Lipid containing formulations

An association complex comprising:

• a. one or more compounds, each individually having a structure defined by formula (I) or a pharmaceutically acceptable salt thereof
• wherein:
• each Xa and Xb, for each occurrence, is independently C1-6 alkylene;
• n is 0, 1, 2, 3, 4, or 5;
• each R is independently H or
• wherein:
• at least n+2 of the R moieties in at least about 80% of the molecules of the compound of formula (I) in the preparation are not H;
• m is 1, 2, 3 or 4;
• Y is O, NR2, or S;
• R1 is alkyl or alkenyl;
• each of which is optionally substituted with one or more substituents;
• and
• R2 is H, alkyl or alkenyl;
• each of which is optionally substituted each of which is optionally substituted with one or more substituents;
• provided that, if n=0, then at least n+3 of the R moieties are not H;
• b. PEG-lipid having the structure shown in formula (XV)
• wherein:
• each L1 and L2 are independently a bond or C(O);
• each R1 and R2 are independently alkyl alkenyl or alkynyl;
• each of which is optionally substituted with one or more substituents;
• X is —C(O)NH—, C(S)NH, —C(O)C1-3alkylC(O)NH—;
• or —C(O)C1-3alkyl-C(O)O—;
• m is an integer from 0-11 and
• n is an integer from 1-500;
• c. a steroid;
• and
• d. a nucleic acid.