We describe a novel manifestation of rigidochromic behavior in a series of tetranuclear Cu(I)–pyrazolate (Cu4pz4) macrocycles, with implications for solid-state luminescence at deep-blue wavelengths ...(<460 nm). The Cu4pz4 emissions are remarkably sensitive to structural effects far from the luminescent core: when 3,5-di-tert-butylpyrazoles are used as bridging ligands, adding a C4 substituent can induce a blue shift of more than 100 nm. X-ray crystal and computational analyses reveal that C4 units influence the conformational behavior of adjacent tert-butyl groups, with a subsequent impact on the global conformation of the Cu4pz4 complex. Emissions are mediated primarily through a cluster-centered triplet (3CC) state; compression of the Cu4 cluster into a nearly close-packed geometry prevents the reorganization of its excited-state structure and preserves the 3CC energy at a high level. The remote steric effect may thus offer alternative strategies toward the design of phosphors with rigid excited-state geometries.
The nucleocapsid (N) protein is one of the four structural proteins of the SARS-CoV-2 virus and plays a crucial role in viral genome organization and, hence, replication and pathogenicity. The ...N-terminal domain (NNTD) binds to the genomic RNA and thus comprises a potential target for inhibitor and vaccine development. We determined the atomic-resolution structure of crystalline NNTD by integrating solid-state magic angle spinning (MAS) NMR and X-ray diffraction. Our combined approach provides atomic details of protein packing interfaces as well as information about flexible regions as the N- and C-termini and the functionally important RNA binding, β-hairpin loop. In addition, ultrafast (100 kHz) MAS 1H-detected experiments permitted the assignment of side-chain proton chemical shifts not available by other means. The present structure offers guidance for designing therapeutic interventions against the SARS-CoV-2 infection.
A method for conjugation of ligands to the surface of exosomes was developed using click chemistry. Copper-catalyzed azide alkyne cycloaddition (click chemistry) is ideal for biocojugation of small ...molecules and macromolecules to the surface of exosomes, due to fast reaction times, high specificity, and compatibility in aqueous buffers. Exosomes cross-linked with alkyne groups using carbodiimide chemistry were conjugated to a model azide, azide-fluor 545. Conjugation had no effect on the size of exosomes, nor was there any change in the extent of exosome adherence/internalization with recipient cells, suggesting the reaction conditions were mild on exosome structure and function. We further investigated the extent of exosomal protein modification with alkyne groups. Using liposomes with surface alkyne groups of a similar size and concentration to exosomes, we estimated that approximately 1.5 alkyne groups were present for every 150 kDa of exosomal protein.
A sensitive label-free electrochemical immunosensor was designed using a novel signal amplification system for quantitative detecting hepatitis B surface antigen (HBsAg). Nitrogen-doped graphene ...quantum dots (N-GQDs) supported surfactant-free AuPdCu ternary nanoparticles (AuPdCu/N-GQDs), which featured with good conductivity and excellent catalytic properties for the reduction of hydrogen peroxide (H2O2), was synthesized by a simple and benign hydrothermal procedure. At the same time, the electroactive polymer nanospheres (PS) was synthesized by infinite coordination polymers of ferrocenedicarboxylic acid, which could play as carrier and electronic mediator to load AuPdCu/N-GQDs. The PS not only improved the ability to load antibodies because of the good biocompatibility, but also accelerated electron transport of the electrode interface attribute to plentiful ferrocene unit. Thus, the prepared AuPdCu/N-GQDs@PS has abilities of good biocompatibility, catalytic activity and electrical conductivity to be applied as transducing materials to amplify electrochemical signal in detection of HBsAg. Under optimal conditions, the fabricated immunosensor exhibited high sensitivity and stability in the detection of HBsAg. A linear relationship between current signals and the concentrations of HBsAg was obtained in the range from 10fg/mL to 50ng/mL and the detection limit of HBsAg was 3.3fg/mL (signal-to-noise ratio of 3). Moreover, the designed immunosensor with excellent selectivity, reproducibility and stability shows excellent performance in detection of human serum samples. Furthermore, this label-free electrochemical immunosensor has promising application in clinical diagnosis of HBsAg.
•The AuPdCu/N-GQDs was synthesized through a benign and surfactant-free method.•AuPdCu/N-GQDs@PS was applied as signal amplification platform in the immunosensor for the first time.•The PS was used to load more antibodies and accelerate electron transfer of the electrode interface.•The novel AuPdCu/N-GQDs@PS based immunosensor possesses excellent sensitivity, special selectivity and good stability.
A tubular micromotor with spatially resolved compartments is presented toward efficient site‐specific cargo delivery, with a back‐end zinc (Zn) propellant engine segment and an upfront cargo‐loaded ...gelatin segment further protected by a pH‐responsive cap. The multicompartment micromotors display strong gastric‐powered propulsion with tunable lifetime depending on the Zn segment length. Such propulsion significantly enhances the motor distribution and retention in the gastric tissues, by pushing and impinging the front‐end cargo segment onto the stomach wall. Once the micromotor penetrates the gastric mucosa (pH ≥ 6.0), its pH‐responsive cap dissolves, promoting the autonomous localized cargo release. The fabrication process, physicochemical properties, and propulsion behavior are systematically tested and discussed. Using a mouse model, the multicompartment motors, loaded with a model cargo, demonstrate a homogeneous cargo distribution along with approximately four‐fold enhanced retention in the gastric lining compared to monocompartment motors, while showing no apparent toxicity. Therapeutic payloads can also be loaded into the pH‐responsive cap, in addition to the gelatin‐based compartment, leading to concurrent delivery and sequential release of dual cargos toward combinatorial therapy. Overall, this multicompartment micromotor system provides unique features and advantages that will further advance the development of synthetic micromotors for active transport and localized delivery of biomedical cargos.
Tubular micromotors with spatially resolved compartments are fabricated with a Zn engine and a cargo‐loaded gelatin segment further protected by a pH‐responsive cap. The multicompartment motors display powerful propulsion in gastric fluid while showing enhanced distribution and localized cargo delivery in the gastric mucosa. Such capabilities make these compartmentalized motors a promising platform for transport and active delivery of a variety of therapeutic payloads.
Rapid increase in use of fungicides for the agricultural and industrial purposes has marked the deterioration of water resources which ultimately affects the human life. Accordingly, various attempts ...have been made in the removal of these noxious compounds. In the same context, we are presenting biopolymers based nanohydrogel sheets; guar gum-crosslinked-Soya lecithin nanohydrogel sheets (GG-crosslinked-SY NHS) used for the effective removal of a fungicide; thiophanate methyl from aqueous solution. Guar gum and soya lecithin were employed as the biopolymers in the fabrication of nanohydrogel sheets due to their non- toxic nature, easy availability, cheapness and significant properties. Due to the presence of highly reactive functional groups onto the surface of GG-crosslinked-SY NHS, good adsorption results have been obtained. Maximum adsorption capacity of 59.205mg/g was observed with 20mg GG-crosslinked-SY NHS and 25ppm thiophanate methyl solution concentration as calculated from the Langmuir isotherm. Results showed that neutral pH favoured the adsorption process. Kinetics results were indicative of the physical interactions between the thiophanate methyl and GG-crosslinked-SY NHS surface. Thermodynamic results have shown the spontaneous and endothermic adsorption process.
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•GG-crosslinked-SY nanohydrogel sheets prepared via facile greener microwave method•GG-crosslinked-SY NHS was used as an adsorbent for removal of thiophanate methyl.•The adsorption capacity was found to be 59.205mg/g.•H bonding and π-π interactions mainly governed between GG-crosslinked-SY NHS and thiophanate methyl
Bioorthogonal reactions are chemical reactions that neither interact with nor interfere with a biological system. The participating functional groups must be inert to biological moieties, must ...selectively reactive with each other under biocompatible conditions, and, for in vivo applications, must be nontoxic to cells and organisms. Additionally, it is helpful if one reactive group is small and therefore minimally perturbing of a biomolecule into which it has been introduced either chemically or biosynthetically. Examples from the past decade suggest that a promising strategy for bioorthogonal reaction development begins with an analysis of functional group and reactivity space outside those defined by Nature. Issues such as stability of reactants and products (particularly in water), kinetics, and unwanted side reactivity with biofunctionalities must be addressed, ideally guided by detailed mechanistic studies. Finally, the reaction must be tested in a variety of environments, escalating from aqueous media to biomolecule solutions to cultured cells and, for the most optimized transformations, to live organisms. Work in our laboratory led to the development of two bioorthogonal transformations that exploit the azide as a small, abiotic, and bioinert reaction partner: the Staudinger ligation and strain-promoted azide–alkyne cycloaddition. The Staudinger ligation is based on the classic Staudinger reduction of azides with triarylphosphines first reported in 1919. In the ligation reaction, the intermediate aza-ylide undergoes intramolecular reaction with an ester, forming an amide bond faster than aza-ylide hydrolysis would otherwise occur in water. The Staudinger ligation is highly selective and reliably forms its product in environs as demanding as live mice. However, the Staudinger ligation has some liabilities, such as the propensity of phosphine reagents to undergo air oxidation and the relatively slow kinetics of the reaction. The Staudinger ligation takes advantage of the electrophilicity of the azide; however, the azide can also participate in cycloaddition reactions. In 1961, Wittig and Krebs noted that the strained, cyclic alkyne cyclooctyne reacts violently when combined neat with phenyl azide, forming a triazole product by 1,3-dipolar cycloaddition. This observation stood in stark contrast to the slow kinetics associated with 1,3-dipolar cycloaddition of azides with unstrained, linear alkynes, the conventional Huisgen process. Notably, the reaction of azides with terminal alkynes can be accelerated dramatically by copper catalysis (this highly popular Cu-catalyzed azide–alkyne cycloaddition (CuAAC) is a quintessential “click” reaction). However, the copper catalysts are too cytotoxic for long-term exposure with live cells or organisms. Thus, for applications of bioorthogonal chemistry in living systems, we built upon Wittig and Krebs’ observation with the design of cyclooctyne reagents that react rapidly and selectively with biomolecule-associated azides. This strain-promoted azide–alkyne cycloaddition is often referred to as “Cu-free click chemistry”. Mechanistic and theoretical studies inspired the design of a series of cyclooctyne compounds bearing fluorine substituents, fused rings, and judiciously situated heteroatoms, with the goals of optimizing azide cycloaddition kinetics, stability, solubility, and pharmacokinetic properties. Cyclooctyne reagents have now been used for labeling azide-modified biomolecules on cultured cells and in live Caenorhabditis elegans, zebrafish, and mice. As this special issue testifies, the field of bioorthogonal chemistry is firmly established as a challenging frontier of reaction methodology and an important new instrument for biological discovery. The above reactions, as well as several newcomers with bioorthogonal attributes, have enabled the high-precision chemical modification of biomolecules in vitro, as well as real-time visualization of molecules and processes in cells and live organisms. The consequence is an impressive body of new knowledge and technology, amassed using a relatively small bioorthogonal reaction compendium. Expansion of this toolkit, an effort that is already well underway, is an important objective for chemists and biologists alike.
•Physicochemical and structural modification of starch depended on its type and annealing method.•Annealing could reduce the molecular weight of wheat starch.•Repeated annealing exhibited its ...superiority in improving crystal order of normal wheat starch.•Repeated annealing was more effective in increasing molecule interaction of starch.
Effects of repeated annealing treatments (8 cycles, 12 h each) or continuous annealing treatments (12–96 h) at 50 °C on structural, physicochemical, and digestive properties of normal and waxy wheat starches were investigated. Wheat starches retained the original crystalline structure of A-type after annealing. Annealing treatments increased crystallinity, short chain of amylopectin, viscosity, and gelatinization temperatures of starch. However, molecular weight, long chain of amylopectin, solubility, and swelling power of starch decreased after annealing. Additionally, annealing reduced the in vitro digestibility of wheat starches. The changes in properties of starch varied depending on starch type, normal or waxy, and annealing methods, repeated or continuous. The repeated annealing was found to be more effective in modification of normal wheat starch properties. However, continuous annealing efficiently modified properties of the waxy wheat starch. The obtained results may help in choosing appropriate applications of annealed wheat starches in the food industry.
Networks of single-walled carbon nanotubes (SWCNTs) decorated with Au-coated Pd (Au/Pd) nanocubes are employed as electrochemical biosensors that exhibit excellent sensitivity (2.6 mA mM−1 cm−2) and ...a low estimated detection limit (2.3 nM) at a signal-to-noise ratio of 3 (S/N = 3) in the amperometric sensing of hydrogen peroxide. Biofunctionalization of the Au/Pd nanocube-SWCNT biosensor is demonstrated with the selective immobilization of fluorescently labeled streptavidin on the nanocube surfaces via thiol linking. Similarly, glucose oxidase (GOx) is linked to the surface of the nanocubes for amperometric glucose sensing. The exhibited glucose detection limit of 1.3 μM (S/N = 3) and linear range spanning from 10 μM to 50 mM substantially surpass similar CNT-based biosensors. These results, combined with the structureʼs compatibility with a wide range of biofunctionalization procedures, would make the nanocube-SWCNT biosensor exceptionally useful for glucose detection in diabetic patients and well suited for a wide range of amperometric detection schemes for clinically important biomarkers.
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