α-Diimine Cisplatin Derivatives: Synthesis, Structure, Cyclic Voltammetry and Cytotoxicity

Three new Pt(II) complexes [(dpp-DAD)PtCl₂] (I), [(Mes-DAD(Me)₂)PtCl₂] (II) and [(dpp-DAD(Me)₂)PtCl₂] (III) were synthesized by the direct reaction of [(CH₃CN)₂PtCl₂] and corresponding redox-active 1,4-diaza-1,3-butadienes (DAD). The compounds were isolated in a single crystal form and their molecular structures were determined by X-ray diffraction. The purity of the complexes and their stability in solution was confirmed by NMR analysis. The Pt(II) ions in all compounds are in a square planar environment. The electrochemical reduction of complexes I-III proceeds in two successive cathodic stages. The first quasi-reversible reduction leads to the relatively stable monoanionic complexes; the second cathodic stage is irreversible. The coordination of 1,4-diaza-1,3-butadienes ligands with PtCl₂ increases the reduction potential and the electron acceptor ability of the DAD ligands. The synthesized compounds were tested in relation to an adenocarcinoma of the ovary (SKOV3).

Sterically Hindered Tellurium(IV) Catecholate as a Lewis Acid

Sterically hindered tellurium catecholate Te(Cat³⁶)₂ (Cat³⁶ = 3,6-di-tert-butyl-catecholate) was synthesized with the reaction of amorphous Te with 3,6-di-tert-butyl-o-benzoquinone. Adducts of Te(Cat³⁶)₂ with various O- and N-donors were isolated and characterized by means of single-crystal X-ray diffraction along with IR, UV-vis, and NMR (¹H, ¹³C, and ¹²⁵Te) spectroscopies. In the crystal structure of the adduct with 2,2'-bipyridine (bipy), the unprecedented μ-κ²N,N':κ²N,N'-bridging coordination mode of bipy was observed. Various intermolecular interactions Te...O, Te...N, and Te...C in adducts were analyzed using density functional theory calculations and quantum theory of atoms in molecules analysis. The estimated strength for appropriate short contacts varies from 0.9 to 5.3 kcal/mol, and they are attractive and purely non-covalent.

Simultaneous 15 N polarization of several biocompatible substrates in ethanol-water mixtures by signal amplification by reversible exchange (SABRE) method

Signal amplification by reversible exchange (SABRE) is a popular method for generating strong signal enhancements in nuclear magnetic resonance (NMR). In SABRE experiments, the source of polarization is provided by the nonthermal spin order of parahydrogen (pH₂ , the H₂ molecule in its nuclear singlet spin state). Polarization formation requires that both pH₂ and a substrate molecule bind to an Ir-based complex where polarization transfer occurs. Subsequently, the complex dissociates and free polarized substrate molecules are formed. In this work, we present approaches towards biocompatible SABRE, meaning that several small biomolecules are simultaneously polarized by using the SABRE method in water-ethanol solutions at room temperature. We are able to demonstrate significant ¹⁵ N-NMR signal enhancements in water-ethanol solutions for biomolecules like nicotinamide, metronidazole, adenosine-5'-monophosphate, and 4-methylimidazole and found that the first three substrates are polarized at the same level as a well-known pyridine. We show that simultaneous polarization of several molecules is indeed feasible when the reactions are carried out at an ultralow field of about 400-500 nT. The achieved enhancements are between 100-fold and 15,000-fold. The resulting ¹⁵ N polarization (maximal value about 4% achieved for metronidazole and pyridine at 45°C) strongly depends on the sample temperature, pH₂ bubbling pressure, and pH₂ flow. One more parameter, which is important for optimizing the enhancement, is the solvent pH. Hence, this study presents a step in developing biocompatible SABRE polarization and gives a clue on how such SABRE experiments should be optimized to achieve the highest NMR signal enhancement.

Paramagnetic Rhenium Iodide Cluster with N-Heterocyclic Carbene

triangulo-Trirhenium nonaiodide Re₃I₉ reacts with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) to produce the novel 13-electron paramagnetic cluster Re₃I₈(IMes)₂, which was characterized by means of X-ray diffraction analysis, ESR spectroscopy, magnetometry, and quantum chemistry.

Tantalum(iv) pyrazolate: new wine in the old wineskin

Homoleptic binuclear Ta(iv) pyrazolate [Ta₂(pz)₈] with Ta–Ta distance of 3.1895(7) Å was obtained in a reaction of Ta(NMe₂)₅ with unsubstituted pyrazole Hpz.

A Sterically Hindered Derivative of 2,1,3-Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium-Nitrogen Radical Anion

Interaction of the tetradentate redox-active 6,6'-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H₄ L) with TeCl₄ leads to neutral diamagnetic compound TeL (1) in high yield. The molecule of 1 has a nearly planar TeN₂ O₂ fragment, which suggests the formulation of 1 as Te^II L^2- , in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp₂ ] leads to quantitative formation of the paramagnetic salt [CoCp₂ ]⁺ [1]^.- , which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp₂ ]⁺ [1]^.- at room temperature features a quintet due to splitting on two equivalent ¹⁴ N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the ¹²⁵ Te nucleus. Two-component relativistic DFT calculations perfectly reproduce the a(¹⁴ N) HFI constants and A_∥ (¹²⁵ Te) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in 1^.- is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1^.- can be regarded as the first example of a structurally characterised monomeric tellurium-nitrogen radical anion.

Di-tert-butylcatecholate derivatives of titanocene

Titanocene dichloride reacts with sodium 3,5-di-tert-butyl-catecholate to give the mixed-valence binuclear Ti(iii,iv) complex Cp₂Ti(μ-Cat³⁵)₂TiCp.

The first heterocubane cluster with a [W3GaS4] core

The paramagnetic cuboidal clusters [Mo₃(GaCl)(μ₃-S)₄(dppe)₃Cl₃] and [W₃(GaBr)_0.81(μ₃-S)₄(dppe)₃Br₃] were synthesized by treatment of the corresponding triangular clusters [M₃S₄(dppe)₃X₃]X with [Ga(η⁵-C₅Me₅)]₆.

Coherent evolution of singlet spin states in PHOTO-PHIP and M2S experiments

A consistent theoretical description of the spin dynamics underlying photo-PHIP (para-hydrogen induced polarization) experiments is given and validated experimentally: spectra from zero-quantum coherence (ZQC) "in-phase" and "out-of-phase" were obtained and evolution of ZQCs and the population of singlet spin state was tracked and modeled. Data from recent literature [O. Torres et al., J. Am. Chem. Soc., 2014] are reinterpreted. Advantages of using M2S sequences such as APSOC for detecting photo-PHIP are demonstrated. A sequence for 2D ZQ spectroscopy based on APSOC is proposed and the fundamental principles of ZQ spectroscopy are formulated. This investigation opens a new way to obtain information on the sign of J-couplings using ZQ spectroscopy. The proposed method is also useful to track the redistribution of the singlet spin population in various PHIP related experiments, which is essential for efficient polarization transfer to target nuclei.

Synthesis, molecular structures and EPR spectra of the paramagnetic cuboidal clusters with Mo3S4Ga cores

The paramagnetic cuboidal clusters [Mo₃(GaBr)(μ₃-S)₄(diphos)₃Br₃] (diphos = dppe, dmpe) were synthesized by the reduction of triangular clusters [Mo₃S₄(diphos)₃Br₃]Br with elemental Ga.

NHC adducts of tantalum amidohalides: the first example of NHC abnormally coordinated to an early transition metal

The first abnormally coordinated NHC complex of an early transition metal, [(aIMes)TaCl₂(NMe₂)₃], is prepared.

A Site-Specific Study of the Magnetic Field-Dependent Proton Spin Relaxation of an Iridium N-Heterocyclic Carbene Complex

We report a study of proton spin relaxation of an Iridium N-heterocyclic carbene complex [Ir(COD)(IMes)Cl] complex (where COD=1,5-cyclooctadiene, Imes=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene). This compound is a pre-catalyst of the most efficient complex allowing the signal amplification by reversible exchange (SABRE) effect, relevant for enhancing weak signals in nuclear magnetic resonance (NMR). An important feature of the study is a combination of relaxation measurements over a wide field range with high-resolution NMR detection. As a result, we are able to measure nuclear magnetic relaxation dispersion (NMRD) curves in the field range 0.1 mT–16.4 T (corresponding to the frequency range 4 kHz–700 MHz) for individual protons in the complex under study. This attractive possibility enables determination of the motional correlation times, τc , for the individual protons by analyzing the features in the NMRD curves (increase of the relaxation times) appearing at the magnetic fields where ωτc ≈1 (here ω is the proton Larmor precession frequency at a given field strength). The following correlation times were determined: (1.3±0.1) ns for the protons of imidazol-2-ylidene, (0.96±0.1) ns for the ortho-protons of two phenyl moieties and (0.95±0.2) ns for the protons of methyl groups. Additionally, we report low-field features coming from “strong coupling” of the protons. One should note that such features must not be misinterpreted by associating them with motional features. From the low-field features we obtain consistent estimates for the proton spin-spin interactions. The analysis of motional correlation times is also of importance for interpretation of spin order transfer from parahydrogen to various substrates in transient organometallic complexes (termed the SABRE effect) at high magnetic field.

Spin polarization transfer mechanisms of SABRE: A magnetic field dependent study

We have investigated the magnetic field dependence of Signal Amplification By Reversible Exchange (SABRE) arising from binding of para-hydrogen (p-H2) and a substrate to a suitable transition metal complex. The magnetic field dependence of the amplification of the (1)H Nuclear Magnetic Resonance (NMR) signals of the released substrates and dihydrogen, and the transient transition metal dihydride species shows characteristic patterns, which is explained using the theory presented here. The generation of SABRE is most efficient at low magnetic fields due to coherent spin mixing at nuclear spin Level Anti-Crossings (LACs) in the SABRE complexes. We studied two Ir-complexes and have shown that the presence of a (31)P atom in the SABRE complex doubles the number of LACs and, consequently, the number of peaks in the SABRE field dependence. Interestingly, the polarization of SABRE substrates is always accompanied by the para-to-ortho conversion in dihydride species that results in enhancement of the NMR signal of free (H2) and catalyst-bound H2 (Ir-HH). The field dependences of hyperpolarized H2 and Ir-HH by means of SABRE are studied here, for the first time, in detail. The field dependences depend on the chemical shifts and coupling constants of Ir-HH, in which the polarization transfer takes place. A negative coupling constant of -7Hz between the two chemically equivalent but magnetically inequivalent hydride nuclei is determined, which indicates that Ir-HH is a dihydride with an HH distance larger than 2Å. Finally, the field dependence of SABRE at high fields as found earlier has been investigated and attributed to polarization transfer to the substrate by cross-relaxation. The present study provides further evidence for the key role of LACs in the formation of SABRE-derived polarization. Understanding the spin dynamics behind the SABRE method opens the way to optimizing its performance and overcoming the main limitation of NMR, its notoriously low sensitivity.

Synthesis, molecular and electronic structure of an incomplete cuboidal Re3S4 cluster with an unusual quadruplet ground state

A Re(IV) cluster complex [Re(3)(μ(3)-S)(μ-S)(3)(dppe)(3)Br(3)](+) with nine cluster skeletal electrons (CSE) and a quadruplet ground state has been prepared by treatment of [Re(3)S(7)Br(6)]Br with 1,2-bis(diphenylphosphino)ethane (dppe) in MeCN.

Tris(tetra-butyl-ammonium) hexa-kis-(tert-butane-thiol-ato-κS)hepta-μ(3)-chlorido-μ(3)-sulfido-hexa-molybdate dihydrate

The octa­hedral cluster core of the anion in the structure of the title compound, (C₁₆H₃₆N)₃[Mo₆(C₄H₉S)₆(μ₃-Cl)₇(μ₃-S)]·2H₂O, has -3 site symmetry. Two μ₃-Cl atoms fully occupy positions in the cluster core, while the remaining six positions are statistically occupied by Cl and S atoms in a 1:5 ratio. The fully occupied Cl-atom positions are located on sites with 3 symmetry, and the N atom of tetra­butyl­ammonium cation is located on a site with 2 symmetry. The structure contains also two disordered solvent water mol­ecules, one of which is located on a threefold rotation axis and the other in a general position, both with an occupancy of 0.25. The water mol­ecules are localized in cavities formed by the tetra­butyl­ammonium cations and the tert-butane­thiol­ate groups. The metal clusters are stacked in a cubic close packing arrangement along [001].

Olivopontocerebellar atrophy in a large Iakut kinship in eastern Siberia

One-hundred cases of olivopontocerebellar atrophy, type 1, were found and studied in the Iakut population of Eastern Siberia. The disease followed a slowly progressive course of cerebellar insufficiency caused by degeneration in the cerebellar cortex, nuclei pontis, and inferior oliva. The disorder shows an autosomal dominant pattern of inheritance with a lower penetrance in females. The disease spread from a small region in the Aldan valley 200 to 300 years ago.

[Effect of the economic activity of man on natural foci of plague]

Under the effect of human economic activity in the natural plague foci there occurred changes in the structures of local biocenoses. The extent and the direction of these changes were determined by the character and the scale of the economic activity. The final outcome of ploughing up, irrigation and supply with water of the vast areas is elimination of the focus or of its autonomic areas, but excessive exploitation of the desert pastures not infrequently leads to the opposite result. Large industrial construction and building of means of communications decreased the territories of the natural foci of plague only slightly, although no significant action was produced by them on the structure of biocenoses and the state of the foci.

Estimate of the genome size by renaturation studies in Streptomyces

The genome sizes of Streptomyces coelicolor and Streptomyces rimosus as calculated by deoxyribonucleic acid reassociation kinetics are approximately 10.5 X 10(6) nucelotide pairs.