Comparison of ‘soft ionization’ techniques with electron impact mass spectrometry for desoxinojirimycin and folic acid derivatives

Seven desoxinojirimycin and three folic acid derivatives were investigated using the soft ionization techniques of desorption chemical ionization (DCI), laser desorption (LAMMA), field desorption (FD), secondary ion mass spectrometry (SIMS) and fast atom bombardment (FAB). The mass spectra were compared with electron impact (EI) spectra and interpreted in terms of their suitability for analytical purposes.     

Structural diversity in native cyclodextrins/folic acid complexes--from [2]-rotaxane to exclusion compound

The formation of different complexes of folic acid depending on the size of the host cyclodextrin resulting in either an exclusion compound (with the smallest α-cyclodextrin) or 2-rotaxane, where cyclodextrin is threaded over folic acid (with β- and γ-cyclodextrins), is presented. The formation is carried out in water which allows both possible application in pharmaceutical sciences and usage of environmentally friendly "green chemistry". The obtained compounds are thoroughly characterized using one and two dimensional NMR, mass spectrometry, differential scanning calorimetry and thermogravimetric analysis.     

Kinetic spectrophotometric method as a new strategy for the determination of vitamin B9 in pharmaceutical and biological samples

In this study, a new method is proposed for the determination of trace amounts of folic acid (vitamin B(9)). This method is based on the inhibitory effect of folic acid on the reaction of Thionine and bromate in sulfuric acid media. The reaction can be monitored spectrophotometrically by measuring the decrease in absorbance at 601 nm (λ(max)). The effective variables on the reaction rate were investigated. Under optimum experimental conditions, the method allows to determine of the folic acid in a wide linear range with two linear segments. The limit of detection was 0.36 μg mL(-1) of folic acid. Relative standard deviations of six replicate determinations of 5.0 and 50.0 μg mL(-1) of folic acid were 1.18 and 1.02%, respectively. The interfering effect of the different species was also investigated. The method was evaluated by quantifying of folic acid in biological and pharmaceutical samples with satisfactory assay results.     

Purification of folic acid candidate reference material by preparative high-performance liquid chromatography

An effective process for the purification of folic acid candidate reference material with preparative high-performance liquid chromatography (Pre-HPLC) was developed in this study. During the process of experimental operation, parameters including the influences of mobile phase, flow rate, and injection volume on the purity and yield were investigated, and the optimized conditions were as follows: the mobile phase was acetonitrile and water in a gradient mode with flow rate of 16?mL/min and injection volume of 2.0?mL at concentration of 10?mg/mL. Under the conditions, the purity and yield of folic acid product were up to 99.4% and 21.0%, respectively, whereas the purity of folic acid raw material was 95.2%. The purified folic acid product was characterized by LC–MS, HPLC, Karl Fischer coulometer, and quantitative nuclear magnetic resonance (qNMR). Results proved that the main component of the product was folic acid and the purities determined by HPLC and qNMR were consistent. Two impurities including N-(4-aminobenzoyl)-L-glutamic acid and pteroic acid were further quantified by LC–MS. Compared with the recrystallization approach, the purity of folic acid obtained by Pre-HPLC increased from 98.2% to 99.4%.     

聚次甲基蓝修饰玻碳电极测定叶酸

利用循环伏安法将次甲基蓝修饰到玻碳电极表面,制备了聚次甲蓝修饰电极(PMB/GCE),并研究了此电极的化学性质及对叶酸的电化学响应特性.在磷酸盐缓冲液中PMB/GCE电极对叶酸有良好的催化作用并出现一个灵敏的还原峰,用循环伏安法测得峰电流与叶酸的浓度在0.1×10-3～2.9×10 -3 mol/L范围内呈良好线性关系...     

Highly Sensitive Spectrofluorimetric Determination of Trace Amounts of Folic Acid using a Oxytetracycline-Terbium(III) Probe

Abstract

A new spectrofluorimetric method was developed for the determination of trace amounts of folic acid using oxytetracycline–terbium ion complex as a fluorescent probe. In the buffer solution of pH 6.00, folic acid remarkably reduced the fluorescence intensity of the oxytetracycline–terbium complex at λ = 545 nm. The reduced fluorescence intensity of the Tb³⁺ ion was proportional to the concentration of folic acid. Optimum conditions for the determination of folic acid were investigated. This method was simple, practical, and relatively free of interference from coexisting substances. Furthermore, it was successfully applied to assess folic acid in tablet, injection, and urine samples.     

Thermal Stability Of Folic Acid in the solid-state

This study attempts to identify the degradative process which folic acid undergoes in the solid-state under thermal stress. In order to facilitate the process, the various pieces of the chemical structure, namely, p-amino benzoic acid, pterin and glutamic acid as both its d- and l-isomers were investigated as separate entities. These structured solid-state pieces were then compared to the composite solid state folic acid degradative curves in order to identify the peaks seen and provide direction for the interpolation of the degradative mechanism. It was observed that none of the structural pieces could be superimposed as assumed earlier and hence an attempt was made to identify the decomposition products using various analytical techniques such as infrared spectroscopy, mass spectroscopy and X-ray diffraction which suggested that the glutamic acid fragment is lost first as evidenced by acid loss and amide enhancement in the IR spectra. The vitamin was ultimately degrading to carbon fragments and that further identification was not necessary. This revised version was published online in August 2006 with corrections to the Cover Date.     

蔬菜中叶酸的催化氧化荧光法测定

建立了催化氧化荧光法间接测定叶酸的新方法。在pH5.0的HAc-NaAc缓冲溶液中,Co2+催化KIO4氧化叶酸产生强荧光,以262 nm为激发波长,在445 nm处测定叶酸的氧化产物蝶呤-6-羧酸的荧光强度,研究了反应的适宜条件及动力学参数,并探讨了反应机理。在优化实验条件下,叶酸浓度在1.0×10-8~1.0×10-5mol/L范围内与荧光强度呈良好线性关系,回归方程为ΔIF=10.82c(μmol/L)+2.867,相关系数r=0.998 5,方法的检出限为5×10-9mol/L。对5×10-7mol/L叶酸标准溶液进行11次平行测定,相对标准偏差(RSD)为0.1%。该法使用Co2+为催化剂,大大提高了方法的灵敏度。方法用于蔬菜中叶酸的测定,加标回收率为93%~104%,6次测定的相对标准偏差为0.98%~2.1%,结果令人满意。     

Synthesis, characterisation and photo-stability of a folate-modified β-cyclodextrin as a functional food additive

A novel two-step synthetic route was developed and gave the mono-substituted derivative 6-deoxy-6-[(1-(2-amino)ethylamino)folate]-β-cyclodextrin (CDEnFA) with high yield (60?%). Elemental analysis, mass spectrometry, ¹H and ¹³C NMR, FTIR and Raman spectroscopies demonstrated the successful synthesis of the γ isomer only with no evidence of the presence of other isomers or free folic acid. Electronic absorption spectroscopy was used to study the photochemical properties of CDEnFA and showed that in both the solid state and aqueous solution CDEnFA is considerably more photo-stable than free folic acid.     

Fluorescent carbon dots derived from lactose for assaying folic acid

The fluorescent carbon dots were successfully synthesized by simply heating the mixture of lactose and Na OH solution. The as-synthesized carbon dots had been systematically characterized by fluorescence, Fourier transform infrared(FTIR), high resolution transmission electron microscopy(HR-TEM) and ~(13)C NMR. Since the fluorescence of the carbon dots was efficiently quenched by folic acid, the carbon dots were employed as selective fluorescence probes for detecting folic acid, depending on the formation of hydrogen bond among the functional group of folic acid(–OH, –COOH and –NH_2) and –OH and –COOH of the carbon dots. Moreover, the decrease of fluorescence intensity was capable of detecting folic acid in a linear range of 6×10~(-5)–8×10~(-8) mol/L with a detection limit of 1.2×10~(-9)mol/L at a signal-to-noise ratio of 3, suggesting a promising assay for folic acid. Significantly, the practicability of this fluorescence probe to assay folic acid in human urine samples was further evaluated.     

Chemiluminescence flow sensor for folic acid with immobilized reagents.

A novel chemiluminescence (CL) sensor for folic acid combined flow-injection (FI) technology was presented in this paper. The analytical reagents involved in the CL reaction, including luminol and hexacyanoferrate(III), were both immobilized on an anion-exchange column in FI system. The CL signal produced by the reaction between luminol and hexacyanoferrate(III), which were eluted from the column through sodium phosphate injection, was decreased in the presence of folic acid. The CL emission was correlated with the folic acid concentration in the range from 0.01 to 15 microg ml(-1), and the detection limit was 3.5 ng ml(-1) folic acid (3sigma). At a flow rate of 2.0 ml min(-1), including sampling and washing, could be performed in 2 min with a relative standard deviation of < 2.5%. The flow sensor could be reused more than 300 times and has been applied to the analysis of folic acid in pharmaceutical preparations. and the recovery was from 97.4% to 100.4%.     

Photophysical behaviour of asymmetrically substituted metal free, Mg and Zn phthalocyanines in the presence of folic acid

This work reports on the synthesis, characterisation and photophysical properties of new asymmetric metal free, magnesium and zinc phthalocyanines containing a mono carboxylic acid group for possible linking to biological molecules via an amide bond. Successful synthesis of the phthalocyanines was achieved through the statistical condensation method. The phthalocyanines were mixed with folic acid and their photophysical properties were examined. The triplet quantum yield values for all the complexes in DMSO were between 0.49 and 0.74 and in the presence of folic acid they were between 0.37 and 0.63. The lifetimes were generally good ranging from 70 to 290 μs in the absence or presence of folic acid.     

原子吸收光谱法间接测定叶酸的含量

在pH5．0的NaOAc-HOAc缓冲溶液中，过量的硝酸银完全沉淀叶酸，用原子吸收光谱法测定剩余的硝酸银，间接计算出叶酸的含量。方法简单快速，回收率在98％～104％之间，相对标准偏差为2．4％。     

Effect of gamma radiation on folic acid and its cobalt complex solutions

Gamma-radiolysis of folic acid and its cobalt complex were studied in aqueous solutions at doses ranged from 2 to 10 krad and from 2 to 10 Mrad using⁶⁰Co source. The variations in their spectra of IR, UV, and visible due to their radiolysis were shown. Also the change in pH after radiolysis was determined. The results showed that decomposition of folic acid by gamma-radiation occurred without variation of pH. Fine measurements of pH for irradiated CoCl₂ and cobalt-folic acid complex solutions can be utilized for dose determination in the studied range of 2–10 Mrad. IR spectra showed that addition of cobalt chloride to folic acid decreased its decomposition by gamma-radiation. This result proved the importance of addition of cobalt chloride in keeping foodstuffs, which contain folic acid, by irradiation. The mechanism for the effect of radiation on cobalt chloride and cobalt-folic acid complex was discussed.     

Optically active supramolecular complexes of water-soluble achiral polythiophenes and folic acid: spectroscopic studies and sensing applications

Optically active supramolecular complexes of water-soluble achiral polythiophene (PT) derivatives, PMTPA or PMTEA (Chart 1), and folic acid have been prepared; and the complex formation processes have been studied by absorption, emission, and circular dichroism (CD) spectroscopies. The complexes exhibited unique split-type induced CDs in the pi-pi* transition region of PTs, indicating that the molecular chirality of the glutamic acid moiety in folic acid was expressed in PT backbones. The influences of temperature, solvent composition, and the structures of the inducing molecules on the chirality induction to PTs were also investigated, and a possible mechanism for the formation of chiral superstructures was proposed. Furthermore, it was found that, upon addition of folic acid into aqueous solution of PTs (PMTPA or PMTEA), a dramatic color change from yellow to purple along with the emission quenching of PT derivatives was observed. PMTEA, having one fewer carbon in the hydrophobic side chain relative to PMTPA, showed better selectivity toward folic acid sensing over ATP because of its higher solubility in water and the appropriate hydrophilic/hydrophobic balance in the complex. Therefore, it can be applied as a colorimetric and fluorescent probe for detecting folic acid with high selectivity and sensitivity. Besides naked-eye detection of folic acid, the detection limit can be extended to be 10 (-8) M by using fluorometry and PMTEA as the probing molecule.     

Self-assembly of folic acid derivatives: induction of supramolecular chirality by hierarchical chiral structures

Hierarchical chiral structures made up of dendritic oligo(L- or D-glutamic acid) moieties of folic acid derivatives induce supramolecular chirality in the self-assembled columnar structures of the folic acids. These folic acids self-assemble through the intermolecular hydrogen bonds of the pterin rings to form disklike tetramers. In the neat states, the stacked tetramers form thermotropic hexagonal columnar phases over wide temperature ranges, including room temperature. Addition of alkali metal salts induces chirality in the columnar phases. In dilute solution states in a relatively polar solvent (chloroform), the folic acid derivatives form non-chiral, self-assembled structures. In the presence of sodium triflate, the folic acid forms chiral columnar assemblies through the oligo(L-glutamic acid) moiety, similar to those formed in the liquid-crystalline (LC) states. The enantiomer of the folic acid induces columnar assemblies with reversed helicity. In the case of the diastereomer, no induced helicity is observed. Application of an apolar solvent (dodecane) drives the folic acid derivatives to form chiral assemblies in the absence of ions. In this case, lipophilic interactions promote nanophase segregation, which enhances the formation of chiral columns. Interestingly, the chiral supramolecular structure of the diastereomer induces the most intense circular dichroism. In both cases, the molecular chirality in the oligo(glutamate) moieties yields supramolecular chirality of the folic acids that self-assemble through cooperative molecular interactions.     

Ultraviolet photodegradation of folic acid

The vitamin folate is vital for all living creatures. Scientists have suggested that ultraviolet degradation of folate in vivo played a role in the evolution of mankind. In order to better understand the photodegradation of folate, we have provided a spectroscopic study of the ultraviolet photodegradation of aqueous folic acid under aerobic conditions. We found strong indications that the folic acid molecule is cleaved into p-aminobenzoyl-L-glutamic acid and 6-formyl pterin when exposed to ultraviolet radiation. When the irradiation continues, 6-formyl pterin is degraded to pterin-6-carboxylic acid. The photodegradation of folic acid is divided into three phases. In the first phase, the formation of photoproducts follows a zero order rate law. In the second phase the presence of photoproducts sensitizes the degradation of folic acid and the degradation process is accelerated. In the third phase the degradation of 6-formyl pterin to pterin-6-carboxylic acid is the dominating process. This reaction follows a first order rate law. We show that both 6-formyl pterin and pterin-6-carboxylic acid sensitize the photodegradation of folic acid. However, experiments performed in heavy water indicate that generation of singlet oxygen is probably not the explanation for the photosensitizing of folic acid.     

Radioenzymatic determination of subpicomole quantities of folic acid and dihydrofolate based on differential reduction by dihydrofolate reductase

A sensitive method for the determination of folic acid in the presence of dihydrofolate has been described. The analysis is based on the difference in reactivity of dihydrofolate reductase toward folic acid and dihydrofolate. The tetrahydrofolate formed was measured by stoichiometric entrapment into a covalent, ternary complex with thymidylate synthase and [³H]fluorodeoxyuridylate. Differentiation between folic acid and dihydrofolate was accomplished by the use of two levels of dihydrofolate reductase. Recovery of both folic acid and dihydrofolate was quantitative in the range of 0.1 to 2.0 pmol.     

Novel Copper(II)-Selective Potentiometric Sensor Based on a Folic Acid-Functionalized Carbon Nanotube Material

Abstract

A folic acid-functionalized carbon nanotube nanomaterial was prepared by immobilizing folic acid molecules on the carbon nanotubes through covalent bonds. The material was characterized using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy. Fourier transform infrared spectroscopy confirmed that folic acid molecules were grafted on the carbon nanotube surfaces through the amide bonds between the carboxylic acid functional groups of the oxidized carbon nanotubes and the amine groups of the folic acid molecules. The folic acid molecules bonded to carbon nanotube surfaces led to appreciable changes in the morphology. By using currently obtained folic acid-functionalized carbon nanotube nanomaterial as electroactive material in a polyvinyl chloride membrane, a potentiometric copper (II)-selective sensor was developed. Membrane optimization studies showed that the composition exhibiting the best potentiometric properties was 4.0% (w/w) folic acid–carbon nanotube, 64.0% (w/w) o-nitrophenyl octylether, and 32.0% (w/w) polyvinyl chloride. The developed sensor displayed a linear response in the copper (II) concentration ranging from 1.0?×?10^–6 to 1.0?×?10^–1 M with a correlation coefficient of 0.9993 and a slope of 29.8?±?0.6?mV/decade of activity. The response time, detection limit, and pH working range were determined to be 4?s, 3.8?×?10^–7 M and 4.0–8.0, respectively. The developed sensor showed highly selective and satisfactory potentiometric response for the determination of copper (II) in a Turkish coin.     

Determination of fortified and endogenous folates in food-based Standard Reference Materials by liquid chromatography-tandem mass spectrometry

The National Institute of Standards and Technology (NIST) is developing a wide variety of Standard Reference Materials (SRMs) to support measurements of vitamins and other nutrients in foods. Previously, NIST has provided SRMs with values assigned for the folate vitamer, folic acid (pteroylglutamic acid), which is fortified in several foods due to its role in prevention of neural tube defects. In order to expand the number of food-based SRMs with values assigned for folic acid, as well as additional endogenous folates, NIST has developed methods that include trienzyme digestion and isotope-dilution liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis. Sample preparation was optimized for each individual food type, but all samples were analyzed under the same LC-MS/MS conditions. The application of these methods resulted in folic acid values for SRM 1849a Infant/Adult Nutritional Formula and SRM 3233 Fortified Breakfast Cereal of (2.33?±?0.06) μg/g and (16.0?±?0.7) μg/g, respectively. In addition, the endogenous folate vitamer 5-methlytetrahydrofolate (5-MTHF) was detected and quantified in SRM 1849a Infant/Adult Nutritional Formula, candidate SRM 1549a Whole Milk Powder, and candidate SRM 1845a Whole Egg Powder, resulting in values of (0.0839?±?0.0071) μg/g, (0.211?±?0.014) μg/g, and (0.838?±?0.044) μg/g, respectively. SRM 1849a Infant/Adult Nutritional Formula is the first food-based NIST SRM to possess a reference value for 5-MTHF and the first certified reference material to have an assigned 5-MTHF value based on LC-MS/MS. The values obtained for folic acid and 5-MTHF by LC-MS/MS will be incorporated into the final value assignments for all these food-based SRMs.