Review on Microbial Sources, Production, Purification and Potential Industrial Applications of Laccases

Laccase (EC 1.10.3.2) is a multicopper blue oxidase which are involved in the oxidation of a broad range of organic substrates, including phenols, polyphenols, anilines, and even certain inorganic compounds by a one-electron transfer mechanism. Laccases are widely distributed in bacteria, fungai, insects and higher plants. There are mainly two production techniques for cultivation of laccase such as submersed fermentation and solid- state fermentation. This paper briefly discuss the effect of carbon source, effect of nitrogen source, effect of inducers, effects of surfactants, effect of agitator, influence of metal ions and use of agro-industrial waste in production medium. The paper also discussed the purification techniques such as ammonium sulphate precipitation for extraction purpose followed by dialysis and ion-exchange chromatography as well characterization techniques. Laccases are known to show application ranging from pharmaceutical industries to textile sector as well as in biosensor development.

Photosynthetic reaction center variants made via genetic code expansion show Tyr at M210 tunes the initial electron transfer mechanism

Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides were engineered to vary the electronic properties of a key tyrosine (M210) close to an essential electron transfer component via its replacement with site-specific, genetically encoded noncanonical amino acid tyrosine analogs. High fidelity of noncanonical amino acid incorporation was verified with mass spectrometry and X-ray crystallography and demonstrated that RC variants exhibit no significant structural alterations relative to wild type (WT). Ultrafast transient absorption spectroscopy indicates the excited primary electron donor, P*, decays via a ∼4-ps and a ∼20-ps population to produce the charge-separated state P+HA− in all variants. Global analysis indicates that in the ∼4-ps population, P+HA− forms through a two-step process, P*→ P+BA−→ P+HA−, while in the ∼20-ps population, it forms via a one-step P* → P+HA− superexchange mechanism. The percentage of the P* population that decays via the superexchange route varies from ∼25 to ∼45% among variants, while in WT, this percentage is ∼15%. Increases in the P* population that decays via superexchange correlate with increases in the free energy of the P+BA− intermediate caused by a given M210 tyrosine analog. This was experimentally estimated through resonance Stark spectroscopy, redox titrations, and near-infrared absorption measurements. As the most energetically perturbative variant, 3-nitrotyrosine at M210 creates an ∼110-meV increase in the free energy of P+BA− along with a dramatic diminution of the 1,030-nm transient absorption band indicative of P+BA– formation. Collectively, this work indicates the tyrosine at M210 tunes the mechanism of primary electron transfer in the RC.

Mechanistic insight into deep holes from interband transitions in Palladium nanoparticle photocatalysts

Photocatalysis of metallic nanoparticles, especially utilizing hot electrons generated from localized surface plasmon resonance, is of widespread interest. However, the role of hot holes, especially generated from interband transitions, has not been emphasized in exploring the photocatalytic mechanism yet. In this study, a photocatalyzed Suzuki-Miyaura reaction using mesoporous Pd nanoparticle photocatalyst served as a model reaction to study the role of hot holes by accurately measuring the quantum yields of the photocatalyst. The quantum yields increase under shorter wavelength excitations and correlate to the “deeper” energy of the holes from the Fermi level. Our mechanistic study suggests that deeper holes in the d-band can catalyze the oxidative addition of aryl halide R-X onto Pd0 at the surface of nanoparticles to form the R-PdII-X complex, the rate-determining step of the established catalytic cycle. We pointed out that this deep hole mechanism should deserve as much attention as the well-known hot electron transfer mechanism in previous studies.

Deformation of polyiodides in Cs2I8 crystals at high pressure

Dicaesium octaiodide is composed of layers of zigzag polyiodide units (I8 2−) intercalated with caesium cations. Each I8 2− unit is built of two triiodides bridged with one diiodine molecules. This system was subjected to compression up to 5.9 GPa under hydrostatic conditions. Pressure alters the supramolecular architecture around I8 2−, leading to bending of the triiodide units away from their energetically preferred geometry (D ∞h). Short I2...I3 − contacts compress significantly, reaching lengths typical for the covalently bonded polyiodides. Unlike in reported structures at ambient conditions, pressure-induced catenation proceeds without symmetrization of the polyiodides, pointing to a different electron-transfer mechanism. The structure is shown to be half as compressible [B0 = 12.9 (4) GPa] than the similar CsI3 structure. The high bulk modulus is associated with higher I—I connectivity and a more compact cationic net, than in CsI3. The small discontinuity in the compressibility trend around 3 GPa suggests formation of more covalent I—I bonds. The potential sources of this discontinuity and its implication on the electronic properties of Cs2I8 are discussed.