Transcript The Effect of Amino Acids on the Solubility of Copper (II) Citraconate

The Effect of Amino Acids on the Solubility of Copper (II) Citraconate
Rhomesia Ramkellowan
Mentor: Sabrina G. Sobel, Department of Chemistry, Hofstra University, Hempstead, New York, 11549
Project SEED
Abstract
Copper (II) Citraconate + Amino Acids
Copper(II) Citraconate + Glycine
• Copper dissolved starts at ~26% without added
glycine.
80%
70%
% Cu(Citr)
Dissolved
Zinc and copper salts are known to be important in general human nutrition and surface
wound healing. The success formulations that provide zinc and copper(II) ions locally at the
wound site may depend on the bioavailability of zinc and copper(II) ions. A study of the
influence that amino acids have on the solubility of zinc citraconate may be relevant to such
therapy. In this research, copper(II) citraconate was combined with varying molar amounts of
amino acids (glycine, alanine and serine) and each solution was titrated with Na2EDTA to
determine the total copper(II) ion content in the solutions, and therefore the percent of zinc
citraconate that dissolved and the percent copper(II) titrated. It is hoped that this research may
help aid future development of medical copper(II) salt treatments.
Relevant Equilibria
• Added glycine gradually increases the solubility of
Copper (II) citraconate.
60%
50%
2
40%
y = -0.0093x + 0.122x + 0.2709
R2 = 0.9675
30%
• Maximum solubility of ~65% was seen at a glycine
to total copper molar ratio of 5:1
20%
0
2
4
6
8
10
Rel. Moles of Glycine
Introduction
Copper(II) Citraconate + Alanine
Alanine is less polar than
glycine, and serine is
more polar that glycine
70%
• Maximum solubility of
~60% was seen at a alanine
to copper salt molar ratio of
5:1
% CuCitr Dissolved
Determination of interaction of strong and weak complexing agents and effect on free
copper(II) ion content can lead to useful insight for development of applications
• Copper(II) complexes are important in biological and industrial contexts
– General Nutrition (RDA 900mcg)
– Wound healing (promotes debridement and healing of burn wounds)
– Plant nutrition (provides an essential nutrient)
• What form of copper(II) is best for each situation?
– Are free copper(II) ions (weakly complexed) or strongly complexed copper(II) ions more
beneficial?
– Strong complexes for the removal of copper(II) ; weak complexes for the delivery of
•Added alanine gradually
increases the solubility of
Copper (II) Citraconate.
60%
50%
40%
2
y = -0.0076x + 0.0976x + 0.3464
2
R = 0.6993
30%
20%
0
2
4
6
8
Rel. Moles of Alanine
10
12
% CuCitr Dissolved
• Added serine increases the solubility of Copper (II)
Citraconate.
• Maximum solubility of ~61% was seen at a serine to
total copper molar ratio of 5:1
60%
50%
y = 0.0557x + 0.3588
R2 = 0.6372
40%
1.5†*
to be determined
to be determined
to be determined
to be determined
to be determined
Conclusion
30%
1
2
3
4
5
UV-Vis Spectra with Added Glycine
Copper Citraconate Plus Glycine
6
• Attempted synthesis of copper (II) citraconate was mostly successful
• Composition of copper(II) citraconate is still unclear
• Significant initial solubility of copper(II) citraconate (0.6454g/25 mL, or 0.0258 g per mL)
• Percent copper(II) citraconate dissolved increased as amino acid ratio increased
• Added amino acid dramatically enhances solubility of copper (II) citraconate prepared
• Speciation diagrams of citraconic acid and glycine were calculated using known equilibrium
constants (Table above)
• Enhancement of solubility cannot solely be due to protonation of salt anion by free amino acid
as pK’s of anions and amino acids are comparable
Future Work
0.7
0.6
Absorbance
KHL’
KL’1
KL’2
not be important at pH 5.5, [L’] = 0.0132% of total [glycine]
*not important: K < 1
0.5
1:0
1:1
1:2
1:5
0.4
0.3
0.2
• Create new method to synthesize pure zinc citraconate and copper (II) citraconate.
• Analysis of salt will be done before titrations with amino acids.
• Complete trials and UV-Vis analyses with other amino acids.
• Expect percent zinc dissolved and percent copper dissolved to increase as amino acid ratio
increase.
• Measure free [Cu2+] in all solutions using ion specific electrode
• Expect to see an increase in free [Cu2+] as the amino acid : zinc salt ratio increases.
0.1
0
400
500
600
700
800
Bibliography
900
Wavelength (nm)
Organic Molecules Used
Peak Maxima
Serine
0.12
4.90†
9.01†
KHL
KL1
† may
Rel. Moles Serine
Alanine
Cu+2 + HL’  ZnHL’
Cu+2 + L’  ZnL’
CuL’ + L’  ZnL’2
CuHL + HL’  Cu(HL)HL’
CuL + HL’  Cu(L)HL’
CuL + L’  CuLL’
70%
Procedure
Glycine
Kgly2
Kgly3
Cu+2 + HL  ZnHL
Cu+2 + L  ZnL
2.34
9.60
logK
to be determined
3.4
H2gly+  H+ + Hgly (zwitterion) (HL’)
Hgly  H+ + gly- (L’)
Glycine Addition to Copper(II) Citraconate
Copper(II) Citraconate + Serine
0
Citraconic acid
Symbol
Kcitr1
Kcitr2
CuL + L’  CuL’ + L
CuHL + HL’  CuHL’ + HL
CuL + HL’  CuHL’ + L
20%
Citraconic acid, copper (II) carbonate and all amino acids were used as received. Na2EDTA was
dried for >1 hr at 100°C before use.
Preparation of Copper (II) Citraconate
Citraconic acid was stirred in 20 mL Nanopure H2O until completely dissolved. Copper (II)
carbonate was stirred in 20 mL Nanopure H2O on medium heat. Citraconic acid solution was
added to stirred copper (II) carbonate solution by pipette. Mixture was left to stir overnight and
filtered. Filtrate was placed in rotary evaporator and the solids were dried in a desiccator to
yield potentially copper (II) citraconate.
Preparation of Solutions
One gram copper (II) citraconate was combined with varying molar amounts of amino acid and
20 mL Nanopure H2O, stirred overnight and diluted to 25 mL. Mixtures were quantitatively
filtered after 48 hrs.
Analysis of Total Copper(II) Ion Content
Small aliquots of filtered solution (~2 mL) were combined with 25.0 mL pH 5.5 acetate buffer,
and titrated with 0.0100 M Na2EDTA to endpoint using Xylenol Orange indicator.
Calculation of Percent Dissolved Copper(II) Citraconate
All titration results were entered into an Excel spreadsheet. Then, based on the stoichiometry of
1:1 Cu2+:EDTA2-, moles copper, and grams copper (II) citraconate, percent copper (II)
citraconate dissolved was calculated.
pK
2.23
5.46
Other Possible Equilibria
(citr  gly) Ligand Exchange
copper(II).
• Copper(II) complex characteristics
– Strong complexing agents (e.g. citraconate) and weak complexing agents (e.g. amino
acids) are well known.
– The interaction of the strong and weak complexing agents and effect on free copper(II) ion
content is not known.
– Initial research with zinc gluconate + glycine showed a modest increase in free zinc ion
content (93% vs.91%). Will copper(II) complexes act the same?
– Previous research in this group has shown an increase of zinc citrate solubility with the
addition of amino acids (w/glycine, 0 - 50 molar excess: range of 10% - 50% soluble)
Equilibrium
H2citr  H+ + Hcitr- (HL)
Hcitr-  H+ + citr-2 (L)
Analytical Articles
Shoulders
Cu(Citr):Glycine Ratio
1:0
Wavelength (nm)
750
Absorbance
0.290
Wavelength (nm)
none
Absorbance
1:1
1:2
1:5
742
736
724
0.402
0.539
0.617
640-665
630-665
600-665
0.20-0.24
0.27-0.30
0.26-0.36
Bobtelsky, M.; Jordan, J. J. Am. Chem. Soc. 1945, 67, 1824-31.
Campi, E.; Ostacoli, G. et al. J. Inorg. Nucl. Chem. 1964, 26, 553-64.
Childs, C.W.; Perrin, D.D. J. Chem. Soc. A 1969, 1039 - 44.
Novick, S.G. J. Chem. Educ. 1997, 74, 1463.
Zarembo, J.E.; Godfrey, J.C.; Godfrey, N.J. J. Pharm. Sci. 1992, 81, 128-30.
Medical/Agricultural Articles
Novick, S.G.; Godfrey, J.C. et al. Med. Hypoth. 1996, 46, 295-302.
Henzel, J.; DeWase, M. et al. Arch. Surg. 1970, 100, 349.
Cunningham, J.J.; Lydon, M.K.; et al. J. Am. Coll. Nutr. 1991, 10, 57-62.
Haertl, E. J. Agric. Food Chem. 1963, 11, 108-11.
Thanks to:
Allison Haigney: additional
mentor, Lois and Mike:
helpful co-researchers,
Hofstra U. Chemistry
Department: site sponsor,. Dr.
Sat Bhattacharya and Harlem
Children Society, Ms. Susan
Fahrenholtz, Project Seed and
the American Chemical
Society.
Partially funded by Godfrey Science & Design, Inc., Huntingdon Valley, PA 2006