Critical-zone reactions involve inorganic and biogenic colloids in a cation-rich environment. The present research defines the rates and structure of purified Mg-montmorillonite aggregates formed in the presence of monovalent (K+) and divalent (Ca2+, Mg 2+) cations using light-extinction measurements. Time evolution of turbidity was employed to determine early-stage aggregation rates. Turbidity spectra were used to measure the fractal dimension at later stages. The power law dependence of the stability ratios on cation concentration was found to vary with the reciprocal of the valence rather than the predicted reciprocal of valence-squared, indicating that the platelet structure may be a factor influencing aggregation rates. The critical coagulation concentrations (CCC) (3 mM for CaCl2, 4 mM for MgCl2, and 70 mM for KCl) were obtained from the stability ratios. At a later time and above a minimal cation concentration, turbidity reached a quasi-stable state, indicating the formation of large aggregates. Under this condition, an approximate turbidity forward-scattering correction factor was applied and the fractal dimension was determined from the extinction spectra. For the divalent cations, the fractal dimensions were 1.65 ± 0.3 for Ca2+ and 1.75 ± 0.3 for Mg2+ and independent of cation concentrations above the CCC. For the monovalent cation, the fractal dimension increased with K+ concentration from 1.35 to 1.95, indicating a transition to a face-to-face geometry from either an edge-to-edge or edge-to-face orientation.

Bacteria play an important role in determining the properties and behavior of clay minerals in natural environments and such interactions have great potential for creating stable biofilms and carbon storage sites in soils, but our knowledge of these interactions are far from complete. The purpose of this study was to understand better the effects of bacteria-generated biofilms on clay interlayer expansion. Mixtures of a colloidal, 2-water hectorite clay and Pseudomonas syringae in a minimal media suspension evolve into a polysaccharide-rich biofilm aggregate in time-series experiments lasting up to 1 week. X-ray diffraction analysis reveals that upon aggregation, the clay undergoes an initial interlayer contraction. Short-duration experiments, up to 72 h, result in a decrease in the d001 value from 1.50 to 1.26 nm. The initial interlayer contraction is followed in long-duration (up to 1 week) experiments by an expansion of the d001 value of 1.84 nm. The expansion is probably a result of large, biofilm-produced, polymeric molecules being emplaced in the interlayer site. The resultant organo-clay could provide a possible storage medium for carbon in a microbial colony setting.

“Substantial downzoning” is defined as the exercise of police power to significantly reduce the legally permitted density on undeveloped land in a community. This contentious practice is typically challenged by those who perceive the action to limit their market opportunities (e.g., farmers and developers), their sympathizers, and others who prefer the status quo. Supporters tend to be those who perceive positive benefits (e.g., environmentalists, conservationists, and homeowners) and those who see it as a supplement to other preservation techniques, based on concerns over such things as growing public costs of land acquisition, limited effectiveness of existing alternatives, or the perceived urgency to act to manage growth.

Given the complexity of the issue and the lack of previous research, this paper develops a conceptual model of the public choice to “substantially downzone” and presents specific hypotheses to be empirically tested, using New Jersey as a case study. The probability of implementing substantial downzoning is found to increase with (i) the amount of open space that remains to be protected, (ii) declining farm population, (iii) recent growth in non-farm population, (iv) recent growth in land values, and (v) the presence of alternative growth management tools. Results also suggest its use as a substitute for other preservation tools when the financial and/or political ability of communities to afford other approaches is limited. Hence, the likelihood of substantial downzoning may increase over time if alternatives become more difficult to implement.

The trpRNA-binding Attenuation Protein (TRAP) from Bacillus subtilis is an 11-subunit protein that binds a series of 11 GAG and UAG repeats separated by two to three-spacer nucleosides in trp leader mRNA. The structure of TRAP bound to an RNA containing 11 GAG repeats shows that the RNA wraps around the outside of the protein ring with each GAG interacting with the protein in nearly identical fashion. The only direct hydrogen bond interactions between the protein and the RNA backbone are to the 2′-hydroxyl groups on the third G of each repeat. Replacing all 11 of these guanosines with deoxyriboguanosine eliminates measurable binding to TRAP. In contrast, a single riboguanosine in an otherwise entirely DNA oligonucleotide dramatically stabilizes TRAP binding, and facilitates the interaction of the remaining all-DNA portion with the protein. Studies of TRAP binding to RNAs with between 2 and 11 GAGs, UAGs, AAGs, or CAGs showed that the stability of a TRAP-RNA complex is not directly proportional to the number of repeats in the RNA. These studies also showed that the effect of the identity of the residue in the first position of the triplet, with regard to binding to TRAP, is dependent on the number of repeats in the RNA. Together these data support a model in which TRAP binds to RNA by first forming an initial complex with a small subset of the repeats followed by a cooperative interaction with the remaining triplets.

The trpRNA-binding Attenuation Protein (TRAP) from Bacillus subtilis binds a series of GAG and UAG repeats separated by 2–3 nonconserved spacer nucleotides in trp leader mRNA. To identify chemical groups on the RNA required for stability of the TRAP–RNA complex, we introduced several different nucleoside analogs into each pentamer of the RNA sequence 5′-(UAGCC)-3′ repeated 11 times and measured their effect on the TRAP–RNA interaction. Deoxyribonucleoside substitutions revealed that a 2′-hydroxyl group (2′-OH) is required only on the guanosine occupying the third residue of the RNA triplets for high-affinity binding to TRAP. The remaining hydroxyl groups are dispensable. Base analog substitutions identified all of the exocyclic functional groups and N1 nitrogens of adenine and guanine in the second and third nucleotides, respectively, of the triplets as being involved in binding TRAP. In contrast, none of the substitutions made in the first residue caused any detectable changes in affinity, indicating that elements of these bases are not necessary for complex formation and stability. Studies using abasic nucleotides in the first residue of the triplets and in the two spacer residues confirmed that the majority of the specificity and stability of the TRAP–RNA complex is provided by the AG dinucleotide of the triplet repeats. In addition to direct effects on binding, we demonstrate that the N7-nitrogen of adenosine and guanosine in UAG triplet and the 2′-OHs of (UAGCC)11 RNA are involved in the formation of an as yet undetermined structure that interferes with TRAP binding.