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PMR studies of palladium(II)-glycyl-L-aspartic acid complexes in aqueous solution
Volume 4% number 2
1 September 1976
CHEMICAL PHYSICS LE’ITERS
2MR STUDjIBS OF PALLADIUM(II)-GLYCYLGASPARTIC IN AQUEOUS SOLUTION
ACID COMPLEXES
H. KOZ-EOWSKI and B. JEiOVlSKA-TRZEBIATOWSKA of Chemistry, University of Woczizw. SC-383 IVro&zw. Pobd
institute
Received 21 April 1976 The PhfR technique has been used to establish the coordinations in 1 : 1 and 1 : 2 Pd(I1) to glycyl-L-aspartic acid complexes In the 1 : 1 complex both nitrogens and the a-carboxyl group are coordinated to the metal ion and the p-carboxyi group is in a pseudoaxial position. in the 1 : 2 comp!ex only nitrogen atoms are coordinated to Pd(II) ions and the conformations of the ligands in this complex are also established.
1. Introduction
3. Results
Palladium (II) ions ha= the capability of forming stable diamagnetic square planar complexes both with aminoacids and peptides [l-5] , and they are most effective in the promotion of peptide hydrogen ionization [l] _ The NMR method, as well as CD spectroscopy [1,2] can be used to establish the structure of Pd(II)peptide complexes, especially to find the conformation of the coordinated ligands. As part of our investigations of interactions between transition metal ions and molecules of biological interest [6-81 we present here the results of our PMR studies on Pd(II)-glycyl-Caspartic acid complexes in aqueous solution.
3.1. 1 : I mob-ratio
2. Experimental Glycyl-Gaspartic acid was used as received from Fluka. QPdCI, was obtained by crystallization of KC1 and PdCl, solutions containing HCl. Titration data showed its 99% purity. PMR spectra were made on a JEOL 100 MHz JNM PS-100 spectrometer using (CIi3)4NCl(TMA) as an internal standard. All spectra were recorded at 26 f: 1°C. pH was adjusted with KOD (KO2H> and HCl in D,O solution and measured
on a Mera-Elmat
N-5 12 pH-meter.
Analysis
of the NklR spectra were made on a JEC-6 computer.
246
system
PMR spectra for PI-I = l-53,8.4 and 12.48 are given in fig. 1. The shapes of all PMR spectra for pH higher than 3 are the same and only slight changes in chemical shift values are observed for c&H and BCH, protons of the aspartic acid residue. In extremely high pH (see pH = 12.48, fig. 1) the triplet of the a-CH proton and the doublet of the /3-CH, protons, vanish and new ones (Y;, 0; appear at somewhat higher field (= 5 Hz). The character of the obtained spectra indicates that the formed complexes are inert in NMR scale and separated lines for different species in solution can be observed. Protons of the aspartic acid residue in the whole pH range have an A,X type of spectrum contrary to metalfree peptide, or to complexes of this peptide with Zn(I1) ions [9], where at pH higher than 3 the spectrum was of the ABX type. The vi&al coupling constant for the 1 : 1 palladium complex JAx is equal to 4 Hz and is considerably smaller than for metai-free peptide (in solutionJAX = 6.2 Hz). 3.2. 2 : I molarrario system PMR spectra at pH up to 3 for this molar ratio are the same as for the 1 : 1 one. For pH higher than 3 the PMR spectra are much more complicated than in the previous case (some of them are given in fig. 2).
CHEMICAL PHYSICS LETTERS
Volume 42. number 2
1
September 1976
B
d.
. -ISO
-100
-50
6
si3
Fig. 1. PhIR spectra of 1 : 1 Pd(I1) - glycyl-L-aspartic acïd solution at pH = 1.53 (A), 8.4 (B), 12.48 (0. q, Pi and ri are Proton rnultiplets of metal-free peptide (O), 1 : 1 complex (1).
Fig. 2. P&$R spectra of 1 : 2 Pd(II) - gIycyI-baspartic acid solution at pH = 2.36 (Ah 4.94 (Bh 10.6L(Ch 2M KOH(D)- Qif & 7 are proton rmdtiplets for metal-free peptide (0), 1 : 1 complex (1). 1 : 2 complex with uncomPIetelY coordinated second kand (2,3), 1 : 2 complex (4).
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Fig. 3. Rotamers of glycyl-L-aspartic acid molecule.
A spectrum characteristic of a 1 : 1 molar ratio system can be observed additionally up to pH = 11 and it decays with increasing pH. In strong basic solution tbe spectra of the glycine Cl-$ protons are of the AB type and the Q:CH and p CHz ones of the aspartic acid residue are of the ABX type. Using a rotamer notation as in fig. 3 for the aspartic acid residue the analysis can be made, and the population of each rotamer can be calculated with the equations (see for example ref. IlOl)
J BX = PI
Jg + PII:It + PIL Jg,
1 September 19+6
ligand (e.g. lVH2 group and the peptide linkage) at very low pH. High up-field shifting is caused by the negative charges of the coordinated atoms : Cl’, N of the peptide linkage and eventually COO-. There is no change in chemical shift of the at line (coordinated glycine) for pH increasing from 1.53 up to 8.4 or í 2.48, which allows USto state that rl corresponds to the chelate complex with both nitrogen atoms bound to Pd(lI). Both other mdtiplets of coordinated peptide ar and PI are shifted to higher field (deprotonation of the p-COOH group), but the A,X type of spectra is maintained in the whole pH region. According to eqs. (1) the populations of rotamers 1 and 11 (fig. 3) ior the AZX type of spectra and for JaX = 4Hz should be equal, plrl = 0.76 and pl = prl = 0.12. These results suggest, that the structure of the 1 : 1 Pd(II)peptide complex is as given in fig. 4, in which the cy or P’carboxyl group is coordinated to the Pd(Il) ion and other one is in a pseudoaxial position (perpendicular to the complex plane).
(1)
4. Discussion 4.1. Cbrnplexes
in the
I : I molar ratio solutbns
At pH 1.53 the PMR spectrum consists of metal-free peptide multiplats (oo, /Zr-,,7 ) and of the multiplets of peptide coordinated to Pd(l 6 ions (ai, PI, 71 and 7;). Considembte changes of rhe chemical shifts of the glycine CHL prutons and the
- Pd (lil @a -c á -Cl_orow
0-N 0
-
H
Fig. 4. Probable structures for 1 : 1 complex with coordinated ecarboxyl group
Volume42, number 2
CHEMICAL PHYSICS LETTERS
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September1976
In the case of the structure “B” only two rotamers 11 and 111of the peptide are possible and pl shouId not be eqd p, (JAx f Jsxs ABX spectrum). Thus the structure “A” for the 1 : 1 complex wit11the crcarboxyl group coordinated to the metal ion is more probable. This is consistent with the general view that a five-membered chelate ring is more favourable than a six-membered one. The change of Qrland S1 chemical shîfts at very high pH (pH = 10 - 13) is probably caused by exc-bange of the Cl- ion for an OH- group at the fourth coordination site of the centra1 ion.
the lower pH region (pEI = 3 - 11); the 1 : 1 complex as described in the previous section (7, in the glycine part of the spectrum), the 1 : 2 complex with the second ligand bonded by only one rütrogen (72 and r3 lines) and the 1 : 2 complex with four coordinated nitrogens. The structural conclusions from these complexes could be useful for the interpretation of square planar Cu(I1) and Ni(H) complexes, which are also of interest [9], becausc of the similarities of the structures of tetragonal Cu(H), Ni(H) and Pd(II) complexes [ 1,2] .
4.2. Complexes in the I : 2 mokar rdio system
Acknowledgement
The interpretation of the PMR specrra for pH values up to about 3 is the same as for the 1 : I case. Another complex which could be distinguished among the species in solution is the 1 : 2 Pd(II) to peptide one with spectrum as given in fig. 2 for 2M KOD solution. CH, protons of glycine exhibit an AB type of spectrum with AvAB = 15.5 Hz, JAB = 16.2 Hz with the centre at vc = -2 1.5 Hz with respect to TMA. The inequivalente of these protons caused by the carbonyl goup of the peptide linkage is observed probably because of slow conformational (S + X) changes of chelate rings in the 1 : 2 complex. The protons of the aspartic acid residue have a spectrum of the ABX type: JAx = 10.5 Hz, J,, = 4.4 Hz and JAB = 14.85 Hz and vA = i80.7 Hz, vg = i54.3 Hz and vx = -102.2 Hz with respect to TMA. The rotamer populations in the complex can be found from eqs. (1) and for the 1 : 2 complex we have pI = 0.72, pn = 0.16 = 0.12. These data show that only two nitrogens -JPm are coorclinated from each peptide molecule and carboxyl groups are directed outward the complex core, one in pseudoequatorial and the other in pseudoaxial position. There are few species existing in the solution in
Wc thank Mr. 2. Siatecki MSci for allowing us to use bis programme for NMR spectra1 analyses.
References 111E.W. Wiion Jr. and R.B. Martin, Inorg. Chem. 9 (1970) 528.
121T.P. Pïnter, E.W. Wikon Jr. and R.B. Martin, Inorg. Chem. 11 (1972) 738, and referencesthereïn. [31 S.T. Chow. C.A. McAuliffe and B.J. Sayle, J. Inorg. Nucl. Chem. 37 (1975)
451.
t41 C.P. Trvediand R.C. Kapoor,Proc. Natl. Acad. Sci. India Sec. A (1971) 101. [SI J. KoUman, Cb. Schroeter and E. Hoyer, J. Prakt. Chem. 317 (1975)
515.
161 B. Jezowska-Trzebiatowska,
G. FormickaXo5owska and H. Kozlowski, submitted for publication 171 B. Jeiowska-Trzebiatowska, G. Formicka-Kozlowska and H. KozPowski, submittcd for publication. L. Latos-GraZy&ki and H. Vl B. Jeiowska-Trzeóiatowska, KozPowski, submitted for publication 191 H. Kozlowski and B. Jekowska-Trzebiatowska, in preparation. [lol H. Oya, Y. Arata and S. Fujiwara, J. MOL Spectry. 23 (1967) 78. and references therein.
249
1 September 1976
CHEMICAL PHYSICS LE’ITERS
2MR STUDjIBS OF PALLADIUM(II)-GLYCYLGASPARTIC IN AQUEOUS SOLUTION
ACID COMPLEXES
H. KOZ-EOWSKI and B. JEiOVlSKA-TRZEBIATOWSKA of Chemistry, University of Woczizw. SC-383 IVro&zw. Pobd
institute
Received 21 April 1976 The PhfR technique has been used to establish the coordinations in 1 : 1 and 1 : 2 Pd(I1) to glycyl-L-aspartic acid complexes In the 1 : 1 complex both nitrogens and the a-carboxyl group are coordinated to the metal ion and the p-carboxyi group is in a pseudoaxial position. in the 1 : 2 comp!ex only nitrogen atoms are coordinated to Pd(II) ions and the conformations of the ligands in this complex are also established.
1. Introduction
3. Results
Palladium (II) ions ha= the capability of forming stable diamagnetic square planar complexes both with aminoacids and peptides [l-5] , and they are most effective in the promotion of peptide hydrogen ionization [l] _ The NMR method, as well as CD spectroscopy [1,2] can be used to establish the structure of Pd(II)peptide complexes, especially to find the conformation of the coordinated ligands. As part of our investigations of interactions between transition metal ions and molecules of biological interest [6-81 we present here the results of our PMR studies on Pd(II)-glycyl-Caspartic acid complexes in aqueous solution.
3.1. 1 : I mob-ratio
2. Experimental Glycyl-Gaspartic acid was used as received from Fluka. QPdCI, was obtained by crystallization of KC1 and PdCl, solutions containing HCl. Titration data showed its 99% purity. PMR spectra were made on a JEOL 100 MHz JNM PS-100 spectrometer using (CIi3)4NCl(TMA) as an internal standard. All spectra were recorded at 26 f: 1°C. pH was adjusted with KOD (KO2H> and HCl in D,O solution and measured
on a Mera-Elmat
N-5 12 pH-meter.
Analysis
of the NklR spectra were made on a JEC-6 computer.
246
system
PMR spectra for PI-I = l-53,8.4 and 12.48 are given in fig. 1. The shapes of all PMR spectra for pH higher than 3 are the same and only slight changes in chemical shift values are observed for c&H and BCH, protons of the aspartic acid residue. In extremely high pH (see pH = 12.48, fig. 1) the triplet of the a-CH proton and the doublet of the /3-CH, protons, vanish and new ones (Y;, 0; appear at somewhat higher field (= 5 Hz). The character of the obtained spectra indicates that the formed complexes are inert in NMR scale and separated lines for different species in solution can be observed. Protons of the aspartic acid residue in the whole pH range have an A,X type of spectrum contrary to metalfree peptide, or to complexes of this peptide with Zn(I1) ions [9], where at pH higher than 3 the spectrum was of the ABX type. The vi&al coupling constant for the 1 : 1 palladium complex JAx is equal to 4 Hz and is considerably smaller than for metai-free peptide (in solutionJAX = 6.2 Hz). 3.2. 2 : I molarrario system PMR spectra at pH up to 3 for this molar ratio are the same as for the 1 : 1 one. For pH higher than 3 the PMR spectra are much more complicated than in the previous case (some of them are given in fig. 2).
CHEMICAL PHYSICS LETTERS
Volume 42. number 2
1
September 1976
B
d.
. -ISO
-100
-50
6
si3
Fig. 1. PhIR spectra of 1 : 1 Pd(I1) - glycyl-L-aspartic acïd solution at pH = 1.53 (A), 8.4 (B), 12.48 (0. q, Pi and ri are Proton rnultiplets of metal-free peptide (O), 1 : 1 complex (1).
Fig. 2. P&$R spectra of 1 : 2 Pd(II) - gIycyI-baspartic acid solution at pH = 2.36 (Ah 4.94 (Bh 10.6L(Ch 2M KOH(D)- Qif & 7 are proton rmdtiplets for metal-free peptide (0), 1 : 1 complex (1). 1 : 2 complex with uncomPIetelY coordinated second kand (2,3), 1 : 2 complex (4).
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Volume 42, number 2
CHEMICAL PHYSLCS LETTERS
Fig. 3. Rotamers of glycyl-L-aspartic acid molecule.
A spectrum characteristic of a 1 : 1 molar ratio system can be observed additionally up to pH = 11 and it decays with increasing pH. In strong basic solution tbe spectra of the glycine Cl-$ protons are of the AB type and the Q:CH and p CHz ones of the aspartic acid residue are of the ABX type. Using a rotamer notation as in fig. 3 for the aspartic acid residue the analysis can be made, and the population of each rotamer can be calculated with the equations (see for example ref. IlOl)
J BX = PI
Jg + PII:It + PIL Jg,
1 September 19+6
ligand (e.g. lVH2 group and the peptide linkage) at very low pH. High up-field shifting is caused by the negative charges of the coordinated atoms : Cl’, N of the peptide linkage and eventually COO-. There is no change in chemical shift of the at line (coordinated glycine) for pH increasing from 1.53 up to 8.4 or í 2.48, which allows USto state that rl corresponds to the chelate complex with both nitrogen atoms bound to Pd(lI). Both other mdtiplets of coordinated peptide ar and PI are shifted to higher field (deprotonation of the p-COOH group), but the A,X type of spectra is maintained in the whole pH region. According to eqs. (1) the populations of rotamers 1 and 11 (fig. 3) ior the AZX type of spectra and for JaX = 4Hz should be equal, plrl = 0.76 and pl = prl = 0.12. These results suggest, that the structure of the 1 : 1 Pd(II)peptide complex is as given in fig. 4, in which the cy or P’carboxyl group is coordinated to the Pd(Il) ion and other one is in a pseudoaxial position (perpendicular to the complex plane).
(1)
4. Discussion 4.1. Cbrnplexes
in the
I : I molar ratio solutbns
At pH 1.53 the PMR spectrum consists of metal-free peptide multiplats (oo, /Zr-,,7 ) and of the multiplets of peptide coordinated to Pd(l 6 ions (ai, PI, 71 and 7;). Considembte changes of rhe chemical shifts of the glycine CHL prutons and the
- Pd (lil @a -c á -Cl_orow
0-N 0
-
H
Fig. 4. Probable structures for 1 : 1 complex with coordinated ecarboxyl group
Volume42, number 2
CHEMICAL PHYSICS LETTERS
1
September1976
In the case of the structure “B” only two rotamers 11 and 111of the peptide are possible and pl shouId not be eqd p, (JAx f Jsxs ABX spectrum). Thus the structure “A” for the 1 : 1 complex wit11the crcarboxyl group coordinated to the metal ion is more probable. This is consistent with the general view that a five-membered chelate ring is more favourable than a six-membered one. The change of Qrland S1 chemical shîfts at very high pH (pH = 10 - 13) is probably caused by exc-bange of the Cl- ion for an OH- group at the fourth coordination site of the centra1 ion.
the lower pH region (pEI = 3 - 11); the 1 : 1 complex as described in the previous section (7, in the glycine part of the spectrum), the 1 : 2 complex with the second ligand bonded by only one rütrogen (72 and r3 lines) and the 1 : 2 complex with four coordinated nitrogens. The structural conclusions from these complexes could be useful for the interpretation of square planar Cu(I1) and Ni(H) complexes, which are also of interest [9], becausc of the similarities of the structures of tetragonal Cu(H), Ni(H) and Pd(II) complexes [ 1,2] .
4.2. Complexes in the I : 2 mokar rdio system
Acknowledgement
The interpretation of the PMR specrra for pH values up to about 3 is the same as for the 1 : I case. Another complex which could be distinguished among the species in solution is the 1 : 2 Pd(II) to peptide one with spectrum as given in fig. 2 for 2M KOD solution. CH, protons of glycine exhibit an AB type of spectrum with AvAB = 15.5 Hz, JAB = 16.2 Hz with the centre at vc = -2 1.5 Hz with respect to TMA. The inequivalente of these protons caused by the carbonyl goup of the peptide linkage is observed probably because of slow conformational (S + X) changes of chelate rings in the 1 : 2 complex. The protons of the aspartic acid residue have a spectrum of the ABX type: JAx = 10.5 Hz, J,, = 4.4 Hz and JAB = 14.85 Hz and vA = i80.7 Hz, vg = i54.3 Hz and vx = -102.2 Hz with respect to TMA. The rotamer populations in the complex can be found from eqs. (1) and for the 1 : 2 complex we have pI = 0.72, pn = 0.16 = 0.12. These data show that only two nitrogens -JPm are coorclinated from each peptide molecule and carboxyl groups are directed outward the complex core, one in pseudoequatorial and the other in pseudoaxial position. There are few species existing in the solution in
Wc thank Mr. 2. Siatecki MSci for allowing us to use bis programme for NMR spectra1 analyses.
References 111E.W. Wiion Jr. and R.B. Martin, Inorg. Chem. 9 (1970) 528.
121T.P. Pïnter, E.W. Wikon Jr. and R.B. Martin, Inorg. Chem. 11 (1972) 738, and referencesthereïn. [31 S.T. Chow. C.A. McAuliffe and B.J. Sayle, J. Inorg. Nucl. Chem. 37 (1975)
451.
t41 C.P. Trvediand R.C. Kapoor,Proc. Natl. Acad. Sci. India Sec. A (1971) 101. [SI J. KoUman, Cb. Schroeter and E. Hoyer, J. Prakt. Chem. 317 (1975)
515.
161 B. Jezowska-Trzebiatowska,
G. FormickaXo5owska and H. Kozlowski, submitted for publication 171 B. Jeiowska-Trzebiatowska, G. Formicka-Kozlowska and H. KozPowski, submittcd for publication. L. Latos-GraZy&ki and H. Vl B. Jeiowska-Trzeóiatowska, KozPowski, submitted for publication 191 H. Kozlowski and B. Jekowska-Trzebiatowska, in preparation. [lol H. Oya, Y. Arata and S. Fujiwara, J. MOL Spectry. 23 (1967) 78. and references therein.
249