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1.
Inorg Chem ; 2020 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-32672944

RESUMO

Herein, we combine for the first time SQUID magnetometry, cw-EPR, THz-EPR, and paramagnetic NMR spectroscopies to study the magnetic properties of a high-spin cobalt(II) heteroscorpionate complex. Complementary information provided by these methods allowed precise determination of the magnetic interaction parameters, thereby removing the ambiguity inherit to single-method studies. We systematically investigate the extent to which information about the magnetic interaction parameters can be deduced from reduced data sets. The detailed study revealed significant different magnetic properties in solid state and solution. To further exploit the information content of the solution NMR experimental results, we introduce the new concept of reduced paramagnetic shift. It allows for the determination of the magnetic axes and, subsequently, full NMR signal assignment. It is shown that even in complicated cases, in which common NMR analytics (integral intensities, relaxation factors, etc.) fail, it yields robust results.

2.
Org Biomol Chem ; 18(4): 755-766, 2020 01 28.
Artigo em Inglês | MEDLINE | ID: mdl-31912862

RESUMO

The design of small organic molecules with a predictable and desirable DNA-binding mechanism is a topical research task for biomedicine application. Herein, we demonstrate an attractive supramolecular strategy for controlling the non-covalent ligand-DNA interaction by binding with cucurbituril as a synthetic receptor. With a combination of UV/vis, CD and NMR experiments, we demonstrate that the bis-styryl dye with two suitable binding sites can involve double stranded DNA and cucurbituril in the formation of the supramolecular triad. The ternary assembly is formed as a result of the interaction of macrocyclic cucurbituril with one pyridinium fragment of the bis-styryl dye, while the second pyridinium fragment of the dye is effectively associated with DNA backbones, which leads to a change in the ligand-DNA binding mode from aggregation to a minor groove. This exciting outcome was supported by molecular docking studies that help to understand the molecular orientation of the supramolecular triad and elucidate the destruction of dye aggregates caused by cucurbituril. These studies provide valuable information on the mechanisms of DNA binding to small molecules and recognition processes in bioorganic supramolecular assemblies constructed from multiple non-covalent interactions.


Assuntos
Hidrocarbonetos Aromáticos com Pontes/química , Corantes/química , DNA/química , Imidazóis/química , Estirenos/química , Animais , Bovinos , Ligantes , Compostos Macrocíclicos/química , Simulação de Acoplamento Molecular
3.
Phys Chem Chem Phys ; 21(16): 8201-8204, 2019 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-30950488

RESUMO

Here we report a combined use of THz-EPR and NMR spectroscopy for obtaining a detailed electronic structure of a long-known high-spin complex, cobalt(ii) bis[tris(pyrazolyl)borate]. The lowest inter-Kramers transition was directly measured by THz-EPR spectroscopy, while the energies of higher Kramers doublets were estimated by a recently proposed NMR-based approach. Together, they produced magnetic parameters for a full model that explicitly includes spin-orbit coupling. This approach is applicable to all transition metal ions for which the spin-orbit coupling cannot be treated perturbatively.

4.
Chemphyschem ; 20(8): 1001-1005, 2019 04 16.
Artigo em Inglês | MEDLINE | ID: mdl-30897255

RESUMO

Herein, we report a new trigonal prismatic cobalt(II) complex that behaves as a single molecule magnet. The obtained zero-field splitting, which is also directly accessed by THz-EPR spectroscopy (-102.5 cm-1 ), results in a large magnetization reversal barrier U of 205 cm-1 . Its effective value, however, is much lower (101 cm-1 ), even though there is practically no contribution from quantum tunneling to magnetization relaxation.

5.
Inorg Chem ; 57(24): 15330-15340, 2018 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-30495930

RESUMO

Zero-field splitting (ZFS) of three high-spin Co(I) ( S = 1) clathrochelate complexes was determined by frequency-domain Fourier-transform THz-EPR (FD-FT THz-EPR). The following axial and rhombic ZFS values ( D and E, respectively) were determined: [N( n-Bu)4]CoI(GmCl2)3(BPh)2 (1, D/ hc = +16.43(1) cm-1, E/ hc = 0.0(1) cm-1), [P(Me2N)4]CoI(GmCl2)3(BPh)2 (2, D/ hc = +16.67(4) cm-1, E/ hc = 0.0(1) cm-1), and [P(C6H5)4]CoI(GmCl2)3(BPh)2 (3, D/ hc = +16.72(2) cm-1, E/ hc = 0.24(3) cm-1). Complementary susceptibility χ T measurements and quantum chemistry calculations on 1 revealed hard-axis-type magnetic anisotropy and allowed for a correlation of ZFS and the electronic structure. Increased rhombicity of 3 as compared to 1 and 2 was assigned to symmetry changes of the ligand structure induced by the change of the counterion. 1 and 3 exhibited temperature-dependent ZFS values. Possible reasons for this phenomenon, such as structural changes and weak chain-like intermolecular antiferromagnetic interactions, are discussed.

6.
Chem Commun (Camb) ; 54(28): 3436-3439, 2018 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-29424850

RESUMO

The first synthesized and X-ray structurally characterized "classical" iron(i) dioximate showed an unrivaled stability towards strong acids, thus calling for a reassessment of the origins of the electrocatalytic activity of similar low-valent cobalt and iron cage complexes with electron-withdrawing ribbed substituents, shown previously to be effective electrocatalysts of the HER.

7.
ACS Omega ; 3(5): 4941-4946, 2018 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-31458710

RESUMO

Variable-temperature NMR spectroscopy has recently emerged as a new alternative to the magnetometry methods for studying single molecule magnets. Its use is based on an accurate determination of magnetic susceptibility tensor anisotropy Δχ, which is not always achievable due to some contact contribution to NMR chemical shifts and possible conformational dynamics. Here, we applied this approach to cholesteryl-substituted cage cobalt(II) complexes featuring a very large magnetic anisotropy. Conformational rigidity and large size of the cholesteryl substituent with many magnetically nonequivalent nuclei resulted in an excellent convergence of experimental and calculated 1H and 13C chemical shifts, thus allowing for the determination of Δχ value for all of the synthesized cobalt(II) complexes with a very high accuracy and providing a more reliable zero-field splitting energy for further calculations.

8.
Inorg Chem ; 56(24): 14759-14762, 2017 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-29206025

RESUMO

Spin transitions in spin-crossover compounds are now routinely studied in the solid state by magnetometry; however, only a few methods exist for studies in solution. The currently used Evans method, which relies on NMR spectroscopy to measure the magnetic susceptibility, requires the availability of a very pure sample of the paramagnetic compound and its exact concentration. To overcome these limitations, we propose an alternative NMR-based technique for evaluating spin-state populations by only using the chemical shifts of a spin-crossover compound; those can be routinely obtained for a solution that contains unknown impurities and paramagnetic admixtures or is contaminated otherwise.

9.
Chemistry ; 23(61): 15424-15435, 2017 Nov 02.
Artigo em Inglês | MEDLINE | ID: mdl-28853186

RESUMO

The thermodynamics of chloride dissociation from the 18e arene ruthenium iminophosphonamides [(η6 -arene)RuCl{(R'N)2 PR2 }] (1 a-d) [previously known with arene=C6 Me6 , R=Ph, R'=p-Tol (a); R=Et, R'=p-Tol (b); R=Ph, R'=Me (c); and new with arene=p-cymene, R=Ph, R'=p-Tol (d)] was assessed in both polar and apolar solvents by variable-temperature UV/Vis, NMR, and 2D EXSY 1 H NMR methods, which highlighted the influence of the NPN ligand on the equilibrium parameters. The dissociation enthalpy ΔHd decreases with increasing electron-donating ability of the N- and P-substituents (1 a, 1 d>1 b>1 c) and solvent polarity, and this results in exothermic spontaneous dissociation of 1 c in polar solvents. The coordination of neutral ligands (MeCN, pyridine, CO) to the corresponding 16e complexes [(η6 -arene)Ru{(R'N)2 PR2 }]+ PF6- (2 a-d) is reversible; the stability of the 2⋅L adducts depends on the π-accepting ability of L. Carbonylation of 2 a and 2 d resulted in rare examples of cationic arene ruthenium carbonyl complexes (3 a, 3 d), while the monocarbonyl adduct derived from 2 c reacts further with a second equivalent of CO with conversion to carbonyl-carbamoyl complex 3 c, in which one CO molecule is inserted into the Ru-N bond. The new complexes 1 d, 2 d, 3 a, 3 c, and 3 d were isolated and structurally characterized.

10.
Beilstein J Org Chem ; 13: 639-643, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28487757

RESUMO

1,11-Dien-6-ynes undergo cycloisomerization in the presence of the cobalt catalytic system CoBr2/phosphine ligand/Zn/ZnI2 giving cyclohexene, diene or cyclopropane structures depending on the type of the phosphine ligand. This unpredictable behaviour suggests that, although the availability of the cobalt catalytic system is appealing, the development of well-defined catalysts is desirable for further progress.

11.
Inorg Chem ; 56(12): 6943-6951, 2017 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-28541691

RESUMO

High magnetic anisotropy is a key property of paramagnetic shift tags, which are mostly studied by NMR spectroscopy, and of single molecule magnets, for which magnetometry is usually used. We successfully employed both these methods in analyzing magnetic properties of a series of transition metal complexes, the so-called clathrochelates. A cobalt complex was found to be both a promising paramagnetic shift tag and a single molecule magnet because of it having large axial magnetic susceptibility tensor anisotropy at room temperature (22.5 × 10-32 m3 mol-1) and a high effective barrier to magnetization reversal (up to 70.5 cm-1). The origin of this large magnetic anisotropy is a negative value of zero-field splitting energy that reaches -86 cm-1 according to magnetometry and NMR measurements.

12.
ACS Omega ; 2(10): 6852-6862, 2017 Oct 31.
Artigo em Inglês | MEDLINE | ID: mdl-31457271

RESUMO

The study tackles one of the challenges in developing platinum-free molecular electrocatalysts for hydrogen evolution, which is to seek for new possibilities to ensure large turnover numbers by stabilizing electrocatalytic intermediates. These species are often much more reactive than the initial electrocatalysts, and if not properly stabilized by a suitable choice of functionalizing substituents, they have a limited long-time activity. Here, we describe new iron and cobalt(II) cage complexes (clathrochelates) that in contrast to many previously reported complexes of this type do not act as electrocatalysts for hydrogen evolution. We argue that the most probable reason for this behavior is an excessive stabilization of the metal(I) species by perfluoroaryl ribbed groups, resulting in an unprecedented long-term stability of the metal(I) complexes even in acidic solutions.

13.
Inorg Chem ; 55(22): 11867-11882, 2016 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-27801586

RESUMO

The first hybrid di- and trinuclear iron(II)-zirconium(IV) and iron(II)-hafnium(IV) macrobicyclic complexes with one or two apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using transmetalation reaction between n-butylboron-triethylantimony-capped or bis(triethylantimony)-capped iron(II) clathrochelate precursors and dichlorozirconium(IV)- or dichlorohafnium(IV)-5,10,15,20-tetraphenylporphyrins under mild conditions. New di- and trinuclear porphyrinoclathrochelates of general formula FeNx3((Bn-Bu)(MTPP)) and FeNx3(MTPP)2 [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinato(2-); Nx = nioximo(2-)] were characterized by one-dimensional (1H and 13C{1H}) and two-dimensional (COSY and HSQC) NMR, high-resolution electrospray ionization mass spectrometry, UV-visible, and magnetic circular dichroism spectra, single-crystal X-ray diffraction experiments, as well as elemental analyses. Redox properties of all complexes were probed using electrochemical and spectroelectrochemical approaches. Electrochemical and spectroelectrochemical data suggestive of a very weak, if any, long-range electronic coupling between two porphyrin π-systems in FeNx3(MTPP)2 complexes. Density functional theory and time-dependent density functional theory calculations were used to correlate spectroscopic signatures and redox properties of new compounds with their electronic structures.

14.
J Phys Chem Lett ; 7(20): 4111-4116, 2016 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-27689621

RESUMO

A large barrier to magnetization reversal, a signature of a good single-molecule magnet (SMM), strongly depends on the structural environment of a paramagnetic metal ion. In a crystalline state, where SMM properties are usually measured, this environment is influenced by crystal packing, which may be different for the same chemical compound, as in polymorphs. Here we show that polymorphism can dramatically change the magnetic behavior of an SMM even with a very rigid coordination geometry. For a cobalt(II) clathrochelate, it results in an increase of the effective barrier from 109 to 180 cm-1, the latter value being the largest one reported to date for cobalt-based SMMs. Our finding thus highlights the importance of identifying possible polymorphic phases in search of new, even more efficient SMMs.

15.
Artigo em Inglês | MEDLINE | ID: mdl-26855085

RESUMO

In medical and pharmaceutical applications, chitosan is used as a component of hydrogels-macromolecular networks swollen in water. Chemical hydrogels are formed by covalent links between the crosslinking reagents and amino functionalities of chitosan. To date, the most commonly used chitosan crosslinkers are dialdehydes, such as glutaraldehyde (GA). We have developed novel GA like crosslinkers with additional functional groups-dialdehyde derivatives of uridine (oUrd) and nucleotides (oUMP and oAMP)-leading to chitosan-based biomaterials with new properties. The process of chitosan crosslinking was investigated in details and compared to crosslinking with GA. The rates of crosslinking with oUMP, oAMP, and GA were essentially the same, though much higher than in the case of oUrd. The remarkable difference in the crosslinking properties of nucleoside and nucleotide dialdehydes can be clearly attributed to the presence of the phosphate group in nucleotides that participates in the gelation process through ionic interactions with the amino groups of chitosan. Using NMR spectroscopy, we have not observed the formation of aldimine bonds. It can be concluded that the real number of crosslinks needed to cause gelation of chitosan chains may be less than 1%.


Assuntos
Materiais Biocompatíveis/química , Quitosana/química , Reagentes para Ligações Cruzadas/química , Glutaral/análogos & derivados , Nucleosídeos/química , Nucleotídeos/química , Monofosfato de Adenosina/análogos & derivados , Géis/química , Glutaral/química , Uridina/análogos & derivados , Uridina Monofosfato/análogos & derivados
16.
Chem Commun (Camb) ; 52(7): 1397-400, 2016 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-26620770

RESUMO

An atom-economical methodology for the synthesis of sterically hindered tertiary amines was developed, which is based on complementary Rh- and Ru-catalyzed direct reductive amination of ketones with primary and secondary amines using carbon monoxide as a deoxygenating agent.


Assuntos
Aminas/química , Aminação , Isomerismo , Oxirredução , Difração de Raios X
17.
J Am Chem Soc ; 137(31): 9792-5, 2015 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-26199996

RESUMO

Single-molecule magnets (SMMs) with one transition-metal ion often rely on unusual geometry as a source of magnetically anisotropic ground state. Here we report a cobalt(II) cage complex with a trigonal prism geometry showing single ion magnet behavior with very high Orbach relaxation barrier of 152 cm(-1). This, to our knowledge, is the largest reported relaxation barrier for a cobalt-based mononuclear SMM. The trigonal prismatic coordination provided by the macrocyclic ligand gives intrinsically more stable molecular species than previously reported SMMs, thus making this type of cage complexes more amendable to possible functionalization that will boost their magnetic anisotropy even further.

18.
Inorg Chem ; 54(12): 5827-38, 2015 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-26017024

RESUMO

Template condensation of dichloroglyoxime with n-hexadecylboronic acid on the corresponding metal ion as a matrix under vigorous reaction conditions afforded n-hexadecylboron-capped iron and cobalt(II) hexachloroclathrochelates. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-vis, (1)H and (13)C{(1)H} NMR, (57)Fe Mössbauer spectroscopies, SQUID magnetometry, electron paramagnetic resonance, and cyclic voltammetry (CV) and by X-ray crystallography. The multitemperature single-crystal X-ray diffraction, SQUID magnetometry, and differential scanning calorimetry experiments were performed to study the temperature-induced spin-crossover [for the paramagnetic cobalt(II) complex] and the crystal-to-crystal phase transitions (for both of these clathrochelates) in the solid state. Analysis of their crystal packing using the molecular Voronoi polyhedra and the Hirshfeld surfaces reveals the structural rearrangements of the apical long-chain alkyl substituents resulting from such phase transitions being more pronounced for a macrobicyclic cobalt(II) complex. Its fine-crystalline sample undergoes the gradual and fully reversible spin transition centered at approximately 225 K. The density functional theory calculated parameters for an isolated molecule of this cobalt(II) hexachloroclathrochelate in its low- and high-spin states were found to be in excellent agreement with the experimental data and allowed to localize the spin density within a macrobicyclic framework. CV of the cobalt(II) complex in the cathodic range contains one reversible wave assigned to the Co(2+/+) redox couple with the reduced anionic cobalt(I)-containing species stabilized by the electronic effect of six strong electron-withdrawing chlorine substituents. The quasireversible character of the Fe(2+/+) wave suggests that the anionic iron(I)-containing macrobicyclic species undergo substantial structural changes and side chemical reactions after such metal-centered reduction.

19.
Chemistry ; 21(13): 4923-5, 2015 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-25688543

RESUMO

Melittin is a membrane-active peptide from bee venom with promising antimicrobial and anticancer activity. Herein we report on a simple and selective method for labeling of the tryptophan residue in melittin by the organometallic fragment [(C5 H5 )Ru](+) in aqueous solution and in air. Ruthenium coordination does not disturb the secondary structure of the peptide (as verified by 2D NMR spectroscopy), but changes the pattern of its intermolecular interactions resulting in an 11-fold decrease of hemolytic activity. The high stability of the organometallic conjugate allowed the establishment of the biodistribution of the labeled melittin in mice by inductively coupled plasma MS analysis of ruthenium.


Assuntos
Venenos de Abelha/química , Meliteno/química , Rutênio/química , Triptofano/química , Sequência de Aminoácidos , Animais , Camundongos , Dados de Sequência Molecular , Estrutura Molecular , Peptídeos
20.
Dalton Trans ; 44(8): 3773-84, 2015 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-25607531

RESUMO

Pentafluorophenylboron-capped iron and cobalt(II) hexachloroclathrochelate precursors were obtained by the one-pot template condensation of dichloroglyoxime with pentafluorophenylboronic acid on iron and cobalt(II) ions under vigorous reaction conditions in trifluoroacetic acid media. These reactive precursors easily undergo nucleophilic substitution with (per)fluoroarylthiolate anions, giving (per)fluoroarylsulfide macrobicyclic complexes with encapsulated iron and cobalt(II) ions; nucleophilic substitution of the cobalt(II) hexachloroclathrochelate precursor with a pentafluorophenylsulfide anion gave the target hexasulfide monoclathrochelate and the mixed-valence Co(III)Co(II)Co(III) bis-clathrochelate as a side product. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV-Vis, (57)Fe Mössbauer (for the X-rayed iron complexes), (1)H, (11)B, (13)C and (19)F NMR spectroscopies and by X-ray diffraction; their redox and electrocatalytic behaviors were studied using cyclic voltammetry and gas chromatography. As can be seen from the single-crystal X-ray diffraction data, the second superhydrophobic shell of such caged metal ions is formed by fluorine atoms of both the apical and ribbed (per)fluoroaryl peripheral groups. The main bond distances and chelate N=C-C=N angles in their molecules are similar, but rotational elongation (contraction) along the molecular C3-pseudoaxes, accompanied by changes in the geometry of the corresponding MN6-coordination polyhedra from a trigonal prism to a trigonal antiprism, allowed encapsulating Fe(2+), Co(2+) and Co(3+) ions. The nature of an encapsulated metal ion and its oxidation state affect the M-N bond lengths, and, for cobalt(ii) clathrochelate with an electronic configuration d(7) the Jahn-Teller structural effect is observed as an alternation of the Co-N distances. Pentafluorophenylboron-capped hexachloroclathrochelate precursors, giving stable catalytically active metal(I)-containing intermediates due to the electron-withdrawing effect of their six ribbed chlorine substituents, were found to show moderate electrocatalytic activity in a 2H(+)/H2 hydrogen-forming reaction. In the case of their ribbed-functionalized sulfide derivatives, the strong electron-withdrawing (per)fluoroaryl groups do not stabilize the reduced electrocatalytically active metal(i)-containing species as their mesomeric effect is absent or substantially decreased by steric hindrances between them.

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