Interaction Of Metal Cations Research Articles

Thermoelectric engineered cementitious composites with low thermal conductivity for efficiency improvement of buildings

Thermoelectric cement-based materials are getting noticed for their ability to convert heat into electricity and reduce surface temperatures. This study developed thermoelectric ultra-lightweight engineered cementitious composites (ULW-ECC) with low thermal conductivity (0.478 – 0.668 W/(mK)) and low density (1003 – 1157 kg/m3). Carbon fibre (CF) of varying lengths (1 – 20 mm) and concentrations (0, 0.5, and 1.0 vol%) were incorporated, and the mechanical, electrical conductivity and thermoelectric performance of the composite were thoroughly examined. Additionally, the impact of saturation and drying treatment on thermoelectric conversion efficiency was assessed. The results revealed that the inclusion of mineral admixtures and fly ash cenospheres within the composite could decrease the content of OH– ions in pore solution due to the pozzolanic effect. This phenomenon led to the creation of a high-performance p-type ionic thermoelectric effect, with a Seebeck coefficient of 3.14 mV/℃. Moreover, treatments involving saturation and drying were found to respectively enhance and diminish conversion efficiency. Incorporating CF into ULW-ECC generates an ionic-electronic thermoelectric effect through the collaborative interaction of metal cations and positive hole carriers from both the pore solution and CF, respectively. Thermoelectric conversion efficiency varied with CF length and dosage, with a peak improvement in the Seebeck coefficient reaching 5.9 mV/℃. However, a sharp decline occurred when a continuous conductive network was formed.

Distinct ion transport behavior between graphene oxide and UV-irradiated reduced graphene oxide membranes

Graphene oxide (GO) membranes are promising materials for achieving selective ion permeation in aqueous solutions. However, the swelling of GO laminates, caused by the affinity of water molecules for oxygen-containing groups (OCGs) on GO, significantly limits the practical prospects of GO membranes for selective ion transport and separation applications. Selectively removing OCGs from GO has been shown to decrease the interlayer distance between individual GO sheets, thereby improving the ability of laminate membranes to discriminate between different ions based on a size-exclusion mechanism. In this work, GO reduced through exposure to ultraviolet light (UV-rGO) is shown to display ion transport behavior that raises questions about size-exclusion as the dominant mechanism determining selective ion transport in GO membranes. Notably, smaller monovalent Li+ cations are found to permeate more slowly through UV-rGO membranes than larger divalent metal cations such as Ca2+ and Mg2+. This unexpected behavior results in a 3 – 4 fold improvement in the separation selectivity between these representative cations with UV-rGO compared to pristine GO membranes. Through a joint experimental and theoretical study, we identified the factors influencing selective ion transport through the nanochannels in UV-rGO membranes. We demonstrate that the selective removal of hydroxyl (–OH) groups from the basal planes of GO enhances the interactions of metal cations with functional groups located at the edges of GO, thereby resulting in a lower ratio of free Li+ in solution, rather than stationary Li+ adsorbed onto the surface GO, compared to Ca2+ cations. Based on these results, we propose a separation mechanism analogous to chromatography, which emphasizes the crucial role of different OCGs on GO surfaces in controlling selective ion transport through GO membranes.

Interfacial interactions controlling adsorption of metal cations on montmorillonite

Abstract Montmorillonite (Mt) is a ubiquitous swelling clay mineral and major component of soft rocks, sediments, and soils with an inherent capability to sorb metal cations. This unique feature renders Mt important for the enrichment and mobilization of environmentally important metal cations, retardation of heavy metals and radionuclide ions, the evolution of clay mineral itself, soils and sediments, and other geological processes. Understanding the interfacial interactions of Mt with metal cations at the molecular level is of fundamental importance in all these processes, but still remains elusive, due to the chemical and structural complexity of Mt surfaces and the diverse chemistries of metal cations. In this Review, we aim to provide the reader with a comprehensive overview of the adsorption modes of metal cations on basal and edge surfaces of Mt, local chemical environments of the cation binding sites, the driving forces for metal sorption, and factors influencing the dynamics of cation uptake onto Mt surfaces. Various surface complexation models [i.e., nonelectrostatic model (NEM), constant capacitance model (CCM), diffuse layer model (DLM), and triple-layer model (TLM)], advanced spectroscopic techniques (i.e., NEM, CCM, DLM, and TLM), and atomistic simulation methods (i.e., MD, DFT, and FPMD) have been used in conjunction with macroscopic adsorption experiments to gain detailed insights into the interfacial interactions of metal cations on Mt. Mt adsorbs metal cations via three independent pathways: (1) cation exchange; (2) surface complexation; and (3) nucleation and surface precipitation. The principal driving force for cation exchange is electrostatic interaction, while chemical bonding governs the two other mechanisms that depend on the basal and edge surface properties of Mt. The siloxane cavities on the tetrahedral basal plane exhibit the strongest adsorption sites for cation exchange and are greatly affected by the the degree of Al3+/Si4+ tetrahedral substitutions. At the amphoteric edge surfaces bearing hydroxyl groups, metal cations could form mono/multiden-tate surface complexes on Mt [010] and [110] edges. Ionic strength, pH, the presence of competing cations, temperature, and layer charge have been shown to affect the adsorption mechanisms and quantity of adsorbed cations. The updated information on the interfacial interactions of metal cations with Mt basal and edge surfaces presented in this review provides an improved understanding of the enrichment of metals, formation of metal ores, and natural biogeochemical cycles, as well as may promote technological and engineering applications of this important clay mineral in environmental remediation, geological repository, petroleum exploration and extraction, and extraterrestrial research.

Colorimetric detection of SARS‐CoV‐2 variants with paper‐based analytical devices

Colorimetric detection of SARS‐CoV‐2 variants with paper‐based analytical devices

Sodium Cationization Enables Exotic Deprotonation Sites on Gaseous Mononucleotides.

We report observation and photoelectron spectroscopic characterization of sodium cationization on four doubly deprotonated mononucleotide dianions Na+·[dNMP-2H]2- (N = A, G, C, or T) in the gas phase. Multiple tautomers with distinct deprotonated sites are identified, in which Na+ enables novel double deprotonation patterns and folds the resultant mononucleotide dianions. The most stable isomer for the whole family is derived from detaching one proton from the phosphate and the other from the nucleobase (amino group for N = A, G, and C, but nitrogen atom for T), whereas high-lying isomers with protons detached separately from the phosphate and the hydroxy group of sugar coexist. Particularly, an exotic deprotomer with both protons deprived from guanosine is populated as well. This work thus displays a remarkably diverse binding landscape enabled by sodium cationization, a potentially critical element in developing a general formulism to better model metal cation and nucleotide interactions.

Conformation and Metal Cation Binding of Zwitterionic Alanine Tripeptide in Saline Solutions by Infrared Vibrational Spectroscopy and Molecular Dynamics Simulations.

In this work, linear infrared (IR) spectroscopy and molecular dynamics (MD) simulations were used to examine the interaction of different metal cations (Na+, Ca2+, Mg2+, and Zn2+) with backbone (amide C═O) and C-terminal carboxylate (COO-) groups in zwitterionic alanine tripeptide (Ala3) in aqueous solutions with varying saline concentrations. Circular dichroism spectra and MD results suggest that Ala3 is predominantly in polyproline-II (PPII) conformation, whose amide-I and asymmetric carboxylate stretching IR vibration signatures are also supported by quantum-chemistry calculations. The zwitterionic form of Ala3 separates the two amide-I modes in frequency, which are weakly coupled modes, as revealed by two-dimensional IR measurement, and can be used to probe backbone-cation interactions at different scenarios (near charged or neutral chemical groups respectively). Cation concentration-dependent IR frequency red shifts in the amide-I mode are seen for both amide-I modes, whereas blue shifts are also seen in the amide-I mode far from the NH3+ group. The observed spectral changes are discussed from the perspective of the salting-in and salting-out abilities of the cations. In addition, all the metal cations studied here (except Zn2+) can specifically coordinate to the COO- group in bidentate and pseudo-bridging forms simultaneously. For Zn2+, only the pseudo-bridging form exists. Our results shed light on the macroscopic protein salting-in and salting-out phenomena from the perspective of key chemical bonds in peptides.

Solvation of Isoelectronic Halide and Alkali Metal Ions by Argon Atoms.

This work systematically examines the interactions of alkali metal cations and their isoelectronic halide counterparts with up to six solvating Ar atoms (M+Arn and X-Arn, where M = Li, Na, K, and Rb; X = H, F, Cl, and Br; and n = 1-6) via full geometry optimizations with the MP2 method and robust, correlation-consistent quadruple-ζ (QZ) basis sets. 116 unique M+Arn and X-Arn stationary points have been characterized on the MP2/QZ potential energy surface. To the best of our knowledge, approximately two dozen of these stationary points have been reported here for the first time. Some of these new structures are either the lowest-energy stationary point for a particular cluster or energetically competitive with it. The CCSD(T) method was employed to perform additional single-point energy computations upon all MP2/QZ-optimized structures using the same basis set. CCSD(T)/QZ results indicate that internally solvated structures with the ion at/near the geometric center of the cluster have appreciably higher energies than those placing the ion on the periphery. While this study extends the prior investigations of M+Arn clusters found within the literature, it notably provides one of the first thorough characterizations of and comparisons to the corresponding negatively charged X-Arn clusters.

The mechanisms of fluorescence quenching of carbon dots upon interaction with heavy metal cations

The paper presents the results of a study of the interaction of heavy metal cations Fe3+, Cr3+, Cu2+, Pb2+, Zn2+, Ni2+, Ag+ with carbon dots synthesized by the hydrothermal method in water. It was found that all the studied cations quench the fluorescence of nanoparticles to one degree or another. The series of cations were determined according to the degree of their influence on the fluorescence of carbon dots. The mechanisms of quenching the fluorescence of carbon dots upon interaction with cations have been investigated. It is shown that the quenching of the luminescence of nanoparticles in the presence of the investigated cations of heavy metals has a complex character. The observed changes in the intensity of fluorescence of carbon dots are the result of a superposition of several factors—electrostatic interactions of metal cations with surface fluorophores of carbon dots, aggregation of nanoparticles, and the effect of an inner filter for iron ions.

Interactions of divalent metal cations with headgroups of monomers, dimers, and trimers of anionic surfactant

The goal of this work was to investigate the interaction and binding of the metal divalent cations, Me2+, with the headgroups of monomers, dimers, and trimers of anionic surfactant, for the alkaline earth metal cations (Me2+ = Be2+, Mg2+, Ca2+, Sr2+, Ba2+), the transition metal ions (Me2+ = Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+), and Sn2+ and Pb2+ ions. Herein, sodium dodecyl sulfate, SDS, was applied as an anionic surfactant. In this study mass spectrometry with electrospray ionization was used, which allowed determination of the preference of Me2+ binding to DS monomers (PMemon) and dimers (PMedim) and the total energies of interaction (bonding), Ebind, of divalent metal ions with DS trimers. The PMemon, PMedim, and Ebind parameters were correlated with different ion properties to characterize the interactions between Me2+ ions and a given anionic surfactant. The metal ions were ordered according to their affinity to DS monomers and dimers and their strength of binding with DS trimers. As follows from the results presented, from among the alkaline earth metal cations, the Ca2+ ions are the easiest to bind with DS monomers, dimers, and trimers and make the strongest bonds with them, while among the other Me2+ ions considered, the Hg2+, Sn2+, and Pb2+ cations interact very weakly and poorly with DS monomers, dimers, and trimers. From the results obtained in this work, it can be concluded which divalent metal ions should be used to introduce more or less significant changes in the aggregate structures of anionic surfactants.

Quantum-Chemical Modeling of the Interactions of IIA Group Metal Cations with Humic Acids

Quantum-Chemical Modeling of the Interactions of IIA Group Metal Cations with Humic Acids

Application of Chemometrics Tools to the Study of the Fe(III)-Tannic Acid Interaction.

Chemometric techniques were applied to the study of the interaction of iron(III) and tannic acid (TA). Modeling the interaction of Fe(III)–TA is a challenge, as can be the modeling of the metal complexation upon natural macromolecules without a well-defined molecular structure. The chemical formula for commercial TA is often given as C76H52O46, but in fact, it is a mixture of polygalloyl glucoses or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 up to 12. Therefore, the data treatment cannot be based on just the stoichiometric approach. In this work, the redox behavior and the coordination capability of the TA toward Fe(III) were studied by UV-vis spectrophotometry and fluorescence spectroscopy. Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) and Parallel Factor Analysis (PARAFAC) were used for the data treatment, respectively. The pH range in which there is the redox stability of the system Fe(III)–TA was evaluated. The binding capability of TA toward Fe(III), the spectral features of coordination compounds, and the concentration profiles of the species in solution as a function of pH were defined. Moreover, the stability of the interaction between TA and Fe(III) was interpreted through the chemical models usually employed to depict the interaction of metal cations with humic substances and quantified using the concentration profiles estimated by MCR-ALS.

Chelate formation and stability analysis of cobalt, nickel and copper with lomatiol

The pH-metric studies on the interaction of divalent metal cations, Co (II), Ni (II) and Cu (II) with lomatiol have been performed under the thermodynamic conditions achievable at constant ionic strength and infinite dilution in which a mole of divalent metal, combined with 02 mol of lomatiol. Lomatiol being bidentate could replace two water molecules at a time. The values of stepwise formation constants showed no conspicuous difference at 25 °C and 35 °C, and the complexes, registered a decrease in their stability values suggesting the low temperature as a favorable condition under which the chelation of metal with lomatiol is feasible. The reaction takes place without the use of any specific catalyst although under alkaline conditions. The reactions of lomatiol with metal cations in solution had been adjudged as the spontaneous reaction on account of the negative ΔG value in all the metal lomatiol systems. Also the study showed the positive experimental values of entropy changes in all the systems and negative value of free energy. The continuous fall in the values of the stepwise formation constants (k1 > k2 > k3) in the divalent metal-lomatiol system has been assigned to the statistical factor.

Tripartite Mechanism of Neural Memory: Proof-of-Concept with Neuromimetic Impedence Electrodes

The idea that neural signaling is the basis of mental processes has a long history. We graphically summarize salient developments in the neurobiology of signaling, as a Timeline. In particular, we review the “tripartite mechanism” of neural memory, which centers on the interactions between a neuron with its surrounding extracellular matrix (nECM) doped with metals and neurotransmitters (NTs). Essentially, the neuron employs the nECM as its “memory material”, wherein it uses dopants to encode cognitive units of information (termed “cuinfo”). The NTs, which elicit bodily reactions (feelings), also encode past feelings as emotions, which “color” mental states in real-time and in memory. In the interest of developing experimental tests of the tripartite mechanism, impedance glass electrodes were covalently coated with an exemplar NT (oxytocin) or a sulfated tetra-saccharide analog of the nECM, were constructed and tested. The two types of coated, neuro-mimetic electrodes, termed “neulectrodes”, were capable of detecting metals, such as Hg+2, Pb+2, Cd+2, Cu+2, and Zn+2 with very high selectivity and sensitivity. The “neulectrodes” demonstrated that the chemodynamic interactions of metal cations with NTs or nECM-saccharide analogues can translate into electrodynamic signals. They experimentally validate the concept of the tripartite mechanism that underlies the chemo-electric encoding of neural memory.

Nucleobase Pair-Metal Dimer/Dinuclear Metal Cation Interaction: A Theoretical Study.

Nucleobase pair–metal dimer/dinuclear metal cation interactions play an important role in biological applications because of their highly symmetrical structures and high stabilities. In this work, we have selected five adenine–adenine hydrogen bonding, adenine–thymine (AT), adenine–uracil, adenine–adenine stacking pairs, and Watson–Crick AT stacking pairs and studied their interaction with the coinage metal dimer M2 and M22+ metal cations, where M = Ag, Au, and Cu. Quantum chemical calculations have been carried out with density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Electronic structures were analyzed by the partial density of states method. During interactions, we find that M–M distances are shorter than the sum of van der Waals radii of the corresponding two homocoinage metal atoms, which show the existence of significant metallophilic interactions. Results indicated that nucleobase–M22+ complexes are stronger as compared to nucleobase–M2 complexes. Also, the replacement of the hydrogen bond by the dinuclear metal cation-coordinated bond forms more stable alternative metallo-DNA sequences in AAST base pairs. TDDFT calculations reveal that nucleobase–Cu2 complexes and nucleobase–Ag22+/Au22+ complexes can be used for fluorescent markers and logic gate applications. Atom-in-molecules analysis predicted the noncovalent interaction in these complexes.

Hofmeister Series for Metal-Cation-RNA Interactions: The Interplay of Binding Affinity and Exchange Kinetics.

A large variety of physicochemical properties involving RNA depends on the type of metal cation present in solution. In order to gain microscopic insight into the origin of these ion specific effects, we apply molecular dynamics simulations to describe the interactions of metal cations and RNA. For the three most common ion binding sites on RNA, we calculate the binding affinities and exchange rates of eight different mono- and divalent metal cations. Our results reveal that binding sites involving phosphate groups preferentially bind metal cations with high charge density (such as Mg2+) in inner-sphere conformations while binding sites involving N7 or O6 atoms preferentially bind cations with low charge density (such as K+). The binding affinity therefore follows a direct Hofmeister series at the backbone but is reversed at the nucleobases leading to a high selectivity of ion binding sites on RNA. In addition, the exchange rates for cation binding cover almost 5 orders of magnitude, leading to a vastly different time scale for the lifetimes of contact pairs. Taken together, the site-specific binding affinities and the specific lifetime of contact pairs provide the microscopic explanation of ion specific effects observed in a wide variety of macroscopic RNA properties. Finally, combining the results from atomistic simulations with extended Poisson–Boltzmann theory allows us to predict the distribution of metal cations around double-stranded RNA at finite concentrations and to reproduce the results of ion counting experiments with good accuracy.

Roles of pH, cation valence, and ionic strength in the stability and aggregation behavior of zinc oxide nanoparticles

The effects of pH, cation valence, and ionic strength (IS) on the stability and aggregation behavior of zinc oxide nanoparticles (ZnO NPs) were investigated in this study. Results showed that ZnO NPs were most prone to aggregation at the isoelectric point (pH = 8.7), with an aggregation rate (ΔD/Δt) of 30.1. ZnO NPs showed a greater propensity for dissolution at lower pH (pH < 7), and Zn2+ was more rapidly released into the aqueous phase in acidic solutions than neutral or alkaline conditions. The C/C0 of ZnO NPs was about 21.56% and remained stable in acidic solution of pH 4.0. Additionally, slow sedimentation with a C/C0 ratio of 95.0% was observed due to an increase in repulsive interactions between nanoparticles under pH = 10. The effect of cations on the ΔD/Δt of ZnO NPs decreased in strength as follows: Ca2+ > Mg2+ > K+ > Na+. High-valence metal cations (Ca2+, Mg2+) were more competitively adsorbed onto the surface of ZnO NPs with a hydrogen atom due to Coulomb's law, increasing the zeta potential and stabilizing the suspension of ZnO NPs at IS < 10 mM. Furthermore, compression of the electric double layer (EDL) became stronger than electrostatic adsorption with increasing IS, reaching a maximum ΔD/Δt of 23.3 (Ca2+, pH = 7, IS = 1 M). The C/C0 ratio of ZnO NPs decreased from 100% to 56.5% (Na+), 52.2% (K+), 45.2% (Mg2+), and 40.1% (Ca2+) at pH = 7 and an IS of 0.5 M. In addition to the cation valence, the hydration forces and ionic radii of the metal cations might be other factors that affected the interactions of metal cations with ZnO NPs. Finally, the total interaction energy between ZnO NPs was calculated using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theoretical formula, and the calculated results were in agreement with the experimental outcomes under various aquatic environmental conditions.

Poly(ethylene oxide) helical conformation and alkali metal cation selectivity studied using electrospray ionization mass spectrometry.

The poly(ethylene oxide) (PEO)-alkali metal cation interaction is widely used in many areas. The conformation of the PEO-alkali metal cation complex has been studied extensively, but the conformational mechanism is still unclear. Simulations have been used to explain the mechanism, but there is a lack of experimental data from long PEO chains to verify the simulation results. The relative peak abundance of PEO (iso-C10 H21 (OC2 H4 )n OH (naverage = 7, where n denotes the number of ethylene oxide (EO) units) oligomers complexed to five alkali metal cations (Li+ , Na+ , K+ , Rb+ and Cs+ ) was studied using positive electrospray ionization mass spectrometry (ESI-MS). The ion selectivity of PEO oligomers to alkali metal cations corresponded to the peak abundance in competitive ESI-MS. PEO formed its first helix when the number of EO units reached six and the helix played an important role in the ion selectivity of PEO. For larger PEO oligomers with a helix, the ion selectivity of PEO depended on the degree of host-guest matching of the cations and the helix. The highest selectivity of PEO to K+ was due to K+ providing the best shape matching with the helical cavity. For smaller PEO oligomers without a helix, the selectivity was mainly determined by the surface charge density of the cations. The formational mechanism of the PEO-alkali metal cation complex was predicted. The results gave straightforward evidence to explain the conformational mechanism of the PEO-alkali metal cation complex and provided experimental data for further simulation studies.

Structural, Optical, and Magnetic Properties of the New (1-x)Bi0.5Na0.5TiO3 + xMgCoO3-δ Solid Solution System

A new (1-x)Bi0.5Na0.5TiO3 + xMgCoO3-δ solid solution system was synthesized using the simple sol–gel method. The structure that was investigated via X-ray diffraction and Raman scattering analysis indicated that the MgCoO3-δ materials were highly soluble into the host Bi0.5Na0.5TiO3 crystals. The random incorporation of Mg and Co cations into the host crystal of the Bi0.5Na0.5TiO3 materials reduced the optical band gap energy and induced a complex magnetic behavior as a function of MgCoO3−δ concentration solute in the host matrix. The optical band gap energy values decreased from 3.05 eV for pure Bi0.5Na0.5TiO3 materials to 2.22 eV with 9 mol% MgCoO3-δ solution for the Bi0.5Na0.5TiO3 compounds. A weak ferromagnetic property with strongly induced diamagnetism was obtained at room temperature for the pure Bi0.5Na0.5TiO3 materials, whereas ferromagnetic properties were observed for the MgCoO3-δ-modified Bi0.5Na0.5TiO3 compounds. The addition of paramagnetic and/or antiferromagnetic-like behavior was obtained for the MgCoO3-δ solid solution with over 5 mol% in the host Bi0.5Na0.5TiO3 materials. This work contributes to the current understanding of the interaction of transition metal cations in the host crystal ABO3 perovskite of lead-free ferroelectric materials due to the co-modification of A and B sites.

Conformational insight into radiation-chemical transformations of dicyclohexano-18-crown-6 complexes with alkaline earth metal chlorides: Effect of cation size

Effects of cation size on relative yields of macrocycle cleavage under irradiation of stereoisomeric dicyclohexano-18-crown-6 complexes with alkaline earth metal chlorides were studied to mimic the radiolysis of the macrocyclic components of metal-loaded extractants applicable for radioactive waste reprocessing. Chloride-anions was found to prevent the macrocycle from destruction at early stage of radiolysis. However, radiolytic atomic chlorine was generated as a result of anion decay that promoted radiation-chemical transformations of the crown ether in secondary radical reactions. Interaction of metal cation with donor oxygen atoms of crown ether led to conformational rearrangement of the macrocycle and induced additional channel of C–O bond cleavage at post-radiation stages of radiolysis. Total fraction of acyclic radical products increased as follows: Ca2+ > Sr2+ > Ba2+. This sequence order is correlated with data of vibrational spectroscopy and implies more radiation sensitivity of the folded, asymmetric conformation of macrocycle in complexes with calcium chloride in contrast to symmetric complexes with barium chloride.

Luminophore Formation in Various Conformations of Bovine Serum Albumin by Binding of Gold(III).

The purpose of the presented protocols is to study the process of Au(III) binding to BSA, yielding conformation change-induced red fluorescence (λem = 640 nm) of BSA-Au(III) complexes. The method adjusts the pH to show that the emergence of the red fluorescence is correlated with the pH-induced equilibrium transitions of the BSA conformations. Red fluorescent BSA-Au(III) complexes can only be formed with an adjustment of pH at or above 9.7, which corresponds to the "A-form" conformation of BSA. The protocol to adjust the BSA to Au molar ratio and to monitor the time-course of the process of Au(III) binding is described. The minimum number of Au(III) per BSA, to produce the red fluorescence, is less than seven. We describe the protocol in steps to illustrate the presence of multiple Au(III) binding sites in BSA. First, by adding copper (Cu(II)) or nickel (Ni(II)) cations followed by Au(III), this method reveals a binding site for Au(III) that is not the red fluorophore. Second, by modifying BSA by thiol capping agents, another nonfluorophore-forming Au(III) binding site is revealed. Third, changing the BSA conformation by cleaving and capping of the disulfide bonds, the possible Au(III) binding site(s) are illustrated. The protocol described, to control the BSA conformations and Au(III) binding, can be generally applied to study the interactions of other proteins and metal cations.