Comprehensive Understanding of Host- and Guest-Dependent Helix Inversion in Chiral Nematic Liquid Crystals: Experimental and Molecular Dynamics Simulation Study.

Nematic liquid crystals (LCs) are known to transform into chiral nematic LCs with helical structures upon doping with enantiomeric compounds (called chiral dopants or guests). Here, we investigated the mechanism of host LC- and guest-dependent helix inversion by using octahedral metal complexes as guests. The helical twisting powers (HTPs/µm-1) of eight metal complexes with Δ, Λ chirality were examined in five nematic LC hosts. For example, Δ-[Ru(acac)2(trop)] (Ru-trop, Hacac = 2,4-pentanedione, Htrop = tropolone) induces a left-handed ( M) helix upon doping with N-(4-methoxybenzylidene)-4-butylaniline (MBBA), whereas it induces an opposite right-handed ( P) helix in 4-cyano-4'-pentylbiphenyl (5CB). The monobrominated complex of Ru-trop, Δ-[Ru(acac)2(Brtrop)] (Ru-Br1trop, HBr1trop = 5-bromotropolone), induces P helices in both MBBA and 5CB, whereas the dibrominated complex, Δ-[Ru(acac)2(Br2trop)] (Ru-Br2trop, HBr2trop = 3,7-dibromotroplone) induces M helices in both the media. The molecular dynamics simulation performed in parallel confirmed the drastic effect of the bromo groups on the microscopic ordering direction of guests in nematics. Further, HTPs of all Δ isomers of metal complexes investigated were found to shift in the positive direction as the dielectric constant anisotropy (Δε) of the host LCs increases (and vice versa for Λ isomers). These experimental and calculated results highlight the interplay of steric (excluded volume effect) and electrostatic (dipole-dielectric body) interactions between the host LCs and guest metal complexes.

Seasonal Occurrence and Interspecific Interactions of Egg Parasitoids of Megacopta cribraria (Heteroptera: Plataspidae) in Japan.

We conducted a field study to determine seasonal egg parasitism rates of the kudzu bug Megacopta cribraria (F.) on the kudzu plant, Pueraria montana (Lour.) Merr. var. lobata (Willd.) Maesen et Almeida ex Sanjappa and Pradeep, in Tokyo, Japan, during the period from May 2014 to September 2014. The eggs of M. cribraria per 1 m2 of kudzu at four locations in Tokyo were collected weekly and parasitism rates were assessed. Eggs of M. cribraria were laid on the kudzu plant from May to September. Megacopta cribraria eggs were parasitized by two parasitoid species, Paratelenomus saccharalis (Dodd) and Ooencyrtus nezarae Ishii. Paratelenomus saccharalis first appeared in May, and its parasitism rates peaked in July and September. Ooencyrtus nezarae first appeared in June and its parasitism rates peaked in July. Except for one location which could not be statistically analyzed because of the small sample size, occurrence of parasitism by P. saccharalis and O. nezarae in M. cribraria egg masses was independent at one location and positively associated at two locations, suggesting that the use of host egg masses by P. saccharalis and O. nezarae is not mutually exclusive. Parasitism rates by P. saccharalis and O. nezarae were significantly lower for egg masses parasitized by both species than for those parasitized by a single species. The proportion of males among O. nezarae progeny was significantly higher for egg masses parasitized by O. nezarae together with P. saccharalis than for those parasitized by O. nezarae alone. These results suggest that parasitism of host egg masses by the two species is influenced by their interspecific interactions.