Nanoparticle PEG modification with H-phosphonates

A compound of the formula:

• wherein
• each L1, L2, L3 and L4 is independently selected from the group consisting of a bond and a linking group;
• R1 is selected from the group consisting of a nanoparticle, an attachment component, a targeting agent, a diagnostic agent, a stealth agent, and a tetrapodal presentation component;
• each R2 is independently selected from the group consisting of a stealth agent, C1-C10 alkyl, a carboxylic acid or ester, a phosphonic acid or ester, a sulfonic acid or ester, and a hydroxy;
• each R3 and R4 is independently selected from the group consisting of H, a nanoparticle, an attachment component, a targeting agent, a diagnostic agent, and a stealth agent, wherein at least one of R3 or R4 is other than H;
• and
• n is an integer of from 0 to 2.