Spectral Signatures of a Negative Polaron in a Doped Polymer Semiconductor: Energy Levels and Hubbard U Interactions

The modern picture of negative charge carriers on conjugated polymers invokes the formation of a singly occupied (spin-up/spin-down) level within the polymer gap and a corresponding unoccupied level above the polymer conduction band edge. The energy splitting between these sublevels is related to on-site Coulomb interactions between electrons, commonly termed Hubbard U. However, spectral evidence for both sublevels and experimental access to the U value is still missing. Here, we provide evidence by n-doping the polymer P(NDI2OD-T₂) with [RhCp*Cp]₂, [N-DMBI]₂, and cesium. Changes in the electronic structure after doping are studied with ultraviolet photoelectron and low-energy inverse photoemission spectroscopies (UPS, LEIPES). UPS data show an additional density of states (DOS) in the former empty polymer gap while LEIPES data show an additional DOS above the conduction band edge. These DOS are assigned to the singly occupied and unoccupied sublevels, allowing determination of a U value of ∼1 eV.

Biotinylation as a tool to enhance the uptake of small molecules in Gram-negative bacteria

Antibiotic resistance is a major public health concern. The shrinking selection of effective antibiotics and lack of new development is making the situation worse. Gram-negative bacteria more specifically pose serious threat because of their double layered cell envelope and effective efflux systems, which is a challenge for drugs to penetrate. One promising approach to breach this barrier is the “Trojan horse strategy”. In this technique, an antibiotic molecule is conjugated with a nutrient molecule that helps the antibiotic to enter the cell through dedicated transporters for the nutrient. Here, we explored the approach using biotin conjugation with a florescent molecule Atto565 to determine if biotinylation enhances accumulation. Biotin is an essential vitamin for bacteria and is obtained through either synthesis or uptake from the environment. We found that biotinylation enhanced accumulation of Atto565 in E. coli. However, the enhancement did not seem to be due to uptake through biotin transporters since the presence of free biotin had no observable impact on accumulation. Accumulated compound was mostly in the periplasm, as determined by cell fractionation studies. This was further confirmed through the observation that expression of streptavidin in the periplasm specifically enhanced the accumulation of biotinylated Atto565. This enhancement was not observed when streptavidin was expressed in the cytoplasm indicating no significant distribution of the compound inside the cytoplasm. Using gene knockout strains, plasmid complementation and mutagenesis studies we demonstrated that biotinylation made the compound a better passenger through OmpC, an outer membrane porin. Density functional theory (DFT)-based evaluation of the three-dimensional geometries showed that biotinylation did not directly stabilize the conformation of the compound to make it favorable for the entry through a pore. Further studies including molecular dynamics simulations are necessary to determine the possible mechanisms of enhanced accumulation of the biotinylated Atto565.

Attitudes toward prenatal diagnosis and termination of pregnancy for genetic disorders among healthcare workers in a selected setting in Sri Lanka

OBJECTIVES

Assess attitudes toward prenatal diagnosis (PND) and termination of pregnancy (TOP) for Down syndrome (DS), hemophilia, lethal autosomal recessive disorder (LRD) and a hypothetical late-onset neurodegenerative disorder (NDD) among healthcare workers in one Sri Lankan district.

METHODS

Self-administered questionnaire (tested for content validity) completed by medical (n = 218) and nursing (n = 368) students, nurses (n = 178) and doctors (n = 127).

RESULTS

Acceptability of PND was 94%, 91%, 86% and 71% respectively for LRD, DS, hemophilia and NDD. Favorable attitudes toward TOP for DS (84%), and LRD (82%) were higher compared with hemophilia (65%) and NDD (53%). There was willingness to consider TOP for self/spouse for DS (79%), LRD (78%), hemophilia (60%) and NDD (54%). The proportions willing to participate in a pregnancy termination (DS 54%, LRD 51%, hemophilia 38%, NDD 38%) were lower. Religious affiliation influenced attitudes regarding TOP with Christians being more opposed than Buddhists.

CONCLUSIONS

There is acceptance of and willingness to participate in TOP for fetal anomalies among Sri Lankan healthcare workers. These findings have relevance for developing prenatal diagnostic services in Sri Lanka. Religious affiliation among Asian doctors, nurses (and patients) in developed countries is likely to determine permissiveness toward PND and TOP.