1,721,068 research outputs found
Functionalization Pattern of Graphene Oxide Sheets Controls Entry or Produces Lipid Turmoil in Phospholipid Membranes
Full text linkMolecular dynamics,
coarse-grained to the level of hydrophobic and hydrophilic interactions,
shows that graphene oxide sheets, GOSs, can pierce through the phospholipid
membrane and navigate the double layer only if the hydrophilic groups
are randomly dispersed in the structure. Their behavior resembles
that found in similar calculations for pristine graphene sheets. If
the oxidation is located at the edge of the sheets, GOSs hover over
the membrane and trigger a major reorganization of the lipids. The
reorganization is the largest when the radius of the edge-functionalized
sheet is similar to the length of the lipophilic chain of the lipids.
In the reorganization, the heads of the lipid chains form dynamical
structures that pictorially resemble the swirl of water flowing down
a drain. All effects maximize the interaction between hydrophobic
moieties on the one hand and lipophilic fragments on the other and
are accompanied by a large number of lipid flip-flops. Possible biological
consequences are discussed
Binding and recognition mechanisms of the human tyrosylprotein sulfotransferase isoform-2 (TPST-2) towards its natural ligands. A computational investigation.
No full textLUIGI BOLONDI FELICITATIONS VOLUME
Studies in Medicine and Its History
Studi medici
e di storia della medicina in onore di Luigi Bolond
Hajos-Parrish-Eder-Sauer-Wiechert reaction: The definitive reaction mechanism deciphered by DFT calculations
No full textThe use of (S)-proline as a catalyst for intramolecular aldol reactions pioneered by Hajos, Parrish, Eder, Sauer and Wiechert paved the way for modern organo-catalysis, which earned MacMillan and List the Nobel Prize in Chemistry in 2021. The work reported herein shed light on mechanistic aspects regarding the "prototypal " H-P-E-S-W reaction that, up to date, are unclear. The DFT calculations determined i) the mechanism of the dehydration step of the ketol intermediate that proceeds via an E1cB (elimination, unimolecular, conjugate base) mechanism; ii) the rate-determining steps (RDS) of the H-P-E-S-W reaction that correspond to enamine formation and dehydration; iii) the catalytic role of the water molecule formed during the reaction, that behaves as a proton shuttle during the enamine and C-C bond formation and determines a significant lowering of the activation barriers
Use of a coordination complex or compound for the measurement of temperature
No full textUse for measuring temperatures of a coordination complex presenting formula I, wherein M1, M2, M3, M4, M5 are chosen, each independently of the others, in the group consisting of: CuI, AgI, AuI, PdII; n is equal to the sum of the oxidation states of M1, M2, M3, M4, M5 minus 3; II represents a respective portion of each tridentate ligand having the formula III in which R1 is chosen in the group consisting of: Ph, C1-C4 alkyl, halo-alkyl C1-C4 substituted phenyl; R2 is chosen in the group consisting of: Ph, C1-C4 alkyl, C1-C4 halo-alkyl-, substituted phenyl; R3 is chosen in the group consisting of: C3-C18 alkyl, benzyl, substituted benzyl, C1-C20 hydroxy-alkyl, C1-C20 alkoxy silane
Graphene Materials Strengthen Aqueous Polyurethane Adhesives
Full text linkCarboxyl-functionalized graphene platelets (GP) and graphene oxide (GO) sheets were added to a commercial aqueous adhesive dispersion of thermoplastic polyurethane (TP) (Idrotex 200 from FacGB s.r.l.). For both additives, the weight percentage was of industrial interest, 0.01 and 10.1 wt %. The addition of GP/GO was carried out in a simple and scalable-up process that can be applied to other materials and additives. Mechanical, peel tests were applied on polyurethane strips (75 mm long, IS mm wide, and 1.5 mm thick) prepared cutting extruded sheets obtained using Estane 58091, a 70D aromatic polyester-based TP. The tests with 0.01 wt % of GP showed statistically significant higher forces at first failure and maximum forces with respect to the pristine adhesive. Sample characterization was carried out with scanning electron microscopy, infrared spectroscopy, X-ray diffraction, and thermal analysis. A mechanism is suggested for the improved performance of the low-dose GP adhesive
A Full QM Computational Study of the Catalytic Mechanism of α-1,4-Glucan Lyases
No full textWe investigated the catalytic mechanism of α-1,4-glucan lyases using a full QM DFT approach based on the M06-2X functional. The reaction profile of the whole catalytic process can be divided into three phases: glycosylation, deglycosylation-elimination and tautomerization. Glycosylation is a highly asynchronous SN1-like process with an energy barrier of 10.2 kcal mol−1. A proton moves from the Asp665residue to the glycosidic oxygen. Asp553acts as a nucleophile and attacks the anomeric carbon causing the cleavage of the glycosidic bond. Deglycosilation-elimination is the rate-determining step of the entire process with an overall barrier of 18.3 kcal mol−1. The final step (restoring the catalyst and tautomerization) occurs rather easily, since the Asp553carboxylate group “assists” the proton transfer in the tautomerization process. Our computations clearly indicate that tautomerization must occur inside the enzyme before leaving the active site rather than in the aqueous solution. Outside of the protein environment the enol-AF→keto-AF process “assisted” by a water molecule has a barrier of 35.8 kcal mol−1
C60bioconjugation with proteins: Towards a palette of carriers for all pH ranges
Full text linkThe high hydrophobicity of fullerenes and the resulting formation of aggregates in aqueous solutions hamper the possibility of their exploitation in many technological applications. Noncovalent bioconjugation of fullerenes with proteins is an emerging approach for their dispersion in aqueous media. Contrary to covalent functionalization, bioconjugation preserves the physicochemical properties of the carbon nanostructure. The unique photophysical and photochemical properties of fullerenes are then fully accessible for applications in nanomedicine, sensoristic, biocatalysis and materials science fields. However, proteins are not universal carriers. Their stability depends on the biological conditions for which they have evolved. Here we present two model systems based on pepsin and trypsin. These proteins have opposite net charge at physiological pH. They recognize and disperse C60in water. UV-Vis spectroscopy, zeta-potential and atomic force microscopy analysis demonstrates that the hybrids are well dispersed and stable in a wide range of pH's and ionic strengths. A previously validated modelling approach identifies the protein-binding pocket involved in the interaction with C60. Computational predictions, combined with experimental investigations, provide powerful tools to design tailor-made C60@proteins bioconjugates for specific applications
Biocompatible and Light-Penetrating Hydrogels for Water Decontamination
Full text linkSolar
light-activated photocatalyst nanoparticles (NPs) are promising
environment-friendly low cost tools for water decontamination, but
their dispersion in the environment must be minimized. Here, we propose
the incorporation of TiO2-NPs (also in combination with
graphene platelets) into highly biocompatible hydrogels as a promising
approach for the production of photoactive materials for water treatment.
We also propose a convenient fluorescence-based method to investigate
the hydrogel photocatalytic activity in real time with a conventional
fluorimeter. Kinetics analysis of the degradation profile of a target
fluorescent model pollutant demonstrates that fast degradation occurs
in the matrix bulk. Fluorescence anisotropy proved that small pollutant
molecules diffuse freely in the hydrogel. Rheological and scanning
electron microscopy characterization showed that the TiO2-NP incorporation does not significantly alter the hydrogel mechanical
and morphological properties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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