Enantioselective Glutamic Acid Discrimination and Nanobiological Imaging by Chiral Fluorescent Silicon Nanoparticles.

Enantioselective discrimination of chiral molecules is essential in chemistry, biology, and medical science due to the configuration-dependent activities of enantiomers. Therefore, identifying a specific amino acid and distinguishing it from its enantiomer by using nanomaterials with outstanding performance are of great significance. Herein, blue- and green-emitting chiral silicon nanoparticles named bSiNPs and gSiNPs, respectively, with excellent water solubility, salt resistance, pH stability, photobleaching resistance, biocompatibility, and ability to promote soybean germination, were fabricated in a facile one-step method. Especially, chiral gSiNPs presented excellent fluorescence recognition ability for glutamic acid enantiomers within 1 min, and the enantiomeric recognition difference factor was as high as 9.0. The mechanism for enantiomeric fluorescence recognition was systematically explored by combining the fluorescence spectra with density functional theory (DFT) calculation. Presumably, the different Gibbs free energy and hydrogen-bonding interaction of the chiral recognition module with glutamic acid enantiomers mainly contributed to the difference in the fluorescence signals. Most noteworthy was the fact that the chiral gSiNPs can showcase not only the ability to recognize l- and d-glutamic acids in living cells but also the test strips fabricated by soaking gSiNPs can be applied for d-glutamic acid visual detection. As a result, this study provided insights into the design of multifunctional chiral sensing nanoplatforms for enantiomeric detection and other applications.

Composite materials based on covalent organic frameworks for multiple advanced applications.

Covalent organic frameworks (COFs) stand for a class of emerging crystalline porous organic materials, which are ingeniously constructed with organic units through strong covalent bonds. Their excellent design capabilities, and uniform and tunable pore structure make them potential materials for various applications. With the continuous development of synthesis technique and nanoscience, COFs have been successfully combined with a variety of functional materials to form COFs-based composites with superior performance than individual components. This paper offers an overview of the development of different types of COFs-based composites reported so far, with particular focus on the applications of COFs-based composites. Moreover, the challenges and future development prospects of COFs-based composites are presented. We anticipate that the review will provide some inspiration for the further development of COFs-based composites.

Controlled packing of chiral assembly scaffolds to promote chiral J-aggregation of carbocyanine dyes.

Controlled aggregation of dyes is crucial to achieve their desired optical and electronic properties. Here, we report the induction of chiral J-aggregation of carbocyanine dyes by using lysine-derived amphiphile assemblies as scaffolds in water. The molecular structure of the amphiphiles affected the packing of the assembly. The tight packing with some flexibility promoted the formation of J-aggregates of the dyes with strong chiroptical properties.

Sequential chiral induction between organic and inorganic supramolecular helical assemblies for the in situ formation of chiral carbon dots.

Self-organised helical bilayers of dicationic gemini surfactants confined in helical silica nanospace were transformed in situ to carbon dots (CDots) via pyrolysis. These water-dispersible CDots exhibit electronic absorption spanning the UV and visible range and possess symmetrical circular dichroism (CD) signals, the sign of which depends on the handedness of the helices.

Chiral H-aggregation-induced large stokes shift with CPL generation assisted by α-helical poly(L-lysine) substructure.

Fluorescent materials with large Stokes shifts have significant potential for use in optical applications. Typically, a synthetic design strategy is utilized for this purpose. In this study, we demonstrated a novel method by binding a chiral template to a nonchiral fluorescent agent without chemical modification. Specifically, α-helical poly(L-lysine) was employed as the chiral template, which interacted with a disulfonic fluorescent dye, such as NK2751. The dye caused excimer luminescence by inducing the formation of a chirally H-aggregated dimer only when poly(L-lysine) was in an α-helical shape. The result was a Stokes shift of 230 nm. Similar effects were not observed when the chiral template was in a random coil condition and the Stokes shift was less than 40 nm. These findings imply that H-aggregated dimerization, which often results in quenching, permits the electronic transitions necessary for fluorescence events by the formation of the chirally twisted state. In addition, we introduce for the first time the generation of circularly polarized luminescence using the chirality induction phenomena in a dye supported by poly(L-lysine).

Zwitterionic polymer-terminated porous silica stationary phases for highly selective separation in hydrophilic interaction chromatography.

We described two novel zwitterionic polymer-terminated porous silica stationary phases containing the same pyridinium cation and anions of different side chains (carboxylate and phosphonate groups) for use in hydrophilic interaction liquid chromatography (HILIC). These two novel columns were prepared by polymerizing 4-vinylpyridine and grafting it onto a silica surface, followed by quaternization reaction with 3-bromopropionic acid (Sil-VPC24) and (3-bromopropyl) phosphonic acid (Sil-VPP24), which possess positively charged pyridinium groups, and negatively charged carboxylate and phosphonate groups, respectively. The products obtained were verified through relevant characterization techniques such as elemental analysis, Fourier-transform infrared spectroscopy, thermogravimetric analysis, Zeta potential analysis, and Brunauer-Emmett-Teller analysis. The retention properties and mechanisms of different types of compounds (neutral, cationic, and anionic) on the two zwitterionic-modified silica stationary phases were studied by varying the buffer salt concentration and pH of the eluent. The separation of phenol and aromatic acids, disubstituted benzene isomers, sulfonamide drugs, as well as nucleosides/nucleobases were investigated on the two packed novel columns and a commercial zwitterionic column in identical HILIC mode, ensuring a thorough comparison between both novel columns and with a commercial standard. The results illustrated that various compounds could be separated up to various efficiencies based on the mechanism of hydrophilic interaction-based retention between the solutes and the two zwitterionic polymer stationary phases. The Sil-VPP24 column demonstrated the best separation performance out of the three, as well as flexible selectivity and excellent resolution. Both novel columns exhibited excellent stability and chromatographic repeatability for the separation of seven nucleosides and bases.

Carbonized π-conjugated polymer-coated porous silica: preparation and evaluating its extraction ability for berberine.

In view of the limitations of existing berberine solid-phase extraction adsorbents, this paper proposes a novel carbonized π-conjugated polymer-coated porous silica (SiO2@C-π-CP) adsorbent with simple process and low cost for efficient extraction of berberine by multiple interactions. Characterization methods, including Brunner-Emmet-Teller measurement, thermogravimetric analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy techniques, were used to verify the successful modification of carbonized π-conjugated polymer on the surface of porous silica. The berberine was selected as target molecule, and the adsorption mechanism and process were investigated through adsorption kinetics, adsorption isotherms, and thermodynamic studies. The fitting results show that the adsorption of berberine by SiO2@C-π-CP well conforms to the pseudo-second-order and Langmuir models. By optimizing the main SPE parameters, the SPE method based on SiO2@C-π-CP was developed. Excellent results were obtained, including low limit of detection (0.75 ng mL-1) and limit of quantification (2 ng mL-1), wide linearity (2-13,000 ng mL-1), and satisfactory relative standard deviations (RSD) of inter-day (1.5%) and intra-day (6.2%). Finally, the SiO2@C-π-CP also has been successfully used to the enrichment of berberine in real urine samples. This research makes clear that SiO2@C-π-CP has outstanding potential for trace enrichment of berberine alkaloids.

Chemical redox-induced chiroptical switching of supramolecular assemblies of viologens.

A chiral supramolecular assembly exhibiting redox-induced changes in its chiroptical properties was prepared using viologen-modified glutamide (G-V2+) derivatives. Achiral viologen moieties in the G-V2+ assembly were chirally orientated by glutamide groups, affording a unique orange-colored solution, with a visible absorption band at around 470 nm, having electronic circular dichroism (CD) signals (molar ellipticity [θ] = 0.58 × 105 deg cm2 dmol-1: absorption dissymmetry factors (g) = 5.2 × 10-3 at 512 nm). The G-V2+ could be reduced to its cation radical (G-V+˙) but retains its chiral assembly. After chemical reduction, the color change from orange to blueish violet, indicating an absorption band at approximately 560 nm, and the sign change of the CD signal from positive to negative ([θ] = -0.36 × 105 deg cm2 dmol-1; g = -2.9 × 10-3 at 580 nm) were observed in water. Subsequent oxidation re-introduces the G-V2+ chiroptical behavior before reduction.

Decreased physical activity with subjective pleasure is associated with avoidance behaviors.

The main hypothesis for the relation between physical activity and mental health is that autonomous motivation, such as subjective pleasure for the activity, plays an important role. However, no report has described empirical research designed to examine the role of subjective pleasure in the relation between objectively measured physical activity and psychological indexes. We used accelerometers to collect data indicating participants' physical activity intensity during a week. Participants recorded their subjective pleasure of activity per hour. In 69% of them, the individual correlation coefficients between physical activity and pleasure in an hour (an index of Physical Activity-Pleasure; PA-PL) were positive (r = 0.22, 95%Cl = [0.11-0.38]), indicating that pleasant sensations increased concomitantly with increasing physical activity. Conversely, 31% participants exhibited negative values of PA-PL, which means that the increase in physical activity had the opposite effect, decreasing pleasure. Multiple linear regression analysis showed that avoidance/rumination behaviors decreased significantly with increased PA-PL (ß = -6.82, 95%CI: [-13.27 to -0.38], p < .05). These results indicate that subjective pleasure attached to the PA is more important than the PA amount for reducing depressive behavior.

A Molecular Shape Recognitive HPLC Stationary Phase Based on a Highly Ordered Amphiphilic Glutamide Molecular Gel.

Chiral glutamide-derived lipids form self-assembled fibrous molecular gels that can be used as HPLC organic phases. In this study, HPLC separation efficiency was improved through the addition of branched amphiphilic glutamide lipids to the side chains of a terminally immobilized flexible polymer backbone. Poly(4-vinylpyridine) with a trimethoxysilyl group at one end was grafted onto the surface of porous silica particles (Sil-VP15, polymerization degree = 15), and the pyridyl side chains were quaternized with a glutamide lipid having a bromide group (BrG). Elemental analysis indicated that the total amount of the organic phase of the prepared stationary phase (Sil-VPG15) was 38.0 wt%, and the quaternization degree of the pyridyl groups was determined to be 32.5%. Differential scanning calorimetric analysis of a methanol suspension of Sil-VPG15 indicated that the G moieties formed a highly ordered structure below the phase transition temperature even on the silica surface, and the ordered G moieties exhibited a gel-to-liquid crystalline phase transition. Compared with a commercially available octadecylated silica column, the Sil-VPG15 stationary phase showed high selectivity toward polycyclic aromatic hydrocarbons, and particularly excellent separations were obtained for geometrical and positional isomers. Sil-VPG15 also showed highly selective separation for phenol derivatives, and bio-related molecules containing phenolic groups such as steroids were successfully separated. These separation abilities are probably due to multiple interactions between the elutes and the highly ordered functional groups, such as the pyridinium and amide groups, on the highly ordered molecular gel having self-assembling G moieties.

Chirality induction to achiral molecules by silica-coated chiral molecular assemblies.

Hybrid silica-organic nanohelices are used to organize a large variety of nonchiral small organic molecules or inorganic anions to nanometer-sized assemblies. Such chiral organization of achiral molecules induces chiroptical properties as detected by vibrational or electronic circular dichroism (CD), as well as from circularly polarized luminescence (CPL).

Enantioselective Self-Assembled Nanofibrillar Network with Glutamide-Based Organogelator.

A chiral molecular gelation system, as a chiral host, was used to effectively realize enantioselectivity using the simple carboxylic acid functional group. For this purpose, an L-glutamic-acid-based lipidic amphiphile (G-CA) with a carboxylic head group was selected and its responsiveness to cationic guest molecules was investigated. The dispersion morphology of G-CA in its solution state was examined by confocal and transmission electron microscopies, while interactions between the G-CA, as the host system, and guest molecules were evaluated by UV-visible, circular dichroism, and fluorescence spectroscopies. As a result, enantioselectivity was effectively induced when G-CA formed highly ordered aggregates that provide negatively charged surfaces in which carboxyl groups are assembled in highly ordered states, and when the two cationic groups of the guest molecule are attached to this surface through multiple interactions.

Lanthanide ion-doped silica nanohelix: a helical inorganic network acts as a chiral source for metal ions.

We demonstrate that lanthanide ions doped in nanometrical silica helices with a chirally arranged siloxane network without any organic mediates show induced chiroptical properties such as circular dichroism and circularly polarized luminescence.

Hetero-network hydrogels crosslinked with silica nanoparticles for strategic control of thermal responsive property.

Two thermoresponsive copolymers with different lower critical solution temperatures (LCSTs) were crosslinked using silica nanoparticles to afford hybrid hydrogels exhibiting two distinct thermo-responsivities. The thermo-responsive copolymers were synthesised by free radical polymerisation from a monomer with a reactive side chain (3-methacryloxypropyl trimethoxysilane (S)) and water-soluble monomers with different thermo-responsivities (N-isopropyl acrylamide (N) or N-(3-methoxy propyl)acrylamide (M)). The obtained reactive copolymers, poly(N-isopropyl acrylamide-co-3-methacryloxypropyl trimethoxysilane) (pNS) and poly(N-(3-methoxy propyl acrylamide-co-3-methacryloxypropyl trimethoxysilane)) (pMS), were characterized by multiple techniques including 1H NMR and FTIR spectroscopy. The hetero-network hybrid hydrogels were easily prepared by mixing aqueous solutions of the copolymer with an aqueous colloidal silica suspension; their gelation properties could be tuned by varying the amounts of pNS, pMS, and Si. Differential scanning calorimetric analysis showed that the hetero-network hydrogel exhibited a critical two-step phase transition at temperatures around the LCST of each copolymer (33 °C for pNS, 73 °C for pMS), indicating that each polymer does not disturb the phase transitions of the other. The deswelling of the hetero-network hydrogel could be controlled with respect to temperature and time.

Remarkable enhancement of thermal stability of epoxy resin through the incorporation of mesoporous silica micro-filler.

For the first time, we incorporated mesoporous micro-silica (5 µm, pore size = 50 nm) as a filler in epoxy resin aiming to enter polymer into the pore of the silica. As expected, the thermal stability of the composite increased remarkably, followed by noteworthy thermal degradation kinetics when compared to the controlled cured epoxy resin. Composites were prepared by the direct dispersion of modified nano-silica, modified mesoporous micro-silica, unmodified mesoporous micro-silica, non-porous micro-silica, and irregular micro-silica of various pore sizes as fillers in diglycidyl ether of bisphenol-A epoxy resin via ultra-sonication and shear mixing, followed by oven-curing with 4,4-diaminodiphenyl sulfone. DSC and TGA analyses demonstrated a higher glass transition temperature (increased by 3.65-5.75 °C) and very high activation energy for thermal degradation (average increase = 46.2%) was obtained for the same unmodified silica composite compared to pure epoxy, respectively.

Fabrication of Carbon-Like, π-Conjugated Organic Layer on a Nano-Porous Silica Surface.

This paper presents a new type of black organic material-porous silica composite providing an extremely highly selective adsorption surface. This black composite was prepared by lamination on nano-sized pores with a carbon-like, π-extended structure, which can be converted via the on-site polymerization of 1,5-dihydroxynaphthalene with a triazinane derivative and a thermally induced condensation reaction with denitrification. This bottom-up fabrication method on porous materials had the great advantage of maintaining the pore characteristics of a raw porous material, but also the resultant black surface exhibited an extremely high molecular-shape selectivity; for example, that for trans- and cis-stilbenes reached 14.0 with the black layer-laminated porous silica, whereas it was below 1.2 with simple hydrophobized silica.

Preparation of Vortex Porous Graphene Chiral Membrane for Enantioselective Separation.

Chiral materials are usually the key to the separation of chiral membranes. In this work, we propose a new strategy that chiral porous graphene membrane can be fabricated from nonchiral porous graphene by mechanical stirring to induce vortex structure. Porous graphene with controlled, nanosized pores was synthesized by a newly designed, one-pot process directly from graphite as opposed to graphene oxide. Then porous graphene was immobilized on ultrafiltration membrane through filtering while stirring to form porous graphene membrane, which was applied for enantioselective separation toward DL-amino acids: for example, the separation factor of l-/d-phenylalanine reached 4.76. Interestingly, we first observed that the front and back sides of the porous graphene membrane exhibited opposite optical activities.

Chirality induction on non-chiral dye-linked polysilsesquioxane in nanohelical structures.

We demonstrate the direct induction of chirally arranged organic dye-linked polysilsesquioxane through a sol-gel transcription using a chiral supramolecular template. The chiral arrangement was confirmed by using electronic and vibrational circular dichroism and circularly polarized luminescence spectroscopies.

Chiroptical property tuning of supramolecular assemblies in polymer matrices.

Chiroptical materials have received much attention in diverse fields for applications such as displays, sensors, smart memory devices, and catalysis. Here, we develop a simple fabrication method for polymer films with tunable chiroptical properties using small amounts of self-assembling fluorescent dye as an additive. Both the circular dichroism and circularly polarized luminescence signals of the film can be tuned between positive and negative values by thermal treatment. The chiroptical properties can be varied by slight changes in the orientation of chiral pyrene moieties in self-assembled nanofibril networks.

Dispersible chitosan particles showing bacteriostatic effect against Streptococcus mutans and their dental polishing effect.

Nontoxic and biodegradable chitosan is potentially useful in various applications. We prepared submicron chitosan particles with high dispersibility in aqueous solution utilizing the electrostatic interaction phase separation method described in a previous report, but using citric acid as the polyvalent anionic compound instead of sodium sulfate. The submicron chitosan particles showed significant antibacterial activity and anti-adhesive action against Streptococcus mutans, even at around neutral pH. However, chitosan granules showed no antibacterial activity under the same conditions. The addition of the chitosan particles to dental polishing paste provided stainless steel discs (the same hardness as dental enamel) with a smoother surface than polishing paste without additives. In view of their submicron size and antibacterial activity, chitosan particles could potentially be multifunctional components of oral and dental cleaning materials.