Hydrogen-Ion Titrations of Amino Acids and Proteins in Solutions Cont aining Concentrated Electrolyte

This report describes a first attempt to quantify the net charge as a function of solution pH for lysozyme and {alpha}-chymotrypsin at 0.1 M, 1.0 M and 3.0 M ionic strength, (IS). The calculations are based on the residue (titratable group) pK{sub a}`s in the amino-acid sequence of the protein. To determine these pK{sub a}`s, a simple theory was used which assumes that the pK{sub a}`s are independent from each other in the protein and are equal to their pK{sub a} values in free amino-acid solution (Independent-Site Theory, IST). Residue pK{sub a}`s were obtained from amino-acid hydrogen-ion titrations at three different KCl concentrations corresponding to 0.1M, 1.0M and 3.0M ionic strength. After construction of a suitable apparatus, the experimental procedure and data reduction were computerized to perform a large number of titrations. Most measured pK{sub a}`s showed high reproducibility (the difference of pK{sub a} values observed between two experiments was less than 0.05). For IS = 0.1M, observed pK{sub a}`s agreed with literature values to within a few hundredths of a pH unit. Furthermore, the ionic-strength dependence of the pK{sub a}`s followed the trends reported in the literature, viz. pK{sub a} values decrease with increasing ionic strength until they reach a minimum at about IS = 0.5M. At still higher IS, pK{sub a}`s increase as the ionic strength rises to 3M. The known pK{sub a}`s of all titratable groups in a protein were used with the IST to give a first approximation of how the protein net charge varies with pH at high ionic strength. A comparison of the titration curves based on the IST with experimental lysozyme and {alpha}-chymotrypsin titration data indicates acceptable agreement at IS = 0.1M. However, comparison of measured and calculated titration curves at IS = 1M and IS = 3M indicates only quantitative agreement

Schlussbericht zur Definitionsstudie ueber ein MIPAS-Experiment auf der EOM-Nutzlast

TIB Hannover: FR 2603 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The chopped pyrgeometer: a new step in pyrgeometry

A new type of pyrgeometer, which uses modulation of the atmospheric radiation by a mechanical chopper has built for the use of ground based and airborne measurement of broadband infrared atmospheric irradiances. The instrument basically consists of two radiometers - a target radiometer and a reference radiometer - using a specially developed chopper. The reference radiometer is used to measure the radiation of the chopper which has to be known additionally to calculate the atmospheric radiation from the signal of the target radiometer. The radiometer equations take into account the non-flat spectral response. A spectral correction factor is introduced to describe the relation between the weighted irradiance at the detector and the irradiance coming from the source. One important advantage of the chopped pyrgeometer is its nonsensitivity to the temperature distribution inside the instrument as well as its fast response. The chopped pyrgeometer has been used during a number of airborne missions. During the Pre-EUCREX Intercomparison Campaign flown in January 1992, two Eppley pyrgeometers, two pyrgeometers of the Foot-type and a chopped pyrgeometer were flown besides other instruments on three aircraft. During a rectangular flight pattern (box) the absolute irradiance values measured by the five instruments differ by about #+-# 10% from the average value (#approx# 85 W/m"2) of all instruments, the chopped pyrgeometer indicating the smallest values throughout. Since a detailed error budget of all instruments was not available, special emphasis was placed on relative quantities (ratios) to describe the trends measured by the various instruments along the flight tracks. It has been found, that the measurements of the chopped pyrgeometer show a much better correlation to the measurement of the Foot pyrgeometers, than to the Eppley instruments. A comparison of four different model calculations with the measured data of all participating instruments at ground and at three flight levels is presented. (orig.)38 refs.Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Definitionsstudie ueber ein MIPAS-Experiment auf der EOM-Nutzlast Schlussbericht

SIGLETIB Hannover: FR 2603 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Kinetic analysis of cryotropic gelation of poly(Vinyl Alcohol)/water solutions by small-angle neutron scattering

Aqueous poly(vinyl alcohol) (PVA) solutions subjected to cryogenic treatment form strong physical gels. The cryogenic treatment basically consists of freezing an initially homogeneous polymer solution at low temperatures, storing in the frozen state for a definite time, and defrosting. These gels are of great interest for biotechnology, medicine, the food industry, and many other applications. The outstanding properties of these systems depend on a complex macroporous architecture, whereby PVA chains and water molecules are organized over different hierarchical length scales. The structure and the principal processes subtending the formation of these systems are discussed in the framework of our current understanding of polymer gels. These processes involve formation of ice crystals, PVA crystallization, liquid–liquid phase separation, hydrogen bonding, and entanglements. Small angle neutron scattering is used to follow the cryotropic gelation of PVA/water solutions and detailed information is extracted concerning the gelation mechanism and kinetic parameters related to the formation of these complex systems