The role of humic substances in chromium sorption onto natural organic matter (peat).

To elucidate mechanisms of Cr3+ sorption onto the unaltered solid natural organic matter, the comparative studies of this ion binding from a solution at pH 4.0 onto three selected particle size fractions: 2000-1000 microm, 630-200 microm and 63-20 microm of markedly different HS content and structure, separated by a wet sieving from an overall sample of peat (Brushwood Peat Humus) were carried out. Comparable patterns of COOH groups and CEC(t) confirmed that for cation exchange capacity were responsible mainly cations connected with COO- functional groups. It was though found that aliphatic acids in the solid state did not take part in Cr3+ binding, thus the finest studied fraction 63-20 microm of the highest contents of functional groups showed the lowest sorption capacity for Cr3+, while similar patterns of sorbed Cr3+, soluble HS content and base CEC(0) indicated that these parameters were directly interrelated. The base ion exchange processes determined by CEC(0) (with Ca2+ as a predominant exchangeable cation) appeared to be not the major mechanisms responsible for Cr3+ sorption. For this metal, strong binding to insoluble large molecular weight organic pool two- to threefold prevailed over the ion exchange processes. Very low acid desorption indicated generally low mobility of Cr3+ -organic compounds.

Structure of N,4-dinitroaniline and its complex with sulfolane at 85 K; on the proton donor-acceptor affinity of the primary nitramine (HNNO2) group.

The NNO2 group of the title compound is significantly less twisted with respect to the aromatic ring in comparison to a typical secondary nitramine. The amide nitrogen is trigonally hybridized. The nitramino group is almost planar. The C-C-N-N torsion angles vary between ca 13 and 42 degrees, whereas the twist along the N-N bond is much smaller and amounts to between ca 1 and 15 degrees. Those twist angles are governed by a crystal packing and are much larger in the case of crystals of pure N,4-dinitroaniline in comparison to that of its complex with sulfolane. The deviations of the internal angles of the aromatic ring from 120 degrees do not exceed 3 degrees. The presence of the nitro group increases the C-C-C valence angle of ca 2.0-2.6 degrees, whereas an analogous effect associated with the nitramino group is much smaller (ca 0.3-1.3 degrees), pointing to its weak electron-withdrawing properties. The nitramino group displays no tendency to conjugate with an electron-demanding substituent across the ring. It participates in hydrogen bonding only as a hydrogen-bonding donor. It does not act as a proton acceptor, despite the fact that nitramine rearrangement is catalysed by acids.

1-methyl-4-nitraminopyridinium nitrate and 4-nitraminopyridinium methanesulfonate.

In the title compounds, C6H8N3O2+*NO3- and C5H6N3O2+*-CH3SO3-, respectively, the cations are almost planar; the twist of the nitramino group about the C-N and N-N bonds does not exceed 10 degrees. The deviations from coplanarity are accounted for by intermolecular N-H...O interactions. The coplanarity of the NHNO2 group and the phenyl ring leads to the deformation of the nitramino group. The C-N-N angle and one C-C-N angle at the junction of the phenyl ring and the nitramino group are increased from 120 degrees by ca 6 degrees, whereas the other junction C-C-N angle is decreased by ca 5 degrees. Within the nitro group, the O-N-O angle is increased by ca 5 degrees and one O-N-N angle is decreased by ca 5 degrees, whereas the other O-N-N angle remains almost unchanged. The cations are connected to the anions by relatively strong N-H...O hydrogen bonds [shortest H.O separations 1.77 (2)-1.81 (3) A] and much weaker C-H...O hydrogen bonds [H...O separations 2.30 (2)-2.63 (3) A].

Two trans-4-aminoazoxybenzenes.

Two isomeric trans-4-aminoazoxybenzenes, trans-1-(4-aminophenyl)-2-phenyldiazene 2-oxide (alpha, C(12)H(11)N(3)O) and trans-2-(4-aminophenyl)-1-phenyldiazene 2-oxide (beta, C(12)H(11)N(3)O), have been characterized by X-ray diffraction. The alpha isomer is almost planar, having torsion angles along the C(aryl)-N bonds of only 4.9 (2) and 8.0 (2) degrees. The relatively short C(aryl)-N bond to the non-oxidized site of the azoxy group [1.401 (2) A], together with the significant quinoid deformation of the respective phenyl ring, is evidence of conjugation between the aromatic sextet and the pi-electron system of the azoxy group. The geometry of the beta isomer is different. The non-substituted phenyl ring is twisted with respect to the NNO plane by ca 50 degrees, whereas the substituted ring is almost coplanar with the NNO plane. The non-oxidized N atom in the beta isomer has increased sp(3) character, which leads to a decrease in the N-N-C bond angle to 116.8 (2) degrees, in contrast with 120.9 (1) degrees for the alpha isomer. The deformation of the C-C-C angles (1-2 degrees ) in the phenyl rings at the substitution positions is evidence of the different character of the oxidized and non-oxidized N atoms of the azoxy group. In the crystal structures, molecules of both isomers are arranged in chains connected by weak N-H.O (alpha and beta) and N-H.N (beta) hydrogen bonds.

1-Nitroindoline.

In the title compound, C(8)H(8)N(2)O(2), the nitramino group is planar and only slightly twisted with respect to the indoline rings. The bridgehead N--C bond is slightly shorter than in typical secondary aromatic nitramines. The N--N bond has some double-bond character. The molecules are connected by weak C--H...O hydrogen bonds, forming chains parallel to the z direction.

2,3-Dihydro-3-methyl-2-nitrimino-1,3-thiazole.

The title compound ¿alternatively, 3-methyl-2-[oxido(oxo)hydrazono]-2,3-dihydro-1,3-thiazole¿, C(4)H(5)N(3)O(2)S, was obtained by methylation of N-(2-thiazolyl)nitramine. The molecule lies on a mirror plane and the thiazole ring is planar, regular in shape and aromatic. The S atom participates in the aromatic sextet via an electron pair on the 3p(z) orbital. In the crystal, the molecules are arranged in parallel layers, bound to each other by weak C-H.O and C-H.N hydrogen bonds and by S.O dipolar interactions, with an interlayer separation of 3.23 A.

Binding and chemical fractionation of heavy metals in typical peat matter.

Laboratory batch studies were conducted to evaluate the binding capacity and the mobility of metal species bound to typical humus peat matter. The identification of phase composition of mineral fractions and functional groups in the organic matter was assessed. The results showed generally high, but different retention capacity and binding strength, suggesting distinct diversity in binding mechanisms, phases and chemical nature of binding sites, depending on the metal species and their input concentrations. In general, the binding capacity of peat for the metal ions studied follows the order: Cr(3+) > Cu(2+) > Zn(2+) > Cd(2+) and results in the decrease of pH in the same order, due to displacement of H(3)O(+) from the peat by metal ions. The highest metal enrichment occurs in fractions F1(EXC), F2(CARB), F4(MRO) and F5(OM) of different binding strength adequate to exchangeable, carbonatic, moderately reducible amorphous Fe-oxide and organic/ sulphidic fractions in soils and sediments. In relation to species distribution in peats, the prevailing part of Cr(3+) is strongly bound in oxidizable organic substrate, while Cu(2+) is highly enriched in the moderately reducible F4(MRO) and the most labile F2(EXC) fractions. Cd(2+) and Zn(2+) are predominantly bound in the labile F1(EXC) and F2(CARB) fractions. Diversity of the predominant binding phases for the studied metals suggests rather weak competition for binding sites between chromium and copper ions; the strongest competition between the sorbed metal ions is anticipated for F1(EXC) and F2(CARB) fractions.