Monoatomic Anions Research Articles

Identifications of False Positives Amongst Sodium(I) Cations in Protein Three-Dimensional Structures—A Validation Approach Extendible to Any Alkali or Alkaline Earth Cation and to Any Monoatomic Anion

Validation of the data deposited in the Protein Data Bank is of the upmost importance, since many other databases, data mining processes, and artificial intelligence tools are strictly grounded on them. The present paper is divided into two parts. The first part describes and analyzes validation methods that have been designed and used by the structural biology community. Everything began with the Ramachandran plot, with its allowed and disallowed types of backbone conformations, and evolved in different directions, with the inclusion of additional stereochemical features, distributions’ analyses of structural moieties, and scrutiny of structure factor amplitudes across the reciprocal lattice. The second part of the paper is focused on the largely unexplored problem of the high number of false positives amongst the sodium(I) cations observed in protein crystal structures. It is demonstrated that these false positives, which are atoms wrongly identified with sodium, can be identified by using electrostatic considerations and it is anticipated that this approach can be extended to other alkali and alkaline earth cations or to monoatomic anions. In the end, I think a global initiative, accessible to all volunteers and possibly overseen by the Protein Data Bank, should take the place of the numerous web servers and software applications by providing the community with a select few reliable and widely accepted tools.

Application of the CL&P-Pol polarizable force field in the determination of the excess chemical potential of thiophene within the [C4mim] [BF4, Cl, Br, CH3COO] ionic liquids

The combustion of fossil fuels is an important source of air pollution due to the presence of sulfur-based compounds. In this regard, a reliable atomistic forcefield is required in order to provide insights on solute-solvent interactions, and in designing high aromatic sulfur extracting solvents. In the present work, the excess chemical potentials of thiophene within four 1-butyl-3-methylimidazolium-based ionic liquids were evaluated through the free energy perturbation with replica exchange molecular dynamics methodology by using the CL&Pol polarizable force fields based on Drude oscillators. First, in order to validate the accuracy of the polarizable force fields, a series of thermodynamic properties of pure ionic liquids such as diffusion coefficient, liquid density, dielectric constant, and heat of vaporization were computed using the CL&Pol force field and compared against experimental values. The results from the calculated thiophene excess chemical potential values, indicated that the [C4mim][CH3COO] ionic liquid presents the more favorable excess chemical potential (higher solubility) with respect to the thiophene molecule at both 300 K and 343 K in comparison to the other ionic liquids studied. The structural analysis revealed that the ionic liquid anion interacts more closely and with well-defined RDF peaks with the thiophene molecule, the larger anions present higher surrounding particle densities with the thiophene molecules (solvation shell), while the monoatomic anions interact preferentially with the hydrogens close to the sulfur thiophene atom; In contrast no marked solvation layers were observed with the ionic liquid cations.

Abstract 5387: Host-derived CCL2 drives prostate cancer bone metastasis via CCND2/STAT3 pathway

Abstract Overexpression of tumor-derived CCL2 has been shown to partially promote prostate cancer (PCa) bone metastasis, but the function of host-derived CCL2 is not fully understood. We first developed a mouse model using intracardiac injection and obtained highly metastatic PCa cell subclones through in vivo selection. The highly metastatic tumor cells were injected intracardially into CCL2 knockout (CCL2 KO) mice and wild-type (WT) controls, and the tumor cell growth and metastasis were monitored weekly by bioluminescence imaging. The osteolytic lesions were evaluated by radiography, micro-computed tomography (microCT) and immunohistochemistry (IHC) staining. The cells in the bone microenvironment were analyzed by flow cytometry. Also, RNA sequencing (RNA-seq) analysis was performed on the cells either from CCL2 KO mice or WT controls. We found that a loss of host-derived CCL2 significantly retarded tumor growth in bone and prolonged mouse survival. In addition, bone density analysis revealed a decrease in osteolytic lesion in CCL2 KO mice, compared to WT controls. Systemically, CCL2 deficiency reduced the proportion of granulocyte-myeloid-derived suppressor cell (G-MDSC) populations with immunosuppressive function and decreased the PCa conditioned medium (CM)-induced osteoclast formation. The enrichment analysis revealed that the dysregulated genes in bone metastatic cells from CCL2 KO mice were significantly enriched in several biological processes, including vitamin metabolism, monoatomic anion homeostasis, immune response, and bone growth. Additionally, we also confirmed that the CCND2/STAT3 pathway is apparently suppressed in the cells from CCL2 KO mice. This study demonstrated that targeting the host-derived CCL2 might be a novel potential anti-metastatic approach. Supported by the NSFC projects (81972766, 81972420, 82173336), as well as grants from the Science and Technology Project of Shenzhen (JCYJ20190809161811237, JCYJ20210324104214040). Key words Host-derived CCL2; Prostate cancer; Bone metastasis; osteoclast; CCND2 Citation Format: Jie Meng, Ming Chang, Siyuan Qin, Xin Huang, Weiping Liang, Haibo Tong, Jian Zhang. Host-derived CCL2 drives prostate cancer bone metastasis via CCND2/STAT3 pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5387.

On the halide aggregation into the [Au4(PPh3)4]4+ cluster core. Insights from structural, optical and interaction energy analysis in [(Ph3PAu)4X2]2+ and [(Ph3PAu)4X]3+ species (X = Cl-, Br-, I-).

The aggregation of halide atoms into gold clusters offers an interesting scenario for the development of novel metal-based cavities for anion recognition and sensing applications. Thus, further understanding of the different contributing terms leading to efficient cluster-halide aggregation is relevant to guide their synthetic design. In this report, we evaluate the formation of [(Ph3PAu)4X2]2+ and [(Ph3PAu)4X]3+ species (X = Cl-, Br-, I-) in terms of different energy contributions underlying the stabilization of the cluster-halide interaction, and the expected UV-vis absorption profiles as a result of the variation in frontier orbital arrangements. Our results denote that a non-planar Au4 core shape enables enhanced halide aggregation, which is similar for Cl-, Br-, and I-, in comparison to the hypothetical planar Au4 counterparts. The electrostatic nature of the interaction involves a decreasing ion-dipole term along with the series, and for iodine species, higher-order electrostatic contributions become more relevant. Hence, the obtained results help in gaining further understanding of the different stabilizing and destabilizing contributions to suitable cluster-based cavities for the incorporation of different monoatomic anions.

Differential Gene Expression of Malaria Parasite in Response to Red Blood Cell-Specific Glycolytic Intermediate 2,3-Diphosphoglycerate (2,3-DPG)

Innovative strategies to control malaria are urgently needed. Exploring the interplay between Plasmodium sp. parasites and host red blood cells (RBCs) offers opportunities for novel antimalarial interventions. Pyruvate kinase deficiency (PKD), characterized by heightened 2,3-diphosphoglycerate (2,3-DPG) concentration, has been associated with protection against malaria. Elevated levels of 2,3-DPG, a specific mammalian metabolite, may hinder glycolysis, prompting us to hypothesize its potential contribution to PKD-mediated protection. We investigated the impact of the extracellular supplementation of 2,3-DPG on the Plasmodium falciparum intraerythrocytic developmental cycle in vitro. The results showed an inhibition of parasite growth, resulting from significantly fewer progeny from 2,3-DPG-treated parasites. We analyzed differential gene expression and the transcriptomic profile of P. falciparum trophozoites, from in vitro cultures subjected or not subjected to the action of 2,3-DPG, using Nanopore Sequencing Technology. The presence of 2,3-DPG in the culture medium was associated with the significant differential expression of 71 genes, mostly associated with the GO terms nucleic acid binding, transcription or monoatomic anion channel. Further, several genes related to cell cycle control were downregulated in treated parasites. These findings suggest that the presence of this RBC-specific glycolytic metabolite impacts the expression of genes transcribed during the parasite trophozoite stage and the number of merozoites released from individual schizonts, which supports the potential role of 2,3-DPG in the mechanism of protection against malaria by PKD.

Exploring the Nature of Anion-π Interactions: Complexes of π-Acceptors with Fluoro- or Oxoanions Compared to the Associations with Halides.

The variations in the nature and properties of the anion-π complexes with different types of anions are identified via experimental (UV-vis and X-ray crystallographic) measurements and computational analysis of the associations of tetracyanopyrazine, tetrafluoro-, or dichlorodicyano-p-benzoquinone. Co-crystals of these π-acceptors with the salts of fluoro- and oxoanions (PF6-, BF4-, CF3SO3-, or ClO4-) comprised anion-π bonded alternating chains or 1:2 complexes showing interatomic contacts of up to 15% shorter than the van der Waals separations. DFT computations confirmed that binding energies between the neutral π-acceptors and polyatomic noncoordinating oxo- and fluoroanions are comparable to those in the previously reported anion-π complexes with more nucleophilic halides. Yet, while the latter show distinct charge-transfer bands in the UV-vis range, the absorption spectra of the solutions containing oxo- and fluoroanions and the π-acceptors were close to those of the individual reactants. The natural bond orbital (NBO) analysis revealed a very small charge transfer of Δq = 0.01-0.02 e in the complexes with oxo- or fluoroanions as compared to the Δq = 0.05-0.22 e found for analogous complexes with halides. These distinctions were related to the smaller frontier orbital energy gap and better overlap in the complexes with halides (since the highest occupied orbitals of these monoatomic anions are closer in energy to the lowest unoccupied orbitals of the π-acceptors) as compared to that in the multicenter-bonded associations with polyatomic oxo- and fluoroanions. In accordance with these data, the energy decomposition analysis showed that while the complexes of neutral π-acceptors with the fluoro- and oxoanions are formed predominantly via electrostatic interaction, the associations with halides comprised significant orbital (charge-transfer) interactions and they explain their spectral and structural features.

Isolation of Homo-/Mixed-Valence Ag12 , Ag29 , and Ag8 Clusters Stabilized by Cyclic Alkyl(amino) Carbene-Anchored Monoanionic Phosphorus Ligand.

Silver clusters are attractive candidates for their promising optical properties, and biomedical activities. Herein, we report on the first syntheses and isolation of three homo-/mixed-valence silver nanoclusters (NCs) with Ag12 Cl3 , Ag29 , and Ag8 cores [((cAAC)P)6 Ag12 Cl3 ](OTf)3 (1), [((cAAC)P)6 Ag29 ] (2), and [((cAAC)P)4 Ag8 ] (3) having three-/twofold symmetry, employing cyclic alkyl(amino) carbene (cAAC)-supported phosphinidenide (cAACP- ) as the π-accepting stabilizing ligand. The average diameters of Ag NCs 1, and 2 are approximately 1.6 to 2 nm. The redox non-innocent mono-atomic phosphorus anions (P- ) anchored with cAAC ligands are generated in situ by the reaction of AgOTf with a boryl-phosphaalkene (cAAC)P-B(Ni Pr2 )2 through cleavage of the P-B bond with the help of a triflate anion (OTf- ) as a weak nucleophile. Equivalent number of the (cAAC)P- anions generated in situ are oxidized to produce the corresponding bis-phosphinidene (cAAC)2 P2 leading to the generation of Ag0 ions in solution for the formation of the unprecedented mixed-valence Ag NC 2. Complex 3 is achieved by treating potassium phosphinidenide cAACPK with AgNTf2 . The ligand field and the steric hindrance of the (cAAC)P units play crucial roles in stabilizing complexes 1-3, further providing a three- (1, 2)/two- (3) fold stand. The Ag12 Cl3 NC (1) with a tricationic core [AgI 12 Cl3 ] was found to be diamagnetic, and fluorescent, emitting green light at 563 nm when excited at 400 nm. In contrast, the neutral Ag29 (2) and Ag8 (3) clusters were found to be paramagnetic, and NMR silent showing characteristic EPR signals for Ag0 at room temperature.

Quantification of the interactions in halide-anion-based imidazolium ionic liquids

Non-covalent interactions between constituent ions of ionic liquids (ILs) define their distinctive physicochemical properties and are critical for understanding their micro and bulk structures as well as designing new task-specific ILs. Therefore, the quantification of these interactions can improve our understanding of this unique class of materials. A set of 20 halide-anion-based imidazolium ILs (Cnmim X, X = Cl, Br, I, and BF4; n = 2, 4, 6, 8, and 10) was selected for this study. The variation of the anion (hydrogen-bond-acceptor property and size), presence of water, and the alkyl chain length of the imidazolium ring have all been considered as parameters when attempting to address mainly the following two fundamental questions: How does the strength of hydrogen bonding in these selected Coulomb systems change? How much do dispersion forces play a role in the net attractive interaction energy despite being weak? To this end, dispersion-corrected density functional theory (DFT) computations were executed to acquire the optimized structures of all the considered ILs, followed by an ensemble of NCI and QATIM analyses to explore the strength of non-covalent interactions. Further, quantum mechanical energy decomposition analysis (QM-EDA) based on symmetry-adapted-perturbation-theory (SAPT) has been employed to dissect the total interaction energy into its components. An assessment of QM-EDA demonstrates that the electrostatic interaction dominates the intermolecular attraction, although induction and dispersion components also play a substantial role. The dispersion energies are amplified when water is present, as well as when anion size and alkyl chain length increase. We quantified the non-covalent interactions between ion pairs using NCI-RDG and Bader's QTAIM analyses. Strong hydrogen bonding with a partial covalent character was observed between monoatomic anions and C2-proton of the imidazolium ring, but for the multiatomic anion (BF4−) and interaction between imidazolium ring alkyl groups and anions, a weak electrostatic hydrogen bonding was found. The hydrogen bonding strength decreases with increasing anion size; it is strongest in the C2mim Cl ion pair. NBO analysis gives a clear indication of nX→σC−H*(X=Cl,Br,I,andF) type intermolecular interaction with highest stabilization energy (En→σ*(2)). A clear correlation between E(2) and hydrogen bond lengths were observed. Overall, the current study illuminates the intricate network of covalent-like and non-covalent interactions in selected imidazolium ILs based on halide anions.

Experimental and COSMO-RS Simulation Studies on the Effects of Polyatomic Anions on Clay Swelling.

Ionic liquids (ILs) can play a vital role in clay swelling inhibition during hydraulic fracturing. Previous studies highlighted the effect of side-chain length attached to the cationic core and different anions possessing almost the same chemical properties on inhibition performance. However, polyatomic anions have the potential to superiorly inhibit swelling compared to monoatomic anions. In this study, three ILs, namely, 1-butyl-3-methylimidazolium chloride (BMIMCl), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6), were utilized to assess the effects of polyatomic anions on clay swelling inhibition. These performances were compared with the performances of a conventional inhibitor, potassium chloride (KCl). X-ray diffraction (XRD) testing was applied to check the mineral components present in the bentonite clay sample studied in this research. Clay swelling inhibition performance and rheological properties of these ILs were evaluated by the bentonite plate soaking test, linear swelling test, and rheological test. The swelling inhibition mechanisms were investigated through ζ-potential measurement, Fourier transform infrared (FT-IR) spectroscopy, and contact angle measurement. Moreover, COSMO-RS computer simulation was conducted to explain the inhibition mechanisms theoretically. The results demonstrated that BMIMPF6 showed superior inhibition performance and reduced the swelling by 21.55%, while only 9.26% reduction was attained by potassium chloride (KCl). The adsorption ability on the bentonite surface through electrostatic attraction, higher activity coefficient, and less electronegativity of PF6– anion played a vital role in attaining such superior inhibition performance by BMIMPF6.

Induced circular dichroism of monoatomic anions: silica-assisted the transfer of chiral environment from molecular assembled nanohelices to halide ions.

We demonstrate the first example of induced CD of monoatomic anions. This was detected using chirally-arranged molecular assemblies of non-chiral cationic gemini surfactants (16-2-16) with monoatomic anions stabilized with silica-coating. Furthermore, we have also achieved multi-step transfer of a chiral environment through an in situ chemical reaction via chiralized monoatomic anions.

Effect of counter anions on ferroelectric properties of diisopropylammonium‐cation based molecular crystals

Diisopropylammonium cation based single crystals with different counter anions (F−, Cl−, Br−, I−, , and ) were prepared. Their crystal structures and ferroelectric properties were investigated by single‐crystal X‐ray diffraction spectroscopy, differential scanning calorimetry, and dielectric measurements. The experimental results illustrate that the ferroelectric properties of diisopropylammonium‐based single crystals are closely related to the electronegativity and structure of the counter anions. For monoatomic anions, higher electronegativity results in higher polarization and phase‐transition temperature of the corresponding molecular–ionic ferroelectrics. The results of density‐functional theory (DFT) calculations also support the experimental results.

Ionic liquids and their bases: Striking differences in the dynamic heterogeneity near the glass transition.

Ionic liquids (ILs) constitute an active field of research due to their important applications. A challenge for these investigations is to explore properties of ILs near the glass transition temperature Tg, which still require our better understanding. To shed a new light on the issues, we measured ILs and their base counterparts using the temperature modulated calorimetry. We performed a comparative analysis of the dynamic heterogeneity at Tg for bases and their salts with a simple monoatomic anion (Cl–). Each pair of ionic and non-ionic liquids is characterized by nearly the same chemical structure but their intermolecular interactions are completely different. We found that the size of the dynamic heterogeneity of ILs near Tg is considerably smaller than that established for their dipolar counterparts. Further results obtained for several other ILs near Tg additionally strengthen the conclusion about the relatively small size of the dynamic heterogeneity of molecular systems dominated by electrostatic interactions. Our finding opens up new perspectives on designing different material properties depending on intermolecular interaction types.

Polychalcogenide Anions: Structural Diversity and Ligand Versatility

AbstractThe structures and ligand binding modes of polychalcogenide anions are reviewed in this article. Participation in hypervalent 3c‐4e bonds and/or weaker secondary np2 → nσ* bonds leads to a strikingly more diverse homopolytaomic anion chemistry for selenium and tellurium in comparison to sulfur, for which only unbranched chain anions Sn2– with n = 2–9 have been reported. Trapped S2·– and S3·– radicals are responsible for the characteristic colours of the ultramarine pigments and S3·– is the dominant sulfur species at the high temperatures and pressures of deep metamorphic settings. Hypervalent linear TeTe24–, T‐shaped TeTe34– and square‐planar TeTe46– units generate a remarkable variety of structural motifs and connectivity patterns for 1 to 3D polytelluride anions. Electron‐deficient polytelluride sheets are, however, prone to periodic spatial modifications of their charge density (CDWs) with a lower total free energy, whose formation is driven by nesting effects in the electronic band structure causing Fermi surface instabilities. Polychalcogenide ligands augment the typical terminal and bridging coordination modes of monoatomic chalcogenide anions through their ability to participate in chelation, side‐on and combination binding modes. In addition to the electrical conductivity and thermoelectric energy conversion properties of the polytellurides, potential applications of the polychalcogenides range from the manufacture of synthetic zeolite pigments and ion‐exchangeable polysulfide aerogels to NIR‐emissive lanthanide polyselenides with high quantum efficiency.

Modeling the hydration of mono-atomic anions from the gas phase to the bulk phase: The case of the halide ions F−, Cl−, and Br−

In this work, we investigate the hydration of the halide ions fluoride, chloride, and bromide using classical molecular dynamics simulations at the 10 ns scale and based on a polarizable force-field approach, which treats explicitly the cooperative bond character of strong hydrogen bond networks. We have carried out a thorough analysis of the ab initio data at the MP2 or CCSD(T) level concerning anion/water clusters in gas phase to adjust the force-field parameters. In particular, we consider the anion static polarizabilities computed in gas phase using large atomic basis sets including additional diffuse functions. The information extracted from trajectories in solution shows well structured first hydration shells formed of 6.7, 7.0, and 7.6 water molecules at about 2.78 Å, 3.15 Å, and 3.36 Å for fluoride, chloride, and bromide, respectively. These results are in excellent agreement with the latest neutron- and x-ray diffraction studies. In addition, our model reproduces several other properties of halide ions in solution, such as diffusion coefficients, description of hydration processes, and exchange reactions. Moreover, it is also able to reproduce the electrostatic properties of the anions in solution (in terms of anion dipole moment) as reported by recent ab initio quantum simulations. All the results show the ability of the proposed model in predicting data, as well as the need of accounting explicitly for the cooperative character of strong hydrogen bonds to reproduce ab initio potential energy surfaces in a mean square sense and to build up a reliable force field.

Observation of poly(ethylene glycol) clusters with the chlorine anion in the gas phase under electrospray conditions

It is demonstrated herein that poly(ethylene glycol) (PEG) oligomers can form stable complexes with the chlorine anion in the gas phase as evidenced by results from electrospray ionization mass spectrometry (ESI-MS) and molecular dynamics simulation. While the formation of crown-ether-like structures by acyclic polyethers in their complexes with alkali metal cations coordinated by the ether oxygen atoms has been extensively studied, the possibility of forming 'inversed' quasi-cyclic structures able to bind a monoatomic anion has not been proved till now. We have observed the formation of stable gas-phase complexes of oligomers of PEG-400 with the Cl(-) anion experimentally by ESI-MS for the first time. It is suggested that a necessary precondition for obtaining the polyether-chlorine anion clusters is the prevention of the formation of neutral ion pairs. Molecular dynamics simulation has demonstrated the wrapping of the Cl(-) anion by the PEG chain, to stabilize the PEG(n)•Cl(-) clusters in the gas phase. The conformation of the polyether chain in such quasi-cyclic or quasi-helical complexes is 'inversed' compared with that in the complexes with cations: that is its hydrogen atoms are turned towards the central anion. Awareness of the possibility of the Cl(-) anion being trapped in quasi-cyclic PEG structures may be of practical importance when considering the intermolecular interactions of PEGs.

ChemInform Abstract: Anion Binding in Covalent and Self‐Assembled Molecular Capsules

AbstractReview: 149 refs.

Study of the orbital hardness and the Kohn-Sham radius on single monoatomic anions

Within the Kohn-Sham framework and for a series of single charged monatomic anions, the orbital hardness is calculated as a change in the frontier eigenvalue, which is equivalent to integrate the local hardness function obtained through the derivative of the KS effective potential respect to the occupation number. The local hardness function is composed by the sum of two terms with opposite sign that describe the electrostatic and exchange-correlation interactions. Moreover, it is found that, at the KS radii, the last term vanishes with the result that the orbital hardness of the anion is a measure of the electrostatic potential exerted by the frontier density at the KS radii. A further derivation leads to establish a direct relationship between hardness and the inverse of the KS radii. The polarizability of the anion is also examined by computing it from the volume of a sphere having the KS radii. These results show that anions from the halide group are hard and little polarizable, whereas anions from the alkali group are soft and highly polarizable. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

High-pressure study of solvation properties of room-temperature ionic liquids

The solvation properties of some room-temperature ionic liquids consisting of imidazolium cations and various anions were examined by means of the high-pressure spectroscopy with solvatochromic probes. We measured the pressure dependence of Kamlet-Taft solvatochromic parameters (π*, β) and microviscosity (η). It was found that π* and β were not so sensitive to the types of imidazolium cations and polyatomic anions, but the type of monoatomic anions. The pressure dependence of microviscosity was found to obey the empirical power-law equation.

Anion binding in covalent and self-assembled molecular capsules

This critical review describes selected examples extracted from the extensive literature generated during the past 42 years on the topic of anion binding in molecular capsules. The goal of including anions in molecular capsules emerges from the idea of incorporating the traits exhibited by biological receptors into synthetic ones. At the outset of this research area the capsules were unimolecular. The scaffold of the receptor was designed to covalently link a series of functional groups that could converge into a cavity and to avoid its collapse. The initial examples involved the encapsulation of one monoatomic spherical anion. With time, the cavity size of the receptor was increased and encapsulation of polyatomic anions and co-encapsulation became a reality. Synthetic economy fueled the use of aggregates of self-complementary molecules rather than one large molecule as capsules. The main purpose of this review is to give a general overview of the topic which might be of interest to supramolecular or non supramolecular chemists alike (149 references).

The chemistry of gold as an anion

Due to relativistic and classical shell structure effects, the 6s orbital of gold is significantly contracted and energetically stabilized. This is reflected by a strikingly high electron affinity, and a distinct tendency to adopt negatively polarized valence states. This tutorial review focuses on the chemistry of gold as an anion, displaying the integral ionic charge number of 1-. Two synthetic approaches to compounds containing monoatomic gold anions have become available: (1) reacting elemental gold with molten caesium and an oxide, e.g. Cs2O; (2) metathesis reactions involving Au- dissolved in liquid ammonia. Both procedures have proven to be rather versatile. Aurides synthesized along these routes are surveyed, in particular with respect to their structures and bonding properties.