The closest thing I could find that matches, "the general economic concept where interest groups with disproportionate amounts of power shape public policy," comes from Karl Marx's Communist Manifesto.
Having destroyed the social power of the nobility and the guildmasters, the bourgeois also destroyed their political power. Having raised itself to the actual position of first class in society, it proclaims itself to be also the dominant political class. This it does through the introduction of the representative system which rests on bourgeois equality before the law and the recognition of free competition, and in European countries takes the form of constitutional monarchy. In these constitutional monarchies, only those who possess a certain capital are voters – that is to say, only members of the bourgeoisie. These bourgeois voters choose the deputies, and these bourgeois deputies, by using their right to refuse to vote taxes, choose a bourgeois government. (pg 46)
Karl Marx certainly believed that different groups of people had disproportionate political power. His forward in the German edition mentions that the French Revolution was the first time the proletariat (working class) held political power.
first in the February Revolution, and then, still more, in the Paris Commune, where the proletariat for the first time held political power for two whole months
He didn't come up with the concept of Regulator Capture, that was George Stigler.
The theory of regulatory capture is associated with Nobel laureate economist George Stigler, one of its main developers.