Structural and spectroscopic studies of a new 2-naphthylmethyl ester of lasalocid acid

Article abstract of DOI:10.1016/j.molstruc.2008.07.024

A new lasalocid 2-naphthylmethyl ester (NAFB) has been synthesised and studied by X-ray, ¹H NMR, ¹³C NMR, FT-IR, UV-vis, fluorescence-spectroscopy as well as by the PM5 semiempirical method. The crystals of NAFB are monoclinic, space

Full text of DOI:10.1016/j.molstruc.2008.07.024

Journal of Molecular Structure 918 (2009) 108–115
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Structural and spectroscopic studies of a new 2-naphthylmethyl ester
of lasalocid acid
a
a
a
a
´
Adam Huczynski , Izabela Paluch , Małgorzata Ratajczak-Sitarz , Andrzej Katrusiak ,
Bogumil Brzezinski a, , Franz Bartl
b
*
a Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
b Institute of Medical Physics and Biophysics Charité, Universitätsmedizin Berlin Campus, Charité Mitte, Ziegelstr. 5/9, 10117 Berlin, Germany
a r t i c l e i n f o
a b s t r a c t
A new lasalocid 2-naphthylmethyl ester (NAFB) has been synthesised and studied by X-ray, 1H NMR, 13
C
Article history:
Received 16 June 2008
Accepted 21 July 2008
Available online 3 August 2008
NMR, FT-IR, UV–vis, fluorescence-spectroscopy as well as by the PM5 semiempirical method. The crystals
of NAFB are monoclinic, space group P21 with a = 10.120(2) Å, b = 18.245(3) Å, c = 12.354(3) Å,
b = 109.65(3ꢀ) and Z = 2. The molecular conformation of NAFB in the solid state is stabilized by three intra-
molecular hydrogen bonds, and no intermolecular H-bonds are formed. The FT-IR spectrum of NAFB in
chloroform indicates equilibrium between two NAFB conformers. In the first conformer the keto group
forms an intramolecular hydrogen bond, while in the second one this group is not involved in any hydro-
gen bonds. The two structures of NAFB are calculated by the PM5 method and discussed in detail.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Ionophores
Lasalocid ester
X-ray
Spectroscopic methods
PM5 calculation
1. Introduction
2. Experimental
Ionophores are biologically interesting groups of compounds
capable of transporting various cations across biological mem-
branes [1–11]. Lasalocid isolated from Streptomyces lasaliensis is a
representative of these compounds. It has important and useful
biological activities such as the growth inhibition of the Gram-
positive bacteria and the effective control of coccidiosis in
chickens, beef and cattle [12–17].
Recently, some esters of lasalocid, in particular those with poly-
oxaalkyl chains or aromatic substituents have been synthesised
and their structures have been studied by different methods [18–
24]. According to the results of these papers, the increasing length
of the oxaalkyl chains of the respective derivatives results in an en-
hanced effectiveness of the complexation process of the monova-
lent cations. For the esters with aromatic substituents no
influence of these rings on the complexation process was observed.
Crucial points for the biological activity of these compounds are
molecular conformation and intermolecular interactions. In this
paper we report the structures of a new lasalocid 2-naphthyl-
methyl ester (Scheme 1) in the solid state and in the solution as
elucidated by X-ray crystallography, FT-IR, 1H NMR, 13C NMR,
UV–vis, fluorescence-spectroscopy and PM5 methods.
2.1. Preparation lasalocid 2-naphthylmethyl ester (NAFB)
Lasalocid sodium salt was extracted from Avatec (Fa. Spezialfut-
ter Neuruppin). It was dissolved in dichloromethane and stirred
vigorously with
a layer of diluted aqueous sulphuric acid
(pH = 1.5). The organic layer containing lasalocid acid was washed
with distilled water. Subsequently dichloromethane was evapo-
rated under reduced pressure to dryness.
A
mixture
of
2-(bromomethyl)naphthalene
(221 mg,
1.00 mmol, Fluka), LAS (500 mg, 0.85 mmol) and 1,8-diazabicy-
clo[5.4.0]undec-7-en (DBU) (130 mg, 0.85 mmol) and 40 ml tolu-
ene was heated at 90 °C for 5 h. After cooling, the precipitate
DBU-hydrobromide (DBUꢀHBr) was filtered and washed with hex-
ane. Hexane was evaporated under reduced pressure and the resi-
due was purified by chromatography on silica gel (Fluka type 60)
yielding NAFB (343 mg, 55% yield, m.p. 97 °C). The crystals of NAFB
were obtained by crystallization from dried acetonitrile solutions.
Elemental analysis: Calculated: C 73.94%; H 8.55%, Found:
C 73.79%; H 8.71%.
2.2. X-ray measurements
The crystals selected for single-crystal X-ray diffraction mea-
surements formed colourless parallelepipeds with well-developed
faces. They were stable under normal conditions and the X-ray
diffraction measurements were carried out on a Kuma KM-4 CCD
* Corresponding author. Tel.: +48 618291330.
E-mail address: bbrzez@main.amu.edu.pl (B. Brzezinski).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.07.024

´
109
A. Huczynski et al. / Journal of Molecular Structure 918 (2009) 108–115
Table 2
40
Atomic coordinates (ꢂ 104) and equivalent isotropic displacement parameters
41
39
38
(Å2 ꢂ 103)
x
y
z
U(eq)
42
37
45
43
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
8201(4)
10064(5)
10340(4)
7268(3)
4225(3)
6779(4)
9560(4)
10259(3)
8988(8)
8528(7)
9249(6)
8861(8)
7753(8)
7047(6)
7391(7)
6539(4)
7358(4)
6489(5)
6039(5)
5056(5)
4515(5)
4365(5)
5863(6)
6147(6)
7682(5)
7922(6)
9314(5)
9444(5)
10842(5)
11167(6)
10923(5)
12061(4)
12671(5)
13066(6)
7651(7)
8712(8)
5679(5)
3534(5)
2018(5)
3720(4)
7312(5)
9754(6)
8707(6)
8023(10)
8668(6)
7923(12)
8586(8)
7856(15)
6423(16)
5695(16)
5908(10)
6602(13)
6528(12)
7764(2)
7839(3)
6950(2)
7555(2)
8329(2)
8618(2)
8778(2)
7381(2)
7536(4)
6822(3)
6576(4)
5938(4)
5556(3)
5776(3)
6414(3)
6549(2)
6308(2)
6344(3)
7114(3)
7167(2)
7961(3)
8256(3)
8323(3)
8832(3)
8998(3)
9045(3)
8677(3)
7881(3)
7599(2)
7766(3)
8600(3)
9130(2)
7504(4)
7735(4)
9828(3)
10269(4)
8454(4)
8999(3)
8910(3)
6647(2)
5950(2)
5693(3)
8428(3)
9091(4)
9525(4)
10197(4)
10632(6)
11264(5)
11355(8)
10935(6)
9830(7)
9220(5)
10269(5)
3421(4)
5016(4)
6625(3)
530(2)
ꢁ456(3)
ꢁ1324(3)
411(4)
1509(2)
4434(6)
4773(6)
5931(6)
6363(6)
5688(7)
4539(6)
4087(5)
2840(4)
2024(4)
729(4)
112(1)
182(2)
140(2)
83(1)
90(1)
83(1)
86(1)
93(1)
98(2)
78(2)
35
36
44
31
15
O(2)
O(1)
1
32
12
O
O
33
30
29
8
2
16
HO
O(3)
3
7
13
11
14
10
17
9
28
21
93(2)
34
H3C
OH
O(4)
O
O
6
4
18
100(2)
108(2)
108(2)
76(2)
83(2)
77(1)
68(1)
70(1)
73(1)
73(2)
84(2)
92(2)
103(2)
113(2)
85(2)
76(2)
89(2)
88(2)
83(2)
O(5)
27
20
O(6)
5
19
O(7)
O
26
23
C(9)
25
22
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
C(41)
C(42)
C(43)
C(44)
C(45)
24
OH
335(4)
O(8)
ꢁ924(4)
ꢁ1144(5)
ꢁ2365(4)
ꢁ2393(5)
ꢁ3302(5)
ꢁ2782(5)
ꢁ1477(5)
ꢁ770(5)
ꢁ1025(4)
ꢁ227(5)
1032(5)
1169(4)
978(4)
1733(5)
2890(5)
ꢁ1071(7)
ꢁ1074(7)
ꢁ4514(5)
ꢁ2585(4)
ꢁ2691(4)
ꢁ1219(3)
61(4)
7618(4)
3034(4)
3362(7)
4233(6)
4443(8)
5346(7)
5509(9)
4740(12)
3936(11)
2865(9)
2637(8)
3758(9)
Scheme 1. The structures and atom numbering of NAFB.
diffractometer at 296 K. The structure was solved by direct meth-
ods [25] and refined by full-matrix least-squares [26]. The positions
of all H-atoms were determined on the basis of the molecular
geometry (C–H 0.93–0.98, O–H 0.82 Å) and recalculated after each
refinement cycle. Uiso’s were related to the thermal vibrations of
their carriers. The absolute conformation of NAFB in the crystal
was consistent with the chemical information. Selected details
about the crystal structure, experiment and structure solution
and refinement are given in Table 1. The fractional atomic coordi-
nates are listed in Table 2. The crystallographic-information-file
(CIF) has been deposited at the Cambridge Crystallographic Data-
base Centre as a Supplementary Publication No. CCDC 688478.
92(2)
119(2)
143(2)
167(3)
174(3)
291(5)
174(3)
111(2)
138(2)
90(2)
102(2)
157(3)
141(3)
93(2)
2.3. NMR measurements
The NMR spectra were recorded in CDCl3 using a Varian Gemini
300 MHz spectrometer. All spectra were locked to deuterium reso-
94(2)
Table 1
103(2)
150(3)
200(5)
225(7)
221(7)
166(4)
145(4)
112(2)
Crystal data and structure refinement
Empirical formula
Formula weight
C45H62O8
730.95
Temperature (K)
293(2)
Wavelength (Å)
0.71073
Crystal system, space group
Monoclinic, P21
Unit cell dimensions
a (Å)
10.120(2)
U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
b (Å)
c (Å)
18.245(3)
12.354(3)
109.65(3)
2148.2(8)
nance of CDCl3. The error in ppm values was 0.01. All 1H NMR mea-
surements were carried out at the operating frequency
300.075 MHz; flip angle, pw = 45°; spectral width, sw = 4500 Hz;
acquisition time, at = 2.0 s; relaxation delay, d1 = 1.0 s; T = 293.0 K
and TMS as the internal standard. No window function or zero fill-
ing was used. Digital resolution was 0.2 Hz/point. 13C NMR spectra
were recorded at the operating frequency 75.454 MHz; pw = 60°;
sw = 19,000 Hz; at = 1.8 s; d1 = 1.0 s; T = 293.0 K and TMS as the
internal standard.
b (ꢀ)
Volume (Å3)
Z
2
Calculated density (g cmꢁ3
)
1.130
0.076
792
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm)
h Range for data collection (°)
Limiting indices
Reflections collected/unique
Completeness to h = 29.85 (%)
Refinement method
0.30 ꢂ 0.20 ꢂ 0.075
2.14–29.85
ꢁ13 6 h 6 13, ꢁ23 6 k 6 24, ꢁ17 6 l 6 16
29,068/10,641 Rint = 0.1206
90.7
The 1H and 13C NMR signals were assigned independently for
each species using one or two-dimensional (COSY, HETCOR) spectra.
Full-matrix least-squares on F2
10641/1/478
Data/restraints/parameters
Goodness-of-fit on F2
0.796
2.4. FT-IR measurements
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0494, wR2 = 0.0480
R1 = 0.3316, wR2 = 0.0626
ꢁ0.4(9)
Absolute structure parameter
In the mid infrared region the FT-IR spectra of NAFB were
recorded in chloroform solution and potassium bromide in the
Largest diff. peak and hole (e Åꢁ3
)
0.224 and ꢁ0.204

´
110
A. Huczynski et al. / Journal of Molecular Structure 918 (2009) 108–115
Table 3 (continued)
Table 3
Bond lengths (Å) and angles (°)
C(7)–C(8)–C(9)
C(10)–C(9)–C(8)
111.5(4)
114.4(4)
115.0(4)
112.3(4)
108.3(4)
108.6(4)
111.4(4)
114.0(4)
107.9(4)
107.2(4)
113.9(4)
124.1(5)
121.8(5)
114.1(5)
105.9(4)
113.8(4)
109.7(4)
110.3(4)
102.8(4)
119.2(5)
103.2(5)
115.7(5)
110.9(5)
103.5(4)
107.9(4)
104.6(4)
111.0(5)
102.3(5)
116.2(5)
113.6(5)
110.3(4)
109.8(5)
115.6(5)
108.7(5)
115.7(4)
112.2(4)
105.4(4)
110.3(5)
106.6(4)
108.7(4)
113.6(5)
107.8(4)
110.9(4)
115.5(4)
111.4(6)
108.6(8)
113.2(4)
109.5(4)
121.8(8)
123.6(8)
114.6(9)
119.4(7)
124.7(10)
118.9(11)
115.9(8)
117.2(9)
116.9(12)
129(2)
O(1)–C(1)
O(1)–C(35)
O(2)–C(1)
1.305(6)
1.457(5)
1.218(6)
1.335(5)
1.432(4)
1.194(5)
1.439(4)
1.460(5)
1.408(4)
1.420(5)
1.431(5)
1.490(8)
1.393(6)
1.442(6)
1.391(6)
1.346(6)
1.574(6)
1.416(6)
1.385(5)
1.511(5)
1.569(5)
1.546(5)
1.506(5)
1.534(5)
1.541(5)
1.540(6)
1.590(4)
1.561(6)
1.532(5)
1.569(5)
1.557(6)
1.499(5)
1.571(6)
1.550(5)
1.540(5)
1.568(7)
1.501(5)
1.516(5)
1.508(6)
1.551(6)
1.562(6)
1.580(5)
1.413(6)
1.343(8)
1.504(4)
1.515(7)
1.319(6)
1.435(9)
1.506(7)
1.349(8)
1.387(7)
1.420(9)
1.451(13)
1.274(13)
1.536(13)
1.337(8)
1.394(9)
C(11)–C(10)–C(33)
C(11)–C(10)–C(9)
C(33)–C(10)–C(9)
O(4)–C(11)–C(10)
O(4)–C(11)–C(12)
C(10)–C(11)–C(12)
C(13)–C(12)–C(11)
C(13)–C(12)–C(32)
C(11)–C(12)–C(32)
O(5)–C(13)–C(12)
O(5)–C(13)–C(14)
C(12)–C(13)–C(14)
C(15)–C(14)–C(13)
C(15)–C(14)–C(30)
C(13)–C(14)–C(30)
O(6)–C(15)–C(14)
O(6)–C(15)–C(16)
C(14)–C(15)–C(16)
C(17)–C(16)–C(15)
C(17)–C(16)–C(29)
C(15)–C(16)–C(29)
C(16)–C(17)–C(18)
O(6)–C(18)–C(19)
O(6)–C(18)–C(17)
C(19)–C(18)–C(17)
O(6)–C(18)–C(27)
C(19)–C(18)–C(27)
C(17)–C(18)–C(27)
O(7)–C(19)–C(20)
O(7)–C(19)–C(18)
C(20)–C(19)–C(18)
C(19)–C(20)–C(21)
C(22)–C(21)–C(20)
O(8)–C(22)–C(21)
O(8)–C(22)–C(25)
C(21)–C(22)–C(25)
O(8)–C(22)–C(23)
C(21)–C(22)–C(23)
C(25)–C(22)–C(23)
O(7)–C(23)–C(22)
O(7)–C(23)–C(24)
C(22)–C(23)–C(24)
C(26)–C(25)–C(22)
C(28)–C(27)–C(18)
C(31)–C(30)–C(14)
O(1)–C(35)–C(36)
C(37)–C(36)–C(44)
C(37)–C(36)–C(35)
C(44)–C(36)–C(35)
C(36)–C(37)–C(38)
C(39)–C(38)–C(45)
C(39)–C(38)–C(37)
C(45)–C(38)–C(37)
C(38)–C(39)–C(40)
C(39)–C(40)–C(41)
C(42)–C(41)–C(40)
C(41)–C(42)–C(45)
C(45)–C(43)–C(44)
C(43)–C(44)–C(36)
C(43)–C(45)–C(38)
C(43)–C(45)–C(42)
C(38)–C(45)–C(42)
O(3)–C(3)
O(4)–C(11)
O(5)–C(13)
O(6)–C(15)
O(6)–C(18)
O(7)–C(19)
O(7)–C(23)
O(8)–C(22)
C(1)–C(2)
C(2)–C(7)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(4)–C(34)
C(5)–C(6)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
C(10)–C(33)
C(11)–C(12)
C(12)–C(13)
C(12)–C(32)
C(13)–C(14)
C(14)–C(15)
C(14)–C(30)
C(15)–C(16)
C(16)–C(17)
C(16)–C(29)
C(17)–C(18)
C(18)–C(19)
C(18)–C(27)
C(19)–C(20)
C(20)–C(21)
C(21)–C(22)
C(22)–C(25)
C(22)–C(23)
C(23)–C(24)
C(25)–C(26)
C(27)–C(28)
C(30)–C(31)
C(35)–C(36)
C(36)–C(37)
C(36)–C(44)
C(37)–C(38)
C(38)–C(39)
C(38)–C(45)
C(39)–C(40)
C(40)–C(41)
C(41)–C(42)
C(42)–C(45)
C(43)–C(45)
C(43)–C(44)
112.7(19)
121.1(11)
118.1(10)
123.1(9)
117.7(13)
118.9(11)
C(1)–O(1)–C(35)
C(15)–O(6)–C(18)
C(19)–O(7)–C(23)
O(2)–C(1)–O(1)
O(2)–C(1)–C(2)
O(1)–C(1)–C(2)
C(7)–C(2)–C(3)
C(7)–C(2)–C(1)
C(3)–C(2)–C(1)
O(3)–C(3)–C(4)
O(3)–C(3)–C(2)
C(4)–C(3)–C(2)
C(5)–C(4)–C(3)
C(5)–C(4)–C(34)
C(3)–C(4)–C(34)
C(4)–C(5)–C(6)
C(7)–C(6)–C(5)
C(6)–C(7)–C(2)
C(6)–C(7)–C(8)
C(2)–C(7)–C(8)
114.3(6)
112.0(4)
116.6(4)
123.9(7)
122.3(7)
113.6(7)
118.5(6)
124.6(7)
116.7(6)
117.4(8)
120.8(6)
121.8(6)
118.7(7)
123.1(7)
118.2(7)
120.6(6)
122.2(6)
118.1(6)
114.4(6)
127.2(6)
form of pellets. A cell with Si windows and wedge-shaped layers
was used to avoid interferences (mean layer thickness 170 m).
The spectra were taken with an IFS 113v FT-IR spectrophotometer
(Bruker, Karlsruhe) equipped with a DTGS detector; resolution
2 cm–1, NSS = 64. The Happ–Genzel apodization function was used.
l
2.5. UV–vis and fluorescence measurements
The absorption spectra of LAS and NAFB were recorded in 1 cm
cells on a Jasco V-550 spectrophotometer (JASCO, Tokyo, Japan).

´
111
A. Huczynski et al. / Journal of Molecular Structure 918 (2009) 108–115
Table 4 (continued)
Table 4
Selected torsion angles (°)
O(8)–C(22)–C(25)–C(26)
C(21)–C(22)–C(25)–C(26)
C(23)–C(22)–C(25)–C(26)
O(6)–C(18)–C(27)–C(28)
C(19)–C(18)–C(27)–C(28)
C(17)–C(18)–C(27)–C(28)
C(15)–C(14)–C(30)–C(31)
C(13)–C(14)–C(30)–C(31)
C(1)–O(1)–C(35)–C(36)
O(1)–C(35)–C(36)–C(37)
O(1)–C(35)–C(36)–C(44)
C(35)–C(36)–C(37)–C(38)
C(35)–C(36)–C(44)–C(43)
ꢁ66.0(7)
172.7(5)
50.3(7)
174.7(7)
57.5(9)
ꢁ73.2(9)
173.3(4)
ꢁ68.2(5)
ꢁ93.1(7)
103.2(6)
ꢁ77.4(6)
176.3(5)
ꢁ178.5(6)
C(35)–O(1)–C(1)–O(2)
C(35)–O(1)–C(1)–C(2)
O(2)–C(1)–C(2)–C(7)
O(1)–C(1)–C(2)–C(7)
O(2)–C(1)–C(2)–C(3)
O(1)–C(1)–C(2)–C(3)
C(7)–C(2)–C(3)–O(3)
C(1)–C(2)–C(3)–O(3)
C(1)–C(2)–C(3)–C(4)
ꢁ0.7(9)
ꢁ174.9(4)
ꢁ173.0(6)
1.3(7)
12.5(8)
ꢁ173.2(5)
ꢁ179.6(5)
ꢁ4.7(7)
176.5(5)
179.1(5)
ꢁ1.6(7)
O(3)–C(3)–C(4)–C(5)
O(3)–C(3)–C(4)–C(34)
C(2)–C(3)–C(4)–C(34)
C(34)–C(4)–C(5)–C(6)
C(5)–C(6)–C(7)–C(8)
C(1)–C(2)–C(7)–C(6)
C(3)–C(2)–C(7)–C(8)
C(1)–C(2)–C(7)–C(8)
C(6)–C(7)–C(8)–C(9)
C(2)–C(7)–C(8)–C(9)
177.2(4)
ꢁ175.7(5)
178.9(5)
ꢁ177.0(5)
ꢁ176.6(4)
9.0(8)
The UV–vis spectra of LAS and NAFB (1 ꢂ 10ꢁ5 mol dmꢁ3) were
recorded for these compounds in spectral–grade. The intensity of
fluorescence emission was measured for LAS and NAFB at the angle
90° relative to the incident excitation light. During the absorption
and fluorescence measurements the samples were kept at room
temperature. The samples were excited at 260 nm. The fluores-
cence quantum yield of NAFB was estimated from the equation:
ꢁ98.8(5)
75.4(6)
C(7)–C(8)–C(9)–C(10)
C(8)–C(9)–C(10)–C(11)
C(8)–C(9)–C(10)–C(33)
C(33)–C(10)–C(11)–O(4)
C(9)–C(10)–C(11)–O(4)
C(33)–C(10)–C(11)–C(12)
C(9)–C(10)–C(11)–C(12)
O(4)–C(11)–C(12)–C(13)
C(10)–C(11)–C(12)–C(13)
O(4)–C(11)–C(12)–C(32)
C(10)–C(11)–C(12)–C(32)
C(11)–C(12)–C(13)–O(5)
C(32)–C(12)–C(13)–O(5)
C(11)–C(12)–C(13)–C(14)
C(32)–C(12)–C(13)–C(14)
O(5)–C(13)–C(14)–C(15)
C(12)–C(13)–C(14)–C(15)
O(5)–C(13)–C(14)–C(30)
C(12)–C(13)–C(14)–C(30)
C(18)–O(6)–C(15)–C(14)
C(18)–O(6)–C(15)–C(16)
C(13)–C(14)–C(15)–O(6)
C(30)–C(14)–C(15)–O(6)
C(13)–C(14)–C(15)–C(16)
C(30)–C(14)–C(15)–C(16)
O(6)–C(15)–C(16)–C(17)
C(14)–C(15)–C(16)–C(17)
O(6)–C(15)–C(16)–C(29)
C(14)–C(15)–C(16)–C(29)
C(15)–C(16)–C(17)–C(18)
C(29)–C(16)–C(17)–C(18)
C(15)–O(6)–C(18)–C(19)
C(15)–O(6)–C(18)–C(17)
C(15)–O(6)–C(18)–C(27)
C(16)–C(17)–C(18)–O(6)
C(16)–C(17)–C(18)–C(19)
C(16)–C(17)–C(18)–C(27)
C(23)–O(7)–C(19)–C(20)
C(23)–O(7)–C(19)–C(18)
O(6)–C(18)–C(19)–O(7)
C(17)–C(18)–C(19)–O(7)
C(27)–C(18)–C(19)–O(7)
O(6)–C(18)–C(19)–C(20)
C(17)–C(18)–C(19)–C(20)
C(27)–C(18)–C(19)–C(20)
O(7)–C(19)–C(20)–C(21)
C(18)–C(19)–C(20)–C(21)
C(19)–C(20)–C(21)–C(22)
C(20)–C(21)–C(22)–O(8)
C(20)–C(21)–C(22)–C(25)
C(20)–C(21)–C(22)–C(23)
C(19)–O(7)–C(23)–C(22)
C(19)–O(7)–C(23)–C(24)
O(8)–C(22)–C(23)–O(7)
C(21)–C(22)–C(23)–O(7)
C(25)–C(22)–C(23)–O(7)
O(8)–C(22)–C(23)–C(24)
C(21)–C(22)–C(23)–C(24)
C(25)–C(22)–C(23)–C(24)
173.2(4)
63.3(5)
ꢁ168.7(3)
ꢁ63.8(5)
60.6(5)
61.0(5)
ꢀ
ꢁ
2
AR FS nS
ꢁ174.6(3)
ꢁ65.1(5)
171.7(4)
176.1(3)
52.8(5)
US
¼
UR
ꢃ
ꢃ
FR
AS
nR
where
U
R is the quantum yield of the standard, A is the absorbance
at the wavelength of the excitation, F is the integrated intensity of
ꢁ37.5(6)
85.6(6)
142.7(4)
ꢁ94.3(4)
112.1(6)
ꢁ68.0(5)
ꢁ11.1(7)
168.7(4)
ꢁ149.4(4)
ꢁ21.3(5)
ꢁ41.4(5)
79.2(5)
ꢁ159.9(5)
ꢁ39.3(7)
35.4(5)
157.6(5)
159.8(4)
ꢁ77.9(6)
ꢁ35.8(5)
ꢁ157.0(5)
ꢁ118.9(5)
ꢁ0.7(6)
118.0(5)
23.4(6)
139.4(5)
ꢁ87.4(5)
63.6(5)
ꢁ167.8(4)
ꢁ70.6(5)
175.4(4)
43.5(6)
54.9(6)
ꢁ59.1(6)
169.1(5)
ꢁ52.5(5)
ꢁ177.8(4)
50.2(5)
67.6(5)
ꢁ175.3(4)
ꢁ50.1(6)
ꢁ62.1(5)
65.2(5)
ꢁ69.5(5)
51.7(5)
174.9(4)
165.9(4)
ꢁ72.9(5)
50.3(7)
Fig. 1. (a) A perspective view of NAFB in the crystal structure. Hydrogen bonds have
been indicated by dashed lines; (b) The structures of NAFB without the engagement
of the C@O carbonyl group in hydrogen bond (type A), calculated by semiempirical
PM5 method (WinMopac 2003).

´
A. Huczynski et al. / Journal of Molecular Structure 918 (2009) 108–115
112
the emission spectra, n is the refractive index of solution, the index
(S) means sample and (R) means reference. The standard fluoro-
phore for the quantum yield measurements was Quinine sulphate
crystal. In this conformation the carbonyl group C@O(5) is not in-
volved in any hydrogen bonds, which is consistent with the bal-
ance of H-donors and H-acceptors in this structure, and with the
close location of O(5) to the potential donor hydroxyl group –
O(4)H. Due to their close location the potential O(4)HꢃꢃꢃO(5) bond
would be strongly strained. However the formation of the
O(4)HꢃꢃꢃO(5) bond is possible and would considerably change the
molecular conformation as has been shown by the semiempirical
calculations presented below (Section 3.5). There are no strong
intermolecular hydrogen bonds in this crystal structure (Fig. 3
and Table 5).
in 0.2 mol dmꢁ3 H2SO4 R = 0.51) [27].
(U
2.6. Semiempirical calculations
PM5 semiempirical calculations were performed using the
WinMopac 2003 program. In all cases full geometry optimisation
of NAFB was carried out without any symmetry constraints [28–
32].
2.7. Elemental analysis
3.2. NMR measurements
The 1H and 13C NMR data of NAFB are collected in Table 6. In the
1H NMR spectrum of NAFB in CDCl3 solution the most significantly
shifted signal at 11.47 ppm is assigned to the donor proton of the
O(3)H group at the salicylic ring involved in the intramolecular
O(3)HꢃꢃꢃO(2)@C hydrogen bond. The signal of the O(4)H and
The elemental analysis of NAFB was carried out on Vario ELIII
(Elementar, Germany).
2.8. Melting point
Corrected melting point was determined on a Mettler FP900.
3. Results and discussion
The structures and the numbering of the atoms of NAFB are
shown in Scheme 1.
3.1. X-Ray structure analysis
NAFB crystallizes as a non-solvate in acetonitrile solution. The
molecular dimensions (Table 3) fully confirm the chemical formula
of the substance. Three intramolecular hydrogen bonds are charac-
teristic of all the NAFB structures (Table 5). The very short
O(3)ꢃꢃꢃO(2) bond (Table 4) is likely to stabilize the nearly coplanar
conformation of the C(1)O(1)O(2) group and phenyl ring C(2–7).
This hydrogen bond is resonance assisted in the system of conju-
gated
p-electron bonds. A considerable distortion of planarity –
the torsion angle O(2)C(1)C(2)C(3) is 12.5(8)° (Table 4) – is due
to the overcrowding effect, as also testified by the strongly bent
OHꢃꢃꢃO angle. The other hydrogen bonds, between O(8)HꢃꢃꢃO(4)H
and O(4)HO(6) groups are considerably longer. The intramolecular
hydrogen bonds, O(3)HꢃꢃꢃO(2), O(4)HꢃꢃꢃO(6) and O(8)HꢃꢃꢃO(4), are
strong stabilizing effects of the molecular conformation in the
Fig. 3. Arrangement of complex NAFB in the crystal lattice, projected along the
[100] crystal direction.
Table 5
The parameters (length and angle) of intramolecular hydrogen bonds of NAFB
determined from X-ray studies and calculated by PM5 semiempirical method
Used method
Compound
Atoms engaged in
hydrogen bonds
Length
(Å)
Angle
(°)
X-ray
NAFB(type
O(3)ꢁHꢃꢃꢃO(2)
O(8)ꢁHꢃꢃꢃO(4)
O(4)ꢁHꢃꢃꢃO(6)
2.509(6)
2.874(4)
2.912(4)
149
165
179
A
– crystal)
PM5
NAFB(type
O(3)ꢁHꢃꢃꢃO(2)
O(8)ꢁHꢃꢃꢃO(4)
O(4)ꢁHꢃꢃꢃO(6)
2.60
2.85
2.95
145
160
171
A)
NAFB(type
O(3)ꢁHꢃꢃꢃO(2)
O(8)ꢁHꢃꢃꢃO(4)
O(4)ꢁHꢃꢃꢃO(5)
2.60
2.84
2.90
145
127
149
B)
(type A), structure of NAFB in which the C(13)@O group is not engaged in hydrogen
bond.
Fig. 2. The structures of NAFB with the engagement of the C@O carbonyl group in
hydrogen bond (type B) calculated by the semiempirical PM5 method (WinMopac
2003).
(type B), structure of NAFB in which the C(13)@O group is engaged in hydrogen
bond.

´
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A. Huczynski et al. / Journal of Molecular Structure 918 (2009) 108–115
the geminal (2J) spin–spin coupling (Fig. 4). This kind of coupling
indicates that both protons are located in different electronic envi-
Table 6
1H NMR and 13C NMR chemical shifts (ppm) of NAFB in CDCl3
No. atom
1H NMR
13C NMR
ronments and
observed.
a typical AB spin–spin coupling structure is
1
2
3
4
5
6
7
8
9
–
–
–
–
171.80
111.06
160.86
124.04
135.16
121.76
143.63
34.04
36.37
33.71
71.46
49.26
215.05
54.70
85.01
35.04
39.22
85.81
73.33
20.94
29.98
70.50
76.57
14.05
29.34
6.41
The most interesting signals in the 13C NMR spectrum of NAFB
are those of C(1) and C(3) carbon atoms, which suggest the exis-
tence of enol and/or ketol tautomeric forms of the lasalocid esters.
These signals arise at 171.80 ppm and 160.86 ppm, respectively,
indicating that NAFB exists in solution predominantly in the enol
form as shown in Scheme 1.
7.16
6.65
–
2.81
1.44–1.68
1.18
3.43
2.72
–
2.70
3.77
2.20
1.51–1.81
–
3.78
1.42–1.64
1.36–1.42
–
3.76
1.16
1.58
0.88
1.29
0.80
1.00
1.34–1.81
0.66
0.55
0.84
2.21
5.56
–
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
O(3)H
O(4)H
O(8)H
3.3. FT-IR measurements
In Fig. 5a and b, the spectra of NAFB in chloroform (dashed line)
and in KBr (solid line) are compared. In the spectrum of NAFB in
KBr only one band assigned to the m(OH) vibrations of O(4)H and
O(8)H groups is observed at 3448 cmꢁ1 indicating that these OH
groups form relatively weak hydrogen bonds of comparable
strength. This observation is in good agreement with the X-ray
structure of NAFB. The vibration of the proton in the intramolecu-
lar O–HꢃꢃꢃO@C hydrogen bond, which is the strongest of all hydro-
gen bonds should be observed in the FT-IR spectrum in the region
below 3000 cmꢁ1. However, this absorption does appear very
clearly neither in the NAFB solid state spectrum nor in the spec-
trum of chloroform solution. The reason for the low intensity of
this absorption is probably a strong coupling of the proton motion
30.61
8.45
in the intramolecular hydrogen bond with the
p-electrons within
15.97
18.21
12.23
12.94
12.68
15.86
67.61
133.22
133.14
133.14
128.28
127.67
126.30
127.67
128.54
127.47
132.52
–
the pseudo-aromatic structure which results in a loss of proton
polarizability [33].
In the spectrum of NAFB in chloroform solution a broad band
with a maximum at about 3443 cmꢁ1 and a new weak one at about
3580 cmꢁ1 are observed (Fig. 5a, dashed line). The latter band indi-
cates that in chloroform solution one of the weak hydrogen bonds
is partially broken. This indicates that the structure of NAFB under-
goes slight changes in solution as compared to the solid state. A
similar conclusion can be drawn from the spectra in the region of
7.91
–
ꢄ7.85
7.49
7.55
ꢄ7.85
ꢄ7.85
7.47
–
11.47
3.28
3.28
the
trum of the solid state (solid line) exhibits only one band at
1715 cmꢁ1 assigned to the
(C@O) vibrations of C(13)@O group.
m(C@O) vibrations (Fig. 5b). It is obvious, that the NAFB spec-
m
However, in chloroform solution the intensity of this band de-
creases and an additional shoulder at 1702 cmꢁ1 arises. The exis-
tence of the shoulder at 1702 cmꢁ1 indicates that in chloroform
solution the keto C(13)@O group becomes partially hydrogen-
bonded. This supports the statement that the solution structure
of NAFB is slightly different compared to the solid state structure.
Furthermore, the band characteristic of the ester group at about
1650 cmꢁ1 seems to be unchanged in both states.
–
–
O(8)H protons arises as one broadened signal at 3.28 ppm indicating
that both protons are involved in relatively weak hydrogen bonds.
The signals of the naphthalene ring protons are found in the
range between 7.47–7.91 ppm, whereas the C(5)H and C(6)H pro-
ton signals of the salicylic moiety arise as two doublets at 7.16 and
6.65 ppm, respectively (Fig. 4). The signal of the methylene group
protons is observed at 5.56 ppm as a doublet of doublets due to
3.4. UV–vis and fluorescence studies
The absorption and emission spectra of NAFB are shown in
Fig. 6 and the spectral characteristics are given in Table 7. In the
Fig. 4. 1H NMR spectrum of NAFB in region of aromatic proton signals.

´
114
A. Huczynski et al. / Journal of Molecular Structure 918 (2009) 108–115
100
50
0
a
3443
3448
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber [cm
]
b
100
50
0
1711
1652
1702
1715
1800
1750
1700
1650
1600
1550
-1
Wavenumber [cm
]
Fig. 5. FT-IR spectra of NAFB: (—) in KBr pallet, (- - -) in chloroform: (a) 4000–400 cmꢁ1; (b) 1800–1550 cmꢁ1
.
absorption spectrum of NAFB an intense band at 226 nm together
with less intense satellite bands in the region 260–350 nm are ob-
served (Fig. 6 left, solid line). The absorption maxima at 274 and
1.0
0.5
0.0
1.0
0.5
0.0
286 nm in the UV–vis spectrum of NAFB is caused by p–
p* transi-
tions in the naphthalene ring. The respective spectrum of lasalocid
acid is less structured. Only three bands with maxima at 215 nm,
248 nm and 318 nm (Fig. 6, dashed line) are observed. The fluores-
cence spectrum of NAFB shows a band with a maximum at ca.
378 nm (kexc = 260 nm) (Fig 6 right, solid line). In the fluorescence
emission spectrum of lasalocid acid this band is shifted to 381 nm
(kexc = 260 nm) (Fig 6 right, dashed line). The quantum yield of the
fluorescence emission of lasalocid acid was calculated to be
U
= 0.15, which is quite high. Note that the salicylic acid moiety
of the lasalocid molecule actively contributes to the emission
[34]. In contrast, the new 2-naphthylmethyl ester of lasalocid acid
shows a two orders of magnitude lower quantum yield of fluores-
cence (Table 7), which indicates an influence of the carboxylic
group on this process.
200
250
300
350
400
450
500
Wavelength [nm]
Fig. 6. Absorption (left) and emission corrected spectra (right) of: NAFB (—) and LAS
(- - -).
3.5. PM5 calculations
Table 7
UV–vis and fluorescence spectral characteristics of NAFB
On the basis of the spectroscopic as well as X-ray results, the
structure of NAFB (type A) was calculated by the PM5 semiempir-
ical method and compared to the crystal structure (Fig. 1). The
hydrogen bond parameters of NAFB are collected in Table 5 to-
gether with the respective X-ray data. On the basis of the spectro-
scopic observations the respective structure of NAFB was
calculated (type B structure, Fig. 2). In this structure the C(13)@O
is involved in the formation of an intramolecular hydrogen bond.
The calculated hydrogen bond parameters for the type A struc-
ture are comparable with those determined by the X-ray method,
although these two methods describe two different states, i.e. the
UV–vis
Fluorescence
kexc (nm)
260
kmax (nm)
Log
e
kem (nm)
U
228.0
250.0
274.5
286.0
318.5
4.41
4.15
3.80
3.70
3.73
378
3.7 ꢂ 10ꢁ2
kmax
, maximum of the absorption band; e, molar extinction coefficient
(dmꢁ3 molꢁ1 cmꢁ1); kexc, excitation wavelength; kem, maximum of the fluorescence
band;
[27].
U, quantum yield of fluorescence relative to Quinine sulphate in 0.1 N H2SO4

´
115
A. Huczynski et al. / Journal of Molecular Structure 918 (2009) 108–115
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method is a reliable tool for visualization of structures also in the
solid state.
The structure of NAFB (B type) is stabilized by the formation of
three intramolecular hydrogen bonds that cause the formation of
two different parts of the ester molecule (Table 5). One part includes
the salicylic group and is stabilized by the O(3)ꢃꢃꢃO(2) intramolecular
hydrogen bond. The rest of the molecule is stabilized by two O(8)–
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Acknowledgement
´
Dr. Adam Huczynski wishes to thank the Foundation for Polish
Science for a fellowship.
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