Hg2+-mediated aggregation of gold nanoparticles for colorimetric screening of biothiols

In this work, we report a colorimetric assay for the screening of biothiols including glutathione (GSH), cysteine (Cys), and homocysteine (Hcys) based on Hg(2+)-mediated aggregation of gold nanoparticles (AuNPs). Hg(2+) can induce aggregation of thiol-containing naphthalimide (1) capped AuNPs due to the cross-linking interactions from the resulting "thymine-Hg(2+)-thymine" (T-Hg(2+)-T) analogous structure. When Hg(2+) is firstly treated with biothiols, followed by mixing with 1-capped AuNPs suspension, AuNPs undergo a transformation from an aggregation to a dispersion state depending on the concentration of biothiols. This anti-aggregation or re-dispersion of AuNPs is due to the higher affinity of Hg(2+) for biothiols relative to compound 1. The corresponding color variation in the process of anti-aggregation of AuNPs can be used for the quantitative screening of biothiols through UV-vis spectroscopy or by the naked eye. Under optimized conditions, a good linear relationship in the range of 0.025-2.28 μM is obtained for GSH, 0.035-1.53 μM for Cys, and 0.040-2.20 μM for Hcys. The detection limits of this assay for GSH, Cys, and Hcys are 17, 9, and 18 nM, respectively. This colorimetric assay exhibits a high selectivity and sensitivity with tunable dynamic range. The proposed method has been successfully used in the determination of total biothiol content in human urine samples.     

A tryptophan-containing open-chain framework for tuning a high selectivity for Ca2+ and 13C NMR observation of a Ca2+-indole interaction in aqueous solution

Two molecular architectures featuring the cation-responsive tryptophan indole were designed and investigated for the development of a novel fluorescent chemosensor for Ca2+. We observed that the Trp-based open-framework chemosensor EW2 exhibits remarkable selectivity for Ca2+ over Mg2+, Ba2+, K+, Na+, and Li+ in water between pH 4.6 and 7.0 on the basis of Ca2+-induced high fluorescence enhancement of the Trp residue. A combined 13C NMR and CD spectroscopic study has demonstrated a dynamic reorientation of the indole ring due to the cation-indole interaction accompanying the Ca2+-induced dramatic fluorescence enhancement. The results suggest that the highly sensitive, metal-ion-dependent Trp indolyl C(3) chemical shifts may serve as a promising indicator for monitoring metal ion-indole noncovalent interaction in solution.     

Modulator binding protein antagonizes activation of (Ca2+ + Mg2+)-ATPase and Ca2+ transport of red blood cell membranes.

Red blood cells contain a protein that activates membrane-bound (Ca2+ + Mg2+)-ATPase and Ca2+ transport. The red blood cell activator protein is similar to a modulator protein that stimulates cyclic AMP phosphodiesterase. Wang and Desai [Journal of Biological Chemistry 252:4175--4184, 1977] described a modulator-binding protein that antagonizes the activation of cyclic AMP phosphodiesterase by modulator protein. In the present work, modulator-binding protein was shown to antagonize the activation of (Ca2+ + Mg2+)-ATPase and Ca2+ transport by red blood cell activator protein. The results further demonstrate the similarity between the activator protein from human red blood cells and the modulator protein from bovine brain.     

A proposed mechanism underlying the process of Ca2+-mediated transfer of DNA across biological membranes

Interaction studies between negatively charged membrane lipids and DNA demonstrate that these molecules interact specifically with each other provided Ca²⁺ is present. On the basis of these results, a mechanism has been proposed which might account for the transfer of nucleic acids through the biological membrane.     

Exploration of the Ca2+ interaction modes of the nifedipine calcium channel antagonist.

A comprehensive study is carried out using quantum chemical computation and molecular dynamics (MD) simulations to gain insight into the interaction between Ca(2+) ions and the most important class of calcium channel antagonists--nifedipine. First, the chelating structures and energetic characters of nifedipine-Ca(2+) in the gas phase are explored, and 25 isomers are found. The most favorable chelating mode is a tridentate one, that is, Ca(2+) binds to two carbonyl O atoms and one nitryl O atom, where Ca(2+) is above the plane of the three O atoms to form a pyramidal structure. Accurate geometric structures, relative stabilities, vertical and adiabatic binding energies, and charge distributions are discussed. The differences in the geometries and energies among these isomers are analyzed from the contributions of chelating sites, electrostatics and polarizations, steric repulsions, and charge distributions. The interconversions among isomers with similar geometries and energies are also investigated because of the importance of the geometric transformation in the biological system. Furthermore, certain numbers of water molecules are added to the nifedipine-Ca(2+) system to probe the effect of water. A detailed study is performed on the hydrated geometries on the basis of the most stable isomer 1. Stepwise hydration can weaken the nifedipine-Ca(2+) interaction, and the chelating sites of nifedipine are gradually replaced by the added water molecules. Hexacoordination is found to be the most favorable geometry no matter how many water molecules were added, which can be verified by the MD simulations. The transfer of water molecules from the inner shell to the outer shell is also supported by MD simulations of the hexahydrated complexes.     

Iminodiacetic acid-functionalized gold nanoparticles for optical sensing of myoglobin via Cu2+ coordination

A novel gold nanoparticle (AuNP)-based optical sensing system has been developed for the detection of myoglobin (Mb), which is of significant importance for early disease diagnosis. Two thiol molecules containing an iminodiacetic acid moiety (IDA) were synthesized. This detection is based on the Mb-induced aggregation of IDA-functionalized AuNPs resulting from the structures of Mb sandwiched between the functionalized AuNPs via Cu(2+) bridges in the coordination interactions of IDA-Cu(2+)-histidine residues available on the Mb surface, which was confirmed by UV-vis spectroscopy, transmission electron microscopy, dynamic light scattering, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The induction aggregation resulted in a red shift in plasmon resonance band of the AuNPs concomitant with a change in solution color from red to purple. The qualitative and quantitative detections of Mb can be achieved by colorimetric observations and UV-vis spectral measurements, respectively. The selectivity of protein assay with the functionalized AuNPs was further investigated, and it is found that the optical sensing of histidine-rich proteins is closely related to number and distribution of surface histidine residues as well as size of proteins.     

Gas-phase reactions between thiourea and Ca2+: new evidence for the formation of [Ca(NH3)]2+ and other doubly charged species.

The gas-phase reactions between Ca(2+) and thiourea are investigated by means of electrospray ionization/mass spectrometry experiments. The MS/MS spectra of [Ca(thiourea)](2+) complexes show the appearance of new doubly charged species formed by the loss of NH(3) and HNCS. Other intense peaks at m/z 43, 56, 60, 73, 76 and 98 are also observed, and assigned to monocations produced in different coulomb-explosion processes. The structures and bonding characteristics of the different stationary points of the [Ca(thiourea)](2+) potential energy surface (PES) were theoretically studied by DFT calculations carried out at B3LYP/cc-pWCVTZ level. The analysis of the topology of this PES permits to propose different mechanisms for the loss of ammonia and HNCS, and to identify, the m/z 43, 56, 60, 73, 76 and 98 peaks as H(2)NCNH(+), CaNH(2) (+), H(2)NCS(+), CaSH(+), thiourea(+) and CaNCS(+) ions respectively. There are significant dissimilarities between the reactivity of urea and thiourea, which are related to the lower ionization energy of the latter, and to the fact that thioenols are intrinsically more stable than enols with respect to the corresponding keto forms.     

Active calcium treatment transport via coupling between the enzymatic and the ionophoric sites of Ca2+ + Mg2+-ATPase.

The 20K dalton fragment of Ca2+ + Mg2+-ATPase obtained from th tryptically digested sarcoplasmic reticulum has been further purified using Bio-Gel P-100. This removed low-molecular-weight UV-absorbing and positive Lowry-reacting contaminants. The ionophoric activity of the 20K fragment in both oxidized cholesterol and phosphatidylcholine:cholesterol membranes is unaltered by this further purification. The 20K selectivity sequence in phosphatidylcholine:cholesterol membrane is Ba2+ greater than Ca2+ greater than Sr2+ greater than Mn2+ Mg2+. Digestion of intact sarcoplasmic reticulum vesicles with trypsin, which results in the dissection of the hydrolytic site (30K) from the ionophoric site (20K), is shown to disrupt energy transduction between ATP hydrolysis and calcium transport. This further implicates the 20K dalton fragment as a calcium transport site. These data and previous evidence are discussed in terms of a proposed model for the ATPase molecular structure and the mechanisms of cation transport in sarcoplasmic reticulum.     

The hyperfine interaction in the A 2Pi1/2 and X 2Sigma+ states of ytterbium monofluoride

The fine and hyperfine interaction parameters in the A (2)Pi(1/2)(v=0) and X (2)Sigma(+)(v=0) states of the odd metal nuclear spin isotopologues of ytterbium monofluoride, (171)YbF and (173)YbF, have been determined from an analysis of high-resolution laser induced fluorescence spectra of the A (2)Pi(12)<--X (2)Sigma(+)(0,0) band. The observed ground X (2)Sigma(+)(v=0) state (171)Yb(I=1/2) Fermi contact parameter is significantly smaller than that determined from the matrix isolation electron spin resonance measurement [Van Zee et al., J. Phys. Chem. 82, 1192 (1978)]. An interpretation of the (173,171)Yb magnetic hyperfine and nuclear electric quadrupole coupling parameters is given.     

An ab initio quantum chemical investigation of 43Ca NMR interaction parameters for the Ca2+ sites in organic complexes and in metalloproteins

We have carried out an extensive ab initio quantum chemical (QC)43Ca NMR study on a series of Ca-O organic compounds and three different Ca-bound proteins and found that the HF/6-31G* level of function can reliably predict 43Ca NMR interaction parameters (delta(iso) and chi(q)), especially for organic solids. This QC study finds correlations between Ca-O bond environment (mean distance and coordination number) and delta(iso)(43Ca). Although relatively small values of chi(q)(43Ca) are found for Ca-O organic compounds with a coordination number between 6 and 10, the QC shows that chi(q)(43Ca) is sensitive to the Ca-O coordination geometry of the Ca2+ sites in metalloproteins--a potentially important observation. An application of such ab initio QC 43Ca NMR studies is in characterizing the Ca-O bonding environment around target Ca2+ sites. As an example, we propose a new potential analytical approach using the absolute (43)Ca chemical shielding constant to investigate the hydration shell of Ca2+ in a dilute CaCl2 aqueous solution. Furthermore, by adopting a NMR methodology similar to that reported in Wong et al. Chem. Phys. Lett. 2006, 427, 201, natural abundance 43Ca MAS NMR spectra of Ca(L-glutamate)(2) x 4H2O were recorded, and delta(iso)(43Ca) and the quadrupolar parameter (Pq) were estimated to be 6.6 ppm and 0.8 MHz, respectively.     

Thermodynamic quantities for the interaction of SO 4 2− with H+ and Na+ in aqueous solution from 150 to 320°C

The aqueous reactions,

A microfluidic-based system for analysis of single cells based on Ca2+ flux

A microfluidic format-based system has been developed for in situ monitoring of the calcium flux response to agonists using Chinese hamster ovary (CHO) cells. The assay is based on measuring the fluorescent intensity of the calcium-sensitive indicator, Fluo-4 AM, and was performed in a modified glass chip channel, whose surface was functionalised using a silanisation method with 3-aminopropyltriethoxysilane (APTS) (enabling the cells to be immobilised on the channel surface). CHO cells calcium flux response was measured for different agonists over a range of concentrations. Cells and reagents were introduced into the chip in a continuous flow as a series of plugs in a given sequence.     

Thermodynamic modeling for the removal of Cs+, Sr2+, Ca2+and Mg2+ions from aqueous waste solutions using zeolite A</p> </p>

Summary The batch removal ofCs⁺, Sr²⁺, Ca²⁺and Mg²⁺ions from aqueous solutions using synthetic zeolite A was investigated. The influence of the initial ion concentration, pH and temperature was studied. The obtained isotherm data have been correlated with Langumir, Freundlich, and Dubinin-Radushkevich(D-R) isotherm models. The effect of the temperature on the equilibrium distribution values has been utilized to evaluate the standard thermodynamic parameters such as free energy (DG), enthalpy (DH) and entropy (DS). Based on the D-R isotherm expression, the maximum ion-exchange capacity and the mean free energy of each studied ion has been determined. The selectivity sequence, deduced from the equilibrium isotherm data is: Sr²⁺>Ca²⁺>Mg²⁺>Cs⁺>Na⁺.</p> </p>     

The interaction of [Pd(N,N-dimethylaminopropylamine)(H2O)]2+ with dicarboxylic acids and inosine: Thermodynamic model for carboplatin drug

The Pd(DMPA)Cl₂ complex, where DMPA = N,N-dimethylaminoproylamine, was synthesized and characterized. The stoichiometry and stability constants of the complexes formed between various dicarboxylic acids and [Pd(DMPA)(H₂O)₂]²⁺ were investigated. The effect of solvent dielectric constant, chloride ion concentration of the medium and temperature on the stability constant of the cyclobutanedicaroxylic acid (CBDCA) complex was investigated. The equilibrium constants for the displacement of coordinated CBDCA by inosine, taken as an example of DNA constituents, were calculated. The results are expected to contribute to the chemistry of antitumour agents.      

Cathodic carboxylation of gold in thick {Au-CO2}n layers. A model for reversible electrochemical sequestration of CO2

Catalytic reduction of CO₂ (saturated in organic polar solvents, e.g. N,N-dimethylfomamide, containing Me₄NX or NaBF₄) was achieved at smooth gold electrodes and at glassy carbon electrodes galvanostatically capped with a thin layer of gold. Under these quite explicit conditions, very sharp reduction steps were observed near − 1.5 V vs. Ag/AgCl. With small cations listed above, an unexpected behavior was observed, a progressive electrode inhibition occurring upon several scans or after a fixed-potential electrolysis at E < − 1.7 V. This phenomenon could be attributed to the insertion of CO₂ into gold, leading to the formation of a thick iono-metallic multi-strata layer (less conducting than pure metal) that grows with the electrode charge. The formation of this new interface is due to the concur of three elements: transient CO₂ anion radical, the metal, and rather small-sized cations (M⁺ = Na⁺ or TMA⁺), the three possibly associated in a form {Au-CO₂⁻,M⁺} apparently very reactive with oxygen, moisture, and with some organic π-acceptors. Upon multi-scans up to − 2.2 V, the thickness of formed layer progressively increases reaching more than 10^− 7 to 10^− 6 mol cm^− 2. Such multi-layers undergo decomposition in the anodic domain at about + 1.7 V liberating CO₂ beforehand trapped in Au. Coulometric analyses demonstrated that insertion (cathodic) and release (anodic) steps are quite equivalent, which permits to consider this process as chemically reversible sequestration of carbon dioxide.     

The solubility of CaMoO4(c) and an aqueous thermodynamic model for Ca2+-MoO 4 2 -ion-interactions

The solubility of powellite [CaMoO₄(c)] was studied in aqueous Na₂MoO₄, CaCl₂ and Ca(NO₃)₂ solutions ranging in concentrations from 1×10^–4M to 1.0M and over equilibration times extending to 36 days. Our experimental data were interpreted using the aqueous ion-interaction model of Pitzer and coworkers. The Ca²⁺–MoO ₄ ^2– ion-interactions were found to be analogous to Ca²⁺–SO ₄ ^2– . The use of Ca²⁺–MoO ₄ ^2– ion-interactions parameters (⁽⁰⁾=0.2, ⁽¹⁾ = 3.1973 and ⁽²⁾) and a logK _sp of –7.93 gave excellent predictions of all of the experimental data. Commonion ternary interaction parameters such as MoO ₄ ^2– –Cl^– or MoO ₄ ^2– –NO ₃ ^– were not required.     

An application of electrospray ionization tandem mass spectrometry to probe the interaction of Ca2+/Mg2+/Zn2+ and Cl- with gramicidin A

The peptide, gramicidin A (GrA), has been demonstrated to interact with divalent salts (CaCl2, MgCl2, and ZnCl2) using electrospray ionization mass spectrometry (ESI-MS). The ESI-MS analysis revealed different complexes formed due to the interaction of Val-GrA and Ile-GrA with divalent salts: [Val or Ile-GrA-H+M]+, [Val or Ile-GrA+MCl]+ and [Val or Ile-GrA+M]2+, where M is Ca or Mg or Zn. All these complexes have been subjected to collisionally activated dissociation (CAD). CAD of singly and doubly charged GrA and metal complexes exhibited the losses of water molecules, indicating the ligand preference of GrA. MS/MS and MS3 of [Val or Ile-GrA+MCl]+ resulted in the elimination of chloride ion and water, respectively. The tandem mass spectrometry data of the complex [Val-GrA+MCl]+ suggest that chloride interaction is stronger in the presence of Ca than of Mg and Zn. This study reveals that GrA could interact with Ca, Mg, and Zn in metal ion form as well as in ion pair (MCl) form. The interactions of GrA with Ca support the proposal of a physical basis for the messenger role of Ca (Urry et al., J. Biol. Chem. 1982, 257: 6659-6661).     

Thermodynamic quantities for the interaction of H+ and Na+ with C2H3O 2 − and Cl− in aqueous solution from 275 to 320°C

The aqueous reactions, {ie865-1}were studied as a function of ionic strength at 275, 300, and 320°C using a flow calorimetric technique. Log K, H and S values were determined from the fits of the calculated and experimental heats while Cp values were calculated from the variation of H values with temperature. The log K and H values for the first two reactions agree well with literature values at these temperatures. No previous results have been reported for the third reaction. The use of equations containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the log K values determined in this study. The resulting plots of log K for the isocoulombic reactions vs. I/T were approximately linear, which demonstrates that the Cp values for these reactions are approximately zero.Deceased 5 September 1987     

A new family of Ru(II) polypyridyl complexes containing open-chain crown ether for Mg2+ and Ca2+ probing

Six polypyridyl bridging ligands BL(1-6) containing open-chain crown ether, where BL(1-3) formed by the condensation of 4,5-diazafluoren-9-hydrazine with 1,7-bis-(4-formylphenyl)-1,4,7-trioxaheptane, 1,10-bis-(4-formylphenyl)-1,4,7,10-tetraoxadecane, and 1,13-bis-(4-formylphenyl)-1,4,7,10,13-pentaoxatridecane, respectively, BL(4-6) formed by the reaction of 9-(4-hydroxy)phenylimino-4,5-diazafluorene with diethylene glycol di-p-tosylate, triethylene glycol di-p-tosylate, and tetraethylene glycol di-p-tosylate, respectively, have been synthesized. Reaction of Ru(bpy)(2)Cl(2).2H(2)O with BL(1-6), respectively, afforded six bimetallic complexes [(bpy)(2)RuBL(1-6)Ru(bpy)(2)](4+) as PF(6)(-) salts. Cyclic voltammetry of these complexes is consistent with one Ru(II)-centered oxidation around 1.32V and three ligand-centered reductions. These complexes show metal-to-ligand charge transfer absorption at 413-444 nm and emission at 570 nm. Binding behavior of complexes with alkali and alkaline-earth metal ions are investigated by UV-vis absorption, fluorescence, and cyclic voltammetry. Addition of alkali and alkaline-earth metal ions to the solution of [(bpy)(2)RuBL(1-6)Ru(bpy)(2)](PF(6))(4) all result in a progressive quenching of fluorescence, a hyperchromic effect of UV-vis absorption, and a progressive cathodal shift of Ru(II)-centered E(1/2). Ru-BL(2) and Ru-BL(5) show the highest binding ability toward Mg(2+) among the five cations examined while Ru-BL(3) and Ru-BL(6) exhibit good selective recognition ability to Ca(2+).     

A gold nanorod based colorimetric probe for the rapid and selective detection of Cu2+ ions

A gold nanorod (AuNR) based colorimetric probe was reported for the rapid and selective detection of Cu(2+) ions. The probe was fabricated by functionalizing cysteine (Cys) onto AuNR (Cys-AuNR) with an aspect ratio of 2.3. The strong coordination of Cu(2+) with cysteine resulted in a stable Cys-Cu-Cys complex, and induced the aggregation of the colloidal nanorods along with a rapid colour change from blue-green to dark gray. Potential factors affecting the performance of the probe for the detection of Cu(2+) were carefully optimized, including the pH value of the buffer media, the concentration of cysteine, and the kinetics for the coordination of Cu(2+) with Cys-AuNR. Under optimal conditions, the developed colorimetric method gave a linear range of 1-100 μM for Cu(2+), and a detection limit (3s) of 0.34 μM. Moreover, the developed method exhibited excellent selectivity for Cu(2+), and quantitative spike-recoveries from 90% to 107% in environmental water samples. The proposed colorimetric approach can in principle be used to detect other metal ions by functionalizing various specific ligands onto the AuNR that can selectively bind the other target metal ions.