Adsorption of designed pyrimidine derivative ligands on an activated carbon for the removal of Cu(II) ions from aqueous solution.

The adsorption of five Nalpha-substituted amino acids with a 5-nitroso-6-oxo pyrimidine as substituent on a commercial activated carbon (AC) has been studied in aqueous solution at several pH values. The adsorption processes of these organic compounds have been analyzed on the basis of the electrolytic behavior of the adsorbates. In all cases, the adsorption process is highly irreversible due to strong pi-pi interactions between the arene centers of the AC and the pyrimidine residue of the adsorbates. This interaction is consistent with XPS data and HOMO-LUMO theoretical calculations. The adsorption of these organic compounds provides a new route for the functionalization of the AC surface with carboxyl groups. In addition, the adsorption capacity of the AC/organic compound systems for Cu(II) ions in aqueous solution has been studied at different pH values. These systems show an increase of the adsorption capacity for Cu(II) compared to the AC, which is related to the AC functionalization with carboxyl groups due to the adsorbed organic compounds.

N-(6-Amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)leucine: a three-dimensional hydrogen-bonded framework structure.

In the title compound, C11H17N5O4, the bond distances show evidence of a highly polarized molecular-electronic structure. The molecules are linked into a three-dimensional framework by a combination of O-H...O and N-H...O hydrogen bonds, including a very short O-H...O hydrogen bond [H...O=1.67 A, O...O=2.494 (2) A and O-H...O=166 degrees].

Ligand adsorption on an activated carbon for the removal of chromate ions from aqueous solutions.

The results presented in this work are related to the design of a guideline to develop specific properties at the surface of an activated carbon (AC). For this, two model aromatic compounds have been synthesized and their electrolytic behavior in aqueous solutions was studied by a potentiometric method. The textural characteristics of the activated carbon were determined by porosimetry methods. The nature of oxygen-carrying functions and the acid-base behavior of the AC surface were characterized by TPD and potentiometric titration methods, respectively. The adsorption and desorption equilibria of the aromatic compounds on activated carbon were measured in aqueous solutions, and the hysteresis between adsorption and desorption, which reveals irreversible adsorption, was discussed on the basis of the frontier orbital theory. HOMO and LUMO orbitals of the adsorbent and adsorbates were calculated, and irreversible adsorption was attributed to the small energy difference between HOMO and LUMO of the aromatic adsorbates and the adsorbent. Adsorption equilibria of K2CrO4 in aqueous solution on the AC alone and on the AC-aromatic ligand adsorbents, respectively, prove the efficient development of specific chemical functions at the carbon surface provided by the adsorbed aromatic compounds.

Hydrated metal(II) complexes of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl) derivatives of glycine, glycylglycine, threonine, serine, valine and methionine: a monomeric complex and coordination polymers in one, two and three dimensions linked by hydrogen bonding.

Nine hydrated complexes of Group 2 (alkaline earth) cations with organic ligands which are N-substituted amino acids containing the 6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl group have been structurally characterized. The octahydrated calcium glycinate complex, where the six-coordinate Ca cation lies on an inversion centre in the space group P(-)1, forms a finite (zero-dimensional) complex. The hexahydrated barium glycinate complex contains eight-coordinate Ba and it is isostructural with the known Sr analogue, and its one-dimensional coordination polymer takes the form of a simple chain. The octahydrated calcium and strontium threonine complexes are isostructural, with eight-coordinate cations lying on twofold rotation axes in the space group C2: the one-dimensional coordination polymers take the form of a chain of spiro-fused rings and a similar chain of spiro-fused rings is found in the heptahydrated barium serine complex, although here the ten-coordinate cation lies in a general position. In the tetrahydrated strontium and barium glycylglycinate complexes, the eight-coordinate cations lie on twofold rotation axes in the space group C2/c, but in the Sr complex the coordination polymer is a chain of spiro-fused rings, while in the Ba complex the coordination polymer forms deeply puckered sheets. There are two types of Ca site in the hexahydrated calcium valine complex: one is eight coordinate and gives rise to a two-dimensional coordination polymer, while the other is seven coordinate forming a finite, zero-dimensional coordination complex. In the heptahydrated barium methionine complex, the coordination polymer is three dimensional. In all of the complexes, the coordination aggregates are further linked by an extensive series of hydrogen bonds.

Bis[6-amino-3-methyl-5-nitrosopyrimidine-2,4(1H,3H)-dionato]diaquazinc(II) dihydrate, redetermined at 120 K: a three-dimensional hydrogen-bonded framework.

The title compound, whose structure has been redetermined at 120 K, contains almost centrosymmetric trans-[Zn(C(5)H(5)N(4)O(3))(2)(H(2)O)(2)].2H(2)O units, together with two uncoordinated water molecules. An extensive series of O-H.O, O-H.N and N-H.O hydrogen bonds gives rise to a three-dimensional framework structure.

Barium bis[6-amino-3-methyl-5-nitrosopyrimidine-2,4(1H,3H)-dionate] trihydrate: coordination polymer chains linked by hydrogen bonds.

The title complex, catena-poly[[triaquabarium(II)]-di-mu-6-amino-3-methyl-5-nitrosopyrimidine-2,4(1H,3H)-dionato], [Ba(C(5)H(5)N(4)O(3))(2)(H(2)O)(3)](n), forms a coordination polymer chain in which the two distinct anions use different ligating atoms to bridge pairs of cations. Adjacent pairs of cations are also linked by pairs of bridging water molecules. The chains are linked into a single three-dimensional framework by an extensive series of hydrogen bonds.

6-Amino-3-methyl-5-nitrosopyrimidine-2,4(1H,3H)-dione forms a three-dimensional hydrogen-bonded framework structure.

Molecules of the title compound, C(5)H(6)N(4)O(3), are linked into a single three-dimensional framework by a two-centre N-H.O hydrogen bond [H.O = 1.92 A, N.O = 2.785 (2) A and N-H.O = 168 degrees ], a two-centre N-H.H hydrogen bond [H.N = 2.19 A, N.N = 3.017 (2) A and N-H.N = 157 degrees ] and the intermolecular component of an effectively planar three-centre N-H.(O)(2) hydrogen bond [H.O = 2.03 and 2.31 A, N.O = 2.645 (2) and 2.957 (2) A, N-H.O = 126 and 130 degrees, and O.H.O = 101 degrees ].