Nanomaterials in photocatalysed organic transformations: development, prospects and challenges

Photoredox catalysis has gained widespread attention in recent years as a powerful tool to drive chemical transformations in the presence of light, particularly for molecules that are capable of showing redox activity. A typical photocatalytic pathway may involve electron or energy transfer processes. To date, photoredox catalysis has been explored mainly with Ru, Ir and other metal or small molecule based photocatalysts. Due to their homogeneous nature, they cannot be reused and are not economical. These factors have motivated researchers to look for an alternate class of photocatalysts which are more economical and reusable, thus paving the way for protocols that can be easily transferred to the industrial sectors as well. In this regard, scientists have come up with various nanomaterials as sustainable and economical alternatives. These have unique properties that arise from their structure, surface functionalization, etc. Apart from that, at the lower dimensions, they bear an increased surface to volume ratio, which can provide an enhanced number of active sites for catalysis. Nanomaterials have been used for various applications like sensing, bioimaging, drug delivery, energy generation, etc. However, their potential as photocatalysts for organic transformations has been taken up as a subject of research quite recently. This article focusses on the use of nanomaterials in photo-mediated organic transformations with a wider goal to motivate readers from materials as well as organic synthetic backgrounds to dig deeper into this area of research. Various reports have been included to cover the plethora of reactions that have been explored with nanomaterials as a photocatalyst. The scientific community has also been introduced to the challenges and prospects of the field, which will further help in its growth. In a nutshell, this writeup will help to cater to the interest of a large group of researchers to highlight the prospects of nanomaterials in photocatalysis.

Time resolved fluorescence sensor array for discrimination of phosphate anions by using transition metal dichalcogenide quantum dots and Tb (III)

Phosphate detection has garnered widespread attention due to their biological and environmental impact. Among several optical techniques, time resolved fluorescence (TRF) provides a sensitive way for discrimination of analytes in a complex mixture as it suffers less interference from the background, thus providing a high signal to noise ratio. The sensitization of rare earth metal (REM) ions by semiconducting quantum dots (QDs) can help the former overcome the drawback of low absorption coefficient, thus allowing one to exploit the additional advantage of the REM, viz, the long-excited state lifetime. Herein, we have developed a TRF based sensor array consisting of three QDs, i.e., MoS₂ , WS₂ and MoSe₂ as energy sensitizers to Tb³⁺ ion. Different QDs possess variable energy transfer ability to Tb³⁺ ion. Hence, they can be used for discrimination of phosphates. It was also observed that CrO₄ ^2- can competitively bind to Tb³⁺ and further, enhance the efficiency of the sensor array which could discriminate six different phosphates at 200 μM concentration in aqueous as well as serum media with a detection limit of 10 μM in aqueous media. Thus, the sensitivity of the TRF based sensor array is rarely compromised in a complex mixture, which is advantageous over a fluorescence-based sensor array.

Dual Role of MoS2 Quantum Dots in a Cross-Dehydrogenative Coupling Reaction

Modern day research focuses on the development of greener and eco-friendlier protocols to fabricate biologically relevant targets with minimal waste generation. C-C bond formation reactions are of prime importance in this regard. In a typical photocatalytic hydrogen evolution reaction, three components are used, viz, catalyst, photosensitizer, and sacrificial amine donor. Among these, the photosensitizer and sacrificial amine donors are wasted at the end of the reaction. Considering these drawbacks, in this work, we have developed a methodology targeted at the utilization of sacrificial amine donors for C-H functionalization with MoS2 quantum dots (QDs) as the catalyst as well as the photosensitizer. QDs indeed emerged to be an active participant in the heterogeneous electron transfer process. This concept opens up new possibilities in the field of nanomaterial-based photomediated organic transformations without the aid of any external photosensitizers via a clean and sustainable protocol with no side product.

2D-MoS2 photocatalyzed cross dehydrogenative coupling reaction synchronized with hydrogen evolution reaction

The chemically exfoliated 2D-MoS₂ has a mixture of 1T (metallic) and 2H (semiconducting) phases.

Abstract P6-02-02: Increased interval cancers after the 2009 U.S. preventive services task force guidelines: A single-center, retrospective analysis

Background: In late 2009, the U.S. Preventive Services Task Force (USPSTF) increased the recommended time between screening mammography from one year to two years. We examined the effect of USPSTF recommendations in an integrated safety-net system whose patients often have intermittent access to care. The purpose of this study was to determine if changes in screening guidelines were associated with stage migration or changes in rate of interval cancers.

Methods: We conducted a retrospective cohort analysis of breast cancer patients diagnosed between 2005-2013 at one safety-net hospital. We abstracted stage at diagnosis, time intervals between screening and diagnostic imaging, as well as BIRADS classification from clinical and administrative billing data. We divided patients into two cohorts: Those diagnosed with breast cancer "pre-2010" (2005 – 2010) and "post-2010" (2011-2013). We compared stage of diagnosis between cohorts using Chi-Square tests. In a subset of patients for whom we had prior screening imaging information, we determined the rate of interval cancers. Interval cancers were defined as patients whose diagnosis occurred within 14 months (pre-2010) or within 26 months (post-2010) of normal screening mammography. Logistic regression was used to determine the unadjusted odds of interval cancer as a function of being post-2010 versus pre-2010.

Results: There were 521 unique, breast cancer patients between 2005-2013,

Distribution of Breast Cancer by Stage Stage 0Stage IStage IIStage IIIStage IVTotal2005-200941816142242492010-20134679824421272

249 in the 'pre-2010' cohort, and 272 in the 'post-2010' cohort. In the 2005-2009 cohort, 32.5% and 24.5% of patients were stage I and Stage II respectively. In 2010-2013, 29.0% and 30% were stage I and stage II, respectively. The difference in stage at diagnosis was not statistically significant (p=0.62). In a subset of 178 patients with available screening imaging data, we determined the rate of interval cancers. Pre-2010, 7.4% (8/108) of patients had an interval cancer. Post-2010, 20% (14/70) patients had an interval cancer. Patients diagnosed post-2010 had three times the odds of having an interval cancer compared to pre-2010 patients (OR = 3.13, 95% CI 1.24-7.91, p=0.01).

Discussion: The USPSTF 2009 recommendation is associated with a statistically significant increase in interval cancers in a safety-net population, but we cannot conclude that this contributes to stage migration in this limited population. Investigation of larger groups is needed to further assess how USPSTF guidelines affect outcomes in underserved populations.

Citation Format: Townsend NT, Everhart RM, Bayliss EA, Jaiswal K. Increased interval cancers after the 2009 U.S. preventive services task force guidelines: A single-center, retrospective analysis. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-02-02.

Bone marrow progenitor cells contribute to esophageal regeneration and metaplasia in a rat model of Barrett's esophagus

Barrett's esophagus develops when refluxed gastric juice injures the esophageal squamous lining and the injury heals through a metaplastic process in which intestinal-type columnar cells replace squamous ones. The progenitor cell that gives rise to Barrett's metaplasia is not known, nor is it known why the condition is predisposed to malignancy. We studied the contribution of bone marrow stem cells to the development of Barrett's esophagus in an animal model. Twenty female rats were given a lethal dose of irradiation followed by tail vein injection of bone marrow cells from male rats. Ten days later, the female rats were randomly assigned to undergo either esophagojejunostomy, a procedure that causes reflux esophagitis with intestinal metaplasia, or a sham operation. The rats were killed at 8 weeks and serial sections of the snap-frozen esophagi were cut and mounted on slides. The first and last sections were used for histological evaluation and the intervening sections were immunostained for cytokeratin to identify epithelial cells and analyzed for Y chromosome by fluorescence in situ hybridization (FISH). Histological evaluation of the esophagi from rats that had esophagojejunostomy revealed ulcerative esophagitis and multiple areas of intestinal metaplasia. FISH analyses showed that some of the squamous epithelial cells and some of the columnar epithelial cells lining the glands of the intestinal metaplasia were positive for Y chromosome. These observations suggest that multi-potential progenitor cells of bone marrow origin contribute to esophageal regeneration and metaplasia in this rat model of Barrett's esophagus.

Effect of age and caloric restriction on bleomycin-chelatable and nonheme iron in different tissues of C57BL/6 mice

The objective of this study was to test the hypothesis that the widely observed age-associated increase in the amounts of macromolecular oxidative damage is due to an elevation in the availability of redox-active iron, that is believed to catalyze the scission of H2O2 to generate the highly reactive hydroxyl radical. Concentrations of bleomycin-chelatable iron and nonheme iron were measured in various tissues and different regions of the brain of mice fed on ad libitum (AL) or a calorically restricted (to 60% of AL) diet at different ages. The concentrations of these two pools of iron varied markedly as a function of tissue, age, and caloric intake. There was no consistent ratio between the amounts of nonheme and the bleomycin-chelatable iron pools across these conditions. Nonheme iron concentration increased with age in the liver, kidney, heart, striatum, hippocampus, midbrain and cerebellum of AL animals, whereas bleomycin-chelatable iron increased significantly with age only in the liver. Amounts of both nonheme and bleomycin-chelatable iron remained unaltered during aging in the cerebral cortex and hindbrain of AL mice. Caloric restriction had no effect on iron concentration in the brain or heart, but caused a marked increase in the concentration of both bleomycin-chelatable and nonheme iron in the liver and the kidney. The results do not support the hypothesis that accumulation of oxidative damage with age, or its attenuation by CR, are associated with corresponding variations in redox-active iron.

Effects of hormones on the number, distribution and degranulation of mast cells in the ovarian complex of mice

The changes in the number and degranulation pattern of mast cells varied with the types of hormonal treatment and ovarian compartment. Luteinizing hormone (LH), follicle stimulating hormone (FSH), thyroid stimulating hormone (TSH) and 17-beta estradiol (E2) treatment caused increase (P < 0.05) in the number of mast cells in the hilum as compared with the controls. Increase (P < 0.05) in the number of mast cells in the whole ovarian complex was observed only following FSH and E2 treatment. All the hormones used in the present study increased the percentage degranulation of mast cells in the hilum. However, only LH, FSH and E2 increased the percentage degranulation of mast cells in other compartments of the ovary (medulla, bursa and cortex). TSH and ACTH failed to cause any increase in the percentage degranulation of mast cells in these compartments. The present findings indicate E2 to be the most potent among the hormones tested in causing degranulation of mast cells in all ovarian compartments.

Effects of cimetidine, H2 receptor antagonist, on follicular and luteal development in the mice

The effects of various doses, duration and frequency of cimetidine treatment on vaginal cycle, ovulation, ovarian histology and follicular kinetics were investigated. In addition, studies were performed to assess the reversibility in ovarian functions following withdrawal of cimetidine treatment. A statistically significant (P < 0.05) decline in ovarian and uterine weights, but not in body and adrenal weights, were observed in females treated with cimetidine four times daily for long-term as compared with the controls. Ovarian and uterine weights recovered to pretreatment levels following withdrawal of the treatment. Cimetidine treatment caused irregularities in the reproductive cyclicity of mice. Cimetidine treatment causes adverse effect on ovarian function depending on the time, duration and frequency of treatment. Treatment for only one day at proestrus induced significant (P < 0.05) decline in ovulatory efficiency. However, administration of cimetidine, four times daily, for either 6 or 14 days caused ovarian dysfunction. The treatment depressed the number of healthy preantral and antral follicles as well as number of healthy corpus luteum (CL) in the ovary. Absence of healthy CL, presence of several atretic late antral follicles and reproductive acyclicity provide evidence for the failure of ovulation in mice treated with cimetidine four times per day for 14 days. Moreover, when cimetidine was administered twice daily, the ovaries also showed newly formed CL. The results, thus, suggest that the effects of cimetidine on ovulation are dependent on dose, duration and frequency of treatment. Blockage of ovulation in long-term cimetidine treated mice could be due to its influence on follicular atresia. Ovulation had occurred in these females after withdrawal of cimetidine treatment.