Quantum theory of electron transport in molecular nanostructures

This thesis addresses the fundamental aspects of controlling transport through organic molecules by presenting a series of studies in the electronic properties of molecular junctions. The exploration and understanding of the electronic characteristics of single molecules connected to electrodes is an essential part in the application of electronics. Here, I implemented transport calculations based on the Landauer formula combined with Kohn–Sham orbitals extracted from density functional theory (DFT). Chapter 4 elucidates the validity of a ‘curly arrow rule’, which has been used widely by chemists and physicists to predict the electronic properties of molecular junctions. Anthraquinone is found to break this rule in the case of meta connectivity to electrodes. This is significant, because changing the redox state of meta-connected dihydroxyanthracene to meta-connected anthraquinone, increases the conductance by a couple of orders of magnitude, due to the transition from constructive to destructive QI, which can help in the design of the QI based single-molecule switches such as data storage elements. Finally, chapter 5 presents a theoretical investigation of electron transport through dimethyldihydropyrene (DHP) and Cyclophanediene (CPD) systems focusses on changes in the conductance as a consequence of photochemical stimuli. These molecules could be exploited in the function of electronic devices, when responding to external stimul

Breakdown of Curly Arrow Rules in Anthraquinone

Understanding and controlling quantum interference QI in single molecules is fundamental to the development of QI based single molecule electronics. Over the past decade, simple rules such as counting rules, curly arrow rules, circuit rules and more recently magic ratio rules have been developed to predict QI patterns in polycyclic aromatic hydrocarbons. These rules have been successful in explaining observed electronic transport properties of molecular junctions and provide helpful design tools for predicting properties of molecules before their synthesis. Curly arrow rules are widely used by chemists, material scientists and physicists to predict destructive QI. Here we examine the validity of curly arrow rules in fully conjugated anthracene and dihydroxyanthracene, cross‐conjugated anthraquinone and broken conjugated dihydroanthracene attached to graphene or gold electrodes through pi‐pi stacking or thiol and Au‐C anchors. For the first time, we demonstrate that curly arrow rules break down in molecular junctions formed by cross‐conjugated anthraquinone. In contrast with the destructive QI predicted by curly arrow rules for a meta connected anthraquinone core, we demonstrate that QI is constructive. This behavior is independent of the choice of electrode material or anchor groups. This is significant, because by changing the redox state of meta connected dihydroxyanthracene to form meta connected anthraquinone, the conductance of the junction increases by couple of orders of magnitude due to the cross over form constructive to destructive QI. This opens new avenues for realization of quantum interference based single molecule switches

Influence of environmental fluctuations on quantum interference in naphthalene and azulene

Both naphthalene and azulene have the same number of carbon and hydrogen atoms, but the former is an alternant hydrocarbon and the latter is a nonalternant hydrocarbon. This leads to a large difference in their electronic and transport properties. Herein, quantum transport is investigated through these two molecules and it is shown how quantum interference (QI) affects their electrical conductance. It is demonstrated that the orbital rule to predict QI breaks down in both naphthalene and azulene. The influence of environmental fluctuations on their QI and electrical conductance is also investigated. The results show that QI in azulene is more sensitive to environmental fluctuations than in naphthalene. In particular, destructive QI can be changed to constructive QI in azulene by small environmental fluctuations

SARS-CoV-2 susceptibility and COVID-19 disease severity are associated with genetic variants affecting gene expression in a variety of tissues

Variability in SARS-CoV-2 susceptibility and COVID-19 disease severity between individuals is partly due to genetic factors. Here, we identify 4 genomic loci with suggestive associations for SARS-CoV-2 susceptibility and 19 for COVID-19 disease severity. Four of these 23 loci likely have an ethnicity-specific component. Genome-wide association study (GWAS) signals in 11 loci colocalize with expression quantitative trait loci (eQTLs) associated with the expression of 20 genes in 62 tissues/cell types (range: 1:43 tissues/gene), including lung, brain, heart, muscle, and skin as well as the digestive system and immune system. We perform genetic fine mapping to compute 99% credible SNP sets, which identify 10 GWAS loci that have eight or fewer SNPs in the credible set, including three loci with one single likely causal SNP. Our study suggests that the diverse symptoms and disease severity of COVID-19 observed between individuals is associated with variants across the genome, affecting gene expression levels in a wide variety of tissue types

A first update on mapping the human genetic architecture of COVID-19

peer reviewe

Measuring Empathy among Dental Students and Interns: A Cross-Sectional Study from Dammam, Saudi Arabia

Objective. To evaluate empathy and its related factors among undergraduate dental students and interns enrolled in a public dental college in Dammam, Saudi Arabia. Materials and Methods. This cross-sectional study used the Jefferson Scale of Empathy-Health Profession Students (JSE-HPS) version to determine empathy in 362 dental students and interns in Dammam, Saudi Arabia. The JSE-HPS is a 20-item 7-point Likert scale questionnaire, and its score ranges from 20 to 140 with high values indicating increased empathy. Influences of age, gender, class year, previous year’s grade point average (GPA), educational attainment of parents, and monthly family income on empathy were evaluated. Results. Of 501 enrolled students and interns, 362 returned completed questionnaires, and the response rate of the study was 72%. The sample’s empathy score (JSPE-HPS scale) ranged from 70 to 129 with a mean of 96.75 (±13.76). Most participants believed that empathy is important for effective communication with patients (96.1%) and can improve the provider-patient relationship (95.6%). Females demonstrated a significantly higher mean empathy score (99.98 ± 14.01) than males (92.72 ± 12.35) (P<0.001). Similarly, the participants with high GPA (98.06 ± 13.69) had significantly greater mean empathy scores than those with low GPA (94.84 ± 13.68) (P=0.029). The mean empathy score increased significantly from junior students (3rd and 4th year students) to senior students (5th and 6th year students) and interns (P=0.008). Multiple linear regression analysis showed that class year (B = 2.03, P=0.006) and GPA (B = 8.67, P=0.003) were significant factors associated with empathy. Conclusions. Empathy is important for effective patient communication and improved provider-patient relationship. Female gender, high GPA, and class years were associated with empathy. Empathy should be integrated into dental curricula for effective student learning and positive patient care outcomes

Antihyperglycemic Effect of <i>Lavandula pedunculata</i>: In Vivo, In Vitro and Ex Vivo Approaches

Lavandula pedunculata (Mill.) Cav. (LP) is one of lavender species traditionally used in Morocco to prevent or cure diabetes, alone or in the form of polyherbal preparations (PHP). Therefore, the primary objective of this study was to test the antihyperglycemic effect of the aqueous extract of LP, alone and in combination with Punica granatum L. (PG) and Trigonella foenum-graecum L. (FGK). The secondary objective was to explore some mechanisms of action on the digestive functions. The antihyperglycemic effect of the aqueous extract of LP, alone and in combination with PG and FGK, was studied in vivo using an oral glucose tolerance test (OGTT). In addition, LP extract was tested on the activities of some digestive enzymes (pancreatic α-amylase and intestinal α-glucosidase) in vitro and on the intestinal absorption of glucose ex vivo using a short-circuit current (Isc) technique. Acute and chronic oral administration of LP aqueous extract reduced the peak of the glucose concentration (30 min, p p 50 almost identical to acarbose (0.44 ± 0.05 mg/mL and 0.36 ± 0.02 mg/mL, respectively), as well as the intestinal α-glucosidase, (IC50 = 131 ± 20 µg/mL) and the intestinal glucose absorption (IC50 = 81.28 ± 4.01 µg/mL) in concentration-dependent manners. LP aqueous extract exhibited potent actions on hyperglycemia, with an inhibition on digestive enzymes and glucose absorption. In addition, the combination with PG and FGK enhanced oral glucose tolerance in rats. These findings back up the traditional use of LP in type 2 diabetes treatment and the effectiveness of the alternative and combinative poly-phytotherapy (ACPP)

2,7- and 4,9-Dialkynyldihydropyrene molecular switches : syntheses, properties, and charge transport in single-molecule junctions

This paper describes the syntheses of several functionalized dihydropyrene (DHP) molecular switches with different substitution patterns. Regioselective nucleophilic alkylation of a 5-substituted dimethyl isophthalate allowed the development of a workable synthetic protocol for the preparation of 2,7-alkyne-functionalized DHPs. Synthesis of DHPs with surface-anchoring groups in the 2,7- and 4,9-positions is described. The molecular structures of several intermediates and DHPs were elucidated by X-ray single-crystal diffraction. Molecular properties and switching capabilities of both types of DHPs were assessed by light irradiation experiments, spectroelectrochemistry, and cyclic voltammetry. Spectroelectrochemistry, in combination with density functional theory (DFT) calculations, shows reversible electrochemical switching from the DHP forms to the cyclophanediene (CPD) forms. Charge-transport behavior was assessed in single-molecule scanning tunneling microscope (STM) break junctions, combined with density functional theory-based quantum transport calculations. All DHPs with surface-contacting groups form stable molecular junctions. Experiments show that the molecular conductance depends on the substitution pattern of the DHP motif. The conductance was found to decrease with increasing applied bias

A multinational Delphi consensus to end the COVID-19 public health threat

Despite notable scientific and medical advances, broader political, socioeconomic, and behavioural factors continue to undercut the response to the coronavirus disease 2019 (COVID-19) pandemic1,2. This Delphi study convened a diverse, multidisciplinary panel of 386 academic, health, NGO, government and other experts in COVID-19 response from 112 countries and territories to recommend specific actions to end this persistent global public health threat. The panel developed a set of 41 consensus statements and 57 recommendations to governments, health systems, industry, and other key stakeholders across six domains: communication; health systems; vaccination; prevention; treatment and care; and inequities. In the wake of nearly three years of ragmented global and national responses, it is instructive to note that three of the highest-ranked recommendations call for the adoption of whole-of-society and whole-of-government approaches1, while maintaining proven prevention measures using a vaccines-plus approach2 that employs a range of public health and financial support measures to complement vaccination. Other recommendations with at least 99% combined agreement advise governments and other stakeholders to improve communication, rebuild public trust, and engage communities3 in the management of pandemic responses. The findings of the study, which have been further endorsed by organisations globally, include points of unanimous agreement, as well as six recommendations with >5% disagreement, that provide health and social policy actions to address inadequacies in the pandemic response and help bring this public health threat to an end