Synthesis, spectroscopic, structural and theoretical characterization of hydrogensquarate and mononuclear Au(III)-complex of dipeptide phenylalanyltyrosine

Article abstract of DOI:10.1016/j.molstruc.2007.10.015

The mononuclear Au(III)-complex ([Au(C₁₈H₁₈N₂O₄)Cl]) and hydrogensquarate ([C₂₂H₂₁N₂O₈]) of dipeptide phenylalanyltyrosine (H-Phe-Tyr-OH) have been synthezised, characterized spectroscopically and structurally by means of solid-state linear-polarized IR-spectroscopy, ¹H- and ¹³C-NMR, ESI-MS, HPLC-MS-MS, FAB-MS, TGS and DSC methods. The structure of the Au(III)-complex has been predicted theoretically by DFT calculations. The dipeptide coordinated in a tridentate manner via -NH₂, -COO^- and N^--groups. One Cl^- ion is attached to the metal centre as a terminal ligand, yielding a planar AuN₂OCl chromophor. The hydrogensquarate consists in positive charged dipeptide moiety and negative one hydrogensquarate (HSq^-) anion stabilizing by strong intermolecular hydrogen bonds.

Full text of DOI:10.1016/j.molstruc.2007.10.015

Available online at www.sciencedirect.com
Journal of Molecular Structure 885 (2008) 104–110
www.elsevier.com/locate/molstruc
Synthesis, spectroscopic, structural and theoretical characterization
of hydrogensquarate and mononuclear Au(III)-complex
of dipeptide phenylalanyltyrosine
a,
b,c
a
d
*
Bojidarka B. Koleva , Tsonko Kolev , Sonya Y. Zareva , Michael Spiteller
a Sofia University ‘‘St. Kl. Ohridsky’’, Faculty of Chemistry, Department of Analytical Chemistry, 1164 Sofia, Bulgaria
b Institute of Organic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. build. 9, 1113 Sofia, Bulgaria
c Plovdiv University ‘‘P. Hilendarski’’, Faculty of Chemistry, Department of Organic Chemistry, Plovdiv 4000, Bulgaria
d Institut fu¨r Umweltforschung, University of Dortmund, Otto-Hahn-Strasse 6, 44221 Dortmund, Germany
Received 3 June 2007; received in revised form 10 October 2007; accepted 17 October 2007
Available online 25 October 2007
Abstract
The mononuclear Au(III)-complex ([Au(C18H18N2O4)Cl]) and hydrogensquarate ([C22H21N2O8]) of dipeptide phenylalanyltyrosine
(H–Phe–Tyr–OH) have been synthezised, characterized spectroscopically and structurally by means of solid-state linear-polarized IR-
1
spectroscopy, H- and 13C-NMR, ESI-MS, HPLC-MS–MS, FAB-MS, TGS and DSC methods. The structure of the Au(III)-complex
has been predicted theoretically by DFT calculations. The dipeptide coordinated in a tridentate manner via –NH2, –COOꢀ and Nꢀ-
groups. One Clꢀ ion is attached to the metal centre as a terminal ligand, yielding a planar AuN2OCl chromophor. The hydrogensquarate
consists in positive charged dipeptide moiety and negative one hydrogensquarate (HSqꢀ) anion stabilizing by strong intermolecular
hydrogen bonds.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Solid-state linear-polarized IR-spectroscopy; 1H- and 13C-NMR; ESI-MS; HPLC-MS–MS; FABMS; TGS and DSC methods; H–Phe–Tyr–
OH dipeptide; Au(III)-complexes; Hydrogensquarate
1. Introduction
VLA-4 integring antagonists [10] or potassium channel
openers [11–13] have been also reported. These results have
been in the basis of our previous spectroscopic and struc-
tural studies of some optically active hydrogensquarate
derivatives of amino acids amides [8,9] as well as of
Au(III)-complexes and salts with aliphatic and aromatic
di- and tripeptides [14–19].
We now present a spectroscopic and theoretical charac-
terization of hydrogensquarate and Au(III)-complex of
dipeptide phenylalnyl–tyrosine (H–Phe–Tyr–OH) (Scheme 1)
by means of linear-polarized IR-LD spectroscopy of ori-
ented solid samples as a nematic liquid crystal suspension,
1H- and 13C-NMR, ESI-MS, HPLC-MS–MS, FAB-MS,
TGS and DSC methods. The theoretical DFT calculations
(B3LYP and Lanl2DZ (Au)/6-31+G(3df) (Cl, C, H)) using
polarization function alpha 0.2 and 1.2 (Au) is also demon-
strated, obtaining the structure of Au(III)-complex. As far
Au(III)-complexes and salts of amino acid derivatives
and peptides are of interest for a range of preparative
and pharmaceutical applications as potential anticancer
agents. Moreover, the investigations of complexation abil-
ity of these biological active compounds could be explained
the way for coordination of metals to DNA in living cell
[1–4]. Furthermore, the squaric acid salts with optically
active amino acid amides crystallized noncentrosymmetri-
cally and are of great interest for nonlinear optical and
electro optical application [5–9]. In last years the bioactiv-
ity of squaric acid and some derivatives as inhibitors and
*
Corresponding author.
E-mail address: BKoleva@chem.uni-sofia.bg (B.B. Koleva).
0022-2860/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.10.015

B.B. Koleva et al. / Journal of Molecular Structure 885 (2008) 104–110
105
O
O
O
OH
OH
H3N
NH
O
H3N
NH
O
O
OH
HO
×
O
O
H-Phe-Tyr-OH
H2Sq×H-Phe-Tyr-OH
Scheme 1. Chemical diagram of compounds studied.
as the exact structures of the Au(III)-complexes with pep-
tides are rare in the literature, only three structures with
dipeptide glycylhistidine: ([(Au(H–Gly–L–His–OH)Hꢀ1)-
Cl]Cl ꢁ 3H2O) and [(Au(H–Gly–L–His–OH)Hꢀ3)]4 ꢁ 10H2O
and with tripeptide glycylglycylhistidine: [(Au(H–Gly–
Gly–His–OH)Hꢀ2)]Cl ꢁ H2O are known [20,21], and any
studied, developing the new approaches for structural
information receiving in solid state are reasonable.
54.7° (magic angle), and negative ones corresponding to
transition moments between 54.7° and 90°. In the reduc-
ing-difference procedure, the perpendicular spectrum multi-
plied by the parameter c, is subtracted from the parallel one
and c is varied until at least one band or sets of bands are
eliminated. The simultaneous disappearance of these bands
in the reduced IR-LD spectrum (IRp–cIRs) obtained indi-
cates co-linearity of the corresponding transition moments,
thus yielding to information regarding the mutual disposi-
tion of the molecular fragments. This elimination method is
carried out graphically using a subtraction procedure
attached to the program for processing of IR spectra.
HPLC MS–MS measurements are made using TSQ
7000 (Thermo Electron Corporation) instrument under
the conditions presented in Table 1. Two flows were used:
(i) A–H2O and 0.1% HCOOH and (ii) B–CH3CN and 0.1%
HCOOH.
2. Experimental
2.1. Materials and methods
The dipeptide H–Phe–Tyr–OH (P99.00%) was pur-
chased from Bachem Organics (Switzerland) and was used
without further purification.
The 4000–400 cmꢀ1 solid-state IR-spectra were recorded
on a Bomem Michelson 100 FT-IR spectrometer (resolu-
tion 2 cmꢀ1, 150 scans) equipped with a Perkin-Elmer
wire-grid polarizer. The oriented solid samples were
obtained as a suspension in a nematic liquid crystal of
the 40-cyano-40-alkylbicyclohexyl type (ZLI 1695, Merck),
mesomorphic at room temperature. Its weak IR-spectrum
permits the recording of the guest-compound bands in
the whole 4000–400 cmꢀ1 range. The presence of an iso-
lated nitrile stretching IR-band at 2236 cmꢀ1 serves addi-
tionally as an orientation indicator. The effective
orientation of the samples was achieved through the fol-
lowing procedure: 5 mg of the compound to be studied
was mixed with the liquid crystal substance until a slightly
viscous suspension was obtained. The phase thus prepared
was pressed between two KBr-plates for which, in advance,
one direction had been rubbed out by means of fine sand-
paper. The grinding of the mull in the rubbing direction
promotes an additional orientation of the sample [15–19].
IR-LD spectroscopy and the interpretation of the linear-
polarized IR-spectra are described in [22–26]. The method
consists of subtraction of the perpendicular spectrum, (IRs,
resulting from a 90° angle between the polarized light beam
electric vector and the orientation of the sample) from the
parallel one (IRp) obtained with a co-linear mutual orienta-
tion. The recorded difference (IRp–IRs) spectrum divides
the corresponding parallel (Ap) and perpendicular (As)
integrated absorbencies of each band into positive values
originating from transition moments, which form average
angles with the orientation direction (n) between 0° and
The FAB mass spectra were recorded on a Fisons VG
autospect instrument employing 3-nitrobenzylalcohol as
matrix. The elemental analysis was carried out according
to the standard procedures for C and H (as CO2, and
H2O) and N (by the Dumas method). The thermogravimet-
ric study was carried out using a Perkin-Elmer TGS2
instrument. The calorimetry was performed on a DSC-2C
Perkin-Elmer apparatus under argon.
2.1.1. ESI mass spectrometry
A triple quadruple mass spectrometer (TSQ 7000
Thermo Electron, Dreieich, Germany) equipped with an
ESI 2 source was used and operated with the following
conditions: capillary temperature 180 °C; sheath gas
60 psi, corona 4.5 lA and spray voltage 4.5 kV. The sample
was injected in the ion source by an autosampler
(Surveyor) with a flow rate of 0.2 ml/min a pure acetoni-
trile. About 1 mg/ml of the sample was dissolved in aceto-
Table 1
HPLC-MS–MS conditions
N
t (min)
A (%)
B (%)
Rate (ll minꢀ1
)
0
1
2
3
4
5
6
0.00
3.00
8.00
100
100
65
0
0
0
0
35
100
100
0
200
200
200
200
200
200
200
9.00
14.00
14.50
20.00
100
100
0

106
B.B. Koleva et al. / Journal of Molecular Structure 885 (2008) 104–110
nitrile. The data obtained was processed using an Excalibur
1.4 software.
4.80; N, 6.35%. Yield 78%). TGV and DSC analysis in
the range 300–500 K showed that no solvent was included
in the complex.
1H- and 13C-NMR measurements, referred to sodium
3-(trimethylsilyl)-tetradeuteropropionate, were made at
298 K with a Bruker DRX-400 spectrometer using 5 mm
tubes and D2O as solvent.
3. Results and discussion
Optimisation of the structure of Au(III)-complex of H–
Phe–Tyr–OH was carried out by density funclional theory
calculations (B3LYP) and Lanl2DZ (Au)/6-31+G(3df)
(Cl, C, H) basis set [24,27] with polarization function alpha
0.2 and 1.2 (Au). The theoretical analysis was carried out
using the Dalton 2.0 program package [28].
3.1. Theoretical calculations
The predicted geometry parameters of Au(III)-complex
of H–Phe–Tyr–OH are listed in Scheme 2 and are made
in the basis of the experimental spectroscopic results about
the way for coordination of metal center with dipeptide
(see below). The predicted geometry assumed a co-linear
orientation of following transition moments in the frame
of the complex molecule: out-of-plane aromatic ones (11-
cCH and 4-cAr according Wilson notation [29]), typical
for mono- and para-disubstituted benzene fragments and
mC@O stretchingfrequency of carboxylic group. These
results supported as well the conclusions obtained [30–32]
about the application of DFT calculations at B3LYP and
Lanl2DZ (Au)/6-31+G(3df) (Cl, C, H) with polarization
function alpha 0.2 and 1.2 (Au) as far as the calculated
bond length and angles are compared with crystallographic
data about the known Au(III)-complexes with di- and trip-
2.2. Synthesis
Au(III)-complex of H–Phe–Tyr–OH, [Au(C18H18-
N2O4)Cl], was obtained by a mixing of 0.5670 g of
HAuCl4 ꢁ 3H2O in 5 ml water to 5 ml of H2O solution
containing 0.2787 g of dipeptide at (metal to ligand) mole
ratio of 1:2. After 15 days, the isolated yellow precipitate
was filtered off, washed with water and dried over P2O5.
Yield: 61%, mp 353 °C. (Found: C, 38.55; H, 3.25; N,
5.01; [Au(C18H18N2O4)Cl] calcd.: C, 38.69; H, 3.25; N,
5.01%). TGV and DSC analysis in the range 300–500 K
showed that no solvent was included in the complex.
The hydrogen squarate of H–Phe–Tyr–OH (H2Sq ꢁ
H–Phe–Tyr–OH), [C22H21N2O8], was obtained according
the procedure: an aqueous solution of dipeptide H–Phe–
Tyr–OH (5 ml, 0.3291 g) was mixed with 5 ml 0.1140 g
squaric acid in same solvent at equimolar ratio 1:1. The
white crystals are formed after 10 days and were filtered,
washed with H2O and dried at 298 K in air. (Found: C,
59.88; H, 4.80; N, 6.34; [C22H21N2O8] calcd.: C, 59.86; H,
˚
eptides [33–36] and the values are not differ that 0.098 A
and 3.3(4)°. Furthermore, the shown geometry of the com-
plex is confirmed from the linear polarized IR-data
obtained and included in next part.
3.2. IR- and IR-LD data
The comparison of IR-spectral characteristics of
Au(III)-complex and hydrogensquarate of H–Phe–Tyr–OH
Scheme 2. Optimized geometry of the Au(III)-complex of H–Phe–Tyr–OH.

B.B. Koleva et al. / Journal of Molecular Structure 885 (2008) 104–110
107
Fig. 1. Solid-state IR-spectra of H–Phe–Tyr–OH complex with Au(III)
(a) and its hydrogensquarate (b).
Fig. 2. Nonpolarized IR (a) and reduced IR-LD spectrum (b) of Au(III)-
complex of H–Phe–Tyr–OH after elimination of the peak at 1725 cmꢀ1
.
is made towards the known theoretical and experimental
data about pure dipeptide and its hydrochloride salt [37].
The main characteristic IR-bands are listed as: (i) H–Phe–
Tyr–OH: 3220 cmꢀ1 (mNH), 1681 cmꢀ1 ðdaNsH3þÞ, 1670 cmꢀ1
(amide I), 1630 cmꢀ1 (8a(Phe)), 1614 cmꢀ1 (8a(Tyr)),
1594 cmꢀ1 (8b(Phe)), 1585 cmꢀ1 (8b(Tyr)), 1564 cmꢀ1
(19a(Phe)), 1554 cmꢀ1 (amide II), 1525 cmꢀ1 ðmCasOOꢀÞ,
1511 cmꢀ1 (19a(Tyr)); (ii) H–Phe–Tyr–OH hydrochloride
salt: 3160 cmꢀ1 (mNH), 1731 cmꢀ1 (mC@O, COOH group)
1656 cmꢀ1 ðdaNsH3þÞ, 1650 cmꢀ1 (amide I), 1612 cmꢀ1 (8a),
1593 cmꢀ1 (8b(Phe)), 1587 cmꢀ1 (8b(Tyr)), 1600 cmꢀ1 (amide
II), 1514 cmꢀ1 (19a(Tyr)), 1498 cmꢀ1 (19a(Phe)).
1590 cmꢀ1 (8b(Tyr)), 1523 cmꢀ1 (Amide II), 1516 cmꢀ1
(19a(Tyr)), 1500 cmꢀ1 (19a(Phe)). Like in hydrochloride salt
[37] the interactions with squaric acid leads to protonation
of COOꢀ group and disappearance of mas
and msCOOꢀ
COOꢀ
maxima. The IR-spectrum of hydrogensquarate shows as
well series of IR-peaks characteristic for HSqꢀ ion at
1818 cmꢀ1, 1703 cmꢀ1 and 1600 cmꢀ1 assigned to combina-
tion of mCꢀO, mCꢀC and mC@C modes. The peaks positions
are typical for the other obtained hydrogensquarates of
peptides and amino-acid amides [35].
Polarized IR-LD data of Au(III)-complex leads to fol-
lowing conclusions based on the applied reducing-differ-
ence procedure. The elimination of carboxylic mC@O
stretching peak at 1725 cmꢀ1 resulted to disappearance of
out-of-plane modes characteristic for mono- and para-
disubstituted benzene fragments (Fig. 2b) at 821 cmꢀ1
(11-cAr(Tyr)), 748 cmꢀ1 (11-cAr(Phe)) and 701 cmꢀ1 (4-
The comparison with neutral peptide and its Au(III)-
complex indicated the following main differences: (i) the
m
NH and amide II peaks are disappeared after complexation
as
(Fig. 1a). (ii) the pairs of m
and msCOOꢀ maxima are also
COOꢀ
absent in the IR-spectrum of the complex and a new band
at 1722 cmꢀ1 is at hand belonging to mC@O; (iii) the new
cAr(Phe)). This result indicated a co-linear orientation of
peaks at 3386 cmꢀ1
,
3205 cmꢀ1
,
3070 cmꢀ1 and
corresponding transition moment, which is realized in the
frame of the shown structure in Scheme 2. In parallel dur-
ing the last procedure the peak of amide I at 1675 cmꢀ1 is
observed also supported the presented structure due to the
mutual cross-oriented transition moments of both mC@O
modes closing an torsion angle of 65.7°.
1658 cmꢀ1 could be explained with mNasH2, Fermi-resonance
splitted msNH2 and dNH2 stretching and bending modes. This
assignment is supported by the disappearance of NH3þ
characteristic bands, typical for neutral dipeptide. These
data assumed a tridentate coordination of H–Phe–Tyr–
OH through its –NH2, –COOꢀ and deprotonated –NH
(amide) groups. Other characteristic IR-bands of Au(III)-
complex are: 1675 cmꢀ1 (amide I), 1627 cmꢀ1 (8a(Phe)),
1614 cmꢀ1 (8a(Tyr)), 1596 cmꢀ1 (8b(Phe)), 1587 cmꢀ1
(8b(Tyr)), 1566 cmꢀ1 (19a(Phe)), 1513 cmꢀ1 (19a(Tyr)),
840 cmꢀ1 (4-cAr(Tyr)), 738 cmꢀ1 (11-cAr(Phe)) and 701 cmꢀ1
(4-cAr(Phe)).
1
3.3. H- and 13C-NMR data
The nuclear magnetic resonance spectra Au(III)-complex
and hydrogensquarate of H–Phe–Tyr–OH are compared
with zwitterion form of dipeptide [38–41]. The a-(1H) and
b-(2H) protons in Phe-residues are observed generally about
4.50 and 3.00 ppm as doublets dd and 2dd, respectively. The
aromatic protons (5H) are obtained over 7.00 ppm as mul-
tiplet (m). The Tyr-side chain shown signals about 3.00 ppm
(1H, dd, b-Tyr), 3.30 ppm (m, 1H, b–Tyr), 4.90 ppm (dd,
1H, a-Tyr), 5.83 ppm (d, 2H), 6.51 (d, 1H), 6.70 ppm (d,
1H), respectively. The corresponding 13C-NMR chemical
shifts are about 35.00 (CH2, Phe), 55.70 (CH, Phe),
The complicated IR-spectrum of hydrogensquarate of
H–Phe–Tyr–OH (Fig. 1b) due to the strong intermolecular
interactions between dipeptide and HSqꢀ ions required a
preliminary deconvolution and curve-fitting for obtaining
the numꢀb1er of maxima and their position: 3340ꢀc1mꢀ1 (mNH),
1740 cm
(mC@O
,
COOH group) 1669 cm
ðdaNsH3þÞ,
1645 cmꢀ1 (amide I), 1613 cmꢀ1 (8a), 1598 cmꢀ1 (8b(Phe)),

108
B.B. Koleva et al. / Journal of Molecular Structure 885 (2008) 104–110
129.35, 131.23, 131.2 (Phe), 38.9 (b-Tyr), 55.0 (a-Tyr), 83.5,
98.0, 97.5, 100.1 (Tyr), 166.0 (COH, Tyr), respectively, The
signals about 165.00 ppm and 175.00 ppm correspond to
COOꢀ and CONH, respectively.
[43]. The dipeptide signals in the salt are 39.4 (b-Phe),
56.9 (a-Phe), 130.0, 132.0, 135.5 (Phe), 37.5 (b, Tyr), 59.2
(a-Tyr), 125.9, 128.9, 131.8, 132, 5 (Tyr), 159.7 (COH,
Tyr), 175.5 ppm (COOH) and 172.5 (CONH), respectively.
The complexation with Au(III) leads to following differ-
1
ences in the H- and 13C-NMR spectra of the dipeptide.
3.4. ESI-MS and HPLC-MS–MS data
The b-Phe (2H, dd) and b-Tyr (m, dd, 1H) signals are
downfield shifted and overlapped about 4.50 ppm. The
a-Phe and a-Tyr dd (1H) signals are shifted as well and
are observed at 5.20 ppm and 5.35 ppm. The other signals
are practically insignificant shifted and are observed in the
6.00–7.50 ppm range. These data assumed a tridentate
coordination of dipeptide with Au(III) center through –
NH2, –COOꢀ and –Nꢀof amide group. The 13C-NMR
data of Au(III)-complexes are 37.5 (b-Phe), 56.0 (a-Phe),
130.5, 131.0, 135.0 (Phe), 38.5 (b-Tyr), 55.2 (a-Tyr),
125.5, 128.0, 128.9, 129, 5 (Tyr), 159.0 (COH, Tyr),
169.5 ppm (COOꢀ) and 172.5 (CONH), respectively.
The 1H-NMR data of hydrogensquarate of H–Phe–
Tyr–OH are: (i) The chemical shifts of b-Phe (2H, dd), a-
Phe (dd, 1H) and aromatic 5H are practical unaffected after
the protonation of COO- group in zwitterion dipeptide; (ii)
b–Tyr (m, dd, 1H) and a–Tyr dd (1H) signals are downfield
shifted with about 1.00 ppm and 4. ppm, respectively. The
aromatic signals in the 6.00–7.50 ppm range are practically
insignificant. These data correlated well with known ones
about the protonated forms of tyrosine and phenylalanine
containing dipeptides [42]. However, the 13C-NMR data of
hydrogensquarate are significant differ than the neutral
dipeptide one due to an observation of four new signals
at 184.6, 180.9, 176.9, 170.0 ppm, belonging to HSqꢀ ion
The most intense peak in the FAB mass spectrum of the
Au(III)-complex is at 559.2 m/z, corresponding to the sin-
gle charged [C18H19N2O4AuCl]+ ion with molecular weight
559.7.
The ESI-MS spectrum of hydrogensquarate is given in
Fig. 3. The most intensive peak is at m/z 357.0. As far as
the molecule weight of protonated H–Phe–Tyr–OH,
[C18H20O4N2]+, is 329.12, the signals should be corre-
sponds to an NHþ4 adduct with dipeptide. The peak at
467.08 could be assigned to Na+ adduct with H–Phe–
Tyr–OHꢂ ꢂ ꢂHSqꢀ specie, which have a molecule weight of
443.01. It is well-known that the Na+ and NH4þ adducts
are typical for ESI-MS and for that reason for the analysis
of peptides and their derivatives is preferable a combina-
tion of HPLC-MS–MS determination [44–48]. The HPLC
separation of system studied is presented in Fig. 4A as a
dependence of relative abundance vs. time (t). Two peaks
are observed at t = 1.94 min and t = 11.51 min. The MS
data of first one given a peak at m/z 329.2, which correlated
with the molecule weigh of protonated peptide with for-
mula [C18H20O4N2]+ (Fig. 4B). The maximum at 657.4
belongs to dimmers of the dipeptide studied. The second
peak in Fig. 4B corresponds to molecule species with m/z
119.9 corresponds to protonated hydrogensquarate. The
Fig. 3. ESI mass-spectrum of H2Sq ꢁ H–Phe–Tyr–OH.

B.B. Koleva et al. / Journal of Molecular Structure 885 (2008) 104–110
109
Fig. 4. HPLC-MS–MS spectra of H2Sq ꢁ H–Phe–Tyr–OH.
MS–MS spectrum given in Fig. 4C gives a peak at m/z
4. Conclusions
329.1 exactly given the molecule mass of the dipeptide stud-
ied and confirmed the synthesis of hydrogensquarate salt of
H–Phe–Tyr–OH.
On the basis of solid-state IR-LD spectroscopy, 1H- and
13C-NMR, ESI-MS, HPLC-MS–MS, FAB-MS, TGS and

110
B.B. Koleva et al. / Journal of Molecular Structure 885 (2008) 104–110
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DSC as well as by DFT calculations at B3LYP level of and
Lanl2DZ (Au)/6-31+G(3df) (Cl, C, H) basis set using
polarization function alpha 0.2 and 1.2 (Au) the following
essential conclusions can be drown: (i) A mononuclear
Au(III)- complex of H–Phe–Tyr–OH has been synthesised
and is characterized with a tridentate coordination of
dipeptide through its –NH2, –COOꢀ and –Nꢀ-groups.
One Clꢀ is attached as a terminal ligand in four position
to metal ion, forming a planar geometry of the Au(III) cen-
ter; (ii) hydrogensquarte of H-Phe–Tyr–OH has been
obtained consists in positive charged dipeptide moiety
and negative one hydrogensquarate anion (HSqꢀ) stabiliz-
ing by strong intermolecular hydrogen bonds; (iii) A pre-
cise vibrational assignment of both system studied has
been obtained by means of solid-state IR-LD spectroscopy
of oriented samples in nematic liquid crystal suspension;
1
(iv) The comparison with IR-spectroscopic and H- and
13C-NMR data as well as with all mass spectral ones indi-
cated the same type of Au(III) coordination with dipeptide
both in solid-state and in solution.
Acknowledgements
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