query: instance_of abelsonite
supports: Porphyrins are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their  carbon atoms via methine bridges (=CH). The parent porphyrin is porphin, and substituted porphines are called porphyrins. The porphyrin ring structure is aromatic, with a total of 26 electrons in the conjugated system. Various analyses indicate that not all atoms of the ring are involved equally in the conjugation or that the molecule's overall nature is substantially based on several smaller conjugated systems. One result of the large conjugated system is that porphyrin molecules typically have very intense absorption bands in the visible region and may be deeply colored; the name "porphyrin" comes from the Greek word  ("porphyra"), meaning "purple". An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are very small; typical sizes are around 100 picometers (a ten-billionth of a meter, in the short scale). Abelsonite is a nickel porphyrin mineral with chemical formula C31H32N4Ni . It was discovered in 1969 in the U.S. State of Utah and described in 1975 . The mineral is named after geochemist Philip H. Abelson . It is the only known crystalline geoporphyrin . A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge. However, in quantum physics, organic chemistry, and biochemistry, the term "molecule" is often used less strictly, also being applied to polyatomic ions. An organic compound is virtually any chemical compound that contains carbon, although a consensus definition remains elusive and likely arbitrary. Organic compounds are rare terrestrially, but of central importance because all known life is based on organic compounds. The most basic petrochemicals are considered the building blocks of organic chemistry. The connectivity of a molecule often has a strong influence on its physical and chemical properties and behavior. Two molecules composed of the same numbers of the same types of atoms (i.e. a pair of isomers) might have completely different chemical and/or physical properties if the atoms are connected differently or in different positions. In such cases, a structural formula is useful, as it illustrates which atoms are bonded to which other ones. From the connectivity, it is often possible to deduce the approximate shape of the molecule. The structural formula of a chemical compound is a graphic representation of the molecular structure, showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly. Unlike chemical formulas, which have a limited number of symbols and are capable of only limited descriptive power, structural formulas provide a complete geometric representation of the molecular structure. For example, many chemical compounds exist in different isomeric forms, which have different enantiomeric structures but the same chemical formula. A structural formula is able to indicate arrangements of atoms in three dimensional space in a way that a chemical formula may not be able to do. In chemistry, a conjugated system of connected p-orbitals with delocalized electrons in molecules with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pairs, radicals or carbenium ions may be part of the system. The compound may be cyclic, acyclic, linear or mixed. A macrocycle is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule". In the chemical literature, macrocycles varyingly include molecules containing rings of 8 or more atoms, or 12 or more atoms. Well-known examples are the group of drugs known as macrolides. The IUPAC definition notes that a "cyclic macromolecule has no end-groups but may nevertheless be regarded as a chain", and that ""macrocycle" is sometimes used [in the literature] for molecules of low relative molecular mass that are not considered macromolecules. Many macrocycles are employed as macrocyclic ligands. Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula CHNH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., "N"-methylpyrrole, CHNCH. Porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as heme. An isomer (from Greek , isomerès; isos = "equal", méros = "part") is a molecule with the same molecular formula as another molecule, but with a different chemical structure. That is, isomers contain the same number of atoms of each element, but have different arrangements of their atoms. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are two main forms of isomerism (or ): structural isomerism (or constitutional isomerism) and stereoisomerism (or spatial isomerism). Porphin, sometimes spelled porphine, is the parent chemical compound for types of biochemically significant compounds called porphyrins. The chemical formula of porphin is CHN. Porphin is an organic compound that is aromatic and heterocyclic since its chemical structure, shown at right, essentially consists of four pyrrole rings joined together by four methine (=CH) groups to form a larger macrocycle ring. The compound itself is a solid. An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by either chemical or physical means, via ionization.
candidates: 12 chain charge chemical chemical compound definition energy five formula gas group ion liquid literature mass matter may molecule number ordinary organic compound part physics region ring structure system ten two
answer: chemical compound