Post-synthesis of a titanium-rich magnetic COF nanocomposite with flexible branched polymers for efficient enrichment of phosphopeptides from human saliva and serum.

A Ti4+-functionalized magnetic covalent organic framework material with flexible branched polymers (mCOF@ε-PL@THBA-Ti4+) built via an immobilized metal ion affinity chromatography (IMAC) enrichment strategy was proposed through post-synthesis modification. Hydrophilic ε-poly-L-lysine (ε-PL) rich in amino active groups was first introduced in the fabrication of the phosphopeptide enrichment material to increase the hydrophilicity while providing more functional modification pathways of the material. 2,3,4-Trihydroxy-benzaldehyde (THBA) provides abundant binding sites for the immobilization of numerous Ti4+, which is advantageous for the subsequent efficient phosphopeptide enrichment. The magnetic nanocomposite exhibited outstanding performance of phosphopeptide enrichment with good selectivity (1 : 5000), a low detection limit (2 fmol), and relatively high loading capacity (66.7 mg g-1). What's more, after treatment with mCOF@ε-PL@THBA-Ti4+, 16 endogenous phosphopeptides from fresh saliva of healthy people were recognized by MALDI-TOF MS, and 50 phosphopeptides belonging to 35 phosphoproteins from the serum of uremia patients were detected by nano-LC-MS/MS. Proteomics data analysis for the differential protein selection between uremia and normal controls was conducted using R software, and four down-regulated and three up-regulated proteins were obtained. The results suggested that the prepared material has potential applications in biomarker discovery.

Spectroscopic characterization of heteronuclear iron-chromium carbonyl cluster anions.

Infrared photodissociation spectroscopy has been used to investigate CrFe(CO)n- (n = 4-9) clusters in the gas phase. Comparison of the observed spectra in the carbonyl stretching frequency region with those predicted for low-lying isomers by DFT calculations showed that the observed CrFe(CO)n- (n = 4-8) clusters could be characterized to have Cr-Fe bonded (OC)4Fe-Cr(CO)n-4 structures. The coexistence of isomers with the (OC)Fe-Cr(CO)5 and (OC)3Fe-Cr(CO)4 structures was also observed for CrFe(CO)6- and CrFe(CO)7- anions, respectively. The CrFe(CO)n- (n = 4-8) complexes were strongly bonded systems. The CrFe(CO)8- complex was a coordination-saturated cluster, and the CrFe(CO)9- anion was characterized to contain a CrFe(CO)8- core tagged by one CO molecule. Bonding analysis revealed that the Cr-Fe bonds in the CrFe(CO)n- (n = 4-8) clusters were predominantly σ-type single bonds. The iron center in the Fe(CO)4 moiety and the chromium center in the Cr(CO)5 moiety fulfilled the 18-electron configuration for the CrFe(CO)n- (n = 4-6) clusters. As in the CrFe(CO)n- (n = 7, 8) complexes, the iron center in the Fe(CO)4 moiety exhibited a 17-electron configuration, while the chromium center in the Cr(CO)4 moiety exhibited a 16-electron configuration. These findings provide valuable insights into the structure and bonding mechanism of heterometallic carbonyl clusters.

Cis- and trans-binding influences in [NUO·(N2)n].

Uranium nitride-oxide cations [NUO]+ and their complexes with equatorial N2 ligands, [NUO·(N2)n]+ (n = 1-7), were synthesized in the gas phase. Mass-selected infrared photodissociation spectroscopy and quantum chemical calculations confirm [NUO·(N2)5]+ to be a sterically fully coordinated cation, with electronic singlet ground state of 1A1, linear [NUO]+ core, and C5v structure. The presence of short N-U bond distances and high stretching modes, with slightly elongated U-O bond distances and lowered stretching modes, is rationalized by attributing them to cooperative covalent and dative [ǀN≡U≡Oǀ]+ triple bonds. The mutual trans-interaction through flexible electronic U-5f6d7sp valence shell and the linearly increasing perturbation with increase in the number of equatorial dative N2 ligands has also been explained, highlighting the bonding characteristics and distinct features of uranium chemistry.

Infrared photodissociation spectroscopy of heteronuclear group 15 metal-iron carbonyl cluster anions AmFe(CO)n- (A = Sb, Bi; m, n = 2, 3).

Heteronuclear group 15 metal-iron carbonyl cluster complexes of AmFe(CO)n- (A = Sb, Bi; m, n = 2-3) were generated in the gas phase and studied by infrared photodissociation spectroscopy in the carbonyl stretching region. Their structures were determined by comparing the experimental spectra with predicted spectra derived from DFT calculations at the B3LYP and BP86 levels. All of the AmFe(CO)n- cluster anions were determined to have Fe(CO)n- fragments with all of the CO ligands terminally bonded to the iron center, and they can be regarded as being formed via the interactions of the neutral group 15 metal clusters with the Fe(CO)n- fragments. Bonding analyses indicated that each A2Fe(CO)n- (n = 2, 3) cluster anion contained two A-Fe single bonds and one A-A double bond. Each A3Fe(CO)n- (n = 2, 3) cluster anion involved three A-Fe single bonds and three A-A single bonds. There is an isolobal relationship between the Fe(CO)3- group and the group 15 atoms. The substitution of an Fe(CO)3- group in place of one A atom in the tetrahedral A4 molecule resulted in an A3Fe(CO)3- cluster anion with the closed-shell electronic configuration for all the group 15 metals and iron atoms.

Infrared Photodissociation Spectroscopy of Heteronuclear Arsenic-Iron Carbonyl Cluster Anions.

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+1 with 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.

Octacarbonyl Ion Complexes of Actinides [An(CO)8 ]+/- (An=Th, U) and the Role of f Orbitals in Metal-Ligand Bonding.

The octacarbonyl cation and anion complexes of actinide metals [An(CO)8 ]+/- (An=Th, U) are prepared in the gas phase and are studied by mass-selected infrared photodissociation spectroscopy. Both the octacarbonyl cations and anions have been characterized to be saturated coordinated complexes. Quantum chemical calculations by using density functional theory show that the [Th(CO)8 ]+ and [Th(CO)8 ]- complexes have a distorted octahedral (D4h ) equilibrium geometry and a doublet electronic ground state. Both the [U(CO)8 ]+ cation and the [U(CO)8 ]- anion exhibit cubic structures (Oh ) with a 6 A1g ground state for the cation and a 4 A1g ground state for the anion. The neutral species [Th(CO)8 ] (Oh ; 1 A1g ) and [U(CO)8 ] (D4h ; 5 B1u ) have also been calculated. Analysis of their electronic structures with the help on an energy decomposition method reveals that, along with the dominating 6d valence orbitals, there are significant 5f orbital participation in both the [An]←CO σ donation and [An]→CO π back donation interactions in the cations and anions, for which the electronic reference state of An has both occupied and vacant 5f AOs. The trend of the valence orbital contribution to the metal-CO bonds has the order of 6d≫5f>7s≈7p, with the 5f orbitals of uranium being more important than the 5f orbitals of thorium.

Alkali Metal Covalent Bonding in Nickel Carbonyl Complexes ENi(CO)3.

The alkali metal-nickel carbonyl anions ENi(CO)3 - with E=Li, Na, K, Rb, Cs have been produced and characterized by mass-selected infrared photodissociation spectroscopy in the gas phase. The molecules are the first examples of 18-electron transition metal complexes with alkali atoms as covalently bonded ligands. The calculated equilibrium structures possess C3v geometry, where the alkali atom is located above a nearly planar Ni(CO)3 - fragment. The analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms.

Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3- (A=As, Sb, Bi) Complexes.

Heteronuclear transition-metal-main-group-element carbonyl complexes of AsFe(CO)3- , SbFe(CO)3- , and BiFe(CO)3- were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass-selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)3- . Chemical bonding analyses on the whole series of AFe(CO)3- (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp-p) type of transition-metal-main-group-element multiple bonding. The σ-type three-orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)3- (A=As, Sb, Bi) complexes.

CO Oxidation by Group 3 Metal Monoxide Cations Supported on [Fe(CO)4 ]2.

Infrared photodissociation spectroscopy of mass-selected heteronuclear cluster anions in the form of OMFe(CO)5- (M=Sc, Y, La) indicates that all these anions involve an 18-electron [Fe(CO)4 ]2- building block that is bonded with the M center through two bridged carbonyl ligands. The OLaFe(CO)5- anion is determined to be a CO-tagged complex involving a [Fe(CO)4 ]2- [LaO]+ anion core. In contrast, the OYFe(CO)5- anion is characterized to have a [Fe(CO)4 ]2- [Y(η2 -CO2 )]+ structure involving a side-on bonded CO2 ligand. The CO-tagged complex and the [Fe(CO)4 ]2- [Sc(η2 -CO2 )]+ isomer co-exist for the OScFe(CO)5- anion. These observations indicate that both the ScO+ and YO+ cations supported on [Fe(CO)4 ]2- are able to oxidize CO to CO2 . Theoretical analyses show that [Fe(CO)4 ]2- coordination significantly weakens the MO+ bond and decreases the energy gap of the interacting valence orbitals between MO+ and CO, leading to the CO oxidation reactions being both thermodynamically exothermic and kinetically facile.

Preparation and Characterization of Uranium-Iron Triple-Bonded UFe(CO)3- and OUFe(CO)3- Complexes.

We report the preparation of UFe(CO)3- and OUFe(CO)3- complexes using a laser-vaporization supersonic ion source in the gas phase. These compounds were mass-selected and characterized by infrared photodissociation spectroscopy and state-of-the-art quantum chemical studies. There are unprecedented triple bonds between U 6d/5f and Fe 3d orbitals, featuring one covalent σ bond and two Fe-to-U dative π bonds in both complexes. The uranium and iron elements are found to exist in unique formal U(I or III) and Fe(-II) oxidation states, respectively. These findings suggest that there may exist a whole family of stable df-d multiple-bonded f-element-transition-metal compounds that have not been fully recognized to date.