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Biomedical subjects

G Cuevas

Publications and source records attributed to G Cuevas.

13 recordsLinked to original sources
PubMed2003

Effects on run-off water quantity and quality of urban organic wastes applied in a degraded semi-arid ecosystem.

Biosolids and composted municipal solid wastes were surface-applied (0 and 80 Mg ha(-1)) to a degraded soil in a semi-arid environment to determine their effects on the quantity and quality of run-off water. Three and 4 years after application, a simulated rainfall was performed (intensity=942.5 ml min(-1) and kinetic energy=3.92 J m(-2)) on 0.078 m(2) plots using a portable rainfall simulator. The run-off from the different treatment plots was collected and analysed. The type of treatment was highly related to infiltration, run-off and sediment production. The biosolid-treated plots showed the minimum value of total run-off, maximum time to the beginning of run-off and maximum run-off ratio (the relationship between total rainfall and run-off). The MSW-treated plots showed values intermediate between biosolid-treated plots and control plots. Soil losses were also closely related to treatment type. Control plots showed the maximum sediment yield, MSW-treated plots showed intermediate values, and biosolid plots the minimum values for washout. The concentrations of NH(4)-N and PO(4)-P in the run-off water were significantly higher in the treated plots than in control plots. The highest PO(4)-P value, 0.73 mg l(-1), was obtained in the soil treated with biosolids; NO(3)-N concentration also increased significantly with respect to the control and MSW treatments. NH(4)-N concentrations of 15.6 and 15.0 mg l(-1) were recorded in the soils treated with biosolids and MSW, respectively, values approximately five times higher than those obtained in run-off water from untreated soil. However, the concentrations of all these constituents were lower than threshold limits cited in water quality standards for agricultural use. With the exception of Cu, all trace metals analysed in the run-off water were below detection limits.

Conservation of Natural Resources↗
PubMed2002

Relationship between molecular structure and electron targets in the electroreduction of benzocarbazolediones and anilinenaphthoquinones. Experimental and theoretical study.

We report the synthesis and voltamperometric reduction of 5H-benzo[b]carbazole-6,11-dione (BCD) and its 2-R-substituted derivatives (R = -OMe, -Me, -COMe, -CF(3)). The electrochemical behavior of BCDs was compared to that of the 2-[(R-phenyl)amine]-1,4-naphthalenediones (PANs) previously studied. Like PANs, BCDs exhibit two reduction waves in acetonitrile. The first reduction step for the BCDs represents formation of the radical anion, and the half-wave potential (E(1/2)) values for this step are less negative than for that of the PANs. The second reduction wave, corresponding to the formation of dianion hydroquinone, has E(1/2) values that shift to more negative potentials. A good linear Hammett-Zuman (E(1/2) vs sigma(p)) relationship, similar to that for the PAN series, was also obtained for the BCDs. However, unlike the PANs, in the BCDs, the first reduction wave was more susceptible to the effect of the substituent groups than was the second wave, suggesting that the ordering of the two successive one-electron reductions in BCDs is opposite that in PANs. This is explained by the fact that the electron delocalizations in the two systems are different; in the case of BCDs there is an extra aromatic indole ring, which resists loss of its aromatic character. The electronic structures of BCD compounds were, therefore, investigated within the framework of the density functional theory, using the B3LYP hybrid functional with a double zeta split valence basis set. Our theoretical calculations show that the O(1).H-N hydrogen bond, analogous to that previously described for the PAN series, is not observed in the BCDs. Laplacians of the critical points (nabla(2)rho) and the natural charges for the C-O bonds indicate that the first reduction wave for the BCDs corresponds to the C(4)-O(2) carbonyl, while in the PAN series the first one-electron transfer occurred at the C(1)-O(1) carbonyl. Natural bond orbital analysis showed that, in all the BCDs, the lowest unoccupied molecular orbital (LUMO) is located at C(4), whereas for the PANs, the LUMO is found at C(1). The good correlation between the LUMO energy values and the E(1/2) potentials (wave I) established that the first one-electron addition takes place at the LUMO. Analysis of the molecular geometry confirmed that, in both series of compounds, the effect of the substituent groups is mainly on the C(4)-O(2) carbonyl. These results explain the fact that reduction of the C(4)-O(2) carbonyl (voltammetric wave II in the PANs and voltammetric wave I in the BCDs) is more susceptible to the effect of the substituent groups than is reduction of the C(1)-O(1) carbonyl (wave I in the PANs and wave II in the BCDs).

Carbazoles↗
PubMed2001

Molecular structure of substituted phenylamine alpha-OMe- and alpha-OH-p-benzoquinone derivatives. Synthesis and correlation of spectroscopic, electrochemical, and theoretical parameters.

Thirteen C(6) para-substituted anilinebenzoquinones derived from perezone (PZ) (2-(1,5-dimethyl-4-hexenyl)-3-hydroxy-5-methyl-1,4-benzoquinone) were prepared to analyze the effect of the substituents on quinone electronic properties. The effect of a hydrogen bond between the alpha-hydroxy and carbonyl C(4)-O(4) groups was determined in perezone derivatives by substituting electron-donor and electron-acceptor groups such as -OMe, -Me, -Br, and -CN and comparing the -OH (APZs) and -OMe (APZms) derivatives. Reduction potentials of these compounds were measured using cyclic voltammetry in anhydrous acetonitrile. The typical behavior of quinones, with or without alpha-phenolic protons, in an aprotic medium was not observed for APZs due to the presence of coupled, self-protonation reactions. The self-protonation process gives rise to an initial wave, corresponding to the irreversible reduction reaction of quinone (HQ) to hydroquinone (HQH(2)), and to a second electron transfer, attributed to the reversible reduction of perezonate (Q(-)) formed during the self-protonation process. This reaction is favored by the acidity of the alpha-OH located at the quinone ring. To control the coupled chemical reaction, we considered both methylation of the -OH group (APZms) and addition of a strong base, tetramethylammonium phenolate (Me(4)N(+)C(6)H(5)O(-)), to completely deprotonate the APZs. Methylation led to recovery of reversible, bi-electronic behavior (Q/Q(*)(-) and Q(*)(-)/Q(2)(-)), indicating the nonacidic properties of the NH group. The addition of a strong base resulted in reduction of perezonate (Q(-)) obtained from the acid-base reaction of APZs with Me(4)N(+)C(6)H(5)O(-) to produce the dianion radical (Q(*)(2)(-)). Although the nitrogen atom interferes with direct conjugation between both rings by binding the quinone with the para-substituted ring, the UV-vis spectra of these compounds showed the existence of intramolecular electronic transfer from the respective aniline to the quinone moiety. (13)C NMR chemical shifts of the quinone atoms provided additional evidence for this electron transfer. These findings were also supported by linear variation in cathodic peak potentials (E(pc)) vs Hammett sigma(p) constants associated with the different electrochemical transformations: Q/Q(*)(-), Q(*)(-)/Q(2)(-) for APZms or HQ/HQH(2) and Q(-)/Q(*)(2)(-) for APZs. The electronic properties of model anilinebenzoquinones were determined at a B3LYP/6-31G(d,p) level of theory within the framework of the density functional theory. Our theoretical calculations predicted that all the compounds are floppy molecules with a low rotational C-N barrier, in which the degree of conjugation of the lone nitrogen pair with the quinone system depends on the magnitude of the electronic effect of the substituents of the aniline ring. Natural charges show that C(1) is more positive than C(4) although the LUMO orbital is located at C(4). Hence, if the natural charge distribution in the molecule controls the first electron addition, this should occur at carbon atom C(1). If the process is controlled by the LUMO orbitals, however, electron addition would first occur at C(4). For the APZms series susceptibility of the first reduction wave to the substitution effect (rho(pi) = 147 mV) is lower than that of the second reduction wave (rho(pi) = 156 mV). Thus, the first, one-electron transfer in the quinone system is controlled by the natural charge distribution of the molecule and therefore takes place at C(1).

Acetonitriles↗
PubMed2001

Electronic delocalization contribution to the anomeric effect evaluated by computational methods.

This study proposes the determination of the electronic delocalization contribution to the Anomeric Effect (EDCAE, Delta Delta E(deloc), eq 3) as a computational alternative in the evaluation of the excess of the axial preference shown by an electronegative substituent located at alpha position to the annular heteroatom of a heterocyclic compound (anomeric position) in both the presence and the absence of electronic delocalization retaining the same molecular geometry. The determination of the EDCAE is computationally accessible through the application of the natural bond orbital analysis (NBO). This type of analysis allows the comparison of hypothetical molecules lacking electronic delocalization (Lewis molecules, in which the electrons are strictly located in bonds and lone pairs) with the fully delocalized molecules retaining the same geometry and the evaluation of the anomeric effect in terms of eq 3. The role of the Lewis molecules is the same as the cyclohexane used experimentally to evaluate the anomeric effect. The advantage of doing this is that Lewis molecules are stereoelectronically inert. Applying this methology to cyclic and acyclic molecules at B3LYP/6-31G(d,p) and HF/6-31G(d,p)//B3LYP/6-31G(d,p) levels of theory, we found that the anomeric effect shown by Cl in 1,3-dioxane; F, Cl, SMe, PH(3), and CO(2)Me groups in 1,3-dithiane is of stereoelectronic nature while the preference of F, OMe, and NH(2) in 1,3-dioxane and the P(O)Me(2) group in 1,3-dithiane is not. Furthermore, this methodology shows that anomeric effects without stereoelectronic origin can modify the molecular geometry in agreement with the geometric pattern required by the double-bond no-bond model, as recently proposed by Perrin.

Journal Article↗
PubMed2001

Rigorous interpretation of electronic density functions of axial and equatorial conformers of dimethylphosphinoylcyclohexane, 2-(dimethylphosphinoyl)-1,3,5-trithiane, and 2-(dimethylphosphinoyl)-1,3-dithiane-1,1,3,3-tetraoxide.

Theoretical analysis within the frame of the Topological Theory of Atoms in Molecules confirms the repulsive steric interaction between an axial dimethylphosphinoyl group and the syn-diaxial hydrogens in cyclohexane derivative 2-ax. In seemingly good agreement with experiment, equatorial isomer 2-eq was calculated to be 1.49 kcal/mol more stable than 2-ax. (Experimental energy difference in (diphenylphosphinoyl)cyclohexane, Delta H(o) = 1.96 kcal/mol.) In contrast, axial 2-(dimethylphosphinoyl)-1,3,5-trithiane, 3-ax, was calculated to be 6.38 kcal/mol more stable than 3-eq. (Experimentally, the axial conformer of 2-(diphenylphosphinoyl)-1,3,5-trithiane, was found to be 1.43 kcal/mol more stable than the equatorial conformer, in solvent chloroform.) Theoretical analysis, in particular the electron density at the bond critical point within the C(4,6)-H...O=P bonding trajectory, implies significant bonding in this segment of interacting atoms. By the same token, substantial positive charge is acquired by the C--H bonds adjacent to the sulfonyl groups in disulfone 4. Hydrogen bonding between the phosphoryl group and H(4,6) leads to stabilization of 4-ax, which is estimated to be 5.0 kcal/mol lower in energy than 4-eq. This conclusion is supported by examination of P==O...H--C(4,6) bond trajectories, as well as from evaluation of the critical point properties along those interacting moieties. By contrast, fluorinated derivative 5 is more stable in the equatorial conformation, indicating a repulsive electrostatic interaction of the C--F...O-P entity in 5-ax.

Journal Article↗
PubMed2001

[Risk factors for morbidity and mortality in patients with essential hypertension, followed for 25 years].

BACKGROUND: Among hypertensive patients, other risk factors for mortality and morbidity, besides blood pressure, must be considered when therapeutic decisions are done. AIM: To assess the incidence and relevance of cardiovascular risk factors in a cohort of patients with essential hypertension. MATERIAL AND METHODS: A cohort of 1,072 treated patients with essential hypertension was followed for a period up to 25 years. Four hundred eighty six were men and 586 were women, age ranged from 31 to 70 years. At entry, 56% of subjects did not have any organic complications associated to hypertension (stage I WHO criteria), 30% had mild alterations (Stage II) and 14% had major complications (myocardial infarction, stroke, heart failure or renal failure). Likewise, 43.8% had mild, 14.5%, moderate and 41.7%, severe hypertension. Patients were treated with monotherapy or combined therapy based on diuretics, beta blockers, calcium antagonists and angiotensin converting enzyme inhibitors. Goal of therapy was 140/90 mm Hg. Risk factors associated diseases and complications were registered carefully. Causes of death were obtained from hospital records and death certificates. Mortality was analyzed using life tables (intention to treat method included). RESULTS: Blood pressure dropped significantly during follow up from a mean of 182/110 to 154/92 mm Hg. During follow up, 143 patients died and 429 complications (lethal or non lethal) were recorded. Twenty four percent of patients smoked, 24% reported alcohol intake, 56% had hypercholesterolemia, 11% were obese, 13% had diabetes and 3% had gout. The proportional hazard model showed that the existence of previous complications, the presence of more than 3 risk factors, and age over 60 and mean systolic and diastolic pressure during therapy, were independent and significant risk factors for mortality. CONCLUSIONS: The incidence of risk factors among our hypertensive patients is very similar to that of other national or international cohorts.

Adult↗
PubMed1998

[Influence of risk factors and pharmacological treatment on mortality in patients with essential hypertension].

BACKGROUND: The V JNC consensus stated that although new antihypertensive agents, such as angiotensin converting enzyme inhibitors and calcium channel blockers, are considered safer drugs, there is no firm evidence from large controlled trials that these drugs are associated with a lower cardiovascular mortality. AIM: To study the association between cardiovascular risk factors, blood pressure levels, pharmacological treatment and mortality in a group of hypertensive patients followed at an hypertension outpatient clinic. PATIENTS AND METHODS: Patients with essential hypertension were treated with different antihypertensive medications, according to physicians criteria, and controlled until death or loss from follow up. Causes of death were obtained from hospital records and death certificates. Survival was analyzed using life tables, comparisons between groups of patients were done using chi square or a Cox's proportional hazards model. RESULTS: Three hundred thirty-nine hypertensive patients aged 33 to 80 years old were followed for a mean period of 9.8 +/- 4.9 years. Eighty-six were treated with beta blockers, 64 with diuretics, 133 with calcium antagonists and 56 with ACE inhibitors. Blood pressure dropped similarly with all medications. During follow up, 79 patients died. Life table analysis showed that patients with a history of angina, diabetes or myocardial infarction had higher mortality rates. Similarly, patients treated with beta blockers and diuretics had higher mortality than patients treated with calcium antagonists or angiotensin converting enzyme inhibitors. The proportional hazards model showed that the effect of treatment modality persisted after correction for the other risk factors for mortality. CONCLUSIONS: In this series of hypertensive patients, those treated with beta blockers or diuretics had higher mortality rates than those receiving calcium channel antagonists or angiotensin converting enzyme inhibitors.

Adrenergic beta-Antagonists↗
PubMed1995

[Blood insulin in fasting conditions as a simple marker of insulin resistance in hypertensive patients].

Insulin resistance is associated to hypertension, obesity and diabetes and may be an independent cardiovascular risk factor. The exact assessment of insulin resistance requires complex metabolic studies. However, there is a good correlation between this parameter and fasting serum insulin levels. The aim of this work was to study fasting serum insulin levels by radio immuno analysis in 43 hypertensive patients aged 56 +/- 5.5 years old (27 male, 17 obese and 8 diabetics) and 20 normotensive controls aged 50 +/- 4.8 years old (13 male). Insulin levels were 3.8 UI/L in controls, 12.1 UI/L in normal weight, 15.5 UI/L in obese and 18.3 UI/L in diabetic hypertensives (ANOVA p < 0.001). These levels were above two standard deviations of control values in 50% of normal weight, 66% of obese and 62% of diabetic hypertensives. It is concluded that normal weight, obese and diabetic hypertensive subjects have high fasting insulin levels.

Adult↗
PubMed1992

[Percutaneous mitral valvuloplasty during pregnancy].

The mitral valve stenosis is the most frequently valvuloplasty in pregnant patients. When it carries a significant risk of mortality for both mother and fetus, it can be performed a surgical commissurotomy, with a high risk for the fetus. We report our experience in percutaneous mitral valvuloplasty (PMV) in 3 patients during the third trimester of pregnancy with severe mitral stenosis. In this cases, we performed PMV in NYHA (New York Heart Association) CF III patients refractory to medical treatment. We used the transseptal double balloon technique protecting the abdominal wall using a lead apron. The mitral areas increased from 1 to 2 cm2, without a significant development of mitral regurgitation. In all cases, the infants delivered at term without complications and with normal weight. The PMV arise like an ideal intervention for the treatment of mitral stenosis during pregnancy.

Adult↗
PubMed1991

[Celiprolol in the treatment of chronic stable angina].

Celiprolol is a third generation beta blocking drug with intrinsic vasodilator effect. We evaluated the effect of this drug at a fixed dose of 400 mg daily in 20 patients with coronary artery disease and stable angina having 2 to 40 episodes of pain a week. All patients had positive exercise stress test with greater than 1 mm ST depression. Compared to the 1 month baseline placebo phase, patients after 3 months of treatment with celiprolol had less episodes of angina (2.4 vs 7.2 a week, p less than 0.001), higher angina threshold (667 vs 337 sec, p less than 0.025), higher ischemia threshold (614 vs 401 sec, p less than 0.001) and were able to perform more work (3937 vs 2403 kgm/min. p less than 0.01). 9 patients had no pain during exercise. A decrease in blood pressure, heart rate and double product was evident in the stress tests of the active phase. Adverse effects included headache (4 patients), sweating (1) and fatigue (1) not requiring modification of drug dose. No adverse effects were seen in 13 patients. Thus, celiprolol is effective to decrease angina during daily life and increase exercise tolerance in patients with chronic stable angina pectoris.

Adrenergic beta-Antagonists↗
PubMed1991

[Morbidity and mortality of essential arterial hypertension treated in Chile: a 15 years' follow-up study].

In order to establish morbidity and mortality in treated patients with essential hypertension, a prospective study was started in 1974. 714 patients were followed for 15 years. Admission criteria included diastolic blood pressure over 95 mmHg during one month on placebo, absence of malignant or accelerated hypertension and no recent (6 month) cardiovascular complication. According to target organ damage, 51% of patients were in WHO stage I, 35% in stage II and 14% in stage III. There were 342 males and 372 females, with mean age 58.7 +/- 9.8 years. Mean initial blood pressure was 181/110 +/- 12/8.9 mmHg. Treatment schedules included diuretics alone (23%), beta blockers alone (32%), diuretic and betablocker (38%), combined therapy with vasodilators (9%) and other forms of therapy (5%). 75 subjects failed to comply with therapy but were maintained in the analysis (intention to treat). A significant reduction in blood pressure was observed in the group as a whole (154/93 +/- 7/9 mmHg). Sustained normalization of BP (< 90 mmHg) was obtained in 40.2% of patients, reductions to between 91 and 100 mmHg in 37.2% and reductions to over 101 mmHg in 22.5% 47 patients died from cerebro vascular complications (15-year cumulative death rate of 12.3%). Total morbidity rate was 40.1% (232 events) with 61 coronary events (13.3%), 43 cerebrovascular events (8.7%), 30 cases of heart failure (12.9%) and 21 cases of renal failure (4.3%). These figures are in agreement with internationally reported ones with the exception of coronary morbidity which appears lower in this study.

Adult↗
PubMedDate not supplied

Biowaste effects on soil and native plants in a semiarid ecosystem.

Many soils of the Mediterranean region with a semiarid climate are subjected to progressive degradation as a result of water erosion. Biosolids and municipal solid wastes (MSW) were surface-applied once at three rates (40, 80, and 120 Mg ha(-1)) to different plots in a degraded semiarid ecosystem. The study was conducted to determine the effects of such applications on soil chemical properties and native vegetation over a three-year period. Soil N, P, and K initially increased with increasing biowaste application rates, but then decreased over time. Levels of Zn and Cu were higher in MSW than biosolid-treated plots, and increased in both years after application. Concentrations of soil Cd, Pb, Ni, and Cr did not change as a result of biowaste amendment in the study period. The growth of native plants was enhanced by the addition of biowastes. Total plant canopy and plant biomass increased significantly and remained higher in all treatments than in the control plot over the three-year period. The species richness of native plants decreased with increasing biowaste rates. Differences in the development of native plant communities between treatments were observed, and were more remarkable three years after biowaste application. Tissue N, P, K, Zn, and Cu levels increased with the biowaste application rate, but concentrations of tissue Pb, Cd, Ni, and Cr did not increase significantly. Biowastes applied at the rate of 80 Mg ha(-1) gave rise to the most favorable soil and native vegetation results while avoiding environmental risks.

Agriculture↗