Assessment of lisdexamfetamine dimesylate stability and identification of its degradation product by NMR spectroscopy

Lisdexamfetamine dimesylate (LDX), a long-acting prodrug stimulant indicated for the treatment of the attention-deficit/hyperactivity disorder (ADHD), was subjected to forced degradation studies by acid and alkaline hydrolysis and the degradation profile was studied. To obtain between 10–30% of degraded product, acid and alkaline conditions were assessed with solutions of 0.01?M, 0.1?M, 0.5?M, and 1?M of DCl and NaOD. These solutions were analyzed through 1?H NMR spectra. Acid hydrolysis produced no degradation in 0.01?M and 0.1?M DCl and 4.38%, 9.69%, and 17.75% of degradation LDX, respectively, in 0.5?M, 1?M (4h) and 1?M (4?+?12?h) DCl. And alkaline hydrolysis produced no degradation in 0.01?M and 0.1?M DCl and a degradation LDX extension of 8.5%, 14.30%, and 22.91%, respectively, in 0.5?M, 1?M (4h) and 1?M (4?+?12?h) NaOD. LDX solutions subjected to 1?M (4?+?12?h) acid and alkaline hydrolysis were evaluated by NMR spectra (1?H NMR, 13?C NMR, HSQC and HMBC). LDX degradation product (DP) was identified and its structure elucidated as a diastereoisomer of LDX: (2R)-2,6-diamino-N-[(2S)-1-phenylpropan-2-yl] hexanamide without their physical separation.     

Synergistic extraction of REE and TPE from HNO<Subscript>3</Subscript> solutions with a mixture of CCD and HDBP ZS (1: 6) in a polar diluent

Extraction of Ce(III), Am(III), and Eu(III) from HNO₃ solutions with acidic zirconium salt of dibutyl hydrogen phosphate (HDBP ZS) at the ratio Zr: HDBP = 1: 6 and with a mixture of HDBP ZS (1: 6) and chlorinated cobalt dicarbollide (CCD) in a polar diluent, mixture of o-chloronitrobenzene and CCl₄ (1: 1), was studied. A synergistic effect was observed at a definite ratio of CCD and HDBP in the mixture. The maximal synergistic effect was observed for a mixture of HDBP ZS with CCD and an HDBP to CCD molar ratio of 6:1. The largest magnitude of the synergistic effect was 5 for all the examined elements. The synergistic effect observed in the HDBP ZS (1: 6)-CCD system in extraction of rare-earth and transplutonium elements can be attributed to interaction of Zr, CCD, and HDBP leading to the formation of a complex acid, which is stronger and more hydrophobic than the initial compounds. The stoichiometry of the extraction of Ce and Eu with such acid corresponds to the stoichiometry of the extraction with HDBP ZS and CCD, and in the extraction of Am it is somewhat different. In the extraction ability, this acid considerably surpasses CCD and somewhat surpasses HDBP ZS. The extractability order of metals corresponds to the order of their extractability with HDBP ZS and is opposite to the order of their extractability with CCD. High extraction ability of the complex extractant allows REE and TPE to be recovered directly from the Purex process raffinate.     

Hexacyanoferrate(III) oxidation of arsenic and its subsequent removal from the spent reaction mixture

Inorganic arsenic is the most toxic form and has been classified in group 1 as carcinogenic to humans which induces lung, urinary bladder and primary skin cancer. Worldwide concern over its presence in water bodies have prompted much research and policy development focusing on the removal of this chronic human carcinogen. It has been observed that the ash of Unio (Lamellidens marginalis--the fresh water mussel) can be used successfully for the removal of arsenic(V) from the aqueous solutions at low pH (～9.0). Initially the kinetics of oxidation of arsenic(III) by alkaline hexacyanoferrate(III), both with and without adding iridium(III) chloride was studied. Subsequently after complete removal of ferrocyanide, the removal of arsenic(V) produced in the spent reaction mixture was taken up. Out of the five ashes obtained from different sources, the ash of Unio was found to be the best which results in decreasing arsenic(V) concentration from 1000 ppb to >10 ppb, TDS from 16.9 ppt to 8.5 ppt and conductivity from 33.8 mS to 17.1 mS. Kinetic results show the possibility of graphical separation of the reaction proceeding in the absence of iridium(III) from that proceeding in the presence of iridium(III) chloride.     

Hyphenation of capillary HPLC to microcoil (1)H NMR spectroscopy for the determination of tocopherol homologues

Highly selective reversed phases (C(30) phases) are self-packed in 250 microm inner diameter fused-silica capillaries and employed for capillary HPLC separation of shape-constrained natural compounds (tocopherol homologues, vitamin E). Miniaturized hyphenated systems such as capillary HPLC-ESI-MS (positive ionization mode) and, with special emphasis, continuous-flow capillary HPLC- NMR are used for structural determination of the separated compounds. Despite the small amount of sample available (1.33 microg of each tocopherol), the authors have been able to monitor the capillary HPLC separation under continuous-flow (1)H NMR conditions, thus allowing an immediate peak identification. Further structural assignment was carried out in the stopped-flow NMR mode as shown, for example, by a 2D (1)H,(1)H COSY NMR spectrum of alpha-tocopherol. We demonstrate in this paper the considerable potential of hyphenated capillary separations coupled to MS and NMR for the investigation of restricted amounts of sample.     

Screening and identification of organophosphorus compounds related to the chemical weapons convention with 1D and 2D NMR spectroscopy

Two-dimensional 1H-31P Fast-HMQC was tested for determination of the presence in low concentrations of organophosphorus compounds related to the Chemical Weapons Convention. This method, based on inverse detection, demonstrated high sensitivity and selectivity. Background signals, such as solvent peaks, are suppressed with good efficiency, and organophosphorus compounds present at a concentration level 1-10 microg/mL can be detected within a few hours. In addition, phosphorus-selective one-dimensional 1H-31P HSQC-TOCSY was applied to produce a complete proton spectrum of selected organophosphorus compound from a sample containing intense background resonances. Application of the methods presented in this paper resulted in considerably improved performance of NMR spectroscopy as a complementary technique for screening as well as identification of chemical warfare agents in environmental samples.     

Method performance and validation for quantitative analysis by (1)h and (31)p NMR spectroscopy. Applications to analytical standards and agricultural chemicals

Nuclear magnetic resonance (NMR) can be used to provide an independent and intrinsically reliable determination of chemical purity. Unlike chromatography, it is possible to employ a universal reference standard as an internal standard for the majority of chemical products assayed by quantitative NMR (QNMR). This is possible because the NMR response can be made the same for all chemical components, including the internal standard, by optimizing certain instrumental parameters. Experiments were performed to validate the quantitative NMR method described in this paper for the analysis of organic chemicals. Experimental precision, accuracy, specificity, linearity, limits of detection and quantitation, and ruggedness were systematically addressed, and system suitability criteria were established. The level of the major chemical ingredient can be determined with accuracy and precision significantly better than 1%, and impurities may be quantified at the 0.1% level or below. Thus, QNMR rivals chromatography in sensitivity, speed, precision, and accuracy, while avoiding the need for a reference standard for each analyte. Examples are given of (1)H and (31)P NMR used for quantitative analysis of agricultural chemicals, and a method for characterization of analytical standards is presented.     

Chain order and mobility of high-density c(18) phases by solid-state NMR spectroscopy and liquid chromatography

C(18) phases prepared by different synthetic pathways are examined by solid-state NMR spectroscopy. Silane functionality is clearly indicated by (29)Si CP/MAS NMR spectroscopy. Order and mobility of the alkyl chains are investigated with high-speed (1)H MAS and (13)C CP/MAS NMR spectroscopy. Differences in coverage are monitored by (1)H line widths,( 13)C chemical shifts, (13)C cross-polarization constants, and (1)H relaxation times in the rotating frame. It is shown that C(18) phases prepared by the surface polymerization technique exhibit a more regular surface coverage than sorbents prepared by conventional polymeric synthesis. The findings from solid-state NMR investigations are discussed in the context of liquid chromatography (LC) separations of linear and bulky polycyclic aromatic hydrocarbon (PAH) solutes.     

Determination of the composition of acetylglycerol mixtures by (1)H NMR followed by GC investigation

Commercially available partly acetylated glycerols (mono- and diacetins) are a mixture of glycerol, 1- and 2-acetylglycerol, 1,2- and 1,3-diacetylglycerol, and triacetin. No exact analysis method is available. Comparisons of (1)H NMR measurements obtained using deuterated dimethyl sulfoxide (DMSO-d6) and DMSO-d6/15% D2O are sufficient to identify and determine quickly all the components. Advantages compared with the commonly used NMR solvent CDCl3 for fatty acid glycerides include the solubility of all the components and a highly informative OH signal pattern in a region between 4.36 and 5.26 ppm almost free of other signals. 2-Acetylglycerol (2-acetin) is shown to disproportionate even at 50 degrees C into a mixture of glycerol and acetylglycerol thereby making it difficult to quantify by liquid chromatography (LC) and gas chromatography (GC) methods. Complete (1)H chemical shift data for all five components allow for the identification of the components in the mixture and thus the determination of the composition. The NMR method with DMSO-d6 as solvent was used for acetins, propionins, and butyrins. Semipreparative high-performance liquid chromatography (HPLC) on an RP18 column led to moderately pure 1-monoacetin and a mixture of diacylated species. Electron impact mass spectra show for all the components very characteristic fragmentation patterns with loss of AcOCH2 radicals, in contrast to the well-known pattern of longer-chained fatty acid derivatives that show preferred first-step loss of acyl-O radicals.     

Synergistic extraction of REE and TPE from HNO<Subscript>3</Subscript> solutions with a mixture of CCD and HDPB ZS (1 : 8) in a polar diluent

Extraction of Ce(III), Am(III), and Eu(III) from HNO₃ solutions with an acidic zirconium salt of dibutyl hydrogen phosphate (HDBP ZS) at the Zr: HDBP ratio of 1: 8 and with a mixture of HDBP ZS (1: 8) and chlorinated cobalt dicarbollide (CCD) in an o-chloronitrobenzene-CCl₄ mixture (1: 1) was studied. At a definite molar ratio of CCD and HDBP in a mixture, a considerable synergistic effect is observed, reaching a maximum (30–40 for all the examined elements) at HDBP: CCD = 2: 1. The synergistic effect observed in the system HDBP ZS (1: 8)-CCD in extraction of rare-earth and transplutonium elements can be attributed to interaction of Zr, CCD, and HDBP, leading to the formation of a complex acid that is stronger and more hydrophobic than the starting compounds. The stoichiometry of the extraction of REE and TPE with such an acid corresponds to the stoichiometry of their extraction with HDBP ZS or CCD, and the extraction ability of the system is considerably enhanced relative to the components taken separately. The metal extractabilility series corresponds to the extractability series with HDBP ZS and is opposite to the extractability series with CCD. The Zr atom in the complex extractant binds in the first coordination sphere two CCD anions, two DBP anions, and four HDBP molecules.     

Isolation and identification of sialylated glycopeptides from bovine alpha1-acid glycoprotein by off-line capillary electrophoresis MALDI-TOF mass spectrometry

Sialylated glycopeptides contained in liquid chromatographic fractions of bovine alpha1-glycoprotein tryptic digests were isolated from asialo peptides using capillary electrophoresis (CE). CE effluents were deposited directly onto a metallic target and analyzed using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. This method allowed the characterization of four N-glycosylation sites in the glycoprotein, and each site was observed as a set of sialylated peptide glycoforms. Tandem mass spectrometry was used to confirm peptide sequences and glycan content in glycoforms. The CE method developed for this study resulted in a very clear separation of the sialylated from the asialo content of glycoprotein digests and proved very useful in the determination of the nature and location of sialylated glycans along the protein chain. This article is the first report describing the use of on-target CE fraction collection using a MALDI removable sample concentrator.     

Application of nonselective 1D (1)H-(31)P inverse NMR spectroscopy to the screening of solutions for the presence of organophosphorus compounds related to the chemical weapons convention

1D nonselective (1)H-(31)P HSQMBC, HSQC, and (31)P decoupled HSQC NMR experiments were applied to the screening of original OPCW proficiency test samples for the presence of organophosphorus (OP) compounds related to the Chemical Weapons Convention. The HSQC and HSQMBC spectra are compared to 1D (1)H NMR spectra with WET solvent suppression and (31)P[(1)H] spectra of the same samples. The 1D nonselective HSQC and HSQMBC experiments are shown to be the most sensitive NMR experiments to selectively screen samples for the presence of organophosphorus(OP) compounds. These experiments are at least three times more sensitive than the (31)P[(1)H] NMR experiment and allow the determination of the number of OP compounds present in the sample and their alkyl group bound to the phosphorus atom. Samples spiked at the 5-10 ppm level can be screened within an hour for the presence of OP compounds, whereas for the (31)P[(1)H] experiments, an overnight acquisition is necessary. The sensitivity of the experiments decreases in the order (31)P decoupled HSQC, HSQMBC, and HSQC. For the different alkyl groups, the sensitivity of these experiments decreases in the order methyl approximately isopropyl > ethyl > propyl.     

Synergistic extraction of REE and TPE from HNO3 solutions with a CCD-HDBP ZS (1: 12) mixture in a polar diluent

Extraction of Ce(III), Am(III), and Eu(III) from HNO₃ solutions with an acidic zirconium salt (HDBP ZS) of dibutyl hydrogen phosphate (HDBP) at Zr: HDBP = 1: 12 and with a mixture of HDBP ZS with chlorinated cobalt dicarbollide (CCD) in a polar diluent, a 1: 1 o-chloronitro-benzene-CCl₄ mixture, was examined. This system exhibits a substantial synergistic effect, which is at a maximum (30–40 for all the elements examined) at the 1: 1 HDBP to CCD molar ratio. The synergistic effect observed in the HDBP ZS (1: 12)-CCD system in extraction of REE and TPE can be associated with interaction of Zr, CCD, and HDBP, resulting in formation of a complex acid, more hydrophobic and stronger than the initial compounds. The trends in variation of the metal extractability are identical to those for HDBP ZS and opposite to those for CCD. The Zr atom in the complex extractant binds three CCD anions, as well as DBP anion and HDBP molecules.     

Drug release from cast films of ethylene vinyl acetate (EVA) copolymer: Stability of drugs by <Superscript>1</Superscript>H NMR and solid state <Superscript>13</Superscript>C CP/MAS NMR

The study utilizes an oral biocompatible material based on ethylene vinyl acetate copolymer (EVA) designed to release drugs in vitro at therapeutic levels over several days. We examined the drug stability during film casting process using proton and solid state NMR techniques. The drug-loaded EVA films were prepared from the dry sheet obtained by solvent (dichloromethane) evaporation of polymer casting solutions. Drugs tested include chlorhexidine diacetate (CDA), doxycycline hydrochloride (DOH), tetracycline hydrochloride (TTH) and nystatin (NST). Drug release from the films was examined for at least 14 days in 10 ml ddH₂O (NST in water/ethanol (4:1)) which was replaced daily. Changes in optical density were followed spectraphotometrically. Effect of temperature on rate measurements was studied and the energies of activation (E^∗) were calculated using Arrhenius plots. Effect of EVA copolymer composition on CDA release rate was also investigated. The enhanced rates with temperature increase may be attributed to the formation of channels with increased geometry in the polymer. The highest E^∗ observed for CDA compared to DOH and TTH may be related to their average molecular weights. Spectral analyses for CDA and NST revealed that the chemical and physical structures of the drugs remained unaffected during the film casting process.     

Synergic extraction of Ce(III) from HNO<Subscript>3</Subscript> solutions with a mixture of CCD and HDBP ZS in a polar diluent

The extraction of Ce(III) from HNO₃ solutions with a mixture of chlorinated cobalt dicarbollide (CCD) and dibutyl hydrogen phosphate (HDBP) or its zirconium salt (HDBP ZS) in m-nitrobenzotrifluoride was studied by the method of isomolar series. A considerable synergic effect S was observed, reaching a maximum in a mixture of HDBP with CCD at the molar ratio HDBP : CCD = 7 : 1 (S = 100). The highest Ce(III) distribution ratios D _Ce are observed with mixtures of CCD and HDBP ZS (1 : 6 and 1 : 4). An increase in the HNO₃ concentration causes changes in D _Ce and S to different extents depending on the type of HDBP ZS. The synergic effect was attributed to the formation of coordination compounds that are more hydrophobic than the initial compounds and have stronger bonds of Ce(III) with the ligands.     

Characterization of silicon dioxide films on a 4H-SiC Si(0001) face by fourier transform infrared (FT-IR) spectroscopy and cathodoluminescence spectroscopy

We used Fourier transform infrared (FT-IR) spectroscopy to characterize silicon dioxide (SiO(2)) films on a 4H-SiC(0001) Si face. We found that the peak frequency of the transverse optical (TO) phonon in SiO(2) films grown on a 4H-SiC substrate agrees well with that in SiO(2) films grown on a Si substrate, whereas the peak frequency of the longitudinal optical (LO) phonon in SiO(2) films on a 4H-SiC substrate is red-shifted by approximately 50 cm(-1) relative to that in SiO(2) films on a Si substrate. We concluded that this red-shift of the LO phonon is mainly caused by a change in inhomogeneity due to a decrease in density in the SiO(2) films. Furthermore, cathodoluminescence (CL) spectroscopy results indicated that the channel mobility of the SiC metal-oxide-semiconductor field-effect transistor (MOSFET) decreases roughly in proportion to the increase in the intensity of the CL peak at 460 and 490 nm, which is attributed to the increase in the number of oxygen vacancy centers (OVCs). FT-IR and CL spectroscopies provide us with a large amount of data on OVCs in the SiO(2) films on a 4H-SiC substrate.     

Synthesis of poly(methyl methacrylate)-block-poly(L-histidine) and its use as a hybrid silver nanoparticle conjugate

Poly[(methyl methacrylate)-block-poly(L-histidine)] (PMMA-b-PHIS) was synthesized by combining atom transfer radical polymerization and living ring-opening polymerization of alpha-amino acid-N-carboxyanhydride. The resulting hybrid block copolymer forms reverse micelles in the mixture solution of water and N,N-dimethylformamide (DMF) and self-assembles into PHIS/PMMA core/shell spheres with controllable size in the range of 80 to 250 nm depending on the micellization temperature. The self-assembly of PMMA-b-PHIS was carried out in H2O/DMF (3/7) mixture in the presence of AgNO3. Reduction of the resulting Ag ions encapsulated inside of the reverse micelles yielded an attractive Ag nanoparticle core/polymer shell conjugate system.