Studies on the interaction of phosphate anions with N-functionalised polyaza[n]paracyclophanes: The role of N-methylation

Article abstract of DOI:10.1039/b315717b

The synthesis and interaction of N,N′ N″ ,N?- tetramethyl-2,6,9,13-tetraaza[14]paracyclophanes (B323Me₄) with nucleotides and inorganic phosphates is described. An easy methodology is used to define thermodynamic selectivity. The interaction of

Full text of DOI:10.1039/b315717b

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Studies on the interaction of phosphate anions with
N-functionalised polyaza[n]paracyclophanes:
the role of N-methylation
M Teresa Albelda,a Juan C. Frías,b Enrique García-España*a and Santiago V. Luis*b
a Departamento de Química Inorgánica, Universitat de València, Dr. Moliner 50,
46100 Burjassot (Valencia), Spain. E-mail: enrique.garcia-es@uv.es
b Departamento de Química Inorgánica y Orgánica. U. A. de Materiales Orgánicos Avanzados,
Universitat Jaume I-CSIC, Castellón, Spain. E-mail: luiss@mail.uji.es
Received 4th December 2003, Accepted 2nd February 2004
First published as an Advance Article on the web 18th February 2004
The synthesis and interaction of N,NЈ,NЉ,Nٞ-tetramethyl-2,6,9,13-tetraaza[14]paracyclophanes (B323Me4) with
nucleotides and inorganic phosphates is described. An easy methodology is used to define thermodynamic selectivity.
The interaction of B323Me4 and ATP has been monitored by 1H, 31P NMR and by molecular mechanics, ruling out
the possibility of the participation of π-stacking interactions. Results show that N-methylation is accompanied by a
strong increase in the interaction of the resulting macrocycle with ATP.
Polyazacyclophanes are versatile molecules able to complex
either organic or inorganic substrates.1 The presence of nitro-
gen donor atoms provides a way for the interaction with transi-
tion metal cations, but, at the same time, those receptors are
able to strongly interact with anions in their protonated forms.
On the other hand, the aromatic spacer plays an essential role
increasing the hydrophobicity of the site, incorporating poten-
tial π interactions and precluding the involvement of all the
nitrogen donors in the coordination to a single metal center. In
polyazamacrocycles, the presence of nitrogen atoms facilitates
the introduction of a variety of different arms through their
N-functionalisation. Tuning the nature of the N-attached arms,
for example introducing carboxylic arms or hydrophobic sub-
stituents, represents a simple way to improve selectivity towards
some given guests and to incorporate specific activities, so we
can consider those macrocycles as molecules with smart func-
tions.2 During the last years, there has been an increasing inter-
est in the study and complexation of anionic species, according
to the fact that a large number of the substances and cofactors
engaged in biological processes are anions.3 In this context,
polyaza[n]paracyclophanes have shown interesting properties in
their interaction with different anions.4
modification of conformational equilibria can strongly affect
the expected interaction of this receptor with different guests.
In this work, we have focused our attention on the interaction
of B323Me4 (2) with the nucleotides ATP, ADP and AMP and
the inorganic anions pyrophosphate and tripolyphosphate.
Results and discussion
Synthesis of receptors
The synthesis of the precursor polyaza[n]paracyclophane
(B323, 1) was carried out according to literature procedures.1a
Permethylation of this polyazamacrocycle was obtained using
an Eschweiler–Clarke procedure,6 affording quantitative yields
of 2 (see Scheme 1).
The same synthetic procedure was used to prepare, also in
quantitative yields, other N-methylated macrocycles such as
B222Me4 (4) and D222Me4 (6) from B222 (3) and D222 (5)
(see Chart 1).
Here we report on the synthesis and on the interaction
studies of N,NЈ,NЉ,Nٞ-tetramethyl-2,6,9,13[14]paracyclophane
(B323Me4) with different organic and inorganic phosphate
anions. The interaction of polyazamacrocycles with phosphate
anions is of great interest due to the important role that
phosphates play in biological processes.5 N-Methylation of
B323 can provide important differences in the properties of
B323Me4 with regards to the parent macrocycle. The increase
in hydrophobicity, the changes in acid–base properties and the
Chart 1
Scheme 1 Synthesis of B323Me4: i) K2CO3, CH3CN; ii) Na/Hg, Na2HPO4; iii) HCOOH, H2CO.
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2, 8 1 6 – 8 2 0
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
816

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Table 1 Logarithms of the stepwise protonation constants for the protonation of different polyazacyclophanesa
Reactionb
B323Me4
B323
D323
D323Me4
B222
B222Me4
H ϩ L = HL
H ϩ HL = H2L
H ϩ H2L = H3L
H ϩ H3L = H4L
Log β
8.99 (3)c
8.22 (3)
6.59 (3)
3.69 (4)
27.49
9.93d
9.09
7.44
3.61
30.07
10.54e
9.32
7.44
3.59
30.89
11.15 (4)
9.12 (4)
7.34 (4)
3.84 (5)
31.45
9.39 (2)
8.45 (2)
5.38 (2)
2.51 (1)
25.73
9.07 (4)
7.96 (4)
3.88 (4)
<2.0
<22.91
a Determined in 0.15 mol dmϪ3 NaCl at 298.1 K. b Charges omitted for clarity. c Values in parentheses are standard deviations in the last significant
figure. d Taken from reference 1b. e Taken from reference 10.
Table 2 Logarithms of the stepwise stability constants for the interaction of B323Me4 (2) with different nucleotides and phosphate anionsa
Reactionb
ATP
ADP
AMP
PYR
TPP
H4L ϩ H2A = H6LA
H3L ϩ H2A = H5LA
H3L ϩ HA = H4LA
H2L ϩ HA = H3LA
H3L ϩ A = H3LA
HL ϩ HA = H2LA
H2L ϩ A = H2LA
HL ϩ A = HLA
5.40 (4)c
6.10 (3)
5.59 (3)
—
5.39 (3)
—
3.94 (3)
4.69 (3)
4.53 (2)
—
4.42 (3)
—
—
3.83 (5)
3.98 (5)
4.15 (3)
4.04 (3)
—
—
3.97 (3)
3.70 (4)
4.10 (4)
4.35 (4)
4.40 (4)
4.19 (4)
—
4.22 (4)
4.18 (4)
3.76 (6)
3.71 (5)
4.32 (2)
—
4.44 (3)
—
4.08 (3)
3.82 (4)
4.73 (2)
4.24 (4)
4.01 (1)
3.67 (3)
a Determined in 0.15 mol dmϪ3 NaCl at 298.1 K. b Charges omitted for clarity. c Values in parentheses are standard deviations in the last significant
figure.
Scheme 2 Preferential protonation sites for the successive protonation steps.
Protonation studies
ational factors that could make minimisation of electrostatic
repulsion difficult, clearly compensate for the favourable elec-
tronic effects provided by the introduction of methyl groups on
the nitrogen atoms
Acid–base properties of compound 2 were studied by the use
of pH-metric titrations, as the first step for the analysis of its
properties as a receptor. All the titrations were carried out as
has been fully described,7 at 298.1 K using NaCl 0.15 M to
maintain a constant ionic strength. The program PASAT was
used for data acquisition.8 The program HYPERQUAD was
employed for the analysis of those data and stability con-
stant calculations, and the program HYSS was used to obtain
the distribution diagrams.9 The stability constants for the pro-
tonation of B323Me4 obtained in this way are presented in
Table 1. For comparison, the stability constants for the proton-
ation of related polyazacyclophanes 1 and 3–6 have been also
included.10
As can be seen in the table, stepwise protonation constants
for B323Me4 follow similar trends to those found for related
receptors such as B323,7,10 with the presence of two large con-
stants for the two first protonation steps, an intermediate one
and a smaller one corresponding to the last protonation step.
The N-methylation is accompanied by a slight decrease in the
basicity of B323Me4 as compared with that of B323. This
decrease in basicity affects the first three protonation steps and
is not very important for the last one. The same is true for the
receptor B222Me4, for which the value of the global basicity
constant is about 2.5 logarithmic units smaller than that for
B222. Only in the case of D323Me4 is the basicity comparable
with that of the parent compound D323. In this case, the first
protonation constant is larger for D323Me4 than for any other
of the macrocycles in Table 1. It has to be taken into account
that D323 itself contains four methyl groups on the aromatic
subunit. According to the former data, the increase in hydro-
phobicity that accompanies N-methylation, and conform-
In the case of B323Me4, 1H and 13C NMR spectra at variable
pH give information about its average protonation (see Scheme
2).11 For instance, the benzylic protons experience a significant
downfield shift from pH 12 to 4, the region corresponding to
the uptake of the first two protons, remaining essentially
unchanged at lower pH values. On the contrary, the downfield
shift for the protons of the central ethylene bridge is more pro-
nounced between pH 4 and 2, the region involving the third and
fourth protonation steps. These NMR data suggest that the
first two protonation steps mainly affect the benzylic nitrogen
atoms. The same results can be obtained by the use of 15N
NMR spectroscopy, the signal of the benzylic nitrogens being
essentially shifted downfield (from Ϫ340 to Ϫ335 ppm)
between pH 12 and 4.12
According to those data, N-methylation of B323 does not
produce significant changes on the protonation scheme of the
resulting macrocycle.10 The same seems to apply to the other
N-methylated macrocycles prepared (4 and 6).
Anion binding studies
The interaction of B323Me4 with ATP, ADP, AMP, pyrophos-
phate and tripolyphosphate was also studied by pH-metric
titrations. Table 2 gathers the stability constants, determined at
298.1 K in 0.15 mol dmϪ3 NaCl, for the species formed in those
systems.
Several features regarding the speciation and the stability of
those interactions deserve discussion. First of all, the stoichio-
metries found for the adducts formed in all systems are always
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2, 8 1 6 – 8 2 0
817

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Table 3 Logarithms of the stepwise stability constants for the inter-
action of ATP with B323 and B323Me4.a
1 : 1. The protonation degrees of the adducts vary from 1 to 6
for all the species except in the case of AMP for which only
pentaprotonated species are formed. Since the receptor and the
anions themselves participate in several protonation equilibria
that are often overlapped, care has to be taken in order to
decide which are the right stepwise equilibria involved in the
formation of a given adduct species. To overcome this problem,
first of all, one has to consider which are the relevant basicity
equilibria for the host and the guest at the pH value for the
formation of a given species.13 Considering all these factors, the
stepwise stability constants shown in Table 2 can be proposed as
the most feasible ones for the interaction of B323Me4 with ATP,
ADP, AMP, pyrophosphate (PYR) and tripolyphosphate
(TPP). In the case of TPP, for the H2LA species a clear-cut
separation cannot be made and this species would be formed
either by the reaction of HL and HA or H2L and A with
percentages of participation that would depend on pH.
Reactionb
B323
B323Me4
H4L ϩ H2A = H6LA
H3L ϩ H2A = H5LA
H3L ϩ HA = H4LA
H3L ϩ A = H3LA
H2L ϩ A = H2LA
HL ϩ A = HLA
3.82 (1)c
4.08 (1)
3.39 (1)
2.58 (2)
—
5.50 (4)
6.10 (3)
5.59 (3)
5.39 (3)
4.73 (2)
4.24 (4)
—
a Determined in 0.15 mol dmϪ3 NaCl at 298.1 K. b Charges omitted for
clarity. c Values in parentheses are standard deviations in the last signifi-
cant figure.
However using the conditional stability constants a simpler
picture of the situation defined according to the following
equation can be attained.13
logKs = Σ[Hi ϩ jAL]/Σ[HiA]Σ[HjL]
(1)
Fig.
2
Representation of the values of the logarithms for the
conditional stability constants for the interaction of ATP with
This procedure permits a straightforward comparison of the
different systems and obtainment of the appropriate selectivity
ratios, at the different pH values, just by dividing the corre-
sponding conditional constants. Fig. 1 shows the plots of the
conditional stability constants vs. pH for the different phos-
phate anions. In such a graphic, it can be seen that ATP is the
substrate exhibiting the largest conditional constants through-
out the entire pH range. At acidic pH values, AMP is the
species showing the lowest interaction. At basic pH values,
AMP, ADP, PYR and TPP present similar conditional con-
stants. In order to explain this trend, the charge of the anions
must be the most relevant factor. From the data in Fig. 1,
quantitative selectivity ratios can be obtained. Thus, for
instance, at pH 4, ligand 2 is 65, 52 and 19 times more selective
for ATP than for TPP, AMP and ADP, respectively.
B323Me4 (black) and B323 (magenta).
We have made use of 1H and 31P nuclear magnetic resonance
spectroscopy and molecular mechanics calculations to study
the interaction of B323Me4 with ATP, in order to better under-
1
stand this behaviour. As has been described before, H NMR
spectra of the macrocycle displays significant changes in the
aliphatic region upon protonation (see Fig. 3). One of the main
features for the spectrum of the fully protonated receptor is the
presence of a broad band corresponding to the benzylic pro-
tons at 4.57 ppm. This can be assigned to a slow rotation of the
polynitrogenated chain around the macrocycle.14 Addition of
1 mol of ATP is accompanied by substantial changes in the
signals corresponding to the macrocycle. The benzylic band
at 4.57 splits into two broad signals at 4.26 and 4.72 ppm.
The same happens for the signal corresponding to the central
methylene of the propylenic groups, which is split into two
broad signals at 1.99 and 2.25 ppm. This strongly suggests a
clear differentiation of the two sides of the macrocyclic plane
upon interaction with ATP. A general broadening of the other
aliphatic signals is observed and they appear overlapped at 2.9–
3.5 ppm. A very significant broadening is also found for the
aromatic signal that only experiences a minor change in its
chemical shift. If the signals corresponding to ATP are con-
Fig.
1
Representation of the values of the logarithms for the
conditional stability constants for the interaction of B323Me4 with
different phosphate anions: ATP-red; ADP-green; PYR-black; TPP-
blue; AMP-magenta.
The former data allow an evaluation of the influence of
N-methylation in the interaction of polyazamacrocycles with
anions. Table 3 gathers the stepwise stability constants obtained
for the interaction of B323 and B323Me4 with ATP.
As it can be seen, the permethylated receptor (2) has stability
constants that are always two orders of magnitude larger than
the corresponding ones for the parent B323 (1). Accordingly,
although B323Me4, taking into account the data in Table 1, is
less basic than B323, it interacts much more strongly with ATP
species. Fig. 2 shows the plots of the conditional stability con-
stants (calculated using eqn. 1) vs. pH for the interaction of
B323 and B323Me4 with ATP. From those data, it can be
inferred that selectivity ratios range from ca. 30000 at basic pH
values to 50 at acidic pH values, reaching a value of about 100
at the neutral region.
Fig.
3
1H NMR spectra for ATP, B323Me4 and the complex
B323Me4–ATP formed at acidic pH values (pH = 1.6).
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2, 8 1 6 – 8 2 0
818

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sidered, it can be seen that only minor changes occur, with the
observation of a slight downfield shift for the protons of the
sugar moiety (∆δ < 0.2 ppm). The aromatic signals of ATP
remain essentially unchanged. The former observations seem to
rule out the existence of π-stacking interactions between the
adenine fragment of the ATP and the aromatic subunit of
B323Me4.
Conclusions
The present results clearly show how very minor structural
changes can have a large influence in defining the nature and the
strength of the interaction of protonated polynitrogenated
receptors with anions of biological relevance, in this case ATP.
In the present work, it has been observed that N-methylation of
B323 (1) is a very favourable feature when the interaction with
ATP is considered. The resulting receptor, B323Me4 (2), is very
selective for ATP over other phosphate anions such as ADP,
AMP, PYR or TPP, with conditional constants, measured in
water, being one to two orders of magnitude larger for ATP.
When B323Me4 is compared with B323, it can be seen that
N-methylation is accompanied by an increase in the corre-
sponding conditional constants of at least two orders of magni-
tude over the entire range of pH. These results can be related
with the observations reported by different authors regarding
the improvement in DNA–receptor interaction with the use of
polynitrogenated macrocycles containing alkyl chains.16 Appar-
ently, the increase in hydrophobicity can play a significant role.
The lower ligand solvation is likely to contribute to the higher
affinity constants observed as a consequence of the energetic-
ally less expensive desolvation.
The interaction ATP–B323Me4 was also followed by 31P
NMR. As can be seen in Fig. 4, small changes in the chemical
shifts of the three phosphorous atoms are observed along with
a significant broadening of the three signals. This suggest that
the three phosphate groups would be involved in the binding to
the fully protonated B323Me4, even if the Pα could be involved
at a lower extent. The large broadenings found can be explained
through the existence of several complexes in equilibrium,
but with the interaction taking place from a single side of the
macrocyclic plane.
Experimental
General synthetic procedure for the preparation of permethylated
polyaza[n]paracyclophanes.
Synthesis of N,NЈ,NЉ,Nٞ-tetramethyl-2,6,9,13-tetraaza[14]-
paracyclophane (B323Me4, 2)
Compound 1 (0.13 g, 0.48 mmol) was dissolved in a mixture
of formic acid (0.78 g, 13.55 mmol), formaldehyde (0.57 g,
6.19 mmol) and water (0.05 mL). The resulting solution was
stirred and heated under reflux for 48 h and then cooled in an
ice bath. The solution was then basified with NaOH until pH >
12 and extracted with CH2Cl2 (3 × 30 mL). The organic phase
was dried and the solvent vacuum evaporated at reduced pres-
Fig. 4 31P NMR spectra for ATP and its complex with B323Me4.
The use of molecular modelling was very helpful in rational-
izing the former observations. Molecular mechanics calcu-
lations were carried out using the program MACROMODEL
5.0 with the AMBER force field, as implemented in this pack-
age, and with a GB/SA simulation of water as the solvent.15 The
minimum energy conformer found from calculations agrees
very well with the experimental data obtained by NMR
experiments.
The calculated structure is depicted in Fig. 5 and shows how
all the phosphate groups interact with the ammonium groups
of the receptor on one side of the plane of the macrocyclic ring.
Nevertheless, according to its location and to the calculated
distances to the nearest ammonium groups, the Pα phosphate
group should interact less strongly than the other two. At the
same time, the aromatic adenine subunit is located far away
from the aromatic spacer of the polyazacyclophane. Calcu-
lations also show the existence of several structures related to
the one displayed in Fig. 5, very close in energy and differing
only in minor conformational changes.
1
sure to give an oily product (0.158 g, 99%). H NMR (CDCl3,
δ ppm): 1.28 (m, 4H), 1.96 (s, 6H), 1.97–2.22 (m, 12H), 2.26 (s,
6H), 3.40 (s, 4H), 7.24 (s, 4H). 13C NMR (CDCl3, δ ppm): 26.6,
45.8, 46.9, 54.9, 56.3, 58.4, 65.2, 139.2, 140.4. MS (ESI)-
(M ϩ H): 333. This compound was stored as its hydrobromide
and the elemental analysis was obtained from the correspond-
ing salt. Calc. for C20H36N4ؒ4HBrؒH20: C, 36.6; H, 6.1; N, 8.5.
Found: C, 36.6; H, 6.3; N, 8.6%.
N,NЈ,NЉ,Nٞ-Tetramethyl-2,5,8,11-tetraaza[12]paracyclophane
(B222Me4, 4)
99% Yield. 1H NMR (CDCl3, δ ppm): 1.89 (s, 4H), 2.02 (s, 6H),
2.00–2.25 (m, 8H), 2.27 (s, 6H), 3.46 (s, 4H), 7.29 (s, 4H). 13C
NMR (CDCl3, δ ppm): 45.6, 47.7, 54.2, 55.2, 57.1, 65.2, 133.6,
140.7. MS (ESI)(M ϩ H): 305. This compound was stored as a
hydrobromide and the elemental analysis was obtained from
the corresponding salt. Calc. for C18H32N4ؒ4HBrؒ5H20: C, 34.4;
H, 5.7; N, 8.9. Found: C, 34.3; H, 5.9; N, 9.0%.
N,NЈ,NЉ,Nٞ-Tetramethyl-16,17,19,20-tetramethyl-2,5,8,11-
tetraaza[12]paracyclophane (D222Me4, 6)
1
99% Yield. H NMR (CDCl3, δ ppm): 1.96 (s, 4H), 2.05 (m,
4H), 2.12–2.24 (m ϩ s, 10H), 2.31 (s, 12H), 2.39 (s, 6H), 3.62 (s,
4H). 13C NMR (CDCl3, δ ppm): 16.8, 44.1, 44.7, 51.4, 52.3,
55.9, 56.8, 134.0, 134.6. MS (ESI)(M ϩ H): 361. Elemental
analyses always gave inconsistent results with this compound.
Emf measurements
The potentiometric titrations were carried out at 298.1 0.1 K
using 0.15 mol dmϪ3 NaCl as a supporting electrolyte. The
Fig. 5 Minimum energy conformer calculated for the interaction of
tetraprotonated B323Me4 with ATP.
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2, 8 1 6 – 8 2 0
819

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(i) K. Sato, T. Onitake, S. Arai and T. Yamagishi, Heterocycles, 2003,
60, 779.
experimental procedure (burette, potentiometer, cell, stirrer,
microcomputer, etc.) has been fully described elsewhere.7 The
acquisition of the emf data was performed with the computer
program PASAT.8 The reference electrode was a Ag/AgCl
electrode in saturated KCl solution. The glass electrode was
calibrated as a hydrogen-ion concentration probe by titration
of previously standarised amounts of HCl with CO2-free
NaOH solutions and the equivalent point was determined by
the Gran method,17 which gives the standard potential, EЊЈ, and
the ionic product of water (pKw = 13.73(1)).
The computer program HYPERQUAD was used to calculate
the protonation and stability constants.9 The pH range investi-
gated was 2.5–10.5. The different titration curves for each
system (at least two) were treated either as a single set or as
separated curves without significant variations in the values of
the stability constants. Finally, the sets of data were merged
together and treated simultaneously to give the final stability
constants.
2 E. Kimura, Tetrahedron, 1992, 48, 6175.
3 (a) Supramolecular Chemistry of Anions, eds. A. Bianchi,
K. Bowman-James, E. García-España, Wiley, New York, 1997;
(b) P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed., 2001, 40, 486;
(c) J. M. Llinares, D. Powell and K. Bowman-James, Coord. Chem.
Rev., 2003, 240, 57.
4 (a) J. A. Aguilar, E. García-España, J. A. Guerrero, S. V. Luis, J. M.
Llinares, J. F. Miravet, J. A. Ramirez and C. Soriano, J. Chem. Soc.,
Chem. Commun., 1995, 2237; (b) M. I. Burguete, E. García-España,
S. V. Luis, J. F. Miravet, L. Payá, M. Querol and C. Soriano, Chem.
Commun., 1998, 1823; (c) M. I. Burguete, S. V. Luis, J. F. Miravet,
M. Querol and E. García-España, Chem. Commun., 1999, 649;
(d ) C. Bazzicaluppi, A. Bencini, A. Bianchi, M. Cechi, B. Escuder,
V. Fusi, E. García-España, C. Giorgi, S. V. Luis, G. Maccagni,
V. Marcelino, P. Paoletti and B. Valtancoli, J. Am. Chem. Soc., 1999,
121, 6807; (e) J. A. Aguilar, B. Celda, E. García-España, S. V. Luis,
M. C. Martinez, J. A. Ramirez, C. Soriano and R. Tejero, J. Chem.
Soc., Perkin Trans. 2, 2000, 1323; ( f ) P. Arranz, A. Bencini,
A. Bianchi, P. Diaz, E. García-España, C. Giorgi, S. V. Luis,
M. Querol and B. Valtancoli, J. Chem. Soc., Perkin Trans. 2, 2001,
1765.
NMR measurements
5 For biological phosphate receptors see: (a) H. Luecke and F. A.
Quiocho, Nature, 1990, 347, 402; (b) J. J. He and F. A. Quiocho,
Science, 1991, 251, 1497 For synthetic receptors see:; (c) F. P.
Schmidtchen, A. Gleich and A. Schummer, Pure Appl. Chem., 1989,
61, 1535; (d ) E. Kimura, Y. Kuramoto, T. Koike, H. Fujioka and
M. Kodama, J. Org. Chem., 1990, 55, 42; (e) D. A. Nation,
J. Reibenpies and A. E. Martell, Inorg. Chem., 1996, 35, 4597;
( f ) K. Metori and M. Miyaka, Heterocycles, 2003, 60, 1441; (g) H. J.
Schneider, L. Tianjun and N. Lomazde, Angew. Chem., Int. Ed.,
2003, 42, 3544.
The 1H, 13C and 31P spectra were recorded on VARIAN
MERCURY 300 and VARIAN INOVA 500 spectrometers,
1
operating at 300 and 500 MHz for H, 75.43 and 125.75 MHz
for 13C, and 121.44 and 202.40 MHz for 31P. The 15N spectra
were measured on a VARIAN INOVA 500 spectrometer
equipped with a 5 mm, tunable, broadband, inverse-detection
probe at 50.7 MHz.12
6 (a) J. C. Frias, Ph. D. Thesis University Jaume I, 2000;
(b) W. Eschweiler, Ber., 1905, 38, 880; (c) H. T. Clarke, H. B.
Gillespie and S. Z. Wisshaus, J. Am. Chem. Soc., 1933, 55, 4571.
7 E. García-España, M.-J. Ballester, F. Lloret, J.-M. Moratal, J. Faus
and A. Bianchi, J. Chem. Soc., Dalton Trans, 1988, 101.
8 M. Fontanelli, M. Micheloni, Proceedings of the I Spanish-Italian
Congress on Thermodynamics of Metal Complexes, Diputación de
Castellón, Spain, 1990. Program for the automatic control of the
microburette and the acquisition of the electromotive force readings.
9 P. Gans, A. Sabatini and A. Vacca, Talanta, 1996, 43, 1739.
10 Stability constants for the protonation of macrocycles 1, 3 and 5
have been taken from: A. Bianchi, B. Escuder, E. García-España,
S. V. Luis, V. Marcelino, J. F. Miravet and J. A. Ramírez, J. Chem.
Soc., Perkin Trans. 2, 1994, 1253.
11 (a) A. K. Convington, M. Paabo, R. A. Robinson and R. G. Bates,
Anal. Chem., 1968, 40, 700; (b) J. E. Sarnesky, H. L. Surprenant,
F. K. Molen and C. N. Reiley, Anal. Chem., 1975, 47, 2116.J.
12 M. T. Albelda, M. I. Burguete, J. C. Frías, E. García-España,
S. V. Luis, J. F. Miravet and M. Querol, J. Org. Chem., 2001, 66,
7505–7510.
Molecular mechanics calculations
Calculations were carried out on a Silicon Graphics work-
station using the package of programs implemented in
MACROMODEL 5.0.15 Conformational searches were made
using the Monte-Carlo method in the automatic mode and with
standard parameters and cut-offs. At least three conform-
ational searches were used for each case under study using 1000
structures. Solvents were simulated using the continuous
method GB/SA as implemented in MACROMODEL.
Acknowledgements
This work has been supported by the Spanish Dirección
General de Enseñanza Superior (project BQU2003-0215) and
the Generalitat Valenciana (project CTIDIB/2002/244).
13 M. T. Albelda, M. A. Bernardo, E. García-España, M. L. Rodino-
Salido, S. V. Luis, M. J. Melo, F. Pina and C. Soriano, J. Chem.Soc.,
Perkin Trans. 2, 1999, 2545.
14 (a) M. I. Burguete, B. Escuder, E. García-España, S. V. Luis and
J. F. Miravet, J. Org. Chem., 1994, 59, 1067; (b) B. Altava, M. I.
Burguete, B. Escuder, E. García-España, S. V. Luis and C. Muñoz,
Tetrahedron, 1997, 53, 2629; (c) M. I. Burguete, B. Escuder, S. V.
Luis, J. F. Miravet, M. Querol and E. García-España, Tetrahedron
Lett., 1998, 39, 3799.
15 (a) F. Mohamadi, N. G. J. Richards, W. C. Guida, R. Liskamp,
G. Lipton, G. Chang, T. Hendrickson and W. C. Still, J. Comput.
Chem., 1990, 11, 440; (b) W. C. Still, A. Tempczyk, R. C. Hawley and
T. Hendrickson, J. Am. Chem. Soc., 1990, 112, 6127; (c) For the use
of this program for related systems see: M. I. Burguete, M. Bolte,
J. C. Frías, E. García-España, S. V. Luis and J. F. Miravet,
Tetrahedron, 2002, 58, 4179.
16 J. W. Sibert, A. H. Cory and J. G. Cory, Chem. Commun., 2002, 154.
17 (a) G. Gran, Analyst (London), 1952, 77, 881; (b) F. J. Rossotti and
H. Rossotti, J. Chem. Educ., 1965, 42, 375.
References and notes
1 (a) A. Bencini, M. I. Burguete, E. García-España, S. V. Luis,
J. F. Miravet and C. Soriano, J. Org. Chem., 1993, 58, 4749;
(b) A. Andrés, M. I. Burguete, E. García-España, S. V. Luis,
J. F. Miravet and C. Soriano, J. Chem.Soc., Perkin Trans. 2, 1993,
749; (c) A. Andrés, M. I. Burguete, B. Escuder, J. C. Frías, E. García-
España, S. V. Luis and J. F. Miravet, J. Org. Chem., 1998, 63, 1810;
(d ) S. Andrés, B. Escuder, A. Domenech, E. García-España, S. V.
Luis, V. Marcelino, J. M. Llinares, J. A. Ramirez and C. Soriano,
J. Phys. Org. Chem., 2001, 14, 495; (e) M. I. Burguete, B. Escuder,
E. García-España, L. López, S. V. Luis, J. F. Miravet and M. Querol,
Tetrahedron Lett., 2002, 1817; ( f ) M. B. Inoue, M. Inoue, R. Sugich-
Miranda, L. Machi, E. F. Velazquez and Q. Fernando, Inorg. Chim.
Acta, 2001, 317, 181; (g) M. A. Heuft and A. G. Fallis, Angew.
Chem., Int. Ed., 2002, 41, 4520; (h) S. E. Gibson, J. O. Jones, S. B.
Kalindjian, J. D. Knight, J. W. Steed and M. J. Tozer, Chem.
Commun., 2002, 1938; Y. Yuan, G. Gao, Z. L. Jiang, J. S. You, Z. Y.
Zhou, D. Q. Yuan and R. G. Xie, Tetrahedron, 2002, 58, 8993;
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2, 8 1 6 – 8 2 0
820