Semenogelins Armed in Zn(II) and Cu(II): May Bioinorganic Chemistry Help Nature to Cope with Enterococcus faecalis?

Proteolytic degradation of semenogelins, the most abundant proteins from human semen, results in the formation of 26- and 29-amino acid peptides (SgIIA and SgI-29, respectively), which share a common 15 amino acid fragment (Sg-15). All three ligands are effective Zn(II) and Cu(II) binders; in solution, a variety of differently metalated species exist in equilibrium, with the [NH2, 3Nim] donor set prevailing at physiological pH in the case of both metals. For the first time, the Cu(II)-induced antimicrobial activity of Sg-15 against Enterococcus faecalis is shown. In the case of the two native semenogelin fragment metal complexes, the strong local positive charge in the metal-bound HH motif correlates well with their antimicrobial activity. A careful analysis of semenogelins' metal coordination behavior reveals two facts: (i) The histamine-like Cu(II) binding mode of SgI-29 strongly increases the stability of such a complex below pH 6 (with respect to the non-histamine-like binding of SgIIA), while in the case of the SgI-29 Zn(II)-histamine-like species, the stability enhancement is less pronounced. (ii) The HH sequence is a more tempting site for Cu(II) ions than the HXH one.

CH vs. HC-Promiscuous Metal Sponges in Antimicrobial Peptides and Metallophores.

Histidine and cysteine residues, with their imidazole and thiol moieties that deprotonate at approximately physiological pH values, are primary binding sites for Zn(II), Ni(II) and Fe(II) ions and are thus ubiquitous both in peptidic metallophores and in antimicrobial peptides that may use nutritional immunity as a way to limit pathogenicity during infection. We focus on metal complex solution equilibria of model sequences encompassing Cys-His and His-Cys motifs, showing that the position of histidine and cysteine residues in the sequence has a crucial impact on its coordination properties. CH and HC motifs occur as many as 411 times in the antimicrobial peptide database, while similar CC and HH regions are found 348 and 94 times, respectively. Complex stabilities increase in the series Fe(II) < Ni(II) < Zn(II), with Zn(II) complexes dominating at physiological pH, and Ni(II) ones-above pH 9. The stabilities of Zn(II) complexes with Ac-ACHA-NH2 and Ac-AHCA-NH2 are comparable, and a similar tendency is observed for Fe(II), while in the case of Ni(II), the order of Cys and His does matter-complexes in which the metal is anchored on the third Cys (Ac-AHCA-NH2) are thermodynamically stronger than those where Cys is in position two (Ac-ACHA-NH2) at basic pH, at which point amides start to take part in the binding. Cysteine residues are much better Zn(II)-anchoring sites than histidines; Zn(II) clearly prefers the Cys-Cys type of ligands to Cys-His and His-Cys ones. In the case of His- and Cys-containing peptides, non-binding residues may have an impact on the stability of Ni(II) complexes, most likely protecting the central Ni(II) atom from interacting with solvent molecules.

Uracil Derivatives for Halogen-Bonded Cocrystals.

Among non-covalent interactions, halogen bonding is emerging as a new powerful tool for supramolecular self-assembly. Here, along with a green and effective method, we report three new halogen-bonded cocrystals containing uracil derivatives and 1,2,4,5-tetrafluoro-3,6-diiodobenzene as X-bond donor coformer. These multicomponent solids were prepared both by solvent-drop grinding and solution methods and further characterized by powder and single-crystal X-ray diffraction, Fourier-transformed infrared spectroscopy, and thermal methods (TGA-DSC). In order to study the relative importance of hydrogen versus halogen bonds in the crystal packing, computational methods were applied.

Deciphering the H-Bonding Preference on Nucleoside Molecular Recognition through Model Copper(II) Compounds.

The synthetic nucleoside acyclovir is considered an outstanding model of the natural nucleoside guanosine. With the purpose of deepening on the influence and nature of non-covalent interactions regarding molecular recognition patterns, three novel Cu(II) complexes, involving acyclovir (acv) and the ligand receptor N-(2-hydroxyethyl)ethylenediamine (hen), have been synthesized and thoroughly characterized. The three novel compounds introduce none, one or two acyclovir molecules, respectively. Molecular recognition has been evaluated using single crystal X-ray diffraction. Furthermore, theoretical calculations and other physical methods such as thermogravimetric analysis, infrared and UV-Vis spectroscopy, electron paramagnetic resonance and magnetic measurements have been used. Theoretical calculations are in line with experimental results, supporting the relevance of the [metal-N7(acv) + H-bond] molecular recognition pattern. It was also shown that (hen)O-H group is used as preferred H-donor when it is found within the basal coordination plane, since the higher polarity of the terminal (hen)O-H versus the N-H group favours its implication. Otherwise, when (hen)O-H occupies the distal coordination site, (hen)N-H groups can take over.

Silver(I)-mediated base pairing in DNA involving the artificial nucleobase 7,8-dihydro-8-oxo-1,N6-ethenoadenine.

The artificial nucleobase 7,8-dihydro-8-oxo-1,N6-ethenoadenine (X) was investigated with respect to its ability to engage in Ag(I)-mediated base pairing in DNA. Spectroscopic data indicate the formation of dinuclear X-Ag(I)2-X homo base pairs and mononuclear X-Ag(I)-C base pairs (C, cytosine). Density functional theory calculations and molecular dynamics simulations indicate that the nucleobase changes from its lactam tautomeric form prior to the formation of the Ag(I)-mediated base pair to the lactim form after the incorporation of the Ag(I) ions. Fluorescence spectroscopy indicates that the two Ag(I) ions of the homo base pair are incorporated sequentially. Isothermal titration calorimetry confirms that the affinity of one of the Ag(I) ions is about tenfold higher than that of the other Ag(I) ion. The computational analysis by means of density functional theory confirms a much larger reaction energy for the incorporation of the first Ag(I) ion. The thermal stabilization upon the formation of the dinuclear Ag(I)-mediated homo base pair exceeds the one previously observed for the closely related nucleobase 1,N6-ethenoadenine by far, despite very similar structures. This additional stabilization may stem from the presence of water molecules engaged in hydrogen bonding with the additional oxygen atom of the artificial nucleobase X. The highly stabilizing Ag(I)-mediated base pair is a valuable addition to established dinuclear metal-mediated base pairs.

Adipato bridged novel hexanuclear Cu(ii) and polymeric Co(ii) coordination compounds involving cooperative supramolecular assemblies and encapsulated guest water clusters in a square grid host: antiproliferative evaluation and theoretical studies.

Two new coordination compounds involving hexanuclear Cu(ii), viz., [Cu6(phen)6(µ4-adpt)4(H2O)2](NO3)4·10H2O (1) and polymeric Co(ii), viz., {[(µ2-adpt)4Co(µ2-H2O)2Co(H2O)4]·4H2O}n (2) (phen = 1,10-phenanthroline; adpt = adipate) have been synthesized and characterized using elemental analysis, TGA, spectroscopic (IR, electronic and ESR), PXRD and single crystal X-ray diffraction techniques. Discrete nitrate-water clusters involving the [(H2O)3NO3]- core in 1 and linear (H2O)4 core in 2 provide stability to the layered network of the structures of the compounds. Interestingly, the water clusters in polymer 2 are encapsulated as guests in the voids of the host square grid that extends in 2D architecture. Theoretical studies have revealed the presence of interesting energetically significant cooperativity effects of π-stacking contacts that are responsible for the hexanuclear structure of compound 1. Both complexes significantly inhibit cell viability by inducing apoptotic cell death in the DL cancer cell line with negligible cytotoxicity in normal cells (PBMC). An assessment of ROS (reactive oxygen species) level study revealed a rapid increase of ROS in DL cells indicating cytotoxicity of the compounds against the DL cells. A decrease in MMP (mitochondrial membrane potential) is associated with an opening of the mitochondrial permeability transition pores which corroborates the apoptotic features of 1 and 2. The mode of action of the cytotoxic activities of the compounds has been explored with respect to their in silico docking ability and further inhibition of antiapoptotic proteins as evidenced by western blot analysis. SAR analyses based on pharmacophore modelling reveal that the molecular features of the structures of the compounds play important roles in biological activities.

Synthesis, X-ray characterization and regium bonding interactions of a trichlorido(1-hexylcytosine)gold(iii) complex.

Herein we report the synthesis and X-ray characterization of a gold(iii) complex of 1-hexylcytosine via N(3). The AuCl3N complexes stack on top of each other by reciprocal [AuCl] regium bonding interactions. After the first example 35 years ago, this is the second available structure of a cytosine nucleobase model complexed to gold(iii).

Iridium(III) coordination of N(6) modified adenine derivatives with aminoacid chains.

In this manuscript we report the preparation of three N6-aminoacid-adenine-derivatives: N-(7H-purin-6-yl)glycine·0.5H2O (N6-GlyAde), N-(7H-purin-6-yl)-ß-alanine·1.5H2O (N6-ß-AlaAde) and N-(7H-purin-6-yl)-γ-aminobutyric·2H2O (N6-GabaAde) and the synthesis and X-ray characterization of three Ir(III) NAMI-A derivatives (NAMI-A is [imidazoleH][trans-RuIIICl4(DMSO-κS)(imidazole)]) [trans-IrIIICl4(DMSO-κS)(N3-H)-(7H-purin-6-yl)glycine-κN9] (1), [trans-IrIIICl4(DMSO-κS)(N3-H)-(7H-purin-6-yl)-ß-alanine-κN9] hydrate (2) and [trans-IrIIICl4(DMSO-κS)(N3-H)-(7H-purin-6-yl)-γ-aminobutyryl-κN9] (3). In all complexes the metal center shows octahedral geometry with coordination to four chlorido ligands and one S coordinated dimethylsulfoxide (DMSO-κS). The coordination sphere of the metal is completed by the modified adenine molecule which is bound via N(9) and protonated at N(3). In two complexes the importance of lone pair (lp)-π interactions involving the adenine ring have been studied using density functional theory (DFT) calculations and the Bader's theory of atoms in molecules. Furthermore, the ability of complexes (1-3) to affect the cell viability was evaluated against three different cancer cell lines: human lung carcinoma cells (A549), human cervical carcinoma cells (HeLa) and human breast cancer cells (MCF7). We have also analyzed their ability to cleave the DNA experimentally and their affinity for two models of DNA has been studied using molecular docking simulations.

Synthesis, reactivity, X-ray characterization and docking studies of N7/N9-(2-pyrimidyl)-adenine derivatives.

The reaction of adenine with 2-chloropyrimidine yields as a major product the unexpected N7-(2-pyrimidyl)-adenine (1) and as a minor one N9-(2-pyrimidyl)-adenine (2). Both compounds have been characterized by X-ray diffraction analysis. Moreover, we report the formation of a 1:1 co-crystal (3) composed by compound (1) and adenine that was formed serendipitously during the synthesis of (1). Unexpectedly, the treatment of (1) with Brönsted acids like HCl or HNO3 causes the opening of the imidazole ring of the N7-substituted adenine, yielding N5-(pyrimidin-2-yl)pyrimidine-4,5,6-triamine (4-7) which we have X-ray characterized in its neutral, (4), monoprotonated [nitrate salt (6)] and diprotonated forms [hydrochloride salt (5) and, also, a tetrachlorozincate salt (7)]. Finally, we have used compound (5) as ligand to synthesize and X-ray characterize its complexes with Ir(III) and Ag(I) (compounds (8) and (9), respectively), where the latter is a 2D coordination polymer and the former is a discrete mononuclear complex. We have studied the supramolecular assemblies formed in the solid state by using density functional theory (DFT) calculations. Finally, DNA-docking studies of several compounds have been carried out in order to analyze their ability to interact with the DNA.

Probing the effect of N-alkylation on the molecular recognition abilities of the major groove N7-binding site of purine ligands.

The study of the metal binding pattern of N-methyladenines (1-, 3-, 7- or 9-Meade) towards CuII-iminodiacetate-like chelates is addressed on the basis of XRD crystal structures of sixteen novel ternary compounds. Except for three compounds, all others feature an square-based Cu(II) coordination, type 4 + 1, and the efficient cooperation of a CuN7 bond with an intra-molecular N6-H⋯O(coord. carboxylate) interligand interaction as the major metal-binding pattern. The three referred exceptions to this behavior are: (1) the compound [Cu(MIDA)(7Meade)(H2O)]·4H2O, which evidence the CuN3 binding pattern; the (2) [Cu(IDA)(1Meade)(H2O)2]·4H2O, which molecular recognition consist in the CuN9 bond and a (distal aqua)⋯⋯N3(1Meade) intra-molecular interaction, within an octahedral Cu(II) center; and (3) [Cu(IDA)(9Meade)(H2O)2]·3H2O, also with a 4 + 1 + 1 Cu(II) coordination, where the CuN7 bond exists along with an extremely weak N6-H⋯O(coord. carboxylate) interaction (3.33 Å, 140.2°). This former interaction is determined by packing forces that promote the participation of the N6H group in a 'trifurcated' H-bond. In conclusion, the cooperation between the CuN7 bond (not possible for 7Meade) and the intra-molecular N6-H⋯O interaction is clearly favored (a) by the H-accepting role of the O-coordinated carboxylate atoms from the iminodiacetate ligands in mer-NO2 conformation and (b) in compounds where the Cu(II) atom exhibits an elongated square-base pyramidal coordination, type 4 + 1.

The Role of Lead(II) in Nucleic Acids.

Although lead(II) is naturally not associated with nucleic acids, this metal ions has been applied with DNA and RNA in various contexts. Pb2+ is an excellent hydrolytic metal ion for nucleic acids, which is why it is mainly used as probing agent for secondary structure and to determine metal ion binding sites both in vitro and in vivo. A further application of lead(II) is in structural studies, i.e., NMR, but also in X-ray crystallography, mostly using this heavy metal to solve the phase problem in the latter method. The structures of tRNAPhe, RNase P, HIV-1 DIS, and the leadzyme are discussed here in detail. A major part of this review is devoted to the cleavage properties of lead(II) with RNA because of its excellence in catalyzing phosphodiester cleavage. Metal ion binding sites in large naturally occurring ribozymes are regularly determined by Pb2+ cleavage, and also in the in vitro selected socalled leadzyme, this metal ion is the decisive key to backbone cleavage at a specific site. Lead(II) was used in the first in vitro selection that yielded a catalytic DNA, i.e., the DNAzyme named GR5. Next to the GR5, the so-called 8-17E is the second most prominent DNAzyme today. Derivatives of these two lead(II)-dependent DNAzymes, as well as the G-quadruplex forming PS2.M have been applied to detect lead(II) in the lower nanomolar range not only in the test tube but also in body fluids. Due to the toxicity of lead(II) for living beings, this is a highly active research field. Finally, further applications of lead(II)-dependent DNAzymes, e.g., in the construction of nanocomputers, are also discussed.

X-ray Crystal Structure of a Metalled Double-Helix Generated by Infinite and Consecutive C*-AgI -C* (C*:N1 -Hexylcytosine) Base Pairs through Argentophilic and Hydrogen Bond Interactions.

The synthesis of a metalled double-helix containing exclusively silver-mediated C*-C* base pairs is reported herein (C*=N1 hexylcytosine). Remarkably, it is the first crystal structure containing infinite and consecutive C*-AgI -C* base pairs that form a double helix. The AgI ion occupies the center between two C* residues with N(3)-Ag bond lengths of 2.1 Šand short AgI -AgI distances (3.1 Å) suggesting an interesting argentophilic attraction as a stabilization source of the helical disposition. The solid-state structure is further stabilized by metal-mediated base-pairs, hydrogen bonding and π-stacking interactions. Moreover, the angle N(3)-Ag-N(3) is almost linear in the [Ag(N1 hexylcytosine)2 ]+ motif and the bases are not coplanar, thus generating a double-strand helical aggregate in the solid state. The noncovalent and argentophilic interactions have been rationalized based on DFT calculations.

Triple-bridged ferromagnetic nickel(II) complexes: a combined experimental and theoretical DFT study on stabilization and magnetic coupling.

Two dinuclear [Ni2L2(o-(NO2)C6H4COO)2(H2O)] (1), [Ni2L2(p-(NO2)C6H4COO)2(H2O)]·0.5CH3OH (2) complexes and one trinuclear [Ni3L2(p-(NO2)C6H4COO)4]·C2H5OH (3) Ni(II) complex have been synthesized using a tridentate Schiff base ligand, 1-[(3-dimethylamino-propylimino)-methyl]-naphthalen-2-ol (HL) along with ortho- and para-nitro benzoate as co-ligands. All these three (1-3) complexes have been characterized by spectral analysis, X-ray crystallography and variable temperature magnetic susceptibility measurements. The structural analyses reveal that complexes 1 and 2 are dinuclear in which two µ2-phenoxido and a water molecule bridge the two Ni(ii) centers to make the complexes face sharing bioctahedra. Complex 3 is a linear triple bridged (phenoxido and carboxylato) trinuclear Ni(II) complex. Variable-temperature magnetic susceptibility studies indicate the presence of ferromagnetic exchange coupling in complexes 1-3 with J values of 25.4, 28.1 and 6.2 cm(-1) respectively. Theoretically obtained J values of 21.4 cm(-1) (for 1), 22.0 cm(-1) (for 2) and 9.3 cm(-1) (for 3) corroborate very well the experimental results. DFT calculation also shows that stronger H-bonding interactions present in the case of carboxylate based coligands stabilise the triple oxido-bridged complexes.

Crystal structures and DFT calculations of new chlorido-dimethylsulfoxide-M(III) (M = Ir, Ru, Rh) complexes with the N-pyrazolyl pyrimidine donor ligand: kinetic vs. thermodynamic isomers.

New chlorido-dimethylsulfoxide-iridium(III), ruthenium(III) and rhodium(III) complexes with the 2-(1H-pyrazol-1-yl)-pyrimidine (pyrapyr) ligand (OC-6-N1)-[Rh(III)Cl3(DMSO-κS)(pyrapyr)] (1a, N = 3 and 1b, N = 4); (OC-6-N1)-[Ru(III)Cl3(DMSO-κS)(pyrapyr)] (2a, N = 3 and 2b, N = 4) and (OC-6-N1)-[Ir(III)Cl3(DMSO-κS)(pyrapyr)] (3a, N = 3 and 3b, N = 4) have been synthesized and characterized by spectroscopic techniques and by single crystal X-ray diffraction studies (1a, 1b, 2a, 2b, a disordered crystal 3a/3b and a cocrystal 3a·3b). In all cases, the metal centers show octahedral geometry coordinated to three chloride ligands and one S coordinated dimethylsulfoxide (DMSO-κS). The coordination sphere of the metal is completed by the pyrapyr molecule. Two different coordination modes are observed: (i) the DMSO-κS is opposite to the pyrimidinic N atom (IUPAC nomenclature is OC-6-31 denoted herein as trans); (ii) DMSO-κS is opposite to the pyrazolic N atom (IUPAC nomenclature is OC-6-41 denoted as cis). For Rh(III) the kinetic product (cis) yields the thermodynamic (trans) upon heating a solution of the kinetic product and both isomers have been X-ray characterized. Conversely for Ru(III), both kinetic and thermodynamic complexes have been obtained by using different procedures. Both isomers have been characterized by X-ray crystallography and the kinetic product does not yield the thermodynamic upon heating a solution of the former. Furthermore, the Ir(III) behaves differently, since both isomers are energetically equivalent and both isomers co-crystallize in the solid state. The kinetic/thermodynamic mechanism that yields the different isomers has been studied by using theoretical DFT calculations for each metal. Finally, two Ru(II) complexes (OC-6-N1)-[Ru(II)Cl2(DMSO-κS)2(pyrapyr)] (1a, N = 3 and 4b, N = 4) are also described and X-ray characterized. They were obtained as minor products during the synthesis of 2a.

Syntheses, structures, properties and DFT study of hybrid inorganic-organic architectures constructed from trinuclear lanthanide frameworks and Keggin-type polyoxometalates.

In this paper we report the synthesis and X-ray characterization of four novel hybrid inorganic-organic assemblies generated from H4SiW12O40 as Keggin-type polyoxometalates (POM) and, in three of them, a trinuclear lanthanide cluster of type {Na(H2O)3[Ln(HCAM)(H2O)3]3}(4+) is formed, where Ln metal is La in compound 1, Ce in compound 2, and Eu in compound 3 (H3CAM = chelidamic acid or 2,6-dicarboxy-4-hydroxypyridine). These compounds represent the first POM-based inorganic-organic assemblies using chelidamic acid as an organic ligand. The thermal stability of the organic ligand is crucial, since pyridine-2,6-bis(monothiocarboxylate) instead of chelidamic acid is used (compound 4) under the same synthesis conditions, the decomposition of the ligand to pyridine was observed leading to the formation of colorless crystals of a pseudo hybrid inorganic-organic assembly. In compound 4 the hybrid inorganic-organic assembly is not formed and the organic part simply consists of four molecules of protonated pyridine acting as counterions of the [SiW12O40](4-) counterpart. The luminescent properties of compounds and have been investigated and their solid state architectures have been analyzed. Whereas compound only shows ligand emission, the Eu(3+) emission in compound 3 is discussed in detail. We have found that unprecedented anion-π interactions between the POM, which is a tetra-anion, and the aromatic rings play a crucial role in the crystal packing formation. To the best of our knowledge, this is the first report that describes and analyzes this interaction in Keggin-type POM based inorganic-organic frameworks. The energetic features of these interactions in the solid state have been analyzed using DFT calculations in some model systems predicted by us.

Use of metalloligands [CuL] (H2L = salen type di-Schiff bases) in the formation of heterobimetallic copper(II)-uranyl complexes: photophysical investigations, structural variations, and theoretical calculations.

Five heterobimetallic copper(II)-uranium(VI) complexes [(CuL(1))UO2(NO3)2] (1), [{CuL(1)(CH3CN)}UO2(NO3)2] (2), [{CuL(1)(CH3COCH3)}UO2(NO3)2] (3), [{CuL(2)(CH3CN)}UO2(NO3)2](4), and [{CuL(2)(CH3COCH3)}UO2(NO3)2][{CuL(2)}UO2(NO3)2] (5) have been synthesized by reacting the Cu(II)-derived metalloligands [CuL(1)] and [CuL(2)] (where, H2L(1) = N,N'-bis(α-methylsalicylidene)-1,3-propanediamine and H2L(2) = N,N'-bis(salicylidene)-1,3-propanediamine) with UO2(NO3)2·6H2O in 1:1 ratio by varying the reaction temperature and solvents. Absorption and fluorescence quenching experiments (steady-state and time-resolved) indicate the formation of 1:1 ground-state charge transfer copper(II)-uranium(VI) complexes in solution. X-ray single-crystal structure reveals that each complex contains diphenoxido bridged Cu(II)-U(VI) dinuclear core with two chelated nitrato coligands. The complexes are solvated (acetonitrile or acetone) in the axial position of the Cu(II) in different manner or desolvated. The supramolecular interactions that depend upon the co-ordinating metalloligands seem to control the solvation. In complexes 2 and 3 a rare NO3(-)···NO3(-) weak interaction plays an important role in forming supramolecular network whereas an uncommon U═O···NO3(-) weak interaction helps to self-assemble heterobinuclear units in complex 5. The significance of the noncovalent interactions in terms of energies and geometries has been analyzed using theoretical calculations.

Metallomacrocycles as anion receptors: combining hydrogen bonding and ion pair based hosts formed from Ag(I) salts and flexible bis- and tris-pyrimidine ligands.

Two self-assembled hosts are formed from Ag(I) salts and bis-pyrimidyl ligands and X-ray characterized. Both are able to incorporate two anions into the structure combining hydrogen bonding and electrostatic interactions.

Experimental and theoretical studies on the coordination chemistry of the N1-hexyl substituted pyrimidines (uracil, 5-fluorouracil and cytosine).

N(1)-Hexyl substituted pyrimidines were shown to present solubility properties closer to the real bases than the commonly used methyl and ethyl derivatives, yielding bi-layered structures in the solid state. The study of their coordination capabilities, mainly with Ag(I) and Hg(II), is presented in order to prove their reactivity. A series of coordination complexes, namely, [Hg(N(1)-hexyl-5-fluorouracilate)2]4·6H2O (1), (Ag(+))·[Ag(N(1)-hexyl-5-fluorouracilate)2](-) (2), [Ag(NO3)(N(1)-hexyluracil-κO(4))4] (3), [ZnBr2(N(1)-hexylcytosine)2] (4), [CdBr2(N(1)-hexylcytosine)2] (5), [HgBr2(N(1)-hexylcytosine)2] (6) and [CoBr2(N(1)-hexylcytosine)2] (7), have been synthesized in good yields and X-ray characterized. The presence of the hexyl chains and the fluorine atoms causes the formation of interesting 3D architectures in the solid state. Their structures have been further characterized by infrared spectra (IR) and elemental analyses. In addition, DFT-D3 calculations are used to study interesting noncovalent interactions observed in the solid state, like fluorine-fluorine, fluorine-π and hydrophobic interactions.

RNAs' uracil quartet model with a non-essential metal ion.

We have recently communicated the resemblance of 1-hexyluracil in the crystal state with a lipid bilayer (CrystEngComm, 2010, 12, 362-365). Treatment of this molecule with silver nitrate yields a model, using a non-essential metal ion, of a uracil quartet with geometric parameters comparable to those previously found in RNA strands.

Intermolecular C-H...pi interactions in 1,5-diphenyl-3-(2-pyridyl)-2-pyrazoline.

The title compound, C(20)H(17)N(3), is a derivative of 1,3,5-triaryl-2-pyrazoline and can act as an N,N'-bidentate ligand. This molecule features strong fluorescence that can be explained by an extended pyridyl-C=N-N-phenyl system. The three-dimensional structure is formed by means of an extended network of weak C-H...pi hydrogen bonds supported by pi-pi interactions.