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US20120070378A1 - Lanthanide ion complexes and imaging method - Google Patents

Lanthanide ion complexes and imaging method Download PDF

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US20120070378A1
US20120070378A1 US13/128,766 US200913128766A US2012070378A1 US 20120070378 A1 US20120070378 A1 US 20120070378A1 US 200913128766 A US200913128766 A US 200913128766A US 2012070378 A1 US2012070378 A1 US 2012070378A1
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complex
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lanthanide
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compound
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Yi Pang
Qinghui Chu
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University of Akron
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
    • C07F5/00—Compounds containing elements of Groups 3 or 13 of the Periodic Table
    • C07F5/003—Compounds containing elements of Groups 3 or 13 of the Periodic Table without C-Metal linkages
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K49/00—Preparations for testing in vivo
    • A61K49/001—Preparation for luminescence or biological staining
    • A61K49/0013—Luminescence
    • A61K49/0017—Fluorescence in vivo
    • A61K49/0019—Fluorescence in vivo characterised by the fluorescent group, e.g. oligomeric, polymeric or dendritic molecules
    • A61K49/0021—Fluorescence in vivo characterised by the fluorescent group, e.g. oligomeric, polymeric or dendritic molecules the fluorescent group being a small organic molecule
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K2211/00—Chemical nature of organic luminescent or tenebrescent compounds
    • C09K2211/10—Non-macromolecular compounds
    • C09K2211/1018—Heterocyclic compounds
    • C09K2211/1025—Heterocyclic compounds characterised by ligands
    • C09K2211/1029—Heterocyclic compounds characterised by ligands containing one nitrogen atom as the heteroatom
    • C09K2211/1033—Heterocyclic compounds characterised by ligands containing one nitrogen atom as the heteroatom with oxygen
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K2211/00—Chemical nature of organic luminescent or tenebrescent compounds
    • C09K2211/18—Metal complexes
    • C09K2211/182—Metal complexes of the rare earth metals, i.e. Sc, Y or lanthanide

Definitions

  • the present exemplary embodiment relates to lanthanide ion complexes. It finds particular application in conjunction with complexes that absorb or fluoresce in the visible or near-infrared (NIR) region of the electromagnetic spectrum, a process for preparing such complexes, and their NIR emission properties that render the complexes useful in imaging applications such as methods of imaging or therapy using such complexes.
  • NIR near-infrared
  • the present exemplary embodiment is also amenable to other like applications.
  • Imaging techniques are used for a variety of applications, including drug discovery and preclinical testing, studies of disease, treatment and medical diagnosis.
  • Molecular imaging is a rapidly emerging field, as it provides noninvasive visual quantitative representations of fundamental biological processes (T. F. Massoud, S. Gambhir, “Integrating noninvasive molecular imaging into molecular medicine: an evolving paradigm,” Trends in Molecular Medicine 2007, 13, 183-191).
  • Molecular imaging differs from conventional diagnostic imaging in that it uses probes known as biomarkers, which interact chemically with their surroundings and give signals according to molecular changes/response occurring within the area of interest. This ability to image fine molecular changes can directly or indirectly reflect specific cellular and molecular events that can reveal pathways and mechanisms responsible for disease (R. Weissleder, V.
  • luminescence-based imaging is non-invasive, involves non-ionizing radiation, and can provide high sensitivity, thus combining some of the best qualities of PET (positron emission tomography), SPECT, ultrasound, and MRI.
  • Optical imaging uses the fluorescence as optical contrast. Like ultrasound, optical imaging does not have strong safety concerns in comparison with the other medical imaging modalities, which is a valuable attribute (E. M. Sevick-Muraca, J. C. Rasmussen, “Molecular Imaging with Optics: Primer and Case for Near-Infrared Fluorescence in Personalized Medicine,” Journal of Biomedical Optics 2008, 13, 041303-1-041303/16).
  • Fluorescent molecules that absorb and emit light in the near-infrared (NIR) region are of particular interest for potential in vivo imaging applications.
  • the spectral range of interest is approximately 850-1100 nm, where the background noise arising from the fluorescence of the biological material itself (cellular autofluorescence) noise is minimal.
  • cellular autofluorescence the background noise arising from the fluorescence of the biological material itself
  • the fluorophores are subject to photo-irradiation and detectability is limited by cellular autofluorescence and auto-absorption.
  • One approach to overcoming the autofluorescence problem is to develop fluorescent probes that display long emission wavelengths, long decay times, and high quantum yield and high fluorescence brightness (see, for example, Z.
  • lanthanide chelates as luminescent labels has been increasingly recognized as a technique for detecting biomolecules with high sensitivity.
  • One feature of lanthanide chelate luminescence is that the excited state lifetime is unusually long (often over 1 millisecond) in comparison with the lifetime of organic fluorescent compounds. Therefore, time-resolved fluorometric measurement of lanthanide chelate compounds eliminates the undesired background fluorescence, which decays within several nanoseconds.
  • Other attractive features of lanthanide chelates are their emission in the NIR region, narrow emission bands which originate from the f-f transition of the lanthanide atom, and high detection sensitivity.
  • the lanthanide elements are considered to be the sequence of 15 elements with atomic numbers from 57 (lanthanum) to 71 (lutetium). All lanthanide elements are f-block elements, corresponding to the gradual filling of the 4f electron shell. The characteristic f ⁇ f transitions are quite narrow, and substantially unaffected by the chemical environment of the ion. These transitions are easily recognizable, making lanthanide ions candidates for optical probes. Most of the lanthanide cations are luminescent, either fluorescent (e.g., Pr 3+ , Nd 3+ , Ho 3+ , Er 3+ , and Yb 3+ ) or phosphorescent (e.g.
  • NIR signals generated with such ligands can be weak and can be masked by autofluorescence signals in imaging.
  • a lanthanide complex comprising at least one lanthanide ion and at least one polydentate ligand derived from a molecule having the general formula of Structure 2:
  • E represents a heteroatom or heteroatom-containing group
  • R 1 -R 8 are independently selected from H; —OH; —SO 3 H; —CO 2 H; —NH 2 ; X, where X represents a halide; optionally substituted organic groups; and conjugated linking groups which link two of the polydentate ligands of structure 2 together.
  • a method of forming a lanthanide complex comprising combining a lanthanide ion with a ligand-forming molecule having the general formula of Structure 2:
  • E represents a heteroatom or heteroatom-containing group and R 1 -R 8 are independently selected from H; —OH; —SO 3 H; —CO 2 H; —NH 2 ; X, where X represents a halide; and optionally substituted organic groups.
  • FIG. 1 illustrates an x-ray structure of a representative lanthanide complex of Yb 2 (HBO) 6 ;
  • FIG. 2 illustrates an x-ray structure of a representative lanthanide complex of Yb(HBO) 3 .DMSO;
  • FIG. 3 shows emission spectra of HBO-coordinated lanthanide complexes in the powder form which were formed in a heterogeneous reaction scheme.
  • FIG. 4 shows absorption in the UV-visible range of exemplary complexes formed in situ from HBO and lanthanide ions in DMSO, with and without triethylamine;
  • FIG. 5 shows photoluminescence spectra of HBO lanthanide complexes formed in-situ in DMSO solution in the presence of NEt 3 ;
  • FIG. 6 shows phosphorescence spectra of HBI-, HBO-, and HBT-ligands of Gadolinium complexes in DMSO at 77K in which the different spectral positions show that the triplet-state energy levels of the attached ligands are dependent on the heteroatoms present in the heterocyclic rings;
  • FIG. 7 shows time-resolved decay curves taken with a 1.0 ms delay of HBI-Gd, HBO-Gd and HBT-Gd complexes in DMSO at 77K (formed by a homogeneous reaction scheme), in the absence of O 2 ;
  • FIG. 8 is a simplified diagram showing the energy flow path during sensitization of lanthanide luminescence: (singlet excited state 1 S) ⁇ (triplet excited state 3 T) ⁇ (excited states of lanthanide ions Ln 3+ ). To achieve an efficient energy transfer, the triplet energy levels ( 3 T) are matched to the luminescence energy levels of lanthanide ions (Ln 3+ ); and
  • FIG. 9 illustrates luminescence intensities from Nd 3+ complexes formed in situ from HBO, HBI, and quinoline (Qin) in DMSO (1.0 ⁇ 10 ⁇ 5 M).
  • the lanthanide complex includes at least one lanthanide ion and at least one negatively charged ligand L 1 .
  • the negatively charged ligand L 1 is derived from an optionally substituted, 2-(2′-hydroxyphenyl)benzene-fused azole compound, where the azole ring includes, in addition to nitrogen, a hetero atom or group E.
  • E can be O, S, P, Si, B or an N-containing hetero group.
  • Example ligands include ligands of 2-(2′-hydroxyphenyl)benzoxazole (HBO), where E represents oxygen, 2-(2′-hydroxyphenyl)benzothiazole (HBT), where E represents sulfur, and 2-(2′-hydroxyphenyl)benzimidazole (HBI), where E represents N—H, and substituted derivatives thereof.
  • HBO 2-(2′-hydroxyphenyl)benzoxazole
  • HBT 2-(2′-hydroxyphenyl)benzothiazole
  • HBI 2-(2′-hydroxyphenyl)benzimidazole
  • Compounds including such complexes may be in solid or solution form.
  • ligands L 1 of this class can chelate with various lanthanide ions to form stable complexes.
  • the exemplary ligands have significant absorption coefficients, appropriate triplet state energy levels that match the energy levels of lanthanide f-orbitals, and a suitable structure to form polydentate chelation with lanthanide ions (through the hydroxyl group of the phenyl and the nitrogen of the azole).
  • the exemplary ligands can provide improved sensitizing capacity for the lanthanide ions and increased NIR signals, when compared with existing ligands.
  • One reason for the improvement may be that the sensitizing molecule (here, ligand L 1 ) is closer to the Ln 3+ ion than in existing complexes, thus allowing for more efficient energy transfer.
  • the exemplary complex may be in the form of a compound represented by the general formula of Structure 1.
  • L 1 represents the negatively charged ligand, and will be described in further detail below.
  • M + represents an optional monovalent cation.
  • Exemplary monovalent cations include L 1+ , NH 4 + and combinations thereof.
  • Ln represents a lanthanide ion.
  • Lanthanide ions are ions of lanthanide elements (now referred to as lanthanoids in IUPAC terminology) which include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
  • Exemplary lanthanide ions include Pr 3+ , Nd 3+ , Sm 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ and Yb 3+ .
  • A represents an optional anionic ligand.
  • Exemplary anions which may be used as the anionic ligand include those which are capable of forming a soluble salt of a lanthanide element.
  • Exemplary anions include halides, such as Cl ⁇ , AcO ⁇ , CF 3 SO 3 ⁇ , nitride, and combinations thereof.
  • L 2 represents an optional neutral ligand, examples of which are provided below.
  • m, n, p, q, and z each represent a number where n and p are independently at least 1 and m, q, and z, can independently be 0 or greater. Values of m, n, p, q, and z can be selected to provide a charge balanced compound in which each lanthanide ion does not exceed its maximum coordination of 8.
  • L 1 has a valency of greater than 1, e.g., is a divalent anion, in which case, the values of m, n, p, q, and z may be appropriately selected accordingly.
  • L 1 may be a polydentate ligand derived from a molecule having the general formula represented by Structure 2.
  • E represents a heteroatom or heteroatom-containing group.
  • exemplary heteroatoms/groups include O (oxygen), S (sulfur), P (phosphorus), B (boron), Si (silicon) and N—R, where R represents a stabilizing group, such as H, alkyl, aryl, or the like, e.g., of from 1 to about 6 carbon atoms.
  • R represents a stabilizing group, such as H, alkyl, aryl, or the like, e.g., of from 1 to about 6 carbon atoms.
  • E is selected from O, S, and N—R.
  • R is H or CH 3 .
  • the E group or atom is an electron donating group which helps to stabilize the 5-membered azole ring and give it aromatic character.
  • the E group affects the emission characteristics, as discussed below.
  • R and R 1 -R 8 may be independently selected from H; —OH; —SO 3 H; —NH 2 ; —CO 2 H; X, where X represents a halide; and organic groups, e.g., optionally substituted C 1 -C 30 groups selected from alkoxy (—OR 9 ), amino (e.g., —NHR′, —NR′R′′) and alkyl amino (e.g., —R′′′NHR′, —R′′′NR′R′′); alkyl, alkenyl, alkynyl, cycloalkyl, aryl, alkylaryl, heterocyclic groups, ring structures formed by two or more of R 1 -R 8 ; and combinations thereof.
  • alkoxy —OR 9
  • amino e.g., —NHR′, —NR′R′′
  • alkyl amino e.g., —R′′′NHR′, —R′′′NR′R′′
  • R′, R′′ and R 9 can be selected from optionally substituted C 1 -C 15 groups selected from alkyl, alkenyl, alkynyl, cycloalkyl, aryl, and alkylaryl;
  • R′′′ can be an optionally substituted alkyl bridging group of up to three carbon atoms in length; and one or more of R 1 -R 8 may be a linking group which links two such ligands L 1 . In general these groups are not destabilizing in the complex.
  • polydentate it is meant that the ligand provides two or more coordination sites for the lanthanoid ion. In general, each of these coordination sites is associated with a different ring of the ligand.
  • Exemplary halides X in the above can include Cl and Br.
  • R 10 can be as described above for R 9 .
  • “optionally substituted” means that the group in question can include a substituent for one or more of its hydrogen or carbon atoms, such as alkyl, aryl, alkoxy, aryloxy, a heteroatom containing substituent, X, O, S, N or the like.
  • a polyaminocarboxylic acid-containing group is a group containing one or more nitrogen atoms connected through one or more carbon atoms to one or more carboxyl groups, and wherein the nitrogen is optionally linked to the complex via an alkyl bridge.
  • Such groups are useful chelating groups and thus may be useful in tuning the ion-binding properties of the complex.
  • Another useful chelating group for the R 1 and/or R 5 positions is —COOH.
  • Structure 2 corresponds respectively to 2-(2′hydroxyphenyl)benzoxazole (HBO), 2-(2′-hydroxyphenyl)benzothiazole (HBT), and 2-(2′-hydroxyphenyl)benzimidazole (HBI).
  • Exemplary neutral ligands L 2 in Structure 1 include, but are not limited to:
  • TPPO triphenylphosphine oxide
  • the complex may have the general formula of Structure 3:
  • R 3 ⁇ H, X, —OR 9 , —NHR′ or CH 3 and/or R 5 ⁇ —H,
  • R 12 can be as for R 6 , e.g., R 12 ⁇ H or C(CH 3 ) 3 and R 6 ⁇ H or C(CH 3 ) 3 .
  • R 5 can be as described above for structure 5.
  • L 1 may have the general formula of Structure14:
  • E and E′ can independently be as for E above;
  • R 14 and R 15 each represent a substituent independently selected from R 1 , R 2 , and R 4 as above, i.e., in the R 1 , R 2 , and/or R 4 position, e.g., both may be in the R 1 position; and
  • R 16 represents a conjugated linking group, such as one of structures 15 and 16:
  • the structure of the complex comprising the ligand of Structure 14 can be represented by Structure 20:
  • L 2 ′ and L 2 may be independently selected from neutral ligands, as for L 2 above;
  • X′ and X may be independently selected from anions, as for X above;
  • q 1 and q 2 may be as for q;
  • z 1 and z 2 may be as for z.
  • composition may be a polymer of the general form shown in Structure 21:
  • R 14 -R 16 are as described above and t can be an integer which is ⁇ 2, e.g., from 2-100.
  • the exemplary complexes and compounds comprising them can be used as effective photosensitizers for lanthanide ions.
  • HBI derivatives have been found to form NIR luminescent complexes with eight lanthanide ions (Pr, Nd, Sm, Dy, Ho, Er, Tm, and Yb).
  • HBO and HBT derivatives have been found to form NIR luminescent complexes with six lanthanide ions (Pr, Nd, Sm, Ho, Er, and Yb).
  • the relative luminescent intensity of the resulting complexes follows the general trend HBT>HBO>HBI complexes.
  • compositions are suitable for use with a variety of other modalities including X-rays, magnetic resonance, and radiographic imaging.
  • Biomolecule refers to all natural and synthetic molecules that play a role in biological systems. Biomolecules include hormones, amino acids, peptides, peptidomimetics, proteins, nucleosides, nucleotides, nucleic acids, carbohydrates, lipids, albumins, mono- and polyclonal antibodies, receptor molecules, receptor binding molecules, and aptamers.
  • biomolecules include inulins, prostaglandins, growth factors, growth factor inhibitors like somatostatin, liposomes, and nucleic acid probes.
  • synthetic polymers include polylysine, polyaspartic acid, polyarginine, aborols, dendrimers, and cyclodextrins. Coupling of such complexes to biomolecules can be accomplished by several known methods (see, for example, Hnatowich, et al., Science, 1983, 220, 613).
  • the exemplary complexes thus find application in a variety of imaging techniques of which the following are examples:
  • the complex may serve as a reporter for a targeting biomolecule which is specific for the disease.
  • a probe comprising the complex and a coupled targeting biomolecule is introduced to the body of a human or other animal subject, e.g. as a pill or liquid to be swallowed, or by injection. Due to the targeting biomolecule, the probe concentrates in regions of diseased cells, such as cancer cells.
  • the exemplary complex luminesces.
  • a detector is positioned proximate the subject. The detector detects the emitted radiation in a selected NIR range at which the luminescence occurs. The detector sends signals to a reconstruction processor which generates an image of the subject or portion of the subject, based on the received signals. In general, such images use color or grayscale to indicate the determined concentration of the luminescing complex.
  • the image can be superimposed over or otherwise combined with a second image which shows features of the body, such as organs, bone or tissue.
  • the second image can be generated by another imaging technique, such as positron emission spectroscopy (PET), (SPECT), or magnetic resonance imaging (MRI).
  • PET positron emission spectroscopy
  • SPECT positron emission spectroscopy
  • MRI magnetic resonance imaging
  • the exemplary complex-containing probe can be administered along with a marker for the second imaging technique.
  • the hybrid image may be generated by detecting luminescence at two wavelengths, one for the complex, the other selected for detecting auto-luminescence from the body.
  • the exemplary complex allows early detection of diseases, even at the molecular level. Such techniques can be used to detect whether a subject has a particular disease or to follow the progress of a disease.
  • a probe includes the complex linked to a candidate therapeutic agent, such as a drug.
  • a candidate therapeutic agent such as a drug.
  • the ability of the drug to target a known disease site, such as a cancer, can be tracked by the complex.
  • the complex acts as a reporter for the drug movement, in a similar manner to that described for detection. If the detected concentration of the complex at the known disease site is higher than in surrounding tissue, it can be inferred that the candidate therapeutic agent is specific for the disease site
  • compositions comprising the exemplary compounds and probes containing them, an effective amount of one or more of the exemplary compounds alone or in the form of a probe may be dispersed in a pharmaceutically acceptable composition and administered to a patient either systemically or locally to the organ or tissue to be studied.
  • These compositions may also include stabilizing agents, such as amino acids, peptides and mono- or poly-carboxylic acids, amines, nucleotides, or saccharides.
  • parenteral administration advantageously contains a sterile aqueous solution or suspension of the complexe(s) whose concentration ranges from about 1 nM to about 0.5 M.
  • the complex may be present in the pharmaceutical composition at a concentration of at least 0.1% by weight and up to about 90% by weight.
  • Such solutions also may contain pharmaceutically acceptable buffers, emulsifiers, surfactants, and, optionally, electrolytes, such as sodium chloride.
  • enteral compositions may optionally include buffers, surfactants, emulsifiers, thixotropic agents, and the like.
  • Compositions for oral administration may also contain flavoring agents and other ingredients for enhancing their organoleptic qualities.
  • the diagnostic compositions are administered in doses effective to achieve the desired diagnostic or therapeutic objective. Such doses may vary widely depending upon the particular complex employed, the organs or tissues to be examined, the equipment employed in the clinical procedure, and the like.
  • the complex also finds application in telecommunication applications, for example, in a transmitting material such as an optical fiber. It may also find application in lasers and as a light emitting material, for example, in a light emitting diode (LED). In an LED, for example, a layer comprising the complex may be excited by electrical current and emit light at a wavelength, e.g., in the visible or Near-IR region.
  • a transmitting material such as an optical fiber. It may also find application in lasers and as a light emitting material, for example, in a light emitting diode (LED).
  • LED light emitting diode
  • a layer comprising the complex may be excited by electrical current and emit light at a wavelength, e.g., in the visible or Near-IR region.
  • Scheme 1 illustrates exemplary methods for synthesis of near infrared-emitting materials in a heterogeneous reaction.
  • a complex of the form Ln 2 L 1 6 can be formed by reaction of a lanthanide salt LnX 3 (e.g., a lanthanide chloride), with a ligand L 1 in neutral form such as any one or more of those illustrated in Structures 5-13 in an approximately 1:3 molar ratio of Ln to L 1 .
  • the reaction may be carried out in a suitable solvent, such as C 1 -C 6 alcohol, e.g., ethanol or methanol, and optionally also a base capable of reacting with the halide in the lanthanide salt, but which does not tend to complex with the lanthanide ion, such as KOH or NaOH.
  • the reaction generally proceeds at room temperature (e.g., 15-25° C.) to form a precipitate of Ln 2 L 1 6 .
  • a complex of the form LnL 1 3 L 2 can be formed as a precipitate by reaction of a lanthanide salt LnX 3 (e.g., a lanthanide chloride), with a ligand L 1 and a ligand L 2 ; where L 1 is in neutral form such as any one or more of those illustrated in Structures 5-13 and L 2 can be any neutral ligand.
  • the reactants can be in an approximately 1:3:1 molar proportion of Ln:L 1 :L 2 .
  • the reaction can be conducted in a suitable solvent, such as ethanol, at a suitable reaction temperature, such as room temperature.
  • a complex of the form MLnL 1 4 can be formed as a precipitate by reaction of a lanthanide salt LnX 3 (e.g., a lanthanide chloride), with a ligand L 1 and a cation M + , as described above, e.g., in the form of a base, MOH.
  • the reaction can be conducted in a suitable solvent, such as ethanol, at a suitable reaction temperature, such as room temperature.
  • a complex of the form LnL 1 3 DMSO can be formed by recrystallization of Ln 2 L 1 6 (formed in reaction A) in dimethylsulfoxane (DMSO) at a suitable reaction temperature, such as room temperature.
  • DMSO acts as ligand L 2 .
  • Scheme 2 illustrates the synthesis of Near IR Emitting Materials by Homogeneous Reaction.
  • lanthanide halide such as LnCl 3 (or other LnA 3 compound)
  • ligand L 1 are reacted to form a complex of the general form LnL 1 m A 3-m .
  • the value of m depends on the molar proportions of the starting materials. For example, a ratio of LnA 3 :L 1 may be approximately 1:1 to 1:2.
  • the reaction may be conducted in a suitable solvent, such as an alcohol (e.g., methanol or ethanol), or DMSO, and optionally further in the presence of a tertiary amine, such as triethylamine, pyridine, or other nitrogenous base.
  • a suitable solvent such as an alcohol (e.g., methanol or ethanol), or DMSO
  • a solution comprising the complex formed by reaction scheme 2 may include the complex at a concentration of at least 1 nanomole (10 ⁇ 9 mole/liter).
  • the solution comprises at least 1 wt % of the complex and can comprise up to 90 wt % of the complex.
  • ⁇ indicates the reaction was completed. ⁇ indicates precipitation occurred from the reaction. x indicates no reaction was observed. NIR indicates the complex gave NIR emission. N/A indicates that the combination was not investigated. ⁇ indicates the reaction occurs partially (or incomplete reaction).
  • each of the lanthanide ions shown formed a complex and exhibited fluorescence in at least one of the solvents tested.
  • the complexation can proceed completely without the promotion of triethylamine, indicating the strong likelihood of coordinating ability of the ligand of structure 6. It is suggested that its Y-type geometry structure is favorable for entropy driven complexation.
  • the complexation of several lanthanide ions was also tested in chloroform and dioxane, both with and without NEt 3 , but no reaction took place.
  • the addition of triethylamine is advantageous for the complete reaction in the case of DMSO, reflecting the impact of solvent and base on the complexation.
  • Table 2 shows that complexes of HBO with various lanthanide ions are formed.
  • triethylamine was generally beneficial, except in the case of dioxane as a solvent where no reaction took place.
  • FIG. 1 shows an X-ray crystal structure of Compound 1, Yb 2 (HBO) 6 , recrystallized from DMF.
  • FIG. 2 depicts an X-ray crystal structure of Yb(HBO) 3 .DMSO, which is the product of Compound 1, after recrystallization from DMSO solvent.
  • FIG. 3 shows emission spectra of various HBO-coordinated lanthanide complexes (compounds 1, 2, 4, and 5) in the powder form (Reaction Scheme 1). As can be seen, the compounds have peaks at different wavelengths in the NIR range. The spectra exhibited different characteristics of lanthanide emission, such as pure and multiplicity of spectrum peaks.
  • FIG. 4 shows absorption in the UV-visible range of various complexes formed in situ from HBO and lanthanide ions in DMSO (Reaction Scheme 2), with and without triethylamine.
  • FIG. 5 shows photoluminescence spectra of HBO lanthanide complexes formed in-situ in DMSO solution in the presence of triethylamine.
  • Table 3 provides a comparison of photophysics data of lanthanide complexes of benzoxazole derivatives: HBO, a ligand derived from structure 6 (Ligand 6) and a ligand derived from structure 19 (Ligand 19) formed in-situ in DMSO solution in the present of triethylamine. Maximum absorption wavelengths were detected in the UV-Visible range, and maximum emission wavelengths were detected in the NIR range, by photoluminescence.
  • Table 4 provides a comparison of similar photophysics data of lanthanide complexes of benzimidazole derivatives: HBI, a ligand derived from structure 12 (Ligand 12) and a ligand derived from structure 13 (Ligand 13), formed in-situ in DMSO solution in the presence of triethylamine.
  • Table 5 provides a comparison of photophysics data lanthanide complexes of benzothiazole derivatives: HBT, a ligand derived from structure 9 (Ligand 9) and a ligand derived from structure 10 (Ligand 10) formed in-situ in DMSO solution in the presence of triethylamine.
  • the sensitization of lanthanide ions involves an intramolecular energy transfer via the sequential process of ligand singlet ⁇ ligand triplet ⁇ lanthanide luminescent energy levels.
  • the overall efficiency of the process is dependent on the relative positions of the lowest triplet energy level of the ligand, which can be perturbed (or adjusted) via chemical modification of the ligand structure. Only those ligands which exhibit the triplet energy level above the lanthanide luminescent energy levels are found to transfer the energy by an intramolecular process.
  • the lifetime of the ligand triplet state also has profound effect on the efficiency of energy transfer.
  • FIGS. 6 and 7 show phosphorescence spectra and time-resolved decay curves of HBI-Gd, HBO-Gd and HBT-Gd complexes (formed by Reaction Scheme 2).
  • the phosphorescence spectra were taken at 77K with 1.0 ms delay in DMSO solution in the absence of O 2 . As can be seen in the FIG.
  • HBI possesses the highest triplet energy, which accounts for its sensitization ability of all the lanthanide ions tested, followed by that of HBO and then HBT.
  • the phosphorescence lifetimes of the three compounds, shown in FIG. 7 are all of about the same scale (half life t 1 of about 3 ms). This is significant larger than that of quinolinol derivatives (half life of about 0.5 ms), which are known as ligands for the lanthanide ion sensitization.
  • the longer lifetime of ligand triplets increases the probability of energy transfer, so does the sensitization ability.
  • the matched energy level and prolonged lifetime illustrates the great sensitization ability of the compounds and complexes disclosed herein.
  • the neodymium cation Nd 3+ gives emission lines at 887 nm and 1060 nm, corresponding to energy transitions 4 F 3/2 ⁇ 4 I 9/2 and 4 F 3/2 ⁇ 4 I 11/2 (shown in FIG. 5 ).
  • the emission peak at 1060 nm is widely used in the commercial YAG laser system, the emission peak at 887 nm may play a particular role in imaging applications for the exemplary complex.
  • FIG. 9 shows the emission of Nd 3+ complexes formed in situ from HBO, HBI, and quinoline (Qin) in DMSO (1.0 ⁇ 10 ⁇ 5 M).
  • the HBO-Nd 3+ complex gives higher intensity from the 4 F 3/2 ⁇ 4 I 9/2 transition (at ⁇ 890 nm), than that from the 8-hydroxyquinoline complex, Qin-Nd 3+ .
  • the exemplary ligands are also capable of adjusting the emission ratio between the two emission lines, with HBI-Nd 3+ showing stronger emission at 1060 nm while HBO-Nd 3+ shows stronger emission at ⁇ 887 nm.

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ITMI20130908A1 (it) 2013-06-03 2014-12-04 Univ Milano Bicocca Materiale fotoluminescente a lunga persistenza a base di ossicarbonato di gadolinio drogato con itterbio e metodi per la sua produzione

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CN107383385A (zh) * 2017-08-02 2017-11-24 金华职业技术学院 一种2‑碘苯甲酸双核镧(iii)配合物及其制备方法

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