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The HCN1-4 channel family is responsible for the hyperpolarization-activated cation current I f /I h that controls automaticity in cardiac and neuronal pacemaker cells. We present cryoelectron microscopy (cryo-EM) structures of HCN4 in the presence or absence of bound cAMP, displaying the pore domain in closed and open conformations. Analysis of cAMP-bound and -unbound structures sheds light on how ligand-induced transitions in the channel cytosolic portion mediate the effect of cAMP on channel gating and highlights the regulatory role of a Mg 2+ coordination site formed between the C-linker and the S4-S5 linker. Comparison of open/closed pore states shows that the cytosolic gate opens through concerted movements of the S5 and S6 transmembrane helices. Furthermore, in combination with molecular dynamics analyses, the open pore structures provide insights into the mechanisms of K + /Na + permeation. Our results contribute mechanistic understanding on HCN channel gating, cyclic nucleotide-dependent modulation, and ion permeation., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Cu(II) ion was selected as an additive to improve the enantioseparation efficiency of three dihydroflavone enantiomers in high-speed counter-current chromatography (HSCCC), using hydroxypropyl-β-cyclodextrin (HP-β-CyD) as the chiral selector. The influences of important parameters, including the metal ion, the concentrations of HP-β-CyD and the Cu(II) ion, and the sample size were investigated. Under optimal conditions, three dihydroflavone enantiomers, including (±)-hesperetin, (±)-naringenin, and (±)-farrerol, were successfully enantioseparated. The chiral recognition mechanism was investigated. The enantioseparation was attributed to the different thermodynamic stabilities of the binary complexes of HP-β-CyD and (±)-hesperetin, and Cu(II) ion could enhance this difference by forming ternary complexes with the binary complexes. This Cu(II) ion-improved complexation HSCCC system exhibited improved performance for chiral separation, and therefore it has great application potential in the preparative enantioseparation of other compounds with similar skeletons., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The controlled self-assembly of protein cages is vital for the use of these nanocompartments in biomedical and nanotechnological applications. Recently, we showed that by combining different structural peptide elements, it is possible to assemble viral capsid proteins in distinct well-defined morphologies. In this chapter, a triblock copolypeptide is discussed, consisting of a metal ion-coordinating hexahistidine tag, a stimulus-responsive elastin-like polypeptide and a pH-responsive self-assembling viral capsid protein. This protein is able to form two different types of capsids, depending on the assembly pathway that is followed. Here, we focus on the metal ion-induced assembly process and describe the relevant experimental procedures to induce and utilize this assembly behavior.

Metal ion detection is critical in a variety of areas. The past decade has witnessed great progress in the development of metal ion sensors using functional nucleic acids (FNAs) and nanomaterials. The former has good recognition selectivity toward metal ions and the latter possesses unique properties for enhancing the performance of metal ion sensors. This review offers a summary of FNA- and nanomaterial-based metal ion detection methods. FNAs mainly include DNAzymes, G-quadruplexes, and mismatched base pairs and nanomaterials cover gold nanoparticles (GNPs), quantum dots (QDs), carbon nanotubes (CNTs), and graphene oxide (GO). The roles of FNAs and nanomaterials are introduced first. Then, various methods based on the combination of different FNAs and nanomaterials are discussed. Finally, the challenges and future directions of metal ion sensors are presented., (Copyright © 2017 Elsevier B.V. All rights reserved.)

We present the development of a facile phase-inversion method for forming asymmetric membranes with a precise high metal ion loading capacity in only the dense layer. The approach combines the use of macromolecule-metal intermolecular complexes to form the dense layer of asymmetric membranes with nonsolvent-induced phase separation to form the porous support. This allows the independent optimization of both the dense layer and porous support while maintaining the simplicity of a phase-inversion process. Moreover, it facilitates control over (i) the thickness of the dense layer throughout several orders of magnitude from less than 15 nm to more than 6 μm, (ii) the type and amount of metal ions loaded in the dense layer, (iii) the morphology of the membrane surface, and (iv) the porosity and structure of the support. This simple and scalable process provides a new platform for building multifunctional membranes with a high loading of well-dispersed metal ions in the dense layer.

In this work, the behavior of several metal ions with different globular proteins was investigated by affinity capillary electrophoresis. Screening was conducted by applying a proper rinsing protocol developed by our group. The use of 0.1M EDTA in the rinsing solution successfully desorbs metal ions from the capillary wall. The mobility ratio was used to evaluate the precision of the method. Excellent precision for repeated runs was achieved for different protein metal ion interactions (RSD% of 0.05-1.0%). Run times were less than 6 min for all of the investigated interactions. The method has been successfully applied for the interaction study of Li(+), Na(+), Mg(2+), Ca(2+), Ba(2+), Al(3+), Ga(3+), La(3+), Pd(2+), Ir(3+), Ru(3+), Rh(3+), Pt(2+), Pt(4+), Os(3+), Au(3+), Au(+), Ag(+), Cu(1+), Cu(2+), Fe(2+), Fe(3+), Co(2+), Ni(2+), Cr(3+), V(3+), MoO4(2-) and SeO3(2-) with bovine serum albumin, ovalbumin, β-lactoglobulin and myoglobin. Different interaction values were obtained for most of the tested metal ions even for that in the same metal group. Results were discussed and compared in view of metal and semimetal group's interaction behavior with the tested proteins. The calculated normalized difference of mobility ratios for each protein-metal ion interaction and its sign (positive and negative) has been successfully used to detect the interaction and estimate further coordination of the bound metal ion, respectively. The comprehensive platform summarizes all the obtained interaction results, and is valuable for any future protein-metal ion investigation., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Biometal ions are crucial in the structure and function of living organisms and have extensively been employed to promote bone tissue regeneration. Nevertheless, the biological functions of biometal ions and the underlying mechanisms responsible for their pro-regenerative effects remain incompletely understood, since bone repair is an intricate physiological process involving multiple cell types and signals. Recent accomplishments in the osteoimmunological field have revealed the momentous involvement of the immune system in mediating the therapeutic effects of biometal ions. The inflammatory factors secreted by immune cells contribute to bone cell migration, activation, and proliferation. This review summarizes the immune system and its constituent cells, followed by the current perspective on immunomodulation during bone healing. Next, the physicochemical and physiological properties of various biometal ions, including lithium, sodium, potassium, magnesium, calcium, strontium, vanadium, iron, cobalt, copper, and zinc, are thoroughly reviewed. In addition, the interactions between biometal ions, immune cells, and bone tissue are discussed, aiming to provide insights into the prospective development of novel approaches to bone tissue regeneration by harnessing the therapeutic potential of these biometal ions. [ABSTRACT FROM AUTHOR]

Terminal 2′-deoxynucleotidyl transferase (TdT) is a unique enzyme capable of catalysing template-independent elongation of DNA 3′ ends during V(D)J recombination. The mechanism controlling the enzyme's substrate specificity, which is necessary for its biological function, remains unknown. Accordingly, in this work, kinetic and mutational analyses of human TdT were performed and allowed to determine quantitative characteristics of individual stages of the enzyme–substrate interaction, which overall may ensure the enzyme's operation either in the distributive or processive mode of primer extension. It was found that conformational dynamics of TdT play an important role in the formation of the catalytic complex. Meanwhile, the nature of the nitrogenous base significantly affected both the dNTP-binding and catalytic-reaction efficiency. The results indicated that neutralisation of the charge and an increase in the internal volume of the active site caused a substantial increase in the activity of the enzyme and induced a transition to the processive mode in the presence of Mg2+ ions. Surrogate metal ions Co2+ or Mn2+ also may regulate the switching of the enzymatic process to the processive mode. Thus, the totality of individual factors affecting the activity of TdT ensures effective execution of its biological function. [ABSTRACT FROM AUTHOR]

Novel 1,8-naphthalimide-based fluorescent probes NI-1 and NI-2 were designed and screened for use as chemosensors for detection of heavy metal ions. Two moieties, methylpyridine (NI-1) and hydroxyphenyl (NI-2), were attached via piperazine at the C-4 position of the napthalimide core resulting in a notable effect on their spectroscopic properties. NI-1 and NI-2 are pH sensitive and show an increase in fluorescence intensity at around 525 nm (switch "on") in the acidic environment, with pKa values at 4.98 and 2.91, respectively. Amongst heavy metal ions only Cu2+ and Hg2+ had a significant effect on the spectroscopic properties. The fluorescence of NI-1 is quenched in the presence of either Cu2+ or Hg2+ which is attributed to the formation of 1:1 metal-ligand complexes with binding constants of 3.6 × 105 and 3.9 × 104, respectively. The NI-1 chemosensor can be used for the quantification of Cu2+ ions in sub-micromolar quantities, with a linear range from 250 nM to 4.0 μM and a detection limit of 1.5 × 10−8 M. The linear range for the determination of Hg2+ is from 2 μM to 10 μM, with a detection limit of 8.8 × 10−8 M. Conversely, NI-2 behaves like a typical photoinduced electron transfer (PET) sensor for Hg2+ ions. Here, the formation of a complex with Hg2+ (binding constant 8.3 × 103) turns the green fluorescence of NI-2 into the "on" state. NI-2 showed remarkable selectivity towards Hg2+ ions, allowing for determination of Hg2+ concentration over a linear range of 1.3 μM to 25 μM and a limit of detection of 4.1 × 10−7 M. [ABSTRACT FROM AUTHOR]

Rhodamine Schiff bases as fluorescent chemo-sensors, fluorogenic cation sensors, is scientifically exigent work. Rhodamine Schiff base derivatives have gained attention due to their structural variability. The combination of donor and acceptor groups with delocalized π-orbital results in excellent fluorescent properties due to intramolecular charge transfer (ICT) and opening of spirolactam ring of Rhodamine moiety. In this review, we summarize information about Rhodamine Schiff bases sensors reported over the past two decades (2002–2022). We focused on the design, synthesis, and sensing mechanism (ON/OFF, OFF/ON, and ON-OFF-OFF) of these sensors for Fe3+ and Cu2+ metal ions, as well as their practical applications. We also examined how the photophysical properties of these sensors change when they coordinate with the metal ions, resulting in changes in the typical sensing behaviour, such as a hypochromic/hyperchromic or hypsochromic/bathochromic shift. We anticipate that this review will provide a fundamental framework for researchers to further investigate Rhodamine Schiff-based sensors. [ABSTRACT FROM AUTHOR]

Ion-imprinted polymers (IIPs) have been widely used in different fields of Analytical Sciences due to their intrinsic selective properties. However, the success of chemical imprinting in terms of selectivity, as well as the stability, specific surface area, and absence of swelling effect depends on fully understanding the preparation process. Therefore, the proposal of this review is to describe the influence of relevant parameters on the production processes of ion-imprinted polymers, including the nature (organic, inorganic, or hybrid materials), structure, properties of the salt (source of the metal ion), ligand, crosslinking agent, porogenic solvent, and initiator. Additionally, different polymerization methods are discussed, the classification of IIPs as well as the applications of these adsorbent materials in the last years (2017–2022). [ABSTRACT FROM AUTHOR]

In this study, a novel fluorescent probe (graphene quantum dots functionalized d‐penicillamine [GQDs‐DPA]) was developed for the selective identification of Cu2+, V5+, and Fe3+ among 26 types of metal ions, which considerably quench the fluorescence intensity of GQD. So, GQDs‐DPA was applied as a simple fluorescent probe for facile metal ions recognition in standard solution. The proposed DPA‐GQD supported amino acids respond to Cu2+, V5+, and Fe3+, with high sensitivity. The intensity of the fluorescence histogram of this probe significantly diminished in exposure to metal ions such as Cu(II), V(V), and Fe(III). Moreover, a microfluidic paper‐based device (μPAD) was fabricated through a facile and cost‐effective protocol. Cu2+, V5+, and Fe3+ can be selectively recognized by GQDs‐DPA using μPAD by naked eye. Also, GQDs‐DPA exhibits a linear response for the detection of ions in concentrations ranging from 0.01 to 1 ppm, with a low limit of quantification of 0.01 ppm in standards samples. The boosted color uniformity, low instrumental needs of the stamp, and disposability of μPADs enable the application of the proposed device for commercial applications in environmental science and technology. [ABSTRACT FROM AUTHOR]

The study of metal ions in the context of cell signaling has historically focused mainly on Ca2+, the second messenger par excellence. But recent studies support an emerging paradigm in which other metals, including magnesium and d -block metals, play a role in signal transduction as well. Armed with the right indicators, fluorescence microscopy offers a unique combination of spatial and temporal resolution perfectly suited to reveal metal transients in real time, while also helping identify possible sources of ion mobilization and molecular targets. With a focus on Mg2+, we highlight recent advancements in the development of molecular indicators and imaging strategies for the study of metal ions in signaling. We discuss remaining conceptual and technical challenges in the field, and we illustrate through the case of Mg2+ how the study of nontraditional ions in signaling is inspiring technological developments applicable more broadly to the study of metals in biology. [ABSTRACT FROM AUTHOR]

A fluorescent probe for the detection of lead ions in complete aqueous solution was synthesized by covalently combining a fluorescent 1,8-naphthalimide dye with cellulose nanocrystals (CNCs). The dye-labelled CNCs have lots of carboxyl and hydroxyl groups on the surface, which make them disperse well in water. There is little fluorescence discrimination for 1,8-naphthalimide dye in the presence of different metal ions, while the fluorescent CNCs exhibit selective and sensitive response to Pb(II) with remarkably enhanced emission intensity. The limit of detection of the fluorescent CNCs is as low as 1.5 × 10−7 mol/L, and there is good linear relationship between the fluorescence maxima and the Pb(II) concentration in a wide range of 2.5 × 10−7–5.0 × 10−5 mol/L. The sensing ability of the dye-labeled CNCs to Pb(II) is ascribed to the synergistic complexation of Pb(II) with both the grafted dye groups and the adjacent carboxyl groups on the surface of the CNCs. The combination ratio of Pb(II) to the fluorophore on CNCs is determined to be 1.2:1 via Job's plot experiment, which is basically consistent with the theoretical value of 1:1. The offered fluorescent CNCs can be employed as a nanosensor for the detection of metal ions and can be further promoted for many applications in chemical, environmental, and biological systems. Water-dispersible fluorescent probe via covalent immobilization of 1,8-naphthalimide on cellulose nanocrystals (CNCs) exhibits selective and sensitive detection of lead ions in complete aqueous solution. The inhibited intramolecular charge transfer process (ICT) of the fluorophores loaded on CNCs contributes to the remarkably enhanced fluorescence emission in the presence of lead ions. [ABSTRACT FROM AUTHOR]

We report an IR-IR double resonance study of the structural landscape present in the Na(glucose) complex. Our experimental approach involves minimal modifications to a typical IR predissociation setup, and can be carried out via ion-dip or isomer-burning methods, providing additional flexibility to suit different experimental needs. In the current study, the single-laser IR predissociation spectrum of Na(glucose), which clearly indicates contributions from multiple structures, was experimentally disentangled to reveal the presence of three α-conformers and five β-conformers. Comparisons with calculations show that these eight conformations correspond to the lowest energy gas-phase structures with distinctive Na coordination. [ABSTRACT FROM AUTHOR]

As an important component of flexible electronic devices, strain sensing hydrogels have attracted extensive attention in the field of wearable sensors. However, the hydrogel matrix has some problems such as weak mechanical strength, lack of adhesion and poor performance stability. Herein, an ionic conductive poly (hydroxyethyl methacrylate) (PHEMA) hydrogel with good toughness and adhesion strength was prepared which was initiated by dynamic REDOX reaction of phenolic hydroxyl group and metal ions. The resulting PHEMA/ tannic acid (TA)-Fe hydrogel exhibits high flexibility (2227% elongation at break) and excellent adhesion properties (238 kPa on pig skin) due to the presence of TA and Fe3+ ion. Rheological results demonstrated self-healing performance of the hydrogels, and cyclic compression experiments displayed the hydrogels exhibit very good fatigue resistance. Furthermore, the hydrogel showed well strain sensing ability under different stretch and compress conditions and could maintain the stability performance for at least 100 cycles within 100% strain. Therefore, the PHEMA/TA-Fe hydrogels prepared with a simple and convenient redox catalytic polymerization method possess great potential to be used in flexible electronic devices. [Display omitted] • PHEMA/TA-Fe hydrogel was prepared inducing with a facile redox reaction of TA-Fe. • PHEMA hydrogel was crosslinked with dynamic hydrogen bonds and metal coordination. • PHEMA hydrogel showed high flexibility, excellent adhesion and self-healing abilities. • PHEMA hydrogel exhibits well strain sensing ability under vary stretch or compress. [ABSTRACT FROM AUTHOR]

Background: The potential risks associated with hip resurfacing arthroplasty (HRA) are controversial and underestimated. The aim of this study was to explore intermediate-term trends for the levels of cobalt (Co), chromium (Cr), and molybdenum (Mo) ions after HRA. Methods: Forty patients who underwent HRA from October 2005 to December 2010 were recruited to this study. The serum levels of metal ions were examined preoperatively and 3, 12, 24, and 60 months after surgery. Trends and differences in levels of metal ions with respect to sex, operated side, and body mass index (BMI) were analyzed. Results: There were no significant differences in levels of Cr, Co, and Mo at each time point with respect to sex, operated side, and BMI (p > 0.05). The postoperative levels of Cr, Co, and Mo ions were significantly higher than the preoperative levels across sex, operated side, and BMI groups. Postoperative levels of Cr, Co, and Mo peaked at 12, 24, and 60 months, respectively. Cr levels peaked earlier (at 12 months) in the overweight (BMI ≥25 kg/m²) group compared to the normal-weight group (BMI <25 kg/m²), Co levels (at 12 months) peaked in women compared to men, and Mo levels (at 3 months) peaked in the bilateral HRA group compared to the unilateral HRA group. Conclusions: Serum levels of Cr, Co, and Mo increased significantly after HRA. Cr levels peaked earlier in the overweight patients, Co levels peaked in women, and Mo levels peaked in patients who underwent bilateral HRA. However, there were no significant differences with respect to sex, operated side, and BMI. [ABSTRACT FROM AUTHOR]

Transport of carbonate ions was explored through fiber supported solid membrane. A novel fiber supported solid membrane was prepared by chemical modification of cellulose fiber with citric acid, 2'2-bipyridine and magnesium carbonate. The factors affecting the permeability of carbonate ions such as immobilization of citric acid-magnesium metal ion -2'2-bipyridine complex (0 to 2.5 mmol/g range) over cellulose fiber, carbon-ate ion concentration in source phase and NaOH concentration in receiving phase were investigated. Ki-netic of carbonate, sulfate, and nitrate ions was investigated through fiber supported solid membrane. Transport of carbonate ions with/without bubbling of CO2 (0 to 10 ml/min) in source phase was explored from source to receiving phase. The novel idea is to explore the adsorptive transport of CO2 from source to receiving phase through cellulose fiber containing magnesium metal ion organic framework. [ABSTRACT FROM AUTHOR]

Cationic metal ion-coordinated N-diisopropyloxyphosphoryl dipeptides (DIPP-dipeptides) were analyzed by electrospray ionization multistage tandem mass spectrometry (ESI-MS). Two novel rearrangement reactions with hydroxyl oxygen or carbonyl oxygen migrations were observed in ESI-MS/MS of the metallic adducts of DIPP-dipeptides, but not for the corresponding protonated DIPP-dipeptides. The possible oxygen migration mechanisms were elucidated through a combination of MS/MS experiments, isotope (O, N, and H) labeling, accurate mass measurements, and density functional theory (DFT) calculations at the B3LYP/6-31 G(d) level. It was found that lithium and sodium cations catalyze the carbonyl oxygen migration more efficiently than does potassium and participation through a cyclic phosphoryl intermediate. In addition, dipeptides having a C-terminal hydroxyl or aromatic amino acid residue show a more favorable rearrangement through carbonyl oxygen migration, which may be due to metal cation stabilization by the donation of lone pair of the hydroxyl oxygen or aromatic π-electrons of the C-terminal amino acid residue, respectively. It was further shown that the metal ions, namely lithium, sodium, and potassium cations, could play a novel directing role for the migration of hydroxyl or carbonyl oxygen in the gas phase. This discovery suggests that interactions between phosphorylated biomolecules and proteins might involve the assistance of metal ions to coordinate the phosphoryl oxygen and protein side chains to achieve molecular recognition. [ABSTRACT FROM AUTHOR]

Competitive adsorption of Ag+, Pb2+, Ni2+, and Cd2 ions on vermiuculite in a binary, ternary, and quaternary mixture was investigated in batch experiments. The effects of the presence of Ag+, Ni2+, and Cd2+ ions on the adsorption of Pb2+ ions were investigated in terms of the equilibrium isotherm. Experimental results indicated that Pb2+ ions always favorably adsorbed on vermiculite over Ag+, Ni2+, and Cd2+ ions. The adsorption equilibrium data of Pb2+ ions better fitted the Langmuir model than the Freundlich model. The results showed that the pseudo-second-order kinetics model was in good agreement with the experimental results for all metal ions, and the adsorption rate among the metal ions followed Ag+ > Pb2+ > Ni2+ > Cd2+. The desorption and regenration study indicated that vermiculite can be used repeatedly and be suitable for the design of a continuous process. [ABSTRACT FROM AUTHOR]

The binding of ions Li+, Na+, K+, NH4+ (group I), Mg2+, Al3+, Ga3+ (group II), Ca2+, Pb2+ (group III) ions, Ba2+ and paraquat by heterocyclophanes containing biindolizine and quinoxaline fragments connected by 3,6,9-trioxaundecane and 5,8,11,14,17-pentaoxageneicosane spacers, and also their acyclic analogues, in the acetonitrile-0.1 M Bu4NBF4 is studied by cyclic voltammetry. A conclusion is drawn that the ions of the group I are not bound by these compounds; the paraquat is not bound by heterocyclophane with the 5,8,11,14,17-pentaoxageneicosan spacers. For ions of the group II, reversible redox-switchable binding by the macrocycles with the 3,6,9-trioxaundecane and 5,8,11,14,17-pentaoxageneicosan spacers is observed: the initial compounds show the binding; their radical cations and dications do not. The binding of the ions of the group III and Ba2+ is determined by the macrocycles' size. In particular, these ions are bound not only by the heterocyclophane with 3,6,9-trioxaundecane spacers but also by its radical cation or dication. The binding results in the corresponding dication stabilization. The heterocyclophane with the 5,8,11,14,17-pen-taoxageneicosan spacers demonstrates the redox-switchable binding of Ca2+ and Pb2+ ions; no effect of Ba2+ ions on the cyclic voltammograms of this heterocyclophane was observed. In the ternary system "heterocyclophane with 3,6,9-trioxaundecane spacers + ions of the group II (Al3+, Ga3+) + ions of the group III (Ca2+, Pb2+)" either primary binding of the group III ion Pb2+ or concurrent binding of the ions of the group II and the group III, with the system's reversible redox-switching from one metal complex to another, was observed. [ABSTRACT FROM AUTHOR]

Abstract: We describe an ultraviolet (UV) absorbance titration method that can be used to determine complexing capacities (C L) and conditional stability constants (log K) of humic substances (HSs) with metal ions such as Cu(II) and Hg(II). Two fulvic acids (FA) and one humic acid (HA) were used for this study. UV absorbance of HSs gradually increased with the addition of Cu(II) or Hg(II) after blank correction, and these increases followed the theoretical 1:1 (ligand:metal ion) binding model. The results from the absorbance titration calculation for HSs with Cu(II) and Hg(II) compared well with those from fluorescence quenching titration. The titration of the model compound l-tyrosine with Cu(II) proved the validity of this method, and the K and C L were within 2.3% and 7.4% of the fluorescence quenching titration. The results suggest that the UV absorbance titration can be used to study the binding capacities of HSs and/or dissolved organic matter (DOM) with trace metals. The advantages and disadvantages of the absorbance titration method were also discussed. [Copyright &y& Elsevier]

Abstract: New chromogenic diazophenylcalix[4]arenes 1 and 2 were synthesized in cone conformation. Compound 1 with the ortho-carboxyl groups in CH3CN solution preferentially binds with alkaline earth and transition metal ions, whereas no significant changes in absorption spectra are observed in the presence of alkali metal ions. While 2 with the ortho-ester groups shows selective complexation properties towards transition metal ions over alkali and alkaline earth metal ions. The detection of metal ions gives rise to bathochromic shifts in the absorption spectra (from orange/yellow to red), which is clearly visible even to the naked eye. According to the selective color changes using both receptors upon cation complexation, one can set up a qualitative analytical routine to screen alkali, alkaline earth, and transition metal ions. [Copyright &y& Elsevier]

Abstract: A series of insoluble chitosan (CTS) derivatives were prepared by grafting ester- and amino-terminated dendrimer-like polyamidoamine (PAMAM) into CTS using a divergent method by repeating two processes: (1) Michael addition of methyl acrylate (MA) to surface amino groups, and (2) amidation of the resulting esters with ethylenediamine (EDA). Their structures were characterized by infrared spectra (IR) and wide-angle X-ray diffraction (WAXD). The adsorption capabilities of the products for Au3+, Pd2+, Pt4+, Ag+, Cu2+, Zn2+, Hg2+, Ni2+, and Cd2+ were studied. The results showed that the products exhibited better adsorption capabilities for Au3+ and Hg2+ than for other metal ions, and the adsorption capabilities of amino-terminated products were higher than those of ester-terminated ones. Also it was observed that a high percentage of grafting of PAMAM into CTS does not ensure a high adsorption capacity. [Copyright &y& Elsevier]

Abstract: A novel complexing membrane was used for the removal of heavy metal ions such as Pb(II), Cd(II) and Cu(II) from aqueous solutions. The membrane consists in a semi-interpenetrating polymer network of crosslinked poly(vinyl alcohol) as the matrix and poly(ethyleneimine) as the complexing polymer. The absorption reactions followed pseudo-first-order kinetics with similar rate constants for the three cations. A model is proposed for the absorption–desorption process in order to rationalize the data obtained for the retention ratio and the retention efficiency ratio. The corresponding equilibrium constants were determined for the three metal ions, showing that the affinity order of the membrane is Pb>Cu>Cd. This sequence is consistent with the order of maximum uptake of the ions per gram of membrane: 0.59, 0.47 and 0.33mmolg−1, respectively. On the other hand, the uptake order is different on a mass basis: 123, 30 and 37mgg−1, respectively. Regeneration of the membrane and metal recovery were studied with HCl and HNO3 at different concentrations. Filtration of solutions of each metal ion showed large elimination ratios (96–99.5%) with a retention sequence Cd>Cu>Pb. The membrane remained efficient until complete saturation of its sites. Moreover, Cu retention is larger than expected, indicating possible additional chelation by the PVA matrix. Better retention ratios were observed when the concentration of the feed solution was kept constant. Filtration of a mixture of the three cations (all at 100ppm concentration) resulted in the same retention sequence, but the elimination ratios were smaller and Pb was eventually displaced by Cu and Cd that were present in larger molar concentrations. [Copyright &y& Elsevier]

Abstract: In order to prevent engine failure, the oil must be changed before it loses its protective properties. It is necessary to monitor the actual physical and chemical condition of the oil to reliably determine the optimum oil-change interval. Our study focuses on the condition of the lubricating oil in an operated car engine. Shear stress curves and viscosity curves as a function of the shear rate for fresh and used lubricating oil were examined. Metal nitrate was detected in the lubricating oil from the operated car engine through the use of a chelating self-assembled monolayer. [Copyright &y& Elsevier]

Abstract: Calreticulin (CRT) is a chaperone of the endoplasmic reticulum. We dissected CRT into its two structural domains, N-/C-domain and P-domain, to identify its metal ion-responsive region. For this, we constructed bacterial expression systems for the N-/C-domain (1–180 fused by a linker to 290–400) and P-domain (189–280). Circular dichroism (CD) studies showed that calcium ions increased tertiary packing and thermal stability of apo N-/C-domain, whereas zinc ions had a strong destabilizing effect. Interestingly, neither calcium nor zinc ions altered the structural properties of apo P-domain. These results indicate that the calcium- and zinc-responsive regions reside strictly in the N-/C-domain. Analysis of thermal denaturation curves of CRT, N-/C-domain, and P-domain suggested a structural role for the P-domain in CRT. Rotary shadowing electron microscopy (EM) analysis of CRT and calnexin provided convincing evidence for their structural relatedness. This analysis also revealed that apo P-domain adopts various curved shapes suggesting conformational flexibility. EM images of apo N-/C-domain revealed objects having wide gaps suggesting weak interactions between the N- and C-domains. This is consistent with the larger size of apo N-/C-domain on the gel filtration column. Our studies provide a framework for correlating the structural organization of CRT with its metal ion-responsive region. [Copyright &y& Elsevier]

Structural features of clusters involving a metal ion (Li+, Na+, Be2+, Mg2+, Zn2+, Al3+, or Ti4+) surrounded by a total of 18 water molecules arranged in two or more shells have been studied using density functional theory. Effects of the size and charge of each metal ion on the organization of the surrounding water molecules are compared to those found for a Mg[H2O]• [H2O]12 cluster that has the lowest known energy on the Mg2+• [H2O]18 potential energy surface (Markham et al. in J Phys Chem B 106:5118–5134, 2002). The corresponding clusters with Zn2+ or Al3+ have similar structures. In contrast to this, clusters with a monovalent Li+ or Na+ ion, or with a very small Be2+ ion, differ in their hydrogen-bonding patterns and the coordination number can decrease to four. The tetravalent Ti4+ ionizes one inner-shell water molecule to a hydroxyl group leaving a Ti4+(H2O)5 (OH−) core, and an H3O+• • • H2O moiety dissociates from the second shell of water molecules. These observations highlight the influence of cation size and charge on the local structure of hydrated ions, the high-charge cations causing chemical changes and the low-charge cations being less efficient in maintaining the local order of water molecules. [ABSTRACT FROM AUTHOR]

Distinct spatio-temporal variations of metal ions and Taxol production were observed for Taxus cuspidata cells immobilized on polyurethane foam. The Taxol content in the inner foam layer reached 215 μg g−1 at day 30, which was 40-fold higher than that in the outer foam layer, and the Ca2+ and Mg2+ contents were 5.3 and 3.7 times higher, while the K+ content was 5.5 times lower. Thus higher intracellular Ca2+ and Mg2+ contents and lower intracellular K+ content may favor the Taxol biosynthesis in immobilized Taxus cuspidata. [ABSTRACT FROM AUTHOR]

A quantitative analysis has been carried out to determine the concentration of Zr4+ ion in aqueous solution by using alizarin red S (ARS) as reagent to form ARS-Zr complex. ARS-Zr complex gives a maximum absorption peak at wavelength of 520 nm with pH 2.5. The repeatability study at two different Zr4+ ion concentrations of 10 mg/l and 200 mg/l was found to give RSD values of 1.16% and 0.55%, respectively. The study of interfering ions was carried out with K+, Na+, Ca2+, Pb2+, Al3+ and Fe3+ ions with Zr4+ ion: interfering ions at mole ratio of 1:1, 1:10 and 1:100. The study showed a significant interfering effect at the ratio of 1:100 for all the ions except K+ and Na+ ions. Characterization of ARS-Zr complex gives a dynamic Zr4+ concentration range of 5-35 mg/l. However, the use of artificial neural network (ANN) was able to extend the dynamic concentration range of Zr4+ to a larger range of 5-200 mg/l with optimized ANN parameters of 14 hidden neurons, 20 epochs, and training rate of 0.001. The sum square error (SSE) was found to have a value of 0.33 with an average error of 0.38. [ABSTRACT FROM AUTHOR]

Abstract: The effect of four metal ions Cu2+, Ni2+, Zn2+ and Co2+ on the interaction between bovine serum albumin (BSA) and berberine chloride (BC) extracted from a traditional Chinese Herb coptis chinensis franch, was investigated mainly by means of UV and fluorescence spectroscopy in this paper. The four metal ions make the quenching efficacy of BC to BSA higher than that in the absence of these metal ions because of the possible transition of BSA molecular conformation caused by metal ions. It was found that the quenching mechanism is a combination of static quenching with nonradiative energy transfer. In the presence of metal ions, the apparent association constant K A and the number of binding sites of BC on BSA are both decreased in a range of 8–19% and 25–28%, respectively, which indicates that the metal ions decrease the binding efficacy of BC on BSA and increase the concentration of free BC simultaneously. The scheme of interaction between BC and BSA in the presence of metal ions is a strong quenching but a weak binding. [Copyright &y& Elsevier]

2,3-Dihydroxypyridine loaded (via -N=N-linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1?g packed in a column of 1?cm diameter; surface area 135.5?m2?g-1) was found to be an effective solid phase sorbent for enriching Zn2+, Mn2+, Ni2+, Pb2+, Cd2+, Cu2+, Fe3+ and Co2+ at pH 3.5 to 7.0 using flow rates between 1.0-5.0?mL?min-1. For desorption (recovery 97.0-99.8%) of the metal ions, 8 to 10?mL of 2.0?mol?L-1 HCl or 1.5?mol?L-1 HNO3 at a flow rate of between 2.0 and 4.0?mL?min-1 were found most suitable. The t1/2 (time for 50% sorption) is between 2 and 10?min when a 50?mL solution (containing a total amount of metal of 2?mg) was equilibrated with 0.5?g of resin. Sorption of all metal ions except Pb2+ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmol?g-1. The resin can withstand an acid concentration of =6?mol?L-1 and can be reused for thirty cycles of sorption-desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca2+ and Mg2+ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30?µg?L-1 for Zn2+, Mn2+, Ni2+, Pb2+, Cd2+, Cu2+, Fe3+ and Co2+, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018-1.0, 0.067-5.0, 0.2-5.0, 0.9-20, 0.028-2.0, 0.077-5.0, 0.19-10 and 0.1-3.5?µg?mL-1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry. [ABSTRACT FROM AUTHOR]

The concepts embodied in de novo structure-based drug design are being adapted for the computer-aided design of metal ion sequestering agents. This adaptation requires the development of methods for (i) generating candidate structures and (ii) evaluating and prioritizing these structures with respect to their binding affinity for a specific guest. This article summarizes recent progress in this area that includes the creation of a new computer software program, called HostDesigner, that can generate and evaluate millions of new molecular structures per minute on a desktop personal computer. Several methods for evaluating the degree of binding site organization in a host structure are presented. An example is provided to demonstrate how these methods have been used to identify ligand architectures that provide enhanced metal ion binding affinity. [Copyright &y& Elsevier]

Alkaline phosphatase (AP) displays significant structural changes during metal-ion binding, supporting cooperative interactions between the subunits of the dimeric enzyme. Here, we present data on the dynamic properties of AP from E. coli, and characterize the structural changes that accompany variations in metal-ion content, combining limited proteolysis and MALDI-TOF mass spectrometry. Limited proteolysis revealed an internal cleavage site at Arg-293, reflecting a position of conformational flexibility supporting subunit communication essential for catalysis. A specific shielding of a region distant from the metal-binding site has been demonstrated, implying transmission of conformational changes, induced by metal-ion binding to the adjacent subunit, across the subunit interface. [Copyright &y& Elsevier]

Summary: In current study, the diphenylaminomethylcalix[4]arene(3) was synthesized and immobilized onto silica surface to prepare a selective, regenerable and stable resin-4. The synthesized resin-4 has been characterized by FT-IR spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy(EDX) and Brunauer-Emmett-Teller(BET) techniques. To check the adsorption capacity of resin-4, the batch and column adsorption methodology were applied and it has observed that the resin-4 was selectively removed Hg 2+ ions under the optimized parameters. The maximum adsorption capacity was obtained at pH 9 using 25 mg/L of resin-4. Under the optimal conditions, different equilibrium, kinetic and thermodynamic models were applied to experimental data. The results show that adsorption mechanism is chemical in nature following Langmuir model with good correlation coefficient(R 2 =0.999) and having 712.098(mmol/g) adsorption capacity. The energy of calculated from D-R model suggests the ion exchange nature of the adsorption phenomenon. Dynamic adsorption experiments were conducted using Thomas model. The maximum solid phase concentration(qo) was 7.5 and rate constant THk was found to be 0.176 with(R 2 =0.938) for Hg 2+ ions. The kinetic study describes that the adsorption mechanism follows pseudo second order(R 2 =0.999). The thermodynamic parameters such as ΔH(0.032 KJ/mol) and ΔS(0.127 KJ/mol/K) and ΔG(-5.747,-6.306,-7.027 KJ/mol) shows that the adsorption of Hg 2+ ion is endothermic and spontaneous. The reusability of resin-4 was also checked and it has observed that the after 15 cycle only 1.2% adsorption reduces. Moreover, the resin-4 was applied on real wastewater samples obtained from local industrial zone of Karachi, Sindh-Pakistan. [ABSTRACT FROM AUTHOR]