Illuminate Proteins and Peptides by Elemental Tag for HPLC-ICP-MS Detection

Abstract

High-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC-ICP-MS) is becoming a significant complementary technique of HPLC–molecular mass spectrometry for proteins and peptides quantification. However, the naturally occurring heteroelements inside proteins and peptides, such as sulfur, phosphor, and selenium, are not sensitive enough in ICP-MS for low-abundance proteins and peptides, due to their low ionization efficiency or polyatomic spectral interference. In order to make the low-abundance proteins and peptides “visible” by HPLC-ICP-MS, a foreign elemental tag can be employed. The foreign elemental tags are highly sensitive in ICP-MS and almost absent in common biological matrices, which leads to significantly low limits of detection. This review summarizes the major applications of elemental tags in combination with HPLC-ICP-MS detection. The organic mercury tags, iodine tags, ferrocene tags, and macrocyclic metal chelate complex tags are discussed in detail. The recent development of HPLC-ICP-MS in combination with elemental tags demonstrates the great potential in sensitive and accurate proteins and peptides quantification.     

Sensitized emission of luminescent lanthanide complexes based on 4-naphthalen-1-yl-benzoic acid derivatives by a charge-transfer process.

The photophysical properties of 4-naphthalen-1-yl-benzoic acid ligands and their Eu(III)-cored complexes were systematically investigated to elucidate the effective energy-transfer pathway in luminescent lanthanide complexes. A series of 4-naphthalen-1-yl-benzoic acid ligands, such as 4-naphthalen-1-yl-benzoic acid (NA-1), 4-[4-(4-methoxyphenyl)-naphthalen-1-yl]-benzoic acid (NA-2), and 4-{4-[4-(4-methoxyphenyl)-naphthalen-1-yl]-benzyloxy}-benzoic acid (NA-3), were synthesized and utilized for the synthesis of their Eu(III)-cored complexes, corresponding to NAC-1, NAC-2, and NAC-3. The fluorescence spectra of NA-1 and NA-2 show large Stokes shifts with increasing solvent polarity. These large Stokes shifts might be dominantly due to the formation of an intramolecular charge transfer (ICT) complex in the excited state. Also, the intensive luminescence of the Eu(III) ions by the photoexcitation of the ligand in NAC-1 and NAC-2 in polar solvents supports that the energy transfer from the ligand to the Eu(III) ion takes place efficiently. In the case of NA-3, which has a -CH2OPh- group that acts as a blocking group, there is no dependence of the fluorescence spectrum on the solvent nature and no luminescence of the Eu(III) ions by the photoexcitation of the ligand, indicating no formation of the ICT state. This can be due to the fact that the formation of the ICT state in NA-3 was prevented because the -OCH2- group acts as a blocking group by interrupting the pi-conjugation between the benzoic acid and the naphthalene unit. From these photophysical studies, we suggest that the ICT state plays a very important role in the energy-transfer pathway from the ligand to the Eu(III) ion. To our best knowledge, this is the first demonstration of sensitized emission of luminescent lanthanide complexes based on 4-naphthalen-1-yl-benzoic acid derivatives by the charge-transfer process.     

Aqueous Geochemistry of Rare Earth Elements and Yttrium. XII: Potentiometric Stability Constant Determination of Bis-Tris Complexes with La, Nd, Eu, Gd, Yb, Dy, Er, Lu, and Y

Conditional stability constants of 2-[bis(2-hydroxyethyl)amino]-2(hydroxymethyl)-1,3-propanediol (BT) complexes of trivalent rare earth element (Ln) ions (La, Nd, Eu, Gd, Yb, Dy, Er, Lu) and Y were determined potentiometrically in aqueous NaCl solutions at 30°C and 0.1 M ionic strength. Least-squares fitting shows that, at <0.04 molal BT, the complex LnBT³⁺ is dominant, with LnBT₂ ³⁺ forming a secondary complex, where:

Relaxometric Study of Copper [15]Metallacrown‐5 Gadolinium Complexes Derived from α‐Aminohydroxamic Acids

Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded between 0.24 mT and 1.4 T for lanthanum(III )‐ and gadolinium(III )‐containing [15]metallacrown‐5 complexes derived from α‐aminohydroxamic acids and with copper(II ) as the ring metal. The influence of the different R‐groups on the proton relaxivity was investigated, and a linear relationship between the relaxivity and the molecular mass of the metallacrown complex was found. The selectivity of the metallacrown complexes was tested by transmetalation experiments with zinc(II ) ions. The crystal structure of the copper [15]metallacrown‐5 gadolinium complex with glycine hydroximate ligands is reported.     

Sonoluminescence of aqueous solutions of lanthanide salts

The influence of salts (TbCl₃, Tb(NO₃)₃, PrCl₃, EuCl₃, CeCl₃, and DyCl₃) on the spectrum and intensity of multi-bubble sonoluminescence (SL) of water was observed at a frequency of 20 kHz. Luminescence bands of the lanthanide ions were detected in the SL spectra of concentrated solutions of the Ce^III, Tb^III, and Dy^III chlorides (0.1—1 mol L^–1). No luminescence was observed for solutions of the other salts, and the shape of the spectra is due to the absorption of the water SL by the lanthanide ions. Possible mechanisms of the appearance of SL of lanthanides were considered. The first mechanism is the excitation of the lanthanide aqua ions in the solution bulk due to the absorption of the short-wave portion of glow of the excited water molecules and OH radicals emitted from the cavitation gas-vapor bubbles. The second mechanism involves the transfer of the lanthanide ions to the gas phase from the liquid layer adjacent to the cavitation bubble and their excitation in the bubble volume upon collisions with other hot or electron-excited particles.     

Preparation, Spectral and Thermal Studies of Y(III) and Lanthanide(III) 1-Hydroxy-2-Naphthoates

Complexes of lanthanide(III) (La–Lu) and Y(III) with 1-hydroxy-2-naphthoic acid were obtained as crystalline compounds with a general formula Ln[C₁₀H₆(OH)COO]₃⋅nH₂O:n=6 for La–Tm and Y, n=2 for Yb and n=0 for Lu. IR spectra of the prepared complexes were recorded, and their thermal decomposition in air were investigated. Spectroscopic data suggest that in the coordination of metal-organic ligand only oxygen atoms from the carboxylate group take part. When heated, the complexes decompose to the oxides Ln₂O₃, CeO₂, Pr₆O₁₁ and Tb₄O₇ with intermediate formation of Ln(C₁₁H₇O₃)(C₁₁H₆O₃). This revised version was published online in August 2006 with corrections to the Cover Date.     

In situ high temperature NMR and EXAFS experiments in rare-earth fluoride molten salts

The local structure in molten YF₃–LiF and LaF₃–LiF binaries has been investigated by NMR and EXAFS spectroscopy. For YF₃–LiF, the high-temperature ¹⁹F and ⁷Li NMR spectra have been recorded in situ in the molten state for compositions ranging from pure LiF to pure YF₃. The LaF₃–LiF system has been studied by ¹⁹F and ¹³⁹La NMR and EXAFS spectroscopy at the LIII edge of La. The local environment around the La³⁺ in the molten state does not depend on the composition, while ¹⁹F chemical shift evolution confirms the progressive formation of bridged species. To cite this article: A.-L. Rollet et al., C. R. Chimie 7 (2004).

Résumé

Étude in situ par spectroscopies RMN et EXAFS à haute température de fluorures de terres rares fondus. La structure locale des mélanges fondus YF₃–LiF et LaF₃–LiF a été étudiée par spectroscopies RMN et EXAFS à haute température. Pour le système YF₃–LiF, les spectres RMN à haute température de ¹⁹F et ⁷Li ont été enregistrés in situ dans le liquide pour différentes compositions variant de LiF pur à YF₃ pur. Le système LaF₃–LiF a été étudié par RMN de ¹⁹F et ¹³⁹La, et par EXAFS au seuil LIII du lanthane. L’environnement autour du La³⁺ à l’état fondu ne dépend pas de la composition, alors que les évolutions du déplacement chimique du fluor confirment la formation progressive d’espèces pontantes. Pour citer cet article : A.-L. Rollet et al., C. R. Chimie 7 (2004).     

A new pyridine-2,6-bis(oxazoline) for efficient and flexible lanthanide-based catalysts of enantioselective reactions with 3-alkenoyl-2-oxazolidinones

A new pyridine-2,6-bis(oxazoline) (4) has been easily synthesised from the reaction of (1S,2S)-2-amino-1-phenylpropane-1,3-diol (1) and dimethyl pyridine-2,6-dicarboximidate (2), followed by TIPS (TIPS=triisopropylsilyl) protection of the 4'-CH2OH group. The catalysts derived from 4 and eight lanthanide(III) triflates have been tested over three reactions involving 3-acryloyl- and 3-crotonoyloxazolidinones (5 a,b): the Diels-Alder (DA) reaction with cyclopentadiene, the 1,3-dipolar cycloaddition with diphenyl nitrone and the Mukaiyama-Michael reaction with 2-trimethylsilyloxyfuran. Several reactions exhibit very good enantioselectivity (ee>90 %), and the opposite enantiomers can be easily obtained simply by changing the cation. This specific feature of the ligand can be appreciated in the DA reaction of 5 a, since the catalyst [Sc(III)4] gives the adduct (2'S)-9 a with 99 % ee, whereas the catalyst [Y(III)4] gives the opposite enantiomer with 95 % ee. A rationale of the enantioselectivity is proposed on the basis of the NMR spectra of La-based complexes involving 4 and 5 as ligands.