He Ion ammonia Is a positively charged polyatomic cation whose chemical formula is NH 4 + . The molecule is not flat, but has the shape of a tetrahedron.
The positively charged ammonium ion NH 4 + , The four hydrogen atoms make up the four corners of the tetrahedron.
Figure 1: Structure of the ammonium ion.
The nitrogen of the ammonia possesses a pair of non-shared electrons capable of accepting a proton (Lewis base) whereby the ammonium ion is formed by the protonation of the ammonia according to the reaction:
NH 3 + H + → NH 4 +
They are also referred to as ammonium substituted amines or substituted ammonium cations. For example, methyl ammonium chloride is an ionic salt of formula CH 3 NH 4 Cl where the chloride ion is bound to a methylamine.
The ammonium ion has properties very similar to the heavier alkali metals and is often considered a close relative. Ammonium is expected to behave like a metal at very high pressures, such as inside giant gas planets like Uranus and Neptune.
Ammonium ion plays an important role in the synthesis of proteins in the human body. In short, all living things need proteins, which are made up of about 20 different amino acids. While plants and microorganisms can synthesize most of the amino acids from the nitrogen in the atmosphere, animals can not.
For humans, some amino acids can not be synthesized at all and should be consumed as essential amino acids.
Other amino acids, however, can be synthesized by microorganisms in the gastrointestinal tract with the help of ammonia ions. Thus, this molecule is a key figure in the nitrogen cycle and in protein synthesis.
Properties
Solubility and molecular weight
The ammonium ion has a molecular weight of 18.039 g / mol and a solubility of 10.2 mg / ml of water (National Center for Biotechnology Information, 2017). When ammonia is dissolved in water, the ammonium ion is formed according to the reaction:
NH 3 + H 2 O → NH 4 + + OH -
This increases the hydroxyl concentration in the medium by increasing the pH of the solution (Royal Society of Chemistry, 2015).
Properties base acid
The ammonium ion has a pKb of 9.25. This means that at pH above this value will have an acidic behavior and at lower pH will have a basic behavior.
For example, by dissolving ammonia in acetic acid (pKa = 4.76), the free nitrogen pair of nitrogen takes one proton from the medium by increasing the concentration of hydroxyl ions according to the equation:
NH 3 + CH 3 COOH ⇌ NH 4 + + CH 3 Coo -
However, in the presence of a strong base, such as sodium hydroxide (pKa = 14.93), the ammonium ion yields a proton to the medium according to the reaction:
NH 4 + + NaOH ⇌ NH 3 Na + + H 2 OR
In conclusion, at pH lower than 9.25, the nitrogen will be protonated, while at pH greater than that value will be deprotonated. This is of paramount importance in understanding titration curves and understanding the behavior of substances such as amino acids.
Ammonium salts
One of the most characteristic properties of ammonia is its ability to combine directly with acids to form salts according to the reaction:
NH 3 + HX → NH 4 X
Thus, with hydrochloric acid it forms ammonium chloride (NH 4 Cl); With nitric acid, ammonium nitrate (NH 4 DO NOT 3 ) With carbonic acid will form ammonium carbonate ((NH 4 ) 2 CO 3 ) etc. It has been shown that perfectly dry ammonia will not combine with perfectly dry hydrochloric acid, the moisture being required to provoke the reaction (VIAS Encyclopedia, 2004).
Most simple ammonium salts are very soluble in water. One exception is ammonium hexachloroplatinate, the formation of which is used as a test for ammonium. The salts of ammonium nitrate and especially perchlorate are highly explosive, in these cases the ammonium is the reducing agent.
In an unusual process, ammonium ions form an amalgam. Such species are prepared by electrolysis of an ammonium solution using a mercury cathode. This amalgam eventually decomposes to release ammonia and hydrogen (Johnston, 2014).
One of the most common ammonium salts is ammonium hydroxide, which is simply ammonia dissolved in water. This compound is very common and found naturally in the environment (in air, water and soil) and in all plants and animals, including humans.
Applications
Ammonium is an important source of nitrogen for many plant species, especially those growing on hypoxic soils. However, it is also toxic to most crop species and seldom applied as the sole source of nitrogen (Database, Human Metabolome, 2017).
Nitrogen (N), bound to proteins in dead biomass, is consumed by microorganisms and converted to ammonium ions (NH4 +) that can be directly absorbed by plant roots (eg, rice).
The ammonium ions are usually converted to nitrite ions (NO2-) by the nitrosomonas bacteria, followed by a second conversion to nitrate (NO3-) by Nitrobacter bacteria.
The three major sources of nitrogen used in agriculture are urea, ammonium and nitrate. Biological oxidation of ammonium to nitrate is known as nitrification. This process considers several steps and is mediated by obligate aerobic, autotrophic bacteria.
In flooded soils, Oxidation of NH4 + is restricted. Urea is decomposed by the enzyme urease or chemically hydrolyzed to ammonia and CO 2.
In the ammonia step, the ammonia is converted by ammoniating bacteria into the ammonium ion (NH4 +). In the next step the ammonium is converted by nitrifying bacteria into nitrate (nitrification).
This highly mobile form of nitrogen is most commonly absorbed by plant roots as well as by microorganisms in the soil.
To close the nitrogen cycle, the nitrogen gas in the atmosphere is converted into biomass nitrogen by Rhizobium bacteria that live in the root tissues of legumes (eg, alfalfa, peas and beans) and legumes (such as alder) And by cyanobacteria and Azotobacter (Sposito, 2011).
Through ammonia (NH4 +) aquatic plants can absorb and incorporate nitrogen into proteins, amino acids and other molecules. High concentrations of ammonia can increase the growth of algae and aquatic plants.
Ammonium hydroxide and other ammonium salts are widely used in food processing. Food and Drug Administration (FDA) regulations state that ammonium hydroxide is safe ("generally recognized as safe"or GRAS) as a yeast agent, pH control agent and a finishing agent Superficial in food.
The list of foods in which ammonium hydroxide is used as a direct food additive is extensive and includes baked goods, cheeses, chocolates, other confectionery (for example, candies) and puddings. Ammonium hydroxide is also used as an antimicrobial agent in meat products.
Ammonia in other forms (eg, ammonium sulfate, ammonium alginate) is used in seasonings, soy protein isolates, snacks, jams and jellies and non-alcoholic beverages (PNA potassium nitrate association, 2016).
Ammonium measurement is used in the RAMBO test, particularly useful in diagnosing the cause of an acidosis (Test ID: RAMBO Ammonium, Random, Urine, S.F.). The kidney regulates acid excretion and systemic acid base balance.
Changing the amount of ammonia in the urine is an important way for the kidneys to carry out this task. Measuring the level of ammonia in the urine can provide an understanding of the cause of an altered acid-base balance in patients.
The level of ammonia in the urine can also provide much information about the daily production of acid in a given patient. Since most of an individual's acid burden comes from ingested proteins, the amount of ammonia in the urine is a good indicator of protein intake in the diet.
Measurements of urine ammonia may be particularly useful for the diagnosis and treatment of patients with kidney stones:
- High ammonium levels in the urine and low urine pH suggest ongoing gastrointestinal bleeding. These patients are at risk for uric acid and calcium oxalate stones.
- A little urine ammonia and high urine pH suggest renal tubular acidosis. These patients are at risk of calcium phosphate stones.
- Patients with calcium oxalate and calcium phosphate stones are often treated with citrate to raise urine citrate (a natural inhibitor of calcium oxalate and calcium phosphate crystal growth).
However, since the citrate is metabolized to bicarbonate (a base), this drug can also increase the pH of the urine. If the pH of urine is too high with citrate treatment, the risk of calcium phosphate stones may be unintentionally increased.
Monitoring of ammonium urine is a way to titrate the citrate dose and avoid this problem. A good dose of initial citrate is about half of the ammonium excretion in the urine (in mEq of each).
The effect of this dose on the ammonium, citrate and urine pH values can be monitored and the citrate dose adjusted based on the response. A drop in urine ammonia should indicate whether the current citrate is sufficient to partially (but not completely) counteract the daily acid load of that given patient.
References
- Database, Human Metabolome. (2017, March 2). Showing metabocard for Ammonium. Retrieved from: hmdb.ca.
- Johnston, F.J. (2014). Ammonium salt. Retrieved from accessscience: accessscience.com.
- National Center for Biotechnology Information. (2017, February 25). PubChem Compound Database; CID = 16741146. Retrieved from PubChem.
- PNA potassium nitrate association. (2016). Nitrate (NO3-) versus ammonium (NH4 +). Retrieved from kno3.org.
- Royal Society of Chemistry. (2015). Ammonium ion. Recovered from chemspider: chemspider.com.
- Sposito, G. (2011, September 2). Soil. Recovered from encyclopedia britannica: britannica.com.
- Test ID: RAMBO Ammonium, Random, Urine. (S.F.). Recovered from encyclopediamayomedicallaboratorie.com.
- VIAS Encyclopedia. (2004, December 22). Ammonium Salts. Recovered from encyclopedia vias.org.