Methyl Hexadecyl Viologen Inclusion in Cucurbit[8]uril: Coexistence of Three Host-Guest Complexes with Different Stoichiometry in a Highly Hydrated Crystal

The host-guest inclusion complexes of cucurbiturils with alkyl viologen have interesting architectures, chemical properties, and potential applications in sensors and nanotechnology. A highly hydrated triclinic crystal of cucurbit[8]uril (CB[8]) complexed by methyl hexadecyl viologen (MVC16) is characterized by the unprecedented coexistence in the crystal of three host-guest complexes with 3:2, 2:2, and 1:1 stoichiometries. In all these complexes, the hook-shaped alkyl chain of the MVC16 is hosted in the CB[8] macrocycles, while the methyl viologen moieties have various environments. In the Z-shaped 3:2 complex, a central CB[8] unit hosts two viologen heads in the cavity, while the 2:2 complex is held together by \u3c0-stacking interactions between two viologen units. In the square 2D tiling crystal packing of CB[8] macrocycles, the same site which favors the dimerization observed in the 2:2 complex is also statistically occupied by a single methyl viologen moiety of the 1:1 complex. The rational interpretation of the crystal structure represented an intriguing challenge, due to the complicated statistical disorder in the alkyl chains hosted in CB[8] units and in the methyl viologen moieties of 2:2 and 1:1 complexes. In contrast with the solution behavior dominated by the 2:1 complex, the coexistence of three host-guest complexes with 3:2, 2:2, and 1:1 ratios highlights the fundamental importance of packing effects in the crystallized supramolecular complexes. Therefore, the crystallization process has permitted us to capture different host-guest systems in a single crystal, revealing a supramolecular landscape in a single photo

The Role of Chain Length in Cucurbit[8]uril Complexation of Methyl Alkyl Viologens

Viologens are among the most studied guests for cucurbit[8]uril (CB[8]) and their complexation is usually driven by bipyridyl core inclusion inside the cavity to maximize both hydrophobic and cation-dipole interactions. The presence of alkyl substituents on the guest alters this complexation mode, switching to aliphatic chain inclusion in U-folded conformation. Herein, we report a thorough study of the influence of the alkyl chain length on the binding mode of methyl alkyl viologens. The chain length of the studied guests was increased by two methylene groups starting from methyl dodecyl viologen (MVC12) to the octadecyl analogue (MVC18). Complexation in water, investigated by NMR spectroscopy and ITC, revealed a clear switch from 1 : 1 to 2 : 1 host/guest stoichiometry moving from 12 to 16 carbon atoms, as a consequence of the chain folding of the major portion of the longer alkyl chain in one CB[8] cavity and the inclusion of the full viologen unit by another host molecule. The CB[8]2.MVC18 complex crystal structure evidences the unprecedented 2 : 1 stoichiometry and quantified in 12 the number of carbon atoms necessary to fill the CB[8] cavity in U-shaped conformation

Combined Approach of Mechanochemistry and Electron Crystallography for the Discovery of 1D and 2D Coordination Polymers

Mechanochemical synthesis is an attractive preparative method that combines a green approach with versatility, efficiency, and rapidity of reaction. However, it often yields microcrystalline materials, and their small crystal size is a major hindrance to structure elucidation with conventional single-crystal or powder X-ray diffraction methods. This work presents the novel approach of combining mechanochemistry with electron diffraction techniques to elucidate the crystal structure of metal−organic compounds of zinc(II) and copper(II) with 2,6-pyridinedicarboxylic acid and 4,4′-bipyridine

Characterization of metabolic resting rate and proposal of a new equation for a female Brazilian population

OBJETIVOS: Os objetivos do estudo foram normatizar o gasto metabólico de repouso (GMR) de mulheres brasileiras, avaliar a adequação da fórmula de Harris Benedict (HB), a relação entre suas variáveis e propor novas equações para estimativa do GMR. SUJEITOS E MÉTODOS: Para tanto, foram utilizados 760 exames de calorimetria indireta (CI) de mulheres com idade entre 18 e 65 anos. Os resultados foram tabulados, a população foi dividida de acordo com quintis de peso e, então, realizaram-se as análises estatísticas. RESULTADOS: A média de GMR variou entre 1.226 calorias/dia a 1.775 calorias/dia. A fórmula de HB superestimou o GMR em torno de 7%.Concluímos, a partir da correlação entre as variáveis, que o peso possui correlação positiva com o GMR, e a idade, uma correlação negativa. CONCLUSÃO: GMR assim como coeficiente respiratório (QR) podem ser utilizados como preditores de obesidade. Nosso estudo trouxe duas novas propostas de equações, uma para a população com índice de massa corpórea (IMC) &gt; 35 kg/m² e outra para a população com IMC < 35 kg/m².OBJETIVES: The goals of this study were to standardize resting metabolic rate (RMR) in the Brazilian female population and evaluate the suitability of the HB equation. SUBJECTS AND METHODS: In order to do so, 760 indirect calorimetry (CI) measurements performed in Brazilian female patients between 18 and 65 years old, were used. The results were tabulated, the population distributed according to the quintiles of weight, and the statistical analyses applied. RESULTS: The average RMR varied from 1,226 to 1,775 calories/day. The HB equation overestimated the RMR by about 7%. From the correlation between the variables, we conclude that weight has a positive correlation with RMR and age a negative correlation. CONCLUSION: The RMR and respiratory quotient (QR) can be used as obesity predictors. Two new equations were proposed in our study, one for the population with body mass index (BMI) &gt; 35 kg/m² and another for the population with BMI < 35 kg/m²

Drinking water quality governance: A comparative case study of Brazil, Ecuador, and Malawi

Human health is greatly affected by inadequate access to sufficient and safe drinking water, especially in low and middle-income countries. Drinking water governance improvements may be one way to better drinking water quality. Over the past decade, many projects and international organizations have been dedicated to water governance; however, water governance in the drinking water sector is understudied and how to improve water governance remains unclear. We analyze drinking water governance challenges in three countries—Brazil, Ecuador, and Malawi—as perceived by government, service providers, and civil society organizations. A mixed methods approach was used: a clustering model was used for country selection and qualitative semi-structured interviews were used with direct observation in data collection. The clustering model integrated political, economic, social and environmental variables that impact water sector performance, to group countries. Brazil, Ecuador and Malawi were selected with the model so as to enhance the generalizability of the results. This comparative case study is important because similar challenges are identified in the drinking water sectors of each country; while, the countries represent diverse socio-economic and political contexts, and the selection process provides generalizability to our results. We find that access to safe water could be improved if certain water governance challenges were addressed: coordination and data sharing between ministries that deal with drinking water services; monitoring and enforcement of water quality laws; and sufficient technical capacity to improve administrative and technical management of water services at the local level. From an analysis of our field research, we also developed a conceptual framework that identifies policy levers that could be used to influence governance of drinking water quality on national and sub-national levels, and the relationships between these levers

(Invited) intrinsic reliability assessment of 650V rated AlGaN/GaN based power devices:an industry perspective

Although astounding performance is already proven by many research papers, the widespread adoption of GaN power devices in the market is still hampered by (1) yield and reproducibility ; (2) cost ; (3) reliability. All three factors are to be considered, but to convince customers to adopt GaN power devices, proven device and product reliability is a must. Cost is kept acceptably low by growing the GaN epi stack on 6 inch and 8inch Si substrates, and by processing the GaN power device technology in standard CMOS production lines. This paper will focus on the most important intrinsic reliability mechanisms for GaN power devices. It will cover gate dielectric reliability, Ohmic contact reliability, accelerated drain stress testing (high temperature reverse bias--HTRB) and high voltage device wear-out testing (high voltage off-state stress--HVOS). Acceleration models are discussed A measurement strategy to extract valuable information about the physical properties of the buffer layers (e.g. activation energies of the traps, conduction mechanisms, \u2026) based on simple transmission line structures, is outlined

Giant regular polyhedra from calixarene carboxylates and uranyl

Self-assembly of large multi-component systems is a common strategy for the bottom-up construction of discrete, well-defined, nanoscopic-sized cages. Icosahedral or pseudospherical viral capsids, built up from hundreds of identical proteins, constitute typical examples of the complexity attained by biological self-assembly. Chemical versions of the so-called 5 Platonic regular or 13 Archimedean semi-regular polyhedra are usually assembled combining molecular platforms with metals with commensurate coordination spheres. Here we report novel, self-assembled cages, using the conical-shaped carboxylic acid derivatives of calix[4]arene and calix[5]arene as ligands, and the uranyl cation UO22+ as a metallic counterpart, which coordinates with three carboxylates at the equatorial plane, giving rise to hexagonal bipyramidal architectures. As a result, octahedral and icosahedral anionic metallocages of nanoscopic dimensions are formed with an unusually small number of components