Synthesis and different molecular recognition of two dye-modified cyclodextrins with spacer of different length

Two β-cyclodextrin derivatives (1 and 2) bearing a hydroxyazobenzene unit, each having a butylene or a 4,7-dioxadecylene spacer between the cyclodextrin and the dye, were prepared, which showed guest-induced color changes with a marked difference in molecular recognition behavior in aqueous solution.     

Reaction of isoquinolinium methylide derivatives with trimethylsilylketene

Our investigation on the reaction of isoquinolinium methylide derivatives with trimethylsilylketene (TMS ketene), giving [3+2] cycloadducts, pyrroloisoquinolines, is described. TMS ketene is found to function as the C2 unit introducing reagent in the reaction of isoquinolinium methylide derivatives. Furthermore, the advantage of TMS ketene in comparison with ketene (CH₂CO) is shown.     

Host-guest complexation affected by pH and length of spacer for hydroxyazobenzene-modified cyclodextrins

Three modified beta-cyclodextrins appended with a hydroxyazobenzene as a dye unit, 1, 2, and 3, each incorporating a different length spacer between the beta-CD and the dye unit with a bis(propyl(oxyethylene)), butylene, and amide bond spacer, respectively, were synthesized in order to investigate their spectroscopic changes induced by pH and host-guest complexation as well as to investigate their conformations and guest-binding properties by means of absorption and induced circular dichroism spectroscopies in aqueous solutions. All hosts accommodated the dye unit in their own CD cavities with an orientation parallel to the CD axis, forming intramolecular complexes. When the pH of the solution changed, the structure changed in response to pH without conformational changes. Existing as the phenol form under acidic condition, they were converted to the yellow phenolate form by dissociation of a proton of the hydroxyl group in the dye unit with increasing pH (pK(a1); 7.62 for 1, 7.44 for 2, 8.00 for 3). Further increase in pH led to the dissociation of the ammonium proton in the secondary amine group in the spacer of 1 and 2 (pK(a2); 8.76 for 1, 8.67 for 2). Upon addition of 1-adamantanol (AN) as a guest, all hosts accommodated AN in their CD cavities, forming 1:1 host-guest inclusion complexes. The complexation phenomena were accompanied with changes in the conformation of the hosts, in which the dye units of 1 and 2 are excluded to outside of the cavity, but not for 3. The dye unit of 3 remained in the cavity, where the guest was also included partly. Therefore, the guest-binding abilities of 1 and 2 were larger than that of 3, which has poor binding ability. The binding constants of 1, 2, and 3 for AN are estimated to be 7400, 1940, and 140 M(-1) at pH 3.2, respectively. However, the guest-binding abilities of 1 and 2 were dependent on the pH of the solution. The ability of 1 under weak alkaline condition was stronger than under acidic or alkaline conditions, while that of 2 increased with increasing pH. Under the condition from neutral to weak alkaline media, 1 and 2 demonstrated color changes from colorless to yellow upon formation of inclusion complexes. When 1-adamantanecarboxylic acid (AC) was used as the charged guest, 1 and 2 bound to AC with a larger binding constant than AN. On the other hand, 1 and 2 bound to 1-adamantineamine (AA) with a smaller binding constant than AN. All these results demonstrate that the complexation phenomena depend on the pH of the solution as well as the length of the spacer of the hosts and that the electrostatic interaction between the host and the guest is also important for forming a stable complex.     

Introduction of single mutation changes arylmalonate decarboxylase to racemase

The introduction of only one mutation based on the estimated reaction mechanism endowed arylmalonate decarboxylase with a racemase activity, which catalyses racemisation of alpha-arylpropionates.     

Molecular dynamics study on the ligand recognition by tandem SH3 domains of p47phox, regulating NADPH oxidase activity

The phagocyte NADPH oxidase complex plays a crucial role in host defense against microbial infection through the production of superoxides. Chronic granulomatous disease (CGD) is an inherited immune deficiency caused by the absence of certain components of the NADPH oxidase. Key to the activation of the NADPH oxidase is the cytoplasmic subunit p47phox, which includes the tandem SH3 domains (N-SH3 and C-SH3). In active phagocytes, p47phox forms a stable complex with the cytoplasmic region of membrane subunit p22phox that forms a left-handed polyproline type-II (PPII) helix conformation. In this report, we have analyzed the conformational changes of p47phox-p22phox complexes of wild-type and three mutants, which have been detected in CGD patients, using molecular dynamics simulations. We have found that in the wild-type, two basal planes of PPII prism in cytoplasmic region of p22phox interacted with N-SH3 and C-SH3. In contrast, in the modeled mutants, the residue at the ape of PPII helix, which interacts simultaneously with both of the tandem SH3 domains in the wild-type, moved toward C-SH3. Furthermore, interaction energies of the cytoplasmic region of p22phox with C-SH3 tend to decrease in these mutants. All these findings led us to conclude that interactions between N-SH3 of p47phox and PPII helix, which is formed by cytoplasmic region of p22phox, may play a significant role in the activation of the NADPH oxidase.     

Highly stereoselective asymmetric Pummerer reactions that incorporate intermolecular and intramolecular nonbonded S...O interactions

New chiral sulfoxides (R(S),S)-3, (S(S),S)-3, (R(S),S)-4, and (S(S),S)-4 and known chiral sulfoxides (R(S))-5, (R(S))-6, and (R(S))-7 were synthesized, and the stereochemistry of the new sulfoxides (R(S),S)-3 and (R(S),S)-4 was determined by X-ray crystallographic analysis. In their crystallographic structures, the intramolecular nonbonded S...O close contacts were recognized. Analyses of several sulfoxide complexes including rac-11 with N,N-dimethylacetamide (DMAC) or N-methyl-2-pyrrolidone (NMP) in a MeOH solution utilizing cold-spray ionization mass spectrometry provided, for the first time, direct information for intermolecular nonbonded S...O interactions between sulfoxides and amide (or lactam) in a solution. Highly diastereoselective and enantioselective Pummerer reactions based on the concept of intermolecular and intramolecular nonbonded S...O interactions were performed by treatment of several chiral sulfoxides (R(S), S)-3, (S(S), S)-3, (R(S), S)-4, (S(S), S)-4, (R(S))-5, (R(S))-6, and (R(S))-7 with acetic anhydride and trimethylsilyl triflate (TMSOTf) in DMAC, NMP, N,N-dimethylformamide, and N-formylpiperidine. Mechanistic studies on these facile stereoselective Pummerer reactions revealed the necessity for the amide/TMSOTf complex, such as 26 or 27, to be an efficient activation reagent for Ac(2)O and a trapping reagent for the released acetate ion, and that DMAC and NMP had a positive effect on this highly stereoselective chiral transfer reaction.     

Anti versus syn opening of epoxides derived from 9-(3-deoxy-beta-D-glycero-pent-3-enofuranosyl)adenine with Me3Al: factors controlling the stereoselectivity

Upon epoxidation with dimethyldioxirane, the 2',5'-bis-O-silyl derivatives of 9-(3-deoxy-beta-D-glycero-pent-3-enofuranosyl)adenine gave the respective "3',4'-up" epoxides exclusively. Reaction between these epoxides and Me3Al was investigated in detail. It was found that the stereoselectivity of epoxide ring opening (anti versus syn) varied significantly upon changing the amount of Me3Al, the solvent, the O-silyl protecting group, and the reaction temperature. A possible reaction mechanism is proposed.     

Perfectness and imperfectness of unit disk graphs on triangular lattice points

Given a finite set of 2-dimensional points P⊆R² and a positive real d, a unit disk graph, denoted by (P,d), is an undirected graph with vertex set P such that two vertices are adjacent if and only if the Euclidean distance between the pair is less than or equal to d. Given a pair of non-negative integers m and n, P(m,n) denotes a subset of 2-dimensional triangular lattice points defined by where . Let T_m,n(d) be a unit disk graph defined on a vertex set P(m,n) and a positive real d. Let be the kth power of T_m,n(1).In this paper, we show necessary and sufficient conditions that [ is perfect] and/or [ is perfect], respectively. These conditions imply polynomial time approximation algorithms for multicoloring (T_m,n(d),w) and .     

Single-shot full-field interferometric polarimeter with an integrated calibration scheme

A simple interferometric polarimeter with an integrated calibration scheme is proposed for accurate and fast mapping of the state of polarization (SOP). Conventional single-shot polarimeters that detect the amplitude and phase of orthogonally polarized field components by interferometry using Fourier fringe analysis suffers from errors caused by the imperfect reference beam and ambiguity in the spatial carrier frequency in the fringe pattern. In the proposed system, the integrated calibration scheme eliminates those error sources and enables accurate measurement of SOP without prior knowledge of the reference beam and the spatial carrier frequency.     

Inteferences in neutron and photon activation analysis

The effect of following interferences was quantitatively assessed in terms of interference factor by irradiating samples together with highly pure reagents at two reactor sites of diferent neutron spectra and fluxes for neutron activation analysis (NAA) and an electron LINAC for photon activation analysis (PAA). The interfering reactions studied are 91) fast neutron-induced reactions, (2) uranium fission (3) (n,γ) reactions of other target elements in NAA, and (4) reactions induced by secondary neutrons in PAA. Corrections for these interferences were successfully applied to the activation analysis of some geological reference rock samples and biological samples.