The emission of a bright blue fluorescence is a unique feature common to the vast variety of polymer carbon dots (CDs) prepared from carboxylic acid and amine precursors. However, the difficulty to ...assign a precise chemical structure to this class of CDs yet hampers the comprehension of their underlying luminescence principle. In this work, we show that highly blue fluorescent model types of CDs can be prepared from citric acid and ethylenediamine through low temperature synthesis routes. Facilitating controlled polycondensation processes, the CDs reveal sizes of 1–1.5 nm formed by a compact network of short polyamide chains of about 10 monomer units. Density functional theory calculations of these model CDs uncover the existence of a spatially separated highest occupied molecular orbital and a lowest unoccupied molecular orbital located at the amide and carboxylic groups, respectively. Photoinduced charge transfer between these groups thus constitutes the origin of the strong blue fluorescence emission. Hydrogen-bond-mediated supramolecular interactions between the polyamide chains enabling a rigid network structure further contribute to the enhancement of the radiative process. Moreover, the photoinduced charge transfer processes in the polyamide network structure easily explain the performance of CDs in applications as revealed in studies on metal ion sensing. These findings thus are of general importance to the further development of polymer CDs with tailored properties as well as for the design of technological applications.
The p.(Tyr400_Phe402del) mutation in the LDL receptor (
) gene is the most frequent cause of familial hypercholesterolaemia (FH) in Gran Canaria. The aim of this study was to determine the age and ...origin of this prevalent founder mutation and to explore its functional consequences. For this purpose, we obtained the haplotypic information of 14 microsatellite loci surrounding the mutation in one homozygous individual and 11 unrelated heterozygous family trios. Eight different mutation carrier haplotypes were identified, which were estimated to originate from a common ancestral haplotype 387 (110-1572) years ago. This estimation suggests that this mutation happened after the Spanish colonisation of the Canary Islands, which took place during the fifteenth century. Comprehensive functional studies of this mutation showed that the expressed LDL receptor was retained in the endoplasmic reticulum, preventing its migration to the cell surface, thus allowing us to classify this
mutation as a class 2a, defective, pathogenic variant.
Cardiac glycosides (CGs) are secondary compounds found in plants and amphibians and are widely distributed in nature with potential cardiovascular action. Their mechanism is based on the blockage of ...the heart's sodium potassium ATPase, with a positive inotropic effect. Some of the most well-known CGs are digoxin, ouabain, oleandrin, and bufalin. They have similar chemical structures: a lactone ring, steroid ring, and sugar moiety. Digoxin, ouabain, and oleandrin are classified as cardenolides, consisting of a lactone ring with five carbons, while bufalin is classified as bufodienolides, with a six-carbon ring. Small structural differences determine variations in the toxicokinetics and toxicodynamics of such substances. Most case reports of poisoning caused by CGs are associated with cardiovascular toxicity, causing a variety of arrhythmias and lesions in the heart tissue. Experimental studies also describe important similarities among different CGs, especially regarding species sensitivity. Recent studies furthermore focus on their antineoplastic potential, with controversial results. Data from research studies and case reports were reviewed to identify the main characteristics of the CGs, including toxicokinetics, toxicodynamics, clinical signs, electrocardiographic, pathological findings, antineoplastic potential and the main techniques used for diagnostic purposes.
•Cardiac glycosides bind and inhibit the sodium and potassium pump affecting the heart.•Digoxin, ouabain, oleandrin and bufalin are the most well known cardiac glycosides.•Recent findings report additional mechanisms of action and also contribute to the diagnosis of poisoning.•Antineoplastic potential is under investigation but data interpretation should be careful due to current studies limitations.
Thus book examines the spatial morphologies represented in a wide range of contemporary ethnic American literary and cinematic works. Drawing from Henri Lefebvre’s theorization of space as a living ...organism, Edward Soja’s writings on the postmetropolis, Marc Augé’s notion of the non-place, Manuel Castells’ space of flows, and Michel de Certeau’s theories of walking as a practice, the volume extends previous theorizations by examining how spatial uses, appropriations, strictures, ruptures, and reconfigurations function in literary texts and films that represent inhabitants of racial-ethnic borderlands and migrational U.S. cities. The authors argue for the necessity of an alternative poetics of place that makes room for those who move beyond the spaces of traditional visibility—displaced and homeless people, undocumented workers, hybrid and/or marginalized populations rendered invisible by the cultural elite, yet often disciplined by agents of surveillance. Building upon Doreen Massey’s conceptualization of liminal space as a sphere in which narratives intersect, clash, or cooperate, this study recasts spatial paradigms to insert an array of emergent geographies of invisibility that the volume traverses via the analysis of works by Chuck Palahniuk, Helena Viramontes, Karen Tei Yamashita, Gloria Anzaldúa, Alejandro Morales, and Li-Young Lee, among others, and films such as Thomas McCarthy’s The Visitor, Steven Spielberg’s The Terminal, and Alejandro Gonzalez Iñárritu’s Babels.
Purpose
– The purpose of this paper is to explore customer engagement in Twitter via data mining.
Design/methodology/approach
– This study’s intended contributions are twofold: to find a clear ...connection among customer engagement, presumption, and Web 2.0 in a context of service-dominant (S-D) logic; and to identify social networks created by prosumers. To this end, the study employed data mining techniques. Tweets about IKEA were used as a sample. The resulting algorithm based on 300 tweets was applied to 4,000 tweets to identify the patterns of electronic word-of-mouth (eWOM).
Findings
– Social networks created in IKEA’s tweets consist of three forms of eWOM: objective statements, subjective statements, and knowledge sharing. Most objective statements are disseminated from satisfied or neutral customers, while subjective statements are disseminated from dissatisfied or neutral customers. Satisfied customers mainly carry out knowledge sharing, which seems to reflect presumption behavior.
Research limitations/implications
– This study provides partial evidence of customer engagement and presumption in IKEA’s tweets. The results indicate that there are three forms of eWOM in the networks: objective statements, subjective statements, and knowledge sharing. It seems that IKEA successfully engaged customers in knowledge sharing, while negative opinions were mainly disseminated in a limited circle.
Practical implications
– Firms should make more of an effort to identify prosumers via data mining, since these networks are hidden behind “self-proclaimed” followers. Prosumers differ from opinion leaders, since they actively participate in product development. Thus, firms should seek prosumers in order to more closely fit their products to consumer needs. As a practical strategy, firms could employ celebrities for promotional purposes and use them as a platform to convert their followers to prosumers. In addition, firms are encouraged to make public how they resolve problematic customer complaints so that customers can feel they are a part of firms’ service development.
Originality/value
– Theoretically, the study makes unique contributions by offering a synergic framework of S-D logic and Web 2.0. The conceptual framework collectively relates customer engagement, presumption, and Web 2.0 to social networks. In addition, the idea of examining social networks based on different forms of eWOM has seldom been touched in the literature. Methodologically, the study employed seven algorithms to choose the most robust model, which was later applied to 4,000 tweets.
In this communication we present a potentiometric aptasensor based on chemically modified graphene (transducer layer of the aptasensor) and aptamers (sensing layer). Graphene oxide (GO) and reduced ...graphene oxide (RGO) are the basis for the construction of two versions of the aptasensor for the detection of a challenging living organism such as Staphylococcus aureus. In these two versions, DNA aptamers are either covalently (in the GO case) or non-covalently (in the RGO case) attached to the transducer layer. In both cases we are able to selectively detect a single CFU/mL of S. aureus in an assay close to real time, although the noise level associated to the aptasensors made with RGO is lower than the ones made with GO. These new aptasensors, that show a high selectivity, are characterized by the simplicity of the technique and the materials used for their construction while offering ultra-low detection limits in very short time responses in the detection of microorganisms.
•A new potentiometric biosensor based on graphene and aptamers is presented.•Graphene (graphene oxide and reduced graphene oxide) act as outstanding transducer of the biosensor.•The biosensor is able to detect a single CFU/mL of Staphylococcus aureus in a few minutes.•These results outperform existing detection methods in simplicity and performance parameters.
Objective:
We set out to analyze the incidence and predictive factors of pulmonary embolism (PE) in hospitalized patients with Covid-19.
Methods:
We prospectively collected data from all consecutive ...patients with laboratory-confirmed Covid-19 admitted to the Hospital de la Santa Creu i Sant Pau, a university hospital in Barcelona, between March 9 and April 15, 2020. Patients with suspected PE, according to standardized guidelines, underwent CT pulmonary angiography (CTPA).
Results:
A total of 1,275 patients with Covid-19 were admitted to hospital. CTPA was performed on 76 inpatients, and a diagnosis of PE was made in 32 (2.6% 95%CI 1.7–3.5%). Patients with PE were older, and they exhibited lower PaO
2
:FiO
2
ratios and higher levels of D-dimer and C-reactive protein (CRP). They more often required admission to ICU and mechanical ventilation, and they often had longer hospital stays, although in-hospital mortality was no greater than in patients without PE. High CRP and D-dimer levels at admission (≥150 mg/L and ≥1,000 ng/ml, respectively) and a peak D-dimer ≥6,000 ng/ml during hospital stay were independent factors associated with PE. Prophylactic low molecular weight heparin did not appear to prevent PE. Increased CRP levels correlated with increased D-dimer levels and both correlated with a lower PaO
2
:FiO
2
.
Conclusions:
The 2.6% incidence of PE in Covid-19 hospitalized patients is clearly high. Higher doses of thromboprophylaxis may be required to prevent PE, particularly in patients at increased risk, such as those with high levels of CRP and D-dimer at admission. These findings should be validated in future studies.
The preparation, characterization, and photophysical and electrocatalytic properties of carbon dot (CD)/MoS2 ensembles is reported. Based on electrostatic interactions, ammonium‐functionalized MoS2, ...which was prepared upon reaction of 1,2‐dithiolane tert‐butyl carbamate with MoS2 followed by acidic deprotection, was coupled with CDs bearing multiple carboxylates on their periphery, as derived upon microwave‐assisted polycondensation of citric acid and ethylenediamine followed by alkaline treatment. Insights into electronic interactions between the two species within CD/MoS2 ensembles emanated from absorption and photoluminescence titration assays. Efficient fluorescence quenching of CDs by MoS2 was observed and attributed to photoinduced electron/energy transfer as the decay mechanism for the transduction of the singlet excited state of CDs. Finally, the electrocatalytic performance of the CD/MoS2 ensemble was assessed towards the hydrogen evolution reaction and found to be superior to that of individual CDs species.
Dotting C and attracting MoS2: Aqueous, stable carbon dot (CD)/MoS2 ensembles form through electrostatic interactions (see figure). The efficient photoluminescence quenching of CDs by MoS2, together with the improved electrocatalytic performance of CD/MoS2 towards the hydrogen evolution reaction, advance the field of energy‐conversion applications.
We report on the modification of graphene oxide (GO) with poly(vinyl alcohol) (PVA) leading to the mechanical improvement of GO based materials. First, GO was covalently functionalised with PVA by ...esterification of carboxylic groups on GO with hydroxyl groups of PVA resulting in functionalised f-(PVA)GO. This was carried out for PVA of six different molecular weights. This functionalised graphene oxide could be formed into a paper-like material by vacuum filtration. Papers prepared from f-(PVA)GO showed significant increases in mechanical properties compared to those prepared with GO or with simple mixtures of GO and PVA. The best performance was achieved for PVA functional groups with molecular weights between 50 and 150kg/mol. Improvements in Young’s moduli of 60% and tensile strength of 400% were observed relative to GO-only paper. The improved mechanical properties are attributed to enhanced inter-flake stress transfer due to the covalently bonded PVA. Second, functionalised f-(PVA)GO was used as filler in PVA-based composites. The application of a pre-selection method allowed the use of only the largest functionalised f-(PVA)GO flakes. This resulted in substantially reinforced PVA–f-(PVA)GO composites. Both modulus and strength increased by 40% relative to the pure polymer for f-(PVA)GO loadings below 0.3 vol.%.
The type and distribution of oxygen functional groups in graphene oxide (GO) and reduced graphene oxide (RGO) remain still a subject of great debate. Local analytic techniques are required to access ...the chemistry of these materials at a nanometric scale. Electron energy loss spectroscopy in a scanning transmission electron microscope can provide the suitable resolution, but GO and RGO are extremely sensitive to electron irradiation. In this work we employ an optimized experimental setup to reduce electron illumination below damage limit. GO oxygen maps obtained at a few nanometers scale show separated domains with different oxidation levels. The C/O ratio varies from about 4:1 to 1:1, the latter corresponding to a complete functionalization of the graphene flakes. In RGO the residual oxygen concentrates mostly in regions few tens of nanometers wide. Specific energy-loss near-edge structures are observed for different oxidation levels. By combining these findings with first-principles simulations we propose a model for the highly oxidized domains where graphene is fully functionalized by hydroxyl groups forming a 2D-sp3 carbon network analogous to that of graphane.
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