Fabrication of a novel graphene oxide based magnetic nanocomposite and its usage as a highly effectual catalyst for the construction of N,N′-alkylidene bisamides

Abstract

At first, a novel graphene oxide-based magnetic nanocomposite namely Si-propyl-functionalized N¹,N¹,N²,N²-tetramethylethylenediamine-N¹,N²-diium hydrogen sulfate anchored to graphene oxide-supported Fe₃O₄ (nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄]) was fabricated. After full characterization of the nanocomposite, its catalytic performance was examined for the solvent-free construction of N,N′-alkylidene bisamides from aryl aldehydes (1 eq.) and primary aromatic and aliphatic amides (2 eq.), in which the products were acquired in short times (15–30 min) and high to excellent yields (89–98%). Nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] could be magnetically isolated form the reaction medium, and reused three times without remarkable loss of catalytic activity.

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1. Introduction

Graphene oxide (GO) is made from flat sheets with hydroxyl, epoxide and carboxylic acid groups; in these sheets, carbon atoms with sp² and sp³ hybridization are placed into a honeycomb network. Besides the unique characteristics of GO such as high structural strength, appropriate durability (chemical and thermal), safety, high adsorption capacity, high hydrophilic nature, high thermal conductivity and suitable mechanical properties, it can be readily functionalized using inorganic (magnetic/non-magnetic) and organic components to fabricate GO derivatives for different uses.^1–22 For example, GO and its functionalized derivatives (magnetic nanocomposites, etc.) have been used for treatment of hazardous environmental contaminants,¹ targeted delivery of quercetin to cancer cells,² sustainable water purification,³ extracting and determining metoprolol in exhaled breath condensate,⁴ removing dyes from wastewater⁵ and cancer therapy.⁶ They have been also applied as adsorbents,⁷ heat exchangers,⁸ bioinks for three-dimensional mesenchymal stem cell printing⁹ and biosensors.¹⁰ In organic synthesis, GO and its derivatives have been utilized as efficacious catalysts.^11–22

The high importance and numerous applications of magnetic nanomaterials have been reported in the literature.^{3–7,17–23} Some advantages of these materials include safety, suitable thermic and chemical durability, easy detaching from the process reactor, non-corrosiveness, effectiveness and aptitude to graft with diverse inorganic and organic components for a wide range of usages.^{3–7,17–23} It is worth noting that in magnetic nanocomposites based on GO, the advantages of magnetic nanomaterials and graphene oxide have been studied.

A valuable, useful, advantageous and applicable protocol, which has been extensively utilized for the construction of numerous organic substances, is the use of solvent-free conditions.^24–28 Utilization of this protocol not only is in accordance with the principles of green chemistry, but it can also lead to cleaner reaction medium, easier workup, increasing yield, decrement of reactor size and decreasing energy consumption, time and cost.²⁵

Bisamide scaffolds exist in the structure of numerous industrial and bioactive compounds.^29–37 For instance, these compounds have been applied for selective dye uptake,²⁹ selective detection of metal ions,³⁰ removal of Hg²⁺ and Pb²⁺ ions³¹ and ampere sensing.³² Moreover, they have been utilized as additives to control formation of methane hydrate for gas storage and flow assurance,³³ highly stable MRI contrast,³⁴ tyrosinase inhibitors,³⁵ antitumor³⁶ and antiviral³⁷ agents. A group of these compounds is the N,N′-alkylidene bisamides, which have been manufactured through the condensation of aryl aldehydes (1 eq.) with primary amides (2 eq.) using a catalyst.^38–47

Having the above issues in mind, developing a novel graphene oxide-based magnetic nanocomposite as a catalyst for the construction of N,N′-alkylidene bisamides can be valuable and desirable. Herein, we have developed Si-propyl-functionalized N¹,N¹,N²,N²-tetramethylethylenediamine-N¹,N²-diium hydrogen sulfate anchored to graphene oxide-supported Fe₃O₄ (nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] or NGFRNH) to catalyze the construction of N,N′-alkylidene bisamides.

2. Experimental

2.1. Materials and instruments

The details of the materials and instruments used have been described in the ESI.†

2.2. Fabrication of NGFRNH

GO and GO@Fe₃O₄ (I) were constructed through the reported protocols.^48,49 (3-Chloropropyl)trimethoxysilane (3 mmol, 0.596 g) and toluene (30 mL) were added to I (1.5 g), and stirred in reflux conditions for 12 h; the solid was magnetically isolated, washed with toluene (2 × 5 mL), and dried under vacuum (at 100 °C) to furnish II. Thereupon, N¹,N¹,N²,N²-tetramethylethylenediamine (3 mmol, 0.349 g) and compound II were stirred and refluxed in toluene (30 mL) for 12 h; the solid was separated by an external magnet, washed with toluene (2 × 5 mL), and dried under vacuum (at 100 °C) to produce III. Lastly, H₂SO₄ (3 mmol, 0.16 mL) was gradually added to III in CH₂Cl₂ (20 mL) at ambient temperature, and stirred for 5 h at the same temperature and 2 h under reflux conditions; the solid was magnetically separated, washed by CH₂Cl₂ (2 × 5 mL), and dried at 100 °C (under vacuum) to fabricate NGFRNH (Scheme 1).

Scheme 1 The fabrication of NGFRNH.

Note: Before each stage, the reaction mixture was irradiated with ultrasound waves to disperse it.

2.3. The construction of N,N′-alkylidene bisamides (general protocol)

A mixture of an aldehyde (0.5 mmol), amide (1 mmol) and NGFRNH (0.040 g) in a reaction vessel was strongly stirred at 110 °C using a glass rod. After observing consumption of the aldehyde and amide by TLC, the mixture was cooled to ambient temperature, warm EtOAc (10 mL) was added to it, and stirred for 1 min; then, NGFRNH was magnetically isolated (this action was done two times); the recycled NGFRNH was washed with EtOAc (2 × 3 mL), dried and used for next run. The acquired solutions after the double extraction of the product were collected and distilled; the remaining solid was recrystallized from ethanol (95%) to construct the pure bisamide.

Note: Selected original spectra of the bisamides are provided in the ESI.†

2.4. Selected spectral data of the constructed bisamides

Bisamide 3. ¹H NMR (300 MHz, DMSO-d₆): δ (ppm) 7.20 (t, J = 7.1 Hz, 1H, methine CH), 7.50–7.62 (m, 6H, H_Ar), 7.73 (t, J = 7.9 Hz, 1H, H_Ar), 8.00 (d, J = 7.7 Hz, 5H, H_Ar), 8.23 (d, J = 8.0 Hz, 1H, H_Ar), 8.42 (s, 1H, H_Ar), 9.32 (d, J = 7.2 Hz, 2H, 2NH); ¹³C NMR (75 MHz, DMSO-d₆): δ (ppm) 59.1, 121.9, 123.3, 128.1, 128.8, 130.4, 132.2, 134.1, 134.2, 142.9, 148.3, 166.5.

Bisamide 8. ¹H NMR (300 MHz, DMSO-d₆): δ (ppm) 7.10 (t, J = 6.6 Hz, 1H, methine CH), 7.51–7.60 (m, 6H, H_Ar), 7.85 (t, J = 8.5 Hz, 2H, H_Ar), 7.97 (d, J = 7.6 Hz, 4H, H_Ar), 8.24 (s, 1H, H_Ar), 9.27 (d, J = 6.6 Hz, 2H, 2NH); ¹³C NMR (75 MHz, DMSO-d₆): δ (ppm) 58.7, 124.4, 124.6, 128.2, 128.8, 132.0, 132.2, 132.8, 134.0, 141.8, 148.0, 166.5. Mass: m/z 409 (M⁺).

Bisamide 10. ¹H NMR (300 MHz, DMSO-d₆): δ (ppm) 7.12 (t, J = 7.5 Hz, 1H, methine CH), 7.25 (t, J = 8.8 Hz, 2H, H_Ar), 7.49–7.61 (m, 8H, H_Ar), 7.98 (d, J = 7.0 Hz, 4H, H_Ar), 9.12 (d, J = 7.6 Hz, 2H, 2NH); ¹³C NMR (75 MHz, DMSO-d₆): δ (ppm) 58.9, 115.4, 115.7, 128.0, 128.8, 129.1, 129.2, 132.1, 134.3, 137.1, 160.6, 163.8, 166.2.

3. Results and discussion

3.1. Characterization of NGFRNH

At first, GO was produced by oxidation of graphite using a rectified Hummers' protocol. Then, Fe₃O₄ nanoparticles was supported on GO nanosheets using co-precipitation method to synthesize GO@Fe₃O₄. In continue, GO@Fe₃O₄ was functionalized by (3-chloropropyl)trimethoxysilane, N¹,N¹,N²,N²-tetramethylethylenediamine and sulfuric acid to fabricate nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] (NGFRNH) as a novel graphene oxide based magnetic nanocomposite. The structure of NGFRNH was proposed on basis of the reported structures for this category of materials.^19,20,49 Energy-dispersive X-ray spectroscopy (EDX), elemental mapping, field emission scanning electron microscopy (FE-SEM), FT-IR, X-ray diffraction (XRD), thermogravimetric (TG), derivative thermogravimetry (DTG) and vibrating-sample magnetometery (VSM) analyses were used to characterize the nanocomposite.

The EDX (Fig. 1) and elemental mapping (Fig. 2) analyses of nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] showed carbon, which is pertained to GO and the organic moiety anchored to Fe₃O₄. The analyses indicated oxygen, which is ascribed to GO, Fe₃O₄ and HSO₄⁻. Observation of the peak related to iron in the EDX spectrum, and observing iron in the elemental mapping images confirmed existing Fe₃O₄ in the nanocomposite structure. Both analyses verified existing silicon, which is belong to Si-propyl-functionalized N¹,N¹,N²,N²-tetramethylethylenediamine-N¹,N²-diium moiety. The peak assigned to nitrogen of N¹,N¹,N²,N²-tetramethylethylenediamine-N¹,N²-diium component was observed in the EDX spectrum; nitrogen was also seen in the elemental mapping analysis. The chlorine (related to Cl⁻) was observed in both analyses. Observation of S in the EDX and elemental mapping analyses approved existing HSO₄⁻ in the structure of NGFRNH. Furthermore, the elemental mapping images demonstrate good distribution of the elements in the nanocomposite surface.

Fig. 1 The EDX analysis of NGFRNH.

Fig. 2 The elemental mapping images of NGFRNH.

Fig. 3 illustrates the FE-SEM pictures of NGFRNH; the pictures showed nanosheets of GO with diameter of 35.4, 50.3, 51.1 nm, etc. and crumpled structure in their edges, and also the nanoparticles of the functionalized Fe₃O₄ supported on GO.

Fig. 3 The FE-SEM pictures of the nanocomposite.

The FT-IR spectrum of nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] is represented in Fig. 4, and the interpretation of the spectrum is given in Table 1. The spectrum showed the peaks related to all bonds and functional groups presented in the nanocomposite structure (graphene oxide, Fe₃O₄, OSi-R′-NHMe₂ and HSO₄⁻); thus, the spectrum confirmed successful fabrication of the catalyst, i.e. supporting Fe₃O₄ on GO to produce GO@Fe₃O₄, and functionalization of GO@Fe₃O₄ by the organic component and HSO₄⁻.

Fig. 4 The FT-IR spectrum of NGFRNH.

Table 1 The results on interpreting the FT-IR spectrum of NGFRNH

Peak (cm^−1)	Bond or functional group
464	Si–O (rocking)
590	Fe–O (stretching vibration)
1125	SO2 of HSO4^− (symmetric stretching)
1249	SO2 of HSO4^− (asymmetric stretching)
1470	Aliphatic C–H (bending)
1630	C=C of GO (stretching vibration)
1714	C=O of GO (stretching vibration)
2926	Aliphatic C–H (stretching vibration)
∼2570–3630	OH groups of HSO4^− and GO (stretching)

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The XRD pattern of nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] is displayed in Fig. 5. The peak located at 11.37° can be related to GO; the low intensity of the peak is because of supporting Fe₃O₄ on GO nanosheets and also functionalization by Si-R′-NHMe₂ and hydrogen sulfate. The diffraction lines appeared at 31.99, 35.91, 38.72, 43.78, 53.39, 58.38 and 63.01° verified existing Fe₃O₄ (a cubic spinel form) in the nanocomposite structure, and consequently, successful supporting Fe₃O₄ on GO nanosheets. The other data obtained from the XRD pattern, such as FWHM (width at half maximum), interplanar distance, relative intensity of the peaks and crystalline sizes of the particles, are illustrated in Table 2; the crystalline sizes, which were calculated by Debye–Scherrer equation, were in the range of 3.63–54.13 nm, and are in acceptable compliance with the sizes gained from the FE-SEM analysis (Fig. 3).

Fig. 5 The XRD spectrum of NGFRNH.

Table 2 The XRD data of for NGFRNH

2θ (°)	FWHM (°)	Interplanar distance (nm)	Rel. int. (%)	Crystalline size (nm)
5.197	0.2952	1.7006	100.00	26.96
8.658	0.1968	1.0213	71.04	40.52
11.373	0.1476	0.7780	27.83	54.13
15.793	0.2952	0.5611	23.25	27.19
18.993	0.3936	0.4673	48.69	20.48
25.137	0.3936	0.3543	42.09	20.70
26.920	0.3936	0.3312	42.21	20.77
31.997	0.3936	0.2797	18.55	21.01
35.909	1.5744	0.2500	13.94	5.30
38.717	0.9840	0.2326	8.49	8.56
43.779	2.3616	0.2068	2.83	3.63
63.014	0.5904	0.1475	8.53	15.79

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Thermal durability of NGFRNH was determined by TG and DTG analyses (Fig. 6); the corresponding diagrams demonstrate weight losing in three stages. The weight loss occurred up to 175 °C (with T_max at 166.5 °C in the DTG diagram) can be related to thermal desorption of water and solvents adsorbed on the nanocomposite surface. The second and third stages of the weight losing which took place at 175–320 °C (with T_max at 265.7 °C in the DTG diagram) and 320–600 °C (with T_max at 513.2 °C in the DTG diagram) can be due to the decomposition of oxygen-containing groups in GO (carboxylic acid, hydroxyl and epoxide) and the organic constitute grafted with GO@Fe₃O₄ (i.e. Si-R′-NHMe₂). The weight loss after 470 °C is related to decomposition of GO nanosheets.

Fig. 6 The TG and DTG curves of NGFRNH.

Magnetic behavior of nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] was studied by VSM analysis; Fig. 7 depicts the analysis result. Considering the VSM diagram, saturation magnetization (M_s) of the nanocomposite was ∼5.4 emu g⁻¹. Lower M_s of NGFRNH compared to Fe₃O₄ is due to supporting Fe₃O₄ on graphene nanosheets and functionalization with the organic component and hydrogen sulfate. Nevertheless, NGFRNH had sufficient magnetic property to recycle from the reaction mixture by an external magnet.

Fig. 7 The VSM diagram of the magnetic nanocomposite.

3.2. Application of NGFRNH as catalyst for manufacturing N,N′-alkylidene bisamides

Investigating catalytic property of nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] was done on the construction of N,N′-alkylidene bisamides from aryl aldehydes and primary amides. In this regard, the condensation of 4-chlorobenzaldehyde (0.5 mmol) and benzamide (1 mmol) was tested using 0.035, 0.040 and 0.045 g of NGFRNH at 90, 100, 110 and 115 °C in the absence of solvent; Scheme 2 illustrates the model reaction, and Table 3 indicates the obtained results. The best results were attained when the reaction was performed using 0.040 g of the nanocomposite at 110 °C (entry 2); so, 0.040 g was chosen as the optimal catalyst dosage, and 110 °C was selected as the optimized temperature. To compare catalytic efficacy of nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] with the precursors used for its synthesis, and determine the role of graphene oxide, the model reaction was examined without catalyst and also in the presence of the precursors (GO, II and III) under identical conditions. As Table 3 exemplifies, these conditions were not efficient, and afforded low or moderate yields of product 6 (entries 7–10). Thus, our plan to design nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] as catalyst for the fabrication of N,N′-alkylidene bisamides was logical. Furthermore, considering the results acquired in entries 7 and 8, GO role was not only as a support, but also it could act as a co-catalyst. In another study, the gram scale synthesis of product 6 was studied; for this purpose, 5 mmol (0.703 g) of 4-chlorobenzaldehyde was reacted with 10 mmol (1.211 g) of benzamide in the presence of 0.400 g of NGFRNH at 110 °C, in which the bisamide was obtained in 93% after 20 min.

Scheme 2 The model reaction to acquire the best conditions.

Table 3 Optimization of the reaction conditions

Entry	Catalyst	Catalyst amount (g)	Temp. (°C)	Time (min)	Yield^a (%)
a Isolated yield.
1	NGFRNH	0.035	110	25	93
2	NGFRNH	0.040	110	15	98
3	NGFRNH	0.045	110	15	98
4	NGFRNH	0.040	90	35	76
5	NGFRNH	0.040	100	25	91
6	NGFRNH	0.040	115	15	98
7	—	—	110	15	<10
8	GO	0.040	110	15	27
9	Material II	0.040	110	15	38
10	Material III	0.040	110	15	42

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After attaining the optimized conditions, the domain and performance of the nanocatalyst for the construction of N,N′-alkylidene bisamides were assessed through usage of miscellaneous aromatic aldehydes (carrying diverse electron-attracting and electron-releasing substituents on their ortho, meta or para positions), and also aromatic and aliphatic amides in the reaction; the gained results are reported in Table 4. It was found that all substrates afforded the relevant bisamides in short times and high to excellent yields; these results confirmed wide domain and high efficiency of NGFRNH to catalyze the reaction.

Table 4 The construction of various derivatives of N,N′-alkylidene bisamide using NGFRNH

Product no.	Ar	R	Time (min)	Yield^a (%)	M.p. (°C) [lit.]
a Isolated yield.
1	C6H5	C6H5	20	94	222–225 (220–221)^45
2	2-O2NC6H4	C6H5	20	93	255–257 (257–259)^41
3	3-O2NC6H4	C6H5	25	97	226–228 (228–230)^47
4	4-O2NC6H4	C6H5	20	96	260–262 (261–263)^42
5	2-ClC6H4	C6H5	15	97	243–245 (242–244)^47
6	4-ClC6H4	C6H5	15	98	256–259 (258–261)^43
7	2,4-Cl2C6H3	C6H5	25	97	203–205 (201–203)^44
8	4-Cl,3-O2NC6H3	C6H5	25	94	247–249 (250–252)^38
9	4-BrC6H4	C6H5	15	97	254–257 (252–254)^42
10	4-FC6H4	C6H5	15	97	230–233 (227–229)^44
11	4-MeOC6H4	C6H5	30	89	220–222 (223–225)^44
12	4-MeC6H4	C6H5	15	95	241–244 (241–244)^43
13	4-O2NC6H4	CH3	25	97	257–260 (260–265)^39
14	4-ClC6H4	CH3	15	96	254–257 (252–255)^38
15	4-MeOC6H4	CH3	20	92	213–215 (215–217)^39

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On basis of the literature,^42,43,47 a reasonable mechanism was suggested for the construction of N,N′-alkylidene bisamides (Scheme 3). Nano-[GO@Fe₃O₄@R-NHMe₂][HSO₄] can catalyze the reaction by its acidic group (hydrogen sulfate); its roles involve: (i) activating the electrophiles in steps 1 and 3 to accept nucleophilic attack of amide, and (ii) conversion of the hydroxyl group to a good leaving group in step 2 for elimination of a H₂O molecule.

Scheme 3 The mechanism.

Capability of NGFRNH for recovering and reusing was perused on the reaction of 4-chlorobenzaldehyde and benzamide (Scheme 2); it was recovered pursuant to the described way in experimental section, and reused for three times without remarkable loss of catalytic activity (Fig. 8). However, in fourth recycling (run 5), the reaction yield was significantly decreased.

Fig. 8 The recoverability results of NGFRNH.

To compare NGFRNH with the reported catalysts, the construction of bisamides 1, 6 and 12 was chosen, and the catalysts were compared in terms the reaction conditions, time and yield; Table 5 illustrates this comparison. The reaction yields of our catalyst are higher than the reported ones, and the reaction times are shorter than most of the reported catalysts showed in Table 5. The reaction conditions of NGFRNH are better than some catalysts, and are same with the others (in terms of performing the reaction under solvent-free conditions or in solvent). The reaction temperature of NGFRNH is as same as some catalysts, and is higher than the others. The another advantage of NGFRNH with respect to some catalysts reported in Table 5 is ability to catalyze the reaction in the case of aromatic and aliphatic amides.

Table 5 The construction of bisamides 1, 6 and 12 using NGFRNH and some reported catalysts

Catalyst	Conditions	Time (min) for products 1/6/12	Yield (%) for products 1/6/12	Ref.
a Nano-Mn-[phenyl-salicylaldimine-methyl-pyranopyrimidinedione]Cl2.b In the research, this product has not been constructed.c H5[PV2W10O40] immobilized on clay.d GO grafted with SO3H-functionalized glycerin.e Nano-2-[N′,N′-dimethyl-N′-(silica-n-propyl)ethanaminium chloride]-N,N-dimethylaminium bisulfate.
NGFRNH	Solvent-free, 110 °C	20/15/15	94/98/95	This work
Nano-[Mn-PSMP]Cl2^a	EtOH, reflux	—^b/150/270	—^b/85/75	38
Ph3CCl	EtOH, 60 °C	—^b/35/—^b	—^b/90/—^b	39
HPVAC-20^c	Solvent-free, 110 °C	35/25/40	93/96/90	40
Montmorillonite K10	Solvent-free, 100 °C	80/—^b/—^b	85/—^b/—^b	41
GO@Gl-SO3H^d	Solvent-free, 110 °C	15/10/15	91/96/90	42
3D-network polymer supported ionic liquid	Toluene, reflux	30/25/30	85/83/87	43
Nano-[DSPECDA][HSO4]^e	Solvent-free, 90 °C	30/—^b/30	91/—^b/79	44
ZnO/KIT-6@NiFe2O4	Solvent-free, 60 °C	10/10/10	90/94/75	45
C/TiO2–SO3H	Solvent-free, 100 °C	90/120/120	93/93/90	46
KH2PO4 supported on silica	Solvent-free, 80 °C	15/15/15	87/90/71	47

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4. Conclusions

Briefly, we have fabricated a novel graphene oxide-based magnetic nanocomposite possessing an acidic group (HSO₄⁻); it may catalyze organic transformations which require acidic catalyst to carry out. In this research, we have successfully applied the nanocomposite as catalyst to construct N,N′-alkylidene bisamides from aryl aldehydes (1 eq.) and primary amides (2 eq.); the privileges of this approach comprise wide domain, high performance, construction of the products in short times and excellent yields, efficiency of the protocol to fabricate the bisamides from aromatic and aliphatic amides, utilization of solvent-free conditions, magnetically recovering the catalyst, recoverability of the catalyst for three times without significant loss of its activity and good accordance with principles of green chemistry.

Data availability

The data supporting this article have been included as part of the ESI.†

Author contributions

Abdolkarim Zare: investigation, project administration, supervision, formal analysis, writing – original draft, writing – review & editing. Marziyeh Barzegar: methodology, formal analysis, writing – original draft. Esmael Rostami: investigation, supervision, formal analysis. Ahmad Reza Moosavi-Zare: investigation, writing – review & editing, formal analysis.

Conflicts of interest

There are no conflicts to mention.

Acknowledgements

The authors are thankful from Payame Noor and Persian Gulf Universities due to helping this research.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra04136d

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