Determination of molecular descriptors for illegal drugs by GC-FID using
Abraham solvation model
Syeda Sabrina AkhterUniversity of North Texas
June 24, 2013
Outline• Drugs• Abraham Solvation Model• Gas Chromatography
GC instrumentation Method development
• ResultLinear regression studiesPrediction of molecular descriptors
• Summary• Future Work
Objective• To utilize commonly used GC columns with desired stationary phases
to characterize the drugs and drug like molecules
• To build up a large data set of organic compounds with similar functional groups as the drugs
• To combine gas chromatography retention time with Abraham solvation parameter model to develop correlation between the partitioning behavior of the drug and
several biological phases to predict properties of drug molecules such as- basicity, acidity,
polarizability from the molecular descriptors
Drugs• A chemical substance that has a physiological effect when injected or
otherwise introduced to the body
• Drugs need to cross certain biological and chemical barriers to enter into the
central nervous system (CNS)
• Partitioning behavior is an important property governing the transport of the
drug in the central nervous system
• Partition coefficients between the phases predict drug permeability across
the membranes
Abraham Solvation Model• An approach for predicting biological activities and
partitioning coefficients
• A good way to predict absorption, distribution, metabolism,
elimination and toxicity of the drug – no animal studies needed
• Less time consuming and minimizes waste of valuable
resources
Abraham Solvation Model Cont.• It is made of two linear free energy relationships (LFER)
the partitioning of a solute from a gas phase to a condensed phase
SP= c + eE + sS+ aA +bB + lL
the partitioning between two condensed phases
SP= c + eE + sS+ aA +bB + vV
• SP is the solute property
• E, S, A, B, V and L are called the Molecular descriptors
• c, e, s, a, b, v and l are called the process coefficients
Abraham Solvation Model Cont.
SP = c + e.E + s.S + a.A + b.B + l.L (gas-condensed phase)
• E = excess molar refraction
• S = dipolarity/polarizability
• A = solute hydrogen bond acidity
• B = solute hydrogen bond basicity
• L = logarithm of solute gas phase Ostwald partition coefficient into hexadecane at 298K
Abraham Solvation Model Cont.SP = c + e.E + s.S + a.A + b.B + l.L
• e = measure of the solvent dispersion interactions
• s = the ability of the solvent phase to undergo dipole-dipole induced interaction with a solute
• a = complementary hydrogen bond basicity of the solvent
• b = complementary hydrogen bond acidity of the solvent
• l = the endoergic and exoergic solute-solvent effects that arise through solute polarizability
Abraham Solvation Model Cont.
• William E. Acree, Jr., Laura M. Grubbs and Michael H. Abraham, Toxicity and drug testing, Intech, 2012
Gas Chromatography
Separation of the components of a sample based upon the
partition, or distribution, in which the components are distributed
between two phases --
• Stationary phase – solid or liquid Retention mechanism depends on the intermolecular interactions between
the solute and stationary phase
• Mobile phase – gas Transports the analyte through the column but does not participate in the
retention mechanism
Instrumentation of GC
• Carrier Gas (mobile phase)- He or N
• Sample injection Split injection
Splitless injection
• Columns (stationary phase) Packed
Open tubular or capillary
• Detectors - FID
• Recorders Figure: Schematic diagram for GC instrumentation
Instrumentation of GC
Column Stationary Phase Polarity Max. Temp.
Recommended
TR-1MS
100% dimethyl polysiloxane
non- polar 380ºC
Chlorinated and nitroaromatic compounds
TG-5MS
5% diphenyl 95% dimethyl polysiloxane
low- polarity
350ºC
Semivolatiles, Phenols, Amines
TR-5 5% phenyl methyl polysiloxane
Low-Polarity
350ºC Alcohols, free fatty acids, aromatics, flavours and low polarity pesticides
TG-
1301MS
6% cyanopropylphenyl 94% dimethyl polysiloxane
Mid-
polarity280ºC
Alcohols, Volatile organics, Oxygenates, Residual Solvents
ZB-35 35% diphenyl 65%
dimethylpolysiloxaneMid-
polarity360ºC Aroclors, Semi-volatiles Amines, Drugs
of Abuse, Pharmaceuticals, Steroids, Pesticides
ZB-Wax Plus
polyethylene glycol
polar
280ºC
Esters, Alcohols, Ketones, Glycols, Aromatic Isomers
30m x 0.32mm (ID) x 0.25um film thickness
Method Development• Sample: 1 mg/mL each in MeOH, DCM or DMSO
• Injection: 1.0µL
• Split ratio: 50:1
• Split Mode: Split
• Injection Temperature : 240oC
• Carrier Gas: He
• Carrier gas flow rate : 1.5 mL/min
• Oven Temp: 50o C (hold 5 min)
to 250oC-3600C (hold 5min)
@ 15oC/min
• Detector: FID
• Detector temperature: 200oC
Time (min)
Tem
p. (
ºC)
15ºC/ m
in
Samples of Illegal DrugsCompound Chemical
StructureMolecular Formula
Molecular Weight (g/mol)
Boiling Point (°C)
Lidocaine C14H22N2O 234.34 181
Cocaine C17H21NO4 303.35 187-188
Codeine C18H21NO3 299.36 250
Morphine C17H19NO3 285.34 254
Samples of Chemical compounds
• Samples of organic compounds used which have similar functional groups with the drugs samples
• Over 75 compounds have been run in six columns to build on the training sets
• The chemical compounds selected have wide range of boiling points
Resultsc,e,s,a,b and l are obtained for the six columns from the natural logarithm of average retention time
• TR-5: c= 0.410, e= -0.144, s=0.154, a= 0.297, b= -0.195, l= 0.341, R2= 0.921, N=67
• TR-1MS: c= 1.011, e= -0.062, s= 0.121, a= 0.190, b= -0.061, l= 0.248, R2= 0.9470, N=63
• ZB-WAX Plus: c= 0.473, e= 0.030, s= 0.630, a= 0.797, b= -0.102, l= 0.269, R2= 0.8655, N=54
• TG-1301MS: c= 0.846, e= 0.127, s= 0.262, a= 0.319, b= -0.214, l= 0.207, R2= 0.6512, N=53
• TG-5MS: c= 0.855, e= 0.212, s= 0.328, a= 0.346, b= -0.382, l= 0.167, R2= 0.6596, N= 69
• ZB-35: c= 0.612, e= 0.006, s= 0.227, a= 0.139, b= -0.006, l= 0.269, R2= 0.9111, N=68
SP= c + eE + sS+ aA +bB + lL
ResultsThe coefficients are then used to get the mathematical equation for six columnsTR-5:
LnRT (calculated) = 0.410- 0.144E + 0.154S + 0.297A - 0.195B + 0.341L • TR-1MS: LnRT (calculated) = 1.011 - 0.062E + 0.121S + 0.190A - 0.061B + 0.248L • ZB-WAX PLUS: LnRT(calculated) = 0.473 + 0.030E + 0.630S + 0.797A - 0.102B + 0.269L
• TG-1301MS: LnRT (calculated) = 0.846 + 0.127E + 0.262S + 0.319A - 0.214B + 0.207L • TG-5MS: LnRT (calculated) = 0.855 + 0.212E + 0.328S + 0.346A – 0.382B + 0.167L • ZB-35: LnRT (calculated) = - 0.612 + 0.006E + 0.227S + 0.139A – 0.006B + 0.269L
SP= c + eE + sS+ aA +bB + lL
LnRT(calc) vs LnRT(exp)
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.81.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
LnR
Tcal
cula
ted
LnRTexperimental
y=0.8657x+0.2758R2=0.8656
(e)
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.81.0
1.5
2.0
2.5
3.0 y=0.9123x+0.1771R2=0.9111
LnR
Tcal
cula
ted
LnRTexperimental
(f)
0.5 1.0 1.5 2.0 2.5 3.0
1.0
1.5
2.0
2.5
3.0
LnR
Tcal
cula
ted
LnRTexperimental
y=0.9220x+0.1468R2=0.9210
(d)
1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
LnR
Tcal
cula
ted
LnRTexperimental
y=0.9458x+0.1132R2=0.9470
(a)
0.5 1.0 1.5 2.0 2.5 3.0
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
LnR
Tcal
cula
ted
LnRTexperimental
y=0.6595x+0.6250R2=0.6596
(c)
0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.61.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
LnR
Tcal
cula
ted
LnRTexperimental
y=0.6519x+0.6449R2=0.6512
(b)
TR-1MS TG-1301MS TG-5MS
TR-5 ZB-WAX PLUS ZB-35
TR-1MS (100% dimethylpolysiloxane)1,2-dichlorobenzene1-bromohexane2-acetyl pyridine2-butanone2-chlorophenol2-methyl cyclohexanone2-picoline3-amino-1-propanolacetic acidacetophenonealpha-pineneamyl acetateanilinebenzenebenzoic acidbenzonitrilebenzyl chloridebromobenzenechlorobenzeneethyl acetateethyl alcohol
ethyl benzoateisopentylacetatemesitylenemethyl acetatemethyl benzoatemethyl isobutyl ketonemorpholineN,N-diethyl anilineN,N-dimethyl anilineN,N-dimethyl formamidenaphthalenenitrobenzenenonyl amineo-anisaldehydeoctylaminepentane-1-olphenolpyridinequinolinetetrachloroethylenetetrahydrofurantoluene
c= 0.801, e= -0.055, s= 0.129, a= 0.224, b= -0.065, l= 0.303, N=43
LnRT (calculated) = 0.801 - 0.055E + 0.129S + 0.224A - 0.065B + 0.303L
1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
1.4
1.6
1.8
2.0
2.2
2.4y=0.8047x+0.3842R2=0.9905
Ln R
Tcal
cula
ted
LnRTexperimental
(a)
TR-5 (5% phenyl 95% methylpolysiloxane) 1,2-dichlorobenzene1,2-dimethyl benzene1-bromohexane1-chloronaphthalene2-butanone2-chlorobenzoic acid2-chlorophenol3-nitrobenzoic acidacetamideacetic acidacetonealpha-pineneamyl acetatebenzoic acidbenzyl chloridebromobenzenechlorobenzeneethanolethyl acetate
ethyl benzoateiso-pentyl acetateisoquinolinemesitylenemethyl acetatemethyl benzoatemethyl isobutyl ketoneN,N-diethylanilineN,N-dimethylformamidenaphthalenenitrobenzenenonylamineo-anisaldehydeoctyl aminepentan-1-olphenolpyridinequinolineresorcinoltetrachloroethylenetoluene
c= 0.096, e= -0.184, s=0.229, a= 0.319, b= -0.285, l= 0.420, N=40; LnRT (calculated) = 0.096- 0.184E + 0.229S + 0.319A - 0.285B + 0.420L
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.60.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6y=0.8089x+0.3374R2=0.9904
Ln R
Tcal
cula
ted
LnRTexperimental
(c)
TG-5MS (5% diphenyl 95% dimethylpolysiloxane) 1,2-dichlorobenzene
1,2-dimethylbenzene
2-butanone
2-chlorobenzoic acid
2-chlorophenol
3-nitrobenzoic acid
acetamide
acetanilide
acetone
aniline
benzoic acid
benzonitrile
benzyl chloride
biphenyl
chlorobenzene
ethanol
ethyl acetate
formamide
isoquinoline
lactic acid
methyl acetate
naphthalene
N-propyl alcohol
phenol
phenylacetic acid
pyridine
quinoline
tetrachloroethylenetetrahydrofuran
toluene
vanillin
c= -0.161, e= -0.156, s= 0.509, a= 0.398, b= -0.523, l= 0.290, N=31
LnRT (calculated) = - 0.161 - 0.156E + 0.509S + 0.398A – 0.523B + 0.290L
0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6y=0.6695x+0.7114R2=0.9862
Ln R
Tcal
cula
ted
LnRTexperimental
(e)
TG-1301MS (6%cyanopropylphenyl 94% dimethylpolysiloxane)1,2-dichlorobenzene
1,2-dimethyl benzene
2-acetylpyridine
2-butanone
2-chlorophenol
acetic acid
acetophenone
aniline
benzoic acid
benzonitrile
benzyl chloride
bromobenzene
chlorobenzene
ethanol
ethyl acetate
ethyl benzoate
isoquinoline
lactic acid
mesitylene
N,N-diethylaniline
N,N-dimethylaniline
nitrobenzene
o-anisaldehyde
phenol
pyridine
quinoline
tetrahydrofuran
toluene
c= 0.072, e= -0.009, s= 0.515, a= 0.418, b= -0.312, l= 0.357, N=33
LnRT (calculated) = 0.072 - 0.009E + 0.515S + 0.418A - 0.312B + 0.357L
0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.41.2
1.4
1.6
1.8
2.0
2.2
2.4
Ln R
Tcal
cula
ted
LnRTexperimental
y=0.6342x+0.7545R2=0.9811
(d)
ZB-35 (35% diphenyl 65% dimethylpolysiloxane)
c= -0.612, e= 0.006, s= 0.227, a= 0.139, b= -0.006, l= 0.269, N=43
LnRT(calculated) = - 0.612 - 0.006E + 0.227S + 0.139A – 0.006B + 0.269L
1,2-dichlorobenzene1,2-dimethyl benzene1-bromohexane2-acetyl pyridine2-butanone2-chlorophenol2-methyl cyclohexanone2-picolineacetic acidacetoneacetophenonealpha-pineneamyl acetatebenzenebenzoic acidbenzonitrilebenzyl chloridechlorobenzeneDecaneethyl acetateethyl benzoate
isopentylacetatemesitylenemethyl acetatemethyl benzoatemethyl isobutyl ketonemorpholinem-toluic acidN,N-diethyl anilineN,N-dimethyl anilineN,N-dimethyl formamidenitrobenzenenonyl amineo-anisaldehydeo-cresoloctylaminepentane-1-olphenolpyridineResorcinoltetrachloroethylenetetrahydrofurantoluene
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
1.2
1.4
1.6
1.8
2.0
2.2
2.4y=0.7526x+0.4410R2=0.9911
Ln R
Tcal
cula
ted
LnRTexperimental
(f)
ZB-WAX PLUS (100% polyethelene glycol)1,2-dichlorobenzene
1,2-dimethylbenzene
1-bromohexane
2-acetylpyridine
2-butanone
2-chlorophenol
Acetone
Acetophenone
alpha pinene
amyl acetate
Aniline
Benzene
Benzonitrile
Benzyl chloride
Bromobenzene
Chlorobenzene
DiiodomethaneEthyl AcetateEthyl benzoatemesityleneMethyl AcetateMethyl Benzoatemethyl isobutyl ketoneN,N-DimethylanilineN,N-DimethylformamidenitrobenzeneNonylamineN-propyl alcoholOctylaminephenoltetrachloroethyleneTetrahydrofuranToluene
c= 0.027, e= -0.021, s= 0.830, a= 0.996, b= -0.174, l= 0.354, N=32
LnRT(calculated) = 0.027 - 0.021E + 0.830S + 0.996A - 0.174B + 0.354L
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.81.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6 y=0.7798x+0.4531R2=0.9907
Ln R
Tcal
cula
ted
LnRTexperimental
(b)
Process coefficients for the six columns
Stationary Phases c e s a b l v
TR-1MS0.348 -0.024 0.056 0.097 -0.028 0.131 0.000
TR-50.042 -0.080 0.099 0.139 -0.124 0.182 0.000
TG-1301MS0.031 -0.004 0.223 0.182 -0.136 0.155 0.000
TG-5MS0.070 0.068 0.221 0.173 -0.227 0.126 0.000
ZB-WAX PLUS0.012 -0.009 0.360 0.432 -0.076 0.154 0.000
ZB-350.266 0.003 0.099 0.060 -0.003 0.117 0.000
Octanol/water0.088 0.562 -1.054 0.034 -3.460 0.000 3.814
SP= c + eE + sS+ aA +bB + lL SP= c + eE + sS+ aA +bB + vV
Molecular descriptors for Lidocaine
Descriptors ValueE 1.100S 0.147A 0.000B 1.792L 8.448V 2.059
Phase Experimental LogRT
Calculated LogRT
TR-1MS1.214 1.389
TR-51.199 1.285
TG-1301MS1.060 1.129
TG-5MS1.063 0.834
ZB-WAX PLUS -- --
ZB-351.014 1.265
Octanol2.196
2.204
SD= 0.199
SD=√(exp-calc)²/n-1
Molecular descriptors for Cocaine
Descriptors Value
E 1.355S -1.328A 0.000B 2.523L 10.530V 2.298
Phase Experimental LogRT
Calculated LogRT
TR-1MS 1.078 1.553
TR-5 0.998 1.407
TG-1301MS 1.063 1.022
TG-5MS 1.003 0.622
ZB-WAX PLUS -- --
ZB-35 1.013 1.362
Octanol2.275
2.283
SD= 0.407
SD=√(exp-calc)²/n-1
Molecular descriptors for Morphine
Descriptors Value
E 2.120S -0.994A 0.000B 2.543L 10.120V 2.065
Phase Experimental logRT
Calculated logRT
TR-1MS1.078 1.499
TR-50.998 1.302
TG-1301MS1.007 1.027
TG-5MS1.061 0.691
ZB-WAX PLUS -- --
ZB-351.014 1.349
Octanol1.394
1.403
SD= 0.360
SD=√(exp-calc)²/n-1
Molecular descriptors for Codeine
Descriptors ValueE 1.960S -0.486A 0.000B 2.669L 11.040V 2.206
Phase Experimental logRT
Calculated logRT
TR-1MS 1.261 1.649
TR-5 1.261 1.517
TG-1301MS 1.193 1.267
TG-5MS 1.271 0.880
ZB-WAX PLUS -- --
ZB-35 1.166 1.506
Octanol0.872
0.882
SD= 0.306
SD=√(exp-calc)²/n-1
Summary• GC-FID is used to obtain retention time of the drugs and organic chemicals
• LnRT(exp) and LnRT(calc) is compared
• Mathematical correlations between the logarithm of retention time of illegal drugs with GC system and the solute molecular descriptor from the Abraham model is developed
Future work• By increasing number of stationary phases and data points the equation can be modified
• Some drug compounds are not volatile enough. So HPLC can be used
• HPLC is also a good method for analyzing drugs with high boiling point
References[1]. William E. Acree, Jr., Laura M. Grubbs and Michael H. Abraham, Toxicity and drug testing, Intech, 2012[2]. C. Keck; S. Kobierski, R. Mauludin, R.H. Muller, Dosis, 2, 2008, 24, 124-128 .
[3]. A. N. Lukyanov, V. P. Torchilin, Advanced Drug Delivery Reviews, 2004, 56 (9), 1273-1289.
[4]. Ian A. Fowlis. Gas chromatography, 2nd ed.; John wiley & sons, 1994.
[5]. C.F. Poole, S.K. Poole, Chromatography Today, Amsterdam, 1991.
[6]. J.R. Conder, C.L. Young, Physicochemical Measurements by Gas Chromatography, Wiley, New York, 1979.
[7] V.G. Berezkin, A.A. Korolev, I.V. Malyukova, J. High Resolut. Chromatogr., 1997, 20, 333.
[8]. Michael H. Abrahama, Colin F. Pooleb, Salwa K. Poole, Journal of Chromatography A, 1999, 842, 79–114.
[9]. M.H.Abraham, F.Martins, R.C. Mitchell, C.J. Salter, J. Pharm. Sci., 1999, 88, 241.
[10]. M.H. Abraham, J. Le, W.E. Acree Jr., Coll. Czech. Chem. Comm., 1999, 64, 1748.
[11]. M.H. Abraham, J. Le, W.E. Acree Jr., P.W. Carr, J. Phys. Org. chem., 1999, 12, 675.
[12]. X.R. Xia, R.E. Baynes, N.A. Monterio-Riviere, J.E. Riviere, SAR QSAR Environ. Res., 2007, 18, 579.
[13]. L. Sprunger, A. Protctor, W.E. Acree Jr., M.H. Abraham, Journal of chromatography A, 2007, 1175, 162-173
[14]. J.A. Gratton, M.H. Abraham, M.W. Bradbury, H.S. Chadha, J. Pham. Pharmacol, 1997, 49, 1211-1216
Acknowledgements Thanks to committee members• Dr. Teresa Golden, Advisor• Dr. William E. Acree• Dr. Sushama Dandekar
Special thanks• Golden Group Members• Michele Stovall
GC training• Dr. Verbeck’s lab
Drugs• Dylan Harbour and
Timothy Stephens SPSS and EXCEL