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DNA nanotechnology has been employed to develop devices based on i-motif structures. The protonated cytosine-cytosine base pairs that stabilize i-motif conformations are favored under slightly acidic conditions. This unique property has enabled development of the first DNA molecular motor driven by pH changes. The ability to alter the stability and pH transition range of such DNA molecular motors is desirable. Understanding how i-motif structures are influenced by modifications, and which modifications enhance stability and/or affect the pH characteristics, are therefore of great interest. Here, the influence of 5-halogenation of the cytosine nucleobases on the base pairing of protonated cytidine nucleoside analogue base pairs is examined using complementary threshold collision-induced dissociation techniques and computational methods. The nucleoside analogues examined here include the 5-halogenated forms of the canonical DNA and RNA cytidine nucleosides. Comparisons among these systems and to the analogous canonical base pairs previously examined enable the influence of 5-halogenation and the 2′-hydroxy substituent on the base pairing to be elucidated. 5-Halogenation of the cytosine nucleobases is found to enhance the strength of base pairing of DNA base pairs and generally weakens the base pairing for RNA base pairs. Trends in the strength of base pairing indicate that both inductive and polarizability effects influence the strength of base pairing. Overall, the present results suggest that 5‑halogenation, and in particular, 5-fluorination and 5-iodination, provide effective means of stabilizing DNA i-motif conformations for applications in nanotechnology, whereas only 5-iodination is effective for stabilizing RNA i-motif conformations but the enhancement in stability is less significant. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop a simple biological system suitable for the treatment of dairy parlor wash waters. A novel horizontal-flow biofilm system with step feed was designed, constructed, and tested in the laboratory for organic carbon removal, nitrification, and denitrification of a synthetic dairy wastewater with average filtered chemical oxygen demand ([COD.sub.f]) of 2,060 mg/L, total nitrogen (TN) of 288 mg/L, and ammonia nitrogen ([NH.sub.4]-N) of 127 mg/L. The novel biofilm system consisted of two reactor units placed on top of one another, each comprising a stack of horizontal plastic sheets. Part of the wastewater was pumped onto Sheet 1 (top feed) and the remainder onto Sheet 11 (step feed) and flowed over the horizontal sheets down through the system. Three hydraulic loading rates were examined: 32.3, 25.1, and 19.3 L/[m.sup.2] day, based on the top plan area, and the respective removals of [COD.sub.f] were 96, 96, and 97% and of TN, 86, 83, and 75% were achieved. The system was simple and cheap to construct and operate. DOI: 10.1061/(ASCE)0733-9372(2007)133:6(569) CE Database subject headings: Agriculture; Biofilm; Biological treatment; Environmental engineering; Nitrification; Denitrification; Wastewater management.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2006.03.005 Byline: M.G. Healy, M. Rodgers, J. Mulqueen Keywords: Recirculating sand filters; Dairy parlor wastewaters; Forward flow; Organic loading rate Abstract: A stratified sand filter column, operated in recirculation mode and treating synthetic effluent resembling high-strength dairy wastewaters was studied over a 342-d duration. The aim of this paper was to examine the organic, total suspended solids (TSS) and nutrient removal rates of the sand filter, operated in recirculation mode, under incrementally increasing hydraulic and organic loading rates and to propose a field filter-sizing criterion. Best performance was obtained at a system hydraulic loading rate of 10Lm.sup.-2 d.sup.-1; a higher system hydraulic loading rate (of 13.4Lm.sup.-2 d.sup.-1) caused surface ponding. The system hydraulic loading rate of 10Lm.sup.-2 d.sup.-1 gave a filter chemical oxygen demand (COD), TSS, and total kjeldahl nitrogen (TKN) loading rate of 14, 3.7, and 2.1gm.sup.-2 d.sup.-1, respectively, and produced consistent COD and TSS removals of greater than 99%, and an effluent NO.sub.3-N concentration of 42mgL.sup.-1 (accounting for an 86% reduction in total nitrogen (Tot-N)). As the proportional surface area requirement for the sand filter described in this study is less than the recommended surface area requirement of a free-water surface (FWS) wetland treating an effluent of similar quality, it could provide an economic and sustainable alternative to conventional wetland treatment. Author Affiliation: Department of Civil Engineering, National University of Ireland, Galway, Ireland Article History: Received 23 June 2005; Revised 21 January 2006; Accepted 15 March 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2005.07.003 Byline: M. Rodgers, M.G. Healy, J. Prendergast Abstract: A laboratory continuous feed biofilm reactor, comprising a bulk fluid reactor, a biofilm plastic module, a feed tank, and pneumatic devices and controls, was operated for a total period of 257 days, including seeding time, to treat domestic-strength synthetic wastewater under increasing ammonium nitrogen (NH.sub.4.sup.+-N) loading rates, ranging from 0.17[+ or -]0.01 (0.71[+ or -]0.06gm.sup.-2 d.sup.-1) to 0.70[+ or -]0.02kgm.sup.-3 d.sup.-1 (2.9[+ or -]0.1gm.sup.-2 d.sup.-1). The biofilm plastic module was moved vertically in and out of the wastewater in continuous cycles. The maximum NH.sub.4.sup.+-N removal rate was reached during the maximum loading phase, when a NH.sub.4.sup.+-N loading rate of 0.70[+ or -]0.02kgm.sup.-3 d.sup.-1 (2.9[+ or -]0.1gm.sup.-2 d.sup.-1) was applied to the system. During this loading period, the average NH.sub.4.sup.+-N removal rate was 0.30[+ or -]0.10kgm.sup.-3 d.sup.-1 (1.30[+ or -]0.40gm.sup.-2 d.sup.-1). Author Affiliation: Department of Civil Engineering, National University of Ireland, Galway, Ireland Article History: Received 23 December 2004; Revised 7 June 2005; Accepted 26 July 2005

Accumulation of biomass and deposition of suspended solids at the surface of a sand filter can lead to clogging of the filter media. A laboratory intermittent sand filter column, which included three sand strata, was operated for a period of 806 d before failure occurred through surface clogging. Upon dismantling the column, the cause and effects of the surface clogging were investigated. The main mechanism responsible for sand clogging appeared to be biomass buildup. Maximum loss on ignition of filter media samples was 2.35%, and it occurred in the upper 0.01 m of the sand. There was a reduction in field-saturated hydraulic conductivity in the top 0.01 m of the upper sand stratum from a value of 1.9 x [10.sup.-3] [+ or -] 1.7 x [10.sup.-4] m [s.sup.-1] (for virgin sand with an effective size, [d.sub.10], of 0.45 mm) to 3.5 x [10.sup.-5] [+ or -] 7.5 x [10.sup.-6] m [s.sup.-1]. The soil-water characteristic curve, which relates the volumetric water content ([[theta].sub.v]) to the soil suction, also reflected the changes in the filter media due to clogging. The water-holding capacity greatly increased as biomass accumulated in the filter media. Scanning electron microscopy (SEM) confirmed the existence of a clogging organic layer on the surface of the top sand layer.

Threshold collision-induced dissociation of M(super +1) (adenine) with xenon is studied using guided ion beam mass spectrometry. Theoretical calculations on Cu(super +) indicate distinct differences in the binding site propensities of adenine to the alkali vs transition metal ions, a consequence of s-d sigma hybridization on the latter.