Selective Recognition Research Articles

Selective recognition of Fe2+ in aqueous solution by chalcones

Recognition of metal ions in aqueous media has direct impact for designing new supramolecular hosts for targeting biochemical pathways. In the present work we have studied the binding behavior of three simple chalcones with variation in number of phenolic OH groups. These chalcones showed very good binding capabilities towards metal ions in CH3OH-H2O (1:1, v/v) solvent system. The receptors R1 has interacted with all metal ions, which are used in the present study through 2:1 mode of complexation whereas R2 have showed equilibrium between the complexes of 2:1 and 1:1 with few exceptions. The highest association constants (K21) of R1 and R2 for Fe2+ is observed as 1.1 × 109 (4) M−1 and 2.3 × 108 (7) M−1 respectively by fluorescence titration method. But R3, which is lack of any phenolic OH group, binds all the metal ions through the formation of 1:1 mode of complex formation by exploiting the only one donor site as carbonyl ‘O’ atom resulting lower association constant for all the metal ions. So intermolecular hydrogen bonding as well as π- π stacking interaction forced the receptors R1 and R2 to arrange in a pseudo cleft orientation for the recognition of metal ions in 2:1 mode of complex formation. The binding behaviour of the receptors with few alkali metal ions (Na+, K+ and Cs+) and alkaline-earth metal ions (Mg2+, Ca2+ and Ba2+) are also studied and observed weak binding nature in compared with the transition metal ions.

Highly Selective Fluorescent Sensors: Polyethylenimine Derivatives of Triphenylamine and Coumarin for GTP and ATP Interaction via Fluorescence Lifetime Imaging Microscopy.

Chemical derivatives of polyethylenimine (PEI) receptors with either triphenylamine (TPA) or 7-hydroxy-4-methyl-coumarin (Cou) form stable complexes with adenine and guanine nucleotides in water. The host-guest complex modulation is found to be based on noncovalent molecular interactions such as π-π stacking and hydrogen bonding, which are dependent on the aromatic moieties attached to the polyaminic (PEI) backbone. PEI-TPA acts as a chemosensor with a recognition driving force based on aggregation-induced emission (AIE), involving π-π interaction between the nucleic base and TPA. It detects GTP by a chelation enhancement quenching effect of fluorescence (CHEQ) with a measured logarithm stability constant, log β = 7.7. By varying the chemical characteristics of the fluorophore, as in the PEI-Cou system, the driving force for recognition changes from a π-π interaction to an electrostatic interaction. The coumarin derivative detects ATP with a log β value one order of magnitude higher than that for GTP, allowing for the selective recognition of the two nucleotides in a 100% aqueous solution. Furthermore, fluorescence lifetime imaging microscopy (FLIM) allows for a correlation between the selectivity of PEI-TPA toward nucleotides and the morphology of the structures formed upon ATP and GTP recognition. This study offers valuable insights into the design of receptors for the selective recognition of nucleotides in water.

A novel method to prepare water-soluble cellulose-based fluorescent probes for highly sensitive and selective detection and removal of Hg2+/Hg22+ ions

Improving the water solubility of natural product cellulose and using it to treat heavy metal ions is very important. In this work, cellulose-based fluorescent probes containing BODIPY fluorophore were synthesized by simple chemical method, which realized the selective recognition and removal of Hg2+/Hg22+ ions in an aqueous system. Firstly, fluorescent small molecule (BOK-NH2) bearing -NH2 group was synthesized through Knoevenagel condensation reaction between BO-NH2 and cinnamaldehyde. Secondly, via the etherification of -OH on the cellulose, substituents bearing -C ≡ CH groups with different lengths at the end are grafted on the cellulose. Finally, cellulose-based probes (P1, P2, and P3) were prepared by amino-yne click reaction. The solubility of cellulose is improved greatly, especially the cellulose derivative with branched long chains has excellent solubility in water (P3). Benefiting from the improved solubility, P3 could be processed into solutions, films, hydrogels, and powders. Upon the addition of Hg2+/Hg22+ ions, the fluorescence intensity enhanced, which are “turn-on” probes. At the same time, the probes could be utilized as efficient adsorbents for Hg2+/Hg22+ ions. The removal efficiency of P3 for Hg2+/Hg22+ is 79.7 %/82.1 %, and the adsorption capacity is 159.4 mg·g−1/164.2 mg·g−1. These cellulose-based probes are expected to be employed in the treatment of polluted environments.

Novel AIEE pillar[5]arene-fluorene fluorescent copolymer for selective recognition of paraquat by forming polypseudorotaxane

A novel conjugated polymer (Co-P[5]Flu) was synthesized by copolymerizing a difunctionalized pillar[5]arene and a fluorene derivative monomer. Co-P[5]Flu displayed an aggregation-induced emission enhancement (AIEE) effect because of the restricted intramolecular rotations of the pillar[5]arene unit. Co-P[5]Flu exhibited high selectivity and sensitivity towards the pesticide paraquat (PQ) with excellent anti-interference properties. It presented fluorescence quenching response (1–I/I0=96.6%) only towards paraquat and not towards other competitive guests. The fluorescence titration experiments revealed that the detection limit (LOD) for paraquat was as low as 1.69×10−8 M, and the Stern-Volmer constant (KSV) was determined to be 2.11×104 M−1. The recognition mechanism was studied using both 1H NMR titration and theoretical calculations. The Co-P[5]Flu showed fluorescence quenching for PQ due to the synergistic effect of polypseudorotaxane formation and photoinduced electron transfer (PET). Additionally, the polymer chemosensor demonstrated potential for the detection of paraquat in practical samples.

An ultrasensitive colorimetric biosensor for the detection of Gram-positive bacteria by integrating paper-based enrichment and carbon dot-based selective recognition

Rapid screening of bacteria by low-cost and eco-friendly material-based approaches is still a major challenge. Herein, a colorimetric biosensor was designed for the ultrasensitive and rapid detection of Gram-positive bacteria. The biosensor exploited polydopamine and polyethyleneimine (PDA-PEI)-modified papers for separating bacteria and carbon dots (CDs) for selective colorimetric detection of Gram-positive bacteria. Noble metal-free CDs can target Gram-positive bacteria by binding with peptidoglycan and possess peroxidase-like activity. Thus, they can avert the step of modifying recognition probes, facilitating biosensor fabrication, and reducing the cost. This biosensor can detect S. aureus as low as 1 cfu mL−1, L. monocytogenes as low as 5 cfu mL−1, and B. subtilis as low as 9 cfu mL−1 within 55 min. In addition, a portable device was constructed to enable convenient and on-site quantitative detection of Gram-positive bacteria. The feasibility of the biosensor was verified by detecting Gram-positive bacteria in eggshell and sausage samples with recoveries ranging from 91.2% to 110%.

Preparation of lysozyme-imprinted mesoporous Zr-based metal-organic frameworks with remarkable specific recognition

The development of high-performance protein-imprinted materials remains challenging due to defects concerning high mass transfer resistance and non-specific binding, which are crucial for protein purification and enrichment. In this paper, lysozyme-imprinted mesoporous Zr-based MOF (mesoUiO-66-NH2@MIPs) with specific and selective recognition of lysozyme (Lyz) were prepared by surface imprinting technology. In particular, the excellent hydrophilicity mesoporous MOFs (mesoUiO-66-NH2) with a pore size of 10 nm was prepared as a carrier for Lyz immobilization by an auxiliary modulation strategy to regulate the microporous structure of UiO-66-NH2 with the propionic acid solution, enabling massive loading of the macromolecular protein Lyz. The mesoUiO-66-NH2@MIPs reached a maximum saturation adsorption of 206.54 mg g−1 on Lyz in 20 min at 25 °C with an imprinting factor of 2.57 and selection factors of 2.02, 2.34, and 2.45 for cytochrome c (Cyt c), bovine serum albumin (BSA) and bovine hemoglobin (BHb), respectively. More importantly, the mesoUiO-66-NH2@MIPs could specifically recognize Lyz from the mixed protein system. The adsorption capacity of Lyz could still reach 78.55% after 5 cycles with good cyclic regeneration performance. This provides a new research option for developing and applying novel porous MOF in biomolecule imprinting technology and the specific separation of biomolecules.

Designing Nonconventional Luminescent Materials with Efficient Emission in Dilute Solutions via Modulation of Dynamic Hydrogen Bonds.

Nonconventional luminescent materials (NLMs) which do not contain traditional aromatic chromophores are of great interest due to their unique chemical structures, optical properties, and their potential applications in various areas, such as cellular imaging and chemical sensing. However, most reported NLMs show weak or no emission in dilute solutions, which severely limits their applications. In this work, dynamic hydrogen bonds were utilized to design NLMs with efficient emission in dilute solutions. To further validate the results, polymers P1 and P2 were successfully prepared and investigated. It was found that the luminescence quantum efficiency of P1 and P2 at a concentration of 0.1 mg/mL in water solution was 8.9 and 0.6%, respectively. The high efficiency can be attributed to the fact that polymer P1 has more intra- or intermolecular dynamic hydrogen bonds and other short interactions than P2 in dilute solutions, allowing P1 to achieve the through-space conjugation effect to increase the degree of system conjugation, restrict molecular motion, and decrease nonradiative transitions, which can effectively improve luminescence. In addition, polymer P2 exhibits the characteristics of clustering-triggered emission, excitation wavelength-dependent and concentration-dependent fluorescence properties, excellent photobleaching resistance, low cytotoxicity, and selective recognition of Fe3+. The present study investigates the manipulation of luminescence properties of NLMs in dilute solutions through the modulation of dynamic hydrogen bonds. This approach can serve as a semi-empirical technique for designing and building innovative NLMs in the times ahead.

Thermo-responsive ion imprinted polymer on the surface of magnetic carbon nanospheres for recognizing and capturing low-concentration lithium ion

Ion imprinted polymer (IIP) on the surface of magnetic carbon nanospheres, using N-propylacrylamide and benzo-12-crown 4-ether (B12C4) as bi-functional monomers, is designed and synthesized for the selective recognition and recovery of Li+ from aqueous medium. The adsorption behaviors of Li+-IIP including adsorption kinetics, isotherms, selective recognition, and regeneration are investigated in detail by inductively coupled plasma-optical emission spectroscopy. The adsorption capacity of Li+-IIP towards Li+ reaches a maximum value of 23.46 mg g−1 at 25 ˚C within 60 min. The Langmuir and pseudo-second-order models manifest the apparent adsorption behavior dominated by single layer chemisorption. The Li+-IIP realized selective adsorption of Li+ against Na+, K+, Mg2+, Al3+, and Fe3+ in their coexistence solution. It is reused five times without a significant decrease with the assistance of externally applied magnetic field for solid/liquid separation. The recognition mechanism of Li+-IIP towards Li+ is the combined action of dehydration effect, electrostatic attraction, and size and imprinting effect, as identified by theoretical simulated calculation based on density functional theory and experimental data. The temperature-responsive adsorption of Li+-IIP towards Li+ facilitates the adsorption/desorption operations. Li+-IIP shows good separation from the treated solution by applying an external magnetic field. This work provides new insights into the recovery of lithium.

Impact of Asialoglycoprotein Receptor and Mannose Receptor Deficiency on Murine Plasma N-glycome Profiles

The asialoglycoprotein receptor (ASGPR) and the mannose receptor C-type 1 (MRC1) are well known for their selective recognition and clearance of circulating glycoproteins. Terminal galactose and N-Acetylgalactosamine are recognized by ASGPR, while terminal mannose, fucose, and N-Acetylglucosamine are recognized by MRC1. The effects of ASGPR and MRC1 deficiency on the N-glycosylation of individual circulating proteins have been studied. However, the impact on the homeostasis of the major plasma glycoproteins is debated and their glycosylation has not been mapped with high molecular resolution in this context. Therefore, we evaluated the total plasma N-glycome and plasma proteome of ASGR1 and MRC1 deficient mice. ASGPR deficiency resulted in an increase in O-acetylation of sialic acids accompanied by higher levels of apolipoprotein D, haptoglobin, and vitronectin. MRC1 deficiency decreased fucosylation without affecting the abundance of the major circulating glycoproteins. Our findings confirm that concentrations and N-glycosylation of the major plasma proteins are tightly controlled and further suggest that glycan-binding receptors have redundancy, allowing compensation for the loss of one major clearance receptor.

Selective molecular recognition of amino acids and their derivatives by cucurbiturils in aqueous solution: An MD/3D-RISM study

The three-dimensional reference interaction site model theory was utilized to investigate cucurbituril–guest binding and its corresponding solvation structure. In this study, glycine, tryptophan, phenylalanine and their derivatives were employed as representatives of guest molecules. In the case of aromatic amino acids, phenylalanine shows the most significant binding affinity in cucurbit-7-uril, whereas tryptophan provides the highest binding affinity in cucurbit-8-uril. Although these guest molecules are very similar in molecular volumes, their chemical and physical properties are different. These findings agree well with reports from previous studies. We also found that the substitution of the tert-butyl (–C(CH3)3) group at the para-position in phenylalanine provides the highest binding affinity gain among all derivatives. Moreover, the unbound state of glycine is pointed out.

Conjugated Polymeric Materials in Biological Imaging and Cancer Therapy.

Conjugated polymers (CPs) have attracted much attention in the fields of chemistry, medicine, life science, and material science. Researchers have carried out a series of innovative researches and have made significant research progress regarding the unique photochemical and photophysical properties of CPs, expanding the application range of polymers. CPs are polymers formed by the conjugation of multiple repeating light-emitting units. Through precise control of their structure, functional molecules with different properties can be obtained. Fluorescence probes with different absorption and emission wavelengths can be obtained by changing the main chain structure. By modifying the side chain structure with water-soluble groups or selective recognition molecules, electrostatic interaction or specific binding with specific targets can be achieved; subsequently, the purpose of selective recognition can be achieved. This article reviews the research work of CPs in cell imaging, tumor diagnosis, and treatment in recent years, summarizes the latest progress in the application of CPs in imaging, tumor diagnosis, and treatment, and discusses the future development direction of CPs in cell imaging, tumor diagnosis, and treatment.

Highly Selective Transport and Enrichment of Lithium Ions through Bionic Ion Pair Receptor Nanochannels.

Inspired by ion pair cotransport channels in biological systems, a bionic nanochannel modified with lithium ion pair receptors is constructed for selective transport and enrichment of lithium ions (Li+). NH2-pillar[5]arene (NP5) is chosen as ion pair receptors, and the theoretical simulation and NMR titration experiments illustrate that NP5 has good affinity for the ion pair of LiCl through a strong host-guest interaction at the molecular level. Due to the confinement effect and ion pair cooperation recognition, an NP5-based receptor was introduced into an artificial PET nanochannel. An I-V test indicated that the NP5 channel realized the highly selective recognition for Li+. Meanwhile, transmembrane transport and COMSOL simulation experiments proved that the NP5 channel achieved the transport and enrichment of Li+ through the cooperative interaction between NP5 and LiCl. Moreover, the receptor solution of transmembrane transport LiCl in the NP5 channel was used to cultivate wheat seedlings, which obviously promoted their growth. This nanochannel based on the ion pair recognition will be much useful for practical applications like metal ion extraction, enrichment, and recycle.

A new pyridine-dicarbohydrazide-based turn-off fluorescent and colorimetric chemosensor for selective recognition of Cu2+

A new pyridine-dicarbohydrazide-based turn-off fluorescent and colorimetric chemosensor for selective recognition of Cu2+

Molecularly imprinted CaCO3/polydopamine hybrid composite for selective protein recognition

Molecularly imprinted CaCO3/polydopamine hybrid composite for selective protein recognition

Ultrasensitive Pesticide Detection and Specific Recognition in Microenvironment-Modulated Fluorescent Micro-/Mesoporous Polyaminals.

Two new carbazole-based monomers 6,6'-(9-n-butyl-9H-carbazole-3,6-diyl)bis(1,3,5-triazine-2,4-diamine) and 6,6'-(9H-carbazole-3,6-diyl)bis(1,3,5-triazine-2,4-diamine) are synthesized and employed to polymerize with formamide and N,N-dimethylformamide, respectively, to afford thee fluorescent micro-/mesoporous polyaminals with physicochemical microenvironment modulated by -NH2, -NH-, -N(CH3)2, and n-butyl groups. Their chemosensing properties for five pesticides trifluralin (TFR), triflumizole, imidacloprid, lambda-cyhalothrin, and cyfluthrin are studied. Surprisingly, the polymers exhibit exceptionally high recognition for TFR, and the fluorescent quenching coefficients measured in water reach 4.1 × 106 M-1, being 2 orders of magnitude higher than those of other porous polymers reported in the literature. The limit of detection (0.7 ppb) for TFR can compete with that of the electrochemical method. The fluorescence response at an extremely low concentration of 3 × 10-8 M and selective recognition for TFR are confirmed by the visual observation using the portable polymer plates. Additionally, the different water mediums including varied acid-basic conditions and the presence of heavy metal ions have nearly no effect on the detection sensitivity. The ultrasensitive recognizable response for TFR is explained in terms of the photoinduced electron transfer, inner filter effect, improved hydrophilicity of polymer skeleton and porous trapping effect, and the dimensions and geometric configurations of pesticide molecules.

Covalent Modification of Nanoparticle‐Imprinted Matrices for Selective Nanoparticle Recognition

AbstractNanoparticle‐imprinted matrices (NAIMs) were prepared using ammonium‐terminated SiO2 nanoparticles (NPs) as templates initially attached to activated glassy carbon. After electrodeposition of a matrix of polyplumbagin and polyphenol, the selectivity of the polymer matrix was tuned towards the ligand shell of the Au analyte NPs by conjugate addition of substituted thiols to the plumbagin moiety within the matrix. The reactions were followed by cyclic voltammetry (CV) and the presence of thiols and amino groups in the film was verified by X‐ray photoelectron spectroscopy (XPS). After dissolution of the template NPs, the matrix had complementary cavities for the uptake of Au NPs. The amount of Au NP inside the cavities was quantified by the charge transferred during electrodissolution of the Au NPs in 3 M KCl in linear sweep voltammetry, which depended on the covalent modification of the polyplumbagin matrix, the pH during uptake and the size of the Au analyte NPs. The NAIM system modified with 1,2‐ethanedithiol showed the best uptake with 9.6×107 NPs cm−2 at pH 10, which is five times higher than the uptake of the same matrix at pH 5. In contrast, the cysteamine‐modified NAIM exhibited the highest uptake at pH 5.

Evaluating the Activity of Neuraminidase in Bacterial Vaginosis Microflora and Imaging Sialic Acid on the Cell Membrane by Boron and Nitrogen Codoped Fluorescent Carbon Dots.

Sialic acids (SAs) are commonly located on the cell surface as terminal ends of glycoproteins and glycolipids. Neuraminidase (NEU) is a class of glycoside hydrolase enzymes that can cleave SAs from receptors. Both SA and NEU play important roles in human physiological and pathological processes of cell-cell interaction, communication, and signaling. Additionally, bacterial vaginosis (BV), a form of gynecological inflammation caused by dysbiosis of the vaginal microbiome, results in the abnormal activity of NEU in vaginal fluid. Here, we developed a novel probe for rapidly and selectively sensing SA and NEU based on a one-step prepared boron and nitrogen codoped fluorescent carbon dots (BN-CDs). The selective recognition reaction between SA and the phenylboronic acid groups on the surface of BN-CDs inhibits fluorescence emission from BN-CDs, while the NEU-catalyzed hydrolysis of SA bound on BN-CDs leads to fluorescence recovery. The probe was applied in diagnosing BV and showed consistent results to Amsel criteria. Moreover, the low cytotoxicity of BN-CDs facilitates its application in fluorescence imaging of SA on the membrane of red blood cells (RBCs) and leukemia cell lines (U937, KAS-1). The excellent sensitivity, accuracy, and applicability of the developed probe support its broad potential applications in future clinical diagnosis and treatment.

Binaphthyl-Based Chiral Macrocyclic Hosts for the Selective Recognition of Iodide Anions.

In this study, we explorethe synthesis of binaphthyl-based chiral macrocyclic hosts for the first time. They exhibited the selective recognition abilities of iodide anions which can be favored over those of other anions (AcO-, NO3-, ClO4-, HSO4-, Br-, PF6-, H2PO4-, BF4-, and CO3F3S-), as confirmed by UV-vis, HRMS, and 1H NMR spectroscopy experiments, as well as DFT calculations. Neutral aryl C-H···anion interactions play an important role in the formation complexes. The recognition process can be observed by the naked eye.

Introduction: Laboring in the Extractive University

The twin pressures of dwindling state funding and widening student access has created a crisis of higher education that reverberates into the hidden abode of teaching and learning. In this special issue we reconnect pedagogy to its context of determination (and nondetermination) by bringing theories of the labor process to bear on the dilemmas and challenges faced by teaching assistants (TAs). Our project of auto-ethnography was suspended between two crises—COVID-19 and an unprecedented university-wide strike by graduate students. Elizabeth Torres Carpio advances the idea of the university's “selective recognition” that expands the work of street-level educators -TAs facing increasing numbers of students from economically poor and culturally diverse backgrounds. Natalie Pasquinelli considers the way faculty manage TAs as apprentices through hegemonic “status control.” Justin Germain focuses on the autonomy that allows TAs to turn teaching into “innovation games,” offering the players a sense of accomplishment. Thomas Gepts examines the “arrhythmic” time bind in which graduate students are caught between commitments to future-oriented research and present-oriented teaching. Margaret Eby shows how the “power of silence” allows TAs to conceal their anxiety and defend their autonomy. The university extracts the labor of TAs by giving them “constrained autonomy” to absorb, divert, and conceal the pressures descending from a top-heavy administrative structure. We extend the idea of “constrained autonomy” to other occupations.

Street-Level Educators: The Selective Recognition of Students and Invisible TA Labor

Drawing on my experience as a teaching assistant (TA), I expand on Michael Lipsky's concept of the street-level bureaucrat by focusing on how an agency's construction of the client shapes the work of the bureaucrat. I call this selective recognition. The university classifies students into three types: the archetypal student for whom the university is designed, the partially recognized student who receives accommodations, and the unrecognized student with responsibilities that make learning difficult. The result is an adaptation of the TA's three dimensions of the labor process: teaching, administration, and care work. The labor contract stipulates the first and a modicum of the second but not the third. Changing student demographics have increased all dimensions of TA labor, especially administrative tasks and the amount of invisible care work performed. The extractive university relies on this invisible and often overextended labor to dampen and conceal the reality of its own failing mission.