Encyclopedia
This picture displays Carlos M. Villalón research group.
18 Jul 2023
Transmission electron microscopy (TEM) micrograph of graphite oxide (GO) synthesized by the Hummers' method.
20 Nov 2023
Oxidative stress is a physiological condition characterized by an imbalance between reactive oxygen species (ROS) production and the body's antioxidant defense mechanisms. ROS, including superoxide anion, hydrogen peroxide, and hydroxyl radicals, can be generated by various cellular sources, such as mitochondria, peroxisomes, and NADPH oxidase.
04 Sep 2023
Transmission electron microscopy (TEM) of multi-walled carbon nanotubes (MW-CNTs).
04 Dec 2023
Graphite bisulphate (GBS) is the first graphite intercalation compound to be prepared. It was synthesized by Brodie in the 1855 by using a mixture of sulphuric and nitric acids. This reaction implies surface oxidation of the graphite crystal and insertion of molecules and ions in the lattice. Graphite intercalation compounds (GICs) are generally categorized as covalent and ionic types. Nowadays, research in this area is principally focused on ionic GICs, because of their use in energy storage systems (e.g., Li-ion batteries), superconductivity at low temperature, reagents and catalysts in organic synthesis, etc. GBS has both an ionic and covalent nature, indeed it contains two types of intercalated species: HSO4- ions and H2SO4 molecules. Owing to the electrostatic interactions with the graphene plane, the HSO4- molecules originate point defects in the graphite crystalline structure, that cannot move from the lattice positions where they have been formed. Differently, the H2SO4 molecules are free to move by diffusion in the space between the adjacent graphite crystallographic planes and segregate in order to maximize all physical interactions, thus forming a network of linear defects in the structure of the graphite matrix. For such a reason GBS is a chemical substance not very stable, especially in presence of moisture. GBS has been extensively used for producing expanded graphite, graphite nanoplatelets (GNPs), single- and few-layer graphene, graphene oxide, graphene aerogels[1] and many other types of graphite-based industrial products.
27 Dec 2023
Definition of nanostructureOwing to the very large number of nanostructure types with strongly differing shapes (let's compare, for example, graphene with fullerenes or SW-CNTs with atomic clusters)[1], it is quite difficult to formulate an universal definition for such a type of advanced material. However, based on some features common to all kinds of nanostructures, the following definition could be developed:"Nanostructures are artificial or natural tiny solid corpuscles, belonging to the microscopic world and precisely to the nanoscopic dimensional scale (that is, 10-9m), that are characterized by anomalous chemical and physical properties in comparison with the corresponding bulk (massive) solid phases, because of effects like: quantum-confinement, band structure discretization, prevalence of surface on bulk matter, change of the prevaling type of surface atoms, high surface free energy content, etc. and these properties can be widely tuned by morphological variations (i.e., by nanostructure size and shape modification)."
26 Jun 2024
Nanomaterials are classified according to their nature, number of finite dimensions, shape and chemical composition. Similarly to other chemical substances, nanomaterials are distinct as organic and inorganic solids. Such a distinction is based on the presence of C-H bonds in the nanomaterial chemical structure. Organic nanomaterials contain C-H bonds in their chemical structure; differently, inorganic nanomaterials do not contain C-H bonds. For example, graphite oxide (GO) is an organic nanomaterial while graphene, fullerenes (C60, C70), and carbon quantum-dots are inorganic nanomaterials. A further information concerns the number of finite X-Y-Z dimensions in the nanostructure (that is, the number of non nanometric dimensions in the nanostructure) [1]. As a consequence, nanoparticles are 0-D nanostructures, nanotubes are 1-D nanostructures and nanoplatelets are 2-D nanostructures. Recently, the term 3-D is being reserved to the ‘nanostructured materials’, that is solids with nanometric features in their structure. Therefore, a nanocrystalline metallic or ceramic solid is a 3-D nanostructure. The currently adopted nomenclature always specify the nanostructure shape in the name formulation (e.g., triangles, cubes, platelets, wires, rods, filaments). When nanoparticles have a quasi-spherical shape, they can be also named pseudo-spherical nanoparticles, if the shape is not perfectly spherical, or polyhedral nanoparticles in the case they are very small and therefore closely resemble this highly regular solid figure. In the formulation of the nanostructure name also the chemical composition must be provided, in this case the chemical formula or the chemical nomenclature is used (e.g., gold nanoplatelets, ZnO nanocubes, carbon nanoparticles, silver nanotubes).
07 Jun 2024
Long-chain normal-alkyl thiolates of noble metals (Me-SCnH2n+1, with n>10) are covalent chemical compounds, that thermally decompose, producing the zero-valent metal and an organic waxy by-product (disulfide, RSSR). For example, silver-dodecylthiolate (Ag-C12H25) decomposes at ca. 150°C, producing elemental silver. Owing to the possibility for the metal alkyl-thiolate molecules to organize in nano-sized micellar forms, frequently the metallic phase generated by thermal decomposition has nanometric size and regular geometry (e.g., mono-dispersed nano-spheres, nano-cylinders with identical diameters, lamellas, etc.). Indeed, the thermally generated solid phase of elemental silver is made of continuous nano-wires because the silver-dodecylthiolate precursor contains molecules organized in a tubular structure with the metallic atoms placed inside this structure. Metal thiolates, like silver-dodecylthiolate, are easily synthesized by precipitation from an alcoholic solution (ethanol) of the metallic salt (silver nitrate, AgNO3) and the thiol (dodecylthiol, C12H25-SH) [1].
13 Nov 2023
Transmission electron microscopy (TEM) micrograph of gold nanoparticles embedded in a polyvinylpyrrolidone matrix (40,000X).
20 Nov 2023
The amorphous nature of silica contained in the diatomite frustules implies an abundance of silanol groups (Si-OH) and siloxane bridges (Si-O-Si) on its surface. Infra-red analysis (FT-IR) can confirm the presence of the characteristic absorption bands of silica at around 3600 cm-1, that is ascribed to the O-H stretching vibration of absorbed water molecules on its surface (the same water molecules produce also a low-intensity absorption band located at 1630 cm-1, due to bending vibrations). A very broad and strong band at ca. 1100 cm-1, which is related to the Si-O-Si asymmetric vibrations and the band at ca. 800 cm-1, which is produced by the symmetric Si-O-Si stretching vibrations.
18 Jan 2024
Gold(I) chloride (AuCl) is a covalent solid quite soluble in non-polar organic media. Therefore, it is possible to prepare films of AuCl solid solution in amorphous polystyrene by the solution-casting technology, using chloroform as solvent. Gold chloride is not thermally stable and therefore it decomposes by heating at ca. 120°C, thus generating gold atoms (and chloride radicals), that first saturate the polymeric matrix and then precipitate in form of polydispersed and shapeless nanosized particles. However, owing to the Ostwald ripening process, prolonged thermal annealing (1-4 hours) of this gold/polystyrene systems transforms the metallic phase from its irregular form to large 2D particles shaped in form of triangles, hexagons and other polygonal shapes, with very low thickness (only few atomic layers). Probably, the polymer side-groups have a role in inhibiting the crystal growth in the direction perpendicular to the basal planes. Owing to their very low thickness, these 2D-gold particles (quantum-wells) are quite transparent and an interference image is produced by the interaction with the electron beam of the transmission electron microscope (TEM) [1].
13 Nov 2023
Nanostructures can be obtained also by top-down approaches like the ball milling technology. For example, diatomite is a very useful industrial product also in form of a finely grounded powder. Indeed, micrometric diatomite fragments are glass pieces with very sharp edges that can be used for different applications. A very important possibility is to use these sharp pieces of glass as a natural non-toxic insecticide for domestic and farmyard animals. Indeed, the sharp edges of diatomite fragments cut the coticule of insects, causing their dehydration and death. Diatomite micro-powder is also a very good abrasive for the same reason. In addition, it is used as dryer agent, sorbent for liquids, ionic dye adsorbent, toxic cations adsorbent, etc.
29 Nov 2023
Microporosity in the single-lamellar crystals of natural clinoptilolite is organized in a very unique manner; indeed, it involves only the lateral surfaces of the crystals and not the basal planes. In particular, the channels form a two-dimensional array, which is placed in parallel to the crystal basal planes. In this two-dimensional array, A (0.72-0.44 nm) and B (8-member ring, 0.41-0.47 nm) channels are parallel each other, while C (8-member ring, 0.55-0.40 nm) channels are located perpendicularly to them. Such unique characteristics of clinoptilolite microporosity allows these 40nm thick single-lamellar crystals to be easily placed on a planar support (paper foil, polymer film, etc.) without occluding the microporosity and thus allowing mechanisms of molecular release or absorption to take place [1]. In addition, since the basal planes of clinoptilolite crystals do not contain any porosity, a binder can be placed at substrate-lamellas interface in order to stably connect them to the substrate without influencing the material microporosity.
10 Jan 2024
Transmission electron microscopy (TEM) micrograph of a MW-CNT bundle.
04 Dec 2023
Gold nanocrystals, that precipitate in molten polymers by saturating them with gold atoms, always show regular 2D or 3D-shapes. Planar triangles is the most common geometrical shape for gold nanocrystals. However, these nano-particles occasionally develop other geometries like, for example, the pentagonal bipyramid.
13 Dec 2023
This infographic reveals fascinating facts about these vital pollinators, from their complex social structures to their crucial role in our ecosystem. Learn how bees support biodiversity and agriculture.
24 Jul 2024
Papaya ringspot virus (PRSV) Leaf symptoms include: 1. "Shoestrings" (i.e., the leaf lobes become narrow, chlorotic, deformed and stringlike) 2. "Green islands" (i.e., raised spots having a dark green color 3. Leaf deformity; reduction in leaf size.
Wikimedia Commons, Plant pests and diseases, Scot Nelson
15 Mar 2024
Owing to the small number of graphene sheets contained inside of graphite nano-platelet (GNP), these nanostructures are characterized by a quite low internal cohesion. As a consequence, they can be easily spread on the surface of a flat, non-polar substrate by acting on it with a friction force. It has been shown that the surface of a polyethylene (LD-PE) film is a perfect substrate for graphite coatings [1]. These coatings are at same time electrically conductive, optically transparent and semi-reflective (i.e., slightly silvery). However, if the adopted non-polar substrate has a fibrous surface, like in the case of a film of bi-axially oriented polypropylene (BOPP), when GNPs are spread by friction against this surface, some of them spontaneously scrolls, thus producing tubular structures, similar to nano-scrolls [2]. The structures obtained by this easy micromechanical approach have a micronic size, but their walls have a thickness of only few nanometers. This type of structures can have a number of technological applications mainly related to the possibility for them to act as a reservoir; for example, they can be used for drug delivery, aroma release, absorbent, etc. The TEM micrograph shows the typical microstructure of a carbon nanoscroll prepared by spreading graphite nanoplatelets on a BOPP substrate [3].
08 Dec 2023
Some examples of the organization of biosynthetic gene clusters (BGCs) for the production of secondary metabolites (SMs) in fungi [1]. (a) BGCs for production of SMs based on so-called “central” gene, which encodes one type of megasynthase or another: (i) NRPS (nonribosomal peptide synthetase), (ii) PKS (polyketide synthase), or (iii) NRPS-PKS hybrid. (b) “Early” and “late” BGCs for production of cephalosporin C in Acremonium chrysogenum. (c) BGCs for production of lovastatin in Aspergillus terreus: P450—cytochrome P450. (d) BGCs for production of terpenoid SM: TPC—terpene cyclase. (e) BGCs for production of meroterpenoid with unique structure. BGC for production of biscognienyne B is given as an example. (f) BGC for production of kojic acid in Aspergillus oryzae. Gene loci for enzymes of the biosynthetic pathways of the SMs are colored in red; gene loci for protein transporters of biosynthetic products are colored in blue; gene locus for protecting the microorganism from the produced secondary metabolite is colored in green; gene locus for the specific regulator of this biosynthetic pathway is colored in white; locus for gene with unknown function is colored in brown. Genes for backbone enzymes (NRPS, PKS, and TPC) responsible for the production of the core structure of SMs are colored in red.
18 Jul 2023
Localization of biosynthetic gene clusters (BGCs) for the production of secondary metabolites (SM) on the chromosomes of Penicillium chrysogenum [1]. 4 chromosomes of P. chrysogenum are compared with 4 keyboards of the organ; the relative localization of BGCs on keys of chromosomes-keyboards is shown, as previously described [2]. BGCs for which the product is unknown ("orphan" clusters) are designated according to the previously entered numbering [2] and are marked in black. The BGC for which the product is known is indicated by its name and marked in red; the formula given for this target metabolite is marked in yellow.
19 Jul 2023
