An automated procedure for the simultaneous determination of specific conductance and pH in natural water samples

An automated, continuous-flow system is utilized to determine specific conductance and pH simultaneously in natural waters. A direct electrometric procedure is used to determine values in the range pH 4–9. The specific conductance measurements are made with an electronically modified, commercially available conductivity meter interfaced to a separate module containing the readout control devices and printer. The system is designed to switch ranges automatically to accommodate optimum analysis of widely varying conductances ranging from a few μmhos cm^-1 to 15,000 μmho cm^-1. Thirty samples per hour can be analyzed. Comparison of manual and automated procedures for 40 samples showed that the average differences were 1.3% for specific conductance and 0.07 units for pH. The relative standard deviation for 25 replicate values for each of five samples was significantly less than 1% for the specific conductance determination; the standard deviation for the pH determination was ? 0.06 pH units.     

A new approach to intermolecular forces in non-bonding regions

A new method to compute intermolecular energies in non-bonding regions is presented. It is based on the assumption that in such regions molecules can be reviewed as the sum of distorted, possibly overlapping, and electron exchanging atoms. The intermolecular energy change at a given distance is due to the sum of the atomic energy changes caused by these distortions. The energy change of any particular atom is computed in a Hartree—Fock model in which the effect of the other atom is represented by an effective potential. This potential in turn is computed from a calculation at a slightly larger intermolecular distance of the potential seen by an external electron in the field of the “other” atom. This potential computed in the RPA approximation and involves the distorted Hartree—Fock orbitals of the other atom (computed in a similar manner to the above) and the RPA response function of the other distorted atom.     

Obtaining partial widths from siegert wavefunctions

It is shown that a simple expression for the partial widths in a multichannel decay problem can be readily obtained from a Siegert wavefunction.     

Birefringence changes in vertebrate striated muscle.

The changes in birefringence in the rigor to relax transition of single Triton-extracted rabbit psoas muscle fibers have been investigated. The total birefringence of rigor muscle fibers was dependent on sarcomere length and ranged from (1.46 +/- 0.08) X 10(-3) to (1.60 +/- 0.06) X 10(-3) at sarcomere lengths from 2.70 mum to 3.40 mum. An increase in total birefringence was measured dependent on sarcomere length when 55 single fibers were relaxed from the rigor state with Mg-ATP. Pyrophosphate relaxation produced a smaller increase in retardation when compared to Mg-ATP. The expected change in intrinsic birefringence during the rigor to relax transition was calculated assuming a hinge function of the subfragment 2 moiety of myosin. The changes in birefringence during isometric contraction and relaxation have been discussed in relation to possible structural changes.     

Highly substituted pyridines via tethered imine-enamine (TIE) methodology

A tethered imine-enamine methodology has been developed for the direct conversion of 1,2,4-triazines into highly substituted pyridines via the inverse electron demand Diels-Alder reaction which avoids the need for a discrete aromatisation step. This TIE methodology has also been applied in one pot reaction cascades involving 1,2,4-triazines and utilising MnO(2)-mediated tandem oxidation processes (TOPs).     

The structures of fluorides. XV. Neutron diffraction-kubic harmonic profile analysis of the body-centered cubic phase of sulfur hexafluoride at 193°K

Sulfur hexafluoride has a body-centered cubic phase (a = 5.915(3) Å) between its melting point (222.4°K) and 93°K, below which a lower symmetry phase exists. NMR studies show that in both phases there is rapid reorientation of the sulfur hexafluoride molecules. From a neutron diffraction pattern collected at 193°K with λ = 1.086 Å, the data were not satisfied by a model with a spherically symmetrical fluorine density nor by a refinement with conventional ellipsoidal-shaped atoms. The latter gave systematically low S-F distances and abnormally high β_ij thermal factors. Good agreement was obtained by a combination of Kubic Harmonics with full-matrix least-squares analysis of the neutron profile pattern. The refinement was made with one variable Kubic Harmonic coefficient a₂ = 5.94(11), with $\text{R}{}_{\mathrm{w}}\text{= {}\text{∑ w[y}{}_0\text{? (}\text{1}\text{s}\text{)y}{}_{\mathrm{c}}\text{]}{}^2\text{∑ wy}{}_0{}^2\text{}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.079}$ and $\text{χ}{}^2\text{=}\text{∑ w[y}{}_0\text{? (}\text{1}\text{s}\text{)y}{}_{\mathrm{c}}\text{]}{}^2\text{(NO-NV)}\text{= = 1.2}$. Only four least-squares variables were required with 225 observations in the range of one or more hkl reflections to 2θ = 58.3°. AS-F distance of 1.542(4) Å, obtained from the neutron diffraction data, is in good agreement with the reported value of 1.564(10) Å found from electron diffraction measurements of the vapor. The disordered fluorine distribution has broad maxima on the cell edges similar to those found in the plastic cubic phases of MoF₆ and WF₆.     

Metal cyanurate compounds formed directly from metal salts and urea

Compounds which have been identified as metal cyanurates have been prepared by heating certain metal oxides or salts directly with urea. Copper, nickel, cobalt, zinc, iron and manganese compounds have been formed in this manner. X-ray diffraction data and possible structures for some of these compounds are presented.