Proline–cyclodextrin conjugates: synthesis and evaluation as catalysts for aldol reaction in water

The synthesis of six conjugates of l-proline and β-cyclodextrin and their evaluation as catalysts of aldol reaction in water are described. The results indicated that the nature of the linker between proline and β-cyclodextrin is important for catalytic activity; the one with the most flexible linker gave the best results. Inhibition experiments showed that the cavity of β-cyclodextrin plays a role in the catalysis. Permethylation of the cyclodextrin hydroxyl groups led to higher conversion rates.     

Evidence for conformational differences in aqueous and crystalline structures of α-bungarotoxin and cobratoxin

Laser Raman spectroscopy has been employed to investigate the structures of α-bungarotoxin (Bungarus multicinctus) and cobratoxin (Naja naja siamensis) in H₂O and D₂O solutions. Structures of the aqueous neurotoxins are compared with one another and with the X-ray crystal structures. The results indicate that the solution and crystal molecular structures of cobratoxin are in substantial agreement with one another, but those of α-bungarotoxin are not. Raman data provide no evidence for strained disulfides in aqueous α-bungarotoxin, although strained CSSC dihedral angles are indicated for the X-ray crystal structure. The data are interpreted as evidence for a strained molecular conformation of α-bungarotoxin in the crystal, which converts to a relaxed, more energetically favorable conformation in aqueous solution. Raman spectra also suggest more β-strand secondary structure in aqueous α-bungarotoxin (47 ± 5%) than in the crystalline form ( < 10%). The high β-strand content measured by Raman spectroscopy could be due to either a secondary structure in solution that is appreciably different than that of the crystal, or to the imprecision of the Raman method in distinguishing peptide configurations that are vibrationally equivalent but conformationally inequivalent. Aqueous α-bungarotoxin and cobratoxin also differ from one another in amino acid side chain orientations and interactions, though not in main chain conformations. Different geometries are indicated for cystine CCSS dihedral angles, and different hydrogen bonding states are indicated for internal tyrosines. Tyrosine-24 of α-bungarotoxin is shown to donate a strong hydrogen bond to a negative acceptor, deduced to be glutamate-41, whereas the equivalently positioned residue of cobratoxin is apparently hydrogen bonded to solvent molecules.     

Yellow-green fluorescent carbon dots as fluorescent/colorimetric dual-mode probe for the detection of pH value and its application in fluorescent paintingEI北大核心CSCD

Yellow-green fluorescent carbon dotsY-G-CDswas used as a fluorescent/colorimetric dual-mode nanoprobe for the detection of pH value in solution and fluorescent painting. The fluorescent intensity and absorbance of the nanoprobe showed strong pH dependence. The fluorescent intensity at 520 nm and the ratio of absorbance at 438 and 386 nm showed good linear relationships with the pH valuein the ranges of pH 5.9-7.7 and pH 5.9-8.0respectively. As a fluorescent nanoprobeY-G-CDs had good photo stability at pH 5.96.8 and 8.0and good reversibility between pH 5.9 and pH 7.7. The detection of pH value of solution was not affected by other interfering substances. In additionthe Y-G-CDs with excellent fluorescent performance have been successfully applied in fluorescent painting as a fluorescent ink. Under the irradiation of 365 nm UV lightthe drawing image emitted bright green fluorescence with clear outline. © 2022, Youke Publishing Co.,Ltd. All rights reserved.     

C–H...O and C–H...N interactions in RNA structures

Small molecule studies indicate that C–H...X interactions (X: O,N) constitute weak H-bonds. We have performed a comprehensive analysis of their occurrence and geometry in RNA structures. Here, we report on statistical properties of the total set of interactions identified and discuss selected motifs. The distance/angle distribution of all interactions exhibits an excluded region where the allowed C–H...X angle range increases with an increasing H...X distance. The preferred short C–H...X interactions in RNA are backbone-backbone contacts between neighbour nucleotides. Distance/angle distributions generated for various interaction types can be used for error recognition and modelling. The axial C2′(H)...O4′ and C5′(H)...O2′ interactions connect two backbone segments and form a seven-membered ring that is specific for RNA. An AA base pair with one standard H-bond and one C–H...N interaction has been identified in various structures. Despite the occurrence of short C–H...X contacts their free energy contribution to RNA stability remains to be assessed. Received: 17 May 1998 / Accepted: 4 August 1998 / Published online: 2 November 1998     

Dynamical and structural properties of flavin adenine dinucleotide in aqueous solutions and bound to free and sol–gel immobilized glucose oxidase

Journal of Sol-Gel Science and Technology - Optical properties of flavin adenine dinucleotide moiety are nowadays widely used for biotechnological applications. In particular when flavin adenine...     

Novel naphthalimide–aminobenzamide dyads as OFF/ON fluorescent supramolecular receptors in metal ion binding

A series of novel naphthalimide–aminobenzamide (NAPIM-2ABZ) dyads 3 connected by different length polymethylene chains were synthesized and studied as fluorescent supramolecular receptors in metal ion binding. The photophysical properties were evaluated and compared with separated chromophores. The electronic absorption spectra of dyads 3 showed no interaction between chromophores in the ground state. The fluorescence quantum yields were lower in dyads 3 in comparison with N-propyl-2-aminobenzamide (8). The fluorescence quenching is attributed to a PET mechanism between fluorophores (from 2ABZ to NAPIM), which is dependent on the polymethylene chain length. In metal binding study was found a response towards transition metal ions such as Hg(II), Cu(II), Zn(II) and Ni(II). Dyad 3b presented selectivity towards Cu(II). The UV-vis, IR and ¹H-NMR studies demonstrated the interaction with 2ABZ moiety in the ground state, and interestingly dyads with shorter polymethylene chains 3a (n = 0), 3b (n = 1) and 3c (n = 2) exhibited an OFF/ON fluorescence behaviour due to the PET inhibition and the quenching of 2ABZ fluorescence. Dyads 3d (n = 4) and 3e (n = 6) presented opposite response ON/OFF in the complex with metal ions evidencing the absence of PET in these dyads.     

Synthesis and characterization of quinoline-derivated fluorescent sol–gel-imprinted polymer as a chemosensor for sensing of uranyl ion

Journal of Sol-Gel Science and Technology - In this work, chemosensor that contains 3-aminoquinoline derivative of silane coupling agent grafted to the sol–gel polymer has been synthesized...     

A simple Schiff base as ‘naked eye’ and fluorescent ‘on–off’ sensor for detecting cyanide in mixed aqueous solution

A simple Schiff base sensor (L₁) derived from N-(1-naphthyl) ethylenediamine dihydrochloride was designed and synthesised by simple chemistry procedures. The sensor exhibited a visible colour change observed by both colorimetric and fluorimetric responses for cyanide ion in aqueous solution. The detection of cyanide was performed via the nucleophilic attack of cyanide anion on the imine group of the sensor with a 1?:?1 binding stoichiometry. Moreover, test strips based on the sensor were fabricated, which served as convenient and efficient CN^? test kits and the sensor L₁ is a good way to detect hydrogen cyanide in aqueous extracts of sprouting potatoes.     

Technology and structural characteristics of electrode material in the Pt/C–Taunite-MD–Nafion system

Laboratory technique was developed for fabrication of an electrode material containing a platinized carbon black, carbon nanofibers, and proton-conducting polymer Nafion. Scanning and transmission electron microscopy was used to study the structure of the material and experimental dependences were obtained that relate the properties and structure of the electrode material to its structure and fabrication technique and make it possible to obtain a material with prescribed service characteristics.     

O-Aryloxime ether analogues as novel and efficient ligands for palladium-catalyzed Suzuki–Miyaura coupling in water

O-Aryloxime ether analogues L1–L3 were studied as ligands in palladium-catalyzed Suzuki–Miyaura cross-coupling reaction of aryl bromides and aryl boronic acids in water at room temperature. Reaction conditions for the cross-coupling were optimized using PdCl₂ and Pd(OAc)₂ under aerobic condition. From the three electronically diverse O-aryloxime ether ligands studied herein, the use of 1-phenyl-ethanone O-(4-chloro-phenyl)-oximeL2 exhibits the best catalytic system in the presence of K₂CO₃ as the base and TBAB as the promoter.     

Synthesis and evaluation of peptide–fentanyl analogue conjugates as dual µ/δ-opioid receptor agonists for the treatment of pain

Novel peptide-fentanyl analogue conjugates were synthesized by the covalent coupling of carfentanyl derivatives to the C-terminus or N-terminus of the conformationally constrained dermorphin tetrapeptide BVD03 via a chemical linker. The carfentanyl-related analogues displayed distinct binding and functional activities at µ/δ opioid receptors (MOR/DOR) and antinociceptive effects when conjugated to the peptide. The most potent compound, SW-LJ-11, displayed mixed MOR/DOR agonist properties in the low nanomolar range and significant analgesic efficacy in vivo in four classic mouse models of pain. Interestingly, SW-LJ-11 did not exhibit any physical dependence or respiratory depression, in contrast to an equipotent analgesic dose of morphine or BVD03, indicating that the use of opioid peptide–fentanyl analogue conjugates as dual MOR/DOR agonists may be a promising strategy for obtaining safer opioids.     

Advances and trends in the design, analysis, and characterization of polymer–protein conjugates for “PEGylaided” bioprocesses

In addition to their use as therapeutics and because of their enhanced properties, PEGylated proteins have potential application in fields such as bioprocessing. However, the use of PEGylated conjugates to improve the performance of bioprocess has not been widely explored. This limited additional industrial use of PEG-protein conjugates can be attributed to the fact that PEGylation reactions, separation of the products, and final characterization of the structure and activity of the resulting species are not trivial tasks. The development of bioprocessing operations based on PEGylated proteins relies heavily in the use of analytical tools that must sometimes be adapted from the strategies used in pharmaceutical conjugate development. For instance, to evaluate conjugate performance in bioprocessing operations, both chromatographic and non-chromatographic steps must be used to separate and quantify the resulting reaction species. Characterization of the conjugates by mass spectrometry, circular dichroism, and specific activity assays, among other adapted techniques, is then required to evaluate the feasibility of using the conjugates in any operation. Correct selection of the technical and analytical methods in each of the steps from design of the PEGylation reaction to its final engineering application will ensure success in implementing a "PEGylaided" process. In this context, the objective of this review is to describe technological and analytical trends in developing successful applications of PEGylated conjugates in bioprocesses and to describe potential fields in which these proteins can be exploited.     

An in situ generated CuI/metformin complex as a novel and efficient catalyst for C–N and C–O cross-coupling reactions

An in situ generated complex of copper(I) and a biguanide, namely metformin, was found to be a highly efficient homogeneous catalyst in N/O-arylation reactions. The O-arylation of substituted phenols with various aryl iodides and bromides was also achieved using this copper catalyst to afford diaryl ethers in good to excellent yields in DMF. This heterogeneous copper catalyst also promotes the N-arylation of imidazole with a variety of aryl halides (Cl, Br, I) in acetonitrile.     

Nonpolar organic compounds in fine particles: quantification by thermal desorption–GC/MS and evidence for their significant oxidation in ambient aerosols in Hong Kong

Nonpolar organic compounds (NPOCs) in ambient particulate matter (PM) commonly include n-alkanes, branched alkanes, hopanes and steranes, and polycyclic aromatic hydrocarbons (PAHs). The recent development of thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) has greatly reduced time and labor in their quantification by eliminating the laborious solvent extraction and sample concentration steps in the traditional approach that relies on solvent extraction. The simplicity of the TD-GCMS methods has afforded us concentration data of NPOCs in more than 90 aerosol samples in two aerosol field studies and 20 vehicular emissions-dominated source samples in Hong Kong over the past few years. In this work, we examine the interspecies relationships between select NPOCs and their concentration ratios to elemental carbon (EC) among the ambient samples and among the source samples. Our analysis indicates that hopanes were mainly from vehicular emissions and they were significantly oxidized in ambient PM. The hopane/EC ratio in ambient samples was on average less than half of the ratio in vehicular emissions-dominated source samples. This highlights the necessity in considering oxidation loss in applying organic tracer data in source apportionment studies. Select PAH/EC ratio–ratio plots reveal that PAHs had diverse sources and vehicular emissions were unlikely a dominant source for PAHs in Hong Kong. Biomass burning and other regional sources likely dominated ambient PAHs in Hong Kong.     

Gold nanoparticle–antibody conjugates for specific extraction and subsequent analysis by liquid chromatography–tandem mass spectrometry of malondialdehyde-modified low density lipoprotein as biomarker for cardiovascular risk

Oxidized low-density lipoproteins (OxLDLs) like malondialdehyde-modified low-density lipoprotein (MDA-LDL) play a major role in atherosclerosis and have been proposed as useful biomarkers for oxidative stress. In this study, gold-nanoparticles (GNPs) were functionalized via distinct chemistries with anti-MDA-LDL antibodies (Abs) for selective recognition and capture of MDA-LDL from biological matrices. The study focused on optimization of binding affinities and saturation capacities of the antiMDA-LDL-Ab-GNP bioconjugate by exploring distinct random and oriented immobilization approaches, such as (i) direct adsorptive attachment of Abs on the GNP surface, (ii) covalent bonding by amide coupling of Abs to carboxy-terminated-pegylated GNPs, (iii) oriented immobilization via oxidized carbohydrate moiety of the Ab on hydrazide-derivatized GNPs and (iv) cysteine-tagged protein A (cProtA)-bonded GNPs. Depending on immobilization chemistry, up to 3 antibodies per GNP could be immobilized as determined by ELISA. The highest binding capacity was achieved with the GNP-cProtA-Ab bioconjugate which yielded a saturation capacity of 2.24 ± 0.04 μg mL⁻¹ GNP suspension for MDA-LDL with an affinity K_d of 5.25 ± 0.11 × 10⁻¹⁰ M. The GNP-cProtA-antiMDA-LDL bioconjugate revealed high specificity for MDA-LDL over copper(II)-oxidized LDL as well as native human LDL. This clearly demonstrates the usefulness of the new GNP-Ab bioconjugates for specific extraction of MDA-LDL from plasma samples as biomarkers of oxidative stress. Their combination as specific immunoextraction nanomaterials with analysis by LC–MS/MS allows sensitive and selective detection of MDA-LDL in complex samples.     

A novel naphthalimide–glutathione chemosensor for fluorescent detection of Fe3+ and Hg2+ in aqueous medium and its application

By rationally introducing glutathione functionalized 1, 8–naphthalimide, a novel fluorescent chemosensor (NG) was successfully synthesized. NG can high selectively and sensitively recognize Fe³⁺/Hg²⁺ ions through quenching of fluorescence among all kinds of common metal ions in aqueous medium. The binding stoichiometry ratio of NG–Fe³⁺ is verified as 2:1and NG–Hg²⁺ as 1:2 confirmed by Job's plot method, FT-IR, ¹H NMR and ESI–MS spectrum, and the possible sensing mechanism were also proposed. The chemosensor NG toward Fe³⁺ and Hg²⁺ displays the excellent advantages of high selectivity and sensitivity, low detection limits (7.92?×?10^?8 and 4.22?×?10^?8?M), high association constants (3.37?×?10⁸ and 8.14?×?10⁴?M^?2), instataneous response (about 10s) and wide pH response range (3.0–8.0). Importantly, the chemosensor NG was successfully applied to determine Hg²⁺ in tap water. Meanwhile, the test strips based on NG were prepared, which could conveniently and efficiently detect Fe³⁺ and Hg²⁺. Moreover, the complex of NG and Fe³⁺ (NG–Fe³⁺) showed high selectivity and sensitivity for H₂PO₄￣ over many other anions in the same medium.     

Characterization and application of quantum dot nanocrystal–monoclonal antibody conjugates for the determination of sulfamethazine in milk by fluoroimmunoassay

Quantum dot (Qdot) nanocrystals have been increasingly used as fluorescence labels in fluoroimmunoassays recently because of their excellent optical characteristics. In this paper, a new monoclonal antibody (MAb) against sulfamethazine (SMZ) was successfully produced and linked to Qdot nanocrystals by covalent coupling. The Qdot–MAb conjugates were characterized by SDS-PAGE and high-performance capillary electrophoresis (HPCE). An enzyme-linked immunosorbent assay (ELISA) method was utilized to evaluate the antigen–antibody binding affinity and then a novel direct competitive fluorescence-linked immunosorbent assay (cFLISA) for the detection of SMZ in milk by using Qdots as fluorescent labels was evaluated. The results showed that the 50% inhibition values (IC₅₀) of the cFLISA were 4.3 ng/mL in milk and 5.2 ng/mL in PBS, and the limits of detection (LODs) were 0.6 ng/mL in milk and 0.4 ng/mL in PBS, respectively. The recoveries of SMZ from spiked milk samples at levels of 10–100 ng/mL ranged from 94 to 106%, with coefficients of variation (CVs) of 2.1–9.2%. Figure Shematic diagram of the direct cFLISA procedure Jianzhong Shen and Fei Xu contributed equally to this work.     

Thiourea linked peracetylated glucopyranosyl–anthraquinone conjugate as reversible ON–OFF receptor for fluoride in acetonitrile

A new thiourea linked peracetylated glucopyranosyl–anthraquinone conjugate (L) has been synthesized and characterized. The binding properties of L have been studied with nineteen different anions. The L exhibited selective chromogenic as well as fluorescent chemosensor property toward F⁻ by a ∼13-fold increase in the emission intensity upon binding with F⁻. The minimal detection limit for F⁻ is 185 ± 5 ppb in acetonitrile. Interaction of F⁻ led to a bathochromic shift of 80 nm in the absorption band. An INHIBIT logic gate has been proposed using the output obtained from the fluorescence studies. The structure of the species formed upon the interaction of F⁻ with L has been established by DFT computations.     

Simple and sensitive detection method for chromium(VI) in water using glutathione—capped CdTe quantum dots as fluorescent probes

Water-soluble and stable CdTe quantum dots (QDs) were synthesized in aqueous solution with glutathione (GSH) as the stabilizer. GSH is employed by nature to detoxify heavy metal ions. As a result of specific interaction, the fluorescence intensity of GSH-capped QDs is selectively reduced in the presence of Cr(VI). Under the optimum conditions, the relative fluorescence intensity decreases linearly with the Cr(VI) concentration in the range from 0.01 to 1.00?µg mL^?1, and the detection limit is 0.008?µg mL^?1. The luminescence response of the QDs to ions markedly depended on the particle size, and a new strategy for tuning the selectivity of luminescent QDs to certain ions without changing the capping layer of the QDs can be achieved by changing the crystallite size of the QDs.     

Mono- and dinuclear cyclopalladates as catalysts for Suzuki–Miyaura cross-coupling reactions in predominantly aqueous media

Suzuki–Miyaura cross-coupling reactions of aryl halides with arylboronic acids were performed in predominantly aqueous media employing two mono- and two dinuclear cyclopalladated complexes as catalysts. These complexes are [Pd(HL)Cl] (I), [Pd(L)(PPh₃)] (II), [Pd₂(μ-dppb)(L)₂] (III) and [Pd₂(μ-dppf)(L)₂] (IV); where H₂L, dppb and dppf represent 4-methoxy-N′-(mesitylidene)benzohydrazide, 1,4-bis(diphenylphosphino)butane and 1,1′-bis(diphenylphosphino)ferrocene, respectively. The reactions were conducted using potassium carbonate as base in presence of tetrabutylammonium bromide (TBAB) at 70/90 °C in dimethylformamide–water (1:20) mixture. Among the four catalysts used, the dinuclear complex IV turned out to be the most effective and afforded moderate to excellent yields with broad substrate scope.