Nanostructures as the Substrate for Single-Molecule Magnet Deposition

Anchoringsingle-molecule magnets (SMMs) on the surface of nanostructures is gaining particular interest in the field of molecular magnetism. The accurate organization of SMMs on low-dimensional substrates enables controlled interactions and the possibility of individual molecules' manipulation, paving the route for a broad range of nanotechnological applications. In this comprehensive review article, the most studied types of SMMs are presented, and the quantum-mechanical origin of their magnetic behavior is described. The nanostructured matrices were grouped and characterized to outline to the reader their relevance for subsequent compounding with SMMs. Particular attention was paid to the fact that this process must be carried out in such a way as to preserve the initial functionality and properties of the molecules. Therefore, the work also includes a discussion of issues concerning both the methods of synthesis of the systems in question as well as advanced measurement techniques of the resulting complexes. A great deal of attention was also focused on the issue of surface-molecule interaction, which can affect the magnetic properties of SMMs, causing molecular crystal field distortion or magnetic anisotropy modification, which affects quantum tunneling or magnetic hysteresis, respectively. In our opinion, the analysis of the literature carried out in this way will greatly help the reader to design SMM-nanostructure systems.

Synthetic Opals or Versatile Nanotools-A One-Step Synthesis of Uniform Spherical Silica Particles

Synthetic opals, a composition of homogeneous silica spheres in the mesoscale size range, have attracted the attention of scientists due to their favorable chemical and physical properties. Their chemical inertness and stability, biocompatibility, homogeneity, elevated specific surface area, and ease of functionalization of their surfaces make them a versatile nanotool. In the present study, the Stöber process was used to investigate the effect of parameters, such as reagent concentration and synthesis temperature, on the resulting silica particle size and structure. The optimal conditions for successfully obtaining homogeneous particles in the mesoscale range with high reproducibility were investigated. Several synthesis procedures and their dependence on the reaction temperature were presented to allow the selection of the assumed diameter of silica spheres. The numerous samples obtained were examined for size, homogeneity, structure, and specific surface area. On the basis of specific surface area measurements and nuclear magnetic resonance studies, the internal hierarchical structure of the spherical silica was confirmed as consisting of a solid core and layers of secondary spheres covered by a solid shell. Structural studies (X-ray Spectroscopy, X-ray Absorption Near-Edge Structure, and nuclear magnetic resonance), together with infrared vibrational spectroscopy, showed no dependence of the structure of the obtained mesospheres on the concentration of reagents and the size of the obtained particles.

Synthesis, thermal evolution and magnetic investigations of SBA-15 silica functionalized with anchored iron phosphonate molecules

In the current work, we report on synthesizing a series of novel nanocomposite materials obtained by functionalizing the SBA-15 silica matrix with anchored iron phosphonate molecules and following thermal treatment. Obtained results reveal the formation of a unique amorphic layer of Fe-based compounds on the surface of silica walls of SBA-15 channels as a result of the organic groups' decomposition after the moderate thermal treatment. Due to their unique structure, represented in an active Fe-containing amorphous coating spread over a large surface area, these materials are of great interest for their potential applications in fields such as catalysis, adsorption, and non-linear optics. Obtained materials remain amorphous, preserving the SBA-15 mesoporous structure up to the temperatures of approximately 800 °C, after which the partial melting of the silica backbone is observed with simultaneous formation of nanocrystals inside the newly-formed glassy mass. All obtained materials were characterized using such techniques as thermogravimetry, transmission and scanning electron microscopy combined with energy dispersive X-ray spectroscopy mapping, Raman spectroscopy, N₂sorption analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and SQUID measurements.

Aluminium(III) Oxide-The Silent Killer of Bacteria

In this article, we describe the antimicrobial properties of pristine anodised aluminium oxide matrices-the material many consider biologically inert. During a typical anodisation process, chromium and chlorine compounds are used for electropolishing and the removal of the first-step aluminium oxide. Matrices without the use of those harmful compounds were also fabricated and tested for comparison. The antibacterial tests were conducted on four strains of Escherichia coli: K12, R2, R3 and R4. The properties of the matrices were also compared to the three types of antibiotics: ciprofloxacin, bleomycin and cloxacillin using the Minimal Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) tests. Moreover, DNA was isolated from the analysed bacteria which was additionally digested with formamidopyrimidine-DNA glycosylase (Fpg) protein from the group of repair glycosases. These enzymes are markers of modified oxidised bases in nucleic acids produced during oxidative stress in cells. Preliminary cellular studies, MIC and MBC tests and digestion with Fpg protein after modification of bacterial DNA suggest that these compounds may have greater potential as antibacterial agents than the aforementioned antibiotics. The described composites are highly specific for the analysed model Escherichia coli strains and may be used in the future as new substitutes for commonly used antibiotics in clinical and nosocomial infections in the progressing pandemic era. The results show much stronger antibacterial properties of the functionalised membranes on the action of bacterial membranes in comparison to the antibiotics in the Fpg digestion experiment. This is most likely due to the strong induction of oxidative stress in the cell through the breakdown of the analysed bacterial DNA.

Spherical Silica Functionalized by 2-Naphthalene Methanol Luminophores as a Phosphorescence Sensor

Photoluminescence is known to have huge potential for applications in studying biological systems. In that respect, phosphorescent dye molecules open the possibility to study the local slow solvent dynamics close to hard and soft surfaces and interfaces using the triplet state (TSD: triplet state solvation dynamics). However, for that purpose, probe molecules with efficient phosphorescence features are required with a fixed location on the surface. In this article, a potential TSD probe is presented in the form of a nanocomposite: we synthesize spherical silica particles with 2-naphthalene methanol molecules attached to the surface with a predefined surface density. The synthesis procedure is described in detail, and the obtained materials are characterized employing transmission electron microscopy imaging, Raman, and X-ray photoelectron spectroscopy. Finally, TSD experiments are carried out in order to confirm the phosphorescence properties of the obtained materials and the route to develop phosphorescent sensors at silica surfaces based on the presented results is discussed.

Pyridine Derivatives-A New Class of Compounds That Are Toxic to E. coli K12, R2-R4 Strains

A preliminary study of 2-amino-4-aryl-3,5-dicarbonitrile-6-thiopyridines as new potential antimicrobial drugs was performed. Special emphasis was placed on the selection of the structure of target pyridine derivatives with the highest biological activity against different types of Gram-stained bacteria by lipopolysaccharide (LPS). Herein, Escherichia coli model strains K12 (without LPS in its structure) and R2–R4 (with different lengths of LPS in its structure) were used. Studied target compounds were provided with yields ranging from 53% to 91% by the lipase-catalyzed one pot multicomponent reaction of various aromatic aldehydes with malononitrile, and thiols. The presented work showed that the antibacterial activity of the studied pyridines depends on their structure and affects the LPS of bacteria. Moreover, the influence of the pyridines on bacteria possessing smooth and rough LPS and oxidative damage to plasmid DNA caused by investigated compounds was indicated. Additionally, the modification of the bacterial DNA with the tested compounds was performed to detect new potential oxidative damages, which are recognized by the Fpg protein. The obtained damage modification values of the analyzed compounds were compared with the modifications after antibiotics were used in this type of research. The presented studies demonstrate that 2-amino-4-aryl-3,5-dicarbonitrile-6-thiopyridines can be used as substitutes for known antibiotics. The observed results are especially important in the case of the increasing resistance of bacteria to various drugs and antibiotics.

A Low-Dimensional Layout of Magnetic Units as Nano-Systems of Combinatorial Logic: Numerical Simulations

Nanotechnology has opened numerous ways for physically realizing very sophisticated nanodevices that can be fabricated exclusively using molecular engineering methods. However, the synthesis procedures that lead to the production of nanodevices are usually complicated and time consuming. For this reason, the destination materials should be well designed. Therefore, numerical simulations can be invaluable. In this work, we present numerical simulations of the magnetic behaviour of magnetic units shaped into nanometric strips as a low dimensional layout that can be used as nano-systems of combinatorial logic. We showed that magnetic layouts that contain fewer than 16 magnetic units can take on a specific configuration as a response to the input magnetic field. Such configuration can be treated as an output binary word. The layouts that contained various numbers of magnetic units showed different switching characteristics (utterly different order of inverting of strips' magnetic moments), thus creating numerous combinations of the output binary words in response to the analog magnetic signal. The number of possible output binary words can be increased even more by adding parameters--the system's initial magnetic configuration. The physical realization of the model presented here can be used as a very simple and yet effective encryption device that is based on nanometric arrays of magnetic units rather than an integrated circuit. The same information, provided by the proposed system, can be utilized for the construction of a nano-sensor for measuring of magnetic field with the possibility of checking also the history of magnetization.

All That Glitters Is Not Silver-A New Look at Microbiological and Medical Applications of Silver Nanoparticles

Silver and its nanoparticles (AgNPs) have different faces, providing different applications. In recent years, the number of positive nanosilver applications has increased substantially. It has been proven that AgNPs inhibit the growth and survival of bacteria, including human and animal pathogens, as well as fungi, protozoa and arthropods. Silver nanoparticles are known from their antiviral and anti-cancer properties; however, they are also very popular in medical and pharmaceutical nanoengineering as carriers for precise delivery of therapeutic compounds, in the diagnostics of different diseases and in optics and chemistry, where they act as sensors, conductors and substrates for various syntheses. The activity of AgNPs has not been fully discovered; therefore, we need interdisciplinary research to fulfil this knowledge. New forms of products with silver will certainly find application in the future treatment of many complicated and difficult to treat diseases. There is still a lack of appropriate and precise legal condition regarding the circulation of nanomaterials and the rules governing their safety use. The relatively low toxicity, relative biocompatibility and selectivity of nanoparticle interaction combined with the unusual biological properties allow their use in animal production as well as in bioengineering and medicine. Despite a quite big knowledge on this topic, there is still a need to organize the data on AgNPs in relation to specific microorganisms such as bacteria, viruses or fungi. We decided to put this knowledge together and try to show positive and negative effects on prokaryotic and eukaryotic cells.

Nanostructured Silica with Anchoring Units: The 2D Solid Solvent for Molecules and Metal Ions

The ability to organize, separate and manipulate individual molecules and ions on a surface opens up almost unlimited opportunities. However, it often requires complex techniques and a proper support material. With this in mind, we show a new concept of 2D solid solvents and review a simple and efficient procedure which is based on nanostructured forms of silica with anchoring units. We describe silica supports, such as spherical nanoparticles and mesoporous silica structures, as well as review the methods for chemical modification of the surface of silica with the functional groups. Finally, we present a few particular examples of the immobilization of molecules and ions on the surface of 2D solid solvents along with the experimental investigation of the obtained materials.

Synthesis in Silica Nanoreactor: Copper Pyrophosphate Quantum Dots and Silver Oxide Nanocrystallites Inside Silica Mezochannels

The synthesis routes are presented for the preparation of nanocomposites composed of nanocrystals placed inside SBA-15 silica pores. The procedures assume treating the silica channels as nanoreactors, where nanocrystals are created as a result of thermal decomposition of internal functional units. Its sizes and chemical composition can be modified by the change of functional group types and density inside silica channels. The procedure is demonstrated by the example of copper pyrophosphate quantum dots and silver oxide nanoparticles inside silica mezochannels. The method can be easily adopted to other types of nanocrystals that can be synthesized inside silica nanoreactors.

How to Control the Distribution of Anchored, Mn12-Stearate, Single-Molecule Magnets

Controlling the distribution of the Mn₁₂–stearate, single-molecule magnets (SMMs) anchored on a select surface is expected to be a new method for tuning its interactions, and an investigation on the magnetic properties of separated magnetic molecules is also lacking. The anchoring of the SMMs at the surface with an assumed statistic distance between each other is not an easy task; nevertheless, in this work, we show a synthesis which allows for this in detail. The immobilization of the Mn₁₂–stearate was demonstrated with the use of FTO glasses and spherical silica as substrates. Based on differential pulse anodic stripping voltammetry (DPASV) and transmission electron microscopy (TEM) observations, we proved the efficiency of the method proposed. We observed continuous decreasing the number of bonds, and afterward, decreasing in the number of immobilized molecules with an increasing the number of spacer units used for separation of the magnetic particles.

Mesoporous Silica-Based Materials for Electronics-Oriented Applications

Electronics, and nanoelectronics in particular, represent one of the most promising branches of technology. The search for novel and more efficient materials seems to be natural here. Thus far, silicon-based devices have been monopolizing this domain. Indeed, it is justified since it allows for significant miniaturization of electronic elements by their densification in integrated circuits. Nevertheless, silicon has some restrictions. Since this material is applied in the bulk form, the miniaturization limit seems to be already reached. Moreover, smaller silicon-based elements (mainly processors) need much more energy and generate significantly more heat than their larger counterparts. In our opinion, the future belongs to nanostructured materials where a proper structure is obtained by means of bottom-up nanotechnology. A great example of a material utilizing nanostructuring is mesoporous silica, which, due to its outstanding properties, can find numerous applications in electronic devices. This focused review is devoted to the application of porous silica-based materials in electronics. We guide the reader through the development and most crucial findings of porous silica from its first synthesis in 1992 to the present. The article describes constant struggle of researchers to find better solutions to supercapacitors, lower the k value or redox-active hybrids while maintaining robust mechanical properties. Finally, the last section refers to ultra-modern applications of silica such as molecular artificial neural networks or super-dense magnetic memory storage.

Functionalized mesoporous silica thin films as a tunable nonlinear optical material

The article is about a novel material for application in optoelectronic devices: mesoporous silica in the form of thin films with vertically aligned channels containing anchored propyl-copper-phosphonate functional groups. We described a synthesis route and carried out characterization of the structure to obtain its nonlinear optical (NLO) properties (second and third order harmonic generation). A quasi phase transition was found in the material resulting from modification of the functional group content. We also demonstrated that it is possible to modify NLO susceptibilities by tuning the distance between active polar units.

Relaxation and magnetocaloric effect in the Mn12 molecular nanomagnet incorporated into mesoporous silica: a comparative study

Successful incorporation of the Mn₁₂ molecules into silica channels has been attested with AC susceptometry and magnetocaloric effect measurements.

A novel hybrid-maximum neural network in stereo-matching process

In the present paper, the completely innovative architecture of artificial neural network based on Hopfield structure for solving a stereo-matching problem-hybrid neural network, consisting of the classical analog Hopfield neural network and the Maximum Neural Network-is described. The application of this kind of structure as a part of assistive device for visually impaired individuals is considered. The role of the analog Hopfield network is to find the attraction area of the global minimum, whereas Maximum Neural Network is finding accurate location of this minimum. The network presented here is characterized by an extremely high rate of work performance with the same accuracy as a classical Hopfield-like network, which makes it possible to use this kind of structure as a part of systems working in real time. The network considered here underwent experimental tests with the use of real stereo pictures as well as simulated stereo images. This enables error calculation and direct comparison with the classic analog Hopfield neural network as well as other networks proposed in the literature.