A negatively charged molecule is filtered with more difficulty compared to a positive one because

Functionally, the glomerular membrane permits the free passage of neutral substances up to 4 nm in diameter and almost totally excludes those with diameters greater than 8 nm. However, the charges on molecules, as well as their diameters, affect their passage into Bowman's capsule. The negatively charged sialoproteins on the filtering membrane make it difficult for the negative paicles to pass through. The total area of glomerular capillary endothelium across which filtration occurs in humans is about 0.8 m 2Ref: Ganong&;s Review of Medical Physiology, 23rd edition, page no: 640