Do carbyne radicals really exist in aqueous solution?

They do exist! Free carbyne radicals can be prepared at room temperature in an aqueous solution by the decomposition of mono- or trinuclear metal (M) complexes containing alkylidyne ligands (see scheme; red C, blue M, green H). The generated radicals then react to form a variety of organic compounds by chain-lengthening reactions in solution. They also exhibit hydrogen, oxygen, or carbon abstraction from solvent, reactant, or product molecules.