Long-chain saturated hydrocarbons and alkoxysilanes are ligands that are commonly used to passivate perovskite quantum dots (PQDs) to enhance their stability and optical properties. However, the insulating nature of these capping ligands creates an electronic energy barrier and impedes interparticle electronic coupling, thereby limiting device applications. One strategy to solve this problem is the use of short conductive aromatic ligands that allow delocalization of the electronic wave function from the PQDs, which, in turn, facilitates charge transport between PQDs by lowering the energy barrier. This is demonstrated with methylammonium lead bromide (MAPbBr 3 ) QDs prepared using benzylamine (BZA) and benzoic acid (BA) capping ligands. Optimized BZA-BA-MAPbBr 3 QDs are highly stable and show very high photoluminescence (PL) quantum yield (QY) (86%). More importantly, the BZA-BA-MAPbBr 3 QD film exhibits higher conductivity and carrier lifetime and more efficient charge extraction compared to PQDs with insulating ligands, as indicated by electrochemical measurements and transient photocurrent and photovoltage spectroscopy.

Magic sized clusters (MSCs), small nanoparticles with a single size or narrow size distribution, possess unique chemical and physical properties. CH3NH3PbBr3 perovskite MSCs (PMSCs) were synthesized using butylamine (BTYA) and valeric acid (VA) as well as 3,3-diphenylpropylamine (DPPA) and VA as capping ligands in an excess amount. The PMSCs were characterized using UV–vis and photoluminescence (PL) spectroscopy. For BTYA-VA PMSCs, there is an excitonic absorption peak at 424 nm and PL peak at 434 nm, while the DPPA-VA PMSCs exhibit an absorption peak at 428 nm and PL peak at 451 nm. The size and optical properties of the PMSCs are found to be dependent on the ligands used for passivation. Additionally, in a series dilution of DPPA-VA PMSCs in toluene, it was discovered that different sized perovskite quantum dots (PQDs) can be synthesized with tunable PL emission with peaks ranging between 451 and 525 nm. This phenomenon was not observed for BTYA-VA PMSCs. This contrast indicates the unique interaction between the DPPA ligand and the toluene solvent for the dilution-induced PQD formation. These findings provide new insights into the mechanism of growth and stability of PMSCs that are useful for generating and understanding the formation of larger nanostructures such as QDs.

Compared to bulk perovskites, charge transport in perovskite quantum dot (PQD) solids is limited. To address this issue, energetically aligned capping ligands were used to prepare methylammonium lead bromide (MAPbBr3) PQDs toward enhancing surface charge carrier density in PQD solids. Trans-cinnamic acid (TCA) and its derivates, functionalized with electron-donating or electron-withdrawing groups to modulate energy levels, are used as passivating exciton-delocalizing ligands (EDLs) to decrease the energy gap with respect to the PQD core. 3,3-Diphenylpropylamine (DPPA) ligand is shown to stabilize EDLs on the PQD surface through π–π stacking intermolecular interaction, mitigating charge trapping and nonradiative decay. Passivation using EDLs in combination with DPPA increases the photoluminescence (PL) quantum yield (QY) (90%), photoconductivity, extraction, mobility, transport time, and lifetime of charge carriers in PQD solids. Prototype PQD-based light-emitting diodes (LEDs) were demonstrated with a low turn-on voltage of 2.5 V.

Background: High protein calorie restriction diets have shown clinical efficacy for obesity, but the mechanisms are not fully known. The intestinal microbiome is a mediator of obesity and preclinical data support an effect of high protein diet (HPD) on the gut microbiome of obesity, but there are few studies in humans. Methods: To address this, we conducted a dietary intervention trial of 80 overweight and obese subjects who were randomized to a calorie-restricted high protein diet (HPD) (30% calorie intake) or calorie-restricted normal protein diet (NPD) (15%) for 8 weeks. Baseline dietary intake patterns were assessed by the Diet History Questionnaire III. Longitudinal fecal sampling was performed at baseline, week 1, week 2, week 4, week 6, and week 8, for a total of 365 samples. Intestinal microbiome composition was assessed by 16S rRNA gene sequencing. Results: At baseline, microbial composition was associated with fiber and protein intake. Subjects on the HPD showed a significant increase in microbial diversity as measured by the Shannon index compared to those on the NPD. The HPD was also associated with significant differences in microbial composition after treatment compared to the NPD. Both diets induced taxonomic shifts compared to baseline, including enrichment of Akkermansia spp. and Bifidobacterium spp. and depletion of Prevotella spp. Conclusion: These findings provide evidence that weight loss diets alter the gut microbiome in obesity and suggest differential effects of HPDs compared to NPDs which may influence the clinical response to HPD.

Background: The microbiome has been shown in pre-clinical and epidemiological studies to be important in both the development and treatment of obesity and metabolic associated fatty liver disease (MAFLD). However, few studies have examined the role of the microbiome in the clinical response to calorie restriction. To explore this area, we performed a prospective study examining the association of the intestinal microbiome with weight loss and change in hepatic steatosis on a calorie-restricted diet.Methods: A prospective dietary intervention study of 80 overweight and obese participants was performed at the Greater West Los Angeles Veterans Affair Hospital. Patients were placed on a macronutrient standardized diet for 16 weeks, including 14 weeks of calorie restriction (500 calorie deficit). Body composition analysis by impedance, plasma lipid measurements, and ultrasound elastography to measure hepatic steatosis were performed at baseline and week 16. Intestinal microbiome composition was assessed using 16S rRNA gene sequencing. A per protocol analysis was performed on all subjects completing the trial (n = 46).Results: Study completers showed significant reduction in weight, body mass index, total cholesterol, low density lipoprotein, and triglyceride. Subjects who lost at least 5% of their body weight had significantly greater reduction in serum triglyceride and hepatic steatosis than those with <5% body weight loss. Enterococcus and Klebsiella were reduced at the end of the trial while Coprococcus and Collinsella were increased. There were also significant baseline microbiome differences between patients who had at least 5% weight loss as compared to those that did not. Lachnoclostridium was positively associated with hepatic steatosis and Actinomyces was positively associated with hepatic steatosis and weight. Baseline microbiome profiles were able to predict which patients lost at least 5% of their body weight with an AUROC of 0.80.Conclusion: Calorie restriction alters the intestinal microbiome and improves hepatic steatosis in those who experience significant weight loss. Baseline microbiome differences predict weight loss on a calorie–restricted diet and are associated with improvement in hepatic steatosis, suggesting a role of the gut microbiome in mediating the clinical response to calorie restriction.