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The S‐glycosyltransferase LmbT, involved in the biosynthesis of lincomycin A, is the only known enzyme that catalyzes the enzymatic incorporation of rare amino acid L‐ergothioneine (EGT) into secondary metabolites. Here, we show the structure and function analyses of LmbT. Our in vitro analysis of LmbT revealed that the enzyme shows promiscuous substrate specificity toward nitrogenous base moieties in the generation of unnatural nucleotide diphosphate (NDP)‐D‐α‐D‐lincosamides. Furthermore, the X‐ray crystal structures of LmbT in its apo form and in complex with substrates indicated that the large conformational changes of the active site occur upon binding of the substrates, and that EGT is strictly recognized by salt‐bridge and cation‐π interactions with Arg260 and Trp101, respectively. The structure of LmbT in complex with its substrates, the docking model with the EGT‐S‐conjugated lincosamide, and the structure‐based site‐directed mutagenesis analysis revealed the structural details of the LmbT‐catalyzed SN2‐like S‐glycosylation reaction with EGT. [ABSTRACT FROM AUTHOR]

Following the events which took place on September 11, 2001, and the anthrax attacks which occurred after that date, US authorities became concerned with the idea that an assault with chemical or biological weapons could take place on American territory or in American ships or planes. A worrisome model for such an assault was the 1995 terrorist attack carried out on the Tokyo, Japan, subway system, using sarin gas. This paper discusses the possible ways to do in order to prevent casualties if such an attack took place. One idea was to use sensors that, like smoke detectors, would warn of impending danger. That concept became the foundation of the "detect to warn" strategy that served as the basis of efforts to protect public places. With a close examination of this strategy, this paper reveals that there are three major flaws that reduce the value of this approach and risk creating a false sense of security.

The utility and performance of label-free, oligonucleotide probes for reagentless detection of dilute target analytes was examined using a voltammetric transduction principle in an array format. Multistep, solid-state fabrication yielded preproduction arrays of 16 individually addressable, 30 [micro]m diameter microelectrodes in a 30 mm x 6.5 mm x 0.5 mm dipstick disposable device. The specificity of 16 nucleotide (nt) 2'-O-methylribonucleic acid and 22 nt DNA backbone probes bound through [Mg.sup.2+] phosphonate bridges to polypyrrole films on the microelectrodes were studied using microbial target RNAs of various lengths. Probe-specific interactions with Escherichia coli O157 H7 23S rRNA (2907 nt) and Candida albicans 18S rRNA (1788 nt) were detected at 65 and 58 fmol/mL, respectively, in volumes as low as 0.5 mL Specificity studies showed that, for a given probe, 'non-target' transcripts can contribute to changes in the voltammetric detection signal, though with responses that never exceed 70% of the detection signal acquired for specifically designed complementary targets. These results statistically validate the use of the voltammetric microelectrode array for obtaining a 'yes--no' answer on complementary specific binding. The study also identifies challenges and pitfalls for the selection strategies of oligonucleotide probes. 10.1021/ac102002k

Here we report the fabrication of two types of microirradiators, consisting of a recessed disk and protruding wire with low-[beta]-energy radionuclide Ni-63 electrodeposited onto a 25 [micro]m diameter Pt wire. Ni-63 is constricted to a small surface area of the microelectrode; hence, this tool provides a means of delivery of localized, large dose density of [beta] radiation to the object but a minimal dose exposure to the user. The activity levels of Ni-63 emitted from the recessed disk and protruding wire are 0.25 and 1 Bq, respectively. The corresponding [beta] particles flux levels emitted from the recessed disk and protruding wire are 51 and 11 kBq/[cm.sup.2], respectively. These values, measured experimentally using liquid scintillation counting, fit very well the expected values of activity for each microirradiator, calculated considering the self-absorption effect, typical for low-energy [beta] particles. In order to determine the optimal configuration the dose rates for varying distances from the object were calculated.

A sensing layer for a chemically sensitive field-effect transistor (CHEMFET) based on a composite of camphorsulfonic acid (CSA)-doped polyaniline (PANI) and the room-temperature ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethanesuffonyl)-imide, BMI([Tf.sub.2]N), has been developed and characterized for the sensing of ammonia gas. The work function responses of the cast films with and without IL were analyzed by 'stepwise' changes of ammonia gas concentration from 0.5 to 694 ppm in air as a function of the mole fraction of IL to PANI. The PANI. CSA/BMI([Tf.sub.2]N) layers showed enhanced sensitivities, lower detection limits, and shorter response times. There is experimental evidence that PANI forms a charge-transfer complex with imidazolium cation.

When an object approaches a vibrating quartz crystal microbalance (QCM) the resonant frequency changes. This 'proximity effect' was seen at the distance of 10 mm in air and became more pronounced as the distance decreased. This effect depends on the quality factor (Q-factor) value of a QCM, conductivity of the object, and electrical connection of the object to QCM electrodes. A special setup was constructed to test the impact of the proximity effect on a QCM. Damping fluid was placed on one side of QCM, to change the Q-factor. A conducting metal disk was brought close to the other side of the QCM exposed to air. By varying the distance between the QCM and an object (metal disk), a shift in frequency was observed. This proximity effect was largest (>200 Hz for 10 MHz QCM) when the Q-factor was low and a conducting metal disk (e.g., Cu) was electrically shorted to the proximal (nearest) QCM electrode. The finite element modeling showed that the proximity effect was likely due to interaction of the object with the fringing electromagnetic field of the QCM. A simple modified Butterworth Van-Dyke model was used to describe this effect. It must be recognized that this effect may lead to large experimental artifacts in a variety of analytical QCM applications where the Q-factor changes. Therefore, in order to avoid artifacts, QCM and similar mass acoustic devices should not operate in the low Q-factor (< 1000) regime.

Here we show that an array of sensors can provide information about the spatial and temporal distribution of chemicals in liquid turbulent plumes. Planar laser induced fluorescence (PLIF) and amperometric sensor arrays were used to record signals from modulated chemical plumes released into a recirculating flume. Coherence analysis was applied to extract the frequency components contained in the sensor response. Effects due to release distance, modulation frequency, and array orientation were investigated. This study has demonstrated that frequency encoded information can be extracted from a turbulent chemical plume using an array of amperometric sensors with optimized three-dimensional geometry and tuning.

Doping of glass with lithium ion can be accomplished by exposing the glass to a solution of organic solvent containing a soluble lithium ion salt, such as LiBr and a small amount of water. Under such conditions, the activity of solvated [Li.sup.+] is very high causing it to partition into the hydrated glass surface. Laser-induced breakdown spectroscopy and atomic absorption spectroscopy have been used to monitor the partitioning between glass and organic phase, respectively.

Strong protonic acids such as triflic acid and as tetrafluoroboric acid lower both the work and function and increase the conductivity of PANI-EB according to the known protonic form of the doping mechanism. The difference between these two kinds of doping is demonstrated by measurement of the work function, conductivity, UV-vis, and IR spectroscopy.

Dynamic characteristics of the amperometric sensing system for tracking of turbulent chemical plumes have been studied. The correlation analysis requires that such sensors respond rapidly and have long-term stability and minimal or low-flow sensitivity. Moreover, for practical purposes, such sensors must respond to an electrochemical marker that would be found in or at least be compatible with the diet of marine animals. Ascorbic acid is such a compound and can be electrochemically oxidized. Its long-term dynamic behavior on several types of electrodes has been studied. It has been found that a Pt electrode coated with polyaniline satisfies all the above requirements. However, this system has a peculiar dynamic behavior that affects the results of the correlation analysis, namely, at the higher frequencies. The behavior of such system in the virtual plume setup has been characterized and its usability for detection of fluctuating concentration of ascorbic acid in saline solution has been confirmed.

Results show that fundamental differences exist in the acid doping behavior of polyaniline film between a strong and a weak acid. Data indicate that both protons and anions of the dopant acids influence the structure and redox properties of polyaniline.

A review of published literature on chemical sensors for the period Dec 1, 1993 to Nov 30, 1997 is presented. The sensors covered by the papers included amperometric, conductometric, optical, mass, thermal, and potentiometric devices. Papers on books, general reviews, calibration rules, machine olfaction, the history and manufacture of chemical sensors and their applications were also included in the review.

A sensor array for analyzing hydrogen and ammonia gas mixtures in humid air has been developed, built into a rugged system, and calibrated for laboratory testing. The sensor array is comprised of four chemically sensitive field-effect transistors (CHEMFETs). Chemically sensitive layers for the sensors were developed and tested using a Kelvin probe. A combination of catalytic and noncatalytic thin layers (palladium and polyaniline) was selected for the four-sensor array. The work function responses of the CHEMFET sensor array to mixtures of hydrogen, ammonia, and humid air were measured. Chemometric multivariate methods, linear and nonlinear partial least squares, were used for the calibration of the sensor array using gas mixtures in the concentration range from 0 to 10 000 ppm hydrogen and ammonia in humid air. The sensor array for ammonia showed good sensitivity, selectivity, response time, and stability and is recommended for field deployment. In contrast, the sensor array for hydrogen, though highly sensitive to hydrogen, demonstrated inadequate stability, requiring further development before deployment is recommended.

The Kelvin probe (KP) is an analytical instrument composed of Cu and Pd plates that generate an alternating current in an external circuit. The KP was commonly utilized for the quantitative analysis of work function, contact and surface potentials of materials. A new class of chemical sensors can be developed based on the combination of the principles of KP and the Nernst equation. These chemical sensors such as insulated gate field-effect transistors can be utilized for the quantitative analysis of electrically neutral species based on the semiconductor effect.

A rapid, automated, microanalytical procedure for the determination of 90Sr in aged nuclear waste has been developed. It is based on a sequential injection analysis (SIA) system which rapidly separates 90Sr from 90Y, 137Cs, and other radionuclides. The isolated 90Sr is then detected on-line with a flow-through liquid scintillation counter. The separation is achieved using a sorbent extraction minicolumn containing a resin (EIChrom, Sr-Spec) that selectively binds 90Sr as a crown ether complex under acidic conditions. The 90Sr is eluted with water, mixed with liquid scintillation cocktail, and detected in the flow cell of the counter. Sample 90Sr activity can be quantified from peak areas, giving linear calibration curves. The instrument can also be operated in a stopped-flow mode for longer counting times. Analyses of aged nuclear waste samples from the Hanford site by the SIA method and a manual method were in excellent agreement: correlation coefficient R = 0.994. Sample analysis by the SIA method is complete in less than 40 min. The advantages of the new 90Sr analyzer include faster analysis, greater precision, reduced labor costs, and reduced secondary waste. Worker safety is improved because solution handling operations are fully automated and contained.

A selection of chemical sensor literature, published during the period Jan. 1, 1992-Nov. 1, 1993, are classified using four categories. These are books and reviews, reviews of sensors by their type, fabrication and selectivity and data processing. Entries for the four different types of chemical sensors namely, thermal sensors, mass sensors, electrochemical sensors and optical sensors, are evaluated based on the four categories. The books and reviews category registered the biggest percentage increase.

Ion optodes can be used in optically-monitored electrochemical ion detection without the use of an additional reference electrode. However, several optodes based on chromoionophores and field-sensitive dyes that feature either whole membrane or hydrophobic interactions require references during single ion-sensing studies. This dependency can be attributed to the extended membrane thickness created by the indicator and solute-solvent interactions and the solvation effects in hydrophobic conditions. Nevertheless, the ability of ion optodes to measure ion concentration in electrically neutral media makes it more valuable over other chemical sensors.

Research concerning chemical sensors and sensing techniques for the past two years failed to bring about any major new development. Most advances centered on new devices and fabrication procedures. The application of these new developments provided greater selectivity and higher sensing properties to the chemical detectors. Thermal, mass, electrochemical and optical sensors were used in researches to determine their performance in different experimental conditions.

Polyaniline (PANI) sensing layers incorporated with metal atoms can be used in electrochemical detection of hydrogen cyanide (HCN) within the 0.13 to 20 parts-per-million concentration range. The Kelvin probe work function sensor selectively measures the reversible and reproducible reaction caused by the charge-transfer interaction between the gas and PANI layer. The results show a concentration dependence between 20 and 35 mV/decade of HCN and a logarithmic response involving bulk mechanism. In addition, the confined space charge within the layer thickness and the total thickness of the matrix affect the sensitivity of the film.