The Destination

It is sometimes difficult to realize that you are making progress, especially in medical school. You fight your way through the dark woods, getting scratched by loose branches, not quite sure if your feet are pointed in the right direction. Sometimes the journey feels like the mountain is collapsing, your feet are falling under you, your fingers throb from frost bite. Yet, there are the days where you stop and see the beauty of the journey in front of you. The winter is not always a cold, barren place, it holds so much beauty and it is worth the fight to continue

The Effect of Explicit Solvent on Photodegradation of Decabromodiphenyl Ether in Toluene: Insights from Theoretical Study

Polybrominated diphenyl ethers (PBDEs) have received special environmental concern because of their potential toxicity to humans and wildlife worldwide. However, their photochemical degradation mechanisms remain largely unknown. Herein, a PCM/TD-DFT scheme (time-dependent density functional theory combined with the polarizable continuum model) augmented with explicit solute–solvent interactions is used to explore the promotive effects of the toluene solvent on the photochemical degradation debromination of deca-BDE (BDE209). The face-to-face π–π interactions between penta-bromine-substituted phenyl and toluene are investigated. The calculations indicate that the face-to-face π–π interaction plays an important role in the low-lying π→σ* transitions of BDE209–toluene π-stacking complex at around 300 nm in the sunlight region, which leads to notable changes for the πσ* excited states and which promotes the breaking of the C–Br bonds. The photodegradation reaction via an intermolecular charge-transfer excited state formed by the electronic transition from a π orbital of toluene to a σ* orbital of BDE209 is found to be a dominant mechanism. Our calculation results reveal the mechanism of how the participation of an explicit toluene solvent molecule catalyzes the photodegradation of BDE209 and explain the experimental results successfully. The present study may provide helpful information for the removal of PBDE contamination

Table3_Systematic review of ethnomedicine, phytochemistry, and pharmacology of Cyperi Rhizoma.docx

Cyperi Rhizoma (CR) is the dry rhizome of Cyperus rotundus L., a Cyperaceae plant. It has a long history of clinical medication and is known as the “holy medicine” of gynecology. CR smells sweet and bitter. It has the effect of soothing the liver and relieving depression, regulating qi, regulating meridian and relieving pain. It can be used to treat liver qi stagnation, chest pain, spleen and stomach qi stagnation, hernia pain, irregular menstruation and other diseases. At present, the main chemical constituents isolated from CR are volatile oil, flavonoids and terpenes. Modern pharmacological studies have shown that CR has a wide range of pharmacological activities, including antidepressant, hypoglycemic, antioxidant, anti-inflammatory, antipyretic and analgesic effects. In this paper, the botany, traditional application, phytochemistry, pharmacological effects, processing and other aspects of CR are reviewed. At the same time, the shortcomings of current research of CR are discussed in depth, and the possible solutions are put forward in order to find a breakthrough point for future research of CR.</p

Electronic Structure Theory Study of the Microsolvated F^–(H₂O) + CH₃I S_N2 Reaction

The potential energy profile of microhydrated fluorine ion reaction with methyl iodine has been characterized by extensive electronic structure calculations. Both hydrogen-bonded F^–(H₂O)---HCH₂I and ion–dipole F^–(H₂O)---CH₃I complexes are formed for the reaction entrance and the PES in vicinity of these complexes is very flat, which may have important implications for the reaction dynamics. The water molecule remains on the fluorine side until the reactive system goes to the S_N2 saddle point. It can easily move to the iodine side with little barrier, but in a nonsynchronous reaction path after the dynamical bottleneck to the reaction, which supports the previous prediction for microsolvated S_N2 systems. The influence of solvating water molecule on the reaction mechanism is probed by comparing with the influence of the nonsolvated analogue and other microsolvated S_N2 systems. Taking the CCSD­(T) single-point calculations based on MP2-optimized geometries as benchmark, the DFT functionals B97-1 and B3LYP are found to better characterize the potential energy profile for the title reaction and are recommended as the preferred methods for the direct dynamics simulations to uncover the dynamic behaviors

Table1_Systematic review of ethnomedicine, phytochemistry, and pharmacology of Cyperi Rhizoma.DOCX

Cyperi Rhizoma (CR) is the dry rhizome of Cyperus rotundus L., a Cyperaceae plant. It has a long history of clinical medication and is known as the “holy medicine” of gynecology. CR smells sweet and bitter. It has the effect of soothing the liver and relieving depression, regulating qi, regulating meridian and relieving pain. It can be used to treat liver qi stagnation, chest pain, spleen and stomach qi stagnation, hernia pain, irregular menstruation and other diseases. At present, the main chemical constituents isolated from CR are volatile oil, flavonoids and terpenes. Modern pharmacological studies have shown that CR has a wide range of pharmacological activities, including antidepressant, hypoglycemic, antioxidant, anti-inflammatory, antipyretic and analgesic effects. In this paper, the botany, traditional application, phytochemistry, pharmacological effects, processing and other aspects of CR are reviewed. At the same time, the shortcomings of current research of CR are discussed in depth, and the possible solutions are put forward in order to find a breakthrough point for future research of CR.</p

Table4_Systematic review of ethnomedicine, phytochemistry, and pharmacology of Cyperi Rhizoma.docx

Cyperi Rhizoma (CR) is the dry rhizome of Cyperus rotundus L., a Cyperaceae plant. It has a long history of clinical medication and is known as the “holy medicine” of gynecology. CR smells sweet and bitter. It has the effect of soothing the liver and relieving depression, regulating qi, regulating meridian and relieving pain. It can be used to treat liver qi stagnation, chest pain, spleen and stomach qi stagnation, hernia pain, irregular menstruation and other diseases. At present, the main chemical constituents isolated from CR are volatile oil, flavonoids and terpenes. Modern pharmacological studies have shown that CR has a wide range of pharmacological activities, including antidepressant, hypoglycemic, antioxidant, anti-inflammatory, antipyretic and analgesic effects. In this paper, the botany, traditional application, phytochemistry, pharmacological effects, processing and other aspects of CR are reviewed. At the same time, the shortcomings of current research of CR are discussed in depth, and the possible solutions are put forward in order to find a breakthrough point for future research of CR.</p

Table2_Systematic review of ethnomedicine, phytochemistry, and pharmacology of Cyperi Rhizoma.docx

Cyperi Rhizoma (CR) is the dry rhizome of Cyperus rotundus L., a Cyperaceae plant. It has a long history of clinical medication and is known as the “holy medicine” of gynecology. CR smells sweet and bitter. It has the effect of soothing the liver and relieving depression, regulating qi, regulating meridian and relieving pain. It can be used to treat liver qi stagnation, chest pain, spleen and stomach qi stagnation, hernia pain, irregular menstruation and other diseases. At present, the main chemical constituents isolated from CR are volatile oil, flavonoids and terpenes. Modern pharmacological studies have shown that CR has a wide range of pharmacological activities, including antidepressant, hypoglycemic, antioxidant, anti-inflammatory, antipyretic and analgesic effects. In this paper, the botany, traditional application, phytochemistry, pharmacological effects, processing and other aspects of CR are reviewed. At the same time, the shortcomings of current research of CR are discussed in depth, and the possible solutions are put forward in order to find a breakthrough point for future research of CR.</p

Theoretical Studies on F^– + NH₂Cl Reaction: Nucleophilic Substitution at Neutral Nitrogen

The S_N2 reactions at N center, denoted as S_N2@N, has been recognized to play a significant role in carcinogenesis, although they are less studied and less understood. The potential energy profile for the model reaction of S_N2@N, chloramine (NH₂Cl) with fluorine anion (F^–), has been characterized by extensive electronic structure calculations. The back-side S_N2 channel dominates the reaction with the front-side S_N2 channel becoming feasible at higher energies. The minimum energy pathway shows a resemblance to the well-known double-well potential model for S_N2 reactions at carbon. However, the complexes involving nitrogen on both sides of the reaction barrier are characterized by NH---X (X = F or Cl) hydrogen bond and possess C₁ symmetry, in contrast to the more symmetric ion-dipole carbon analogues. In the F^– + NH₂Cl system, the proton transfer pathway is found to become more competitive with the S_N2 pathway than in the F^– + CH₃Cl system. The calculations reported here indicate that stationary point properties on the F^– + NH₂Cl potential energy surface are slightly perturbed by the theories employed. The MP2 and CAM-B3LYP, as well as M06-2X and MPW1K functionals give overall best agreement with the benchmark CCSD­(T)/CBS energies for the major S_N2 reaction channel, and are recommended as the preferred methods for the direct dynamics simulations to uncover the dynamic behaviors of the title reaction

How a Solvent Molecule Affects Competing Elimination and Substitution Dynamics. Insight into Mechanism Evolution with Increased Solvation

Competiting S_N2 substitution and E2 elimination reactions are of central importance in preparative organic synthesis. Here, we unravel how individual solvent molecules may affect underlying S_N2/E2 atomistic dynamics, which remains largely unclear with respective to their effects on reactivity. Results are presented for a prototype microsolvated case of fluoride anion reacting with ethyl bromide. Reaction dynamics simulations reproduce experimental findings at near thermal energies and show that the E2 mechanism dominates over S_N2 for solvent-free reaction. This is energetically quite unexpected and results from dynamical effects. Adding one solvating methanol molecule introduces strikingly distinct dynamical behaviors that largely promote the S_N2 reaction, a feature which attributes to a differential solute–solvent interaction at the central barrier that more strongly stabilizes the transition state for substitution. Upon further solvation, this enhanced stabilization of the S_N2 mechanism becomes more pronounced, concomitant with drastic suppression of the E2 route. This work highlights the interplay between energetics and dynamics in determining mechanistic selectivity and provides insight into the impact of solvent molecules on a general transition from elimination to substitution for chemical reactions proceeding from gas- to solution-phase environments