Structure, acidity and basicity of a benzene disulfonamide inhibitor of carbonic anhydrase

Article abstract of DOI:10.1016/j.molstruc.2013.11.047

N-(4-Diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide) (I-3) and its hydrochloride salt (I-3·HCl) were prepared. The X-ray molecular structure of (I-3·HCl) has been determined. The gas phase geometry of free base, its anion, cation and hydrochloride h

Full text of DOI:10.1016/j.molstruc.2013.11.047

Journal of Molecular Structure 1059 (2014) 124–131
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structure, acidity and basicity of a benzene disulfonamide inhibitor
of carbonic anhydrase
c
c
ˇ d
Milan Remko a,b, , Peter Herich , Fridrich Gregán , Jozef Kozíšek
ˇ
⇑
a Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Comenius University Bratislava, Odbojarov 10, 832 32 Bratislava, Slovakia
b Center for Hemostasis and Thrombosis, Hemo Medika Bratislava, 851 04 Bratislava, Slovakia
c Department of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, 81237 Bratislava, Slovakia
d Department of Chemistry, Faculty of Natural Sciences, Matej Bel University, 974 01 Banská Bystrica, Slovakia
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
N-(4-Diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide) (I-3) and its hydrochloride salt (I-3ÁHCl)
were prepared. The X-ray molecular structure of this compound has been determined. The gas phase
geometry of these ligands has been computed using Becke3LYP/6-311++G(d,p) and B97D/
6-311++G(d,p) model chemistry.
ꢀ
ꢀ
Molecular structure of CAI I-3 and its
HCl salt.
The crystal packing is stabilized by
intermolecular hydrogen-bond and
p–p stacking interactions.
ꢀ
ꢀ
This structure is also present in the
gas phase and/or in water solution.
The I-3 behaves as a weak acid and/or
base.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 October 2013
Received in revised form 18 November 2013
Accepted 18 November 2013
Available online 25 November 2013
N-(4-Diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide) (I-3) and its hydrochloride salt (I-3ÁHCl)
were prepared. The X-ray molecular structure of (I-3ÁHCl) has been determined. The gas phase geometry
of free base, its anion, cation and hydrochloride has been computed using Becke3LYP/6-311++G(d,p) and
B97D/6-311++G(d,p) model chemistry. The conformational behavior of these systems in water was
examined using the solvation CPCM model. In the solid state this compound possesses a sandwich-like
structure. According to the density functional calculations using B97D Grimme’s functional including dis-
persion this structure is also present in the gas phase and/or in water solution. On the other hand, the
B3LYP functional calculations prefer extended conformer in gas phase. The calculated gas-phase acidity
and basicity are conformationally dependent and low, indicating that I-3 behaves as a weak acid and/or
base.
Keywords:
Aromatic sulfonamides
Synthesis
X-ray structure
DFT calculation
Solvent effect
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
⇑
Corresponding author at: Department of Pharmaceutical Chemistry, Faculty of
Pharmacy, Comenius University Bratislava, Odbojarov 10, 832 32 Bratislava,
Slovakia. Tel.: +421 2 50117225; fax: +421 2 50117100.
The sulfonamide group –SO2NH– is present in many organic
compounds that are known as potent inhibitors of the carbonic
anhydrases (CA) [1–3]. In addition to their established role as
E-mail address: remko@fpharm.uniba.sk (M. Remko).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.11.047

M. Remko et al. / Journal of Molecular Structure 1059 (2014) 124–131
125
diuretics and antiglaucoma drugs, it has recently emerged that CA
inhibitors could have potential as novel anti-obesity, anticancer
and anti-infective drugs [4]. Furthermore, recent studies suggest
that CA activation may provide a novel therapy for Alzheimer’s dis-
ease [4] and antibiotic therapy [5]. Various substituted aromatic
and heterocyclic sulfonamides have been synthesized and evalu-
ated for possible therapeutic use as antiglaucoma agents [6–9].
Commonly used sulfonamide antiglaucomatics include orally
administered acetazolamide, ophthalmic suspension of brinzola-
mide and ophthalmic solution of dorzolamide [8,9]. They bind as
anions to the Zn2+ ion within the enzyme active site [10–12] with
abnormally high affinities for isozyme CAII, ref. [13–15]. Because
therapeutically useful antiglaucoma drugs are aromatic and het-
erocyclic sulfonamides, it is evident that for optimal in vivo activity
the balanced hydro- and liposolubility is necessary. It is well estab-
lished [16,17] that a water-soluble sulfonamide, also possessing
relatively balanced lipid solubility, would be an effective antiglau-
coma drug via the topical route. One of the conditions [16] needed
for a sulfonamide to act, as an effective intraocular pressure-lower-
ing agent, is to possess modest lipid solubility attributable to its
unionized form.
Hydrochloride of N-(4-diethylaminoethoxy-benzyl)benzene-
1,4-bis(sulfonamide) (I-3ÁHCl) was prepared by followed proce-
dure: The solution of 20% hydrochloride in anhydrous methanol
was added slowly to stirred solution of N-(4-diethylaminoeth-
oxybenzyl)benzene-1,4-bis(sulfonamide) 0.9 g (0.0021 mol) in
methanol (10 ml) to pH = 4. After then the mixture was stirred
15 min at room temperature. The solvent was evaporated and
the residue was purified by crystallization from ethanol:water
(10:1). Colorless solid, yield 0.72 g (80%), m. p. 210–211 °C. TLC
in acetone: Rf = 0.40. Elemental analysis for C19H28ClN3O5S2 (M.r.
478.03), calculated (found): C 47.74 (47.90), H 5.90 (5.76), Cl
7.42 (7.31), N 8.79 (8.88), S 13.41 (13.19). 1H NMR (DMSO) 1.24
(t, 6H, CH3), 3.20 (m, 4H, CH2-N), 3.47 (t, 2H, CH2-N), 3.97 (t, 2H,
CH2-Phenyl), 4.31 (t, 2H, CH2-O), 6.90 (d, 2H, Har), 7.16 (d, 2H,
Har), 7.62 (s, 2H, SO2-NH2), 7.93 (d, 2H, Har), 7.98 (d, 2H, Har),
8.37 (t, 1H, SO2NH), 10.17 (s, 1H, NH+).
2.2. X-ray crystallographic data
The single-crystal, X-ray data collection for compound I-3ÁHCl
In this work we report the synthesis, molecular structure, basi-
city and acidity of a novel drug-like aromatic sulfonamide (N-(4-
was performed on an Oxford Diffraction Gemini R four circle j-axis
diffractometer equipped with a Ruby CCD detector and a graphite
monochromator, using Mo-Ka radiation at 298(1) K. CrysAlis pro-
gram package (Oxford Diffraction, 2012) was used for data reduc-
tion [20]. The structure was solved by direct methods using
SHELXS-2008 and SHELXS-2013 programs [21,22]. Refinement
was carried out on F2, and scattering factors incorporated in SHEL-
XL-2013 program were used. All non-hydrogen atoms were refined
with anisotropic thermal parameters. Crystal data for I-3ÁHCl data
collection procedures, structure determination methods and
refinement results are summarized in Table 1. All hydrogen atoms
were placed geometrically and refined using a mixed model, with
Uiso(H) = 1.2 Ueq(C, or N), C–H distances fixed for CH2 groups at
0.97 Å, for aromatic groups at 0.93 Å, for methyl group at 0.96 Å
and N–H distances for NH2 and NH groups fixed at 0.83 Å and for
the N3-H3 N group at 0.97 Å. The DIAMOND program package
was used for molecular structure drawing [23].
diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide)
(I-3),
and its hydrochloride (N-(4-diethylaminoethoxybenzyl)benzene-
1,4-bis(sulfonamide), I-3ÁHCl) with favorable biological properties
comparable to those obtained for therapeutically useful acetazola-
mide, dorzolamide and brinzolamide [18]. The solid-state structure
of novel aromatic sulfonamides has been examined by X-ray crys-
tallography. Theoretical quantum chemical methods were applied
for structural characterization of these compounds in the gas phase
and water solution.
2. Experimental section
2.1. Synthesis
N-(4-Diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide)
(I-3) was prepared as depicted in Scheme 1 [19]. To the cold solution
4-diethylaminoethoxy benzylamine (1) in acetone (12 ml) solution
of sodium carbonate 2.34 g (0.022 mol) in water (10 ml) in a small
portion during 5 min was added. To this stirred mixture 4-sul-
famoylbenzenesulfonylchloride (2) 5.12 g (0.02 mol) during
30 min at 10 °C was added. After then the reaction mixture was stir-
red 12 h at room temperature. The solid inorganic salt was filtered,
washed with acetone (5 ml). The solvent from filtrate was evapo-
rated using a vacuum rotatory evaporator. The residue was mixed
three times with cold water (3 Â 10 ml). The crude solid was filtered
and purified by crystallization from 2-propanol. Colorless solid,
yield 6.10 g (69.3%), m.p. 158 °C. TLC in acetone Rf = 0.50. Elemental
analysis for C19H27N3O5S2 (M.r. 441.57), calculated (found): C 51.68
(51.86), H 6.16 (6.02), N 9.52 (9.38), S14.52 (14.23). 1H NMR (DMSO)
1.07 (t, 6H, CH3), 2.64 (q, 4H, CH2-N), 2.87 (t, 2H, CH2-N), 4.04 (t, 2H,
CH2-O), 6.89 (d, 2H, Har.), 7.12 (d, 2H, Har.-O), 7.63 (s, 2H, SO2-NH2),
8.00 (dd, 4H, Har.-SO2), 8.39 (t, 1H, NH-SO2).
Table 1
Crystallographic data and structure refinement for compound I-3ÁHCl.
Compound
I-3 Â HCl
C:_1005
C19 H28 Cl N3 O5 S2
478.01
293(1) K
0.71073 Å
Orthorhombic
P b c a
a = 11.2348(2) Å
b = 16.0525(3) Å b = 90°
Identification code
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell dimensions
a = 90°
c = 25.2170(4) Å
4547.80(14) Å3
8
c = 90°
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
1.396 Mg/m3
0.387 mmÀ1
2016
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to 2
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
0.22 Â 0.08 Â 0.03 mm
2.74–26.37°
À14 6 h 6 14, À20 6 k 6 20, À31 6 l 6 31
79865
4629 [R(int) = 0.0924]
99.5%
H = 25.00°
Full-matrix least-squares on F2
4629/3/283
1.016
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 = 0.0445, wR2 = 0.0945
R1 = 0.0818, wR2 = 0.1080
0.265 and À0.300 e.ÅÀ3
Scheme 1.

126
M. Remko et al. / Journal of Molecular Structure 1059 (2014) 124–131
Crystallization of free base N-(4-diethylaminoethoxyben-
using density functional theory [25–27] with the B3LYP hybrid
functional [28–30] and B97D Grimme’s functional including dis-
persion [31] and the polarized triple-f 6-311++G(d,p) basis set
[32]. The enthalpies and Gibbs energies of protonation and
deprotonation of base N-(4-diethylaminoethoxybenzyl)benzene-
1,4-bis(sulfonamide) (I-3) was computed by the same way as in
our previous publication [33]. Solvent effects on the species stud-
ied were evaluated using the polarizable conductor calculation
model (CPCM) [34–37]. The structures of all gas-phase and
condensed-phase (CPCM) species were fully optimized without
any geometrical constraint. The calculations of the macroscopic
zyl)benzene-1,4-bis(sulfonamide) (I-3) did not give single crystals
suitable for X-ray diffraction studies. Thus its solid-state structure
is still unknown. Crystallographic data of the title compound has
been deposited with the Cambridge Crystallographic Data Center
as supplementary publication No.: CCDC 966739.
2.3. Computational details
The geometry (Fig. 1) of all molecular species investigated has
been completely optimized with the Gaussian 09 program [24],
Fig. 1. Molecular structure of two stable conformers of hydrochloride of the N-(4-diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide) and ortep drawing of its X-ray
structure. Thermal ellipsoids are drawn at 30% probability.

M. Remko et al. / Journal of Molecular Structure 1059 (2014) 124–131
127
pKa were performed using the program SPARC developed by Carre-
ira et al. [38–40].
3. Results and discussion
3.1. X-ray structure
The compound investigated belongs to the effective carbonic
anhydrase inhibitors and consists of common benzene-1,4-disulf-
onamide pharmacophoric structural unit. Extended tail of this
derivative contains diethylaminoethoxybenzyl moiety and exploit
the strategy of enhanced hydrophobic interactions between hydro-
phobic moieties of both active site of enzyme and inhibitor [18].
The diethylamino nitrogen atom of the parent base I-3 is principal
basic center with the computed pKa = 8.87, and is at physiological
pH = 7.4 slightly protonated (hydrogen bond acceptor site). Two
sulfonamide NH groups are slightly acidic (the computed
pKa = 9.18 and 10.14 for terminal –SO2NH2 and central –SO2NH–
moieties, respectively) and provide hydrogen bond donors. The
crystal packing of the molecule shows a system of four intermolec-
ular hydrogen bonds, five hydrogen interactions and one intramo-
lecular hydrogen interaction (Fig. 2, Table 2). Crystal structure has
crystallized in the centrosymmetric P bca group (No. 61). There are
eight molecules in the unit cell.
Fig. 2. Intermolecular N–HÁ Á ÁO hydrogen bonds of I-3ÁHCl (dashed lines) deter-
mining the packing of molecules in the crystal structure. Only H atoms participating
in hydrogen bonds are shown.
Chlorine anion ClÀ is bonded by three hydrogen bonds (H3 N,
H2 N and H1N1, with distances 2.12(3) Å, 2.347(6)
Å and
Table 2
Hydrogen bonds and hydrogen interactions for I3.HCl [Å and °].
2.478(6) Å, as well) and two Van der Waals interactions (H6A and
H14A of 2.74 Å and 2.88 Å). The sulfonamide NH2 group is engaged
in two intermolecular hydrogen bonds. One H-bond arises from the
N1–H2N1Á Á ÁO4 interaction with adjacent SO2 group and the other
is N1–H1N1Á Á ÁCl1 (2.270(11) Å and 2.478(6) Å, as well). Weak
C14–H14BÁ Á ÁO2 of 2.50 Å and C14–H14AÁ Á ÁCl1 of 2.88 Å contacts
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
2.74
2.63
2.60
2.50
2.88
2.50
2.478(6)
2.270(11)
2.347(6)
2.12(3)
d(DÁ Á ÁA)
<(DHA)
C(6)–H(6A)Á Á ÁCl(1)#1
C(7)–H(7A)Á Á ÁO(1)#2
C(12)–H(12A)Á Á ÁO(4)#3
C(14)–H(14B)Á Á ÁO(2)#4
C(14)–H(14A)Á Á ÁCl(1)#1
C(18)–H(18A)Á Á ÁO(5)
N(1)–H(1N1)Á Á ÁCl(1)#1
N(1)–H(2N1)Á Á ÁO(4)#3
N(2)–H(2N)Á Á ÁCl(1)#5
N(3)–H(3N)Á Á ÁCl(1)
0.93
0.97
0.93
0.97
0.97
0.97
0.830(3)
0.830(3)
0.829(3)
0.97(3)
3.609(3)
3.339(3)
3.504(3)
3.171(3)
3.447(3)
3.086(3)
3.300(2)
3.061(3)
3.169(2)
3.082(2)
156.2
130.0
164.8
126.4
118.6
118.8
171(3)
159(3)
172(3)
172(2)
and
p–p [centroid–centroid distance = 3.842 Å] stacking interac-
tions also occur. Shorter distance is between carbons C4 and C8
with value of 3.361 Å.
In the molecule there are two sulfonamide groups with the dis-
tances S1–O1, S1–O2, S1–N1, S1–C1 1.422(2), 1.427(2), 1.597(2)
and 1.770(2) Å, and S2–O3, S2–O4, S2–N2, S2–C4 1.427(2),
1.428(2), 1.592(2) and 1.766(2) Å, which are within the interval
found for 153 crystal structures in the Cambridge Structural Data-
base with R-value lower as 0.030. For S–O bonds in similar aro-
matic sulfonamides the shorter distance of 1.389 Å was found
[41], refcode UKAXEK and longer of 1.500 Å [42], refcode MEZGON.
For S-N bond the shorter distance of 1.542 Å [43], refcode YAZNIY
and longer of 1.695 Å [44], refcode YODCUQ was found. For S-C
bond the shorter distance of 1.760 Å [41] and longer of 1.838 Å
[45], refcode HOFPEX was found.
Symmetry transformations used to generate equivalent atoms: #1 Àx + 1, Ày,
Àz + 2 #2 Àx + 1, yÀ1/2, Àz + 3/2 #3 x + 1/2, y, Àz + 3/2 #4 Àx + 3/2, y À 1/2, z #5
Àx + 3/2, Ày, z À 1/2.
An X-ray analysis of this compound showed that the proton is
located on the basic nitrogen atom N3. Three intermolecular
hydrogen bonds mediated by the Cl1 atoms and one hydrogen
bond between O4Á Á ÁH2N1–N1 stabilize the crystal structure. Each
Cl1 atom bridges three molecules via N–HÁ Á ÁCl1 hydrogen bond.
Similar stabilizing effect on the structure exhibit the five intermo-
lecular and one intramolecular C18–H18AÁ Á ÁO5 hydrogen interac-
tion (Fig. 3, Position 1 and 2).
The carbonic anhydrase inhibitor I-3 possesses benzene-1,4-
bis(sulfonamide) functionality, connecting aromatic ring and a ba-
sic diethylaminoethoxy substituent. Their relative molecular orien-
tation is described by sixteen dihedral angles. The relevant bond
lengths, bond angles and dihedral angles for X-ray conformations
and calculated values of the fully optimized structures are given
in Tables 3 and 4, respectively. The bond lengths and bond angles
of the sulfonamide moieties in I-3ÁHCl are similar. The Carom–S
bond length of about 1.76–1.77 Å is a single bond length between
sp2 hybridized carbon atom and sulfur since the sulfonamide group
Fig. 3. Ortep drawing of crystal packing detail in two positions for I3.HCl, red-
hydrogen bonds, blue-hydrogen interactions. (For interpretation of the references
to colour in this figure legend, the reader is referred to the web version of this
article.)

128
M. Remko et al. / Journal of Molecular Structure 1059 (2014) 124–131
Table 3
Experimental and theoretically optimized relevant bond lengths (Å), bond angles (degrees) and dihedral angles (degrees) of the I-3ÁHCl.
I-3ÁHCl, conformation II I-3ÁHCl, conformation I
Parameter
X-ray
B3LYP
B97D
B3LYP-CPCM
B3LYP
B97D
B3LYP-CPCM
d[C(1)–S(1)]
d[C(4)–S(2)]
d[C(7)–N(2)]
d[C(7)–C(8)]
d[C(11)–O(5)]
d[C(14)–O(5)]
d[C(14)–C(15)]
d[C(15)–N(3)]
d[C(16)–N(3)]
d[C(18)–N(3)]
d[N(1)–S(1)]
d[N(2)–S(2)]
d[O(1)–S(1)]
d[O(2)–S(1)]
d[O(3)–S(2)]
d[O(4)–S(2)]
1.770(2)
1.766(2)
1.468(3)
1.513(3)
1.373(3)
1.424(3)
1.510(3)
1.494(3)
1.508(3)
1.483(4)
1.597(2)
1.592(2)
1.422(2)
1.427(2)
1.4266(18)
1.4275(19)
118.5(2)
119.46(19)
117.3(2)
120.2(2)
124.9(2)
108.7(2)
117.1(2)
123.56(18)
117.49(18)
120.05(14)
106.82(13)
106.85(13)
107.96(12)
120.18(12)
106.83(11)
107.31(12)
107.34(11)
129.9(3)
À80.2(3)
À65.9(3)
64.8(3)
1.8100
1.8034
1.4799
1.5123
1.3713
1.4264
1.5174
1.4969
1.5037
1.5018
1.6957
1.6957
1.4556
1.4557
1.4612
1.4613
119.13
119.33
113.42
120.66
124.57
109.45
117.36
118.89
118.66
123.36
105.57
105.57
107.20
122.25
105.16
109.24
104.11
125.05
À68.21
À82.77
54.12
1.8210
1.8210
1.4783
1.5209
1.3784
1.4477
1.5195
1.5001
1.5044
1.5037
1.6956
1.6999
1.4647
1.4705
1.4671
1.4677
118.96
118.77
115.62
121.07
124.86
109.15
116.26
120.54
118.43
123.11
105.20
105.20
106.07
123.69
105.69
104.84
107.06
129.98
À67.60
À70.00
59.53
1.8057
1.8032
1.4841
1.5117
1.3697
1.4284
1.5169
1.5107
1.5146
1.5150
1.6673
1.6750
1.4634
1.4633
1.4672
1.4685
119.04
119.24
113.24
120.75
124.56
109.05
116.68
119.72
119.72
120.59
105.92
105.94
108.87
119.67
111.29
105.48
104.16
122.77
À72.91
À79.24
57.04
1.8027
1.8108
1.4753
1.5110
1.3688
1.4251
1.5271
1.4939
1.5040
1.5019
1.6886
1.6700
1.4597
1.4598
1.4582
1.4586
119.09
119.36
110.09
120.67
115.64
104.53
113.23
120.97
118.54
122.70
107.29
107.28
103.27
122.82
105.54
106.55
107.22
61.22
1.8163
1.8213
1.4861
1.5112
1.3734
1.4331
1.5289
1.4940
1.5052
1.5026
1.7153
1.6970
1.4703
1.4701
1.4680
1.4677
118.91
119.18
109.23
120.52
115.53
105.05
112.07
117.89
117.47
122.87
107.44
107.52
102.03
123.06
105.84
106.40
105.23
65.63
1.8013
1.8082
1.4846
1.5098
1.3688
1.4271
1.5257
1.5022
1.5155
1.5144
1.6760
1.6664
1.4656
1.4664
1.4645
1.4651
119.06
119.01
109.74
120.79
115.58
104.58
113.18
120.08
118.71
119.66
105.84
111.46
102.48
120.55
105.67
106.72
108.95
72.56
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
[C(6)–C(1)–S(1)]
[C(5)–C(4)–S(2)]
[N(2)–C(7)–C(8)]
[ C(9)–C(8)–C(7)]
[O(5)–C(11)–C(10)]
[O(5)–C(14)–C(15)]
[N(3)–C(15)–C(14)]
[C(7)–N(2)–S(2)]
[C(11)–O(5)–C(14)]
[O(1)–S(1)–O(2)]
[O(1)–S(1)–N(1)]
[O(2)–S(1)–N(1)]
[N(1)–S(1)–C(1)]
[O(3)–S(2)–O(4)]
[O(3)–S(2)–N(2)]
[O(4)–S(2)–N(2)]
[N(2)–S(2)–C(4)]
U[N(2)–C(7)–C(8)–C(9)]
U[O(5)–C(14)–C(15)–N(3)]
U[C(8)–C(7)–N(2)–S(2)]
U[C(19)–C(18)–N(3)–C(15)]
U[C(14)–C(15)–N(3)–C(18)]
U[C(14)–C(15)–N(3)–C(16)]
U[C(17)–C(16)–N(3)–C(15)]
U[C(10)–C(11)–O(5)–C(14)]
U[C(15)–C(14)–O(5)–C(11)]
U[C(6)–C(1)–S(1)–O(1)]
U[C(6)–C(1)–S(1)–O(2)]
U[C(6)–C(1)–S(1)–N(1)]
U[C(7)–N(2)–S(2)–C(4)]
U[C(5)–C(4)–S(2)–O(3)]
U[C(5)–C(4)–S(2)–O(4)]
U[C(5)–C(4)–S(2)–N(2)]
179.87
À166.37
À176.33
161.60
À67.66
À66.01
177.08
176.19
À22.94
À156.59
90.22
À176.04
À177.01
À176.02
167.39
À62.45
À64.07
179.21
177.92
À23.28
À157.44
89.59
À169.86
À166.56
À175.25
173.75
À56.92
À63.16
177.98
À179.02
À29.36
À160.13
82.38
65.6(3)
74.24
80.64
69.01
À64.8(3)
À159.6(3)
8.0(3)
À171.73(19)
À55.0(2)
174.6(2)
59.9(2)
77.0(2)
143.0(2)
12.6(2)
À57.42
À163.05
1.53
À178.86
À21.93
À156.10
90.96
103.60
150.95
17.86
À97.84
À50.80
À163.50
À9.07
À60.43
À161.66
À1.27
179.04
À2.20
À177.96
À25.03
À156.31
89.32
À136.80
109.75
67.42
93.32
134.82
4.66
À113.39
À65.25
À20.54
À153.77
93.31
À58.99
À22.79
À157.16
90.18
À62.30
À19.82
À150.69
95.19
154.98
20.14
À92.92
À102.5(2)
Table 4
Geometry of NÁ Á ÁH–Cl and N–H+ bonds in I-3ÁHCl and I-3-H(+) species.
I-3ÁHCl, conformation II
I-3ÁHCl, conformation I
Parameter
X-ray
B3LYP
B97D
B3LYP-CPCM
B3LYP
B97D
B3LYP-CPCM
d[N(3)–H]
0.970
2.126
3.089
3.396
1.1329
1.7550
2.8853
6.2658
6.9276
102.19
174.91
À170.17
26.64
1.0232
6.0652
4.4547
104.83
À166.36
1.1664
1.7043
2.8686
3.0133
3.7550
102.81
175.43
À163.33
42.03
1.0262
3.1610
3.8360
104.90
À169.68
1.0545
2.0752
3.1249
5.0631
6.0645
103.54
173.21
À174.69
16.25
1.0237
7.5579
5.9296
104.49
À176.29
1.1288
1.7609
2.8897
13.4721
12.5392
106.53
178.96
47.70
À63.77
1.0237
13.7993
12.5392
106.44
57.11
1.1609
1.7081
2.8689
12.8740
11.4285
106.49
178.82
53.27
À50.77
1.0257
13.0261
11.5928
106.90
59.50
1.0568
2.0469
3.1022
13.4720
12.1885
106.28
176.17
59.60
d[HÁ Á ÁCl]
d[N(3)Á Á ÁCl]
d[N(1)Á Á ÁO(5)]
d[S(1)Á Á ÁO(5)]
4.698
H
H
[C(15)–N(3)–H]
[N(3)–HÁ Á ÁCl]
100.80
172.01
À176.43
À34.26
U[C(14)–C(15)–N(3)–H]
U
[C(15)–N(3)–HÁ Á ÁCl]
20.91
d[N(3)–H]
1.0233
13.4581
12.1602
106.84
54.18
d[N(1)Á Á ÁO(5)]
d[S(1)Á Á ÁO(5)]
H
[C(15)–N(3)–H]
U[C(14)–C(15)–N(3)–H]

M. Remko et al. / Journal of Molecular Structure 1059 (2014) 124–131
129
Table 5
Relative energy stability (kJ/mol) of individual conformers of N-(4-diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide) (I-3) and its hydrochloride salt (I-3ÁHCl).
Conformer
B3LYP/6-311++G(d,p)
Gas-phase
B97D/6-311++G(d,p)
Gas-phase
In water (CPCM)
In water (CPCM)
I-3 (I)
I-3 (II)
0
0.3
0
2.9
0
0
6.8
0
39.0
0
57.3
0
x
0
43.5
0
45.2
0
x
0
6.5
43.4
0
17.2
0
I-3 (I) NH+
I-3 (II) NH+
I-3 (I) SO2NHÀ
I-3 (II) SO2NHÀ
I-3ÁHCl (I)
I-3ÁHCl (II)
0
11.6
31.7
0
41.5
0
1.3
X Conformer (I) converged to the conformer (II).
Table 6
Computed gas-phase acidity and basicity of N-(4-diethylaminoethoxybenzyl)benzene-1,4bis(sulfonamide) (I-3).
No.
Species
B97D/6-311++G(d,p)
H298 (kJ/mol)
B3LYB/6-311++G(d,p)
D
D
S298 (J/K mol)
D
G298 (kJ/mol)
D
H298 (kJ/mol)
D
S298 (J/K mol)
D
G298 (kJ/mol)
I
II
I
I-3-SO2NH2 (NH-anion)
I-3-SO2NH2 (NH-anion)
I-3-SO2NH2 (N3-cation)
I-3-SO2NH2 (N3-cation)
1342.40
1380.86
À975.23
À995.91
53.46
125.97
1326.47
1343.32
À937.56
À948.44
1390.23
119.71
121.90
1357.23
1333.07
À916.85
À972.62
1369.44
À956.32
À1007.07
À126.27
À132.41
II
À160.39
À115.69
Fig. 4. Molecular superimposition of the X-ray structure of I-3ÁHCl (red) and its B97D/6-311++g(d,p) optimized conformer II (blue). (For interpretation of the references to
colour in this figure legend, the reader is referred to the web version of this article.)
and aromatic rings are approximately perpendicular (dihedral an-
gles [C(6)–C(1)–S(1)–N(1) and [C(5)–C(4)–S(2)–N(2)], Table 3).
two functionals of the density functional theory. The hybrid Beck-
e3LYP functional is, in combination with the triple-f basis set, one
of the best DFT functionals for the accuracy of geometries [48]. The
Grimme’s B97D uses the empirical dispersion energy correction
specifically designed for accurate evaluation of van der Waals
interactions [31]. Two initial conformations of the N-(4-diethyla-
minoethoxybenzyl)benzene-1,4-bis(sulfonamide) for use in the
calculations were selected. First one, based on the our previous
investigations of aromatic sulfonamides [49,50] represent ‘‘ex-
tended’’ conformer (I). A second, ‘‘sandwich-type’’ conformer (II)
resulted from the X-ray structure of a solid sample of the N-(4-
diethylaminoethoxybenzyl) benzene-1,4-bis(sulfonamide) hydro-
chloride. An analysis of the harmonic vibrational frequencies of
the optimized species computed at the B3LYP and B97D levels of
theory also proved that all of them are minima (zero number of
imaginary frequencies). Important geometrical parameters of the
U
U
The S–N bond length is about 1.60 Å, and is much shorter than the
S–N single bond distance of about 1.75 Å [46]. The arrangement of
bonds around sulfur atom is distorted tetrahedral, a common
structural feature found in aromatic and heterocyclic sulfonamides
[43,47]. The largest deviation of about 120° is in the O–S–O angle
(Table 3). The X-ray structure of I-3ÁHCl provides the sandwich-like
conformer in which both aromatic rings are almost in parallel
arrangement (Fig. 1).
3.2. Theoretical calculations
The conformational structure of the N-(4-diethylaminoeth-
oxybenzyl)benzene-1,4-bis(sulfonamide) and its hydrochloride
salt in the gas phase and in water solution was investigated using

130
M. Remko et al. / Journal of Molecular Structure 1059 (2014) 124–131
neutral molecules and ionic species investigated are given in
Tables 3 and 4. The hydrochloride salt was considered as 1:1
complexes of base I-3 with hydrochloric acid. Hydrochloride was
selected because it is one of the favorite counterions for the salt
formation of the drugs [51]. HCl bridges the basic N(3) nitrogen
atom and in the solid state the extent of proton transfer has been
determined from single-crystal X-ray diffraction.
unambiguously prefers ‘‘sandwich-like’’ conformation as the most
stable structure. This conformation is also most stable species in
the solid state. The superposition of the 3-D structures of the
I-3ÁHCl manifesting the overall difference in experimental solid
state and gas phase geometries of this salt is shown in Fig. 4.
Solvent effect did not change appreciably geometry of isolated
molecule (Table 3). The sulfonamide studied contains an acidic –
NH2 group and thus it may undergo deprotonation reactions. It is
well known [10,53] that the anion is bound to the enzyme active
site and therefore represents the active species. Table 5 contains
acidities of I-3 computed by two model chemistry methods. The
absolute value of computed acidity is conformationally dependent.
Average values of gas phase acidities computed by two methods
(1334.9 (B97D) and 1345.2 kJ/mol (B3LYP), respectively) fit well
to each other and are close to those values calculated for a series
of substituted aromatic sulfonamides [33].
Initial conformations to use in the density functional theory cal-
culations of the N-(4-diethylaminoethoxybenzyl)benzene-1,4-
bis(sulfonamide), its hydrochloride salt, protonated and ionized
species were build using of the Gauss View graphical interface of
Gaussian. As an initial conformation of these species an ‘‘extended’’
structure I was applied (Fig. 1). However, it is common in the com-
putational study of biologically active compounds also use avail-
able structural data obtained from X-ray crystallography as
guides to the quality of theoretical computations. Thus, as a second
conformer for calculations we took the ‘‘sandwich-like’’ conformer
II, Fig. 1 resulted from the experimental X-ray data of the crystal
structure of I-3ÁHCl discussed in the previous paragraph. Important
geometric parameters of hydrochloride salt of the N-(4-diethyla-
minoethoxybenzyl)benzene-1,4-bis(sulfonamide) and protonated
species are given in Tables 3 and 4. The hydrochloride salt was con-
sidered as 1:1 complex of base I-3 with hydrochloric acid. HCl
bridges basic N(3) nitrogen atom by means of proton transfer
hydrogen bond of the N+–HÁ Á ÁCl– type (Table 4). In the solid state
the I-3ÁHCl salt exists as stable sandwich-like conformer which
is, besides hydrogen bonds, also stabilized by interatomic contacts
resulting from the aromatic-aromatic interaction. Thus, the disper-
sion interaction may also play important part in stabilization of
stable conformation of this salt in the gas state. The relative ener-
gies of individual conformations of the I-3, I-3ÁHCl, protonated and
ionized I-3 species with respect to the most stable conformers
computed for the gas phase and solvated molecules are reported
in Table 6. Owing to the different accounting of nonbonding inter-
actions the optimized geometry of hydrochloride I-3 using B3LYP
and B97D functionals differs considerably, especially in the values
of selected dihedral angles describing the mutual position of the
4. Conclusions
This study was set out to synthesize, determine stable confor-
mations, study solvent effect, acidity and basicity of aromatic sul-
fonamide, potent inhibitor of carboanhydrase and its
hydrochloride salt for which a relatively small amount of experi-
mental and theoretical physicochemical data exist, considering
its biological importance. Using the experimental and theoretical
methods the following conclusions can be drawn.
(1) In the solid state the 3D structure of I-3ÁHCl provides the
sandwich-like conformer in which both aromatic rings are
almost in parallel arrangement. Examination of X-ray data
showed that the proton resides on the base, it means that
the proton transfer has occurred and the crystalline complex
of I-3ÁHCl is a salt.
(2) According to the density functional calculations using B97D
Grimme’s functional including dispersion the ‘‘sandwich-
like’’ conformer II is the most stable species also in the gas
phase and in water solution. The B3LYP functional calcula-
tions prefer extended conformer I in both gas phase and in
water. The ‘‘sandwich-like’’ conformation II is less stable
by 11.6 kJ/mol.
two aromatic ring moieties (dihedral angles
U[C(8)–C(7)–N(2)–
S(2)] and [C(7)–N(2)–S(2)–C(4)]). In the solid state this com-
U
pound possesses a unique sandwich-like structure (conformer II).
According to the density functional calculations using B97D Grim-
me’s functional including dispersion the conformer II is the most
stable species also in the gas phase and/or in water solution. The
B3LYP functional calculations prefer extended conformer I in both
gas phase and in water. The ‘‘sandwich-like’’ conformation II is less
stable by 11.6 kJ/mol (Table 6). The same ordering of stability of
two conformations resulting from calculations was also observed
for base N-(4-diethylaminoethoxybenzyl)benzene-1,4-bis(sulfon-
amide) (I-3). Protonation of the basic N3 nitrogen atom of I-3 re-
sults in an appreciable stabilization of the ‘‘sandwich-like’’
conformer II. As regards of anionic species initial geometry of con-
former I converged to the conformer II (B97D functional). Con-
former II resulted also from B3LYP calculations as the most
stable species (Table 6). As it was shown previously [52] for correct
theoretical description of interactions in complex molecules like
DNA using the DFT method the study may include the ability to
treat covalent and dispersion interactions along with treatment
of solvent effects. Thus, the B97D Grimme’s functional including
dispersion and treatment of solvent effects within a CPCM model
represents more realistic description of conformational behavior
of N-(4-diethylaminoethoxybenzyl)benzene-1,4-bis(sulfonamide)
studied by us. Treatment of solvent effect within B3LYP and
B97D functionals produced a different relative energy stability of
the species studied (Table 6). The B3LYP method shows that rela-
tive stability of both conformers in water is almost the same. How-
ever, the application of the DFT method including dispersion
(3) The calculated gas-phase acidity and basicity are conforma-
tionally dependent and low, indicating that I-3 behaves as a
weak acid and/or base. In the condensed phase the diethyl-
amino nitrogen atom of the parent base I-3 is principal basic
center with the computed pKa = 8.87, and is at physiological
pH = 7.4 slightly protonated. Two sulfonamide NH groups
are slightly acidic (the computed pKa = 9.18 and 10.14 for
terminal -SO2NH2 and central –SO2NH– moieties, respec-
tively) and provide hydrogen bond donors.
Supplementary data
Crystallographic data for the molecule I-3ÁHCl have been depos-
ited at the Cambridge Crystallographic Data Center with the depo-
sition number CCDC 966739. Copy of the data can be obtained free
of charge via External link http://ccdc.cam.ac.uk/retrieving.html.
Acknowledgments
This work was supported by the Science and Technology Assis-
tance Agency (Contract No. APVV-0202-10) and the Slovak Grant
Agency VEGA (Contracts Nos. 1/0679/11 and 1/0634/13).

M. Remko et al. / Journal of Molecular Structure 1059 (2014) 124–131
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