The Reaction between Sodium Hydroxide and Atomic Hydrogen in Atmospheric and Flame Chemistry.

We report the first direct kinetic study of the gas-phase reaction NaOH + H → Na + H2O, which is central to the chemistry of sodium in the upper atmosphere and in flames. The reaction was studied in a fast flow tube, where NaOH was observed by multiphoton ionization and time-of-flight mass spectrometry, yielding k(NaOH + H, 230-298 K) = (3.8 ± 0.8) × 10-11 cm3 molecule -1 s-1 (at 2σ confidence level), showing no significant temperature dependence over the indicated temperature range and essentially in agreement with previous estimates of the rate constant in hydrogen-rich flames. We show, using theoretical trajectory calculations, that the unexpectedly slow, yet T-independent, rate coefficient for NaOH + H is explained by severe constraints in the angle of attack that H can make on NaOH to produce H2O. This reaction is also central to explaining Na-catalyzed flame inhibition, which has been proposed to occur via the sequence Na + OH (+ M) → NaOH followed by NaOH + H → Na + H2O, thereby effectively recombinating H and OH to H2O. RRKM calculations for the recombination of Na and OH yield k(Na + OH + N2, 300-2400 K) = 2.7 × 10-29 (300/T)1.2 cm6 molecule-2 s-1, in agreement with a previous flash photolysis measurement at 653 K and Na-seeded flame studies in the 1800-2200 K range. These results therefore provide strong evidence to support the mechanism of flame inhibition by Na.

The reactive collision mechanism evinced: stereodynamical control of the elementary Br + H2 → H + HBr reaction.

From a kinetics standpoint, reactive molecular collisions are the building blocks of the mechanisms of chemical reactions. In contrast, a dynamics standpoint reveals molecular collisions to have their own internal mechanisms, which are not mere theoretical abstractions: through suitable preparation of the reactants internal and stereochemical states, features of the mechanisms of a reactive molecular collision can be made evident and used as "handles" to control the reaction outcome. Using time-independent quantum dynamical calculations, we demonstrate this for the Br + H2(v = 0-1, j = 2) → H + HBr reaction in the 1.0-1.6 eV range of total energies. Despite its pronounced effect on reactivity, which is in agreement with the predictions from Polanyi rules, reactant vibration is found to have little effect on the mechanism of this endoergic, late-barrier reaction. Analysis of the correlations between directional reaction properties shows that the collision stereochemistry strongly depends on the total energy, but not on how this energy is partitioned between reactant translation and vibration. The stereodynamical preferences implied by the collision mechanisms determine how and to what extent one can control the reaction. Regarding the overall reaction, the extent of control is found to be large near the reaction threshold but not when the total energy is high. Regarding state-to-state reactions, the effect of reactant stereochemistry on the product rotational state distribution is found to be nontrivial and energy dependent.

Rotational alignment effects in NO(X) + Ar inelastic collisions: a theoretical study.

Rotational angular momentum alignment effects in the rotational inelastic scattering of NO(X) with Ar have been investigated by means of close-coupled quantum mechanical, quasi-classical trajectory, and Monte Carlo hard shell scattering calculations. It has been shown that the hard shell nature of the interaction potential at a collision energy of Ecoll = 66 meV is primarily responsible for the rotational alignment of the NO(X) molecule after collision. By contrast, the alternating trend in the quantum mechanical parity resolved alignment parameters with change in rotational state Δj reflects differences in the differential cross sections for NO(X) parity conserving and changing collisions, rather than an underlying difference in the collision induced rotational alignment. This suggests that the rotational alignment and the differential cross sections are sensitive to rather different aspects of the scattering dynamics. The applicability of the kinematic apse model has also been tested and found to be in excellent agreement with exact quantum mechanical scattering theory provided the collision energy is in reasonable excess of the well depth of the NO(X)-Ar potential energy surface.

Three-vector correlation in statistical reactions: the role of the triatomic parity.

This article presents a methodology for the determination of the k-j-k' three-vector correlation assuming a statistical model for atom-diatom reactions; k and k' are the reagent-approach and product-recoil directions, respectively, and j is the rotational angular momentum of the reagent diatomic. Although the polarization of reagent angular momentum is in most cases negligible, conservation of the triatomic parity imposes a certain polarization for some combinations involving low reagent and product rotational states. Statistical and quantum-mechanical polarization-dependent differential cross sections were calculated for the barrierless D(+) + H(2)(v = 0,j) → HD(v' = 0,j') + H(+) reaction. The agreement between the two is in most cases excellent, confirming the statistical character of the reaction at low and moderate collision energies.

Orientation effects in Cl + H2 inelastic collisions: characterization of the mechanisms.

Based on quantum mechanical scattering (QM) calculations, we have analyzed the polarization of the product hydrogen molecule in Cl + H(2) (v = 0, j = 0) inelastic collisions. The spatial arrangements adopted by the rotational angular momentum and internuclear axis of the departing molecule have been characterized and used to prove that two distinct mechanisms, corresponding to different dynamical regimes, are responsible for the inelastic collisions. Such mechanisms, named as low-b and high-b, correlate with well defined ranges of impact parameter values, add in an essentially incoherent way, and can be clearly differentiated through the quantum mechanical polarization moment that measures the orientation of the products rotational angular momentum with respect to the scattering plane. Other directional effects turn out to fail when it comes to distinguishing the mechanisms. Quasiclassical trajectories (QCT) calculations have been used as a supplement to the purely quantum mechanical analysis. By combining QM and QCT results, which are in very good agreement, we have succeeded in obtaining a clear and meaningful picture of how the two types of collisions take place.

Liver transplantation in bearers of hepatitis B associated or not with delta hepatitis in the age of the new antiviral drugs: is hyperimmune globulin still necessary?

Hepatitis B (HBV) is a public health problem worldwide; one-third of the population has already been in contact with HBV, and 350 million people are chronic carriers of virus. The appearance of hyperimmune gamma globulin and antiviral drugs has allowed that group to undergone hepatic transplantation, achieving satisfactory results to prevent a relapse. But the use of hyperimmune gamma globulin has an extremely high cost, and combined therapies with new antiviral drugs seem to be a therapeutic alternative. We analyzed 21 patients with hepatitis B associated or not with Delta hepatitis over a mean follow-up period of 19.5 months, concluding that use of only nucleotide analogues has sufficient to achieve satisfactory results.

Simultaneous pancreas-kidney transplantation in a human immunodeficiency virus-positive recipient: a case report.

BACKGROUND: After the development of highly active antiretroviral therapy (HAART) for patients with human immunodeficiency virus (HIV), there has been increased interest in organ transplantation for this selected population. There is a lack of reports about pancreas transplant in HIV+ recipients. CASE REPORT: We report the case of a 43-year-old HIV+ man who presented with type 1 diabetes for 25 years and end-stage-renal disease. He underwent dialysis therapy for the prior 3 years. His CD4 count was 830 cells/mL and a negative viral load was achieved after 3 months of antiretroviral therapy. His nutritional status was favorable; no opportunistic infections had occurred. A simultaneous pancreas-kidney transplantation (SPKT) was performed from a 19-year-old deceased trauma victim. Pancreas implantation was enteric-portal drainage. No induction immunosuppression was used, but rather tacrolimus, sodium mycophenolate, and steroids. In the postoperative period, there was a delayed kidney graft function requiring hemodialysis for 14 days. On postoperative day 11, a kidney biopsy specimen showed mild rejection, which was successfully treated with steroids. The patient was discharged after 22 days; he was normoglycemic and insulin-independent with a serum creatinine value of 1.9 mg/dL. Currently, his outcome has been uneventful, without a readmission or opportunistic infections. After 5 months postoperation, the viral load is negative and the CD4 count is 460 cells/mL. The current serum creatinine level is 1.1 mg/dL; no insulin has been required. COMMENT: HIV has been considered to be an absolute contraindication to organ transplantation, because of the infection risk due to severe immunosuppression, to interactions between antiretroviral and immunosuppressive drugs, and to reluctance to offer an organ to a terminal patient. However, transplants in HIV+ patients have shown good results, when a patient has an acceptable CD4 level, a low viral load, and minimal antiretroviral therapy.

The collisional depolarization of (2S+1)Sigma radicals by closed shell atoms: Theory and application to OH(A (2)Sigma(+))+Ar.

Classical and quantum mechanical expressions for the j-j(') vector correlation (also referred to as the rotational tilt) are presented for the situation in which the initial and final relative velocity directions are unresolved. The quantum mechanical expressions are compared with previous descriptions in the literature. It is shown that in the case of (2S+1)Sigma radicals in collision with closed shell species, a tensor opacity formalism can be employed in quasiclassical trajectory calculations to provide classical estimates of both open shell spin-rotation state and nuclear hyperfine state changing (or conserving) cross sections. Polarization parameters are also obtained from the same formalism. The method is applied to calculations on the OH(A (2)Sigma(+))-Ar system using a recently developed potential energy surface. The results of both the closed and open shell quasiclassical trajectory calculations are found to compare favorably with those from close-coupled closed and open shell quantum mechanical scattering calculations. The accompanying paper provides an experimental test of these calculations and of the potential energy surface they employ.

Constraints at the transition state of the D + H2 reaction: quantum bottlenecks vs. stereodynamics.

This article presents a quasiclassical trajectory method for the calculation of cumulative reaction probabilities by sampling of the helicity quantum number of the reagents (k). The method is applied to the D + H(2) reaction at various total angular momentum (J) values, and the helicity-resolved quasiclassical cumulative reaction probabilities are compared to their quantum mechanical counterparts. The agreement between the two sets of results is fairly good. In particular, k-dependent, J-independent reaction thresholds found with quantum methods are reproduced by the quasiclassical calculations. The shift of these thresholds with increasing k, which has been previously attributed to the quantum bottleneck states taking part in the reaction, is revisited and discussed also in terms of the reaction stereodynamics.

Analysis of the H + D2 reaction mechanism through consideration of the intrinsic reactant polarisation.

The effect of reactant polarisation on the dynamics of the title reaction at collision energies up to 1.6 eV is analysed in depth. The analysis takes advantage of two novel theoretical concepts: intrinsic reaction properties and stereodynamical portraits. Exact quantum methods are used to determine the polarisation moments that quantify the intrinsic reactant polarisation at various levels of detail, including or not product state and/or scattering angle resolution. The data is then examined with the aid of stereodynamical portraits, which facilitate the rationalisation of the stereochemical effects that are relevant for the reaction dynamics. This allows for detailed characterisations of the so-called direct and delayed reaction mechanisms.

Mechanism and control of the F+H2 reaction at low and ultralow collision energies.

This article uses theoretical methods to study the dependence on stereodynamical factors of the mechanism and reactivity of the F+H2 reaction at low and ultralow collision energies. The impact of polarization of the H2 reactant on total and state-to-state integral and differential cross sections is analyzed. This leads to detailed pictures of the reaction mechanism in the cold and ultracold regimes, accounting, in particular, for distinctions associated with the various product states and scattering angles. The extent to which selection of reactant polarization allows for external control of the reactivity and reaction mechanism is assessed. This reveals that even the simplest of reactant polarization schemes allows for fine, product state-selective control of differential and (for reactions involving more than a single, zero orbital angular momentum partial wave) integral cross sections.

Use of a donor aortic cross for arterial reconstruction of the pancreaticoduodenal allograft.

Combined liver-pancreas procurement generally requires back bench reconstruction of the arterial blood supply with a donor Y-iliac graft to the pancreas graft. A modified vascular reconstruction that uses donor aortic cross including the brachiocephalic trunk and the left carotid artery as a single arterial patch is presented. This is useful when iliac grafts are unavailable or are being used as an alternative technique.

Cholelithiasis in cirrhotic patients. (Analysis of cholelithiasis among patients with liver cirrhosis in São Paulo, Brazil).

During the past 20 years, several authors have reported increased prevalence of cholelithiasis in liver cirrhosis. This biliary disease has been implicated with the deterioration of liver function, liver disease of alcoholic origin or even the presence of hypersplenism in this patient population. This study analyzes the incidence and possible factors which are responsible for promoting cholelithiasis in cirrhosis. The study included 110 cirrhotic patients of a private center specialized in treating liver diseases. The incidence of cholelithiasis was 27.3% (25.3% in males and 33.3% in females). There was no correlation between liver function defined by Child's classification or through the laboratory examinations (AST, ALT, AP, GGT, PT, Alb, TB, DB, PA) and the presence of gallstones. No evidence was found that the etiology of cirrhosis or the presence/absence of hypersplenism affected the prevalence of cholelithiasis in this population. In conclusion, an increased prevalence of cholelithiasis was verified in this population of cirrhotics but the pathogenesis is still obscure.

[Hepatic hemangioma. Analysis of 103 cases. Clinical considerations and imaging methods]. / Hemangiomas hepáticos. Análise de 103 casos. Considerações clínicas e dos métodos de imagem.

Hemangiomas are the most common benign vascular tumor found in the liver. In this study, 103 cases of hepatic hemangiomas were analysed in a retrospective manner. Image aspects such as those seen in ultrassonography, computed tomography, nuclear magnetic resonance and arteriography are discussed. The incidence was higher amongst the female sex, between individuals from 40 to 60 years old, which presented predominantly without symptoms (66%) and localized mainly in the right hepatic lobe (74%). The meaning of those aspects, when adopted, permits the clinicians to differentiate benign from malignant nodular lesions in the liver.

Laparoscopic cholecystectomy in cirrhotic patients.

Cholecystectomy in cirrhotic patients is commonly followed by high morbidity and mortality. In our study, laparoscopic cholecystectomy was performed in 12 cirrhotic patients (eight Child A and four Child B) in an effort to obtain lower complication and mortality rates. The mean age of the group was 51.8 years; seven of the 12 patients were men. Four patients had liver disease from virus B, five from virus C, one because of alcohol, and two had cryptogenic liver cirrhosis. The average operative time was 157 min. Intraoperative cholangiography could be performed in eight cases. No mortality or need to perform laparotomy occurred. Only one patient required blood transfusion (8.3%). Postoperative complications occurred in four patients, but these were easily controlled and included renal failure, diabetic impairment, hematoma with ascitic leakage through the wound, and wound abscess, one case each. No postoperative liver failure was observed. All patients walked and were refed in the first 24 h after surgery. They were dismissed in an average period of 2.5 days. Our primary view demonstrated that laparoscopic cholecystectomy was safe and well tolerated by selected cirrhotic patients (Child A and B) with clear indication for surgery.

[Pyogenic liver abscesses: analysis of 36 cases treated by percutaneous drainage]. / Abscessos piogênicos do fígado: análise de 36 casos tratados por punção percutânea.

Thirty-six patients with pyogenic liver abscess treated by percutaneous drainage plus antibiotic therapy were reviewed. The most frequent symptoms were fever (75%) and pain (72.2%), and the most common physical signs were liver enlargement (58.3%) and jaundice (33.3%). The mean time interval from admission to diagnosis was 16 days. CT scans and ultrasonography were diagnostic in 100% of the patients. The percutaneous drainage was effective in one attempt in 19 patients, two attempts in 8, three attempts in 8 patients and more than four attempts in only one patient. There were three patients with hemoperitoneum (8.7%) as a post-drainage complication, one of them needed to be treated surgically. Mean hospital stay was of 24.8 days and the mortality rate was 5.5%. Percutaneous drainage plus antibiotic therapy is then an efficient therapeutic approach to the treatment of pyogenic liver abscess.

Intestinal anastomoses.

Anastomotic dehiscence remains the main cause of morbidity and mortality of intestinal resections, mainly the colorectal (77, 95, 110). Very often in the literature the words dehiscence and fistula are misused for the same meaning. Nevertheless, attention must be paid to the fact that these two situations may be distinct. Dehiscence is defined as the failure of healing of the anastomoses, while fistula is the leakage of the intestinal content into the peritoneal cavity. So, the evidence of fistula is always accompanied by dehiscence, although a dehiscence may not develop into a fistula, should it be blocked by omentum or surrounding organs (110, 117). The incidence of overt dehiscence varies from 0.1% to 30% in the literature (13, 15, 17, 27, 31, 40, 44, 46, 76, 77, 81, 96, 113, 120, 123, 126, 133, 135). The Colon Cancer Project of the Saint Mary's Hospital in London, a multicentric study of patients submitted to bowel resections revealed a post operative mortality of 22% in patients with dehiscence and 7% for uncomplicated anastomoses. This led to the struggle various authors to achieve better results, regarding techniques and suture materials, such as the number of planes involved, inverted or everted sutures, wound healing and the influence of local and systemic factors, like infections, antibiotics, NSAIDs on sutures. Recently, surgical stapling gained importance among surgeons, due to its technical advantages. However, this is still very controversial and must undergo further investigations (93, 107, 109, 112, 115, 116). So, in order to understand the pathophysiology of the complications and to reduce morbidity and mortality, related to intestinal anastomoses, it is necessary to study the events involved in intestinal healing after resection, as well as the technique, materials used and the factors related to anastomotic failure.

[Immunological parameters in the differential diagnosis of ascites secondary to peritoneal carcinomatosis, hepatic cirrhosis, and congestive heart failure]. / Parâmetros imunológicos no diagnóstico differencial de ascite secundária à carcinomatose peritoneal, cirrose hepática e insuficiência cardíaca congestiva.

As a contribution to the study of ascites in patients with liver cirrhosis, congestive heart failure and peritoneal carcinomatosis evaluate in serum and ascites the concentrations of alphafetoprotein, carcinoembryonic antigen and fibronectin, they might suggest a diagnosis for the basic pathology. Forty-seven patients were studied, from whom 23 with cirrhosis, 17 peritoneal carcinomatosis and 7 with congestive heart failure. We conclude that: a) none of the tools usually employed in the analysis of ascitic fluid alone can make the base pathological process responsible for producing ascites; b) fibronectins were more useful for differential diagnosis between cirrhosis and carcinomatosis; c) alpha-fetoprotein and carcinoembryonic antigen were not useful for the definition for differential diagnosis.

[Hepatic hemangiomas. The importance of the image]. / Hemangiomas hepáticos. Importância da imagem.

In the authors' experience, 0.24% of the patients submitted to liver imaging (ultrasound or computerized tomography) have hemangiomas. These are shown as solid nodular lesions, mostly found by chance. Sometimes they do not appear as typical solid vascular lesions. The authors' experience and the literature are discussed. A clear and concise approach to this benign neoplasm is suggested.

Prognostic value of preoperative tests in the surgical treatment of ascites with the implant of Le Veen shunts in cirrhotics.

In the period of January 1978 to October 1988, 32 Le Veen shunts (LVS) were implanted in 20 patients, out of which 16 were alcoholic cirrhotics and 4 postnecrotic cirrhotics. In the present study, we correlated preoperative laboratory data of these patients with their postoperative evolution, comparing the clinical results of patients who survived more than 30 days (13 patients = 65%) with the results of those who died within the same period (7 patients = 35%). For that matter, 14 laboratory tests were performed in order to measure the serum levels of hematocrit, hemoglobin, urea, creatinine, sodium, potassium, bilirubin, albumin, AST, ALT, alkaline phosphatase, fibrinogen, gamma GT and prothrombin activity. After statistical analysis, we observed that 6 of the 14 tests performed could be considered of prognostic value in the following decreasing order of importance: fibrinogen, alkaline phosphatase, prothrombin activity, urea, gamma GT and bilirubin. We observed that all the 7 patients who died prematurely presented 3 or more of these levels altered, when compared with standard values. Based on these data, we concluded that serum levels of fibrinogen, alkaline phosphatase, urea, gamma GT, bilirubin and activity of prothrombin proved to be important factors in determining the prognosis of immediate survival in cirrhotic patients who underwent LVS implantation. We also concluded that when 3 or more of these factors are altered, the implant of LVS is contraindicated, whatever clinical criteria for indication and contraindication were taken into account.