Showing papers on "Aquation published in 2001"

4-Cyanopyridine and amide-N and amide-O linkage isomers of 4-pyridinecarboxamide on trans-chloro(1,4,8,11-tetraazacyclotetradecane)ruthenium(II/III).

Abstract: The synthesis, UV-vis spectra, and electrochemical behavior of the nitrile-bonded trans-[Ru(II)Cl(cyclam)(4-NCpyH(+))](BF(4))(2) (4-Ncpy = 4-cyanopyridine; cyclam = 1,4,8,11-tetraazacyclotetradecane) and of trans-[Ru(III)Cl(cyclam)(NHC(O)-4-pyH(+))](2+) are described. The UV-vis spectrum of the Ru(II) nitrile complex shows a MLCT band at 548 nm at pH 1, which is shifted to 440 nm at pH approximately 6, for the unprotonated species. trans-[Ru(II)Cl(cyclam)(4-NCpyH(+))](2+) was electrolytically oxidized (+600 mV vs Ag/AgCl) at pH 1 to Ru(III), followed by hydrolysis (k = 0.25 s(-1)) of the coordinated nitrile to give trans-[Ru(III)Cl(cyclam)(NHC(O)-4-pyH(+))](2+), in which the amide is deprotonated and coordinated through nitrogen. The identity of the species is pH dependent, the nitrogen-bonded amide prevailing at low pH ( 8). Reduction of trans-[Ru(III)Cl(cyclam)(NHC(O)-4-pyH)](2+) in acidic media does not result in fast aquation (k = approximately 2.4 x 10(-5) s(-1)) as for other amides on ruthenium(II) pentaammine, but instead linkage isomerization occurs, resulting in the oxygen-bonded species, with an estimated rate constant of approximately 2 x 10(-2) s(-1), smaller than in the pentaammine analogues.

Isomer formation in the binding of [PtCl2(cis-cyclohexane-1,3-diamine)] to oligonucleotides and the X-ray crystal structure of [PtCl2(cis-cyclohexane-1,3-diamine)]·dimethylformamide

Abstract: The crystal structure of [PtCl2(cis-1,3-chxn)] (cis-1,3-chxn = (cis-cyclohexane-1,3-diamine)) as the dimethyformamide solvate is reported. When [PtCl2(cis-1,3-chxn)] binds to d(GpG), two isomers are formed that are readily separated by HPLC. Both the HPLC and GFAAS studies of the products show that the isomers form in a 1 ∶ 1 ratio. Competition experiments involving d(GpG) and the aquated and nonaquated forms of [PtCl2(cis-1,3-chxn)] and [PtCl2(NH3)2] showed that the slower binding of the former complex was due to slower aquation and not steric bulk. 1D and 2D NMR studies of the [Ptd(GpG)(cis-1,3-chxn)] isomers showed that both the dinucleotide and the diamine were highly fluxional, even at low temperatures, and this prevented formation of strong cross peaks in the NOESY and ROESY spectra and hence identification of the isomers. [PtCl2(cis-1,3-chxn)] was reacted with a 52-mer oligonucleotide having six GpG binding sites and the products were enzymatically digested and separated by HPLC. The two [Ptd(GpG)(cis-1,3-chxn)] stereoisomers were the only significant platinated products, again forming in a 1 ∶ 1 ratio although it had been anticipated that stereoselectivity would be observed in the reaction with the 52-mer because of the potential for steric interactions with the cis-1,3-chxn ligand. Molecular modelling revealed that the observed lack of stereoselectivity was due to the ability of the cis-1,3-chxn ligand to adopt a continuum of conformations that allow it to avoid severe steric clashes with the DNA.

A kinetic study on the iron(III)-promoted aquation of [Cr(C2O4)2(picolinato)]2− and [Cr(C2O4)2(2-pyridineacetato)]2− complexes

Abstract: Two [Cr(C2O4)2(AB)]2− type complexes, obtained from the reaction of cis-[Cr(C2O4)2(H2O)2]− with the AB ligand, [AB = picolinic (pyac) or 2-pyridine-ethanoic acid (pyeac) anions], were converted into [Cr(C2O4)(pyac)(H2O)2]0 and [Cr(C2O4)(pyeac)(H2O)2]0 compounds, respectively via FeIII-induced substitution of the oxalato ligand. The aquation products were separated chromatographically and their spectral characteristics and acid dissociation constants determined. The kinetics of the oxalato ligand substitution were studied with a 10–40 fold excess of FeIII over [CrIII] at [H+] = 0.2 M and at constant ionic strength 1.0 M (Na+, H+, Fe3+, ClO−4). The reaction rate law is of the form: r = kobs[CrIII], where kobs = kQ[FeIII]/(1 + Q[FeIII]). The first-order rate constants (k), preequilibria quotients (Q) and activation parameters derived from the k values have been determined. The reaction mechanism is discussed in terms of a Lewis acid catalyzed (induced) ligand substitution.

Activation Volumes for a Series of Spontaneous, Acidand Base-Catalysed Aquation Reactions of Aniono trans- [Co(MeNH2)(NH3)4X]2,1+ Complexes (X=Cl-, Br-,ΝO3-,SO42-)

Abstract: Abstract The volumes of activation for the spontaneous, base-, and acid- catalysed path of the hydrolysis reaction of a series of trans-[Co(MeNH2)(NH3)4X](3-n)+ ions (X = Cl-, Br-, (ONO2)- (OSO3)2-) have been determined in order to establish analogies with the dissociative trends found in previous work with the spontaneous hydrolysis of neutral ligands from the same cores. While for the base catalysed path a significant decrease in the activation volume is found on going from the {Co(NH3)5} to the trans- {Co(MeNH2)(NH3)4} inert skeleton (i.e. 9.8, 12.5, 4.0 and 9.1 cm3 mol-1 for the chloro, bromo, nitrato and sulfato derivatives), no significant changes are observed for the same complexes in the spontaneous reaction. The trends are rationalized in terms of the important changes occurring in electrostriction factors for the DCB and Id intimate mechanisms operating and the important increase in the degree of dissociativeness due to the presence of a trans-methylamino ligand. For the acid catalysed path the differences are much more difficult to assess, specially taking into account the limited information available as well as the inherent errors involved in the rate constant determination.

A radiochromatograpic study of the reaction of 51CrO3 with hydrochloric acid

Abstract: The objective of the present work is to verify the reduction of CrO 3 in concentrated hydrochloric acid, using 5 1 Cr as a tracer For the study, 5 1 CrO 3 was added to 37% HCI and maintained under agitation at 20°C for specified time periods Aliquots were diluted to approximately pH 2 and analyzed by open column cation and anion chromatography, either immediately or after storage for specified time periods The separations, which were made by stepwise elution using HClO 4 and Ca(ClO 4 ) 2 solutions as eluents with fraction collection, followed by counting with a NaI(Tl) detector and a single channel analyzer, permitted construction of elution profiles whose peaks were identified by comparison with authentic samples The results show that CrO 3 is reduced to Cr(III) in 37% HCl and that the initial identifiable product is [CrCl 3 (H 2 O) 3 ], a product which undergoes slow aquation at pH 2 to [Cr(H 2 O) 4 Cl 2 ] + , [Cr(H 2 O) 5 Cl] 2 + and [Cr(H 2 O) 6 ] 3 +

A Radiochromatograpic Study Of The Reaction Of 51cro3 With Hydrochloric Acid

Abstract: The objective of the present work is to verify the reduction of CrO 3 in concentrated hydrochloric acid, using 5 1 Cr as a tracer. For the study, 5 1 CrO 3 was added to 37% HCI and maintained under agitation at 20°C for specified time periods. Aliquots were diluted to approximately pH 2 and analyzed by open column cation and anion chromatography, either immediately or after storage for specified time periods. The separations, which were made by stepwise elution using HClO 4 and Ca(ClO 4 ) 2 solutions as eluents with fraction collection, followed by counting with a NaI(Tl) detector and a single channel analyzer, permitted construction of elution profiles whose peaks were identified by comparison with authentic samples. The results show that CrO 3 is reduced to Cr(III) in 37% HCl and that the initial identifiable product is [CrCl 3 (H 2 O) 3 ], a product which undergoes slow aquation at pH 2 to [Cr(H 2 O) 4 Cl 2 ] + , [Cr(H 2 O) 5 Cl] 2 + and [Cr(H 2 O) 6 ] 3 + .

Pentacyanochromate(III) Complexes: Ground- and Excited-State Chemistry

Abstract: An overview is presented of the available information on pentacyanochromate(III) complexes, including some recent work in our laboratory. Several aspects of the chemistry of this little explored class of anionic compounds are considered, such as the preparative methods, the absorption and emission spectra, and some thermal aquation and anation reactions. The photochemistry is given special attention; various photoaquation and photoanation results are discussed in the light of current models.