Abstract: As a feed and nutritional supplement, trace element amino acid chelate has the advantages of moderate chemical stability, high bio-valency, special absorption mode and special metabolic pathway, and has dual nutrition and therapeutic effects. Lysine is the first limiting amino acid, and its trace element chelate has special use and broad market prospects. This paper describes two methods for synthesizing zinc chelates of lysine from lysine hydrochloride and L-lysine. The important influencing factor for the synthesis of lysine zinc chelate by lysine hydrochloride is the pH value of the reaction system. The optimum pH is 8, and the yield can reach more than 85%. L-lysine is used. The raw material synthesizes lysine zinc chelate, the system is anhydrous, and the yield can reach more than 94%.

Key words: lysine; chelate; feed additive

The study of the complexes of amino acids and metal elements is one of the hot topics in today's research, both in the theoretical study of coordination compounds and in the application of animal feeding practices. The trace element amino acid chelate has moderate chemical stability, and the amino acid protects the metal ion, preventing the trace element from forming an insoluble compound in the intestinal tract or being adsorbed on the insoluble colloid which hinders the absorption of the element, and is also a trace of the divalent ion. The element has a competitive absorption effect with calcium, and the trace element amino acid chelate compound which is firstly complexed in vitro can further digest and absorb the pathway, so that the efficiency is greatly increased. At the same time, it also prevents the adverse effects of anti-nutritional factors such as phytic acid, oxalic acid and citric acid contained in natural feed to a considerable extent, and thus is beneficial to the absorption of the body. Inorganic trace elements pass through the cell membrane, and it is necessary for the carrier molecule to coat the metal ions and form an organic fat-soluble complex outside the cell membrane to pass the cations through the cell membrane.

Founed (1974) believes that the metal ion of the chelate center can pass through the small intestine fluff brush border, and all amino acid chelate can be absorbed in the form of amino acids. Generally, the molecular weight limit of the amino acid is wide in the animal, and the molecular weight of the chelate is below 1000, which can be absorbed through the cell membrane, which indicates that the chelate of the amino acid has higher bioavailability than the trace element of the inorganic substance.

After the trace element amino acid chelate enters the body, according to the different ratios and amounts of certain amino acids required by different tissues and enzyme systems, the trace elements of the corresponding amino acid can be directly transported to each specific target tissue and enzyme system. The release of trace elements by the action of the target tissue to meet the needs of the body, which eliminates the biochemical process required to absorb the inorganic derivative, thereby improving the absorption and utilization of trace elements. According to research reports, amino acids can play a special role in the body as a "single unit", such as changing the animal's fur condition and reducing early embryonic death. Trace element amino acid chelate compound has the functions of enhancing bactericidal ability, improving immune response, reducing the number of somatic cells in milk and improving reproductive ability, and the like. At the same time, the trace element chelate formed with the amino acid ligand is both fully nutritious and most suitable. However, EDTA and phytic acid, etc., which are complex element trace chelate compounds, are not suitable for this purpose.

Trace element amino acid chelate has achieved good results as a feed additive. It has been reported that feeding trace element amino acid chelate has a good effect on chicken weight gain, egg production rate and feed conversion rate. In addition, the addition of amino acid chelated iron to early weaned piglets was significantly higher than the additive ferrous sulfate weight gain, the addition of iron glycinate increased by 7.0%, and the addition of methionine iron increased by 12.9%. Adding methionine copper and adding the same amount of copper sulfate, the weight gain rate is 1.2 times that of the latter.

In short, the absorption mode and metabolic pathway of amino acid chelate in vivo are different from inorganic mineral salts. A certain amount of trace element amino acid chelate can stimulate certain biological processes. Therefore, the organic state of amino acid chelate is traced. Elements are more beneficial to the growth of the body than inorganic trace elements.

Lysine is the first essential amino acid in the human body. It is a synthetic amino acid, hemoglobin and an important amino acid that promotes the regeneration of nerve cells in the brain. An important carrier of fat metabolism in the body, carnitine, is formed by lysine and methionine. The addition of a small amount of lysine to the food can increase the secretion of pepsin and gastric acid, thereby promoting the appetite of the elderly and children. L-lysine has certain adjuvant effects on malnutrition, hepatitis B, bronchitis, etc. Lysine and ferrous compound together have significant effects in treating anemia.

Zinc is the second most abundant element in trace elements in humans and other organisms. Moreover, zinc enzymes are present in all six types of enzymes. Therefore, the amount of zinc in the cells directly regulates the activity of these enzymes, which in turn controls various metabolic processes, especially the metabolism of proteins, sugars and fats, as well as the synthesis and degradation of ribozymes. The situation of zinc also affects the hormonal regulation of organisms, especially for insulin, growth hormone, and sex hormones. Among trace elements, zinc has the most obvious effect on immune function. Decreased zinc levels in both human and animal bodies can cause cellular immune function to be low. Zinc deficiency in the body can cause diseases such as Yilang village disease, intestinal dermatitis, diabetes, rheumatoid arthritis, anorexia, abnormal ammonia metabolism, loss of taste, and impaired metabolism of connective tissue. It can also lead to inadequate male gonads; female anemia, stunting and secondary sexual insufficiency. Because lysine is a limiting amino acid that is essential for living organisms and cannot be synthesized by itself, it plays an important role in humans and animals, while zinc is an essential trace element for humans and animals. Zinc lysine has high absorption and high utilization rate. It also has dual nutritional and therapeutic effects and can be used as an ideal nutritional fortifier and feed additive. Moreover, as far as the literature on amino acid chelates we have reviewed is concerned, the synthetic preparation methods of metal chelates of methionine and glycine have been reported, and the preparation methods of lysine metal chelates have not been reported in China.

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1 test

1.1 Main instruments and reagents

DF-10lB collector thermostatic magnetic stirrer; SHZ-D circulating water pump vacuum pump; constant temperature drying oven.

Lysine hydrochloride (feed grade), zinc chloride [ZnCl2·7H20] (analytical grade), zinc chloride [ZnCl2] (analytical grade), L-lysine (L-Lysine) (biochemical reagent), Zinc sulfate [ZnS04·7H20] (analytical grade), sodium hydroxide [NaOH] (chemically pure), methanol [CH30H] (analytical grade), ethanol [CH3CH20H] (analytical grade), lithium hydroxide [LiOH·H20] ( Chemically pure).

1.2 Synthesis of lysine zinc

1.2.1 Method 1 Weigh 18.2 g of lysine hydrochloride (0.1 mol1), add 15 ml of water, heat to 70 ° C to dissolve completely, and weigh 6.82 g of zinc chloride (0.05 mol) in 20 ml of water. Adding to the above lysine hydrochloride solution, adjusting the pH of the reaction system to 8 with 2 mol/1 sodium hydroxide solution, and reacting for 1 hour at 80 ° C on a heat collecting thermostatic magnetic stirrer. The filtrate was concentrated by heating to a crystallized film, cooled, and allowed to stand overnight. A large amount of solid was precipitated, and filtered, and the obtained solid was washed twice with ethanol and dried to give a pale yellow solid of 23.86 g.

1.2.2 Method 2 Weigh 3.0g L-lysine into a 250ml round bottom bottle, add 100ml methanol and 0.84g (0.02mo1) lithium hydroxide (LiOH·H2O), heat to reflux for 1h, cool, filter to remove excess L-lysine gives the lithium salt of lysine. A solution of 1.36 g (0.01 mol) of zinc chloride (ZnCl2) and 30 ml of methanol was added to the filtrate to rapidly precipitate, and 2.0 g of the product was obtained as a milky white powdery solid with a yield of 94.79%. The product placed in the air quickly deliquescent and turned yellow and became viscous.

2 Results and discussion

2.1 Comparison of several synthetic methods

The authors have attempted to synthesize Zn(Lsy)2 with high zinc content using inexpensive and readily available lysine hydrochloride. The method is to first destroy the lysine hydrochloride to make it a lysine and then chelate it with zinc. However, it is not possible to synthesize zinc lysine in the pH of the system, but a large amount of zinc hydroxide precipitate is formed. Improved, zinc lysine was synthesized in two other ways in this experiment. The method 1 is synthesized by using lysine hydrochloride, sodium hydroxide and the corresponding zinc salt in an aqueous solution, the reaction conditions are easy to control, the raw materials are cheap and easy to obtain, the product properties are stable, but the yield can only reach about 85%, and finally The product was lysine zinc hydrochloride hydrate. Method 2 is to synthesize a lithium salt of lysine by using pure lysine and lithium hydroxide in methanol, and then reacting with zinc chloride to obtain zinc lysine. The method requires anhydrous system, harsh conditions, expensive raw materials, and very good product properties. It is unstable and difficult to store, but the yield is high, up to 95%, and the product purity is high.

2.2 Composition and related properties of zinc lysine

2.2.1 Method 1 The product obtained is a pale yellow solid, soluble in water, not

Soluble in ethanol, the content of zinc is 11.84%, is lysine zinc hydrochloride hydrate, the molecular formula is Zn (Lsy) 2 · 2HCl · 7H20, the molecular weight is 556, the theoretical percentage of zinc is 11.73%, and the actual measurement The values ​​are close.

2.2.2 Method 2 The obtained product is milky white powder, insoluble in methanol, the content of zinc is 17.86%, is L-lysine zinc, the molecular formula is Zn (Lsy) 2, the theoretical percentage of zinc is 18.41%, and the actual The measured values ​​are relatively close. However, since L-lysine is easy to absorb water to form hydrates, it is easy to absorb carbon dioxide in the air to form carbonates, and because of free amino groups, it is prone to yellowing and deterioration. Therefore, zinc L-lysine is easily deliquescent in the air. And reacts with carbon dioxide in the air to form carbonates and hydrates, and is pale yellow.

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2.3 Effect of system pH on synthesis

In solution, lysine is mainly present as a facultative ion. Can be expressed as:

When the acidity of the solution is very strong, the amino acid is mostly in the form of -NH3+, and the hydroxyl group is in the form of -COOH, which is obviously not conducive to the formation of the complex; but when the solution is too basic, the metal ion will form a hydroxide precipitate. It is also not conducive to the formation of complexes, therefore, a suitable pH is a key condition for the preparation of the product. In this paper, the range of pH value 6~9 was selected to investigate the effect of pH on the chelation reaction (operating according to method 1, the reaction temperature was 80oC, and the reaction time was lh).

Table 1 Effect of different pH values ​​on the yield of zinc lysine

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PH value 6 7 8 9

Production (g) 20.50 22.20 23.86 20.36

Yield (%) 73.74 79.86 85.83 73.24

When the solution pH ≥ 10, the Zn in the product is greater than 54.8%, and it can be seen that most of the Zn2+ at this time is a precipitate. It can be seen from the data in the table that the optimum pH of the product is about 8, and the isoelectric point of lysine is 9,47, and the optimum pH value of the complex is slightly smaller than the isoelectric point, which can be interpreted as lysine. When the acid complex is formed, the unsupported s-position amino group in the lysine molecule still exists in the form of -NH3+, from which it can be inferred that the lysine zinc molecule still contains two HCl molecules, which can be expressed as Zn (Lys). 22.2 HCl, which is consistent with the composition of the previously analyzed product.

2.4 Effect of reaction temperature on synthesis

According to the method 1, the pH of the reaction system was adjusted to 8 with a 5 M sodium hydroxide solution, and the reaction time was 1 h.

Table 2 Effect of temperature on lysine zinc

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Reaction temperature (oC) 80 90 100

Production (g) 23.86 23.12 22.86

Yield (%) 85.83 83.16 82.23

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It can be seen from the data in the table that in the case where lysine and zinc chloride are completely dissolved, the lower the temperature of the system is, the more favorable the chelation reaction is, but the effect is not significant.

2.5 Effect of different zinc sources on synthesis

When zinc lysine was synthesized by the method 1, zinc sulfate [ZnSO4·7H20] and zinc chloride [ZnCl2·7H20] were used as the zinc source. The molar ratio of lysine to zinc sulfate is 2:1, at a pH of 8, the temperature is 80 ° C, the reaction time is 1 h, the Zn of the obtained product is 10.6%, and the Zn of the product obtained from zinc chloride is 11.84. %, from which it can be inferred that the product obtained from zinc sulfate is a complex mixture of Zn(Lys)2·2HCl·7H20, Zn(Lys)2·2H2S04·7H20 and Zn(Lys)2·HCl·H2S04·7H20, The calculation of the yield and the research have brought unnecessary troubles. The use of zinc chloride [ZnCl2·7H20] as the zinc source avoids the interference of S042-, and the smaller the molecular weight of the organic matter, the better the absorption angle of the organism is. Absorption of the body, therefore, it is more reasonable to use zinc chloride as a source of zinc.