Detection of homocysteine and cysteine

Conjugated polymer with carboxylate groups-Hg2+ system as a turn-on fluorescence probe for label-free detection of cysteine-containing compounds

In this work, a turn on fluorescent sensor, based on Hg²⁺ coordination conjugated polymer, was developed to detect cysteine-containing compounds. The fluorescence of conjugated polymer (poly(2,5-bis (sodium 4-oxybutyrate) -1,4 - phenylethynylene-alt-1,4-phenyleneethynylene; PPE-OBS) would be quenched by Hg²⁺ because of the coordination-induced aggregation and electron transfers of PPE-OBS toward Hg²⁺. When there were some cysteine-containing compounds in PPE-OBS-Hg²⁺ system, the fluorescence of PPE-OBS would be recovered. It indicated that the PPE-OBS-Hg²⁺ system could be used to detect cysteine-containing compounds. Under the optimized conditions, the experiment results showed that there were particularly linear range, high sensitivity and selectivity over other amino acids. The limit of detection (LOD) of cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) were 0.725μmolL^-1, 0.982μmolL^-1 and 1.21μmolL^-1 by using this sensor. In addition, Cys standard recovery in several green tea drink and honey samples was also demonstrated. The recovery of Cys was range from 96.3 to 105.0% and RSD was less than 3.25%. The satisfactory results demonstrated that the proposed method could be as a potential fluorescent method for determining cysteine-containing compounds in real samples.

3-(2-Bromoacetamido)-N-(9-ethyl-9H)-carbazol fluorescent probe and its application for the determination of thiophenols in rubber products by HPLC with fluorescence detection and atmospheric chemical ionization mass spectrometry identification

A rapid, sensitive, and selective precolumn derivatization method for the simultaneous determination of eight thiophenols using 3-(2-bromoacetamido)-N-(9-ethyl-9H)-carbazol as a labeling reagent by high-performance liquid chromatography with fluorescence detection has been developed. The labeling reagent reacted with thiophenols at 50°C for 50 min in aqueous acetonitrile in the presence of borate buffer (0.10 mol/L, pH 11.2) to give high yields of thiophenol derivatives. The derivatives were identified by online postcolumn mass spectrometry. The collision-induced dissociation spectra for thiophenol derivatives gave the corresponding specific fragment ions at m/z 251.3, 223.3, 210.9, 195.8, and 181.9. At the same time, derivatives exhibited intense fluorescence with an excitation maximum at λ_ex = 276 nm and an emission maximum at λ_em = 385 nm. Excellent linear responses were observed for all analytes over the range of 0.033-6.66 μmol/L with correlation coefficients of more than 0.9997. Detection limits were in the range of 0.94-5.77 μg/L with relative standard deviations of less than 4.54%. The feasibility of derivatization allowed the development of a rapid and highly sensitive method for the quantitative analysis of trace levels of thiophenols from some rubber products. The average recoveries (n = 3) were in the range of 87.21-101.12%.

Non-protein thiol imaging and quantification in live cells with a novel benzofurazan sulfide triphenylphosphonium fluorogenic compound

Thiols (-SH) play various roles in biological systems. They are divided into protein thiols (PSH) and non-protein thiols (NPSH). Due to the significant roles thiols play in various physiological/pathological functions, numerous analytical methods have been developed for thiol assays. Most of these methods are developed for glutathione, the major form of NPSH. Majority of these methods require tissue/cell homogenization before analysis. Due to a lack of effective thiol-specific fluorescent/fluorogenic reagents, methods for imaging and quantifying thiols in live cells are limited. Determination of an analyte in live cells can reveal information that cannot be revealed by analysis of cell homogenates. Previously, we reported a thiol-specific thiol-sulfide exchange reaction. Based on this reaction, a benzofurazan sulfide thiol-specific fluorogenic reagent was developed. The reagent was able to effectively image and quantify total thiols (PSH+NPSH) in live cells through fluorescence microscopy. The reagent was later named as GUALY's reagent. Here we would like to report an extension of the work by synthesizing a novel benzofurazan sulfide triphenylphosphonium derivative [(((7,7'-thiobis(benzo[c][1,2,5]oxadiazole-4,4'-sulfonyl))bis(methylazanediyl))bis(butane-4,1-diyl))bis(triphenylphosphonium) (TBOP)]. Like GUALY's reagent, TBOP is a thiol-specific fluorogenic agent that is non-fluorescent but forms fluorescent thiol adducts in a thiol-specific fashion. Different than GUALY's reagent, TBOP reacts only with NPSH but not with PSH. TBOP was effectively used to image and quantify NPSH in live cells using fluorescence microscopy. TBOP is a complementary reagent to GUALY's reagent in determining the roles of PSH, NPSH, and total thiols in thiol-related physiological/pathological functions in live cells through fluorescence microscopy. Graphical Abstract Live cell imaging and quantification of non-protein thiols by TBOP.

Synthesis, resolution and crystal structures of two enanti-omeric rhodamine derivatives

The title mol-ecule, rac-6'-bromo-3'-di-ethyl-amino-3H-spiro-[2-benzo-furan-1,9'-xanthen]-3-one, C24H20BrNO3, was synthesized and the two enanti-omers which formed were separated. The structures of all three compounds were determined and compared with those of a variety of related derivatives. A notable feature is the fold of the xanthene portion which ranges from 15.15 (13)° in the racemate to 2.42 (2)° in one mol-ecule of the R enanti-omer with that for the S enanti-omer having an inter-mediate value. The differences are attributed to the number and severity of inter-molecular inter-actions which include C-H⋯O hydrogen bonds, C-H⋯π(ring) and, in the S enanti-omer, a π-stacking inter-action between the carbonyl group and an aromatic ring.

Enhanced G-Quadruplex DNA Stabilization and Telomerase Inhibition by Novel Fluorescein Derived Salen and Salphen Based Ni(II) and Pd(II) Complexes

Metal based salen complexes have been considered as an important scaffold toward targeting of DNA structures. In the present work, we have synthesized nickel(II) and palladium(II) salen and salphen complexes by using readily available fluorescein as the backbone to provide an extended aromatic surface. The metal complexes exhibit affinity toward the human telomeric G-quadruplex DNA with promising inhibition of telomerase activity. This has been ascertained by their efficiency in the long term cell proliferation assay which showed significant cancer cell toxicity in the presence of the metal complexes. Confocal microscopy showed cellular internalization followed by localization in the nucleus and mitochondria. Considerable population at the sub-G1 phase of the cell cycle showed cell death via apoptotic pathway.

Fluorescein-Based Chromogenic and Ratiometric Fluorescence Probe for Highly Selective Detection of Cysteine and Its Application in Bioimaging

A dual mode fluorescent probe, which is based on an integration of fluorescein and coumarin fluorophores, was developed for the discrimination of Cys from Hcy and GSH. This probe (2) shows the advantage of quick reaction (5 min) with Cys, resulting in a strong fluorescence turn-on response when excited at 450 nm. Notably, it also demonstrates the ratiometric fluorescence property while excited by a shorter wavelength (332 nm). All of results suggest probe 2 has a high selectivity toward Cys even in the presence of other amino acids, cations and anions. The detection limit of Cys was calculated as 0.084 μM, which was much lower than the intracellular concentration. ¹H NMR, MS and DFT calculation were used to reveal the detection mechanism further. Finally, this low cytotoxic probe was successfully applied in bioimaging within HepG2 cells.

A dual-signal sensing system based on organic dyes-LDHs film for fluorescence detection of cysteine

It is of great significance to sense cysteine (Cys) in a simple and fast way because of its potential applications in biological processes.

Orchestration of dual cyclization processes and dual quenching mechanisms for enhanced selectivity and drastic fluorescence turn-on detection of cysteine

Synergistic dual cyclizations and dual quenching mechanisms of acrylate and maleimide groups for improved turn-on fluorescence detection of cysteine.

A fluorescein-based chemosensor for relay fluorescence recognition of Cu(ii) ions and biothiols in water and its applications to a molecular logic gate and living cell imaging

Relay recognition of copper(ii) ions and biothiolsviaa fluorescence “on–off–on” cascade has been realized in 100% aqueous solution when excited by the visible light.

A fast-response two-photon fluorescent probe for the detection of Cys over GSH/Hcy with a large turn-on signal and its application in living tissues

Cysteine (Cys), a small-molecule aminothiol, plays important roles in various physiological processes in connection with various diseases, such as skin lesions, edema, hair depigmentation and liver damage. We developed a novel two-photon fluorescent probe for sensing Cys in presence of GSH and Hcy in vivo. The two-photon fluorescent probe exhibited favorable properties, including fast response (about 20 min), good selectivity, and low cytotoxicity. Furthermore, it was successfully applied for imaging Cys in living cells and tissues.

A Simple and Effective Ratiometric Fluorescent Probe for the Selective Detection of Cysteine and Homocysteine in Aqueous Media

Biothiols such as cysteine (Cys) and homocysteine (Hcy) are essential biomolecules participating in molecular and physiological processes in an organism. However, their selective detection remains challenging. In this study, ethyl 2-(3-formyl-4-hydroxyphenyl)-4-methylthiazole-5-carboxylate (NL) was synthesized as a ratiometric fluorescent probe for the rapid and selective detection of Cys and Hcy over glutathione (GSH) and other amino acids. The fluorescence intensity of the probe in the presence of Cys/Hcy increased about 3-fold at a concentration of 20 equiv. of the probe, compared with that in the absence of these chemicals in aqueous media. The limits of detection of the fluorescent assay were 0.911 μM and 0.828 μM of Cys and Hcy, respectively. ¹H-NMR and MS analyses indicated that an excited-state intramolecular proton transfer is the mechanism of fluorescence sensing. This ratiometric probe is structurally simple and highly selective. The results suggest that it has useful applications in analytical chemistry and diagnostics.

Quinones as novel chemiluminescent probes for the sensitive and selective determination of biothiols in biological fluids

Altered plasma aminothiol concentrations are thought to be a valuable risk indicator and are interestingly utilized for routine clinical diagnosis and for the monitoring of various metabolic disorders and human diseases, and accordingly there is a need for an accurate and reliable assay capable of simultaneously determining aminothiols including glutathione (GSH), N-acetylcysteine (NAC), homocysteine (Hcys), and cysteine (Cys) in human plasma. Herein, a highly sensitive, selective, and very fast HPLC-chemiluminescence (HPLC-CL) coupled method is reported, exploiting for the first time the strong nucleophilicity and high reactivity of aminothiols toward quinones for a CL assay. The unique redox-cycling capability of quinone and/or Michael addition adducts, thioether-quinone conjugates, was utilized to establish a novel analytical method based on the reaction of adducts with dithiothreitol (DTT) to liberate reactive oxygen species (ROS), which are detected by using a luminol-CL assay. Specimen preparation involved the derivatization of aminothiols with menadione (MQ) for 5 minutes at room temperature. A unique green chemistry synthesis of thioether-quinones in HEPES buffer (pH 8.5) was introduced by using our reaction methodology without needing any hazardous organic solvent or catalyst. The aminothiol-MQ adducts were separated using solid-phase extraction followed by isocratic elution on an ODS column. Linearity was observed in the range of 2.5-500, 5-500, 10-1500, and 20-2000 nM with detection limits (S/N of 3) of 3.8, 4.2, 8, and 16 (fmol per injection) for GSH, NAC, Hcys, and Cys, respectively. The method was successfully applied for the selective determination of aminothiols in human plasma from healthy people and patients with rheumatic arthritis and diabetes mellitus. The obtained results postulated the usefulness of our method for investigating the relationship between aminothiol metabolism and related human disorders.

Mitochondria-Targeting Chromogenic and Fluorescence Turn-On Probe for the Selective Detection of Cysteine by Caged Oxazolidinoindocyanine

We report a chromogenic and fluorescence turn-on probe based on crotonoyl ester-functionalized oxazolidinoindole for the selective detection of cysteine in neutral buffer. The probe rapidly formed indocyanophenolate through the Michael addition and a subsequent cyclization reaction of cysteine, inducing both a dramatic bathochromic shift (>130 nm) and a large fluorescence turn-on response (F/F0 12) in the UV-vis and fluorescence spectra and affording a micromolar limit of detection (LOD = 5.0 μM) of cysteine in HEPES buffer. When cysteine was added, the probe exhibited a dual optical change with strong green fluorescence and dramatic red color by the oxazolidinoindole-to-hydroxyethylindolium transformation. Further cellular application of the probe was successfully performed for the mitochondrial imaging of HeLa cells.

Assembling of a functional cyclodextrin-decorated upconversion luminescence nanoplatform for cysteine-sensing

A novel rhodamine-oxaldehyde (RHO) functionalized β-NaYF4:Yb(3+)/Er(3+) upconversion nanoparticle (UCNP) for specific detection of cysteine (Cys) in aqueous solution was achieved through a Förster resonance energy transfer (FRET) process. Based on self-assembling interaction, hydrophobic upconversion nanoparticles could be modified with α-cyclodextrin to make them water dispersible.

Physiologically relevant plasma d,l-homocysteine concentrations mobilize Cd from human serum albumin

Although low-level chronic exposure of humans to cadmium (Cd(2+)) can result in a variety of adverse health effects, little is known about the role that its interactions with plasma proteins and small molecular weight (SMW) ligands in the bloodstream may play in delivering this metal to its target organs. To gain insight, a Cd-human serum albumin (HSA) 1:1 (molar ratio) complex was analyzed by size exclusion chromatography (SEC) coupled on-line to a flame atomic absorption spectrometer (FAAS). Using a phosphate buffered saline (PBS)-buffer mobile phase, the stability of the Cd-HSA complex was investigated in the presence of 2.0mM of SMW ligands, including taurine, acetaminophen, l-methionine, l-cysteine (Cys), d,l-homocysteine (hCys) or l-cysteine methyl-ester (Cys-Me). While taurine, acetaminophen and l-methionine did not affect its integrity, Cys, hCys and Cys-Me completely abstracted Cd from HSA. Subsequent investigations into the effect of 1.5, 1.0 and 0.5mM Cys and hCys on the integrity of the Cd-HSA complex revealed clear differences with regard to the nature of the eluting SMW-Cd species between these structurally related endogenous thiols. Interestingly, the Cd-specific chromatograms that were obtained for 0.5mM hCys revealed the elution of an apparent mixture of the parent Cd-HSA complex with a significant contribution of a structurally uncharacterized CdxhCysy species. Since this hCys concentration is encountered in blood plasma of hyperhomocysteinemia patients and since previous studies by others have revealed that a SH-containing carrier mediates the uptake of Cd into hepatocytes, our results suggest that plasma hCys may play a role in the toxicologically relevant translocation of Cd from the bloodstream to mammalian target organs.

Tuning interionic interaction for highly selective in vivo analysis

The development of highly selective methodologies to enable in vivo recording of chemical signals is of great importance for studying brain functions and brain activity mapping. However, the complexity of cerebral systems presents a great challenge in the development of chem/(bio)sensors that are capable of directly and selectively recording bioactive molecules involved in brain functions. As one of the most important and popular interactions in nature, interionic interaction constitutes the chemical essence of high specificity in natural systems, which inspires us to develop highly selective chem/(bio)sensors for in vivo analysis by precisely engineering interionic interaction in the in vivo sensing system. In this tutorial review, we focus on the recent progress in the tuning of interionic interaction to improve the selectivity of biosensors for in vivo analysis. The type and property of the interionic interaction is first introduced and several strategies to improve the selectivity of the biosensors, including enzyme-based electrochemical biosensors, aptamer-based electrochemical biosensors, and the strategies to recruit recognition molecules are reviewed. We also present an overview of the potential applications of the biosensors for in vivo analysis and thereby for physiological investigations. Finally, we present the major challenges and opportunities regarding the high selectivity of in vivo analysis based on tuning interionic interaction. We believe that this tutorial review provides critical insights for highly selective in vivo analysis and offers new concepts and strategies to understand brain chemistry.

A novel pyrene based fluorescent probe for selective detection of cysteine in presence of other bio-thiols in living cells

This manuscript reports the synthesis of pyrene-based fluorescent probe (PA-1) containing α,β-unsaturated carbonyl moiety and its application towards the selective and sensitive detection of cysteine (Cys) over other bio-thiols. The probe, 3-(2-hydroxyphenyl)-1-pyrenyl-2-propenone (PA-1) was synthesized through Claisen-Schmidt condensation between acetyl pyrene and salicylaldehyde. The formed product was characterized by (1)H NMR, (13)C NMR and GC-MS techniques. The probe exhibited absorption maximum at 374nm and emission maximum at 467nm (λex=342nm). The emission intensity of PA-1 was greatly enhanced while adding 2.5nM Cys. This can be attributed to the nucleophilic attack of Cys to the α,β-unsaturated ketone resulting in switching off, intramolecular charge transfer (ICT) from pyrene moiety to the phenolic nucleus. This was confirmed by DFT measurements. The PA-1 exhibited an excellent selectivity towards the determination of 40nM cys in the presence of 250,000-fold higher concentration of common interferents. The emission intensity was linearly increased and the limit of detection was found to be 10pM/L (S/N=3). Interestingly, the response of the PA-1 towards Cys is less than 1min. The confocal laser scanning micrographs of HeLa cells confirmed the cell permeability of the PA-1 and its ability to selectively detect Cys in living cells. In addition, the proposed probe was successfully applied for the determination of Cys in blood serum samples.

Fluorescein Tri-Aldehyde Promotes the Selective Detection of Homocysteine

Elevated homocysteine levels are a well-known independent risk factor for cardiovascular disease. To date, relatively few selective fluorescent probes for homocysteine detection have been reported. The lack of sensing reagents and remaining challenges largely derive from issues of sensitivity and/or selectivity. For example, homocysteine is a structural homologue of the more abundant (ca, 20-25 fold) aminothiol cysteine, differing only by an additional methylene group side chain. Fluorescein tri-aldehyde, described herein, has been designed and synthesized as a sensitive and selective fluorophore for the detection of homocysteine in human plasma samples. It responds to analytes selectively via a photoinduced electron transfer (PET) inhibition process that is modulated by predictable analyte-dye product hybridization and ionization states. Mulliken population analysis of fluorescein tri-aldehyde and its reaction products reveals that the characteristic formation of multiple cationic of homocysteine-derived heterocycles leads to enhanced relative negative charge build up on the proximal phenolate oxygen of the fluorophore as a contributing factor to selective emission enhancement.

A fluorescent probe for relay recognition of homocysteine and Group IIIA ions including Ga(iii)

Relay fluorescence recognition of homocysteine and gallium ions was realized by sequential chemodosimeter and chemosensor approaches for the first time.

Differentiation of biothiols from other sulfur-containing biomolecules using iodide-capped gold nanoparticles

We describe here a simple method based on the aggregation of iodide-capped gold nanoparticles (GNPs) to differentiate biothiols from other sulfur-containing biomolecules.

An “off–on” fluorescent probe for the detection of cysteine /homocysteine and its imaging in living cells

Based on the NCL reaction, we prepared an off/on fluorescent probe BQ for the selective sensing of Cys/Hcy. The discrimination of Cys and Hcy is achieved through the different rates of the transthioesterification reaction of Cys/Hcy with BQ.

An ultrafast turn-on thiol probe for protein labeling and bioimaging

A novel ultrafast turn-on thiol probe was developed that can be successfully applied to label protein thiols and imaging them in living cells.

Single fluorescent probe for reversibly detecting copper ions and cysteine in a pure water system

In this work, we have engineered a novel fluorescent probe PI, which remarkably can reversible detect copper ion and cysteine in pure water system for the first time.

Colorimetric and ON–OFF–ON fluorescent chemosensor for the sequential detection of Cu(ii) and cysteine and its application in imaging of living cells

An easy-to-prepare colorimetric and ON–OFF–ON fluorescent naphthol derivative 1 has been used for sequential detection of Cu²⁺ and cysteine.

A dual-site two-photon fluorescent probe for visualizing mitochondrial aminothiols in living cells and mouse liver tissues

In this work, we developed a dual-site two-photon (TP) fluorescent RSH probe (CA-TPP) for imaging mitochondrial RSH in living systems. In particular, probe CA-TPP was capable of using TP fluorescence to track mitochondrial RSH over a long period for the first time.

Highly selective colorimetric and fluorescent BODIPY dyes for sensing of cysteine and/or homocysteine

Selective “naked eye” and fluorescent sensing of biothiols by visible-light excitable α- and β-formyl BODIPYs1and3was developed.

A colorimetric and fluorometric investigation of Cu(ii) ion in aqueous medium with a fluorescein-based chemosensor

A colorimetric and fluorometric chemosensor, 1,4-bis(1-fluorescein)-2,3-diaza-1,3-butadiene (L, 3) as Schiff base is developed for naked-eye detection of Cu²⁺ ion in aqueous medium due to the formation of a 1 : 1 copper–ligand complex.

Colorimetric and fluorescence probe for the detection of nano-molar lysine in aqueous medium

A new BODIPY based lysine selective probe,THBPY, is synthesized and detects nano-molar lysine in aqueous medium, exhibiting both a visible change in color from yellow-green to orange and a change in the fluorescence profile.