Adenine Complexes Research Articles

Spectroscopic and potentiometric studies of the interaction of adenine with trivalent metal ions

Potentiometric titration was used to determine the potentiometric diagrams of complexes of adenine with Al3+, Cr3+, and Fe3+. IR and Raman spectra of solids show that the interaction of adenine with Cr3+ is not as strong as the other metals. Fe3+ binds to adenine at low and medium pH values at an Fe3+–adenine ratio of 6, while Al3+ binds to adenine at all pH values at an Al3+–adenine ratio of 8. The IR band associated with N-9–H is split into two components at high and low wavenumbers; IR band splitting has been observed for groups with a large dipole moment such as carbonyl and phosphate. To the best of our knowledge, this is the first time to see the splitting of IR bands involving a nitrogen. We also obtained potentiometric titration plots for adenine with Al3+, Cr3+, and Fe3+, independently, in various molar ratios which showed an interaction with adenine, consistent with the IR and Raman findings. Metal–adenine-hydroxo complexes were formed.

Voltammetric Study of Adenine Complex with Copper on Mercury Electrode

AbstractThe determination of adenine (Ade), adenosine (Ado) and hydrolyzed adenosine (h‐Ado) in the presence of copper(II) ions is described by cyclic (CV) and elimination voltammetry with linear scan (EVLS) in connection with adsorptive stripping technique. Signals of adenine and copper‐adenine complex were measured on a hanging mercury drop electrode (HMDE) in buffered solutions with different pH. The differences in electrochemical behavior of Ade and Ado were found not only in dependence on the presence of copper ions, scan rate, Ade concentration and pH, but also on the accumulation time and potential where a copper‐Ade complex is formed. A deeper evaluation of voltammetric responses was carried out by EVLS. The EVLS function E4 eliminating charging and kinetic current components and conserving the diffusion current component was capable of enhancing the current sensitivity of CV peaks and of detecting electron transfer in adsorbed state. The irreversible electrode process of a totally adsorbed electroactive species is indicated by means of a peak‐counterpeak signal. Our results show that EVLS in connection with the adsorptive stripping procedure is not only a useful tool for both qualitative and quantitative microanalysis of Ade but also for revealing certain details in electrode processes.

On the importance of electrostatics in stabilization of stacked guanine–adenine complexes appearing in B-DNA crystals

In this paper, the importance of the first-order electrostatic energy in stabilization of stacked guanine–adenine complexes is discussed for conformations of the complexes appearing in B-DNA crystals. The interaction energy components were calculated at the SCF level of theory using variational–perturbational scheme and compared with the total MP2 intermolecular interaction energy. It is demonstrated that electrostatic energy plays an important role in the stabilization of analyzed structures. Moreover, the results of calculations show that the electrostatic component is much more dependent on the conformations of guanine–adenine complexes than the total MP2 interaction energy.

Theoretical Study on the Gas-Phase Acidity of Multiple Sites of Cu+−Adenine and Cu2+−Adenine Complexes

The acidities of multiple sites in Cu(+)-adenine and Cu(2+)-adenine complexes have been investigated theoretically. To compare, the acidities of adenine (A) and adenine radical cation (A(*+)) have also been included. The results clearly indicate that the acidities of C-H and N-H groups in Cu(+/2+)-adenine are significantly enhanced relative to the neutral adenine. The acidic order for a given site on adenine and adenine derivatives is as follows: Cu(2+)-adenine > A(*+) > Cu(+)-adenine > A. For Cu(+)-adenine and Cu(2+)-adenine, N3-coordination exhibits N9-H acid, and N1- and N7-coordination exhibits N6-H(a) and N6-H(b) acid, respectively. Additionally, it is found that C2-H group is surprisingly acidic in the coordination complexes. Calculations in aqueous solution reveal that our results can be extrapolated to aqueous solution. Analyses of the electronic properties interpret the highest acidity of Cu(2+)-adenine among the adenine derivatives studied. Also, Electrostatic potential calculations of [A(-H(+))](-) and [A(-H(+))](*) indicate that the removal of H(a) or H(b) from the amino group favors the bidentate coordination, which provides a dative bond from the deprotonated N and the original coordination ligand to copper ion besides the electrostatic interaction between them and thereby stabilizes the [A(-H(+))](-)/[A(-H(+))](*). NBO analysis confirms the electrostatic potential result.

Metal ion interactions with nucleobases in the tripodal tris(2-aminoethyl)amine (tren) ligand-system. Crystal structures of [Zn(tren)(adeninato)] · ClO 4, [Cd(tren)(adeninato)] · ClO 4, [Ni(tren)(adeninato)(ClO 4)], [Zn(tren)(hypoxanthinato)] · ClO 4 · H 2O, [{Cd(tren)} 2(hypoxanthinato)] · (ClO 4) 3 · 0.5H 2O, [Ni(tren)(uracilato)(H 2O)] · ClO 4 · (0.5H 2O) 2, and [Cu(tren)(uracilato)] · ClO 4 · 0.5H 2O

Reaction between nucleobases (adenine, hypoxanthine, cytosine, and uracil), tris(2-aminoethyl)amine (tren) and M(ClO 4) 2 (M 2+ = Zn 2+, Cd 2+, Ni 2+ or Cu 2+) under pH 8–9 gave eight ternary tren-metal ion-nucleobase complexes, among which seven crystal structures, [Zn(tren)(adeninato)] · ClO 4 ( 1), [Cd(tren)(adeninato)] · ClO 4 ( 2), [Ni(tren)(adeninato)(ClO 4)] ( 3), [Zn(tren)(hypoxanthinato)] · ClO 4 · H 2O ( 4), [{Cd(tren)} 2(hypoxanthinato)] · (ClO 4) 3 · 0.5 H 2O ( 5), [Ni(tren)(uracilato)(H 2O)] · ClO 4 · (0.5H 2O) 2 ( 7), and [Cu(tren)(uracilato)] · ClO 4 · 0.5H 2O ( 8) were determined by X-ray diffraction. In each of the adenine complexes with Zn 2+ ( 1), Cd 2+ ( 2), and Ni 2+ ( 3), among which 1 and 2 are isostructural to each other, a tren-capped metal ion binds to an adeninato ligand through N(9) with the formation of an intramolecular interligand hydrogen bond between the amino nitrogen of tren and N(3) of the base. In the hypoxanthine complexes 4 and 5, a tren-capped Zn 2+ ion in 4 binds to a hypoxanthinato ligand through N(9) with the formation of an intramolecular N(tren)–H⋯N(3) hydrogen bond, while in 5 two tren-capped Cd 2+ ions bind to a hypoxanthinato ligand, one through N(7) with the formation of an intramolecular N(tren)–H⋯O(6) hydrogen bond and the other through N(9) to form an intramolecular N(tren)–H⋯N(3) hydrogen bond. In each of the uracil complexes with Ni 2+ ( 7) and Cu 2+ ( 8), a tren-capped metal ion binds to an uracilato ligand through N(1) with the formation of an intracomplex O(aqua)–H⋯O(2) hydrogen bond in 7 or an intramolecular N(tren)–H⋯O(2) hydrogen bond in 8. Tren-capped metal ion-bonded nucleobases act as building blocks for the assembly of supramolecular structures, by versatile hydrogen bonding and/or stacking abilities of nucleobases. The significance of intramolecular interligand interaction as a factor that affects metal-binding site(s) on nucleobases is emphasized.

Copper–adenine complex, a compound, with multi-biochemical targets and potential anti-cancer effect

A series of adenine–copper complexes ( 1– 6) with various ligands (Cl −, SCN −, BF 4 − and acac [acetylacetonate ion]) have been synthesized and characterized by elemental analysis, infrared spectroscopy and thermal analysis. Among the six complexes only complex ( 1), Cu 2(adenine) 4Cl 4·2EtOH (abbreviated as Cu–Ad), demonstrated some toxic effect on different cell lines. In vitro investigations of the biological effect of Cu–Ad complex have shown that it: (1) binds genomic DNA; (2) decreases significantly, the viability of cells in culture in a concentration (15–125 μM)-dependant manner; an estimated IC 50 of: 45 μM with HepG2; 73 μM with C2C12; 103 μM with NIH3T3; and 108 μM with MCF7. Cu–Ad had no effect on A549 cells; (3) inhibits Taq polymerase-catalyzed reaction; (4) inhibits the binding of the transcription factor GATA-5 to labeled DNA probes; (5) inhibits mitochondrial NADH-UQ-reductase with an estimated IC 50 of 2.8 nmol, but had no effect on succinate dehydrogenase activity; (6) increases reactive oxygen species (60%) at 45 μM Cu–Ad; and (7) decreases ATP (80%) at 50 μM Cu–Ad. The new compound Cu 2(adenine) 4Cl 4·2EtOH (Cu–Ad), belongs to a class of copper–adenylate complexes that target many biochemical sites and with potential anti-cancer activity.

Density functional theory study on hydrogen‐bonded complexes of adenine with polyformamide molecules

AbstractThe structures of hydrogen‐bonded complexes A–Fn(n= 2–7) of adenine with polyformamide molecules have been fully optimized at B3LYP/6‐31G(d) basis set level. All the formamide molecules prefer to be NH proton donor rather than CH proton donor and are favorably bound to the five‐numbered moiety of adenine. A displacement of formamide molecules to one side of adenine mean plane has happened with an increasing number of formamide molecules. An obvious effect of hydrogen‐bonding cooperativity can be seen during the complex process. The most interesting geometrical change of adenine upon the complex is the shortening of the bond C4N6 resulting from the strengthening of the conjugation between the π system of the adenine ring and the lone pair of the nitrogen atom. An existence of weak NH···π bonding interaction between the π system of adenine and NH bond of F7 is found and further conformed by an natural bond orbital analysis specially carried out on A–F7. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Controlled aggregation of adenine by sugars: physicochemical studies, molecular modelling simulations of sugar–aromatic CH–π stacking interactions, and biological significance

CH-Pi stacking interactions between carbohydrates and aromatic compounds play a central role in biomolecular recognition, especially in lectin-sugar and protein-glycolipid systems. In the present study, we have measured the solubility of the sparingly soluble aromatic base adenine in presence of various saccharides as an approach to investigate the interaction between adenine and sugars. Above 82.5 mM, adenine solutions gradually formed a crystalline precipitate which could be quantified by spectrophotometric turbidity measurements. Precipitation of adenine was increased by salts (NaCl and NaF) whereas it was prevented by DMSO, in agreement with the involvement of hydrophobic interactions (pi-pi stacking) in the vertical stacking of adenine molecules. Several monosaccharides and disaccharides were found to increase adenine solubility, with the following order: D-galactose = D-lactose > D-sucrose > D-glucose = D-maltose > D-ribose > D-fructose. Molecular mechanics simulations indicated that the potent cosolvent effect of beta-D-galactopyranose was probably mediated by CH-pi stacking interactions between its apolar surface and the aromatic structure of adenine. The polar OH groups of the sugars interacted with surrounding water molecules, ensuring the solubility of sugar-adenine complexes. In contrast, beta-D-fructofuranose, which has two polar faces, did not stack onto adenine and had a weak cosolvent effect. CH-pi stacking interactions were also demonstrated between 6-methylpurine and the sugar head group of glycolipids (glucosyl-, galactosyl- and lactosylceramide) but not with the charged head group of phosphatidylinositol-4,5-diphosphate. These data indicate that galactose-containing molecules have a high stacking propensity for aromatic compounds such as adenine, due to the specific structure of the galactose cycle.

The origin of deficiency of the supermolecule second-order Møller-Plesset approach for evaluating interaction energies

Calculations for the complex of thymine and adenine are used to show that the supermolecule second-order Moller-Plesset perturbation theory (MP2) approach for evaluating interaction energies fails in certain cases because of the behavior of one of its components: the uncoupled Hartree-Fock dispersion energy. A simple approach for correcting the MP2 supermolecule interaction energies is proposed. It focuses on correcting a relatively small difference between the MP2 and coupled cluster interaction energies, which is a very appealing feature of the new approach considering a benchmark role played by coupled cluster results.

Metal-ion binding and metal-ion induced folding of the adenine-sensing riboswitch aptamer domain

Divalent cations are important in the folding and stabilization of complex RNA structures. The adenine-sensing riboswitch controls the expression of mRNAs for proteins involved in purine metabolism by directly sensing intracellular adenine levels. Adenine binds with high affinity and specificity to the ligand binding or aptamer domain of the adenine-sensing riboswitch. The X-ray structure of this domain in complex with adenine revealed an intricate RNA-fold consisting of a three-helix junction stabilized by long-range base-pairing interactions and identified five binding sites for hexahydrated Mg2+-ions. Furthermore, a role for Mg2+-ions in the ligand-induced folding of this RNA was suggested. Here, we describe the interaction of divalent cations with the RNA–adenine complex in solution as studied by high-resolution NMR spectroscopy. Paramagnetic line broadening, chemical shift mapping and intermolecular nuclear Overhauser effects (NOEs) indicate the presence of at least three binding sites for divalent cations. Two of them are similar to those in the X-ray structure. The third site, which is important for the folding of this RNA, has not been observed previously. The ligand-free state of the RNA is conformationally heterogeneous and contains base-pairing patterns detrimental to ligand binding in the absence of Mg2+, but becomes partially pre-organized for ligand binding in the presence of Mg2+. Compared to the highly similar guanine-sensing riboswitch, the folding pathway for the adenine-sensing riboswitch aptamer domain is more complex and the influence of Mg2+ is more pronounced.

Structural and Energetic Properties of Organometallic Ruthenium(II) Diamine Anticancer Compounds and Their Interaction with Nucleobases.

We rationalize the chemoselectivity of the monofunctional ruthenium anticancer compound [(η(6)-arene)Ru(II)(en)(OH2)](2+) (en=ethylenediamine; arene=benzene 1, p-cymene 2) toward guanine, using static DFT (BP86) and MP2 calculations together with Car-Parrinello molecular dynamics. The calculated binding energies for the three investigated nucleobases (G, A, C) decreases in the order G(N7) ≫ C(O2) ∼ C(N3) > A(N7) > G(O6) > OH2. The G(N7) complex is the most stable product due to a hydrogen bond of its O6 with one of the H2N-amine groups of en, while the corresponding NH2-H2N(en) interaction in the adenine complex is repulsive. A very low rotational barrier of 0.17 kcal/mol (BP86) and 0.64 kcal/mol (MP2) was calculated for the arene rotation in [(η(6)-C6H6)Ru(en)(Cl)](+) (3) allowing complexes containing arenes with bulky side chains like p-cymene to minimize steric interactions with, e.g., DNA by simple arene rotation. All [(η(6)-arene)Ru(en)(L)](2+) compounds exist in two stable conformers obtained for different diamine dihedral angle (NCCN) orientation, which, in the case of asymmetric ligands L, differ by up to ∼2.8 kcal/mol. Car-Parrinello dynamics reveal a chelating transition state for the interconversion between N7 and O6 binding of guanine to [(η(6)-arene)Ru(en)](2+).

Metal ion interactions with nucleic acid bases in the tripodal tris(2-aminoethyl)amine (tren) ligand-system: Crystal structures of [Ni(tren)(adeninato)(ClO 4)] · adenine, [Cu(tren)(9-ethylguanine)] · (ClO 4) 2, [{Ni(tren)(H 2O)} 2(hypoxanthinato)] · (ClO 4) 3 · 1.5H 2O, [Ni(tren)(hypoxanthinato)(H 2O)] · ClO 4 · 2H 2O, and [{Ni(tren)(H 2O)} 2(hypoxanthinato)] 2 · (NO 3) 6 · 4.5H 2O

Reaction of tris(2-aminoethyl)amine (tren) and Cu(ClO 4) 2, Ni(ClO 4) 2, or Ni(NO 3) 2 with purine nucleobases (adenine, 9-ethylguanine, and hypoxanthine) gave five ternary tren–metal ion–nucleobase complexes, [Ni(tren)(adeninato)(ClO 4)] · adenine ( 1), [Cu(tren)(9-ethylguanine)] · (ClO 4) 2 ( 2), [{Ni(tren)(H 2O)} 2(hypoxanthinato)] · (ClO 4) 3 · 1.5H 2O ( 3), [Ni(tren)(hypoxanthinato)(H 2O)] · ClO 4 · 2H 2O ( 4), and [{Ni(tren)(H 2O)} 2(hypoxanthinato)] 2 · (NO 3) 6 · 4.5H 2O ( 5), where 1 and 4 were prepared under pH 8–9 while 2, 3, and 5 were under pH 6–7, and their crystal structures were determined by X-ray diffraction. In the adenine complex 1, the tren-capped metal ion binds to the base through N(9) with the formation of an intramolecular interligand hydrogen bond between the amino group of tren and N(3) of the base, and the 9-ethylguanine complex 2 involves the metal bonding to N(7) of the base with the formation of an intramolecular hydrogen bond between the amino group of tren and O(6) of the base. In the hypoxanthine complexes 3 and 5, the metal ions bind to N(7) in addition to N(9), forming three intramolecular hydrogen bonds, two involving O(6) with the amino nitrogen of tren and the aqua ligand and one between the aqua ligand and N(3) of the base, whereas the hypoxanthine complex 4 involves the metal bonding solely to N(9) with the formation of an intramolecular hydrogen bond between the aqua ligand and N(3) of the base, where N(7) as well as N(1) are hemi-protonated. The absence of the metal–N(7) bonding for adenine in 1 while the metal bonding to N(7) specific for guanine derivatives in 2, 3 and 5 are rationalized in terms of interligand interactions.

Stability of Nucleic Acid Base Pairs in Organic Solvents: Molecular Dynamics, Molecular Dynamics/Quenching, and Correlated Ab Initio Study

The dynamic structure and potential energy surface of adenine...thymine and guanine...cytosine base pairs and their methylated analogues interacting with a small number (from 1 to 16 molecules) of organic solvents (methanol, dimethylsulfoxide, and chloroform) were investigated by various theoretical approaches starting from simple empirical methods employing the Cornell et al. force field to highly accurate ab initio quantum chemical calculations (MP2 and particularly CCSD(T) methods). After the simple molecular dynamics simulation, the molecular dynamics in combination with quenching technique was also used. The molecular dynamics simulations presented here have confirmed previous experimental and theoretical results from the bulk solvents showing that, whereas in chloroform the base pairs create hydrogen-bonded structures, in methanol, stacked structures are preferred. While methanol (like water) can stabilize the stacked structures of the base pairs by a higher number of hydrogen bonds than is possible in hydrogen-bonded pairs, the chloroform molecule lacks such a property, and the hydrogen-bonded structures are preferred in this solvent. The large volume of the dimethylsulfoxide molecule is an obstacle for the creation of very stable hydrogen-bonded and stacked systems, and a preference for T-shaped structures, especially for complexes of methylated adenine...thymine base pairs, was observed. These results provide clear evidence that the preference of either the stacked or the hydrogen-bonded structures of the base pairs in the solvent is not determined only by bulk properties or the solvent polarity but rather by specific interactions of the base pair with a small number of the solvent molecules. These conclusions obtained at the empirical level were verified also by high-level ab initio correlated calculations.

The Effect of V(III)-Adenine Complex on Yeast as a Model of Eukaryotic Cells

The dinuclear micro-okso vanadium (III) complex compound H(4)V(2)OCl(4)(Ad)(2) synthesized in our laboratory was investigated as a potential cytotoxic agent against yeast cells. The results of these studies could be helpful in the explanation of the mechanism governing the V (III) compound action on yeast as a simple model of eukaryotic cells. The important factors influencing the toxicity of this complex compound are: the stage of the yeast life cycle, the rate of growth and the pH of reaction mixture. The lethal effect was distinctly stronger when the reaction mixture was slightly acidic (pH = 4). In such solutions V(III) mononuclear species with adenine was relatively stable, and during the time of experiment possibly only a slow oxidation process to V(IV) occurred. In the solutions with pH = 7, several hydrolytic, perhaps mixed-valence, polynuclear species were present and their action on the yeast cells was rather weak. The increased lethal activity of this compound in acidic solutions may be useful in specific treatment against cancer cells whose cytoplasm and/or closest surrounding has lower pH value. The next important result was an observation that the killing activity of this compound was enhanced for yeast cells being in log phase. Also these which had a slower rate of growth (possessing some auxotrophic mutations) were more resistant than those growing faster. The extent of yeast mutagenesis caused by the complex compound is negligible, as the number of mutants found in experiments was within the limit of experimental error. These results are promising and the investigated complex can be considered as a potential anti cancer agent.

Valence Anions in Complexes of Adenine and 9-Methyladenine with Formic Acid: Stabilization by Intermolecular Proton Transfer

Photoelectron spectra of adenine-formic acid (AFA(-)) and 9-methyladenine-formic acid (MAFA(-)) anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and anionic complexes of adenine/9-methyladenine and formic acid were also studied computationally at the B3LYP, second-order Møller-Plesset, and coupled-cluster levels of theory with the 6-31++G** and aug-cc-pVDZ basis sets. The neutral complexes form cyclic hydrogen bonds, and the most stable dimers are bound by 17.7 and 16.0 kcal/mol for AFA and MAFA, respectively. The theoretical results indicate that the excess electron in both AFA(-) and MAFA(-) occupies a pi* orbital localized on adenine/9-methyladenine, and the adiabatic stability of the most stable anions amounts to 0.67 and 0.54 eV for AFA(-) and MAFA(-), respectively. The attachment of the excess electron to the complexes induces a barrier-free proton transfer (BFPT) from the carboxylic group of formic acid to a N atom of adenine or 9-methyladenine. As a result, the most stable structures of the anionic complexes can be characterized as neutral radicals of hydrogenated adenine (9-methyladenine) solvated by a deprotonated formic acid. The BFPT to the N atoms of adenine may be biologically relevant because some of these sites are not involved in the Watson-Crick pairing scheme and are easily accessible in the cellular environment. We suggest that valence anions of purines might be as important as those of pyrimidines in the process of DNA damage by low-energy electrons.

Does the A·T or G·C Base-Pair Possess Enhanced Stability? Quantifying the Effects of CH···O Interactions and Secondary Interactions on Base-Pair Stability Using a Phenomenological Analysis and ab Initio Calculations

An empirically based relationship between overall complex stability (-DeltaG degrees ) and various possible component interactions is developed to probe the question of whether the A.T/U and G.C base-pairs exhibit enhanced stability relative to similarly hydrogen-bonded complexes. This phenomenological approach suggests ca. 2-2.5 kcal mol-1 in additional stability for A.T owing to a group interaction containing a CH...O contact. Pairing geometry and the role of the CH...O interaction in the A.T base-pair were also probed using MP2/6-31+G(d,p) calculations and a double mutant cycle. The ab initio studies indicated that Hoogsteen geometry is preferred over Watson-Crick geometry in A.T by ca. 1 kcal mol-1. Factors that might contribute to the preference for Hoogsteen geometry are a shorter CH...O contact, a favorable alignment of dipoles, and greater distances between secondary repulsive sites. The CH...O interaction was also investigated in model complexes of adenine with ketene and isocyanic acid. The ab initio calculations support the result of the phenomenological approach that the A.T base-pair does have enhanced stability relative to hydrogen-bonded complexes with just N-H...N and N-H...O hydrogen bonds.

Copper–adenine complex: A new class of compounds with multi-in vitro biochemical effects on cancer cells

Copper–adenine complex: A new class of compounds with multi-in vitro biochemical effects on cancer cells

Interaction of porphyrins with adenine and adenosine complexes. Effect of a metal nature

Reactions of complex formation of 5,10,15,20-tetraphenylporphine (H2TPP) and tetra-tert-butylphthalocyanine (H2(t-Bu)4Pc) with adenine and adenosine complexes of d-metals in DMSO and ethanol are studied. It was found that H2TPP reacts with Cu(II) and Hg(II) adeninates and adenosinates in DMSO, but does not react with Zn(II), Co(II), and Cd(II) adeninates and adenosinates (with both bridging and monodentate type of the ligand coordination). H2(t-Bu)4Pc enters the complex formation reaction with adeninates and adenosinates of all studied metals in DMSO at almost equal rates. The states of adenine and adenosine complexes of different d-metals in DMSO and ethanol are proposed on the basis of kinetic data obtained.

Conserved supramolecular architecture in polymetallic nucleobase complexes

The single crystal X-ray structures of two different polynuclear metal–nucleobase complexes are reported. Crystals isolated from the reaction of CdBr 2 with ethylenediamine-N9-ethyladenine, A-Et-en, were characterised by X-ray structural analysis as a coordination polymer [μ-{CdBr( N3, N7-A-Et-en)} 2CdBr 4] ( 2). Reaction of the Pd(II)–adenine complex, [PdCl( N3-A-Et-en)] +, with sodium uracilate yielded [(Pd( N3-A-Et-en) 2( N1, N3-U)][ClO 4] 2 ( 3). Despite the considerable differences in the nature of the compounds the crystal structures feature essentially similar supramolecular architectures. A building block analysis demonstrates how this arises and reveals an approach, based on bond-type substitution and molecular replacement, to conserving such features. This may be a useful approach that could be more widely adopted in crystal engineering strategies.

Watson–Crick pairing of nucleobases functionalized with open-shell molecular entities in crystalline solids

A Watson-Crick type molecular complex of adenine and thymine bases substituted with the stable radical of nitronylnitroxide has been synthesized, which forms a double-chain spin system in the crystal.