Brian L. Silver

Infrared Absorption Spectra of the 18O‐Labeled Acetylacetonates of Cr(III) and Mn(III)

The 18O‐induced isotopic shifts of the Cr(III) and Mn(III) acetylacetonate (of over 90 at % 18O) infrared absorption bands were measured in the 400–1650‐cm−1 region. The hitherto accepted assignments of these bands are discussed in the light of these measurements. It is found that the band at about 1520 cm−1 is due to C=C stretching while that at about 1570 cm−1 has a C=O stretching character. The ∼1425‐cm−1 band must be due to the asymmetrical CH3 bending while the one at 661 cm−1 probably belongs to an out‐of‐plane deformation and that at 590 cm−1 to an M—O stretching.

ESR of Cu2+(H2O)6. II. A quantitative study of the dynamic Jahn‐Teller effect in copper‐doped zinc Tutton's salt

The X‐band ESR spectra of 63Cu2+ doped zinc Tuttons salt enriched to 16 at.% in 17O isotope was studied in a single crystal at 20, 77, and 290°K. The powder spectrum of the same material was studied over the temperature range 10–350°K at X band and 120–290°K at Q band. The observed values of the g tensor and 63Cu and 17O hyperfine tensors were found to be strongly temperature dependent except when the magnetic field was parallel to g3, one of the principal axes of the g tensor. The directions of the principal axes of the g tensor and 63Cu hyperfine tensor were shown to be temperature independent, in opposition to the findings of other workers. In the single crystal, marked mI dependent linewidth variations in the 63Cu hyperfine components were observed in the temperature range 14–80°K, except when the external field was parallel to g3. The experimental data are explicable in terms of a dynamic Jahn‐Teller effect, in contrast to the previously held assumption that dilute copper Tuttons salt is a static J...

Polycation-induced fusion of negatively-charged vesicles

Sonicated vesicles of 20-50 nm in diameter consisting of neutral phospholipids and a variety of acidic phospholipids were interacted with polylysine, cytochrome c, Ca2+ and Mg2+. The addition of polycations caused massive aggregation accompanied by an increase of membrane permeability as determined by leakage of fluorescent dye. Aggregation was followed by fusion of the vesicles into structures that in some cases exceeded 1 micron in diameter. Polylysine induced aggregation and appreciable fusion at charge ratios (polylysine/phospholipid) of 0.5-2, while divalent cations did so only at charge ratios (cation/phospholipid) greater than 10. Aggregation and fusion induced by polylysine were dependent also on the size of the polycation, i.e., the longer the molecule the less needed to induce similar aggregation. It appears that, due to the concentration of charges on a single molecule, polylysine is at least an order of magnitude more effective than divalent cations at inducing fusion of membranes. Cytochrome c induced fusion of similar vesicles at moderately acidic pH (pH 4.2).

Order and Disorder

Molecules never rest. The formally rigid all-trans chains in crystalline phospholipids have a measure of vibrational freedom that increases toward the methyl group tail of the chain (Figure 9). In liquid crystal phases the chains are disordered, any given segment rapidly changing its orientation. We expect the motion of a given segment to be more limited near the tightly packed head groups than at the tail ends of the chains but since the orientation of a given segment is time-dependent and unpredictable, we can only make statistical statements about motion. In this chapter we show that a variety of spectroscopic techniques allow us to make such statements since they provide quantitative measures of order, a term we shortly shall define. The theoretic framework that we use was invented to deal with the physical properties of liquid crystals.

Oxygen Isotope Exchange Reactions of Organic Compounds

Publisher Summary Isotope exchange reactions are reversible chemical processes in which two isotopes C and C* of the same element exchange places. No net chemical change takes place in these reactions, but only interchange of the isotopic label occurs. The large majority of exchange reactions studied are those between organic compounds and water. These reactions significantly provide a great deal of information on the mechanisms of the reaction of organic compounds. The isotopic exchange of oxygen in organic compounds involves the use of O 18 . The isotopic exchange of O 18 with organic compounds is important as a control in tracer studies, particularly in the systems of biological interest where water plays a prominent role. This chapter describes exchange reactions that deal with simple oxygen-containing organic molecules, such as alcohols, phenols, ketones, aldehydes, and carboxylic acids and their derivatives. It examines many organic derivatives of inorganic oxyacids, such as esters of phosphoric and sulphuric acids, for oxygen exchange with water. Few exchanges not involving water, such as the exchange of O 18 between organic compounds and alumina and other metal oxides, are also presented.

ESR of Cu2+ (H2O)6. I. The oxygen‐17 superhyperfine tensors in 63Cu2+ doped zinc Tutton's salt at 20 °K

The X‐band ESR spectrum of 63Cu2+ doped zinc Tuttons salt enriched to 16 at.% in oxygen‐17 isotope was studied in a completely deuterated single crystal at 20°K. Satellites from both singly and doubly labelled molecules were observed and the oxygen‐17 superhyperfine tensors were found to differ for the two trans pairs of equatorial oxygens. The two tensors are −21.0, −11.9, and −10.9×104 cm−1 and −16.1, −9.9, and −8.8×104 cm−1, where the largest principal value in each case is directed along the copper‐oxygen bond and the tensors are associated, respectively, with the shorter and longer of the equatorial copper‐oxygen bonds. The tensors, after correction for a distant dipolar contribution from the metal, were shown to imply a value of 1/6 for the ratio 2s0/2p0 in the molecular orbital containing the unpaired electron. This result is discussed in terms of the known geometry of the Cu2+(H2O)6 complex in Tuttons salts.

Oxygen−17 Hyperfine Splitting Constants in the ESR Spectra of p‐Semiquinones—17O

Oxygen−17 hyperfine splitting constants have been determined for a number of semiquinones—17O. The results were correlated with the spin density distribution in the radicals. It was found that the splitting constants aO can be very well fitted to an expression of the form, aO=QOC O ρO+QCO O  ρC, where ρO and ρC are pπ spin densities on the oxygen and carbon atoms of the carbonyl group, and the Qs are sigma—pi interaction constants. QOC O is about −40 G, but the analysis does not allow the value of QCOO to be determined, although its magnitude is certainly much less than that of QOC O. These interaction constants are discussed in terms of the general theory of Karplus and Fraenkel. Solvent effects on aO were observed, especially in going from apropic to hydrogen‐bonding solvents and are discussed in terms of radical—solvent interaction at the carbonyl oxygen. In the Appendixes molecular orbital parameters for oxygen and chlorine are derived from the analysis of proton hyperfine splitting constants in simp...

An NADH:Quinone oxidoreductase of the halotolerant bacterium Ba1 is specifically dependent on sodium ions☆

The rate of NADH oxidation by inverted membrane vesicles prepared from the halotolerant bacterium Ba1 of the Dead Sea is increased specifically by sodium ions, as observed earlier in whole cells. The site of this sodium effect is identified as the NADH: quinone oxidoreductase, similarly to the other such system known, Vibrio alginolyticus (H. Tokuda and T. Unemoto (1984) J. Biol. Chem. 259, 7785-7790). Sodium accelerates quinone reduction severalfold, but oxidation of the quinol, with oxygen as terminal electron acceptor, is unaffected. The sodium-dependent pathway of quinone reduction exhibits higher apparent affinity to extraneous quinone (Q-2) than the sodium-insensitive pathway, and is specifically inhibited by 2-heptyl-4-hydroxyquinoline N-oxide. ESR spectra of the membranes contain a feature at g = 1.98 which is tentatively identified as one originating from semiquinone. This feature is increased by NADH and decreased by addition of Na+, suggesting that, as proposed from different kinds of evidence for the V. alginolyticus system, sodium affects the semiquinone reduction step. As in the other system, the site of sodium stimulation in Ba1 probably corresponds to the site of sodium translocation, which was shown earlier (S. Ken-Dror, R. Shnaiderman, and Y. Avi-Dor (1984) Arch. Biochem. Biophys. 229, 640-649) to be linked directly to a redox reaction in the respiratory chain.

ESR of 17O‐Labeled Nitrogen Dioxide Trapped in a Single Crystal of Sodium Nitrite

A study is reported of the ESR spectrum of NO2–17O formed by γ irradiation of single crystals of NaNO2–17O at 77°K. Hyperfine splittings due to 14N and 17O were studied as a function of orientation, and the principal values and directions of the hyperfine tensors determined. The results for the nitrogen hyperfine and g tensor agree with those of Zeldes and Livingston. In a general orientation, splittings are observed due to two magntically inequivalent oxygens. The magnitudes of the principal values for the hyperfine tensors of both oxygens are:4.27, 54.90, and 1.74 G. The directions of the largest principal values are in the molecular plane at angles of + 7.5° and − 7.5° to the molecular axis. The results are used to derive values for the MO coefficients of the 4a1 orbital which contains the unpaired electron. An attempt is made to interpret the g tensor in terms of the electronic structure of NO2.

The infrared absorption spectrum of 18O-labelled nitrobenzene

The absorption spectrum of a sample which was composed of about 49 per cent C6H5N16O18O, 32 per cent C6H5N16O2 and 19 per cent C6H5N16O2 was measured, in solution in carbon disulphide or carbon tetrachloride or as a liquid, in the 3700–390 cm−1 region, in comparison to the corresponding spectrum of normal nitrobenzene. Only the bands at 2860, 1531, 1349, 850, 790, 702, 681, 532 and 417 cm−1 were observed to be affected by the 18O-labelling. The band at 850 cm−1 is re-assigned to an NO2 symmetric deformation while the 681 cm−1 band is assigned to an out-of-plane ring deformation. The band at 532 cm−1 is shown to be very sensitive to the mass of the oxygen atoms and is therefore due to a mode of vibration which has a strong NO (out-of-plane) bending character.