Cobalt ions inhibit electron-transport activity of Photosystem II without affecting Photosystem I

Investigations on photosynthesis have greatly benefited by the use of specific inhibitors that affect a specific site of inhibition on the electron-transport chain. We show here for the first time that cobalt (Co²⁺) ions can be used specifically to inactivate electron donation to the reaction centre of Photosystem (PS) II without affecting PS I reactions. This conclusion is based on the following observations: (1) addition of exogenous electron donors such as NH₂OH does not relieve Co²⁺-induced inactivation of photoelectron transport or the lowering of steady-state chlorophyll a fluorescence yield; this suggests that the inhibition is beyond the NH₂OH donation site and before the fluorescence quencher Q, i.e., on the reaction centre complex itself. (2) Washing of Co²⁺-pretreated chloroplasts with isolation buffer to remove Co²⁺ does not relieve Co²⁺-induced inhibition of Hill activity, suggesting that the Co²⁺ effect is irreversible. (3) Co²⁺ did not alter the PS I reactions. Thus, Co²⁺-treated chloroplasts can be used to study PS I functions free from PS II reactions in isolated chloroplasts.     

A novel optical probe based on d‐penicillamine‐functionalized graphene quantum dots: Preparation and application as signal amplification element to minoring of ions in human biofluid

In this study, d ‐penicillamine‐functionalized graphene quantum dots (DPA‐GQD) has been synthesized, which significantly increases the fluorescence intensity of GQD. We used this simple fluorescent probe for metal ions detection in human plasma samples. Designed DPA‐GQD respond to Hg²⁺, Cu²⁺, Au²⁺, Ag⁺, Co²⁺, Zn²⁺, and Pb²⁺ with high sensitivity. The fluorescence intensity of this probe decreased significantly in the presence of metal ions such as, Hg²⁺, Cu²⁺, Au²⁺, Ag⁺, Co²⁺, Zn²⁺, and Pb²⁺. In this work, a promising probe for ions monitoring was introduced. Moreover, DPA‐GQD probe has been tested in plasma samples. The functionalized DPA‐GQDs exhibits great promise as an alternative to previous fluorescent probes for bio‐labeling, sensing, and other biomedical applications in aqueous solution.     

A new rhodamine‐based fluorescent chemodosimeter for mercuric ions in water media

A new rhodamine–ethylenediamine–nitrothiourea conjugate (RT) was synthesized and its sensing property as a fluorescent chemodosimeter toward metal ions was explored in water media. Analytical results from absorption and fluorescence spectra revealed that the addition of Hg²⁺ ions to the aqueous solution of the chemodosimeter RT caused a distinct fluorescence OFF–ON response with a remarkable visual color change from colorless to pink; however, no clear spectral and color changes were observed from other metal ions including: Zn²⁺, Cu²⁺, Cd²⁺, Pb²⁺, Ag⁺, Fe²⁺, Cr³⁺, Co³⁺, Ni²⁺, Ca²⁺, Mg²⁺, K⁺ and Na⁺. The sensing results and the molecular structure suggested that a Hg²⁺‐induced a desulfurization reaction and cyclic guanylation of the thiourea moiety followed by ring‐opening of the rhodamine spirolactam in RT are responsible for a distinct fluorescence turn‐on signal, indicating that RT is a remarkably sensitive and selective chemodosimeter for Hg²⁺ ions in aqueous solution. Hg²⁺ within a concentration range from 0.1 to 25 μM can be determined using RT as a chemodosimeter and a detection limit of 0.04 μM is achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

Metal cations as synaptosomal calcium blockers in studies with Fura-2

Metal ions are often used to block calcium channels in various tissues, including synaptosomes. In the present study, Fura-2 was used to determine the effectiveness of various metal ions as calcium channel blockers in rat brain synaptosomes in vitro. In buffer solutions, La³⁺ and Cd²⁺ increased the Fura-2 fluorescence in a manner similar to Ca²⁺. Ni²⁺ and Mn²⁺ appeared to be fluorescence quenching cations, and Sr²⁺ and Co²⁺ had little effect on the fluorescence of Fura-2. In suspensions of synaptosomes under resting conditions, Cd²⁺, Ni²⁺ and Mn²⁺ were found to be not suitable for use in synaptosome studies. On the other hand, La³⁺ and Co²⁺ had little effect on the Fura-2 fluorescence of resting synaptosomes, and under depolarizing conditions, La³⁺ and Co²⁺ decreased the Fura-2 fluorescence. These resuls, therefore, suggest that La³⁺ and Co²⁺ may be suitable as calcium channel blockers in synaptosome studies.     

A new fluorescent chemosensor for Hg2+ in aqueous solution

We prepared an aminothiourea‐derived Schiff base (DA) as a fluorescent chemosensor for Hg²⁺ ions. Addition of 1 equiv of Hg²⁺ ions to the aqueous solution of DA gave rise to an obvious fluorescence enhancement and the subsequent addition of more Hg²⁺ induced gradual fluorescence quenching. Other competing ions, including Pb²⁺, Cd²⁺, Cr³⁺, Zn²⁺, Fe²⁺, Co³⁺, Ni²⁺, Ca²⁺, Mg²⁺, K⁺ and Na⁺, did not induce any distinct fluorescence changes, indicating that DA can selectively detect Hg²⁺ ions in aqueous solution. Copyright © 2012 John Wiley & Sons, Ltd.     

Study of fluorescence quenching of mercaptosuccinic acid‐capped CdS quantum dots in the presence of some heavy metal ions and its application to Hg(II) ion determination

In this study, CdS quantum dots (QDs) capped with mercaptosuccinic acid (MSA) were prepared in one step. The size, shape, component and spectral properties of MSA‐capped CdS QDs were characterized by transmission electron microscopy (TEM), photoluminescence (PL) and infrared (IR) spectrometry. The results showed that the prepared QDs with an average diameter of 6 nm have favorable fluorescence, which is greatly influenced by the pH of the environment. The interaction of some heavy metal ions including Ag⁺, Hg²⁺, Cu²⁺, Ni²⁺ and Co²⁺ with MSA‐capped CdS QDs was investigated in different buffering pH media. Based on the fluorescence quenching of the QDs in the presence of each of the metal ions, the feasibility of their determinations was examined according to the Stern–Volmer equation. The investigations showed that Hg(II) ions can be determined in the presence of many co‐existing metal ions at a buffering pH of 5. This method was satisfactorily applied to the measurement of Hg(II) ions in some environmental samples. Copyright © 2014 John Wiley & Sons, Ltd.     

Spectroscopic Analysis of the Cu<Superscript>2+</Superscript>-Induced Fluorescence Quenching of Fluorescent Proteins AmCyan and mOrange2

Fluorescent proteins show fluorescence quenching by specific metal ions, which can be applied towards metal biosensing applications. In order to develop metal-biosensor, we performed spectroscopic analysis of the fluorescence quenching of fluorescent protein AmCyan and mOrange2 by various metal ions. The fluorescence intensity of AmCyan was reduced to 48.54% by Co²⁺ and 67.77% by Zn²⁺; Cu²⁺ reduced the fluorescence emission of AmCyan to 19.30% of its maximum. The fluorescence intensity of mOrange2 was quenched by only Cu²⁺, to 11.48% of its maximum. When analyzed by Langmuir equation, dissociation constants for AmCyan and mOrange2 were 56.10 and 21.46 µM, respectively. The Cu²⁺ quenching of AmCyan and mOrange2 were reversible upon treatment with the metal chelator EDTA, indicating that the metal ions were located on the protein surface. Their model structures suggest that AmCyan and mOrange2 have novel metal-binding sites.     

Interaction of divalent metal ions with the carboxyl-terminal domain of human voltage-gated proton channel Hv1

The voltage-gated proton channel Hv1 functions as a dimer, in which the intracellular C-terminal domain of the protein is responsible for the dimeric architecture and regulates proton permeability. Although it is well known that divalent metal ions have effect on the proton channel activity, the interaction of divalent metal ions with the channel in detail is not well elucidated. Herein, we investigated the interaction of divalent metal ions with the C-terminal domain of human Hv1 by CD spectra and fluorescence spectroscopy. The divalent metal ions binding induced an obvious conformational change at pH 7 and a pH-sensitive reduction of thermostability in the C-terminal domain. The interactions were further estimated by fluorescence spectroscopy experiments. There are at least two binding sites for divalent metal ions binding to the C-terminal domain of Hv1, either of which is close to His²⁴⁴ or His²⁶⁶ residue. The binding of Zn²⁺ to the two sites both enhanced the fluorescence of the protein at pH 7, whereas the binding of other divalent metal ions to the two sites all resulted fluorescence quenching. The orders of the strength of divalent metal ions binding to the two sites from strong to weak are both Co²⁺, Ca²⁺, Ni²⁺, Mg²⁺, and Mn²⁺. The strength of Ca²⁺, Co²⁺, Mg²⁺, Mn²⁺ and Ni²⁺ binding to the site close to His²⁴⁴ is stronger than that of these divalent metal ions binding to the site close to His²⁶⁶.     

Transition metal ions and selenite modulate the methylation of arsenite by the recombinant human arsenic (+3 oxidation state) methyltransferase (hAS3MT)

This report demonstrates that transition metal ions and selenite affect the arsenite methylation by the recombinant human arsenic (+3 oxidation state) methyltransferase (hAS3MT) in vitro. Co²⁺, Mn²⁺, and Zn²⁺ inhibited the arsenite methylation by hAS3MT in a concentration-dependent manner and the kinetics indicated Co²⁺ and Mn²⁺ to be mixed (competitive and non-competitive) inhibitors while Zn²⁺ to be a competitive inhibitor. However, only a high concentration of Fe²⁺ could restrain the methylation. UV-visible, CD and fluorescence spectroscopy were used to study the interactions between the metal ions above and hAS3MT. Further studies showed that neither superoxide anion nor hydrogen peroxide was involved in the transition metal ion or selenite inhibition of hAS3MT activity. The inhibition of arsenite methylating activity of hAS3MT by selenite was reversed by 2 mM DTT (dithiothreitol) but neither by cysteine nor by β-mercaptoethanol. Whereas, besides DTT, cysteine can also prevent the inhibition of hAS3MT activity by Co²⁺, Mn²⁺, and Zn²⁺. Free Cys residues were involved in the interactions of transition metal ions or selenite with hAS3MT. It is proposed that the inhibitory effect of the ions (Co²⁺, Mn²⁺, and Zn²⁺) or selenite on hAS3MT activity might be via the interactions of them with free Cys residues in hAS3MT to form inactive protein adducts.     

A new principle for activity measurement of ADP or ATP dependent enzymes: fluorescence quenching of epsilon-ADP and epsilon-ATP by divalent metal ions.

The divalent metal ions Cu²⁺, Co²⁺, Mn²⁺, and Zn²⁺ form complexes with the fluorescent etheno analogs of the adenine nucleotides. The fluorescence intensity is thereby diminished. The binding strength of the metals to etheno-adenosine triphosphate is higher than to etheno-adenosine di- and monophosphate. The quenching effect of the divalent metal ions can be exploited as a simple routine activity measurement for various kinases and phosphohydrolases.     

Interaction of β‐cyclodextrin‐capped CdSe quantum dots with inorganic anions and cations

A facile method was developed for the preparation of water soluble β‐Cyclodextrin (β‐CD)‐modified CdSe quantum dots (QDs) (β‐CD‐QDs) by directly replacing the oleic acid ligands on the QDs surface with β‐CD in an alkaline aqueous solution. The as‐prepared QDs show good stability in aqueous solution for several months. Oxoanions, including phosphoric acid ion, sulphite acid ion and carbonic acid ion, affect the fluorescence of β‐CD‐QDs. Among them, H₂PO₄^– exhibited the largest quenching effect. For the polyprotic acids (HO)₃AO, the effect of acidic anions on the fluorescence of β‐CD‐QDs was in the order: monoanion (HO)₂AO₂^– > dianion (HO)AO₃^2– >> trianion AO₄^3–. After photoactivation for several days in the presence of anions at alkaline pH, the β‐CD‐QDs exhibited strong fluorescence emission. The effect of various heavy and transition metal ions on the fluorescence properties of the β‐CD‐QDs was investigated further. It was found that Ag⁺, Hg²⁺ and Co²⁺ have significant quenching effect on the fluorescence of the β‐CD‐QDs. The Stern–Volmer quenching constants increased in the order: Hg²⁺ < Co²⁺ <Ag⁺. The adsorption model of metal ions on β‐CD‐QDs was explored. Copyright © 2011 John Wiley & Sons, Ltd.     

An Engineered Palette of Metal Ion Quenchable Fluorescent Proteins

Many fluorescent proteins have been created to act as genetically encoded biosensors. With these sensors, changes in fluorescence report on chemical states in living cells. Transition metal ions such as copper, nickel, and zinc are crucial in many physiological and pathophysiological pathways. Here, we engineered a spectral series of optimized transition metal ion-binding fluorescent proteins that respond to metals with large changes in fluorescence intensity. These proteins can act as metal biosensors or imaging probes whose fluorescence can be tuned by metals. Each protein is uniquely modulated by four different metals (Cu²⁺, Ni²⁺, Co²⁺, and Zn²⁺). Crystallography revealed the geometry and location of metal binding to the engineered sites. When attached to the extracellular terminal of a membrane protein VAMP2, dimeric pairs of the sensors could be used in cells as ratiometric probes for transition metal ions. Thus, these engineered fluorescent proteins act as sensitive transition metal ion-responsive genetically encoded probes that span the visible spectrum.     

The high‐molecular‐weight kininogen Domain 5 is an intrinsically unstructured protein and its interaction with ferritin is metal mediated

High‐molecular‐weight kininogen domain 5 (HK5) is an angiogenic modulator that is capable of inhibiting endothelial cell proliferation, migration, adhesion, and tube formation. Ferritin can bind to a histidine–glycine–lysine‐rich region within HK5 and block its antiangiogenic effects. However, the molecular intricacies of this interaction are not well understood. Analysis of the structure of HK5 using circular dichroism and nuclear magnetic resonance [¹H, ¹⁵N]‐heteronuclear single quantum coherence determined that HK5 is an intrinsically unstructured protein, consistent with secondary structure predictions. Equilibrium binding studies using fluorescence anisotropy were used to study the interaction between ferritin and HK5. The interaction between the two proteins is mediated by metal ions such as Co²⁺, Cd²⁺, and Fe²⁺. This metal‐mediated interaction works independently of the loaded ferrihydrite core of ferritin and is demonstrated to be a surface interaction. Ferritin H and L bind to HK5 with similar affinity in the presence of metals. The ferritin interaction with HK5 is the first biological function shown to occur on the surface of ferritin using its surface‐bound metals.     

A highly selective fluorescence and absorption sensor for rapid recognition and detection of Cu2+ ions in aqueous solution and film

A fluorescence and absorption chemosensor (SAAT) based on 5-(hydroxymethyl)-salicylaldehyde (SA) and o-aminothiophenol (AT) was designed and synthesized. SAAT in DMSO–HEPES (20.0 mM, v/v, 1:99, pH = 7.0) solution shows a highly selective and sensitive absorption and an ‘on–off’ fluorescence response to Cu²⁺ ions in aqueous solutions over all other competitive metal ions including Na⁺, Ag⁺, Ba²⁺, Ca²⁺, Cd²⁺, Mg²⁺, Zn²⁺, Cr³⁺, Al³⁺, Hg²⁺, K⁺, Mn²⁺, Ni²⁺, Sr²⁺, Tb³⁺ and Co²⁺. SAAT exhibits ratiometric absorption sensing ability for Cu²⁺ ions. Importantly, SAAT also can sense Cu²⁺ ions using fluorescence quenching, the fluorescence intensity of SAAT showed a good linear relationship with Cu²⁺ concentration, and the detection limit of Cu²⁺ was 0.34 μM. The results of Job's plot, Benesi–Hildebrand plot, mass spectra, and density functional theory calculations confirmed that the selective absorption and fluorescence response were attributed to the formation of a 1:1 complex between SAAT and Cu²⁺. SAAT in test film could identify Cu²⁺ in water samples using the intuitive fluorescence colour change under a UV lamp. SAAT has great application value as a selective and sensitive chemosensor to discriminate and detect Cu²⁺ ions.     

Excellent Comprehensive Performance of Na‐Based Layered Oxide Benefiting from the Synergetic Contributions of Multimetal Ions

Na‐ion batteries are promising for large‐scale energy storage applications, but few cathode materials can be practically used because of the significant difficulty in synthesizing an electrode material with superior comprehensive performance. Herein, an effective strategy based on synergetic contributions of rationally selected metal ions is applied to design layered oxides with excellent electrochemical performances. The power of this strategy is demonstrated by the superior properties of as‐obtained NaFe_0.45Co_0.5Mg_0.05O₂ with 139.9 mA h g^?1 of reversible capacity, 3.1 V of average voltage, 96.6% of initial Coulombic efficiency, and 73.9 mA h g^?1 of capacity at 10 C rate, which benefit from the synergetic effect of Fe³⁺ (high redox potential), Co³⁺ (good kinetics), and inactive Mg²⁺ with compatible radii (stabilizing structure). Moreover, it is clarified that the superior property is not the simple superposition of performance for layered oxides with single metal ions. With the assistance of density functional theory calculations, it is evidenced that the wide capacity range (>70%) of prismatic Na⁺‐occupied sites during sodiation/desodiation is responsible for its high rate performance. This rational strategy of designing high‐performance cathodes based on the synergetic effect of various metal ions might be a powerful step forward in the development of new Na‐ion‐insertion cathodes.     

Luminescent properties of 4‐aminobenzo‐15‐crown‐5 after preferential binding of ferric ions in aqueous solutions

We report a combined approach that introduces the use of 4‐aminobenzo‐15‐crown‐5 (4AB15C5) for the detection of ferric(III) ions by colorimetric, ultraviolet (UV)–visible light absorption, fluorescence, and live‐cell imaging techniques along with density functional theory (DFT) calculations. We have found that 4AB15C5 is sensitive and selective for binding ferric(III) ions in aqueous solutions. DFT calculations using the polarizable continuum model have been used to explain the strong binding of the ferric ion by 4AB15C5 in aqueous solutions. The detection limit in the fluorescence quenching measurements was found to be as low as 50 μM for the ferric ion with a determined Stern–Volmer constant of 1.52 × 10⁴ M^?1. Fluorescence intensity did not change for other ions tested, Fe²⁺, Co²⁺, Mn²⁺, Mg²⁺, Zn²⁺, Ca²⁺, NH₄⁺, Na⁺, and K⁺ ions. Live‐cell fluorescence imaging was also used to check the intracellular variations in ferric ion levels. Our spectroscopic data indicated that 4AB15C5 can bind ferric ions selectively in aqueous solutions.     

Types of interaction of meso‐tetraphenylporphyrin with alkali and alkaline‐earth metal ions

The cavity in a porphyrin can accommodate metal ions through electron donor–acceptor (EDA) interaction in acetonitrile media without any specially designed fabrication with the porphyrin subunit. Alkali metal ion forms a complex with meso‐tetraphenylporphyrin (TP) in 2:1 stoichiometry, while the bivalent Mg²⁺ ion follows a 1:1 stoichiometry. A fluorescence interaction study indicated that TP can behave like a chemosensor for these ions present in the blood electrolytes. Specifically, for the alkali metal ions intensity‐based sensing was observed, due to inhibition of photoinduced electron transfer (PET), entailing enhancement of fluorescence intensity, and for the alkaline‐earth Mg²⁺ a mixed quenching was observed. Na⁺ and K⁺ ions can be differentiated depending upon the extent of fluorescence enhancement. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of transition metal ions on the fluorescence and Taq-catalyzed polymerase chain reaction of tricyclic cytidine analogs

The cytosine analogs 1,3-diaza-2-oxophenothiazine (tC) and 1,3-diaza-2-oxophenoxazine (tCo) stand out among fluorescent bases due to their unquenched fluorescence emission in double-stranded DNA. Recently, we reported a method for the generation of densely tCo-labeled DNA by polymerase chain reaction (PCR) that relied on the use of the extremely thermostable Deep Vent polymerase. We have now developed a protocol that employs the more commonly used Taq polymerase. Supplementing the PCR with Mn²⁺ or Co²⁺ ions dramatically increased the amount of tCo triphosphate (dtCoTP) incorporated and, thus, enhanced the brightness of the PCR products. The resulting PCR products could be easily detected in gels based on their intrinsic fluorescence. The Mn²⁺ ions modulate the PCR by improving the bypass of template tCo and the overall catalytic efficiency. In contrast to the lower fidelity during tCo bypass, Mn²⁺ improved the ability of Taq polymerase to distinguish between dtCoTP and dTTP when copying a template dA. Interestingly, Mn²⁺ ions hardly affect the fluorescence emission of tC(o), whereas the coordination of Co²⁺ ions with the phosphate groups of DNA and nucleotides statically quenches tC(o) fluorescence with small reciprocal Stern–Vollmer constants of 10–300 μM.     

A simply synthesized biphenyl substituted piperidin‐4‐one for the fluorescence chemosensing of Cd2+

Ion‐induced change in fluorescence is a straight‐forward method for detection of toxic metal ions showing immediate response. Cadmium ions are toxic to the environment. We report in this paper a piperidine‐4‐one‐based fluorescent chemosensor of Cd²⁺ ions, designed and synthesized by a simple method. The compound is characterized using infra‐red (IR) and ¹H–NMR spectral techniques. The chemosensor showed Cd²⁺ ion selectivity and sensitivity in aqueous solution. The stoichiometry and the binding constants were determined using fluorescence spectroscopy. Piperidine‐4‐one shows a 1:1 stoichiometric binding to Cd²⁺. The limit of detection of Cd²⁺ was reported.     

SDS-capped 1-pyrenecarboxaldehyde nanoprobe for selective detection of Cu2+ ion from water samples: Spectroscopic approach

Sodium dodecyl sulfate (SDS)-capped 1-pyrenecarboxaldehyde nanoparticles (PyalNPs) were prepared using a reprecipitation method in an aqueous medium and exhibited red-shifted aggregation-induced enhanced emission (AIEE). The dynamic light scattering (DLS) examination showed narrower particle size distribution with an average particle size of 41 nm, whereas −34.5 mV zeta potential value indicate the negative surface charge and good stability of nanoparticles (NPs) in an aqueous medium. The AIEE was seen at λ_max = 473 nm in a fluorescence spectrum of a PyalNP suspension. In the presence of Cu²⁺ ions, the fluorescence of PyalNPs quenches very significantly, even in the presence of other metal ions like Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Al³⁺, Fe²⁺, Hg²⁺, Ni²⁺ and Mg²⁺. The changes in the fluorescence lifetime of PyalNPs in the presence of Cu²⁺ ions suggested that the type of quenching was dynamic. The fluorescence quenching data for the NPs suspension fitted well into a typical Stern–Volmer relationship in the concentration range 1.0–25 μg/ml of Cu²⁺ ions. The estimated value of the correlation coefficient R² = 0.9877 was close to 1 and showed the linear relationship between quenching data and Cu²⁺ ion concentration. The limit of detection (LOD) was found to be 0.94 ng/ml and is far below the tolerable intake limit value of 1.3 μg/ml accepted by the World Health Organization for Cu²⁺ ions in drinking water. The fluorescence quenching approach for a SDS-capped Pyal nanosuspension for copper ion quantification is of high specificity and coexisting ions were found to interfere very negligibly. The developed method was successfully applied for the estimation of copper ions in river water samples.