Synthesis and characterization of fac-[M(CO)3(P)(OO)] and cis-trans-[M(CO)2(P)2(OO)] complexes (M = Re, (99m)Tc) with acetylacetone and curcumin as OO donor bidentate ligands

The Homoleptic Curcumin-Copper Single Crystal (ML2): A Long Awaited Breakthrough in the Field of Curcumin Metal Complexes

The first single crystal structure of the homoleptic copper (II) ML2 complex (M=Cu (II), L = curcumin) was obtained and its structure was elucidated by X-ray diffraction showing a square planar geometry, also confirmed by EPR. The supramolecular arrangement is supported by C-H···O interactions and the solvent (MeOH) plays an important role in stabilizing the crystal packing Crystallinity was additionally assessed by XRD patterns. The log P value of the complex (2.3 ± 0.15) was determined showing the improvement in water solubility. The cytotoxic activity of the complex against six cancer cell lines substantially surpasses that of curcumin itself, and it is particularly selective against leukemia (K562) and human glioblastoma (U251) cell lines, with similar antioxidant activity to BHT. This constitutes the first crystal structure of pristine curcumin complexed with a metal ion.

Bio-Evaluation of 99mTc-Labeled Homodimeric Chalcone Derivative as Amyloid-β-Targeting Probe

Chalcone derivatives have been successfully utilized for a range of biological applications and can cross the blood–brain barrier easily. β-amyloid-specific bis-chalcone derivative, 6,9-bis(carboxymethyl)-14-(4-[(E)-3-(4-(dimethylamino)phenyl)acryloyl]phenoxy)-3-(2-[(2-(4-[(E)-3-(4-(dimethylamino)phenyl)acryloyl]phenoxy)ethyl)amino]-2-oxoethyl)-11-oxo-3,6,9,12-tetraazatetradecanoic acid, DT(Ch)₂, was analyzed using molecular modeling to explain the binding modes of the ligand with amyloid fibril and monomer followed by ^99mTc-complexation in 95% yield and 98.7% efficiency. High-binding specificity of the radiocomplex was established following in vitro evaluation against 100-fold excess of DT(Ch)₂. ^99mTc–DT(Ch)₂ exhibited <3% trans-complexation in human serum after 24 h, indicating high stability. A fast clearance rate in pharmacokinetics studies displayed a biphasic pattern with t_1/2(F) = 30 min ± 0.09 and t_1/2(S) = 4 h 20 min ± 0.06. In vivo single-photon emission computed tomography (SPECT) imaging in rabbits reiterated the pharmacokinetics data with initially high brain uptake followed by rapid washout. Biodistribution studies confirmed the initial brain uptake as 1.16 ± 0.02% ID/g after 2 min and the brain_2min/brain_30min ratio was 3.74. Radioactivity distribution in the brain was >40% in the cingulate cortex followed by >25% in the hippocampus, a distribution pattern aligned to Alzheimer’s affected brain regions. Radiocomplex also displayed rapid plasma clearance followed by hepatobolic and renal modes of excretion.

Synthesis of Novel Pyrazolo[3,4-b]pyridines with Affinity for β-Amyloid Plaques

Three novel pyrazolo[3,4-b]pyridines were synthesized via the cyclization of 5-amino-1-phenylpyrazole with the corresponding unsaturated ketone in the catalytic presence of ZrCl4. The ketones were afforded by modifying a stabilized ylide facilitated Wittig reaction in fairly high yields. The novel compounds exhibited exciting photophysical properties with the dimethylamine phenyl-bearing pyrazolopyridine showing exceptionally large Stoke’s shifts. Finally, both the dimethylamino- and the pyrene-substituted compounds demonstrated high and selective binding to amyloid plaques of Alzheimer’s disease (AD) patient brain slices upon fluorescent confocal microscopy observation. These results reveal the potential application of pyrazolo[3,4-b]pyridines in the development of AD amyloid plaque probes of various modalities for AD diagnosis.

Effective Labeling of Amine Pharmacophores through the Employment of 2,3-Pyrazinedicarboxylic Anhydride and the Generation of fac-[M(CO)3(PyA)P] and cis-trans-[M(CO)2(PyA)P2] Complexes (PyA = Pyrazine-2-carboxylate, P = Phosphine, M = Re, 99mTc)

The fac-[M(CO)₃(PyA)(P)] and cis-trans-[M(CO)₂(PyA)(P)₂] neutral complexes (M is Re or ^99mTc), based on the mixed ligand strategy with pyrazine-2-carboxylic acid (PyAH) as the bidentate N,O and triphenylphosphine as the monodentate P ligand, are presented. Through the employment of the anhydride of pyrazine-2,3-dicarboxylic acid (PyDA), the PyAH scaffold was conveniently derivatized with the model bioactive amine 1-(2-methoxyphenyl)piperazine, the active part of the 5-HT_1A antagonist WAY100635. Reaction of either PyAH or the pharmacophore-bearing PyAH ligand (L¹H) with fac-[M(CO)₃]⁺ core in water yielded the intermediate fac-[M(CO)₃(PyA)(H₂O)] complexes. The labile aqua ligand was easily replaced by PPh₃ to yield the fac-[Re(CO)₃(PyA)(PPh₃)] complexes, while in toluene under reflux, the cis-trans-[Re(CO)₂(PyA)(PPh₃)₂] complexes were obtained. The latter complexes were alternatively obtained from mer-[Re(CO)₃(PPh₃)₂Cl] by refluxing with the PyA ligand in toluene. The analogous ^99mTc complexes were synthesized quantitatively, showing excellent stability in competition studies. The methodology described herein represents a practical procedure for the effective integration of the fac-[M(CO)₃]⁺ core with amine-bearing biologically active compounds for diagnosis/therapy.

Naphthalene Exchange in [Re(η6 -napht)2 ]+ with Pharmaceuticals Leads to Highly Functionalized Sandwich Complexes [M(η6 -pharm)2 ]+ (M=Re/99m Tc)

Bis‐arene sandwich complexes are generally prepared by the Fischer‐Hafner reaction, which conditions are incompatible with most O‐ and N‐ functional groups. We report a new way for the synthesis of sandwich type complexes [Re(η⁶‐arene)₂]⁺ and [Re(η⁶‐arene)(η⁶‐benzene)]⁺ from [Re(η⁶‐napht)₂]⁺ and [Re(η⁶‐napht)(η⁶‐benzene)]⁺, with functionalized arenes and pharmaceuticals. N‐methylpyrrolidine (NMP) facilitates the substitution of naphthalene with the incoming arene. A series of fully characterized rhenium sandwich complexes with simple arenes, such as aniline, as well as with active compounds like lidocaine and melatonin are presented. With these rhenium compounds in hand, the radioactive sandwich complexes [^99mTc(η⁶‐pharm)₂]⁺ (pharm=pharmaceutical) can be unambiguously confirmed. The direct labelling of pharmaceuticals with ^99mTc through η⁶‐coordination to phenyl rings and the confirmation of the structures with the rhenium homologues opens a path into molecular theranostics.

Synthesis and evaluation of new mixed "2 + 1" Re, 99mTc and 186Re tricarbonyl dithiocarbamate complexes with different monodentate ligands

A series of "2 + 1" mixed ligand tricarbonyl complexes of the general formula fac-[Re/^99mTc/¹⁸⁶Re(CO)₃(DDTC)(L)] containing diethyldithiocarbamate (DDTC) as a monoanionic bidentate ligand and a series of monodentate ligands L was synthesized, characterized and evaluated. The impact of ligand L on the radiochemical yield (RCY) and biodistribution of the final compounds was also investigated. DDTC and the appropriate L ligand [cyclohexyl isocyanide (cisc), tert-butyl isocyanide (tbi), triphenylphosphine (PPh₃), methyldiphenylphosphine (PPh₂Me), triphenylarsine (AsPh₃), imidazole (im), and 4-aminopyridine (4AP)] readily reacted in equimolar amounts with the [Et₄N]₂[Re(CO)₃Br₃] precursor to afford fac-[Re(CO)₃(DDTC)(cisc)], Re1, fac-[Re(CO)₃(DDTC)(tbi)], Re2, fac-[Re(CO)₃(DDTC)(PPh₃)], Re3, fac-[Re(CO)₃(DDTC)(PPh₂Me)], Re4, fac-[Re(CO)₃(DDTC)(AsPh₃)], Re5, fac-[Re(CO)₃(DDTC)(im)], Re6 and fac-[Re(CO)₃(DDTC)(4AP)], Re7, complexes in high yields (>80%). All Re complexes were fully characterized by IR, NMR, and in addition Re4, Re5, and Re7 with X-ray crystallography. Analogous reactions as performed with Re were subsequently explored on the ^99mTc and ¹⁸⁶Re-tracer levels using the corresponding fac-[^99mTc/¹⁸⁶Re(CO)₃(H₂O)₃]⁺ precursor. Complexes ^99mTc1 - ^99mTc5, ¹⁸⁶Re1 and ¹⁸⁶Re3 were obtained in high radiochemical yield (>91%), while the complexes ^99mTc6, ^99mTc7 and ¹⁸⁶Re7 formed with radiochemical yields of 55%, 28%, and 75%, respectively. The ^99mTc and ¹⁸⁶Re-complexes were characterized by comparative HPLC analysis using the analogous Re complexes. During histidine and cysteine challenge experiments at 37 °C through 6 h, complexes ^99mTc1 - ^99mTc5 remained > 92% stable, while complexes ^99mTc6 and ^99mTc7 remained only 8% stable through 3 h. Similar studies for ¹⁸⁶Re-complexes showed that ¹⁸⁶Re1 and ¹⁸⁶Re3 remained > 95% stable for up to 48 h, while ¹⁸⁶Re7 had decreased to 7% after 3 h. LogD_7.4 data of ^99mTc1 - ^99mTc5, ¹⁸⁶Re1, and ¹⁸⁶Re3 complexes, which ranged from 2.59 to 3.39, suggested high lipophilicity. Biodistribution studies in healthy Swiss albino mice showed hepatobiliary excretion for ^99mTc1, ^99mTc2, and ^99mTc4, fast blood clearance for ^99mTc4, while high liver uptake and retention for ^99mTc3 and ^99mTc5 were measured. Moreover, ^99mTc2 showed high accumulation in the lungs with sustained retention (52.80% ID/g at 4 h p.i.) and significant brain uptake at 2 min p.i. (1.89% ID/g). The study showed the great influence of monodentate ligand in the synthesis and biodistribution of the mixed ligand complexes.

Applications of Radiolabelled Curcumin and Its Derivatives in Medicinal Chemistry

Curcumin is a natural occurring molecule that has aroused much interest among researchers over the years due to its pleiotropic set of biological properties. In the nuclear medicine field, radiolabelled curcumin and curcumin derivatives have been studied as potential radiotracers for the early diagnosis of Alzheimer’s disease and cancer. In the present review, the synthetic pathways, labelling methods and the preclinical investigations involving these radioactive compounds are treated. The studies entailed chemical modifications for enhancing curcumin stability, as well as its functionalisation for the labelling with several radiohalogens or metal radionuclides (fluorine-18, technetium-99m, gallium-68, etc.). Although some drawbacks have yet to be addressed, and none of the radiolabelled curcuminoids have so far achieved clinical application, the studies performed hitherto provide useful insights and lay the foundation for further developments.

Ruthenium(II) 1,4,7-trithiacyclononane complexes of curcumin and bisdemethoxycurcumin: Synthesis, characterization, and biological activity

Two cationic ruthenium(II) 1,4,7-trithiacyclononane ([9]aneS₃) complexes of curcumin (curcH) and bisdemethoxycurcumin (bdcurcH), namely [Ru(curc)(dmso-S)([9]aneS₃)]Cl (1) and [Ru(bdcurc)(dmso-S)([9]aneS₃)]Cl (2) were prepared from the [RuCl₂(dmso-S)([9]-aneS₃)] precursor and structurally characterized, both in solution and in the solid state by X-ray crystallography. The corresponding PTA complexes [Ru(curc)(PTA)([9]aneS₃)]Cl (3) and [Ru(bdcurc)(PTA)([9]aneS₃)]Cl (4) have been also synthesized and characterized (PTA = 1,3,5-triaza-7-phosphaadamantane). Bioinorganic studies relying on mass spectrometry were performed on complexes 1-4 to assess their interactions with the model protein lysozyme. Overall, a rather limited reactivity with lysozyme was highlighted accompanied by a modest cytotoxic potency against three representative cancer cell lines. The moderate pharmacological activity is likely connected to the relatively high stability of these complexes.

Strategies for the Molecular Imaging of Amyloid and the Value of a Multimodal Approach

Protein aggregation has been widely implicated in neurodegenerative diseases such as Alzheimer's disease, frontotemporal dementia, Parkinson's disease, and Huntington disease, as well as in systemic amyloidoses and conditions associated with localized amyloid deposits, such as type-II diabetes. The pressing need for a better understanding of the factors governing protein assembly has driven research for the development of molecular sensors for amyloidogenic proteins. To date, a number of sensors have been developed that report on the presence of protein aggregates utilizing various modalities, and their utility demonstrated for imaging protein aggregation in vitro and in vivo. Analysis of these sensors highlights the various advantages and disadvantages of the different imaging modalities and makes clear that multimodal sensors with properties amenable to more than one imaging technique need to be developed. This critical review highlights the key molecular scaffolds reported for molecular imaging modalities such as fluorescence, positron emission tomography, single photon emission computed tomography, and magnetic resonance imaging and includes discussion of the advantages and disadvantages of each modality, and future directions for the design of amyloid sensors. We also discuss the recent efforts focused on the design and development of multimodal sensors and the value of cross-validation across multiple modalities.

Energy transfer mechanisms in pH-tuned aggregates of curcumin

Curcumin ((1,7-bis-(4-hidroxi-3-metoxifenil)-1,6-heptadieno-3,5-diona)), is a natural yellow-orange polyphenol dye, obtained from Curcuma longa rhizomes, with vast potential in the biotechnology field, such as anti - inflammatory and cancer preventive properties, and a very environmental-sensible structure, mostly resulting in aggregate formations, with low solubility in aqueous solvents and remarkable pH dependence. Hence, it is essential to comprehend its aggregation mechanisms, optical properties and conformational equilibrium to develop curcumin-based drugs and biomaterials for several applications. With the purpose of understand such concepts and its properties, the results presented in this work, obtained through spectroscopic measurements and the Hill's modeling, show a conformational equilibrium, driven by pH, between the enol-enolate and aggregated forms in curcumin, and the respective energy transfer processes between these species. Additionally, the photophysical mechanisms for the energy transfer between aggregated forms, observed with the ellipsometry measurements, showed an "all-or-nothing" character, pointing to a very complex conformation for curcumin aggregates.

Synthesis, characterization, kinetic investigation and biological evaluation of Re(i) di- and tricarbonyl complexes with tertiary phosphine ligands

Kinetics of Re(i) complexes illustrated the ability to ‘tune’ the metal centre; phosphine-based complexes were more stable and more cytotoxic.

Zn(II) Curcuminate Complexes with 2,2'-bipyridine and Carboxylates

Two novel zinc(II) compounds with curcuminate (abbreviated as cur-), [Zn(CH3COO)(cur)(bpy)](1)·CH3OH·2H2O (bpy = 2,2'-bipyridine) and [Zn(PhCOO)(cur)(bpy)] (2)·CH3OH, have been synthesized and characterized. Their composition has been determined by single-crystal X-ray structure analysis. Complexes 1 and 2 are similar: in both a five-fold coordination environment of zinc(II) consists of a monodentate carboxylate, a chelating bidentate 2,2'-bipyridine, and curcuminate, which is bound via a deprotonated 1,3-dione moiety. In 1, 2,2'-bipyridine nitrogen atoms and curcuminate oxygen atoms form the base of a square pyramid, whereas the acetate oxygen occupies its apex. The O3N2 donor set in 2 defines a polyhedron which more closely resembles a trigonal bipyramid. The packing in the crystal lattices of both compounds is governed by hydrogen-bonds. Complexes 1 and 2 display higher stability than curcumin in buffered media at pH = 7.0, however, the degradation of coordinated cur- is comparable to that of yellow pigment curcumin (curH) when the pH is raised to 7.2. Both complexes 1 and 2 in DMSO exhibit fluorescence with Stokes shifts of 5367 and 4634 cm-1, respectively.

Crystal structure of fac-aqua-[(E)-4-(benzo[d]thia-zol-2-yl)-N-(pyridin-2-yl-methyl-idene)aniline-κ2 N,N']tricarbonylrhenium(I) hexa-fluorido-phosphate methanol monosolvate

In the title compound, fac-[Re(C19H13N3S)(CO)3(H2O)]PF6·CH3OH, the coordination environment of the ReI atom is octa-hedral with a C3N2O coordination set. In this mol-ecule, the N,N' bidentate ligand, (E)-4-(benzo[d]thia-zol-2-yl)-N-(pyridin-2-yl-methyl-idene)aniline, and the monodentate aqua ligand occupy the three available coordination sites of the [Re(CO)3]+ core, generating a '2 + 1' mixed-ligand complex. In this complex, the Re-C bonds of the carbonyl ligands trans to the coordinating N,N' atoms of the bidentate ligand are longer than the Re-C bond of the carbonyl group trans to the aqua ligand, in accordance with the intensity of their trans effects. The complex is positively charged with PF6 - as the counter-ion. In the structure, the complexes form dimers through π-π inter-molecular inter-actions. O-H⋯O and O-H⋯N hydrogen bonds lead to the formation of stacks parallel to the a axis, which further extend into layers parallel to (01). Through O-H⋯F hydrogen bonds between the complexes and the PF6 -counter-anions, a three-dimensional network is established.

Complexes of Technetium(V) and Rhenium(V) with β-Diketonates

Reactions of (NBu₄)[MOCl₄] complexes (M = Tc or Re) with an excess of hexafluoroacetylacetone (Hhfac) give products with a composition of (NBu₄)[MOCl₃(hfac)] as bright yellow (Tc) or red (Re) solids. The products are stable as solids but rapidly decompose in solution. A number of related phenylimidorhenium(V) complexes were synthesized starting from [Re(NPhF)Cl₃(PPh₃)₂], where (NPhF)^2- is a para-fluorinated phenylimido ligand. Products with compositions of [Re(NPhF)Cl₂(PPh₃)(acac)], [Re(NPhF)Cl₂(PPh₃)(hfac)], [Re(NPhF)Cl₂(PPh₃)(tfac)], [Re(NPhF)Cl₂(PPh₃)(naphtfac)], and [Re(NPhF)Cl₂(PPh₃)(^tbutfac)] (Hacac = acetylacetone, Htfac = trifluoroacetylacetone, Hnaphtfac = naphthoyltrifluoroacetylmethane, and H^tbutfac = tert-butyroyltrifluoroacetylmethane) were isolated from reactions of the quite soluble [Re(NPhF)Cl₃(PPh₃)₂] with the corresponding β-diketones and studied spectroscopically and by X-ray diffraction. The β-diketonates are coordinated in a meridional arrangement with the phenylimide. The formation of two isomers was detected for nonsymmetric β-diketones with a preference for the "equatorial" position for the more bulky substituents. Products with more than one chelating ligand were not obtained. The technetium complexes [Tc(NPhX)Cl₃(PPh₃)₂] (X = p-F or p-CF₃) were prepared from reactions of pertechnetate, PPh₃, HCl, and substituted arylacetylhydrazines and isolated as green solids. They are sufficiently stable as solid but rapidly decompose in moist solvents upon hydrolysis of the Tc-N bonds. From reactions of [Tc(NPh)Cl₃(PPh₃)₂] or [Tc(NPhF)Cl₃(PPh₃)₂] in dry solvents, the complexes [Tc(NPh)Cl₂(PPh₃)(hfac)] and [Tc(NPhF)Cl₂(PPh₃)(hfac)] were prepared and isolated in crystalline form. An X-ray diffraction study shows that fluorination of the para position of the phenylimido ligand results in a slight lengthening of all bonds in the coordination sphere of technetium.

Dicarbonyl cis-[M(CO)2(N,O)(C)(P)] (M = Re, 99mTc) Complexes with a New [2 + 1 + 1] Donor Atom Combination

The synthesis and characterization of the dicarbonyl mixed ligand cis-[Re(CO)₂(quin)(cisc)(PPh₃)] complex, 4, where quin is the deprotonated quinaldic acid, cisc is cyclohexyl isocyanide, and PPh₃ is triphenylphosphine, is presented. The synthesis of 4 proceeds in three steps. In the first, the intermediate fac-[Re(CO)₃(quin)(H₂O)] aqua complex 2 is generated from the fac-[NEt₄]₂[Re(CO)₃Br₃] precursor, together with the brominated products fac-[Re(CO)₃(quinH)(Br)] 1a and fac-[NEt₄][Re(CO)₃(quin)(Br)] 1b, in low yield. In the following step, replacement of the aqua ligand of complex 2 by the monodentate isocyanide ligand leads to the formation of fac-[Re(CO)₃(quin)(cisc)], 3. In the third step replacement of the species trans to the isocyanide carbonyl group of 3 by a phosphine generates complex 4. The Re complexes 2-4 were prepared in high yield and fully characterized by elemental analysis, spectroscopic methods, and X-ray crystallography. At the technetium-99m (^99mTc) tracer level, the analogous complexes 3' and 4' were produced in high radiochemical purity, characterized by comparative reverse phase high-performance liquid chromatography and showed high resistance to transchelation by histidine or cysteine. This new [N,O][C][P] donor atom combination with the cis-[M(CO)₂]⁺ core (M = Re, ^99mTc) is a promising scaffold for the development of novel diagnostic and therapeutic targeted radiopharmaceuticals.

Crystal structure of fac-(acetylacetonato-κ2 O,O′)tricarbonyl(tri-m-tolyl phosphane-κP)rhenium(I), C29H28O5PRe

C29H28O5PRe, monoclinic, P21/n (no. 14), a = 10.548(5) Å, b = 22.996(5) Å, c = 11.022(5) Å, β = 98.011(5)°, V = 2647.4(18) Å3, Z = 4, R gt(F) = 0.0306, wRref (F2) = 0.0911, T = 100 K.

Crystal structure of fac-(acetylacetonato-κ2O,O′)tricarbonyl(tri(p-tolyl)phosphine-κP)rhenium(I), C29H28O5PRe

C29H28O5PRe, triclinic, P1̄ (no. 2), a = 12.733(7) Å, b = 18.668(11) Å, c = 24.779(15) Å, α = 101.442(20)°, β = 100.844(18)°, γ = 104.240(19)°, V = 5419(9) Å3, Z = 8, Rgt(F) = 0.0307, wRref(F2) = 0.0772, T = 100 K.

Crystal structure of fac-(acetylacetonato-κ2O,O′)tricarbonyl(benzyldiphenylphosphine-κP)rhenium(I), C27H24O5PRe

C27H24O5PRe, triclinic, P1̄ (no. 2), a = 9.0305(17) Å, b = 12.084(2) Å, c = 12.403(2) Å, α = 89.688(6)°, β = 70.083(6)°, γ = 76.315(6)°, V = 1232.2(4) Å3, Z = 2, Rgt(F) = 0.0180, wRref(F2) = 0.0432, T = 100(2) K.

Technetium-99m radiochemistry for pharmaceutical applications

Technetium-99m (^99m Tc) is a widely used radionuclide, and the development of ^99m Tc imaging agents continues to be in demand. This overview discusses basic principles of ^99m Tc radiopharmaceutical preparation and design and focuses on the ^99m Tc radiochemistry relevant to its pharmaceutical applications. The ^99m Tc complexes are described based on the most typical examples in each category, keeping up with the state-of-the-art in the field. In addition, the main current strategies to develop targeted ^99m Tc radiopharmaceuticals are summarized.

Synthesis of Oxorhenium(V) and Oxotechnetium(V) Complexes That Bind to Amyloid-β Plaques

Alzheimer's disease is characterized by the presence of amyloid plaques in the brain. The primary constituents of the plaques are aggregated forms of the amyloid-β (Aβ) peptide. With the goal of preparing technetium-99(m) complexes that bind to Aβ plaques with the potential to be diagnostic imaging agents for Alzheimer's disease, new tetradentate ligands capable of forming neutral and lipophilic complexes with oxotechentium(V) and oxorhenium(V) were prepared. Nonradioactive isotopes of technetium are not available so rhenium was used as a surrogate for exploratory chemistry. Two planar tetradentate N3O ligands were prepared that form charge-neutral complexes with oxorhenium(v) as well as a ligand featuring a styrylpyridyl functional group designed to bind to Aβ plaques. All three ligands formed complexes with oxorhenium(V), and each complex was characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The oxorhenium(V) complex with a styrylpyridyl functional group binds to Aβ plaques present in post-mortem human brain tissue. The chemistry was extrapolated to technetium-99(m) at the tracer level for two of the ligands. The resulting oxotechnetium(V) complexes were sufficiently lipophilic and charge-neutral to suggest that they have the potential to cross the blood-brain barrier but exhibited modest stability with respect to exchange with histidine. The chemistry presented here identifies a strategy to integrate styrylpyridyl functional groups into tetradentate ligands capable of forming complexes with [M═O](3+) cores (M = Re or Tc).

Crystal structure of tetraethylammonium fac-tricarbonyl(hexafluoroacetylacetonato-κ 2O,O′)-(nitrato-κO)rhenium(I), C16H21O8N2F6Re

C16H21O8N2F6Re, triclinic, P1̅, a = 9.161(5) Å, b = 10.283(5) Å, c = 12.974(5) Å, α = 87.739(5)°, β = 78.339(5)°, γ = 75.047(5)°, V = 1156.3(10) Å3, Z = 2, R gt (F) = 0.037, wR ref (F 2 ) = 0.1012, T = 100(2) K.

A gallium(III) Schiff base-curcumin complex that binds to amyloid-β plaques

Gallium-68 is a positron-emitting isotope that can be used in positron-emission tomography imaging agents. Alzheimer's disease is associated with the formation of plaques in the brain primarily comprised of aggregates of a 42 amino acid protein called amyloid-β. With the goal of synthesising charge neutral, low molecular weight, lipophilic gallium complexes with the potential to cross the blood-brain barrier and bind to Aβ plaques we have used an ancillary tetradentate N₂O₂ Schiff base ligand and the β-diketone curcumin as a bidentate ligand to give a six-coordinate Ga³⁺ complex. The tetradentate Schiff base ligand adopts the cis-β configuration with deprotonated curcumin acting as a bidentate ligand. The complex binds to amyloid-β plaques in human brain tissue and it is possible that extension of this chemistry to positron-emitting gallium-68 could provide useful imaging agents for Alzheimer's disease.

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.

Synthesis, characterization and biological evaluation of (99m)Tc/Re-tricarbonyl quinolone complexes

New rhenium(I) tricarbonyl complexes with the quinolone antimicrobial agents oxolinic acid (Hoxo) and enrofloxacin (Herx) and containing methanol, triphenylphosphine (PPh3) or imidazole (im) as unidentate co-ligands, were synthesized and characterized. The crystal structure of complex [Re(CO)3(oxo)(PPh3)]∙0.5MeOH was determined by X-ray crystallography. The deprotonated quinolone ligands are bound bidentately to rhenium(I) ion through the pyridone oxygen and a carboxylate oxygen. The binding of the rhenium complexes to calf-thymus DNA (CT DNA) was monitored by UV spectroscopy, viscosity measurements and competitive studies with ethidium bromide; intercalation was suggested as the most possible mode and the DNA-binding constants of the complexes were calculated. The rhenium complex [Re(CO)3(erx)(im)] was assayed for its topoisomerase IIα inhibition activity and was found to be active at 100μM concentration. The interaction of the rhenium complexes with human or bovine serum albumin was investigated by fluorescence emission spectroscopy (through the tryptophan quenching) and the corresponding binding constants were determined. The tracer complex [(99m)Tc(CO)3(erx)(im)] was synthesized and identified by comparative HPLC analysis with the rhenium analog. The (99m)Tc complex was found to be stable in solution. Upon injection in healthy mice, fast tissue clearance of the (99m)Tc complex was observed, while both renal and hepatobiliary excretion took place. Preliminary studies in human K-562 erythroleukemia cells showed cellular uptake of the (99m)Tc tracer with distribution primarily in the cytoplasm and the mitochondria and less in the nucleus. These preliminary results indicate that the quinolone (99m)Tc/Re complexes show promise to be further evaluated as imaging or therapeutic agents.

Metal complexes of curcumin--synthetic strategies, structures and medicinal applications

This Tutorial Review presents an overview on the synthesis, characterization and applications of metal complexes containing curcumin (=1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) and its derivatives as ligands. Innovative synthetic strategies leading to soluble and crystallizable metal curcumin complexes are outlined in detail. Special emphasis is placed on the highly promising and exciting medicinal applications of metal curcumin complexes, with the three most important areas being anticancer activity and selective cytotoxicity, anti-Alzheimer's disease activity, and antioxidative/neuroprotective effects. Overall, this Tutorial Review provides the first general overview of this emerging and rapidly expanding field of interdisciplinary research.

Metal complexes containing natural and and artificial radioactive elements and their applications

Recent advances (during the 2007–2014 period) in the coordination and organometallic chemistry of compounds containing natural and artificially prepared radionuclides (actinides and technetium), are reviewed. Radioactive isotopes of naturally stable elements are not included for discussion in this work. Actinide and technetium complexes with O-, N-, N,O, N,S-, P-containing ligands, as well π-organometallics are discussed from the view point of their synthesis, properties, and main applications. On the basis of their properties, several mono-, bi-, tri-, tetra- or polydentate ligands have been designed for specific recognition of some particular radionuclides, and can be used in the processes of nuclear waste remediation, i.e., recycling of nuclear fuel and the separation of actinides and fission products from waste solutions or for analytical determination of actinides in solutions; actinide metal complexes are also usefulas catalysts forcoupling gaseous carbon monoxide, as well as antimicrobial and anti-fungi agents due to their biological activity. Radioactive labeling based on the short-lived metastable nuclide technetium-99m (^99mTc) for biomedical use as heart, lung, kidney, bone, brain, liver or cancer imaging agents is also discussed. Finally, the promising applications of technetium labeling of nanomaterials, with potential applications as drug transport and delivery vehicles, radiotherapeutic agents or radiotracers for monitoring metabolic pathways, are also described.

Rhenium and technetium bi- and tricarbonyl complexes in a new strategy for biomolecule incorporation using click chemistry

A versatile strategy to prepare fac-[M(I)(CO)3](+) and cis-[M(I)(CO)2](+) (M = Re, (99m)Tc) complexes was developed using Huisgen click chemistry and monodentate phosphine ligands to readily incorporate biomolecules and tailor the chemical properties.

Metal complexes designed to bind to amyloid-β for the diagnosis and treatment of Alzheimer's disease

Alzheimer's disease is the most common form of age-related neurodegenerative dementia. The disease is characterised by the presence of plaques in the cerebral cortex. The major constituent of these plaques is aggregated amyloid-β peptide. This review focuses on the molecular aspects of metal complexes designed to bind to amyloid-β. The development of radioactive metal-based complexes of copper and technetium designed as diagnostic imaging agents to detect amyloid burden in the brain is discussed. Separate sections of the review discuss the use of luminescent metal complexes to act as non-conventional probes of amyloid formation and recent research into the use of metal complexes as inhibitors of amyloid formation and toxicity.