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