An accurate and reliable analysis of trimethylamine using thermal desorption and gas chromatography–time of flight mass spectrometry

Trimethylamine (TMA) is well-known for manifesting the odor of rotting fish and urine. The analysis of TMA in environmental samples generally suffers from low reproducibility and poor sensitivity. In this study, a technique for the quantitative analysis of gas phase TMA was developed using thermal desorption (TD)-gas chromatography (GC)-time of flight mass spectrometry (TOF-MS). This new approach yielded good linearity (R² = 0.9930), precision (RSE = 1.59%), and high sensitivity with the method detection limit (MDL) of 51 pg, i.e., detection of 0.021 ppb of TMA at 1 L sample (limit of detection (LOD): 5.32 pg (0.002 ppb). This method was tested against gas samples collected from two representative sources of TMA: (1) rotten thornback fish and (2) cat urine-soaked clay. The concentration of TMA in these samples, when analyzed after treatment at varying dilution ratios, averaged 293 ± 29.7 ppm (RSE = 3.82%) and 74.1 ± 5.78 ppb (RSE = 3.19%), respectively. The feasibility of this approach, when tested with TD–GC–Quadruple (Q) MS, showed a good compatibility with moderately reduced sensitivity. The results of this study demonstrated that one can achieve highly reliable and reproducible analysis of TMA from environmental samples when using thermal desorption (for pretreatment) and detection (by the TOF or Q-MS system).     

Facies architecture related to sea-level changes of the Upper Cretaceous (Santonian) Taneichi Formation,northeast Japan: evidence of actual sea-level fluctuation during the Late Cretaceous

Well-exposed transgressive and regressive sequence of the Santonian Taneichi Formation occurs along the Pacific Coast of northeastern Honshu, Japan. Although the studied sequence is of only 60 m thickness, the outcrops show various sedimentary facies accompanied with two disconformities, suggesting a small-scale but substantial sea-level rise and fall. Orientations of some sedimentary structures, such as ripples and bipolar cross-stratification, indicate that the paleostrandline of the Taneichi Formation made a high angle with the present coastline. Compared with the Santonian Kunitan Formation that is exposed about 50 km south of the studied section and that consists of thick deposits due to an incised valley sedimentation, the thin sediments of the Taneichi Formation are thought to have been supplied from the broad coastal plain along the eastern margin of the Eurasian continent.     

Assessment of range‐separated exchange functionals and nonempirical functional tuning for calculating the static second hyperpolarizabilities of streptocyanines

DFT method can severely overestimate the response properties for π‐conjugation systems. The range‐separated exchange and recently developed optimal IP‐tuning process are evaluated on the prediction of static second hyperpolarizabilities of streptocyanines of increasing molecular length. The finite field results have shown that the exact exchange at midium and long distance can relieve only a part of the overshooting but still beyond satisfaction. The exact exchange at short distance has the oppsite effects showing the failure of converntional hGGA. The optimal tuned range‐separated exchange functionals show little improvements performing worse than the default ones. Importantly, the electronic structure–property relationship, bond order alternation‐γ , is not well established with DFT method. © 2017 Wiley Periodicals, Inc.     

The Driving Force for the Acylation of β-Lactam Antibiotics by L,D-Transpeptidase 2: Quantum Mechanics/Molecular Mechanics (QM/MM) Study

β-lactam antibiotics, which are used to treat infectious diseases, are currently the most widely used class of antibiotics. This study focused on the chemical reactivity of five- and six-membered ring systems attached to the β-lactam ring. The ring strain energy (RSE), force constant (FC) of amide (C−N), acylation transition states and second-order perturbation stabilization energies of 13 basic structural units of β-lactam derivatives were computed using the M06-2X and G3/B3LYP multistep method. In the ring strain calculations, an isodesmic reaction scheme was used to obtain the total energies. RSE is relatively greater in the five-(1a–2c) compared to the six-membered ring systems except for 4b, which gives a RSE that is comparable to five-membered ring lactams. These variations were also observed in the calculated inter-atomic amide bond distances (C−N), which is why the six-membered ring lactams C−N bond are more rigid than those with five-membered ring lactams. The calculated ΔG^# values from the acylation reaction of the lactams (involving the S−H group of the cysteine active residue from L,D transpeptidase 2) revealed a faster rate of C−N cleavage in the five-membered ring lactams especially in the 1–2 derivatives (17.58 kcal mol⁻¹). This observation is also reflected in the calculated amide bond force constant (1.26 mDyn/A) indicating a weaker bond strength, suggesting that electronic factors (electron delocalization) play more of a role on reactivity of the β-lactam ring, than ring strain.     

中华乌塘鳢对性外激素嗅电反应的比较

用电生理方法研究中华乌塘鳢嗅上皮对PGE2、PGF2α、17α P和17α,20β P4种人工合成激素和对性成熟中华乌塘鳢贮精囊、精巢、卵巢和性未成熟卵巢4种提取液的嗅电反应(Electro olfactogram,EOG),观察嗅觉对不同刺激物的敏感性以及性成熟度对EOG的影响,以探讨中华乌塘鳢嗅上皮对何种性外激素最为敏感及嗅觉敏感性与性成熟度的关系.结果表明:性成熟鱼嗅上皮对4种人工合成激素的EOG大小顺序为:PGE2>PGF2α>17α P>17α,20β P,雄鱼对PGE2、PGF2α的EOG明显大于雌鱼(P<0.05);性成熟鱼嗅上皮对4种提取液的EOG大小顺序为:性成熟贮精囊液>性成熟精巢液>性成熟卵巢液>性未成熟卵巢液,它们之间的相对刺激有效性(Relativestimuluseffectiveness,RSE)差异在雄鱼为显著(P<0.05),在雌鱼则为极显著(P<0.01);性成熟鱼嗅上皮对性外激素的敏感性明显高于性未成熟鱼(P<0.01).