Converting an Esterase into an Epoxide Hydrolase

Entering the fold : A common structural motif in hydrolytic enzymes is the α,β‐hydrolase fold. The interconversion of one enzyme into another by introduction of mechanistically important residues is not enough; only substitution of a loop allows epoxide hydrolase activity in the esterase scaffold to be formed (see picture; structure comparison of epoxide hydrolases (green) with the esterase (orange)). The result is an enantioselective chimeric enzyme.

     

Multicut-HDMR with an application to an ionospheric model

A new High Dimensional Model Representation (HDMR) tool, Multicut-HDMR, is introduced and applied to an ionospheric electron density model. HDMR is a general set of quantitative model assessment and analysis tools for improving the efficiency of deducing high-dimensional input-output system behavior. HDMR describes an output [f(x)] in terms of its input variables (x = [x(1), x(2), em leader, x(n)]) via a series of finite, hierarchical, correlated function expansions. Various forms of HDMR are constructed for different purposes such as modeling laboratory or field data, or reproducing a complicated mathematical model. The Cut-HDMR technique, which expresses f(x) with respect to a specified reference point x in the input space, is appropriate when the input space is sampled in an orderly fashion. However, if the desired domain of the input space is too large, the HDMR function expansion may not converge, and Cut-HDMR will be unable to accurately approximate f(x). The new Multicut-HDMR technique addresses this problem through the use of multiple reference points in the input space.     

Synthesis of an isostere of an O-linked glycopeptide

[reaction: see text] A route for the synthesis of an electrophilic, carbocyclic galactose equivalent from D-galactose is described. The strategy utilizes ring-closing metathesis with Grubbs's second-generation catalyst as the key step. The galactose-derived electrophile reacted in an S(N)2 fashion with N-Boc-cysteine methyl ester to provide an alpha-galactosylserine isostere. The method was extended to the synthesis of a glycopeptide isostere.     

Activating an enzyme by an engineered coiled coil switch

We designed a de novo protein based on a circular permutant of RNaseT1, in which the enzymatic activity can be manipulated by engineered peptide binding. The circular permutant of RNaseT1 was obtained by tethering the original C- and N-termini with a GPAG linker and cleaving the molecule between Glu82 and Asn83. This mutant lacked enzymatic activity, due to the destabilization of entire protein structure. We previously reported the construction of ABC-type heterotrimeric coiled coil peptides, in which the A- and B-type peptides cannot form the folded trimeric structure without the C-type peptide. The introduction of the A- and B-type coiled coil peptides to the C- and N-termini of the circular permutant of RNaseT1, respectively, and the subsequent addition of the C-type coiled coil peptide enabled the RNaseT1 domain to refold properly, thus, restoring the enzymatic activity. The formation of the trimeric coiled coil structure should bring the cleaved sites of RNaseT1 close enough to refold the RNaseT1 domain spontaneously.     

Effect of an electric field on an interfacial profile

We consider the interface between two dielectric liquids in an electric field which is parallel to the interface. Using the Ginsburg-Landau model for binary fluids we add a term for the electric field energy and show that near the critical point the effect of the electric field is to change both the interface width and the critical temperature.     

Interfacing an atomic absorption spectrometer with an inexpensive desktop computer

A Commodore PET microcomputer and a Duoprint electro-sensitive printer are employed, with little additional equipment, to control a Varian-Techtron AA6 spectrometer in conjunction with power supplies, and to process and record the results of atomic absorption and emission measurements.     

The Thermal Rearrangement of an NHC-Ligated 3-Benzoborepin to an NHC-Boranorcaradiene

An N-heterocyclic-carbene-ligated 3-benzoborepin with a bridged structure has been synthesized by double radical trans-hydroboration of benzo[3,4]cycloundec-3-ene-1,5-diyne with an N-heterocyclic carbene borane. The thermal reaction of the NHC-ligated borepin at 150 °C gives an isolable NHC-boranorcaradiene. Experiments and density functional theory calculations support a mechanism whereby the borepin initially rearranges to a boranorcaradiene by a thermal 6π-electrocyclic reaction. This is followed by 1,5-boron shift to give a rearranged boranorcaradiene. This shift occurs with stereoinversion at boron through a transition state with open-shell diradical character. This is the first example of the isolation of a boranorcaradiene from a thermal reaction of a borepin.     

Pi-dimer of an aniline dimer: an ESR-UV-vis spectroelectrochemical study

It is shown for the first time that the most important intermediate formed during aniline polymerization, the p-aminodiphenylamine, forms a pi-dimer under oxidation at room temperature in acidified organic solvents that are used in electropolymerization. N-Phenylquinonediimine, which is generally assumed to be formed under oxidation, is only formed in basic solutions and in ionic liquids. Most of the mechanistic studies reported so far take the formation of N-phenylquinonediimine under consideration, although it is not consistent with the UV-vis spectra measured during oxidation of p-aminodiphenylamine. The formation of a pi-dimer is very well consistent with the electronic spectra of the oxidation product. In this way the pi-dimer is very important for the interpretation of the UV-vis spectra of higher oligomers and polyaniline as well. Furthermore, it offers a new interpretation of the redox behavior of p-aminodiphenylamine as found by cyclic voltammetry and has to be considered in the mechanism of the electrochemical polyaniline formation.     

ESCA-Untersuchungen an Prussiaten

X-Ray Photoelectron Spectroscopic Studies of Prussiates The ionization energies of some prussiates are reported. The results are discussed in terms of the effects of σ-donor and π-acceptor bonds on ESCA data. Based on the foregoing discussion it is shown that charge equalization depends to a great extend on the number of possible π-bonds. Iron(II) and iron(III) salts of prussiates don't give any evidence for a ?valency exchange.”?     

Integration of an electrochemical-based biolithography technique into an AFM system

An ordinary atomic force microscopy (AFM) was functionalized and applied to electrochemically draw micropatterns of biomolecules. To fabricate an electrochemical AFM probe having an electrode at the tip, a metal-coated AFM probe was first insulated with Parylene C, and then the apex of the tip was ground mechanically to expose the electrode. The effective electrode diameter was estimated to be ca. 500 nm. The electrode probe was positioned close to a heparin-coated antibiofouling substrate and used to locally generate hypobromous acid from a dilute Br⁻ solution to render the substrate surface protein-adhesive. In situ topographical imaging after the electrochemical treatment suggested the heparin layer became detached to allow the adsorption of proteins, in this case fibronectin. The diameter of the drawn fibronectin pattern was 2 μm, which is one order of magnitude smaller than we achieved previously using a microdisk electrode (tip diameter 10 μm). Figure AFM configuration integrated with the electrochemical-based surface modification and resultant micropatterns of fluorescence-labeled fibronectin Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and DNA triplex formation of an oligonucleotide containing an urocanamide

An urocanamide nucleoside designed and previously tested as its protected ribose derivative in aprotic solvents for binding a cytosine-guanine (CG) Watson-Crick base pair was successfully incorporated into a triplex forming oligonucleotide. Binding affinity and specificity of this nonnatural nucleoside were studied in a triple helix with duplex targets containing all four possible Watson-Crick base pairs opposite the nucleoside analog in the third strand. UV melting experiments indicate the formation of a well-defined triplex with specific binding of the urocanamide analog to a CG inversion of the homopurine-homopyrimidine target. However, binding affinities in the triplex are weak and much lower when compared to the canonical base triads.     

The silver salt of 12-tungstophosphoric acid: an efficient catalyst for the three-component coupling of an aldehyde, an amine and an alkyne

A three-component coupling of an aldehyde, an alkyne and an amine to prepare propargylamines was performed using the silver salt of 12-tungstophosphoric acid (Ag₃PW₁₂O₄₀) as a heterogeneous catalyst under mild reaction conditions in the absence of any co-catalyst. A variety of aldehydes and amines were converted to the corresponding propargylamines demonstrating the versatility of the reaction. The Ag₃PW₁₂O₄₀ (AgTPA) catalyst was recovered quantitatively by a simple filtration and reused several times.     

Interaction of an infrared surface plasmon with an excited molecular vibration

The interaction of an infrared surface plasmon and an excited molecular vibration was investigated by using a square array of subwavelength holes in a Ni film which supports propagating, surface-plasmon-mediated, transmission resonances. The largest transmission resonance [the (1,0)(-)] was tuned through the rocking vibration of the hexadecane molecule (at 721 cm(-1)) in a hexadecane film on the mesh by varying the thickness of the film. The interaction of the rocking vibration and surface plasmon is characterized spectroscopically by an increase in the intensity of the vibrational band by more than a factor of 2, variation of the vibrational line shape relative to the spectrum on a nonmetallic surface, and shifts in vibrational peak position by as much as 3.0 cm(-1). Relationships are developed between the transmission resonance position and the thickness and dielectric properties of the coating.     

Amperometric biosensors employing an insoluble oxidant as an interference-removing agent

A strong oxidant membrane is introduced to amperometric biosensors in order to solve the problem associated with interference from readily oxidizable species. The proposed biosensors are in planar format, and are composed of four components, i.e. a base amperometric transducer, an enzyme layer, a protecting membrane, and an oxidant membrane. In this sensor format, interfering species are removed by an oxidation reaction during their diffusion through the oxidant membrane. The oxidant membrane is introduced by dispensing a mixture of an oxidant and a polymer matrix as dissolved in an organic solvent, and thus, could be easily adapted to mass fabrication of miniature biosensors. In this work, several different reagents are examined as oxidants: BaO₂, CeO₂, MnO₂ and PbO₂. Of these, PbO₂ is shown to yield biosensors with the best performance, in terms of reducing interfering signals. Two different matrix systems are devised for use in formulating oxidant membranes: hydrophilic polyurethane (HPU) and cellulose acetate incorporating poly(ethylene glycol) (CA/PEG). While the CA/PEG-type sensor displays better sensitivity and faster response behavior, the HPU-type is shown to exhibit more pronounced interference-removing ability. The analytical utility of the proposed oxidant membrane is demonstrated by fabricating amperometric glucose and creatinine sensors as the model biosensor systems, and by investigating their response characteristics.     

Self-Assembly of an Amino Acid Derivative into an Antimicrobial Hydrogel Biomaterial

N-(4-Nitrobenzoyl)-Phe self-assembled into a transparent supramolecular hydrogel, which displayed high fibroblast and keratinocyte cell viability. The compound showed a mild antimicrobial activity against E. coli both as a hydrogel and in solution. Single-crystal XRD data revealed packing details, including protonation of the C-terminus due to an apparent pK_a shift, as confirmed by pH titrations. MicroRaman analysis revealed almost identical features between the gel and crystal states, although more disorder in the former. The hydrogel is thermoreversible and disassembles within a range of temperatures that can be fine-tuned by experimental conditions, such as gelator concentration. At the minimum gelling concentration of 0.63 wt %, the hydrogel disassembles in a physiological temperature range of 39–42 °C, thus opening the way to its potential use as a biomaterial.     

Synthesis of an Azasteroid Using an Acyl Iminium Ion-Initiated Tandem Cyclization

An acyl iminium ion-initiated tandem cyclization gave an unexpected dienone product, a seco-azasteroid (2). The factors governing the formation of 2 were investigated in an attempt to optimize its formation. The reaction was applied to a more elaborate system, resulting in the synthesis of the full steroid skeleton of 13-azaandrosta-1,4-diene-3,17-dione (3), which contains the unusual substitution of a chlorine atom for the axial 19-methyl.     

Error in an approximate wave function and an error minimization scheme

An estimate of error in an approximate wave function for a stationary state is put forward that does not require any information about the exact state. The measure is sensitive and direct. Parameters embedded in a trial wave function can be varied to minimize this error as well, leading to a variational principle. Such a scheme works nicely for bound states and the more so for Siegert states, for which the standard energy minimization principle does not apply. Pilot calculations on the anharmonic oscillator system and the radial Stark effect in the hydrogen atom reveal the worth of the endeavor. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

The first example of an ene reaction between an ester of cyclopropenecarboxylic acid and an alkyne

Methyl cyclopropenecarboxylate (I) enters into the ene reaction with the cyclic acetylene (II), giving vinylcyclopropene (III) with a high yield.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1229–1230, May, 1991.     

Functional regulation of an immobilized redox protein on an oriented metal coordinated peptide monolayer as an electron mediator

We fabricated a vertically and unidirectionally oriented metal coordinated α-helical peptide monolayer, Leu(2)Ala(Pyri)(Co(II))Leu(6)Ala(4-Pyri)(Co(II))Leu(6), by stepwise polymerization on a mixed self-assembled monolayer consisting of amino-alkanethiol, dialkyl disulfide, and ferrocenyl alkanethiol acted as a photoresponsive electron donor. Redox-active protein, nitrate reductase (NR), was fixed on the surface of the peptide monolayer. By contrast, we fixed NR on the mixed self-assembled monolayer directly. Upon photoirradiation, electron flow occurred from the excited ferrocenyl group on the substrate to the electron acceptor, NR, on the surface of the molecular layers. The activated NR on the molecular layers reduced the nitrate to nitrite. The amount of the bioelectrocatalytic product, nitrite, generated by the immobilized NR on the peptide monolayer was larger than that produced by the immobilized NR on the mixed self-assembled monolayer directly. That is to say, the NR on the peptide monolayer has been more activated rather than that on the peptide absent monolayer by photoirradiation. The effective activation of the NR on the peptide monolayer can be explained in terms of enhancement of the vectorial electron flow along the macro-dipole moment of the α-helical peptide that arranged unidirectionally. It suggested that the ordered metal coordinated α-helical peptide monolayer acted as an efficient electron mediator to achieve a communication between the electron donor and the redox-active moiety. Such a hybrid molecular system looks promising for novel nanodevices, such as nano-photoreactors.     

Strukturuntersuchungen an Mannanderivaten

H-NMR investigations using a high resolution 220 MHz spectrometer were performed on methyl, acetyl and benzoyl derivatives of mannan from ivory nuts and Tubera salep, and on the corresponding d-mannopyranose derivatives. With the exception of the C(1) configuration the structure of these polysaccharides may be determined by comparing the coupling constants and chemical shifts of the substituted polysaccharides with those of the corresponding monosaccharide derivatives. The particularly broad signals in the spectra of low as well as high molecular weight acetyl and benzoyl mannans and furthermore, the differences between the chemical shifts of protons in 1,2,3,4,6-penta-O-acetyl-d-mannopyranose and those of the benzoylated mannans, are discussed in terms of relatively small flexibility of the polymer chains or chain segments in solution. In addition studies to determine the type of glycosidic bonds in polysaccharides from a comparison of the δ_H(1)-values of various polyglycan derivatives are reported.