Inhibition of dextransucrase by α-D-Glucose derivatives

alpha-D-Glucopyranosyl fluoride was modified at positions 2, 3, or 5 and these analogs were tested as substrates and inhibitors of dextransucrase from Leuconostoc mesenteroides B-512F. The analogs studied were 2-deoxy-2-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-thio-alpha-D-glucopyranosyl fluoride, and 5-thio-alpha-D-glucopyranosyl fluoride. Kinetic constants for alpha-D-glucopyranosyl fluoride were also determined. None of the alpha-D-glucopyranosyl fluorides were accepted as substrates for dextransucrase. 2-Deoxy-2-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-fgluoro-alpha-D-glucopyranosyl fluoride, and 3-deoxy-3-thio-alpha-D-glucopyranosyl fluoride were competitive inhibitors with Ki values of 63, 93, and 53 mM, respectively. The Km for alpha-D-glucopyranosyl fluoride was found to be 26 mM. The data indicate that the hydroxyl groups at C2 and C3 are important for proper binding of alpha-D-glucopyranosyl fluoride for the active site of dextransucrase and that the C3-hydroxyl probably acts as a hydrogen-bond donor.     

A New Method for the Preparation of Sulphuryl Chloro Fluoride

It has been observed that a suspension of sodium fluoride in boiling acetonitrile could be used for the preparation of fluorine compounds such as silicon tetrafluoride [1], thiophosphoryl fluoride [2], sulphur tetrafluoride [3,4], and fluorocyclophosphazenes [5]. This method, when adopted for the fluorination of sulphuryl chloride [6], it is observed that a mixture of sulphuryl fluoride and sulphuryl chloro fluoride is obtained. On the other hand, when lead fluoride is substituted for sodium fluoride, pure sulphuryl chloro fluoride is evolved. Based on this observation, a new method has been standardised for the preparation of a pure sample of sulphuryl chlorofluoride by fluorinating sulphuryl chloride by lead fluoride in acetonitrile medium.     

大气中氟污染对牡丹影响的调查分析

对大气氟污染与观赏植物牡丹叶片中的含氟量之间的关系进行了分析。结果表明：(1)一定时间内牡丹叶片的吸氟量和积累量成正相关。(2)牡丹叶片中的含氟量与测定点距污染源的距离呈负相关。(3)牡丹叶尖枯病是因大气氟污染所致，并非病理原因。     

Adsorption of fluoride ions onto carbonaceous materials

The characteristics of fluoride ion adsorption onto carbonaceous materials were derived as adsorption isotherms at different temperatures and in different pH solutions. The fluoride ion was adsorbed into pores in carbonaceous materials produced from wood; the larger the specific surface area, the more fluoride ions adsorbed. Bone char was the most effective adsorbent. The composition of bone char includes calcium phosphate, calcium carbonate, and so on. This suggests that the phosphate ion in bone char was exchanged with a fluoride ion. Moreover, the mechanism of fluoride ion adsorption onto bone char is clearly chemical in nature because the amount of fluoride ion adsorbed onto bone char increased with increasing temperature and decreasing pH. The amount of fluoride ion adsorbed onto bone char was also shown to depend on the concentration of sodium chloride in solution because of the "salting-out" effect. The adsorption of fluoride ion onto bone char is endothermic. Bone char can be utilized to remove fluoride ions from drinking water.     

氟-铁恒电位配位滴定法测定铁离子研究

以氟离子溶液作滴定剂,氟离子选择性电极作指示电极,在pH=1.5的条件下,对恒电位配位滴定法测定铁离子进行了研究。对pH=1.5的条件下使用氟离子选择性电极的可行性,氟-铁的反应速率及电极的响应速率进行了讨论。     

Determination of submicromolar concentrations of fluoride in biological samples

The fluorescence of a Morin-thorium complex provides a more sensitive fluoride reagent than has been previously used. It has immediate stability and a linear response to fluoride up to 50% reduction in fluorescence. The values for serum fluoride, as measured with this reagent after diffusion at room temperature, agree with those obtained with the fluoride electrode and with those predicted by the renal clearance of radioactive fluoride. The relative standard deviation when measuring 10(-6)M fluoride in 2 ml of serum is +/-10%.     

竹炭对饮用水中氟离子的吸附条件研究

研究了竹炭对饮用水中氟离子的吸附能力以及pH值、投料量、吸附作用时间、再生方法、再生效果等因素对除氟效果的影响。结果发现，竹炭对氟具有较好的吸附效果，是较为理想的饮水除氟材料。     

Sintering of kaolinite with ammonium fluoride

The present work represents a study of the influence of ammonium fluoride on the thermal behaviour of kaolinite by using a derivatograph. The sintering of kaolinite with ammonium fluoride was found to be complicated. Different products of sintering are obtained, depending on the temperature and the amount of ammonium fluoride. They were identified microscopically and by using a Siemens Crystalloflex diffratometer. These include an ammonium aluminium fluoride complex, cryptohalite, aluminium fluoride, mullite, topaz and corundum. The DTA curves (using kaolinite and ammonium fluoride mixes of ratio 1:1) indicate the formation of the ammonium aluminum fluoride complex and cryptohalite at 120–280°C and the appearance of aluminium fluoride, topaz and mullite at 640°C. The intensive formation of topaz takes place at 750°C and its subsequent dissociation at 940°C with corundum formation. The very small endothermic peak at 1010°C represents the formation of mullite. In experiments using mixes of kaolinite—ammonium fluoride in the ratios 1:1 and 1:1.3 the end-product of sintering consists of corundum and mullite. When using mixes of the ratio 1:1.7, aluminium fluoride constitutes the main composition of the end-product.     

The effect of hydrolysed aluminium species in fluoride ion determinations

The limited ability of added ligands to mask the interference of Al(III) in fluoride determination by means of ion-selective electrode measurements has been re-examined, and an explanation based on competing equilibria developed. When the Al(III) level exceeds the fluoride content, the excess of A1(III) forms colloidal hydrous oxide particles in the pH range 4-9, and this solid strongly sorbs fluoride. Under these conditions, masking ligands have to promote both decomposition of AlF(x), soluble complexes and release of sorbed fluoride by substrate dissolution. The latter is a slow process, particularly with an "aged" gel, and long equilibration periods can be required for total fluoride release. Ion-chromatography studies have shown that the amount of fluoride lost through sorption on the hydrous oxide particles (isolated during the membrane filtration/degassing step) can be quite high. By analogy, preliminary phase separation of natural water samples must also separate sorbed fluoride and soluble fluoride complexes. In the presence of A1(III), accurate analysis for fluoride requires removal of the aluminium, or isolation of fluoride from the matrix, or very careful pretesting of masking efficiencies.     

Elimination of fluoride ions in water for human consumption using hydroxyapatite as an adsorbent

In this work, a synthetic hydroxyapatite, Bio-gel HTP, marketed by BIO-RAD®, has been studied in order to propose a method to remove the excess fluoride present in drinking water. The removal of fluoride ions by this adsorbent has been studied as a function of solution pH, and fluoride ion concentration. Experiments of fluoride ions sorption have been carried out with the use of ¹⁸F radiotracer in solutions of NaF at several concentrations with an ion selective electrode used for fluoride analysis. The adsorption isotherms show that the best fluoride adsorption on hydroxyapatite occurs at a pH range of 7.0–7.5. At this pH value the solid presents an important capacity of subtraction of fluoride, of around of 100 mmol/100 g.     

Buffers for fluoride electrode calibration in the low concentration range

Thorium-buffered fluoride standards for calibration of fluoride electrodes at low fluoride concentration are described. Fluoride electrodes give Nernstian response down to very low fluoride levels, but the practical limit is set at about pF 6 by contamination from distilled water, reagents etc.     

Interaction between organic molecules and electrogenerated nickel fluoride films: the choice of organic reactants for electrochemical perfluorination

The interactions of organic molecules such as acetonitrile, propylene carbonate, and sulfolane on the electrogenerated nickel fluoride films were investigated using cyclic voltammetry and scanning electron microscopy. The effect of water, alkali metal fluorides, fluoride content, and acidity are also reported. Based on these studies, the potential effect of these factors on electrochemical perfluorination processes are projected. Water and alkali metal fluorides would enhance the dissolution of nickel fluoride film. Organic molecules like acetonitrile dissolve nickel fluoride film, while propylene carbonate forms thick polymeric layers on nickel surface. Higher acidity and fluoride ion content enhance the stability of a thin, catalytically active nickel fluoride film. Organic reactants like sulfolane form a composite film with nickel fluoride and, thus, enhance the long-term stability and electrocatalytic activity.     

Highly selective optical fluoride ion sensor with submicromolar detection limit based on aluminum(III) octaethylporphyrin in thin polymeric film

A highly selective, sensitive, and reversible fluoride optical sensing film based on aluminum(III)octaethylporphyrin as a fluoride ionophore and a lipophilic pH indicator as the optical transducer is described. The fluoride optical sensing films exhibit a submicromolar detection limit and high discrimination for fluoride over several lipophilic anions such as nitrate, perchlorate, and thiocyanate.     

The determination of microgram quantities of fluoride : The use of the aluminium-haematoxylin complex

This paper describes a method for the spectrophotometric determination of fluoride. The fluoride is separated from interfering ions by the standard method of distillation as hydrofluosilicic acid. The fluoride in this distillate is determined by its destruction of the aluminium-haematoxylin complex; the amount of complex destroyed which is directly proportional to the concentration of fluoride is measured spectrophotometrically using radiation of 5700 A. The method will detect down to 0.05 p.p.m. of fluoride on a 10 gram sample with precision of rather better than ± 10% with larger amounts of fluoride. references p. 368.     

Composition Profiles of Dental Enamel Studied by X-Ray Photoelectron Spectroscopy (ESCA)

Abstract

The surfaces of both normal and fluoride treated human dental enamel were examined with x-ray photoelectron spectroscopy (ESCA). Using argon-ion etching to remove thin layers of enamel, subsurface layers were also analyzed. The resulting composition-depth profile showed that stannous fluoride produced a subsurface layer containing both tin and fluoride whereas fluorine was absent from the surface layer. Acid fluoride treatments, however, converted the surface to calcium fluoride which steadily decreased in concentration with depth.     

Effects of airborne fluoride on soil and vegetation

The study was initiated by the sudden uncontrolled release of airborne fluorides in 2005 into the environment from aluminium smelter factory that caused damage of vegetation. Samples of corn leaves and corn male flower heads with visible symptoms of fluoride intoxication had been collected in autumn 2005. Increased contents of total fluoride, which exceeded the maximum allowable content of fluorine in feeding stuffs, including meadow grass, were detected. During continuation of the study some commercially available herbal teas and plants used for preparing herbal teas infusions, collected in the field in 2010, were investigated to investigate possible uptake of fluoride from the soil. Nettle (Urtica dioica) has been found to be a promising passive bioindicator for monitoring phytotoxic effects of fluoride in the soil on the vegetation. Good correlation between labile free fluoride in the soil and total fluoride in the nettle has been found, while total fluoride in the soil, soil pH and the dominant wind direction were also proven as important factors influencing the uptake of fluoride by the nettle.     

The acidimetric estimation of fluoride. A comparison of the glass with the lanthanum fluoride electrode

A rapid potentiometric titration using cerium (III) chloride as titrant with a glass electrode indicator system is proposed for fluoride estimations. The alkali fluoride (0.002-0.02 M) initially adjusted to a pH of 6.3 ± 0.05 is titrated continuously. The equivalence point is measured directly from the recorder chart as the mean of two well defined points. Calibrations are carried out with fluoride solutions of about the same salt content, or by repeating the titration on another aliquot with a standard addition of fluoride. This procedure gives results as precise as those obtained previously with the fluoride electrode without elaborate computations. A direct comparison of glass and fluoride electrode systems with different titrants is provided.     

NH4F对化学镀镍液的作用机理及镀层性能的影响

氟元素是周期表中最活泼的非金属元素,有着最强的电负性,氟化物有着特殊的化学性能。关于氟化物在化学镀镍磷工艺中的应用已有报道,在镁基体上化学镀的前处理过程中,常用氢氟酸或氟化氢铵来进行活化处理;硅片表面上的化学镀也通常用HF与HNO3或HCl的混酸来活化,使硅片表面产生Si-H键。另外,如果在化学镀液中添加少量的氟化钠,则起到加速的作用[1]。对于氟化物在化学镀镍磷工艺中的报道仅限于此,未见有关氟化物在化学镀中其它作用的研究。鉴于此,本工作以氟化铵为研究对象,对其在弱碱性的条件下对化学镀液的缓冲能力、沉积速度以及所得镀层性能的影响进行了研究。     

A method for the simultaneous detection of hydrogen fluoride and fluorine

A relatively simple and rapid method for detecting hydrogen fluoride and elemental fluorine is described. A solution containing sodium bicarbonate and potassium bromide is treated with the gas. Hydrogen fluoride immediately liberates carbon dioxide from the bicarbonate; elemental fluorine immediately colours the solution and then causes the evolution of oxygen, hydrogen peroxide and hydrogen fluoride. A mixture of fluorine and hydrogen fluoride simultaneously colours the solution and evolves carbon dioxide.     

Potentiometric determination of fluoride in coal ores and slags after direct fusion

A potentiometric procedure is described for the determination of 0.001–1.7 % of fluoride in ores and refractory materials. The sample is first sintered with sodium carbonate to oxidize any carbon and then fused. After dissolution of the fused cake, fluoride is measured in a suitable citrate-buffered aliquot with a fluoride ion-selective electrode. Data are given for reference standards; the relative standard deviation was 0.6% for 1.7% fluoride in a basic slag.