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At least 1,009 records · Page 56Linked to original sources
PubMed1993

Recognition of enantiomers by Chirasil-Val and oligopeptide analogues as studied by gas-phase calorimetry and 1H NMR spectroscopy in solution.

A series of oligopeptides, L-Valn-NHtBu (n = 1-4), were linked to poly(beta-methyl)siloxy-alpha-methylpropanoic acid copolymer; the resulting chirally modified polydimethylsiloxanes were used for the resolution of enantiomers by gas chromatography. Chiral recognition proved most effective for n = 1 (known as Chirasil-Val), as judged from the resolution factors (alpha) and the thermodynamic parameters delta delta H, delta delta S and chi = delta delta H/delta H', where delta H' = delta HChir -delta HSE30. Likewise, 1H NMR spectroscopy in carbon tetrachloride solution revealed a maximum chemical shift non-equivalence of the amide N-H signal of racemic N-TFA-amino acid methyl esters on addition of the chiral polymer, for n = 1. From circular dichroism spectroscopy of L-Valn-NH'Bu (n = 2, 3, 4 and 6) and polyoxyethylene-bound pivaloyl-L-Valn-Gly-NH-POE3000 (n = 2-8), it is concluded that the peptide moiety of the stationary phase mostly adopts the unfavourable random coil conformation, whereas the beta-sheet structure was only partially found and only for n > or = 6.

Amino Acid Sequence↗
PubMed1982

Power and heat measurement by direct calorimetry of individual insect response to allelo- and toxic compounds.

A microcalorimeter was constructed for the individual insect in order to measure the insect's power output as a function of time (the thermogram). The instrument has a figure of merit of 7 microW/microV. It includes a Peltier pumped thermoelectric control loop which protects from intruding ambient thermals, and holds baseline drift to less than 2 microV/day. the design is a conventional twin, or differential heat conduction calorimeter, with two insect-holding vessels of glass. The vessels are connected by a stopcock, to give the insect the option of crawling from the sample chamber to the reference chamber. Continuous, metered air flow is provided. A small pulse of compound may be born in, as vapor with the air flow, for the study of attractants, toxic compounds, anesthetics and allelochemicals. The insect's reaction to such compounds, appears in the thermogram. Cabbage looper larvae were examined in their irritative exothermic reaction to microgram amounts of benzene, and in their neutral behavior toward similar amounts of aliphatic hydrocarbons delivered as a single pulse of vapor. The male northern corn rootworm was monitored in his attraction to female rootworm extract ("pheromone') and his tendency to move upwind, or up airflow, toward the pheromone. The instrument enables discrimination of the transient metabolism of muscle use, from that of the resting state power which is probably the true basal metabolic rate power.

Animals↗
PubMed1984

The use of flow calorimetry in antigen-antibody reactions.

The binding of anti-IgM IgG to human monoclonal IgM has been studied calorimetrically and results have been compared with parallel turbidity measurements of the same reaction. In the first series of experiments using the flow calorimeter equipped with a mixing cell, varied flow rates gave identical values for the thermic contribution, indicating that the same quantity of heat was evolved in the different time intervals in which the reaction mixture was in the calorimetric cell. In the second set of experiments a flow-through cell was used. Reactants were mixed outside the calorimeter and no heat was detected upon entry of the pre-mixed reactants into the calorimetric cell. Results suggest that heat is evolved instantaneously upon mixing and no heat is produced during aggregation. Antibody-antigen binding can be followed in the absence of precipitation, as may occur in reactions involving monoclonal antibodies.

Animals↗
PubMed1994

Rates of heat and water loss in female mink (Mustela vison) measured by direct calorimetry.

The energy expenditure (EE) of adult female mink was studied by continuous 24-hr measurement of rates of total heat loss (THL) in a controlled environment using a 24 m3 calorimeter allowing separate on-line determination of sensitive (SHL) and evaporative (EHL) heat loss within the range of 20-200 W (72-720 kJ/hr). In four adult female mink (scanblack colour mutant), studied in transparent cages and given free access to feline food pellets and water, the mean 24-hr energy expenditure (= THL) under controlled experimental conditions was 8.9 W/kg (range: 5.5-13.1 W/kg) at 18 degrees C and 5.8 W/kg (range: 4.3-9.5 W/kg) at 24 degrees C. The results are in agreement with the data reported in the literature on the metabolic rate of adult farm-raised mink, calculated from rates of oxygen uptake under controlled experimental conditions, and with the energy requirement for maintenance, 586 kJ/kg/day (6.8 W/kg) recommended by the NRC. Under the experimental conditions of the present study the mean rate of total evaporative water loss (TEWL) amounted to 3.7 g/kg/hr at 18 degrees C and 5.5 g/kg/hr at 24 degrees C. The contributions of SHL and EHL to 24-hr THL in female mink were inversely related and markedly dependent on chamber temperature. When corrected for evaporated urinary and faecal water, SHL and EHL amounted to 76 and 24% of THL at 18 degrees C, but at 24 degrees C the corresponding values were 41 and 59%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗