TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preparation: No general preparation given. Preferred Compounds: The compound (I) is a compound in which NEG is a group comprising an anion, which is capable of bonding to a proton or other cation; and the radical of RAD is not pi -conjugated to the anion of NEG; and the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than in the corresponding structure (I) when the anion of NEG is bonded to a proton or other cation. The compound (I) is a compound in which NEG is a group comprising an anion, which is capable of bonding to proton or other cation; RAD is not pi -conjugated to the anion of NEG; and the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than a Doubly-Coupled Molecular Orbital (D0MO) of NEG and the SOMO of RAD is higher in energy than the DOMOs of NEG when the anion of NEG is bonded to a proton or other cation. The radical protecting group comprises the compound (I) in which NEG is a group comprising an anion, which is capable of bonding to a proton or other cation; the radical of RAD is not pi -conjugated to the anion of NEG; and the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than a Doubly-Occupied Molecular Orbital (DOMO) of NEG; and the SOMO of RAD is higher in energy than the DOMOs of NEG when the anion of NEG is bonded to a proton or other cation; and the radical of RAD is capable of forming a bond to a radical to be protected to give the protected radical when the anion of NEG is bonded to a proton or other cation; and the radical to be protected is de-protectable when the anion of NEG is not bonded to a proton, or other cation. Preferred Components: The cation is a metal ion or metal containing ionic species or is an ammonium or phosphonium ion. The protected radical, the radical to be protected, or the radical protecting groups are detectable by a sensor, where the sensor comprises a profluorescent probe. The sensor is useful for determining pH; medical imaging; degree of oxidation or reduction; or detecting and quantifying free radical species that may be present (preferably the sensor is useful in determining pH). The radical to be protected, or radical protecting group is an antioxidant; or is an industrial antioxidant inclusive of light stabilizers; or is a biological active antioxidant. The radical of RAD is stabilized; or the radical of RAD is delocalized or the radical of RAD is in conjugation with L. The radical of RAD is electronically and/or sterically stabilized by groups which are proximate to the radical. The anion of NEG is destabilized. The negative charge of the anion of NEG is not delocalized to any groups outside of that anion. The anion of NEG is not in pi -conjugation with L. The NEG comprises a sterically and/or electronically destabilized anion. The anion of NEG is electronically and/or sterically destabilized by groups which are proximate to that anion. The NEG comprises an electronically destabilized anion. Preferred Method: The process (M5) of deprotecting a radical protected with radical protecting group involves the removal of the proton or other cation bonded to the anion of NEG; or increasing the pH of the reaction medium to remove the proton bonded to the anion of NEG; or addition of a metal chelate to the reaction medium to remove metal cations bonded to the anion of NEG; or addition of anions to the reaction medium, where the added anions form a precipitate with cations present in the reaction medium, thereby removing those cations from bonding with the anions of NEG. The method (M19) of modifying a biological macromolecule involves incorporation of a radical into that biological macromoleeule, where the resultant structure formed is compound (I) in which NEG is group comprising an anion, which is capable of bonding to a proton or other cation, the radical of RAD is not conjugated to the anion of NEG; and after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAP is lower in energy than in the corresponding compound (I) when the anion of NEG is bonded to a proton or other cation. The method (M20) of modifying a biological macromolecule involves the incorporation of radical into that biological macromolecule, where the resultant compound is of formula (I), where NEG is a group comprising an anion, which is capable of bonding to a proton or other cation, where after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than a Doubly-Occupied Molecular Orbital (DOMO) of NEG, where the SOMO of RAD is higher in energy than the DOMO of NEG when the anion of NEG is bonded to a proton or other cation; or incorporation of an anion into a biological macromolecule, where the resultant compound formed is compound (I) in which NEG is a group comprising the anion, which is capable of bonding to proton or other cation, where after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAP is lower energy than the corresponding compound (I), where the anion of NEG is bonded to a proton or other cation; or incorporation of an anion into a biological macromolecule, where the resultant compound is of formula (I), in which NEG is a group comprising the anion, which is capable of bonding to a proton or other canon, where after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than a Doubly-Occupied Molecular Orbital (DOMO) of NEG, where the SOMO of RAD is higher in energy than the DOMO of NEG when the anion of NEG is bonded to a proton or other cation; or incorporation of a radical and an anion into the biological macromolecule, where the resultant compound formed is compound (I), where NEG is a group comprising the anion, which is capable of bonding to a proton or other cation and after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than in the corresponding compound (I) when the anion of NEG is bonded to a proton or other cation; or incorporation of a radical and an anion into that biological macromolecule, where the resultant compound is (I) in which NEG is a group comprising the anion, which is capable of bonding to proton or other cation, where after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than a Doubly-Occupied Molecular Orbital (DOMO) of NEG and the SOMO of RAD is higher in energy than the DOMOs of NEG when the anion of NEG is bonded to a proton or other cation. The method (M22) of modifying a biological macromolecule, such that the resultant biological macromolecule will form a complex with a substrate, where that resultant substrate-complex formed is of formula (I), in which NEG is a group comprising an anion, which is capable of bonding to a proton or other cation and after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than in the corresponding compound (I) when the anion of NEG is bonded to a proton or other cation; or NEG is a group comprising an anion, which capable of bonding to a proton or other cation and after modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than a Doubly-Occupied Molecular Orbital (DOMO) of NEG and the SOMO of RAD is higher in energy than the DOMO of NEG when the anion of NEG is bonded to a proton or other cation. The method (M23) of modifying a substrate such that the resultant modified substrate with form a complex with a biological macromolecule, where that resultant substrate-complex formed is compound of formula (I), where NEG is a group comprising an anion, which is capable of bonding to proton or other cation and after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than the corresponding compound (I) when the anion of NEG is bonded to a proton or other cation; or after modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than Doubly-Occupied Molecular Orbital (DOMO) of NEG and the SOMO of RAD is higher in energy than the DOMOs of NEG when the anion of NEG is bonded to a proton or other cation. In method (M13), the negative point charge has been neutralized, and the oxidation removes an impaired electron. In method (M13), when NEG is bonded to a proton or other cation, the oxidation removes an unpaired electron. The species to be oxidized in method (M13) are interconvertible by the introduction or removal of a negative point charge. The specie to be oxidized is interconvertible by the addition or removal of protons or other cations. The method (M21) of modifying a biological macromolecule, where the resultant compound formed is of formula (I), where NEG is a group comprising an anion, which is capable of bonding to proton or other cation and after the modification, the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than in the corresponding compound (I) when the anion of NEG is bonded to a proton or other cation; or after modification, the lowest Singly-Occupied Molecular Orbital (SOMO) is lower in energy than a Doubly-Occupied Molecular Orbital (DOMO) of NEG and the SOMO of RAD is higher in energy than the DOMOs of NEG when the anion of NEG is bonded to a proton or other cation. The method (M24) of modifying a biological macromolecule and a substrate, such that the resultant modified biological macromolecule and substrate will form a complex, where that resultant substrate-complex formed is of formula (I) in which NEG is a group comprising anion which is capable of bonding to a proton or other cation and after the modification, the lowest SOMO of RAD is lower in energy than the corresponding compound (I) when the anion of NEG is bonded to a proton or other cation; or modification, the lowest SOMO of RAD is lower in energy than DOMO of NEG and the SOMO of RAD is higher in energy than the DOMOs of NEG when the anion of NEG is bonded to a proton, or other cation.    TECHNOLOGY FOCUS - PHARMACEUTICALS - Preferred Components: At least one of the radical to be protected or the radical protecting group or its resultant metabolite or its resultant product is biologically active. The biological active species is released in the body. The biological active species is released in the body in response to a change in physiological conditions, and in particular as the result of increase in pH. The biological active species is selected from nitric oxide; nitrogen dioxide; a structure comprising a nitric oxide and/or nitrogen dioxide radical; or non-steroidal antiinflammatory drug. Preferred Method: The modification is to the active site of that biological macromolecule.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The chain extending polymer radical is capped with the radical protecting group (I). Preferred Method: In methods (M1), (M2), (M5), (M8) and (M10), the deprotected radical reacts with itself or with at least one reagent in the reaction medium. The radical reaction is selected from radical coupling; Wurtz reaction; nitroxide mediated polymerization; nitroxide radical coupling; double bond addition; cyclization reactions; atom abstraction; and oxidation. The deprotected radical participates in a polymerization reaction. The capped radical is deprotected, allowing further polymerization of that deprotected radical. The polymer substrate prior to capping is different from the polymer substrate after deprotection. The polymerization reaction is a block co-polymerization. The polymerization is conducted at a temperature of up to 120 degrees C, preferably 25 to 80 degrees C. The reaction medium is buffered. Preferred Definitions:    NEG=a surface or structure capable of bearing and/or carrying a negative point charge, where the negative point charge is capable of being neutralized and the negative point charge is selected from electron, an electric charge, negative potential or a negative coulombic charge; and the negative point charge is capable of being neutralized by removal, dissipation or inversion of that charge, where the surface or structure capable of bearing and/or carrying a negative point charge is an electrode or is metallic or non-metallic or the surface or structure capable or bearing and/or carrying negative point charge comprises graphene or is a group comprising an anion, which is capable of being neutralized by bonding to a proton or other cation (preferably comprises anion selected from -C(O)-O-, -C(O)-S-, -C(O)-O-O-, O-, S-, -NH-C(O)-CH-(CH3)-NH-C(O)-, -O-P(O)(O-CH3)-O-, -O-P(O)(O-)(O-), -S(O)2-O-, -O-SO2-O-, -C-O-O-, -N-O-, -C?=C-, C- or -CF2-SO2-O-);    RAD=stearic and/or electronically stabilized radical (preferably electronically stabilized radical) or radical selected from 17 groups as given in the specification e.g. -N-O., -N-S., -N-Se., -P-O., -N., -P., -O-O., -S-S., -S-O., -Se-O., -O-S., -O-Se., O.-phenyl, or S.-phenyl; DNA/RNA-base based radical or is an amino acid based radical, where DNA/RNA base is selected front guanine (g), adenine (a), cytosine (c), thymine (t) or uracil (u); or comprises a radical group selected from 2,2',6,6'-tetramethylpuperidine-N-oxyl (TEMPO), 2,2',5,5'-tetramethylpyrrolidine-N-oxyl (PROXYL), 2,2,5,5-tetramethyl-4-phenyl-3-azahexane-3-oxyl (TIPNO), N,N-(1,1-dimethylethyl-1-)-(1-diethyl-phosphono-2,2-dimethyl-propyl-1)-N-oxyl (SG1) or guanine based or glycyl-based radical;    L=linker comprised of at least two portions, where at least two of the portions are non-covalently bonded together, where the non-covalent bonding is hydrogen bonding or electrostatic bonding and the at least one portion comprises at least one of DNA/RNA-bases, amino acids, peptides, cofactors, enzymes, enzyme fragments, activating enzymes, biological macromolecules or enzyme substrates, where the portions ate naturally occurring, modified from those naturally occurring, or are synthetic or linker that comprises at least two portions, where at least one of the portions bond to at least one metal center, where the metal center is selected from alkali metal cations and transition metal cations or linker that comprises at least one polymeric portion; or at least one of a bond, a hydrogen bond: a non-covalent bond; an electrostatic bond;: metal bonding; alkyl, cyclic alkyl, aryl, alkene, alkyne, heterocyclic, heteroaromatic, sugar, metal complex, or is a through-space interaction; or is a bond; phenyl; biphenyl; 1-20C alkyl, 2-20C cycloalkyl, RNA-based sugar or DNA-based sugar.    The L comprises conjugation to RAD or does not comprise pi -conjugation to NEG. The L links more than one NEG and/or RAD groups.    ACTIVITY - None given.    MECHANISM OF ACTION - None given.    SPECIFIC COMPOUNDS - 41 Compounds are specifically claimed as the compound (I) but the unclear structures given in claim 114 in the original specification cannot be included.    EXAMPLE - No suitable example given.