Palladium-catalyzed stereoselective formation of alpha-O-glycosides

A novel method for palladium-catalyzed stereoselective formation of alpha-O-glycosides has been developed. This strategy relies on the palladium-biaryl phosphine catalyst-glycal donor complexation to control the anomeric selectivity. It does not depend on the nature of the protecting groups on the substrates, thus eliminating the need for cumbersome protecting group manipulations.     

Quantitative thermodynamic analysis of sublimation rates using an atomic force microscope

Atomic force microscopy (AFM) has been successfully used to study the activation energy for evaporation of pentaerythritol tetranitrate (PETN) nanoislands formed by spin coating. These islands are annealed isothermally in the temperature range of 30-70 degrees C for a given time and are scanned with AFM in contact mode at room temperature. The volume of these islands does not change significantly up to about 35-40 degrees C indicating that sublimation is not significant below 40 degrees C. Above 40 degrees C, the islands start shrinking, and the rate of weight loss is analyzed as a function of temperature. The activation energy of evaporation using AFM was found to be similar to that for bulk PETN crystals using thermogravimetric analysis (TGA) at higher temperatures (110-135 degrees C). These results demonstrate that AFM is a useful tool to measure thermodynamic properties with a nanoscale probe.     

Chemoselective derivatization of a bionanoparticle by click reaction and ATRP reaction

Horse spleen apoferritin, the hollow protein shell derived from ferritin, a special biological nanoparticle, can be chemoselectively modified at the lysine residues, which affords a robust scaffold for further chemical reactions including Cu(i)-catalyzed azide-alkyne cycloaddition reaction and atom transfer radical polymerization reaction.     

A microwave-assisted synthesis of julolidine-9-carboxamide derivatives and their conversion to chalcogenoxanthones via directed metalation

9-formyljulolidine was oxidized via a microwave-assisted Willgerodt-Kindler reaction to the N-piperidine or N-morpholine julolidine-9-thioamide. 9-formyl-1,1,7,7-tetramethyljulolidine gave the corresponding N-piperidine tetramethyljulolidine-9-thioamide. The thioamides were converted to the corresponding carboxamides with trifluoroacetic anhydride. The amide group directed ortho-metalation in the julolidine system, but not in the tetramethyljulolidine system. The resulting anion was captured by dichalcogenide electrophiles. The resulting products were converted to chalcogenoxanthones with phosphorus oxychloride and triethylamine (POCl3/Et3N).     

Reaction of Aplysia limacina metmyoglobin with hydrogen peroxide

Myoglobin (Mb) from gastropod mollusc Aplysia limacina shows only 20% sequence homology to the 'prototype' sperm whale Mb but exhibits a typical Mb fold and can reversibly bind oxygen. An intriguing feature of aplysia Mb is that it lacks the distal histidine and displays a ligand stabilisation based on an arginine. Here we report the reaction of aplysia metMb with hydrogen peroxide studied by optical and electron paramagnetic resonance (EPR) spectroscopies. Two electron oxidation of the protein by H2O2 results in formation of two intermediates typical for this class of reactions, the oxoferryl haem state and a globin-bound free radical. An unusual characteristic of the aplysia Mb reaction is formation, prior to haem oxidation, of an optically distinct compound with an EPR spectrum typical of the low spin Fe3+ haem state. This compound is interpreted as the complex between H2O2 and the ferric haem state (Compound), formed prior to cleavage of the dioxygen bond. We conclude that H2O2 is singly deprotonated in Compound which can thus be notated as [Fe3+--OOH]. A new low spin ferric haem state has been observed over the period of Compound decay, and hypotheses have been formulated as to its identity and role. The location of the protein bound radical observed in aplysia Mb is discussed in light of the fact that the protein does not have any tyrosine residues, the most common site of free radical formation in the haem protein/peroxide systems. All intermediates of the reaction are kinetically characterised.     

Modular syntheses of multidentate ligands with variable N-donors: applications to tri- and tetracopper(I) complexes

A general method for the preparation of multidentate ligands comprised of a multi-imine platform derived from 1,1,1-tris(aminomethyl)ethane or tris(aminoethyl)amine connected to bi- and tridentate N-donor chelates has been developed. The feasibility of the method has been demonstrated through the synthesis and characterization of a large set of these ligand types. Complexation to Cu(I) was accomplished for several cases, yielding tri- and tetracopper(I) complexes that have been characterized in solution by NMR spectroscopy and conductivity, and in the solid state by elemental analysis, mass spectrometry, and/or X-ray crystallography. These complexes are potentially useful for modeling multicopper protein active sites.     

有限元技术用于研究熔体生长中的小面化现象

开发了一种基于边界保角变换技术的有限元方法来处理自由边界问题,并成功地将其用于晶体定向生长过程中的界面动力学影响的研究。所建立的基于石榴石熔体生长过程的各向异性的界面动力学模型可导致相界面上小面的出现。讨论了界面动力学模型中的最大偏移角θｍａｘ对小面的形状和计算误差的影响,给出了一种十分有效地降低计算误差的措施：在模型方程中适当计人表面张力的影响。     

Domain Analysis and Motif Matcher (DAMM): A Program to Predict Selectivity Determinants in Monosiga brevicollis PDZ Domains Using Human PDZ Data

Choanoflagellates are single-celled eukaryotes with complex signaling pathways. They are considered the closest non-metazoan ancestors to mammals and other metazoans and form multicellular-like states called rosettes. The choanoflagellate Monosiga brevicollis contains over 150 PDZ domains, an important peptide-binding domain in all three domains of life (Archaea, Bacteria, and Eukarya). Therefore, an understanding of PDZ domain signaling pathways in choanoflagellates may provide insight into the origins of multicellularity. PDZ domains recognize the C-terminus of target proteins and regulate signaling and trafficking pathways, as well as cellular adhesion. Here, we developed a computational software suite, Domain Analysis and Motif Matcher (DAMM), that analyzes peptide-binding cleft sequence identity as compared with human PDZ domains and that can be used in combination with literature searches of known human PDZ-interacting sequences to predict target specificity in choanoflagellate PDZ domains. We used this program, protein biochemistry, fluorescence polarization, and structural analyses to characterize the specificity of A9UPE9_MONBE, a M. brevicollis PDZ domain-containing protein with no homology to any metazoan protein, finding that its PDZ domain is most similar to those of the DLG family. We then identified two endogenous sequences that bind A9UPE9 PDZ with <100 μM affinity, a value commonly considered the threshold for cellular PDZ–peptide interactions. Taken together, this approach can be used to predict cellular targets of previously uncharacterized PDZ domains in choanoflagellates and other organisms. Our data contribute to investigations into choanoflagellate signaling and how it informs metazoan evolution.     

The Benefits of Using Web-Based Enhancements in an Environmental Chemistry Class

Four semesters of student evaluations of an environmental chemistry class have been analyzed for differences that can be attributed to Web-based enhancements. The enhancements included Web-based lecture notes, reading and problem assignments, bookmark files, and videotaped lectures. We developed these materials as part of a larger project to provide university-level technical courses over the Internet. Student perceptions of the course improved significantly (α = 0.10) after adding Web-based enhancements. Student’s opinion of the instructor improved, but the change is not significant at the 90% confidence level. The student responses to “Was the course challenging?” “Was my interest stimulated?” and “Was the instructor concerned?” were unchanged in the two groups of students. Drop rates were unchanged between the two student groups. The grade-average was nearly identical for the two student groups (82.9% vs. 83.5%), but the grade-distribution changed significantly. The percentage of A’s decreased slightly when Web-based enhancements were added, but the number of B’s increased from 22% to 40%. The percentage of C’s, D’s and F’s decreased for the students with access to Web-based enhancements. These results indicate that Web-based materials helped weaker students improve their performance and, therefore, their opinion of the class and of the instructor was more favorable.     

Coupling Microdroplet Microreactors with Mass Spectrometry: Reading the Contents of Single Droplets Online

Fully integrated : Mass spectrometry has been integrated into a detection scheme for microdroplets that are created within microfluidic channels (see picture, scale bar 200 μm). This technique allows droplets to be identified based on the compounds they contain, and combines fluorescence screening with MS analysis. These experiments indicate how similar approaches can be applied to the ambitious goals of on‐chip protein evolution and chemical synthesis.