Ruiqiong Li

The effect of midpolar regime mimics on anion transport mediated by amphiphilic heptapeptides

Nine amphiphilic heptapeptides, synthetic anion transporters (SATs) of the form (C18H37)2N–Y–(Gly)3-Pro-(Gly)3–OCH2Ph were prepared. The unit (OH2)Y represents the diacids succinic, glutaric, diglycolic, 3-thiaglutaric, N-methyliminodiglycine, isophthalic, and terephthalic acids. Additionally, Y was absent or present as acetic acid affording the structure (C18H37)2N–(Gly)3-Pro-(Gly)3–OCH2Ph or (C18H37)2N–(Gly)4-Pro-(Gly)3–OCH2Ph. The diglycolic acid derivative was reported previously but the remaining compounds are new. These nine peptides mediated release of Cl– from DOPC/DOPA vesicles with varying efficacy. Chloride release diminished for the Y-containing amphiphilic heptapeptides in the order glutaric, succinic > 3-thiaglutaric > terephthalic > acetic, N-methyliminodiacetic, > no Y, isophthalic. The release of Cl– was generally exponential over time but the curve shapes were distinctly sigmoidal for the more flexible diacids. Computational studies were undertaken to assess differences in conformation. Overall, it appeared that Cl– release for those SATs that could adopt a linear conformation on the N-terminal side of proline correlated best with the polarity of the diacid.

Pyrogallarene-based ion-conducting pores that show reversible conductance properties

Pyrogallol[4]arene macrocycles prepared from pyrogallol and n-dodecanal insert in phospholipid bilayers and form conducting pores that undergo reversible switching over a wide range of potentials.

Alkali metal and ammonium cation–arene interactions with tetraphenylborate anion

Sodium, potassium, rubidium, caesium, ammonium and tetramethylammonium tetraphenylborates were studied by both positive and negative ion electrospray mass spectrometry. An affinity order of Cs+ > Rb+ > K+ ∼ Na+ was obtained. The results obtained were compared with both calculations and solid-state structures, where available. The previously reported high affinity of caesium for tetraphenylborate concluded from NMR experiments was confirmed for the gas phase. The affinity does not appear to result from steric effects and a cation–pi interaction seems likely. In the positive ion mode, a unique acetonitrile complex of NaBPh4 was observed.

Aplosspan: a bilayer-length, ion-selective ionophore that functions in phospholipid bilayers.

A structurally simple, novel, membrane-active ionophore has been designed, prepared, characterized, and shown to conduct Na(+), Cl(-), and carboxyfluorescein anions, probably as a dimer, across liposomal bilayers.

Anion transport properties of amine and amide-sidechained peptides are affected by charge and phospholipid composition

Four synthetic anion transporters (SATs) having the general formula (n-C(18)H(37))(2)N-COCH(2)OCH(2)CO-(Gly)(3)Pro-Lys(epsilon-N-R)-(Gly)(2)-O-n-C(7)H(15) were prepared and studied. The group R was Cbz, H (TFA salt), t-Boc, and dansyl in peptides 1, 2, 3, and 4 respectively. The glutamine analog (GGGPQAG sequence) was also included. A dansyl-substituted fluorescent SAT was used to probe peptide insertion; the dansyl sidechain resides in an environment near the bilayers midpolar regime. When the lysine sidechain was free or protected amine, little effect was noted on final Cl(-) transport rate in DOPC : DOPA (7 : 3) liposomes. This stands in contrast to the significant retardation of transport previously observed when a negative glutamate residue was present in the peptide sequence. It was also found that Cl(-) release from liposomes depended on the phospholipid composition of the vesicles. Chloride transport diminished significantly for the free lysine containing SAT, 2, when the lipid was altered from DOPC : DOPA to pure DOPC. Amide-sidechained SATs 1 and 5 showed a relatively small decrease in Cl(-) transport. The effect of lipid composition on Cl(-) transport was explained by differences in electrostatic interaction between amino acid sidechain and lipid headgroup, which was modeled by computation.