1,721,050 research outputs found
The route towards nanoparticle shape metrology
No full textAn approach to identify and classify different shapes of nanomaterials starting from transmission electron microscopy images could be a powerful instrument to categorize the different shapes of nanoparticles and fingerprint the geometrical variability of an ensemble
In Vivo Application of Carboranes for Boron Neutron Capture Therapy (BNCT): Structure, Formulation and Analytical Methods for Detection
Full text linkCarboranes have emerged as one of the most promising boron agents in boron neutron capture therapy (BNCT). In this context, in vivo studies are particularly relevant, since they provide qualitative and quantitative information about the biodistribution of these molecules, which is of the utmost importance to determine the efficacy of BNCT, defining their localization and (bio)accumulation, as well as their pharmacokinetics and pharmacodynamics. First, we gathered a detailed list of the carboranes used for in vivo studies, considering the synthesis of carborane derivatives or the use of delivery system such as liposomes, micelles and nanoparticles. Then, the formulation employed and the cancer model used in each of these studies were identified. Finally, we examined the analytical aspects concerning carborane detection, identifying the main methodologies applied in the literature for ex vivo and in vivo analysis. The present work aims to identify the current strengths and weakness of the use of carboranes in BNCT, establishing the bottlenecks and the best strategies for future applications
A Mechanistic Insight into the Cu(II)-Catalyzed C–N and C–O Coupling Reaction of Arylglyoxylic Acids with Isatins; A DFT Investigation
No full textWe carried out a DFT computational investigation on the mechanism of the copper(II) catalyzed C–N, C–O cross coupling reaction involving isatin and phenylglyoxylic acid recently reported by Gogoi. The mechanistic hypothesis proposed by this author is overall confirmed. Our computations demonstrated that the initial decarboxylation is an exergonic reaction (–15.3 kcal mol–1). This process, which can occur rather easily under the used experimental conditions (95 °C for 24 hours), triggers the catalytic cycle with the formation of the initial active organometallic complex (I1). A copper acetate ligand deprotonates the isatin nitrogen. This enhances its nucleophilic character and makes possible the attack of nitrogen on the Cu atom. A reversible transformation connects the initial encounter complex between isatin and the active intermediate I1 and the intermediate where the metal atom inserts into the amide bond. The decarbonylation step represents the rate-determining step of the entire process (activation free energy = 23.3 kcal mol–1). Copper does not change its oxidation state (II) in the course of the catalytic reaction. The mechanism never involves directly the isatin benzene ring: this is consistent with the fact that only slight changes in the reaction yield are observed when substituents are inserted at different positions of the aromatic ring
Exploiting Blood Transport Proteins as Carborane Supramolecular Vehicles for Boron Neutron Capture Therapy
Full text linkCarboranes are promising agents for applications in boron neutron capture therapy (BNCT), but their hydrophobicity prevents their use in physiological environments. Here, by using reverse docking and molecular dynamics (MD) simulations, we identified blood transport proteins as candidate carriers of carboranes. Hemoglobin showed a higher binding affinity for carboranes than transthyretin and human serum albumin (HSA), which are well-known carborane-binding proteins. Myoglobin, ceruloplasmin, sex hormone-binding protein, lactoferrin, plasma retinol-binding protein, thyroxine-binding globulin, corticosteroid-binding globulin and afamin have a binding affinity comparable to transthyretin/HSA. The carborane@protein complexes are stable in water and characterized by favorable binding energy. The driving force in the carborane binding is represented by the formation of hydrophobic interactions with aliphatic amino acids and BH-π and CH-π interactions with aromatic amino acids. Dihydrogen bonds, classical hydrogen bonds and surfactant-like interactions also assist the binding. These results (i) identify the plasma proteins responsible for binding carborane upon their intravenous administration, and (ii) suggest an innovative formulation for carboranes based on the formation of a carborane@protein complex prior to the administration
Theoretical design of an ultrafast supramolecular rotor composed of carbon nano-rings
No full textThe design of molecular rotors that can rotate at ultrahigh speeds is important for the development of artificial molecular machines. Based on theoretical calculations, we demonstrate that two kinds of carbon nano-rings,i.e.[n]cycloparaphenylenes ([n]CPP) and cyclo[18]carbon (C18), can form an ultrafast ring-in-ring nano-rotor through π-π interaction. As a high-symmetry and low-barrier rotator, the rotational frequency of C18in [11]CPP is close to the THz regime. At low temperatures, the motion of the [11]CPP:C18system is purely rotational. As temperature increases, precession movements start to be observed and the motion resembles the behaviour of a gyroscope. The [11]CPP:C18rotor can serve as a building block for bottom-up construction of more complex molecular machines
CNT-Catalyzed Oxidative Dehydrogenation of Ethylbenzene to Styrene: DFT Calculations Disclose the Pathways
No full textOxygen atoms, in the form of epoxy or carbonyl groups present at the edges of carbon nanotubes, trigger oxidative dehydrogenation of ethylbenzene to styrene. DFT calculations reveal that the process can occur along three pathways. The first two bifurcate from the initial transformation of an epoxide into a hydroxyl group, which occurs via a biradical transition state and the formation of a benzyl-like intermediate. The epoxide can further react to release styrene and form a water molecule, as observed experimentally, via a highly exothermic process. Alternatively, in the presence of a second adjacent epoxide, styrene is also produced without water formation along a less exothermic pathway that leaves two hydroxyl groups on the nanotube surface. Along the third pathway, two adjacent carbonyl groups (quinone functionality) also promote the formation of styrene, with energy barriers similar to those calculated in the presence of epoxy groups. These are in the range 36–37 kcal mol −1 . These values that can be easily surmounted at the working temperature used in the experiment (between 450 and 550 °C)
Oriented External Electric Fields Affect Rate and Stereoselectivity of Electrocyclic Reactions
No full textWe carried out a computational investigation at the density functional theory (M06-2X) level on the effects of oriented external electric fields (OEEF) on activation barriers and stereochemical output of the thermal ring opening of 3-substituted cyclobutenes (C4H5X) to butadienes. It is well known that with π-electron-donor substituents (X = CH3, NH2), the conrotatory outward rotation is preferred, while with π-electron-acceptor substituents (X = CHO, NO, BH2), the conrotatory inward process becomes favored. In the presence of the OEEF applied along the three axes x, y, and z in either positive or negative direction, for both π-donor and π-acceptor substituents, we observed either catalysis or inhibition. Both effects were consistent with the change of the induced dipole along the direction of the applied field. An interesting effect was observed for X = CHO and NO. The simultaneous catalysis and inhibition of the outward and inward transformation leads to a reversed ratio between outward and inward transformation, with the former being favored (stereochemical inversion). Such effect was not observed for X = BH2 (the strongest π-acceptor examined here). In this case, in the absence of the applied field, the difference between the inward and outward barriers is too large and the simultaneous catalysis and inhibition of the outward and inward transformation is not capable of determining the stereochemical inversion
Incorporation of Molecular Nanoparticles Inside Proteins: The Trojan Horse Approach in Theranostics
Full text linkCONSPECTUS: Molecular nanoparticles, MNPs, characterized by well-defined chemical formulas, structures, and sizes can interact with a variety of proteins. Fullerenes, carboranes, and gold nanoclusters well represent the diversity of MNPs properties available in nanoscience. They can have diameters smaller than 1.5 nm, be hydrophilic or hydrophobic, and can use a paraphernalia of means to establish local and global interactions with the amino acidic residues of proteins. Proteins, endowed as they are with an assortment of pockets, crevices, and gaps are natural supramolecular hosts to incorporate/hide/transport MNPs directly in water with a facile and "green" approach.This Account identifies and discusses the rules that govern the interactions and binding between MNPs and proteins. Fullerenes are composed solely by carbon atoms arranged to form hollow polyhedra. Hydrophobic interactions occur between aliphatic residues and the fullerene surface. The amino acids most effectively interacting with fullerenes are aromatic residues that establish p-p stacking interactions with the cage. Amphiphilic and charged residues produce also cation-p, anion-p, and surfactant-like interactions with the cages.Carboranes are composed of boron, carbon, and hydrogen atoms, also arranged to form cages. They are hydrophobic with unusual properties originating from the presence of boron atoms. Hydride-like hydrogens bound to the boron atoms govern carborane chemistry. These negatively charged hydrogens do not participate in classic hydrogen bonding with water and promote hydrophobic interactions with proteins. On the contrary, the electronegativity of these hydrogens drives the formation of unconventional dihydrogen bonds with the acidic hydrogen atoms of positively charged amino acid. Carboranes also establish C-H center dot center dot center dot p and B-H center dot center dot center dot p interactions with aromatic residues.Gold nanoclusters, AuNCs, are synthesizable with atomically precise stoichiometry. Amino acid residues with sulfur atoms or with nitrogen-containing heterocycles are the strongest Au binders. The proteins can act as supramolecular hosts but also as templates for the synthesis of AuNCs directly inside the protein core. Of the pristine amino acids, tryptophan, tyrosine, phenylalanine, and aspartic acid are the most efficient reducing groups. In a peptide sequence, the best Au-reducing moieties are obtained by nitrogencontaining residue such as glutamine, asparagine, arginine, and lysine. The investigation of the interactions between AuNCs and proteins therefore adds further complexity with respect to that of fullerenes and carboranes. The selection of the host proteins should consider that they will have to contain active sites for metal ion accumulation and ion reduction where AuNC can form and stabilize. This Account further discusses the hybridization of MNPs with proteins in view of creating innovative multifunctional theranostic platforms where the role of proteins is akin to that of "Trojan Horses" since they can (i) hide the MNPs, (ii) control their cellular uptake, (iii) drive their crossing of physiological barriers, and (iv) ultimately govern their biological fate
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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