Lewis J. Noe

Polarizability and dipole moment changes of the lowest 1ππ* state of azulene; an example of the use of the Stark effect on polar and nonpolar mixed molecular crystals

The relatively high representative electric fields present at molecular sites in a polar molecular crystal, ∼ 107 V cm−1, make possible the determination of excited‐state dipolar and polarizability properties of a guest molecule dispersed in the polar host from a consideration of field induced moments. The determination of the magnitudes and directions of these guest properties is particularly dependent on an analysis interrelating Stark measurements made separately on the spectroscopically accessible states of the guest when dispersed in a polar and in nonpolar host lattice. The azulene‐benzophenone, azulene‐naphthalene mixed‐crystal systems were chosen to demonstrate this method of analysis for the lowest 1ππ* state of azulene. The magnitude of the dipole moment change for azulene dispersed in the nonpolar (zero field) naphthalene lattice Δμzf = 1.21 D, has already been determined. Using this magnitude and the results of Stark measurements on azulene in benezophenone we find that (1) the molecular dipol...

In situ surface plasmon study of the electropolymerization of Fe(vbpy)32+ onto a gold surface

Abstract Sequential multilayer electropolymerization of Fe(vbpy)32+ (vbpy=4-vinyl-4′-methyl-2,2′-bipyridine) onto a thin gold electrode was followed in situ with surface plasmon spectroscopy (SPS) using a 1 mW HeNe laser at 6328 A. The robustness of the gold film electrode necessary for electrochemical deposition in 0.10 M tetraethylammonium perchlorate+acetonitrile is imparted by use of a thin film of 3-mercaptopropyl-trimethoxysilane attached to a SF10 slide to which the metal is covalently bonded. As each polymer layer is deposited by cycling a potentiostat from 0.0 to −1.75 and back to 0.0 V, a plasmon spectrum (reflectivity versus prism angle) is obtained. SP analysis of the angular shift of the spectrum, which increases as the polymer layer thickens, yields an estimate of both the thickness and index of refraction of the polymer film. We found that the plasmon spectrum shifts to higher angles as the polymer layer thickens, along with a progressive decrease in the depth of the resonance minimum. Our modeling shows this unusual spectral behavior involving the resonance minimum is consistent with a Fe(vbpy)32+ chromophore absorption at 6328 A, along with thickening of the polymer film. This work demonstrates that SPS is a viable in situ technique for obtaining thickness measurements of electrodeposited thin films.

Acid dissociation constants of diphytanylglycerolphosphorylglycerol-methylphosphate, and diphytanylglycerolphosphorylglycerophosphate and its deoxy analog

Abstract Acid dissociation constants of 2,3-diphytanyl- sn -glycero-1-phosphoryl- sn -3′-glycero-1′-methylphosphate (PGP-Me), the major phospholipid in extreme halophiles (Halobacteriaceae) , and of the demethylated 2,3-diphytanyl- sn -glycero-1-phosphoryl- sn -3′-glycero-1′-phosphate (PGP) and its deoxy analog 2,3-diphytanyl- sn -glycero-1-phosphoryl-1′-(1′,3′-propanediol-3′-phosphate) (dPGP), were calculated by an original mathematical procedure from potentiometric titration data in methanol/water (1:1, v/v) and found to be as follows: for PGP-Me (and presumably PGP), p K 1 =3.00 and p K 2 =3.61; for PGP, p K 3 =11.12; and for dPGP, p K 1 =2.72, p K 2 =4.09, and p K 3 =8.43. High-resolution 31 P NMR spectra of intact PGP-Me in benzene/methanol or in aqueous dispersion showed two resonances corresponding to the two P-OH groups, each of which exhibited a chemical shift change in the pH range 2.0–4.5, corresponding to acid dissociation constants p K 1 =p K 2 =3.2; no further ionization (p K 3 ) was detected at higher pH values in the range 5–12. The present results show that PGP-Me titrates as a dibasic acid in the pH range 2–8, but above pH 8, it titrates as a tribasic acid, presumably PGP, formed by hydrolysis of the methyl group during the titration with KOH. Calculation of the concentrations of the ionic molecular species of PGP-Me, PGP and dPGP as a function of pH showed that the dianionic species predominate in the pH range 5–9, covering the optimal pH for growth of Halobacteriaceae. The results are consistent with the concept that the hydroxyl group of the central glycerol moiety in PGP-Me and PGP is involved in the formation of an intramolecular hydrogen-bonded cyclic structure of the polar headgroup, which imparts greater stability to the dianionic form of PGP-Me and PGP in the pH range 5–9 and facilitates lateral proton conduction by a process of diffusion along the membrane surface of halobacterial cells.