Exploring potential crossing seams in periodic systems: Intersystem crossing pathways in the benzene crystal.

The intersystem crossing (ISC) pathways of triplet benzene molecules in a benzene crystal were investigated theoretically. A combination of the gradient projection (GP) method, which is a standard method for optimizing the crossing seam of two potential energy surfaces, and the single-component artificial-force-induced reaction (SC-AFIR) method (GP/SC-AFIR) was used. This is the first reported use of a GP/SC-AFIR calculation using a density functional theory calculation with periodic boundary conditions. A systematic search for the minimum-energy structures in the seams of crossing of the singlet (S0) and triplet (T1) potential energy surfaces (S0/T1-MESX structures) found 39 independent S0/T1-MESX structures. Energy barriers between the S0/T1-MESX and the stationary structure of the triplet state (T1-MIN) were computed, and then two competing ISC pathways were extracted; the calculated overall energy barrier to the intermolecular C-C-bonded type (SX3) and the out-of-plane bent C-H type (SX15) S0/T1-MESX structures from T1-MIN were 0.26 and 0.27 eV, respectively. The rate constants for SX3 and SX15 formation were estimated to be 5.07 × 108 and 2.17 × 108 s-1 (at 273 K), respectively, or 9.73 × 10-5 and 4.78 × 10-6 s-1 (at 77 K), respectively. At 273 K, which is close to the melting point of the benzene crystal (278.5 K), SX3 and SX15 are easily accessible from T1-MIN, and ISC could occur through the S0/T1-MESX points. By contrast, at 77 K, T1-MIN survives long enough for phosphorescence to compete with ISC.

Solid phase extraction of phosphorus-containing amino acid-type herbicides and their metabolites from human blood with titania for determination by capillary electrophoresis.

Phosphorus-containing amino acid-type herbicides (PAAHs) and their metabolites in human plasma and whole blood were extracted with titania and determined by capillary electrophoresis (CE). The recoveries of glyphosate (GLYP), aminomethylphosphonic acid (AMPA), gluphosinate (GLUF), and 3-methylphosphonico-propionic acid (MPPA) from human plasma were 84.6, 76.8, 90.4, and 89.6%, respectively. The recoveries of GLYP, AMPA, GLUF, and MPPA from whole blood were 79.6, 84.4, 36.9, and 31.8%, respectively. The low recoveries of GLUF and MPPA from whole blood were improved by the dilution of whole blood with water to 4-fold.

Cloud point extraction and preconcentration for the gas chromatography of phenothiazine tranquilizers in spiked human serum.

Cloud point extraction was successfully applied to the preconcentration of phenothiazine derivatives, such as pericyazine (PC), chlorpromazine (CP) and fluphenazine (FUL), for gas chromatography (GC). Phenothiazine derivatives were separated from surfactants by passing the surfactant-rich phase through a cation exchange column after cloud point extraction, permitting the determination of the phenothiazine derivatives extracted in the surfactant-rich phase by GC. The optimal condition for the cloud point extraction of phenothiazine derivatives was also investigated using Triton X-100, Triton X-114, and PONPE10. Triton X-114 provided the most efficient recovery of phenothiazine derivatives among the surfactants used. The addition of sodium chloride and excess ammonia to the sample solution resulted in a decrement of the recovery of the phenothiazine derivatives. The proposed method was applied to the determination of phenothiazine derivatives in spiked human serum by GC. The recoveries of PC, CP, and FUL in spiked human serum were 95.1%, 87.1%, and 84.7%, respectively.