodies. PDG-PAGE provides researchers with an electrophoretic technique to preparatively purify proteins under nonreducing conditions with molecular mass differences of 2 kDa.     

Destructive adsorption of CCl4 over lanthanum-based solids: linking activity to acid-base properties

The relative activities of a low-surface crystalline and high-surface amorphous LaOCl, further denoted as S1 and S2, have been compared for the destructive adsorption of CCl4. It was found that the intrinsic activity of S2 is higher than that of S1. Both samples were characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2-physisorption, and Raman and infrared (IR) spectroscopy. IR was used in combination with CO2, CO, and methanol as probe molecules. The CO2 experiments showed that different carbonate species are formed on both materials. For S1, a high surface concentration of bidentate carbonate species and a lower concentration of monodentate carbonate were observed. In the case of S2, bulk carbonates were present together with bridged carbonates. CO adsorption shows that S2 and S1 have very similar Lewis acid sites. However, methanol adsorption experiments showed that S2 had a higher number of stronger Lewis acid sites than S1 and that twofold coordinated methoxy species were more strongly bound than threefold coordinated methoxy species. Because of the analogy between methanol dissociation and the removal of the first chlorine atom in the destructive adsorption of CCl4, the sites enabling twofold coordination were likely to be the same Lewis acid sites actively involved in the destructive adsorption of CCl4. La2O3 was less active than the two LaOCl materials, and therefore, the intrinsic activity of the catalyst increases as the strength of the Lewis acid sites increases. S2 contains more chlorine at the surface than S1, which is expressed by the higher number of sites enabling twofold coordination. Moreover, this explains the difference in destructive adsorption capacity for CCl4 that was observed for the samples S1 and S2. Since LaCl3, being the most acidic phase, is not active for the destructive adsorption of CCl4, basic oxygen atoms, however, remain needed to stabilize the reaction intermediate CCl3 as La-O-CCl3.     

Singlet oxygen generation versus O–O homolysis in phenyl-substituted anthracene endoperoxides investigated by RASPT2, CASPT2, CC2, and TD-DFT methods

Peptidylarginine deiminase 4 (PAD4), also known as protein arginine deiminase 4, performs a post-translational deimination that converts arginine to citrulline. The dysregulation of PAD4 has been implicated in a number of diseases, including rheumatoid arthritis (RA) and cancer. This makes PAD4 an important therapeutic target. To develop small-molecule inhibitors as potential treatments, it is advantageous if the catalytic mechanism is well understood. The protonation states of the active site residues, which have long been under controversy, have a direct impact on the catalytic mechanism. Two competing mechanisms are under investigation in the current literature. The first is a reverse protonation mechanism that depends on the active site histidine and cysteine existing as an ion pair. The second is a substrate-assisted mechanism that depends on the active site histidine and cysteine being neutral. This study uses the semimicroscopic protein dipoles Langevin dipoles (PDLD/S) linear response approximation method in the MOLARIS software package to calculate the change in solvation energy of moving the residue from water to the protein interior, and then using that information to assess the protonation states of the active site residues of PAD4. Results from these calculations suggest that in the enzyme–substrate complex of PAD4, the cysteine and histidine are protonated and deprotonated, respectively, and are therefore both neutral, analogous to the proposed protonation states of the active site residues in the Michaelis complex in the substrate-assisted mechanism.     

Molecular dynamics simulation of DNA‐directed assembly of nanoparticle superlattices using patterned templates

DNA‐directed assembly is a well developed approach in constructing desired nano‐architectures. On the other hand, E‐beam lithography is widely utilized for high resolution nano‐scale patterning. Recently, a new technique combining these two methods was developed to epitaxially grow DNA‐mediated nanoparticle superlattices on patterned substrates. However, defects are observed in epitaxial layers which restricts this technique from building large‐scale superlattices for real applications. Here we use molecular dynamics simulations to study and predict defect formation on adsorbed superlattice monolayers. We demonstrate that this epitaxial growth is energetically driven by maximizing DNA hybridization between the epitaxial layer and the substrate and that the shape anisotropy of the DNA‐mediated template posts leads to structural defects. We also develop design rules to dramatically reduce defects on epitaxial layers. Ultimately, with the assist of the computational study, this technique will open the door to constructing well‐ordered, three‐dimensional novel nanomaterials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1687–1692     

Artificial Spin-Ice and Vertex Models

In classical and quantum frustrated magnets the interactions in combination with the lattice structure impede the spins to order in optimal configurations at zero temperature. The theoretical interest in their classical realisations has been boosted by the artificial manufacture of materials with these properties, that are of flexible design. This note summarises work on the use of vertex models to study bidimensional spin-ices samples, done in collaboration with R. A. Borzi, M. V. Ferreyra, L. Foini, G. Gonnella, S. A. Grigera, P. Guruciaga, D. Levis, A. Pelizzola and M. Tarzia, in recent years. It is an invited contribution to a J. Stat. Mech. special issue dedicated to the memory of Leo P. Kadanoff.     

Low‐Fouling Electrosprayed Hemoglobin Nanoparticles with Antioxidant Protection as Promising Oxygen Carriers

Despite all the attempts to create advanced hemoglobin (Hb)‐based oxygen carriers (HBOCs) employing an encapsulation platform, major challenges including attaining a high Hb loading and long circulation times still need to be overcome. Herein, the fabrication, for the first time, of nanoparticles fully made of Hb (Hb‐NPs) employing the electrospray technique is reported. The Hb‐NPs are then coated by antioxidant and self‐polymerized poly(dopamine) (PDA) to minimize the conversion of Hb into nonfunctional methemoglobin (metHb). The PDA shell is further functionalized with poly(ethylene glycol) (PEG) to achieve stealth properties. The results demonstrate that the as‐prepared Hb‐NPs are hemo‐ and biocompatible while offering antioxidant protection and decreasing the formation of metHb. Additionally, decoration with PEG results in decreased protein adsorption onto the Hb‐NPs surface, suggesting a prolonged retention time within the body. Finally, the Hb‐NPs also preserve the reversible oxygen‐binding and releasing properties of Hb. All in all, within this study, a novel HBOCs with high Hb content is fabricated and its potential as an artificial blood substitute is evaluated.     

Development of a method for quantitative determination of the cytotoxic agent piplartine (piperlongumine) in multiple skin layers

This study reports the development of a simple and reproducible method, with high rates of recovery, to extract the cytotoxic agent piplartine from skin layers, and a sensitive and rapid UV‐HPLC method for its quantification. Considering the potential of piplartine for topical treatment of skin cancer, this method may find application for formulation development and pharmacokinetics studies to assess cutaneous bioavailability. Porcine skin was employed as a model for human tissue. Piplartine was extracted from the stratum corneum (SC) and remaining viable skin layers (VS) using methanol, vortex homogenization and bath sonication, and subsequently assayed by HPLC using a C₁₈ column, and 1:1 (v/v) acetonitrile–water (adjusted to pH 4.0 with acetic acid 0.1%) as mobile phase. The quantification limit of piplartine was 0.2 μg/mL (0.6 μm ), and the assay was linear up to 5 μg/mL (15.8 μm ), with within‐day and between‐days assay coefficients of variation and relative errors <15%. Piplartine recovery from SC and VS varied from 86 to 96%. The method was suitable to assay samples from skin penetration studies, enabling detection of differences in cutaneous delivery in different skin compartments resulting from treatment with various formulations and time periods.     

Short time deposition of TiO2 nanoparticles on SiC as photocatalysts for the degradation of organic dyes

The deposition of TiO₂ nanoparticles on SiC was carried out by mechanical milling under different conditions. SiC–TiO₂ samples were used as photocatalysts for the degradation of organic dyes such as methylene blue and rhodamine B. A short time deposition of TiO₂ nanoparticles was observed during mechanical milling (2 min at 200 rpm) to cover the SiC particles. The presence of SiC and TiO₂ (anatase and rutile) was confirmed by means of X-ray diffraction after thermal treatment at 450 °C. The deposition of TiO₂ on SiC was corroborated by scanning electron microscopy analysis; the thickness of the thin layer of TiO₂ deposited on SiC increases as the proportion of TiO₂ increases. The energy band gap values obtained for these compounds were around 3.0 eV. SiC–TiO₂ photocatalysts prepared by mechanical milling exhibited better activity under UV-light irradiation for the degradation of methylene blue and rhodamine B than commercial TiO₂ powder (titania P25).