A MASS SPECTROMETRY STUDY OF BIOCOMPATIBLE POLYESTERS Magdalena Cristina STANCIU*, Marieta NICHIFOR Institute of Macromolecular Chemistry “Petru Poni”, 41 A Gr. Ghica-Voda Alley, Iasi 700487, Romania A new biocompatible and biodegradable polyester based on litocholic acid was prepared by a two-step procedure. Both the final product and the corresponding intermediate were characterized by elemental analysis, 1 H-, 13 C-NMR, FT-IR as well as ESI-mass spectrometry spectra. Thermal and X-ray diffraction studies for the novel polymer have been achieved. INTRODUCTION Bile acids are compounds biosynthesized in the liver that play an important biological role in the body [ 1-2,3 ]. Biocompatibility, amphiphilicity, self- assembling capacity, high stability of the steroid skeleton, chirality and reactivity of the side groups [ 4 ] are properties of bile acids that can be preserved by their derivatives. Polymers made of bile acids are promising materials in chemistry, biomedicine [ 5,6 ], biomimicry [ 7 ] and supramolecular science [ 8,9 ]. Bile acids were included in the main chain of the polymers 10 1
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A MASS SPECTROMETRY STUDY OF BIOCOMPATIBLE POLYESTERS
Magdalena Cristina STANCIU*, Marieta NICHIFOR
Institute of Macromolecular Chemistry “Petru Poni”, 41 A Gr. Ghica-Voda Alley, Iasi 700487, Romania
A new biocompatible and biodegradable polyester based on litocholic acid was prepared by a two-step
procedure. Both the final product and the corresponding intermediate were characterized by elemental analysis,
1H-, 13C-NMR, FT-IR as well as ESI-mass spectrometry spectra. Thermal and X-ray diffraction studies for the
novel polymer have been achieved.
INTRODUCTION
Bile acids are compounds biosynthesized in the liver that play an important biological role in the body [1-2,3].
Biocompatibility, amphiphilicity, self-assembling capacity, high stability of the steroid skeleton, chirality and
reactivity of the side groups [4] are properties of bile acids that can be preserved by their derivatives. Polymers
made of bile acids are promising materials in chemistry, biomedicine [5,6], biomimicry [7] and supramolecular
science [8,9]. Bile acids were included in the main chain of the polymers10 or were attached to polymeric
materials as pendent groups [11-13] or chain-end groups [14-17]. Homopolycondensation of BA led to very rigid,
non-degradable and insoluble polyesters [18-20]. Thus, the present study goal was the synthesis and
characterization of a new biocompatible and biodegradable polyester by the polycondensation of 3-
(succinoyloxy)-litocholic acid with diethylene glycol (DEG). These polymers could have potential applications
in controlled drug release.
. The procedure for the synthesis of polyesters is described in details and the polymers crystallinity and thermal
The mass spectrometry analysis of various biopolymers has become important due to the high demand to develop newer and better materials formulations. ESI-MS is a relatively soft ionization technique used for the analysis of biomolecules and some synthetic polymers, becoming a very effective method for structure elucidation and determination of the molecular associations [1, 2]. The HPLC-ESI-MS
20 . S. Gouin, X. X. Zhu and S. Lehnert, Macromolecules, 2000, 33, 5379-5383.
21 . A. W. Coats and J. P. Redfern, Nature, 1964, 68-69.
22 . E. Urbanovici and E. Segal, Thermochim. Acta, 1984, 80, 389-393.
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analysis was performed in order to estimate their number-average (Mn) and weight-average (Mw) molar masses of the polyesters synthesized by polycondensation.
Mass spectrometry experiments were performed with a quadrupole-time-of-flight (Q-TOF) MS instrument equipped with an electrospray ionization source operated in the negative ion mode. The polyesters were dissolved in methanol to obtain a concentration of 100 μg/mL and 10 μL was injected into the HPLC system directly connected to the electrospray ion source. The Q-TOFMS optimal conditions were set as follows: electrospray ionization in negative ion mode, drying gas (N2) flow rate 10.0 L/min; drying gas temperature 325 ºC; nebulizer pressure 15 psig, capillary voltage 4200 V; fragmentation voltage 75-400 V; the full-scan mass spectra of the investigated compounds were acquired in the range m/z 50–3000.
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Fig. xxx. Negative ion ESI mass spectrum of (a) SC_CA, (b) SC_DCA, (c)SC_LA, spectra recorded in chloroform/methanol solution (1:1,v/v).
In the figure xxx is presented the mass specta acquired for the cholic acid (SC_CA), deoxycholic acid (SC_DCA) and litocholic acid (SC_LA) hemiesters. The base peaks observed at m/z = 507.13, 491.187 and 475.31 are associated with the presence of the singly charged deprotonated molecular ions [M-H]-. The negative electrospray ionization mode favors the formation of chlorine aducts ions of the form [M+Cl]-. Therefore, the peaks witht m/z: 543.10, 527.11 and 511.29 can be assigned to the hemiesters chlorine aducts.
Electrospray ionization also determines the formation of molecular dimers, [2M-H] -. Relative intensity of the corresponding dimers pick sites is close to the pick-sized molecular ions as the polarity of the two types of compounds is similar, in ESI-MS spectra, the signal intensity on the polarity of the molecule and not found in mass percentage it. Pick-ups from m / z 1015.59 and m / z 983.60 attributable to that product molecular dimers 1 and 2, respectively.
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Fig. xxx. Negative ion ESI mass spectrum of (a) PES_CA, (b) PES_DCA, (c)PES_LA, spectra recorded in chloroform/methanol solution (1:1,v/v).
The recorded mass spectrum for the polyesters of 3-succinoyloxy-bile acid (CA, DCA and LA) with DEG is presented in figure xxx. The base peaks was observed at m/z =595.21, 579.33 and 563.22 it was assigned as single charge deprotonated ion, corresponds to [M-H]- (where M is the molecular weight for the polyester structure when n=1). Furthermore, other ions coresponding to the polyester with n=2–5, are also detectable. These ions arise with the dehydrations and losses of one or more water molecules of the oligomer unit.
As can be observed in XXX, the signal to noise ratio and resolution of each peak decrease gradually with the molar masses of oligomers. Consequently, peak intensities, rather than peak areas, were used to calculate the Mn, Mw and polydispersity index (PI). Standard procedures were used for these calculations [17 D. Vitalini, P. Mineo, E. Scamporrino, Macromolecules 30 (1997) 5285.].We measured the intensity maximum of each peak (primary and secondary) and used these values to generate our oligomer distributions.
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[1] MWF. Nielen, FA Buijtenhuijs, Anal. Chem.,71, 1809-1814, 1999.[2] SM Weidner, S Trimpin, Anal. Chem. 80, 4349–4361, 2008.[3] D. Vitalini, P. Mineo, E. Scamporrino, Macromolecules 30 (1997) 5285[4] Julien E. Gautrot, X.X. Zhu, Molar mass of main-chain bile acid-based oligo-esters measured by SEC, MALDI-TOF spectrometry and NMR spectroscopy: A comparative study, Analytica Chimica Acta 581 (2007) 281–286
Acknowledgement. This research was financially supported by National Plan PNII Programme Human Resources, Postdoctoral research project number 54/2010, code 675/28.07.2010 and CNCSIS-UEFISCDI, project number 644/2009 PN II – IDEI code 989/2008.
CONCLUSIONS
New polyesters of 3-succinoyloxy-bile acid (CA and DCA) with DEG were obtained and characterized
by means of qualitative analyses and spectral measurements, as well as by cristallinity and thermal analysis. The
new polyesters have a good solubility in many organic solvents, high thermal stability and crystalline/amorphous
properties. These biocompatible polymers can be used as biodegradable matrices for drug delivery systems,
either as such or after their grafting to a polysaccharide backbone.
Acknowledgements: We gratefully acknowledge the financial support from Ministry of Education and Research
of Romania (Consiliul Naţional al Cercetǎrii Ştiinţifice din Învăţământul Superior-PCE-“Idei”-2008).