Time-series analysis of rhenium(I) organometallic covalent binding to a model protein for drug development

Metal-based complexes with their unique chemical properties, including multiple oxidation states, radio-nuclear capabilities and various coordination geometries yield value as potential pharmaceuticals. Understanding the interactions between metals and biological systems will prove key for site-specific coordination of new metal-based lead compounds. This study merges the concepts of target coordination with fragment-based drug methodologies, supported by varying the anomalous scattering of rhenium along with infrared spectroscopy, and has identified rhenium metal sites bound covalently with two amino acid types within the model protein. A time-based series of lysozyme-rhenium-imidazole (HEWL-Re-Imi) crystals was analysed systematically over a span of 38 weeks. The main rhenium covalent coordination is observed at His15, Asp101 and Asp119. Weak (i.e. noncovalent) interactions are observed at other aspartic, asparagine, proline, tyrosine and tryptophan side chains. Detailed bond distance comparisons, including precision estimates, are reported, utilizing the diffraction precision index supplemented with small-molecule data from the Cambridge Structural Database. Key findings include changes in the protein structure induced at the rhenium metal binding site, not observed in similar metal-free structures. The binding sites are typically found along the solvent-channel-accessible protein surface. The three primary covalent metal binding sites are consistent throughout the time series, whereas binding to neighbouring amino acid residues changes through the time series. Co-crystallization was used, consistently yielding crystals four days after setup. After crystal formation, soaking of the compound into the crystal over 38 weeks is continued and explains these structural adjustments. It is the covalent bond stability at the three sites, their proximity to the solvent channel and the movement of residues to accommodate the metal that are important, and may prove useful for future radiopharmaceutical development including target modification.

Shedding Light on the Enigmatic TcO2 ⋅ xH2 O Structure with Density Functional Theory and EXAFS Spectroscopy

The β-emitting ⁹⁹ Tc isotope is a high-yield fission product in ²³⁵ U and ²³⁹ Pu nuclear reactors, raising special concern in nuclear waste management due to its long half-life and the high mobility of pertechnetate (TcO₄ ^- ). Under the conditions of deep nuclear waste repositories, Tc is retained through biotic and abiotic reduction of TcO₄ ^- to compounds like amorphous TcO₂  ⋅ xH₂ O precipitates. It is generally accepted that these precipitates have linear (Tc(μ-O)₂ (H₂ O)₂ )_n chains, with trans H₂ O. Although corresponding Tc-Tc and Tc-O distances have been obtained from extended X-ray absorption fine structure (EXAFS) spectroscopy, this structure is largely based on analogy with other compounds. Here, we combine density-functional theory with EXAFS measurements of fresh and aged samples to show that, instead, TcO₂  ⋅ xH₂ O forms zigzag chains that undergo a slow aging process whereby they combine to form longer chains and, later, a tridimensional structure that might lead to a new TcO₂ polymorph.

Introduction of Re(CO)3+/99mTc(CO)3+ Organometallic Species into Vinylpyrrolidone-Allyliminodiacetate Copolymers

N-vinylpyrrolidone-co-allylamine copolymers (VP-co-AA) containing iminodiacetic (IDA) chelation units were prepared in the range of molecular masses of the copolymers from 9000 to 30,000 Da depending on polymerization conditions. Non-radioactive organometallic species Re(CO)₃⁺ were introduced into polymeric carriers under mild conditions; the prepared metal–polymeric complexes were characterized by IR, NMR, ESI-MS and HPLC. IR spectra data confirmed the coordination of M(CO)₃⁺ moiety to the polymeric backbone via IDA chelation unit (appearance of characteristic fac-M(CO)₃⁺ vibrations (2005, 1890 cm⁻¹), as well as the appearance of group of signals in ¹H NMR spectra, corresponding to those inequivalent to methylene protons CH₂COO (dd, 4.2 ppm), coordinated to metal ions. The optimal conditions for labeling the PVP-co-AA-IDA copolymers with radioactive ^99mTc(CO)₃⁺ species were determined. The radiochemical yields reached 97%. The obtained radiolabeled polymers were stable in blood serum for 3 h. In vivo distribution experiments in intact animals showed the high primary accumulation of technetium-99m MPC (MM = 15,000 Da) in blood with subsequent excretion via the urinary tract.

Crystal structure of fac-tricarbonyl-(nitrato-k1 O)-bis(pyridine-κN)-rhenium, C13H10O6N3Re

C13H10O6N3Re, monoclinic, P21/c (no. 14), a = 7.9325(9) Å, b = 13.811(2) Å, c = 13.458(2) Å, β = 92.637(4)°, V = 1472.83(4) Å3, Z = 4, R gt(F) = 0.0249, wR ref(F 2) = 0.0568, T = 100(2) K. CCDC no.: 2024932

Rhenium(V)-oxo complexes [ReOX2(N∩O)(EPh3)] (X=Cl, Br, I; E=P, As) – synthesis, structure, spectroscopy, and catalytic properties

The present review aims to give a comprehensive survey about the chemistry of rhenium(V)-oxo complexes of general formula [ReOX2(N∩O)(EPh3)], where X=Cl, Br, I, E=P, As, and N∩O stands for uninegative chelating N∩O-ligand, carried out within the last four decades. In addition to the synthesis aspects, the available structural data as well as the results issued from techniques such as infrared and ultraviolet-visible spectroscopies are collected and discussed. Furthermore, a brief description of the applications of these compounds in catalysis is included.

The bio-relevant metals of the periodic table of the elements

The bio-relevant metals (and derived compounds) of the Periodic Table of the Elements (PTE) are in the focus. The bulk elements sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) from the s-block, which are essential for all kingdoms of life, and some of their bio-activities are discussed. The trace elements of the d-block of the PTE as far as they are essential for humans (Mn, Fe, Co, Cu, Zn, Mo) are emphasized, but V, Ni, Cd, and W, which are essential only for some forms of life, are also considered. Chromium is no longer classified as being essential. From the p-block metals only the metalloid (half-metal) selenium (Se) is essential for all forms of life. Two other metalloids, silicon and arsenic, are briefly mentioned, but they have not been proven as being essential for humans. All metals of the PTE and a plethora of their compounds are used in industry and many of them are highly toxic, like lead (Pb), which is discussed as a prime example. Several metals of the PTE, that is, their ions and complexes, are employed in medicine and we discuss the role of lithium, gallium, strontium, technetium, silver, gadolinium (the only f-block element), platinum, and gold.

Influence of the chelator structures on the stability of Re and Tc tricarbonyl complexes with iminodiacetic acid tridentate ligands: a computational study

The development of novel radiopharmaceuticals for nuclear medicine based on M(CO)3 (M = Tc, Re) complexes has attracted great attention. The versatility of this core and the easy production of the fac-[M(CO)3(H2O)3](+) precursor could explain this interest. The main characteristics of these tricarbonyl complexes are the high substitution stability of the three CO ligands and the corresponding lability of the coordinated water molecules, yielding, via easy exchange of a variety of bi- and tridentate ligands, complexes xof very high kinetic stability. Here, a computational study of different tricarbonyl complexes of Re(I) and Tc(I) was performed using density functional theory. The solvent effect was simulated using the polarizable continuum model. These structures were used as a starting point to investigate the relative stabilities of tricarbonyl complexes with various tridentate ligands. These complexes included an iminodiacetic acid unit for tridentate coordination to the fac-[M(CO)3](+) moiety (M = Re, Tc), an aromatic ring system bearing a functional group (-NO2, -NH2, and -Cl) as a linking site model, and a tethering moiety (a methylene, ethylene, propylene butylene, or pentylene bridge) between the linking and coordinating sites. The optimized complexes showed geometries comparable to those inferred from X-ray data. In general, the Re complexes were more stable than the corresponding Tc complexes. Furthermore, using NH2 as the functional group, a medium length carbon chain, and ortho substitution increased complex stability. All of the bonds involving the metal center presented a closed shell interaction with dative or covalent character, and the strength of these bonds decreased in the sequence Tc-CO > Tc-O > Tc-N.

Crystal structure of fac-tricarbon-yl(quinoline-2-carboxyl-ato-κ(2) N,O)(tri-phenyl-arsane-κAs)rhenium(I)

In the title compound, [Re(C10H6NO2)(CO)3{As(C6H5)3}], the coordination environment of Re(I) is that of a distorted octa-hedron. Three coordination sites are occupied by three carbonyl groups in a facial arrangement and the remaining three sites by tri-phenyl-arsane and deprotonated quinaldic acid in As-mono- and N,O-bidentate fashions, respectively. In the crystal, the complexes are linked through weak C-H⋯O hydrogen bonds, forming a three-dimensional network. It worth noting that, as far as we know, this complex is the first Re(I) tri-phenyl-arsane tricarbonyl compound to be reported.

Quantum chemistry calculations of technetium and rhenium compounds with application in radiopharmacy: review

Quantum chemistry calculations are a powerful tool in the development of new ^99mTc and ^186/188Re radiopharmaceuticals.

SPECT/CT imaging of radiolabeled cubosomes and hexosomes for potential theranostic applications

We have developed a highly efficient method for the radiolabeling of phytantriol (PHYT)/oleic acid (OA)-based hexosomes based on the surface chelation of technetium-99m ((99m)Tc) to preformed hexosomes using the polyamine 1, 12-diamino-3, 6, 9-triazododecane (SpmTrien) as chelating agent. We also report on the unsuccessful labeling of cubosomes using the well-known chelating agent hexamethylpropyleneamine oxime (HMPAO). The (99m)Tc-labeled SpmTrien-hexosomes ((99m)Tc-SpmTrien-hexosomes) were synthesized with good radiolabeling (84%) and high radiochemical purity (>90%). The effect of radiolabeling on the internal nanostructure and the overall size of these aqueous dispersions was investigated by using synchrotron small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and transmission electron cryo microscopy (cryo-TEM). Further, we show the utility of (99m)Tc-SpmTrien-hexosomes for the in vivo imaging of healthy mice using single photon emission computed tomography (SPECT) in combination with computed tomography (CT), i.e. SPECT/CT. SPECT/CT experiments of subcutaneously administered (99m)Tc-SpmTrien-hexosomes to the flank of mice showed a high stability in vivo allowing imaging of the distribution of the radiolabeled hexosomes for up to 24 h. These injected (99m)Tc-SpmTrien-hexosomes formed a deposit within the subcutaneous adipose tissue, displaying a high biodistribution of ≈ 343% injected dose/g tissue (%ID/g), with negligible uptake in other organs and tissues. The developed (99m)Tc labeling method for PHYT/OA-based hexosomes could further serve as a useful tool for investigating and imaging the in vivo performance of cubosomal and hexosomal drug nanocarriers.