Application of plug–plug technique to ACE experiments for discovery of peptides binding to a larger target protein: A model study of calmodulin‐binding fragments selected from a digested mixture of reduced BSA

To discover peptide ligands that bind to a target protein with a higher molecular mass, a concise screening methodology has been established, by applying a “plug–plug” technique to ACE experiments. Exploratory experiments using three mixed peptides, mastoparan‐X, β‐endorphin, and oxytocin, as candidates for calmodulin‐binding ligands, revealed that the technique not only reduces the consumption of the protein sample, but also increases the flexibility of the experimental conditions, by allowing the use of MS detection in the ACE experiments. With the plug–plug technique, the ACE–MS screening methodology successfully selected calmodulin‐binding peptides from a random library with diverse constituents, such as protease digests of BSA. Three peptides with K_d values between 8–147 μM for calmodulin were obtained from a Glu‐C endoprotease digest of reduced BSA, although the digest showed more than 70 peaks in its ACE–MS electropherogram. The method established here will be quite useful for the screening of peptide ligands, which have only low affinities due to their flexible chain structures but could potentially provide primary information for designing inhibitors against the target protein.     

Total synthesis of unsaturated imine venom alkaloids of Costa Rican ant by way of Schmidt reaction via allyl/pentadienyl cations

Total synthesis of α,β-, and α,β,γ,δ-unsaturated imine ant venom alkaloids is described. The labile two conjugated imine alkaloids were synthesized by late stage intramolecular Schmidt reaction via allyl and pentadienyl cation intermediates.     

Synthesis of chlorophyll-a derivatives possessing (un)substituted 13-exo-methylene moiety and their optical properties

Chlorophyll-a derivatives possessing an un/mono/disubstituted methylene moiety at the 13¹-position were prepared by (un)substituted methylation of the 13-carbonyl group and successive dehydration. Substitution of the 13¹-oxo to the methylene group slightly blue-shifted electronic absorption and emission bands in a solution and decreased chemical stability to give an oxidation product cleaved at the E-ring. Further mono/disubstitution at the methylene terminal increased wavelengths of absorption and emission maxima as well as oxidative tolerance.     

Rhenium complex-catalyzed coupling reaction of enol acetates with alcohols

The reaction of enol acetates with alcohols in the presence of a catalytic amount of a rhenium complex, such as ReBr(CO)₅, produced the corresponding ketones and aldehydes in moderate to good yields. It was suggested that the preparation of an ether, an intermolecular dehydrated product, was the first step of the reaction.     

Rod-packing arrangements of invariant tori in solenoidal vector fields with cubic symmetries

Journal of Mathematical Chemistry - The arrangements of invariant tori that resemble rod packings with cubic symmetries are considered in three-dimensional solenoidal vector fields. To find them...     

Morphological changes in the cellulose and lignin components of biomass occur at different stages during steam pretreatment

Morphological changes to the different components of lignocellulosic biomass were observed as they occurred during steam pretreatment by placing a pressure reaction cell in a neutron beam and collecting time-resolved neutron scattering data. Changes to cellulose morphology occurred mainly in the heating phase, whereas changes in lignin morphology occurred mainly in the holding and cooling phases. During the heating stage, water is irreversibly expelled from cellulose microfibrils as the elementary fibrils coalesce. During the holding phase lignin aggregates begin to appear and they increase in size most noticeably during the cooling phase. This experiment demonstrates the unique information that in situ small angle neutron scattering studies of pretreatment can provide. This approach could be useful in optimizing the heating, holding and cooling stages of pretreatments to allow the exact size and nature of lignin aggregates to be controlled in order to enhance enzyme accessibility to cellulose and therefore the efficiency of biomass conversion.     

Diversity of potential hydrogen bonds in cellulose I revealed by molecular dynamics simulation

We have performed molecular dynamics calculations using a revised version of the Gromos56A_carbo force field to understand the consequences of the different potential hydrogen bonding patterns on the structural stability and thermal behavior of the I_α and I_β forms of native cellulose. For each allomorph, we considered three patterns of hydrogen bonds: two patterns obtained from neutron diffraction data refinement and a regular mixture of the two. Upon annealing, the hydrogen bonding schemes of cellulose I_β, irrespective of the starting structure, re-arranged into the main hydrogen bond pattern experimentally observed (pattern A). On the other hand, the I_α structures, irrespective of the starting hydrogen bonding pattern, converged to a non-experimental structure where the adjacent chains are shifted along the chain direction by 0.12 nm in the hydrogen-bonded plane, and the hydroxymethyl group conformation alternates between gt and tg along the chain. The exotic structure in I_α might be a consequence of a deficiency in force field parameters and/or potential molecular arrangement in less crystalline cellulose.     

Catalytic oxidation of benzene at low temperature over novel combination of metal oxide based catalysts: CuO,MnO2, NiO with Ce0.75Zr0.25O2 as support

Mesoporous Ce_0.75Zr_0.25O₂ solid solution powders were successfully synthesized by a co-precipitation method. A combination of 10 wt% copper oxide, manganese oxide, and nickel oxide was added to the Ce_0.75Zr_0.25O₂ support by impregnation method and calcined in the air with a flow rate of 2 ml s^?1 at 400 °C for 4 h. All catalysts were characterized using Hydrogen Temperature Programmed Reduction (H₂-TPR), X-ray Diffraction (XRD), and Brunauer-Emmet-Teller (BET) isotherm methods to find the interaction between metals, the crystallinity of the catalyst, surface area and pore volume of the catalyst, respectively. The 3.3% CuO-3.3% MnO₂-3.3% NiO/Ce_0.75Zr_0.25O₂ catalyst showed higher catalytic activity for benzene oxidation with benzene conversion of 90% at 250 °C and weight hourly space velocity (72,000 mL g^?1 h^?1) when compared to one metal oxide only. This finding presents a high activity and low-cost catalysts for removing a very lean concentration of benzene containing in the industrial flue gas at low temperatures.     

Dehydration‐fragmentation mechanism of cathinones and their metabolites in ESI‐CID

Various cathinone‐derived designer drugs (CATs) have recently appeared on the drug market. This study examined the mechanism for the generation of dehydrated ions for CATs during electrospray ionization collision‐induced dissociation (ESI‐CID). The generation mechanism of dehydrated ions is dependent on the amine classification in the cathinone skeleton, which is used in the identification of CATs. The two hydrogen atoms eliminated during the dehydration of cathinone (primary amine) and methcathinone (secondary amine) were determined, and the reaction mechanism was elucidated through the deuterium labeling experiments. The hydrogen atom bonded to the amine nitrogen was eliminated with the proton added during ESI, in both of the tested compounds. This provided evidence that CATs with tertiary amine structures (such as dimethylcathinone and α‐pyrrolidinophenones [α‐PPs]) do not undergo dehydration. However, it was shown that the two major tertiary amine metabolites (1‐OH and 2″‐oxo) of CATs generate dehydrated ions in ESI‐CID. The dehydration mechanisms of the metabolites of α‐pyrrolidinobutiophenone (α‐PBP) belongs to α‐PPs were also investigated. Stable‐isotope labeling showed the dehydration of the 1‐OH metabolite following a simple mechanism where the hydroxy group was eliminated together with the proton added during ESI. In contrast, the dehydration mechanism of the 2″‐oxo metabolite involved hydrogen atoms in three or more locations along with the carbonyl group oxygen, indicating that dehydration occurred via multiple mechanisms likely including the rearrangement reaction of hydrogen atoms. These findings presented herein indicate that the dehydrated ions in ESI‐CID can be used for the structural identification of CATs.     

Macrocyclic Metal Complexes Bearing Rigid Polyaromatic Ligands: Synthesis and Catalytic Activity

We synthesised palladium and platinum complexes possessing cyclic and acyclic pincer‐type polyaromatic ligands and investigated their structural effect on the catalysis. The pincer‐type bis(6‐arylpyridin‐2‐yl)benzene skeleton was constructed via Kröhnke pyridine synthesis under transition metal‐free conditions on gram‐scale quantity. Ligand structure significantly influenced catalytic activity toward the platinum‐catalysed hydrosilylation of diphenyl acetylenes, despite the ligand‐independence of the conformations and electronic properties of these complexes.