the magnitude of the gain. Thus, the delay time of -0.5 s observed in Fig. 4 increases to 12 s at E, = 46 V/pin. Furthermore, the use of additional polymer layers will not decrease the threshold for oscillation noticeably unless an index-matching liquid is used to reduce the reflection losses accordingly. Once oscillation has been achieved, however, the P C reflectivity will increase significantly faster with EL, for a larger multilayer stack.Finally, predicting the threshold for oscillation or the value of R from measurements of tw o-beam coupling galn is not a simple matter. Recent work has shown that these ~o l v -L , mers benefit from gain enhanceinent due to very slow motion of the index eratine, which -l n e k that the cavity beam is expected to be frequency-shifted from the pumping beam. This complicates the theoretical analysis to a level beyond the scope of this report (25).

Antibodies generated by candidate HIV-1 vaccines in a phase I clinical trial were assessed for neutralizing activity with a panel of eight well-characterized, genetically diverse clade B primary isolates having an R5 phenotype. The vaccines consisted of one of three different recombinant canarypox vectors expressing membrane-anchored HIV-1(MN)gp120 (ALVAC vCP205, vCP1433, and vCP1452) followed by boosting with a soluble gp160 hybrid consisting of MNgp120 and the majority of gp41 from strain IIIB. Serum samples from a subset of volunteers in each arm of the trial, containing moderate to high titers of neutralizing antibodies to HIV-1 MN, were analyzed. Competition assays with peptides revealed that the majority of neutralizing activity was specific for the MN-V3 loop. Despite MN-specific neutralization titers that sometimes exceeded 1:500, no neutralization of primary isolates was detected and, in some cases, mild infection enhancement was observed. In addition, little or no neutralization of the HIV-1 IIIB heterologous T cell line-adapted strain of virus was detected. These results reinforce the notion that monovalent HIV-1 ENV is a poor immunogen for generating cross-reactive neutralizing antibodies.

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The hydration of polar natural and synthetic lipids yields a variety of lipid phases including various inverted cubic phases and the inverted hexagonal (HII) phase. The HII phase can be considered as aqueous columns encased with a monolayer of lipids and arranged in a hexagonal pattern. The polar head groups are well-ordered at the water interface, whereas the lipid tails are disordered to fill the volume between the tubes of water. A particularly interesting characteristic of the HII phase is the large temperature effect on the basis vector length d of the hexagonal lattice. Previous studies indicate that polymerization of the lipid region of the HII phase might reduce the sensitivity of the basis vector to temperature. A phosphoethanolamine (PE) was designed and synthesized with dienoyl groups in each lipid tail in an attempt to cross-link the lipids around and along the water core of the HII phase. The synthesis of the the PE was accomplished by acylation of 3-(4-methoxybenzyl)-sn-glycerol with 2,4,13-(E,E,Z)-docosatrienoic acid, followed by deprotection, then phosphorylation with dichloro-[[N-[(2,2,2-trichloroethoxy)carbonyl]-2-amino]ethyl]phosphinic acid to give the Troc-PE, which was converted to the PE with activated zinc and acetic acid. The hydrated PE (1/1 weight lipid/water) formed the HII phase over an extended temperature range. Polymerization to high conversion was accomplished at 60 °C with the aid of redox initiators. Polymerization was followed in-situ using X-ray diffraction over a period of 48 h. The scattering, which weakened over the course of the reaction, remained consistent with a hexagonal phase. Temperature cycling of the polymerized HII phase showed an unaltered pattern on decreasing temperature while maintaining the same lattice parameter, unlike that of the unpolymerized phase where the value increased with decreasing temperature. Thus it is possible to fix the dimensions of the HII phase by cross-linking polymerization of appropriately designed reactive lipids.

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Several attempted syntheses of Ti-TMS1, a hexagonal mesoporous TiO2 reported by Antonelli and Ying, have resulted in a lamellar structure as determined by two-dimensional powder X-ray diffraction and transmission electron microscopy (TEM). Regions of partially calcined lamellar materials, when observed by TEM can be mistaken for hexagonal material. In no cases are specimens produced that were unambiguously hexagonal. It is concluded that the hexagonal material exists, if at all, only as a minor component of a larger lamellar structure when phosphate surfactants are used. Ti-TMS1 therefore remains elusive.