Measurement and summary of photoionization data for biomass-derived compounds.

RATIONALE: Biomass is a potential feedstock for making liquid fuels and valuable chemicals. Quantitative analysis of biomass conversion in real time by photoionization mass spectrometry (PIMS) is an important way to understand the reaction process. However, the lack of photoionization data for biomass-derived compounds limits the research using PIMS. METHODS: Measurements of photoionization data were performed with synchrotron vacuum ultraviolet PIMS. Toluene and methanol were used as calibrated references and solvents in this experiment since their photoionization cross-sections (PICS) are well documented in the literature. RESULTS: The ionization energies (IEs) of 23 biomass-derived compounds were measured. Among them, the PICSs of 14 compounds were calibrated and presented. Besides, the IEs of 95 other biomass-derived compounds and their typical fragment ions were also summarized. CONCLUSIONS: A photoionization database related to IEs and PICSs of biomass-derived compounds (m/z < 200) is established. PICSs of most biomass-derived compounds have low values at the most frequently used photoionization energy of 10.5 eV. Lignin-derived compounds have lower IEs than carbohydrate-derived compounds.

Efficient preparation of carbon nanospheres-anchored porous carbon materials and the investigation on pretreatment methods.

Manufacturing high-performance activated carbon (AC) materials from abundant biomass at low temperature and short activation time is targeted by the green and sustainable chemical industry. Here, a 1980 m2/g of carbon nanospheres-anchored porous carbon material (PHAC) derived from waste sawdust was prepared by a method of H3PO4 hydrothermal combined with fast activation at 450 °C within 2.8 min. It is found that H3PO4 hydrothermal pretreatment could promote the dehydration of carbohydrates to form more unstable C = O structures, which were decomposed in the subsequent fast activation to form pore structures. In addition, this process is also conducive to the formation of carbon nanospheres, increasing the degree of graphitization and producing more graphite defects. The prepared PHAC showed good adsorption performance for different types of pollutants. This work provides a new insight for the preparation of high performance biomass based carbon materials under mild conditions.

Evidence of a Phenolic Pool as a Key Intermediate for Zeolite-Catalyzed Lignin Pyrolysis.

The phenolic pool is considered to be an important intermediate during the catalytic conversion of biomass. However, no direct evidence has been reported on its full picture on a molecular level due to the huge challenges in probing the reactive and lowly volatile phenolic oligomers with state-of-the-art technologies. Herein, we report the online detection and structural identification of a phenolic pool by utilizing in-situ atmospheric-pressure photoionization mass spectrometry, demonstrating that the phenolic pool is formed through repolymerization of monomers with an equidistant group pattern and acts as a key mechanistic step for both valuable aromatic products and undesired coke. The exploration of the real reactive species is also of great importance for the rational design and synthesis of advanced catalysts with high activity.

Interactions of disulfide-constrained cyclic tetrapeptides with Cu(2+).

The purpose of this work is to characterize the interactions of two disulfide-constrained cyclic tetrapeptides [c(Ac-Cys-Pro-Phe-Cys-NH(2)), SS1; c(Ac-Cys-Pro-Gly-Cys-NH(2)), SS2] with Cu(2+) ions in order to facilitate the design of cyclic peptides as sensors for metal ions. The Cu(2+)-peptide complex cations at m/z 569.1315 for Cu(2+)-SS1 and m/z 479.0815 for Cu(2+)-SS2 were detected by mass spectrometry. The gas-phase fragmentation of the Cu(2+)-peptide complexes was studied by collision-induced dissociation and suggests the atoms involved in the coordination. Cu(2+) ion binds to a single SS1 or SS2 with K (d(app)) of 0.57 ± 0.02 and 0.55 ± 0.01 µM, respectively. Isothermal titration calorimetry data indicate both enthalpic and entropic contributions for the binding of Cu(2+) ion to SS1 and SS2. The characteristic wavenumber of 947 cm(-1) and the changes at 1,664 and 1,530 cm(-1) in the infrared spectrum suggest that the sulfydryl of cysteine, the carbonyl group, and amide II are involved in the coordination of Cu(2+). The X-ray absorption near-edge structure signal from the Cu(2+)-peptide complex corresponds to the four-coordination structure. The extended X-ray absorption fine structure and electron paramagnetic resonance results demonstrate the Cu(2+) ion is in an S/N/2O coordination environment, and is a distinct type II copper center. Theoretical calculations further demonstrate that Cu(2+) ion binds to SS1 or SS2 in a slightly distorted tetragonal geometry with an S/N/2O environment and the minimum potential energy.

On-line product analysis of pine wood pyrolysis using synchrotron vacuum ultraviolet photoionization mass spectrometry.

The pyrolysis process of pine wood, a promising biofuel feedstock, has been studied with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry. The mass spectra at different photon energies and temperatures as well as time-dependent profiles of several selected species during pine wood pyrolysis process were measured. Based on the relative contents of three lignin subunits, the data indicate that pine wood is typical of softwood. As pyrolysis temperature increased from 300 to 700 °C, some more details of pyrolysis chemistry were observed, including the decrease of oxygen content in high molecular weight species, the observation of high molecular weight products from cellulose chain and lignin polymer, and potential pyrolysis mechanisms for some key species. The formation of polycyclic aromatic hydrocarbons (PAHs) was also observed, as well as three series of pyrolysis products derived from PAHs with mass difference of 14 amu. The time-dependent profiles show that the earliest products are formed from lignin, followed by hemicellulose products, and then species from cellulose.

Selectivity of arsenite interaction with zinc finger proteins.

Arsenic is a carcinogenic element also used for the treatment of acute promyelocytic leukemia. The reactivity of proteins to arsenic must be associated with the various biological functions of As. Here, we investigated the selectivity of arsenite to zinc finger proteins (ZFPs) with different zinc binding motifs (C2H2, C3H, and C4). Single ZFP domain proteins were used for the direct comparison of the reactivity of different ZFPs. The binding constants and the reaction rates have been studied quantitatively. Results show that both the binding affinity and reaction rates of single-domain ZFPs follow the trend of C4 > C3H ≫ C2H2. Compared with the C2H2 motif ZFPs, the binding affinities of C3H and C4 motif ZFPs are nearly two orders of magnitude higher and the reaction rates are approximately two-fold higher. The formation of multi-domain ZFPs significantly enhances the reactivity of C2H2 type ZFPs, but has negligible effects on C3H and C4 ZFPs. Consequently, the reactivities of the three types of multi-domain ZFPs are rather similar. The 2D NMR spectra indicate that the As(III)-bound ZFPs are also unfolded, suggesting that arsenic binding interferes with the function of ZFPs.

Note: Laser-induced acoustic desorption∕synchrotron vacuum ultraviolet photoionization mass spectrometry for analysis of fragile compounds and heavy oils.

In this work, we coupled synchrotron vacuum ultraviolet photoionization (SVUV PI) method with the laser-induced acoustic desorption (LIAD) technique for mass spectrometric analysis. The LIAD technique is a "soft" desorption method, which could avoid the degradation of analytes during desorption process. Meanwhile, SVUV PI is an efficient "soft" ionization source. The new combination of the "soft" desorption technique and "soft" photoionization method is well suitable to reduce the difficulty for interpreting the mass spectra of the fragile compounds and heavy oils.

Synchrotron vacuum ultraviolet (VUV) photo-induced fragmentation of cyclic dipeptides radical cations.

Cyclic dipeptides, due to their chemical properties and various bioactivities, are very attractive for medicinal chemistry. Fragmentations of three simple cyclic dipeptides including cyclo(Gly-Gly), cyclo(Ala-Ala) and cyclo(Gly-Val) in the gas-phase are determined with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (VUV PIMS) and theoretical calculations. Cyclo(Gly-Gly) and cyclo(Ala-Ala) show the similar fragmentation pathways. The primary decomposition reactions of cyclo(Gly-Gly) and cyclo(Ala-Ala) radical cations are found to be HNCO loss and CO elimination. The appearance energies (AEs) of fragment ions [CH2NHCOCH2]+• and [CH3CHNHCOCHCH3]+• are measured to be 10.21 and 9.66±0.05 eV, respectively, which are formed from cyclo(Gly-Gly) and cyclo(Ala-Ala) radical cations with HNCO elimination. Due to the stabilization of the radical cation of cyclo(Gly-Val) with isopropyl side group, the dominant fragment ion m/z 114 assigned as [C4H6N2O2]+• is produced by γ-H migration and i cleavage to lose propylene. The ionization energies (IEs) of three cyclic dipeptides decrease in the order cyclo(Gly-Gly) (9.33±0.05 eV)>cyclo(Ala-Ala) (9.21±0.05 eV)>cyclo(Gly-Val) (9.09±0.05 eV) from measurements of photoionization efficiency spectra. It implies that IEs of cyclic dipeptides are affected by substituent groups and symmetrical characterization of molecular structures. These observations of the chemical properties of cyclic dipeptides radical ion (M+•) may be important for understanding gas-phase molecular reactivity of 2,5-diketopiperazines and guiding diketopiperazine-based drug design.

Identification of [PtCl2(phen)] binding modes in amyloid-ß peptide and the mechanism of aggregation inhibition.

Platinum phenanthroline complexes inhibit amyloid-ß (Aß) aggregation and reduce Aß-caused neurotoxicity [Proc. Natl. Acad. Sci., 2008, 105, 6813-6818]. In this study, we investigated the interactions of Aß(1-16) with [PtCl(2)(phen)] (phen=1,10-phenanthroline) using HPLC, ESI-MS, and NMR spectroscopy , and characterized the identity of products using tandem mass spectrometry. Results indicated that the phenanthroline ligand could induce noncovalent interactions between Aß peptide and platinum complexes, leading to rapid Aß platination. Multiple products were generated in the reaction, in which His6/His14 chelation was preferentially formed. Coordination of Asp7, His13, and Lys16 was also detected in other products. The majority of products were monoplatinated adducts with binding of the {Pt(phen)} scaffold, which impeded intermolecular interactions between Aß peptides. Moreover, noncovalent interactions were confirmed by the interaction between Aß peptide and [Pt(phen)(2)]Cl(2). The synergistic roles of the phen ligand and platinum(II) atom in the inhibition of Aß aggregation are discussed.

VUV photon-induced ionization/dissociation of antipyrine and propyphenazone: mass spectrometric and theoretical insights.

Two analgesic and anti-inflammatory drugs, antipyrine and propyphenazone, were investigated with infrared laser desorption/tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (IR LD/VUV PIMS) and theoretical calculations. Mass spectra of the two drugs were measured at various photon energies. Fragment ions were gradually produced as photon energy increases. The structural assignment of the dominant fragment ions was supported by the results from a commercial electron impact time-of-flight mass spectrometer (EI-TOF MS). Primary fragmentation pathways were established from experimental observations combining with theoretical calculations. Methyl radical elimination is a common fragmentation pathway for two analytes. However, for propyphenazone cation, isopropyl group elimination to form antipyrine cation is another competitive pathway.

Vacuum ultraviolet photofragmentation of sarcosine: photoionization mass spectrometric and theoretical insights.

Vacuum ultraviolet (VUV) photon-induced ionization and fragmentation of N-methyl glycine (sarcosine) were investigated with infrared laser desorption/tunable synchrotron VUV photoionization mass spectrometry (IR LD/VUV PIMS) and theoretical calculations. Fragment-controllable mass spectra of sarcosine were measured at various photon energies. By tuning the photon energy, the fragments at m/z 44, 45, 43, 42, 30, and 60 were gradually detected. The ionization energy of the precursor was obtained by measuring the photoionization efficiency spectrum. Possible formation pathways of the fragment ions at m/z 44 (CH(3)NHCH(2)(+)), 45 (CH(3)NH(2)CH(2)(+)), 43 (CH(2)NHCH(2)(+)), 42 (CH(2)NCH(2)(+)), 30 (CH(2)NH(2)(+)), and 60 (CH(2)COOH(2)(+)) were discussed in detail with the help of calculations at the G3B3 and B3LYP/6-31++G(d,p) levels.