A theoretical study on bond dissociation energies and oxidation potentials of monolignols

A theoretical study on the proton affinity of sulfur ylides

The proton affinities of sulfoxide ylides, carbonyl ylides, allyl ylides, benzenyl ylides and heterocyclic ylides with typical substituents were investigated using the SOGGA11-X functional.

Theoretical study on adiabatic electron affinity of fatty acids

The AEA of saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids with typical substituents were calculated by the ωB97X method.

Unlocking high-potential non-persistent radical chemistry for semi-aqueous redox batteries

Stabilizing non-persistent radical opens the gate to low-cost high-potential cathode for all-organic aqueous redox batteries with fast reversible rate capability.

Following laser induced changes of plant phenylpropanoids by Raman microscopy

Raman microscopy is a powerful imaging technique for biological materials providing information about chemistry in context with microstructure. A 532 nm laser is often used as excitation source, because high spatial resolution and signal intensity can be achieved. The latter can be controlled by laser power and integration time, whereby high power and long times give good signal to noise ratio. However, most biological materials absorb in the VIS range and fluorescence masking the signal or even sample degradation might be hindering. Here, we show that on lignified plant cell walls even very short integration times and low laser powers induce a change in the ratio of the lignin bands at 1660 and 1600 cm-1. Time series on lignin model compounds revealed this change only in aromatic molecules with two OH-groups, such as coniferyl alcohol. Therefore, we conclude that monolignols are present in the cell wall and responsible for the observed effect. The solvent selectivity of the changes points to a laser induced polymerization process. The results emphasize how crucial careful adjustment of experimental parameters in Raman imaging of biological materials is and show the potential of time series and repeated imaging to get additional insights (e.g. monolignols).

Characterization of Dye-decolorizing Peroxidase (DyP) from Thermomonospora curvata Reveals Unique Catalytic Properties of A-type DyPs

Dye-decolorizing peroxidases (DyPs) comprise a new family of heme peroxidases, which has received much attention due to their potential applications in lignin degradation. A new DyP from Thermomonospora curvata (TcDyP) was identified and characterized. Unlike other A-type enzymes, TcDyP is highly active toward a wide range of substrates including model lignin compounds, in which the catalytic efficiency with ABTS (kcat(app)/Km(app) = (1.7 × 10(7)) m(-1) s(-1)) is close to that of fungal DyPs. Stopped-flow spectroscopy was employed to elucidate the transient intermediates as well as the catalytic cycle involving wild-type (wt) and mutant TcDyPs. Although residues Asp(220) and Arg(327) are found necessary for compound I formation, His(312) is proposed to play roles in compound II reduction. Transient kinetics of hydroquinone (HQ) oxidation by wt-TcDyP showed that conversion of the compound II to resting state is a rate-limiting step, which will explain the contradictory observation made with the aspartate mutants of A-type DyPs. Moreover, replacement of His(312) and Arg(327) has significant effects on the oligomerization and redox potential (E°') of the enzyme. Both mutants were found to promote the formation of dimeric state and to shift E°' to a more negative potential. Not only do these results reveal the unique catalytic property of the A-type DyPs, but they will also facilitate the development of these enzymes as lignin degraders.

Identification and characterization of a multifunctional dye peroxidase from a lignin-reactive bacterium

Plant biomass represents a renewable feedstock that has not yet been fully tapped because of the difficulty in accessing the carbon in its structural biopolymers. Lignin is an especially challenging substrate, but select microbes have evolved complex systems of enzymes for its breakdown through a radical-mediated oxidation process. Fungal systems are well-characterized for their ability to depolymerize lignin, but the ability of bacteria to react with this substrate remains elusive. We have therefore focused on elucidating strategies used by lignin-reactive soil bacteria and describing their oxidative enzyme systems. We now report the identification and characterization of an unusual C-type dye-decolorizing peroxidase from Amycolatopsis sp. 75iv2 (DyP2), which belongs to a family of heme peroxidases reported to be involved in bacterial lignin degradation. Biochemical studies indicate that DyP2 has novel function for this family, with versatile and high activity both as a peroxidase and Mn peroxidase (k(cat)/K(M) ≈ 10(5)-10(6) M(-1) s(-1)). It also has a Mn-dependent oxidase mode of action that expands its substrate scope. Crystallographic studies of DyP2 at 2.25 Å resolution show the existence of a Mn binding pocket and support its key role in catalysis.

Single-conformation ultraviolet and infrared spectra of jet-cooled monolignols: p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol

Single-conformation spectroscopy of the three lignin monomers (hereafter "monolignols") p-coumaryl alcohol (pCoumA), coniferyl alcohol (ConA), and sinapyl alcohol (SinA) has been carried out on the isolated molecules cooled in a supersonic expansion. Laser-induced fluorescence excitation, dispersed fluorescence, resonant two-photon ionization, UV-UV hole-burning, and resonant ion-dip infrared spectroscopy were carried out as needed to obtain firm assignments for the observed conformers of the three molecules. In each case, two conformers were observed, differing in the relative orientations of the vinyl and OH substituents para to one another on the phenyl ring. In pCoumA, the two conformers have S(0)-S(1) origins nearly identical in size, split from one another by only 7 cm(-1), in close analogy with previous results of Morgan et al. on p-vinylphenol ( Chem. Phys. 2008 , 347 , 340 ). ConA, with its methoxy group ortho to the OH group, also has two low-energy conformers forming a syn/anti pair, in this case with the OH group locked into an orientation in which it forms an intramolecular H-bond with the adjacent methoxy group. The electronic frequency shift between the two conformers is dramatically increased to 805 cm(-1), with the dominant conformer of ConA (with S(0)-S(1) origin at 32 640 cm(-1)) about 5 times the intensity of its minor counterpart (with S(0)-S(1) origin at 33 444 cm(-1)). The presence of an OH···OCH(3) intramolecular H-bond is established by the shift of the OH stretch fundamental of the OH group to 3599 cm(-1), as it is in o-methoxyphenol ( Fujimaki et al. J. Chem. Phys. 1999 , 110 , 4238 ). Analogous single-conformation UV and IR spectra of o-methoxy-p-vinylphenol show a close similarity to ConA and provide a basis for a firm assignment of the red-shifted (blue-shifted) conformer of both molecules to the syn (anti) conformer. The two observed conformers of SinA, with its two methoxy group straddling the OH group, have S(0)-S(1) origins split by 239 cm(-1) (33 055 and 33 294 cm(-1)), a value between those in pCoumA and ConA. A combination of experimental data and calculations on the three monolignols and simpler derivatives is used to establish that the conformational preferences of the monolignols reflect the preferences of each of the ring substituents separately, enhanced by the presence of the intramolecular OH···OCH(3) H-bond. Taken as a whole, the presence of multiple flexible substituents locks in certain preferred orientations of the groups relative to one another, even in the apparently flexible allyl alcohol side chain (-CH═CH-CH(2)OH), where the OH group orients itself so that the hydrogen is pointed back over the vinyl π cloud in order to minimize interactions between the oxygen lone pairs and the π electrons.