A Highly Selective Luminescent Switch-On Probe for Histidine/Histidine-Rich Proteins and Its Application in Protein Staining

A DMSO-assisted iridium(III) complex as a luminescent "turn-on" sensor for selective detection of L-histidine and bacterial imaging

Histidine (His) is a semi-essential amino acid and a unique key neurotransmitter involved in numerous physiological processes. An excessive or deficient amount of His in the body can lead to various related diseases. However, since the chemical structures of L-His and its metabolites (such as histamine (Ha), imidazole-4-acetate (ImA), etc.) are very similar, simple and efficient selective detection of L-His and its related metabolites is of great importance but remains a great challenge. Herein, we successfully designed and synthesized a DMSO-assisted iridium(III) complex (Ir1-DMSO), which can be applied as a "turn-on" photoluminescence (PL) probe for the selective detection and quantification of L-His/Ha. More importantly, Ir1-DMSO exhibited good sensitivity, high selectivity, and anti-interference capability for L-His/Ha/His-containing proteins, which is advantageous due to its simple fabrication and low technical demands. This was attributed to the reaction of Ir1-DMSO with imidazole and amino groups of L-His/Ha. Furthermore, we show the utility of Ir1-DMSO as a PL imaging agent in cultures of E. coli and S. aureus. Considering its diversity of composition and structural flexibility, it can be extended to other solvents and Ir-ligand complexes for various analyses based on specific molecular recognition sensing platforms.

2-Phenylbenzothiazolyl iridium complexes as inhibitors and probes of amyloid β aggregation

The aggregation of amyloid β (Aβ) peptides is a significant hallmark of Alzheimer's disease (AD), and the detection of Aβ aggregates and the inhibition of their formation are important for the diagnosis and treatment of AD, respectively. Herein, we report a series of benzothiazole-based Ir(III) complexes HN-1 to HN-8 that exhibit appreciable inhibition of Aβ aggregation in vitro and in living cells. These Ir(III) complexes can induce a significant fluorescence increase when binding to Aβ fibrils and Aβ oligomers, while their measured log D values suggest these compounds could have enhanced blood-brain barrier (BBB) permeability. In vivo studies show that HN-1, HN-2, HN-3, and HN-8 successfully penetrate the BBB and stain the amyloid plaques in AD mouse brains after a 10-day treatment, suggesting that these Ir(III) complexes could act as lead compounds for AD therapeutic and diagnostic agent development.

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

A Water-Soluble Wavy Coordination Polymer of Cu(II) as a Turn-On Luminescent Probe for Histidine and Histidine-Rich Proteins/Peptides

Histidine plays an essential role in most biological systems. Changes in the homeostasis of histidine and histidine-rich proteins are connected to several diseases. Herein, we report a water-soluble Cu(II) coordination polymer, labeled CuCP, for the fluorimetric detection of histidine and histidine-rich proteins and peptides. Single-crystal structure determination of CuCP revealed a two-dimensional wavy network structure in which a carboxylate group connects the individual Cu(II) dimer unit in a syn-anti conformation. The weakly luminescent and water-soluble CuCP shows turn-on blue emission in the presence of histidine and histidine-rich peptides and proteins. The polymer can also stain histidine-rich proteins via gel electrophoresis. The limits of quantifications for histidine, glycine-histidine, serine-histidine, human serum albumin (HSA), bovine serum albumin, pepsin, trypsin, and lysozyme were found to be 300, 160, 600, 300, 600, 800, 120, and 290 nM, respectively. Utilizing the fluorescence turn-on property of CuCP, we measured HSA quantitatively in the urine samples. We also validated the present urinary HSA measurement assay with existing analytical techniques. Job's plot, 1H NMR, high-resolution mass spectrometry (HRMS), electron paramagnetic resonance (EPR), fluorescence, and UV-vis studies confirmed the ligand displacement from CuCP in the presence of histidine.

Enhanced TNT vapor sensing through a PMMA-mediated AIPE-active monocyclometalated iridium(III) complex: a leap towards real-time monitoring

Based on the explosive nature and harmful effects of nitro-based explosive materials on living beings and the environment, it is extremely important to develop luminescence-based probe molecules for their detection with excellent selectivity and sensitivity. Two AIPE (aggregation-induced phosphorescence emission)-active iridium(III) complexes (M1 and M2) were developed for the sensitive detection of TNT in both contact and non-contact modes. The aggregate solutions of both complexes (M1 and M2 in THF/H2O, 1/9 by volume) detected TNT at the pico-molar (pM) level. These complexes showed greatly enhanced emission intensity while embedded in a PMMA(polymethyl methacrylate) matrix film. The amplified quantum efficiency, improved phosphorescence lifetime, and enhanced porous network of M2-PMMA composite helps to improve the sesitivity of TNT vapor detection. Interestingly, the sensitivity of the detection of TNT by the M2 complex was significantly improved (5-fold) in a PMMA-incorporated complex (CP) with an observed limit of detection (LOD) of 12.8 ppb. From the BET analysis of CP, it was observed that the mesoporous network of CP has an average pore diameter of 8.52 nm and a surface area of 2.03 m2 g-1. The porous network of CP assists in trapping TNT vapor in a polymeric network containing an electron-rich probe (iridium(III) complex, M2), which helps to effectively trap TNT, thus enhancing electronic communication. As a result, significant emission quenching was observed.

Photoluminescence-Electrochemiluminescence Dual-Mode Sensor Arrays for Histidine and Its Metabolite Discrimination and Disease Identification

Histidine (His) and its metabolite analysis is significant due to their vital roles in the diagnosis of diseases. In practical applications, simple and effective detection and discrimination of these metabolic species are still a great challenge due to their highly similar structures. Herein, photoluminescence (PL)-electrochemiluminescence (ECL) dual-mode sensor arrays consisting of a series of sensing elements were proposed for simultaneous quantitation and accurate discrimination of His and its four key metabolites (including histamine, imidazole-4-acetic acid, N-acetylhistamine, and imidazole propionate). The sensing elements of these sensor arrays were constructed by employing two solvent iridium(III) complexes ([Ir(pbz)2(DMSO)Cl] and [Ir(ppy)2(DMSO)Cl], pbz = 3-(2-pyridyl)benzoic acid, ppy = 2-phenylpyridine) with excellent PL and ECL performances as cross-responsive sensing units. Based on diverse coordination abilities of the two complexes with the imidazole group of the five targets, PL and ECL responses of each sensing unit can be enhanced to various degrees, which generate unique fingerprint patterns for the corresponding targets. Through principal component analysis, the multifarious patterns (two-, three-, and four-element sensor arrays) can be transformed into simple visualization modes, from which His and its four key metabolites can be effectively discriminated against each other. Moreover, the quantitation of an individual metabolic species at different concentrations and the recognition of the mixtures with different ratios were also accurately achieved. Notably, His and its four key metabolites in urine can also be successfully discriminated by the as-fabricated sensor arrays, and the patients with kidney diseases can be identified clearly, providing a promising way for disease diagnosis.

A Core Structural Protein That Builds the Locust Mandible with a Mechanical Gradient

Natural materials, such as locust mandibles and squid beaks, define significant mechanical gradients that have been attributed to the chemical gradients of their specialized structural proteins (SPs). However, the mechanism by which SPs form chemical gradients in these materials remains unknown. In this study, a highly abundant histidine-rich structural protein (LmMHSP) was identified in the mandible of a migratory locust (Locusta migratoria). LmMHSP was proven by both in vivo and in vitro evidence to act as a core building block of the mandible with a variety of synergistic functions including chitin binding, matrix formation via liquid-liquid phase separation, chemical cross-linking, and metal coordination. Furthermore, we found that the SP gradient in the locust mandible stems from the chitin-binding activity of LmMHSP and different microstructures of chitin scaffolds in different regions. These findings advance our understanding of the formation mechanisms of natural biomaterials and have implications for the fabrication of biomimetic materials.

Novel Electrochemiluminescent Biosensor to Ultrasensitively Detect U94 Gene in Human Herpesvirus 6 Using Metal-Organic Framework-Based Nanoemitters Comprising Iridium(III) Complexes via One-Pot Coordination Reaction Strategy

The detection of the U94 gene in human herpesvirus 6 is crucial for early diagnosis of HHV-6 infections, which could induce acute febrile illness in infants. In this work, the first ultrasensitive electrochemiluminescence (ECL) biosensor for detecting U94 gene in Human Herpesvirus 6 was successfully designed by utilizing efficient novel metal-organic framework (MOF)-based ECL nanoemitters comprising iridium(III) complexes (Ir-ZIF-8-NH2) synthesized via one-pot coordination reaction strategy as an ECL indicator and a target-catalyzed hairpin assembly (CHA) signal amplification strategy. The as-prepared ECL indicator Ir-ZIF-8-NH2 exhibited an approximately 2.7-fold ECL intensity compared with its small molecular analogue of emissive iridium(III) complex named IrppymIM formed by in situ coordination reaction between iridium(III) solvent complex and imidazole ligands. In addition, a target-catalyzed hairpin assembly (CHA) strategy was employed to further improve the sensitivity of the proposed ECL biosensor, which demonstrated a wide linear range from 1 fM to 1 μM and the limit of detection as low as 0.113 fM (S/N = 3). Significantly, this biosensor was successfully applied to detect U94 gene in plasmids and real virus samples. The recoveries were in the range of 97.0-109.0% for plasmids and 95.7-107.5% for real virus samples with a relative standard deviation (RSD) of 1.87-2.53%. These satisfactory experimental results from the proposed ECL biosensor in this work would inevitably promote the development of new time/cost-effective and sensitive methods to detect HHV-6 with a major global health threat and substantial burden on healthcare in the future.

Unexpected reactivity of cyclometalated iridium(III) dimers. Direct synthesis of a mononuclear luminescent complex

A new synthetic method has been developed for the preparation of unexpected emissive iridium(III) complexes (A and B), directly obtained from the established [Ir(ppy)2(μ-Cl)]2 dimer, under reaction conditions in which such compounds are usually considered stable. Complex A ([Ir(ppy)2(Oppy)], where Hppy = 2-phenylpyridine and HOppy = 2-(o-hydroxyphenyl)pyridine) was obtained from the dimer without the addition of further ancillary ligands in the reaction environment, but in the presence of a basic water environment in 2-ethoxyethanol as solvent at 165 °C. The complex evidences the unexpected insertion of an oxygen atom between the iridium(III) center and the carbon atom of one ppy moiety. Under specific reaction conditions, the mer-[Ir(ppy)3] complex (B) was obtained. The presence of the right amount of water is important to maximize the formation of A relative to B. Both compounds were fully characterized by NMR spectroscopy and mass spectrometry (MS), and the X-ray structure of A was also determined. DFT calculations were used to shed light on the reaction mechanism leading to the unexpected formation of A, suggesting that the Oppy ligand is generated intramolecularly once the [Ir(ppy)2(μ-OH)]2 dimer is formed. The process is probably assisted by a redox reaction involving the second iridium(III) center in the dimer. The electrochemical and photophysical properties of complexes A and B were investigated in comparison with the well-known fac-[Ir(ppy)3] analogue (C). Complex A displays a green emission (λmax = 545 nm) with a photoluminescence quantum yield (PLQY) of nearly 40%, whereas the oxygen-free counterpart B is poorly emissive, exhibiting an orange emission (λmax = 605 nm) with a PLQY below 10%. These findings may pave the way for the direct synthesis of neutral luminescent complexes with the general formula [Ir(C^N)2(OC^N)], even using dimers with non-commercial or highly substituted C^N ligands, without the need for synthesizing the corresponding hydroxyl-substituted ancillary ligand, which may be hardly obtainable.

Polymeric copper(ii) and dimeric oxovanadium(v) complexes of amide-imine conjugate: bilirubin recognition and green catalysis

An exceptionally simple amide-imine conjugate, (E)-N'-(4-(diethylamino)-2-hydroxybenzylidene)-4-methylbenzohydrazide (L), derived by the condensation of 4-methyl-benzoic acid hydrazide (PTA) with 4-(diethylamino)-2-hydroxybenzaldehyde was utilized to prepare a dimeric oxo-vanadium (V1) and a one-dimensional (1D) copper(ii) coordination polymer (C1). The structures of L, V1 and C1 were confirmed by single crystal X-ray diffraction analysis. The experimental results indicate that V1 is a promising green catalyst for the oxidation of sulfide, whereas C1 has potential for a C-S cross-coupling reaction in a greener way. Most importantly, C1 is an efficient 'turn-on' fluorescence sensor for bilirubin that functions via a ligand displacement approach. The displacement equilibrium constant is 7.78 × 105 M-1. The detection limit for bilirubin is 1.15 nM in aqueous chloroform (chloroform/water, 1/4, v/v, PBS buffer, and pH 8.0).

A novel fluorescent probe based on a tripeptide-Cu(II) complex system for detection of histidine and its application on test strips and smartphone

Herein, we reported a novel peptide-based fluorescent probe DSSH for highly selective and sensitive detections of both Cu²⁺ and _l-histidine (_l-His). DSSH exhibited different color changes and fluorescence "on-off" response toward Cu²⁺ with a 2:1 binding stoichiometry, and the limit of detection (LOD) for Cu²⁺ was calculated to be 22.9 nM. The in situ formed DSSH-Cu²⁺ ensemble showed obvious fluorescence "off-on" response to _l-His based on replacement reaction with Cu²⁺, as well as the discernable color changes under 365 nm UV lamp irradiation with "naked eye". The specificity of Cu²⁺/_l-His interactions allowed _l-His to be determined without interference from other amino acids, and the detection limit of DSSH-Cu²⁺ ensemble response to _l-His was determined as 25.7 nM. Notably, DSSH was successfully applied for detecting Cu²⁺ and _l-His in RKO living cells owing to its remarkable fluorescence behavior and low cytotoxicity. Test strips experiments suggested that DSSH can recognize Cu²⁺ and _l-His together by a remarkable fluorescence change. More importantly, smartphone was combined with _l-His solutions of different concentrations and converted into digital values through RGB channels, which was successfully used for semi-quantitative identification of _l-His, and the limit of detection (LOD) was 0.97 μM.

Iridium(III) solvent complex-based electrogenerated chemiluminescence and photoluminescence sensor array for the discrimination of bases in oligonucleotides

Development of rapid and sensitive method for the discrimination of bases in oligonucleotides is of great importance in clinical diagnosis. Here, we demonstrate the first case of single iridium(III) solvent complex-based electrogenerated chemiluminescence (ECL) and photoluminescence (PL) sensor array for the discrimination of bases in oligonucleotides. One iridium (III) solvent complex ([Ir(ppy)₂(DMSO)Cl], ppy = 2-phenylpyridine, probe 1) was designed as both ECL and PL probe while five bases (guanine, adenine, cytosine, thymine and uracil) were chosen as analytes. Two-element sensor array was built for the discrimination of five bases based on the fingerprint response of probe 1 to bases via coordination interactions. The combination of unique ECL and PL variations with principal component analysis was applied for the quantitative analysis of five bases in a linear range of 1.0 μM-10 μM and for the effective discrimination of individual base, the mixture of bases and oligonucleotides. Moreover, the sensor array was successfully applied to discriminate different mismatched ss-DNAs from HIV gene (a fully-matched ss-DNA), even at single-base difference. This work demonstrates that the sensor array using single iridium (III) solvent complex is a promising approach for the discrimination of bases with good sensitivity and simpleness in clinical diagnosis.

Recent advances and challenges in developing electrochemiluminescence biosensors for health analysis

This Feature Article simply introduces principles and mechanisms of electrochemiluminescence (ECL) biosensors for the determination of biomarkers and highlights recent advances of ECL biosensors on key aspects including new ECL reagents and materials, new biological recognition elements, and emerging construction biointerfacial strategies with illustrative examples and a critical eye on pitfalls and discusses challenges and perspectives of ECL biosensors for health analysis.

One Molecular Probe with Opposite Enantioselective Fluorescence Enhancement at Two Distinct Emissions

It is discovered that one enantiomer of a chiral substrate can greatly enhance the fluorescence of one molecular probe at one emitting signal (λ₁ = 517 nm), while the opposite enantiomer of the substrate greatly enhances the fluorescence of the same probe at a distinctively different emission (λ₂ = 575 nm). This probe is made of a 1,1'-binaphthyl-based chiral dialdehyde that in combination with Zn²⁺ under slightly acidic conditions shows a chemoselective and enantioselective fluorescent response to histidine. The opposite enantioselective fluorescent responses of the probe at two emissions allow it to be used to determine both the concentration and the enantiomeric composition of the substrate using a single probe. The mechanistic study has revealed two very different reaction pathways when the two enantiomers of the substrate are treated with the probe. These reaction pathways generate two different products, one dimeric and another polymeric, with very different emissions.

Design, synthesis, and applications of ring-functionalized histidines in peptide-based medicinal chemistry and drug discovery

Modified and synthetic α-amino acids are known to show diverse applications. Histidine, which possesses numerous applications when subjected to synthetic modifications, is one such amino acid. The utility of modified histidines varies widely from remarkable biological activities to catalysis, and from nanotechnology to polymer chemistry. This renders histidine residue an important place in scientific research. Histidine is a well-studied scaffold and constitutes the active site of various enzymes catalyzing important reactions in the biological systems. A rational modification in histidine structure with a distinctly developed protocol extensively changes its physical and chemical properties. The utilization of modified histidines in search of potent, target selective and proteostable scaffolds is vital in the development of bioactive peptides with enhanced drug-likeliness. This review is a compilation and analysis of reported side-chain ring modifications at histidine followed by applications of ring-modified histidines in the synthesis of various categories of bioactive peptides and peptidomimetics.

Rational design of photoactivatable metal complexes to target and modulate amyloid-β peptides

The accumulation of amyloid-β (Aβ) aggregates is found in the brains of Alzheimer's disease patients. Thus, numerous efforts have been made to develop chemical reagents capable of targeting Aβ peptides and controlling their aggregation. In particular, tunable coordination and photophysical properties of transition metal complexes, with variable oxidation and spin states on the metal centers, can be utilized to probe Aβ aggregates and alter their aggregation profiles. In this review, we illustrate some rational strategies for designing photoactivatable metal complexes as chemical sensors for Aβ peptides or modulators against their aggregation pathways, with some examples.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Iridium tetrazolato complexes as efficient protein staining agents

Iridium tetrazolato complexes have been illustrated as one kind of efficient protein staining agent.

A resin containing motifs of maleic acid and glycine: a super-adsorbent for adsorptive removal of basic dye pararosaniline hydrochloride and Cd(II) from water

The cyclocopolymerization of N,N-diallylglycine hydrochloride, maleic acid and 1,1,4,4-tetraallylpiperazinium dichloride afforded a cross-linked polyzwitterionic acid, which, upon treatment with NaOH, gave the corresponding cross-linked anionic polyelectrolyte (CAPE) in quantitative yield. The pH-responsive resins contained a high density of CO2 - motifs as well as the chelating motifs of glycine residues. The resin CAPE was found to be a super-adsorbent for the removal of pararosaniline hydrochloride (PRH); having a q max of 1534 mg/g. The adsorption process followed pseudo-second-order kinetics and was found to be a nearly irreversible process as suggested by the parameters obtained from Elovich kinetic model. The resin demonstrated excellent adsorption/desorption efficiencies, thereby ensuring its recycling and reuse in potent applications like remediation of industrial dye-waste water. The resin's chelating motifs were also efficient in the adsorptive removal of Cd(II) ions with a q max of 248 mg/g. It was also employed for the simultaneous and effective trapping of Cd(II) and the dye from industrial wastewater. The resin's impressive performance accords it a prestigious place among many sorbents in recent works.

Single nanoparticle identification coupled with auto-identify algorithm for rapid and accurate detection of L-histidine

In this work, an auto-identify sensor was constructed for rapid and high-precision detection of L-histidine. The proposed strategy is based on the auto-identify algorithm and the aggregation of alkynyl and azide functionalized gold nanoparticles induced by the Cu⁺ catalyzed azides and alkynes cycloaddition (CuAAC) reaction. Specially, the color of scattering light spots for the aggregated gold nanoparticle (AuNPs) caused by CuAAC reaction was quite different from that of the monomers. However, L-histidine can bind to Cu²⁺ and inhibits the production of Cu⁺, hence preventing the aggregation of AuNPs. Therefore, there is a distinct change of color as the addition of L-histidine under dark-field microscopy. Then, L-histidine can be quantitatively detected by combining the color change with the Meanshift algorithm accurately and automatically. Such proposed method has been successfully applied for the detection of L-histidine in serum sample with satisfying result.

A novel electrochemical sensor for the determination of histidine based on a molecularly imprinted copolymer

The present study aimed to report a novel electrochemical sensor through electropolymerization of o-aminophenol (o-AP) and m-dihydroxy benzene (m-DB) as monomers on the surface of the glassy carbon electrode (GCE) for the determination of histidine (His) as a template molecule. The developed sensor exhibited satisfactory sensitivity and high selectivity, and also offered a linear range between 0.005 and 10.0 μM with a detection limit of 0.9 nM. Finally, it is worth mentioning that we also aimed at employing the proposed sensor for the detection of His in blood serum samples.

Structural insights into the enhanced thermostability of cysteine substitution mutants of L-histidine decarboxylase from Photobacterium phosphoreum

Enzymatic amino acid assays are important in physiological research and clinical diagnostics because abnormal amino acid concentrations in biofluids are associated with various diseases. L-histidine decarboxylase from Photobacterium phosphoreum (PpHDC) is a pyridoxal 5'-phosphate-dependent enzyme and a candidate for use in an L-histidine quantitation assay. Previous cysteine substitution experiments demonstrated that the PpHDC C57S mutant displayed improved long-term storage stability and thermostability when compared with those of the wild-type enzyme. In this study, combinational mutation experiments of single cysteine substitution mutants of PpHDC were performed, revealing that the PpHDC C57S/C101V/C282V mutant possessed the highest thermostability. The stabilizing mechanism of these mutations were elucidated by solving the structures of PpHDC C57S and C57S/C101V/C282V mutants by X-ray crystallography. In the crystal structures, two symmetry-related PpHDC molecules form a domain-swapped homodimer. The side chain of S57 is solvent exposed in the structure, indicating that the C57S mutation eliminates chemical oxidation or disulfide bond formation with a free thiol group, thereby providing greater stability. Residues 101 and 282 form hydrophobic interactions with neighboring hydrophobic residues. Mutations C101V and C282V enhanced thermostability of PpHDC by filling a cavity present in the hydrophobic core (C101V) and increasing hydrophobic interactions.

Visible-Light-Mediated Modification and Manipulation of Biomacromolecules

Chemically modified biomacromolecules-i.e., proteins, nucleic acids, glycans, and lipids-have become crucial tools in chemical biology. They are extensively used not only to elucidate cellular processes but also in industrial applications, particularly in the context of biopharmaceuticals. In order to enable maximum scope for optimization, it is pivotal to have a diverse array of biomacromolecule modification methods at one's disposal. Chemistry has driven many significant advances in this area, and especially recently, numerous novel visible-light-induced photochemical approaches have emerged. In these reactions, light serves as an external source of energy, enabling access to highly reactive intermediates under exceedingly mild conditions and with exquisite spatiotemporal control. While UV-induced transformations on biomacromolecules date back decades, visible light has the unmistakable advantage of being considerably more biocompatible, and a spectrum of visible-light-driven methods is now available, chiefly for proteins and nucleic acids. This review will discuss modifications of native functional groups (FGs), including functionalization, labeling, and cross-linking techniques as well as the utility of oxidative degradation mediated by photochemically generated reactive oxygen species. Furthermore, transformations at non-native, bioorthogonal FGs on biomacromolecules will be addressed, including photoclick chemistry and DNA-encoded library synthesis as well as methods that allow manipulation of the activity of a biomacromolecule.

Determining the concentration and enantiomeric composition of histidine using one fluorescent probe

A chemoselective as well as enantioselective fluorescent probe has been developed to determine both the concentration and enantiomeric composition of the biologically important amino acid histidine by measuring the fluorescence responses when excited at two different wavelengths.

Direct preparation of porous cellulose microspheres via a self-growth process on bamboo fibers and their functionalization for specific adsorption of histidine-rich proteins

The traditional preparation of cellulose microspheres always involves tedious synthetic procedures (e.g., dissolution, emulsification and regeneration) and inevitable organic solvents, which undergoes both high production cost and environmental contamination. To overcome these issues, a feasible and green synthesis strategy is proposed to construct porous cellulose microspheres (PCMs) via one-step spontaneous formation relying on sodium periodate oxidation of pure bamboo fibers. By this strategy, a cluster of robust cellulose microspheres grow up on the surface of bamboo fibers in aqueous phase through amorphous oxidized cellulose self-assembly accumulation and then drop out when their sizes increase to about 15 µm. After being immobilized with Cu(II), the prepared cellulose microspheres serve as metal affinity adsorbent for proteins adsorption, showing high adsorption capacity, good selectivity and excellent reusability for bovine hemoglobin (BHb). Together with green and easy synthesis, the novel cellulose microspheres show a promising alternative to commercially available adsorbent support.

Protein Assays on Organic Electronics: Rational Device and Material Designs for Organic Transistor-Based Sensors

Artificial receptor-based protein assays have various attractive features such as a long-term stability, a low-cost production process, and the ease of tuning the target specificity. However, such protein sensors are still immature compared with conventional immunoassays. To enhance the application potential of synthetic sensing materials, organic field-effect transistors (OFETs) are some of the suitable platforms for protein assays because of their solution processability, durability, and compact integration. Importantly, OFETs enable the electrical readout of the protein recognition phenomena of artificial receptors on sensing electrodes. Thus, we believe that OFETs functionalized with artificial protein receptors will be a powerful tool for the on-site analyses of target proteins. In this Minireview, we summarize the recent progress of the OFET-based protein assays including the rational design strategies for devices and sensing materials.

Synthesis and Structural Optimization of Iridium(III) Solvent Complex for Electrochemiluminescence Labeling of Histidine-Rich Protein and Immunoassay Applications for CRP Detection

The reaction between an iridium(III) solvent complex and the histidine site of biomolecules as one kind of novel bioconjugation approaches has received much attention during the past few years. To extend this novel bioconjugation approach into electrochemiluminescence (ECL) immunoassay and optimize the performances, three iridium(III) solvent complexes with different C^∧N bidentate main ligands have been designed and synthesized in this work. Bovine serum albumin (BSA) as the standard histidine-rich protein is initially employed to evaluate the labeling performances by comparing the ECL intensity of the same amount of BSA labeled by different iridium(III) solvent complexes. Importantly, a magnetic beads-based sandwich immunoassay platform using Ir-dmpq (iridium(III) acetonitrile complex with 2-(3,5-dimethylphenyl)quinoline as the main ligand) as a structurally optimized labeling agent has been successfully constructed to detect C-reactive protein (CRP, an important biomarker of systemic inflammation in clinic), and the limit of detection based on this novel labeling agent could reach below 1 ng/mL, which may further pave the way for applications of the iridium(III) solvent complex in histidine-rich protein ECL labeling beyond fluorescence labeling.

New Designs for Phototherapeutic Transition Metal Complexes

In this Minireview, we highlight recent advances in the design of transition metal complexes for photodynamic therapy (PDT) and photoactivated chemotherapy (PACT), and discuss the challenges and opportunities for the translation of such agents into clinical use. New designs for light-activated transition metal complexes offer photoactivatable prodrugs with novel targeted mechanisms of action. Light irradiation can provide spatial and temporal control of drug activation, increasing selectivity and reducing side-effects. The photophysical and photochemical properties of transition metal complexes can be controlled by the appropriate choice of the metal, its oxidation state, the number and types of ligands, and the coordination geometry.

A cyclometalated trinuclear Ir(iii)/Pt(ii) complex as a luminescent probe for histidine-rich proteins

A trinuclear luminescent organometallic Pt–Ir–Pt complex acts as an efficient protein staining agent due to reversible binding to histidine-rich proteins.

Anticancer potency of novel organometallic Ir(iii) complexes with phosphine derivatives of fluoroquinolones encapsulated in polymeric micelles

A 3D model of cell culturing (spheroids) was explored and the anticancer potential of the selected novel organometallic Ir(iii) complex encapsulated in Pluronic p-123 micelles was clearly proved.

A luminescent microRNA nanoprobe based on the target-triggered release of an iridium(III)-solvent complex from mesoporous silica nanoparticles

A luminescent microRNA nanoprobe based on the target-triggered Ir(III)-solvent complex release has been fabricated. The complex is initially embedded into mesoporous silica nanoparticles (MSNs), and then is capped by single-stranded (ss) DNA. In the presence of the target microRNA, the ssDNA hybridize with the microRNA forming a rigid DNA/RNA heteroduplexes and leaving the surface of MSN. Thus, the capped Ir(III) solvent complex is released and re-coordinated with histidine (His) to form a new luminescent complex. The luminescence intensity of the nascent complex (with excitation/emission maxima at 340/570 nm) is positively correlated with the concentrations of the target microRNA in the range from 0.05 to 2 nM, and the detection limit of microRNA is estimated as 0.2 pM (S/N = 3). The ability of this nanoprobe to detect microRNA in cell extract further demonstrates its potential in practical application. Graphical abstractSchematic of a luminescent microRNA nanoprobe based on the target-triggered release of an Ir(III)-solvent complex from mesoporous silica nanoparticles.

Chemical Sensing Platforms Based on Organic Thin-Film Transistors Functionalized with Artificial Receptors

Organic thin-film transistors (OTFTs) have attracted intense attention as promising electronic devices owing to their various applications such as rollable active-matrix displays, flexible nonvolatile memories, and radiofrequency identification (RFID) tags. To further broaden the scope of the application of OTFTs, we focus on the host-guest chemistry combined with the electronic devices. Extended-gate types of OTFTs functionalized with artificial receptors were fabricated to achieve chemical sensing of targets in complete aqueous media. Organic and inorganic ions (cations and anions), neutral molecules, and proteins, which are regarded as target analytes in the field of host-guest chemistry, were electrically detected by artificial receptors. Molecular recognition phenomena on the extended-gate electrode were evaluated by several analytical methods such as photoemission yield spectroscopy in the air, contact angle goniometry, and X-ray photoelectron spectroscopy. Interestingly, the electrical responses of the OTFTs were highly sensitive to the chemical structures of the guests. Thus, the OTFTs will facilitate the selective sensing of target analytes and the understanding of chemical conversions in biological and environmental systems. Furthermore, such cross-reactive responses observed in our studies will provide some important insights into next-generation sensing systems such as OTFT arrays. We strongly believe that our approach will enable the development of new intriguing sensor platforms in the field of host-guest chemistry, analytical chemistry, and organic electronics.

Chemical strategies to modify amyloidogenic peptides using iridium(iii) complexes: coordination and photo-induced oxidation

Effective chemical strategies, i.e., coordination and coordination-/photo-mediated oxidation, are rationally developed towards modification of amyloidogenic peptides and subsequent control of their aggregation and toxicity.

Amyloidogenic peptides are considered central pathological contributors towards neurodegeneration as observed in neurodegenerative disorders [e.g., amyloid-β (Aβ) peptides in Alzheimer's disease (AD)]; however, their roles in the pathologies of such diseases have not been fully elucidated since they are challenging targets to be studied due to their heterogeneous nature and intrinsically disordered structure. Chemical approaches to modify amyloidogenic peptides would be valuable in advancing our molecular-level understanding of their involvement in neurodegeneration. Herein, we report effective chemical strategies for modification of Aβ peptides (i.e., coordination and coordination-/photo-mediated oxidation) implemented by a single Ir(iii) complex in a photo-dependent manner. Such peptide variations can be achieved by our rationally designed Ir(iii) complexes (Ir-Me, Ir-H, Ir-F, and Ir-F2) leading to significantly modulating the aggregation pathways of two main Aβ isoforms, Aβ₄₀ and Aβ₄₂, as well as the production of toxic Aβ species. Overall, we demonstrate chemical tactics for modification of amyloidogenic peptides in an effective and manageable manner utilizing the coordination capacities and photophysical properties of transition metal complexes.

Efficient Generation of Singlet Oxygen and Photooxidation of Sulfide into Sulfoxide via Tuning the Ancillary of Bicyclometalated Iridium(III) Complexes

With 2-phenylquinoline (pq) as a cyclometalated ligand, a series of cationic Ir(III) complexes [Ir(pq)₂(L1)₂](PF₆) (L1 is pyridine (1a), 4-methoxypyridine (1b), 4-dimethylaminopyridine (1c), and 4-acetylpyridine (1d)) and [Ir(pq)₂(L2)](PF₆) (L2 is 2,2'-bipyridine (1e), 2,2'-bipyrimidyl (1f), 4,4'-dimethyl-2,2'-bipyridine (1g), and 4,4'-dimethoxy-2,2'-bipyridine (1h)) were synthesized and characterized. The influence of the metal-based highest occupied molecular orbital on triplet-state lifetime, triplet-state quantum yield, and ¹O₂ generation quantum yield as well as aerobic photo-oxidation of sulfide into sulfoxide was evaluated via tuning the ancillary ligand of Ir(pq)₂ complexes. The results revealed that 1h with chelate ancillary ligand bearing electron-donating group possesses a high ¹O₂ generation quantum yield (0.90) and photocatalytic activity for sulfide oxidation with high chemoselectivity and a low catalyst loading (0.5 mol %) under mild conditions. Moreover, one-pot two-step procedure for preparation of enantiopure sulfoxides, including aerobic photo-oxidation of sulfide using 1h as a photosensitizer and chiral resolution of sulfoxide via a chiral-at-metal strategy, was also developed.

A novel label-free fluorescent detection of histidine based upon Cu2+-specific DNAzyme and hybridization chain reaction

A novel label-free fluorescent sensor for histidine was developed based upon Cu²⁺-specific DNAzyme, hybridization chain reaction(HCR) and triplex DNA. Cu²⁺ can bind to the histidine, in the presence of histidine, leading to the inhibition of the cleavage of substrate strand of Cu²⁺-dependent DNAzyme, then the intact substrate strand trigger the HCR between H1 and H2. The HCR product can be recognized by triplex-forming oligonucleotide (TFO) through triplex formation and reported by the fluorescence of berberine, the fluorescence intensity of the sensing system was proportional to the concentration of histidine during the range of 5.7-455 nmol L^-1, with a detection limit of 2.0 nmol L^-1.

Nucleus-Targeted Organoiridium-Albumin Conjugate for Photodynamic Cancer Therapy

An organoiridium-albumin bioconjugate (Ir1-HSA) was synthesized by reaction of a pendant maleimide ligand with human serum albumin. The phosphorescence of Ir1-HSA was enhanced significantly compared to parent complex Ir1. The long phosphorescence lifetime and high 1 O2 quantum yield of Ir1-HSA are highly favorable properties for photodynamic therapy. Ir1-HSA mainly accumulated in the nucleus of living cancer cells and showed remarkable photocytotoxicity against a range of cancer cell lines and tumor spheroids (light IC50 ; 0.8-5 μm, photo-cytotoxicity index PI=40-60), while remaining non-toxic to normal cells and normal cell spheroids, even after photo-irradiation. This nucleus-targeting organoiridium-albumin is a strong candidate photosensitizer for anticancer photodynamic therapy.

Molecular superoxide radical photogeneration in cancer cells by dipyridophenazine iridium(iii) complexes

The switch from Type II to Type I photochemical mechanism by new Ir(iii) complexes for improved PDT of cancer under hypoxia is demonstrated.