Multiplicity of metal ion binding patterns to nucleobases

Synthesis of a soluble adenine-functionalized polythiophene through direct arylation polymerization and its fluorescence responsive behavior

An adenine-functionalized polythiophene is synthesized via direct arylation polymerization using Boc-protection to overcome catalyst deactivation. The resulting copolymer is highly soluble and shows reversible fluorescence quenching.

Molecular dynamics simulations of alkaline earth metal ions binding to DNA reveal ion size and hydration effects

Classical molecular dynamics simulations reveal size-dependent trends of alkaline earth metal ions binding to DNA are due to ion size and hydration behavior.

Concerted dynamics of metallo-base pairs in an A/B-form helical transition

Metal-mediated base pairs expand the repertoire of nucleic acid structures and dynamics. Here we report solution structures and dynamics of duplex DNA containing two all-natural C-HgII-T metallo base pairs separated by six canonical base pairs. NMR experiments reveal a 3:1 ratio of well-resolved structures in dynamic equilibrium. The major species contains two (N3)T-HgII-(N3)C base pairs in a predominantly B-form helix. The minor species contains (N3)T-HgII-(N4)C base pairs and greater A-form characteristics. Ten-fold different 1J coupling constants (15N,199Hg) are observed for (N3)C-HgII (114 Hz) versus (N4)C-HgII (1052 Hz) connectivities, reflecting differences in cytosine ionization and metal-bonding strengths. Dynamic interconversion between the two types of C-HgII-T base pairs are coupled to a global conformational exchange between the helices. These observations inspired the design of a repetitive DNA sequence capable of undergoing a global B-to-A-form helical transition upon adding HgII, demonstrating that C-HgII-T has unique switching potential in DNA-based materials and devices.

Discovery of and Insights into DNA "Codes" for Tunable Morphologies of Metal Nanoparticles

The discovery and elucidation of genetic codes has profoundly changed not only biology but also many fields of science and engineering. The fundamental building blocks of life comprises of four simple deoxyribonucleotides and yet their combinations serve as the carrier of genetic information that encodes for proteins that can carry out many biological functions due to their unique functionalities. Inspired by nature, the functionalities of DNA molecules have been used as a capping ligand for controlling morphology of nanomaterials, and such a control is sequence dependent, which translates into distinct physical and chemical properties of resulting nanoparticles. Herein, an overview on the use of DNA as engineered codes for controlling the morphology of metal nanoparticles, such as gold, silver, and Pd-Au bimetallic nanoparticles is provided. Fundamental insights into rules governing DNA controlled growth mechanisms are also summarized, based on understanding of the affinity of the DNA nucleobases to various metals, the effect of combination of nucleobases, functional modification of DNA, the secondary structures of DNA, and the properties of the seed employed. The resulting physical and chemical properties of these DNA encoded nanomaterials are also reviewed, while perspectives into the future directions of DNA-mediated nanoparticle synthesis are provided.

Biocompatible organic-inorganic hybrid materials based on nucleobases and titanium developed by molecular layer deposition

We have constructed thin films of organic-inorganic hybrid character by combining titanium tetra-isopropoxide (TTIP) and the nucleobases thymine, uracil or adenine using the molecular layer deposition (MLD) approach. Such materials have potential as bioactive coatings, and the bioactivity of these films is described in our recent work [Momtazi, L.; Dartt, D. A.; Nilsen, O.; Eidet, J. R. J. Biomed. Mater. Res., Part A 2018, 106, 3090-3098. doi:10.1002/jbm.a.36499]. The growth was followed by in situ quartz crystal microbalance (QCM) measurements and all systems exhibited atomic layer deposition (ALD) type of growth. The adenine system has an ALD temperature window between 250 and 300 °C, while an overall reduction in growth rate with increasing temperature was observed for the uracil and thymine systems. The bonding modes of the films have been further characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction, confirming the hybrid nature of the as-deposited films with an amorphous structure where partial inclusion of the TTIP molecule occurs during growth. The films are highly hydrophilic, while the nucleobases do leach in water providing an amorphous structure mainly of TiO₂ with reduced density and index of refraction.

The prediction of intermolecular proton-transfer of guanine-cytosine base pair under the influence of fragments from decomposed MOFs

Metal-organic frameworks (MOFs) can be decomposed into various fragments, including negative/positive charges, Zn⁺ or Cu²⁺ when used as drug delivery materials. To evaluate the safety of MOFs, different mechanisms of intermolecular proton-transfer in guanine-cytosine (GC) base pair under the influence of such fragments were investigated by density functional theory methods. In a vacuum, calculation results show that an excess electron assists proton transfer in the anionic GC radical, and a hole assists proton transfer in the cationic GC radical with small energy barriers. The mechanism for Zn⁺-GC transfer is that the located hole assists proton transfer from G to C. All proton-transfers of Cu²⁺-GC become spontaneous with stable proton-transferred structures, and the driving force is the Cu²⁺ due to its electrostatic and oxidative effects. However, in a micro-water environment, the average energy barrier of all proton-transfer processes increases by 2.8 kcal mol^-1 because of the redistribution of charges. Water molecules play a very important role in buffering, and the influence of fragments on intermolecular proton-transfer processes of GC is reduced.

Balancing ionic and H-bonding interactions for the formation of Au(i) hydrometallogels

Complex [Au(⁹N-adenine)(PMe₃)](CF₃CO₂) displays a supramolecular structure built up through ionic, π-stacking, C–H⋯O, C–H⋯N and C–H⋯Au interactions. This complex forms a stable hydrometallogel consisting of straight molecular nanowires.

Bacterial Resistance and Prostate Cancer Susceptibility Toward Metal-Ion-doped DNA Complexes

DNA nanotechnology has laid a platform to construct a variety of custom-shaped nanoscale objects for functionalization of specific target materials to achieve programmability and molecular recognition. Herein, we prepared DNA nanostructures [namely, synthetic DNA rings (RDNA) and DNA duplexes extracted from salmon (SDNA)] containing metal ions (M²⁺) such as Cu²⁺, Ni²⁺, and Zn²⁺ as payloads for delivery to exterminate highly pathologic hospital bacterial strains (e.g., Escherichia coli and Bacillus subtilis) and prostate cancer cells (i.e., PC3, LNCaP, TRAMP-C1, 22Rv1, and DU145). Morphologies of these M²⁺-doped RDNA were visualized using atomic force microscopy. Interactions between M²⁺ and DNA were studied using UV-vis and Fourier transform infrared spectroscopy. Quantitative composition and chemical changes in DNA without or with M²⁺ were obtained using X-ray photoelectron spectroscopy. In addition, M²⁺-doped DNA complexes were subjected to antibacterial activity studies. They showed no bacteriostatic or bactericidal effects on bacterial strains used. Finally, in vitro cellular toxicity study was conducted to evaluate the effect of pristine DNA and M²⁺-doped DNA complexes on prostate cancer cells. Cytotoxicities conferred by M²⁺-doped DNA complexes for most cell lines were significantly higher than those of M²⁺ without DNA. Cellular uptake of these complexes was confirmed by fluorescence microscopy using PhenGreen FL indicator. On the basis of our observations, DNA nanostructures can be used as safe and efficient nanocarriers for delivery of therapeutics. They have enhanced therapeutic window than bare metals.

7-Methyl-6-furylpurine forms dinuclear metal complexes with N3,N9 coordination

Two dinuclear metal complexes bearing the purine derivative 7-methyl-6-furylpurine (1b) as a ligand are reported. In [Ag2(1b)2(DMSO)2](ClO4)2·DMSO and [Cu2(1b)2(NO3)2], two bridging purine derivatives coordinate the two metal ions via their N3 and N9 positions. In the silver(I) complex, the coordination environment of each metal ion is completed by a DMSO ligand, whereas an additional nitrato ligand coordinates to each copper(I) ion. The intramolecular Ag···Ag distance of 3.1069(5) Å is in agreement with the presence of a weak argentophilic interaction, whereas the Cu···Cu distance of 2.9382(4) Å is too long to be indicative of a cuprophilic interaction. The compounds represent the first examples of dinuclear complexes comprising two N3,N9-bridging purine derivatives without any additional bridging ligand.

Two-stage DNA compaction induced by silver ions suggests a cooperative binding mechanism

The interaction between silver ions and DNA plays an important role in the therapeutic use of silver ions and in related technologies such as DNA sensors. However, the underlying mechanism has not been fully understood. In this study, the dynamics of Ag⁺-DNA interaction at a single-molecule level was studied using magnetic tweezers. AgNO₃ solutions with concentrations ranging from 1 μM to 20 μM led to a 1.4-1.8 μm decrease in length of a single λ-DNA molecule, indicating that Ag⁺ has a strong binding with DNA, causing the DNA conformational change. The compaction process comprises one linear declining stage and another sigmoid-shaped stage, which can be attributed to the interaction mechanism. Considering the cooperative effect, the sigmoid trend was well explained using a phenomenological model. By contrast, addition of silver nanoparticle solution induced no detectable transition of DNA. The dependence of the interaction on ionic strength and DNA concentration was examined via morphology characterization and particle size distribution measurement. The size of the Ag⁺-DNA complex decreased with an increase in Ag⁺ ionic strength ranging from 1 μM to 1 mM. Morphology characterization confirmed that silver ions induced DNA to adopt a compacted globular conformation. At a fixed [AgNO₃]:[DNA base pairs] ratio, increasing DNA concentration led to increased sizes of the complexes. Intermolecular interaction is believed to affect the Ag⁺-DNA complex formation to a large extent.

Antibacterial gluey silver-calcium phosphate composites for dentine remineralization

The development of multifunctional dental-restorative biomaterials with antibacterial activity and remineralization effect for damaged tooth repair is urgent since dental caries is still one of the most common tooth diseases in human beings. Herein, we report a facile strategy for the synthesis of gluey silver-calcium phosphate (GSCP) composites using the rapid microwave-assisted solvothermal method. The as-prepared GSCP composite is an organic-inorganic hybrid, and Ag⁺ ions display a significant influence on the formation of GSCP by interacting with adenosine triphosphate biomolecules. The as-prepared GSCP composite shows good antibacterial properties, in addition, it exhibits a great effect on sheltering dentinal canaliculi and improving the remineralization of dentine in the simulated saliva. The as-prepared GSCP composite is promising for various applications such as oral healthcare, especially, remineralization of dentine, and antibacterial applications.

Supramolecular architectures in metal(II) (Cd/Zn) halide/nitrate complexes of cytosine/5-fluorocytosine

Three new metal(II)-cytosine (Cy)/5-fluorocytosine (5FC) complexes, namely bis(4-amino-1,2-dihydropyrimidin-2-one-κN³)diiodidocadmium(II) or bis(cytosine)diiodidocadmium(II), [CdI₂(C₄H₅N₃O)₂], (I), bis(4-amino-1,2-dihydropyrimidin-2-one-κN³)bis(nitrato-κ²O,O')cadmium(II) or bis(cytosine)bis(nitrato)cadmium(II), [Cd(NO₃)₂(C₄H₅N₃O)₂], (II), and (6-amino-5-fluoro-1,2-dihydropyrimidin-2-one-κN³)aquadibromidozinc(II)-6-amino-5-fluoro-1,2-dihydropyrimidin-2-one (1/1) or (6-amino-5-fluorocytosine)aquadibromidozinc(II)-4-amino-5-fluorocytosine (1/1), [ZnBr₂(C₄H₅FN₃O)(H₂O)]·C₄H₅FN₃O, (III), have been synthesized and characterized by single-crystal X-ray diffraction. In complex (I), the Cd^II ion is coordinated to two iodide ions and the endocyclic N atoms of the two cytosine molecules, leading to a distorted tetrahedral geometry. The structure is isotypic with [CdBr₂(C₄H₅N₃O)₂] [Muthiah et al. (2001). Acta Cryst. E57, m558-m560]. In compound (II), each of the two cytosine molecules coordinates to the Cd^II ion in a bidentate chelating mode via the endocyclic N atom and the O atom. Each of the two nitrate ions also coordinates in a bidentate chelating mode, forming a bicapped distorted octahedral geometry around cadmium. The typical interligand N-H...O hydrogen bond involving two cytosine molecules is also present. In compound (III), one zinc-coordinated 5FC ligand is cocrystallized with another uncoordinated 5FC molecule. The Zn^II atom coordinates to the N(1) atom (systematic numbering) of 5FC, displacing the proton to the N(3) position. This N(3)-H tautomer of 5FC mimics N(3)-protonated cytosine in forming a base pair (via three hydrogen bonds) with 5FC in the lattice, generating two fused R₂²(8) motifs. The distorted tetrahedral geometry around zinc is completed by two bromide ions and a water molecule. The coordinated and nonccordinated 5FCs are stacked over one another along the a-axis direction, forming the rungs of a ladder motif, whereas Zn-Br bonds and N-H...Br hydrogen bonds form the rails of the ladder. The coordinated water molecules bridge the two types of 5FC molecules via O-H...O hydrogen bonds. The cytosine molecules are coordinated directly to the metal ion in each of the complexes and are hydrogen bonded to the bromide, iodide or nitrate ions. In compound (III), the uncoordinated 5FC molecule pairs with the coordinated 5FC ligand through three hydrogen bonds. The crystal structures are further stabilized by N-H...O, N-H...N, O-H...O, N-H...I and N-H...Br hydrogen bonds, and stacking interactions.

Influence of Na+ and Mg2+ ions on RNA structures studied with molecular dynamics simulations

The structure of ribonucleic acid (RNA) polymers is strongly dependent on the presence of, in particular Mg2+ cations to stabilize structural features. Only in high-resolution X-ray crystallography structures can ions be identified reliably. Here, we perform molecular dynamics simulations of 24 RNA structures with varying ion concentrations. Twelve of the structures were helical and the others complex folded. The aim of the study is to predict ion positions but also to evaluate the impact of different types of ions (Na+ or Mg2+) and the ionic strength on structural stability and variations of RNA. As a general conclusion Mg2+ is found to conserve the experimental structure better than Na+ and, where experimental ion positions are available, they can be reproduced with reasonable accuracy. If a large surplus of ions is present the added electrostatic screening makes prediction of binding-sites less reproducible. Distinct differences in ion-binding between helical and complex folded structures are found. The strength of binding (ΔG‡ for breaking RNA atom-ion interactions) is found to differ between roughly 10 and 26 kJ/mol for the different RNA atoms. Differences in stability between helical and complex folded structures and of the influence of metal ions on either are discussed.

Disquisition on the interaction of ibuprofen-Zn(II) complex with calf thymus DNA by spectroscopic techniques and the use of Hoechst 33258 and Methylene blue dyes as spectral probes

The interaction between ibuprofen-Zn(II) complex and calf thymus DNA in physiological buffer (pH 7.4) was studied with the use of Hoechst 33258 and methylene blue dyes as spectral probes by multi-spectroscopic techniques, and viscosity measurements. It was found that ibuprofen-Zn(II) complex molecules could bind with DNA via groove binding mode as evidenced by: i- DNA binding constant (K_b = (1.00 ± 0.2) × 10⁴ M^-1) from Spectrophotometric studies of the interaction of ibuprofen-Zn(II) complex with DNA is comparable to groove binding drugs. ii- Absorption Spectra of Competitive interaction of ibuprofen-Zn(II) complex and Hoechst 33258 with DNA exhibited the reverse process, The results suggested that interaction of the ibuprofen-Zn(II) complex with calf thymus DNA, is similar to Hoechst 33258 interaction with calf thymus DNA (This was verified by the following fluorescence study). iii- Competitive fluorimetric studies with Hoechst 33258 have shown that ibuprofen-Zn(II) complex exhibit the ability of this complex to displace with DNA-bounded Hoechst 33258, indicating that it binds to DNA in strong competition with Hoechst 33258 for the groove binding. iv- There is no significantly change in the fluorescence intensity of the MB-DNA system upon adding the ibuprofen-Zn(II) complex, indicate that MB molecules are not released from the DNA helix after addition of the ibuprofen-Zn(II) complex and are indicative of a non-intercalative mode of binding. v- Small changes in DNA viscosity in the presence of ibuprofen-Zn(II) complex, indicating weak link to DNA, which is consistent with DNA groove binding. As well as, induced CD spectral changes, and the docking results revealed that groove mechanism is followed by ibuprofen-Zn(II) complex to bind with DNA.

Providing evidence for the requirements to achieve supramolecular materials based on metal–nucleobase entities

This article evaluates the strategy to design supramolecular metal–organic frameworks using metal–nucleobase entities as building units.

Metal-mediated base pairs in parallel-stranded DNA

In nucleic acid chemistry, metal-mediated base pairs represent a versatile method for the site-specific introduction of metal-based functionality. In metal-mediated base pairs, the hydrogen bonds between complementary nucleobases are replaced by coordinate bonds to one or two transition metal ions located in the helical core. In recent years, the concept of metal-mediated base pairing has found a significant extension by applying it to parallel-stranded DNA duplexes. The antiparallel-stranded orientation of the complementary strands as found in natural B-DNA double helices enforces a cisoid orientation of the glycosidic bonds. To enable the formation of metal-mediated base pairs preferring a transoid orientation of the glycosidic bonds, parallel-stranded duplexes have been investigated. In many cases, such as the well-established cytosine-Ag(I)-cytosine base pair, metal complex formation is more stabilizing in parallel-stranded DNA than in antiparallel-stranded DNA. This review presents an overview of all metal-mediated base pairs reported as yet in parallel-stranded DNA, compares them with their counterparts in regular DNA (where available), and explains the experimental conditions used to stabilize the respective parallel-stranded duplexes.

Effect on frontier molecular orbitals of substituents in 5-position of uracil base pairs in vacuum and water

The most stable structure of 5-substituted uracil base pairs and metal-mediated-5-substituted uracil complexes are determined. Density functional theory (DFT) method is used in the calculations which are carried out both in vacuum and water. LANL2DZ and 6–311[Formula: see text]G(d,p) basis sets are used for metals and the rest atoms, respectively. Effects on frontier molecular orbitals and energy gaps of substituents in 5-position of uracil base pairs in vacuum and water are found. Conductivity of base pairs or complexes are investigated for single nanowires studied by band theory. It is expected that this study will be an example for future studies that require new nanotechnological applications.

Self-Assembled Ti4+@Biospore Microspheres for Sensitive DNA Analysis

Ti⁴⁺ can be chemically adsorbed and assembled on the surface of the modified spore to form highly monodispersed Ti⁴⁺@spore microspheres. Moreover, we for the first time found that these biomicrospheres exhibit differential affinities toward ssDNA and dsDNA. As a principle-of-proof, we exploited the self-assembled Ti⁴⁺@spore microspheres for a hybridization analysis. Interestingly, in the hybridization analysis, residual ssDNA probes are selectively adsorbed on Ti⁴⁺@spore microspheres at pH 5.0 and then removed via centrifugation. By taking advantage of this property, the signal-to-noise ratio for DNA analysis was considerably increased by reducing the noise caused by the residual ssDNA probes. The proposed method features easy operation, high specificity, and sensitivity and thus exhibits potential for further applications on DNA biosensing.

N3 and O2 Protonated Conformers of the Cytosine Mononucleotides Coexist in the Gas Phase

The gas-phase conformations of the protonated forms of the DNA and RNA cytosine mononucleotides, [pdCyd+H]⁺ and [pCyd+H]⁺, are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy over the IR fingerprint and hydrogen-stretching regions complemented by electronic structure calculations. The low-energy conformations of [pdCyd+H]⁺ and [pCyd+H]⁺ and their relative stabilities are computed at the B3LYP/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) and MP2(full)/6-311+G(2d,2p)//B3LYP/6-311+G(d,p) levels of theory. Comparisons of the measured IRMPD action spectra and B3LYP/6-311+G(d,p) linear IR spectra computed for the low-energy conformers allow the conformers present in the experiments to be determined. Similar to that found in previous IRMPD action spectroscopy studies of the protonated forms of the cytosine nucleosides, [dCyd+H]⁺ and [Cyd+H]⁺, both N3 and O2 protonated cytosine mononucleotides exhibiting an anti orientation of cytosine are found to coexist in the experimental population. The 2'-hydroxyl substituent does not significantly influence the most stable conformations of [pCyd+H]⁺ versus those of [pdCyd+H]⁺, as the IRMPD spectral profiles of [pdCyd+H]⁺ and [pCyd+H]⁺ are similar. However, the presence of the 2'-hydroxyl substituent does influence the relative intensities of the measured IRMPD bands. Comparisons to IRMPD spectroscopy studies of the deprotonated forms of the cytosine mononucleotides, [pdCyd-H]^- and [pCyd-H]^-, provide insight into the effects of protonation versus deprotonation on the conformational features of the nucleobase and sugar moieties. Likewise, comparisons to results of IRMPD spectroscopy studies of the protonated cytosine nucleosides provide insight into the influence of the phosphate moiety on structure. Comparison with previous ion mobility results shows the superiority of IRMPD spectroscopy for distinguishing various protonation sites. Graphical Abstract ᅟ.

DNA-Targeted Inhibition of MGMT

The cationic porphyrin 5,10,15,20-tetrakis (diisopropyl-guanidine)-21H,23H-porphine (DIGPor) selectively binds to DNA containing O⁶ -methylguanine (O⁶ -MeG) and inhibits the DNA repair enzyme O⁶ -methylguanine-DNA methyltransferase (MGMT). The O⁶ -MeG selectivity and MGMT inhibitory activity of DIGPor were improved by incorporating Zn^II into the porphyrin. The resulting metal complex (Zn-DIGPor) potentiated the activity of the DNA-alkylating drug temozolomide in an MGMT-expressing cell line. To the best of our knowledge, this is the first example of DNA-targeted MGMT inhibition.

Aberrant coordination geometries discovered in the most abundant metalloproteins

Metalloproteins bind and utilize metal ions for a variety of biological purposes. Due to the ubiquity of metalloprotein involvement throughout these processes across all domains of life, how proteins coordinate metal ions for different biochemical functions is of great relevance to understanding the implementation of these biological processes. Toward these ends, we have improved our methodology for structurally and functionally characterizing metal binding sites in metalloproteins. Our new ligand detection method is statistically much more robust, producing estimated false positive and false negative rates of ∼0.11% and ∼1.2%, respectively. Additional improvements expand both the range of metal ions and their coordination number that can be effectively analyzed. Also, the inclusion of additional quality control filters has significantly improved structure-function Spearman correlations as demonstrated by rho values greater than 0.90 for several metal coordination analyses and even one rho value above 0.95. Also, improvements in bond-length distributions have revealed bond-length modes specific to chemical functional groups involved in multidentation. Using these improved methods, we analyzed all single metal ion binding sites with Zn, Mg, Ca, Fe, and Na ions in the wwPDB, producing statistically rigorous results supporting the existence of both a significant number of unexpected compressed angles and subsequent aberrant metal ion coordination geometries (CGs) within structurally known metalloproteins. By recognizing these aberrant CGs in our clustering analyses, high correlations are achieved between structural and functional descriptions of metal ion coordination. Moreover, distinct biochemical functions are associated with aberrant CGs versus nonaberrant CGs. Proteins 2017; 85:885-907. © 2016 Wiley Periodicals, Inc.

CheckMyMetal: a macromolecular metal-binding validation tool

Metals are essential in many biological processes, and metal ions are modeled in roughly 40% of the macromolecular structures in the Protein Data Bank (PDB). However, a significant fraction of these structures contain poorly modeled metal-binding sites. CheckMyMetal (CMM) is an easy-to-use metal-binding site validation server for macromolecules that is freely available at http://csgid.org/csgid/metal_sites. The CMM server can detect incorrect metal assignments as well as geometrical and other irregularities in the metal-binding sites. Guidelines for metal-site modeling and validation in macromolecules are illustrated by several practical examples grouped by the type of metal. These examples show CMM users (and crystallographers in general) problems they may encounter during the modeling of a specific metal ion.

Mg2+ ions: do they bind to nucleobase nitrogens?

Given the many roles proposed for Mg2+ in nucleic acids, it is essential to accurately determine their binding modes. Here, we surveyed the PDB to classify Mg2+ inner-sphere binding patterns to nucleobase imine N1/N3/N7 atoms. Among those, purine N7 atoms are considered to be the best nucleobase binding sites for divalent metals. Further, Mg2+ coordination to N7 has been implied in several ribozyme catalytic mechanisms. We report that Mg2+ assigned near imine nitrogens derive mostly from poor interpretations of electron density patterns and are most often misidentified Na+, K+, NH4+ ions, water molecules or spurious density peaks. Consequently, apart from few documented exceptions, Mg2+ ions do not bind to N7 atoms. Without much of a surprise, Mn2+, Zn2+ and Cd2+, which have a higher affinity for nitrogens, may contact N7 atoms when present in crystallization buffers. In this respect, we describe for the first time a potential Zn2+ ribosomal binding site involving two purine N7 atoms. Further, we provide a set of guidelines to help in the assignment of Mg2+ in crystallographic, cryo-EM, NMR and model building practices and discuss implications of our findings related to ion substitution experiments.

N9 substituent mediated structural tuning of copper–purine complexes: chelate effect and thin film studies

Six Cu(ii) complexes of strategically designed derivatives of 6-chloropurine, one of which has been explored as a thin film precursor on quartz and Si(111) surfaces by using chemical vapor deposition (CVD).