Highly Pure Synthesis,Spectral Assignments,and Two‐Photon Properties of Cruciform Porphyrin Pentamers Fused with Benzene Units

Tetrameric porphyrin formation of 2‐hydroxymethylpyrrole fused with porphyrins through a bicyclo[2.2.2]octadiene unit gave bicyclo[2.2.2]octadiene‐fused porphyrin pentamers. Thermal conversion of the pentamers gave fully π‐conjugated cruciform porphyrin pentamers fused with benzene units in quantitative yields. UV/Vis spectra of fully π‐conjugated porphyrin pentamers showed one very strong Q absorption and were quite different from those of usual porphyrins. From TD‐DFT calculations, the HOMO level is 0.49 eV higher than the HOMO?1 level. The LUMO and LUMO+1 levels are very close and are lower by more than 0.27 eV than those of other unoccupied MOs. The strong Q absorption was interpreted as two mutually orthogonal single‐electron transitions (683 nm: 86 %, HOMO→LUMO; 680 nm: 86 %, HOMO→LUMO+1). The two‐photon absorption (TPA) cross section value (σ⁽²⁾) of the benzene‐fused porphyrin pentamer was estimated to be 3900 GM at 1500 nm, which is strongly correlated with a cruciform molecular structure with multidirectional π‐conjugation pathways.     

Nuclear Spin–Lattice Relaxation of Single Crystal Sr14Cu24O41

Nuclear spin–lattice relaxation rate T ₁ ⁻¹ has been measured for the ladder sites of two single crystals Sr₁₄Cu₂₄O₄₁ (Sr14-A,B) by ⁶³Cu NMR/NQR. The hole localization around 100 K appears as a peak in the T variation of T ₁ ⁻¹(NQR). On the other hand, it is suppressed in the T ₁ ⁻¹ (NMR) data under the magnetic field H ∼ 11 T, and a new peak appears around 20 K. T ₁ ⁻¹(NMR) around the peak is more enlarged for Sr14-B than for Sr14-A. Hence, holes on the ladders of Sr14-B tend to be more localized. This is considered to be an origin for the occurrence of the magnetic order in Sr14-B under H ∼ 11 T.     

A chemical model of catechol-O-methyltransferase. Methylation of 3,4-dihydroxybenzaldehyde in aqueous solution

The reaction of 3,4-dihydroxybenzaldehyde (LH2) and dimethylsulfate (DMS) to form the m- and p-O-methylated products (vanillin and isovanillin, respectively) in aqueous 2-(N-morpholino)ethane sulfonate buffer was studied kinetically. The products were determined by means of high-performance liquid chromatography. The O-methylation occurred principally at the p-hydroxyl group in the absence of divalent metal ions. In the presence of Cu(II), the m-methylation was promoted and became predominant. Zn(II) showed a similar but less pronounced effect. The effects were explained in terms of the complex formation of LH2. The second order rate constants for the m- and p-methylation of the species, LH2, CuL and CuL2-2 by DMS were calculated. The values and their ratio for the m-/p-reactions increased in the order of LH2 less than CuL less than CuL2-2. The reaction may serve as a chemical model for catechol-O-methyltransferase, which requires divalent metals and catalyzes the m-methylation.     

Spectral diffusion at the water/lipid interface revealed by two-dimensional fourth-order optical spectroscopy: a classical simulation study

Using a classical simulation protocol for nonlinear optical signals, we predict the two-dimensional (2D) spectra of water near a monolayer of [1,2-dimytristoyl-sn-glycero-3-phosphatidylcholine] (DMPC) generated by three IR probe pulses followed by one visible probe pulse. Sum-frequency-generation 1D spectra show two peaks of the OH stretch representing two environments: near-bulk water nonadjacent to DMPC and top-layer water adjacent to DMPC. These peaks create a 2D pattern in the fourth-order signal. The asymmetric cross-peak pattern with respect to the diagonal line is a signature of coherence transfer from the higher- to the lower-frequency modes. The nodal lines in the imaginary part of the 2D spectrum show that the near-bulk water has fast spectral diffusion resembling that of bulk water despite the orientation by the strong electrostatic field of DMPC. The top-layer water has slower spectral diffusion.     

Analytic energy gradient for second-order Møller-Plesset perturbation theory based on the fragment molecular orbital method

The first derivative of the total energy with respect to nuclear coordinates (the energy gradient) in the fragment molecular orbital (FMO) method is applied to second order M?ller-Plesset perturbation theory (MP2), resulting in the analytic derivative of the correlation energy in the external self-consistent electrostatic field. The completely analytic energy gradient equations are formulated at the FMO-MP2 level. Both for molecular clusters (H(2)O)(64) and a system with fragmentation across covalent bonds, a capped alanine decamer, the analytic FMO-MP2 energy gradients with the electrostatic dimer approximation are shown to be complete and accurate by comparing them with the corresponding numeric gradients. The developed gradient is parallelized with the parallel efficiency of about 97% on 32 Pentium4 nodes connected by Gigabit Ethernet.     

The precise measurement of the (vapour + liquid) equilibrium properties for (CO2 + isobutane) binary mixtures

Recently, it has been suggested that natural working fluids, such as CO₂, hydrocarbons, and their mixtures, could provide a long-term alternative to fluorocarbon refrigerants. (Vapour + liquid) equilibrium (VLE) data for these fluids are essential for the development of equations of state, and for industrial process such as separation and refinement. However, there are large inconsistencies among the available literature data for (CO₂ + isobutane) binary mixtures, and therefore provision of reliable and new measurements with expanded uncertainties is required. In this study, we determined precise VLE data using a new re-circulating type apparatus, which was mainly designed by Akico Co., Japan. An equilibrium cell with an inner volume of about 380 cm³ and two optical windows was used to observe the phase behaviour. The cell had re-circulating loops and expansion loops that were immersed in a thermostatted liquid bath and air bath, respectively. After establishment of a steady state in these loops, the compositions of the samples were measured by a gas chromatograph (GL Science, GC-3200). The VLE data were measured for CO₂/propane and CO₂/isobutane binary mixtures within the temperature range from 300 K to 330 K and at pressures up to 7 MPa. These data were compared with the available literature data and with values predicted by thermodynamic property models.     

A combined effective fragment potential-fragment molecular orbital method. II. Analytic gradient and application to the geometry optimization of solvated tetraglycine and chignolin

The gradient for the fragment molecular orbital (FMO) method interfaced with effective fragment potentials (EFP), denoted by FMO∕EFP, was developed and applied to polypeptides solvated in water. The structures of neutral and zwitterionic tetraglycine immersed in water layers of 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 A? are investigated by performing FMO∕EFP geometry optimizations at the RHF∕cc-pVDZ level of theory for the solutes. The geometries optimized with FMO-RHF∕EFP are compared to those from the conventional RHF∕EFP and are found to be in very close agreement. Using the optimized geometries, the stability of the hydrated zwitterionic and neutral structures is discussed structurally and in terms of energetics at the second-order M?ller-Plesset theory (MP2)∕cc-pVDZ level. To demonstrate the potential of the method for proteins, the geometry of hydrated chignolin (protein data bank ID: 1UAO) was optimized, and the importance of the inclusion of water was examined by comparing the solvated and gas phase structures of chignolin with the experimental NMR structure.     

Catalytic asymmetric allylation of 3,4-dihydroisoquinolines and its application to the synthesis of isoquinoline alkaloids

A catalytic asymmetric allylation of 3,4-dihydroisoquinoline was carried out with allyltrimethoxylsilane-Cu as the nucleophile in the presence of DTBM-SEGPHOS as the chiral ligand to afford corresponding chiral 1-allyltetrahydroisoquinoline derivatives in good yield and stereoselectivity. The allyl adduct thus obtained was applied to the synthesis of several isoquinoline alkaloids such as crispine A and homolaudanosine. The reaction was further used for the synthesis of the isoquinoline moiety of schulzeine A.