Phase equilibrium of binary mixtures of cyclic ethers + chlorobutane isomers: experimental measurements and SAFT-VR modeling

The phase equilibria (experimental and modeled) of eight binary mixtures each formed by a cyclic ether (1,3-dioxolane or 1,4-dioxane) and a chlorobutane isomer (1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, or 2-chloro-2-methylpropane) are presented. New experimental vapor-liquid equilibrium data at isothermal conditions (298.15, 313.15, and 328.15 K) has been obtained, and the statistical associating fluid theory for potentials of variable range (SAFT-VR) is used to model the mixtures. The results are discussed in terms of both the molecular characteristics of the pure compounds and the unlike intermolecular interactions present in the mixtures. The SAFT-VR approach is first used together with standard combining rules without adjustable parameters in order to predict the phase behavior at isothermal conditions. Good agreement between experiment and the prediction is found with such a model. Mean absolute deviations for pressures lie between 1 and 3 kPa, while for vapor phase compositions are less than 0.03 in mole fraction. However, a better agreement, can be obtained by introducing one adjustable parameter kij, which modifies the strength of the dispersion interaction between unlike components in the mixtures. This parameter is adjusted so as to model the phase equilibrium of the whole family of mixtures studied here at isothermal and isobaric conditions. We find that a unique unlike parameter kij is valid for all the studied mixtures and it is not temperature or pressure dependent. This unique transferable parameter together with the SAFT-VR approach provide a description of the vapor-liquid equilibrium of the mixtures that is in excellent agreement with the experimental data. In this case, the absolute deviations are of the order of 0.001 in mole fraction for vapor-phase compositions and less than 1 kPa for pressure.

Clinical significance of persistent left superior vena cava diagnosed in fetal life

OBJECTIVES

To determine the prevalence and clinical significance of persistent left superior vena cava (PLSVC) in fetuses with and without cardiac and extracardiac anomalies.

METHODS

Charts and recorded images were reviewed from high-risk patients who underwent fetal echocardiography between January 2000 and December 2005. This retrospective study included 54 fetuses with confirmed PLSVC who were diagnosed based on the presence of an additional vessel identified to the left of the pulmonary artery in the three-vessel view of the heart. Associated congenital heart defects (CHDs), extracardiac abnormalities, including first trimester nuchal translucency (NT) thickness, and fetal/postnatal outcome were analyzed.

RESULTS

Of 5,737 referrals, 5,233 had a normal heart, and PLSVC was observed in 10 of these fetuses (0.2%; Group 1). CHDs were present in 504 and PLSVC was observed in 44 of these cases (9%). In the latter group, 18/44 (41%) fetuses had heterotaxy syndrome (Group 2) where the most common structural heart defects were atrioventricular septal defect and double-outlet right ventricle. Fetuses without heterotaxy syndrome (Group 3) accounted for 26/44 (59%) cases of CHDs associated with PLSVC. In this group of fetuses the most common CHDs were left outflow tract obstructive defects and conotruncal anomalies. Increased NT was observed in 29%, without differences among the three groups. The survival rates among fetuses in Groups 1, 2 and 3 were 100%, 44% and 50%, respectively. After excluding patients who underwent pregnancy termination, there were no significant differences in the survival rates among the groups, probably due to the small size of the samples. CONCLUSIONS PLSVC is associated with CHDs. The identification of PLSVC should prompt a thorough examination of the fetus to identify additional cardiac and extracardiac anomalies. The prognosis of affected fetuses largely depends on whether or not the PLSVC is associated with a CHD.

Investigation of the Salting Out of Methane from Aqueous Electrolyte Solutions Using Computer Simulations

We calculate the excess chemical potential of methane in aqueous electrolyte solutions of NaCl using Monte Carlo computer simulations. In a recent work [Docherty et al. J. Chem. Phys. 2006, 125, 074510], we presented a new potential model for methane in water which is capable of describing accurately the excess chemical potential of methane in pure water over a range of temperatures, a quantity that can be related to the solubility and which is commonly used to study the hydrophobic effect. Here, we use the same potential model for the water-methane interactions and investigate the effect of added salt on the chemical potential of methane in the solution. The methane molecules are modeled as single Lennard-Jones (LJ) interaction sites, and the water molecules are modeled with the TIP4P/2005 model. A correcting factor of chi = 1.07 for the energetic Berthelot (geometric) combining rule of the methane-water interaction is also used, which mimics the polarization of methane in water. We consider NaCl as the salt and treat the ions with the Smith and Dang model (i.e., as charged LJ interaction sites). Ion-water, ion-ion, and ion-methane interactions are treated using Lorentz-Berthelot combining rules. In addition, the Coulombic potential is used to model charge-charge interactions which are calculated using the Ewald sum. We have carried out isobaric-isothermal (NpT) simulations to determine the equilibrium densities of the solutions. The simulation data is in excellent agreement with experimental densities of aqueous NaCl solutions of different concentration. Hydration numbers are also obtained and found to be in agreement with reported data. Canonical (NVT) simulations at the averaged densities are then performed using the Widom test-particle insertion method to obtain the excess chemical potential of methane in the saline solutions. An increase in the chemical potential of methane, corresponding to a salting out effect, is observed when salt is added to the solution. We investigate different concentrations and ion sizes. An overprediction of the salting out effect as compared with experimental data is observed, which we believe is due to the polarizing effect of the ions in the solution, which is not taken into account by the model. We also find a direct correlation between the increase in the chemical potential and the packing fraction of the solution and argue that the main cause of the observed salting out effect (as represented by an increase in the excess chemical potential) is the increase in the packing fraction of the solutions due to the added salt. Together, with this, we put forward an argument toward explaining the anomalous Hofmeister effect of Li(+).

[Role of malnutrition in intestinal anastomosis collagenization: an analysis of procollagen (PINP) and carboxyterminal telopeptide (ICTP) by radioimmunoassay]

INTRODUCTION

some clinical, anatomo-pathological, and technical factors influence the correct healing of intestinal suture following an intestinal resection. One of the most influential factors is patient nutritional status.

OBJECTIVES

to evaluate the influence of malnutrition on the viability of primary intestinal anastomosis by the analysis of collagen I deposition.

METHODS

40 Wistar rats, radioimmunoassay material. We used 2 groups of rats, 20 animals in each group: a control group (A) and a "malnutrition" group (B).

RESULTS

there was a decrease in PINP (procollagen) deposition in the colon of group B rats as compared to the colon of group A (0.3620 and 0.4340 mg/g respectively) (p = 0.032). There is an increase in ICTP (carboxyterminal telopeptide) in the colon of group B (0.9545 as against 0.8460 mg/g in group A) (p = 0.875). In anastomoses of group B there was a decrease in PINP synthesis as compared to group A (0.376 and 0.468 mg/g respectively, p = 0.002). As regards ICTP, there was an increase in group B (p = 0.330). In relation to the control group no differences were observed in ICTP increases in group B (p = 1).

CONCLUSIONS

colonic anastomosis increases the levels of PINP and ICTP in healed tissue (p = 0.000); malnutrition reduces collagenization in anastomoses (p = 0.000).

Surface ordering and capillary phenomena of confined hard cut-sphere particles

Isothermal-isobaric and Gibbs ensemble Monte Carlo (GEMC) computer simulations of = 1500 and = 3000 hard cut spheres of aspect ratio / = 0.1, respectively, are carried out in order to investigate the effects of confinement on the isotropic (I)-nematic (N) phase transition. We first consider the free system, and confirm the stabilisation of isotropic (I), nematic (N) and columnar (Col) states. We examine in detail the I-N transition and find coexistence densities of =0.355 and =0.368. A slab geometry is then considered for two types of walls: a hard wall, which excludes the particles entirely, and an 'adsorbent' wall which excludes the centre of mass of the particles. The adsorbent wall is found to favour planar (edge-on) alignment, which results in the formation of a first layer of adsorbed molecules, which then acts as a rough hard wall for subsequent particles, and promotes disordered states. Using Gibbs ensemble simulations we determine the capillary phase diagram of the system, and the adsorption as a function of pore width. The capillary phase diagram obtained from Gibbs ensemble simulations corresponds to one with a first-order capillary isotropisation transition, with an associated capillary critical point for a wall separation of ∼3. The hard walls are seen to promote homeotropic (face-on) alignment of the cut spheres, and promote the stabilisation of the nematic phase. In this case the capillary phase diagram obtained from the GEMC simulations exhibits a first-order capillary nematisation transition, and a capillary critical point for a wall separation of ∼4.

Prenatal management of placental chorioangioma: value of the middle cerebral artery peak systolic velocity

Placental chorioangiomas are benign tumors of the placenta. Large chorioangiomas may cause severe complications such as fetal anemia, hydrops and fetal death. We report the use of sonographic findings and peak systolic velocity in the middle cerebral artery in the diagnosis and management of fetal anemia without the occurrence of hydrops fetalis in a pregnant woman with a large placental chorioangioma. Successful intrauterine blood transfusion was performed at 26 weeks. Spontaneous thrombosis of the main supplying blood vessel of the chorioangioma was detected at 33 weeks. The child was delivered at 39 weeks of pregnancy in normal clinical condition.

A potential model for methane in water describing correctly the solubility of the gas and the properties of the methane hydrate

We have obtained the excess chemical potential of methane in water, over a broad range of temperatures, from computer simulation. The methane molecules are described as simple Lennard-Jones interaction sites, while water is modeled by the recently proposed TIP4P/2005 model. We have observed that the experimental values of the chemical potential are not reproduced when using the Lorentz-Berthelot combining rules. However, we also noticed that the deviation is systematic, suggesting that this may be corrected. In fact, by introducing positive deviations from the energetic Lorentz-Berthelot rule to account indirectly for the polarization methane-water energy, we are able to describe accurately the excess chemical potential of methane in water. Thus, by using a model capable of describing accurately the density of pure water in a wide range of temperatures and by deviating from the Lorentz-Berthelot combining rules, it is possible to reproduce the properties of methane in water at infinite dilution. In addition, we have applied this methane-water potential to the study of the solid methane hydrate structure, commonly denoted as sI, and find that the model describes the experimental value of the unit cell of the hydrate with an error of about 0.2%. Moreover, we have considered the effect of the amount of methane contained in the hydrate. In doing so, we determine that the presence of methane increases slightly the value of the unit cell and decreases slightly the compressibility of the structure. We also note that the presence of methane increases greatly the range of pressures where the sI hydrate is mechanically stable.

Prenatal diagnosis and outcome for fetuses with congenital absence of the pulmonary valve

OBJECTIVES

To analyze fetal echocardiographic findings of absent pulmonary valve syndrome (APVS), its association with chromosomal and extracardiac anomalies including nuchal translucency (NT) and the outcome after diagnosis.

METHODS

Data of 14 fetuses with confirmed APVS retrospectively collected in two tertiary referral centers between 1998 and 2004 were analyzed. The variables examined were: reason for referral, gestational age at diagnosis and associated abnormalities, including first trimester NT thickness. Cardiac evaluation included measurement of cardiothoracic ratio, diameter of pulmonary arteries and Doppler flow in the pulmonary trunk. Information was retrieved from clinical files, recorded videotapes and stored images. Karyotyping including examination for the 22q11 deletion was performed in all cases.

RESULTS

Mean gestational age at diagnosis was 28 weeks, with 5/14 (36%) diagnosed before 22 weeks. In 13/14 (93%) there was an associated ventricular septal defect (subaortic in 12 fetuses and inlet-type in one) and all 13 had tetralogy of Fallot. Enlargement of the central pulmonary arteries and cardiomegaly were present in all cases diagnosed after 22 weeks. Of the five fetuses in which APVS was detected before 22 weeks, four (80%) had a normal pulmonary trunk diameter, two (40%) had normal pulmonary branches and three (60%) had normal cardiac size. The arterial duct was absent in 11/14 (79%). A correlation between presence of the arterial duct and the size of the central pulmonary arteries or cardiomegaly could not be established. Increased NT was observed in 4/10 cases (40%) for which this information was available. 22q11 microdeletion was diagnosed in three fetuses (21%). There were five terminations of pregnancy, one intrauterine death, five neonatal deaths and one infant death. Of the six neonates with respiratory distress, only one (17%) survived and of the eight babies in whom there was an intention to treat, two survived (25%).

CONCLUSIONS

APVS can be accurately diagnosed by fetal echocardiography but screening ultrasound in the mid-second trimester is likely to have a low detection rate, probably due to the incomplete expression of the disease at this point. Many fetuses with APVS have an increased NT in the first trimester and this may help an earlier recognition of the defect. The most common associated karyotype anomaly is 22q11 microdeletion. Enlargement of the central pulmonary arteries is mainly related to the gestational age at diagnosis. Our results confirm that the outlook for these patients is extremely poor.

Pulmonary balloon valvuloplasty in a fetus with critical pulmonary stenosis/atresia with intact ventricular septum and heart failure

Outcome of fetuses with critical pulmonary stenosis (critical PS) or atresia of the pulmonary valve (PA) with intact ventricular septum (IVS) is closely related with right ventricle hypoplasia and its consequent hemodynamics. Fetal echocardiography not only allows early detection of this condition but also monitors its normally unfavorable evolution. These cases may benefit from intrauterine intervention relieving outflow tract obstruction in order to achieve a biventricular circulation. Successful valvuloplasty of the pulmonary valve was performed in a fetus with critical PS-IVS and heart failure at 25 weeks. After the procedure there was a significant improvement in fetal hemodynamics. Follow-up scans at 34 weeks detected a significant restenosis with signs of circulatory failure leading to premature delivery of the baby. An immediate postnatal valvuloplasty successfully completed the ultimate objective of biventricular repair. Fetal pulmonary valvuloplasty is feasible and may change the natural history of the disease in fetuses with critical PS-IVS.

Typical isolated ectrodactyly of hands and feet: early antenatal diagnosis

Ectrodactyly is a rare dominant autosomal malformation with variable expression. Herein we report a case early diagnosed by ultrasound at 15 weeks of gestation of isolated ectrodactyly involving the four limbs. The sonographic findings were bilateral split hands and split foot. Diagnosis of typical isolated ectrodactyly was pathologically confirmed. Clinical forms, pathogenesis, differential diagnosis, and early prenatal diagnosis are discussed.

Nematic-nematic phase separation in binary mixtures of thick and thin hard rods: results from Onsager-like theories

The fundamental nature of the nematic-nematic phase separation in binary mixtures of rigid hard rods is analyzed within the Onsager second-virial theory and the extension of Parsons and Lee which includes a treatment of the higher-body contributions. The particles of each component are modeled as hard spherocylinders of different diameter , but equal length . In the case of a system which is restricted to be fully aligned (parallel rods), we provide an analytical solution for the spinodal boundary for the limit of stability of demixing; only a single region of coexistence bounded at lower pressures (densities) by a critical point is possible for such a system. The full numerical solution with the Parsons-Lee extension also indicates that, depending on the length of the particles, there is a range of values of the diameter ratio where the phase coexistence is closed off by a critical point at lower pressure. A second region of coexistence can be found at even lower pressures for certain values of the parameters; this region is bounded by an "upper" critical point. The two coexistence regions can also merge to give a single region of coexistence extending to very high pressure without a critical point. By including the higher-order contributions to the excluded volume (end effects) in the Onsager theory, we prove analytically that the existence of the lower critical point is a direct consequence of the finite size of the particles. A new analytical equation of state is derived for the nematic phase using the Gaussian approximation. In the case of Onsager limit (infinite aspect ratio), we show that the phase behavior obtained using the Parsons-Lee approach substantially deviates from that with the Onsager theory for the transition due to the nonvanishing third and higher order virial coefficients. We also provide a detailed discussion of the phase behavior of recent experimental results for mixtures of thin and thick rods of the same length, for which the Onsager and Parsons-Lee theories can provide a qualitative description.

Density functional theory and simulation of the columnar phase of a system of parallel hard ellipsoids with attractive interactions

A simple molecular model consisting of parallel hard oblate ellipsoids with superimposed square-well attractive interactions of variable range is considered for the study of the phase behavior of thermotropic discotic molecules. A density functional theory appropriate for nonuniform fluids is formulated in which the hard-core contributions to the free energy are treated within a nonlocal weighted-density approximation (WDA) while the attractive contributions are treated at a mean-field level. It is shown that the columnar phase becomes stable relative to the nematic phase at fluid densities for a range of values of the range of the attractive well. In these cases, the region of stability of the columnar phase is bounded at high temperatures by a nematic-columnar-solid triple point. The calculations show that if the attractions are made too long ranged (lambda/D> or approximately =0.84 for particles of aspect ratio of L/D=0.1, where lambda/D is the range of the attractive interaction in units of the molecular diameter D), columnar ordering becomes unstable and the nematic phase dominates at all fluid densities. It is shown that columnar ordering is also predicted when the density functional theory is supplemented with the smoothed-density approximation (SDA). Computer simulations have also been carried out for a particular choice of model parameters; our simulation data confirm the stabilization of the hexagonal columnar phase between the solid and nematic phases. A comparison with simulation data allows us to conclude that the WDA provides a fairly good description of the columnar phase and very good agreement for the nematic-columnar transition properties. On the other hand, our calculations show that the SDA largely underestimates the transition pressure and predicts a too-strongly first-order nematic-columnar transition

Use of a hydrocapillary dressing in the management of highly exuding ulcers: a comparative study

OBJECTIVE

To evaluate the safety and performance of Alione Hydrocapillary dressing (Coloplast A/S) in the management of highly exuding chronic venous leg ulcers and compare it with two hydropolymer dressings,Tielle and Tielle Plus (Johnson & Johnson).

METHOD

A comparative clinical trial was conducted on 97 patients with an ankle brachial pressure index > or = 0.8 and a highly exuding leg ulcer. Ulcer duration was at least four weeks. Treatment continued until healing or for a maximum of 12 months.

RESULTS

There was no statistically significant difference in healing time or wound area reduction between the two treatment protocols. The test dressing (Alione Hydrocapillary) had better absorption capacity and was more comfortable for the patients than the comparator dressings (Tielle/Tielle Plus) and adhered less to the wound bed.Also, more patients preferred the test dressing to their previous treatment. Although severe leakage and maceration were observed more frequently in the comparator group compared with the test group, this was not statistically significant.

CONCLUSION

Both treatment protocols were safe and effective in treating highly exuding chronic venous leg ulcers. The test dressing performed as well as or better than the comparator dressings for all study parameters and more patients preferred the test dressing to their previous dressing compared with the comparator dressings.