Electrocatalytic reduction of carbon dioxide by a polymeric film of rhenium tricarbonyl dipyridylamine

A dipyridylamine ligand with a pendant pyrrole (N-(3-N,N′-bis(2-pyridyl)propylamino)pyrrole, PPP) and its corresponding rhenium(I) complex, Re(CO)₃(κ²-N,N-PPP)Cl, were synthesized. The structure of Re(CO)₃(κ²-N,N-PPP)Cl was determined by X-ray crystallography. Electrochemical polymerization of the pyrrole moiety resulted in the immobilization of poly[Re(CO)₃(κ²-N,N-PPP)Cl] film onto a glassy carbon electrode, which exhibited electrocatalytic activity for the reduction of CO₂ to CO.     

Pyridyl derivatives provide new pathways for labeling protein with fac-[<Superscript>188</Superscript>Re(CO)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>]<Superscript>+</Superscript>

The purpose of this work was to indirect label IgG with fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺ and to check the radiochemical behavior of the labeled product. The compound of (bis(2-pyridylmethyl)-amino)-acetic acid (L²H) was synthesized and labeled with fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺. The labeling yield of ¹⁸⁸Re(CO)₃–L²H was more than 90%. The effects of protein concentration, reaction time, pH and reaction temperature of labeling of IgG with ¹⁸⁸Re(CO)₃–L²H were investigated. The conjugation conditions were optimized. The labeled product was analyzed by size exclusion HPLC and TLC. The stability of ¹⁸⁸Re(CO)₃–L²H–IgG in vitro was high. The results of this study may be useful for [¹⁸⁸Re(CO)₃(H₂O)₃]⁺ labeling of protein for radioimmunotherapy.     

An improved synthesis of S-benzoyl mercaptoacetyltriglycine as BFCA and the labeling of IgG with carrier-free 188Re

S-benzoyl mercaptoacetyltriglycine (S-Bz-MAG₃) was synthesized and labeled with carrier-free ¹⁸⁸Re. The overall yield of S-Bz-MAG₃ is higher than those published in the literature. Dependence of the labeling yield of ¹⁸⁸Re-MAG₃ upon concentration of reducing agent, pH, reaction time, and other parameters was examined and optimum conditions were obtained. The labeling yield of ¹⁸⁸Re-MAG₃ was more than 98%. The concentration procedure was succeeded with Sep-Pak C18 column to obtain highly concentrated ¹⁸⁸Re-MAG₃. The experimental conditions of labeling of IgG with carrier free ¹⁸⁸Re via S-Bz-MAG₃ as a bifunctional chelating agent (BFCA) by pre-radiolabeling of the chelate was studied. The conjugation conditions were optimized. The stability of ¹⁸⁸Re-MAG₃-IgG in vitro was high. The results of this studiy may be useful for ¹⁸⁸Re labeling of MAbs for radioimmunotherapy.     

Conductivity enhancement of PEDOT:PSS film via sulfonic acid modification: application as transparent electrode for ITO-free polymer solar cells

3-Hydroxy-1-propanesulfonic acid(HPSA)was applied as a modification layer on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)film via spin-coating,resulting in a massive boost of the conductivity of PEDOT:PSS film,and thus the as-formed PEDOT:PSS/HPSA bilayer film was successfully used as a transparent electrode for ITO-free polymer solar cells(PSCs).Under the optimized concentration of HPSA(0.2 mol L~(-1)),the PEDOT:PSS/HPSA bilayer film has a conductivity of 1020 S cm~(-1),which is improved by about 1400 times of the pristine PEDOT:PSS film(0.7 S cm~(-1)).The sheet resistance of the PEDOT:PSS/HPSA bilayer film was 98Ωsq~(-1),and its transparency in the visible range was over 80%.Both parameters are comparable to those of ITO,enabling its suitability as the transparent electrode.According to atomic force microscopy(AFM),UV-Vis and Raman spectroscopic measurements,the conductivity enhancement was resulted from the removal of PSS moiety by methanol solvent and HPSA-induced segregation of insulating PSS chains along with the conformation transition of the conductive PEDOT chains within PEDOT:PSS.Upon applying PEDOT:PSS/HPSA bilayer film as the transparent electrode substituting ITO,the ITO-free polymer solar cells(PSCs)based on poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]:[6,6]-phenyl C71-butyric acid methyl ester(PC_(71)BM)(PCDTBT:PC_(71)BM)active layer exhibited a power conversion efficiency(PCE)of 5.52%,which is comparable to that of the traditional ITO-based devices.     

Characterization and application of the fac-[188Re(CO)3(H2O)3]+ core

Summary Fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺ was synthesized with an overall radiochemical yield of 80±5%, and more than 95% radiochemical purity after a QMA Sep-Pak column separation. Fac-[Re(CO)₃(H₂O)₃]⁺ was also synthesized as a reference sample. The structure of the precursor, fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺, was confirmed by high performance of liquid chromatography (HPLC). MN-His (magnetic nanoparticles coated with silica and modified with an amino silane coupling agent, N-[3-(trimethyoxysilyl)propyl]-ethylenediamine (SG-Si900) and immobilized with histidine) was labeled with fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺ and an initial animal test of MN-His was conducted for a magnetic targeting study.     

New chloro- and trifluoroacetato tricarbonylrhenium(I) complexes with a N,N′-bis(benzophenone)-1,2-diiminoethane Schiff base ligand: Spectral and structural studies

The reaction of Re(CO)₅Cl with the chelating ligand N,N′-bis(benzophenone)-1,2-diiminoethane (bz₂en) afforded the neutral fac-[Re(CO)₃(bz₂en)Cl]. The subsequent reaction with AgOCOCF₃ gave fac-[Re(CO)₃(bz₂en)OCOCF₃]. Their pseudooctahedral fac structures have been established by FTIR, UV–Vis, ¹H, ¹³C NMR and have been confirmed by X-ray diffraction analysis. The electrochemical behaviour of the investigated complexes has been studied by cyclic voltammetry.     

The syntheses and coordination properties of M(CO)3X(DAB) (M = Mn,Re; X = Cl,Br, I; DAB = 1,4-diazabutadiene)

M(CO)₅X (M = Mn, Re; X = Cl, Br, I) reacts with DAB (1,4-diazabutadiene = R₁N=C(R₂)C(R₂)′=NR′₁) to give M(CO)₃X(DAB). The ¹H, ¹³C NMR and IR spectra indicate that the facial isomer is formed exclusively. A comparison of the ¹³C NMR spectra of M(CO)₃X(DAB) (M = Mn, Re; X = Cl, Br, I; DAB = glyoxalbis-t-butylimine, glyoxyalbisisopropylimine) and the related M(CO)₄DAB complexes (M = Cr, Mo, W) with Fe(CO)₃DAB complexes shows that the charge density on the ligands is comparable in both types of d⁶ metal complexes but is slightly different in the Fe-d⁸ complexes. The effect of the DAB substituents on the carbonyl stretching frequencies is in agreement with the A′(cis) > A″ (cis) > A′(trans) band ordering.Mn(CO)₃Cl(t-BuNCHCHNt-Bu) reacts with AgBF₄ under a CO atmosphere yielding [Mn(CO)₄(t-BuNCHCHN-t-Bu)]BF₄. The cationic complex is isoelectronic with M(CO)₄(t-BuNCHCHNt-Bu) (M = Cr, Mo, W).     

Chemistry of tricarbonylrhenium(I) chelates of azopyrimidines, azoimidazoles and anion radicals thereof

The azopyrimidine and azoimidazole ligands (general abbreviations, RL) used in the present work are 2-(p-R-C₆H₄NN)C₄H₃N₂, RL_pm (R=H, Cl) and 2-(p-R-C₆H₄NN)-1-(Me)C₃H₂N₂, RL_im (R=Me, Cl), respectively. The reaction of Re(CO)₅Cl with a slight excess of RL in boiling benzene has furnished blue-violet complexes of type Re(CO)₃Cl(RL) which have been spectrally characterized. In Re(CO)₃Cl(HL_pm) and Re(CO)₃Cl(ClL_im) the Re-N^h, Re-N^a distances are 2.173(6), 2.136(6) Å and 2.150(5), 2.166(5) Å, respectively (N^h and N^a are heterocyclic and azo N atoms, respectively). Their N-N lengths (1.271(8), 1.281(7) Å) implicate relatively weak Re-azo(π^*) back-bonding. In the lattice of Re(CO)₃Cl(HL_pm), pair-wise C-H?O hydrogen bonding between symmetry related molecules is present (C?O; 3.264(9) Å, H?O; 2.460(10) Å; C-H?O; 130.6(5)°). The lattice of Re(CO)₃Cl(ClL_im) also consists of centrosymmetric dimers held by aromatic π-π stacking between parallely placed pendant aryl rings (centroid?centroid distance, 3.781(9) Å). Extended Hückel calculations reveal that the LUMO of Re(CO)₃Cl(RL) is ∼60% azo in character. One-electron quasireversible electrochemical reduction occurs near −0.1 and −0.4 V vs. SCE in the cases of Re(CO)₃Cl(RL_pm) and Re(CO)₃Cl(RL_im), respectively. The redox orbital is believed to be to the above noted LUMO. Electrogenerated Re(CO)₃Cl(RL⁻) underwent spontaneous solvolytic chloride displacement in MeCN furnishing Re(CO)₃(MeCN)(RL⁻) which has been isolated. The latter in turn reacted with imidazole and triphenyl phosphine furnishing Re(CO)₃(C₃H₄N₂)(RL⁻) and Re(CO)₃(PPh₃)(RL⁻), respectively. The pattern of carbonyl stretching frequencies of these radical anion complexes is similar to that of Re(CO)₃Cl(RL) but for shifts to lower frequencies by 10-40 cm⁻¹. All the three radical anion systems are one-electron paramagnets (1.7-1.8 μ_B). The unpaired electron is primarily localized in a predominantly azo-π^* orbital. A small metal contribution (^{185, 187}Re, I=5/2) is present and both Re(CO)₃(MeCN)(RL⁻) and Re(CO)₃(C₃H₄N₂)(RL⁻) display six-line EPR spectra (A∼28 G). The line shapes and intensities are characteristic of the presence of g-strain. In the case of Re(CO)₃(PPh₃)(RL⁻) seven nearly equispaced lines are observed due to virtually equal coupling with metal and ³¹P (I=1/2) nuclei. The g values of the radical species span the range 2.0033-2.0066.     

Formulation of a freeze-dried kit for 188Re-MAG3 and its quality control

The synthesis of ¹⁸⁸Re-MAG₃ is described using ¹⁸⁸Re, which was obtained from the alumina based ¹⁸⁸W/¹⁸⁸Re generator. Dependence of the radiolabeling yields of ¹⁸⁸Re-MAG₃ on reducing agent concentration, Bz-MAG₃ concentration, pH, temperature and incubation time was examined. In the case of optimum conditions the yield of ¹⁸⁸Re-MAG₃ was 98%. TLC and HPLC techniques were employed to monitor the different species formed. Biodistribution study of ¹⁸⁸Re-MAG₃ was carried out in rats and compared with behavior of ^99mTc-MAG₃.     

Radiosynthesis and evaluation of 188Re-c(RGDyK)-His as a novel radiotherapeutic agent for integrin αvβ3 targeting tumour

The successes of noninvasive methods to visualize and quantify integrin α_vβ₃ expression in vivo have paved the way for radiolabeling anti-integrin therapy in clinic. Arginine-glycine-aspartice (RGD) peptide and related derivatives labeled with radionuclides for radio-therapy, which specifically targeting integrin α_vβ₃-positive tumors, could be used to treat these tumors. We have labeled c(RGDyK)-His, a RGD derivative, with ¹⁸⁸Re and the radio-therapy efficiency has been evaluated in model nude mice. c(RGDyK)-His was labeled with ¹⁸⁸Re by chelating with [¹⁸⁸Re(CO)₃(H₂O)₃]⁺ under a slightly basic condition. The in vitro specific binding affinity to U87 MG cell lines and the biodistribution of ¹⁸⁸Re-c(RGDyK)-His in the animal tumor models was measured. The inhibitory effects of ¹⁸⁸Re-c(RGDyK)-His were observed more than 1 month, and evaluated by microPET/CT imaging with ¹⁸F-FDG. Results of in vivo, cell uptake demonstrated ¹⁸⁸Re-c(RGDyK)-His had a high specific binding affinity to receptor integrin α_vβ₃. In biodistribution experiment, ¹⁸⁸Re-c(RGDyK)-His was accumulated in the tumor and cleared fast from the normal tissues. In radiotherapy study, tumor growth inhibition was significantly higher in the treatment groups than in the control groups. These studies showed that ¹⁸⁸Re-c(RGDyK)-His could be effectively used for integrin α_vβ₃ targeting therapy. This may offer a potential therapeutic strategy for the treatment of integrin-positive tumors in clinic.     

Λ-doublet populations in CH(A2Δ) produced in the 193 nm multiphoton dissociation of (CH3)2CO, (CD3)2CO, (CH3)2S and CH3NO2

Unequal intensities of the Λ-doublet components were observed in the CH(A²Δ-X²Π) emission following the multiphoton dissociation of (CH₃)₂CO, (CH₃)₂S and CH₃NO₂ by an ArF laser (193 nm). The power dependence of the emission intensity was estimated to be cubic (3.1±0.2) when the laser power was below ≈ 8×10¹⁷ photons cm^?2 pulse^?1. The Λ-doublet populations depended on the rotational quantum number N′ and the preferred level changed at N′ = 20. A similar behavior was observed for the CD(A²Δ) from (CD₃)₂CO. Rotational distributions show bimodal behavior, having a hump around N′ = 13 in CH(A²Δ) and N′ = 11 in CD(A²Δ). These trends indicate that the CH(A²Δ) is produced through multiple processes where stepwise mechanisms are operative via either CH₂ or CH₃, or both radicals as intermediates.     

Synthesis, in vitro and in vivo behavior of 188Re(I)-tricarbonyl complexes for the future functionalization of biomolecules

Radiolabeling of biologically active molecules with fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺ unit has been of primary interest in recent years. Therefore, we herein report ligands L¹−L⁴ (L¹=histidine, L²=nitrilotriacetic acid, L³=2-picolylamine-N,N-diacetic acid, L⁴=bis(2-pyridymethy)amine) that have been evaluated by radiochemical reactions with fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺. These reactions yielded the radioactive complexes of fac-[¹⁸⁸Re(CO)₃L] (L = L¹−L⁴, ¹⁸⁸Re tricarbonyl complexes 1–4), which were identified by HPLC. Complexes 1–4, with log P _o/w values ranging from −2.23 to 2.18, were obtained with yields of ≥95% using ligand concentrations within 10⁻⁶–10⁻⁴M range. Thus, specific activities of 220 GBq/μmol could be achieved. Challenge studies with cysteine and histidine revealed high stability for all of these radioactive complexes, and biodistribution studies in mice indicated a fast rate of blood clearance and high rate of total radioactivity excretion occurring primarily through the renal-urinary pathway. In summary, the ligands L¹–L⁴ are potent chelators for the future functionalization of biomolecules labeling with fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺.     

<Emphasis Type="Italic">N</Emphasis>-allyl and <Emphasis Type="Italic">N</Emphasis>-propargyl trifluoromethanesulfonimides. Theoretical analysis

Tautomers of N-allyl- and N-propargyl-substituted trifluoromethanesulfonimides (CF₃SO₂)₂NR (R = CH₂CH=CH₂, Z/E-CH=CHMe, CH₂C≡CH, CH=CH=CH₂, C≡CCH₂) were calculated by the DFT (B3LYP, wB97XD, PBE1PBE), MP2, and CBS-QB3 methods. The results were compared with the theoretical data for the corresponding amines and amides NHRR¹ (R¹ = H, CF₃SO₂). It was shown that there is no conjugation between the nitrogen atom and C=C bond and that conjugation exists with the C≡C bond with electron density displacement toward the nitrogen atom. The calculations of anions derived from N-allyl- and N-propargyl-trifluoromethanesulfonimides revealed the possibility of their rearrangement with elimination of trifluoromethanesulfinate anion and formation of its H-complex with N-(prop-2-en-1-ylidene)trifluoromethanesulfonamide or N-(prop-2-yn-1-ylidene)trifluoromethanesulfonamide.     

Synthesis and cell uptake of a novel dualmodality (188)Re-HGRGD (D) F-CdTe QDs probe

A novel dualmodality probe was prepared by linking ¹⁸⁸Re-HGRGD (D) F with CdTe QDs, which was monitored using radio-thin layer chromatography (TLC) and -high performance liquid chromatography (HPLC). The ¹⁸⁸Re-HGRGD (D) F-CdTe QDs probe possesses a radiochemistry yield of 92.1% and strong photoluminescence (PL) stability. However, the radiochemical purity of ¹⁸⁸Re-HGRGD (D) F-QDs would reduce to 74.8%, which should be further improved, after incubation with newborn calf serum (NCF) for 24 h. Human glioblastoma U87MG cells, known to express a high-affinity to RGD, were used to assess the in vitro cell binding of probe. The results showed that the radio-signal was in accord with the change of PL intensity, which meant the successful integration of ¹⁸⁸Re and QDs.     

Synthesis of pyridyl derivatives for the future functionalization of biomolecules labeled with the fac-[<Superscript>188</Superscript>Re(CO)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>]<Superscript>+</Superscript> precursor

In this paper, we investigated three ligand systems, symmetric and asymmetric pyridyl-containing tridentate ligands (L¹NH₂ = (bis(2-pyridylmethyl)-amino)-ethylamine, L²H = (bis(2-pyridylmethyl)-amino)-acetic acid, L³NH₂ = [(6-amino-hexyl)-pyridyl-2-methyl-amino]-acetic acid) as bifunctional chelating agents for labeling biomolecules. These ligands reacted with the precursor fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺ and yielded the radioactive complexes fac-[¹⁸⁸Re(CO)₃L] (L = three ligands), which were identified by RP-HPLC. The corresponding stable rhenium tricarbonyl complexes (1–3) were allowed for macroscopic identification of the radiochemical compounds. ¹⁸⁸Re tricarbonyl complexes, with log P _o/w values ranging from −1.36 to −0.32, were obtained with yields of ≥90% using ligand concentrations within the 10⁻⁶−10⁻⁴M range. Challenge studies with cysteine and histidine revealed the high stability properties of these radioactive complexes, and biodistribution studies in normal mice indicated a fast rate of blood clearance and high rate of total radioactivity excretion, primarily through the renal-urinary pathway. In summary, these asymmetric and symmetric pyridyl-containing tridentate ligands are potent bifunctional chelators for the future biomolecules labeling of fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺.     

Tri­carbonyl­[1,1′,1′′-ethyl­idyne­tris­(pyrazole-κN2)]­rhenium(I) bromide and tri­carbonyl­[methyl­idyne­tris­(pyrazole-κN2)]­rhenium(I) iodide ethanol hemisolvate

The two title compounds, [Re(C₁₀H₁₀N₆)(CO)₃]Br and [Re(C₁₁H₁₂N₆)(CO)₃]I·0.5C₂H₆O, have slightly distorted octahedral geometries about the rhenium centers. The distortions result from the constraints of the η³-coordinated tris­(pyrazol-1-yl)­methane ligands in each case which reduce the N—Re—N bond angles well below the preferred value of 90° for facially disposed ligands at a six-coordinate metal center.     

N-Benzyl Derivatives of Leucine Esters

Leucine methyl and ethyl esters reacted with 3-bromobenzaldehyde and 4-chlorobenzaldehyde in anhydrous methanol in the presence of magnesium sulfate to afford the coresponding Schiff bases of the general formula (CH3)2CHCH2CH(COOR¹)N=CHR² [R¹ = CH3, C2H5, R²= 3-BrC6H4, 4-ClC6H4]. Their reduction with sodium tetrahydridoborate yielded N-benzyl derivatives (CH3)2CHCH2CH(COOR¹)NHCH2R², which were converted into N-acyl-N-benzyl derivatives (CH3)2CHCH2CH(COOR¹)N(COR³)CH2R²[R³= CH₃, C₆H₅].     

An improved tungsten-188/rhenium-188 gel generator based on zirconium tungstate

An improved¹⁸⁸W-¹⁸⁸Re gel generator based on Zr tungstate is described. The influence of synthesis parameters and pre-treatment conditions on¹⁸⁸Re elution yields and the¹⁸⁸W breakthrough was studied with 0.15M aqueous solution of NaCl at pH 5.3 to 7.3 as well as with some organic solvents. An elution efficiency of 80% was achieved during 3 month of explotation with 0.15M NaCl at pH=6.3. The¹⁸⁸W breakthrough was 10^–4 to 10^–3%. The¹⁸⁸W breakthrough may be decreased to 10^–6% when converted into tandem generator with an alumina column. However,¹⁸⁸Re yields are reduced by 8–12% with a tandem generator.     

Reactions of the rhenium fragment (η-C5Me5)Re(CO)2 with chlorinated ethylenes: Coordination and C-Cl bond activation

Photochemical reactions of the dinitrogen complex Cp^∗Re(CO)₂N₂ with tetrachloroethylene and trichloroethylene yield the coordination complexes Cp^∗Re(CO)₂(η²-tetrachloroethylene) (1) and Cp^∗Re(CO)₂(η²-trichloroethylene) (2), respectively. Complex 1 reacts thermally in polar organic solvents to produce the C-Cl bond activation product cis-Cp^∗Re(CO)₂(C₂Cl₃)Cl (3). All complexes were isolated and characterized by IR, ¹H and ¹³C NMR spectroscopies and mass spectrometry. Complex 3 was also characterized by X-ray crystallography.     

A Deadly Organometallic Luminescent Probe: Anticancer Activity of a ReI Bisquinoline Complex

The photophysical properties of [Re(CO)₃(L ‐N₃)]Br (L ‐N₃=2‐azido‐N,N‐bis[(quinolin‐2‐yl)methyl]ethanamine), which could not be localized in cancer cells by fluorescence microscopy, have been revisited in order to evaluate its use as a luminescent probe in a biological environment. The Re^I complex displays concentration‐dependent residual fluorescence besides the expected phosphorescence, and the nature of the emitting excited states have been evaluated by DFT and time‐dependent (TD) DFT methods. The results show that fluorescence occurs from a ¹LC/MLCT state, whereas phosphorescence mainly stems from a ³LC state, in contrast to previous assignments. We found that our luminescent probe, [Re(CO)₃(L ‐N₃)]Br, exhibits an interesting cytotoxic activity in the low micromolar range in various cancer cell lines. Several biochemical assays were performed to unveil the cytotoxic mechanism of the organometallic Re^I bisquinoline complex. [Re(CO)₃(L ‐N₃)]Br was found to be stable in human plasma indicating that [Re(CO)₃(L ‐N₃)]Br itself and not a decomposition product is responsible for the observed cytotoxicity. Addition of [Re(CO)₃(L ‐N₃)]Br to MCF‐7 breast cancer cells grown on a biosensor chip micro‐bioreactor immediately led to reduced cellular respiration and increased glycolysis, indicating a large shift in cellular metabolism and inhibition of mitochondrial activity. Further analysis of respiration of isolated mitochondria clearly showed that mitochondrial respiratory activity was a direct target of [Re(CO)₃(L ‐N₃)]Br and involved two modes of action, namely increased respiration at lower concentrations, potentially through increased proton transport through the inner mitochondrial membrane, and efficient blocking of respiration at higher concentrations. Thus, we believe that the direct targeting of mitochondria in cells by [Re(CO)₃(L ‐N₃)]Br is responsible for the anticancer activity.