Maria D.M.C. Ribeiro da Silva

Enthalpies of combustion of 1,2-dihydroxybenzene and of six alkylsubstituted 1,2-dihydroxybenzenes

Abstract The standard ( p o = 101.325 kPa) molar enthalpies of combustion in oxygen at 298.15 K were measured by static-bomb calorimetry and the standard molar enthalpies of sublimation at 298.15 K were measured by microcalorimetry for 1,2-dihydroxybenzene (catechol) and six alkylsubstituted catechols: −Δ c H m o (cr)/(kJ·mol −1 ) Δ sub H m o /(kJ·mol −1 ) Catechol 2864.5 ± 0.8 86.6 ± 1.6 3-Methylcatechol 3505.4 ± 0.5 93.2 ± 1.0 4-Methylcatechol 3504.6 ± 0.6 94.9 ± 1.0 3-isoPropylcatechol 4808.8 ± 1.1 97.8 ± 1.7 4-terButylcatechol 5461.9 ± 0.9 99.3 ± 1.4 3-Methyl-6-isopropylcatechol 5460.2 ± 0.9 96.6 ± 0.9 3,5-diterButylcatechol 8082.7 ± 1.8 100.1 ± 0.6 The increment in the molar enthalpy of formation of the gaseous compound for substitution of alkyl-groups into catechol was found to be approximately the same as the corresponding increment for substitution into benzene.

Prevalence and pattern of cognitive impairment in rural and urban populations from Northern Portugal.

BackgroundDespite worldwide recognition of the burden of dementia, no epidemiological data is yet available in Portugal. The objective of this study is to estimate the prevalence and describe the pattern of cognitive impairment with dementia or no dementia (CIND) in rural and urban populations from Northern Portugal.MethodsTwo random samples of residents aged 55 to 79 years in rural and urban communities were drawn from the health centres registries to be screened for cognitive impairment. The screening criteria for dementia were an abnormal Mini-Mental State Examination (MMSE) score or a Blessed Dementia Scale score. After excluding those who tested positive for dementia, cut-off points for CIND were set at 1 standard deviation below the mean of the MMSE according to educational level. All those who screened positive either for dementia or CIND were examined by a neurologist for establishing a definitive diagnosis.ResultsThe prevalence of cognitive impairment was higher in rural than in urban populations, 16.8% (95% CI: 14.3-19.8%) vs. 12.0% (95%CI: 9.3-15.4%), with a rural/urban prevalence ratio (PR) of 2.16 (95% CI: 1.04-4.50) in the eldest and 2.19 (95% CI: 1.01-4.76) in persons with vascular risk factors. The prevalence of dementia was 2.7% (95% CI: 1.9-3.8%) with a rural/urban PR = 2.1 and the prevalence of CIND was 12.3% (95% CI: 10.4-14.4%) and PR = 1.3. The prevalence of dementia increases exponentially with age and in those with cerebrovascular disease or other comorbid conditions while the prevalence of CIND, besides these factors, is also higher in persons with low levels of education or vascular risk factors. Alzheimers and vascular disease were equally likely aetiologies of dementia (38.7%), the later more common in men PR(F:M = 0.3) as opposed to the former PR(F:M = 2.0). Vascular CIND, associated either with cerebrovascular disease or vascular risk factors was more frequent (39.7%) then depression (18.4%) or any other aetiology.ConclusionsThe prevalence of cognitive impairment is higher in rural compared with urban populations. This is shown in the synergy between age and rurality, with the rural/urban prevalence ratio increasing with age. In this relatively young population from Northern Portugal, cerebrovascular disease as well as vascular risk factors account for 48% of overall cognitive impairment.

Energetics of 6-methoxyquinoline and 6-methoxyquinoline N-oxide: the dissociation enthalpy of the (N-O) bond

Abstract The standard (p o =0.1 MPa ) molar enthalpies of formation, at T=298.15 K , were determined using static-bomb calorimetry for crystalline 6-methoxyquinoline N -oxide (6MeOQUINO), as −(85.6±3.7) kJ · mol −1 and liquid 6-methoxyquinoline (6MeOQUI), −(25.8±2.2) kJ · mol −1 . The standard molar enthalpies of sublimation/vaporization, at T=298.15 K , were measured by microcalorimetry and from the enthalpies of formation of the gaseous compounds, the dissociation enthalpy D m 0 of the (N + –O − ) dative covalent bond was derived, as (269.2±5.0) kJ · mol −1 .

Are Stroke Occurrence and Outcome Related to Weather Parameters? Results from a Population-Based Study in Northern Portugal

Background: Changes in meteorological parameters have been associated with cardiovascular mortality and stroke. The high incidence of stroke in Portugal may be modelled by short- or long-term weather changes whose effect may be different across stroke types and severity. Methods: Data include all patients with a first-ever-in-a-lifetime stroke registered in a population of 86,023 residents in the city of Porto from October 1998 to September 2000. Specific stroke types were considered and ischaemic stroke (IS) subtype was defined according to the Oxfordshire Community Stroke Projet classification and the Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria. Information on daily temperature, humidity and air pressure was obtained from the National Meteorological Office. The Poisson distribution was used to model the daily number of events as a function of each weather parameter measured over different hazard periods, and the binomial model to contrast effects across subgroups. Differential effects of meteorological parameters and hazard periods upon stroke occurrence and outcome were analysed in a stepwise model. Results: Among the 462 patients registered, 19.6% had a primary intracerebral haemorrhage (PICH) and 75.3% an IS. Among patients with IS, 21.6% were total anterior circulation infarcts (TACIs), 19.8% partial anterior circulation infarcts (PACIs), 19.5% posterior circulation infarcts (POCIs) and 39.1% were lacunar infarcts (LACIs). The aetiology of IS was large artery atherosclerosis in 6.9%, cardioembolism in 23.3% and small artery occlusion in 35.6%. The incidence of PICH increased by 11.8% (95% CI: 3.8–20.4%) for each degree drop in the diurnal temperature range in the preceding day. The incidence of IS increased by 3.9% (95% CI: 1.6–6.3%) and cardioembolic IS by 5.0% (95% CI: 0.2–10.1%) for a 1°C drop in minimum temperature in the same hazard period. The incidence of TACIs followed the IS pattern while for PACIs and POCIs there were stronger effects of longer hazard periods and no association was found for LACIs. The relative risk of a fatal versus a non-fatal stroke increased by 15.5% (95% CI: 6.1–25.4%) for a 1°C drop in maximum temperature over the previous day. Conclusions: Outdoor temperature and related meteorological parameters are associated with stroke occurrence and severity. The different hazard periods for temperature effects and the absence of association with LACIs may explain the heterogeneous effects of weather on stroke occurrence found in community-based and hospital admission studies. Emergency services should be aware that specific weather conditions are more likely to prompt calls for more severe strokes.

Enthalpies of combustion of thiobenzamide, N, N-dimethylthiobenzamide, and N, N-diethylthiobenzamide

The standard (po = 0.1 MPa) molar enthalpies of combustion in oxygen at 298.15 K of crystalline thiobenzamide, N, N-dimethylthiobenzamide, and N, N-diethylthiobenzamide to produce CO2(g), N2(g), and H2SO4·115H2O(l) were measured by rotating-bomb calorimetry. The standard molar enthalpies of sublimation at 298.15 K were measured by microcalorimetry. −ΔcHmo(cr)(kJ·mol−1) ΔcrgHmo(kJ·mol−1) Thiobenzamide 4401.4±1.1 103.4±2.2 N, N-Dimethylthiobenzamide 5757.0±1.4 94.8±2.0 N, N-Diethylthiobenzamide 7064.0±1.5 91.4±3.2 These results form the basis of a bond-energy scheme to estimate ΔfHmo(C6H5CSNr2, g).

Energetic studies and phase diagram of thioxanthene.

The molecular stability of thioxanthene, a key species from which very important compounds with industrial relevance are derived, has been studied by a combination of several experimental techniques and computational approaches. The standard (p degrees = 0.1 MPa) molar enthalpy of formation of crystalline thioxanthene (117.4 +/- 4.1 kJ x mol(-1)) was determined from the experimental standard molar energy of combustion, in oxygen, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The enthalpy of sublimation was determined by a direct method, using the vacuum drop microcalorimetric technique, and also by an indirect method, using a static apparatus, where the vapor pressures at different temperatures were measured. The latter technique was used for both crystalline and undercooled liquid samples, and the phase diagram of thioxanthene near the triple point was obtained (triple point coordinates T = 402.71 K and p = 144.7 Pa). From the two methods, a mean value for the standard (p degrees = 0.1 MPa) molar enthalpy of sublimation, at T = 298.15 K (101.3 +/- 0.8 kJ x mol(-1)), was derived. From the latter value and from the enthalpy of formation of the solid, the standard (p degrees = 0.1 MPa) enthalpy of formation of gaseous thioxanthene was calculated as 218.7 +/- 4.2 kJ x mol(-1). Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several homodesmotic reactions in order to derive the standard molar enthalpy of formation of thioxanthene. The ab initio results are in excellent agreement with the experimental data.

Stroke Awareness in Urban and Rural Populations from Northern Portugal: Knowledge and Action Are Independent

Background: Several studies conducted in hospital emergency departments have shown that most patients delay in responding to stroke symptoms. In the general population, recognition of stroke and the appropriate reactions are important for prevention and acute treatment, particularly in areas with a high stroke incidence. The objective of this study was to compare general knowledge about stroke/TIA and prompt action in urban and rural populations. Methods: In the first half of 2007, a cross-sectional study on stroke knowledge was undertaken in rural and urban populations from the Viana do Castelo district. About 1% of people aged at least 18 years registered at three community health centers were asked to check a list of vascular risk factors (VRF), stroke/TIA warning signs, and other non-specific signs, as well as indicate how they would react in the presence of warning signs or stroke/TIA. Results: The 347 urban participants were on average younger than the 316 rural participants (46 vs. 51 years) and fewer had a low educational level (44 vs. 62% had less than 5 years of full education). About 50% identified at least 8 out of 13 VRF and indicated the brain as the body location; 39.7% recognized simultaneously the three key warning signs of the FAST campaign – irrespective of gender, educational level, and residential area. Education and urban environment increased the odds of calling the emergency medical services (EMS), while age had the opposite effect. After adjustment, recognition of brain location and calling EMS in case of paralysis/weakness or dizziness/vertigo increased the odds of calling the EMS in case of stroke, while recognition of the warning signs was not associated with an EMS call. Conclusions: People’s reaction to stroke depends mostly on their sociodemographic profile and their reaction to specific warning signs, independently of recognizing them as ‘originating from stroke’.

Experimental and computational thermochemical study of α-alanine (DL) and β-alanine.

This paper reports an experimental and theoretical study of the gas phase standard (p° = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, of α-alanine (DL) and β-alanine. The standard (p° = 0.1 MPa) molar enthalpies of formation of crystalline α-alanine (DL) and β-alanine were calculated from the standard molar energies of combustion, in oxygen, to yield CO2(g), N2(g), and H2O(l), measured by static-bomb combustion calorimetry at T = 298.15 K. The vapor pressures of both amino acids were measured as function of temperature by the Knudsen effusion mass-loss technique. The standard molar enthalpies of sublimation at T = 298.15 K was derived from the Clausius−Clapeyron equation. The experimental values were used to calculate the standard (p° = 0.1 MPa) enthalpy of formation of α-alanine (DL) and β-alanine in the gaseous phase, Δ(f)H(m)°(g), as −426.3 ± 2.9 and −421.2 ± 1.9 kJ·mol(−1), respectively. Standard ab initio molecular orbital calculations at the G3 level were performed. Enthalpies of formation, using atomization reactions, were calculated and compared with experimental data. Detailed inspections of the molecular and electronic structures of the compounds studied were carried out.

The Dissociation Enthalpies of Terminal (N–O) Bonds in Organic Compounds

Dissociation enthalpies of terminal (N–O) bonds, DH∘(N–O), in amine N-oxides, nitrile N-oxides, pyridine N-oxides, quinoxaline 1,4-dioxides, furoxans, nitrones, azoxy-derivatives, azo-N,N-dioxides, nitro compounds, nitramines, and alkyl nitrates are calculated from published enthalpy of formation, enthalpy of sublimation, and enthalpy of vaporization data. For each class of organic compounds, the calculated DH∘(N–O) values are critically evaluated. The derived DH∘(N–O) values can be used to estimate enthalpies of formation of other molecules in each of these classes of organic compounds.

Is uracil aromatic? The enthalpies of hydrogenation in the gaseous and crystalline phases, and in aqueous solution, as tools to obtain an answer.

The enthalpy of hydrogenation of uracil was derived from the experimental enthalpies of formation, in the gaseous phase, of uracil and 5,6-dihydrouracil, in order to analyze its aromaticity. The enthalpy of formation of 5,6-dihydrouracil was obtained from combustion calorimetry, Knudsen effusion technique and Calvet microcalorimetry results. High-level computational methods were tested for the enthalpy of hydrogenation of uracil, but only with G3 was possible to obtain results in agreement with the experimental ones. It was found that uracil possesses 30.0% of aromatic character in the gaseous phase. Using both implicit, explicit, and hybrid solvation methods, it was possible to obtain a reference value for the enthalpy of hydrogenation of uracil in the aqueous solution and the effect of polarity and hydrogen bonds on the aromaticity of uracil was analyzed. The value of the hydrogenation enthalpy of uracil in aqueous solution was compared with the experimental value in the crystal phase, also dominated by polarity and hydrogen bonds, derived from combustion calorimetry results. The supramolecular effects on the crystal lattice were explored by the computational simulation of π-π staking dimers and hydrogen bonded dimers.