Coordination Of Na Research Articles

Transport and inhibition mechanisms of the human noradrenaline transporter.

The noradrenaline transporter (also known as norepinephrine transporter) (NET) has a critical role in terminating noradrenergic transmission by utilizing sodium and chloride gradients to drive the reuptake of noradrenaline (also known as norepinephrine) into presynaptic neurons1-3. It is a pharmacological target for various antidepressants and analgesic drugs4,5. Despite decades of research, its structure and the molecular mechanisms underpinning noradrenaline transport, coupling to ion gradients and non-competitive inhibition remain unknown. Here we present high-resolution complex structures of NET in two fundamental conformations: in the apo state, and bound to the substrate noradrenaline, an analogue of the χ-conotoxin MrlA (χ-MrlAEM), bupropion or ziprasidone. The noradrenaline-bound structure clearly demonstrates the binding modes of noradrenaline. The coordination of Na+ and Cl- undergoes notable alterations during conformational changes. Analysis of the structure of NET bound to χ-MrlAEM provides insight into how conotoxin binds allosterically and inhibits NET. Additionally, bupropion and ziprasidone stabilize NET in its inward-facing state, but they have distinct binding pockets. These structures define the mechanisms governing neurotransmitter transport and non-competitive inhibition in NET, providing a blueprint for future drug design.

The solid solution in the system NaMgAl(SO4)3–KMgAl(SO4)3

We synthesized six samples in the compositional field NaMgAl(SO4)3–KMgAl(SO4)3 in 20 mol% increments from pure Na to pure K compounds. We investigated them by Powder X-Ray diffraction, 23Na, and 27Al Nuclear Magnetic Resonance spectroscopy. The results confirm NaMgAl(SO4)3 as a unique phase identical to a presumed new mineral found in the fumaroles of Eldfell and Hekla volcanoes in Iceland. It tolerates less than 10 mol% K substitution for Na. There exists a compositional gap to approximately Na0.65K0.35MgAl(SO4)3 from where a solid solution extends to KMgAl(SO4)3. The mineral koryakite [NaKMg2Al2(SO4)6] is a member of the latter solid solution series. The crystal structures of all (Na,K)MgAl(SO4)3 phases are akin to NASICON (NA Super Ionic CONductor). NaMgAl(SO4)3 has R3¯c\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R\\overline{3}c$$\\end{document} symmetry and a disordered distribution of Mg and Al among the octahedral sites with only one unique site for the alkali atom. The members of the solid solution have R3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R\\overline{3}$$\\end{document} symmetry with ordered Mg–Al distribution and two unique alkali sites with different preferences for Na and K. In the crystal structure, the coordination of Na and/or K is trigonal antiprismatic, and these share bases with two octahedral Mg (Na) or Al (K) coordinations. These polyhedra are arranged in columns parallel to [001] and interconnected by SO4 tetrahedral groups. The alkali atoms from a column lie in the same (001) layers as the octahedrally coordinated atoms from the three neighboring rows. On the same level, parallel to (001), there are gaps in the other three neighboring columns forming channels containing Na+ or K+ ions.

High Transference Number of Na Ion in Highly Concentrated Nan(SO2F)2/γ-Butyrolactone Electrolytes for Sodium Batteries

We report here the liquid structures and physicochemical properties of highly concentrated solutions of NaN(SO2F)2 (NaFSA) dissolved in γ-butyrolactone (GBL) for Na-ion batteries. The solvation structure of Na+ was analyzed using Raman spectroscopy. By adding NaFSA to GBL, the Raman band of ring stretching vibration (678 cm−1) of GBL shifted to higher wavenumber because the GBL coordinates to Na+ ion. The concentration dependence of Raman spectral change of GBL suggested the solvation number of Na+ is 5 when the excess GBL molecules exist in the solution. As increasing the concentration of NaFSA, the bound GBL increases and free GBL decreases. At higher concentration of [NaFSA]/[GBL] > 1/2, free GBL does not exist and all of the GBL molecules coordinate to the Na+ ion. Raman spectra of FSA anion suggested that the FSA anion also participates in the coordination of Na+ in the highly concentrated solution. Apparently, the contact ion pairs and ionic aggregates are formed extensively in the highly concentrated solution. This gives significant effects on the Na+ ion conduction mechanism in the liquid. We estimated the transference number of Na+ ion in the electrolytes. The transference number of Na+ in the liquid of [NaFSA]/[GBL] = 1/1 was as high as 0.7. This surprisingly high transference number is probably due to the peculiar conduction mechanism in the ionic aggregates. Na+ ion is considered to exchange the anions dynamically in the ionic aggregates, and this may induce the hopping conduction in the liquid. Charge and discharge tests of a hard carbon electrode were conducted in the liquid of [NaFSA]/[GBL] = 1/1, and the reversible Na+ insertion/extraction into/from the electrode were possible with a high coulombic efficiency. The SEI derived from the FSA anion might contribute to the reversible electrochemical reaction. Acknowledgements This study was supported in part by JSPS KAKENHI (Grant Nos. 18H03926 and 19H05813) from the Japan Society for the Promotion of Science (JSPS) and the MEXT program “Elements Strategy Initiative to Form Core Research Center” of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan.

High Transference Number of Na Ion in Highly Concentrated Sodium Bis(fluorosulfonyl)Amide/γ-Butyrolactone Electrolytes for Sodium Batteries

We report here the liquid structures and physicochemical properties of highly concentrated solutions of NaN(SO2F)2 (NaFSA) dissolved in γ-butyrolactone (GBL) for Na-ion batteries. The solvation structure of Na+ was analyzed using Raman spectroscopy. By adding NaFSA to GBL, the Raman band of ring stretching vibration (678 cm−1) of GBL shifted to higher wavenumber because the GBL coordinates to Na+ ion. The concentration dependence of Raman spectral change of GBL suggested the solvation number of Na+ is 5 when the excess GBL molecules exist in the solution. As increasing the concentration of NaFSA, the bound GBL increases and free GBL decreases. At higher concentration of [NaFSA]/[GBL] > 1/2, free GBL does not exist and all of the GBL molecules coordinate to the Na+ ion. Raman spectra of FSA anion suggested that the FSA anion also participates in the coordination of Na+ in the highly concentrated solution. Apparently, the contact ion pairs and ionic aggregates are formed extensively in the highly concentrated solution. This gives significant effects on the Na+ ion conduction mechanism in the liquid. We estimated the transference number of Na+ ion in the electrolytes. The transference number of Na+ in the liquid of [NaFSA]/[GBL] = 1/1 was as high as 0.7. This surprisingly high transference number is probably due to the peculiar conduction mechanism in the ionic aggregates. Na+ ion is considered to exchange the anions dynamically in the ionic aggregates, and this may induce the hopping conduction in the liquid. Charge and discharge tests of a hard carbon electrode were conducted in the liquid of [NaFSA]/[GBL] = 1/1, and the reversible Na+ insertion/extraction into/from the electrode were possible with a high coulombic efficiency. The SEI derived from the FSA anion might contribute to the reversible electrochemical reaction. Acknowledgements This study was supported in part by JSPS KAKENHI (Grant Nos. 18H03926 and 19H05813) from the Japan Society for the Promotion of Science (JSPS) and the MEXT program “Elements Strategy Initiative to Form Core Research Center” of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan.

Role Reversal of the Carboxylate Group from Coordination to Hydrogen Bonding Only, in Structurally Diverse Metal-2-amino,5-Nitro-benzoates: A First Report

The remarkable structural diversities arising from a small ligand, 2-amino,5-nitro-benzoic acid (L1H), equipped with different functional groups, conferring tunable coordination sites as well as H-bonding abilities, have been explored. Six new crystal structures of Cs(I), Na(I), K(I), and Li(I) ions with L1 have been realized. Notably, for the medium-sized alkali metal ions, a role reversal between the coordination and H-bonding nature of −COO– and −NO2 groups, respectively, has been observed for the first time. Since L1 possesses three potential sites for coordination as well as H-bonding interactions, we realized a delicate control of noncovalent interactions on the resulting supramolecular assemblies. Structural diversities observed range from one-dimensional helices and linear threads to two-dimensional brick-wall types or three-dimensional networks. The electrostatic surface potential (ESP) of three representative complexes provided an insight into the electronic-deficient and electron-rich regions. The coordination of Na(I) and K(I) ions through the nitro groups extends the electron-deficient region of the complexes. The electron densities at the bond critical paths of the representative complexes were calculated to understand the supramolecular outcome of the coordination polymers. Unravelling of such critical electronic information is paramount toward the systematic construction of a new generation of complex coordination polymers.

Elucidating the Impact of Sodium Salt Concentration on the Cathode–Electrolyte Interface of Na–Air Batteries

A promising approach to improve the specific capacity and cyclability in a Na–O2 cell using a pyrrolidinium-based ionic liquid electrolyte in a half-cell has been explored in this work. Increasing the concentration of sodium salt in an ionic liquid electrolyte produces a significant enhancement in the discharge capacity of up to 10 times, a reduction in the overpotential and an increase in the long-term cyclability. Additionally, a distinct discharge morphology is also observed, which is demonstrated to be result of a different oxygen reduction reaction mechanisms. These improvements are likely due to the solvation of Na+ in the electrolyte mixtures containing different Na+ concentrations; the coordination of Na+ by the anion of the ionic liquid dictates the discharge product morphology. At low concentrations, Na+ is strongly coordinated to the anion of the ionic liquid, and this also can have an effect on its mobility; however, at high Na+ concentration, this interaction is weakened and favors mass trans...

One-pot annealing preparation of Na-doped graphitic carbon nitride from melamine and organometallic sodium salt for enhanced photocatalytic H2 evolution

Na-doped graphitic carbon nitride was successfully developed by a one-pot preparation, that was, by simply annealing the mixture of melamine and organometallic sodium salt (ethylenediamine tetraacetic acid disodium salt). Visible-light-driven photocatalytic H2-evolution activity of graphitic carbon nitride was effectively enhanced by Na doping (9.2 times). It was found based on comprehensive analysis that, the absorption of visible light was improved due to the structural change of graphitic carbon nitride by Na doping, thereby promoting the generation of more photo-generated carriers. Meanwhile, the separation and transfer of photo-generated carriers were greatly enhanced by coordination of Na into big C-N rings of the triazine units. Moreover, more active sites for photocatalytic H2-evolution reaction were provided by the increased surface areas.

The ion homeostasis and ROS scavenging responses in ‘NL895’ poplar plantlet organs under in vitro salinity stress

To evaluate salt tolerance and organ-specific responses of Populus deltoides × Populus euramericana cv., ‘NL895’ to salinity stress, plantlets were cultured on half-strength Murashige and Skoog medium containing 0, 50, 100, 150, or 200 mM NaCl for 15–30 d. The growth, ion homeostasis, antioxidant activities, and ultrastructural responses of the roots and leaves were assessed. Sodium chloride, at 50 and 100 mM (there were mostly no statistical differences in the two levels), induced lower Na+ contents, higher K+/Na+ ratio, and lower H2O2 and malondialdehyde (MDA) levels in roots compared to those in leaves. However, salt-stressed roots exhibited greater peroxidase (POD) and glutathione reductase (GR) activities and higher ascorbic acid (AsA) contents compared to leaves. The leaves maintained higher K+ and Ca2+ levels than the roots during NaCl treatment and partly balanced the excess Na+ to decrease Na+ toxicity. Also, leaves reduced oxidative damage by increasing the activities of the antioxidation enzymes superoxide dismutase and catalase, and by increasing AsA and glutathione (GSH) levels. Additionally, an increase in the stomatal density was observed in the NaCl-treated leaves. Overall, roots and leaves displayed different adaptive mechanisms to cope with salt stress and the roots were more tolerant to salt stress than the leaves. Coordination of Na+ and K+ transport in roots and leaves, and the organ-specificity of high POD activity in roots, and high CAT and APX activities in leaves, likely contributed to the salt tolerance of the whole plant. ‘NL895’ poplar could survive at a moderate NaCl level of 100 mM.

Interaction of NaOH solutions with silica surfaces

HypothesisSodium adsorption on silica surfaces depends on the solution counter-ion. Here, we use NaOH solutions to investigate basic environments. SimulationsSodium adsorption on hydroxylated silica surfaces from NaOH solutions were investigated through molecular dynamics with a dissociative force field, allowing for the development of secondary molecular species. FindingsAcross the NaOH concentrations (0.01 M − 1.0 M), ∼50% of the Na+ ions were concentrated in the surface region, developing silica surface charges between − 0.01 C/m2 (0.01 M NaOH) and − 0.76 C/m2 (1.0 M NaOH) due to surface site deprotonation. Five inner-sphere adsorption complexes were identified, including monodentate, bidentate, and tridentate configurations and two additional structures, with Na+ ions coordinated by bridging oxygen and hydroxyl groups or water molecules. Coordination of Na+ ions by bridging oxygen atoms indicates partial or complete incorporation of Na+ ions into the silica surface. Residence time analysis identified that Na+ ions coordinated by bridging oxygen atoms stayed adsorbed onto the surface four times longer than the mono/bi/tridentate species, indicating formation of relatively stable and persistent Na+ ion adsorption structures. Such inner-sphere complexes form only at NaOH concentrations of > 0.5 M. Na+ adsorption and lifetimes have implications for the stability of silica surfaces.

NaCl][Cu(HSeO3)2], NaCl-intercalated Cu(HSeO3)2: synthesis, crystal structure and comparison with related compounds

Abstract Single crystals of [NaCl][Cu(HSeO3)2] have been prepared by the chemical vapor transport reactions. Its crystal structure (monoclinic, C2/c, a = 13.9874(7), b = 7.2594(4), c = 9.0421(5) Å, β = 127.046(2)°, V = 732.81(7) Å3) is based upon electroneutral [Cu(HSeO3)2] sheets formed by corner sharing between the [CuO4] squares and (HSeO3) groups that are parallel to the (100) plane. Each (SeO2OH)– group forms the Oh1...O2 hydrogen bond to an adjacent hydroselenite group to constitute a [(SeO2OH)2]2– dimer that provides additional stabilization of the copper diselenite sheet. The [Cu(HSeO3)2] sheets alternate with the sheets consisting of zigzag–Na–Cl–Na–Cl–chains formed by Cl atoms and disordered Na sites. The chains are parallel to the c axis. The linkage between the alternating electroneutral [Cu(HSeO3)2] and [NaCl] sheets is provided by the Cu–Cl and Na–O bonds. The coordination of Na is fivefold and consists of three O and two Cl atoms. [NaCl][Cu(HSeO3)2] is a new member of the group of compounds based upon the M(HSeO3)2 layers (M2+ = Cu, Co, Cd). The prototype structure for this group is [Cu(HSeO3)2] that does not have any chemical species separating the copper hydroselenite layers. In other compounds, the interlayer space between the [Cu(HSeO3)2]0 layers is occupied by structural units of different complexity. [NaCl][Cu(HSeO3)2] can be considered as [Cu(HSeO3)2] intercalated with the NaCl layers consisting of one-dimensional–Na–Cl–Na–Cl–chains.

Catalytic Conversion of Biomass Pyrolysis Vapours over Sodium‐Based Catalyst: A Study on the State of Sodium on the Catalyst

AbstractIn situ upgrading of biomass pyrolysis vapours over Na2CO3/γ‐Al2O3 catalysts was studied in a laboratory‐scale fixed‐bed reactor at 500 °C. Catalytic oil exhibits a significant improvement over its non‐catalytic counterpart, such as lower oxygen content (12.3 wt % compared to 42.1 wt %), higher energy density (37.0 compared to 19.0 MJ kg−1) and lower acidity. A study using thermogravimetry–mass spectrometry analysis and 23Na and 1H magic‐angle spinning NMR techniques has revealed the formation of a new sodium species in the catalyst, which is responsible for the high catalytic activity. This species is proposed to be formed by the coordination of Na+ ions and the hydroxyl groups on the surface of γ‐Al2O3. Regeneration of the catalyst was performed in air at 600 °C and the regenerated material displays lower activity towards deoxygenation than the fresh catalyst. This deactivation is likely attributed to the change in the active sodium species during regeneration.

Temperature-dependent phase transition and desorption free energy of sodium dodecyl sulfate at the water/vapor interface: approaches from molecular dynamics simulations.

Adsorption of surfactants at the water/vapor interface depends upon their chemical potential at the interface, which is generally temperature-dependent. Molecular dynamics simulations have been performed to reveal temperature influences on the microstructure of sodium dodecyl sulfate (SDS) molecule adsorption layer. At room temperature, SDS molecules aggregate at the interface, being in a liquid-expanded phase, whereas they tend to spread out and probably transit to a gaseous phase as the temperature increases to above 318 K. This phase transition has been confirmed by the temperature-dependent changes in two-dimensional array, tilt angles, and immersion depths to the aqueous phase of SDS molecules. The aggregation of SDS molecules accompanies with larger immersion depths, more coordination of Na(+) ions, and less coordination of water. Desorption free energy profiles show that higher desorption free energy appears for SDS molecules at the aggregate state at low temperatures, but no energy barrier is observed. The shapes of desorption free energy profiles depend upon the distribution of SDS at the interface, which, in turn, is related to the phase state of SDS. Our study sheds light on the development of adsorption thermodynamics and kinetics theories.

Multiple adsorption of CO on Na-exchanged Y faujasite: a DFT investigation

Carbon monoxide is involved in many chemical and industrial processes, and its removal is of great importance to reduce detrimental environmental and climate impacts. CO is also useful to characterise the metal exchanged in zeolites. Multiple adsorption of CO in zeolite faujasites containing Na cations is investigated through quantum chemical calculations. Density functional theory (DFT) calculations were chosen to investigate the structure of sodium-exchanged cations at site II in Y faujasite and to investigate multiple CO adsorption with Na to predict the structure and the infrared CO stretching signal. DFT analysis using B3LYP, B3LYP-D and M062X showed significant differences in the coordination of Na at site II when three CO are adsorbed. From these investigations, polyadsorption of CO in NaY could lead to threefold-coordinated Na at site II in six-membered rings (6MRs) containing two Al and twofold-coordinated Na at site II in 6MRs containing one Al. These results suggest that introduction of non-bonding interactions is necessary to study polyadsorption of CO in NaY.

Degradation of 2,5-Dihydroxy-1,4-benzoquinone by Hydrogen Peroxide under Moderately Alkaline Conditions Resembling Pulp Bleaching: A Combined Kinetic and Computational Study

2,5-Dihydroxy-1,4-benzoquinone (DHBQ) is one of the key chromophores occurring in all types of aged cellulosics. This study investigates the mechanism of H2O2 degradation of DHBQ under conditions relevant to pulp bleaching (3.0% H2O2, NaOH, pH 10), to obtain insights useful for improved pulp processing. DHBQ is degraded quantitatively into malonic acid with an activation energy (E(a)) of 16.1 kcal/mol and activation entropy (Δ(‡)S°) of ~28 cal/mol·K. Higher concentrations of sodium cations increase the reaction rate. Theoretical computations indicate the formation of an intermediate I(O) having an O-O bridge between C-2 and C-5 of the 1,4-cyclohexadione structure. I(O) undergoes O-O homolysis to form a biradical Bt, which is fragmented into malonate anions. The calculated E(a) (17.8 kcal/mol) agrees well with the experimental one. Coordination of Na(+) to I(O) and Bt decreases their energies and enhances the O-O homolysis rate, which is consistent with the acceleration by sodium cation and the negative Δ(‡)S°. The homolysis of I(O) is much favored over that of the neutral counterpart, with the unpaired electrons of Bt being stabilized by the geminal anionic oxygen. This difference in the stability of the intermediates translates into significant variations in the reaction rate and the product distribution between pH 10 and neutral/acidic conditions.

Conformations and hydration structure of hydrophobic polyelectrolyte atactic poly(ethacrylic acid) in dilute aqueous solution as a function of neutralisation

Chain conformations, counter-ion structure, intermolecular hydrogen bonding structure and dynamics of atactic polyethacrylic acid (PEA) in salt-free aqueous dilute solution at 25°C are studied via molecular dynamics (MD) simulations with explicit-solvent and explicit-ion description for the first time. The intermolecular structure was analysed by the radial distribution functions (RDF) for specific atom types between PEA chain, water molecules and Na+ counter-ions, as well as by the hydration near the PEA chain in the solvated system. An increase in f provides an increase in 〈Rg〉 of the chain, consistent with the existence of the compact form of PEA. The simulations show expansion for radius-of-gyration with increase in f, as expected for flexible polyelectrolytes under salt-free condition. The extent of intermolecular hydrogen bonds (H-bonds) between PEA and water is enhanced by increase in f. Chains having a higher counter-ion density show higher values of 〈Rg〉, influenced by intermolecular interactions between PEA and water. The coordination of Na+ counter ions and water molecules to carboxyl oxygens of polyacrylic acid (PAA) increases with charge density of the chain. A comparison of the structure aspects is made with PAA and PMA polyelectrolytes in dilute solution, which brings out the hydrophobic effect of the ethyl side-groups in PEA on conformational properties and counter-ion condensation structure.

Metal-mediated self-assembly of tetrapyridyl porphyrins by Na+ ions

In the presence of the sodium salt of a bulky anion, which allows the solubility of Na(+) in low polarity solvents, various tetra(4-pyridyl)porphyrin derivatives can spontaneously self-assemble from CH(2)Cl(2) into supramolecular nanostructures exhibiting a long-range order, through the coordination of Na(+) ions by the pyridyl moieties at the macrocycle periphery.

A Structural Determinant for the Control of PIP2 Sensitivity in G Protein-gated Inward Rectifier K+ Channels

Inward rectifier K+ (Kir) channels are activated by phosphatidylinositol-(4,5)-bisphosphate (PIP2), but G protein-gated Kir (KG) channels further require either G protein βγ subunits (Gβγ) or intracellular Na+ for their activation. To reveal the mechanism(s) underlying this regulation, we compared the crystal structures of the cytoplasmic domain of KG channel subunit Kir3.2 obtained in the presence and the absence of Na+. The Na+-free Kir3.2, but not the Na+-plus Kir3.2, possessed an ionic bond connecting the N terminus and the CD loop of the C terminus. Functional analyses revealed that the ionic bond between His-69 on the N terminus and Asp-228 on the CD loop, which are known to be critically involved in Gβγ- and Na+-dependent activation, lowered PIP2 sensitivity. The conservation of these residues within the KG channel family indicates that the ionic bond is a character that maintains the channels in a closed state by controlling the PIP2 sensitivity.

NMR resonance assignments of thrombin reveal the conformational and dynamic effects of ligation

The serine protease thrombin is generated from its zymogen prothrombin at the end of the coagulation cascade. Thrombin functions as the effector enzyme of blood clotting by cleaving several procoagulant targets, but also plays a key role in attenuating the hemostatic response by activating protein C. These activities all depend on the engagement of exosites on thrombin, either through direct interaction with a substrate, as with fibrinogen, or by binding to cofactors such as thrombomodulin. How thrombin specificity is controlled is of central importance to understanding normal hemostasis and how dysregulation causes bleeding or thrombosis. The binding of ligands to thrombin via exosite I and the coordination of Na(+) have been associated with changes in thrombin conformation and activity. This phenomenon has become known as thrombin allostery, although direct evidence of conformational change, identification of the regions involved, and the functional consequences remain unclear. Here we investigate the conformational and dynamic effects of thrombin ligation at the active site, exosite I and the Na(+)-binding site in solution, using modern multidimensional NMR techniques. We obtained full resonance assignments for thrombin in seven differently liganded states, including fully unliganded apo thrombin, and have created a detailed map of residues that change environment, conformation, or dynamic state in response to each relevant single or multiple ligation event. These studies reveal that apo thrombin exists in a highly dynamic zymogen-like state, and relies on ligation to achieve a fully active conformation. Conformational plasticity confers upon thrombin the ability to be at once selective and promiscuous.

Formation of nanoporous and non-porous organic–inorganic hybrid materials incorporating α-Keggin phosphotungstate anion: X-ray crystal structure of a 3D polymeric complex [{Na 6(C 9H 5O 6) 3(H 2O) 15}{PW 12O 40}] ∞ with a ‘Ball-in-Bowl’ type molecular structure

Two different synthetic approaches to prepare inclusion complexes of Keggin anion [PW 12O 40] 3− and [Cu 3(BTC) 2(H 2O) 3] n (also known as HKUST-1) have resulted in the formation of two different materials [Cu 3(C 9H 3O 6) 2(H 2O) 3] 2Na 3PW 12O 40· nH 2O ( 1) and [Na 6(BTC-H 2) 3(H 2O) 15][PW 12O 40] ( 2). Compound 1 is a thermally stable, nanoporous material with a type 1 adsorption isotherm. It contains the well-known MOF material [Cu 3(BTC) 2(H 2O) 3] n with half of its pores occupied by the guest Keggin anion. The second product 2 is a crystalline, 3D coordination polymer with a composition of [Na 6(BTC-H 2) 3(H 2O) 15][PW 12O 40] (where BTC-H 3 stands for 1,3,5-benzene-tricarboxylic acid) and is a non-porous, highly water soluble and thermally unstable material. The compound 1 was prepared hydrothermally using precursors of HKUST-1 and Na 3[(PW 12O 40)] whereas 2 was obtained at room temperature from aqueous solutions containing [Cu 3(BTC) 2(H 2O) 3] n and Na 3[(PW 12O 40)] salts. The molecular structure of 2 is unique and features two distinct elements: an anionic Keggin ion [PW 12O 40] 3− and a “bowl type” hexameric [Na 6(C 9H 5O 6) 3(H 2O) 15] 3+ macrocation which is formed by coordination of Na + ions by (BTC-H 2) − anions and water molecules. The macrocation extends in three dimensions due to Y type (BTC-H 2) − to form a porous MOF offering triangular voids. In this framework the globular Keggin ions support themselves above these voids by coordinating to Na + ions and render it completely nonporous. The complex has an unusual structure in the sense that the polyoxoanion is coordinated to [Na 6(C 9H 5O 6) 3(H 2O) 15] 3+ ions by using the three terminal oxygen atoms in a single M 3O 13 triplet, when each one of them is also bridging between two Na + ions. In the crystal structure the POM anion is encapsulated by six octahedrally disposed (BTC-H 2) − moieties. H-bonding interactions among water molecules produce supramolecular water hexamers and dimers.

Structural Basis for Ca2+-Dependent Formation of ALG-2/Alix Peptide Complex: Ca2+/EF3-Driven Arginine Switch Mechanism

ALG-2 belongs to the penta-EF-hand (PEF) protein family and interacts with various intracellular proteins, such as Alix and TSG101, that are involved in endosomal sorting and HIV budding. Through X-ray crystallography, we solved the structures of Ca(2+)-free and -bound forms of N-terminally truncated human ALG-2 (des3-20ALG-2), Zn(2+)-bound form of full-length ALG-2, and the structure of the complex between des3-23ALG-2 and the peptide corresponding to Alix799-814 in Zn(2+)-bound form. Binding of Ca(2+) to EF3 enables the side chain of Arg125, present in the loop connecting EF3 and EF4, to move enough to make a primary hydrophobic pocket accessible to the critical PPYP motif, which partially overlaps with the GPP motif for the binding of Cep55 (centrosome protein 55 kDa). Based on these results, together with the results of in vitro binding assay with mutant ALG-2 and Alix proteins, we propose a Ca(2+)/EF3-driven arginine switch mechanism for ALG-2 binding to Alix.