Preferred Coordination Research Articles

Azobenzene as an Effective Ligand in Europium Chemistry—A Synthetic and Theoretical Study

The preparation and characterization of two novel europium–azobenzene complexes that demonstrate the effectiveness of this ligand for stabilizing reactive, redox-active metals are reported. With the family of rare earth metals receiving attention due to their potential as catalysts, critical components in electronic devices, and, more recently, in biomedical applications, a detailed understanding of factors contributing to their coordination chemistry is of great importance for customizing their stability and reactivity. This study introduces azobenzene as an effective nonprotic ligand system that provides novel insights into rare earth metal coordination preferences, including factors contributing to the coordinative saturation of the large, divalent europium centers. The two compounds demonstrate the impact of the solvent donors (tetrahydrofuran (THF) and dimethoxyethane (DME)) on the overall coordination chemistry of the target compounds. Apart from the side-on coordination of the doubly-reduced azobenzene and the anticipated N-N bond elongation due to decreased bond order, the two compounds demonstrate the propensity of the europium centers towards limited metal-π interactions. The target compounds are available by direct metallation in a straightforward manner with good yields and purity. The compounds demonstrate the utility of the azobenzene ligands, which may function as singly- or doubly-reduced entities in conjunction with redox-active metals. An initial exploration into the computational modeling of these and similar complexes for subsequent property prediction and optimization is performed through a methodological survey of structure reproduction using density functional theory.

Exploring divalent metal ion coordination. Unraveling binding modes in Staphylococcus aureus MntH fragments

Metal ion coordination is crucial in bacterial metabolism, while divalent metal ions serve as essential cofactors for various enzymes involved in cellular processes. Therefore, bacteria have developed sophisticated regulatory mechanisms to maintain metal homeostasis. These involve protein interactions for metal ion uptake, efflux, intracellular transport, and storage. Staphylococcus aureus, a member of the commensal flora, colonizes the anterior nares and skin harmlessly but can cause severe illness. MntH transporter is responsible for acquiring divalent metal ions necessary for metabolic functions and virulence. It is a 450-amino-acid protein analogous to Nramp1 (Natural Resistance-Associated Macrophage Protein 1) in mammals. Herein, the coordination modes of copper(II), iron(II), and zinc(II) ions with select fragments of the MntH were established employing potentiometry, mass spectrometry, and spectroscopic methods. Four model peptides, MNNKRHSTNE–NH2, Ac-KFDHRSS–NH2, Ac-IMPHNLYLHSSI–NH2, and Ac-YSRHNNEE–NH2, were chosen for their metal-binding capabilities and examined to determine their coordination properties and preferences. Our findings suggest that under physiological pH conditions, the N-terminal fragment of MntH demonstrates the highest thermodynamic stability with copper(II) and iron(II) ions. Furthermore, a comparison with other peptides from the S. aureus FeoB transporter indicates different binding affinities.

Solvation structure and thermodynamics for Ln(III), (Ln = Pr, Nd, Tb, and Dy) complexes in phosphonium-based ionic liquids evaluated by Raman spectroscopy and DFT calculation

The coordination states of trivalent praseodymium, neodymium, terbium, and dysprosium complexes in triethyl-n-octylphosphonium bis(trifluoromethylsulfonyl)amide ([P2228][TFSA]) ionic liquid were examined using Raman spectroscopy. In [P2228][TFSA], the concentration dependence of lanthanide (Ln) ions on the Raman spectrum was investigated in the range of 0.24–0.48 mol kg−1 of Ln(III), (Ln = Pr, Nd, Tb, and Dy) in [P2228][TFSA]. Based on classical analysis, solvation numbers n of Ln(III) (Ln = Pr, Nd, Tb, and Dy) in [P2228][TFSA] were determined as 4.80 ± 0.04, 5.08 ± 0.03, 5.15 ± 0.04, and 4.92 ± 0.03, respectively, at 373 K.Based on the temperature dependence of the Raman spectrum measured at temperatures between 298 and 398 K, thermodynamic parameters with ΔisoG, ΔisoH, and ΔisoS for the isomerism of [TFSA]− from the trans- to the cis-coordinated isomer in the bulk and first solvation sphere of the centered Ln3+ (Ln = Pr, Nd, Tb, and Dy) cation in [P2228][TFSA] were evaluated in this study. As indicated by the positive value of ΔisoH(bulk) = 6.86 kJ mol−1, the trans-[TFSA]− was found to be the dominant contributor to enthalpy. In [P2228][TFSA], the value of TΔisoS(bulk) = 7.92 kJ mol−1 was slightly larger than that of ΔisoH(bulk), indicating that cis-[TFSA]− was entropy controlled. Conversely, in the first solvation sphere of the Ln3+ cation, ΔisoH(Ln) became significantly negative, indicating stabilization of cis-[TFSA]− isomers via enthalpic contributions. This result clearly indicates that the cis-[TFSA]− conformer bound to Ln3+ cation is the preferred coordination state of [Ln(III)(cis–TFSA)5]2− in [P2228][TFSA], because ΔisoH(Ln) contributes to a significant decrease in ΔisoG(Ln).Furthermore, DFT calculations using the Amsterdam Density Functional package were used to investigate the optimized geometries and binding energies of [Ln(III)(cis-TFSA)5]2−, (Ln = Pr, Nd, Tb, and Dy) clusters. The bonding energy, ΔEb, was calculated as ΔEb = Etot(cluster) − Etot(Ln3+) − nEtot([TFSA]−), and ΔEb ([Ln(III)(cis-TFSA)5]2−), (Ln = Pr, Nd, Tb, and Dy) were calculated as −4349.2 ± 7.2, −4354.6 ± 7.6, −4278.6 ± 7.2, and −4296.4 ± 7.8 kJ mol−1, respectively. The thermodynamic properties were consistent with the average atomic charges and bond distances of these clusters. Additionally, the highest occupied molecular orbital and lowest unoccupied molecular orbital estimated from DFT methods were consistent with the coordination states of [Ln(III)(cis-TFSA)5]2−, (Ln = Pr, Nd, Tb, and Dy) analyzed by Raman spectroscopy.

Three-dimensional alkaline earth metal-organic framework poly[[μ-aqua-aqua-bis-(μ3-carba-moyl-cyano-nitro-somethanido)barium] monohydrate] and its thermal decomposition.

In the structure of the title salt, {[Ba(μ3-C3H2N3O2)2(μ-H2O)(H2O)]·H2O} n , the barium ion and all three oxygen atoms of the water mol-ecules reside on a mirror plane. The hydrogen atoms of the bridging water and the solvate water mol-ecules are arranged across a mirror plane whereas all atoms of the monodentate aqua ligand are situated on this mirror plane. The distorted ninefold coord-ination of the Ba ions is completed with four nitroso-, two carbonyl- and three aqua-O atoms at the distances of 2.763 (3)-2.961 (4) Å and it is best described as tricapped trigonal prism. The three-dimensional framework structure is formed by face-sharing of the trigonal prisms, via μ-nitroso- and μ-aqua-O atoms, and also by the bridging coordination of the anions via carbonyl-O atoms occupying two out of the three cap positions. The solvate water mol-ecules populate the crystal channels and facilitate a set of four directional hydrogen bonds. The principal Ba-carbamoyl-cyano-nitro-somethanido linkage reveals a rare example of the inherently polar binodal six- and three-coordinated bipartite topology (three-letter notation sit). It suggests that small resonance-stabilized cyano-nitroso anions can be utilized as bridging ligands for the supra-molecular synthesis of MOF solids. Such an outcome may be anti-cipated for a broader range of hard Lewis acidic alkaline earth metal ions, which perfectly match the coordination preferences of highly nucleophilic nitroso-O atoms. Thermal analysis reveals two-stage dehydration of the title compound (383 and 473 K) followed by decomposition with release of CO2, HCN and H2O at 558 K.

Female Rat Behavior Effects from Low Levels of Hexavalent Chromium (Cr[VI]) in Drinking Water Evaluated with a Toxic Aging Coin Approach

We are facing a critical aging crisis, with geriatric populations (65+) growing to unprecedented proportions and ~4 million people (a 6.5-fold increase) expected to become centenarians by 2050. This is compounded by environmental pollution, which affects individuals of all ages and contributes to age-related diseases. As we have a limited understanding of how environmental pollutants affect older populations distinctly from younger populations, these longer-lived geriatric populations present a key knowledge gap. To address this knowledge gap, we employ a “Toxic Aging Coin” approach: heads consider how age impacts chemical toxicity, and tails consider how chemicals act as gerontogens—or how they accelerate biological aging. We employed this approach to investigate hexavalent chromium (Cr[VI]) impacts on female rats exposed to 0.05 or 0.1 mg Cr(VI)/L in drinking water for 90 days; these are the maximum contaminant levels (i.e., the highest levels permitted) from the World Health Organization and U.S. Environmental Protection Agency, respectively. During exposure, rats performed a battery of behavior assays to assess grip strength, locomotor coordination, anxiety, spatial memory, sociability, and social novelty preference. We observed age differences in Cr(VI) neurotoxicity, with grip strength, locomotor function, and spatial memory in middle-aged females being particularly affected. We further compared these results in females to results in males, noting many sex differences, especially in middle-aged rats. These data emphasize the need to consider age and sex as variables in toxicology and to revisit drinking water regulations for Cr(VI).

Computational 3D Models of Fe2+/3+-Aβ1-42 Complexes Associated with Alzheimer's Disease.

The interaction between iron and amyloid-beta (Aβ) peptides has received significant attention in Alzheimer's disease (AD) research due to its potential implications in developing this pathology. However, the coordination preferences of iron and Aβ1-42 have not been thoroughly investigated or remain unknown. This study employs a computational protocol that combines homology modeling techniques with quantum mechanics (DTF-xTB) calculations to build and evaluate several 3D models of Fe2+/3+-Aβ1-42. Our results reveal well-defined complexes for both the metal and peptide moieties, and we discuss the molecular interactions stabilizing these complexes by elucidating the coordinating environments and binding preferences. These proposed models offer valuable insights into the role of iron in Alzheimer's disease (AD) pathology.

Informatics-Based Learning of Oxygen Vacancy Ordering Principles in Oxygen-Deficient Perovskites.

Ordered oxygen vacancies (OOVs) in perovskites can exhibit long-range order and may be used to direct materials properties through modifications in electronic structures and broken symmetries. Based on the various vacancy patterns observed in previously known compounds, we explore the ordering principles of oxygen-deficient perovskite oxides with ABO2.5 stoichiometry to identify other OOV variants. We performed first-principles calculations to assess the OOV stability on a data set of 50 OOV structures generated from our bespoke algorithm. The algorithm employs uniform planar vacancy patterns on (111) pseudocubic perovskite layers and the approach proves effective for generating stable OOV patterns with minimal computational loads. We find as expected that the major factors determining the stability of OOV structures include coordination preferences of transition metals and elastic penalties resulting from the assemblies of polyhedra. Cooperative rotational modes of polyhedra within the OOV structures reduce elastic instabilities by optimizing the bond valence of A- and B cations. This finding explains the observed formation of vacancy channels along low-index crystallographic directions in prototypical OOV phases. The identified ordering principles enable us to devise other stable vacancy patterns with longer periodicity for targeted property design in yet to be synthesized compounds.

Ion association behaviors in the initial stage of calcium carbonate formation: An ab initio study

In this work, we performed static density functional theory calculations and ab initio metadynamics simulations to systematically investigate the association mechanisms and dynamic structures of four kinds of ion pairs that could be formed before the nucleation of CaCO3. For Ca2+–HCO3− and Ca2+–CO32− pairs, the arrangement of ligands around Ca2+ evolves between the six-coordinated octahedral structure and the seven-coordinated pentagonal bipyramidal structure. The formation of ion pairs follows an associative ligand substitution mechanism. Compared with HCO3−, CO32− exhibits a stronger affinity to Ca2+, leading to the formation of a more stable precursor phase in the prenucleation stage, which promotes the subsequent CaCO3 nucleation. In alkaline environments, excessive OH− ions decrease the coordination preference of Ca2+. In this case, the formation of Ca(OH)+–CO32− and Ca(OH)2–CO32− pairs favors the dissociative ligand substitution mechanism. The inhibiting effects of OH− ion on the CaCO3 association can be interpreted from two aspects, i.e., (1) OH− neutralizes positive charges on Ca2+, decreases the electrostatic interactions between Ca2+ and CO32−, and thus hinders the formation of the CaCO3 monomer, and (2) OH− decreases the capacity of Ca2+ for accommodating O, making it easier to separate Ca2+ and CO32− ions. Our findings on the ion association behaviors in the initial stage of CaCO3 formation not only help scientists evaluate the impact of ocean acidification on biomineralization but also provide theoretical support for the discovery and development of more effective approaches to manage undesirable scaling issues.

여성 패션 가방 원단의 텍스쳐(Texture) 디자인에 따른 소비자의 구매 의사 결정에 관한 연구

With the rapid development of modern society, the fabric of bag products is constantly updated, and the purchasing behavior of consumers is constantly changing. This study investigated the effect of the texture design of women's fashion bag fabric on consumers' purchasing decisions by applying the value-attitude-action(VAB) model to adult women aged 18 to 60 in China. According to the analysis results, when looking at consumers' preference for the fabric texture of women's fashion bags, they preferred artificial leather harmonies in homogeneous coordination types, smooth PVC and natural leather in heterogeneous coordination types, and they preferred glitter and spangle textures most in homogeneous coordination. Looking at consumers' preferences for women's bag texture types by age group, those aged 18 to 29 preferred homogeneous coordination of chuede and natural leather, heterogeneous contrast coordination of coarse and smooth natural leather, and those aged 30 to 39 preferred coarse Gretel and smooth natural leather, and those aged 40 to 49 and 50 to 59 preferred rough texture and rough natural leather. According to the analysis of the effect of the texture design of women's fashion bag fabric on consumers' purchasing decisions, it was found that all of the texture designs of women's fashion bag fabric had a significant influence on consumers' purchasing decisions. Among them, heterogeneous harmonious coordination has the greatest impact on consumer value, homogeneous harmonious coordination has the greatest impact on consumer attitudes, and homogeneous contrast coordination has the greatest impact on consumer behavior.

Metal (Mn2+, Co2+ and Cd2+) ions induced differentiation in mixed-ligands MOFs constructed from H3btb and H2bdc: Highly porous Structures, new topology nets and two-step gate-opening behaviors

Mix-ligands strategy is highly efficient for the rational construction of MOFs with particular structure motifs and high porosity, yet challenging and requiring matching in hierarchical coordination assembly and synergetic crystallization. The solvothermal reactions of 1,3,5-tris[4-carboxyphenyl]benzene (H3btb) and 1,4-benzenedicarboxylic acid (H2bdc) with different 3d metal ions, generated highly porous mixed-ligands MOFs of [(CH3)2NH2]2[Mn3(btb)2 (bdc)]·12DMF·3MeOH (Mn-btb-bdc) having anionic 3D frameworks constructed from linear [Mn3(COO)8] nodes, [Co4(btb)2(bdc)(H2O)3]·15DMF·7H2O (Co-btb-bdc) processing neutral frameworks constituted by linear [Co3(COO)6(H2O)4] and paddle-wheel [Co2(COO)4(H2O)2] nodes, as well as one single-ligand MOFs of [(CH3)2NH2][Cd(btb)(H2O)]·8DMF (Cd-btb-2fold) exhibiting 2-fold interpenetrated ths net frameworks due to the unsuccessful introduce of the coexisted bdc ligand. Two new topology net of 2,3,8-connected net with point symbol of (42·6)2(44·66·812·105·12)(6) and 2,3,4,6-connected net with Point Symbol of (4·82)4(42·811·102)2(84·122)(82) were found for Mn-btb-bdc and Co-btb-bdc. All these three MOFs are highly porous with void fractions of 60.9%, 52.2% and 61.4%, stemming from 3D-penetrated, 3D-penetrated and 1D channels, respectively. Such structural differentiations are attributed to the diversified electronic structure and coordination preference of different 3d metal ions, as well as the solvent template and temperature effects. Two-steps gate-opening behaviour in gas sorption isotherms was found in the flexible Mn-btb-bdc MOFs.

Public perceptions on solar geoengineering from focus groups in 22 countries

Solar geoengineering maintains a vocal presence as a stop-gap measure in assessments of climate and sustainability action. In this paper, we map prospective benefits and risks, and corresponding governance approaches, regarding three major proposals for solar geoengineering (stratospheric aerosol injection, marine cloud brightening, and a space-based sunshield). We do so by engaging with 44 focus groups conducted in 22 countries split between the global North and South. We compare results against previous research on the public perceptions of solar geoengineering as well as wider activities in assessment, innovation, and decision-making. We find that global South groups exhibit greater hope but an arguably richer range of concerns for solar geoengineering, in the context of observable inequities in climate action and potential geopolitical conflict. Meanwhile, a strong, global preference for multilateral coordination and public engagement from the conduct of research onwards is offset by skepticism of effective multilateralism and public discourse.

Biological Activity of Complexes Involving Nitro-Containing Ligands and Crystallographic-Theoretical Description of 3,5-DNB Complexes.

Drug resistance in infectious diseases developed by bacteria and fungi is an important issue since it is necessary to further develop novel compounds with biological activity that counteract this problem. In addition, new pharmaceutical compounds with lower secondary effects to treat cancer are needed. Coordination compounds appear to be accessible and promising alternatives aiming to overcome these problems. In this review, we summarize the recent literature on coordination compounds based on nitrobenzoic acid (NBA) as a ligand, its derivatives, and other nitro-containing ligands, which are widely employed owing to their versatility. Additionally, an analysis of crystallographic data is presented, unraveling the coordination preferences and the most effective crystallization methods to grow crystals of good quality. This underscores the significance of elucidating crystalline structures and utilizing computational calculations to deepen the comprehension of the electronic properties of coordination complexes.

Critical Role of Configurational Disorder in Stabilizing Chemically Unfavorable Coordination in Complex Compounds.

The crystal structure of a material is essentially determined by the nature of its chemical bonding. Consequently, the atomic coordination intimately correlates with the degree of ionicity or covalency of the material. Based on this principle, materials with similar chemical compositions can be successfully categorized into different coordination groups. However, counterexamples have recently emerged in complex ternary compounds. For instance, covalent IB-IIIA-VIA2 compounds, such as AgInS2, prefer a tetrahedrally coordinated structure (TCS), while ionic IA-VA-VIA2 compounds, such as NaBiS2, would favor an octahedrally coordinated structure (OCS). One naturally expects that IB-VA-VIA2 compounds with intermediate ionicity or covalency, such as AgBiS2, should then have a mix-coordinated structure (MCS) consisting of covalent AgS4 tetrahedra and ionic BiS6 octahedra. Surprisingly, only the experimental presence of the OCS was observed for AgBiS2. To resolve this puzzle, we perform first-principles studies of the phase stabilities of ternary compounds at finite temperatures. We find that AgBiS2 indeed prefers MCS at the ground state, in agreement with the typical expectation, but under experimental synthesis conditions, disordered OCS becomes energetically more favorable because of its low mixing energy and high configurational entropy. Our work elucidates the critical role of configurational disorder in stabilizing chemically unfavorable coordination, providing a rigorous rationale for the anomalous coordination preference in IB-VA-VIA2 compounds.

Structural features and thermal expansion of zinc aluminosilicate quartz solid solutions

Zinc aluminosilicate (ZAS) glasses were synthesized along the peraluminous join (SiO2 contents between 95 and 50 mol%) by melt-quenching or sol-gel spray-drying and subjected to controlled heat treatments to obtain ZAS quartz solid solutions (Zn-Qz-ss). The precipitation of Zn-Qz-ss is non-stoichiometric with respect to their parent glass and the crystals undergo a compositional evolution during annealing, even in absence of secondary crystalline phases. Near-hexagonal high-quartz-like crystals with negative thermal expansion (down to −3 × 10−6 K−1) can be obtained in the range 50–80 mol% SiO2, while SiO2-richer crystals exhibit positive thermal expansion at room temperature (up to 29 × 10−6 K−1). Zn2+ ions occupy two distinct positions within the structural channels of quartz, with a strong preference for 4-fold coordination. In analogy to lithium aluminosilicate quartz solid solutions (Li-Qz-ss), the low-to-high phase transition exhibits a linear correlation to the composition of the crystals.

Nebulizers.

Nebulizers generate aerosols from liquid-based solutions and suspensions. Nebulizers are particularly well suited to delivering larger doses of medication than is practical with inhalers and are used with a broad range of liquid formulations. When the same drug is available in liquid or inhaler form, nebulizers are applicable for use with patients who will not or cannot reliably use a pressurized metered-dosed inhaler (pMDI) or dry powder inhaler (DPI) due to poor lung function, hand-breath coordination, cognitive abilities (e.g., infants, elderly) or device preference. In a nebulizer, liquid medication is placed in a reservoir and fed to an aerosol generator to produce the droplets. A series of tubes and channels direct the aerosol to the patient via an interface such as mouthpiece, mask, tent, nasal prongs or artificial airway. All nebulizers contain these basic parts, although the technology and design used can vary widely and can result in significant difference in ergonomics, directions for use, and performance. While many types of nebulizers have been described, the three categories of modern clinical nebulizers include: (1) pneumatic jet nebulizers (JN); (2) ultrasonic nebulizers (USN); and (3) vibrating mesh nebulizers (VMN). Nebulizers are also described in terms of their reservoir size. Small volume nebulizers (SVNs), most commonly used for medical aerosol therapy, can hold 5 to 20 mL of medication and may be jet, ultrasonic, or mesh nebulizers. Large volume nebulizers, typically jet or ultrasonic nebulizers, hold up to 200 mL and may be used for either bland aerosol therapy or continuous drug administration.

Navigating through the coordination preferences of heavy alkaline earth metals: Laying the foundations for 223Ra- and 131/135mBa-based targeted alpha therapy and theranostics of cancer

The clinical success of [223Ra]RaCl2 (Xofigo®) for the palliative treatment of bone metastases in patients with prostate cancer has highlighted the therapeutic potential of α-particle emission. Expanding the applicability of radium-223 in Targeted Alpha Therapy of non-osseous tumors is followed up with significant interest, as it holds the potential to unveil novel treatment options in the comprehensive management of cancer. Moreover, the use of barium radionuclides, like barium-131 and -135m, is still unfamiliar in nuclear medicine applications, although they can be considered as radium-223 surrogates for imaging purposes. Enabling these applications requires the establishment of chelators able to form stable complexes with radium and barium radionuclides. Until now, only a limited number of ligands have been suggested and these molecules have been primarily inspired by existing structures known for their ability to complex large metal cations. However, a systematic inspection of chelators specifically tailored to Ra2+ and Ba2+ has yet to be conducted.This work delves into a comprehensive investigation of a series of small organic ligands, aiming to unveil the coordination preferences of both radium-223 and barium-131/135m. Electronic binding energies of both metal cations to each ligand were theoretically computed via Density Functional Theory calculations (COSMO-ZORA-PBE-D3/TZ2P), while thermodynamic stability constants were experimentally determined for Ba2+-ligand complexes by potentiometry, NMR and UV–Vis spectroscopies. The outcomes revealed malonate, 2-hydroxypyridine 1-oxide and picolinate as the most favorable building blocks to design multidentate chelators. These findings serve as foundation guidelines, propelling the development of cutting-edge radium-223- and barium-131/135m-based radiopharmaceuticals for Targeted Alpha Therapy and theranostics of cancer.

Metal Substitutions (M = Al, Ga, In; Sn, Ge; and Mn, Fe, Co) in ZnS: Sphalerite versus Wurtzite Formation.

A series of Zn1-xMxS polycrystalline samples were synthesized via a solid-state reaction in closed vessels to examine the solubility of foreign M cations within the wurtzite ZnS structure, employing quenching or slow cooling processes to favor specific polymorphs. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses revealed diverse structural behaviors across different cations. Group 13 elements (Al and Ga) formed solid solutions with a wurtzite structure, while In showed complex layer stacking defects. For 3d magnetic cations (Mn, Fe, and Co), a broad solubility range in the hexagonal structure was noted for Mn, whereas Fe and Co more readily formed cubic structures, with solubilities similar to Mn in the sphalerite form. Despite structural differences, magnetic susceptibilities and spin freezing temperatures for Fe and Co were comparable. Group 14 elements showed varied behaviors: Sn was insoluble in ZnS, as attested by unchanged unit cell parameters and surface crystallite Sn, whereas Ge only formed in the cubic phase with a solubility limit of x ≈ 0.2. The study discusses these variations in solubility and structure in terms of oxidation states, ionic-covalent radius, and coordination preferences in sulfides.

Diverse crystalline protein scaffolds through metal-dependent polymorphism.

As protein crystals are increasingly finding diverse applications as scaffolds, controlled crystal polymorphism presents a facile strategy to form crystalline assemblies with controllable porosity with minimal to no protein engineering. Polymorphs of consensus tetratricopeptide repeat proteins with varying porosity were obtained through co-crystallization with metal salts, exploiting the innate metal ion geometric requirements. A single structurally exposed negative amino acid cluster was responsible for metal coordination, despite the abundance of negatively charged residues. Density functional theory calculations showed that while most of the crystals were the most thermodynamically stable assemblies, some were kinetically trapped states. Thus, crystalline porosity diversity is achieved and controlled with metal coordination, opening a new scope in the application of proteins as biocompatible protein-metal-organic frameworks (POFs). In addition, metal-dependent polymorphic crystals allow direct comparison of metal coordination preferences.

Differential interactions of essential and toxic metal ions with biologically relevant phosphatidic acid and phosphatidylserine membranes.

Metal pollutants are a growing concern due to increased use in mining and other industrial processes. Moreover, the use of metals in daily life is becoming increasingly prevalent. Metals such as manganese (Mn), cobalt (Co), and nickel (Ni) are toxic in high amounts whereas lead (Pb) and cadmium (Cd) are acutely toxic at low µM concentrations. These metals are associated with system dysfunction in humans including cancer, neurodegenerative diseases, Alzheimer's disease, Parkinson's disease, and other cellular process'. One known but lesser studied target of these metals are lipids that are key membrane building blocks or serve signalling functions. It was shown that Mn, Co, Ni, Pb, and Cd cause rigidification of liposomes and increase the phase transition in membranes composed of both saturated or partly unsaturated phosphatidic acid (PA) and phosphatidylserine (PS). The selected metals showed differential effects that were more pronounced on saturated lipids. In addition, more rigidity was induced in the biologically relevant liquid-crystalline phase. Moreover, metal affinity, induced rigidification and liposome size increases also varied with the headgroup architecture, whereby the carboxyl group of PS appeared to play an important role. Thus, it can be inferred that Mn, Co, Ni, Cd, and Pb may have preferred binding coordination with the lipid headgroup, degree of acyl chain unsaturation, and membrane phase.

Cation induced changes to the structure of cryptophane cages.

Here the monocation complexes of seven anti-cryptophanes are examined with high-resolution ion-mobility mass spectrometry. The relative size of the [cation + cryptophane]+ complexes were compared based on their measured mobilities and derived collisional cross sections. A paradoxical trend of structural contraction was observed for complexes of increasing cation size. Density functional theory confirmed encapsulation occurs for cation = Na+, K+, Rb+, Cs+ and NH4+. However, cation = Li+ preferred oxygen coordination at a linker over encapsulation within the cavity, leading to a slightly larger gas phase structure overall. Protonated cryptophanes yielded much larger collision cross sections via imploded cryptophane structures. Thus, competing physical effects led to the observed non-periodic size trend of the complexes. Trends in complexation from isothermal titration calorimetry and other condensed phase techniques were borne out by the gas phase studies. Further, predicted cavity sizes compared with the gas phase experimental findings reveal more about the encapsulation mechanisms themselves.