Synthesis and characterization of glucosamine-bound near-infrared probes for optical imaging

Tumor-targeted near-infrared fluorophore for fluorescence-guided phototherapy

A tumor-targeted near-infrared (NIR) fluorophore CA800SO3 was developed for fluorescence-guided phototherapy. This new type of NIR fluorophore showed high tumor targetability based on the structure-inherent targeting approach. This fluorophore generated sufficient hyperthermia and reactive oxygen species (ROS) simultaneously for synergistic cancer phototherapy, induced by an 808 nm laser irradiation.

Highly colloidally stable trimodal 125I-radiolabeled PEG-neridronate-coated upconversion/magnetic bioimaging nanoprobes

"All-in-one" multifunctional nanomaterials, which can be visualized simultaneously by several imaging techniques, are required for the efficient diagnosis and treatment of many serious diseases. This report addresses the design and synthesis of upconversion magnetic NaGdF4:Yb3+/Er3+(Tm3+) nanoparticles by an oleic acid-stabilized high-temperature coprecipitation of lanthanide precursors in octadec-1-ene. The nanoparticles, which emit visible or UV light under near-infrared (NIR) irradiation, were modified by in-house synthesized PEG-neridronate to facilitate their dispersibility and colloidal stability in water and bioanalytically relevant phosphate buffered saline (PBS). The cytotoxicity of the nanoparticles was determined using HeLa cells and human fibroblasts (HF). Subsequently, the particles were modified by Bolton-Hunter-neridronate and radiolabeled by 125I to monitor their biodistribution in mice using single-photon emission computed tomography (SPECT). The upconversion and the paramagnetic properties of the NaGdF4:Yb3+/Er3+(Tm3+)@PEG nanoparticles were evaluated by photoluminescence, magnetic resonance (MR) relaxometry, and magnetic resonance imaging (MRI) with 1 T and 4.7 T preclinical scanners. MRI data were obtained on phantoms with different particle concentrations and during pilot long-time in vivo observations of a mouse model. The biological and physicochemical properties of the NaGdF4:Yb3+/Er3+(Tm3+)@PEG nanoparticles make them promising as a trimodal optical/MRI/SPECT bioimaging and theranostic nanoprobe for experimental medicine.

A Near-Infrared Fluorescent Probe Coated with β-Cyclodextrin Molecules for Real-Time Imaging-Guided Intraoperative Ureteral Identification and Diagnosis

Although iatrogenic ureteral injury and its lack of recognition due to ureteral invisibility are serious incidents in open and laparoscopic abdominal surgeries, there are currently no safe and effective methods for intraoperative ureteral identification (IUI) and diagnosis (IUD). In this study, I designed and chemically synthesized a near-infrared fluorescence (NIRF) imaging probe (CD-NIR-1) and evaluated its clearance and ability for IUI and IUD in animal models. CD-NIR-1 demonstrated high specificity and ultrarapid clearance by rat kidneys to the urinary bladder following intravenous administration of a single dose (25 nmol/kg of body weight), with 96% of the dose ultimately excreted at the first urination with no chemical modification. Furthermore, urine containing CD-NIR-1 in ureters showed strong NIRF, thereby enabling IUI and IUD via NIRF imaging. These results demonstrated the efficacy of CD-NIR-1 for clinical use.

Evaluating the Photodynamic Biocidal Activity and Investigating the Mechanism of Thiazolium Cyanine Dyes

In order to develop ideal photosensitizers for photodynamic therapy (PDT), a thiazolium group was introduced in cyanine dyes to possess the advantages of intense absorption in the visible region and anti-microbial activity. We evaluated the anti-bacterial activity of the three thiazolium cyanine dyes against Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria) in vitro. This is the first time that such kinds of cyanine dyes are applied in the photodynamic antibiotic area. Cyanines display excellent anti-bacterial activity to S. aureus and E. coli exposed to white light irradiation, and the corresponding light-induced biocidal efficacy of cyanines increased with irradiation time and concentration. At the same time, there was no observation of dark anti-bacterial abilities. Especially, cyanines show low cell cytotoxicity and excellent biocompatibility. These results suggest that thiazolium cyanine could work as a photosensitizer in PDT with great promise and broad applications for killing bacteria. Mechanistic studies suggest that the reactive oxygen species (ROS) is the vital factor for combating bacteria exposure to white light conditions, whereas it is not the only determining factor of the biocidal activity. The interaction of the cyanine to the cell membrane also plays a critical role in killing bacteria, which has exhibited a synergic effect of electrostatic and hydrophobic interactions. It influences the cell uptake and the membrane perturbation activity of the cyanines, which indirectly affects the biocidal activity.

Novel near-infrared fluorescent probe for live cell imaging

Near infrared (NIR) fluorescent probes play a crucial role in biological system imaging. A novel NIR fluorescent probe, IR787, was designed in the present study. Compared with indocyanine green (ICG), IR787 showed lower background fluorescent interference and higher fluorescence enhancement. Fluorescence intensities were detected by a Cary Eclipse fluorescence spectrophotometer. The interference of intracellular ions (Cu²⁺, Ca²⁺, Mg²⁺ and Zn²⁺) on the measurement was negligible, which indicated a good photostability of IR787. MTT assay demonstrated that cell viability of human lung adenocarcinoma epithelial cell line A549 was not significantly affected by the use of the IR787 probe compared with the ICG probe. This result suggested that the IR787 probe was safe for in vitro cell imaging. In vitro NIR optical imaging experiments further revealed cellular uptake and strong intracellular NIR fluorescence of the IR787 probe in A549 cells. The excitation wavelength was 787 nm for IR787. Compared with the previously reported NIR fluorescent probe ICG, the IR787 NIR fluorescent probe had improved prospects for intracellular imaging. IR787 may play a pivotal role in the understanding cell biology, pharmacology and disease diagnosis.

IR-783 Labeling of a Peptide Receptor for 'Turn-On' Fluorescence Based Sensing

In this study, we examine a means for developing near-IR fluorescent sensors through streamlined, site-specific coupling with peptide-based receptors. As the penultimate step of solid-phase synthesis of a peptide-based receptor, we show a simple means of labeling the N' terminus with the near IR fluorophore IR-783 to afford a viable fluorescent sensor after cleavage from the resin. The proof-of-concept probe utilized a biotin mimetic peptide sequence as the receptive moiety. Here we revealed a "turn-on" fluorescence enhancement upon binding of the biotin mimetic probe to its intended streptavidin target. Not all peptide-receptive moieties tested were able to generate such an enhancement upon target binding, and as such, the rationale for the observed fluorescence response properties is discussed.

Study on feasibility of determination of glucosamine content of fermentation process using a micro NIR spectrometer

N-acetyl-d-glucosamine (GlcNAc) is a microbial fermentation product, and NIR spectroscopy is an effective process analytical technology (PAT) tool in detecting the key quality attribute: the GlcNAc content. Meanwhile, the design of NIR spectrometers is under the trend of miniaturization, portability and low-cost nowadays. The aim of this study was to explore a portable micro NIR spectrometer with the fermentation process. First, FT-NIR spectrometer and Micro-NIR 1700 spectrometer were compared with simulated fermentation process solutions. The R_c², R_p², RMSECV and RMSEP of the optimal FT-NIR and Micro-NIR 1700 models were 0.999, 0.999, 3.226 g/L, 1.388 g/L and 0.999, 0.999, 1.821 g/L, 0.967 g/L. Passing-Bablok regression method and paired t-test results showed there were no significant differences between the two instruments. Then the Micro-NIR 1700 was selected for the practical fermentation process, 135 samples from 10 batches were collected. Spectral pretreatment methods and variables selection methods (BiPLS, FiPLS, MWPLS and CARS-PLS) for PLS modeling were discussed. The R_c², R_p², RMSECV and RMSEP of the optimal GlcNAc content PLS model of the practical fermentation process were 0.994, 0.995, 2.792 g/L and 1.946 g/L. The results have a positive reference for application of the Micro-NIR spectrometer. To some extent, it could provide theoretical supports in guiding the microbial fermentation or the further assessment of bioprocess.

A tumor-targeting probe based on a mitophagy process for live imaging

A pH sensitive probe was designed for mitochondria and autolysosomes monitoring in cell level and tumor targeting imaging.

A simple neridronate-based surface coating strategy for upconversion nanoparticles: highly colloidally stable 125I-radiolabeled NaYF4:Yb3+/Er3+@PEG nanoparticles for multimodal in vivo tissue imaging

In this report, monodisperse upconversion NaYF₄:Yb³⁺/Er³⁺ nanoparticles with superior optical properties were synthesized by the oleic acid-stabilized high-temperature co-precipitation of lanthanide chlorides in octadec-1-ene as a high-boiling organic solvent. To render the particles with biocompatibility and colloidal stability in bioanalytically relevant phosphate buffered saline (PBS), they were modified by using in-house synthesized poly(ethylene glycol)-neridronate (PEG-Ner), a bisphosponate. The NaYF₄:Yb³⁺/Er³⁺@PEG nanoparticles showed excellent long-term stability in PBS and/or albumin without any aggregation or morphology transformation. The in vitro cytotoxicity of the nanoparticles was evaluated using primary fibroblasts (HF) and a cell line derived from human cervical carcinoma (HeLa). The particles were subsequently modified by using Bolton-Hunter-hydroxybisphosphonate to enable radiolabeling with ¹²⁵I for single-photon emission computed tomography/computed tomography (SPECT/CT) bimodal imaging to monitor the biodistribution of the nanoparticles in non-tumor mice. The bimodal upconversion ¹²⁵I-radiolabeled NaYF₄:Yb³⁺/Er³⁺@PEG nanoparticles are prospective for near-infrared (NIR) photothermal/photodynamic and SPECT/CT cancer theranostics.

The photoprocess effects of an amino group located at different positions along the polymethine chain in indodicarbocyanine dyes

The amino group is a-ICT in the even position but is the ICT in the odd position.

Near-infrared indocyanine dye permits real-time characterization of both venous and lymphatic circulation

We investigated the optical properties of a near-infrared (NIR) fluorochrome, di-β-cyclodextrin-binding indocyanine derivative (TK-1), and its pharmacokinetic differences with indocyanine green (ICG). TK-1 was designed to have hydrophilic cyclodextrin molecules and, thus, for higher water solubility and smaller particle sizes than the plasma protein-bound ICG. We compared optical properties such as the absorption and fluorescence spectra, quantum yield, and photostability between both dyes in vitro. In addition, we subcutaneously injected a 1 mM solution of TK-1 or ICG into the hind footpad of rats and observed real-time NIR fluorescence intensities in their femoral veins and accompanying lymphatics at the exposed groin site to analyze the dye pharmacokinetics. These optical experiments demonstrated that TK-1 has high water solubility, a low self-aggregation tendency, and high optical and chemical stabilities. Our in vivo imaging showed that TK-1 was transported via peripheral venous flow and lymphatic flow, whereas ICG was drained only through lymphatics. The results of this study showed that lymphatic and venous transport can be differentially regulated and is most likely influenced primarily by particle size, and that TK-1 can enable real-time NIR fluorescence imaging of whole fluids and solute movement via both microvessels and lymphatics, which conventional ICG cannot achieve.

Review on near-infrared heptamethine cyanine dyes as theranostic agents for tumor imaging, targeting, and photodynamic therapy

A class of near-infrared fluorescence (NIRF) heptamethine cyanine dyes that are taken up and accumulated specifically in cancer cells without chemical conjugation have recently emerged as promising tools for tumor imaging and targeting. In addition to their fluorescence and nuclear imaging-based tumor-imaging properties, these dyes can be developed as drug carriers to safely deliver chemotherapy drugs to tumors. They can also be used as effective agents for photodynamic therapy with remarkable tumoricidal activity via photodependent cytotoxic activity. The preferential uptake of dyes into cancer but not normal cells is co-operatively mediated by the prevailing activation of a group of organic anion-transporting polypeptides on cancer cell membranes, as well as tumor hypoxia and increased mitochondrial membrane potential in cancer cells. Such mechanistic explorations have greatly advanced the current application and future development of NIRF dyes and their derivatives as anticancer theranostic agents. This review summarizes current knowledge and emerging advances in NIRF dyes, including molecular characterization, photophysical properties, multimodal development and uptake mechanisms, and their growing potential for preclinical and clinical use.

A Quick Responsive Fluorogenic pH Probe for Ovarian Tumor Imaging

A novel cell-permeable compound, CypH-1, that is non-fluorescent at neutral pH, but fluoresces under mildly acidic conditions with a near infrared maximum emission wavelength was designed for the detection of tumors in the clinical setting. The potential of CypH-1 in ovarian cancer imaging was demonstrated using a murine model. The intraperitoneally administered CypH-1 results in a robust fluorescence signal of discrete neoplastic lesions with millimeter range resolution within few hours. Moreover, fluorescence signal is strikingly enhanced at peripheral regions of tumors at the microscopic level suggesting a sharp physiological difference at the tumor/normal tissue interface. This robust acid-activated imaging agent is expected to have significant impact in broad surgical and diagnostic applications.

Multimeric Near IR-MR Contrast Agent for Multimodal In Vivo Imaging

Multiple imaging modalities are often required for in vivo imaging applications that require both high probe sensitivity and excellent spatial and temporal resolution. In particular, MR and optical imaging are an attractive combination that can be used to determine both molecular and anatomical information. Herein, we describe the synthesis and in vivo testing of two multimeric NIR-MR contrast agents that contain three Gd(III) chelates and an IR-783 dye moiety. One agent contains a PEG linker and the other a short alkyl linker. These agents label cells with extraordinary efficacy and can be detected in vivo using both imaging modalities. Biodistribution of the PEGylated agent shows observable fluorescence in xenograft MCF7 tumors and renal clearance by MR imaging.

Advances in using MRI probes and sensors for in vivo cell tracking as applied to regenerative medicine

The field of molecular and cellular imaging allows molecules and cells to be visualized in vivo non-invasively. It has uses not only as a research tool but in clinical settings as well, for example in monitoring cell-based regenerative therapies, in which cells are transplanted to replace degenerating or damaged tissues, or to restore a physiological function. The success of such cell-based therapies depends on several critical issues, including the route and accuracy of cell transplantation, the fate of cells after transplantation, and the interaction of engrafted cells with the host microenvironment. To assess these issues, it is necessary to monitor transplanted cells non-invasively in real-time. Magnetic resonance imaging (MRI) is a tool uniquely suited to this task, given its ability to image deep inside tissue with high temporal resolution and sensitivity. Extraordinary efforts have recently been made to improve cellular MRI as applied to regenerative medicine, by developing more advanced contrast agents for use as probes and sensors. These advances enable the non-invasive monitoring of cell fate and, more recently, that of the different cellular functions of living cells, such as their enzymatic activity and gene expression, as well as their time point of cell death. We present here a review of recent advancements in the development of these probes and sensors, and of their functioning, applications and limitations.

pH-responsive near-infrared nanoprobe imaging metastases by sensing acidic microenvironment

A pH responsive near-infrared fluorescence nanoprobe was developed and visualized pulmonary metastases in a mouse model with a volume as small as 0.5 mm³ by sensing the acidic tumor microenvironment.

Up-regulating blood brain barrier permeability of nanoparticles via multivalent effect

PURPOSE

To investigate the multivalent effect for up-regulating the intracerebral delivery of nanoparticles via receptor-mediated transcytosis.

METHODS

Nanoparticles labeled with near-infrared (NIR) fluorophore and different numbers of angiopep-2 peptides that specifically target low-density lipoprotein receptor-related protein (LRP) on the brain capillary endothelial cells were developed. Bio-distribution studies quantified the intracerebral uptakes of these nanoparticles at 2 and 24 h after intravenous injection. In vivo NIR fluorescence imaging, ex vivo autoradiographic imaging and 3D reconstructed NIR fluorescence imaging revealed the nanoparticle distribution pattern in brain. Fluorescence microscopic imaging identified the nanoparticle locations at the cellular level.

RESULTS

The multimetirc association between the angiopep-2 peptides labeled on the nanoparticle and the LRP receptors on the brain capillary endothelial cells significantly increased the intracerebral uptake of the nanoparticles. Nanoparticle Den-Angio4 labeled four angiopep-2 peptides achieved the highest BBB traverse efficacy. After penetrating the BBB, Den-Angio4 distributed heterogeneously and mainly located at hippocampus, striatum and cerebellum in the brains.

CONCLUSIONS

The multivalent effect significantly enhances the BBB permeability of nanoparticles. Den-Angio4 as a nanoparticle prototype provides a two order targeted strategy for diagnosis or treatment of central nerver system diseases by first traversing the BBB via receptor-mediated endocytosis and secondly targeting the leisions with high receptor expression level.

Targeted non-covalent self-assembled nanoparticles based on human serum albumin

Human serum albumin (HSA) is a biological nanocarrier that forms non-covalent complexes with a number of synthetic and biomolecules. Previously we demonstrated radiolabeled HSA-based nanoparticles can form non-covalent complexes with fluorescent cyanine dyes yielding imaging agents for surgical guidance towards tumor draining lymph nodes. Here the self-assembly approach enabled rapid clinical translation. Based on this experience we reasoned it would be interesting to expand this non-covalent technology to a targeted approach. Therefore, the ability of HSA to form non-covalent self-assembled complexes with peptides via near-infrared (NIR) cyanine dyes was explored. Föster resonance energy transfer (FRET) quenching interactions between HSA-Cy5 and the non-covalently bound fluorescent molecules indocyanine green (ICG), IR783-CO(2)H and three IR783-labeled targeting peptides were used to monitor complex assembly and disassembly. The host-guest interactions between HSA and IR783-labeled peptides enabled the formation of (bio)nanoparticles that are coated with peptides, which may target α(v)β(3)-integrins, the chemokine receptor 4 (CXCR4), or somatostatin receptors. The potential of CXCR4-targeted (bio)nanoparticles in sentinel lymph node procedures is demonstrated in vivo. By non-covalently binding NIR-dye labeled peptides to an already clinically approved HSA-scaffold, we have readily formed targeted bionanoparticles.

NEAR-INFRARED DYES: Probe Development and Applications in Optical Molecular Imaging

The recent emergence of optical imaging has brought forth a unique challenge for chemists: development of new biocompatible dyes that fluoresce in the near-infrared (NIR) region for optimal use in biomedical applications. This review describes the synthesis of NIR dyes and the design of probes capable of noninvasively imaging molecular events in small animal models.

Continuous symmetry breaking induced by ion pairing effect in heptamethine cyanine dyes: beyond the cyanine limit

The association of heptamethine cyanine cation 1(+) with various counterions A (A = Br(-), I(-), PF(6)(-), SbF(6)(-), B(C(6)F(5))(4)(-), TRISPHAT) was realized. The six different ion pairs have been characterized by X-ray diffraction, and their absorption properties were studied in polar (DCM) and apolar (toluene) solvents. A small, hard anion (Br(-)) is able to strongly polarize the polymethine chain, resulting in the stabilization of an asymmetric dipolar-like structure in the crystal and in nondissociating solvents. On the contrary, in more polar solvents or when it is associated with a bulky soft anion (TRISPHAT or B(C(6)F(5))(4)(-)), the same cyanine dye adopts preferentially the ideal polymethine state. The solid-state and solution absorption properties of heptamethine dyes are therefore strongly correlated to the nature of the counterion.

Differential-absorption photoacoustic imaging

We present differential-absorption photoacoustic imaging, which detects the difference between transient and ground-state absorption, for contrast enhancement based on suppressing undesired objects. Two tubes were imaged. One contains a Pt(II) octaethylporphine (PtOEP) dye solution and serves as an object of interest, while the other contains an IR-783 (from Sigma-Aldrich) dye solution and serves as an object to suppress. Although the IR-783 tube dominates the conventional photoacoustic image, it is suppressed by 43 dB and consequently significantly overwhelmed by the PtOEP tube in the differential-absorption photoacoustic image. Imaging depth in this mode is also discussed.

Design, synthesis, and structure-affinity relationships of novel series of sialosides as CD22-specific inhibitors

Sialosides incorporating substituted amides or amines at 9-position of sialic acid moiety have been synthesized and evaluated as CD22 inhibitors. Several derivatives exhibited inhibitory potency in sub- to low micromolar range (e. g., 8o, 9d, 9g, and 9k showed IC 50 values 0.40, 0.47, 0.24, and 0.23 microM, respectively, for hCD22, while 8p, 8q, and 9f, showed IC 50 values 1.70, 2.90, and 4.10 microM, respectively, for mCD22). The most significant result was the strongly enhanced affinity of 9g and 9k containing 9-(2' or 4'-hydroxy-4-biphenyl) methylamino substituents (600-fold more potent for hCD22 than the corresponding 9-hydroxy derivative; 7a). Molecular modeling study was carried out to get some insights into the molecular basis of CD22 inhibition. To the best of our knowledge, this is the first systematic structure-affinity relationship study on inhibition of CD22.

Microwave-assisted synthesis of near-infrared fluorescent sphingosine derivatives

Microwave-assisted synthesis of near-infrared fluorescent sphingosine derivatives is described, and the utility of the probes demonstrated by co-localization studies with visible wavelength fluorescent sphingosine derivatives.

Glucosamine-bound near-infrared fluorescent probes with lysosomal specificity for breast tumor imaging

Noninvasive imaging of lysosomes will be useful 1) to elucidate the role of lysosomal parameters in cancer, 2) to diagnose malignant lesions, and 3) to evaluate future lysosome-targeted anticancer therapies. Lysosome-specific labeling of glucosamine-bound near-infrared (NIR) fluorescent probes, IR-1 and IR-2, but not control probe IR-15 without the glucosamine moiety, was observed by fluorescence microscopy in human breast epithelial cell lines. Lysosome labeling and tumor specificity of these NIR probes were investigated by dynamic optical imaging and immunofluorescence staining in human breast tumor xenografts. IR-1 and IR-2 demonstrated faster lysosome labeling rates in highly aggressive MDA-MB-231 and MDA-MB-435 cells compared with less aggressive MCF-7 and nontumorigenic MCF-12A cells. IR-1 and IR-2, but not IR-15, accumulated in human MDA-MB-231, MDA-MB-435, and MCF-7 breast tumor xenografts in vivo. IR-2 demonstrated the highest maximum fluorescence and tumor/normal tissue ratios in all tumor models. Specific lysosome labeling from IR-2 in vivo was validated by colocalization of the NIR fluorescence with CD63 immunofluorescence in tumor sections. IR-1 and IR-2 demonstrated high lysosome-labeling ability and breast tumor-targeting specificity in vitro and in vivo. They are promising for diagnosing malignant lesions and may provide a means for evaluating and monitoring future lysosome-targeted anticancer therapies.

Novel near-infrared fluorescent integrin-targeted DFO analogue

Desferrioxamine (DFO), a siderophore initially isolated from Streptomyces pilosus, possesses extraordinary metal binding properties with wide biomedical applications that include chelation therapy, nuclear imaging, and antiproliferation. In this work, we prepared a novel multifunctional agent consisting of (i) a near-infrared (NIR) fluorescent probe-cypate; (ii) an integrin alpha vbeta3 receptor (ABIR)-avid cyclic RGD peptide, and (iii) a DFO moiety, DFO-cypate-cyclo[RGDfK(approximately)] (1, with approximately representing the cypate conjugation site at the side chain of lysine; f is d-phenylalanine). Compound 1 and two control compounds, cypate-cyclo[RGDfK(approximately)] ( 2) and cypate-DFO ( 3), were synthesized by modular assembly of the corresponding protected RGD peptide cyclo[R(Pbf)GD(OBut)fK] and DFO on the dicarboxylic acid-containing cypate scaffold in solution. The three compounds exhibited similar UV-vis and emission spectral properties. Metal binding analysis shows that DFO as well as 1 and 3 exhibited relatively high binding affinity with Fe(III), Al(III), and Ga(III). In contrast to Ga(III), the binding of Fe to 1 and 3 quenched the fluorescence emission of cypate significantly, suggesting an efficient metal-mediated approach to perturb the spectral properties of NIR fluorescent carbocyanine probes. In vitro, 1 showed a high ABIR binding affinity (10 (-7) M) comparable to that of 2 and the reference peptide cyclo(RGDfV), indicating that both DFO and cypate motifs did not interfere significantly with the molecular recognition of the cyclic RGD motif with ABIR. Fluorescence microscopy showed that internalization of 1 and 2 in ABIR-positive A549 cells at 1 h postincubation was higher than 3 and cypate alone, demonstrating that incorporating ABIR-targeting RGD motif could improve cellular internalization of DFO analogues. The ensemble of these findings demonstrate the use of multifunctional NIR fluorescent ABIR-targeting DFO analogues to modulate the spectral properties of the NIR fluorescent probe by the chelating properties of DFO and visualize intracellular delivery of DFO by receptor-specific peptides. These features provide a strategy to explore the potential of 1 in tumor imaging and treatment as well as some molecular recognition processes mediated by metal ions.