Molecular Properties of Branched Aliphatic α-Amino Acids in Water.

Four branched-chain aliphatic α-amino acids─α-alanine, valine, leucine, and isoleucine (-)─were investigated by quantum-chemical calculations in water as a solvent by two methods. The B3LYP variant of DFT calculations was used to obtain the electronic structure and molecular descriptors of these species in their canonical amino acid form as well as the related zwitterionic form in three oxidation states (cation, neutral molecule, and anion). A total of 24 species were subjected to full geometry optimization and complete vibration analysis.

Molecular Properties of Monoaminergic Catecholamines in Water.

Three neurotransmitters belonging to catecholamines (dopamine, noradrenaline, adrenaline) and related α-amino acids (DOPA and tyrosine) were studied by quantum-chemical and DFT calculations using B3LYP and DLPNO-CCSD(T) methods in water. In addition to the three canonical forms, zwitterionic forms were also investigated, each in three oxidation states (molecular cation L, electroneutral molecule L, and molecular anion L). Each species was subjected to geometry optimization followed by vibrational analysis.

A mononuclear Fe(III) complex showing thermally induced spin crossover and slow magnetic relaxation with reciprocating thermal behaviour.

AC susceptibility measurements of [Fe(L)(NCSe)] reveal a field supported slow magnetic relaxation. On cooling, the relaxation time of the high-frequency fraction decreases which is a sign of reciprocating thermal behaviour. The relaxation time for the low-frequency mode at = 2.

A heptanuclear {DyCu} complex as a single-molecule magnet.

The structure and magnetic properties of a complex containing a {DyCu} core are presented. In 1, the Dy(III) are 9- and the Cu(II) are 4-, 5- and 6-coordinated. Antiferromagnetic interactions cause an irregular energy spectrum with the ground state = 25/2.

Molecular properties of linear amino acids in water.

Four linear amino acids of increased separation of the carboxyl and amino groups, namely glycine (aminoacetic acid), β-alanine (3-aminopropanoic acid), GABA (4-aminobutanoic acid) and DAVA (5-aminopentanoic acid), have been studied by quantum chemical ab initio and DFT methods including the solvent effect in order to get electronic structure and molecular descriptors, such as ionisation energy, electron affinity, molecular electronegativity, chemical hardness, electrophilicity index, dipole moment, quadrupole moment and dipole polarizability. Thermodynamic functions (zero-point energy, inner energy, enthalpy, entropy, and the Gibbs energy) were evaluated after the complete vibrational analysis at the true energy minimum provided by the full geometry optimization. Reaction Gibbs energy allows evaluating the absolute redox potentials on reduction and/or oxidation.

Large Magnetic Anisotropy in Mono- and Binuclear cobalt(II) Complexes: The Role of the Distortion of the Coordination Sphere in Validity of the Spin-Hamiltonian Formalism.

To get a better insight into understanding the factors affecting the enhancement of the magnetic anisotropy in single molecule (single ion) magnets, two cobalt(II) complexes based on a tridentate ligand 2,6-di(thiazol-2-yl)pyridine substituted at the 4-position with -methyl-pyrrol-2-yl have been synthesized and studied by X-ray crystallography, AC and DC magnetic data, FIRMS and HFEPR spectra, and theoretical calculations. The change of the counteranion in starting Co(II) salts results in the formation of pentacoordinated mononuclear [Co(mpyr-dtpy)Cl]·2MeCN () complex and binuclear [Co(mpyr-dtpy)][Co(NCS)] () compound. The observed marked distortion of trigonal bipyramid geometry in and cationic octahedral and anionic tetrahedral units in brings up a question about the validity of the spin-Hamiltonian formalism and the possibility of determining the value and sign of the zero-field splitting parameter.

Magnetic properties of a europium(III) complex - possible multiplet crossover.

A dinuclear complex [(HO)Zn(LH)Eu(NO)] containing a hexadentate Schiff-base {NO}-donor ligand LH was prepared and characterized by X-ray structural analysis and IR, electronic and fluorescence spectroscopy. DC magnetic data show that upon heating the diamagnetic complex with the ground state Eu(III)-F and Zn(II)-S switches to paramagnetic species due to the population of F ( = 1 to 6) magnetic multiplets. The magnetic susceptibility increases from zero, passes through a maximum, and then decreases upon heating.

Electronic structure and molecular properties of nitisinone and mesotrione in water.

Context: Nitisinone is a medium-sized organic molecule that is used in treating hereditary tyrosinemia type 1 (HT-1). The structurally analogous mesotrione, however, is used as a pesticide/herbicide. What molecular properties are responsible for the similarity/dissimilarity of these molecules is investigated here.

Effect of Solvation on Glycine Molecules: A Theoretical Study.

o calculations of HF+MP2 and DFT-B3LYP quality have been used in calculating the molecular geometries and properties of neutral and charged molecules of glycine in amino acid as well as zwitterionic forms. A traditional set of molecular descriptors has been enriched by the molecular chemical potential, expressed the Mulliken electronegativity, and Pearson's chemical hardness. In the global energy minimum, the complete vibrational analysis allowed evaluating the standard Gibbs energy and related thermodynamic quantities.

Limitations on the -Parameter in Ni(II) Complexes.

A number of hexacoordinate, pentacoordinate, and tetracoordinate Ni(II) complexes have been investigated by applying CASSCF + NEVPT2 + SOC calculations and Generalized Crystal Field Theory. The geometry of the coordination polyhedron covers , , , , , , and symmetry. The calculated spin-Hamiltonian parameters and were compared to the available experimental data.

Ab initio study of molecular properties of l-tyrosine.

Context: l-Tyrosine is a naturally occurring agent that acts as a precursor in biosynthesis of monoaminergic neurotransmitters in brain such as dopamine, adrenaline, noradrenaline, and hormones like thyroxine and triiodothyronine. While l-tyrosine in vacuo adopts the canonical aminoacid form with -NH and -COOH functional groups, from neutral solutions, is crystallizes in the zwitterionic form possessing -NH and -COO groups. As l-tyrosine is non-innocent agent with respect to redox processes, redox ability in water expressed by the absolute oxidation and reduction potentials is investigated.

Easy-axis magnetic anisotropy in tetragonally elongated cobalt(II) complexes beyond the spin-Hamiltonian formalism.

Two hexacoordinate Co(II) complexes [Co(hfac)(etpy)] (1) and [Co(hfac)(bzpyCl)] (2) were synthesized and spectrally and structurally characterized. The {CoON} chromophore adopts a geometry of the elongated tetragonal bipyramid with a small -rhombic component. This less common arrangement causes the magnetic data to need be analysed using the Griffith-Figgis model, instead of the commonly used spin-Hamiltonian with zero-field splitting parameters and .

Possible Violation of the Spin-Hamiltonian Concept in Interpreting the Zero-Field Splitting.

The majority of experimental data in electron spin resonance and molecular magnetism are interpreted in terms of the spin-Hamiltonian (SH) formalism. However, this is an approximate theory that requires a proper testing. In the older variant, the multielectron terms are used as a basis in which the -tensor components are evaluated by employing the second-order perturbation theory (PT) for nondegenerate states; here, the spin-orbit interaction expressed the spin-orbit splitting parameter λ serves for the perturbation.

Slow magnetic relaxation in two mononuclear Mn(II) complexes not governed by the over-barrier Orbach process.

Two hexacoordinate Mn(II) complexes containing a chelating residue of hexafluoroacetylacetone and (Cl-substituted) 4-benzylpyridine show DC magnetic functions typical for = 5/2 spin systems: ∼ 2, - small. The AC susceptibility confirms a field supported slow magnetic relaxation in which the over-barrier Orbach relaxation process does not play a role. Both systems possess two or three slow relaxation channels.

Quantified Quasi-symmetry in Metal Complexes.

Shapeness of the coordination polyhedra is quantified by a procedure that moves arbitrary Cartesian coordinates of the complex to the origin, rotates them, reorders them, and compares with the predefined model complex of exact symmetry by calculating the square Euclidian distance and/or -factor as agreement factors. The generalized crystal-field theory has been enriched by considering a non-perfect match of the characters of the irreducible representations borne by the eigenvectors representing the crystal-field terms with those assigned to a perfect symmetry. The agreement of quasi-symmetry with the perfect one is quantified by an array of square Euclidian distances and/or -factors.

-{Er } complex showing field supported slow magnetic relaxation.

The -{Er} complex [ErCl()(OH)(HO)]Cl·HO ( = 9.4; H() = -vanillin) (1) was generated by an method. The isolated Er(iii) complex 1 was characterized by elemental analysis and molecular spectroscopy.

Unusual slow magnetic relaxation in a mononuclear copper(II) complex.

A hexacoordinate Cu(II) complex with the {CuOO'N} donor set shows an intermolecular π-π stacking owing to which a 1D-chain structure is formed. The DC magnetic data at low temperature are consistent with the Curie law. The AC susceptibility shows a field supported slow magnetic relaxation that survives up to 7 K.

Ab initio study of the biogenic amino acids.

Ten amino acids have been subjected to the quantum chemical calculations using the ab initio MO-LCAO-SCF calculations. When the geometry optimization started form the X-ray structure confirming the zwitterionic form, the ab initio calculations in vacuo result in the amino acid (canonical) form with the hydrogen atom attached not to the amine but to the carboxylate group. At the optimum geometry, a number of properties were evaluated: dipole moment, dipole polarizability, molecular surface, molecular volume, HOMO, LUMO, ionization energy, and electron affinity using the ΔSCF approach and their values corrected for electron correlation by the 2nd order perturbation theory (MP2).

A Mixed Valence CoCo Field-Supported Single Molecule Magnet: Solvent-Dependent Structural Variation.

One-pot reaction of the Schiff base ,'-ethylene bis(salicylaldimine) (HL), CoCl.6HO, and [PhSnCl] in acetone produces the mixed valence CoCo compound [CoCo(μ-L)(Ph)(μ-Cl)]·(CH)CO·HO (). Our recent study already revealed that the same reaction mixtures in methanol or ethanol produced a heterometallic SnCo () or monometallic Co complex (), respectively.

Positive zero-field splitting and unexpected slow magnetic relaxation in the magneto-chemical calibrant HgCo(NCS).

DC magnetization data for HgCo(NCS)4 confirm positive value of the zero-field splitting D-parameter. High-frequency and -field EPR gave gz = 2.05, gx = 2.

Spin-crossover in an iron(III) complex showing a broad thermal hysteresis.

A pentadentate Schiff-base ligand 3,5Cl-L2- and NCSe- form an iron(iii) mononuclear complex, namely [Fe(3,5Cl-L)(NCSe)], which shows a thermally induced spin crossover with a broad hysteresis width of 24 K between 123 K (warming) and 99 K (cooling). Analogous complexes of the [Fe(3,5X-L)(Y)] type, where X = Cl or Br and Y = Cl-, N3-, NCS-, and NCSe-, are high-spin over the whole temperature interval.

Effect of the Distant Substituent to Slow Magnetic Relaxation of Pentacoordinate Fe(III) Complexes.

Pentacoordinate Fe(III) complexes [Fe(L)X] and [Fe(L)X], X = Cl and Br, show the slow magnetic relaxation that is enhanced by the applied static magnetic field. A substitution of the distant ethoxy group to the methoxy group residing at the phenyl ring of a Schiff base N,O-donor ligand (L vs L) considerably influences the relaxation characteristics. In the chlorido complex [Fe(L)Cl], the following three slow relaxation channels are recognized as possessing different relaxation times: τ = 0.

New members of the polynuclear manganese family: MnMn single-molecule magnets and MnMn antiferromagnetic complexes. Synthesis and magnetostructural correlations.

The synthesis, crystal structures and magnetic properties are reported for three novel mixed-valence tetranuclear [MnII2MnIII2(HBuDea)2(BuDea)2(EBA)4] (1), [MnII2MnIII2(HBuDea)2(BuDea)2(DMBA)4] (2) and undecanuclear [MnII3MnIII8O4(OH)2(BuDea)6(DMBA)8] (3) clusters, where H2BuDea is N-butyldiethanolamine, HEBA is 2-ethylbutyric acid and HDMBA is 2,2-dimethylbutyric acid. The compounds have been prepared through self-assembly reactions of manganese(ii) chloride with H2BuDea and respective carboxylic acid in methanol solution in air, affording 1 with HEBA, and 2 or 3 with HDMBA, depending on the experimental conditions. The single crystal X-ray analysis reveals that 1 and 2 have similar centrosymmetric structures based on the {M4(μ3-O)2(μ-O)4} core, while 3 discloses the unprecedented {M11(μ-O)4(μ3-O)12} one.

Effect of the distant substituent on the slow magnetic relaxation of the mononuclear Co(ii) complex with pincer-type ligands.

A hexacoordinated complex [Co(pydm)2](mdnbz)2 from the family of pincer complexes was prepared and structurally characterized. The complex behaves as an S = 3/2 spin system with a considerable zero-field splitting parameter D/hc ∼ +50 cm-1. The AC susceptibility measurements show a slow magnetic relaxation with three relaxation channels: at the low-frequency (LF), intermediate-frequency (IF) and high-frequency (HF) domains.

Slow magnetic relaxation in a high-spin pentacoordinate Fe(iii) complex.

A mononuclear pentacoordinate iron(iii) complex shows slow magnetic relaxation with three relaxation channels. The high-frequency relaxation time of the order of microseconds is prolonged on cooling in accordance with the direct and Raman processes. The low frequency relaxation time is little dependent on temperature and varies in the range τ(LF) = 0.