No abstract

Infrared spectra of monomeric acetic acids [CH3COOH(D) and CD3COOH(D)] isolated in Ar and N2 matrices near 4°K are reported. A large anharmonic potential-energy contribution is evident from the observed isotopic frequency shifts. It is proposed that this arises primarily from the double-minimum potential-energy curve for tunneling of the H atom between O atoms via the COH angle bending coordinate. In all cases, important coupling between the COH angle bending and C–O stretching coordinates is observed, with a strong addition of CD3 (umbrella) angle deformation in the case of CD3COOH. Exceptional matrix effects are observed for the coupled vibrations of the –OH molecules. A complete assignment is proposed for these acetic acids on the basis of the new data. As additional supporting evidence, the spectrum of matrix-isolated CH3COF and of acetic acid vapor at low pressure and long path length are reported.

Cell movement and cell-type-specific gene expression during Dictyostelium development are regulated by cAMP, which functions both as an extracellular hormone-like signal and an intracellular second messenger. Previous data indicated that aca-mutants, which lack adenylyl cyclase activity, fail to aggregate and do not express cell-type-specific genes. We show here that overexpression of ACG, a constitutively active adenylyl cyclase, which in wild-type cells is only expressed during spore germination, partially restores the coordination of cell movement and completely restores developmental gene expression. The aca-cells can also be induced to develop into viable spores by synergy with wild-type cells and, furthermore, form small but normal fruiting bodies, after a developmentally relevant regimen of stimulation with nanomolar cAMP pulses followed by micromolar cAMP concentrations. 2'-Deoxy cAMP, a cAMP analog that activates the cell-surface cAMP receptors but not cAMP-dependent protein kinase (PKA), also induces fruiting body formation as well as expression of prespore-specific and prestalk-enriched genes in aca-cells. Intracellular cAMP levels were not altered in aca-cells after stimulation with 2'-deoxy cAMP. Our data indicate that ACA is not required to provide intracellular cAMP for PKA activation but is essential to produce extracellular cAMP for coordination of cell movement during all stages of development and for induction of developmental gene expression.

No abstract

Hyperbranched glycopolymers containing mannose units in the branch point were synthesized through the copolymerization of a mannose inimer and mannose acrylate via atom transfer radical polymerization (ATRP). Incorporating a saccharide residue at the branch point results in a closer analogue to natural branched polysaccharides. Gel permeation chromatography characterization of the polymers qualitatively indicates branching in samples from polymerizations utilizing the mannose inimer. Deprotection of the acetate protecting groups from the hyperbranched mannose polymers yields water-soluble polymers that interact with mannose binding lectin (MBL), a key protein of the innate immunity complement system. MBL interaction increases with increasing polymer molecular weight and increasing branching density. Notably, incorporating mannose into the branching repeat unit also increases the interaction of the glycopolymers with MBL compared with glycopolymers with the same branching density but with no mannose at the branch point.

No abstract

Carbohydrates play prominent roles in immune surveillance and response to infection. Multivalency, molecular weight control, and molecular architecture control are properties that polymer science is well suited to address. Each of these properties has been demonstrated to impact the biological interaction of carbohydrate-bearing chains with their binding partners. This viewpoint highlights synthetic advances and potential applications of carbohydrate-based polymers for immune modulation. It also offers future directions in polymer science necessary for carbohydrate polymers to fulfill their potential as immune modulators.

Infrared spectra for the hydroxyl stretching region of matrix-isolated CF3COOH, CF3COOD, and CH3COOH are reported, and the vapor-phase spectrum of CF3COOH in the region below 500 cm−1 is given. Characteristic line spacings that are found to reproduce the observed spectral features of the high-frequency region are also found to be associated with the low-frequency spectra. Fundamental frequencies for the cyclic dimer ring vibrations are suggested. It is concluded that the well-known band broadening in the hydroxyl stretching region is due to combination bands of the low-frequency modes with the OH fundamental vibration and with nearby binary excitations of the COH(D) bending and the C–O stretching vibrations. A model such as that proposed by Marechal and Witkowski, which considers interactions between the low-frequency and the high-frequency vibrations, seems appropriate in order to explain the intensities of the high combination bands that occur. Further emphasis for the unusual vibrational properties of the mixed COH bending and C–O stretching coordinates in these acids is provided by the spectrum of matrix-isolated monomeric CF3COOH(D). In this case the nominal COH bending vibration of monomeric CF3COOH is clearly doubled while the corresponding COD vibration appears as a single band shifted to lower frequency. The behavior is compared with that for matrix-isolated acetic acid monomers.