Kinetics Study on Reaction between Dihydroartemisinic Acid and Singlet Oxygen: An Essential Step to Photochemical Synthesis of Artemisinin

Artemisinin is an excellent antimalarial drug widely used in clinical medicine.However,due to the limitation of natural source of artemisinin,the chemical synthesis of artemisinin has achieved substantial attention.Dihydroartemisinic acid is a key precursor for the synthesis of artemisinin.The reaction of dihydroartemisinic acid with singlet oxygen to form peroxide is a pivotal step in the photochemical preparation of artemisinin.Nevertheless,the reaction kinetics of dihydroartemisinic acid with singlet oxygen has not been investigated previously.Herein,we report the rate constants of the reaction between dihydroartemisinic acid and singlet oxygen.By directly detecting the luminescence decay kinetics of singlet oxygen at 1270 nm at room temperature,the reaction rate constants of singlet oxygen and dihydroartemisinic acid in different solvents are obtained to be 1.81×10^5(mol/L)^-1·s^-1 in CCl4,5.69×10^5(mol/L)^-1·s^-1 in CH3CN,and 3.27×10^6(mol/L)^-1·s^-1 in DMSO,respec-tively.It is found that the reaction rate constants of dihydroartemisinic acid with singlet oxygen increase as polarity of the solvent increases among the three solvents.These results provide fundamental knowledge to optimize experiment conditions of photochemical synthesis of artemisinin for improving the yields of artemisinin.

Time-Resolved FTIR Study on the Reaction of CHCl2 with NO2

The environmentally important free radical reaction of chlorinated methyl CHCl2 with NO2 was investigated by step-scan time-resolved FTIR （TR-FTIR） emission spectroscopy. Vibrationally excited products of CHClO, NO, CO, and HCl are observed in the high-resolution IR emission spectra and three possible reaction channels are therefore elucidated. In particular, the product CO is newly detected and the product HCl is identified explicitly as a yield from the CHCl2＋NO2 reaction, taking advantage of the sensitive detection of HCl and CO with TR-FTIR. These results are of particular interests to understand the related realistic chemical processes including atmospheric photochemistry, biofuel combustion, waste destruction, and smoking fire.

Reaction of C2HCl2＋O2： Combined TR-FTIR Spectroscopy and Electronic Structure

The product channels and mechanisms of the C2HC12＋O2 reaction are investigated by step-scan time-resolved Fourier transform infrared emission spectroscopy and the G3MP2// B3LYP/6-311G（d,p） level of electronic structure calculations. Vibrationally excited products of HCI, CO, and CO2 are observed in the IR emission spectra and the product vibrational state distribution are determined which shows that HCI and CO are vibrationally excited with the nascent average vibrational energy estimated to be 59.8 and 51.8 kJ/mol respectively. In combination with the G3MP2//B3LYP/6-311G（d,p） calculations, the reaction mechanisms have been characterized and the energetically favorable reaction pathways have been suggested.

Kinetics Study on Reaction of Atenolol with Singlet Oxygen by Directly Monitoring the^(1)O_(2)Phosphorescence

The pharmaceuti-cally active com-pound atenolol,a kind of β-blockers,may result in ad-verse effects both for human health and ecosystems if it is excreted to the surface water resources.To e ectively remove atenolol in the environ-ment,both direct and indirect photodegradation,driven by sunlight play an important role.Among indirect photodegradation,singlet oxygen(^(1)O_(2)),as a pivotal reactive species,is likely to determine the fates of atenolol.Nevertheless,the kinetic information on the re-action of atenolol with singlet oxygen has not been well investigated and the reaction rate constant is still ambiguous.Herein,the reaction rate constant of atenolol with singlet oxy-gen is investigated directly through observing the decay of the^(1)O_(2)phosphorescence at 1270 nm.It is determined that the reaction rate constant between atenolol and^(1)O_(2)is 7.0×10^(5)(mol/L)^(-1)·s^(-1)in D2O,8.0×10^(6)(mol/L)^(-1)·s^(-1)in acetonitrile,and 8.4×10^(5)(mol/L)^(-1)·s^(-1)in EtOH,respectively.Furthermore,the solvent effects on the title reaction were also inves-tigated.It is revealed that the solvents with strong polarity and weak hydrogen donating ability are suitable to achieve high rate constant values.These kinetics information on the reaction of atenolol with singlet oxygen may provide fundamental knowledge to the indirect photodegradation of β-blockers.

Reaction Kinetics between Thiobases and Singlet Oxygen Studied by Direct Detection of the 1O2 Luminescence Decay

Thiobase derivatives have received important investigations due to their wide usage as phototherapeutic agents and their potential carcinogenic side effects as immunosuppressants. The substitution of oxygen atom by the sulfur atom makes the ultraviolet absorption of thiobases redshifted and absorbs UVA light (>300 nm), resulting in unusual high quantum yield of triplet state to generate the singlet oxygen (1O2) through photosensitization. As a type of reactive oxygen species, 1O2 is highly reactive toward thiobases. Herein, we report the measurements of reaction rate constants between di erent thiobases and 1O2 in different solvents through the direct detection of 1O2 luminescence decay kinetics at 1270 nm. The rate constants of thiouracils with 1O2 are five times smaller than that of thioguanine with 1O2, which suggests that thiopurines are more reactive than thiopyrimidines and thus less suitable to be a photosensitive drug on the application of photodynamic therapy. Additionally, the rate constants of thiobases and 1O2 were found to be obviously influenced by the solvent polarity. With the increase of solvent polarity, the rate constants of thiobases and 1O2 decrease.