Accepted Manuscript Structural characterization, AC conductivity, optical properties and biochemical study of a new hybrid phosphate: Scavenger of free radicals Ramzi Fezai, Hanene Hemissi, Ali Mezni, Mohamed Rzaigui PII:
S0022-2860(17)31188-2
DOI:
10.1016/j.molstruc.2017.09.011
Reference:
MOLSTR 24260
To appear in:
Journal of Molecular Structure
Received Date: 24 February 2017 Revised Date:
22 July 2017
Accepted Date: 6 September 2017
Please cite this article as: R. Fezai, H. Hemissi, A. Mezni, M. Rzaigui, Structural characterization, AC conductivity, optical properties and biochemical study of a new hybrid phosphate: Scavenger of free radicals, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.09.011. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Structural characterization, AC conductivity, optical properties and biochemical study of a new hybrid phosphate: scavenger of free radicals
(a)
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Ramzi Fezai(a)*, Hanene Hemissi(a), Ali Mezni(b), Mohamed Rzaigui(a)
Laboratoire de Chimie des Matériaux, Faculté des Sciences de Bizerte, 7021 Zarzouna,
Université de Carthage, Tunisie.
Laboratoire des substances bio-actives, Faculté des Sciences de Bizerte 7021 Zarzouna,
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(b)
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Université de Carthage, Tunisie.
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* For correspondence
Contact Information: Tel: +216 97 069 565; fax: +216 72 590 566
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E-mail:
[email protected]
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[email protected]
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Structural characterization, AC conductivity, optical properties and biochemical study of a new hybrid phosphate: scavenger of free radicals
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Abstract
Single crystal of the hybrid compound [p-(F)C6H4NH3]6P6O18.2H2O has been grown with sizes up to 0.65 x 0.45 x 0.3 mm3 by the slow evaporation method. The crystal structure
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of this material was determined by single crystal X-ray diffraction. It crystallizes in the triclinic space group P1 with the lattice parameters a = 10.16(3) Å, b = 15.87(3) Å, c =
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16.36(4) Å, α = 80.93(2)°, β = 85.92(18)°, γ= 85.31(2)°, V = 2591.1(12) Å3 and Z = 2. Its crystal structure is a packing of alternated inorganic and organic layers parallel to (a, c) planes. The cohesion of the structure is essentially ensured by a hydrogen bonding network as well as electrostatic and Van Der Walls interactions and also F…F interactions so as to
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increase the stability of the 3D-network. The effect of the nature of the substituent in paraposition with respect to amine group on obtained structures and on other studied properties was discussed. Crystal symmetry is confirmed by
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P MAS-NMR. Furthermore, IR
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characteristics and thermal analysis are given. The luminescent properties of this material
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have been carried out at room temperature based on UV absorption spectroscopy data. AC conductivity of this compound has been investigated by means of impedance spectroscopy measurements in the 303–383 K temperature range. The antioxidant study was determined, in vitro, using 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical and reducing power and with ascorbic acid as a control. X-rays structural results are correlated with electrical and antioxidant findings. Key words. Hybrid material; X-ray diffraction; Crystal structure; AC conductivity; Optical properties; Antioxidant activity. 2
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1. Introduction Several studies are devoted to research of organic-inorganic materials, with open structures, with interesting physicochemical properties and therefore can be used in various applications. These compounds represent an advanced field in material sciences. Hybrid
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phosphate materials occupy an important position for their specific physical and chemical properties [1-3]. The study of the electrical properties of these compounds is a dynamic field of research. Impedance spectroscopy is one of the methods that are able to give valuable
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information about conduction mechanism and to understand the nature and the origin of dielectric losses may be useful in the determination of structure and defects in solids [4, 5].
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Up to now, various cyclohexaphosphate structures with interesting topologies and properties have been determined by taking into account many synthetic factors, such as pH values, solvents and temperature. Among them, the most important one in determining the final structure is the functionality and conformation of the organic molecules [6-9]. In this
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context, the organic amines based on aniline have been illustrated to be the most suitable organic bridging ones for the synthesis of hybrid cyclohexaphosphates [10-18]. Particularly, the organic amines reporting a para-substituent with respect to the amine function are largely
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used. As an extension of our previous studies on hybrid organic cyclohexaphosphate
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materials, in this work, we report a new cyclophosphate, [p-(F)C6H4NH3]6P6O18.2H2O. In addition to the structural description, its characterization and electrical study we have discussed the effect of the nature of the substituent in para-position with respect to the amine function on the obtained structures and on the other studied properties. Also, we have investigated the antioxidant activity of this hybrid compound. Recently, scientists are interested in new compounds, either synthesized or obtained from natural sources, which could provide active components to prevent or reduce the impact of oxidative stress on cells. The negative effects of oxidative stress may be mitigated by antioxidants [19, 20].
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2. Materials and Methods 2.1. Chemical preparation Chemistry part of this work consists in carrying out interactions between the cyclohexaphosphoric acid (H6P6O18) and the para-fluoroaniline. The H6P6O18 acid which is
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not commercialized was produced from Li6P6O18.6H2O (Shûlke et al., 1985) [21] by cationexchange on resins (Amberlite IR 120). Crystals of the title compound were prepared by adding dropwise an ethanolic solution (10 mL) of p-fluoraniline (6 mmol) to an aqueous
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solution (20 mL) of cyclohexaphosphoric acid (1 mmol). The reaction mixture was stirred at room temperature for few minutes. Good quality crystals of the title compound appeared after
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a few days.
2.2. Materials and measurements
Experimental details of X-ray diffraction and crystallographic data for a selected crystal are reported in Table 1. The crystallographic data for the structure reported in this paper have
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been deposited with the Cambridge Crystallographic Data Center under CCDC Number 1533105. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, fax: +44 1223 336 033, email:
[email protected]; or
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P MAS-NMR spectrum of the studied compound was performed at room
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The
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on the web: http://www.ccdc.cam.ac.uk.
temperature on a Bruker MSL 300 solid state high-resolution spectrometer operating at 121.495 MHz. The infrared absorption spectrum was recorded in the 400–4000 cm-1 range using a NICOLET IR 200 FT-IR infrared spectrometer. DSC was performed using the “multimodule 92 Setaram analyzer” operating from room temperature up to 400 °C at an average heating rate of 5 °.min-1. The UV absorption spectrum was recorded at room temperature with a Perkin Elmer Lambda 11 UV/Vis spectrophotometer in the range of 200-400 nm. Solid-state emission and
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ACCEPTED MANUSCRIPT excitation spectra were recorded for the solid sample which was loaded into a sample cell (1 cm diameter) which was then fixed on a bracket at room temperature with Perkin-Elmer LS55 spectrofluorometer. The slit widths used for the excitation and emission measurements were 2.5 and 11.5 nm respectively. The scan speed was 1200 nm.min-1.
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The impedance diagrams were recorded in the 5 Hz–13 MHz frequency range using a Hewlett Packard HP 4192A analyzer with 5°C steps. Impedance measurements were performed as function of temperature (303- 383 K). The finely grain sample was pressed into
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pellet of 13 mm diameter and 1.11 mm thickness using a hydraulic press. Both pellet surfaces were coated with silver pastes to act as electrodes and platinum wires attached to the
3. Results and discussion 3.1. Structure description
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electrodes were used as current collectors.
The chemical composition of [p-(F)C6H4NH3]6P6O18.2H2O is depicted in Figure 1. It
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shows the conformation adopted by phosphoric rings, organic cations and water molecules. The atomic arrangement of the title compound is typical of a layer organization (Fig.2). The inorganic layers built up from P6O186- anions, the water molecules and (-NH3) groups develop
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in the (010) planes. Organic cations are located in the interspaced layers and establish
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hydrogen bonds to interconnect the different entities. The projection of one layer along [0 1 0] direction (Fig.3) shows how the basic entities are linked together by O-H…O and N-H…O hydrogen bonds where O-H…O range from 2.843(4) to 3.195(4) Å and N-H…O between 2.707(4) and 3.197(4) Å (Table 2). Despite these bonds are not strong, they allow, by their cumulative effect, a good crystalline stability. This structure is also characterized by the presence of F…F interactions [22]; along the b axis, we report a strong interactions where the distances dF…F range from 3.28 to 3.53 Å in order to increase the stability of the three
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ACCEPTED MANUSCRIPT dimensional network. These interactions were also observed along the c axis, the values of dF... F are between 3.15 and 3.61 Å (Fig.4) improving the stability within each layer. Inside such layer, there are two independent P6O18 rings located around the inversion center (0,1/2,0) and (1/2,1/2,1/2) respectively. These two independent phosphoric rings have
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differences in space representation and angle of orientation relative to the mean plane (Fig.5). In fact, rings built by P1, P2 and P3 are orientated at an angle of 58.55° and that formed by P4, P5 and P6 are oriented at an angle of 63.33°. Examination of the main geometrical
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features (Table S1) of PO4 tetrahedral shows clearly that, despite the P–P–P angles deformation, they are in accordance with others observed cyclohexaphosphates [11, 12, 23].
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In this structure, there are six crystallographically independent organic groups where the aromatic rings are perfectly planar. Interatomic distances and angles C – C, C – N, C - C - C and C - C - N do not reflect any particular deformation. Disposition and orientation of the organic groups are depicted in Fig.2. These cations are oriented in various directions
ammonium groups.
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connecting phosphoric anions of the same layer and the neighboring layers via their
Another characteristic feature of this structure is the presence of a free water molecule,
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O(W2) which is not involved in the Hydrogen-bending scheme. The thermal factor of its oxygen atom (O20) is significantly larger than those generally observed as in these two
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compounds [18, 24].
3.2. Effect of the nature of the substituents in para-position on obtained structures An
examination
of
the
literature
shows
the
existence
of
some
hybrid
cyclohexaphosphates where the organic cations are based on aniline with substituents in paraposition with respect to the amine function [25-29]. We report in table 3 the crystallographic parameters of these structures. The macroscopic structures such as the organization of inorganic anions and organic cations are similar to those of other derivatives of the same
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ACCEPTED MANUSCRIPT cyclohexaphosphates family, but each compound has its specific digital prints atomic positions, hydrogen bonding patterns and physicochemical properties. We note that the first compound (I) crystallized in the monoclinic system with two formula unit per cell, the substituent in the organic amine for this compound is a methyl group
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(-CH3) which is donor (+I). The other compounds form (II) to (VI) crystallized in the triclinic system. The organic amines in these cyclohexaphosphates contain the following substituents: (-OMe), (-OEt), (-NH3), (-Cl) and (-F) which are donor (+M) and attractor (-I). These
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materials present different atomic arrangements and unit cell parameters. The P6O18 rings in these structures are centrosymetric and adopt a chair conformation. In the studied material
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(VI), two independent phosphoric rings where observed, while, in the other compounds we note the presence of only one ring built by three independent PO4 tetrahedral from which the three others are deduced by symmetry. Also, in this structure, we report six independent organic cations whereas, in the other compounds only three protonated nitrogen were
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observed and so three independent organic cations.
These observations explain the difference in volumes where it is around 2591 Å3 with Z = 2 for (VI) while lower than 1653 Å3 from (II) to (V) with Z = 1. Despite this structure is less
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hydrates than the others with the exception of (IV) it presents the denser hydrogen bending network where we note 26 hydrogen bonds while in the other compounds it does not exceed
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20 hydrogen bonds. Also, we note that the two structures with a halogen groups (Cl) and (F) are the least hydrated.
The most compact structure is that formed by the paraphenylendiamine organic amine (V) with a distance between the phosphoric chains (P.C.) equal b = 9.92 Å and then we found (II) with dP.C. = 11.87 Å, then (I) with dP.C. = b/2 = 12.47 Å, then (III) dP.C. = 15.25 Å and finally (VI) and (IV), synthesized from the organic amines with halogen groups in para position, with dP.C. = 15.87 and 16.44 Å respectively.
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ACCEPTED MANUSCRIPT 3.3. Characterization Spectroscopic characterizations have been carried out to elucidate the obtained structure. To confirm the symmetry of the phosphoric anions we have recorded the 31P MASNMR spectrum of [p-(F)C6H4NH3]6P6O18.2H2O reported in Fig. 6. Six resonance peaks are
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observed at: -16.78, -18.68, -20.01, -23.28, -25.35 and -26.82 ppm characteristic of the independent phosphoric sites in this organic cyclohexaphosphate. These sites are due to the presence of two symmetric P6O18 rings formed each one by three crystallographically
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independent PO4 tetrahedral from which the three others are deduced by symmetry. The presence of this number of peaks confirms x-ray results. The NMR study of some reported
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literature compounds shows only three signals due to the presence of only one symmetric P6O18 ring [10, 25, 30] and even for the compound showing two independent phosphoric rings, four peaks have been observed due to the similarity of the chemical environments of some phosphorus sites [18]. Moreover, to analyze the presence of various functional groups in
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the obtained crystals, the synthesized compound has been studied by IR absorption spectroscopy. The infrared spectrum (Fig.7) exhibits the vibrations of different components of this material. Characteristic bands at 1247, 1132 and 1095 cm-1 are related to asymmetric and
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symmetric stretching vibrations of OPO groups, while those at 1023, 958, 830 and 799 cm-1 are assigned to POP groups [31]. Broad bands in the range of 3500-2800 cm-1 correspond to
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OH stretching vibrations of water molecules as well as to that of ammonium groups. The observed bands in the 1680-1350 cm-1 region are due to the deformation vibrations of C=C, OH, and NH3 groups. It is also noted that, in addition to these bands, the band at 830 cm-1 with absence of bands between 675 and 700 cm-1 show that the aromatic ring is paradisubstituted. These vibrations already given confirm the presence of p-fluoroaniline (the amine used in our synthesis).
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ACCEPTED MANUSCRIPT The thermal stability of the synthesized cyclohexaphosphate was studied using differential scanning calorimetry. DSC curve reveals series of endothermic peaks (Figure 8). Based on literature results including thermogravimetric curves, the first peak at 78°C corresponds to the release of water molecules. After the dehydration, the organic entity of the anhydrous
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compound undergoes decomposition in a wide temperature range to give polyphosphoric liquid acid contaminated with black residue of carbon. The departure of water molecules at a low temperature can be explained by the thermal agitation of one of the two water molecules.
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This behavior was observed in the study of [2,3-(CH3)2CH3NH3]6P6O18.2H2O [18] where the dehydration was found at 65°C due to the thermal agitation of water molecules. These
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observations show that the studied material is thermally less stable with compare to others organic cyclohexaphosphates where water molecules have normal thermal agitation [10, 25, 27]. 3.4. Optical properties
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The UV–visible absorbance spectrum of the synthesized compound was studied in a mixture aceton & methanol solution and is shown in Fig. 9(a). It exhibits broad absorption bands at 235 and 288 nm. These absorption bands were attributed to the n–π* transition, due
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to the presence of unshared electron pairs of fluor element, and to the strong π–π* transitions of the delocalized π electrons in the p-fluoroanilinium cation. The gap energy was determined
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from the optical diffuse reflectance spectrum (Fig. 9(b)). The observed gap value is 4.94 eV showing that the studied structure corresponds to a stable system under the ambient conditions (a charge transfer reaction needs variation of environmental conditions). Despite the largest of the band gap, electrical study shows that the electrical conductivity is about 10-7 S.cm-1. These results indicate that the title compound is a semiconductor with wide band gap [32]. Comparatively, fluorescent properties of the synthesized material were determined at room temperature. Fig. 10(a) shows the emission spectrum, of this organic cyclohexaphosphate,
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ACCEPTED MANUSCRIPT studied at the excitation wavelength of 280 nm. It depicts emission bands that occur in the visible region of the electromagnetic spectrum. A broad band is observed around 400 nm accompanied by a shoulder emission peak at 488 nm which are attributed to electron transitions from the lowest energy level of the π* orbital to the n and π orbitals [1, 33]. The
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excitation spectrum which represents the variation of the intensity of the emission band at 400 nm as a function of excitation wavelengths is reported in Fig. 10(b). It exhibits two distinct bands with maximum peaks observed at 288 and 338 nm confirming the selected region of
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excitation wavelength.
3.5.1. Impedance analysis
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3.5. Electrical properties
The Nyquist diagram, (- Z′′) versus (Z′) of the impedance data, of the title compound [p-(F)C6H4NH3]6P6O18.2H2O at different temperatures is given in Fig. 11. This figure shows typical semicircles which become tediously smaller as the temperature increases. The
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electrical response was further fitted with a series network (RP1//CPE1)–(RP2//CPE2). Where the RP1 (Rg), RP2 (Rgb) represent the bulk resistance and the fractal capacitance of the interface CPE1, CPE2 represent the effect of electrode (capacity of the fractal interface CPE).
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Figures 12 and 13 present the real and imaginary parts of impedance Z′ and Z′′ as a function of frequency at different temperatures respectively. The magnitude of Z′ decreases
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with increasing temperature and frequency. While, the variation of the imaginary part of impedance Z′′ reveals that ′ values reach two maximums ( max), which shift to higher frequencies with increasing temperatures. Such behavior indicates the presence of two relaxation process in the system. One related to the grain and the other is due to the presence of grain boundaries.
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Where: -
ω is the angular frequency of measurement,
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A is fitting parameter, which is, principally, temperature dependent.
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The exponent n is related to the interaction of the transferring charge entities with
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-
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the matrix.
Figure 14 shows the frequency-dependent conductivity as a function of temperature. This
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figure shows for T ≤ 313 K two distinct regimes: plateau and dispersion [35]. Then for T ˃ 313 we observe two parts separate at 100 KHz with two distinct regimes (plateau and dispersion), so the equation (*) can be expressed as the following relation: σ(ω) = σ(0) + Aωn1 + σ′ (0) + Bωn2
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The conductivity of the sample has been obtained from the sample’s geometric factor e⁄s and the resistance R (the intercept of the semicircle with the real axis) as
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following:
σ = e/s × 1/R
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We report in Fig. 15 the temperature dependence of the conductivity in a Ln(σT) versus 1000/T. This curve shows two regions separated at 341 K, each one is characterized by a constant activation energy (Ea1 = 1.72 and Ea2 = 0.68 eV) suggesting that the conductivity of the title compound is thermally activated and follows the Arrhenius law very well σT = A0exp(-Ea/kT). We note that this conductivity increases with the temperature showing that this material has semiconductor behavior. Two mechanisms of conductivity are obvious. The first one, corresponding to the starting hydrated compound, occurs before 341 K temperature, the second mechanism, corresponding to the anhydrous phase obtained after dehydration. The
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ACCEPTED MANUSCRIPT conductivity continues to increase rapidly until about 400 K where the compound starts to decompose. 3.5.3. Modulus analysis To analyze the electrical properties we have also used the modulus formalism which
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gives information about the relaxation mechanism. The complex electrical modulus can be represented by the following expression:
M* = 1/ε* = jωC0Z* = M ′ + j M ′′, C0 = ε0S/e
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Where C0 is the vacuum capacitance of cell and ε0 is the permittivity of the free space, S the electrolyte–electrode contact area and e the thickness of the sample.
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The frequency responses of the real part of the electrical modulus M′ at different temperatures is depicted in Figure 16(a). At low frequency region, this variation is characterized by very low value of M′ then an increase in the value of M′ with the frequency approaching to M ∞ for all temperatures due to relaxation process [36, 37].
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Fig. 16(b) shows the imaginary part M′′ of the electrical modulus as a function of frequency at various temperatures. This variation has a different appearance than those typically observed; well-defined maximums (M''max) whose positions shift to higher frequency
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side with the rise in temperature [38-40]. In the present work, we note a first maximum M''max then an increase of the values of M'' which indicates the presence of two relaxation process in
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this material.
3.6. Correlation between electrical and structural properties The study of the electrical properties of this compound showed, differently to other literature results, the presence of two relaxation process. It was found that the imaginary parts of impedance and modulus, Z'' and M'', show two maximums and also the frequency dependence conductivity indicates two parts with two distinct regimes (plateau and dispersion). This behavior has been observed for the organic cyclohexaphosphate [2,3-
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The electrical conduction in the title compound (7.10-7 at 35°C and 77.10-7 S cm-1 at 90°C with activation energy 1.72 and 0.68 eV) is provided by the movement of H+ protons [42]. The structure of this organic cyclohexaphosphate exhibits a three dimensional hydrogen
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bending network where the H+ protons move along a chains, this movement relies on the passage of protons across the two P 6 O 1 8 rings. The conduction strength depends on
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the strength of the involved hydrogen bonds which could explain the difference in the measured conductivity values compared to other materials involving the same conduction type. The conductivity in this structure is greater than in the lamellar structures where the movement of H+ occurs in only two directions [43, 44].
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3.7. In vitro antioxidant activity
The antioxidant capacity of [p-(F)C6H4NH3]6P6O18.2H2O was studied at various concentrations. This capacity was determined, in vitro, using 1,1-diphenyl-2-picrylhydrazyl
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(DPPH), hydroxyl scavenging ability, reducing power and with ascorbic acid as a control. The obtained results were compared to that of the free para-fluoroaniline.
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The antioxidant activities of the studied compound were assessed on the basis of the free radical scavenging effect of the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH•). This activity was determined by modified method (Braca et al., 2002) [45]. The optical density was recorded and percentage (%) of inhibition was calculated using the formula given below: % inhibition of DPPH activity = [(Abs cont−Abs test) /Abs cont] × 100 Where Abs cont = absorbance of the control (reacting mixture without the test sample) and, Abs test sample = absorbance of reacting mixture with the test sample.
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ACCEPTED MANUSCRIPT Figure 17 shows the DPPH• scavenging activity of this compound at different concentration compared to that of ascorbic acid and that of free para-fluoroniline. It was found that this organic cyclohexaphosphate has the highest radical-scavenging activity (RSA) at 1 mg/mL; the percentage of scavenging DPPH radicals is 88.71%±0.06 and the IC50 = 0.48 mg/mL.
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Compared with ascorbic acid at the same concentration, the percentage of inhibition of DPPH is 94.08%±0.26 and the IC50 = 0.45 mg/mL. The ability of this material to scavenge DPPH• has been also observed with the others concentrations showing important percentages of RSA
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which exceeds 84% (%RSA = 84.98%±0.09 at 0.25 mg/mL and 86.02%±0.16 at 0.5 mg/mL). The presence of para-fluoroaniline participate, with important percentages, in this
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effectiveness. This is confirmed by its ability to scavenge free DPPH radicals (75.68%±0.58 at 0.25 mg/mL and 81.43%±0.37 at 1 mg/mL). In addition to the test against DPPH radicals, we have also evaluated the ability of the studied material to scavenge hydroxyl radicals using the method of Halliwell and Gutteridge (1981) [46]. The ability of [p-(F)C6H4NH3]6-
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P6O18.2H2O to prevent Fe2+/H2O2 is a result of deoxyribose decomposition in Fenton reaction. The test results were summarized in Figure 18. All concentrations of the studied phosphate scavenge hydroxyl radicals. The HO• scavenging ability of this compound increase with
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increasing concentration from 76.6%±0.21 at 0.25 mg/mL to 86.52%±0.26 at 1 mg/mL. At the highest concentration the IC50 of the tested compound is about 0.49 mg/mL compared to
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that of ascorbic acid at the same concentration, the percentage of scavenging is 96.16%±0.46 and the IC50 = 0.43 mg/mL. This capacity is mainly due to the impact of the parafluoroaniline which presents an important ability to scavenge hydroxyl radical with percentages of inhibition very close to that of the studied structure (76.07%±0.28 at 0.25 mg/mL and 84.49%±0.68 at 1 mg/mL). Besides, the results of the ferric reducing power (FRP) of the elaborated cyclohexaphosphate were reported in Figure 19. The FRP evaluation was determined according to the method of
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ACCEPTED MANUSCRIPT Pulido et al. (2000) [47] by assessing its ability to reduce a FeCl3 solution. It was found that this organic cyclohexaphosphate exhibits moderate ferric reducing power with compare to the results of radical scavenging capacity (DPPH• and OH•). In fact, at the highest concentration (1 mg/mL), the tested compound has a reducing power, equal to that of the free organic
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amine, about 47% with IC50 = 0.88 mg/mL, compared to that of ascorbic acid at the same concentration (68.22%±1.57, IC50 = 0.56 mg/mL).
3.8. Correlation between antioxidant and structural properties
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The two tests against free radicals (DPPH• and OH•) show that the studied compound is a good scavenger of free radicals compared to ascorbic acid. This effectiveness can be
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explained by the proton diffusion ability as well as the composition of the molecular structure of the tested compound which contains para-fluoroanilinium cations and P6O18 anions reporting reactive sites such as oxygen and nitrogen atoms.
The significant antioxidant activity observed for this material, compared to others compounds
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such as the Benzo(1,3,2)diazaphosphorin-2-oxide and γ-Cyano-α-Hydroxy-phosphonate derivatives [48, 49], can be explained by the structure composition based on P6O18 anions and para-fluoroanilinum cations, which play an important role in this effectiveness, where oxygen
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and nitrogen atoms form a three dimensional hydrogen bending network involved as donor and/or acceptor of electrons and thus by the mobility of H+ protons. This result suggested that
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the tested material has a good ability to donate electrons to reactive free radicals, converting them into more stable products. The proton diffusion ability could explain the behavior of this material as free radical inhibitor or scavenger, acting possibly as primary antioxidant.
4. Conclusions The results of X-ray diffraction on a single crystal of this compound confirm a typical layers structure parallel to the (a, c) planes. Between these layers, the parafluoroanilinium cations are located to ensure the cohesion of the crystalline network by different types of
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ACCEPTED MANUSCRIPT interactions (hydrogen bonds electrostatic, Van Der Waals, F...F). Solid-state 31P MAS-NMR results are in accordance with the X-ray number of phosphoric sites. The vibrational properties of this structure were studied by infrared spectroscopy showing vibrations of all components of the structure. Optical properties show an important Gap energy confirming the
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semiconductor behavior and the blue photoluminescent property. Differential scanning calorimetry and dielectric measurement studies were carried out and showed the appearance of two phases separate at 341 K. The AC conductivity is found to obey the universal power
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law in the both phases I and II. The biochemical study showed that this Compound has an antioxidant character; this is demonstrated by scavenging DPPH radicals, hydroxyl radical
AKNOWLEDGEMENTS
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scavenging significantly to that of ascorbic acid and it has a moderate reducing power.
We acknowledge the team of the materials physics laboratory, Sciences Faculty of Bizerta for their collaboration giving rise to the electrical measurement of the studied
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ACCEPTED MANUSCRIPT [10] R.bel haj salah, L.Khedhiri, C. Ben Nasr, M. Rzaigui, Phosphorus Sulfur. 185 (2010) 595–601. [11] O.S.M. Elmokhtar, S. Abid, M, Rzaigui, A. Durif, Mater. Chem. Phys. 42 (1995) 225– 230.
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[12] E. H. Soumhi, T. Jouini, Acta Cryst. C 52 (1996) 2802–2805.
[13] K. Larafa, A. Mahjoub, M. Rzaigui, Eur. J. Solid. State Inorg. Chem. 34 (1997) 481–494. [14] H. Marouani, M. Rzaigui, M. Bagieu-Beucher, Acta Cryst. C 56 (2000) 356.
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[15] L. Khederi, H. Marouani, M. Rzaigui, Z. Kristallogr. NCS 216 (2001) 429–430. [16] L. Khedhiri, Z. Kristallogr. NCS 218 (2003) 233–234.
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[17] L. Khedhiri, C. B. Nasr, M. Rzaigui, F. Lefebre, Helv. Chim. Acta 86 (2003) 2662–2670. [18] R. Fezai, L. Khedhiri, M. Rzaigui, J. Adv. Chem. 2 (2015) 3490–3504. [19] R.A. Larson, Arch. Insect Biochem. Physiol. 29 (1995) 175–186. [20] W.A. Pryor, Am. J. Clin. Nutr. 53 (1991) 391–393.
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[21] U. Schulke, R. Kayser, Z. Anorg. Allg. Chem. 531 (1985) 167–176. [22] I. Cs¨oregh, T. Brehmer, P. Bombicz, E.Weber, Cryst. Eng. 4 (2001) 343–357. [23] H. Marouani, M. Rzaigui, Solid State Sci. 1 (1999) 395–408.
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[24] M. B. Beucher, M.T.A. Pouchot, M. Rzaigui Acta Cryst. C 47 (1991) 1364–1366. [25] C. Ben Nasr, M. Rzaigui, Mater. Res. Bull. 34 (1999) 557–569.
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[26] M.O. Abdellahi, F. Ben Amor, A. Driss et T. Jouini, Acta Cryst. C 54 (1998) 813. [27] H. Marouani, M. Rzaigui, S. Al-Dheyab. Phopsphorus Sulfur. 186 (2010) 255-262. [28] L. Khediri, E. Jeanneau, F. Lefebvre, M. Rzaigui, C. Ben Nasr, J. mol. Struct. 1105 (2016) 87–95. [29] R. Fezai, A. Mezni, M. Kahlaoui, M. Rzaigui, J. Mol. Struct. 1119 (2016) 54–63. [30] C. Ben Nasr, I. Saıd, M. Rzaigui, Mater. Res. Bull. 36 (2001) 789–798. [31] M. Charfi, A. Jouini, J. Solid. State Chem. 127 (1996) 9–18.
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ACCEPTED MANUSCRIPT [32] S. Z. Wen, W.Q. Kan, H.Y. Hu, Y.H. Kan, Inorg. Chem. Commun 52 (2015) 12. [33] A. Maalaoui, A. Hajsalem, N.R. Ramond, S. Akriche. J. Clust. Sci. 25 (2014) 1525– 1539. [34] B. Louati, M. Gargouri, K. Guidara, T. Mhiri, J. Phys. Chem. Solid 66 (2005) 762.
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[37] A. Ben Rhaiem, F. Hlel, K. Guidara, M. Gargouri, J. Alloys Compd. 463 (2008) 440– 445.
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[38] H. Nefzi , F. Sediri, H. Hamzaoui, N.Gharbi, J. Solid State Chem. 190 (2012) 150–156. [39] H. Chouaib, S.Kamoun, J. Phys. Chem. Solid 85 (2015) 218–225. [40] A. Oueslati, F. Hlel, K. Guidara, M. Gargouri, Journal of Alloys and Compounds 492 (2010) 508–514.
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[41] R. Fezai, A. Mezni, M. Rzaigui, J. Chem. Biol. Phys. Sci. A 6 (2016) 376–386. [42] J. Angyan, M. Allavena, M. Picard, A. Potier, O. Tapia, J. Chem. Phys. 77 (1982) 4723– 4733.
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[43] H. Barbes, G. Mascherpa, R. Fourcade, B. Ducourant, J. Solid State Chem. 60 (1985)
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[44] P. Hagenmuller, W. Van Gool ‘Solid Electrolytes’, Academic Press (1978) 213. [45] A. Braca, N.D. Tommasi, L.D. Bari, C. Pizza, M. Politi, I. Morelli, J. Nat. Prod. 64 (2001) 892–895.
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ACCEPTED MANUSCRIPT Figure Captions Fig. 1: ORTEP Plot of inorganic anions, independent organic cations and water molecules of the title structure. Thermal ellipsoids at 25% of probability. Fig. 2: Projection of the crystal structure of [p-(F)C6H4NH3]6P6O18.2H2O, along the a axis,
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The phosphoric anions are given in tetrahedral representation . Hydrogen bonds are shown as dashed lines.
Fig. 3: Projection along the b axis of the atomic arrangement of [p-(F)C6H4NH3]6P6O18.2H2O.
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The phosphoric anion is given in a tetrahedral representation. The organic cations have been rendered ammonium groups for clarity. Hydrogen bonds are plotted by dashed lines.
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Fig.4: Fragment of the [p-(F)C6H4NH3]6P6O18.2H2O crystal structure. The relatively short intermolecular F···F contacts are given by dashed lines. Fig. 5: Geometry of the two phosphoric rings.
Fig.6: Proton-decoupled 31P MAS-NMR spectrum of [p-(F)C6H4NH3]6P6O18.2H2O.
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* Spinning side bands.
Fig.7: IR spectrum of [p-(F)C6H4NH3]6P6O18.2H2O. Fig.8: DSC curve of [p-(F)C6H4NH3]6P6O18.2H2O.
studied material.
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Fig.9: UV-Visible absorption spectrum (a) and UV diffuse reflectance spectrum (b) of the
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Fig. 10: Emission (a) and excitation (b) spectra for the title compound Fig. 11: Complex impedance diagrams (- Z′′ vs Z′) for [p-(F)C6H4NH3]6P6O18.2H2O at various temperatures.
Fig.12: Plot of the real part of impedance Z′ vs. log(f) of [p-(F)C6H4NH3]6P6O18.2H2O at various temperatures. Fig.13: Plots of the imaginary part of impedance Z′′ vs. log(f) of [p-(F)C6H4NH3]6P6O18.2H2O at various temperatures.
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ACCEPTED MANUSCRIPT Fig.14: The frequency dependence of AC conductivity σAC at various temperatures in the structure of [p-(F)C6H4NH3]6P6O18.2H2O. Fig.15: Variation of Ln(σT) as a function of (1000/T) for. Fig.16 (a)-(b): Variation of the real part M′ (a) and imaginary parts M′′ (b) of the electric as
a
function
of
the
frequency
at
various
temperatures
in
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(F)C6H4NH3]6P6O18.2H2O
[p-
Fig. 17: DPPH Radical Scavenging Activity (AA: ascorbic acid, 4-F: Free amine, 4-F+P6: tested compound).
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Fig.18: OH radical scavenging ability of [p-(F)C6H4NH3]6P6O18.2H2O (AA: ascorbic acid, 4-
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F: Free amine, 4-F+P6: tested compound).
Fig. 19: Reducing power assay (AA: ascorbic acid, 4-F: Free amine, 4-F+P6: tested
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compound).
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ACCEPTED MANUSCRIPT Table 1. Data collection and final results of the structure determination.
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I. Crystal data Formula: [p-(F)C6H4NH3]6P6O18.2H2O Formula weight: 1188.59 System: Triclinic Space group: P-1 Unit-cell parameters: a = 10.157(3) Å, b = 15.868(3) Å, c = 16.365(4)Å α= 80.93(2)°, β = 85.92(18)°, γ= 85.31(2)° Z: 2 3 V (Å ) 2591.1(12) F(000) 1228 -1 Linear absorption factor µ , mm 0.166 3 Crystal size, mm (0.65 x 0.45 x 0.3) Morphology Colorless prisms II. Intensity measurements Diffractometer Enraf-Nonius MACH 3 Monochromator Graphite Radiation AgK α (0.56085) Temperature, K 293 -3 Densit y (calculated), g.cm 1.533 -1 Absorption coefficient, mm 0.177 θ range for data collection, ° 2 - 28 Absorption Correction: refined from Reflections measured 11677 (Rint = 0.029) Independent reflections 9837 III. Structure determination 6033 [(I) > 2 σ(I)] Unique reflections included Number of parameters refined 727 -3 Residual Fourier densit y, e Å -0.37 < ρ < 0.86 R and wR indices (all data) 0.06; 0.18 2 Goodness of fit on F 1.04
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ACCEPTED MANUSCRIPT Table 2. Hydrogen-bonds geometry (Å, °) in [p-(F)C6H4NH3]6P6O18.2H2O. D…A 2.819(4) 2.710(4) 2.830(4) 2.830(4) 2.773(4) 2.981(4) 2.808(4) 2.718(4) 2.724(4) 2.707(4) 2.726(4) 2.788(4) 2.972(4) 2.774(4) 2.890(4) 2.739(4) 3.083(4) 2.777(4) 2.815(4) 2.765(4) 2.715(4) 2.769(4) 3.197(4) 3.195(4) 3.000(4) 2.843(4)
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Symmetry codes : i : -1+x,y,z ; ii : 1-x,1-y,1-z ; iii : 2-x,1-y,-z
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D H…A 135 120 103 110 135 115 117 115 152 168 154 146 129 125 170 165 119 160 157 141 158 128 149 157(3) 126(3) 165(3)
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2.12 2.15 2.49 2.40 2.07 2.50 2.29 2.22 1.90 1.83 1.90 2.00 2.33 2.16 2.01 1.87 2.55 1.92 1.97 2.02 1.87 2.14 2.40 2.39(3) 2.41(3) 1.98(2)
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0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.86(3) 0.86(3) 0.89(2)
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N(1) - H(1A) ...O(18) N(1) - H(1B) ...O(3) N(1) - H(1B) …O(17)iii N(1) - H(1C) ...O(17)iii N(2) - H(2A) ...O(10) N(2) - H(2B) ...O(16) N(2) - H(2B) ...O(15)iii N(2) - H(2C) ...O(17)iii N(3) - H(3A) ...O(6) N(3) - H(3B) ...O(9)i N(3) - H(3C) ...O(10)i N(4) - H(4A) ...O(8)i N(4) - H(4B) ...O(6) N(4) - H(4B) ...O(12)i N(4) - H(4C) ...O(9)ii N(5) - H(5A) ...O(1) N(5) - H(5B) ...O(7) N(5) - H(5B) ...O(5)ii N(5) - H(5C) ...O(8)ii N(6) - H(6A) ...O(18)i N(6) - H(6B) ...O(14) N(6) - H(6C) ...O(5) N(6) - H(6C) ...O(19) O(19)- H(19A) ...O(2) O(19) - H(19A) ...O(5) O(19) - H(19B) ...O(12)
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para-position in the organic cations. Cell parameters b c (Å) β γ ((°)
S. G
V(Å3)
Ref
11.163(4)
2
P21/c
2953(2)
[25]
1
[p-(CH3)C6H4NH3]6 P6O18.8H2O (I)
10.69(6)
[p-(OMe)C6H4NH3]6 P6O18.4H2O (II)
9.69(3)
17.87(4)
9.64(4)
87.27(2)
116.30(3)
92.66(2)
15.25(4)
11.04(2)
10.62(3)
108.35(2)
95.56 (2)
99.16 (2)
9.00 (8)
10.10(9)
16.44(14)
100.48(7)
93.48(7)
115.41(9)
[p-(NH3)C6H4NH3]3 P6O18.6H2O (V)
9.27(2)
9.92(19)
11.06(2)
65.65(2)
74.07(2)
76.32(2)
[p-(F)C6H4NH3]6 P6O18.2H2O (VI)
10.16(3)
15.87(3)
16.36(4)
80.93(2)
85.92(18)
85.31(2)
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P1
1492.8(8)
[26]
P1
1653.7(7)
[27]
1
P1
1313(2)
[28]
1
P1
882.3(3)
[29]
2
P1
2591.1(12)
[*]
1
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[p-(Cl)C6H4NH3]6 P6O18.0.5H2O (IV)
97.53(4)
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[p-( OEt)C6H4NH3]6 P6O18.8H2O (III)
24.952(8)
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Chemical Formula
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Z: number of formula unit per cell; S.G: Space group; V: Volume; [*] This studied structure
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ACCEPTED MANUSCRIPT Highlights Organic–inorganic hybrid cyclohexaphosphate was synthesized at room temperature.
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Layers organization of atomic arrangement showing two independent P6O18 rings.
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The crystal packing stabilized by a set of hydrogen bonds and F…F interactions.
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This material absorbs in the UV region with the observed blue photoluminescence.
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Electric properties were studied showing two mechanisms of conduction and two
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relaxation processes.
Antioxidant study, in vitro, shows significant scavenging capacity of free radicals
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(DPPH• and OH•).
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