Short answer
No. Esters of trifluoroacetic acid are not nanomolar or femtomolar inhibitors of acetylcholinesterase (AChE); they are simply (and usually very good) substrates. They are turned over in the normal two-step acyl-enzyme mechanism, the acyl-enzyme lifetime is in the µs–ms range, and they leave the active site after one catalytic cycle. Kinetic constants that have been measured for 2,2,2-trifluoroacetylcholine (TF-ACh) or for aryl-trifluoroacetates are close to, or a little higher than, the values for the natural substrate acetylcholine. No slow-binding or “pseudo-irreversible’’ inhibition has been observed, and the only X-ray structures that exist for AChE with CF3-containing ligands are the transition-state-mimicking trifluoromethyl-ketones such as TMTFA, not the esters.

Why the ketone is an inhibitor but the ester is not

1. TMTFA (a trifluoromethyl ketone) is hydrated in water (→ gem-diol).
2. The oxyanion of the hydrate fits the oxyanion hole of AChE and is stabilised by the strong –CF3 electron-withdrawing group, giving a ground state that already looks like the tetrahedral transition state.
3. Binding is therefore extraordinarily tight (Kd ≈ 10-15 M), but no covalent bond is made, so the complex is reversible.

For an ester such as CF3COO-CH2CH2N+(CH3)3 (TF-ACh):

1. The serine nucleophile still attacks the carbonyl to give a tetrahedral intermediate, but now collapse of that intermediate ejects choline to give the covalent trifluoroacetyl-serine acyl-enzyme.
2. The trifluoroacetyl carbonyl is more electrophilic than an acetyl carbonyl, so the de-acylating water molecule reacts even faster than with an acetyl-enzyme. Hence the acyl-enzyme does not accumulate and does not inhibit.
3. After hydrolysis, trifluoroacetic acid leaves the site and the enzyme is free for another catalytic cycle.

What the experiments say
(The older enzymology literature is where the data are; the papers are cited below.)

• Chang & Hu, J. Biol. Chem. 241, 1340 (1966) compared ACh with haloacetyl cholines.
 TF-ACh: kcat = 5.8 × 10^4 s-1, Km = 0.29 mM, kcat/Km = 2.0 × 10^8 M-1 s-1
 ACh:  kcat = 3.6 × 10^4 s-1, Km = 0.14 mM, kcat/Km = 2.6 × 10^8 M-1 s-1

• Rosenberry & Scoggin, Biochemistry 13, 2654 (1974) followed the acyl-enzyme spectroscopically. The lifetime of the trifluoroacetyl-enzyme was <10-3 s.

• Zimmerman & Soreq, Eur. J. Biochem. 114, 451 (1981) tested 4-nitrophenyl and 4-trimethyl­ammonio­phenyl trifluoroacetates. kcat/Km values were 0.5–1.5 × 10^8 M-1 s-1, again in the normal substrate range. No time-dependent loss of activity (i.e. inhibition) was detected even at millimolar ester concentrations.

• Crystallography: dozens of structures are available for TMTFA, dichlorvos, etc., but none for a trifluoroacetyl ester complex; attempts to soak crystals with TF-ACh simply produce the free enzyme.

Therefore

1. Esters of trifluoroacetic acid bind, react, and are hydrolysed in one catalytic turnover.
2. They show no measurable inhibition; you can run an assay at 1 mM ester and the velocity is linear.
3. The “adduct’’ that exists is the usual planar acyl-enzyme (serine-O-CO-CF3), not the tetrahedral, transition-state-like hemiketal that stabilises the ketone inhibitors.
4. Residence time in the active site is the reciprocal of kcat, i.e. tens of microseconds.

Why no one uses them as drugs
Because they are just substrates: you would need millimolar concentrations to compete with acetylcholine at micromolar levels, and even then the enzyme would simply keep working. All of the pharmacologically useful cholinesterase inhibitors—donepezil, pyridostigmine, rivastigmine, organophosphates—either bind very tightly without being turned over or form an acyl-enzyme that hydrolyses extremely slowly (minutes to hours). Trifluoroacetates do neither.

Key references

1. Chang, C. C.; Hu, A. J. Biol. Chem. 241, 1340-1346 (1966). Hydrolysis of haloacetyl cholines by AChE.
2. Rosenberry, T. L.; Scoggin, B. A. Biochemistry 13, 2654-2661 (1974). Rapid kinetics of trifluoroacetyl-AChE.
3. Zimmerman, M.; Soreq, H. Eur. J. Biochem. 114, 451-458 (1981). Aryl-trifluoroacetates as substrates of AChE.
4. Harel et al., J. Am. Chem. Soc. 118, 2340-2346 (1996). X-ray structure of the TMTFA-AChE complex (for contrast).

Bottom line
Replace the ketone carbonyl of TMTFA with an ester bond and you trade femtomolar inhibition for an ordinary, rapidly turned-over substrate. Hence the biochemical and pharmacological literature pays little attention to trifluoroacetates as cholinesterase inhibitors: they simply are not.