Thermodynamics of the conversion of aqueous glucose to fructose

The thermodynamics of the conversion of aqueous glucose to fructose has been investigated using both heat conduction microcalorimetry and high pressure liquid chromatography (HPLC). The reaction was carried out in both aqueous Tris/HCl buffer and in aqueous phosphate buffer in the pH range 7–8 using the enzyme glucose isomerase and the cofactors CoCl₂ and MgSO₄. The temperature range over which this reaction was investigated was 298.15–358.15 K. We have found that the enthalpy of reaction is independent of pH over the range investigated. A combined analysis of both the HPLC and microcalorimetric data leads to the following results at 298 15 K:ΔG° = 349 ± 53 J mol^-1, ΔH° = 2.78 ± 0.20 kJ mol^-1, and ΔC _p ^° = 76 ± 30 J mol^-1 K^-1. The stated uncertainties are based upon an analysis of both the random and systematic errors inherent in the measurements. Comparisons are made with literature data. The percent conversion of glucose to fructose has been calculated for the temperature range 300–373.15 K.     

Influence of the pH Value on the Hydrothermal Degradation of Fructose

The hydrothermal treatment of sugars features a promising technology for the production of fine and platform chemicals from renewable resources. In this work the hydrothermal decomposition of fructose was studied in a buffered medium at a pH range between 2.2 and 8.0. It is demonstrated that at lower pH values mainly 5-hydroxymethylfurfural (HMF), levulinic acid and humin are generated, while lactic acid and acetic acid are produced at higher pH values. The work shows that the use of moderate acidic conditions may have advantages for the hydrothermal HMF production over the use of strongly acidic conditions, as especially the degradation into levulinic acid is suppressed. Besides, this study deals with a rather complex reaction network, hence limitations and need for adaption of the kinetic model are discussed.     

离子色谱脉冲安培法测定蜂蜜中的葡萄糖、果糖、蔗糖

利用离子色谱脉冲安培检测器对蜂蜜中葡萄糖、果糖、蔗糖的测定方法进行了研究。采用CARBOPAC^TM PAl分离柱和脉冲安培检测器,对淋洗分离条件进行了实验,选择50mmol/L NaOH作淋洗液,可使蜂蜜中的葡萄糖、果糖、蔗糖很好地分离。检出限分别为：葡萄糖2μg/kg,果糖2μg/kg,蔗糖5μg/kg。加标回收率为90％－108％。该方法只需简单的前处理、无基体干扰,分离效果好,测定准确率高,适用于蜂蜜中葡萄糖、果糖、蔗糖的测定。     

Macrocycle-Derived Functional Xanthenes and Progress Towards Concurrent Detection of Glucose and Fructose

The detection of saccharides in biological media is of great current importance for the monitoring of disease states. We have previously reported that solutions of boronic acid-functionalized macrocycles form acyclic oligomeric materials in situ. The oligomers contain fluorescent xanthene moieties. Current efforts are aimed at modulating the spectroscopic responses of these materials for the analysis of specific sugars. We describe conditions whereby the xanthene boronic acids exhibit high colorimetric fructose selectivity. In contrast, at physiological levels selective glucose monitoring can be achieved via fluorescence. Additionally, we describe a method which exhibits promise for detecting both glucose and fructose at dual wavelengths in the UV-Vis region. Mechanistic rationale for each of these findings is presented.     

Fructose-selective calorimetric biosensor in flow injection analysis

A highly selective, interference free biosensor for the measurement of fructose in real syrup samples was developed. The assay is based on the phosphorylation of d(−)fructose to fructose-6-phosphate by hexokinase and subsequent conversion of fructose-6-phosphate to fructose-1,6-biphosphate by fructose-6-phosphate-kinase. The heat liberated in the second reaction is monitored using an enzyme thermistor. The major advantages of this biosensor are rapid and selective measurement of fructose without the need to eliminate glucose and inexpensive FIA-based, mediator-free calorimetric measurement suitable for regular fructose analysis. This method was optimised for parameters, such as pH, ionic strength, interference, operational stability and shelf life. Good and reproducible linearity (0.5-6.0 mM) with a detection limit of 0.12 mM was obtained. Fructose determination in commercial syrup samples and spiked samples confirmed the reliability of this set-up and technique. The biosensor gave reproducible results with good overall stability for continuous measurements over a period of three months besides a useful shelf life of six months. The method could be used for routine fructose monitoring in food samples.     

d‐Fructose‐Decorated Poly(ethylene imine) for Human Breast Cancer Cell Targeting

The high affinity of GLUT5 transporter for d ‐fructose in breast cancer cells has been discussed intensely. In this contribution, high molar mass linear poly(ethylene imine) (LPEI) is functionalized with d ‐fructose moieties to combine the selectivity for the GLUT5 transporter with the delivery potential of PEI for genetic material. The four‐step synthesis of a thiol‐group bearing d ‐fructose enables the decoration of a cationic polymer backbone with d ‐fructose via thiol‐ene photoaddition. The functionalization of LPEI is confirmed by 2D NMR techniques, elemental analysis, and size exclusion chromatography. Importantly, a d ‐fructose decoration of 16% renders the polymers water‐soluble and eliminates the cytotoxicity of PEI in noncancer L929 cells, accompanied by a reduced unspecific cellular uptake of the genetic material. In contrast, the cytotoxicity as well as the cell specific uptake is increased for triple negative MDA‐MB‐231 breast cancer cells. Therefore, the introduction of d ‐fructose shows superior potential for cell targeting, which can be assumed to be GLUT5 dependent.

     

d‐Fructose Modification Enhanced Internalization of Mixed Micelles in Breast Cancer Cells via GLUT5 Transporters

d ‐Fructose modified poly(ε‐caprolactone)‐polyethylene glycol (PCL‐PEG‐Fru) diblock amphiphile is synthesized via Cu(I)‐catalyzed click chemistry, which self‐assembles with D‐α‐tocopheryl polyethylene glycol 1000 succinate (TPGS) into PCL‐PEG‐Fru/TPGS mixed micelles (PPF MM). It has been proven that glucose transporter (GLUT)5 is overexpressed in MCF‐7 cells other than L929 cells. In this study, PPF MM exhibit a significantly higher uptake efficiency than fructose‐free PCL‐PEG‐N₃/TPGS mixed micelles in both 2D MCF‐7 cells and 3D tumor spheroids. Also, the presence of free d ‐fructose competitively inhibits the internalization of PPF MM in MCF‐7 cells other than L929 cells. PPF MM show selective tumor accumulation in MCF‐7 breast tumor bearing mice xenografts. Taken together, PPF MM represent a promising nanoscale carrier system to achieve GLUT5‐mediated cell specific delivery in cancer therapy.

     

Minimum MD simulation length required to achieve reliable results in free energy perturbation calculations: Case study of relative binding free energies of fructose‐1,6‐bisphosphatase inhibitors

In an attempt to establish the criteria for the length of simulation to achieve the desired convergence of free energy calculations, two studies were carried out on chosen complexes of FBPase‐AMP mimics. Calculations were performed for varied length of simulations and for different starting configurations using both conventional‐ and QM/MM‐FEP methods. The results demonstrate that for small perturbations, 1248 ps simulation time could be regarded a reasonable yardstick to achieve convergence of the results. As the simulation time is extended, the errors associated with free energy calculations also gradually tapers off. Moreover, when starting the simulation from different initial configurations of the systems, the results are not changed significantly, when performed for 1248 ps. This study carried on FBPase‐AMP mimics corroborates well with our previous successful demonstration of requirement of simulation time for solvation studies, both by conventional and ab initio FEP. The establishment of aforementioned criteria of simulation length serves a useful benchmark in drug design efforts using FEP methodologies, to draw a meaningful and unequivocal conclusion. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Spherical and Worm‐Like Micelles from Fructose‐Functionalized Polyether Block Copolymers

This paper presents the synthesis and characterization of d ‐fructose modified poly(ethylene glycol) (Fru‐PEG) and fructose modified poly(ethylene glycol)‐block‐poly(ethyl hexyl glycidyl ether) (Fru‐PEG‐b‐PEHG) that are both prepared by initiation with isopropyliden protected fructose, followed by deprotection of the sugar. The block copolymers are self‐assembled into micelles, and are subsequently characterized by cryo‐TEM and dynamic light scattering. The fluorescent dye Nile red is encapsulated as a model hydrophobic compound and fluorescent marker to perform initial uptake tests with breast cancer cells. The uptake of sugar and nonsugar decorated micelles is compared.