Chiral recognition and supramolecular photoreaction of 1,1′-binaphthol with bovine and human serum albumins

In their pioneering study in 1991, Levi-Minzi and Zandomeneghi discovered that photoirradiation of racemic 1,1′-binaphthol (rac-1) in the presence of bovine serum albumin (BSA) in distilled water gave (R)-1 in 99 % enantiomeric excess (ee) after 77 % of the starting material had been consumed. No similar attempt was made with human serum albumin (HSA). In this study of the effects of phosphate buffer solution on the ground-state affinity and excited-state photobehavior of 1 with serum albumin we found that both BSA and HSA preferentially bind the (S) enantiomer of 1 and that photoreaction of rac-1 mediated by BSA and HSA affords (R)-1 in 98 % ee with 99 % conversion and in 46 % ee with 65 % conversion, respectively.     

Aggregation of Chlorophyll a' in Aqueous Methanol

An aggregate of chlorophyll a' (Chi a' , C13²-epimer of ChI a ) formed in a methanovwater (40160, vol/vol) mixed solvent was examined by visible absorption, circular dichro-ism (CD), fluorescence and resonance Raman spectrosco-pies in relation to its possible involvement in the core of photosystem I reaction center. The Chl a' aggregate exhibited a sharp, double-peaked absorption spectrum (690 and 715 nm) accompanied by an intense, conservative CD signal. The fluorescence excitation polarization spectrum showed that the doublet results from the exciton splitting in a single aggregate species. Time-dependent changes in the spectroscopic properties clearly point to a simple transformation process from one molecular species to another, though a minor component appears to coexist. This conclusion was supported also by the principal multicom-ponent spectral estimation analysis of the transients of absorption spectra. The species formed at the initial stage is most probably a T-shaped dimer or oligomer, which is then gradually converted into the final major product, presumably a stacked dimer. In both of these states, the Chl molecules are linked together via direct coordination of the C13'keto carbonyl oxygen onto the Mg atom of neighboring molecules, as suggested by almost identical resonance Raman spectra in ordinary and deuterated methanovwater mixed solvents. The stacked dimers probably further associate to form a colloidal state in this solvent system. Based on these results, a model for the Chl a' aggregation is proposed.     

Production and excited state dynamics of the photorearranged isomer of benzyl chloride and its methyl derivatives studied by stepwise two-color laser excitation transient absorption and time-resolved thermal lensing techniques

Production and photoexcited dynamics of reaction intermediates with photolyses of benzyl chloride (BzCl) and methyl-substituted benzyl chlorides (MeBzCls) were studied by using stepwise two-color laser excitation transient absorption (TC-TA) and two-color laser excitation time-resolved thermal lensing (TC-TRTL) measurements. With photoexcitation of BzCl the formation of transient photorearranged isomer was suggested in the previous paper [Res. Chem. Intermed. 2001, 27, 137]. Such an isomer formation for MeBzCls was also observed in a 248 nm excitation. It was found that further photoexcitation of the isomers with the 308 nm light caused photodissociation to yield the corresponding benzyl radicals. The reaction quantum yield and the molar absorptivity of the photorearranged isomer of BzCl were estimated. The heat of reaction for the photodissociation of the isomer was successfully determined with the TC-TRTL measurement. These experimental results were consistent with MO calculations.     

Vital significance of addition of “shape similarity” between solutes to shape complementarity for more precise molecular recognition in aqueous binary solvents

Precise and specific molecular recognition is vital to living systems. Discrimination has mainly been studied by using particular host molecules (e.g., crown ethers, cyclodextrin and urea derivatives). Several studies in various fields have pointed out that the famous “lock‐and‐key theory” (the concept of shape complementarity) is, at present, insufficient for understanding precise discrimination. This seems to come from the fact that various types of intermolecular interactions are decisive in such discrimination. This Review intends to describe the novel concept that “shape similarity” between interacting solutes should be added to “shape complementarity” for more precise discrimination to be achieved. Further, the role of shape similarity between solvent and solute molecules is also described. In relation to precise molecular recognition, weak interactions, which depend on the three‐dimensional shape of substituents (shape‐specific weak interactions), are described. Possibility of alterations in solvent structures is discussed in aqueous binary solvents. DOI 10.1002/tcr.201100001     

Krylov subspace methods for computing hydrodynamic interactions in Brownian dynamics simulations

Hydrodynamic interactions play an important role in the dynamics of macromolecules. The most common way to take into account hydrodynamic effects in molecular simulations is in the context of a Brownian dynamics simulation. However, the calculation of correlated Brownian noise vectors in these simulations is computationally very demanding and alternative methods are desirable. This paper studies methods based on Krylov subspaces for computing Brownian noise vectors. These methods are related to Chebyshev polynomial approximations, but do not require eigenvalue estimates. We show that only low accuracy is required in the Brownian noise vectors to accurately compute values of dynamic and static properties of polymer and monodisperse suspension models. With this level of accuracy, the computational time of Krylov subspace methods scales very nearly as O(N(2)) for the number of particles N up to 10 000, which was the limit tested. The performance of the Krylov subspace methods, especially the "block" version, is slightly better than that of the Chebyshev method, even without taking into account the additional cost of eigenvalue estimates required by the latter. Furthermore, at N = 10 000, the Krylov subspace method is 13 times faster than the exact Cholesky method. Thus, Krylov subspace methods are recommended for performing large-scale Brownian dynamics simulations with hydrodynamic interactions.     

Diastereodifferentiating the [2+2] Photocycloaddition of Ethylene to Arylmenthyl Cyclohexenonecarboxylates: Stacking‐Driven Enhancement of the Product Diastereoselectivity That Is Correlated with the Reactant Ellipticity

Upon diastereodifferentiating the [2+2] photocycloaddition of ethylene to a series of p‐substituted (?)‐8‐phenylmenthyl cyclohexenonecarboxylates, the diastereoselectivity was critically controlled by the nature of the substituent introduced to the chiral auxiliary, and the p‐nitro‐substituted substrate afforded the cycloadducts in 90 % diastereomeric excess (de) and with 97 % isolated yield. Detailed experimental and theoretical conformation analyses revealed that the stacking interaction of the aromatic auxiliary with the cyclohexenone moiety plays the decisive role in determining the substrate conformation and is, therefore, responsible for the dramatic enhancement of the de. Of particular interest, the product de was directly related to the ellipticity of the substrate, enabling us to “predict” the de prior to photoirradiation.     

Empirical method for predicting enantioselectivity in catalytic reactions: demonstration with lipase and oxazaborolidine

We derived a novel equation capable of predicting the degree of enantioselectivity in a catalytic reaction without any knowledge of the reaction mechanism and/or the transition-state structure, and tested the validity of this equation by changing substrates systematically in the lipase or oxazaborolidine-catalyzed reactions. A good correlation was observed between the predicted and observed E values, and the stereochemistry of the products could be predicted correctly in most cases (28 out of 30).     

Novel anionic polyaddition of 2‐trifluoromethylacrylate by double Michael reaction with ethyl cyanoacetate

Novel fluorinated polymer synthesis with anionic polyaddition by double Michael addition reaction of 2‐trifluoromethylacrylate derivatives with ethyl cyanoacetate (ECA) was proposed. Diaddition product of ECA with phenyl 2‐trifluoromethylacrylate was yielded in high yield by the catalysis of sodium ethoxide in tetrahydrofuran at 60 °C. Sodium hydroxide catalyzed double Michael addition reaction also produced diaddition product in high yield. Novel anionic polyaddition of 1,4‐phenylene bis(2‐trifluoromethylacrylate) [CH₂?C(CF₃)COOC₆H₄OCOC(CF₃)?CH₂] (PBFA) with ECA afforded the polymer of 1.2 × 10⁴ as the highest molecular weight. The isolated polymer gave the polymer of 2.8 × 10⁴ as a molecular weight by the reaction of the isolated polymer with PBFA in the presence of sodium ethoxide; which proved that the polymer end groups were mainly ECA moieties. The reaction mechanism that the proton abstraction from ECA followed by the addition of 2trifluoromethylacrylate was proposed. The reaction of acetylacetone with PBFA was also examined to give the polymer of 7.6 × 10³ as the highest molecular weight catalyzed by sodium hydroxide at room temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5698–5708, 2009