Competing Metal Cations Research Articles

Diels-Alder clickable furan-thiosemicarbazide cellulose for selective ruthenium (III) imprinting

Developing an efficient adsorbent for Ru3+ ions in wastewater is crucial for both environmental protection and resource recovery. This study introduces a novel approach using cellulose-based adsorbents, specifically modified with furan-thiosemicarbazide (FTC), to enhance their selectivity for Ru3+ ions. By cross-linking the Ru3+/FTC-modified cellulose (FTC-CE) complex with a bis(maleimido)ethane (BME) cross-linker, we created a Ru3+ ion-imprinted sorbent (Ru-II-CE) that exhibits a strong affinity and selectivity for Ru3+ ions. The synthesis process was thoroughly characterized using NMR and FTIR spectroscopy, while the surface morphology of the sorbent particles was examined with scanning electron microscopy. The Ru-II-CE sorbent demonstrated exceptional selectivity for Ru3+ among competing metal cations, achieving optimal adsorption at a pH of 5. Its adsorption capacity was notably high at 215 mg/g, fitting well with the Langmuir isotherm model, and it followed pseudo-second-order kinetics. This study highlights the potential of FTC-CE for targeted Ru3+ removal from wastewater, offering a promising solution for heavy metal decontamination.

Light rare earth elements stabilize G-quadruplex structure in variants of human telomeric sequences

Recently, light rare earth elements (LREEs) are gaining importance in modern-day technologies. Thus, the entry of LREEs into biochemical pathways cannot be ignored, which might affect the conformation of biomacromolecules. Herein, for the first time, we discover the G-quadruplex formation in the human telomeric variants in presence of micromolar concentrations of LREEs. Thermal melting show that the LREE-induced unimolecular G-quadruplex structure. Isothermal titration calorimetry, UV–vis, and CD spectroscopy results suggest the binding stoichiometry of lanthanide ions to telomeric variants is 2:1. The data confirms that the LREE ions coordinate between adjacent G-quartets. The excess LREE ions are most likely binding to quadruplex loops. The CD spectra revealed that the LREE-induced quadruplex in human telomere and its variant have antiparallel orientation. The binding equilibria of LREEs have been studied both in the presence and absence of competing metal cations. Addition of LREEs to the Na+ or K+-induced G-quadruplexes led to conformational change, which may be ascribed to the displacement of K+ or Na+ ions by LREE ions and formation of a more compact LREE-induced G-quadruplex structure in human telomeric variant. Moreover, the thymine in the central loop of the human telomeric sequence stabilizes LREE induced G-quadruplex.

Fast synthesis of Hcy-modified Au nanoclusters under microwave-assisted irradiation and their response to Cu (II) ions

In this work, Cu (II) ion was chosen as an analyte because it is an important trace element in the human body to maintain organism health. AuNCs (gold nanoclusters) with a mean diameter of ∼2 nm were prepared by a microwave-assisted method, using homocysteine (Hcy) as a reducer and stabilizer. The optimal sample showed a red emission peaking at 624 nm with an emission quantum yield of 17.1%, which was assigned as a ligand to metal nanoparticle core charge transfer (LMNCT). This red emission was effectively quenched by Cu (II) but immune to competing metal cations and anions, showing good selectivity. The quenching mechanism was found as the Cu (II) quenching on the LMNCT procedure to AuNCs. The primary advantage of Hcy-modified AuNCs was the easy and quick synthetic procedure, along with acceptable sensing performance, including good selectivity, linear response, and wide working region.

Three new turn-on fluorescent sensors for the selective detection of Zn2+: Synthesis, properties and DFT studies

The design and synthesis of three new 1,8-naphthalimide-based fluorescent sensors ( 1 – 3 ) for the detection of Zn 2+ in aqueous solution is described. The structural architect of these sensors contains 1,8-naphthalimide scaffold as a fluorophore attached to 2,2′-dipicolylamine (DPA) and bis(2-quinolinylmethyl)amine (DQA) receptors through an amide linkage. The addition of Zn 2+ to the solutions of sensors ( 1 – 3 ) led to enhanced fluorescence intensity, ranging between 2.5 and 14 folds. At physiological pH (pH = 7.4), these sensors exhibited high selectivities for Zn 2+ over a wide range of competing metal cations, displaying high sensitivities with a limit of detections of 120, 81.7 and 79.2 nM, respectively. This suggests that these sensors can detect chronic Zn 2+ concentration for freshwater ( > 1.84 μM), designated by the U.S. Environmental Protection Agency. DFT simulations performed on the more stable stacked conformations of unbound and Zn 2+ bounded states suggested that the latter display higher density of excited states than the unbound sensors. Moreover, the stacked conformer of sensor 3 was significantly more stable as compared to sensors 1 and 2 , which was attributed to a stronger Van Der Waals (VDW) interaction between DQA and 1,8-naphthalimide. The Zn 2+ binding leads to enhanced electronic coupling between the HOMOs and LUMOs, making excited states more populated which then undergoes geometric relaxation before emitting light and relaxing back to the ground states. The lower energy separation (5.0 eV) between the HOMO and the first Zn 2+ d-orbital in sensor 3 as compared to sensors 1 and 2 results in enhanced density of the generated states and subsequently higher intensity upon binding with Zn 2+ .

Modular Assembly of Isostructural Mixed-Ligand Uranyl Coordination Polymers Based on a Patterning Strategy.

Controlling the orderly assembly of molecular building blocks for the formation of the desired architectural, chemical, and physical properties of the resulting solid-state materials remains a long-term goal and deserves to be examined. In this work, we propose a patterning strategy for modular assembly and structural regulation of mixed-ligand uranyl coordination polymers (CPs) through the combination of couples of organic ligands with complementary molecular geometry and well-matched coordination modes. By using a 5-(p-tolyldiazenyl)isophthalic acid ligand (H2ptdi) with different rigid linear bicarboxylic acid linkers to construct a well-defined ladder-like pattern, five novel isostructural uranyl coordination polymers, [(UO)2(ptdi)(bdc)0.5](dma) (1), [(UO)2(ptdi)(bpdc)0.5](dma) (2), [(UO)2(ptdi)(tpdc)0.5](dma) (3), [(UO)2(ptdi)(ndc)0.5](dma) (4), and [(UO)2(ptdi) (pdc)0.5](dma) (5) {H2bdc, 1,4-dicarboxybenzene; H2bpdc, 4,4'-biphenyldicarboxylic acid; H2tpdc, terphenyl-4,4″-dicarboxylic acid; H2ndc, 2,6-naphthalenedicarboxylic acid; H2pdc, 1,6-pyrenedicarboxylic acid; [dma]+, [(CH3)2NH2]+}, were successfully synthesized. Structural analysis reveals that 1-5 have similar ladder-like units but different sizes of one-dimensional nanochannels and interlayer spacing due to the different lengths and widths of the linkers. Because of the changes in interlayer spacing of these isostructural cationic frameworks, differences in the performance of Eu3+ ion exchange with [dma]+ are observed. Moreover, those compounds with high phase purity have been further characterized by thermogravimetric analysis, infrared spectroscopy, and luminescence spectroscopy, element analysis, PXRD and UV spectroscopy. Among them, compound 3 with strong fluorescence can selectively detect Fe3+ over several competing metal cations in aqueous solution. This work not only provides a feasible patterning method for effectively regulating the modular synthesis of functional coordination polymers but also enriches the library of uranyl-based coordination polymers with intriguing structures and functionality.

The synthesis of a novel conjugated microporous polymer and application on photocatalytic removal of uranium(Ⅵ) from wastewater under visible light

• A novel porphyrin-based CMP(TT-TPP) showed wide visible light adsorption. • The U(Ⅵ) removal capacity of TT-TPP was 3571.2 mg g −1 . • 80% uranium removal was achieved under solar irradiation. • Good removal rates were reached on high acidity and high salt condition. • TT-TPP displayed a fine selectivity for U(Ⅵ) from simulated radioactive wastewater. Photocatalytic reduction of uranium(Ⅵ) is an efficient and non-pollutant strategy for removal of uranium(Ⅵ) from waste water. However, most current photocatalysts are limited in practical application due to low visible light utilization and low activity on acidic condition. In this work, a new conjugated microporous polymer (CMP) named TT-TPP has been synthesized by C–H arylation between 5, 10, 15, 20-tetrakis(4-bromophenyl)-porphyrin and thieno[3,2-b]thiophene. TT-TPP exhibits excellent chemical stability and photochemical property. It can be used for visible light driven photocatalytic reduction of U(VI) on highly acidic condition (pH = 2–5) with high uranium removal capacity (3571.2 mg g −1 ). Even in 3 M NaNO 3 solution, the removal rate of U(Ⅳ) could reach to 89.9%. TT-TPP still exhibits an excellent uranium selectivity over these competing metal cations, and 97.6% U(Ⅳ) in simulated radioactive wastewater is removed. The X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and the fourier transform infrared spectroscopy (FT-IR) confirmed the reduced uranium was in the form of UO 2 ⋅nH 2 O. In addition, TT-TPP also shows excellent photocatalytic U(VI) reduction performance under natural sunlight irradiation.

A DFT/PCM Study on the Affinity of Salinomycin to Bind Monovalent Metal Cations.

The affinity of the polyether ionophore salinomycin to bind IA/IB metal ions was accessed using the Gibbs free energy of the competition reaction between SalNa (taken as a reference) and its rival ions: [M+-solution] + [SalNa] → [SalM] + [Na+-solution] (M = Li, K, Rb, Cs, Cu, Ag, Au). The DFT/PCM computations revealed that the ionic radius, charge density and accepting ability of the competing metal cations, as well as the dielectric properties of the solvent, have an influence upon the selectivity of salinomycin. The optimized structures of the monovalent metal complexes demonstrate the flexibility of the ionophore, allowing the coordination of one or two water ligands in SalM-W1 and SalM-W2, respectively. The metal cations are responsible for the inner coordination sphere geometry, with coordination numbers spread between 2 (Au+), 4 (Li+ and Cu+), 5/6 (Na+, K+, Ag+), 6/7 (Rb+) and 7/8 (Cs+). The metals’ affinity to salinomycin in low-polarity media follows the order of Li+ > Cu+ > Na+ > K+ > Au+ > Ag+ > Rb+ > Cs+, whereas some derangement takes place in high-dielectric environment: Li+ ≥ Na+ > K+ > Cu+ > Au+ > Ag+ > Rb+ > Cs+.

Viologen‐Based Uranyl Coordination Polymers: Anion‐Induced Structural Diversity and the Potential as a Fluorescent Probe

AbstractFour novel uranyl coordination polymers (CPs) have been synthesized by the utilization of viologen derivative ligand, 1,1’‐bis(3,5‐dicarboxyphenyl)‐4,4’‐bipyridinium (H4bdbp ⋅ 2Cl), and uranyl nitrate under hydrothermal reactions through the regulation of different kinds of inorganic acids (HF, HCl, HNO3, HClO4, H2SO4). Compound 1 features a unique triple‐stranded helix structure with a helical pitch of 31.578 Å. The ligands in compounds 2–4 have similar configurations, while their 3D structures are completely different due to the presence of different kinds of anions. The anions play different roles in the frameworks of these uranyl CPs. In addition, compound 2 possesses strong fluorescence both in solid‐state and aqueous suspension‐state. It is demonstrated that compound 2 can selectively detect Fe3+ over several competing metal cations in aqueous solution.

The emission quenching of upconversion nanoparticles coated with amorphous silica by fluorescence resonance energy transfer: A mercury-sensing nanosensor excited by near-infrared radiation

In this paper, a rhodamine derivative was synthesized as a probe for Hg(II) detection. Its spectral response and sensing mechanism towards Hg(II) were discussed carefully. It was found that its absorption and emission were increased by Hg(II), via a direct bonding stoichiometry of 1:1. Its association constant was determined with absorption titration as 2.59 × 105 M−1, which suggested a coordination procedure between Hg(II) and this rhodamine probe. It showed good selectivity towards Hg(II) over competing metal cations, no increased emission or absorption was observed in the presence of interfering metal cations. It was then covalently grafted onto silica (SiO2)-encapsulated upconversion nanoparticles (UCNPs). Upon near-infrared (NIR) excitation (980 nm), RHO accepted energy from these UCNPs through a FRET (fluorescence resonance energy transfer) procedure, quenching their upconversion emission. A sensing response towards Hg(II) was thus constructed. Good linearity and selectivity were still preserved in this composite sample. On the other hand, this work found a different phenomenon from literature cases, which was the emission absence of rhodamine emission in this composite structure. Detailed analysis suggested that rhodamine emission absence was caused by its self-quenching effect.

Harmonizing the energy band between adsorbent and semiconductor enables efficient uranium extraction

Herein, we harmonized the energy band of defective molybdenum disulfide (MoSx) and reduced graphene oxide (RGO) through manipulating the concentration of S vacancies for efficient U(VI) reduction. The analysis of band structure revealed that the EF and conduction band of MoSx downward shifted with the increase of S vacancies, which lowered the schottky barrier but simultaneous decreased the reducibility of photogenerated electrons. Accordingly, the removal rate of U(VI) under the irradiation of simulated sunlight exhibited a volcanic relationship with the concentration of S vacancies in MoSx/RGO. Specifically, the maximum removal rate reached 91.6% with nearly 83.4% of tetrahydrated uranium (U(IV)) species over MoSx/RGO heterojunction. In addition, the extraction efficiency of MoSx/RGO heterojunction kept steady in 5-cycle test and exhibited less than 4.5% decrease in the presence of non-redox-active competing metal cations.

Efficient uranium reduction of bacterial cellulose-MoS2 heterojunction via the synergistically effect of Schottky junction and S-vacancies engineering

Integration of the schottky junction and defect engineering over the adsorbent-semiconductors is a perspective strategy for the photocatalytic reduction of hexavalent uranium (U(VI)), which not only effectively avoid the limited active sites on semiconductors, but also promote photogenerated electrons are transferred to the adsorbent through the schottky junction. Here, we developed a bacterial cellulose-defective molybdenum disulfide (BC-MoS2-x) heterojunction by integrating schottky junction and sulfur vacancy (S-vacancy), targeting at simultaneous selective U(VI) removal. The carbonized BC served as not only a confined framework for the growing of MoS2, but also an ideal electron acceptor and transporter for improving the charge carrier separation efficiency. Specifically, the Schottky Junction and S-vacancy had been proven to effectively synergistically enhance the photoelectrons transfer from MoS2 to carbonized BC. Accordingly, the BC-MoS2-x heterojunction presented high removal efficiency for U(VI) with a removal rate of up to 91% in a wide range of U(VI) concentrations. The BC-MoS2-x heterojunction possessed excellent cycle stability in multiple U(VI) capture test cycles, and exhibited a highly selective U(VI) removal in the system containing an abundant of non-redox-active competing metal cations. Interestingly, organic matter, as an unfavorable factor for U(VI) removal in the traditional radioactive wastewater, had been proven to be used as the hole trapping agent to improve the U(VI) removal efficiency. This strategy may open a paradigm for the development of rationally designed heterojunctions as the photocatalysts for selective U(VI) removal.

Visible light driven Ti3+ self-doped TiO2 for adsorption-photocatalysis of aqueous U(VI)

The photocatalytic reduction of U(VI) is recognized as an economical and effective way for U(VI) removal/recovery from solutions. To improve the photocatalytic activity of TiO2 under visible light, TiO2 was hydrogenated by NaBH4 to generate Ti3+ self-doped black TiO2 (BTn). The self-doped Ti3+ alongside oxygen vacancies (Ov) could act as interband level to increase visible light capture and reduce the recombination of photogenerated carriers. The obtained BTn samples showed high performance for U(VI) elimination under near neutral conditions, and held an outstanding anti-interference for U(VI) over competing metal cations and anions. Methanol and ethanol could act as sacrificial donors, being favorable for the photocatalytic reduction of U(VI), while the presence of EDTA inhibited the photoreduction of U(VI). The BTn photocatalysts showed relatively high stability and reusability during the photocatalysis and elution processes. The XPS, TEM and XRD results revealed that U(VI) was photo-reduced to form UO2 on the surface of BTn. This work may serve as an important reference for improving the photocatalytic reactivity of TiO2 as well as for the efficient removal/recovery of U(VI) from aqueous solutions.

How mechanical forces can modulate the metal affinity and selectivity of metal binding sites in proteins.

Mechanical forces play a key role in essential biological processes including cell growth, division, deformation, adhesion, migration and intra-cell interactions. The effect of mechanical forces in modulating the structure and properties of metal-occupied protein binding sites has not been fully understood. Here, by employing a combination of density functional theory (DFT) calculations and polarizable continuum model (PCM) computations applied on model metal-loaded EF-hand binding sites, we shed light on the intimate mechanism of the Mg2+/Ca2+ competition impacted by the application of mechanical stimuli. Applying mechanical force with a specific directionality and magnitude may shift the balance between the competing metal cations in favor of a given contestant depending on the composition and strength of the coordinative bonds and robustness of the metal binding site. Furthermore, the calculations help to determine the range of mechanical rupture forces typical for these structures: these range from 0.4 to 1.5 nN depending on the nature of the metal and amino acid residue. This positions the strength of the Mg2+-O and Ca2+-O coordinative bonds between that of typical covalent and hydrogen bonds. The bonds between the metal cation and the charged amino acid residue rupture at higher forces (∼1.2-1.5 nN) relative to those of their metal-noncharged counterparts which dissociate at ∼0.2-0.4 nN.

Powerful uranium extraction strategy with combined ligand complexation and photocatalytic reduction by postsynthetically modified photoactive metal-organic frameworks

Uranium enrichment is perhaps the most critical chemical process throughout the nuclear fuel cycle including uranium mining, uranium extraction from seawater, used fuel reprocessing and disposal, and environmental contamination remediation. New uranium extraction technology is still highly desirable at current stage, although a variety of extraction methods have been established and developed in the past several decades but all with clear demerits. Herein we present a new uranium extraction strategy with combined ligand complexation and photocatalytic reduction based on postsynthetically functionalized metal-organic frameworks (MOFs). The highly robust and photoactive MOF PCN-222 is modified with phosphono- and amino groups that can capture U(VI) from solution. Upon visible light irradiation, the photo-induced electrons from the MOF host can efficiently reduce U(VI) pre-enriched in MOF, affording neutral uranium species that evacuate the MOF structure and regenerating the active site readily for capturing additional U(VI). This auto-recycled process offers an ultrahigh uranium extraction capacity not limited by the number of adsorption sites and more importantly an extra uranium uptake selectivity over these non-redox-active competing metal cations, and can be utilized for uranium separation over extremely wide uranium concentrations and pH ranges, showing a powerful application potential.

A novel sulfur-incorporated naphthoquinone as a selective “turn-on” fluorescence chemical sensor for rapid detection of Ba2+ ion in semi-aqueous medium

A sulfur-functionalised analogue of the naturally available 1,4-naphthoquinone (N) has been synthesized and evaluated as a sensitive and highly selective fluorimetric sensor against the environmentally toxic barium (II) ion in a semi-aqueous medium. The host ligand exhibits a distinct enhancement in its native fluorescence in the presence of barium ions in ethanol/H2O (1:1,v/v). Its sensing activity was further corroborated by a minimum interference offered by a diverse array of other competing metal cations during the fluorimetric sensing of barium ions. The stoichiometry of N:Ba2+ ion system was calculated from the Benesi-Hildebrand plot to be 2:1 with a binding constant of 3.29 mM. The detection limit of the potential fluorescence probe N against aqueous barium ions was observed to be 4.22 mM. In conclusion we propose that sulfur-containing naphthoquinone act as a potential turn-on fluorescence sensor for the selective detection of toxic barium ions in semi-aqueous medium.

Coordination of mycotoxins with lanthanides in luminescent complexes.

The ability of several chelating mycotoxins to form coordination complexes with the lanthanide metals europium and terbium was explored. The mycotoxins examined included ochratoxin A, citrinin, cyclopiazonic acid (CPA), kojic acid, and tenuazonic acid (TeA). Of these compounds, TeA and CPA resulted in the greatest luminescence. Parameters influencing luminescence of TeA were investigated further. These included the type of lanthanide and its concentration, certain environmental factors, and the effect of competing metal cations. Of the two lanthanide metals, the terbium coordination complex (TeA-Tb3+) showed greater luminescence relative to the europium complex (TeA-Eu3+). The effects of solvent type, water content, and pH on the TeA-Tb3+ system suggested that optimal conditions for luminescence were in 90% methanol with 10% aqueous buffer at pH3. In competitive assays, the luminescence of the TeA-Tb3+ complex decreased as the concentration of competing metal cations increased. Among the cations tested, Cu2+ was the best inhibitor followed by Al3+, Au3+, Fe3+, Co2+, Mn2+, Mg2+, and Ca2+. Two cations, Na+ and K+, showed no significant inhibition. This is the first report to describe the coordination of the metal-chelating mycotoxin TeA with lanthanides and the ability of TeA to serve as an "antenna" for the efficient transfer of energy to the lanthanide with resulting luminescence. Understanding the ability of mycotoxins such as TeA to chelate metals provides insight into how they exert their toxic effects.

Role of hydrophobicity in tuning the intracellular uptake of dendron-based fluorophores for in vitro metal ion sensing.

Fluorophores are used for sensing biologically relevant ions, toxic metals or pathogenic markers. However, the mode of entry of such fluorophores into the cell greatly depends on their size, shape, surface charge, functional groups, and hydrophobicity. In particular, the influence of hydrophobicity on the intracellular uptake of fluorophores is poorly investigated. Self-assembly is a recent strategy to tune the intracellular uptake of fluorophores, facilitating increased intracellular sensing and fluorescence. Herein, self-assembly of three novel poly(aryl ether) dendron derivatives that contain rhodamine units was used to investigate the effect of hydrophobicity on the intracellular uptake of self-assembled fluorophores. The results suggest that monomer hydrophobicity plays an important role in the uptake. The dendron-based fluorophores, which upon self-assembly, formed stable spherical aggregates ranging from 300 to 500 nm. The rhodamine-based dendrons could selectively sense Hg2+ ions in the presence of other competing metal cations. Intracellular imaging of the dendron-based fluorophores displayed bright red fluorescence in human embryonic kidney cells. The rate of intracellular uptake of the three dendron-based fluorophores was analyzed by flow cytometry. The results establish the importance of the hydrophilic-lipophilic balance of the self-assembled amphiphiles for tuning the intracellular uptake.

A novel coumarin-based fluorescence enhancement and colorimetric probe for Cu2+ via selective hydrolysis reaction

Abstract A new colorimetric fluorescent probe, 3-benzothiazolyl-coumarin-7-yl picolinate (P1), based on coumarin derivative has been designed and synthesized to detect Cu2+ in CH3CN-water (1:1,v/v) solution. The probe showed highly selective and sensitive fluorescence enhancement response towards Cu2+ via selective hydrolysis reaction of the picolinate moiety followed by generating a strongly fluorescent 3-benzothiazolyl-7-hydroxycoumarin (2) moiety, whereas other competing metal cations (Na+, K+, Mg2+, Ag+, Fe3+, Pb2+, Mn2+, Ca2+, Ni2+, Cr3+, Zn2+, Sn2+, Hg2+, Al3+, Pd2+, Pt2+, Co2+, Au3+) did not possess the property. Upon the addition of Cu2+, the color of P1 changed from colorless to yellow-green, and gave an emission at around 470 nm. Moreover, the detection limit toward Cu2+ was calculated to be as low as 23.9 nM.

Synthesis, characterization and Cu2+ triggered selective fluorescence quenching of Bis-calix[4]arene tetra-triazole macrocycle

A novel fluorescent bis-calix[4]arene macrocycle 9 incorporating metal-binding pockets was successfully prepared. The structure of macrocycle 9 and its precursors were characterized via EI-MS, MALDI-TOF-MS, ESI-MS, 1H NMR, 13CNMR, 2D NMR, and X-ray crystallography. The macrocycle 9 displayed selective fluorescence quenching after interacting with Cu2+ in the presence competing metal cations including Mg2+, Ca2+, Ba2+, Ag+, Zn2+, Ti4+,Cd2+, Hg2+, Pb2+, In3+, La3+, Cr3+, Ni2+, Sb3+, V5+, Fe3+, Co2+, Sn2+, Sn2+, and Tl+. The Cu2+ limit of detection was found to be 40nM much lower than its threshold level (∼20μM) in drinking water permitted by the U.S Environmental Protection Agency (EPA). Furthermore, drinking water samples from Karachi University (Pakistan) spiked with Cu2+ were analysed with the sensing system and the results showed an excellent agreement with the fluorescence quenching phenomenon of macrocycle 9 examined in deionized water. Importantly, the chemosensor 9 could be used to detect Cu2+ in living cells

Radiolabeling of DOTATOC with the long-lived positron emitter 44Sc

The positron-emitting radionuclide 44Sc with a half-life of 3.97h and a β+ branching of 94.3% is of potential interest for clinical PET. As so far it is available from a 44Ti/44Sc generator in Mainz, where long-lived 44Ti decays to no-carrier-added (nca) 44Sc. The 44Sc is a trivalent metal cation and should be suitable for complexation with many well established bifunctional chelators conjugated to peptides or other molecular targeting vectors. Thus, the aim of this work was to investigate the potential of 44Sc for labeling of DOTA-conjugated peptides. DOTA-D-Phe1-Tyr3-octreotide (DOTATOC) was used as a model molecule to study and optimize labeling procedure. Reaction parameters such as buffer conditions, concentration of peptide, pH range, reaction temperature and time were optimized. Addition of 21nmol of DOTATOC to 44Sc in ammonium acetate buffer pH 4.0 provided labeling yields >98% within 25min of heating in an oil-bath at 95°C. This time can be reduced to 3min only by applying microwave supported heating. 44Sc-DOTATOC was found to be stable in 0.9% NaCl, PBS pH 7.4, fetal calf and human serums, and also in the presence of competing metal cations (Fe3+, Ca2+, Cu2+, Mg2+), as well as other ligand competitors, like EDTA and DTPA, even after almost 25h incubation at 37°C. Present study shows that nca 44Sc forms stable complexes with the macrocyclic ligand DOTA and that 44Sc-DOTATOC and analog targeting vectors may be synthesized for further preclinical and clinical investigations.