Zn (II) and Cu (II) Halide Complexes of Poly(propylene amine) Dendrimer Analysed by Infrared and Raman Spectroscopies

Abstract

Two nondestructive and complementary spectral methods as infrared and Raman spectroscopies have been used for characterizations of poly(propylene amine) dendrimers comprising 1,8-naphthalimide units in the dendrimer periphery and their metal complexes with Cu2+ at Zn2+ ions.

Full text

Hindawi Publishing Corporation
International Journal of Inorganic Chemistry
Volume , Article ID , pages
http://dx.doi.org/.//
Research Article
Zn (II) and Cu (II) Halide Complexes of Poly(propylene amine)
Dendrimer Analysed by Infrared and Raman Spectroscopies
Ivo Grabchev,1,2 Ismail Hakki Boyaci,3Ugur Tamer,4and Ivan Petkov5
1Faculty of Medicine, Soa University “St. Kliment Ohridski”, 1407 Soa, Bulgaria
2Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
3Department of Food Engineering, Faculty of Engineering, Hacettepe University, Beytepe Campus, 06800 Ankara, Turkey
4Department of Analytical Chemistry, Faculty of Pharmacy, Gazi University, 06330 Ankara, Turkey
5Faculty of Chemistry and Pharmacy, Soa University “St. Kliment Ohridski”, 1153 Soa, Bulgaria
Correspondence should be addressed to Ivo Grabchev; i.grabchev@chem.uni-soa.bg
Received  April ; Revised  June ; Accepted  June 
Academic Editor: Alfonso Casti ˜
neiras
Copyright ©  Ivo Grabchev et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Two nondestructive and complementary spectral methods as infrared and Raman spectroscopies have been used for character-
izations of poly(propylene amine) dendrimers comprising ,-naphthalimide units in the dendrimer periphery and their metal
complexes with Cu2+ at Zn2+ ions.
1. Introduction
Poly(propylene amine) (PPA) is a new class of commercial
dendrimers possessing tertiary amino groups in the core and
terminal primary amino groups in the dendrimer periphery
[]. eir luminescent characteristics can be customized by
modifying the periphery with dierent uorophores. We have
extensively studied the dendrimer modications with ,-
naphthalimides in response to the needs of vanguard sensors
for preventing environment pollution [–].
Dierent spectral methods and techniques as UV-vis
and uorescence, FTIR and Raman, NMR, AFM, and EPR
are used for identication and characterization of den-
drimers []. Some of these methods used for studying the
vibrations of atoms in dendrimer molecules are infrared
and Raman spectroscopies. e dierence between both
of spectral methods lies in the fact that while in infrared
spectroscopy are important oscillations, changing dipole
moment, in the Raman spectroscopy is characteristic the
change of polarizability of molecules. e main advantage
of Raman spectroscopy compared to Infrared spectroscopy
is the small water absorption, which is oered especially for
biological and medical investigations without further sample
preparations. Surface-enhanced Raman spectroscopy (SERS)
takes the advantage of strongly increased Raman scattering
signal generated by local eld enhancement near metallic
nanostructures []. An example exploits the local plasmon
modes at the interface between two metal nanoparticles. A
key requirement to achieve such detection is the placement of
the analyte close to more than one plasmonic surface []. To
date, isotropic and anisotropic metallic nanoparticles such as
gold and silver have been promising SERS substrates because
of their tunable optical properties, controllable particle size
distribution, easy synthesis procedure, long-term stability,
and high biocompatibility []. On the other hand, the infra-
redspectroscopyismoreinformativeinthecaseoftheinves-
tigations of polar functional groups in organic compounds.
is means that these spectral methods are complementary
and appropriate for researching the structure of organic
molecules [].
In this paper we present Raman and infrared spectral
analyses on Zn (II) and Cu (II) halide complexes of poly(pro-
pylene amine) dendrimers of rst and second generations,
comprising ,-naphthalimide units in the dendrimer periph-
ery. eir spectral characteristics have been investigated in
solidstateandinDMSOsolutioninthepresenceofAg
nanoparticles.

 International Journal of Inorganic Chemistry
NN
N
N
N
N
O
OO
O
O
O
O
O
NN
N
N
N
N
N
N
N
N
N
N
N
N
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
PPA1 PPA2
S : Chemical structure of dendrimers PPA and PPA.
2. Experimental
2.1. Materials. First and second generations PPA dendrimers
modied with ,-naphthalimide derivatives have the struc-
tures shown in Scheme . eir synthesis and metal com-
plexes preparation have been published recently [,].
2.2. Synthesis of Ag Nanoparticles. Before preparation of the
colloids, the whole glassware was washed with aqua regia
and rinsed with deionized water. Hydroxylamine reduced
silver nanoparticles were prepared as reported by Leopold
and Lendl []. Briey, hydroxylamine hydrochloride (1.67 ×
10−3 M) and NaOH (3.33 × 10−3 M) were dissolved in  mL
deionized water. To the basic solution, mL AgNO3(1×
10−2 M) was added dropwise, stirred for  minutes, and
stored in dark place. e concentration of the ultimate silver
colloid solution was assumed as X. e study was carried out
to nd out the optimum concentration of silver colloid. .
times concentrated solution gave the best signal enhancement
for SERS measurements, and this concentration was used for
all SERS measurements in the study.
2.3. Instrumentation. DeltaNu Examiner Raman Microscopy
system with a  nm laser source, a motorized microscope
stagesampleholder,andacooledcharge-coupleddevice
(CCD, at ∘C) detector were used. Instrument parameters
were as follows: x objective,  𝜇mlaserspotsize,mW
laser power, and s acquisition time. Baseline correction
was performed for all of the measurements. In solid sample
measurement, sample was placed on a glace slide and Raman
spectrum of the sample was obtained with micro-Raman
system. In liquid sample measurement, sample was dissolved
in DMSO and then diluted with Milli-Q quality water
( MΩcm) up to −4 M concentration. Aer that  𝜇L
sample was mixed with  𝜇L X Ag nanoparticles in Raman
cuvette, and Raman spectrum of the mixture was obtained
in the range of – cm−1 at a resolution of  cm−1
with constant measurement parameters. Infrared analysis of
both dendrimers and their complexes with metal ions was
carried out using an infrared Fourier transform spectrometer
(IRAnity-) with the diuse-reectance attachment (MIR-
acle Attenuated Total Reectance Attachment) at a cm−1
resolution.
3. Results and Discussion
Stretching and deformation vibrations of the main functions
in the infrared region of PPA dendrimers from rst and
second generations modied with ,-naphthalimides and
their metal complexes are summarised in Tab l e  .
e carbonyl groups from the imide structure give rise
to both of the frequency bands of C=O absorption []. e
IR spectrum of the initial dendrimers PPA and PPA pos-
sesses very similar intensive bands at  cm−1,cm
−1,
 cm−1,andcm
−1.echaracteristicbandsforthe
C–N bonds due to the tertiary amino group from aliphatic
dendrimer structure and C–N–C imidic structure from the
,-naphthalimide are at – cm−1,–cm
−1,
and – cm−1.
e aromatic naphthalene ring from the ,-
naphthalimide units is responsible for the absorptions
due to the C–H stretching vibrations at – cm−1.
e characteristic C–H out-of-plane deformation vibrations

International Journal of Inorganic Chemistry 
T : Experimental infrared wavenumbers of dendrimers in cm−.
]C–H arom ]CH
]AS
C=O ]S
C=O ]C=C arom ]CH]C–N 𝛿C–H arom
PPA  
   
 





PPA/Cu+  
  










PPA/Zn+  
  









PPA  
   
 





PPA/Cu+  
  









PPA/Zn+  
  









1800 1600 1400 1200 1000
50
60
70
80
90
100
PPA1
T(%)
Wavenumber (cm−1)
PPA1/Cu2+
(a)
1700 1650
50
60
70
80
90
100
PPA1
T(%)
Wavenumber (cm−1)
PPA1/Cu2+
(b)
F : Infrared spectra of PPA dendrimer and PPA/Cu2+ complex.
of the aromatic naphthalene rings are at – cm−1 and
– cm−1.
PPA dendrimers under study comprise also aliphatic
methylene (–CH2–) groups in the dendrimer core. e
absorption at – cm−1 for the asymmetric stretch-
ing vibrations and at – cm−1 for the symmetric
stretching vibrations indicates the presence of hydrogen atom
bonded to sp3hybridized carbon atoms (C–H).
Figure  shows the IR spectra of PPA and its metal
complex PPA/Cu2+ givenasacomparison.Itisseenthat
the absorption bends in the region – cm−1 are
dierent (Figure (a)). A new intensive band at  cm−1
wasobservedinthespectraofPPA/Cu
2+ complex which
probably is due to the metal ions complex formation.
e characteristic C–H out-of-plane deformation vibrations
of the aromatic naphthalene rings of PPA and PPA/Cu2+
at the region – cm−1 are also very close. In the region
where absorb C=O groups from the ,-naphthalimide struc-
ture (– cm−1)thedierenceis–cm
−1 (Figure (b))
which can be explained by the possible metal ions coordina-
tion with C=O groups. e same results have been obtained
in the case of PPA dendrimer and its metal complex. In
Figure  theinfraredspectraofPPAandPPA/Zn
2+ are
plottedasanexample.Itisseenthatintheregionwhere
absorb both carbonyl groups the dierence is the same as that
in the case of PPA dendrimer. e dierence has been also
observed and in the spectral region (– cm−1)where
absorb tertiary amine and amide groups.

 International Journal of Inorganic Chemistry
1800 1600 1400 1200 1000
60
70
80
90
100
PPA2
PPA2/Zn2+
T(%)
Wavenumber (cm−1)
F : Infrared spectra of PPA dendrimer and PPA/Zn2+ complex.
400 800 1200 1600
Intensity
Solid
Wavenumber (cm−1)
PPA1/Cu2+
DMSO +Ag np
(a)
400 800 1200 1600
Intensity
Solid
Wavenumber (cm−1)
PPA1/Zn2+
DMSO +Ag np
(b)
F : Raman spectra of PPA dendrimer complex in solid state and in DMSO solutions in the presence of silver nanoparticles.
When Raman active molecules are located near nanopar-
ticles surface within the nanoparticles assembly, Raman sig-
nal intensities are substantially enhanced due to formation of
hotspot. Metal nanoparticles have been used as the substrates
for surface-enhanced Raman scattering (SERS) due to the
enhancement mechanisms. e rst mechanism has a chem-
ical origin, which is due to the formation of a charge-transfer
complexbetweenthesurfaceandtheanalytemolecules.e
second mechanism can be attributed to the enhancement in
electromagnetic eld as a result of strong surface plasmon
resonanceofmetalnanoparticle.esecondmechanism
amplies the incident laser eld and the scattered Raman eld
through their interaction with particle surface. e Raman
scattering enhancement is attributed to plasmonic coupling
between nanoparticles in close proximity, which results in
local electromagnetic eld enhancement on hotspots [].
One of the major research topics is the development
of nanoparticle assemblies which are capable of monitoring
SERS activity for application in environmental monitoring,
diagnosis, and biodetection []. e analytical applications
of Raman are limited due to low Raman cross-section of the
analyte, which is oen the case in inorganic metal species.
However, SERS is a powerful spectroscopy technique for the
monitoring spectral changes aer interactions between metal
cations and nanoparticles.
e metal ions complexes of dendrimers PPA and PPA
have been analyzed by Raman spectroscopy in the region
– cm−1 insolidstateandinDMSO.Respective
Raman spectra of the PPA/Cu2+ and PPA/Zn2+ are plotted
in Figures ,,and. In DMSO solution, silver nanoparti-
cles have been used for better Raman signal enhancement,
if compared to this investigated in solid state. e silver
nanoparticles may aggregate in the presence of DMSO aer
the addition of metal complexes. is process may potentially
aect the SERS signal. erefore the experimental conditions

International Journal of Inorganic Chemistry 
400 800 1200 1600
Solid
Intensity
Wavenumber (cm−1)
DMSO +Ag np
PPA2/Cu2+
(a)
400 800 1200 1600
Intensity
Solid
Wavenumber (cm−1)
PPA2/Zn2+
DMSO +Ag np
(b)
F : Raman spectra of PPA dendrimer complex in solid state and in DMSO solutions in the presence of silver nanoparticles.
400 800 1200 1600
Intensity
Wavenumber (cm−1)
PPA2/Cu2+
PPA1/Cu2+
F : Raman spectra of PPA/Cu2+ and PPA/Cu2+ complex in
DMSO solutions in the presence of silver nanoparticles.
such as the concentrations of silver nanoparticles and the type
of solvent molecule are very important in order to get SERS
signaling as much as possible. From the spectra in solutions
and in solid state, it is seen that there are some changes in
bands and lines intensity in the Raman spectra of both of the
dendrimer complexes.
e strong bands of the Raman spectra of both of the
dendrimer generations at – cm−1 are characteristics
for C–C–C in-plane aromatic vibration. e bands at –
 cm−1 canbeassignedforC–Hout-of-planebending
while those at – cm−1 are for C–H in-plane bending.
e characteristic bands for the C–N bonds which are
due to the tertiary amino group from aliphatic dendrimer
structure are at – cm−1. e C–N–C stretch from
the imidic ,-naphthalimide structure is at – cm−1.
e bands at – cm−1 areassignedtothearomatic
C–C stretching. e bending vibrations of CH2groups from
the aliphatic dendrimer structure give rise to bands at –
 cm−1.ItshouldbestressedthatintheRamanspectra
vibrations of C=O groups do not demonstrate intensive bands
as observed in the infrared spectra. e band attributed to
C=O vibrations is detected with very small intensity near
 cm−1.
Interest was demonstrated to investigate the type of
dendrimer generation on the position of the signals in Raman
spectra. In Figure  the Raman spectra of PPA/Cu2+ and
PPA/Cu2+ complexes at – cm−1 range are presented
as an example. It is seen that both spectra are almost identical
which is due to the similar polarization of the dendrimer
molecules. is is a proof that the generation of the den-
drimers does not aect their polarization. e determining
factor in this process is the type of the uorophore comprised
in the dendrimer.
In summary, it has been demonstrated that the infrared
and Raman spectroscopies can be used as complemen-
tary methods for structural analysis, identication, and
characterization of modied with ,-naphthalimide units
poly(propylene amine) dendrimers from rst and second
generations and their Cu2+ and Zn2+ complexes.
Acknowledgment
e authors wish to acknowledge the COST TD: photo-
synthetic proteins for technological applications: biosensors
and biochips (PHOTOTECH).
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