Ultrasound assisted cleaning of ceramic capillary filter.

Research in the fields of filtration and dewatering connected with the use of ultrasound (US) has been carried out mainly with small laboratory-scale batch or continuously operating devices. So far the only large scale industrial cake filtration applications have been developed and manufactured by Larox Oyj for mining industry. These applications apply ultrasound for cleaning of ceramic capillary action elements having at maximum total filtration area of approximately 150 m(2). Several hundreds of filter units have been delivered worldwide during the past two decades.

Enzymatic synthesis of dipeptide units of the D-D-configuration in aqueous media.

The enzymatic synthesis of dipeptide units of the D-D-configuration in aqueous media, catalysed by muramoyl-pentapeptide carboxypeptidase (E.C.3.4.17.8), is described. Ac-L-Lys(Ac)-D-Ala-D-Lac-OH and Ac-D-Ala-OMe were used as acyl-components. Neutral, basic, and hydrophobic amino acids acting as nucleophiles were incorporated. The enzyme is stereospecific in that only the D-enantiomers of amino acids or amino acid derivatives were incorporated. As nucleophiles, the unmodified amino acids resulted in higher product yields compared with using the corresponding amino acid derivatives. Product yields ranged from 40 to 87%.

The synthesis of an active derivative of cyclomaltoheptaose for the hydrolysis of esters and the formation of amide bonds.

The synthesis is described of a derivative of cyclomaltoheptaose (beta-cyclodextrin) to which the tripeptide Ser-His-Asp, the catalytic triad found in chymotrypsin, has been coupled. The derivative enhanced the rates of hydrolysis of activated esters, as measured by the release of p-nitrophenol, and the formation of amine bonds.

Molecular imprinting of amino acid derivatives at low temperature (0 degrees C) using photolytic homolysis of azobisnitriles.

Molecular imprints of L-phenylalanine anilide (print molecule) were prepared using a number of free radical initiation systems. Polymers were prepared using azobisnitriles as either thermal initiators or photoinitiators at temperatures ranging from 0 to 60 degrees C and evaluated in the high-performance liquid chromatographic mode for enantioselectivity. The results show that preparation of molecular imprints at 0 degrees C using photolytic homolysis of azobisnitriles significantly increases enantioselectivity and allows separations of the enantiomers of the print molecule to be performed at room temperature. This compares to previous reports of molecular imprints where separations needed to be performed at elevated temperatures (80-90 degrees C). The present method is also easier to perform and less time-consuming than those previously described.

Binding of oxytocin to uterine cells in vitro. Occurrence of several binding site populations and reidentification of oxytocin receptors.

Myometrial and endometrial cells of sheep, rat, and calf in monolayer cell culture display at least three populations of binding sites for oxytocin, with dissociation constants (Kd) of approximately 5 X 10(-9), 4 X 10(-7), and greater than 10(-5) mol/liter, respectively. Binding of the tritium-labeled oxytocin (concentration range, 10(-11) to 5 X 10(-4) M) to the first two sites is displaceable by cold oxytocin. The ratio of binding capacities of the high to medium affinity site appears to average 1:18. Dissociation rate constants for these sites (22 degrees C) are roughly 10(-4) and 2 X 10(-3) s-1, respectively. The capacity of the low affinity site varies in individual cell preparations and is between 5 and 66 times that of the medium affinity site. The low affinity binding sites may not be fully saturable and may follow a nonasymptotic binding isotherm. Logarithms of Kd and binding capacity for individual binding sites are linearly correlated. The coexistence of the three sites was also proven by cluster analysis based on similarities between Kd, binding capacity, and Hill coefficient. Only minor systematic species and cell type differences occur in these properties. The value of Kd for the oxytocin receptor in rat myometrium, derived recently from a stepwise irreversible inhibition of uterotonic response to oxytocin, is close to 2.5 X 10(-7) mol/liter. Additional pharmacological data (pA2 values of structural analogues of oxytocin acting as competitive inhibitors) also reveal a Kd value of 3 X 10(-7). It is, therefore, concluded that the receptors for oxytocin in rat myometrium are identical with the medium affinity site.

Histidine racemization in the synthesis of an analog of the luteinizing hormone releasing factor. Investigation by HPLC and enzymatic methods.

To investigate histidine racemization in the synthesis of a LHRH analog, (D-Trp)6-LHRH2-10 was built up by stepwise elongation of the sequence 3-10 using the solid phase technique on a 1% cross-linked chloromethyl polystyrene. For the whole synthesis the tert.-butyloxycarbonyl (BOC) group was used for temporary N-terminal protection. To protect the pi-nitrogen in histidine the benzyl-oxymethyl (BOM) group was utilized. The condensation position in the (D-Trp)6-LHRH analog was chosen so as to be able to investigate the racemization of histidine. We coupled BOC-His(BOM) with the (D-Trp)6-LHRH3-10 fragment using three different activating agents, mixed anhydride, carbonyldiimidazole (1 equiv.)/1-hydroxybenzotriazole (2 equiv.) and dicyclohexylcarbodiimide/1-hydroxybenzotriazole. The racemization was investigated by enzymatic digestion and by HPLC. For HPLC, (D-His(BOM)2-(D-Trp)6-LHRH2-10 was also synthesized. It could be proved that practically no racemization occurs during the actual peptide synthesis. The small amount (1%) of D-histidine found is due to racemization in the synthesis of BOC-His(BOM).