Dynamics in physisorbed monolayers of 5-alkoxy-isophthalic acid derivatives at the liquid/solid interface investigated by scanning tunneling microscopy

Monolayers of isophthalic acid derivatives at the liquid/solid interface have been studied with scanning tunneling microscopy (STM). We have investigated the dynamics related to the phenomenon of solvent co-deposition, which was previously observed by our research group when using octan-1-ol or undecan-1-ol as solvents for 5-alkoxy-isophthalic acid derivatives. This solvent co-deposition has now been visualized in real-time (two frames per second) for the first time. Dynamics of individual molecules were investigated in mixtures of semi-fluorinated molecules with video-STM. The specific contrast arising from fluorine atoms in STM images allows us to use this functionality as a probe to analyze the data obtained for the mixtures under investigation. Upon imaging the same region of a monolayer for a period of time we observed that non-fluorinated molecules progressively substitute the fluorinated molecules. These findings illustrate the metastable equilibrium that exists at the liquid/solid interface, between the physisorbed molecules and the supernatant solution.

Scanning tunneling microscopy: a unique tool in the study of chirality, dynamics, and reactivity in physisorbed organic monolayers.

Scanning tunneling microscopy (STM) is applied to study organic monolayers, physisorbed at the liquid-graphite interface. Due to the very local nature of the probing, the structure of these adlayers has been imaged with very high detail. The high resolution allowed us to investigate the effect of molecular chirality on the monolayer formation and provided a unique way to study chemical reactions at the liquid-graphite interface. Making use of a fast scanning mode, dynamic processes in these adlayers have been visualized.

In utero treatment of toxoplasmic fetopathy with the combination pyrimethamine-sulfadiazine.

The mothers of 52 fetuses with toxoplasma fetopathy diagnosed in utero were treated with a combination pyrimethamine-sulfa drug and spiramycine. Their infants were compared to a group of 51 infants whose mothers had received spiramycine alone. Postnatal treatment was identical in both groups. Parasitological investigation of the placenta was positive in 42 and 76.6%; the newborns had a specific IgM of 17.4 and 69% in groups 1 and 2, respectively. These differences were significant. The mean specific IgG titer was significantly reduced at birth and at 4-6 months of age in group 1. According to the results obtained in the present material the pyrimethamine-sufa drug combination, given to the mothers of fetuses infected with toxoplasma, has a significant effect on the parasitological and serological signs of evolutive fetopathy. It did not significantly alter the clinical pattern, probably because the onset of treatment was too long after maternal infection.

[Fetal toxoplasmosis. In utero treatment with pyrimethamine sulfamides]. / Foetopathie toxoplasmique. Traitement in utero par l'association pyriméthamine-sulfamides.

The mothers of 52 cases of toxoplasmic fetopathy diagnosed in utero by fetal blood and/or amniotic fluid sampling were treated with the combination pyrimethamine-sulfadiazine (or sulfisoxazole) and by spiramycine. The infants were compared with 51 other infants with congenital toxoplasmosis whose mothers had received spiramycine alone. Patients of both groups received the same pyrimethamine-sulfadiazine and spiramycine treatment after birth. Parasitologic examination of the placenta was positive in 42 and 76.6% of patients, in group I and group II respectively. The newborns had specific IgM in 17.4 and 69.2% of cases respectively in both groups. These differences were significant. The mean specific IgG titer was significantly reduced at birth and 4 to 6 months of age in the first group. Patients in group I had more often subclinical infection than patients of the comparison group: 57% vs 33.3%. They had less often a high cerebro-spinal protein content during the first week. Prenatal treatment with pyrimethamine-sulfadrugs resulted in a less progressing infection at birth. However in cases with clinically patent toxoplasmosis, the frequency of overt localizations and their sequellae was not significantly altered. This might be related to a relatively late onset of the treatment. The pyrimethamine-sulfadrug combination given to mothers of proved infected fetuses can be rewarding. The indication might be extended to well-documented seroconverted mothers if, in the future, the acquired experience and necessary pharmacological studies bring the proof of its innocuousness.

Catabolism of bis(5'-nucleosidyl) oligophosphates in Escherichia coli: metal requirements and substrate specificity of homogeneous diadenosine-5',5'''-P1,P4-tetraphosphate pyrophosphohydrolase.

Diadenosine-5',5'''-P1,P4-tetraphosphate pyrophosphohydrolase (diadenosinetetraphosphatase) from Escherichia coli strain EM20031 has been purified 5000-fold from 4 kg of wet cells. It produces 2.4 mg of homogeneous enzyme with a yield of 3.1%. The enzyme activity in the reaction of ADP production from Ap4A is 250 s-1 [37 degrees C, 50 mM tris(hydroxymethyl)aminomethane, pH 7.8, 50 microM Ap4A, 0.5 microM ethylenediaminetetraacetic acid (EDTA), and 50 microM CoCl2]. The enzyme is a single polypeptide chain of Mr 33K, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and high-performance gel permeation chromatography. Dinucleoside polyphosphates are substrates provided they contain more than two phosphates (Ap4A, Ap4G, Ap4C, Gp4G, Ap3A, Ap3G, Ap3C, Gp3G, Gp3C, Ap5A, Ap6A, and dAp4dA are substrates; Ap2A, NAD, and NADP are not). Among the products, a nucleoside diphosphate is always formed. ATP, GTP, CTP, UTP, dATP, dGTP, dCTP, and dTTP are not substrates; Ap4 is. Addition of Co2+ (50 microM) to the reaction buffer containing 0.5 microM EDTA strongly stimulates Ap4A hydrolysis (stimulation 2500-fold). With 50 microM MnCl2, the stimulation is 900-fold. Ca2+, Fe2+, and Mg2+ have no effect. The Km for Ap4A is 22 microM with Co2+ and 12 microM with Mn2+. The added metals have similar effects on the hydrolysis of Ap3A into ADP + AMP. However, in the latter case, the stimulation by Co2+ is small, and the maximum stimulation brought by Mn2+ is 9 times that brought by Co2+. Exposure of the enzyme to Zn2+ (5 microM), prior to the assay or within the reaction mixture containing Co2+, causes a marked inhibition of Ap4A hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)