The synthesis of a new class of chiral mesoporous organosilica hollow nanostructures with tunable architectures is reported using a controlled stepwise sol-gel approach. By modulating the sequence of precursor addition, both yolk-shell and multishelled hollow nanospheres are obtained, enabling precise spatial control over the distribution of chiral and achiral domains. The chiral framework is constructed from enantiopure bridged organosilane monomers, synthesized by reacting 3-isocyanatopropyltriethoxysilane with either (R,R)- or (S,S)-diphenylethane-1,2-diamine (DPEN) or cyclohexane-1,2-diamine (DAC). The achiral component is formed from a mixture of tetraethyl orthosilicate (TEOS) and 1,2-bis(triethoxysilyl)ethane (BTSE), providing structural stability and mesoporosity. By controlling the sequence of precursor addition during the sol-gel process, the chiral framework is selectively introduced at different stages of formation, allowing precise spatial positioning within the hollow architecture. The resulting materials exhibit well-defined morphology, high organic content, and accessible mesoporosity. Enantioselective adsorption studies using tryptophan (Trp) reveal that the spatial location of the chiral framework is a decisive factor in chiral recognition. The highest enantioselectivity is observed when the chiral domains are confined within the interior of the structure, where the nanoconfined environment enhances host-guest interactions, yielding selectivity factors up to 7.0.

Hundreds of minerals are chiral, that is, they appear in nature in two forms—left-handed and right-handed. Yet except for quartz, this key structural property has remained, by and large, in shadow in the world of minerals in research, in museum displays and for collectors. This review is devoted to providing a full picture of chiral minerals in nature. It starts with a general outline of the crystallographic background needed for the characterization of chiral minerals, continues with a detailed description of the many chemical and physical processes leading to their formation and follows with their chemical reactivities and transformations, with their physical properties and with the ways to analyze and identify them. Many tables with listings of various types of chiral minerals are provided. The “missing-glove” situation, in which the recognition that a chiral mineral appears in nature in two distinctly forms is, by and large, missing, is described, and it is hoped that this review will spark interest in this aspect of nature’s crystals.

A positive correlation was observed between the enantiomeric excess (ee) of L-isovaline (L-iVal) and the degree of aqueous alteration (AqA) of carbonaceous meteorites. The origin of this remarkable phenomenon has remained enigmatic from two points of view: First, the correlation is between seemingly unrelated observables–nothing about AqA is of chiral characteristics; and second, following the accepted assumption that circularly polarized light (CPL) was the origin of the observed meteoritic ee of L-amino acids (AAs), it remined unclear why some of the observed levels of the ee of L-iVal in that correlation are significantly higher than those observed in laboratory simulations or those obtained from circular dichroism (CD) g-factor calculations. The current proposition accounting for this picture attributes late AqA conditions of the meteoritic parent bodies as providing the grounds for amplification of early initially CPL-generated low levels of L-ee. For reasons summarized below, this interpretation, which treats the CPL event and the AqA process as occurring in wide-time separated eras, is re-visited. An alternative interpretation of the observed correlation and of the high ee-values, is provided. It focuses on hydrophilic dust-aggregates clouds in wet star-forming regions in early pre-solar times, where both the CPL event and the grounds leading to the later AqA processes of the parent bodies, occurred. This mechanism removes the time separation between the initial ee formation and the AqA of the parent body, and replaces it with parallel processes, providing a scenario to the observation of high ee’s without total destruction, and to the apparent AqA/L-ee correlation. Although iVal is at the focus of this report, the steps of the development of the alternative mechanism and the conclusions that arise from it, are relevant and applicable to the general observations of L-ee’s of meteoritic AA’s.

AbstractAgricultural yields are often limited by damage caused by pathogenic microorganisms, including plant‐pathogenic bacteria. The chemical control options to cope with bacterial diseases in agriculture are limited, predominantly relying on copper‐based products. These compounds, however, possess limited efficacy. Therefore, there is an urgent need to develop novel technologies to manage bacterial plant diseases and reduce food loss. In this study, a new antimicrobial agent was developed using a doping method that entraps small bioactive organic molecules inside copper as the metal matrix. The food preservative agent lauroyl arginate ethyl ester (ethyl lauroyl arginate; LAE) was chosen as the doped organic compound. The new composites were termed LAE@[Cu]. Bactericidal assays against Acidovorax citrulli, a severe plant pathogen, revealed that LAE and copper in the composites possess a synergistic interaction as compared with each component individually. LAE@[Cu] composites were further characterised in terms of chemical properties and in planta assays demonstrated their potential for further development as crop protection agents.

We describe a new process for fabricating chiral organosilica 3D complex structures by combining digital light processing 3D printing with a sol-gel polycondensation process. The fabricated low-density objects have a high surface area with hierarchical porosity based on micropores resulting from the materials' design, and on macropores in the structure resulting from the 3D printing design. Thus, several 3D objects having complex shapes were printed by the polycondensation of 3-acryloxypropyltrimethoxysilane (APTMS) and chiral silane monomers that were obtained by reacting (1R,2R)-cyclohexane-1,2-diamine or (15,2S)-cyclohexane-1,2-diamine with (3-Isocyanatopropyl)triethoxysilane. The dual-function monomer APTMS enabled both localized photopolymerization and polycondensation. Printed gyroids, cubes, and disk-shaped chiral monoliths successfully revealed the enantioselective adsorption of tryptophan enantiomers. It was found that the macroscopic shape of the monolith affects the adsorption performance and its enantioselectivity. High enantioselectivity was obtained when the objects were formed from a chiral silane synthesized from (1R,2R)-cyclohexane-1,2-diamine: L-tryptophan was adsorbed similar to 10 fold higher than D-tryptophan. When the chiral object was fabricated using a chiral silane monomer prepared from (1S,2S)-cyclohexane-1,2-diamine, the enantioselectivity of the adsorption was reversed towards the D-tryptophan isomer. The new approach utilizes the 3D printing methodologies developed here for all-printed enantioselective separation columns; the printed macroporosity facilitates efficient flow, and the meso/microporous walls facilitate enantioselectivity.

Entrapment of glucose oxidase (GOx) within metallic gold converts this widely used enzyme into a general saccharide oxidase. The following sugar molecules were oxidized by the entrapped enzyme (in addition to d -glucose): fructose, xylose, l -glucose, glucose-6-phosphate, sucrose, lactose, methylglucoside, and the tri-saccharide raffinose. With the exception of raffinose, none of these sugars have a natural specific oxidase. The origin of this generalization of activity is attributed to the strong protein-gold 3D interactions and to the strong interactions of the co-entrapped CTAB with both the gold, and the protein. It is proposed that these interactions induce conformational changes in the channel leading to the active site, which is located at the interface between the two units of the dimeric GOx protein. The observations are compatible with affecting the specific conformation change of pulling apart and opening this gate-keeper, rendering the active site accessible to a variety of substrates. The entrapment methodology was also found to increase the thermal stability of GOx up to 100 °C and to allow its convenient reuse, two features of practical importance.

Major attention has been given to safety, environmental, and health hazard issues which arise from using toxic inorganic colorants and pigments in ceramic and glass technologies. A safe alternative is presented, wherein organic colorants approved for human use are entrapped within sol–gel aluminosilicate hybrid matrices and used for glazing porcelain ceramic and glass substrates. Among the colorants used are brilliant blue FCF replacing the toxic cobalt blue, curcumin replacing the toxic cadmium sulfide yellow, and a mixture of carmine and allura-red replacing the toxic cadmium selenide red. Additional advantages of the proposed approach are lowering of energy consumption, offering convenient and efficient recyclability of the colored glasses (thus also solving the current requirements for color-classified recycling), offering a huge library of thousands of organic colorants, opening for the artist and product designer a wide range of visual effects, and opening new artistic coloration methods to be explored. Full characterization was carried out including UV-vis spectroscopy, photoluminescence, topographic thickness analysis, wettability, SEM and XRD analyses, and FIB elemental analyses. The glazes are bright, of the order of 250 microns thick, crack free, chemically stable, with good adherence to both ceramic and glassy surfaces, and recyclable to the pure colorless ceramics or glass by heating. The potential for artistic applications, is demonstrated.

Mesoporous AlPO4 materials have attracted much attention in catalysis due to their high thermal and chemical stability. Of particular interest for catalysis is the pure stoichiometry high surface area (> 500 m2/g) mesoporous AlPO4 (mAlPO4) glass prepared via a template-free aqueous sol–gel synthetic route. Toward the application of this material for catalysis, we have developed methods for loading it with nanoparticles (NPs) of catalytic metals—Pd and Rh—and carried out a detailed characterization study of the resulting doped materials by a wide array of analytical methods, including synchrotron X-ray absorption spectroscopy, inelastic neutron scattering and more. The applicability of this material for catalysis, both by itself and as a support for catalytic NPs, was then evaluated. The pure mAlPO4 exhibited excellent acid-catalyzed [3 + 2] cycloaddition of nitriles and sodium azide. mAlPO4 loaded with the Pd NPs catalyzed very efficiently deoxygenation reactions of benzyl alcohols. mAlPO4 loaded with Rh NPs catalyzed with high selectivity, the hydrogenation of phenols and cresols and full conversion the hydrogenation of the industrially very high-volume toluene to methylcyclohexane. The materials-science aspects of these successful catalysts were studied in detail, leading, for instance, to the understanding of the important role of the interfacial Rh/Pd–O-P bonds.

We report that entrapping glucose oxidase (GOx) within metallic gold, expands its activity to become an oxidase for monosaccharides that do not have a natural enzyme with that activity—fructose and xylose—and that this entrapment also removes the enantioselectivity, rendering this enzyme capable of oxidizing the “wrong” l -enantiomer of glucose. These observations suggest that in this biomaterial adsorptive interactions of the outer regions of the protein with the gold cage, pull apart and widen the tunnel between the two monomeric units of GOx, to a degree that its stereoselectivity is compromised; then, the active sites which are more versatile than currently attributed to, are free and capable of acting on the foreign sugars. To test this proposition, we entrapped in gold l -asparaginase, which is also a dimeric enzyme (a dimer of tight dimers), and found, again, that this metallic biomaterial widens the activity of that enzyme, to include the D-amino acid counter enantiomer as well. Detailed kinetic analyses for all substrates are provided for the gold bio-composites, including determination of the difference between the activation energies towards two opposite enantiomers.

We developed synthetic methods for the doping of metals (M) with metallic nanoparticles (NPs). To the best of our knowledge - unlike oxides, polymers and carbon-based supports - metals were not used so far as supporting matrices for metallic NPs. The composites (denoted M1-NPs@M2) comprise two separate phases: the metallic NPs (the dopant) and the entrapping 3D porous metallic matrix, within which the NPs are intimately held and well dispersed. Two different general synthetic strategies were developed, each resulting in a group of materials with characteristic structure and properties. The first strategy uses pre-prepared NPs and these are entrapped during reductive formation of the metallic matrix from its cation. The second strategy is in situ growth of the doped metallic NPs within the pre-prepared entrapping metallic matrix. These two methods were developed for two types of entrapping metallic matrices with different morphologies: porous aggregated metallic matrices and metallic foams. The leading case in this study was the use of Pt as the NP dopant and Ag as the entrapping matrix, using all of the four combinations - entrapment or growth within aggregated Ag or Ag foam matrices. Full physical and chemical properties analysis of these novel types of materials was carried out, using a wide variety of analytical methods. The generality of the methods developed for these bi-metallic composites was investigated and demonstrated on additional metallic pairs: Au NPs within Ag matrices, Pd NPs within Ni matrices and Ir-NPs within a Rh matrix. As the main application of metallic NPs is in catalysis, the catalytic activity of M1-NPs@M2 is demonstrated successfully for entrapped Pt within Ag for reductive catalytic reactions, and for Pd within Ni for the electrocatalytic hydrogen oxidation reaction.

Aerogels, the lightest solid material known, are low-density nanoporous solids that have found a wide range of applications such as thermal insulation, scaffolds f or tissue engineering, catalysts supports, and micrometeorite collectors. Many types of materials have been used for their preparation, and ceramic/oxide aerogels are by far the most studied and applied family. Here we propose a new comprehensive solution to prepare these materials photochemically and fabricating them in highly complex shapes at all scales, from the macro scale down to the microns scale. The solution to these two challenges is linked, shown in the three photochemical approaches developed, allow unprecedented complexity in shape. The processes are mold irradiation, digital light processing (DLP) 3D printing, and a two-photon printing (TPP) process. The obtained 3D complex silicate objects display low density, high porosity, large surface area, and low thermal conductivity. The fabrication process also enables easy functionalization of the aerogels as inducing in them luminescence or making the printed object superhydrophobic by post printing process. The photochemical approach is ideal for the preparation of components of miniature devices, where low weight is a governing requirement. (c) 2021 Elsevier Ltd. All rights reserved.

We report on the successful fine-tuning of silica aerogel hydrophobicity, through a gas-phase surface modification process. Aerogel hydrophobicity is a widely discussed matter, as it contributes to the aerogel's preservation and determines its functionality. Still, a general procedure for tuning the hydrophobicity, without affecting other aerogel properties was missing. In the developed procedure, silica aerogel was modified with trimethylchlorosilane vapor for varying durations, resulting in gradual hydrophobicity, determined by solid-state NMR and contact angle measurements. The generality of this post-synthesis treatment allows its application on a variety of aerogel materials, while having minimum effect on their porosity and transparency. We demonstrate the applicability of the gradual hydrophobization by tuning drug release rates from the silica aerogel. Two chlorhexidine salts - widely employed as antiseptic agents - were used as model drugs, one representing a soluble drug, and the other an insoluble drug; they were entrapped in silica aerogel, following hydrophobization to varying degrees. The drug release patterns showed that depending on the degree, hydrophobization can increase or decrease release kinetics, compared to the unmodified aerogel. This arises from the effect of the hydrophobic degree on pore structure, diffusional rates and wetting of the aerogel carrier. We suggest the use of the gradual hydrophobization process for other drug-aerogel systems, as well as for other aerogel applications, such as transparent insulation panels, contaminate sorbents or catalysis supports.

We report the successful synthesis of magnetite aerogel, which has been a long-standing un-resolved challenge in magnetic materials and in aerogel materials. It is the first purely magnetic oxide-ceramic aerogel. So far, a leading approach in inducing magnetic properties in aerogels has been the dispersion of magnetic particles in various aerogel supports. This new aerogel has an ultralow density of 55 mg/mL, containing up to 98.7% air. The synthetic challenge required careful tailoring of the various steps, from the magnetite sol, through the gel, and up to the final aerogel. The rationale behind the various synthetic modifications is described in detail. We find that the ability to form monoliths is associated with dual porosity of the aerogel - interstitial microporosity of small magnetite aggregates that build the walls of the material, along with the wide macropores, typical of aerogels. Detailed mechanistic description is provided, along with intensive characterization of the material properties, the superparamagnetic properties, and more. Modifications of the magnetite are described, such as control of its density, mechanical reinforcement with glass fibers and inducing anisotropy by gelation under an external magnetic field. Magnetite aerogel was found to be very dark with extremely low reflectance in the IR range. Various applications of this ultra-light magnetic material are proposed, including lightweight magnetic actuator, support for separable catalysts and more. (C) 2021 The Authors. Published by Elsevier Ltd.

Enantioselective catalytic chiral reactions are important to all aspects of life sciences. Here we present the first utilization of the chiral induced spin selectivity (CISS) effect to form, enantioselectively, sp3 chiral centers in catalytic reactions, starting from achiral reagents. The enantiomeric symmetry is broken by affecting spin-controlled different reaction dynamics toward each of the enantiomers, using magnetic substrates. Two catalytic reactions are used for this purpose: a sulfide to sulfoxide oxidation and a Diels-Alder cycloaddition reaction, both catalyzed by hematite (Fe2O3). The proof of concept was evaluated by circular dichroism measurements and by chiral high-performance liquid chromatography techniques. These results provide direct evidence that the directionality of the electron spin can break enantiomeric symmetry, enabling asymmetric catalysis without using chiral reagents, solvents, or catalysts.

Iron and its alloys have been widely used for variety of medical implants. These are used for long term applications as cheap implants with high inertness and low corrosion rate, and also as implants with high biocompatibility (the fourth-generation type). Such degrading implants can provide a temporary scaffold while the body heals. In addition to the needed mechanical support, it is highly desirable to provide local drug therapy, providing antibacterial properties, preventing rejection of the implant, and more. So far, the combination of a degradable metallic implant which serves also as a three-dimensional matrix for drug release, remained un-answered. Here we present, we believe for the first time realization of this concept: Entrapment of drugs within a 3D degradable metal matrix—iron—from which the entrapped drugs are sustain-released. This new type of material is based on the molecular metals entrapment materials methodology, resulting in drugs@Fe. Two drugs have been successfully entrapped and released: chlorhexidine - an antiseptic drug, and rapamycin—used for avoiding transplant rejection. The delivery profiles of the composites were studied in two forms—powders and pressed discs showing two different types of drug release profiles. The release of the drugs from the powder hasa first order release profile, while the pressed disk is a slower, zero-order release profile, which is highly desirable due to the constant rate of the release. Full characterization of the metallic biomaterials is provided, including XRD, SEM, TGA, elemental analysis, and surface area/porosity analysis.

A fresh look on helicenes' enantiomerization process with a focus on ring conformation reveals that it can be described as a step-by-step mechanism in which maximal distortion is consecutively transferred along the helicene skeleton, head to tail. Density functional theory methods were used to compute the enantiomerization pathway, and continuous symmetry measures were applied to quantify the distortion of even-number helicenes with 8-14 rings. Our findings show that the distortion wave is additive-the process always starts from one edge of the helicene and progresses along the rings until the other edge is reached. As more rings are added to the helicene, extra steps are appended to the distortion wave. Implications of this fundamental process are discussed in light of similar natural phenomena from polymer dynamics to snake locomotion.

The major revolution in modern astronomy recognizing the universe as teeming with exoplanets, the discovery of liquid water in solar moons, and the continuing focus on Mars exploration, all accelerate the re-evaluation of potential biomarkers for extraterrestrial life. Based on life on planet Earth which relies heavily on chiral molecules and especially on homochiral families, the detection of molecules with these structural properties appears in all road-maps as prime indicators of extraterrestrial life. This review analyzes the strengths, bounds and potential weaknesses of relying on chirality and on homochirality as biomarkers, along with recommendations of how to practically use it. Some of the main issues presented, discussed and answered include: what is the extent to which chirality can be expected to be a universal feature of life; is detection of chirality enough or do we need also to detect homochirality; how justified is it to view life on Earth as purely homochiral; what are the weaknesses of the need to invent an arbitrary label of handedness (needed to define homochirality) and what are the pitfalls that emerge from these weaknesses; what stands behind a detected specific value of enantiomeric excess and what affects its values as we consider old, extinct life, just emerging embryonic life, or extant but rare life; how can one quantify the degree of homochirality; and, what are relevant experimental approached for detecting chirality on-ground and from distance? Finally, a summary with a concise list of recommendations is provided, along with a brief outlook.

The majority of oligomeric proteins form clusters which have rotational or dihedral symmetry. Despite the many advantages of symmetric packing, protein oligomers are only nearly symmetric, and the origin of this phenomenon is still in need to be fully explored. Here we apply near-symmetry analyses by the Continuous Symmetry Measures methodology of protein homomers to their natural state, namely their structures in solution. NMR-derived structural data serves us for that purpose. We find that symmetry deviations of proteins are by far higher in solution, compared to the crystalline state; that much of the symmetry distortion is due to amino acids along the interface between the subunits; that the distortions are mainly due to hydrophilic amino acids; and that distortive oligomerization processes such as the swap-domain mechanism can be identified by the symmetry analysis. Most of the analyses were carried out on distorted C2-symmetry dimers, but C3 and D2 cases were analyzed as well. Our NMR analysis supports the idea that the crystallographic B-factor represents non-classical crystals, in which different conformers pack in the crystal, perhaps from the conformers which the NMR analysis provides.

Aerogels, the world's lightest solids, possess extraordinary traits such as very low density, very high surface area, very high porosity and ultra-low heat conductivity. These traits made aerogels favorable in various applications, including high-performance thermal insulators, catalyst supports, electrode materials, random laser matrices, cosmic dust collectors and more. Of the many potential applications of aerogels, one of the most challenging has been the development of a general procedure for bioactive aerogels by the entrapment of enzymes within these air-light materials. The difficulty in reaching this "holy-grail" was dual: The special procedures for obtaining the unique structure of aerogel are destructive to enzymes; and the aerogels are extremely sensitive to any procedural modification. Thus, the use of pure silica aerogel for the entrapment of enzymes was not known. Here we present a generalized, bio-friendly procedure for the entrapment of enzymes in silica aerogel, retaining both the enzymatic activity and the air-light structure of the aerogel. All of the aerogel synthesis steps were modified and optimized for reducing the risk of enzyme denaturation, while preserving the aerogel characteristic structure of the composite. The entrapment of three enzymes of different types was demonstrated: glucose oxidase, acid phosphatase and xylanase. All aerogel-entrapped enzymes showed superior activity over the common method of sol-gel entrapment in xerogels, due to the much wider and open pore network of the former. Michaelis-Menten kinetics was observed for the entrapped enzymes, indicating that the enzymes are highly accessible and diffusional limitations are negligible. The Michaelis-Menten constant, Km, has remained at the same level, indicating that enzyme-substrate affinity was not affected. Thermal stabilization was observed for entrapped acid phosphatase reaching peak activity at 70 degrees C. Large molecular weight substrates such as xylan for xylanase, are no obstacle for the aerogel matrix, while completely inapplicable for the xerogel. All of these properties are highly relevant for biotechnological applications.

A new heterogeneous catalyst for hydrogen oxidation reaction (HOR), metallic palladium within which nanoparticles of ceria are entrapped, CeO 2 @Pd, is described. Its preparation is based on a new materials methodology of molecular doping of metals. The metallic matrix, which encages the nanoparticles, is prepared in foam architecture, to ensure easy molecular diffusion. Characterization of the structural properties of the CeO 2 @Pd composite using SEM, STEM, TEM, XRD, EXAFS and nitrogen adsorption reveals its morphological architecture, which leads to improved catalytic activity. In-situ electrochemical and H 2 temperature-programmed reduction (H 2 -TPR) spectra provide direct experimental evidence of the weakening of Pd‒H bond in the CeO 2 @Pd composites, relative to pure (undoped) Pd catalysts. Gas diffusion electrodes based on the entrapped CeO 2 @Pd catalysts demonstrated one order of magnitude higher activity than pure Pd analog in the HOR reaction in an alkaline medium.