Supramolecular interactions in 2,6-diamino-4-chloropyrimidin-1-ium 5-chlorosalicylate and bis(2,6-diamino-4-chloropyrimidin-1-ium) naphthalene-1,5-disulfonate

The crystals of two new salts, 2,6-diamino-4-chloropyrimidin-1-ium 5-chlorosalicylate, C4H6ClN4 +·C7H4ClO3 −, (I), and bis(2,6-diamino-4-chloropyrimidin-1-ium) naphthalene-1,5-di-sulfonate, 2C4H6ClN4 +·C10H6O6S2 2−, (II), have been synthesized and characterized by single-crystal X-ray diffraction. In both compounds, the N atom of the pyrimidine group in between the amino substituents is protonated and the pyrimidinium cation forms a pair of N—H...O hydrogen bonds with the carboxylate/sulfonate ion, leading to a robust R 2 2(8) motif (supramolecular heterosynthon). In compound (I), a self-complementary base pairing involving the other pyrimidinium ring nitrogen atom and one of the amino groups via a pair of N—H...N hydrogen bonds [R 2 2(8) homosynthon] is also present. In compound (II), the crystallographic inversion centre coincides with the inversion centre of the naphthalene-1,5-disulfonate ion and all the sulfonate O atoms are hydrogen-bond acceptors, generating fused-ring motifs and a quadruple DDAA array. A halogen-bond (Cl...Cl) interaction is present in (I) with a distance and angle of 3.3505 (12) Å and 151.37 (10)°, respectively. In addition, a C—Cl...π interaction and a π–π interaction in (I) and a π–π interaction in (II) further stabilize these crystal structures.

Exploring the Isomer Dependent SERS Spectra of (diphenylphosphoryl)(pyridin-2, -3, and -4-yl)methanol Adsorbed on Gold Nanocolloids

The surface-enhanced Raman scattering (SERS) spectra of three aminophosphonate derivatives of pyridine: (diphenylphosphoryl)(pyridin-2-yl)methanol (α-Pyr), (diphenylphosphoryl)(pyridin-3-yl)methanol (β-Pyr), and (diphenylphosphoryl)(pyridin-4-yl)methanol (γ-Pyr) were measured after immobilization onto colloidal gold surface. Changes in the wavenumber, broadness, and enhancement between the corresponding Raman and SERS bands allowed to deduce orientation of theα-,β-, andγ-isomers (α-,β-, andγ-refer to the position of the substituent relative to the ring nitrogen atom) of aminophosphonate derivatives of pyridine on the gold surface. Briefly, it was demonstrated that theα-Pyr andβ-Pyr show the same mode of adsorption, whereas the adsorption process of theγ-Pyr isomer differs in this regard that pyridine assists in the interaction with the gold surface.

1,5-(1,7)-Biradicals and Nitrenes Formed by Ring Opening of Hetarylnitrenes

Several aromatic and heteroaromatic nitrenes and carbenes undergo photochemical and sometimes also thermal ring opening. Depending on benz-annelation, the ring-opened species may have the character of either nitrenes (for α-annelation) or 1,5-(1,7-)-biradicals (for β-annelation). Both types have been observed, and they are clearly distinguished by their characteristic electron spin resonance spectra. In addition, ring opening of hetarylnitrenes to nitrile ylides can be observed whenever there is a meta-relationship between a ring nitrogen atom and the nitrene (or carbene) centre. The factors governing the two types of ring opening have been investigated. The nitrenes and carbenes are generated by either low temperature Ar matrix photolysis or flash vacuum thermolysis of azides, tetrazoles, triazoles, or diazo compounds with matrix isolation of the products.

Structures of 4-Iminopyrido[1,2-a]pyrimidines, Pyrido[1,2-a]pyrimidin-4-ones, Pyridopyrimidinium Olates, and Thiazolo[3,2-a]pyrimidine Analogues

The Structure-Correlation Principle of Bürgi and Dunitz is invoked in an analysis of the structures of 2-chloro-8-methyl-4-(2-(4-picolinyl)imino-4H-pyrido[1,2-a]pyrimidine 8, 7-chloro-5-(2-thiazolyl)imino-5H-thiazolo[3,2-a]pyrimidine 9, 2-methylamino-4H-pyrido[1,2-a]pyrimidin-4-one 10, 7-methylthio-5H-thiazolo[3,2-a]pyrimidin-5-one 11, 2,3-dihydro-7-methylthio-5H-thiazolo[3,2-a]pyrimidin-5-one 12, and 1-methyl-2-[(o-tert-butylphenyl)imino]-1,2-dihydropyrido[1,2-a]pyrimidin-1-ium-4-olate 13, which have been determined by X-ray crystallography. The most notable structural peculiarities are the long ‘amidine’ and ‘amide’ C–N bonds (1.40–1.50 Å) and the tilting of the ‘amidine’ C=N and ‘amide’ C=O groups towards a ring nitrogen atom (NCX = 114–118°). Also the ‘amidine’ C=N (1.28 Å) and ‘amide’ C=O bonds (1.22–1.24 Å) are long, i.e. in the normal range for resonance-stabilized amidines and amides in spite of the lack of such resonance in these compounds. These features mimic the transition states for ring opening to ketenes. The long amidine and amide C–N bonds and acute NCX angles are in accord with the observed thermal ring opening to ketenimines and ketenes, respectively.

Synthesis and hybridization of oligonucleotides modified at AMP sites with adenine pyrrolidine phosphonate nucleotides

Three structurally diverse types of the protected pyrrolidine nucleoside phosphonates were prepared as the monomers for the introduction of pyrrolidine nucleotide units into modified oligonucleotides on the solid phase. Two different chemistries were used for incorporation of modified and natural units: the phosphotriester method for the former, i.e., monomers containing N-phosphonoalkyl and N-phosphonoacyl moieties attached to the pyrrolidine ring nitrogen atom, and phosphoramidite chemistry for the latter. Since the synthesized pyrrolidine nucleoside phosphonic acids are close mimics of the 3′-deoxynucleoside 5′-phosphates, the incorporation of one modified unit into oligonucleotides gives rise to one 2′,5′ internucleotide linkage. A series of nonamers containing two or three modified units, as well as the fully modified adenine 15-mer, were synthesized in reverse order, i.e., from the 5′ to the 3′ end of the strand. The measurement of thermal characteristics of the complexes of modified nonamers with the complementary strand revealed a destabilizing effect of the introduced modification. The modified adenine homooligonucleotide, was found to form the most stable complex with oligothymidylate of all the tested modified oligonucleotides in terms of ΔTm per modification.

Effect of selenium oxidation state on cadmium translocation in chamomile plants

Syntheses and spectral characteristics of cadmium(II) compounds (CdSeO4, CdSeO3, and Cd(NCSe)2(nia)2) containing selenium in oxidation states (VI), (IV), and (-II) are described. In Cd(NCSe)2(nia)2, nicotinamide (nia) and selenocyanate anions are bonded to Cd atom as N-donor monodentate ligands. Nicotinamide is coordinated through the ring nitrogen atom. The effects of these selenium compounds as well as Cd(NCS)2(nia)2 on the growth and Cd accumulation in roots and shoots of hydroponically cultivated chamomile plants (cultivar Lutea) were studied. In the applied concentration range (12–60 µmol dm−3) Cd(NCS)2(nia)2 affected neither the length nor the dry mass of roots and shoots. Other compounds applied at 24 µmol dm−3 and 60 µmol dm−3 significantly reduced dry mass of roots and shoots. Selenium oxidation state in the cadmium compounds affected Cd accumulation in plant organs as well as Cd translocation within the plants, which was reflected in the values of bioaccumulation (BAF) and translocation factors (S/R). Cd amount accumulated by shoots was lower than that in the roots. The highest BAF values determined for Cd accumulation in shoots were obtained with CdSeO4. Substitution of S with Se in the Cd(NCX)2(nia)2 (X = Se or S) caused an increase of Cd translocation into the shoots.