Fluorescent Recognition Of β-hydroxybutyrate On Rare Earth Complexes

Ketosis has generally been portrayed as an unfavorable pathological state associated with diabetes mellitus. Ketone bodies are normally produced from fat stores as an alternative to glucose during periods of sustained hypoglycemia, which are normally in a proportion of 78% 3-hydroxybutyrate (β-HB),20% acetoacetic acid and 2% acetone. Too much ketones accumulation in the blood can lead to diabetic ketoacidosis (DKA), a medical emergency, which in particular remains an important cause of morbidity and mortality in diabetic populations around the world. When DKA occurs, high level of ketones may get into the brain tissue via the blood circulation and acute brain injury, which may lead to coma even death. As the incidence of diabetes is increasing worldwide, so does the morbidity of DKA. Where medical services are less well developed, the risk of dying from DKA is greater. The prevention of DKA is an issue of national and international consequences.The total concentration of ketone body was mainly affected by that of β-HB. Since β-HB is the major component of serum ketone body, rapid determination of the concentration of β-HB is useful for concluding the level of ketone bodies ulteriorly. The total contents of serum β-HB can help doctors to diagnose diabetes at early stage and to monitor the course of DKA. The American diabetes association advises that blood ketone testing methods that quantify P-HB will be desirable for the diagnosing and monitoring ketoacidosis for diabetic patient management.Rare earth complexes possess many desirable photophysical properties, such as long wavelength emissions (within the visible and the near-infrared (NIR) regions), sharp line-like emission bands and long-lived excited states ([μs-ms-time frame), allowing them to be easily distinguished from shorter-lived (ns-based) autoluminescence. This greatly improves the signal-to-noise ratio of such time-delayed sensors/probes, making them desirable alternatives to fluorescence based systems. The development and use of specific analyte targeting lanthanide based luminescent sensors/probes has recently emerged for various biological applications. Further the application of the hyper-sensitive transition of Eu3+ or Tb3+ has made them suitable for a luminescent sensor.It is well known that the f-f transition of rare earth is forbidden. However, an appropriate antenna can elevate lanthanide ion into an excited state and cause lanthanide emission to occur. Upon addition of the target molecule, a change in lanthanide emission will occur.When effective ligand-to-Ln(III) energy transfer proceeds, the Eu atom located in an asymmetrical coordination environment will emit in the red region of the spectrum at 616 nm ascribed to the 5D0â†'7F2 transition and Tb will emit in the green region of the spectrum at 545 nm ascribed to the 5D4â†' 7F5 transition. These transitions are very sensitive to the change of the symmetry of the coordination sphere around Ln(III) ion and has been named as hypersensitive transition. This property of rare earth complexes can be used to identify the target substrate.The synthesis of 3 lanthanide complexes based β-HB sensors is presented. The experimental results of photophysical properties to test the β-HB sensor are reported as well as the preparation of the sensor. The complexes in methanol-water emitted poorly in the absence of P-HB. Maybe, the vibration of O-H of water molecules quenches the luminescence. Upon addition of 3-HB, which replaced the solvent molecules and coordinated with the terbium(III) atom, gradual enhancements were observed. The detailed work is listed as following:1. The synthesis of Tb complex Cl based on benzoic acid (L+H) is presented in chapter 2. Cl emitted weak luminescence in the green region of the spectrum, which indicated that the ligand-to-Ln(III) energy transfer proceeded. The high-energy vibration of hydroxyl group coordinated with Tb3+may be responsible for the weak emission. Upon addition of β-HB, an increment of the luminescent intensity at 545 nm assigned to 5D4â†'7Fs transition of Tb3+ was observed. A nonlinear least-squares curve fitting of the plot with (Ia-If)/(Ib-If) versus [β-HB] indicated an adduct of 1:1 Cl-β-HB stoichiometry was formed, with K of 9.3×105 M-1. The ratio of the luminescence intensity at 545 to 488 nm can be used to reveal the change in the symmetry of the coordination sphere around Tb(III) ion. Low ratio shows a good symmetry. With the relative luminescence intensity ratio of 545 nm to 485 nm as Y-axis, except NO3- and Cl-, the addition of the other anions induced the ratio decreasing. While only β-HB caused a more significant enhancement. The luminescent titration revealed high selectivity for β-HB.2. In chapter 3, the synthesis of Tb complex C2 based on 2-(methoxycarbonyl)benzoate (MB), the alcoholysis product of o-phthalic anhydride in methanol, was presented and gave a weak green emission with a excitation at 235 nm in methanol-water (V:V,5:1), confirming that the energy transfer from the ligand-centered levels to the metal-centered levels took place. The vibration of O-H of water molecules quenches the luminescence. With the incremental addition of β-HB, the characteristic emission of Tb3+ 5D4-7F5 transition at 545 nm was enhanced gradually. A nonlinear least-squares curve fitting of the plot with (Ia-If)/(Ib-If) versus [p-HB] indicated a 1:1 binding model between the Tb complex and β-HB. The apparent binding constant (K) was obtained as 7.25×105 M-1. Other common anions including Cl-,NO3-,CO32-,PO43-, HPO42-, H2PO4-, C2O42-, P2O74-, SO42", malate, lacticate and citrate can also substitute solvent molecules and coordinate with Tb(III). However, the addition of these anions can cause good symmetry around Tb(III). As a result, an incremental emission of the hypersensitive transition can not occur. The response showed high selectivity for β-HB, which enabled C2 to be a potential real-time luminescent sensor for β-HB.3. A Eu3+ complex C3 based on 1,10-phenanthroline-2-carboxylic was prepared, and emitted a characteristic red luminescence at 618 nm with a excitation at 280nm in methanol-water (V-.V,6:1), which indicated that the energy transfer from the ligand-centered levels to the metal-centered levels took place. The luminescent intensity at 618 nm assigned to 5D0-7F2 transition of Eu3+was larger than that at 592 nm, confirming that the Eu atom lies in a noncentrosymmetric coordination environment. A nonlinear least-squares curve fitting of the plot with (Ia-If)/(Ib-If) versus [β-HB] indicated a 1:1 binding model between the Eu complex and β-HB. The apparent binding constant (K) was obtained as 1.44×104 M-1. Addition of other common anions, such as PO43-, H2PO4-,HPO42-,P2O74-, C2O42-, CO32-,induced fluorescence quenching. Perhaps these oxygen-containing ions coordinated with Eu induced Eu-N bond cleavage, which weakened the energy transfer "antenna effect" from 2-carboxy-1,10-phenanthroline to Eu3+. CH3COO-, NO3-, Cl-induced no difference. Only β-HB caused a more significant fluorescent enhancement. The response showed good selectivity for β-HB compared with other common anions, which enabled C3 to be a potential real-time luminescent sensor for β-HB.