One-dimensional mapping of gamma emitting radionuclides in support of forensic examination

The development of two generations of a one-dimensional gamma mapping system is described. These systems use high-Z shielding, linear stage, and a high-purity germanium detector. Application to items of forensic interest is described and results for such items are presented. The presented results show the fission product (¹³⁷Cs) and activation product (⁶⁰Co) distributions along one-dimension of an archival item.     

Synthesis and evaluation of bioorthogonal pantetheine analogues for in vivo protein modification

In vivo carrier protein tagging has recently become an attractive target for the site-specific modification of fusion systems and new approaches to natural product proteomics. A detailed study of pantetheine analogues was performed in order to identify suitable partners for covalent protein labeling inside living cells. A rapid synthesis of pantothenamide analogues was developed and used to produce a panel which was evaluated for in vitro and in vivo protein labeling. Kinetic comparisons allowed the construction of a structure-activity relationship to pinpoint the linker, dye, and bioorthogonal reporter of choice for carrier protein labeling. Finally bioorthogonal pantetheine analogues were shown to target carrier proteins with high specificity in vivo and undergo chemoselective ligation to reporters in crude cell lysate. The methods demonstrated here allow carrier proteins to be visualized and isolated for the first time without the need for antibody techniques and set the stage for the future use of carrier protein fusions in chemical biology.     

Stereocontrolled Synthesis of syn‐β‐Hydroxy‐α‐Amino Acids by Direct Aldolization of Pseudoephenamine Glycinamide

β‐Hydroxy‐α‐amino acids figure prominently as chiral building blocks in chemical synthesis and serve as precursors to numerous important medicines. Reported herein is a method for the synthesis of β‐hydroxy‐α‐amino acid derivatives by aldolization of pseudoephenamine glycinamide, which can be prepared from pseudoephenamine in a one‐flask protocol. Enolization of (R,R)‐ or (S,S)‐pseudoephenamine glycinamide with lithium hexamethyldisilazide in the presence of LiCl followed by addition of an aldehyde or ketone substrate affords aldol addition products that are stereochemically homologous with L ‐ or D ‐threonine, respectively. These products, which are typically solids, can be obtained in stereoisomerically pure form in yields of 55–98 %, and are readily transformed into β‐hydroxy‐α‐amino acids by mild hydrolysis or into 2‐amino‐1,3‐diols by reduction with sodium borohydride. This new chemistry greatly facilitates the construction of novel antibiotics of several different classes.     

A Conventional Surfactant Becomes CO2‐Responsive in the Presence of Switchable Water Additives

We have developed a new benign means of reversibly breaking emulsions and latexes by using “switchable water”, an aqueous solution of switchable ionic strength. The conventional surfactant sodium dodecyl sulfate (SDS) is not normally stimuli‐responsive when CO₂ is used as the stimulus but becomes CO₂‐responsive or “switchable” in the presence of a switchable water additive. In particular, changes in the air/water surface tension and oil/water interfacial tension can be triggered by addition and removal of CO₂. A switchable water additive, N,N‐dimethylethanolamine (DMEA), was found to be an effective and efficient additive for the reversible reduction of interfacial tension and can lower the tension of the dodecane/water interface in the presence of SDS surfactant to ultra‐low values at very low additive concentrations. Switchable water was successfully used to reversibly break an emulsion containing SDS as surfactant, and dodecane as organic liquid. Also, the addition of CO₂ and switchable water can result in aggregation of polystyrene (PS) latexes; the later removal of CO₂ neutralizes the DMEA and decreases the ionic strength allowing for the aggregated PS latex to be redispersed and recovered in its original state.     

The multi-trip vehicle routing problem

The basic vehicle routing problem is concerned with the design of a set of routes to serve a given number of customers, minimising the total distance travelled. In that problem, each vehicle is assumed to be used only once during a planning period, which is typically a day, and therefore is unrepresentative of many practical situations, where a vehicle makes several journeys during a day. The present authors have previously published an algorithm which outperformed an experienced load planner working on the complex, real-life problems of Burton's Biscuits, where vehicles make more than one trip each day. This present paper uses a simplified version of that general algorithm, in order to compare it with a recently published heuristic specially designed for the theoretical multi-trip vehicle routing problem.     

Complexes of a [2]rotaxane ligand with terminal terpyridine groups

Permanently interlocked [2]rotaxane ligands can be created by capping a pyridine terminated [2]pseudorotaxane with terpyridine containing stoppers. The robust nature of the resulting [2]rotaxane ligand allows coordination to inert metals such as Ru(II) not possible under standard self-assembly conditions.     

Q-switched operation of a Nd:YCOB laser

Q-switched operation of a Nd:YCOB laser is demonstrated. A Nd:YCOB crystal was end-pumped by laser diodes operating at a wavelength of 0.8 μm and with a peak power of 22 W, and Q-switching was achieved by the spinning disc technique. Pulses that were as short as 50 ns and with up to 0.5 mJ of energy were obtained. After optimization, a threshold of 0.5 mJ and a slope efficiency of 13% were achieved.     

The growth of the thermal boundary layer at the inlet to a circular tube

Summary The problem considered is that of the heat transfer occurring at the inlet to a circular tube. Using the method of a previous paper we solve the energy equation in the form of a power series, instead of transforming the equation into an eigenvalue problem by separation of variables, as is usual in such cases. We thus obtain information concerning the temperature distribution at the inlet to the tube which is not provided by the latter method. A sufficient number of coefficients of the power series has been computed to allow the present solution to be joined to one of the second type, thus completing the solution of the problem for all values of the longitudinal variable.