Circular dichroism spectra of N, N-dimethyl-L-amino acids

The circular dichroism spectra in the region 190-300 nm have been measured at pH 1 and pH 13 in aqueous solution for a series of N, N-dimethyl-L-amino acids. A dominant positive Cotton effect is generally observed between 205 and 225 nm as has been found previously for the parent L-amino acids. These results are consistent with the same conformer being dominant for both series of compounds

Circular dichroism spectra of asymmetric unidentate amine complexes of cobalt(III)

The preparations of pentaamminecobalt(III) complexes of a series of asymmetric unidentate amines are reported. The circular dichroism spectra for the (S)-amines show negative Cotton effects under the A → T absorption band, which are somewhat solvent dependent but independent of temperature down to -190°C. The vicinal effect from 1-cyclohexylethylamine was comparable to that from analogous aromatic compounds, but the simpler alkyl derivatives were found to impose smaller rotational strengths on the d-d transitions. The lack of measurable c.d. in the visible region for tetraammine((S)-butane-1, 3-diamine)cobalt(III) is reported and discussed in the light of the other studies

Electrochemistry of macrobicyclic mixed nitrogen-sulfur donor complexes of cobalt(III)

The redox chemistry of the mixed nitrogen-sulfur donor cobalt(III) complexes with the macrobicyclic ligands 8-methyl-6, 10, 19-trithia-l, 3, 14, 16-tetraazabicyclo[6.6.6]icosane (azacapten), l-methyl-8-nitro-3, 13, 16-trithia-6, 10, 19-triazabicyclo[6.6.6]icosane ((NO)capten), and 8-ammonio-1-methyl-3, 13, 16-trithia-6, 10, 19-triazabicyclo[6.6.6]icosane ((NH )capten) qnd of the hexadentate precursor ligand 5-(4-amino-2-thiabutyl)-5-methyl-3,7-dithia-l,9-nonanediamine (ten) has been investigated in aqueous and aprotic solutions. The macrobicyclic complexes exhibit a chemically and electrochemically reversible Co(III)/Co(II) couple near 0 V in aqueous (NHE) and aprotic solutions (Ag/AgCl) and a chemically irreversible but elctrochemically reversible 1-e couple near-1 V, nominally Co(II)/Co(I). In addition, a further multielectron couple is observed for the azacapten complex at more negative potentials. No evidence for oxidation processes was forthcoming. The low-spin d cobalt(II) complex of (NH )capten has been characterized by ESR spectroscopy at 4.2 K, and the nominally d cobalt(I) complex, at 100 K. The former compound exhibits g values at 1.94, 2.21, and 4.22, while the latter compound shows an eight-line pattern at g = 2.17 (A = 67 G) consistent with its formulation as d Co(I) and not as a d Co(II)-S radical state

Comparative formation constants for metal ions with macrocycles based on 1,4,8,11-tetraazacyclotetradecane and carrying diamine, dicarboxylate or amine-carboxylate pendants

Acid dissociation constants for the newly isolated dihydrogen anti-1,4,8,11-tetraazacyclotetradecane-6,13-dicarboxylate (diacmac), as well as for hydrogen anti-6-methyl-1,4,8,11-tetraazacyclotetradecane-6-amine-13-carboxylate (acammac) and anti-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (diammac) are reported. The ligands differ somewhat in their selection of metal ions, which is reflected in the formation constants for complexation (log KML, 25°C) which have been determined for the d10 metal ions Zn2+ (diammac, 14.9; acammac, 14.7; diacmac, 26.3), Cd2+ (diammac, 10.6; acammac, 16.7; diacmac, 15.9), Hg2+ (diammac, 10.5; acammac, 17.3; diacmac, 21.8) and Pb2+ (diammac, 10.8; acammac, 10.7; diacmac, 19.0) and the d5 Mn2+ ion (diammac, 6.2; acammac, 12.0; diacmac, 18.3). Differences arise in part from the increasing availability of potential O donors versus N donors in stepping from diammac to diacmac, and imply a clear role for the pendants in binding metal ions. Copyright ©1996 Elsevier Science Ltd

Circular Dichroism Spectra of Tetraamminecobalt(III) Complexes of Amino Alcohols

The circular dichroism spectra are reported for tetraamminecobalt(III) complexes with the chiral amino alcohols 2-aminopropan-1-ol, 2-aminobutan-1-ol, l-aminopropan-2-ol, 2-amino-1-phenyl- ethanol, ψ-ephedrine and ephedrine with the alcohol groups protonated (OH) and deprotonated (O-). The solvent dependence of the chemical shifts of the NH protons was investigated to determine the effects of stereoselective solvation on the circular dichroism, but, in contrast to some other related systems, the chemical shift difference between the two NH2protons was relatively insensitive to solvent. Consistent with this, the circular dichroism spectra of the tetraphenylborate salts of the deprotonated complexes were found not to be markedly dependent on solvent. Tetraammine- ((-)-ψ-ephedrine)cobalt(III) and tetraammine((-)-ephedrine)cobalt(iii) were found to have the same signs of Cotton effects for the various d-d transitions, whereas bis((-)-ψ-ephedrine)copper(ii) and bis((-)-ephedrine)copper(ii) had opposite signs. This has been explained in terms of different conformer populations in the cobalt(iii) and copper(ii) systems

Solvent-dependent circular dichroism of trans-disubstituted Bis(R-propane-1,2-diamine)cobalt(III) complexes

The circular dichroism spectra of trans-disubstituted bis(R-propane-1,2-diamine)cobalt(III) complexes are reported for an extended series of solvents. The observed variations in the spectra of the dichloro and dibromo complexes are analysed in terms of stereoselective solvation at the diamine N-H protons, and also the ion association between the complexes and their counter-ions. The solvation of these dihalo complexes, which was studied by p.m.r., showed a preference for hydrogen-bond formation with the equatorial N-H protons, rendering the donor nitrogens asymmetric and thus introducing a new source of dissymmetry close to the metal ion chromophore. This affected a decrease in the positive rotational strength of the 1A1g {equivalent to} 1Eg (D4h) transition, and a positive contribution to the rotational strength of the 1A1g {equivalent to} 1A2g (D4h) component. Ion association of the dihalo complexes was evaluated by a comparison of the circular dichroism of the tetraphenylborate and halide salts. The tendency for ion association was much greater for the tripositive diammine complex. However, stereospecific solvation was of little importance and the circular dichroism spectra did not show any marked solvent dependence for the tetraphenylborate salt

Dicopper(II) complexes of spiro macrobicycles with aza and thia aza donor sets

Reaction of the dicopper(II) complex of the binucleating ligand 5, 5-bis(4-amino-2-azabutyl)-3, 7-diazanonane-1, 9-diamine with nitroethane and formaldehyde in water gives the respective macrobicyclic and macromonocyclic binucleating ligands 7, 21-dimethyl-7, 21-dinitro-2, 5, 9, 12, 16, 19, 23, 26-octaazaspiro[13.13]heptacosane and 6, 6-bis(4-amino-2-azabutyl)-13-methyl-13-nitro-l, 4, 8, 11-tetraazacyclotetradecane, both as their dicopper(II) complexes. Similarly, condensation of the dicopper(II) complex of 5, 5-bis(4-amino-2-thiabutyl)-3, 7-dithianonane-1, 9-diamine with nitroethane and formaldehyde results in the binucleating macrobicycle 7, 21-dimethyl-7, 21-dinitro-2, 12, 16, 26-tetrathia-5, 9, 19, 23-tetraazaspiro[13.13]-heptacosane. Physical properties of all complexes are reported and comparisons with mononuclear relatives are made. Structural parameters derived from electron paramagnetic resonance spectra are discussed

Syntheses and Comparative base hydrolysis reactions of chlorocobalt(III) complexes of pendant-arm macrocyclic polyamines and polyamino acids

Chlorocobalt(III) complexes of the pendant-arm macrocycles 1,4,8,12-tetraazacyclopentadecane-10-carboxyiate (2) and 1,5,9,13-tetraazabicyclo[11.2.2]heptadecane-7-carboxylate (4) have been prepared to complement the known complexes of 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine (1) and 7-methyl-1,5,9,13-tetraazabicyclo[11.2.2]heptadecan-7-amine (3). The pairs (1),(3) and (2),(4) differ in replacement of pendant amine and methyl groups in the former pair by a pendant carboxylate group and hydrogen in the latter pair. The macromonocyclic ligands (1) and (2) form cis-chlorocobalt(III) complexes whereas the macrobicyclic ligands (3) and (4) (which contain an additional -CH2-CH2-'strap' linking two amines) form trans-chlorocobalt(III) complexes, defined in terms of location of the pendant donor and the chloride donor. Chloride base hydrolysis kinetics varies with ligand {cis-[Co(1)Cl]2+, kOH 6700 dm3 mol-1 s-1; cis-[Co(2)Cl]+, kOH 1800 dm3 mol-1 s-1 trans-[Co(3)Cl]2+, kOH 3450 dm3 mol-1 s-1; trans-[Co(4)Cl]+, kOH 2250 dm3 mol-1 s-1 at 25°C}. Variations in rate constant are tied mainly to variations in activation enthalpy. Chloride hydrolyses occur with retention of configuration, but slow following isomerization can lead to products such as trans-[Co(2)(OH2)] (ClO4)2.2H2O, which crystallizes in the monoclinic space group P21/c, a 9.581(2), b 16.214(2), c 14.350(2) Å and ß 94.66(1)°. The pendant carboxylate group and two adjacent secondary amines necessarily occupy an octahedral face, with the water molecule bound trans to the pendant carboxylate. The four Co-N distances range from 1.981(2) to 2.022(3) Å, and along with carboxylate Co-O (1.882(3) Å)-and water Co-O (1.934(2) Å) distances are similar to usual distances in cobalt(III) complexes.Australian Research CouncilSupport of this research by the Australian Research Council is gratefully acknowledged. We thank Ms Christine C. Allen for assistance with the structure solution