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Dr. Eng. Monica DINESCU

Assistant Researcher

Laboratory of Optical Processes in Nanostructured Materials

monica[DOT]daescu[AT]infim[DOT]ro

Education

2019-present: PhD student in University POLITEHNICA of Bucharest, Faculty of Applied Chemistry and Materials Science, Romania.

2013-2015: Master in Micro and Nano-materials, University POLITEHNICA of Bucharest, Romania.

2009-2013: Graduate in Chemical Engineering at Faculty of Applied Chemistry and Materials Science; Department: Science and Engineering of Oxide Materials and Nano-materials.

Positions

2013-present: Research Asisitant at National Institute of Materials Physics, Magurele, Romania.

Expertize

 

Specialist in synthesis and different characterization:  UV-vis, FTIR absorption, Raman, Photoluminescence.

Books

 Recent progress in the photoluminescence properties of composites based on conjugated polymers and carbon nanoparticles, M. Baibarac, M. Ilie, A. Matea, M. Daescu, S. Lefrant, Photoluminescence: Advances in Research and Applications 133-166, 2018.

Patents

- Processes for the preparation and use of new crystalline form of 6- (3-Methyl-5-Nitroimidazo-4-il) Sulphanyl-9H-Purine  (Azathioprine), RO133946 (B1), Manta C.M; Samohvalov D; Gherca D; Baibarac M; Lungan M.A; Smaranda I; Man A; Buhal Ţ. L; Udrescu A; Daescu M; Ilie M; Toulbe N., 2019.

 

-Procedeu chimic de asamblare a senzorilor bazati pe oxid de grafena functionalizati cu poli(5-amino-1-naftol) pentru detectia receptorului factorului de crestere epidermal, Dinescu Monica, Udrescu Adelina, Baibarac Mihaela, Fejer Szilard, A00691/02.11.2020

Publications

Open Access
1. Photocatalytic Activity of the Blends Based on TiO2 Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen
Authors: Daescu, M; Chivu, M; Matei, E; Negrila, C; Cramariuc, O; Baibarac, M

Published: JUN 4 2023, MOLECULES, 28, 4546, DOI: 10.3390/molecules28114546

The aim of this work is to highlight the influence of blends based on TiO2 nanoparticles and reduced graphene oxide (RGO) on the photodegradation of acetaminophen (AC). To this end, the catalysts of TiO2/RGO blends with RGO sheet concentrations equal 5, 10, and 20 wt. % were prepared by the solid-state interaction of the two constituents. The preferential adsorption of TiO2 particles onto the RGO sheets' surfaces via the water molecules on the TiO2 particle surface was demonstrated by FTIR spectroscopy. This adsorption process induced an increase in the disordered state of the RGO sheets in the presence of the TiO2 particles, as highlighted by Raman scattering and scanning electron microscopy (SEM). The novelty of this work lies in the demonstration that TiO2/RGO mixtures, obtained by the solid-phase interaction of the two constituents, allow an acetaminophen removal of up to 95.18% after 100 min of UV irradiation. This TiO2/RGO catalyst induced a higher photodegradation efficiency of AC than TiO2 due to the presence of RGO sheets, which acted as a capture agent for the photogenerated electrons of TiO2, hindering the electron-hole recombination. The reaction kinetics of AC aqueous solutions containing TiO2/RGO blends followed a complex first-order kinetic model. Another novelty of this work is the demonstration of the ability of PVC membranes modified with Au nanoparticles to act both as filters for the removal of TiO2/RGO blends after AC photodegradation and as potential SERS supports, which illustrate the vibrational properties of the reused catalyst. The reuse of the TiO2/RGO blends after the first cycle of AC photodegradation indicated their suitable stability during the five cycles of pharmaceutical compound photodegradation.
Open Access
2. Complex Spectroscopy Studies of Nifedipine Photodegradation
Authors: Paraschiv, M; Daescu, M; Bartha, C; Chiricuta, B; Baibarac, M; Ioele, G

Published: NOV 2023, PHARMACEUTICS, 15, 2613, DOI: 10.3390/pharmaceutics15112613

The aim of this work is to highlight the influence of UV light on the hydrolysis reaction of nifedipine (NIF) in the presence of alkaline solutions. In this context, the photodegradation of NIF in the absence of alkaline solutions caused (a) a change in the ratio between the absorbances of three bands in the UV-VIS spectra localized at 224-240 nm, 272-276 nm and 310-340 nm, assigned to the electronic transitions of -COOCH3 groups, -NO2 groups and a heterocycle with six atoms; (b) a red-shift of the photoluminescence (PL) band from 458 nm to 477 nm, simultaneous with an increase in its intensity; (c) a decrease in the ratio of the Raman line intensities, which peaked at 1224 cm-1 and 1649 cm-1, associated with the vibrational modes of -C-C-O in the ester group and C=C stretching; and (d) a decrease in the ratio between the absorbances of the IR bands, which peaked at 1493 cm-1 and 1223 cm-1, associated with the vibrational modes of the -NO2 group and C-N stretching. These changes were explained considering the NIF photodegradation reaction, which leads to the generation of the compound 4-(2-nitrosophenyl)-2.6-dimethyl-3.5-dimethoxy carbonyl pyridine. The interaction of NIF with NaOH in the absence of UV light was demonstrated to induce changes in the vibrational mode of the -C-C-O bond in the ester group. The photodegradation of NIF after its reaction with NaOH induces significant changes highlighted in its (a) UV-VIS spectra, by the shift of the absorption band at 238 nm; (b) PL spectra, by the supraunitary value of the ratio between the emission band intensities at 394-396 nm and 450 nm; (c) Raman spectra, by the change in the ratio between the intensities of the lines that peaked at 1224 cm-1 and 1649 cm-1 from 0.61 to 0.49; and (d) FTIR spectra, by the lowered absorbance of the IR band at 1493 cm-1 assigned to the vibrational mode of the -NO2 group as a result of the generation of the nitroso compound. These changes were explained considering the hydrolysis reaction products of NIF, as the nitroso compound is converted to a lactam-type compound. The photodegradation reaction rate constants of NIF and NIF after interaction with NaOH were also reported. The decrease in thermal stability of NIF samples after interaction with NaOH, as well as of NIF after exposure to UV light compared to NIF prior to exposure to UV light, was demonstrated by thermogravimetry, and the key fragments were confirmed by mass spectrometry.
Open Access
3. New Aspects Concerning the Ampicillin Photodegradation
Authors: Cercel, R; Paraschiv, M; Florica, CS; Daescu, M; Udrescu, A; Ciobanu, RC; Schreiner, C; Baibarac, M

Published: APR 2022, PHARMACEUTICALS, 15, 415, DOI: 10.3390/ph15040415

New aspects concerning the photodegradation (PD) of ampicillin are reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. The exposure of ampicillin in the absence (AM) and in the presence of the excipient (AMP) to UV light leads to an intensity diminution of the photoluminescence excitation (PLE) and photoluminescence (PL) spectra and the emergence of a new IR band at 3450 cm(-1). The photoluminescence studies demonstrate that the AM PD is amplified in the presence of excipients and an alkaline medium. In this last case, the PD process of AM involves the emergence of new compounds, whose presence is highlighted by: (i) the emergence of the isosbestic point at 300 nm in the UV-VIS spectra; (ii) a change in the ratio between the absorbance of IR bands situated in the spectral ranges 1200-1660 and 3250-3450 cm(-1); and (iii) a change in the ratio between the intensities of the Raman lines localized in the spectral ranges 1050-1800 and 2750-3100 cm(-1). A chemical mechanism of the PD processes of AM in an alkaline medium is proposed.
Open Access
4. The Influence of the Ceramic Nanoparticles on the Thermoplastic Polymers Matrix: Their Structural, Optical, and Conductive Properties
Authors: Smaranda, I; Nila, A; Ganea, P; Daescu, M; Zgura, I; Ciobanu, RC; Trandabat, A; Baibarac, M

Published: AUG 2021, POLYMERS, 13, 2773, DOI: 10.3390/polym13162773

This paper prepared composites under the free membranes form that are based on thermoplastic polymers of the type of polyurethane (TPU) and polyolefin (TPO), which are blended in the weight ratio of 2:1, and ceramic nanoparticles (CNs) such as BaSrTiO3 and SrTiO3. The structural, optical, and conductive properties of these new composite materials are reported. The X-ray diffraction studies highlight a cubic crystalline structure of these CNs. The main variations in the vibrational properties of the TPU:TPO blend induced by CNs consist of the following: (i) the increase in the intensity of the Raman line of 1616 cm(-1); (ii) the down-shift of the IR band from 800 to 791 cm(-1); (iii) the change of the ratio between the absorbance of IR bands localized in the spectral range 950-1200 cm(-1); and (iv) the decrease in the absorbance of the IR band from 1221 cm(-1). All these variations were correlated with a preferential adsorption of thermoplastic polymers on the CNs surface. A photoluminescence (PL) quenching process of thermoplastic polymers is demonstrated to occur in the presence of CNs. The anisotropic PL measurements have highlighted a change in the angle of the binding of the TPU:TPO blend, which varies from 23.7 degrees to approximate to 49.3 degrees and approximate to 53.4 degrees, when the concentration of BaSrTiO3 and SrTiO3 CNs, respectively, is changed from 0 to 25 wt. %. Using dielectric spectroscopy, two mechanisms are invoked to take place in the case of the composites based on TPU:TPO blends and CNs, i.e., one regarding the type of the electrical conduction and another specifying the dielectric-dipolar relaxation processes.
Open Access
5. Optical Evidence for the Assembly of Sensors Based on Reduced Graphene Oxide and Polydiphenylamine for the Detection of Epidermal Growth Factor Receptor
Authors: Baibarac, M; Daescu, M; Fejer, SN

Published: FEB 2021, COATINGS, 11, 258, DOI: 10.3390/coatings11020258

Using Raman scattering and FTIR spectroscopy, new optical evidence for the assembly of sensors based on reduced graphene oxide (RGO) and polydiphenylamine (PDPA) for the electrochemical detection of the epidermal growth factor receptor (EGFR) are reported. The assembly process of the RGO sheets electrochemical functionalized with PDPA involves the chemical adsorption of 1,4-phenylene diisothiocyanate (PDITC), followed by an incubation with protein G in phosphate buffer (PB) solution and after that the interaction with EGFR antibodies solution. Taking into account the changes reported by Raman scattering and FTIR spectroscopy, a chemical mechanism of the assembling process for this sensor is proposed. The preliminary testing of the electrochemical activity of the sensors based on RGO and PDPA was reported by cyclic voltammetry.
Open Access
6. Spectroscopic studies on photodegradation of atorvastatin calcium
Authors: Oprica, M; Iota, M; Daescu, M; Fejer, SN; Negrila, C; Baibarac, M

Published: JUL 28 2021, SCIENTIFIC REPORTS, 11, 15338, DOI: 10.1038/s41598-021-94693-5

In this work, the photodegradation process of atorvastatin calcium (ATC) is reported as depending on: (1) the presence and the absence of excipients in the solid state; (2) the chemical interaction of ATC with phosphate buffer (PB) having pH equal to 7 and 8; and (3) hydrolysis reaction of ATC in the presence of aqueous solution of NaOH. The novelty of this work consists in the monitoring of the ATC photodegradation by photoluminescence (PL). The exposure of ATC in solid state to UV light induces the photo-oxygenation reactions in the presence of water vapors and oxygen from air. According to the X-ray photoelectron spectroscopic studies, we demonstrate that the photo-oxygenation reaction leads to photodegradation compounds having a high share of C=O bonds compared to ATC before exposure to UV light. Both in the presence of PB and NaOH, the photodegradation process of ATC is highlighted by a significant decrease in the intensity of the PL and photoluminescence excitation (PLE) spectra. According to PLE spectra, the exposure of ATC in the presence of NaOH to UV light leads to the appearance of a new band in the spectral range 340-370 nm, this belonging to the photodegradation products. Arguments concerning the chemical compounds, that resulted in this last case, are shown by Raman scattering and FTIR spectroscopy.
Open Access
7. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development
Authors: Barbatu, A; Lungan, MA; Toulbe, N; Smaranda, I; Daescu, M; Baibarac, M; Manta, CM

Published: OCT 3 2021, DRUG DEVELOPMENT AND INDUSTRIAL PHARMACY, 47, DOI: 10.1080/03639045.2022.2032131

The physico-chemical properties of two anhydrous AZA forms and their interaction with typical pharmaceutical excipients were assessed by applying various methods (such as PXRD, HPLC, TG/DSC, IR, Raman, PL or UV-Vis) in order to highlight new directions for drug formulation. The stability assessment of AZA anhydrous forms I and II was performed in order to determine the risk of degradation of the active ingredient by accidental exposure to nonstandard conditions in the industrial environment, under different storage, transport or processing conditions. The benefits of form II include increased resistance to chemical degradation over a wide range of pH, but further control of storage and processing conditions is necessary to avoid polymorphic transformation into form I. The solubility assessment on the AZA solid forms in different environments that simulate the conditions of the gastrointestinal tract has the advantage of a significantly increased solubility of form II compared with the commercial form I due to the modification of the crystalline structure. In the case of capsules compared to AZA form I or II as powder, an improvement in their solubility was observed, promoted by the presence of one or more excipients in the formulation mixture.
Open Access
8. Anisotropic Photoluminescence of Poly(3-hexyl thiophene) and Their Composites with Single-Walled Carbon Nanotubes Highly Separated in Metallic and Semiconducting Tubes
Authors: Baibarac, M; Arzumanyan, G; Daescu, M; Udrescu, A; Mamatkulov, K

Published: JAN 2021, MOLECULES, 26, 294, DOI: 10.3390/molecules26020294

In this work, the effect of the single-walled carbon nanotubes (SWNTs) as the mixtures of metallic and semiconducting tubes (M + S-SWNTs) as well as highly separated semiconducting (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of poly(3-hexyl thiophene) (P3HT) was reported. Two methods were used to prepare such composites, that is, the chemical interaction of the two constituents and the electrochemical polymerization of the 3-hexyl thiophene onto the rough Au supports modified with carbon nanotubes (CNTs). The measurements of the anisotropic PL of these composites have highlighted a significant diminution of the angle of the binding of the P3HT films electrochemical synthetized onto Au electrodes covered with M + S-SWNTs. This change was attributed to metallic tubes, as was demonstrated using the anisotropic PL measurements carried out on the P3HT/M-SWNTs and P3HT/S-SWNTs composites. Small variations in the angle of the binding were reported in the case of the composites prepared by chemical interaction of the two constituents. The proposed mechanism to explain this behavior took into account the functionalization process of CNTs with P3HT. The experimental arguments of the functionalization process of CNTs with P3HT were shown by the UV-VIS-NIR and FTIR spectroscopy as well as surface-enhanced Raman scattering (SERS). A PL quenching process of P3HT induced both in the presence of S-SWNTs and M-SWNTs was reported, too. This process origins in the various de-excitation pathways which can be developed considering the energy levels diagram of the two constituents of each studied composite.
Open Access
9. The Influence of UV Light on Photodegradation of Acetylsalicylic Acid
Authors: Daescu, M; Iota, M; Serbschi, C; Ion, AC; Baibarac, M

Published: APR 2021, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 22, 4046, DOI: 10.3390/ijms22084046

Photodegradation of the aqueous solutions of acetylsalicylic acid, in the absence (ASA) and the presence of excipients (ASE), is demonstrated by the photoluminescence (PL). A shift of the PL bands from 342 and 338 nm to 358 and 361-397 nm for ASA and ASE in solid state and as aqueous solutions was reported. By exposure of the solution of ASA 0.3 M to UV light, a decrease in the PL band intensity was highlighted. This behavior was revealed for ASA in the presence of phosphate buffer (PB) having the pH equal to 6.4, 7, and 8 or by the interaction with NaOH 0.3 M. A different behavior was reported in the case of ASE. In the presence of PB, an increase in the intensity of the PL band of ASE simultaneously with a change of the ratio between the intensities of the bands at 361-364 and 394-397 nm was highlighted. The differences between PL spectra of ASA and ASE have their origin in the presence of salicylic acid (SAL). The interaction of ASE with NaOH induces a shift of the PL band at 405-407 nm. Arguments for the reaction of ASA with NaOH are shown by Raman scattering and FTIR spectroscopy.
Open Access
10. Optical Properties of Composites Based on Poly(o-phenylenediamine), Poly(vinylenefluoride) and Double-Wall Carbon Nanotubes
Authors: Baibarac, M; Daescu, M; Matei, E; Nastac, D; Cramariuc, O

Published: AUG 2021, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 22, 8260, DOI: 10.3390/ijms22158260

In this work, synthesis and optical properties of a new composite based on poly(o-phenylenediamine) (POPD) fiber like structures, poly(vinylidene fluoride) (PVDF) spheres and double-walled carbon nanotubes (DWNTs) are reported. As increasing the PVDF weight in the mixture of the chemical polymerization reaction of o-phenylenediamine, the presence of the PVDF spheres onto the POPD fibers surface is highlighted by scanning electron microscopy (SEM). The down-shift of the Raman line from 1421 cm(-1) to 1415 cm(-1) proves the covalent functionalization of DWNTs with the POPD-PVDF blends. The changes in the absorbance of the IR bands peaked around 840, 881, 1240 and 1402 cm(-1) indicate hindrance steric effects induced of DWNTs to the POPD fiber like structures and the PVDF spheres, as a consequence of the functionalization process of carbon nanotubes with macromolecular compounds. The presence of the PVDF spheres onto the POPD fiber like structures surface induces a POPD photoluminescence (PL) quenching process. An additional PL quenching process of the POPD-PVDF blends is reported to be induced in the presence of DWNTs. The studies of anisotropic PL highlight a change of the angle of the binding of the PVDF spheres onto the POPD fiber like structures surface from 50.2 degrees to 38 degrees when the carbon nanotubes concentration increases in the POPD-PVDF/DWNTs composites mass up to 2 wt.%.
Open Access
11. Photoluminescence as a Complementary Tool for UV-VIS Spectroscopy to Highlight the Photodegradation of Drugs: A Case Study on Melatonin
Authors: Daescu, M; Toulbe, N; Baibarac, M; Mogos, A; Lorinczi, A; Logofatu, C

Published: SEP 2020, MOLECULES, 25, 3820, DOI: 10.3390/molecules25173820

In this work, a complementary ultraviolet-visible (UV-VIS) spectroscopy and photoluminescence (PL) study on melatonin (MEL) hydrolysis in the presence of alkaline aqueous solutions and the photodegradation of MEL is reported. The UV-VIS spectrum of MEL is characterized by an absorption band with a peak at 278 nm. This peak shifts to 272 nm simultaneously with an increase in the band absorbance at 329 nm in the presence of an NaOH solution. The isosbestic point localized at 308 nm indicates the generation of some chemical compounds in addition to MEL and NaOH. The MEL PL spectrum is characterized by a band at 365 nm. There is a gradual decrease in the MEL PL intensity as the alkaline solution concentration added at the drug solution is increased. In the case of the MEL samples interacting with an alkaline solution, a new photoluminescence excitation (PLE) band at 335 nm appears when the exposure time to UV light reaches 310 min. A down-shift in the MEL PLE band, from 321 to 311 nm, as a consequence of the presence of excipients, is also shown. These changes are explained in reference to the MEL hydrolytic products.
Open Access
12. Photoluminescence as a Valuable Tool in the Optical Characterization of Acetaminophen and the Monitoring of Its Photodegradation Reactions
Authors: Daescu, M; Matea, A; Negrila, C; Serbschi, C; Ion, AC; Baibarac, M

Published: OCT 2020, MOLECULES, 25, 4571, DOI: 10.3390/molecules25194571

In this work, new evidence for the photodegradation reactions of acetaminophen (AC) is reported by photoluminescence (PL), Raman scattering and FTIR spectroscopy. Under excitation wavelength of 320 nm, AC shows a PL band in the spectral range of 340-550 nm, whose intensity decreases by exposure to UV light. The chemical interaction of AC with the NaOH solutions, having the concentration ranging between 0.001 and 0.3 M, induces a gradual enhancement of the photoluminescence excitation (PLE) and PL spectra, when the exposure time of samples at the UV light increases until 140 min, as a result of the formation of p-aminophenol and sodium acetate. This behavior is not influenced by the excipients or other active compounds in pharmaceutical products as demonstrated by PLE and PL studies. Experimental arguments for the obtaining of p-aminophenol and sodium acetate, when AC has interacted with NaOH, are shown by Raman scattering and FTIR spectroscopy.
Open Access
13. Influence of Reduced Graphene Oxide on the Electropolymerization of 5-Amino-1-naphthol and the Interaction of 1,4-Phenylene Diisothiocyanate with the Poly(5-Amino-1-naphtol)/Reduced Graphene Oxide Composite
Authors: Baibarac, M; Daescu, M; Socol, M; Bartha, C; Negrila, C; Fejer, SN

Published: JUN 2020, POLYMERS, 12, 1299, DOI: 10.3390/polym12061299

A new composite base on reduced graphene oxide (RGO) and poly(5-amino-1-naphthol) (P5A1N) was synthesized by the electrochemical polymerization of 5-amino-1-naphthol (5A1N) in the presence of HClO(4)and H(4)SiW(12)O(40)onto the surface of Au electrode covered with the RGO sheets. The linear dependence of the current densities of the anodic and cathodic peaks with the scan rate of the potential range (0; 0.8) V vs. SCE, reported during electropolymerization of 5A1N, indicates an electron transfer that is controlled by diffusion. A covalent functionalization of the RGO sheets with P5A1N is argued by: (i) the simultaneous disappearance of the IR band at 1584 cm(-1)and the appearance of the new IR bands at 812, 976 and 3744 cm(-1), and (ii) the appearance of two Raman lines at 738 and 1428 cm(-1). An application of the RGO sheets covalently functionalized with P5A1N is demonstrated to support 1,4-phenylene diisothiocyanate (PDITC), a compound used as a cross-linking agent for various biological applications. The chemical adsorption of PDITC onto the RGO sheets covalently functionalized with P5A1N, which involves the appearance of new functional groups of the type thiourea, was proven by Raman scattering and IR spectroscopy.
Open Access
14. Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of α-Lipoic Acid in the Presence of Ag and Au Nanoparticles
Authors: Toulbe, N; Stroe, MS; Daescu, M; Cercel, R; Mogos, A; Dragoman, D; Socol, M; Mercioniu, I; Baibarac, M

Published: NOV 2020, NANOMATERIALS, 10, 2238, DOI: 10.3390/nano10112238

The influence of Ag and Au nanoparticles and reduced graphene oxide (RGO) sheets on the photodegradation of alpha-lipoic acid (ALA) was determined by UV-VIS spectroscopy. The ALA photodegradation was explained by considering the affinity of thiol groups for the metallic nanoparticles synthesized in the presence of trisodium citrate. The presence of excipients did not induce further changes when ALA interacts with Ag and Au nanoparticles with sizes of 5 and 10 nm by exposure to UV light. Compared to the Raman spectrum of ALA powder, changes in Raman lines' position and relative intensities when ALA has interacted with films obtained from Au nanoparticles with sizes between 5 and 50 nm were significant. These changes were explained by considering the chemical mechanism of surface-enhanced Raman scattering (SERS) spectroscopy. The photodegradation of ALA that had interacted with metallic nanoparticles was inhibited in the presence of RGO sheets.
15. Novel anhydrous solid-state form of Azathioprine: The assessing of crystal structure by powder X-Ray diffraction, Infrared Absorption Spectroscopy and Raman scattering
Authors: Covaci, OI; Samohvalov, D; Manta, CM; Buhalteanu, L; Barbatu, A; Baibarac, M; Daescu, M; Matea, A; Gherca, D

Published: FEB 15 2019, JOURNAL OF MOLECULAR STRUCTURE, 1178, 710, DOI: 10.1016/j.molstruc.2018.10.065

Azathioprine (Imuran), one of the oldest immunosuppressants, having been used in transplantation since the early 1960's, is known to have only two crystal forms: an anhydrous form and a dihydrate phase. We report the crystal structure of a new anhydrous solid-state form of Azathioprine, determined directly form powder X-Ray diffraction data, employing the direct-space genetic algorithm technique for structure solution, followed by Rietveld refinement. The new anhydrous polymorph is accessible only by a solid-state dehydration process of the readily obtained monohydrate form of Azathioprine, the form for which a crystal structure has not previously been reported. The IR and Raman spectra confirmed the results obtained from X-Ray diffraction indicating the presence of all functional groups involved in intermolecular hydrogen bonding which dictates different arrangement of molecules in the structural packing. (C) 2018 Elsevier B.V. All rights reserved.
16. Adsorption of 1,4-phenylene diisothiocyanate onto the graphene oxide sheets functionalized with polydiphenylamine in doped state
Authors: Baibarac, M; Daescu, M; Fejer, SN

Published: AUG 19 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-48314-x

Adsorption processes of 1,4-phenylene diisothiocyanate (PDITC) on two new platforms of the type graphene oxide (GO) sheets and GO layers functionalization with polydiphenylamine (PDPA) are studied by Raman scattering and photoluminescence (PL). An interaction in solid state phase of the two constituents, i.e. PDITC and GO sheets, and a deposition of PDITC onto the PDPA functionalized GO layers, respectively, by the drop casting method, were performed. In the first case, it is shown that interaction in solid state phase of GO with PDITC leads to an intercalation of the organic compound between GO sheets simultaneously with the appearance of the o-thiocarbamate groups, that induces: (i) an enhancement of the PDITC Raman lines situated in the 400-800 and 1000-1300 cm(-1) spectral ranges, (ii) a change in the ratio between the relative intensities of the two Raman lines peaked at 1585 and 1602 cm(-1) accompanied by an up-shift in the case of the second line and (iii) a down-shift of the PDTIC PL band from 502 to 491 nm. Using cyclic voltammetry, an electrochemical functionalization of the GO layers with PDPA doped with H3PMo12O40 heteropolyanions takes place, as demonstrated by Raman scattering and FTIR spectroscopy. The presence of the amine groups in the molecular structure of the doped PDPA functionalized GO layers induces a chemical adsorption of PDITC on this platform, when the thiourea groups appear simultaneously with o-thiocarbamate groups. A chemical mechanism is proposed to take place at the interface of the GO sheets and the doped PDPA functionalized GO layers, respectively, with PDITC.
17. Polyaniline photoluminescence quenching induced by single-walled carbon nanotubes enriched in metallic and semiconducting tubes
Authors: Baibarac, M; Matea, A; Daescu, M; Mercioniu, I; Quillard, S; Mevellec, JY; Lefrant, S

Published: JUN 22 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-27769-4

The influence of single-walled carbon nanotubes enriched in semiconductor (S-SWNTs) and metallic (M-SWNTs) tubes on the photoluminescence (PL) of polyaniline (PANI), electrosynthesized in the presence of the H2SO4 and HCl solutions, is reported. The emission bands peaked at 407-418 and 440-520 nm indicate that the electropolymerization of aniline (ANI) leads to the formation of short and longer macromolecular chains (MCs), respectively. We demonstrate that the reaction product consists of ANI tetramers (TT) and trimers (TR) as well as PANI-salt. Using Raman scattering and IR absorption spectroscopy, a covalent functionalization of SWNTs with shorter and longer MCs of PANI-salt is demonstrated. The presence of S-SWNTs and M-SWNTs induces a decrease in ANI TT weight in the reaction product mass consisting in S-SWNTs and M-SWNTs covalently functionalized with PANI-emeraldine salt (ES) and PANI-leucoemeraldine salt (LS), respectively. A PANI PL quenching is reported to be induced of the S-SWNTs and M-SWNTs. A de-excitation mechanism is proposed to explain PANI PL quenching.
18. Electrochemical characterization of the Poly(2, 2 '-Bithiophene-co-Pyrene) Functionalized Single-Walled Carbon Nanotubes Films and Their Applications in Supercapacitors Field
Authors: Baibarac, M; Baltog, I; Daescu, M

Published: MAR 2017, INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE, 12, 2025, DOI: 10.20964/2017.03.60

The performance of the poly(2, 2'-bithiophene-co-pyrene) copolymer doped with bis(2-ethyl hexyl) sulfosuccinate sodium (AOT) anions [(PBTh-Py)(+)AOT(-)] and its composite with single-walled carbon nanotubes (SWNTs) [(PBTh-Py)(+)AOT(-)/SWNTs] as active materials for the electrodes of symmetrical supercapacitors is demonstrated in this work. Using cyclic voltammetry, the influence of the electrolyte concentration and the different cations on the oxidation and reduction processes at the electrolyte/electrode interface is reported. Using charge-discharge galvanostatic measurements in the case of the symmetrical-supercapacitors having as electrode active materials, the (PBTh-Py)(+)AOT(-) copolymer and the (PBTh-Py)(+)AOT(-)/SWNTs composite, values of the specific capacitance equal with 11.5 and 59 F g(-1), respectively, for current densities of 100 mA g(-1), were reported.
19. Optical evidence for chemical interaction of the polyaniline/fullerene composites with N-methyl-2-pyrrolidinone
Authors: Baibarac, M; Baltog, I; Daescu, M; Lefrant, S; Chirita, P

Published: DEC 5 2016, JOURNAL OF MOLECULAR STRUCTURE, 1125, 349, DOI: 10.1016/j.molstruc.2016.07.001

Surface enhanced Raman scattering (SERS) spectroscopic studies reveal a particular chemical interaction of the polyaniline/fullerene (PANI/C-60) composite with N-methyl-2-pyrrolidinone (NMP). The chemical polymerization of aniline in the presence of sulfuric acid, potassium dichromate and fullerene has been used for the preparation of the PANI/C-60 composite. The polymerization reaction involves a doping of PANI with C-60 anion radicals. The interaction of the composite with NMP leads to a de-doping of PANI that involves a transformation of leucoemeraldine salt (LS) repeating units into leucoemeraldine base (LB). Additionally, a gradual increasing in the intensity of the Raman line at 1452 cm(-1) associated to the A(g)(2) pentagonal pinch mode of fullerene and a decrease in the intensity of the Raman lines of PANI are reported. This change arises from the formation of a charge-transfer complex C-60-NMP. The subsequent chemical treatment of PANI-LB with FeCl3 leads to the formation PANI-emeraldine salt. An inhibition of the transformation of PANI doped with C-60 anion radicals into a PANI-LB and the C-60-NMP charge transfer complex in the presence of CdS particles dispersed in NMP is demonstrated by SERS spectroscopy. (C) 2016 Elsevier B.V. All rights reserved.
20. Physico-chemical properties of two anhydrous azathioprine forms and their interaction with typical pharmaceutical excipients: highlighting new findings in drug formulation development
Authors: Barbatu, A; Lungan, MA; Toulbe, N; Smaranda, I; Daescu, M; Baibarac, M; Manta, CM

Published: , DRUG DEVELOPMENT AND INDUSTRIAL PHARMACY, DOI:

The physico-chemical properties of two anhydrous AZA forms and their interaction with typical pharmaceutical excipients were assessed by applying various methods (such as PXRD, HPLC, TG/DSC, IR, Raman, PL or UV-Vis) in order to highlight new directions for drug formulation. The stability assessment of AZA anhydrous forms I and II was performed in order to determine the risk of degradation of the active ingredient by accidental exposure to nonstandard conditions in the industrial environment, under different storage, transport or processing conditions. The benefits of form II include increased resistance to chemical degradation over a wide range of pH, but further control of storage and processing conditions is necessary to avoid polymorphic transformation into form I. The solubility assessment on the AZA solid forms in different environments that simulate the conditions of the gastrointestinal tract has the advantage of a significantly increased solubility of form II compared with the commercial form I due to the modification of the crystalline structure. In the case of capsules compared to AZA form I or II as powder, an improvement in their solubility was observed, promoted by the presence of one or more excipients in the formulation mixture.
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