Histidine hcl o L-Histidine hydrochloride is a chemical compound, an amino acid, hydrochloride salt of histidine, synthesised industrially by fermentation with Escherichia coli. It is found in many parts of the human body, e.g. in the organic matrix of dentin/enamel and helps metabolise trace elements such as Zinc, Iron, Manganese, Copper.

The name describes the structure of the molecule

• "Histidine" refers to the amino acid histidine, one of the essential amino acids that the human body cannot synthesize and therefore must obtain through the diet.
• "HCl" stands for hydrochloride. This indicates that histidine has been combined with hydrochloric acid, forming the hydrochloride salt of the amino acid.

Description of raw materials used in production

• Histidine. An essential amino acid with an imidazole functional group. It plays a crucial role in various proteins and enzymes.
• Hydrochloric Acid (HCl). A strong acid commonly used in chemistry.

Step-by-step summary of industrial chemical synthesis process

Biosynthesis.

• Histidine is biosynthesized in bacteria, fungi, and plants from the sugar phosphate named 5-phosphoribosyl-1-pyrophosphate (PRPP). It undergoes several enzymatic transformations leading to the production of histidine.

Chemical Synthesis.

• While more common in research settings than commercial ones, it is possible to synthesize histidine through various chemical reactions.

Combination with Hydrochloric Acid.

• Histidine is then combined with hydrochloric acid to form histidine hydrochloride, or Histidine HCl.

It occurs as a fine white powder.

What it is used for and where

It is an α-amino acid.

Amino acids play a key metabolic function in the human body and are constituents of proteins. 

As food additives they perform different functions: preservatives, flavour enhancers, food supplements and more.

Amino acids together with their salts are used in cosmetics as conditioning agents for both hair and skin (e.g. as moisturisers and other similar functions). Moisturisers are different in nature: the best are the natural ones that exploit the mechanism of integration between the ingredient and the skin by moisturising the horny hydrolipid film, i.e. the thin protective layer that covers the epidermis protecting it from harmful external microbes, keeping the skin moisturised and supple and its pH or acidity value between 4 and 6.  Then there are the occlusive moisturisers, usually derived from petroleum (Paraffinum, Paraffinum liquidum and others), but also triglycerides, lanolin oil, natural or synthetic waxes, fatty acid esters and others that create an artificial occlusive layer on the stratum corneum of the skin with the advantage of accelerating the protective process but with the disadvantage of preventing the skin's natural transpiration.

α-amino acids that have similar physical structures undergo similar changes with regard to solubility in water/ethanol mixtures, and technologies to separate α-amino acids from industrial residues, which may not even be innocuous, are constantly being improved. However, many data on the solubility in water-ethanol and ethanol of some α-amino acids are contradictory or even lacking, and the effects of ethanol on the solubility of amino acids may be different. Overall, the scientific literature considers that α-amino acids do not pose significant problems for human health when taken orally, except in people with certain genetic diseases.

Food safety: amino acid α generally considered safe.

Cosmetic safety: amino acid α generally considered safe when formulated to be non-irritant.

Animal feeding

Nutritional additive The active ingredient is L-histidine.  Flavouring compound for feed of all animal species, to supplement the diet in adequate quantities to cover requirements, depending on species, physiological state of the animal, performance level, environmental conditions, background amino acid composition of the non-supplemented diet and the status of certain essential trace elements (1).

Medical

Excipient used in parenteral products to stabilise biotherapy. Recent studies have highlighted the usefulness of pH-sensitive micelles also containing Histidine as photosensitising carriers to improve photodynamic cancer therapy (2). It protects brain cells where it formulates a compound called metallothionein.

Cosmetics

Used as a chelating agent in personal care products and as an adjuvant in improving the treatment of skin roughness.

The most relevant studies on this ingredient have been selected with a summary of their contents:

L-Histidine hydrochloride studies

Typical commercial product characteristics L-histidine dihydrochloride

• Molecular Formula  C₆H₁₀ClN₃O₂      C₆H₉N₃O₂ · HCl
• Molecular Weight     191.61
• Exact Mass    191.046158
• CAS  645-35-2   1007-42-7
• UNII    1D5Q932XM6
• EC Number   211-438-9    213-754-2
• DSSTox Substance ID  DTXSID3020700
• IUPAC  (2S)-2-amino-3-(1H-imidazol-5-yl)propanoic acid;hydrochloride
• InChI=1S/C6H9N3O2.ClH/c7-5(6(10)11)1-4-2-8-3-9-4;/h2-3,5H,1,7H2,(H,8,9)(H,10,11);1H/t5-;/m0./s1 
• InChl Key      QZNNVYOVQUKYSC-JEDNCBNOSA-N
• SMILES   C1=C(NC=N1)CC(C(=O)O)N.Cl
• MDL number  MFCD00064556
• PubChem Substance ID    329756297
• RXCUI       1309689
• Beilstein       4168261
• RTECS   MS3116100
• eCl@ss      32160406
• NCACRES  NA.24  

Synonyms

• (2S)-2-amino-3-(1H-imidazol-5-yl)propanoic acid;hydrochloride
• Histidine-L-HCl
• L-Histidine hydrochloride
• L-Histidine, monohydrochloride

References_____________________________________________________________________

(1) EFSA Panel on Additives and Products or Substances used in Animal Feed (FEEDAP), Bampidis V, Azimonti G, Bastos ML, Christensen H, Dusemund B, Fašmon Durjava M, Kouba M, López-Alonso M, López Puente S, Marcon F, Mayo B, Pechová A, Petkova M, Ramos F, Sanz Y, Villa RE, Woutersen R, Herman L, Anguita M, Galobart J, Pettenati E, Tarrés-Call J. Safety and efficacy of a feed additive consisting of l-histidine monohydrochloride monohydrate produced using Escherichia coli  NITE SD 00268 for all animal species (Kyowa Hakko Europe GmbH). EFSA J. 2021 May 31;19(5):e06622. doi: 10.2903/j.efsa.2021.6622.

(2) Debele TA, Mekuria SL, Tsai HC. A pH-sensitive micelle composed of heparin, phospholipids, and histidine as the carrier of photosensitizers: Application to enhance photodynamic therapy of cancer. Int J Biol Macromol. 2017 May;98:125-138. doi: 10.1016/j.ijbiomac.2017.01.103.