Bohdan Balko

High resolution mixer for the study of the kinetics of rapid reactions in solution.

The turbulent wake of a spherical surface was utilized as part of a mixer for fast reaction studies. The mixer is capable of mixing two solutions within 100 μsec at a flow velocity of 30 m/sec. Optical and thermal methods were used to study the mixer. Highly efficient mixing was achieved for 120 cP solutions as well as aqueous solutions.

High Speed Optical Stopped‐Flow Apparatus

A stopped flow apparatus for the study of fast reactions in solution is described. The measured dead time was 270 μsec with an uncertainty in the measurement of 50 μsec. At 410 mμ and an optical density of about 0.09 a change of 0.0044 optical density units could be observed at a flow velocity of 30 m/sec through a 3.0 mm observation tube. Ten milliliters of each of the two reagents are required to fill the system, and less than 1.0 ml of each needs to be expended per experiment.

Measurement and Computation of Thermojunction Response Times in the Submillisecond Range

A simple method is presented for measuring the response of thermocouples in liquid media. Response times down to 50 μsec have been measured. Various coating techniques for obtaining fast responding electrically insulated junctions are discussed. The effect of thermocouple materials and insulation coatings on the response time has been experimentally determined and the results compared with a computer calculation simulating the physical system. The computer calculation involves two difference equations and solves a multilayered media problem without the introduction of heat transfer coefficients. The results agree to within experimental error.

Iron electronic structure in oxyhemoglobin and carboxypeptidase digested derivatives

Mössbauer experiments were performed on the oxy- derivatives of human hemoglobin and its products of digestion with carboxypeptidases. The hemoglobins were chemically enriched to 95% in 57Fe, and were free from hemochrome impurities. Spectra were taken at low temperatures in the presence and absence of a 5.0 T magnetic field. It was observed that the enzymatic digestions which remove residues at least 16 A from the iron of the nearest heme appear to modify the electronic environment of the metal.

Stopped flow microcalorimetry without adiabatic compression: Application to reactions with half-lives between 3 and 50 ms

Abstract A stopped flow apparatus with a thermal sensor has been developed with an uptake syringe mechanically coupled to a set of driving syringes that alleviates the pressure-induced temperature change previously observed at the point of stopping the flow. With this effect eliminated we can now study reactions with total reaction times that are close to the response time of the thermistor (7 ms).

Fast stopped-flow microcalorimeter

A fast stopped-flow microcalorimeter using a thermistor and an a.c. bridge is described. Time resolution, limited by the response of the thermistor, is 3 ms for t 1/2 while sensitivity is 100 mu degree C in this bandpass. A reaction requires 0.3 ml of each reactant. The microcalorimeter is adiabatic to within 2% for 2 s and mixing may be repeated every 5 min. Computer finite element simulation techniques (FEST) are used to correct for the thermistor response time and heat losses. Results of tests with reactions of NaOH and HCl, NaHCO3, and HCl, and glyclyglycine and CO2 agree with published kinetic and thermodynamic values to within an experimental error of less than 2%.

Measurement and simulation of thermistor response time in the millisecond range

The Finite Element Simulation Technique (FEST) has been applied to the design of hermetically‐sealed thermistors with millisecond response times. These thermistors are used in stopped‐flow calorimeters developed especially for investigations of biological reactions. FEST is also used to reconstruct the reaction kinetics obtained with these thermistors by correcting for their finite sensor response times and temperature loss.

The Effect of the Pressure Pulse on Solution Temperature in Stopped-Flow Calorimetry

Abstract The pressure pulse effect, which exhibits itself by a step conductance rise on the response curves of thermistors in the stopped-flow microcalorimeter, is shown theoretically and experimentally to be due to the temperature rise of the solution caused by its adiabatic compression. Thermocouples respond similarly to thermistors in the range of 1 to 400 bars.

Thermal kinetics using a modified commercial stopped flow apparatus

A commercially available optical and fluorescence stopped flow apparatus has been adapted for thermal detection methods. A minor modification was sufficient to permit the measurement of kinetics of chemical reactions with half lives in the range of 15 ms to several seconds. A detection sensitivity of 1 mu2009°C was obtained.