Electrospray ionization tandem mass spectrometry study of six isomeric cationic amphiphiles with ester/amide linker.
BACKGROUND
Isomeric cationic amphiphiles differing only in the orientation of the linker group have been demonstrated to possess dramatically changed gene transfer efficacies. Studies aimed at understanding structure-stability correlations of such isomeric cationic amphiphiles at the molecular level are yet to be undertaken. Such studies may throw significant new insights into the mechanistic origin on their contrasting bioactivities.


METHODS
Electrospray ionization mass spectrometry (ESI-MS) and multi-stage tandem mass spectrometric (MS(n)) experiments were performed on a LCQ ion trap mass spectrometer. The decomposition pathway was confirmed by high-resolution mass spectrometry data from a quadrupole time-of-flight (Q-TOF) mass spectrometer. Dissociation curves were drawn based on the intensities of precursor and product ions.


RESULTS
The collision-induced dissociation (CID) spectra of the M(+) ion of each isomeric pair showed distinct product ions (3 pairs). Normal esters (1 and 3) showed abundant product ions with a neighboring group participation (NGP) reaction and reverse esters (lipid 2 and 4) showed McLafferty rearrangement product ions. The spectra of a normal amide (5) and a reverse amide (6) are similar to that found in the corresponding ester, except for the absence of the McLafferty rearrangement in 6. Dissociation curves revealed that normal esters/amide decompose at lower energy than those of corresponding reverse esters/amide.


CONCLUSIONS
The lipids which easily decompose (flexible) show dramatically enhanced gene delivery capabilities and the lipids which decompose at higher collision energy (CE) values (rigid) are transfection incompetent.
National Centre for Mass Spectrometry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India.
D Vijay
DV
Darshan
B G N
BG
Chandar
M
M
Srujan
A
A
Chaudhuri
S
S
Prabhakar
D000577:Amides / Q000737:chemistry*; D004952:Esters / Q000737:chemistry*; D007536:Isomerism; D008055:Lipids / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods*
D000577:Amides; D004952:Esters; D008055:Lipids