Transesterification in Vitrimer Polymers Using Bifunctional Catalysts: Modeled with Solution-Phase Experimental Rates and Theoretical Analysis of Efficiency and Mechanisms

Recently, thermoset vitrimer polymers have shown significant promise for structural applications because of their ability to be reshaped and remolded due to their covalent adaptive network (CAN). In these vitrimers, the transesterification reaction is responsible for the CAN, where the efficiency of the reaction is controlled either by organic or by organometallic catalysts. Understanding the mechanism of the transesterification reaction in the bulk phase using direct experimental techniques is extremely difficult due to the highly cross-linked complex structure of thermosetting vitrimers. Therefore, we use solution-phase experiments to investigate the catalytic efficiency and to guide density functional theory (DFT) simulations of the transesterification reaction mechanism with catalysts triazabicyclodecene (TBD), zinc acetate (Zn(OAc)₂), 1-methylimidazole (1-MI), and dibutyltin oxide (DBTO). The estimated catalytic efficiency from the detailed DFT reaction path calculations follows the order TBD ≳ DBTO ≳ Zn(OAc)₂ > 1-MI, which agrees with the experimental results. In addition to reaction path modeling, the mechanism and the relative rates of the transesterification reaction are analyzed with the assistance of Fukui indices as a measure of electrophilicity and nucleophilicity of atomic sites and with partial charges. It was found that the sum of the nucleophilicity index of the base and the electrophilicity index of the acid of the bifunctional catalysts correlates with the S_N2 transition state and tetrahedral intermediate energies, which are related to the barrier of the rate-limiting step. This correlation provides a hypothesis for computational prescreening of potentially better catalysts that have an index in a range of values. These results provide a basis for understanding an important part of the mechanism of transesterification in vitrimer systems and may assist with designing new catalysts.

Electronic and Structural Study of ZnxSx [x = 12, 16, 24, 28, 36, 48, 96, and 108] Cage Structures

We present a density functional study on the structural and electronic properties of ZnS bubble clusters, specifically, hollow cages whose spontaneous formation was previously observed in classical molecular dynamics simulations by Spano et al. [J. Phys. Chem. B 2003, 107, 10337]. The hollow ZnS cages in our study were modeled as Zn_xS_x [x = 12, 16, 24, 28, 36, 48, 108], and an onionlike structure was modeled as Zn₉₆S₉₆. The study of energetics and stability, performed using large polarized Gaussian basis sets, indicated all structures to be energetically stable with similar binding energy of 5.5-5.6 eV per ZnS pair. Further computation of electronic properties showed that these cages have large vertical ionization energies and relatively low electron affinities in the ranges of 6.8-8.1 and 1.7-3.0 eV, respectively. They have large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps between 2.5 and 3.3 eV, and quasi-particle gaps vary from 6.2 eV for Zn₁₂S₁₂ to 4.19 for Zn₁₀₈S₁₀₈. The computed vibrational frequencies for selected cages, that is, Zn₁₂S₁₂, Zn₁₆S₁₆, Zn₂₈S₂₈ (O, S₄, and S₈ point groups), and Zn₃₆S₃₆ indicate that these cage structures correspond to local minima on the potential energy surface. Finally, the infrared spectra calculated using large basis sets are also reported.

Plasmablastic Lymphoma

Plasmablastic lymphoma is a rare and aggressive lymphoma reported to be commonly associated with immunodeficiency state. It possesses a challenge to the clinician owing it aggressiveness and poor prognosis. No standard of care treatment is available for the disease. Here we report a case of an immunocompetant 67 years female who is unique in her presentation as she did not have any of the conventional clinical features and had a history of urothelial carcinoma three months back.

Violence against women by their husband and postpartum depression

BACKGROUND

Violence against women in developing countries is very high with very little to choose between the cities and provinces. In Nepal too, violence against women is very rampant. This occurs despite physical violence against women being ascribed as criminal act by Domestic Violence Act. The main objective of the study was to see the association between postpartum depression and violence against women.

METHODS

A prospective cohort study was conducted among pregnant women of reproductive age group in two centers. Standard questionnaires were used to collect data regarding violence and for detecting postpartum depression. Three interviews one in antenatal and two in postnatal period were taken.

RESULTS

The incidence of postpartum depression was found to be 19.4 % (95% CI = 14.73 - 24.06) and 22.22% (95% CI = 17.30 - 27.09) during first (6 week postpartum ) and second (10th week) postpartum interview respectively. The incidence of physical, psychological and sexual violence was found to be 20.8% (95%CI= 16.01 - 25.58), 19.4% (95%CI= 14.73 - 24.06) and 13.9% (95% CI= 9.82 - 17.97) respectively. No statistically significant relationship could be found between different forms of violence and postpartum depression .The study showed that all the women with bad communication or conversation with the husband had postpartum depression while only 17.1% of women with good conversation had postpartum depression.

CONCLUSIONS

No form of violence against women had statistically significant association with development of postpartum depression among Nepalese population.