Comparison of methods for calculating the properties of intramolecular hydrogen bonds. Excited state proton transfer

A series of molecules related to malonaldehyde, containing an intramolecular H-bond, are used as the testbed for a variety of levels of ab initio calculation. Of particular interest are the excitation energies of the first set of valence excited states, nπ∗ and ππ∗, both singlet and triplet, as well as the energetics of proton transfer in each state. Taking coupled cluster results as a point of reference, configuration interaction-singles–second-order Møller–Plesset (CIS–MP2) excitation energies are too large, as are CIS to a lesser extent, although these approaches successfully reproduce the order of the various states. The same may be said of complete active space self-consistent-field (CASSCF), which is surprisingly sensitive to the particular choice of orbitals included in the active space. Complete active space–second-order perturbation theory (CASPT2) excitation energies are rather close to coupled cluster singles and doubles (CCSD), as are density functional theory (DFT) values. CASSCF proton transfer barriers are large overestimates; the same is true of CIS to a lesser extent. MP2, CASPT2, and DFT barriers are closer to coupled cluster results, although yielding slight underestimates. © 1999 American Institute of Physics

Renewable Energy and Sustainable Development Nexus in Selected OECD Countries

This article investigates the relationship between economic growth, renewable energy consumption, gross fixed capital and total number of labor for 1980-2012 in selected OECD countries in terms of sustainability. Four OECD countries are included in our model in order to differentiate the relationship between nuclear energy consumption and economic growth in more developed OECD countries such as the U.S. and Germany with less developed OECD countries such as Turkey and Italy. According to the results of ARDL approach, the effect of renewable energy consumption on GDP is positive in both U.S. and Germany whereas renewable energy consumption has negatively correlated with GDP in Italy and Turkey. It can be concluded that renewable energy consumption has positive effect on economic growth only in more developed countries. Keywords: Economic Growth; Sustainable Development; Renewable Energy; ARDL Bound Test. JEL Classifications: F43; Q01; Q43; Q5

Materiais de base poliuretano com resistência incrementada à fadiga térmica para calçado de segurança

A perda de propriedades ao longo do tempo de vida útil do calçado esta relacionada com a variação térmica e esforço mecânico ocorrido em condições de utilização, o calçado pode ser utilizado de forma intercalada a temperaturas elevc:1das e a temperaturas baixas (p.exe. o calçado usado por militares que operam no deserto). Os materiais de base poliuretano (PUs), nomeadamente os microcelulares, são convencionalmente aplicados na construção de calçado sendo associados a boas propriedades de conforto. Devido as exigências dos consumidores quanto a produtos de elevado desempenho, o desenvolvimento de novos PUs microcelulares com resistência incrementada a fadiga térmica e um tópico de elevado interesse industrial. Assim, o presente trabalho esta focado no desenvolvimento de PUs microcelulares resistentes a fadiga térmica, partindo de uma formulação e de um sistema químico de base poliester tipico para a produção de entressolas para calçado, e onde o incremento desta propriedade e realizado pela aditivação do PU com nanocargas inorgânicas. Produziram-se PUs moldados correspondentes à formulação base e a formulações modificadas com o aditivo inorgânico nano-A (tamanho medio de partícula<1 0 μm) através da incorporação de 1, 3, 5, 7 e 10% (m/m) (Fig.1 (1 a)). Os PUs produzidos foram caracterizados quanto a estrutura celular por microscopia ótica (MO) (Fig.1 (2a)) e Scanning Electron Microscopy (SEM), servindo tambem esta ultima técnica para verificar a distribuição das cargas nas células (Fig. 1 (3a)). As propriedades térmicas foram avaliadas por Differential Scanning Calorimetry (DSC). Para avaliar o efeito da fadiga termica nas propriedades dos PUs, desenvolveu-se um teste laboratorial que consistiu em colocar as amostras numa estufa a 60°C durante 12 horas, seguido de um período a 4 °C (frigorifico) durante 12 horas. Este procedimento foi repetido durante 5 ciclos, seguindo-se a analise por DSC de forma a avaliar o efeito nas propriedades térmicas. Os resultados obtidos por MO permitiram observar que a introdução do aditivo originou distribuições de tamanho de células mais homogéneas, e que esta característica melhorou com o aumento do teor de 1 para 10%. A analise por DSC das amostras após produção evidenciou que a incorporação do aditivo incrementou o valor de Tm de 292.1 (PUbase) para 311.7 oc (PU10nano-A), enquanto após o teste de fadiga térmica os valores de Tm variaram entre 292.7 (PUbase) e 314.7 oc (PU10nano-A). Este resultado aponta para um efeito positivo da utilização deste tipo de cargas no aumento da resistência do PU a temperaturas elevadas.SHOE@FUTURE - Soluções tecnológicas para calçado profissional (projeto SI I&DT - Projetos em Co-Promoção N° 33835) cofinanciado pelo Fundo Europeu de Desenvolvimento Regional (FEDER), através do Programa Operacional Competitividade e lnternacionalização (COMPETE 2020). Laboratório Associado LSRE-LCM (UID/EQU/50020/2019) financiado por fundos nacionais através da FCT/MCTES (PIDDAC) e FCT, e CIMO (UID/AGR/00690/2019) através do FEDER no âmbito do Programa PT2020. Ao financiamento nacional da FCT, P.l., através do contrato de programa institucional de emprego científico de I.P. Fernandes.info:eu-repo/semantics/publishedVersio

A 3-year multicentre randomized controlled trial of etonogestrel- and levonorgestrel-releasing contraceptive implants, with non-randomized matched copper-intrauterine device controls

STUDY QUESTION Is there any difference in the clinical performance of the 3-year one-rod etonogestrel (ENG)- and the 5-year two-rod levonorgestrel (LNG)-releasing contraceptive implants during 3 years of insertion, and between implant and intrauterine device (IUD) contraception, in particular complaints possibly related to hormonal contraceptives? SUMMARY ANSWER The cumulative contraceptive effectiveness after 3 years and method continuation through 2.5 years were not significantly different between ENG and LNG implants, but both outcomes were significantly worse in the non-randomized age-matched group of IUD users than in the combined implant group. WHAT IS KNOWN ALREADY ENG- and LNG-releasing implants are safe and highly efficacious contraceptives with pregnancy rates reported to be 0.0-0.5 per 100 women-years (W-Y). No head-to-head comparative study of the two implants has been undertaken, and little information is available on comparisons of complaints of side effects of implant and copper IUD users. STUDY DESIGN, SIZE, DURATION This was an open parallel group RCT with 1:1 allocation ratio of the ENG and the LNG implants with non-randomized control group of women choosing TCu380A IUD to address lack of reliable data on common side effects typically attributed to the use of progestogen-only contraceptives. After device(s) placement, follow-ups were at 2 weeks, 3 and 6 months, and semi-annually thereafter for 3 years or until pregnancy, removal or expulsion of the implant/IUD occurred. PARTICIPANTS, SETTING, METHODS The study took place in family planning clinics in Brazil, Chile, Dominican Republic, Hungary, Thailand, Turkey and Zimbabwe. Women seeking long-term contraception were enlisted after an eligibility check and informed consent, and 2982 women were enrolled: 1003, 1005 and 974 in the ENG-implant, LNG-implant and IUD groups, respectively; 995, 997 and 971, respectively, were included in the per protocol analysis reported here. MAIN RESULTS AND THE ROLE OF CHANCE ENG and LNG implants each had the same 3-year cumulative pregnancy rate of 0.4 per 100 W-Y [95% confidence interval (CI) 0.1-1.4]. A weight of ≥70 kg at admission was unrelated to pregnancy. Method continuation rates for ENG and LNG implants at 2.5 years were 69.8 (95% CI 66.8-72.6) and 71.8 per 100 W-Y (68.8-74.5), and at 3 years 12.1 (95% CI 5.2-22.0) and 52.0 per 100 W-Y (95% CI 41.8-61.2), respectively. Bleeding disturbances, the most frequent reason for method discontinuation, were significantly more common in the ENG group [16.7 (95% CI 14.4-19.3)] than in the LNG group [12.5 (95% CI 10.5-14.9)] (P 0.019). The 3-year cumulative loss to follow-up was lower in the ENG- than in the LNG-implant group, 8.1 (95% CI 6.4-10.2) and 14.4 per 100 W-Y (95% CI 12.1-17.1), respectively. The median duration of implant removal was 50 s shorter among women with ENG than among women with LNG implant (P < 0.0001). In the observational comparison between IUD and implant users, the 3-year relative risk for pregnancy in IUD group compared with the combined implant group was 5.7 per 100 W-Y (95% CI 4.4-7.3) (P = 0.0003). The 3-year expulsion rate of the IUD was 17.8 per 100 W-Y (95% CI 14.5-21.9), while the discontinuation rate for bleeding disturbances was 8.5 (95% CI 6.7-10.9). Frequency of complaints of headache and dizziness was not significantly different between implant and IUD users (P = 0.16 and 0.77, respectively), acne and bleeding irregularities were more frequent among implant users (P < 0.0001), while heavy bleeding and lower abdominal pain occurred more often among IUD than implant users (P < 0.0001). LIMITATIONS, REASONS FOR CAUTION Few women were ≤19 years old or nulligravida, the proportion of implant users ≥70 kg was <20% and <8% were obese. WIDER IMPLICATIONS OF THE FINDINGS Findings of the study can inform policy makers and clinicians about choice of implant, but also about TCu380A IUD in relation to implants. STUDY FUNDING/COMPETING INTEREST(S) UNDP/UNFPA/WHO/UNICEF/World Bank Special Programme of Research, Development and Research Training in Human Reproduction (HRP), Department of Reproductive Health and Research (RHR), World Health Organization (WHO). This report contains the views of an international expert group and does not necessarily represent the decisions or the stated policy of the WHO. TRIAL REGISTRATION ISRCTN33378571 registered on 22 March 2004. The first participant was enrolled on 12 May 200

Interference of H-bonding and substituent effects in nitro- and hydroxy-substituted salicylaldehydes

Two intramolecular interactions, i.e., (1) hydrogen bond and (2) substituent effect, were analyzed and compared. For this purpose, the geometry of 4- and 5-X-substituted salicylaldehyde derivatives (X = NO2, H or OH) was optimized by means of B3LYP/6-311 + G(d,p) and MP2/aug-cc-pVDZ methods. The results obtained allowed us to show that substituents (NO2 or OH) in the para or meta position with respect to either OH or CHO in H-bonded systems interact more strongly than in the case of di-substituted species: 4- and 3-nitrophenol or 4- and 3-hydroxybenzaldehyde by ∼31%. The substituent effect due to the intramolecular charge transfer from the para-counter substituent (NO2) to the proton-donating group (OH) is ∼35% greater than for the interaction of para-OH with the proton-accepting group (CHO). The total energy of H-bonding for salicylaldehyde, and its derivatives, is composed of two contributions: ∼80% from the energy of H-bond formation and ∼20% from the energy associated with reorganization of the electron structure of the systems in question

Influence of Isotopic Substitution on Strength of Hydrogen Bonds of Common Organic Groups

Although the electronic contribution to the strength of a H–bond is unaffected by isotopic substitution, the heavier mass of deuterium compared with protium lowers some of the vibrational frequencies in the complex. The binding energy of the complex, which includes zero–point and thermal vibrational energies, can thus be altered by several tenths of a kcal mol−1 by H/D substitution. Ab initio calculations are used to analyze this phenomenon in a number of common organic functional groups that are prone to form H–bonds: hydroxyl, carboxyl and amide, both self–complexing as homodimers and with water molecules as partners. It is found that any site of D–substitution increases the complexation energy; however, the bridging sites show a stronger preference for D over H than do the non–bridging, or terminal, sites. Hence D–bonding can be considered to be stronger than H–bonding in these functional groups. Of the groups considered, the energetic preference for D over H is greater in the hydroxyl group, so deuterium would be expected to gravitate toward solvent water molecules in isotopic scrambling experiments. The increments in H–bonding energy resulting from each site of substitution are addititve in cases of multiple substitution

Effect of Nonproximate Atomic Substitution on Excited State Intramolecular Proton Transfer

The central C atom of the OCCCO skeleton of the malonaldehyde molecule is replaced by N, and the effects upon the intramolecular H-bond and the proton transfer are monitored by ab initio calculations in the ground and excited electronic states. The H-bond is weakened in the singlet and triplet states arising from n→π* excitation in both molecules, which is accompanied by a heightened barrier to proton transfer.3ππ* behaves in the same manner, but the singlet ππ* state has a stronger H-bond and lower barrier. Replacement of the central C atom by N strengthens the intramolecular H-bond. Although the proton transfer barrier in the ground state of formimidol is lower than in malonaldehyde, the barriers in all four excited states are higher in the N-analog. The latter substitution also dampens the effect of the n→π* excitation upon the H-bond and increases the excitation energies of the various states, particularly ππ*. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 129–138, 199

Structure, Stability and Bonding of (BC2N)n, n=2,3: An Ab Initio Study

The dimer and trimer of BC2N are studied at the HF and MPn levels using 3-21G, 6-31G∗ and 6-31+G∗ basis sets. It is found that stability is enhanced by maintaining –BN– units together in the cyclic form. Both molecules have cyclic ground state structures with cumulenic-type equal bond lengths in the –BNBN– and polyacetylenic –CCCC– fragments. The linear–cyclic energy difference increases with the size of the cluster. Electron correlation substantially favors the cyclic structures over the linear forms. No general trend of atomic combination has been found in the linear isomers. Diffuse functions have negligible effects on the relative energies and geometries of the dimers

Structure, Stability, and Bonding of BC2N: An Ab Initio Study

Tetra-atomic BC2N, the building block of the mixed carbon and BN clusters, has been studied at the HF, MP2, and CCSD(T) levels using both double- and triple-ζ basis sets with polarization and diffuse functions. In contrast to the parents C4 and (BN)2, the linear triplet (3Π) BCCN is found to be the most stable and the linear−cyclic energy difference is about 28 kcal/mol. In the cyclic structure, isomers with adjacent B and N atoms are more stable, whereas no general trend of atomic combination has been found in the linear isomers. The preferred sequence of atoms in the linear form depends on the cluster size. The nature of bonding and atomization energies of the parent and hybrid molecules are compared and discussed

Excited State Intramolecular Proton Transfer in Anionic Analogues of Malonaldehyde

The transfer of a proton in malonaldehyde takes place within an intramolecular H-bond involving a five-membered ring. This process is compared via ab initio methods with the transfer in analogous systems in which the size of the ring is altered to four and to six and in which the system bears an overall negative charge. In addition to the ground state, calculations are applied to the singlet and triplet ππ* states, as well as to 1nπ* and 3nπ*. The barriers to proton transfer are found to correlate strongly with various geometric and energetic markers of the strength of the H-bond. The H-bond is weakened by n → π* excitation, particularly for the neutral molecule, resulting in a higher transfer barrier. In the case of the two anions, excitation to 3ππ* strengthens the H-bond, while the result is more ambiguous for the 1ππ* state. This trend is reversed in malonaldehyde where the singlet is strengthened by the excitation and the triplet weakened. Some of these patterns are traced directly to the nature of the pertinent orbitals and the density shifts arising from the excitation