Thermodynamic characterization of different actin isoforms

Summary The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of these proteins as well.     

Study of flow rate in pressurized gradient capillary electrochromatography using splitter and separation of peptides using an Amide stationary phase

A pressurized gradient capillary electrochromatograph using a splitter was constructed. The variation in flow rate during gradient elution was investigated and separations of peptides using an Amide stationary phase were demonstrated. The flow rate, which is one of the important factors to control chromatographic behavior, was increased during the gradient elution, and the mismatching of mobile phase between the column and the resistance tubing derived three variation patterns in the flow rate. The electrophoretic migration in electrochromatography could enhance in separation of peptides. The separated peak number of tryptic digest of bovine serum albumin was increased from 30 to 40 by the application of +5 kV.     

Molecular basis for antifreeze activity difference of two insect antifreeze protein isoforms

The insect spruce budworm(Choristoneura fumiferana) produces antifreeze protein(AFP) to assist in the protection of the over-wintering larval stage and contains multiple isoforms. Structures for two isoforms,known as CfAFP-501 and CfAFP-337,show that both possess similar left-handed β-helical structure,although thermal hysteresis activity of the longer isoform CfAFP-501 is three times that of CfAFP-337. The markedly enhanced activity of CfAFP-501 is not proportional to,and cannot be simply accounted for,by the increased ice-binding site resulting from the two extra coils in CfAFP-501. In or-der to investigate the molecular basis for the activity difference and gain better understanding of AFPs in general,we have employed several different computational methods to systematically study the structural properties and ice interactions of the AFPs and their deletion models. In the context of intact AFPs,a majority of the coils in CfAFP-501 has better ice interaction and causes stronger ice lattice disruption than CfAFP-337,strongly suggesting a cooperative or synergistic effect among β-helical coils. The synergistic effect would play a critical role and make significant contributions to the anti-freeze activity β-helical antifreeze proteins. This is the first time that synergistic effect and its implica-tion for antifreeze activity are reported for β-helical antifreeze proteins.     

Generation of functionalized asymmetric benzynes with TMP-zincates. Effects of ligands on selectivity and reactivity of zincates

We have developed new methods for preparing functionalized benzynes through deprotonative zincation as a key reaction using R2Zn(TMP)Li, and we also describes dramatic ligand effects on the benzyne formation. Deprotonative zincation of various meta-substituted bromobenzenes with Me2Zn(TMP)Li proved effective for the one-pot generation of various 3-functionalized benzynes, particularly those electrophilic substituents such as ester, amide, and cyano. On the other hand, zincation with tBu2Zn(TMP)Li, followed by electrophilic trapping (with I2) proved a powerful tool for the preparation of 1,2,3-trisubstituted aromatic compounds.8 The resultant 1,2,3-trisubstituted benzenes are available as precursors for generation of 3-substituted benzynes by halogen-zinc exchange reactions with Me3ZnLi. These methods offer far greater generality than previous methods for the synthesis of functionalized asymmetric benzynes, and should be of value in new syntheses of various natural products and functional materials. In addition, these results underline the utility of spectator ligands on the central metal of ate complexes as a tunable functionality in the development of new ate complex-promoted reactions.     

Do proficiency tests always verify laboratories’ performance? The case of FAPAS PT 0270

In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted. Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in PT 0270 are questionable.     

trans-2,2'-Bi(1-phenyladamantylidene): the most twisted biadamantylidene

The Grignard coupling of 2,2-dibromo-1-phenyladamantane gave trans-2,2'-bi(1-phenyladamantylidene) (1-Ph). Single-crystal X-ray analysis indicated that 1-Ph has a 23.2 degrees twisted double bond, which is much more distorted than that of parent 2,2'-biadamantylidene (1-H) and that of the ethyl-substituted derivative (1-Et). A cyclic voltammogram showed a reversible electron oxidation wave at 0.87 V vs Fc/Fc(+), which is 0.19 V lower than 1-H, indicating a significant increase in the HOMO energy level due to the distortion. The reaction of 1-Ph with 0.9 equiv of bromine gave an intramolecular Friedel-Crafts alkylation product, while bromination of 1-H and 1-Me has been reported to give a bridged bromonium ion and a rearranged product, 2-(1-methyl-2-adamantylidene)-4-bromotricyclo[5,3,1,0(3.9)]undec-4-ene, respectively.     

Evaluation of chiral bidentate ligand–metal complexes in asymmetric 1,3-dipolar cycloaddition reaction of nitrones with 3-alkenoyl-2-oxazolidinones

For evaluation of a chiral C₂-symmetric bis(oxazoline) ligand, its Lewis acid complexes-catalyzed asymmetric 1,3-dipolar cycloaddition reactions of nitrones with electron-deficient dipolarophiles, 3-(2-alkenoyl)-1,3-oxazolidin-2-ones, have been investigated and it was found that the cycloadditions using a Cu(II)-bis(oxazoline) complex under optimized reaction conditions induced extremely high enantioselectivity.     

Reduced Overlap Population Analysis for Triosmium Clusters

The use of reduced overlap population (ROP) analysis from EHMO calculations as a means to gauge the presence of metal–metal bonds in triosmium clusters is examined. A number of triosmium clusters containing bridging ligands have been used as test cases, including the bis-ethoxy bridged cluster Os₃(μ-OEt)₂(CO)₁₀, 1b, and some of its group 15 derivatives Os₃(μ-OEt)₂(CO)₉(EPh₃), 2. These latter clusters are newly synthesized and have been characterized completely, including by single-crystal X-ray crystallographic studies. In honour of Professor Dieter Fenske on his 65th birthday.     

Hydrogen–hydrogen bonding in biphenyl revisited

The evidence for the stabilizing nature of the H–H bonding in planar biphenyl is succinctly reviewed. The stabilizing nature of the H–H bonding is revealed through a comparison of the atomic energy of every atom in planar biphenyl with the same atom in the twisted equilibrium structure. It is shown that the barrier to rotation via the planar transition state is the net resultant of a stabilisation of the four ortho-hydrogen atoms (by 8 kcal/mol each), a stabilisation of the two para-carbon atoms (by 3 kcal/mol each) and by the dominant destabilisation of the two carbon atoms joining the two rings—the two junction carbon atoms—(by 22 kcal/mol each). The energetic stabilisation of the four ortho-hydrogen atoms is further shown to be in large proportion due to the formation of the hydrogen–hydrogen interatomic surface. Furthermore, neither the “bond order” between the two junction carbon atoms nor the total electron delocalisation between the two rings exhibit a significant change in going from the planar to the twisted equilibrium geometry. These findings are in contrast with the classical view of a balance between “steric non-bonded repulsion” and better electron delocalisation as a function of the twist dihedral angle. Similar conclusions have been recently reached by Pacios and Gómez through a study of the electrostatic potential at the position of the hydrogen nuclei. We dedicate this article to Professor TM Krygowski on the occasion of his 70th birthday wishing him a long and productive life.     

Electrochemical investigation of hymecromone at a multi-wall carbon nano-tube/cetyl pyridine bromine composite film electrode

A multi-wall carbon nanotube (MWNT)/cetyl pyridine bromine (CPB) composite film modified glassy carbon electrode (GCE) was developed for the electrochemical determination of hymecromone in phosphonate buffer. Electrochemical behaviour of hymecromone at the composite film electrode was investigated with voltammetry. Compared with an irreversible oxidation of hymecromone at the bare GCE, the oxidation peak current was enhanced greatly at the film electrode. Some parameters such as pH, scan rate, accumulation potential and accumulation time were optimized. Under optimal conditions, an oxidation peak at 0.82 V was employed to determine hymecromone electrochemically. A linearity between the oxidation peak current and the hymecromone concentration was obtained in the range of 3.0 × 10⁻⁷ − 2.0 × 10⁻⁵ mol 1⁻¹ with a detection limit of 8.0 × 10⁻⁸ mol 1⁻¹. The proposed procedure was successfully applied to assay hymecromone in pharmaceutical formulation with satisfactory results. The text was submitted by the authors in English.