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PubMed1995

Effects of the triazine herbicide, simetryn, on freshwater plankton communities in experimental ponds.

The effects of a triazine herbicide, simetryn, on freshwater phyto- and zooplankton communities and water chemistry were investigated using outdoor experimental ponds. Simetryn was applied at a concentration of 0.1 or 1.0 mg l(-1) 18 days after the start of the experiment. Simetryn treatments reduced pH, dissolved oxygen concentration, chlorophyll a concentration and photosynthetic rate in the pond water, whereas they increased the dissolved nutrient concentration. In the phytoplankton community Volvocales and Cryptophyceae were clearly reduced by the herbicide application. In the 0.1 mg l(-1) simetryn-treated ponds, photosynthetic rate of the phytoplankton community recovered slightly about two weeks after the treatment, which coincided with recovery of centric diatoms and Cryptophyceae, whereas it was completely suppressed until the end of the experiment in the 1.0 mg l(-1) simetryn-treated ponds. The decrease in zooplankton density in the treated ponds was not due to the direct toxic effects of simetryn but to indirect effects resulting from reduced algal productivity which in turn reduced the food supply.

Journal Article↗
PubMed2006

Novel derivatives of methyl and ethyl 2-(4-oxo-8-aryl-2H-3,4,6,7-tetrahydroimidazo[2,1-c][1,2,4]triazin-3-yl)acetates from biologically active 1-aryl-2-hydrazinoimidazolines: synthesis, crystal structure and antiproliferative activity.

The 1-aryl-2-hydrazinoimidazolines (2a-h) were directly obtained from appropriate 1-aryl-2-methylthioimidazolines (1a-h) by condensation reaction with hydrazine hydrate. Antimicrobial activities of two 1-aryl-2-hydrazinoimidazolines (2b and 2e) are presented. Their chemical structures were confirmed by IR, (1)H NMR, EI-MS and elemental analysis. The susceptibility of Gram-positive and Gram-negative bacterial strains, mould and yeast-like fungi strains to synthesized compounds and the MIC values against two reference strains of bacteria were determined. The strongest antibacterial activity for compound 2b in relation to reference Gram-negative Escherichia coli ATCC 25922 bacterial strain with minimal inhibitory concentration (MIC) value of 3.91micro g mL(-1) was found. Compound 2b showed superior activity (MIC) to ampicillin and comparable to chloramphenicol. A novel compound 2e was found to be effective against E. coli ATCC 25922 and Staphylococcus aureus ATCC 25923 at concentrations of 7.81micro g mL(-1) and 15.62micro g mL(-1), respectively. Compound 2e revealed antibacterial activity against E. coli ATCC 25922, superior to ampicillin and inferior to chloramphenicol. Against S. aureus ATCC 25923 strain tested, compound 2e demonstrated MIC value inferior to ampicillin and chloramphenicol. Moreover, the synthesis, crystal structure and antiproliferative activity of novel derivatives of methyl and ethyl 2-(4-oxo-8-aryl-2H-3,4,6,7-tetrahydroimidazo[2,1-c][1,2,4]triazin-3-yl)acetates (3a-f and 3g-j) are presented. These compounds were obtained from 1-aryl-2-hydrazinoimidazolines (2a-f) by the addition and cyclization reactions with fumaric acid esters. Molecular structures of these compounds were confirmed by elemental analysis, IR, (1)H NMR, (13)C NMR, EI-MS and by X-ray crystallography (for 3g). The tested imidazotriazines 3e, 3i and 3j exhibited anticancer activities towards the following cancer cells: LS180 (ECACC 87021202, human Caucasian colon adenocarcinoma cells), SiHa (ECACC 85060701, uterus cancer cells), and T47D (ECACC 85102201, human breast carcinoma cells). Compounds 3i and 3j having comparable GI values (above 50%) towards uterus cancer cell line (SiHa) at both examined concentrations (10micro g mL(-1) and 50micro g mL(-1)) were found to be the most effective against this cancer cell line; their GI factors were 53%, 51% and 62%, 55%, respectively, in both examined concentrations (10micro g mL(-1) and 50micro g mL(-1)). Furthermore, the distinctly marked lower cytotoxicity of tested imidazotriazines 3i and 3j against normal cell lines (HSF, human skin fibroblast cells and Vero African Green Monkey Kidney cells, GMK clone) and almost 2-times higher against the majority of cancer cell lines was confirmed.

Cell Line, Tumor↗
PubMed2004

Persistence of four s-triazine herbicides in river, sea and groundwater samples exposed to sunlight and darkness under laboratory conditions.

The persistence of terbuthylazine, simazine, atrazine and prometryn (s-triazine herbicides) was studied in sea, river and groundwaters during long-term laboratory incubation (127 days) under different laboratory conditions (light-darkness at 20 degrees C). Analysis of herbicides was performed by GC-NPD and their identity was confirmed by GC-MSD. A micro on-line method for the isolation of herbicide residues was used. The results showed that light had little effect on the removal of the four herbicides in riverwater but had a marked effect on their removal from sea and groundwater. Surprisingly, this removal appeared to be inversely proportional to the concentration of dissolved organic materials. In general, the degradation order was similar in sea and riverwaters; simazine was the most readily degraded compound (t(1/2)= 29-49 days), while terbuthylazine was the most persistent with the longest half-lives (76-331 days). In groundwater, terbuthylazine also showed greater persistence but prometryn was the compound with a fastest degradation rate, half-lives ranged from 88 days for prometryn to approximately 100 days for the other three compounds in light conditions and 263-366 days for prometryn and terbuthylazine, respectively, in darkness. Only for terbuthylazine was the remaining percentage at the end of the experiment higher than 50% under light conditions in riverwater, while in the other cases, the remaining percentage varied from 7 to 43% for simazine in seawater and atrazine in groundwater, respectively. Finally, a greater persistence was observed in groundwater for the four compounds.

Journal Article↗
PubMed2003

Gas chromatography/mass spectrometry applied for the analysis of triazine herbicides in environmental waters.

The excess use of triazine herbicides in agriculture causes severe contamination to the environment especially for ground water. Gas chromatography coupled with mass spectrometry (GC/MS) was used to analyze simazine, atrazine (ATR), cyanazine, as well as the degradation products of ATR such as deethylatrazine and deisopropylatrazine in environmental water samples. These compounds were baseline separated by the established GC method. The water samples were pre-concentrated by solid-phase-extraction (SPE) and analyzed by ion trap MS at sub- to low-ppt levels. Recovery of ATR by the SPE pre-concentration using a C18 cartridge was determined as 90.5 +/- 3.5%. Detection limit of the method using selected ion monitoring technique for ATR was 1.7 ppt when one liter water was analyzed. The relative analytical error for ATR fortified water samples at 200 ppt was -12.5% (n=12) with triple analysis and the relative standard deviation was 3.2%. Trace levels of ATR at 3.9 and 9.7 ppt were determined in water samples collected from a reservoir and a river in Hong Kong.

Atrazine↗
PubMed1998

Spatial and temporal variations of herbicide (triazines and phenylureas) concentrations in the catchment basin of the Marne river (France).

Triazine and phenylurea concentrations were investigated in four sub-basins of the Marne river (France) in 1992 and 1993. The peak concentrations of atrazine, simazine and isoproturon occurred between March and July. In the four basins, the peaks were in relation with the herbicide application periods and with the important rainfalls, except for the isoproturon. The peaks of terbutryne and ametryne came later in the year, due to their use for weed control on post-emergent corn. For the phenylureas, the peak concentrations were observed in March-April next to the spraying period on winter cereals. The fast transfer of those herbicides was related to their high water solubility. In all the samples, the deethylatrazine (DEA) was detected 1 month after the atrazine due to its degradation within the soils which is of minor importance as compared to its transport by surface waters and also, to interactions between the silt sheet and the stream itself. The DAR evolution showed that the atrazine residence time depends both on the run-off in the first centimetres of the soil and on the treatment periods, particularly in the Grand Morin. The Marne river contamination level was similar to that of the Mélarchez and of the Grand Morin. The minor pollution of the Orgeval was related to minor cultivated areas.

Atrazine↗
PubMed2002

Pyrrolo[2,1-c][1,2,4]triazines from 2-diazopyrroles: synthesis and antiproliferative activity.

Pyrrolo[2,1-c][1,2,4]triazines 4a-g were directly obtained from the reaction of 2-diazopyrroles 1a and b with the sodium salts of beta-diketones, beta-carbonitriles, and beta-dinitriles. Only when the 2-diazopyrroles were coupled with ethyl cyanoacetate, it was possible to isolate, together with the pyrrolotriazines, the intermediate hydrazones 3 which, in turn, cyclised to the title ring system. Pyrrolotriazines 4a-e were evaluated for cytotoxic activity against a panel of 60 human cancer cell lines by the National Cancer Institute and some of them demonstrated inhibitory effects in the growth of a wide range of cancer cell lines generally at 10(-5) M level and in some cases at micromolar concentrations.

Antineoplastic Agents↗
PubMed2001

Evaluation of a multidimensional solid-phase extraction platform for highly selective on-line cleanup and high-throughput LC-MS analysis of triazines in river water samples using molecularly imprinted polymers.

A novel highly selective sample cleanup procedure based on the use of molecularly imprinted polymers (MIPs) as solid-phase extraction materials has been evaluated with respect to its applicability and routine use in environmental analysis. The method comprises the combination of a restricted access material (RAM) and a MIP allowing a selective sample preparation to be achieved in the online mode. This combination is called the size-selective sample separation and solvent switch (six-SPE). The RAM column combines size exclusion and adsorption chromatography, reducing the concentration of matrix molecules by a cutoff of 15 kDa. The MIP column selectively retains the triazine analytes whereas the residual matrix is not retained and separated completely. Thus, the automated RAM-MIP is capable of excluding all matrix and nontarget compounds. The cleaned and enriched extract is subsequently eluted to an HPLC column and analyzed by LC-MS. A complete on-line analysis cycle including multidimensional solid-phase extraction, separation, and detection takes less than 15 min. Terbuthylazine, atrazine, propazine, simazine, ametryn, prometryn, irgarol, and also the metabolites deethylatrazine and deisopropylatrazine can be determined without any matrix interferences, e.g., by humic acids. The whole setup is fully automated and may be continuously operated. Nonspecific interactions with the polymer are below 1% in all cases. The accuracy of the LC-MIP-LC-MS system was controlled using a certified reference material (Aquacheck). The applicability of the method to the cleanup of real samples was demonstrated by injection of contaminated river water samples. The stability of different polymers was tested by consecutive injections, and it was shown that the performance of the materials did not vary even after more than 300 enrichment and desorption cycles.

Journal Article↗
PubMed1994

Mechanism of 2-chloro-(epsilon-amino-Lys75)-[6-[4-(N,N- diethylamino)phenyl]-1,3,5-triazin-4-yl]calmodulin interactions with smooth muscle myosin light chain kinase and derived peptides.

The mechanism of the interactions of 2-chloro-(epsilon-amino-Lys75)-[6-[4-(N,N-diethylamino)phenyl]- 1,3,5-triazin-4-yl]calmodulin (TA-calmodulin) with smooth muscle myosin light-chain kinase (MLCK) and two 17-residue peptides, Ac-R-R-K-W-Q-K-T-G-H-A-V-R-A-I-G-R-L-CONH2 (Trp peptide) and Tyr peptide, in which W is replaced by Y, were studied by measurements of equilibrium and transient fluorescence changes in the nanomolar range. Most reactions were carried out in 100 microM CaCl2 at ionic strength 0.15 M, pH 7.0, and 21 degrees C. In each case association of MLCK or peptide to TA-calmodulin could be described by a two-step process, a bimolecular step and an isomerization. In the case of the interaction between TA-calmodulin and Tyr peptide it was shown that the isomerization involved the binary complex of TA-calmodulin and Tyr peptide as opposed to an isomerization of either TA-calmodulin or Tyr peptide in isolation. These distinctions depended in part on development for transient kinetic experiments of a general theory to quantify relative phase amplitudes in two-step mechanisms. The kinetics for all three association reactions were then interpreted in terms of a bimolecular association (rate constants k+1 and k-1) followed by an isomerization of the binary complex (rate constants k+2 and k-2). For the interaction of TA-calmodulin and Tyr peptide, values of the rate constants are k+1, 8.8 x 10(8) M-1 s-1; k-1, 5.7 s-1; k+2, 0.38 s-1; and k-2, 0.65 s-1. The fluorescence intensities (lambda ex 365 nm, lambda ex 365 nm, lambda em > 400 nm) of TA-calmodulin, the initial binary complex of TA-calmodulin and Tyr peptide, and the isomerized binary complex are in the ratio 1:2.8:1.3. Analogous mechanisms were found for TA-calmodulin binding to Trp peptide and to MLCK, but values for the rate constants and relative fluorescence intensities of the binary complexes were generally not so completely defined. Values for the Trp peptide and MLCK, respectively, are k+1, 8.8 x 10(8) M-1 s-1 and 1.1 x 10(8) M-1 s-1; (k+2 + k-2), 0.97 s-1 and 1.3 s-1; and k-1k-2/(k+2 + k-2), 0.0079 s-1 and 0.025-0.056 s-1. Equilibrium dissociation constants (Kd) for interactions of TA-calmodulin and targets determined from these data are Tyr peptide, 4.1 nM; Trp peptide, 0.011 nM; and MLCK, 0.23-0.51 nM.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed2005

Formation of refractory ring-expanded triazine intermediates during the photocatalyzed mineralization of the endocrine disruptor amitrole and related triazole derivatives at UV-irradiated TiO2/H2O interfaces.

Amitrole (ATz, 3-amino-1H-1,2,4-triazole) is a widely employed herbicide with strong estrogenic activity that can lead to abnormalities of the thyroid gland and can cause mutations. The photocatalytic transformation of ATz was carried out at the UV-irradiated TiO2/H2O interface, along with the triazole derivatives Tz (1H-1,2,4-triazole) and DaTz (3,5-diamino-1H-1,2,4-triazole) to assess the decomposition of these herbicides, to identify intermediates, and to elucidate some mechanistic details of the ATz degradation. Conversion of the nitrogens of these triazoles to NH4+ and/ or NO3- ions occurs competitively and depends on the number of amine functions on the five-membered triazole rings. Photomineralization of the substrates in terms of loss of nitrogen to NH4+/NO3- was rather low (ca. 25-40%) for each of the triazoles, whereas evolution of CO2 (loss of TOC) was more significant (60-70%), indicating considerable retention of nitrogen in the intermediate products. UV-Vis spectroscopy, TOC assays, FT-IR spectroscopy, proton NMR spectrometry, electrospray LC-MS, and molecular orbital calculations were brought to bear in assessing the temporal course of the photocatalyzed process(es). Results show that after cleavage of the triazole ring, the various intermediate fragments recombine to yield ring-expanded six-membered triazine intermediates, which slowly degrade to give the refractory cyanuric acid under the conditions used.

Amitrole↗
PubMed2002

1,3,5-Triazine templated self-assembly of a hexameric copper(I) chloride triphenyl phosphite core.

The reaction of CuCl, P(OPh)(3), and 1,3,5-triazine (Trz) in CHCl(3) produces [(CuCl)(6)(P(OPh)(3))(6)(Trz)(2)] via molecular self-assembly. An X-ray structural study has revealed a D(3d) symmetry hexamer containing an oblate spheroid core. The core consists of a Cu(6)Cl(6) macrocycle, which is capped by two mu(3)-Trz ligands. Seven parallel stacked atom planes are present: P(3), Trz, Cu(3), Cl(6), Cu(3), Trz, and P(3). The six copper atoms are not coplanar with the Trz ligands and form a distorted octahedron. Crystal data: triclinic P macro 1, a = 14.1489(7) A, b = 15.7470(8) A, c = 29.6572(14) A, alpha = 76.4330(10) degrees, beta = 79.5120(10) degrees, gamma = 72.2260(10) degrees, V = 6088.5(5) A(3), Z = 2, 27470 reflections, R = 0.0359.

Journal Article↗
PubMed2003

Five different fluxional processes in polyfluorophenyl palladium(II) complexes with 2,4,6-tris(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine. The driving effect of the solvent.

The polydentate N-donor ligand 2,4,6-tris(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine (Me(2)-TpzT) has been used to synthesize the new palladium derivatives Pd(R)(2)(Me(2)-TpzT), R = C(6)F(5), 1; R = m-C(6)ClF(4), 2. In the case of complex 2, four different atropisomers have been detected at low temperature. The new complexes exhibit a rich dynamic behavior, including three metallotropic processes (metal-hurdling, 1,4-metallotropic shifts, and an intermolecular process) and two processes involving restricted rotation of aromatic rings (the polyfluorophenyl groups and the uncoordinated pyrazole group adjacent to the metal fragment). The fluxional behavior has been studied by (1)H and (19)F NMR spectroscopy using variable temperature NMR studies and (1)H,(1)H and (19)F,(19)F EXSY experiments. The study of solutions of 2 in 1,1',2,2'-tetrachloroethane-d(2) gave the following order for the free energy of activation: pyrazole rotation < 1,4-metallotropic shift < intermolecular exchange < polyfluorophenyl rotation. The process of metal hurdling was not found in this solvent. However, in acetone-d(6) such a process was detected and was found to be of lower energy than the 1,4-metallotropic shift. In dilute acetone-d(6) or 1,1',2,2'-tetrachloroethane-d(2 )()solutions, the intermolecular process was not observed. Conclusions concerning the different mechanisms have been deduced from the data obtained.

Journal Article↗
PubMed2005

Moisture-triggered 1,3,5-triazine-based Cu(II) molecular switch: a combined X-ray single-crystal and powder diffraction study.

A solvothermal synthetic procedure has been exploited to prepare the new [Cu(3)L(NO(3))(6)](n) coordination polymer (1) by reaction of the polydentate N,N'-{2,4-di-[(di-pyridin-2-yl)amine]-1,3,5-triazine}ethylenediamine ligand (opytrizediam L) with copper(II) nitrate. 1 has been structurally characterized by means of the conventional X-ray single-crystal diffraction technique. It crystallizes in the monoclinic C2/c space group with a = 16.830(3), b = 20.701(4), c = 18.170(4) Angstroms, beta = 113.26(3) degrees, V = 5816(2) Angstroms(3), Z = 4. 1 consists of trinuclear Cu(3)L(NO(3))(5) units connected by means of a nitrato-O,O' bridge. The resulting chains are involved in weak interchain head-to-tail pi-pi stacking interactions. In the presence of moisture, 1 is readily converted into the hydrated [Cu(3)L(NO(3))(5)](NO(3)).H(2)O form (2). This second phase, monoclinic P2(1)/c, consists of isolated [Cu(3)L(NO(3))(5)](+) and (NO(3))(-) ions which accommodate water molecules in the crystal lattice. These subtle chemical and structural modifications accompanying the moisture-triggered 1-to-2 transformation have been demonstrated through a X-ray powder diffraction study. A thermodiffractometric analysis has evidenced that this solid-to-solid transformation is fully reversible, i.e., thermally induced dehydration of 2 restores 1. The analysis of the temperature dependence of the magnetic susceptibility for 2 has revealed very weak ferromagnetic interactions, consistent with the large Cu...Cu separation (ca. 7.5 Angstroms) in the trinuclear units.

Journal Article↗
PubMed2005

Characterization and comparison of Cm(III) and Eu(III) complexed with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine using EXAFS, TRFLS, and quantum-chemical methods.

The complexation of Cm(III) and Eu(III) with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (n-C3H7-BTP) in nonaqueous organic solution is studied with extended X-ray absorption spectroscopy. Bond lengths are the same in both complexes. Quantum-chemical calculations performed at different levels support this finding. On the other hand, the Cm.(n-C3H7-BTP)3 complex is formed at much lower ligand-to-metal concentration ratio than the Eu.(n-C3H7-BTP)3 complex, as shown by time-resolved laser-induced fluorescence spectroscopy. This is in good agreement with n-C3H7-BTP's high selectivity for trivalent actinides over lanthanides in liquid-liquid extraction.

Journal Article↗
PubMed2006

2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz)-derived [Ru(II)(tptz)(acac)(CH3CN)]+ and mixed-valent [(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(CH3CN)]+.

Mononuclear [Ru(II)(tptz)(acac)(CH3CN)]ClO4 ([1]ClO4) and mixed-valent dinuclear [(acac)2Ru(III){(mu-tptz-Eta+)-}Ru(II)(acac)(CH3CN)]ClO4 ([5]ClO4; acac = acetylacetonate) complexes have been synthesized via the reactions of Ru(II)(acac)2(CH3CN)2 and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), in 1:1 and 2:1 molar ratios, respectively. In [1]ClO4, tptz binds with the Ru(II) ion in a tridentate N,N,N mode (motif A), whereas in [5]ClO4, tptz bridges the metal ions unsymmetrically via the tridentate neutral N,N,N mode with the Ru(II) center and cyclometalated N,C- state with the Ru(III) site (motif F). The activation of the coordinated nitrile function in [1]ClO4 and [5]ClO4 in the presence of ethanol and alkylamine leads to the formation of iminoester ([2]ClO4 and [7]ClO4) and amidine ([4]ClO4) derivatives, respectively. Crystal structure analysis of [2]ClO4 reveals the formation of a beautiful eight-membered water cluster having a chair conformation. The cluster is H-bonded to the pendant pyridyl ring N of tptz and also with the O atom of the perchlorate ion, which, in turn, makes short (C-H- - - - -O) contacts with the neighboring molecule, leading to a H-bonding network. The redox potentials corresponding to the Ru(II) state in both the mononuclear {[(acac)(tptz)Ru(II)-NC-CH3]ClO4 ([1]ClO4) >> [(acac)(tptz)Ru(II)-NH=C(CH3)-OC2H5]ClO4 ([2]ClO4) > [(acac)(tptz)Ru(II)-NH2-C6H4(CH3)]ClO4 ([3]ClO4) > [(acac)(tptz)Ru(II)-NH=C(CH3)-NHC2H5]ClO4 ([4]ClO4)} and dinuclear {[(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(NC-CH3)]ClO4 ([5]ClO4), [(acac)2Ru(III){(mu-tptz-H+(N+-O-)2)-}Ru(II)(acac)(NC-CH3)]ClO4 ([6]ClO4), [(acac)2Ru(III){(mu-tptz-H+)-}Ru(II)(acac)(NH=C(CH3)-OC2H5)]ClO4 ([7]ClO4), and [(acac)2Ru(III){(mu-tptz-Eta+)-}Ru(II)(acac)(NC4H4N)]ClO4 ([8]ClO(4))} complexes vary systematically depending on the electronic nature of the coordinated sixth ligands. However, potentials involving the Ru(III) center in the dinuclear complexes remain more or less invariant. The mixed-valent Ru(II)Ru(III) species ([5]ClO4-[8]ClO4) exhibits high comproportionation constant (Kc) values of 1.1 x 10(12)-2 x 10(9), with substantial contribution from the donor center asymmetry at the two metal sites. Complexes display Ru(II)- and Ru(III)-based metal-to-ligand and ligand-to-metal charge-transfer transitions, respectively, in the visible region and ligand-based transitions in the UV region. In spite of reasonably high K(c) values for [5]ClO4-[8]ClO4, the expected intervalence charge-transfer transitions did not resolve in the typical near-IR region up to 2000 nm. The paramagnetic Ru(II)Ru(III) species ([5]ClO4-[8]ClO4) displays rhombic electron paramagnetic resonance (EPR) spectra at 77 K (g approximately 2.15 and Deltag approximately 0.5), typical of a low-spin Ru(III) ion in a distorted octahedral environment. The one-electron-reduced tptz complexes [Ru(II)(tptz.-)(acac)(CEta3CN)] (1) and [(acac)2Ru(III){(mu-tptz-Eta+).2-}Ru(II)(acac)(CH3CN)] (5), however, show a free-radical-type EPR signal near g = 2.0 with partial metal contribution.

Journal Article↗
PubMed2006

Toward a clear-cut vision on the origin of 2,6-di(1,2,4-triazin-3-yl)pyridine selectivity for trivalent actinides: insights from theory.

Although BTP (2,6-di(1,2,4-triazin-3-yl)pyridine) has been widely evidenced as the most effective nitrogen ligand for the selective complexation of trivalent actinides from lanthanide counterparts, the origin of its selectivity is still an open question. Neither experimental data nor theoretical calculations have been able to rationalize the role of covalency in real experimental BTP complexes. We show herein with DFT calculations on [M(BTP)3]3+ (M = La, U, Cm, Gd) that, even if back-bonding effects are significant in the U-BTP bond, it is the contrast of donation on 6d and 5f Cm(III) orbitals that explains, at least in part, its selective complexation to BTP.

Journal Article↗
PubMed2003

Melem (2,5,8-triamino-tri-s-triazine), an important intermediate during condensation of melamine rings to graphitic carbon nitride: synthesis, structure determination by X-ray powder diffractometry, solid-state NMR, and theoretical studies.

Single-phase melem (2,5,8-triamino-tri-s-triazine) C(6)N(7)(NH(2))(3) was obtained as a crystalline powder by thermal treatment of different less condensed C-N-H compounds (e.g., melamine C(3)N(3)(NH(2))(3), dicyandiamide H(4)C(2)N(4), ammonium dicyanamide NH(4)[N(CN)(2)], or cyanamide H(2)CN(2), respectively) at temperatures up to 450 degrees C in sealed glass ampules. The crystal structure was determined ab initio by X-ray powder diffractometry (Cu K alpha(1): P2(1)/c (No. 14), a = 739.92(1) pm, b = 865.28(3) pm, c = 1338.16(4) pm, beta = 99.912(2) degrees, and Z = 4). In the solid, melem consists of nearly planar C(6)N(7)(NH(2))(3) molecules which are arranged into parallel layers with an interplanar distance of 327 pm. Detailed (13)C and (15)N MAS NMR investigations were performed. The presence of the triamino form instead of other possible tautomers was confirmed by a CPPI (cross-polarization combined with polarization inversion) experiment. Furthermore, the compound was characterized using mass spectrometry, vibrational (IR, Raman), and photoluminescence spectroscopy. The structural and vibrational properties of molecular melem were theoretically studied on both the B3LYP and the MP2 level. A structural optimization in the extended state was performed employing density functional methods utilizing LDA and GGA. A good agreement was found between the observed and calculated structural parameters and also for the vibrational frequencies of melem. According to temperature-dependent X-ray powder diffractometry investigations above 560 degrees C, melem transforms into a graphite-like C-N material.

Journal Article↗