Enhanced solubilization of zinc and manganese methionine complex salts by addition of ferric ion

Method of enhancing the water solubility of dry zinc methionine complex salts by reacting in water soluble zinc salt with mentionine in the presence of ferric ion with the amount being between about 15 mole percent and 30 mole percent of the amount of zinc present.

BACKGROUND OF THE INVENTION 
This invention relates to an improvement in the properties of dry powder 
complexes of zinc and manganese with methionine in the 1:1 ratio. In that 
sense it represents a significant improvement over the process disclosed 
in commonly owned U.S. Pat. No. 4,764,633, and as well, over commonly 
owned and now expired U.S. Pat. No. 3,941,818 issued Mar. 2, 1976 entitled 
"1:1 ZINC METHIONINE COMPLEXES", and U.S. Letters Pat. No. 3,950,372 
issued Apr. 13, 1976, and entitled "1:1 MANGANESE ALPHA AMINO ACID 
COMPLEXES". Thus U.S. Pat. No. 3,941,818 and U.S. Pat. No. 3,950,372 
relate to 1:1 complexed salts per se of zinc and manganese with the amino 
acid methionine. These salts, as identified in the earlier patents, have 
the useful feature of being highly body absorbable nutritional supplements 
for animals that provide readily available sources of zinc and manganese 
on the one hand, and the essential amino acid methionine on the other. 
The common assignee of both of these patents makes a variety of transition 
metal complexes with alpha amino acids for sale. For example, see U.S. 
Pat. No. 5,061,815 relating to metal lysine complexes and methods for 
producing metal lysine complexes, as well as U.S. Pat. No. 5,278,329 for 
L-form 1:1 metal methionine complexes. 
Complexes of lysine are very easily soluble in water. However, complexes of 
metals such as zinc and manganese and methionine are less soluble in water 
than the complexes of metals and lysine. 
In Anderson, U.S. Pat. No. 4,764,633, an improvement in the complexing 
process is disclosed wherein the complexing of either zinc or manganese 
ions with methionine is conducted in the presence of a catalytically 
effective amount of ferric ion. The amount of ferric ion described is 
about 2% to about 10% based on the dry weight basis of the methionine, 
preferably from about 4% to about 8% based on the dry weight basis of the 
methionine. 
For effective feed supplements, the supplement must be in a powdered, dry 
form, and it must be readily soluble in the gut of animals; otherwise, 
much of the supplement will not be absorbed into the blood stream. It also 
is useful to have water soluble supplements so that the user may 
administer them through aqueous systems. 
While U.S. Pat. No. 4,764,633 enhances the amount of complexation, it does 
not enhance the solubility of the final dry product. 
Accordingly, there has been a real and a continuing need for the discovery 
of a process which will enhance the solubility characteristics of the dry 
1:1 complexes of zinc and manganese with methionine. 
This invention has as its primary objective the fulfillment of this need in 
order that dry 1:1 manganese methionine complexes and dry 1:1 zinc 
methionine complexes have enhanced solubility in comparison with those 
prepared as described in U.S. Pat. No. 3,941,818 and U.S. Pat. No. 
3,950,372. 
For details of the desirability and the utility of 1:1 manganese methionine 
complexes, see the previously referred to U.S. Pat. No. 3,950,372 which is 
incorporated herein by reference. For details of the desirability and the 
utility of 1:1 zinc methionine complexes, see U.S. Pat. No. 3,941,818, 
which is incorporated herein by reference. 
The method of accomplishing each of the above objectives of this invention 
will become apparent from the detailed description of the invention which 
follows hereinafter. 
SUMMARY OF THE INVENTION 
Method of enhancing the water solubility of dry zinc methionine complex 
salts by reacting in water soluble zinc salt with methionine in the 
presence of ferric ion with the amount being between 15 mole percent and 
30 mole percent of the amount of zinc present.

DETAILED DESCRIPTION OF THE INVENTION 
It is important to note that the respective zinc and manganese compounds 
which are prepared in accordance with this invention are referred to as 
complexed salts. These salts are to be carefully distinguished from 
conventional salts such as, for example, zinc chloride or manganese 
chloride. Such conventional salts such as zinc chloride or manganese 
chloride contain only an electrostatic attraction between the cation and 
the anion. The 1:1 complexed salts prepared by this invention differ from 
conventional salts in that while they have an electrostatic attraction 
between the cation and the anion, there is also a coordination bond 
between the cation and the amino moiety of the alpha amino acid. 
With regard to the zinc methionine complexed salts which are prepared in 
accordance with the improved process of this invention, they have the 
general formula: 
##STR1## 
wherein X is an anion and w is an integer equal to the anionic charge of 
X. The cation of these complexed salts is represented by the bracketed 
material in the above formula and represents a 1:1 complex of zinc and 
methionine. 
With regard to the manganese alpha amino acid complex salts of the present 
invention, they have the formula: 
##STR2## 
X and w are as previously defined. 
The process of preparing the desired zinc and methionine 1:1 complex salts 
of methionine as referred to herein is straightforward and direct. 
Commonly it begins with the use of a water soluble zinc salt and/or a 
water soluble manganese salt, respectively. Suitable zinc salts which can 
be employed are the halides, the sulfates, and the phosphates. The desired 
molar ratio of zinc salt to methionine is 1:1. Suitable manganese salts 
which can be employed are likewise halides, sulfates and phosphates. The 
desired molar ratio of manganese to methionine is 1:1. In each instance, 
the sulfate salts are preferred from the standpoint of availability and, 
at least currently, cost. 
In the general process, these salts are at least partially water dissolved, 
preferably at elevated temperatures. Temperatures within the range of from 
about 180.degree. F. to about 205.degree. F. have been found desirable, 
most preferably temperatures within the range of 190.degree. F. to about 
205.degree. F. In actual practice, one common technique is to stir the 
salt into a water solution while simultaneously injecting steam to elevate 
the temperature within the desired range. 
In accordance with the process of our prior patent, U.S. Pat. No. 
4,764,633, along with these reactants, a catalytically effective amount of 
ferric ion is added to enhance complexation yield. The amount added is 
from about 2% to about 10% based upon the dry weight of methionine. The 
earlier patent teaches that levels above the 10 molar percent level based 
upon the dry weight of methionine should be avoided. This corresponds to 
the same molar percentages for zinc, i.e. 2% to 10%, and preferably 4% to 
8%. As previously mentioned in the earlier patent, it was discovered that 
when percentages of ferric ion are added to the reactants at the levels 
there specified, desirable things occur. In the first instance, the 
dissolving of the salt and the amino acid in the water appears to be 
significantly enhanced, and in the second instance there is an increased 
yield of the desirable 1:1 complexes formed. That earlier discovery, 
however, involved formation of the reactants and did not involve solving 
the problems that zinc and manganese methionine complexes are inherently 
difficultly soluble at best after formation. 
It has now been surprisingly discovered that if substantially increased 
amounts of ferric ion are added during the formation reaction for the 
complexes, not only does one get a substantially increased yield of the 
desirable 1:1 complexes, but in addition the dry product produced by the 
process is more soluble, and the solution produced is more stable. 
For purposes of this invention, the amount of dry weight molar basis based 
upon the mole weight of zinc or manganese should be from about 15% to 
about 30% on a mole weight basis. Preferably the amount is within the 
range of from 15% to 20%. As evidenced by the examples, the amount appears 
to be critical in order to achieve the desired solubility of the dry 
weight product. In other words, the enhanced solubility phenomena of the 
present invention is not achieved until the level of ferric ion salt added 
is about 15%. Thus the levels expressed in U.S. Pat. No. 4,764,633 are too 
low to provide the observed enhanced solubility phenomena of the present 
invention. 
While not wishing to be bound by any theory of operability, it is believed 
that the presence of the ferric ion., along with the manganese or the zinc 
ion and methionine, brings about an equilibrium between ferric methionine 
complexes and those of zinc and manganese. Since the ferric ion complexes 
formed are much more soluble than either the zinc or the manganese 
complexes, the equilibrium that occurs seems to shift the equilibrium in 
the reaction of the zinc and the methionine to provide a far more soluble 
product. In any event, the important fact is not theoretically how the 
reaction works, but that it does simply work to provide a product of 
significantly enhanced solubility. 
The ferric ion which is added may be in the form of any water soluble salt 
such as ferric chloride, ferric sulfate, ferric phosphate, ferric acitate, 
or any other suitable water soluble ferric salt. The most preferred, 
however, is ferric chloride and ferric sulfate. 
The following examples are offered to further illustrate the improved 
process of the present invention and the critical levels of ferric ion 
required to achieve the enhanced solubility of the dry products prepared. 
EXAMPLES OF ZINC METHIONINE ACID SULFATE SOLUBILIZATION BY FERRIC CHLORIDE 
The addition of ferric chloride was found to enhance the solubility of zinc 
methionine acid sulfate. However, the concentration of ferric chloride 
required to produce a readily soluble and stable material is critical. The 
following experiment was conducted to determine the optimum concentration 
of ferric chloride. 
Seven samples of zinc methionine acid sulfate containing variable 
concentrations of Fecl.sub.3 were prepared. Zinc sulfate heptahydrate 
(ZnSO.sub.6.7H.sub.2 O; 14.38.sub.g ; 0.05 mole) was dissolved in 30 mL of 
distilled water in a 250 mL beaker. DL-Methionine (7.46 g, 0.05 mole) was 
added. The mixture was heated to boiling, and the heating continued for an 
additional 10 minutes. 
Ferric chloride hexahydrate (Fecl.sub.3.6H.sub.2 O, 13.52.sub.g ; 0.05 
mole) was transferred into a 100 mL volumetric flask. The solid was 
dissolved in approximately 50 mL of H.sub.2 O. Water was added to volume. 
Using a 50 mL burret, a specific volume of the ferric chloride solution was 
added to each of the boiling solutions of zinc methionine acid sulfate 
(Table 1). Each solution was evaporated to dryness under reduced pressure 
at 70.degree. C. using a rotary evaporator. A sample (1.0 g) of each of 
the dried products was transferred into a stoppered test tube. Distilled 
water was added in 0.5 mL increments and thoroughly mixed. The volume 
required for complete solubilization of the sample is reported in Table 2. 
TABLE 1 
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Ferric 
Sam- DL- Chloride 
Ferric Fe/Zn 
ple Zinc Sulfate 
Methionine Solution 
Chloride 
mole 
No. wt. g. mole wt. g. 
mole (mL) mole % 
______________________________________ 
1 14.3% 0.05 7.46 0.05 5 0.0025 5 
2 14.3% 0.05 7.46 0.05 7 0.0035 7 
3 14.3% 0.05 7.46 0.05 9 0.0045 9 
4 14.3% 0.05 7.46 0.05 11 0.0055 11 
5 14.3% 0.05 7.46 0.05 13 0.0065 13 
6 14.3% 0.05 7.46 0.05 15 0.0075 15 
7 14.3% 0.05 7.46 0.05 17 0.0085 17 
______________________________________ 
TABLE 2 
______________________________________ 
Fecl.sub.3 / 
Vol. of Water 
Fe/Zn Methionine to Dissolve 1 g 
Solubility 
Molar % w/w % Sample (mL) g/mL 
______________________________________ 
1 5 5.44 12.5 0.08* 
2 7 7.62 12.5 0.08* 
3 9 9.80 11.0 0.09* 
4 11 11.97 10.5 0.10* 
5 13 14.15 9.5 0.11* 
6 15 16.33 2.5 0.40 
7 17 18.51 2.0 0.50 
______________________________________ 
*Solution was unstable. A white ppt of Methionine was formed upon 
standing. 
From the above Table 1 and Table 2 it can be seen that a critical limit 
occurs with the demarcation line between 13 molar percent and 15 molar 
percent. In practice with other experiments (not specifically shown here), 
it seems that only a little increased value is obtained in going beyond 
15%. In other words, the increased solubility does not significantly 
improve, even though the level might go up to as much as 30%. Thus, about 
15% appears to be the critical distinction and 30% is a practical and 
economic upper limit.