Donald R. Eaton

Concentration of aquatic dissolved organic matter by reverse osmosis

Abstract Dissolved organic carbon (DOC) was concentrated from natural streams using reverse osmosis equipment. Quality control tests show that from 95.6 to 98.5% of total DOC was rejected by the membrane, though only 70% could actually be recovered, most likely because of losses within the plumbing system. Comparison of the acid-base characteristics of the original water sample with re-diluted concentrate show that modifications occurred. Visual evidence showed that polycondensation reactions which modify acid-base characteristics occurred in the concentrate. Analysis of the material passing through the membrane (permeate) shows that it is

Chemical shift anisotropy and second-sphere hydrogen bondin in Cobalt (III) Complexes

The linewidths of the 59Co NMR resonances of 22 Co(III) complexes were measured at fields of 2.114, 5.872, and 9.395 T. The linewidths for octahedral complexes show no field dependence. Less symmetric compounds show differences in linewidth of as much as 10 kHz between the highest field and the lowest field. The linewidth changes parallel the chemical shift anisotropies calculated from optical absorption spectral data. For complexes with high symmetry the increase in width is proportional to the square of the field strength. For complexes of lower symmetry, plots against field squared show a pronounced curvature. If the increase in linewidth is calculated from the chemical shift anisotropies obtained from optical data (or from single-crystal measurements reported in the literature) and correlation times derived from quadrupole coupling constants the calculated increases in width are more than two orders of magnitude smaller than the observed increases. Correlation times of the order 10−9 to 10−10 sec rather than the accepted 10−11 sec for rotational correlation times are required to fit the data. It is suggested that these long correlation times are associated with the lifetimes of hydrogen bonds with second-sphere solvent molecules.

Seasonal variation in the composition of aquatic organic matter in some Nova Scotian brownwaters: a nuclear magnetic resonance approach

Using a novel concentration technique (reverse osmosis and freeze-drying) as well as a standard analytical technique little used with limnological samples (solid state 13C nuclear magnetic resonance), we studied the chemical structure of aquatic organic matter from four closely located freshwater sites in Nova Scotia. The main conclusions drawn from the data are that: (a) the aromatic C fraction which is assumed to be refractory remains at less than 10% of the total, with a slight increase in relative importance in the fall, (b) less structurally complex aliphatic carbon decreases from winter to spring and remains at lower levels into later fall, (c) carbohydrates are at a maximum during the summer, (d) the carboxylic C fraction is at a minimum in the summer and maximum in the fall and winter. Results show roughly the same annual patterns of C composition for the two running water sites. Our data suggest that the hydrological processes which carry terrestrial and wetland DOM to streams and lakes allow a selective adsorption process of DOM to occur in soils. We compare our data to those from other freshwater studies and suggest that the importance of aromatic carbon in freshwaters has probably been overestimated in the past, with a corresponding underestimate of the more biologically labile carbohydrate and aliphatic material.

An N.M.R. study of the interactions between cadoxen and saccharides

Abstract Cadoxen, an aqueous solution of cadmium oxide and ethylenediamine, is an effective solvent for cellulose and is known to form complexes with simpler saccharides. The 1 H-, 13 C-, and 113 Cd-n.m.r. spectra of d -glucose, cellobiose, methyl α- d -glucopyranoside, methyl β- d -glucopyranoside, and cellulose in cadoxen are reported. Cellulose gives a well resolved 13 C spectrum in this solvent, and it is assigned by comparison with the spectra of simpler sugars. The 113 Cd and 13 C results are not consistent with the formation of chelate alcoholate complexes involving the 2- and 3-hydroxyl groups. This form of interaction has been suggested in the literature. It seems rather that hydrogen-bonding interactions are dominant. It is suggested that the effectiveness of cadoxen and similar cellulose solvents is a result of enhanced hydrogen-bonding arising from a combination of steric and electronic factors. The metal ion serves the dual purpose of holding two amino groups in a favorable orientation for hydrogen bonding with a pair of equatorial hydroxyl groups on the carbohydrate, and of decreasing the p Ka of the amino group by withdrawing electrons.Some analogies with the binding of sugars to concanavalin A are discussed.

Studies of exchange equilibria of palladium(II) tertiary phosphine complexes

Abstract The reactions of tertiary phosphine complexes of Pd(II) with phosphine !igand: have been investigated by NMR and conductivity measurements. Depending on the nature of the phosphine ligand either ligand exchange or the formation of cationic complexes can occur. Relative equilibrium constants for these reactions have been obtained. NMR line broadening experiments have enabled the relative rates of ligand exchange between the neutral and cationic complexes and between the cationic complex and free ligand to be obtained. A mechanism for the former process is suggested. The equilibrium constant data suggest that optimum stability for the complexes is achieved with ligands of intermediate donor ability. The significance of this observation is discusssed.

Spin-lattice relaxation in Co complexes of low symmetry

Abstract Spin-lattice relaxation times for 59 Co contained in several low symmetry cobalt complexes are reported. Measurements have been made at two field strengths and, in the case of one complex, in several solvents. Some complementary measurements of 14 N relaxation times on the same complexes are also reported. Linewidth measurements have been made to obtain T 2 values. The relaxation mechanisms depend on the solvent. In a “weakly hydrogen bonding” solvent (acetonitrile) quadrupolar and scalar relaxation through spin coupling to 14 N are the most important mechanisms. Reasonable agreements between experimental and calculated relaxation times at low magnetic field can be obtained using experimental solid state quadrupole coupling constants, spin-spin coupling constants from 15 N data, 14 N T 1 values, and correlation times consistent with those obtained from the Debye formula. In these cases T 1 for 59 Co is greater than T 2 . In hydrogen bonding solvents an additional field dependent term is necessary. Both T 1 and T 2 are affected eliminating the possibility of a chemical exchange process. The field dependent term is associated with chemical shift anisotropy involving the off diagonal (antisymmetric) terms in the chemical shielding tensor. This mechanism requires that T 1 be less than T 2 . The experimental data are consistent with this prediction.

The 19F chemical shifts of fluorophenyl phosphine complexes of group VIII metals

Abstract The 19 F chemical shifts for meta and para fluorophenyl phosphines incorportated in a range of group VIII transition metal complexes are reported. The measured shifts are used to obtain values of the o1 and σ° R parameters used to correlate the electron withdrawing and donating parameters of aromatic compounds. It is concluded that the donor or acceptor properties of a metal ion containing moiety are determined more by the nature of the ligands present than by the formal oxidation state of the metal ion.

Cobalt(II) and zinc(II) complexes of thiourea as catalysts for the reactions between carbonyl compounds and anilines

Abstract The kinetics of the reactions between p-nitro-benzaldehyde and p-toluidine and between acetone and p-anisidine have been examined in non-aqueous solutions and in the presence of Zinc(II) and Cobalt(II) complexes of thiourea which acts as catalysts. The reaction between 2,4-Dinitrophenyl acetate and p-toluidine is not catalysed by these metal complexes. The kinetics of the p-Nitrobenzaldehyde reaction are straight-forward with first order dependence on each of the reactants and on the catalyst and a second order rate determining step. For the reaction in acetonitrile d3 catalysed by tetrakis Zn(II) thiourea perchlorate a third order rate constant of 25.0±1.5 M−2 s−1 has been measured. The kinetics of the acetone/p-anisidine reaction are quite different and closely parallel similar reactions studied previously. The results for the two reactions cannot be fitted to a common mechanism. All three reactions involve nucleophilic attack of an aniline on a carbonyl group but two are catalysed by different mechanisms and the third is not catalysed at all. It is suggested that catalysis can occur either by coordination of the carbonyl compound or by coordination of the adduct formed by the carbonyl compound and the aniline. If neither of these reactants is capable of forming a sufficiently long lived metal complex there will be no catalysis.

Mechanism and kinetics of ligand exchange in Co(II) complexes of thiourea

Abstract The kinetics of ligand exchange of eight Co(II) complexes of thiourea and substituted thioureas have been measured. In each case two mechanisms are involved. The first is a direct associative exchange and the second requires initial displacement of thiourea by the solvent (acetone). Rate constants and activation parameters are presented. The lability of the complexes arises from the low enthalphies of activation.

The reaction of [(η5-cyclohexadienyl)Fe(CO)3]+BF4− with 2-methyl-2-nitrosopropane: an unexpected oscillating reaction

Abstract The reaction of 2-methyl-2-nitrosopropane with the organometallic cation [(η 5 -cyclohexadienyl)tricarbonyliron] + yields the bis(t-butyl)nitroxide radical which is detected by ESR spectroscopy. The intensity of the ESR signal varies in an oscillatory manner with time and the ESR silent period between oscillations ranges from 15 minutes to one hour, depending on the relative concentrations of the reagents. Some years ago, Turcsanyi proposed ( Acta Chim., Acad. Scient. Hungar. , 110 (1982) 305, Chem. Abs. 97 188877w) that a RNO/RNHOH system might exhibit oscillatory behaviour and the data presented are an experimental realization of that prediction. A mechanistic rationale is proposed to account for the observations.