Studies on coherent and incoherent spin dynamics that control the magnetic field effect on photogenerated radical pairs

Since 1970s, magnetic field effects (MFEs) on photogenerated radical pairs have been the centre of focus in the field of spin chemistry. The MFE attributes to quantum mechanical interconversion between the singlet and triplet radical pair states and subsequent spin-selective recombination reactions. In this New View article, the author picks up two hot topics studied during the last two decades, which are (i) so-called low field effect (LFE) and (ii) 2J-resonance MFE on fixed distance donor–acceptor linked molecules. In both of the topics, quantum mechanical explanations are given referring to recent reports, and some novel calculations have been carried out for bridging theoretical and experimental data for long-lived radical pairs. For the first topic, time domain calculations of coherent state mixing have been carried out for elucidation of hyperfine (HF) structure dependence of the LFE. For the second topic, Monte Carlo simulations of the torsional motion of polyaromatic linker unit have been carried out for the demonstration of fast decoherence in such rigid molecules. From these considerations, future possibilities of MFE studies on photo-functional materials and biomolecules have been indicated.     

Poly(p‐benzamide) having isopropyl‐substituted chiral tri(ethylene glycol) side Chain: Synthesis and helical conformation

Isopropyl‐substituted tri(ethylene glycol) is used as a chiral side chain of N‐substituted poly(p‐benzamide) in order to increase the difference of stability between the right‐ and left‐handed helical structures of the polymer. The target polymer is synthesized by the chain‐growth condensation polymerization of the corresponding monomer with an initiator using lithium 1,1,1,3,3,3‐hexamethyldisilazide as a base. A circular dichroism (CD) study of the polymer reveals that the CD signal is due to an excess of a thermodynamically controlled right‐handed helical structure of the polymer, and that the replacement of the methyl group with a bulkier isopropyl group at the side chain of poly(p‐benzamide) increases the abundance of right‐handed helical structure in chloroform. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1623–1628     

Anomalous magnetic field effects on photochemical reactions in ionic liquid under ultrahigh fields of up to 28 T

The magnetic field effects (MFEs) on photoinduced hydrogen abstraction reactions between benzophenone and thiophenol in an ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) imide (TMPA TFSI), were studied by a nanosecond laser flash photolysis technique under ultrahigh fields of up to 28 T. Extremely large and anomalous stepwise MFEs were observed for the first time. The escape yield of benzophenone ketyl radical decreased with increasing magnetic field strength (B) at 0 T相似文献   

Temperature-dependent energy gap of the primary charge separation in photosystem I: study of delayed fluorescence at 77-268 K

The dynamics of fluorescence decay and charge recombination were studied in the ether-extracted photosystem I reaction center isolated from spinach with picosecond resolution over a wide time range up to 100 ns. At all temperatures from 268 to 77 K, a slow fluorescence decay component with a 30-40 ns lifetime was detected. This component was interpreted as a delayed fluorescence emitted from the singlet excited state of the primary donor P700*, which is repopulated through charge recombination that was increased by the lack of secondary acceptor phylloquinone in the sample. Analysis of the fluorescence kinetics allowed estimation of the standard free-energy difference -DeltaG between P700* and the primary radical pair (P700(+)A0(-)) state over a wide temperature range. The values of -DeltaG were estimated to be 160/36 meV at 268/77 K, indicating its high sensitivity to temperature. A temperature-dependent -DeltaG value was also estimated in the delayed fluorescence of the isolated photosystem I in which the secondary acceptor quinone was partially prereduced by preillumination in the presence of dithionite. The results revealed that the temperature-dependent -DeltaG is a universal phenomenon common with the purple bacterial reaction centers, photosystem II and photosystem I reaction centers.     

High-performance olefin polymerization catalysts discovered on the basis of a new catalyst design concept

This critical review highlights the "ligand oriented catalyst design concept", a new catalyst design concept for olefin polymerization that has led to the development of high-activity catalysts. The concept has created a series of highly active ethylene polymerization catalysts, many of which show high activities comparable to those of group 4 metallocene catalysts. Moreover, these catalysts display unique polymerization catalysis to produce a wide variety of polymers that possess unprecedented molecular architectures that are either difficult or impossible to achieve using conventional catalysts (98 references).     

Heterodinuclear M1M2 Complexes (M1=Ni,Pd, Pt; M2=Rh,Ir) Supported by a Tetradentate Phosphine Ligand and Their Application for Hydrosilylation

A new series of cationic heterodinuclear complexes, [M¹M²Cl₂(meso-dpmppp)(RNC)₂]PF₆ (M¹=Ni, M²=Rh, R=^tBu ( 1 a ); M¹=Pd, M²=Rh, R=^tBu ( 2 a ), Xyl ( 2 b ); M¹=Pt, M²=Rh, R=^tBu ( 3 a ), Xyl ( 3 b ); M¹=Pd, M²=Ir, R=^tBu ( 4 a )), supported by a tetradentate phosphine ligand, meso-Ph₂PCH₂P(Ph)(CH₂)₃P(Ph)CH₂PPh₂ (meso-dpmppp), were synthesized by stepwise reactions of meso-dpmppp with NiCl₂ ⋅ 6H₂O or MCl₂(cod) (M=Pd, Pt), forming mononuclear metalloligands of [M¹Cl₂(meso-dpmppp)], and with [M²Cl(cod)]₂ (M²=Rh, Ir) and RNC (R=^tBu, Xyl) in the presence of [NH₄][PF₆]. The related neutral PdRh complex, [PdRhCl₃(meso-dpmppp)(XylNC)] ( 5 ), was also prepared. The structures of 1 – 5 were determined by X-ray analyses to contain two square planar d⁸ metal centers with face-to-face arrangement, where meso-dpmppp supports M¹ and M² metal ions in cis/trans-P,P coordination mode, combining cis-{M¹P₂Cl₂} and trans-{M²P₂(CNR)₂} units. Complexes 1 – 4 showed an intence characteristic absorption around 422–464 nm derived from Rh^I→RNC MLCT transition (HOMO→LUMO+1), which are influenced by changing M¹ (Ni^II, Pd^II, Pt^II) metal ions since HOMO composed of dσ* orbitals appreciably destabilized by changing M¹ from Ni to Pd, and Pt. The electronic structures of 1 a – 4 a were investigated on the basis of DFT calculations and NBO analyses to show weak but noticeable d⁸–d⁸ metallophilic interaction as empirical dispersion energy of 0.9–1.5 kcal/mol without M¹–M² covalent bonding interaction. In addition, 1 – 5 were utilized as catalysts for hydrosilylation of styrene, and the NiRh complex 1 a was found to show higher activity and chemo- and regioselectivity compared with 2 – 5 .     

Protonation and methylation of an Anderson-type polyoxoanion [IMo6O24]5-

A series of protonated and methylated Anderson-type molybdoperiodates as well as the unprotonated [IMo6O24]5- have been synthesized and structurally characterized as tetra-n-butylammonium salts: [(n-C4H9)4N]5[IMo6O24] [monoclinic, space group C2/c, a = 33.6101(3) A, b = 15.2575(1) A, c = 24.0294(2) A, beta = 126.9569(3) degrees , Z = 4], [(n-C4H9)4N]4[IMo6O23(OH)] [monoclinic, space group P21/c, a = 9.5587(1) A, b = 24.1364(2) A, c = 18.2788(2) A, beta = 90.1562(5) degrees , Z = 2], [(n-C4H9)4N]3[IMo6O22(OH)2].2DMF [monoclinic, space group P21/a, a = 17.6105(4) A, b = 15.5432(5) A, c = 29.3316(9) A, beta = 91.475(3) degrees , Z = 4], [(n-C4H9)4N]4[IMo6O23(OMe)].3H2O [orthorhombic, space group Pbca, a = 17.0679(4) A, b = 25.6998(6) A, c = 20.7428(4) A, Z = 4], [(n-C4H9)4N]3[IMo6O22(OMe)2] [monoclinic, space group P21/n, a = 10.4009(1) A, b = 14.6658(3) A, c = 23.5395(4) A, beta = 100.324(1) degrees , Z = 2]. In all of these compounds, the [IMo6O24]5- anion is protonated or methylated selectively at O atoms shared by two Mo atoms. The results have also revealed that the protonated Anderson-type molybdoperiodates readily react with methanol in a very selective manner, while the unprotonated [IMo6O24]5- anion does not react with methanol under similar conditions.     

Coherent positronium molecule Psn and scanning clustering microscopy

The remarkable coherent features are indicated for the positronium molecules Ps_n, which are the lightest molecular system in the universe. The majority of Ps_n molecules undergo the coherent annihilation of all constituent Ps atoms yielding the coherent n‐pair photons which provide a unique method for observing Ps_n with identifying the order of clustering n. This leads to a new microscopy [scanning clustering microscopy (SCM)] in which Ps_n molecules are formed from surface positrons and Ps swarmed around a fine tip of a probe electrically biased with respect to a contacting matter surface to be investigated. It would open up new broad fields to study dynamical aspects of surface layer such as the catalytic activity on a subatomic scale. A method based on the Hunbury Brown–Twiss effect is also presented to determine the dimensions of Ps_n. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 83–99, 1999     

Ligand binding properties of myoglobin reconstituted with iron porphycene: unusual O2 binding selectivity against CO binding

Sperm whale myoglobin, an oxygen storage hemoprotein, was successfully reconstituted with the iron porphycene having two propionates, 2,7-diethyl-3,6,12,17-tetramethyl-13,16-bis(carboxyethyl)porphycenatoiron. The physicochemical properties and ligand bindings of the reconstituted myoglobin were investigated. The ferric reconstituted myoglobin shows the remarkable stability against acid denaturation and only a low-spin characteristic in its EPR spectrum. The Fe(III)/Fe(II) redox potential (-190 mV vs NHE) determined by the spectroelectrochemical measurements was much lower than that of the wild-type. These results can be attributed to the strong coordination of His93 to the porphycene iron, which is induced by the nature of the porphycene ring symmetry. The O2 affinity of the ferrous reconstituted myoglobin is 2600-fold higher than that of the wild-type, mainly due to the decrease in the O2 dissociation rate, whereas the CO affinity is not so significantly enhanced. As a result, the O2 affinity of the reconstituted myoglobin exceeds its CO affinity (M' = K(CO)/K(O2) < 1). The ligand binding studies on H64A mutants support the fact that the slow O2 dissociation of the reconstituted myoglobin is primarily caused by the stabilization of the Fe-O2 sigma-bonding. The IR spectra for the carbon monoxide (CO) complex of the reconstituted myoglobin suggest several structural and/or electrostatic conformations of the Fe-C-O bond, but this is not directly correlated with the CO dissociation rate. The high O2 affinity and the unique characteristics of the myoglobin with the iron porphycene indicate that reconstitution with a synthesized heme is a useful method not only to understand the physiological function of myoglobin but also to create a tailor-made function on the protein.