Haemichrome
Definition
A further oxidation product formed when the globin chains of methaemoglobin denature and the haem group becomes internally coordinated. Associated with the darker brown-to-black colour of older stains.
- Origin
- Oxidation product of methaemoglobin
- Mechanism
- Globin chains denature, haem becomes internally coordinated
- Visual effect
- Associated with darker brown-to-black colour of aged stains
Common questions
Why does a bloodstain's colour change from red toward black as it ages?+
Fresh blood contains oxyhaemoglobin, which oxidises over time to methaemoglobin and then, as the globin protein itself denatures, progresses further to haemichrome. Each stage absorbs and reflects light differently, producing the visible progression from red to brown to near-black.
Can the degree of haemichrome formation be used to estimate a bloodstain's age?+
It gives a rough qualitative indication, since haemichrome formation is a late-stage change associated with older stains, but the rate of progression depends heavily on temperature, humidity, and substrate, so colour alone cannot reliably date a stain to a specific timeframe without other supporting evidence.
Related terms
- Methaemoglobin
- An oxidised form of haemoglobin in which ferrous iron (Fe2+) is converted to ferric iron (Fe3+), unable to carry oxygen. Its formation...
- Oxyhaemoglobin
- The form of haemoglobin in freshly shed arterial blood, where iron in the haem group is in the ferrous (Fe²⁺) state and...
- Photodegradation
- Breakdown of biological molecules driven by ultraviolet and visible radiation. In bloodstains it accelerates haemoglobin oxidation and cleaves DNA strands, hastening ageing...
- Protein Denaturation
- The loss of a protein's three-dimensional structure without breaking peptide bonds, caused by heat, pH change, UV radiation, or chemical agents such...
- Substrate Effect
- The influence of the surface on which a bloodstain lies on the rate and character of chemical change. Porous substrates absorb blood...