Gamma is a programming model where computation is seen as chemical reactions between data represented as molecules floating in a chemical solution. Formally, this model is represented by the rewriting of a multiset where rewrite rules model the chemical reactions. Recently, we have proposed the $\gamma$-calculus, a higher-order extension, where the rewrite rules are first-class citizen. The work presented in this paper increases further the expressivity of the chemical model with generalized multisets: multiplicities of elements may be infinite and/or negative. Applications of these new notions are illustrated by some programming examples.