Search

Heteronuclear arsenic–iron carbonyl cluster anions AsmFe(CO)n–(m, n= 2, 3) have been generated in the gas phase and investigated by mass-selected infrared photodissociation spectroscopy and density functional theory calculations at the B3LYP/BP86/TPSS levels. All the AsmFe(CO)n–(m, n= 2, 3) cluster anions are determined to contain Fe(CO)n–fragments, which can be regarded as being formed by replacing one arsenic atom of the arsenic clusters Asm+1with the Fe(CO)n–group. Bonding analyses indicated that each As2Fe(CO)n–(n= 2, 3) cluster anion involves two Fe–As single bonds and one As–As double bond. Each As3Fe(CO)n–(n= 2, 3) cluster anion has three Fe–As single bonds and three As–As single bonds. The Fe(CO)3–group with a 15-electron configuration is valence isoelectronic to the As atom and can serve as a building block for forming heteronuclear arsenic–iron carbonyl clusters.

An apparatus based on collinear tandem time-of-flight mass spectrometer has been designed for the measurement of infrared photodissociation spectroscopy of mass-selected ions in the gas phase. The ions from a pulsed laser vaporization supersonic ion source are skimmed and mass separated by a Wiley-McLaren time-of-flight mass spectrometer. The ion of interest is mass selected, decelerated and dissociated by a tunable IR laser. The fragment and parent ions are reaccelerated and mass analyzed by the second time-of-flight mass spectrometer. A simple new assembly integrated with mass gate, deceleration and reacceleration ion optics was designed, which allows us to measure the infrared spectra of mass selected ions with high sensitivity and easy timing synchronization.

Fatty acids play a pivotal role in biological processes and have many isomers, particularly at the C═C position, that influence their biological function. Distinguishing between isomers is crucial to investigating their role in health and disease. However, separating the isomers poses a significant analytical challenge. In this study, we developed a simple and rapid strategy combining ion mobility spectrometry and theoretical chemical calculations to differentiate and quantify the C═C positional isomers in 2-/3-butenoic acid (BA), 2-/3-/4-pentenoic acid (PA), and 2-/3-/5-hexenoic acid (HA). C═C positional isomerism was mobility-differentiated by simple complexation with crown ethers (12C4, 15C5, and 18C6) and divalent metal ions (Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+, Sr2+, and Ba2+), that is, converting C═C positional isomers with small structural differences into complexes with large structural differences through the interaction with metal ions and crown ethers. Metallized isomers were formed but could not be differentiated due to their complex and overlapping extracted ion mobiliograms (EIMs). Binary crown ether–isomer complexes were not observed, indicating that C═C positional isomers could not be separated by simple mixing with crown ethers. However, significant EIM differences were obtained for the formed ternary complexes, allowing baseline separation for the isomers. Notably, all crown ethers and metal ions have a separation effect with the isomers, with a calculated separation resolution (Rp–p) of 0.07–2.44. Theoretical chemical calculations were performed to provide in-depth structural information for the complexes and explain the separation principle. Theoretical conformational space showed that the divalent metal ions act as a bridge connecting the crown ether and the isomer. Additionally, the ternary complex becomes more compact as the distance between C═C and −COOH increases. Theoretical results can reflect the features of mobility experiments, with relative errors between the experiment collision cross-section (CCS) and theoretical CCS of no more than ±8.06%. This method was also evaluated in terms of quantification, accuracy, and precision repeatability. Overall, this study establishes that the crown ether–metal ion pair can function as a robust unit for differentiating C═C positional isomerism.