**Core Concept**
The force not acting in an enzyme-substrate complex is related to the concept of lock and key theory, which describes the binding of an enzyme to its substrate. In this theory, the enzyme has a specific active site that binds to the substrate, forming an enzyme-substrate complex. However, the binding of the substrate to the enzyme is not solely due to a single force; rather, it involves a combination of forces including hydrogen bonds, ionic interactions, van der Waals forces, and hydrophobic interactions.

**Why the Correct Answer is Right**
The lock and key theory proposes that the enzyme and substrate have complementary shapes that fit together like a key and a lock. However, this theory has been modified by the induced fit model, which suggests that the binding of the substrate to the enzyme causes a conformational change in the enzyme, allowing it to bind more tightly to the substrate. The force not acting in an enzyme-substrate complex is the **hydrogen bonding** force, as the other forces (ionic interactions, van der Waals forces, and hydrophobic interactions) contribute to the binding of the substrate to the enzyme.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because hydrogen bonding is a significant force in the binding of the substrate to the enzyme.
* **Option B:** This option is incorrect because ionic interactions are a major contributor to the binding of the substrate to the enzyme.
* **Option C:** This option is incorrect because van der Waals forces play a crucial role in the binding of the substrate to the enzyme.
* **Option D:** This option is incorrect because hydrophobic interactions are essential for the binding of the substrate to the enzyme.

**Clinical Pearl / High-Yield Fact**
In enzyme-substrate interactions, the shape complementarity of the enzyme and substrate is crucial for binding, but the induced fit model highlights the dynamic nature of enzyme-substrate interactions.

**Correct Answer:** D.