Halide and hydroxide anion binding in water

The formation of halide and hydroxide anion complexes with two ligands L1 (3,6-bis(morpholin-4-ylmethyl)-1,2,4,5-tetrazine) and L2 (3,6-bis(morpholin-4-ylethyl)-1,2,4,5-tetrazine) was studied in aqueous solution, by means of potentiometric and ITC procedures. In the solid state, HF₂^-, Cl^- and Br^- complexes of H₂L2²⁺ were analysed by single crystal XRD measurements. Further information on the latter was obtained with the use of density functional theory (DFT) calculations in combination with the polarizable continuum model (PCM). The presence of two halide or bifluoride HF₂^- (F-H-F^-) anions forming anion-π interactions, respectively above and below the ligand tetrazine ring, is the leitmotiv of the [(H₂L2)X₂] (X = HF₂, Cl, Br, I) complexes in the solid state, while hydrogen bonding between the anions and protonated morpholine ligand groups contributes to strengthen the anion-ligand interaction, in particular in the case of Cl^- and Br^-. In contrast to the solid state, only the anion : ligand complexes of 1 : 1 stoichiometry were found in solution. The stability of these complexes displays the peculiar trend I^- > F^- > Br^- > Cl^- which was rationalized in terms of electrostatic, hydrogen bond, anion-π interactions and solvent effects. DFT calculations performed on [(H₂L2)X]⁺ (X = F, Cl, Br, I) in PCM water suggested that the ligand assumes a U-shaped conformation to form one anion-π and two salt bridge interactions with the included anions and furnished structural information to interpret the solvation effects affecting complex formation. The formation of hydroxide anion complexes with neutral (not protonated) L1 and L2 molecules represents an unprecedented case in water. The stability of the [L(OH)]^- (L = L1, L2) complexes is comparable to or higher than the stability of halide complexes with protonated ligand molecules, their formation being promoted by largely favourable enthalpic contributions that prevail over unfavourable entropic changes.

[Validation of the INFLESZ scale to evaluate readability of texts aimed at the patient]

BACKGROUND

The readability of written texts aimed at patients is an indicator of quality. Szigriszt made an adaptation of the RES Flesch Score, calling it "Escala de Nivel de Perspicuidad" (Clarity Level Scale), to measure the difficulty in reading a text. But Szigriszt used a text sample that was neither representative nor random, which is why the conclusions are not sufficiently consistent. The aim of this article is to complete the process begun by Szigriszt, review the Szigriszt Scale, comparing it with Flesch's scale, and propose a scale according to Spanish reading habits.

METHODS

Descriptive study. Two hundred and ten documents of 3 types were selected at random: Stationary magazines, school textbooks and scientific magazines. Three fragments of at least 500 words were chosen at random from each one, from the beginning, middle and end. The Flesch-Szigriszt Index (Indice de Legibilidad de Flesch-Szigriszt [IFSZ]), available on the INFLESZ program, was calculated. The scores were classified according to the Flesch and Szigriszt scales.

RESULTS

The readability of the stationary magazines is 60, of scientific magazines 37.9, and school textbooks 67.39.

CONCLUSIONS

Only the scientific magazines are situated between 0 and 50. There are no publications with scores lower than 15. Szigrsizt locates "Normal" from 50; Flesch from 60. An intermediate position is adopted and a new scale is proposed: the INFLESZ Scale, which establishes 5 sections: "Very difficult" (<80), "Somewhat difficult" (40-55), "Normal" (55-65), "Quite easy" (65-80) and "Very easy" (>80). Neither the Clarity Level Scale of Szigriszt nor the RES Flesch Score are adapted to Spanish reading habits. In the case of texts on health, there is a greater probability of their being read and understood if they exceed 55.

Ethyl 6-amino-2-methoxypyridine-3-carboxylate, interplay of molecular and supramolecular structure

The title compound, C(9)H(12)N(2)O(3), crystallizes with two molecules in the asymmetric unit. There is extensive hydrogen bonding which results in the formation of a two-dimensional corrugated sheet. This supramolecular structure is determined by the formation of hydrogen-bonded chains resulting from the presence of a 6-amino group and an ethoxycarbonyl group as substituents on a pyridine ring in relative para positions which constitute a pi-electron 'push-pull' system.

Methyl 4-amino-2,3-dihydro-6-methoxy-1,3-dioxo-1H-pyrrolo[3,4-c]pyridine-7-carboxylate forms hydrogen-bonded sheets built fromR22(8) andR66(42) rings

In the title compound, C10H9N3O5, which was formed by the reaction of 6-amino-2-methoxy-4(3H)-pyrimidinone with dimethyl acetylenedicarboxylate, the molecules are linked by N-H...O hydrogen bonds [N...O 2.8974 (15) and 3.0300 (15) A, and N-H...O 165 and 174 degrees] into planar sheets built from alternating R2(2)(8) and R6(6)(42) rings.

N-(2-Amino-1,6-dihydro-5-nitroso-6-oxopyrimidin-4-yl)-L-isoleucine-water (4/1): interplay of molecular and supramolecular structures

In the title compound, 2C10H15N5O4-0.5H2O, there are two independent molecules of the pyrimidinylisoleucine in general positions and a water molecule lying on a twofold rotation axis. The bond lengths within the organic moieties demonstrate significant polarization of the electronic structure. Each of the organic molecules participates in 12 intermolecular hydrogen bonds, of O-H...O and N-H...O types, while the water molecule acts as a double donor and as a double acceptor of O-H...O hydrogen bonds. The organic components are linked by the hydrogen bonds into a single three-dimensional framework, reinforced by the water molecules.

N-(6-Amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl) derivatives of glycine, valine, serine, threonine and methionine: interplay of molecular, molecular-electronic and supramolecular structures

In each of N-(6-amino-3, 4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)valine, C(10)H(15)N(5)O(4) (3) (orthorhombic, P2(1)2(1)2(1)), N-(6-amino-3, 4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)serine monohydrate, C(8)H(11)N(5)O(5).H(2)O (4) (orthorhombic, P2(1)2(1)2(1)), and N-(6-amino-3, 4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)threonine, C(9)H(13)N(5)O(5)(5) (monoclinic, P2(1)), the C-nitroso fragments exhibit almost equal C-N and N-O bond lengths: the C-N range is 1. 315 (3)-1.329 (3) A and the N-O range is 1.293 (3)-1.326 (3) A. In each compound there are also very short intermolecular O-H.O hydrogen bonds, in which carboxyl groups act as hydrogen-bond donors to the nitrosyl O atoms: the O.O distances range from 2.440 (2) to 2. 504 (4) A and the O-H.O angles lie between 161 and 163 degrees. An interpretation of the relationship between the unusual intramolecular bond lengths and the very short intermolecular hydrogen bonds has been developed based on database analysis and computational modelling. In each of (3)-(5) there is an extensive network of intermolecular hydrogen bonds, generating three-dimensional frameworks in (3) and (5), and two-dimensional sheets in (4).