Temperaturabhängigkeit der ammoniak-diffusion in polymerfilmen

The temperature dependence of the diffusion of ammonia is studied by a new absorption spectroscopic method in 14 transparent filmforming polymers in the range from 15 to 90°C. A linear free-energie-relationship between the activation energy of the diffusion (E_D) and the preexponential factor (D₀) in the Arrhenius-equation corresponds to the behaviour of permanent gases in the glassy state of polymers, but the diffusion coefficients are approximately one order of magnitude lower. A comparison in the activation energies for the diffusion of oxygen and ammonia in three polymers shows that this is due to the decreased activation entropy rather than to a larger Van-der-Waals diameter.     

Effects of Extrusion Temperature and Plasticizers on the Physical and Functional Properties of Starch Films

Cornstarch, at 20% moisture content (dry basis, d.b.), was mixed with glycerol at 3:1 ratio to form the base material for extruded starch films. Stearic acid, sucrose and urea, at varying concentrations, were tested as secondary plasticizers for the starch‐glycerol mixture. The ingredients were extruded at 110 and 120°C barrel temperatures to determine the effects of extrusion temperature, plasticizer type and their concentrations on the film‐forming characteristics of starch, as well as their effects on selected physical and functional properties of the films. The physical and mechanical properties of the films were studied by scanning electron microscopy (SEM) and tensile testing, while the glass transition and gelatinization properties were analyzed using differential scanning calorimetry (DSC). The interactions between the functional groups of starch and plasticizers were investigated using Fourier‐transform infrared (FTIR) spectroscopy. The water vapor permeability (WVP) properties of starch films were determined using ASTM standard E96‐95. Scanning electron micrographs exhibited the presence of native and partially melted starch granules in the extruded films. The tensile stress, strain at break and Young's modulus of starch films ranged from 0.9 to 3.2 MPa, 26.9 to 56.2% and 4.5 to 67.7 MPa, respectively. DSC scans displayed two glass transitions in the temperature ranges of 0.1 to 1°C and 9.6 to 12°C. Multiple melting endotherms, including that of amylose‐lipid complexes, were observed in the thermoplastic extrudates. The gelatinization enthalpies of the starch in the extruded films varied from 0 to 1.7 J/g, and were dependent largely on the extrusion temperature and plasticizer content. The shift in the FTIR spectral bands, as well as the appearance of double‐peaks, suggested strong hydrogen bonding interactions between the starch and plasticizers. The WVP of starch films ranged from 10.9 to 15.7 g mm h^‐1 m^‐2 kPa^‐1, depending on the extrusion temperature and the type of plasticizer used.     

Neonatal blood pressures

Arterial blood pressures were taken by the Doppler ultrasound method in 134 unselected mature neonates (birthweights 2,600-3,900 grams) who were managed in the same manner after birth. Blood pressures were measured at 3-5, 10 and 30 minutes of life and, if indicated, intermittently during the next 24-48 h. Left and right arm pressures were identical or differed by only 1-2 mm Hg. Lower than normal blood pressures were found in 4 groups of infants: those born by cesarean section, those recovering from intrauterine asphyxia, those exposed to maternal anti-hypertensive therapy, and those whose mothers received thiopental within four minutes of delivery. Return of the low pressures to within the normal range was fastest following thiopental induction in the absence of fetal asphyxia and slowest after antihypertensive therapy.     

Extreme catalysts from low-temperature environments

Cold-loving or psychrophilic organisms are widely distributed in nature as a large part of the earth's surface is at temperatures around 0 degrees C. To maintain metabolic rates and to prosper in cold environments, these extremophilic organisms have developed a vast array of adaptations. One main adaptive strategy developed in order to cope with the reduction of chemical reaction rates induced by low temperatures is the synthesis of cold-adapted or psychrophilic enzymes. These enzymes are characterized by a high catalytic activity at low temperatures associated with a low thermal stability. A study of protein adaptation strategies suggests that the high activity of psychrophilic enzymes could be achieved by the destabilization of the active site, allowing the catalytic center to be more flexible at low temperatures, whereas other protein regions may be destabilized or as rigid as their mesophilic counterparts. Due to these particular properties, psychrophilic enzymes offer a high potential not only for fundamental research but also for biotechnological applications.     

Initial steps of the metal-catalysed degradation of L-dehydroascorbic acid in acidic aqueous solutions

The initial steps of the degradation of L-de- hydroascorbic acid (L-DHA) in acidic aqueous solutions and the catalytic effect of different transition metal ions on this reaction were studied. The main product was identified as 3,6-furanosido-2,3-hexodiulosonic acid-2-hydrate (compound I) by GLC-MS and ¹³C-NMR, formed by lactone hydrolysis and hydration of the carbonyl group in the C-2 position of L-dehydroascorbic acid. In addition, number of other compounds were detected; they are formed from compound I by simple enolisation, lactonisation, hydration and dehydration reactions as well as by cleavage and formation of cyclic half acetal bonds. The chemical structures of these compounds were tentatively deduced by the mass spectra of their TMS derivatives and a reaction scheme for their formation is proposed. The velocity and the direction of the reactions were found to be strongly influenced by the presence of catalytic amounts of different transition metal ions. It was concluded that in acidic medium, in contrast to the situation in neutral and alkaline solutions, the opening of the lactone ring of L-DHA is, to a certain degree, a reversible reaction.     

Effects of hydrolyzed spray dried red blood cells in milk replacer on calf intake, body weight gain, and efficiency

An alternative protein ingredient based on spray-dried, hydrolyzed red blood cells was evaluated in calf milk replacers. Two experiments were conducted to determine the value of the ingredient on intake, growth, and feed efficiency in dairy calves. In experiment 1, Holstein bull calves (n = 120) were fed calf milk replacer containing 0, 11, 22, or 43% of crude protein as spray dried hydrolyzed red blood cells. Calves were fed 454 g/d of experimental milk replacer reconstituted to 12% dry matter plus a conventional calf starter for 28 d. Body weight gain, intake of milk replacer and calf starter, feed efficiency, fecal scores, and days scouring were unaffected by source of protein. In experiment 2, Holstein calves (n = 69) at the University of Minnesota, Crookston and Waseca were fed milk replacer containing 0, 22, or 43% of crude protein as spray dried hydrolyzed red blood cells. Calves were fed 454 g/d of experimental milk replacer reconstituted to 12% dry matter plus a conventional calf starter containing 0 or 25% alfalfa meal for 35 d. No calves died during the study. Body weight gain, feed efficiency, intake of calf starter and milk replacer, fecal scores, and days scouring were unaffected by increasing hydrolyzed red blood cells in milk replacer. Similar performance of all calves indicated that spray dried hydrolyzed red blood cells can replace up to 43% of crude protein from whey protein concentrate without detrimental effects on animal performance.     

Microbial Production of Natural and Unnatural Monolignols with Escherichia coli

Phenylpropanoids and phenylpropanoid-derived plant polyphenols find numerous applications in the food and pharmaceutical industries. In recent years, several microbial platform organisms have been engineered towards producing such compounds. However, for the most part, microbial (poly)phenol production is inspired by nature, so naturally occurring compounds have predominantly been produced to date. Here we have taken advantage of the promiscuity of the enzymes involved in phenylpropanoid synthesis and exploited the versatility of an engineered Escherichia coli strain harboring a synthetic monolignol pathway to convert supplemented natural and unnatural phenylpropenoic acids into their corresponding monolignols. The performed biotransformations showed that this strain is able to catalyze the stepwise reduction of chemically interesting unnatural phenylpropenoic acids such as 3,4,5-trimethoxycinnamic acid, 5-bromoferulic acid, 2-nitroferulic acid, and a “bicyclic” p-coumaric acid derivative, in addition to six naturally occurring phenylpropenoic acids.     

New light-sensitive nucleosides for caged DNA strand breaks

Phototriggered bod cleavage has found wide application in chemistry as well as in biology. Nevertheless, there are only a few methods available for site-specific photochemical induction of DNA strand scission despite numerous potential applications. In this study we report the development of new photocleavable nucleotides based on the photochemistry of o-nitrobenzyl esters. The light-sensitive moieties were generated through introduction of o-nitrophenyl groups at the 5'C position of the nucleoside sugar backbone. The newly synthesized, modified nucleosides were incorporated in oligonucleotides and are able to build stable DNA duplexes. In such a way modified oligonucleotides ca cleaved site-specifically upon irradiation with > 360 nm light with high efficiency. Furthermore, we show that these modifications can be bypassed in DNA synthesis promoted by Thermus aquaticus DNA polymerase.     

Different Enzymatic Processing of γ‐Phosphoramidate and γ‐Phosphoester‐Modified ATP Analogues

Monitoring the activity of ATP‐consuming enzymes provides the basis for elucidating their modes of action and regulation. Although a number of ATP analogues have been developed for this, their scope is restricted because of the limited acceptance by respective enzymes. In order to clarify which kind of phosphate‐modified ATP analogues are accepted by the α‐β‐phosphoanhydride‐cleaving ubiquitin‐activating enzyme 1 (UBA1) and the β‐γ‐phosphoanhydride‐cleaving focal adhesion kinase (FAK), we tested phosphoramidate‐ and phosphoester‐modified ATP analogues. UBA1 and FAK were able to convert phosphoramidate‐modified ATP analogues, even with a bulky modification like biotin. In contrast, a phosphoester‐modified analogue was poorly accepted. These results demonstrate that minor variations in the design of ATP analogues for monitoring ATP utilization have a significant impact on enzymatic acceptance.