Tetraethylammonium dihydrogenarsenate bis(arsenic acid) and 1,4‐diazoniabicyclo[2.2.2]octane bis(dihydrogenarsenate) arsenic acid: hydrogen‐bonded networks containing dihydrogenarsenate anions and neutral arsenic acid molecules

The title compounds, (C₈H₂₀N)[H₂AsO₄][H₃AsO₄]₂, (I), and (C₆H₁₄N₂)[H₂AsO₄]₂[H₃AsO₄], (II), are unusual salts containing organic cations, dihydrogenarsenate anions and neutral arsenic acid molecules. In (I), the dihydrogenarsenate anion lies across a twofold rotation axis in the space group C2/c, while the cation is disordered across a centre of inversion. The [H₂AsO₄]⁻ and H₃AsO₄ species interact by way of O—H...O hydrogen bonds, leading to sheets and a three‐dimensional network for (I) and (II), respectively.     

Intake of different chemical species of dietary arsenic by the japanese,and their blood and urinary arsenic levels

We calculated the intake of each chemical species of dietary arsenic by typical Japanese, and determined urinary and blood levels of each chemical species of arsenic. The mean total arsenic intake by 35 volunteers was 195±235 (15.8-1039) μg As day^?1, composed of 76% trimethylated arsenic (TMA), 17.3% inorganic arsenic (As_i), 5.8% dimethylated arsenic (DMA), and 0.8% monomethylated arsenic (MA): the intake of TMA was the largest of all the measured species. Intake of As_i characteristically and invariably occurred in each meal. Of the intake of As_i, 45-75% was methylated in vivo to form MA and DMA, and excreted in these forms into urine. The mean measured urinary total arsenic level in 56 healthy volunteers was 129±92.0 μg As dm^?3, composed of 64.6% TMA, 26.7% DMA, 6.7% As_i and 2.2% MA. The mean blood total arsenic level in the 56 volunteers was 0.73±0.57 μg dl^?1, composed of 73% TMA, 14% DMA and 9.6% As_i. The urinary TMA levels proved to be significantly correlated with the whole-blood TMA levels (r = 0.376; P<0.01).     

Evaluation of the influence of arsenic species on the nitrogen metabolism of a model angiosperm: nasturtium,Tropaeolum majus

How the various organic and inorganic arsenic species affect the nitrogen metabolism of a model plant, Tropaeolum majus, was studied in order to evaluate the toxicological impact of the various chemical forms of arsenic. For this purpose, the effects on the (a) entire nitrogen pool, (b) protein fraction, and (c) non‐protein fraction were distinguished. The arsenic‐dependent effects on the nitrogen cycle were assessed by using ¹⁵N‐labelled KNO₃ as a nutritive substance and optical emission spectroscopy to analyse how ¹⁵N is incorporated into the nitrogen cycle. In addition to the ¹⁵N‐tracer experiments, the uptake and metabolization of the arsenic compounds were examined. The work shows that biochemical indicator systems like ¹⁵N‐tracer studies are able to characterize the degree of the influence of metabolic processes by arsenic species. For example, the incorporated ¹⁵N concentration decreased linearly and independently of the ¹⁵N fraction with increasing dimethylarsinate (DMA) concentrations. This behaviour indicates that DMA has prevented the uptake of ¹⁵N and hence the formation of amino acids and proteins. Arsenite‐treated plants exhibited an elevated concentration of non‐protein ¹⁵N, which could be an indication either for a stimulated uptake of nitrate or for an interrupted amino acid/protein synthesis. Copyright © 2005 John Wiley & Sons, Ltd.     

Species differences in the metabolism of arsenic compounds

Humans are exposed via air, water and food to a number of different arsenic compounds, the physical, chemical, and toxicological properties of which may vary considerably. In people eating much fish and shellfish the intake of organic arsenic compounds, mainly arsenobetaine, may exceed 1000 μg As per day, while the average daily intake of inorganic arsenic is in the order of 10–20 μg in most countries. Arsenobetaine, and most other arsenic compounds in food of marine origin, e.g. arsenocholine, trimethylarsine oxide and methylarsenic acids, are rapidly excreted in the urine and there seem to be only minor differences in metabolism between animal species. Trivalent inorganic arsenic (AsIII) is the main form of arsenic interacting with tissue constituents, due to its strong affinity for sulfhydryl groups. However, a substantial part of the absorbed AsIII is methylated in the body to less reactive metabolities, methylarsonic acid (MMA) and dimethylarsinic acid (DMA), which are rapidly excreted in the urine. All the different steps in the arsenic biotransformation in mammals have not yet been elucidated, but it seems likely that the methylation takes place mainly in the liver by transfer of methyl groups from S-adenosylmethionine to arsenic in its trivalent oxidation state. A substantial part of absorbed arsenate (AsV) is reduced to AsIII before being methylated in the liver. There are marked species differences in the methylation of inorganic arsenic. In most animal species DMA is the main metabolite. Compared with human subjects, very little MMA is produced. The marmoset monkey is the only species which has been shown unable to methylate inorganic arsenic. In contrast to other species, the rat shows a marked binding of DMA to the hemoglobin, which results in a low rate of urinary excretion of arsenic.     

Methylation and Demethylation of Dimethylarsinic Acid in Rats Following Chronic Oral Exposure

Metabolites of dimethylarsinic acid (DMA) were studied in rats chronically exposed to DMA in drinking water. The urine was collected by forced urination at the end of 8, 20 and 30 weeks and the feces at the end of 30 weeks. The samples were analyzed for arsenic species by a combined system of ion chromatography and inductively coupled plasma mass spectrometry (IC–ICP–MS). Increases in arsenite, DMA, trimethylarsine oxide and a still-to-be-identified arsenic compound (which was eluted immediately after monomethylarsonic acid on the chromatogram) were detected in both urine and feces. At the 100 mg l⁻¹ dose, DMA was the main component in the urine; arsenite was a main component in the feces. The results indicate that, besides undergoing methylation, DMA can be demethylated to inorganic arsenic, and demethylation of DMA may be associated with intestinal bacteria     

Speciation of major arsenic species in seawater by flow injection hydride generation atomic absorption spectrometry

Arsenic present at 1 μg L^–1 concentrations in seawater can exist as the following species: As(III), As(V), monomethylarsenic, dimethylarsenic and unknown organic compounds. The potential of the continuous flow injection hydride generation technique coupled to atomic absorption spectrometry (AAS) was investigated for the speciation of these major arsenic species in seawater. Two different techniques were used. After hydride generation and collection in a graphite tube coated with iridium, arsenic was determined by AAS. By selecting different experimental hydride generation conditions, it was possible to determine As(III), total arsenic, hydride reactive arsenic and by difference non-hydride reactive arsenic. On the other hand, by cryogenically trapping hydride reactive species on a chromatographic phase, followed by their sequential release and AAS in a heated quartz cell, inorganic As, MMA and DMA could be determined. By combining these two techniques, an experimental protocol for the speciation of As(III), As(V), MMA, DMA and non-hydride reactive arsenic species in seawater was proposed. The method was applied to seawater sampled at a Mediterranean site and at an Atlantic coastal site. Evidence for the biotransformation of arsenic in seawater was clearly shown.     

ESR. Study of an X-Irradiated Single Crystal of Methylene Diarsonic Acid

X-Irradiation of single crystals of methylene diarsonic acid gives rise to a variety of radicals which have been identified by ESR. spectroscopy; (OH)₂As(O)CHAs(O) (OH)₂, ^?OÅs(OH)₂CH₂As(O)(OH)₂, AsO₃^– and (OH)Ås(O)CH₂As(O)(OH)₂. The spin densities have been obtained from the ⁷⁵As-hyperfine tensors. An additional species - probably a radical anion localized on a pentacoordinated arsenic - is also detected after annealing at room temperature. The radiation damage process is discussed.     

Validation of the thermodynamic model of inorganic arsenic in non polluted river waters of the Basque country (Spain)

The thermodynamic model of inorganic arsenic was validated by comparing the predicted As(III) concentration with the experimentally determined one in several river waters samples of the Basque Country (Spain) collected in two sampling campaigns: spring and autumn 2000. This model takes into account the acid-base equilibria of As(III) and As(V) together with the redox equilibria between the H₃AsO₃ and H₃AsO₄ species. A correct prediction of As(III) concentration requires the knowledge of the total concentration of arsenic, pH, redox potential (referred to hydrogen electrode), and ionic strength values of the solution. The estimation of the activity coefficients of the arsenic species was performed by means of the Modified Bromley’s Methodology (MBM).In order to perform the experimental As(III) determination, an analytical method was implemented by using an ion exchange separation of As(III)/As(V) on a continuous FIA-IE-HG-AAS system. The total arsenic concentration was determined together with total concentration of the main alkaline or alkaline-earth metals and anions in the natural waters. Temperature compensated measurements of the pH and redox potentials were made in-situ at the sampling sites.For both seasonal campaigns, the agreement between predicted and experimental As(III) is really high for those samples belonging to non polluted river waters.     

Arsenic speciation in Chinese brake fern by ion-pair high-performance liquid chromatography-inductively coupled plasma mass spectroscopy

Ion-pair reverse-phase HPLC-inductively coupled plasma (ICP) MS was employed to determine arsenite [As(III)], dimethyl arsenic acid (DMA), monomethyl arsenic (MMA) and arsenate [As(V)] in Chinese brake fern (Pteris vittata L.). The separation was performed on a reverse-phase C18 column (Haisil 100) by using a mobile phase containing 10 mM hexadecyltrimethyl ammonium bromide (CTAB) as ion-pairing reagent, 20 mM ammonium phosphate buffer and 2% methanol at pH 6.0. The detection limits of arsenic species with HPLC-ICP-MS were 0.5, 0.4, 0.3 and 1.8 ppb of arsenic for As(III), DMA, MMA, and As(V), respectively. MMA has been shown for the first time to experimentally convert to DMA in the Chinese brake fern, indicating that Chinese brake fern can convert MMA to DMA by methylation.     

Urinary arsenic speciation by high-performance liquid chromatography/atomic absorption spectrometry for monitoring occupational exposure to inorganic arsenic

Total urinary arsenic determinations are often used to assess occupational exposure to inorganic arsenic. Ingestion of sea food can increase the normal background levels of total arsenic in urine by up to an order of magnitude, but this arsenic has relatively little toxicity; it is tightly bound as arsenobetaine. The excretion of inorganic arsenic and its metabolites dimethylarsenic acid (DMA) and monomethylarsonic acid (MMA) is not influenced by the consumption of arsenic from sea food. Specific measurements of DMA, MMA and inorganic arsenic provide a more reliable indicator or exposure than total urinary arsenic levels. An automated atomic absorption method involving high-performance liquid chromatographic separation of the arsenic species and continuous hydride generation is described for the determination of arsenite, arsenate, DMA and MMA at μg As l^?1 levels. The method is used to study normal urinary arsenic levels in laboratory staff and arsenic excretion by exposed workers.     

On‐Line Determination of Arsenic Species in Sea Water by Selective Hydride Generation Coupled with Inductively Coupled Plasma — Mass Spectrometry

A method for direct de termination of total in organic arsenic (III+V), arsenic (III) and dimethylarsinate (DMA) in sea water was developed by combining continuous‐flow selective hydride generation and inductively coupled plasma mass spectrometry (ICP‐MS) is presented. The principle underlying selective hydride generation is based on proper control of the reaction conditions for achieving separation of the respective arsenic species. The effects of pH and composition of reaction media on mutual interference between the arsenic species were investigated in detail. The results indicate that the appropriate media for the selective determination of total in organic arsenic, DMA and As(III) are 6 M HNO₃, acetate buffer at pH = 4.63 and citrate buffer at pH = 6.54, respectively. The concentrations of total inorganic arsenic species, As(III+V), and As(III) were respectively deter mined and that of As(V) was obtained by the difference between them. As to the concentration of DMA, it was obtained after correction from the interference caused by As(III) and As(V). By following the established procedure, the detection lim its (as based on 3‐sigma criterion) for As(III+V), As(III) and DMA were 0.050, 0.009, and 0.002 ng/mL, respectively. There liability of the pro posed method was evaluated in terms of precision and spike addition. The results indicated that the precision of better than 3% and spike recovery of 95 to 105% for all the arsenic species tested in the natural sea water samples can be obtained.     

Determination of arsenic compounds in beverages by high-performance liquid chromatography-inductively coupled plasma mass spectrometry

Arsenic compounds including arsenous acid (As(III)), arsenic acid (As(V)), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) were separated by high-performance liquid chromatography (HPLC) and detected by inductively coupled plasma mass spectrometry (ICP-MS). A Hamilton PRX-100 anionic-exchange column and a pH 8.5 K₂HPO₄/KH₂PO₄ 5.0 × 10⁻³ mol L⁻¹ mobile phase were used to achieve arsenic speciation. The separation of arsenic species provided peaks of As(III) at 2.75 min, DMA at 3.33 min, MMA at 5.17 min and As(V) at 12.5 min. The detection limits, defined as three times the standard deviation of the lowest standard measurements, were found to be 0.2, 0.2, 0.3 and 0.5 ng mL⁻¹ for As(III), DMA, MMA and As(V), respectively. The relative standard deviation values for a solution containing 5.0 μg L⁻¹ of As(III), DMA, MMA and As(V) were 1.2, 2.1, 2.5 and 3.0%, respectively. This analytical procedure was applied to the speciation of arsenic compounds in drinking (soft drink, beer, juice) samples. The validation of the procedure was achieved through the analysis of arsenic compounds in water and sediment certified reference materials.     

Methyl transfer from a hydrophobic vitamin B12 derivative to arsenic trioxide

The methylation reaction of arsenic trioxide conducted at 37 °C and pH 7.0 for 24 h using hydrophobic methylated vitamin B₁₂, (methyl) (aquo) heptamethylcobyrinate perchlorate, CH₃B₁₂ ester, as a methyl donor in the presence of reduced glutathione (GSH) yielded monomethylarsonous acid (MMA), dimethylarsinic acid (DMA), and trimethylarsine oxide (TMAO) as products with a methylation rate over 95%. In contrast, when methylcobalamin (CH₃B₁₂) was used as the methyl donor, only MMA and DMA were produced and the methylation rate dropped to around 20%. Reductive demethylation of a methyl-corrinoid coordination complex mediated by GSH is suggested as a mechanism of methyl transfer to arsenic trioxide. The differences observed for different corrinoid coordination complexes with respect to the reactivity of methyl transfer to arsenic is ascribable to differences inherent in the base-on (CH₃B₁₂) and base-off (CH₃B₁₂ ester) natures of the compounds.     

Effective,Low‐Cost Recovery of Toxic Arsenate Anions from Water by Using Hollow‐Sphere Geode Traps

Because of the devastating impact of arsenic on terrestrial and aquatic organisms, the recovery, removal, disposal, and management of arsenic‐contaminated water is a considerable challenge and has become an urgent necessity in the field of water treatment. This study reports the controlled fabrication of a low‐cost adsorbent based on microscopic C‐,N‐doped NiO hollow spheres with geode shells composed of poly‐CN nanospherical nodules (100 nm) that were intrinsically stacked and wrapped around the hollow spheres to form a shell with a thickness of 500–700 nm. This C‐,N‐doped NiO hollow‐sphere adsorbent (termed CNN) with multiple diffusion routes through open pores and caves with connected open macro/meso windows over the entire surface and well‐dispersed hollow‐sphere particles that create vesicle traps for the capture, extraction, and separation of arsenate (AsO₄³⁻) species from aqueous solution. The CNN structures are considered to be a potentially attractive adsorbent for AsO₄³⁻ species due to 1) superior removal and trapping capacity from water samples and 2) selective trapping of AsO₄³⁻ from real water samples that mainly contained chloride and nitrate anions and Fe²⁺, and Mn²⁺, Ca²⁺, and Mg²⁺ cations. The structural stability of the hierarchal geodes was evident after 20 cycles without any significant decrease in the recovery efficiency of AsO₄³⁻ species. To achieve low‐cost adsorbents and toxic‐waste management, this superior CNN AsO₄³⁻ dead‐end trapping and recovery system evidently enabled the continuous control of AsO₄³⁻ disposal in water‐scarce environments, presents a low‐cost and eco‐friendly adsorbent for AsO₄³⁻ species, and selectively produced water‐free arsenate species. These CNN geode traps show potential as excellent adsorbent candidates in environment remediation tools and human healthcare.     

Comparison of extraction procedures for arsenic speciation in environmental solid reference materials by high‐performance liquid chromatography–hydride generation‐atomic fluorescence spectroscopy

Water and ‘soft’ extractions (hydroxylammonium hydrochloride, ammonium oxalate and orthophosphoric acid) have been studied and applied to the determination of arsenic species (arsenite, arsenate, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)) in three environmental solid reference materials (river sediment, agricultural soil, sewage sludge) certified for their total arsenic content. The analytical method used was ion exchange liquid chromatography coupled on‐line to atomic fluorescence spectroscopy through hydride generation. Very low detection limits for arsenic were obtained, ranging from 0.02 to 0.04 mg kg^?1 for all species in all matrices studied. Orthophosphoric acid is the best extractant for sediment (mixed origin) and sludge samples (recent origin) but not for the old formation soil sample, from which arsenic is extracted well only by oxalate. Both inorganic forms (As(III) and As(V)) are significant in all samples, As(V) species being predominant. Moreover, organic forms are found in water extracts of all samples and are more important in the sludge sample. These organic forms are also present in the ‘soft’ extracts of sludge. Microwave‐assisted extraction appears to minimize the risk of a redox interconversion of inorganic arsenic forms. This study points out the necessity of combining direct and sequential extraction procedures to allow for initial arsenic speciation and to elucidate the different mineralogical phases–species associations. Copyright © 2002 John Wiley & Sons, Ltd.     

Simultaneous speciation of arsenic (As(III), MMA, DMA, and As(V)) and selenium (Se(IV), Se(VI), and SeCN−) in petroleum refinery aqueous streams

High-performance liquid chromatography (HPLC) coupled to an ICP-MS with an octapole reaction system (ORS) has been used to carry out quantitative speciation of selenium (Se) and arsenic (As) in the stream waters of a refining process. The argon dimers interfering with the ⁷⁸Se and ⁸⁰Se isotopes were suppressed by pressurizing the octapole chamber with 3.1 mL min⁻¹ H₂ and 0.5 mL min⁻¹ He. Four arsenic species arsenite—As(III), arsenate (As(V)), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA)—and three inorganic Se species—selenite Se(IV), selenate Se(VI), and selenocyanate (SeCN⁻)—were separated in a single run by ion chromatography (IC) using gradient elution with 100 mmol L⁻¹ NH₄NO₃, pH 8.5, adjusted by addition of NH₃, as eluent. Repeatabilities of peak position and of peak area evaluation were better than 1% and about 3%, respectively. Detection limits (as 3σ of the baseline noise) were 81, 56, and 75 ng L⁻¹ for Se(IV), Se(VI), and SeCN⁻, respectively, and 22, 19, 25, and 16 ng L⁻¹ for As(III), As(V), MMA, and DMA, respectively. Calibration curve R ² values ranged between 0.996 and 0.999 for the arsenic and selenium species. Column recovery for ion chromatography was calculated to be 97 ± 6% for combined arsenic species and 98 ± 3% for combined selenium species. Because certified reference materials for As and Se speciation studies are still not commercially available, in order to check accuracy and precision the method was applied to certified reference materials, BCR 714, BCR 1714, and BCR 715 and to two different refinery samples—inlet and outlet wastewater. The method was successfully used to study the quantitative speciation of selenium and arsenic in petroleum refinery wastewaters.     

Simultaneous arsenic‐ and selenium‐specific detection of the dimethyldiselenoarsinate anion by high‐performance liquid chromatography–inductively coupled plasma atomic emission spectrometry

The seleno‐bis (S‐glutathionyl) arsinium ion, [(GS)₂AsSe]^?, which can be synthesized from arsenite, selenite and glutathione (GSH) at physiological pH, fundamentally links the mammalian metabolism of arsenite with that of selenite and is potentially involved in the chronic toxicity/carcinogenicity of inorganic arsenic. A mammalian metabolite of inorganic arsenic, dimethylarsinic acid, reacts with selenite and GSH in a similar manner to form the dimethyldiselenoarsinate anion, [(CH₃)₂As(Se)₂]^?. Since dimethylarsinic acid is an environmentally abundant arsenic compound that could interfere with the mammalian metabolism of the essential trace element selenium via the in vivo formation of [(CH₃)₂As(Se)₂]^?, a chromatographic method was developed to rapidly identify this compound in aqueous samples. Using an inductively coupled plasma atomic emission spectrometer (ICP‐AES) as the simultaneous arsenic‐ and selenium‐specific detector, the chromatographic retention behaviour of [(CH₃)₂As(Se)₂]^? was investigated on styrene–divinylbenzene‐based high‐performance liquid chromatography (HPLC) columns. With a Hamilton PRP‐1 column as the stationary phase (250 × 4.1 mm ID, equipped with a guard column) and a phosphate‐buffered saline buffer (0.01 mol dm^?3, pH 7.4) as the mobile phase, [(CH₃)₂As(Se)₂]^? was identified in the column effluent according to its arsenic:selenium molar ratio of 1 : 2. With this stationary phase/mobile phase combination, [(CH₃)₂As(Se)₂]^? was baseline‐separated from arsenite, selenite, dimethylarsinate, methylarsonate and low molecular weight thiols (GSH, oxidized GSH) that are frequently encountered in biological samples. Thus, the HPLC–ICP‐AES method developed should be useful for rapid identification and quantification of [(CH₃)₂As(Se)₂]^? in biological fluids. Copyright © 2003 John Wiley & Sons, Ltd.     

Raman und infrarotspektroskopische Untersuchungen an Alkylderivaten der Arsensäure. III. Die Schwingungsspektren von Methan- und Äthanarsonsäure sowie von Natriumhydrogenmethanarsonat

RAMAN and IR-spectroscopic Investigation of Alkyl Derivatives of Arsenic Acid. III. The Vibrational Spectra of Methane and Ethanearsonic Acid and Sodium Hydrogenmethanearsonate. The RAMAN spectra of CH₃AsO₃H₂, C₂H₅AsO₃H₂ CH₃AsO₃HN₂. 3/2 H₂O (solid and in concentrated aqueous solution) and the IR spectra (400 -4000 cm^?1) of these solid acids – partially deuterated – and of the hydrogenarsonate are discussed. The very probable symmetry of these compounds is C_s. As the IR spectra show (two strong broad OH valence bands at 2820 and 2350 cm^?1; OH deformation frequency at 1220 cm^?1), rather strong H-bonds exist in these acid substances.     

Organoarsenic compounds in plants and soil on top of an ore vein

Plants and soil collected above an ore vein in Gasen (Austria) were investigated for total arsenic concentrations by inductively coupled plasma mass spectrometry (ICP‐MS). Total arsenic concentrations in all samples were higher than those usually found at non‐contaminated sites. The arsenic concentration in the soil ranged from ∼700 to ∼4000 mg kg⁻¹ dry mass. Arsenic concentrations in plant samples ranged from ∼0.5 to 6 mg kg⁻¹ dry mass and varied with plant species and plant part. Examination of plant and soil extracts by high‐performance liquid chromatography–ICP‐MS revealed that only small amounts of arsenic (<1%) could be extracted from the soil and the main part of the extractable arsenic from soil was inorganic arsenic, dominated by arsenate. Trimethylarsine oxide and arsenobetaine were also detected as minor compounds in soil. The extracts of the plants (Trifolium pratense, Dactylis glomerata, and Plantago lanceolata) contained arsenate, arsenite, methylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, the tetramethylarsonium ion, arsenobetaine, and arsenocholine (2.5–12% extraction efficiency). The arsenic compounds and their concentrations differed with plant species. The extracts of D. glomerata and P. lanceolata contained mainly inorganic arsenic compounds typical of most other plants. T. pratense, on the other hand, contained mainly organic arsenicals and the major compound was methylarsonic acid. Copyright © 2002 John Wiley & Sons, Ltd.     

A comparative theoretical study of the reactivities of the Al+ and Cu+ ions toward methylamine and dimethylamine

A very recent laser ablation‐molecular beam experiment shows that an Al⁺ ion can react with a single methylamine (MA, CH₃NH₂) or dimethylamine (DMA, (CH₃)₂NH) molecule to form a 1:1 ion–molecule complex Al⁺[CH₃NH₂] or Al⁺[(CH₃)₂NH)], whereas a dehydrogenated complex ion Cu⁺[CH₃N] or Cu⁺[C₂H₅N] is detected, respectively, in the similar reaction for a Cu⁺ ion. Here, we show a comparative density functional theory study for the reactivities of the Al⁺ and Cu⁺ ions toward MA and DMA to reveal the intrinsic mechanism. It is found that the interactions of the Al⁺ ion with MA and DMA are mostly electrostatic, leading to the direct ion–molecule complexes, Al⁺? NH₂CH₃ and Al⁺? NH( CH₃)₂, in contrast to the non‐negligible covalent character in the corresponding Cu⁺‐containing complexes, Cu⁺? NH₂CH₃ and Cu⁺? NH( CH₃)₂. The general dehydrogenation mechanism for MA and DMA promoted by the Cu⁺ ion has been shown, and the preponderant structures contributing to the mass spectra of the product ions Cu⁺[CH₃N] and Cu⁺[C₂H₅N] are rationalized as Cu⁺? NHCH₂ and Cu⁺? N( CH₂)( CH₃). The presumed dehydrogenation reactions are also discussed for the Al⁺‐containing systems. However, the involved barriers are found to be too high to be overcome at low energy conditions. These results have rationalized all the experimental observations well. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010