Research and Possible Agronomic Applications of C₆₀(OH)₂₄ Adducts with Heavy Metals for Crop Treatment

Abstract

This article describes the synthesis of fullerenol—${\mathrm{C}}_{60}(\mathrm{O}{\mathrm{H})}_{24}$ adducts with some heavy metals—${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2};{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/3}$; Me=Co; Cu; Mn; Zn; Gd; Tb. The identification of adducts was carried out by the methods of: elemental analysis, infrared and electronic spectroscopy, complex thermal analysis, high-performance liquid chromatography and dynamic light scattering. The solubility of adducts in aqueous solutions in the ambient temperature range has been studied. The solubility was significant and ranged from a few tenths to 1 g/dm³. The use of these adducts as micronutrients for spring barley crops in the Republic of Kazakhstan is considered. When using these nanopreparations, a general increase in yield (tens, up to 80 rel.%), nutrient content and moisture content of seeds (4–5 rel. mass %), as well as the resistance of the latter to the effects of pathogenic microorganisms (percentage of healthy seeds growth up to 10 rel.%), was noted.

1. Introduction

This paper describes the synthesis of fullerenol-24 ${\mathrm{C}}_{60}(\mathrm{O}{\mathrm{H})}_{24}$ adducts with some transition metals and lanthanides: ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2}; {\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/3}$; Me=Co; Cu; Mn; Zn; Gd; Tb. One of the possible and potential applications of fullerenols, considered in this work, is the synthesis of fullerenol adducts with transition and 4-f-metals, followed by the use of such adducts for agrochemical goals, as poorly soluble donors of micro-fertilizers of prolonged action, as well as agents that increase the nutrient content and moisture resistance of seeds, and also as well as the resistance of the latter to the effects of pathogenic microorganisms (on the example of spring barley). The most popular and available fullerenol-24 ${\mathrm{C}}_{60}(\mathrm{O}{\mathrm{H})}_{24}$ was used for synthesis [1,2,3], the possible agrotechnical application of which (and some of its derivatives) was previously studied [3,4,5,6,7,8]. The authors, in particular, studied the effect of water-soluble fullerene derivatives on the development of crops of a number of cereals (yield growth and green mass), as well as increasing the stress resistance of cereals to oxidative stress and lack of moisture supply. The main goal of this study in agrotechnical terms is to study the effect of water-soluble metal-adducts of light fullerene C60 on such agrotechnical indicators of spring barley as: yield of spring barley on resistance of seeds, processed by Me-adducts, to the infections, caused by pathogenic microorganisms.

2. Synthesis of Me-Adducts

Synthesis of metal-adducts ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2}; {\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/3}$; Me=Co; Cu; Mn; Zn; Gd; Tb was carried out in 2 stages:

The synthesis of Na-adducts:

$${\mathrm{C}}_{60}({\mathrm{O}\mathrm{H})}_{24}+24\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}={\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{24}+24{\mathrm{H}}_2\mathrm{O}$$

(1)

The synthesis of Me-adducts themselves:

$${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{24}+[(24-\mathrm{x})/2]\mathrm{M}\mathrm{e}{\mathrm{C}\mathrm{l}}_2={\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2}+(24-\mathrm{x})\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$$

(2)

$${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{24}+[(24-\mathrm{x})/3]\mathrm{M}\mathrm{e}{\mathrm{C}\mathrm{l}}_3={\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}({\mathrm{O}}_3\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/3}+(24-\mathrm{x})\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$$

(3)

Moreover, Equation (2) corresponds to the synthesis of adducts with transients, and Equation (3) corresponds to 4f-metals (lanthanides).

Synthesis Scheme

• As a result of dissolution of 2.9 g. ${\mathrm{C}}_{60}(\mathrm{O}{\mathrm{H})}_{24}$ in 30 cm³ 0.1 M NaOH solution, an aqueous solution ${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{24}$ is formed. The pH of the solution is 7.5–8.5 a.u. with the addition of a few drops of 1 M solution of HCl.
• Preparation of 100 cm³ of MeCl_n solution (Me=Co; Cu; Mn; Zn; Gd; Tb) with a concentration of 55 g/dm³ (CoCl₂) ÷ 93 g/dm³ (TbCl₃) at a solution pH~3.5 $÷$ 4.0 a.u. in order to avoid hydrolysis of MeCl_n (by adding a few drops of 1 M HCl solution).
• Adding an aqueous solution of MeCl_n drop by drop to an aqueous solution of ${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{24}$. A loose amorphous colored precipitate is formed. Standing of the resulting solution with the formed precipitate for 24 h. Filtration of the resulting heterogeneous mixture.
• Three-time washing of the sediment with methanol ${\mathrm{C}\mathrm{H}}_3\mathrm{O}\mathrm{H}$ for 50 cm³ of solvent. Final drying of adducts in a vacuum drying cabinet (P ≤ 0.1 mm Hg) at a temperature of ~50 °C for 90 min.
• As a result, we synthesized gram amounts of colored crystal hydrates of Me-adducts: ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6·24{\mathrm{H}}_2\mathrm{O};{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}·18{\mathrm{H}}_2\mathrm{O};{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}·18{\mathrm{H}}_2\mathrm{O};{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8·20{\mathrm{H}}_2\mathrm{O};{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6·22{\mathrm{H}}_2\mathrm{O};{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{T}\mathrm{b}{)}_6·20{\mathrm{H}}_2\mathrm{O}$ with masses 3.8 g (${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6·24{\mathrm{H}}_2\mathrm{O}$) ÷ 4.1 g ${(\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6·22{\mathrm{H}}_2\mathrm{O}$), which corresponds to a practical yield of $\mathsf{\eta }~$65–72% of the theoretically possible.

Typical photos of synthesized adducts, shown in Figure 1, were obtained using a VEGA 3 TESCAN electron microscope (TESCAN, Brno, Czech Republic) at a magnification of ×400 = ×5000.

It should be noted here that in acidic solutions, the formation of adducts of the type ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2};{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/3}$ is not observed in principle, which is unequivocally proven by analyzing solubility diagrams of the type: fullerenol-metal salt–water [2].

3. Identification of Me-Adducts

Identification of Me-adducts: ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2};{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/3}$; Me=Co; Cu; Mn; Zn; Gd; Tb was provided by the following methods of physico-chemical analysis:

• IR spectra of adducts in KBr tablets were obtained on the Shimadzu FTIR-8400S spectrometer (Shimadzu, Kyoto, Japan) in the range of wave numbers $\tilde{\mathsf{\nu }}$= 400 ÷ 4000 cm⁻¹;
• Electronic absorption spectra were obtained on the SPECORD M32 spectrophotometer (Analytik Jena, Jena, Germany) in the wavelength range λ = 200 ÷ 1000 nm (comparison solution–distilled water);
• Complex thermal analysis of adducts was carried out on a NETZSCH TG 209 F1 Libra analyzer (NETZSCH, Selb, Germany) in the temperature range of 30 ÷ 1100 °C in an air atmosphere with a heating rate of 5 K·min⁻¹;
• For high-performance liquid chromatography, a Shimadzu LC-20 Prominence device with spectrophotometric detection at λ = 270 nm was used, equipped with a “Phenomenex^® column NH2” (Phenomenex, Torrance, CA, USA) (150 mm × 2.0 mm, 5 microns, 100 A), input volume 2 × 10⁻² cm³, input speed 0.2 mL·min⁻¹, eluent—acetonitrile/0.1% aqueous solution of acetic acid (5/95);
• Elemental composition analysis was carried out by scanning VEGA 3 TESCAN 4th generation electron microscope in Essence^TM EDS software, using a fully integrated energy dispersion spectrometer (on a VEGA3 TESCAN electron microscope);
• Additionally, elemental analysis for the sulfur content of light atoms was carried out using a PerkinElmer PE 2400 CHN analyzer (PerkinElmer, Waltham, MA, USA);
• Dynamic light scattering in aqueous solutions of adducts was carried out, using Zetasizer Nano ZS (Malvern Panalytical, Malvern, UK);
• Solubility of adducts in aqueous solutions was studied using a standard shaker thermostat with additional temperature stabilization (∆T = 0.05 K, saturation time—8 h, shaking frequency ν = 2 Hz, solution concentrations were determined spectrophotometrically by absorption spectra at λ = 270 nm).

3.1. Elemental Analysis

The data of the elemental analysis are presented below in

Table 1. Elemental composition of Me-adducts: ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2},{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/3}$.

No	Me in Adduct	$\mathbf{Element}\mathbf{Atomic}\mathbf{Content}\mathbf{per}\mathbf{q}\mathbf{Fullerene}\mathbf{Core}({\mathbf{C}}_{60}$) (60 C Atoms).					Me-Adducts Formula
		C	O	H	Na	Me
1	Na	60	44 ± 2	40 ± 2	24 ± 1	0	${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{24}·20{\mathrm{H}}_2\mathrm{O}$
2	Co	60	48 ± 6	48 ± 5	12 ± 3	6 ± 2	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6·24{\mathrm{H}}_2\mathrm{O}$
3	Cu	60	42 ± 8	36 ± 5	4 ± 2	10 ± 4	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}·18{\mathrm{H}}_2\mathrm{O}$
4	Mn	60	42 ± 9	36 ± 4	4 ± 2	10 ± 5	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}·18{\mathrm{H}}_2\mathrm{O}$
5	Zn	60	44 ± 7	40 ± 5	8 ± 3	8 ± 3	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8·20{\mathrm{H}}_2\mathrm{O}$
6	Gd	60	46 ± 8	44 ± 6	6 ± 3	6 ± 3	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6·22{\mathrm{H}}_2\mathrm{O}$
7	Tb	60	44 ± 8	40 ± 7	6 ± 3	6 ± 3	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_2\mathrm{T}\mathrm{b}{)}_6·20{\mathrm{H}}_2\mathrm{O}$

.

It is clearly seen that the composition of the precursor ${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{24}·24{\mathrm{H}}_2\mathrm{O}$ is set fairly accurately. Some variation in the content of O and H is associated with the presence of a large amount of loosely bound crystallization water in all adducts, while partial dehydration of equilibrium crystal hydrates may occur on the surface of the crystal hydrates (when studied in the atmosphere). For Me-adducts with transition metals and lanthanides, Me, the stability of the composition is significantly reduced, first of all, this applies to the content of Me in adducts. In our opinion, all adducts in Table 1 can be considered mixtures of forms with slightly different compositions (related compounds) and their isomers. Indeed, the precursors used for the preparation of adducts are already primary, namely ${\mathrm{C}}_{60}({\mathrm{O}\mathrm{H})}_{24}$, ${\mathrm{C}}_{60}{\mathrm{B}\mathrm{r}}_{24}$ [3], a mixture of isomers, not always strictly stoichiometric in composition. Indeed, a halogen atom can be grafted into a pentagon-hexagonal C atom or a hexagon-hexagonal C atom (then the structure will be inherited by fullerenol, its sodium forms and metalloadducts). Further, the substitution groups can alternatively be located: evenly distributed over the surface of the C₆₀ core, mainly along the equator of the core, mainly circumpolarly, by spots, etc. Already during the formation of Me-adducts with two and three charged cations, binding is possible with groups of one C₆₀ fullerene core, two or even three different cores. Let us evaluate the possibilities of the last substitution. The average distance between neighboring substitution groups (C-O-Na) in the adduct ${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{24}$ can be calculated in the simplest approximation of a uniform distribution of groups over the surface of the core: C₆₀: $\mathrm{r}=(\mathsf{\pi }{\mathrm{d}}^2/\mathrm{N}{)}^{1/2}$, where $\mathrm{d}~$0.73 nm—“diameter of fullerene core”, N = 24. Or: r~0.26 nm. The approximate length of the sum of the bonds ${\mathrm{r}}_{\mathrm{C}-\mathrm{O}-\mathrm{N}\mathrm{a}}~0.3÷0.4\mathrm{n}\mathrm{m}$. In other words, taking into account the ionic radii Me^z+: ${\mathrm{r}}_{{\mathrm{M}\mathrm{e}}^{\mathrm{z}+}}~0.073\left(\mathrm{C}\mathrm{u}\right)÷0.092\left(\mathrm{T}\mathrm{b}\right)\mathrm{n}\mathrm{m}$, it can be stated that geometrically binding one multicharged ion can occur with either one or several fullerene cores. In the case of binding one cation with several fullerene cores at once, the formation of more or less large oligomers should be revived. The formation of rather large associates (with linear dimensions of several microns) is further confirmed by the data of dynamic light scattering. On the other hand, according to the same reason, the electronic spectra of aqueous solutions of adducts will not be completely of the nature of light absorption, but at least partially of the nature of light scattering. In other words, the electronic spectra have a certain turbodimetric character.

3.2. Electronic Spectroscopy

Electronic spectroscopy data are represented in Figure 2 and Figure 3 and in

Table 2. Extinction coefficients in the Bouguer–Lambert–Behr law and coefficients for concentration recalculation at wavelength λ = 270 nm in Me-adduct water solutions.

No	$\mathbf{Me}\mathbf{in}\mathbf{the}\mathbf{Adduct}{\mathbf{C}}_{60}\left({\mathbf{O}\mathbf{H})}_{24-\mathbf{n}}\right({\mathbf{O}}_{\mathbf{n}}\mathbf{M}{\mathbf{e}}_{\mathbf{n}/\mathbf{x}})$	$\mathbf{Extinction}\mathbf{Coefficients}{\mathsf{\epsilon }}_{270}$ (103 cm2/g)	$\mathbf{Coefficients}\mathbf{for}\mathbf{Volume}\mathbf{Concentration}\mathbf{Calculations}{\mathbf{\varkappa }}_{270}$ (g/dm3)
1	Co	0.915	1.093
2	Cu	0.572	1.748
3	Mn	0.850	1.176
4	Zn	0.391	2.557
5	Gd	0.568	1.760
6	Tb	0.733	1.364

. It is clearly visible that the electronic absorption spectra of solutions of all Me-adducts are isomorphic: there are 2 broad absorption peaks at λ₁~340 ÷ 360 nm, λ₂~265 ÷ 275 nm. According to the second peak, we further determined extinction coefficients and the volume concentrations of adducts:

$${\mathrm{D}}_{270}={\mathsf{\epsilon }}_{270}\mathrm{C}\left(\frac{\mathrm{g}}{\mathrm{d}{\mathrm{m}}^3}\right)\mathrm{l}\left(\mathrm{c}\mathrm{m}\right)$$

(4)

$${\mathrm{C}\left(\frac{\mathrm{g}}{\mathrm{d}{\mathrm{m}}^3}\right)=\mathrm{D}}_{270}/{\mathsf{\epsilon }}_{270}\mathrm{l}\left(\mathrm{c}\mathrm{m}\right){=\mathrm{\varkappa }}_{270}{\mathrm{D}}_{270}/\mathrm{l}$$

(5)

where l—width of the cuvette (length of optical way); ${\mathsf{\epsilon }}_{270}$—extinction coefficients in the Bouguer–Lambert–Behr law at wavelength λ = 270 nm; C—volume concentration in $\frac{\mathrm{g}}{\mathrm{d}{\mathrm{m}}^3}$; ${\mathrm{D}}_{270}$—optical density; ${\mathrm{\varkappa }}_{270}$—coefficients for concentration recalculation.

3.3. Infrared Spectroscopy

The absorption IR spectra of all Me-adducts also turned out to be isomorphic. All of them present: vibrations of the fullerene core C₆₀: $\overline{\mathsf{\nu }}\left({\mathrm{c}\mathrm{m}}^{-1}\right)$= 528 ÷ 532; 570 ÷ 577; 1170 ÷ 1183; 1423 ÷ 1429; vibrations of H₂O crystal hydrate molecules: $\overline{\mathsf{\nu }}\left({\mathrm{c}\mathrm{m}}^{-1}\right)$= 3595 ÷ 3620; 3448 ÷ 3454; 1640 ÷ 1651; relatively weak fluctuations of residual and hydrolyzed O-H groups: $\overline{\mathsf{\nu }}\left({\mathrm{c}\mathrm{m}}^{-1}\right)$ = 3417 ÷ 3421; vibrations of C–O groups: $\overline{\mathsf{\nu }}\left({\mathrm{c}\mathrm{m}}^{-1}\right)$= 1716 ÷ 1728; vibrations of O-Na groups: $\overline{\mathsf{\nu }}\left({\mathrm{c}\mathrm{m}}^{-1}\right)$= 540 ÷ 565; the system of peaks, corresponding to the vibrations of Me-O, O-Me-O: $\overline{\mathsf{\nu }}\left({\mathrm{c}\mathrm{m}}^{-1}\right)$= 424 (Zn) ÷ 599 (Tb).

3.4. Complex Thermal Analysis

Complex thermal analysis of crystal hydrates was carried out for the following crystal hydrates of metal products: ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2}·\mathrm{N}{\mathrm{H}}_2\mathrm{O}$ и ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}\prime {)}_{(24-\mathrm{x})/3}·\mathrm{N}\prime {\mathrm{H}}_2\mathrm{O}$ (Me = Co, Cu, Mn, Zn; Me′ = Gd, Tb). Let us denote:${\mathrm{T}}^{\left(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{r}\mathrm{t}\right)}\to {\mathrm{T}}^{\left(\mathrm{e}\mathrm{x}\mathrm{t}\right)}\to {\mathrm{T}}^{\left(\mathrm{f}\mathrm{i}\mathrm{n}\right)}$—temperatures of the beginning, extreme and end of the effect. We denote the following processes: $\mathrm{M}\mathrm{E}\mathrm{D}$—multistage dehydration of crystallohydrates; T-RE-OMD—decomposition with the release of Me oxide; SOD—decomposition with the release of Na₂O oxide; FCO—additional oxidation of fullerene core. In all cases, the effects were consistently observed on the thermograms: $\mathrm{M}\mathrm{E}\mathrm{D}\to \mathrm{T}-\mathrm{R}\mathrm{E}-\mathrm{O}\mathrm{M}\mathrm{D}\to \mathrm{S}\mathrm{O}\mathrm{D}\to \mathrm{F}\mathrm{C}\mathrm{O}—$see

Table 3. Complex thermal analysis of crystal hydrates of metal-adducts of fullerenol-24 with metals: ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2}·\mathrm{N}{\mathrm{H}}_2\mathrm{O}$ and ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}\prime {)}_{(24-\mathrm{x})/3}·\mathrm{N}\prime {\mathrm{H}}_2\mathrm{O}$ (Me = Co, Cu, Mn, Zn; Me′ = Gd, Tb).

No	Process	$$\mathbf{Temperature}\left(\mathbf{C}\right):{\mathbf{T}}^{\left(\mathbf{s}\mathbf{t}\mathbf{a}\mathbf{r}\mathbf{t}\right)}\to {\mathbf{T}}^{\left(\mathbf{e}\mathbf{x}\mathbf{t}\right)}\to {\mathbf{T}}^{\left(\mathbf{f}\mathbf{i}\mathbf{n}\right)}$$
1.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6·24{\mathrm{H}}_2\mathrm{O}\to$ $\to {\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6+24{\mathrm{H}}_2\mathrm{O}$—MED	$75\to 300\to 340$
2.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6\to$ $\to 6\mathrm{C}\mathrm{o}\mathrm{O}+{\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}{\mathrm{O}}_6$—T-RE-OMD	$350\to 405\to 500$
3.	${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}{\mathrm{O}}_6\to$ $\to {\mathrm{C}}_{60}{\mathrm{O}}_{12}+6{\mathrm{N}\mathrm{a}}_2\mathrm{O}$—SOD	$500\to 575\to 645$
4.	${\mathrm{C}}_{60}{\mathrm{O}}_{12}+54{\mathrm{O}}_2\to$ $\to 60{\mathrm{C}\mathrm{O}}_2$—FCO	$680\to 1000\to \cdots$
5.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}·18{\mathrm{H}}_2\mathrm{O}\to$ $\to {\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_2\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}+18{\mathrm{H}}_2\mathrm{O}$—MED	$70\to 285\to 330$
6.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}\to$ $\to 10\mathrm{C}\mathrm{u}\mathrm{O}+{\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_4{\mathrm{O}}_{10}$—T-RE-OMD	$330\to 390\to 485$
7.	${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_4{\mathrm{O}}_{10}\to$ $\to {\mathrm{C}}_{60}{\mathrm{O}}_{12}+2{\mathrm{N}\mathrm{a}}_2\mathrm{O}$—SOD	$490\to 565\to 640$
8.	${\mathrm{C}}_{60}{\mathrm{O}}_{12}+54{\mathrm{O}}_2\to$ $\to 60{\mathrm{C}\mathrm{O}}_2$—FCO	$680\to 1000\to \cdots$
9.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}·18{\mathrm{H}}_2\mathrm{O}\to$ $\to {\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_2\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}·18{\mathrm{H}}_2\mathrm{O}$—MED	$80\to 310\to 355$
10.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}\to$ $\to 10\mathrm{M}\mathrm{n}\mathrm{O}+{\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_4{\mathrm{O}}_{10}$—T-RE-OMD	$345\to 395\to 505$
11.	${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_4{\mathrm{O}}_{10}\to$ $\to {\mathrm{C}}_{60}{\mathrm{O}}_{12}+2{\mathrm{N}\mathrm{a}}_2\mathrm{O}$—SOD	$510\to 585\to 660$
12.	${\mathrm{C}}_{60}{\mathrm{O}}_{12}+54{\mathrm{O}}_2\to$ $\to 60{\mathrm{C}\mathrm{O}}_2$—FCO	$680\to 1000\to \cdots$
13.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8·20{\mathrm{H}}_2\mathrm{O}\to$ $\to {\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8·20{\mathrm{H}}_2\mathrm{O}$—MED	$95\to 315\to 360$
14.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8\to$ $\to 8\mathrm{Z}\mathrm{n}\mathrm{O}+{\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_8{\mathrm{O}}_8$—T-RE-OMD	$355\to 430\to 510$
15.	${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_8{\mathrm{O}}_8\to$ $\to {\mathrm{C}}_{60}{\mathrm{O}}_{12}+4{\mathrm{N}\mathrm{a}}_2\mathrm{O}$—SOD	$515\to 590\to 665$
16.	${\mathrm{C}}_{60}{\mathrm{O}}_{12}+54{\mathrm{O}}_2\to$ $\to 60{\mathrm{C}\mathrm{O}}_2$—FCO	$680\to 1000\to \cdots$
17.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6·22{\mathrm{H}}_2\mathrm{O}\to$ $\to {\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6·22{\mathrm{H}}_2\mathrm{O}$—MED	$90\to 320\to 365$
18.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6\to$ $\to 3\mathrm{G}{\mathrm{d}}_2{\mathrm{O}}_3+{\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_6{\mathrm{O}}_9$—T-RE-OMD	$385\to 470\to 530$
19.	${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_6{\mathrm{O}}_9\to$ $\to {\mathrm{C}}_{60}{\mathrm{O}}_{12}+3{\mathrm{N}\mathrm{a}}_2\mathrm{O}$—SOD	$540\to 610\to 680$
20.	${\mathrm{C}}_{60}{\mathrm{O}}_{12}+54{\mathrm{O}}_2\to$ $\to 60{\mathrm{C}\mathrm{O}}_2$—FCO	$680\to 1000\to \dots$
21.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{T}\mathrm{b}{)}_6·20{\mathrm{H}}_2\mathrm{O}\to$ $\to {\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{T}\mathrm{b}{)}_6·20{\mathrm{H}}_2\mathrm{O}$—MED	$90\to 325\to 370$
22.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{T}\mathrm{b}{)}_6\to$ $\to 3{\mathrm{T}\mathrm{b}}_2{\mathrm{O}}_3+{\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_6{\mathrm{O}}_9$—T-RE-OMD	$375\to 465\to 540$
23.	${\mathrm{C}}_{60}({\mathrm{O}\mathrm{N}\mathrm{a})}_6{\mathrm{O}}_9\to$ $\to {\mathrm{C}}_{60}{\mathrm{O}}_{12}+3{\mathrm{N}\mathrm{a}}_2\mathrm{O}$—SOD	$545\to 615\to 685$
24.	${\mathrm{C}}_{60}{\mathrm{O}}_{12}+54{\mathrm{O}}_2\to$ $\to 60{\mathrm{C}\mathrm{O}}_2$—FCO	$680\to 1000\to \cdots$

.

3.5. High-Performance Liquid-Phase Chromatography (HPLC)

Typical example of a chromatogram of a Me-adduct ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8$ is represented in Figure 4. It is clearly seen from the figure that the mixture of adducts leaves the chromatographic column with a relatively wide peak (with base $~2$ min and half-width $~1$ min), which indirectly indicates the formation of a group of izomers of closely related compounds of very similar composition. Before entering the column, the adduct solution was centrifuged to separate the largest associates with linear dimensions of several microns.

4. Solubility in Water Solutions in the Natural Range of Temperatures

The solubility of Me-adducts in water solutions in the ambient range of temperatures is represented in

Table 4. Solubility in the systems ${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_2\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/2}\mathrm{o}\mathrm{r}{\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{\mathrm{x}}\right({\mathrm{O}}_3\mathrm{M}\mathrm{e}{)}_{(24-\mathrm{x})/3}-{\mathrm{H}}_2\mathrm{O}$; Me: Co; Cu; Mn; Zn; Gd; Tb.

No	System	Crystal Hydrate	Temperature (°C)	Solubility S (g/dm3)
1.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6-{\mathrm{H}}_2\mathrm{O}$	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6·24{\mathrm{H}}_2\mathrm{O}$	25	0.340
2.			0	0.419
3.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}-{\mathrm{H}}_2\mathrm{O}$	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}·18{\mathrm{H}}_2\mathrm{O}$	25	0.503
4.			0	0.636
5.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}-{\mathrm{H}}_2\mathrm{O}$	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}·18{\mathrm{H}}_2\mathrm{O}$	25	0.444
6.			0	0.665
7.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8-{\mathrm{H}}_2\mathrm{O}$	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8·20{\mathrm{H}}_2\mathrm{O}$	25	0.634
8.			0	1.041
9.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6-{\mathrm{H}}_2\mathrm{O}$	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6·22{\mathrm{H}}_2\mathrm{O}$	25	0.552
10.			0	0.627
11.	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_2\mathrm{T}\mathrm{b}{)}_6-{\mathrm{H}}_2\mathrm{O}$	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{T}\mathrm{b}{)}_6·20{\mathrm{H}}_2\mathrm{O}$	25	0.492
12.			0	0.521

and Figure 5. Solubility data confirmed that the solubility of all crystal hydrates of adducts is quite significant for feeding the root system of cereals and amounts to 0.3 $÷$ 1.1 g/dm³. On the other hand, the solubility is not high enough for rapid dissolution and exhaustion of microelements in soils. Figure 5 also shows that the solubility of all Me-adducts (without changing the type of crystal hydrate) increases with decreasing temperature, which can be very valuable from an agrotechnical point of view, since the maximum supply of plants with trace elements will be observed precisely at temperatures of approximately 0 °C (during melting or the first snowfall in the spring–autumn period), when these elements are in maximum demand for the development of cereals.

The temperature dependence of the solubility of crystalline salt hydrates is, in principle, arbitrary; it all depends on the sign of the heat dissolution of the crystalline hydrate in water. In our case, it is negative, which is comparatively rare. But, for example, even in the classical fullerene system ${\mathrm{C}}_{60}-\mathrm{1,2}{\mathrm{C}}_6{\mathrm{H}}_4({\mathrm{C}\mathrm{H}}_3{)}_2$, on the crystallization branch of bi-solvated ${\mathrm{C}}_{60}$, solubility increases with increasing temperature; and on the high-temperature branch of crystallization of non-solvated ${\mathrm{C}}_{60}$, it decreases.

It is likely that the use of the term the “true solubility of metal adducts” in relation to solutions containing suspended micron-sized particles is not correct. In our case, we calculate solubility formally, taking into account all the forms of associates installed in the solution—see

Table 5. Size distribution, electro-kinetic $\mathsf{\xi }$-potentials and mobility of the associates of Me-adducts of fullerenol-24 with some metals.

Me-Adduct	Concentration C (g/dm3)		${\mathsf{\delta }}_0\left(\mathbf{n}\mathbf{m}\right)$	${\mathsf{\delta }}_{\mathbf{I}}\left(\mathbf{n}\mathbf{m}\right)$	${\mathsf{\delta }}_{\mathbf{I}\mathbf{I}}\left(\mathbf{n}\mathbf{m}\right)$	${\mathsf{\delta }}_{\mathbf{I}\mathbf{I}\mathbf{I}}\left(\mathsf{\mu }\mathbf{m}\right)$
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6$	0.34		-	65	105	7
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}$	0.55		-	-	105	5
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}$	0.49		-	-	108	5
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8$	0.88		-	-	120	5
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6$	0.72		-	-	120	6
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_2\mathrm{T}\mathrm{b}{)}_6$	0.50		-	65	103	7
Me-adduct	${\mathrm{N}}_{\mathrm{I}-0}$ $(\mathrm{a}.\mathrm{u}.)$	${\mathrm{N}}_{\mathrm{I}\mathrm{I}-0}$ $(\mathrm{a}.\mathrm{u}.)$	${\mathrm{N}}_{\mathrm{I}\mathrm{I}\mathrm{I}-0}$ $(\mathrm{a}.\mathrm{u}.)$	${\mathrm{N}}_{\mathrm{I}\mathrm{I}-\mathrm{I}}$ $(\mathrm{a}.\mathrm{u}.)$	${\mathrm{N}}_{\mathrm{I}\mathrm{I}\mathrm{I}-\mathrm{I}}$ $(\mathrm{a}.\mathrm{u}.)$	${\mathrm{N}}_{\mathrm{I}\mathrm{I}\mathrm{I}-\mathrm{I}\mathrm{I}}$ $(\mathrm{a}.\mathrm{u}.)$
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6$	$2{\times 10}^4$	$3{\times 10}^4$	$4{\times 10}^9$	2	$3{\times 10}^5$	$1{\times 10}^5$
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}$	-	$3{\times 10}^4$	$2{\times 10}^9$	2	$1{\times 10}^5$	$5{\times 10}^4$
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}$	-	$3{\times 10}^4$	$2{\times 10}^9$	2	$1{\times 10}^5$	$5{\times 10}^4$
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8$	-	$4{\times 10}^4$	$2{\times 10}^9$	3	$1{\times 10}^5$	$4{\times 10}^4$
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6$	-	$4{\times 10}^4$	$3{\times 10}^9$	3	$2{\times 10}^5$	$6{\times 10}^4$
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_2\mathrm{T}\mathrm{b}{)}_6$	$2{\times 10}^4$	$3{\times 10}^4$	$4{\times 10}^9$	2	$3{\times 10}^5$	$2{\times 10}^5$
Me-adduct	${\mathsf{\xi }}_{\mathrm{I}}\left(\mathrm{m}\mathrm{V}\right)$	${\mathsf{\xi }}_{\mathrm{I}\mathrm{I}}\left(\mathrm{m}\mathrm{V}\right)$	${\mathsf{\xi }}_{\mathrm{I}\mathrm{I}\mathrm{I}}\left(\mathrm{m}\mathrm{V}\right)$	${\mathrm{U}}_{\mathrm{I}}$ $($μm∙cm/V∙s$)$	${\mathrm{U}}_{\mathrm{I}\mathrm{I}}$ $($μm∙cm/V∙s$)$	${\mathrm{U}}_{\mathrm{I}\mathrm{I}\mathrm{I}}$ $($μm∙cm/V∙s$)$
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6$	−20	−35	−60	−1.4	−1.8	−0.5
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}$	-	−35	−50	-	−2.1	−0.7
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}$	-	−35	−50	-	−2.0	−0.7
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8$	-	−40	−50	-	−2.3	−0.7
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_3\mathrm{G}\mathrm{d}{)}_6$	-	−40	−55	-	−2.4	−0.6
${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_6\right({\mathrm{O}}_2\mathrm{T}\mathrm{b}{)}_6$	−20	−30	−60	−1.5	−2.1	−0.5

below. Note that the method for determining the concentration of metal-adducts that we use is not spectrophotometry (absorption spectra), but turbidimetry (scattering spectrum), which does not interfere with the use of the Bouguer–Lambert–Beer law.

5. Dynamic Light Scattering in Water Solutions

All solutions of Me-adducts in water turned out to be hierarchically associated in a complex way. Consistent formation of I-order associates with typical linear dimensions was observed in them; ${\mathsf{\delta }}_{\mathrm{I}}$ of the order of tens of nm, II order (${\mathsf{\delta }}_{\mathrm{I}\mathrm{I}}$ of the order of 100 nm); III order (${\mathsf{\delta }}_{\mathrm{I}\mathrm{I}\mathrm{I}}$ of the order of several microns), and the formation of the latter corresponds to a microheterogenic solution. Unassociated metalloadducts (${\mathsf{\delta }}_0$~2 nm were not observed by us). Typical examples of particle size distribution are shown in Table 5 and Figure 6.

Elementary calculation (in spherical approximation) allows us to calculate the number of monomeric Me-adduct molecules in the i-th order associate—${\mathrm{N}}_{\mathrm{i}-0}$ (Table 5):

$${\mathrm{N}}_{\mathrm{i}-0}=({\mathsf{\delta }}_{\mathrm{i}}/{\mathsf{\delta }}_0{)}^3·{\mathrm{K}}_{\mathrm{p}\mathrm{a}\mathrm{c}\mathrm{k}}^{\mathrm{i}};{\mathrm{N}}_{\mathrm{i}+1-\mathrm{i}}=({\mathsf{\delta }}_{\mathrm{i}+1}/{\mathsf{\delta }}_{\mathrm{i}}{)}^3·{\mathrm{K}}_{\mathrm{p}\mathrm{a}\mathrm{c}\mathrm{k}};{\mathrm{K}}_{\mathrm{p}\mathrm{a}\mathrm{c}\mathrm{k}}=\mathsf{\pi }/6$$

(6)

where (${\mathrm{K}}_{\mathrm{p}\mathrm{a}\mathrm{c}\mathrm{k}}$—packing coefficient of “small spheres into a large sphere”).

Also one can calculate the number of i-th order associates of Me-adducts in the (i+1)-th order associate—${\mathrm{N}}_{\mathrm{i}+1-\mathrm{i}}$ (Table 5):

$${\mathrm{N}}_{\mathrm{i}+1-\mathrm{i}}=({\mathsf{\delta }}_{\mathrm{i}+1}/{\mathsf{\delta }}_{\mathrm{i}}{)}^3·{\mathrm{K}}_{\mathrm{p}\mathrm{a}\mathrm{c}\mathrm{k}}$$

(7)

For these calculations, one should estimate the dimensions of hydrated monomers—${\mathsf{\delta }}_0$ also in spherical approximation:

$$\begin{array}{l}{\mathsf{\delta }}_0=\mathsf{\delta }\left({\mathrm{C}}_{60}\right)+2\mathrm{r}\left(\mathrm{C}-\mathrm{O}\right)+2\mathrm{r}\left(\mathrm{O}-\mathrm{M}\mathrm{e}\right)+2\mathsf{\delta }\left({\mathrm{H}}_2\mathrm{O}\right)\approx 0.73+2\times 0.14+\\ +2\left(0.22÷0.33\right)+2\times 0.3\approx 2\mathrm{n}\mathrm{m}\end{array}$$

(8)

The 3th-order associates undoubtedly correspond to the micro-heterogenic colloidal state of the solutions. In Table 5, the electro-kinetic $\mathsf{\xi }$-potentials and mobilities of different-order associates of Me-adducts are also represented. The negative potential of all associates, on the one hand, determines the sedimentation stability of solutions, and, on the other hand, prevents further enlargement of associates of the III order. The latter were isolated, deposited on a quartz substrate and photographed by using a VEGA 3 TESCAN electron microscope (Figure 7). It follows from the obtained data that the main carriers of Me-adducts are probably associates of the second order, since there are relatively many of them in solution, and their mobility in solution is maximal. We did not find unassociated molecules of Me-adducts in solution even at the lowest concentrations (C = 0.01 g/dm³) and we cannot assume their existence in real aqueous solutions.

In our systems, unlike polymers, the molecules of metal-adducts are associated not by strong valence but by weak intermolecular Van der Waals forces. Due to the strictly hierarchical mechanism of association established by us, I-order associates are formed from metal-adduct monomers at certain concentrations; then, with increasing concentrations, II-order associates are formed from I-order associates; and then III-order associates. Thus, either only associates of the same order with the same size and mass (DPI $\approx$ 1) are present in the solution at the same time, or only two orders (when one associate passes into another and then DPI $\approx$ 2), as presented in Table 5 at high concentrations.

6. The Effect of Micro-Fertilizers Based on Me-Adducts on the Yield of Spring Barley

In terms of grain exports, Kazakhstan ranks 9th in the world (5 million tons). The dominant parts in grain production are wheat and barley [9]. Studies of the obtained samples of Me-adducts were carried out from May to October 2022 on experimental fields of peasant farms located in the East of Kazakhstan (Figure 8). The object of research is spring barley on non-irrigated (rainfed) and irrigated plots. The type of soil, the humus content in it and the main agroclimatic indicators according to Kazhydromet and the weather station for 2022 are presented in

Table 6. Main agroclimatic indicators during the period of research in various farms (June–September 2022).

The Name of the Indicator	Polygon I	Polygon II	Polygon III
Soil type	Ordinary chernozem, leached, of medium mechanical composition	Dark brown, light mechanical composition, subject to water and wind erosion	Chestnut, light mechanical composition, highly susceptible to water and wind erosion
Humus content range, %	4. 1 ÷ 5.3	1.0 ÷ 1.6	0.6 ÷ 1.3
The amount of precipitation for the entire growing season, mm	182	123	136
Average temperature for the entire growing season, °C	23.5	18.1	21.2

.

In previous experiments, the consumption of fullerenols and Me-adducts, amounting to $\mathrm{C}\mathrm{o}\mathrm{n}~12.5\mathsf{\mu }\mathrm{g}/{\mathrm{m}}^2$, was preliminarily determined. Introducton of fullerenols and Me-adducts was carried out in the form of water solutions of fullerenols and Me-adducts with the concentration $\mathrm{C}=10\mathrm{m}\mathrm{g}/{\mathrm{d}\mathrm{m}}^3.$ For the effective treatment of spring barley with Me-adducts, it was necessary to ensure the uniformity of the soil at the experimental site, which can be very difficult. An increase in the size of the plot often leads to an increase in the total area of the experiment and the probability of going beyond the uniformity increases. Based on long-term practice [10], it is advisable to set the area of the field experiment plot within 100 m², with a 4-fold repetition of options.

Table 7. Abbreviated name of the corresponding fullerenol and Me-adducts in the field experiment.

The Abbreviated Name of Fullerenol and Me-Adducts in the Field Experiment	Full Name of Fullerenol and Me-Adducts
C	Control (without processing)
F1	Fullerenol-24${-\mathrm{C}}_{60}(\mathrm{O}{\mathrm{H})}_{24}$
F2	Fullerenol-d [13,14]
F3	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{C}\mathrm{u}{)}_{10}$
F4	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_4\right({\mathrm{O}}_2\mathrm{M}\mathrm{n}{)}_{10}$
F5	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_{12}\right({\mathrm{O}}_2\mathrm{C}\mathrm{o}{)}_6$
F6	${\mathrm{C}}_{60}\left({\mathrm{O}\mathrm{N}\mathrm{a})}_8\right({\mathrm{O}}_2\mathrm{Z}\mathrm{n}{)}_8$

shows abbreviated names of fullerenols and Me-adducts in the field experiment, used later in the report. Relatively cheap and more affordable mixed fullerenol-d [11,12]$,{\mathrm{C}}_{60}{\mathrm{O}}_{\mathrm{x}}({\mathrm{O}\mathrm{H})}_{18÷30}$, was used for comparison.

Processing of barley crops was carried out twice in the tillering–tube phase with an interval of 7 days. In variants with non-root treatment with solutions of water-soluble fullerenes, individual fullerenol-24 and mixed fullerenol-d, barley crops were sprayed twice in the tillering phase—at the beginning of the exit into the tube. Barley crops not treated with fullerenol solutions were used as a control sample.

In variants with root treatment with solutions of water-soluble Me-adducts with copper, manganese, cobalt and zinc, barley crops were also treated twice in the tillering phase—the beginning of the exit into the tube. As a control sample, barley crops not treated with solutions of the above fullerenols were used. The treatment was carried out by spraying spring barley from a hand sprayer. The dates of treatment of spring barley crops with fullerenols and Me-adducts are given in

Table 8. Dates of sowing and processing of spring barley in experimental farms with various types of fullerenols and Me-adducts.

	Date of Sowing of Spring Barley	Data of the First Treatment by Fullerenols and Me-Adducts	Data of the Second Treatment by Fullerenols and Me-Adducts
Polygon I	5 May 2022	8 June 2022	15 June 2022
Polygon II	12 May 2022	16 June 2022	23 June 2022
Polygon III	26 May 2022	29 June 2022	6 July 2022
Polygon III-a	26 May 2022	29 June 2022	6 July 2022

.

To determine the biological yield of grain crops at each experimental landfill of all three polygons, a sample was taken from an area $\mathrm{S}=1.0{\mathrm{m}}^2$.

For this purpose, a special frame made of thin but strong slats (a meter frame) was used. The side of the frame in the internal measurement was equal to one meter. To make it easier to apply the frame for sampling, three of its sides are fixed tightly, and the fourth is freely removed and laid. The material was selected from five points of the test site of the landfill in accordance with the methodology for organizing and conducting a survey of grain yields [10].

The positive effect of the studied nanopreparations—fullerenols and Me-adducts—on the yield of spring barley at all the studied polygons was noted. The increase in yield during the processing of experimental plots in comparison with the control samples is shown in Figure 9. Figure 10 show the dependence of the effect of the fullerenol and Me-adduct type on the yield of spring barley on rainfed and irrigated polygons.

This is confirmed by previous studies aimed at increasing the productivity and sustainability of crops, especially under stressful conditions—moisture deficiency [15]. There was practically no positive effect of individual fullerenol-24 and fullerenol-d when spraying spring barley crops at polygon III-a. The effect of nanopreparations was most strongly manifested on the non-irrigated areas of landfill III-a in variants with root treatment with solutions of water-soluble fullerenes—fullerenol adducts with copper, manganese, cobalt and zinc, where the yield of spring barley increased by 54–80 rel.%. On the irrigation experimental plots of the same farm (polygon III), the effect of fullerenols was manifested both during spraying and during root treatment. In the case of spraying with solutions of fullerenol-24 and fullerenol-d, an increase in the yield of spring barley was observed by 23–29 rel.%. Basal treatment with Me-adducts with copper, manganese, cobalt and zinc showed a greater increase in the yield of spring barley by 34–45 rel.%.

Significantly less than expected, the effect of fullerenol and Me-adducts was manifested in polygon I and polygon II. When spraying crops at polygon I with solutions of fullerenol-24 and fullerenol-d, an increase in the yield of spring barley was observed from 2.5 to 21 rel.%. Basal treatment of crops with Me-adducts with copper, manganese, cobalt and zinc at the same landfill showed better results—the increase in the yield of spring barley was in the range of 25–41 rel.%. When spraying crops at landfill II with solutions of fullerenol-24 and fullerenol-d, the increase in the yield of spring barley was in the range of 3–7 rel.%. The root treatment of crops with Me-adducts with copper, manganese, cobalt and zinc at the same landfill showed an increase in the yield of spring barley from 7 to 21 rel.%.

The positive effect of water-soluble fullerene derivativesfullerenols and complexes of either C₆₀ with amino acids in the cultivation of agricultural crops is confirmed by many authors—see, for example, [9,16,17,18]. A number of researchers have found that fullerenols (and its derivatives) have antibacterial and antiviral activity, as well as antioxidant properties in their interaction with microorganisms and biological objects of animal origin [10,19,20,21]. In the review presented in [20], the synthesis of fullerenols is described and several mechanisms of antioxidant activity of fullerenol are proposed. The antioxidant activity of fullerenols indicates the possibility of using these nanomaterials in crop production to increase the productivity and stability of crops, especially under stressful conditions [7]. One of the main stress factors in the cultivation of agricultural crops is a lack of moisture. If regenerative processes develop in normally moistened soil, then in conditions with limited water, oxidative, this leads to the suspension of the plant growth process. Fullerenols and derivatives have the ability to bind reactive oxygen species, so we can expect a positive effect on the process of ammonification–nitrification and, as a consequence, a decrease in the amount of nitrogen fertilizers applied [6,7,13]. Thus, the authors believe that they can confidently assert that the use of fullerenols and derivatives helps to increase yields by stimulating water retention and combating certain pathogens [14]. Also, some research has been presented in the papers [15,22]. It has been shown that fullerenol regulates oxidative stress and homeostasis of tissue ions in spring wheat, improving net primary productivity under salt stress.

7. Quality Control of Seeds, Processed by Fullerenols and Me-Adducts

Quality control of spring barley seeds processed by fullerenols and Me-adducts during the ripening period was carried out according to the main indicators and the State Standard of Russia. The impact of fullerenols and Me-adducts seeds was determined according to the methodology described in the previous Section 6 “The effect of micro-fertilizers based on Me-adducts on the yield of spring barley” at the same times and concentrations. For the experiments, barley seeds obtained from irrigated polygon III were used. Control seeds samples were not treated by fullerenols and Me-adducts during the ripening period. The abbreviated name of fullerenol and Me-adducts in the experiment are shown in Table 7. The following seed quality characteristics were controlled: seed grade purity; weight of 1000 seeds; moisture content in seeds; laboratory germination of seeds; seed germination energy [23,24,25,26].

Separately, the research in the new work [27] should be noted, in which the authors noted the positive effect of fullerenol itself and metal adducts on its main effect on the yield of spring barley, the quality of the grain material and its resistance to pathogenic microflora. In

Table 9. Quality control of seeds, processed by fullerenols and Me-adducts.

Fullerenol and Me-Adduct	Seed Grade Purity (Rel.%)	Weight of 1000 Seeds (g)	Moisture Content in Seeds (Rel. Mass. %)	Laboratory Germination of Seeds (Rel.%)	Seed Germination Energy (Rel.%)
C	95.5	39.2	4.14	87.5	100.0
F1	93.9	41.2	4.31	87.5	97.5
F2	94.8	44.2	4.36	90.0	100.0
F3	95.4	46.4	4.74	87.5	97.5
F4	97.5	42.6.	4.62	87.5	97.5
F5	95.3	41.7	4.07	80.0	92.5
F6	95.0	42.2	4.75	92.5	92.5

and Figure 11 is represented quality control of seeds, processed by fullerenols and Me-adducts