Perturbations produced by electrospray ionization mass spectrometry in the speciation of aluminium(III)/1,6‐dimethyl‐4‐hydroxy‐3‐pyridinecarboxylate aqueous solutions

Electrospray ionization mass spectrometry (ESI‐MS) is very often employed to study metal/ligand equilibria in aqueous solution. However, the ionization process can introduce perturbations which affect the speciation results in an unpredictable way. It is necessary to identify these perturbations in order to correctly interpret the ESI‐MS speciation results. Aluminium(III)/1,6‐dimethyl‐4‐hydroxy‐3‐pyridinecarboxylate (DQ716) aqueous solutions at various pH were analysed by ESI‐MS, and speciation results were compared with those obtained by equilibrium techniques. Differences observed were both qualitative and quantitative. The ESI‐MS spectral changes due to different settings of the following instrumental parameters were analyzed: the solution flow rate (F_S), the nebulizer gas flow rate (F_G), the potential applied at the entrance capillary (E_C), and the temperature of the drying gas (T_G). The effects produced by F_S and E_C on the spectra strongly suggest the key role of surface activity in determining the relative fraction of the ions reaching the detector. The experimental effects of F_S and T_G were interpreted considering the presence of at least two reactions in the gas phase and a dimerization occurring in the droplets. These perturbations cannot be generalized because they appear to be chemical system‐related and instrument‐dependent. Therefore, the identification of perturbations is a required task for any metal‐ligand equilibrium study performed by ESI‐MS. Our results indicate that perturbations can be identified by evaluating the effects produced in the spectra by a change of instrumental parameters. Copyright © 2010 John Wiley & Sons, Ltd.     

A specific LC/ESI-MS/MS method for determination of 25-hydroxyvitamin D3 in neonatal dried blood spots containing a potential interfering metabolite, 3-epi-25-hydroxyvitamin D3

Vitamin D deficiency in an infant is associated with a wide range of adverse health outcomes in later life. A method for the quantification of 25‐hydroxyvitamin D₃ [25(OH)D₃, the best‐established indicator of vitamin D status] in neonatal dried blood spots (DBSs) using LC/ESI‐MS/MS has been developed and validated. The method employed two steps of derivatization, a Diels–Alder reaction with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione followed by acetylation, to enhance the detectability of 25(OH)D₃ in ESI‐MS/MS and to separate 25(OH)D₃ from 3‐epi‐25‐hydroxyvitamin D₃ [3‐epi‐25(OH)D₃], a potent interfering metabolite. 25(OH)D₃ was extracted from two DBS punches (3 mm in diameter, equivalent to 5.3 μL of whole blood), purified using an Oasis HLB^® cartridge, and subjected to derivatization prior to analysis with LC/ESI‐MS/MS. 25‐Hydroxyvitamin D₄ was used as the internal standard. This method was reproducible (intra‐ and inter‐assay RSDs, <6.9%) and accurate (analytical recovery, 95.2–102.7%), and the LOQ was 3.0 ng/mL. The developed method enabled specific quantification of 25(OH)D₃ in neonatal DBSs and detection of vitamin D deficiency without interference from 3‐epi‐25(OH)D₃.     

Application of a low impedance contactless conductometric detector for the determination of inorganic cations in capillary monolithic column chromatography

Poly(glycidyl methacrylate) cation exchange monolithic column was prepared in fused-silica capillaries of 320 μm i.d. by thermally initiated radical polymerization and utilized in capillary ion chromatography. With 15 mM methanesulfonic acid as the mobile phase, the separations of a mixture of inorganic cations (Li⁺, Na⁺, NH₄⁺, K⁺) was tested by using a capacitively coupled contactless conductivity detector (C⁴D) and a low impedance C⁴D (LIC⁴D). The LIC⁴D is the series combination of a C⁴D and a quartz crystal resonator. At the resonant frequency of the series combination, the capacitor impedance from capillary wall was offset by the inductance impedance from the quartz crystal resonator. A minimum impedance was obtained in the impedance-frequency curve of the combination. The responses of the C⁴D and LIC⁴D were analyzed based on an equivalent circuit model. It was shown that the sensitivity of the C⁴D to the change in analyte concentration is rather poor due to the high ratio of the impedance from the capillary wall capacitor to the solution impedance. The LIC⁴D has the similar sensitivity as a contact conductivity detector but a much smaller cell volume. The on-column detection model was realized by LiC⁴D without preparation of optical detection window in monolithic column.     

On‐line solid‐phase extraction coupled with liquid chromatography/electrospray ionization mass spectrometry for the determination of trace tributyltin and triphenyltin in water samples

On‐line solid‐phase extraction (SPE) for pre‐concentration and sample cleanup is one strategy to reduce matrix effects and to simultaneously improve detection sensitivity in liquid chromatography/mass spectrometry (LC/MS). This paper describes an on‐line SPE‐LC/MS method for the determination of tributyltin (TBT) and triphenyltin (TPhT) at trace levels in water samples. The direct coupling of an on‐line C₁₈ pre‐column to LC/MS was used to pre‐concentrate TBT and TPhT at trace levels from waters and to remove interfering matrix effects. Pre‐concentration was followed by separation of TBT and TPhT on a C₁₈ column using a mobile phase containing 0.1% (v/v) HCOOH/5 mM HCOONH₄ and methanol. While both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) can be interfaced with MS for the detection of TBT and TPhT, ESI‐MS was preferred for this application. The calibration curve for the targets was linear in the concentration range 0.1–30 µg L^?1. The detection limit (signal‐to‐noise (S/N) ratio = 3) was 0.02 µg L^?1 when 3.0 mL of sample was enriched on the C₁₈ pre‐column. The recoveries of TBT and TPhT in spiked waters were from 81.0 to 101.9%. The reproducibilities for the analysis of the standard mixture (10 µg L^?1) for TBT and TPhT were 13.1 and 5.0%, respectively. The developed method was an easy and fast way to analyze TBT and TPhT in water samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Simultaneous determination of caffeine,paracetamol, and ibuprofen in pharmaceutical formulations by high‐performance liquid chromatography with UV detection and by capillary electrophoresis with conductivity detection

Paracetamol, caffeine and ibuprofen are found in over‐the‐counter pharmaceutical formulations. In this work, we propose two new methods for simultaneous determination of paracetamol, caffeine and ibuprofen in pharmaceutical formulations. One method is based on high‐performance liquid chromatography with diode‐array detection and the other on capillary electrophoresis with capacitively coupled contactless conductivity detection. The separation by high‐performance liquid chromatography with diode‐array detection was achieved on a C₁₈ column (250×4.6 mm², 5 μm) with a gradient mobile phase comprising 20–100% acetonitrile in 40 mmol L^?1 phosphate buffer pH 7.0. The separation by capillary electrophoresis with capacitively coupled contactless conductivity detection was achieved on a fused‐silica capillary (40 cm length, 50 μm i.d.) using 10 mmol L^?1 3,4‐dimethoxycinnamate and 10 mmol L^?1 β‐alanine with pH adjustment to 10.4 with lithium hydroxide as background electrolyte. The determination of all three pharmaceuticals was carried out in 9.6 min by liquid chromatography and in 2.2 min by capillary electrophoresis. Detection limits for caffeine, paracetamol and ibuprofen were 4.4, 0.7, and 3.4 μmol L^?1 by liquid chromatography and 39, 32, and 49 μmol L^?1 by capillary electrophoresis, respectively. Recovery values for spiked samples were between 92–107% for both proposed methods.     

LC/ESI‐MS/MS characterisation of lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain

Lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain showed an interesting anti‐adhesion activity against biofilm formation of human pathogenic bacterial strains. The chemical characterisation of the crude extract of V9T14 strain was first developed through electrospray ionisation mass spectrometry (ESI‐MS) and ESI‐MS/MS direct infusions: two sets of molecular ion species belonging to the fengycin and surfactin families were revealed and their structures defined, interpreting their product ion spectra. The LC/ESI‐MS analysis of the crude extract allowed to separate in different chromatogram ranges the homologues and the isoforms of the two lipopeptide families. The extract was then fractionated by silica gel chromatography in two main fractions, I and II. The purified biosurfactants were analysed through a new, rapid and suitable LC/ESI‐MS/MS method, which allowed characterising the composition and the structures of the produced lipopeptides. LC/ESI‐MS/MS analysis of fraction I showed the presence of C₁₃, C₁₄ and C₁₅ surfactin homologues, whose structures were confirmed by the product ion spectra of the sodiated molecules [M + Na]⁺ at m/z 1030, 1044 and 1058. LC/ESI‐MS/MS analysis of fraction II confirmed the presence of two main fengycin isoforms, with the protonated molecules [M + H]⁺ at m/z 1478 and 1506 corresponding to C₁₇ fengycin A and C₁₇ fengycin B, respectively. Other homologues (C₁₄ to C₁₆) were revealed and confirmed as belonging to fengycin A or B according to the retention times and the product ions generated, although with the same nominal mass. Finally, a relative percentage content of each homologue for both lipopeptides families in the whole extract was proposed. Copyright © 2010 John Wiley & Sons, Ltd.     

Application of capillary electrophoresis with capacitively coupled contactless conductivity detection (CE‐C4D): An update

Capacitively coupled contactless conductivity detection (C⁴D) has appeared as a powerful technique for the detection of compounds lacking chromogenic or fluorogenic group. Since our last review (Biomedical Chromatography 2014; 28 : 1502–1506) several new capillary electrophoresis (CE)‐C⁴D methods have been reported. This review provides an update of the most recent utilization of CE‐C⁴D in the field of pharmaceutical, biomedical and food analysis covering the period from February 2014 to October 2016. The use of CE with C⁴D in the pharmaceutical field has been shown in many papers. Examples illustrate the applicability of CE‐C⁴D in the fields of pharmaceutical, biomedical and food analysis. Finally, general conclusions and perspectives are provided.     

Conformational Analysis of Thiosugars: Theoretical NMR Chemical Shifts and 3 J H,H Coupling Constants of 5‐Thio‐Pyranose Monosaccharides

The conformational space of D and L, deoxy and nondeoxy, 5‐thio‐pyranoses with biological properties as enzymatic inhibitors was explored using MM and B3LYP/6–31+G* methods in gas phase and solution. The preferred ring conformation for α and β anomers of 5‐thio‐L‐fucopyranose was the ¹C₄ form (about 99%), and for 5‐thio‐D‐glucopyranose and 5‐thio‐D‐mannopyranose, the ⁴C₁ one. The experimental conformational order (⁴C₁>¹C₄>²S_S) for L‐ido derivatives was reproduced only considering the solvent, though for 3‐O‐methyl‐5‐thio‐α‐L‐idopyranose, the inclusion of methyl in C₃ changed the ²S_S form to the B_1,4 one.     

Electrospray Ionization Mass Spectrometry: A Powerful Platform for Noble‐Metal Nanocluster Analysis

Electrospray ionization mass spectrometry (ESI‐MS) is an analytical technique that measures the mass of a sample through “soft” ionization. Recent years have witnessed a rapid growth of its application in noble‐metal nanocluster (NC) analysis. ESI‐MS is able to provide the mass of a noble‐metal NC analyte for the analysis of their composition (n, m, q values in a general formula [M_nL_m]^q), which is crucial in understanding their properties. This review attempts to present various developed techniques for the determination of the composition of noble metal NCs by ESI‐MS. Additionally, advanced applications that use ESI‐MS to further understand the reaction mechanism, complexation behavior, and structure of noble metal NCs are introduced. From the comprehensive applications of ESI‐MS on noble‐metal NCs, more possibilities in nanochemistry can be opened up by this powerful technique.     

One‐Electron Oxidation and Sensitivity of Uric Acid in On‐Line Electrochemistry and in Electrospray Ionization Mass Spectrometry

The sensitivity of detection of uric acid (H₂U) in positive ion mode electrospray ionization mass spectrometry (ESI MS) was enhanced by uric acid oxidation during electrospray ionization. With a carrier solution of pH 6.3>pK_a1=5.4 of H₂U, protonated unoxidized uric acid [H₂U+H]⁺ (m/z 169) was detected together with the protonated uric acid dimer [2H₂U+H]⁺ (m/z 337). The dimer likely forms by 1e^? oxidation of urate (HU^?) followed by rapid radical dimerization. A covalent structure of the dimer was verified by H/D exchange experiments. Efficiency of 2e^?, 2H⁺ oxidation of uric acid is low during ESI in pH 6.3 carrier solution and improves when a low on‐line electrochemical cell voltage is floated on the high voltage of the ES in on‐line electrochemistry ESI MS (EC/ESI MS). The intensity of the uric acid dimer decreases with an increase in the low applied voltage. In a carrier solution with 0.1 M KOH, pH 12.7>pK_a2=9.8 of H₂U, allantoin (Allnt) (MW 158.04), the final 2e^?, 2H⁺ oxidation product of uric acid, was detected as a potassium complex [K(Allnt)+K]⁺ (m/z 235) and the [2H₂U+H]⁺ dimer was not detected. In direct ESI MS analysis of 1000‐fold diluted urine [NaHU+H]⁺ (pK_sp NaHU=4.6) was detected in 40/60 (vol%) water/methanol, 1 mM NH₄Ac, pH ca. 6.3 carrier solution. A new configuration of the ESI MS instrument with a cone‐shaped capillary inlet significantly enhanced sensitivity in ESI and EC/ESI MS measurements of uric acid.     

Studies on the non‐covalent interactions between cyclodextrins and aryl alkanol piperazine derivatives by mass spectrometry and fluorescence spectroscopy

The non‐covalent complexes of α‐ and β‐cyclodextrins (α‐, β‐CDs) with two aryl alkanol piperazine derivatives (Pipe I and Pipe II) have been studied by electrospray ionization mass spectrometry (ESI‐MS) and fluorescence spectroscopy. The ESI‐MS experimental results demonstrated that Pipe I can conjugate to β‐CD and form 1:1 or 1:2 stoichiometric non‐covalent complexes, and Pipe II can only form 1:1 complexes with α‐ or β‐CD. Fluorescence spectra indicated that the fluorescence intensities of Pipe I and Pipe II can be enhanced by increasing the content of β‐CD. The mass spectrometric titration experiments showed that the dissociation constants K_d1 were 5.77 and 9.52 × 10^?4 mol L^?1 for the complexes of α‐CD with Pipe I and Pipe II, respectively, revealing that the binding of α‐CD‐Pipe I was stronger than α‐CD‐Pipe II. The K_d1 and K_d2 values were 9.81 × 10^?4 mol L^?1 and 1.11 × 10^?7 (mol L^?1)² for 1:1 and 1:2 complexes of Pipe I with β‐CD, respectively. The K_d values obtained from fluorescence spectroscopy were in agreement with those from ESI‐MS titration. Copyright © 2010 John Wiley & Sons, Ltd.     

Antioxidant Pathways and One‐Electron Oxidation of Dopamine and Cysteine in Electrospray and On‐Line Electrochemistry Electrospray Ionization Mass Spectrometry

Dopamine [DA]⁺ (m/z 154), DA dimer [2DA‐H]⁺ (m/z 307) and DA quinone [DAQ]⁺ (m/z 152) are detected in positive ion mode electrospray ionization mass spectrometry (ESI MS) of dopamine in 50/1/49 (vol%) water/acetic acid/methanol. H/D exchange experiments support a covalent structure of DA dimer. Thus, ESI of DA may involve 1e^?, 1H⁺ oxidation processes followed by rapid radical dimerization. The DA quinone signal is low in ESI MS, which indicates a low efficiency of the 2e^?, 2H⁺ oxidation reaction. On‐line electrochemistry ESI MS (EC/ESI MS) with low electrochemical cell voltage floated on high ES voltage increases electrospray current and improves sensitivity for DA. The DA quinone signal increases and DA dimer signal decreases. A new configuration of the ESI MS instrument with a cone‐shaped capillary inlet significantly enhanced sensitivity of ESI and EC/ESI MS measurements. A DA quinone‐cysteine adduct [DAQ+Cys]⁺ was detected in solutions of DA with cysteine (Cys). ESI MS and EC/ESI MS indicate formation of the DA quinone‐cysteine adduct by 1e^? pathway. Oxidation pathways in ESI MS are relevant to biological reactivity of DA and Cys.     

Tetrakis(diethyl‐phosphonat)‐, Tetrakis(ethyl‐phenylphosphinat)‐ und Tetrakis(diphenylphosphin‐oxid)‐substituierte Phthalocyanine

Tetrakis(diethyl phosphonate), Tetrakis(ethyl phenylphosphinate)‐, and Tetrakis(diphenylphosphine oxide)‐Substituted Phthalocyanines The title compounds 7, 9 , and 11 are obtained by tetramerization of diethyl (3,4‐dicyanophenyl)phosphonate ( 5 ), ethyl (3,4‐dicyanophenyl)phenylphosphinate ( 8 ), and 4‐(diphenylphosphinyl)benzene‐1,2‐dicarbonitrile ( 10 ). The ³¹P‐NMR spectra of the phthalocyanines 7, 9 , and 11 and of their metal complexes present five to eight signals confirming the formation of four constitutional isomers with the expected C_4h, D_2h, C_2v, and C_s symmetry. In the FAB‐MS of the Zn, Cu, and Ni complexes of 7 and 9 , the peaks of dimeric phthalocyanines are observed. By gel‐permeation chromatography, the monomeric complex [Ni( 7 )] and a dimer [Ni( 7 )]₂ can be separated. These dimers differ from the known phthalocyanine dimers, i.e., possibly the P(O)(OEt)₂ and P(O)(Ph)(OEt) substituents in 7 and 9 are involved in complexation. The free phosphonic acid complex [Zn( 12 )] and [Cu( 12 )] are H₂O‐soluble. In the FAB‐MS of [Zn( 12 )], only the peaks of the dimer are present; the ESI‐MS confirms the existence of the dimer and the metal‐free dimer. In the UV/VIS spectrum of [Zn( 12 )], the hypsochromic shift characteristic for the known type of dimers from 660–700 nm to 620–640 nm is observed. As in the FAB‐MS of [Zn( 12 )], the free phosphinic acid complex [Zn( 13 )] shows only the monomer, an ESI‐MS cannot be obtained for solubility problems. The UV/VIS spectrum of [Zn( 13 )] demonstrates the existence of the monomer as well as of the dimer.     

A Convenient Approach to Simultaneous Analysis of a Pharmaceutical Drug and Its Counter-Ion by CE Using Dual-Opposite End Injection and Contactless Conductivity Detection

Capillary electrophoresis (CE) coupled to a capacitively coupled contactless conductivity detector (C⁴D) was used for the determination in a single analysis of a pharmaceutical drug and its counter-ion. Dual-opposite end injection (DOI) was used to introduce hydrodynamically the analytes at each end of the capillary. No modification of the commercial apparatus is required. After applying the voltage, the cations and anions migrate from each end of the capillary in opposite directions toward the detector placed near the cathode outlet. The electrophoretic conditions were initially developed with three test drugs (chlorpheniramine maleate, metoprolol tartrate, clomiphene citrate) and then applied to two Vinca alkaloids (catharanthine sulfate, vinorelbine ditartrate). The 10 mM histidine–50 mM acetic acid buffer (pH 4.1)–methanol 90:10 (v/v) electrolyte was suitable for the analysis of these high or medium mobile anions by CE–C⁴D due to its low conductivity background and high buffer capacity. Finally, the CE procedure developed was successfully validated for catharanthine sulfate. The method developed herein is fast (<10 min) and accurate (repeatability on migration time < 0.6% and peak areas < 1.3%, n = 6).

     

两种天然齐墩果酸皂苷的合成

3-O-[β-D-Glucopyranosyl-（1→3）-α-L-arabinopyranosyl]-oleanolic acid-28-O-[β-D-glucopyranosyl] ester 1 was synthesized concisely by a convergent strategy. Using stepwise fashion for the synthesis of saponin 2, 3-O-{[β-D-glucopyranosyl-（1→2）]-[α-L-arabinopyranosyl-（1→3）]-α-L-arabinopyranosyl）-oleanolic acid-28-O-（β- D-glucopyranosyl） ester, an abnormal phenomenon, that the terminal arabinosyl residue took the ^1C4 conformation instead of typical ^4C1 form, was observed. Deprotection or heating could not resume the normal conformation, which resulted in the product of 2＇ not 2.     

An experimental and computational investigation on the fragmentation behavior of enaminones in electrospray ionization mass spectrometry

The dissociation pathways of protonated enaminones with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) in positive ion mode. In mass spectrometry of the enaminones, Ar? CO? CH?CH? N(CH₃)₂, the proton transfers from the thermodynamically favored site at the carbonyl oxygen to the dissociative protonation site at ipso‐position of the phenyl ring or the double bond carbon atom adjacent to the carbonyl leading to the loss of a benzene or elimination of C₄H₉N, respectively. And the hydrogen? deuterium (H/D) exchange between the added proton and the proton of the phenyl ring via a 1,4‐H shift followed by hydrogen ring‐walk was witnessed by the D‐labeling experiments. The elemental compositions of all the ions were confirmed by ultrahigh resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR‐MS/MS). The enaminones studied here were para‐monosubstituted on the phenyl ring and the electron‐donating groups were in favor of losing the benzene, whereas the electron‐attracting groups strongly favored the competing proton transfer reaction leading to the loss of C₄H₉N to form a benzoyl cation, Ar‐CO⁺. The abundance ratios of the two competitive product ions were relatively well‐correlated with the σ_p⁺ substituent constants. The mechanisms of these reactions were further investigated by density functional theory (DFT) calculations. Copyright © 2010 John Wiley & Sons, Ltd.     

On‐line 2D‐LC‐ESI/MS/MS determination of rifaximin in rat serum

A highly sensitive and selective on‐line two‐dimensional reversed‐phase liquid chromatography/electrospray ionization–tandem mass spectrometry (2D‐LC‐ESI/MS/MS) method was developed and validated to determine rifaximin in rat serum by direct injection. The 2D‐LC‐ESI/MS/MS system consisted of a restricted access media column for trapping proteins as the first dimension and a Waters C₁₈ column as second dimension using 0.1% aqueous acetic acid:acetonitrile as mobile phase in a gradient elution mode. Rifampacin was used as an internal standard. The linear dynamic range was 0.5–10 ng/mL (r² > 0.998). Acceptable precision and accuracy were obtained over the calibration range. The assay was successfully used in analysis of rat serum to support pharmacokinetic studies. Copyright © 2009 John Wiley & Sons, Ltd.     

Simultaneous determination of atenolol and amiloride in pharmaceutical preparations by capillary zone electrophoresis with capacitively coupled contactless conductivity detection

Capillary zone electrophoresis coupled with a capacitively coupled contactless conductivity detector (CE‐C⁴D) has been employed for the determination of atenolol and amiloride in pharmaceutical formulations. Acetic acid (150 mm ) was used as background electrolyte. The influence of several factors (detector excitation voltage and frequency, buffer concentration, applied voltage, capillary temperature and injection time) was studied. Non‐UV‐absorbing L‐valine was used as internal standard; the analytes were all separated in less than 7 min. The separation was carried out in normal polarity mode at 28°C, 25 kV and using hydrodynamic injection (25 s). The separation was effected in an uncoated fused‐silica capillary (75 μm, i.d. × 52 cm). The CE‐C⁴D method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 5–250 μg/mL for the studied analytes. The relative standard deviations of intra‐ and inter‐day migration times and corrected peak areas were less than 6.0%. The method showed good precision and accuracy and was successfully applied to the simultaneous determination of atenolol and amiloride in different pharmaceutical tablet formulations. Copyright © 2010 John Wiley & Sons, Ltd.     

Fast Determination of Ciprofloxacin by Batch Injection Analysis with Amperometric Detection and Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

We report fast, precise, selective, and sensitive electroanalytical methods for the determination of ciprofloxacin in milk and pharmaceutical samples by batch‐injection analysis with amperometric detection (BIA‐AMP) and by capillary electrophoresis with capacitively‐coupled contactless conductivity detection (CE‐C⁴D). Both methods required simple sample preparation protocols before analysis (milk samples were just diluted and tablets powdered and dissolved in electrolyte/water). The analytical features of BIA‐AMP and CE‐C⁴D methods include, respectively, low relative standard deviation values for repetitive measurements (2.8 % and 1.7 %, n=10), low detection limits (0.3 and 5.0 µmol L^?1), elevated analytical frequency (80 and 120 h^?1) and satisfactory accuracy (based on comparative determinations by HPLC and recovery values for spiked samples).     

CO2 Fixation and Transformation by a Dinuclear Copper Cryptate under Acidic Conditions

CO₂ fixation and transformation by metal complexes continuously receive attention from the viewpoint of carbon resources and environmental concerns. We found that the dinuclear copper(II) cryptate [Cu₂L¹](ClO₄)₄ ( 1 ; L¹=N[(CH₂)₂NHCH₂(m‐C₆H₄)CH₂NH‐(CH₂)₂]₃N) can easily take up atmospheric CO₂ even under weakly acidic conditions at room temperature and convert it from bicarbonate into carbonate monoesters in alcohol solution. The compounds [Cu₂L¹(μ‐O₂COH)](ClO₄)₃ ( 2 ), [Cu₂L¹(μ‐O₂COR)](ClO₄)₃ ( 3 : R=CH₃; 4 : R=C₂H₅; 5 : R=C₃H₇; 6 : R=C₄H₉; 7 : R=C₅H₁₁; 8 : R=CH₂CH₂OH), [Cu₂L¹(μ‐O₂CCH₃)](ClO₄)₃ ( 9 ), and [Cu₂L¹(OH₂)(NO₃)](NO₃)₃ ( 10 ) were characterized by IR spectroscopy and ESI‐MS. The crystal structures of 2 – 6 and 10 were studied by single‐crystal X‐ray diffraction analysis. On the basis of the crystal structures, solution studies, and DFT calculations, a possible mechanism for CO₂ fixation and transformation is given.