A novel route has been developed that yields levulinic acid (4-oxopentanoic acid, LA) and 5-hydroxymethylfurfural (5-HMF) from chitosan. Hydrolysis of chitosan was performed in the presence of a range of Lewis acids with SnCl 4 ·5H 2 O providing the best results. All reactions were performed in sealed vessels under microwave irradiation at 200°C for 30 min. Typical pressures achieved were 17 to 19 bar. 23.9 wt% LA was produced from 100 mg chitosan using 0.24 mmol SnCl 4 ·5H 2 O and 4 mL water. Under more dilute conditions, 10.0 wt% 5-HMF was obtained using 0.12 mmol SnCl 4 ·5H 2 O and 15 mL water. We propose that under more concentrated reaction conditions the 5-HMF formed reacts further to produce LA. When chitin is treated similarly, no 5-HMF is produced but up to 12.7 wt% LA can be obtained. For comparison, 32.0 wt% LA was produced from 100 mg glucosamine hydrochloride using 0.26 mmol SnCl 4 ·5H 2 O and 20 mL water. This corresponds to a yield of 59.4%. The SnCl 4 forms SnO 2 and HCl in solution and under similar conditions using SnO 2 and HCl, chitosan formed 27.4 wt% LA.

How does chemistry scale in complexity to unerringly direct biological functions? Nass Kovacs et al. have shown that bacteriorhodopsin undergoes structural changes tantalizingly similar to the expected pathway even under excessive excitation. Is the protein structure so highly evolved that it directs all deposited energy into the designed function? It is difficult to overstate the importance of having atomic structures to help shape our thinking and understanding of matter. Structural information constrains the number of possible solutions in trying to piece together a puzzle in how matter undergoes transformation from one structure to another and the associated changes in material properties 1,2. In terms of understanding biological processes, this question always reduces to how the protein structure surrounding an active site has evolved to direct chemical processes into biological functions, typically with efficiencies well beyond our current capabilities to exploit chemistry. In this respect, bacteriorhodopsin (bR) serves as a model system for understanding structurefunction relationships for membrane proteins 3-5. This system functions as a light-driven, outward proton pump, which can be triggered by light to use time resolved optical methods to watch it function in real time. Its structure is composed of seven transmembrane α-helices that are covalently bound to a photoactive retinal molecule via a lysine residue through a Schiff base linkage (Fig. 1b). Upon absorbing a photon, the retinal chromophore undergoes rapid isomerization from an all-trans to 13-cis form passing through the I 460 (charge separated), J 625 (highly twisted) and K 590 (isomerized) intermediates. The retinal isomerization acts like a push in changing the electrostatic and structural environment around the active site. These changes in turn lead to a series of cascaded protein conformational changes to facilitate the transport of a proton from the retinal Schiff base to the extracellular side of the membrane via L 550 and M 410 intermediates. The retinal then undergoes reprotonation and thermal re-isomerization through the N 560 and O 630 intermediates, respectively, where it can then return to the bR 568 ground state. These processes have been well characterized spectroscopically and many of the long-lived

A fixed-target approach to high-throughput room-temperature serial synchrotron crystallography with oscillation is described. Patterned silicon chips with microwells provide high crystal-loading density with an extremely high hit rate. The microfocus, undulator-fed beamline at CHESS, which has compound refractive optics and a fast-framing detector, was built and optimized for this experiment. The high-throughput oscillation method described here collects 1–5° of data per crystal at room temperature with fast (10° s−1) oscillation rates and translation times, giving a crystal-data collection rate of 2.5 Hz. Partial datasets collected by the oscillation method at a storage-ring source provide more complete data per crystal than still images, dramatically lowering the total number of crystals needed for a complete dataset suitable for structure solution and refinement – up to two orders of magnitude fewer being required. Thus, this method is particularly well suited to instances where crystal quantities are low. It is demonstrated, through comparison of first and last oscillation images of two systems, that dose and the effects of radiation damage can be minimized through fast rotation and low angular sweeps for each crystal.

Microbial rhodopsins are versatile and ubiquitous retinal-binding proteins which function as light-driven ion pumps, light-gated ion channels and photosensors, with potential utility as optogenetic tools for altering membrane potential in target cells. Insights from crystal structures have been central for understanding proton, sodium, and chloride transport mechanisms of microbial rhodopsins. Two of three known groups of anion pumps, the archaeal halorhodopsins (HRs) and bacterial chloride-pumping rhodopsins (ClRs), have been structurally characterized. Here we report the structure of a representative of a recently discovered third group consisting of cyanobacterial chloride and sulfate ion-pumping rhodopsins, the Mastigocladopsis repens rhodopsin (MastR). Chloride-pumping MastR contains in its ion transport pathway a unique Thr-Ser-Asp (TSD) motif, which is involved in binding of a chloride ion. The structure reveals that the chloride-binding mode is more similar to HRs than ClRs, but the overall structure most closely resembles bacteriorhodopsin (BR), an archaeal proton pump. The MastR structure shows a trimer arrangement reminiscent of BR-like proton pumps and shows features at the extracellular side more similar to BR than the other chloride pumps. We further solved the structure of the MastR-T74D mutant which contains a single amino acid replacement in the TSD motif. We provide insights into why this point mutation can convert the MastR chloride pump into a proton pump, but cannot in HRs. Our study points at the importance of precise coordination and exact location of the water molecule in the active center of proton pumps, which serves as a bridge for the key proton transfer.

It has previously been shown that the easily handled, heat- and air-stable compound Pd(η3-1-PhC3H4)(η5-C5H5) (Vb) reacts rapidly with a wide variety of tertiary phosphines L to produce near-quantitative yields of the corresponding Pd(0) compounds PdL2, which are widely believed to be the active species in many often-used cross-coupling catalyst systems based on Pd(PPh3)4 (I), Pd2(dba)3 (II), PdCl2 (III), and Pd(OAc)2 (IV). However, catalyst precursors I–IV are in fact known to preferentially generate sterically hindered, three-coordinate Pd(0) species rather than two-coordinate PdL2, and thus Vb is hypothetically expected to be a better catalyst precursor for e.g. Suzuki–Miyaura cross-coupling reactions. Utilizing the conventional Suzuki–Miyaura cross-coupling reaction of phenylboronic acid with bromoanisole, comparisons are made of the efficacies of catalyst systems based on Vb with those based on compounds I–IV (L = the representative phosphines PPh3, PCy3, PBu t 3). As anticipated, catalysts generated from Vb are significantly more competent and, as a bonus, Vb makes palladium(0) complexes PdL2 available under rigorously anhydrous conditions.