Andrew Rifkin of DLJ Real Estate Capital Partners has sold his Upper East Side brownstone for $16 million dollars, public records show. The buyer, whose identity remains a mystery, was represented by Matthew Saenger of Green Square Capital Advisors. The 5,700-square-foot townhouse at 11 East 93rd Street sits in the Carnegie Hill Historic District, an enclave of landmarked buildings along the eastern border of Central Park. Built by architect A.B. Ogden in 1901, it’s one