Paramagnetic Complexes Research Articles

Photodynamic Inactivation of Bacteria Using Nickel(II) Complexes with Catecholate and Phenanthroline Ligands.

Metal complexes activated by light can combat infections by triggering the photodynamic inactivation of bacteria. Herein, we report six mixed-ligand nickel(II) complexes with the formulation [Ni(NN)2(L)] (1-6), where NN represents an N,N-donor phenanthroline ligand, specifically 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 5, 6), while L is an O,O donor bidentate ligand derived from catechol (cat2-, in 1, 3, 5) or esculetin (esc2-, in 2, 4, 6). The paramagnetic d8 octahedral complexes demonstrated good dark and photostability in the solution phase and exhibited significant light absorption in the visible (400-700 nm) region. When exposed to low-energy visible light, these complexes demonstrated significant photodynamic inactivation activity against both gram-(+) S. aureus and gram-(-) E. coli bacteria. This resulted in minimum inhibitory concentration (MIC) values ranging from 0.2 to 5.0 μg/mL. The activity was caused by the cell-damaging singlet oxygen species produced by the complexes under light exposure. Notably, the complexes showed no bacterial inhibition activity under dark conditions. This study marks the first examples of Ni(II) complexes designed for light-triggered antibacterial activity, illuminating the path for Ni(II)-based non-macrocyclic complexes for antibacterial PDT applications.

Complexes of Iron(II), Cobalt(II), and Nickel(II) with DOTA-Tetraglycinate for pH and Temperature Imaging Using Hyperfine Shifts of an Amide Moiety.

Paramagnetic complexes of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA4-) derivatives have shown potential for molecular imaging with magnetic resonance. DOTA-tetraglycinate (DOTA-4AmC4-) coordinated with lanthanide metal ions (Ln3+) demonstrates pH/temperature sensing with Biosensor Imaging of Redundant Deviation in Shifts (BIRDS) and Chemical Exchange Saturation Transfer (CEST), respectively, detecting nonexchangeable (e.g., -CHy, where 3 ≥ y ≥ 1) and exchangeable (e.g., -OH or -NHx, where 2 ≥ x ≥ 1) protons. Herein, we report paramagnetic complexes of divalent transition-metal ions (M2+ = Fe2+, Co2+, Ni2+) with DOTA-4AmC4- that endow a unique amide proton (-NH) moiety for pH/temperature sensing. Crystallographic data reveal that DOTA-4AmC4- coordinates with M2+ through oxygen and nitrogen donor atoms, ranging in coordination numbers from 8-coordinate in Fe(II)DOTA-4AmC2-, 7-coordinate in Co(II)DOTA-4AmC2-, and 6-coordinate in Ni(II)DOTA-4AmC2-. The -CHy protons in M(II)DOTA-4AmC2- displayed modest pH/temperature sensitivities, but -NH protons exhibited higher intensity, suggesting prominent BIRDS properties. The pH sensitivity was the highest for Ni(II)DOTA-4AmC2- (1.42 ppm/pH), followed by Co(II)DOTA-4AmC2- (0.21 ppm/pH) and Fe(II)DOTA-4AmC2- (0.16 ppm/pH), whereas temperature sensitivities were comparable (i.e., 0.22, 0.13, and 0.17 ppm/°C, respectively). The CEST image contrast for -NH in M(II)DOTA-4AmC2- was much weaker compared to that of Ln(III)DOTA-4AmC-. Given its high pH sensitivity and low cytotoxicity, Ni(II)DOTA-4AmC2- shows promise for use in preclinical BIRDS-based pH imaging.

The first examples of dirhenium(III,II) paramagnetic complexes with bridging diphenylphosphinomethane and 2-mercaptopyridine ligands: A collective experimental and theoretical studies

2-mercaptopyridine (H-pySH), 5‑chloro-2-mercaptopyridine (Cl-pySH) and 5-trifluoromethyl-2-mercaptopyridine (F3C-pySH) ligands react with the multiply‒bonded paramagnetic dirhenium(III,II) complex [Re2(μ-O2CCH3)Cl4(μ-dppm)2] (1) [dppm is Ph2PCH2PPh2] in refluxing ethanol to afford the paramagnetic substitution products of the type [Re2(μ-dppm)2(μ-R-pyS)2Cl2]Cl (2(R)) [R = H, Cl, CF3]. These are the first examples of paramagnetic dirhenium complexes that contain the bridging mercaptopyridine ligand. These complexes have very similar spectral (UV–vis, IR, EPR) and electrochemical properties which are also reported. The identity of 2(H) and 2(CF3) has been established by single-crystal X-ray structure determination (ReRe distance ∼2.29 Å). The electronic structures and optical properties of the complexes are scrutinized by density functional theory (DFT) and time-dependent DFT studies. DFT calculation shows that the highest occupied molecular orbital (HOMO) corresponds to a δ* interaction between the d-orbitals of rhenium atoms and π* interaction between the sulphur atoms and the rhenium centers whereas the lowest unoccupied molecular orbital (LUMO) is the Re2π* based orbital.

A DNA machine-based magnetic resonance imaging nanoprobe for in vivo microRNA detection

In situ monitoring microRNA (miRNA) expression in vivo holds immense potential for directly visualizing the occurrence and progression of tumors. However, the significant barrier to developing a probe that can overcome the low abundance of miRNAs while providing an output signal with unlimited tissue penetration depth remains formidable. In this study, we developed a DNA machine-based magnetic resonance imaging nanoprobe (MRINP) for amplified detection of miR-21 in vivo. The MRINP was constructed with superparamagnetic Fe3O4 nanoparticles (NPs), paramagnetic Gd-DOTA complexes, and miR-21-activated DNA machines; the DNA machine was composed of hairpin DNAzyme (HD) strands serving as the DNAzyme walker and hairpin substrate (HS) strands serving as the track. Once uptake into tumor cells, the intracellular miR-21 specifically recognized and hybridized with the HD strand, restoring the activity of DNAzyme. Subsequently, the DNAzyme walker autonomously traveled on the surface of MRINP, and each step movement of the DNAzyme walker resulted in the cleavage of its substrate strands and the ensued release of the Gd-DOTA complex-labeled oligonucleotides, turning on the T1 signal of Gd-DOTA complexes for in situ imaging of miR-21 in tumor-bearing mice. This strategy would offer a promising approach for mapping tumor-specific biomarkers in vivo with unlimited penetration depth.

A Caged Neutral 17-Valence-Electron Iron(I) Radical [Fe(CO)2(Cl)(P((CH2)10)3P)]•: Synthetic, Structural, Spectroscopic, Redox, and Computational Studies.

UV irradiation of yellow CH2Cl2 solutions of trans-Fe(CO)3(P((CH2)10)3P) (2a) and PMe3 (10 equiv) gives, in addition to the previously reported dibridgehead diphosphine P((CH2)10)3P (46%), a green paramagnetic complex that crystallography shows to be the trigonal-bipyramidal iron(I) radical trans-[Fe(CO)2(Cl)(P((CH2)10)3P)]• (1a•; 31% after workup). This is a rare example of an isolable species of the formula [Fe(CO)4-n(L)n(X)]• (n = 0-3, L = two-electron-donor ligand; X = one-electron-donor ligand). Analogous precursors with longer P(CH2)nP segments (n = 12, 14, 16, 18) give only the demetalated diphosphines, and a rationale is proposed. The magnetic susceptibility of 1a•, assayed by Evans' method and SQUID measurements, indicates a spin (S) of 1/2. Cyclic voltammetry shows that 1a• undergoes a partially reversible one-electron oxidation, but no facile reduction. The UV-visible, EPR, and 57Fe Mössbauer spectra are analyzed in detail. Complex 2a is similarly studied, and, despite the extra valence electron, exhibits a comparable oxidation potential (ΔE1/2 ≤ 0.04 V). The crystal structure shows a cage conformation, solvation level, disorder motif, and unit cell parameters essentially identical to those of 1a•. DFT calculations provide much insight regarding the structural, redox, and spectroscopic properties.

Exploring the potential of water channels for developing genetically encoded reporters and biosensors for diffusion-weighted MRI

Genetically encoded reporters for magnetic resonance imaging (MRI) offer a valuable technology for making molecular-scale measurements of biological processes within living organisms with high anatomical resolution and whole-organ coverage without relying on ionizing radiation. However, most MRI reporters rely on synthetic contrast agents, typically paramagnetic metals and metal complexes, which often need to be supplemented exogenously to create optimal contrast. To eliminate the need for synthetic contrast agents, we previously introduced aquaporin-1, a mammalian water channel, as a new reporter gene for the fully autonomous detection of genetically labeled cells using diffusion-weighted MRI. In this study, we aimed to expand the toolbox of diffusion-based genetic reporters by modulating aquaporin membrane trafficking and harnessing the evolutionary diversity of water channels across species. We identified a number of new water channels that functioned as diffusion-weighted reporter genes. In addition, we show that loss-of-function variants of yeast and human aquaporins can be leveraged to design first-in-class diffusion-based sensors for detecting the activity of a model protease within living cells.

Nanoprobes based on quantum dots and Gd(III) complexes for dual optical and magnetic resonance imaging

The combination of more than one clinical technique has been increasingly explored to improve imaging diagnosis, suppressing the limitations of individual procedures. Quantum dots (QDs) have been associated with paramagnetic complexes (GdDOTA) to develop optical-magnetic nanoprobes for imaging techniques. Herein, we report the preparation of bimodal nanoprobes by conjugating fluorescent QDs with GdDOTA complexes through dative bonds. These nanoprobes showed an enhancement in their emission intensity compared to bare QDs. Moreover, the nanosystems exhibited r1 values up to 69% higher than the clinical GdDOTA. Therefore, the bimodal systems demonstrated promising performance for both optical and magnetic resonance imaging, exhibiting potential as bimodal contrast agents.

Panoply of P: An Array of Rhenium-Phosphorus Complexes Generated from a Transition Metal Anion.

We expand upon the synthetic utility of anionic rhenium complex Na[(BDI)ReCp] (1, BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate) to generate several rhenium-phosphorus complexes. Complex 1 reacts in a metathetical manner with chlorophosphines Ph2PCl, MeNHP-Cl, and OHP-Cl to generate XL-type phosphido complexes 2, 3, and 4, respectively (MeNHP-Cl = 2-chloro-1,3-dimethyl-1,3,2-diazaphospholidine; OHP-Cl = 2-chloro-1,3,2-dioxaphospholane). Crystallographic and computational investigations of phosphido triad 2, 3, and 4 reveal that increasing the electronegativity of the phosphorus substituent (C < N < O) results in a shortening and strengthening of the rhenium-phosphorus bond. Complex 1 reacts with iminophosphane Mes*NPCl (Mes* = 2,4,6-tritert-butylphenyl) to generate linear iminophosphanyl complex 5. In the presence of a suitable halide abstraction reagent, 1 reacts with the dichlorophosphine iPr2NPCl2 to afford cationic phosphinidene complex 6+. Complex 6+ may be reduced by one electron to form 6•, a rare example of a stable, paramagnetic phosphinidene complex. Spectroscopic and structural investigations, as well as computational analyses, are employed to elucidate the influence of the phosphorus substituent on the nature of the rhenium-phosphorus bond in 2 through 6. Furthermore, we examine several common analogies employed to understand metal phosphido, phosphinidene, and iminophosphanyl complexes.

The paradigm of magnetic molecule in quantum matter: Slow molecular spin relaxation

The quantum nature of single-ion magnets, single-molecule magnets, and single-chain magnets has been manifested among other phenomena by magnetic hysteresis due to slow spin relaxation, competing with fast quantum tunneling at low temperatures. Slow spin relaxation, described by Arrhenius-type law with the effective barrier energies Ueff = 50 cm–1, was discovered 3 decades ago in paramagnetic Mn12-acetate complex of oxy-bridged mixed-valence manganese ions, below the blocking temperature TB = 3 K. In contrast to common magnetic materials, it is governed primarily by magnetic anisotropy, set by zero-splitting of spin states of a magnetic ion in a field of ligands, and spin-lattice coupling. The emerging studies on the border of coordination chemistry, physics of spin systems with reduced dimensionality, and nanotechnologies, were performed in search of routes for enhancement of Ueff and TB characteristics, in line with increase of operation temperature and quantum correlation time, mandatory for quantum applications. The best results with TB ∼ 80 K and Ueff ∼ 1261 cm–1, were obtained for DyIII single-ion magnet, so far. Numerous excellent research and review articles address particular activities behind this achievement. It follows, that present challenges are dictated by the rational development of novel, smart magnetic molecules, featured by butterfly cores, cyano-bridges, 2D metal-organic frameworks, and metal-free graphene nanoclusters, as well as stable free radicals, magnetized by spare electrons. These species are briefly considered here with respect to the unique experience of international collaborative activity, established by Prof. Juan Bartolomé.

NMR spectroscopic investigations of transition metal complexes in organometallic and bioinorganic chemistry

AbstractThe field of coordination chemistry has evolved to intersect with organic chemistry and biochemistry, giving rise to the disciplines of organometallic and bioinorganic chemistry. Nuclear magnetic resonance (NMR) spectroscopy can be applied for characterizing transition metal complexes, spanning both diamagnetic and paramagnetic complexes prevalent in organometallic compounds and metalloproteins. This review offers a comprehensive overview of a wide variety of characterization techniques, ranging from basic 1H and 13C NMR spectroscopy to advanced methods such as heteronuclear experiments, polarization transfer techniques, relaxometry, and multidimensional NMR spectroscopy. The diverse array of NMR spectroscopic methods outlined here promises to enhance our comprehension of transition metal complexes, facilitating the development of innovative catalysts and therapeutics.

Investigation of Earth-Abundant Metal Salts for the Inhibition of Asphalt-Derived Volatile Organic Compounds.

Asphalt is used globally in construction for roads, pavements, and buildings; however, as a fossil-derived material, it is known to generate volatile organic compounds (VOCs) upon exposure to heat and light that can be harmful to human health. Several heterogeneous strategies have been reported for the inhibition of these VOCs; however, the direct use of inexpensive, accessible Earth-Abundant metals has not been extensively explored. In this study, simple metal salts are examined for their coordination capability toward asphalt-derived VOCs. From UV-visible (UV-vis) spectroscopic studies, FeCl3 emerged relative to other metal salts (metal = Mn, Co, Ni, Cu, Zn) as a promising candidate for the adsorption and retention of Lewis basic compounds. Coordination of an example oxygen-containing VOC, benzofuran (Bf), to Fe yielded a paramagnetic semi-octahedral complex Fe(Bf)3Cl3. Evaluation by thermal gravimetric analysis (TGA) coupled to infrared spectroscopy (IR) demonstrated that the complex was stable up to 360 °C. Spectroscopic evaluation demonstrated the stability of the complex upon visible light irradiation and in the presence of a variety of organic pollutants. The potential application of Fe was demonstrated by subjecting biochar to FeCl3 followed by the addition of Bf. It was discovered that this Fe-rich biochar was successful at adsorbing Bf suggesting the possibility of introducing Fe to biochar late-stage in processing to deter asphalt degradation and VOC emissions. An understanding of the binding and stability of Fe salts to VOCs provides insight into how a sustainable infrastructure can be achieved.

Structure-property studies of a four coordinate niobium(IV) amide

The preparation, structure, and magnetic properties of Nb[N(Dipp)TMS]2Cl2 (1) are described. The paramagnetic complex is obtained via treatment of NbCl4(THF)2 with two equivalents of Li[N(Dipp)TMS]. Magnetic studies indicate NbIV (S = ½) ions are present and that slow frequency-dependent magnetization relaxation dynamics are operative below ca. 25 K, under application of non-zero magnetic fields. The relaxation dynamics appear to proceed via a Raman pathway.

Gd(HB-DO3A)]: Equilibrium, Dissociation Kinetic and Structural Differences in a Simple Homolog of [Gd(HP-DO3A)] (Prohance®).

[Gd(HP-DO3A)] (gadoteridol) as an active compound of ProHance® is a widely employed contrast agent in clinical MRI scans in the last 30 years. Recent concerns about the long-term retention of gadolinium-based contrast agents (GBCAs) led to a deeper investigation of the structural features underlying the integrity of the paramagnetic metal complex. Several human and nonclinical studies have noted marked differences among the macrocyclic GBCAs, with the least retention of Gd traces and most rapid elimination consistently being reported for [Gd(HP-DO3A)]. It was deemed of interest to assess how minor structural/electronic changes associated to the ligand structure may affect basic properties of the metal complex with several [Gd(HP-DO3A)] analogues synthesized and characterized in the last years. We recently reported that the closest homolog of [Gd(HP-DO3A)], i. e.: [Gd(HB-DO3A)], in which a (±)-2-hydroxy-1-propyl pendant arm is replaced by a (±)-2-hydroxy-1-butyl moiety, showed a significantly different retention behaviour in the model interaction with collagen, despite the apparently very minor structural difference. In this paper we report a comprehensive study of the structural, thermodynamic, kinetic and relaxation properties of [Gd(HB-DO3A)], compared to the parent [Gd(HP-DO3A)] and to other closely related macrocyclic GBCAs to assess whether very minor structural changes can modulate the physico-chemical properties of Gd3+ complexes.

Metal vs Ligand Oxidation: Coexistence of Both Metal-Centered and Ligand-Centered Oxidized Species.

A series of two-electron-oxidized cobalt porphyrin dimers have been synthesized upon controlled oxidations using halogens. Rather unexpectedly, X-ray structures of two of these complexes contain two structurally different low-spin molecules in the same asymmetric unit of their unit cells: one is the metal-centered oxidized diamagnetic entity of the type CoIII(por), while the other one is the ligand-centered oxidized paramagnetic entity of the type CoII(por•+). Spectroscopic, magnetic, and DFT investigations confirmed the coexistence of the two very different electronic structures both in the solid and solution phases and also revealed a ferromagnetic spin coupling between Co(II) and porphyrin π-cation radicals and a weak antiferromagnetic coupling between the π-cation radicals of two macrocycles via the bridge in the paramagnetic complex.

Nickel Perfluoroalkyl Complexes Supported by Simple Acetate Coligands.

The interaction of tetramethylammonium acetate with [(MeCN)2Ni(CF3)2], [(MeCN)2Ni(C2F5)2], and [NMe4][(MeCN)Ni(CF3)3] was explored by 19F NMR spectroscopy. We show that depending on the nature of the nickel complex, one or two acetate ligands can add to the metal center and replace the nickel-bound MeCN ligands, depending on the acetate concentration. The number of acetates that could bind to nickel, and whether the resulting complex exists as a monomer or dimer, was determined to be dependent on the nature of the fluoroalkyl ligand. Moreover, we observe that oxidation of the nickel center of [(MeCN)2Ni(CF3)2] in the presence of two equivalents of acetate leads cleanly to the octahedral, paramagnetic (EPR spectroscopy), and anionic Ni(III) complex [NMe4][Ni(CF3)2(OAc)2].

Ligand-Induced Intramolecular Redox Diversity in Titanium Complexes with Acenaphthene-1,2-diimine.

A series of the chlorido and alkoxychlorido titanium complexes of the general formula (dpp-Bian)Ti(OiPr)nCl3-n, where dpp-Bian = 1,2-bis[(2,6-iPr2C6H3)imino]acenaphthene n = 0 (2), 1 (3), 2 (4), as well as (dpp-Bian)Ti(OiPr)2 (5) and (dpp-Bian)Ti(OiPr)Cl3 (3-Cl), were isolated and characterized using single-crystal X-ray diffraction analysis and spectroscopic studies combined with density functional theory (DFT) calculations. In the solid state, compounds 2-4 reveal a square-pyramidal geometry at the metal center supported with monoanionic dpp-Bian, whereas 3-Cl with a neutral diimine ligand and 5 bearing a dianionic enebisamide dpp-Bian show, respectively, an octahedral and tetrahedral coordination surrounding the metal ion. Paramagnetic complexes 2-4 exhibit electron paramagnetic resonance spectra in both toluene solution and solid state, confirming the transfer of spin density from the metal ion to the dpp-Bian ligand as the number of alkoxy groups increases. The increase in polarity of the Ti-N bonds in the row 2 < 3 < 4 contributes to enhanced stability of the metal complexes with respect to O-donor molecules. Thus, in tetrahydrofuran (THF), compounds 2 and 3 undergo reversible solvolysis, whereas complex 4 is stable. The charge and spin density distributions as well as molecular orbital energies in 2-4 were analyzed on the basis of DFT calculations which also provided information on the electronic transition energies, absorption band assignments, and thermodynamic parameters of the reactions between the complexes and THF.

Chitosan‐Based Nanogels Containing Ln3+ Chelates (Ln=Gd, Dy) as T1 and T2 MRI Probes

AbstractNovel nanogels, characterized by high stability and incorporating macrocyclic chelates of Gd(III) and Dy(III), were synthesized and assessed for their effectiveness as T1 and T2 relaxation agents, respectively. In this specific design, we employed octacoordinated bifunctional Gd‐1,7‐DOTAGA2 chelate to cross‐link chitosan chains. The results revealed that the sample exhibited a relaxivity value at clinical magnetic field strengths (1.5 T), approximately seven times higher than that of currently available clinical contrast agents and good MRI contrast efficacy at both 7.1 and 1 T. Furthermore, the nanogel displayed excellent stability in biological fluids, with no discernible interactions with serum biomolecules and no release of metal. In addition to Gd(III)‐based probes commonly used as T1 positive contrast agents, the nanogel with the corresponding Dy‐1,7‐DOTAGA2 chelate was prepared to explore its potential as a T2 MRI probe. Dy‐based nanogel demonstrated notably elevated transverse relaxivity values compared to the free chelate at high magnetic fields (&gt;3 T) and significant T2 MRI contrast at 7.1 T, a capability often lacking when employing an equivalent concentration of a low‐molecular‐weight Dy(III) complex. The characterization of paramagnetic complexes was completed through the measurement of 1H NMRD profiles and 17O NMR data.

Reactivity of an Iron Carbonyl Dianion Dictated by a Lewis Basic Appendant

AbstractStudies toward transition metals in negative oxidation states are much less explored compared to those in zero or positive oxidation states. In this study, we present the synthesis and reactivity studies of an Fe(‐II) carbonyl dianion (3) featuring an appended Lewis base, [(L)Fe(CO)3]2− (L=Ph2PCH2CH2NMe2). Unlike the well‐known reactivity of [Fe(CO)4]2− with common electrophiles (E+) which typically forms [(E)2Fe(CO)4], 3 reacted with 2 equiv. of Ph3SnCl to afford a mixture of two products: one being an Fe(II) bis(triphenylstannyl) product (4), and the other an Fe stannylene product (5). Further insights into the reactivity of 3 was elucidated through its reactions with 2 equiv. of Cy3SnCl or Me3SiCl, producing an Fe(II) bis(tricyclohexylstannyl) product (8) and a zwitterionic complex (11), respectively, the latter emerging via THF ring‐opening. Intermediates generated from reactions of 3 with 1 equiv. of each electrophile were isolated to shed light on the reaction mechanisms, highlighting the influence of appended Lewis base on the reactivity of metal carbonyl dianions, especially the generation of the novel stannylene complex 5. The electronic structure of this paramagnetic stannylene complex was also investigated by computational studies.

Reversible structural change of [Co2Fe2] complexes between diamagnetic hydrogen-bonded 1D chains and paramagnetic complexes within a layered structure of amphiphilic anions.

The combination of amphiphilic ions and metal complexes may enable the construction of assemblies in which the assembly structure and electronic state of the metal complexes change concertedly. In this work, an alternating layered structure of [Co2Fe2] complexes and amphiphilic anions was constructed. In the crystal structure, [Co2Fe2] complexes and water molecules formed a hydrogen-bonded supramolecular one-dimensional (1D) chain in the hydrophilic layer. A reversible structural change between the 1D chain and discrete [Co2Fe2] complexes was found to occur concertedly with an electron transfer-coupled spin transition (ETCST) of the [Co2Fe2] complex and desorption/adsorption of water molecules.

Thermal processes in anisotropic metal complexes induced by non-adiabatic switching of magnetic field.

In this article we analyze the thermal processes in magnetically anisotropic metal complexes under the action of non-adiabatic switching of magnetic field. Using the non-stationary perturbation theory for the case of sudden perturbation, we show that this field can cause not only heat release, but also heat absorption, interconnected with the axial zero field splitting (parameter D) in a paramagnetic metal complex. As an illustrative example we consider the simplest S = 1-complexes having "easy axis" and "easy plane" types of anisotropy influenced by the magnetic field that is suddenly turned off. We demonstrate that the character of the thermal processes (heat dissipation or absorption) depends on the sign of D and direction of applied field and so the analysis of these processes can be in principle used as a complementary tool (in addition to SQIUD magnetometry, EPR spectroscopy and INS) for studying magnetic anisotropy. The conditions under which the non-adiabatic switching of the magnetic field gives rise to the heat absorption are revealed. This unusual phenomenon, which can be called "nonadiabatic field switching cooling", may have practical applications.