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The hydration of carbon–carbon triple bonds is an important and atom economic synthetic transformation. Herein, we report a mild and selective method for the catalytic Markovnikov hydration of (E)-aryl enynes to the corresponding enones, mediated through the bench-stable aminium salt, tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBPA). The chemoselective and diastereoselective method proceeds under neutral metal-free conditions, delivering excellent product yields from terminal and internal alkyne units. The synthesis of biologically important (E)-3-styrylisocoumarins, including a formal synthesis of the natural product achlisocoumarin III, demonstrates the utility of this novel transformation.

Diversity Oriented Clicking (DOC) is a unified click-approach for the modular synthesis of lead-like structures through application of the wide family of click transformations. DOC evolved from the concept of achieving "diversity with ease", by combining classic C-C π-bond click chemistry with recent developments in connective SuFEx-technologies. We showcase 2-Substituted-Alkynyl-1-Sulfonyl Fluorides (SASFs) as a new class of connective hub in concert with a diverse selection of click-cycloaddition processes. Through the selective DOC of SASFs with a range of dipoles and cyclic dienes, we report a diverse click-library of 173 unique functional molecules in minimal synthetic steps. The SuFExable library comprises 10 discrete heterocyclic core structures derived from 1,3- and 1,5-dipoles; while reaction with cyclic dienes yields several three-dimensional bicyclic Diels-Alder adducts. Growing the library to 278 discrete compounds through late-stage modification was made possible through SuFEx click derivatization of the pendant sulfonyl fluoride group in 96 well-plates-demonstrating the versatility of the DOC approach for the rapid synthesis of diverse functional structures. Screening for function against MRSA (USA300) revealed several lead hits with improved activity over methicillin.

SuFEx click chemistry is a powerful method designed for the selective, rapid and modular synthesis of functional molecules. Classical SuFEx reactions form stable S-O linkages upon exchange of S-F bonds with aryl silyl-ether substrates, and while near-perfect in their outcome, are sometimes disadvantaged by relatively high catalyst loadings and prolonged reaction times. We herein report the development of 'Accelerated SuFEx Click Chemistry' (ASCC), an improved SuFEx method for the efficient and catalytic coupling of aryl and alkyl alcohols with a range of SuFExable hubs. We demonstrate Barton's hindered guanidine base (2- tert -butyl-1,1,3,3-tetramethylguanidine; BTMG) as a superb SuFEx catalyst that, when used in synergy with silicon additive hexamethyldisilazane (HMDS), yields stable S-O bond linkages in a single step; often within minutes. The powerful combination of BTMG and HMDS reagents allows for catalyst loadings as low as 1.0 mol% and, in congruence with click-principles, provides a scalable method that is safe, efficient, and practical for modular synthesis. ASSC expands the number of accessible SuFEx products and will find significant application in organic synthesis, medicinal chemistry, chemical biology, and materials science .

SuFEx (Sulfur Fluoride Exchange) is a modular, next generation family of click reactions, geared towards the rapid and reliable assembly of functional molecules. This review discusses the growing number of applications of SuFEx, which can be found in nearly all areas of modern chemistry; from drug discovery to materials science.

Selenate-loaded selenium water remediation materials based on polymer fibres have been investigated by dynamic nuclear polarization (DNP) enhanced solid-state NMR. For carbon-13 a significant reduction in experiment time is obtained with DNP even when compared with conventional carbon-13 NMR spectra recorded using larger samples. For the selenium remediation materials studied here this reduction allows efficient acquisition of {1H}-77Se heteronuclear correlation spectra which give information about the nature of the binding of the remediated selenate ions with the grafted side chains which provide the required ion exchange functionality.

A protocol for the efficient conversion of sulfonyl fluorides into sulfonyl azides through Lewis base activation is described. The in situ generated sulfonyl azides are efficient diazo-transfer agents, affording diazo compounds and primary azides in excellent yields.

High-surface area γ-alumina is industrially used as a catalyst support. Catalytically active elements are doped onto the support, where they can bind to AlO4, AlO5 or AlO6 sites on the surface. Pretreating the surface with alkaline earth oxides can alter the availability of these surface sites, hence affecting the catalytic activity. The surface binding sites of strontium oxide (SrO) on γ-alumina were previously unknown. Direct 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) could not detect AlO5 sites at 9.4 T, so 1H‐27Al cross-polarisation (CP) MAS NMR was used to preferentially select the surface environment signals. We directly observed the three surface environments on dehydrated γ-alumina as a function of SrO impregnation up to 4 wt% SrO. We found that Sr2+ preferentially binds to AlO5 and AlO6 surface sites. 1H MAS NMR revealed SrO impregnation causes a reduction in the terminal (−0.3 ppm) and bridging (2.2 ppm) hydroxyl environments, as well as the promotion of a new peak in between these sites, at 0.5 ppm. By using 1H‐27Al CP/MAS NMR the relative proportions of surface sites on γ-alumina can be determined, allowing an optimal level of SrO doping that can saturate all the AlO5 sites. Importantly, this provides a method of subsequently depositing catalytically active elements on just the AlO4 or AlO6 sites, which can provide a different catalytic activity or stability compared to the AlO5 binding site.

We present a selection of elegant and diverse biomimetic syntheses of complex natural product dimers. The dimerisation pathways discussed encompass the most prevalent strategies, including: Diels-Alder, Aldol, Mannich, conjugate addition, oxidative, radical and photochemical approaches; each underpinned through rational biosynthetic speculation.

Technologies that enable surface modification are in high demand and are critical for the implementation of new functional materials and devices. Here, we describe the first modification of a carbon surface (in this case carbon fiber) using the sulfur-fluoride exchange (SuFEx) reaction. The parent sulfur (VI) fluoride moiety can be installed directly to the surface via electrochemical deposition of the fluorosulfate phenyldiazonium tetrafluoroborate salt, or by 'SuFExing' a phenol on the carbon surface followed by treatment of the material with SO2 F2 ; similar to a 'graft to' or 'graft from' functionalization approach. We demonstrate that these SuFEx-able surfaces readily undergo exchange with aryl silyl ethers, and that the subsequent sulfate linkages are themselves stable under electrochemical redox conditions. Finally, we showcase the utility of the SuFEx chemistry by installing a pendant amino group to the fiber surface resulting in interfacial shear strength improvements of up to 130 % in epoxy resin.

The jerantinine family of Aspidosperma indole alkaloids from Tabernaemontana corymbosa are potent microtubule-targeting agents with broad spectrum anticancer activity. The natural supply of these precious metabolites has been significantly disrupted due to the inclusion of T. corymbosa on the endangered list of threatened species by the International Union for Conservation of Nature. This report describes the asymmetric syntheses of (−)-jerantinines A and E from sustainably sourced (−)-tabersonine, using a straight-forward and robust biomimetic approach. Biological investigations of synthetic (−)-jerantinine A, along with molecular modelling and X-ray crystallography studies of the tubulin—(−)-jerantinine B acetate complex, advocate an anticancer mode of action of the jerantinines operating via microtubule disruption resulting from binding at the colchicine site. This work lays the foundation for accessing useful quantities of enantiomerically pure jerantinine alkaloids for future development.

We demonstrate 1,2-dibromoethane-1-sulfonyl fluoride (DESF) as a bench-stable and readily accessible precursor to the robust SuFEx connector, 1-bromoethene-1-sulfonyl fluoride (BESF). The in situ generation of BESF from DESF opens up several new reaction profiles, including application in the syntheses of unprecedented 3-substituted isoxazole-5-sulfonyl fluorides, 1-substituted-1H-1,2,3-triazole-4-sulfonyl fluorides, 2-amino-1-bromoethane-1-sulfonyl fluorides and 4-bromo-β-sultams in good to excellent yields. These new modules comprise a pendant sulfonyl fluoride handle, which further undergoes facile and selective SuFEx reactions with a selection of aryl silyl ethers to generate stable and useful sulfonate connections.

Low levels of transition metal oxides in alkali borosilicate glass systems can drastically influence crystallisation and phase separation properties. We investigated the non-monotonic effect of manganese doping on suppressing crystallisation, and the influence on optical properties by iron oxide doping, in terms of local atomic structure. Structural models based on empirical potential structure refinement were generated from neutron and X-ray scattering data, and compared against multinuclear solid-state NMR. This revealed that a 2.5% manganese doping had a disruptive effect on the entire glass network, supressing crystallisation of an undesired bismuth silicate phase, and that iron species preferentially locate near borate tetrahedra. Preventing phase separation and controlling crystallisation behaviour of glass are critical to the ultimate properties of automotive glass enamels.

Despite considerable research efforts, finding a chemically stable electrolyte mixture in the presence of reduced oxygen species remains a great challenge. Previously, dimethyl sulfoxide (DMSO) and sulfolane-based electrolytes were reported to be stable for Li-O2 battery applications. Recently LiOH-based chemistries have demonstrated to involve supressed side reactions in water-added ether- and DMSO-based electrolytes. Herein, we investigate the impact of dimethyl sulfoxide-based electrolyte and sulfolane co-solvent on the cell chemistry in the presence of water. We found that DMSO-based electrolyte leads to formation of a peroxide-hydroxide mixture as discharge products and the removal of both LiOH and Li2O2 on charging from 3.2 -3.6 V (vs. Li+/Li) is observed. In the presence of sulfolane as co-solvent, a mixture of Li2O2 and LiOH is formed as major discharge products with slightly more dominant LiOH formation than in the absence of sulfolane. The presence of sulfolane has also significant effects in the charging behaviour, exhibiting a clearer 3 e-/O2 oxygen evolution reaction profile during the entire charging process. This work provides insights into understanding the effects of the primary solvent on promoting LiOH formation and decomposition in LiI mediated non-aqueous Li-O2 batteries.

The 1H and 13C NMR spectra in methylammonium lead halide perovskites, CH3NH3PbX3 (X = I, Br and Cl) show that the CH3NH3+ units undergo dynamic reorientation, as the organic component tumbles in the perovskite cage. In addition, the differences in the anomalously long relaxation times of the protons associated with the CH3 and not the NH3 groups indicate that only the amine end of the CH3NH3+ group is interacting with the inorganic network. Using this information, we have refined some single crystal X-ray and neutron diffraction data to probe their unusual structures in more detail. Furthermore, impedance spectroscopy has been used to monitor the high-temperature phase transition of CH3NH3PbI3, which confirms a significant increase in conductivity, when it is in its high temperature and higher symmetry structural regime. The optical band-gaps of each halide perovskite were determined using UV-visible spectroscopy and are consistent with previous reports. NRF (Natl Research Foundation, S’pore) Accepted version

Amide bond formation is one of the most executed reactions in chemistry and biology. This is largely due to the ubiquity of the amide functional group in biological molecules, natural products and pharmaceutically important drugs. We report here the development of "SuFExAmide": a new sulfur-fluoride exchange (SuFEx) click chemistry based protocol for the efficient amidation of carboxylic acids via acyl fluoride intermediates. We have developed benzene-1,3-disulfonyl fluoride as a cost effective, powerful and versatile coupling agent, which delivers challenging secondary and tertiary amides in excellent yields from sterically hindered and electron-deficient amines. The straightforward method offers significant benefits over existing protocols in terms of substrate scope, efficiency and ease of operation and is demonstrated by the synthesis of 44 amides, including GNF6702, an antiprotozoal drug candidate. In the majority of cases, the amide products are obtained in high yield without the need for excess reagents or chromatographic purification.

A protocol for the efficient conversion of sulfonyl fluorides into sulfonyl azides through Lewis base activation is described. The in situ generated sulfonyl azides are efficient diazo-transfer agents, affording diazo compounds and primary azides in excellent yields.

(1)H and (13)C solid- and solution-state NMR have been used to characterise waxes produced in the Fischer-Tropsch reaction, using Co-based catalysts either unpromoted or promoted with approximately 1 wt% of either cerium or rhenium. The aim was to measure average structural information at the submolecular level of the hydrocarbon waxes produced, along with identification of the minor products, such as oxygenates and olefins, which are typically observed in these waxes. A parameter of key interest is the average number of carbon atoms within the hydrocarbon chain (N(C)). A wax prepared using an unpromoted Co/Al(2)O(3) catalyst had N(C)similar to 20, whilst waxes made using rhenium- or cerium-promoted Co/Al(2)O(3) catalysts were found to have N(C)similar to 21. All three samples contained small amounts of oxygenates and alkenes. The subtle differences found in the waxes, in particular the minor species produced, demonstrate that the different promoters have different effects during the reaction, with the Re-promoted catalyst producing the fewest by-products. It is shown in (13)C solid-state NMR spectra that for that for longer chain (compared to the lengths of chain in previous studies) waxes that the lack of resolution and the complexities added by the differential cross-polarisation (CP) dynamics mean that it is difficult to accurately determine N(C) from this approach. However the N(C) determined by (13)C CP magic angle spinning NMR is broadly consistent with the more accurate solution approaches used and suggest that the wax characteristics do not change in solution. On this basis an alternative approach for determining N(C) is suggested based on (1)H solution state NMR that provides a higher degree of accuracy of the chain length as well as information on the minor constituents.

This study reports an automated numerical method for the location of the gel point in oscillatory shear data and demonstrates its potential application in measurements on therapeutically modified (heparinised) samples of healthy coagulating blood. Heparin prolongs the onset of clot formation and has a significant effect on the microstructure of the clot which is eventually formed. The results demonstrate the potential of this rheometrical technique as a new tool for monitoring the effect of heparin on samples of whole blood with significantly better linearity of response within the therapeutic range than another global coagulation monitoring technique (thromboelastography) which has previously been used.

We report studies of the formation of ordered microporous polymer films by the evaporation of polymer solutions following exposure to a humid atmosphere. High-speed microphotographic (HSMP) studies of the formation process reveal that near the surface of the polymer solution, vapor condensation produces near monodisperse water droplets which crystallize to form a close-packed array. Following the evaporation of the solvent, characterization of the solid by Atomic Force Microscopy, confocal microscopy and white light interferometry reveals that the surface of the polymer film features extensive regions of hexagonally close-packed microscopic pores, whose spatial arrangement replicates that of the initial droplet monolayer. Defects recorded by HSMP in the packing of the colloidal monolayer of liquid droplets formed above the surface of the polymer solution are found to correspond to those transferred into the eventual solid film, providing the first direct evidence of the structure templating role of the droplet monolayer.

A method has been developed, using laser ablation–inductively coupled plasma mass spectrometry (LA–ICP-MS), for the semiquantitative determination of 43 elements in diamonds, chromites and garnets. Samples of diamonds from five countries have been analysed and the interrelationship between the trace elements gives distinctive patterns for each source. The data indicate that this technique could form the basis of a provenance identification protocol for diamonds. This would produce an analytical technique to assist police forces in tracing the origin of stolen material. LA–ICP-MS can also be used to establish the trace element distribution in indicator minerals for diamond exploration, such as garnets and chromites. Of particular significance in this data set in the comparison of the relative distributions of the rare earth elements, tantalum and hafnium, which indicates a consistent inter-element relationship for garnets associated with diamondiferous kimberlites. This relationship is considerably different from that found in garnets obtained from non-diamondiferous and other sources. Application of the principle of trace element partitioning pattern recognition to chromites has indicated the potential of the technique to identify also a kimberlitic or non-kimberlitic provenance for this mineral. The data presented here are the result of preliminary investigations. A more detailed study is currently being undertaken and will be the subject of future papers.

High-speed photographic studies and neutron diffraction measurements have been made of water under tension in a Berthelot tube. Liquid water was cooled below the normal ice-nucleation temperature and was in a doubly-metastable state prior to a collapse of the liquid state. This transition was accompanied by an exothermic heat release corresponding with the rapid production of a solid phase nucleated by cavitation. Photographic techniques have been used to observe the phase transition over short time scales in which a solidification front is observed to propagate through the sample. Significantly, other images at a shorter time interval reveal the prior formation of cavitation bubbles at the beginning of the process. The ice-nucleation process is explained in terms of a mechanism involving hydrodynamically-induced changes in tension in supercooled water in the near vicinity of an expanding cavitation bubble. Previous explanations have attributed the nucleation of the solid phase to the production of high positive pressures. Corresponding results are presented which show the initial neutron diffraction pattern after ice-nucleation. The observed pattern does not exhibit the usual crystalline pattern of hexagonal ice [I(h)] that is formed under ambient conditions, but indicates the presence of other ice forms. The composite features can be attributed to a mixture of amorphous ice, ice-I(h)/I(c) and the high-pressure form, ice-III, and the diffraction pattern continues to evolve over a time period of about an hour.

A compact, modular, low-cost, high-density readout system for double-sided silicon strip detectors (DSSD) has been developed. The system, composed of a customized high-density, multi-channel preamplifier unit combined with commercial CAMAC modules, provides for the individual readout of each of the 32 segments in a 16 × 16 crossed-strip DSSD. This system permits X–Y position sensitivity to be achieved for multiple-particle events, making double-sided silicon strip detectors powerful tools for the study of nuclear reactions leading to many-charged-particle final states.

Magic-angle spinning (MAS) NMR spin-echo dephasing is systematically investigated for the spin\ud I = 3/2 11B nucleus in lithium diborate, Li2O.2B2O3. A clear dependence on the quadrupolar\ud frequency (ωQPAS/2π = 3CQ/[4I (2I – 1)]) is observed: the B3 (larger CQ) site dephases more slowly\ud than the B4 site at all investigated MAS frequencies (5 to 20 kHz) at 14.1 T. Increasing the MAS\ud frequency leads to markedly slower dephasing for the B3 site, while there is a much less evident\ud effect for the B4 site. Considering samples at 5, 25, 80 (natural abundance) and 100 % 11B isotopic\ud abundance, dephasing becomes faster for both sites as the 11B isotopic abundance increases. The\ud experimental behaviour is rationalised using density matrix simulations for two and three dipolarcoupled\ud 11B nuclei. The experimentally observed slower dephasing for the larger CQ (B3) site is\ud reproduced in all simulations and is explained by the reintroduction of the dipolar coupling by the\ud so-called “spontaneous quadrupolar-driven recoupling mechanism” having a different dependence\ud on the MAS frequency for different quadrupolar frequencies. Specifically, isolated spin-pair\ud simulations show that the spontaneous quadrupolar-driven recoupling mechanism is most efficient\ud when the quadrupolar frequency is equal to twice the MAS frequency. While for isolated spin-pair\ud simulations, increasing the MAS frequency leads to faster dephasing, agreement with experiment is\ud observed for three-spin simulations which additionally include the homogeneous nature of the\ud homonuclear dipolar coupling network. First-principles calculations, using the GIPAW approach,\ud of the 2J11B-11B couplings in lithium diborate, metaborate and triborate are presented: a clear trend\ud is revealed whereby the 2J11B-11B couplings increase with increasing B-O-B bond angle and B-B\ud distance. However, the calculated 2J11B-11B couplings are small (0.95, 1.20 and 2.65 Hz in lithium\ud diborate), thus explaining why no zero crossing due to J modulation is observed experimentally,\ud even for the sample at 25 % 11B where significant spin-echo intensity remains out to durations of\ud ~200 ms.

Summary form only given. We report studies of ordered microporous and nanoporous polymer films formed by the evaporation of polymer solutions following exposure to a humid atmosphere. High speed microphotographic studies of the formation process reveal that near the surface of the polymer solution, vapour condensation produced near mono-disperse water droplets which form a close-packed monolayer (or 'breath figure'). An interesting feature found in the present study is the occurrence of nano-scale pores at the film surface and at (and within) the walls of the sub-surficial microscopic pores. This finding is particularly important in the context of the possible use of such films as biodegradable scaffolds for Tissue Engineering applications involving extracellular matrix production, or as candidate systems for drug delivery containment systems. Clearly, a failure to account for the presence of large populations of nanoscopic pores at (and within) the walls of the micron-scale pore structure will lead to significant overestimates of the mass of polymer available for bio degradation and hence of the likely lifetime of such structures in vivo. Similarly, given the potential application of porous scaffolds generated using the breath figure technique for slow release in drug delivery processes, the results of the present work suggest the presence of the smaller population of pores could have a significant influence on drug delivery timescale

We report studies of ordered microporous and nanoporous polymer films formed by the evaporation of polymer solutions following exposure to a humid atmosphere. High speed microphotographic (HSMP) studies of the formation process showed that near the surface of the polymer solution, vapour condensation produced near mono-disperse water droplets which form a close-packed monolayer (or ‘breath figure’). Following the evaporation of the solvent, characterisation of the solid by Atomic Force Microscopy and Scanning Electron Microscopy revealed that the surface of the polymer film is characterised by extensive regions of hexagonally close-packed microscopic pores, whose spatial arrangement replicates that of the initial droplet monolayer. Characterisation of sections of the film by Atomic Force Microscopy established that the surficial pores represent open sections of sub-surficial spheroidal cavities formed by encapsulation of the water droplets within the polymer solution. An interesting feature of the results is the occurrence of nano-scale pores at the film surface and at (and within) the walls of the sub-surficial microscopic pores. This is the first physical evidence report of such features in porous polymer films produced by a process involving breath-figures. Their dimensions suggest that more detailed structural investigations will require alternative techniques to conventional, optical methods.

Recently, it has been reported that a series of prostaglandin F2-like compounds (F2-isoprostanes) are produced in vivo during peroxidation of arachidonic acid by a mechanism independent of the cyclooxygenase pathway. Of these, 8-epi-PGF2 alpha is shown to be a potent vasoconstrictor. We describe an improved method for analysing F2-isoprostanes in biological fluids. The method involves solid-phase extraction on an octadecylsilane (C18) and an aminopropyl (NH2) cartridge. After conversion to pentafluorobenzyl ester and trimethylsilyl ether derivatives, F2-isoprostanes are analysed by negative-ion chemical ionization mass spectrometry using tetradeuterated PGF2 alpha as the internal standard. The limit of detection of the assay was 10 pg/ml, with a coefficient of variation ranging from 9.4 to 15.1%. Analysis of plasma samples from healthy volunteers (n = 7) revealed no quantifiable levels of free (unesterified) 8-epi-PGF 2 alpha. However, the plasma samples contained 58 to 166 pg/ml of 8-epi-PGF2 alpha when analyzed for the total (sum of free and esterified) F2-isoprostanes. The main advantages of the method lie in the improved recovery, gas chromatographic separation and speed compared to existing techniques.

Dew or breath figures is a disordered pattern formed by polydisperse water drops that form when a cold surface comes in contact with breath or moist air. Unexpectedly, self-assembled arrays of non-coalescent monodisperse water drops form when dilute solutions of polymers in volatile organic solvents are exposed to moist air. After solvent evaporation is complete, these condensation figures dry out as well, leaving "holey" polymer films, containing hexagonally ordered arrays of pores (0.2 to 10 μm). While the macroporous films are produced easily for a wide variety of solvents and polymers, there is no existing theory that describes how the pore size depends upon tunable parameters like humidity, air temperature and velocity as well as on the choice of solvent and polymer. In this study, we propose a transport model to elucidate the role of the solvent and airflow in determining the rate and extent of evaporative cooling, and contrast our model results with the corresponding experimental measurements for polystyrene/carbon disulfide solutions. We describe how modeling evaporative cooling is essential for the quantitative understanding of dominant processes that lead to growth, non-coalescence and self-assembly of water drops, and the subsequent formation of ordered arrays of pores.

An inhalation exposure system was designed from an all glass aquarium with a volume of 391 liters. A top for the chamber was fabricated from acrylic plastic and Teflone (surface in contact with the test atmosphere) with an inlet, outlet, 5 sampling ports, and handles. Supply air to the chamber was charcoal and HEPA filtered. Air flow through the chamber is horizontal and can range from 50 to 200 liters/minute. Air flow is measured by a glass tube rotameter and regulated by polyvinyl chloride valves. Chamber air was HEPA and charcoal filtered prior to exhausting it to ambient air. The operating characteristics of this exposure system were assessed using test atmospheres of formaldehyde, chlorine, n-hexane and an aerosol of propylene glycol. Expressed as percent of a central sampling point the chamber concentrations of formaldehyde, chlorine and n-hexane ranged from 91.6% to 103.3% with an average of 97.9%. No differences in chamber distribution were noted at 78 or 130 liters/minute (corresponding to 12 and 20 chamber volumes/hour). For propylene glycol, the mass median aerodynamic diameter (MMAD) at a chamber air flow of 79 L/minute varied from 1.37 to 1.63 μm (σg range 1.34 to 1.43). Similar results were found at 130 liters/minute. During mass sampling a concentration gradient was found from the inlet to the outlet of the chamber and ranged from 55 to 99% (¯x = 78.5%) of the inlet concentration. This inhalation exposure system is very suitable for acute or sub-acute inhalation studies of gases or vapors but is only satisfactory for aerosols under certain operating conditions. It should prove to be particularly useful for laboratories wishing to set up a modest inhalation toxicology facility.

Repeated exposure of adult rats to n -hexane produces a central and peripheral neuropathy which may be mediated through metabolic activation to methyl n -butyl ketone (MBK) and 2,5-hexanedione (2,5-HD). The perinatal toxicity of n -hexane and its metabolism in the pregnant rat have not been investigated. Pregnant rats were exposed for 6 hr per day to 1000 ppm n -hexane on Days 8–12, 12–16, or 8–16 of gestation. No significant alterations in fetal resorptions, body weights, visible anomalies, and the incidence of soft tissue and skeletal anomalies were noted in any of the treatment groups. The postnatal growth of pups born from dams exposed to 1000 ppm n -hexane 6 hr/day on Days 8–16 of gestation was significantly depressed compared to controls up to 3 weeks after birth (mean treated litter weight 13.9% less than control at 3 weeks). Litter weights of treated pups had returned to control values by 7 weeks after birth. n -Hexane was metabolized to MBK and 2,5-HD in pregnant rats exposed to 1000 ppm n -hexane on Day 20 of gestation. Concentrations of the three compounds in the fetus were approximately equal to those in maternal blood at all times after exposure. The half-life of 2,5-HD in maternal blood was significantly greater than n -hexane and MBK (3.90 hr vs 1.24 and 0.99 hr, respectively). Thus, n -hexane and its metabolites MBK and 2,5-HD may have only a minimal potential to alter perinatal development of rats.

A subacute study was completed in groups of 10 male and 10 female Fischer 344 rats exposed to air (controls), 1, 3, or 9 ppm chlorine for 6 hr/day, 5 days/week, for 6 weeks. Concentration related decreases in body weight gain were seen at all exposure concentrations in females and at 3 and 9 ppm in males. Additionally, three females at 9 ppm died before the end of Day 30 of exposure. Urinalysis, hematology, and clinical chemistry evaluations were completed on the surviving animals. The urine specific gravity was elevated at all exposure concentrations in the females and at 3 and 9 ppm in the males. The hematocrit and white blood cell count were increased in the females exposed to 9 ppm. Elevations in alkaline phosphatase activity, blood urea nitrogen, γ-glutamyl transpeptidase, and serum glutamic-pyruvic transaminase occurred at 9 ppm; alkaline phosphatase was elevated at 3 ppm in rats of both sexes. Widespread evidence of inflammation was seen throughout the respiratory tract with hyperplasia and hypertrophy of epithelial cells of the respiratory bronchioles, alveolar ducts, and alveoli of male and female rats exposed to 9 ppm. Changes in male rats at 3 or 1 ppm consisted of focal inflammation of the nasal turbinates and a slight to moderate inflammatory reaction around the respiratory bronchioles and alveolar ducts. Increased eosinophilic cytoplasmic homogeneity and decreased granularity of the epithelial cells of the proximal convoluted tubules were seen in the kidneys of male rats exposed to 9 ppm. The livers of rats of both sexes at 9 or 3 ppm had an increased hepato-cellular cytoplasmic vacuolation. These data indicated that repeated exposure of Fischer 344 rats to chlorine resulted in pulmonary effects at all levels of chlorine used, and hepatic and renal effects at 9 and 3 ppm.

For four decades, the Draize test has remained the accepted method for evaluating eye irritation. Criticisms center around the inhumane treatment of animals and the irreproducibility of the subjective scoring procedure. The objective of this study was to determine if changes in corneal thickness obtained using a slit-lamp pachometer could be used to replace the Draize scoring procedure and provide a method for quantifying ocular irritation. Twenty-four chemicals (six surfactants, seven alcohols, four ketones, four acetates, and three aromatics) were instilled in the conjunctival sacs of rabbits and irritation monitored by Draize scoring and changes in corneal thickness. The Draize procedure was more adept at detecting minor conjunctival damage, but corneal thickness exhibited less variation and increased sensitivity for detection of healing reactions. A significant linear correlation (y = 1.736 chi + 92.883) was established between Draize score and corneal thickness changes with a correlation coefficient (r) of 0.86 and an F-value for regression of 261.3. Using these findings, an ocular irritation ranking system is proposed based upon the percentage of corneal swelling. Ocular irritation potential was ranked for the chemical groups tested (surfactants greater than alcohols greater than ketones or acetates greater than aromatics). Quantitation of ocular irritation from changes in corneal thickness provides objective, numerical data applicable to standard parametric statistical procedures. This should eliminate the subjective bias inherent to Draize scoring and decrease intra-and interlaboratory variability.

The sensory irritation potential of a series of saturated and unsaturated aliphatic and cyclic aldehydes was investigated in B6C3F1 and Swiss-Webster mice. With the reflex decrease in respiratory rate as the endpoint response, α,β-unsaturated aliphatic aldehydes yielded RD50 values (concentration which elicits a 50% decrease in respiratory rate) ranging from 1 to 5 ppm while saturated aliphatic aldehydes with two or more carbons produced RD50 values from 750 to 4200 ppm. Cyclic aldehydes produced intermediate RD50 values which ranged from 60 to 400 ppm. No statistically significant differences were found between concentration-response curves of B6C3F1 and Swiss-Webster mice. Saturated aliphatic aldehydes with two or more carbons were nearly 1000 times less potent than formaldehyde. Although the mechanisms responsible for stimulation of trigeminal nerve endings by airborne chemicals are poorly understood, several hypotheses may help to explain the differences seen in this study. For example, the sensory irritation potency of the saturated aliphatic aldehydes diminished with their reported dehydration constants which may determine the degree to which these aldehydes crosslink with receptor proteins. The sensory irritation potency of acrolein and crotonaldehyde was probably due to 1,2 or 1,4 addition reactions. Additionally, molecular conformation and a recently published physical mechanism may contribute to sensory irritation responses, particularly for the less reactive aldehydes. Tentative threshold limit values (TLVs), based upon prevention of sensory irritation, were extrapolated from the RD50 values of Swiss-Webster mice. With the exception of crotonaldehyde, good agreement was found with currently published TLVs.

Numerous in vitro cytotoxicity assays have been proposed as potential alternatives to the Draize eye irritancy test. The results reported, based upon the rank correlation of ocular irritancy with cytotoxicity, have been encouraging. However, direct calibration of in vivo to in vitro data utilizing several categories of chemicals has not been reported. This study evaluated the use of in vitro cytotoxicity data for predicting the ocular irritancy potential of 24 chemicals (six surfactants, seven alcohols, four ketones, four acetates, and three aromatics). BALB/c 3T3 cells were grown overnight, then exposed for 30 min to at least four different concentrations of each chemical (expressed as volume percentage). Linear regression analysis of the log concentration versus percentage of control growth was used to calculate the concentration of toxicant that inhibited the normal growth rate by 50% (GI50). The rank ordering of cytotoxicity based upon the GI50s was surfactants > aromatics > alcohols > ketones or acetates. The larger molecular weight representative of each series (i.e., 2-ethyl-1-hexanol for alcohols) had lower GI50 values than those of the lower molecular weight substances. The GI50 values were then directly calibrated against in vivo ocular irritancy quantitated as percentage corneal swelling following exposure of rabbits to the same test chemicals. A significant linear correlation between cytotoxicity and ocular irritancy was established only for surfactants and alcohols. For acetates, ketones, and aromatics there was little correlation. The overall poor correlation between cytotoxicity and ocular irritancy was attributed to differences in mechanisms of irritancy. The lack of correlation illustrates that in vitro cytotoxicity data cannot be used to predict the ocular irritancy potential of a broad spectrum of chemicals.

The physiological stress imposed upon mice due to the irritating properties of thermal decomposition products of polymeric materials was evaluated. Acute lethality and histopathological evaluation were included in the study. The rankings of the polymeric materials studied from most to least hazardous was concluded to be polytetrafluoroethylene greater than polyvinyl chloride greater than Douglas Fir and flexible polyurethane foam greater than fiber glass reinforced polyester greater than copper coated wire with mineral insulation.

A bleeding diathesis is described which is phenotypically indistinguishable from hemophilia A and which has been transmitted as a dominant trait in three generations of women in a North Carolina kindred. The abnormal phenotype is characterized by clinical mildness and slightly abnormal clotting time, prothrombin consumption, and partial thromboplastin time. Bleeding time, platelet count, clot retraction, tourniquet test, and prothrombin time are normal. Concentration of factors I, II, V, VII, IX, X, and XII are normal, while factor VIII activity is reduced to 2%-5% of control values. De novo synthesis of factor VIII does not occur after transfusion; factor VIII-related antigen is normal; patients'plasmas aggregate platelets normally in the presence of ristocetin, and a typical protein pattern is seen when a chymotryptic digest of cryoprecipitate of the proband is examined by SDS-polyacrylamide gel electrophoresis. Six possible genetic explanations are entertained. Balanced X-autosomal translocation of hemophilia A heterozygotes has been excluded by cytogenetic analysis of metaphase chromosomes. Classes von Willebrand's disease (vWd) is probably excluded on the basis of the laboratory data, and extreme lyonization of hemophilia A heterozygotes on probabilistic grounds. The genetic possibilities which cannot be excluded include a previously unrecognized variant mutation at the vWd locus, a dominant mutation at the hemophilia A locus on the X chromosome, and dominant mutation at a hypothetical fourth locus involved in factor VIII synthesis and control.

The purpose of this study was to investigate the disposition of ethylene (C 2 H 4 ) in the F344 rat and to determine the effects of pretreatment of animals with Aroclor 1254 on the disposition and hepatotoxicity of ethylene. Control or Aroclor 1254-pretreated (500 mg/kg, 5 days before exposure) male rats were exposed to 14 C 2 H 4 (10,000 ppm, 0.04–0.11 μCi/μmol) for 5 hr. Urine, feces, expired CO 2 , and expired 14 C 2 H 4 were collected for 36 hr following the exposure. Aroclor pretreatment did not affect the amount of C 2 H 4 expired (17–18 μmol/rat) but did cause a 4-fold increase in expired 14 CO 2 and a doubled urinary excretion of radioactivity. In control animals the blood, gut, kidney, liver, and lung all had detectable 14 C concentrations (20, 83, 14, 77, and 6 nmol-eq of C 2 H 4 , respectively) 36 hr after exposure. Aroclor pretreatment increased the concentrations in these tissues by factors of 1.5-, 8-, 6-, 17-, and 6-fold, respectively. In contrast to control rats. Aroclor-pretreated animals had detectable concentrations of radioactivity in brain, fat, heart, and muscle. Rats exposed to 10,000 ppm C 2 H 4 exhibited no light microscopic evidence of hepatotoxicity. However, Aroclor-pretreated animals had centrolobular hepatic necrosis as assessed microscopically 36 hr after exposure to C 2 H 4 . These results demonstrate that the metabolism of C 2 H 4 is stimulated by Aroclor pretreatment, and that the hepatic necrosis seen in Aroclor-pretreated rats is the result of a greater amount of metabolism or the production of a metabolite(s) not seen in control animals.

Little information is available on benzene disposition after exposure by inhalation despite the importance of this route in man. Benzene metabolites as a group have been measured in bone marrow, but quantitation of individual metabolites in this target tissue has not been reported. Male Fischer-344 rats were exposed to 500 ppm benzene in air and the uptake and elimination was followed in several tissues. Concentrations of free phenol, catechol, and hydroquinone in blood and bone marrow were also measured. Steady-state concentrations of benzene (11.5, 37.0, and 164.0 μg/g in blood, bone marrow, and fat, respectively) were achieved within 6 hr in all tissues studied. Benzene half-lives during the first 9 hr were similar in all tissues (0.8 hr). A plot of amount of benzene remaining to be excreted in the expired air was biphasic with t 1 2 values for the α and β phases of 0.7 and 13.1 hr, respectively. Phenol was the main metabolite in bone marrow at early times (peak concentration, 19.4 μg/g). Catechol and hydroquinone predominated later (peak concentrations, 13.0 and 70.4 μg/g, respectively). Concentrations of these two metabolites declined very slowly during the first 9 hr. These data indicate that free catechol and hydroquinone persist in bone marrow longer than benzene or free phenol.

A decrease in respiratory rate in mice during exposure to irritating airborne chemicals has been utilized as a response parameter to characterize the degree of upper respiratory tract irritation (sensory irritation) to the thermal decomposition products of plasticized poly(vinyl chloride). The plasticized poly(vinyl chloride) was placed in a low mass vertical furnace and thermally decomposed in an air atmosphere at a programmed heating rate of 20°C min−1. The thermogravimetric study of the plasticized poly(vinyl chloride) demonstrated that two distinct weight loss fractions occurred during the decomposition process. Groups of four male swiss-webster mice were exposed to the thermal decomposition products of the first weight loss fraction in the range 0.03–0.77 mg l−1 and to the second weight loss fraction in the range 0.03–0.38 mg l−1. Dose-response curves were plotted by utilizing the maximum percent decrease in respiratory rate during each exposure as the response parameter. Comparison of these curves to a dose-response curve for hydrogen chloride showed that both the first and second weight loss fraction of plasticized poly(vinyl chloride) were more potent than hydrogen chloride in terms of sensory irritation. From these dose-response relationships qualitative and quantitative predictions of human responses to the thermal decomposition products of plasticized.

Endogenously produced ammonia (NH 3 ) has been quantitated in the expired air of dogs and humans but data for rodents are not available. NH 3 in expired air may have importance in toxicology studies with inhaled gases, vapors, or aerosols because of its ability to form secondary reaction products. Depending upon the reaction product(s) formed, the toxicity of an airborne agent may be increased or decreased. The objective of this study was to quantitate NH 3 in the expired air of unanesthetized Fischer-344 rats, a species commonly used in inhalation toxicity studies. Whole body plethysmography and an indophenol, colorimetric assay were used to quantitate breath NH 3 . Concentrations of NH 3 ranged from 10 to 353 ppb ( x = 78 ppb ) in nose-breathing animals and 34 to 744 ppb ( x = 286 ppb ) in tracheal cannulated animals. These differences were attributed to the absorptive effect of the moist, upper respiratory tract in nose-breathers which was absent in animals with tracheal cannulas. These results compared favorably with published reports using larger species. The presence of NH 3 in the expired air of the rat suggests that reaction products may be formed with a variety of airborne chemicals. This may be particularly significant in low-level, chronic inhalation studies.

To characterize species differences in sensory irritation to formaldehyde (HCHO) and to determine if tidal volume ( V T ) compensation parallels the respiratory rate (ƒ) depression, ƒ, V T , and minute (V E ) of B6C3F1 mice and F-344 rats were measured during 10-min, head-only HCHO exposures. Comparisons also were made between naive (no previous HCHO exposure) and pretreated animals (HCHO, 2, 6, or 15 ppm, 6 hr/day for 4 days). HCHO exposure elicited immediate and simultaneous decreases in ƒ and V E in a concentration-dependent manner. No significant compensation in V T was observed in either species except the 15-ppm-pretreated rats. While ƒ and V E remained maximally depressed in mice for the remainder of the exposure period, recovery occurred in rats. In addition to tolerance development, rats were also less sensitive to HCHO. The RD50 (concentration at which ƒ decreased by 50%) of naive rats was 31.7 ppm vs 4.9 ppm for mice. Similar RD50 values and time-response curves for V E and ƒ were observed among naive and pretreated groups, although the baseline ƒ of pretreated animals was significantly depressed as compared to naive animals. In summary, HCHO exposure depressed V E in both mice and rats. But, because of greater sensitivity and lack of tolerance, mice were able to minimize inhalation of HCHO more than rats. This species difference may contribute to differences in respiratory tract toxicity from inhaled HCHO.

This study examined the effect of acute methyl chloride (MeCl) inhalation on F-344 rat tissue nonprotein sulfhydryl (NPSH), largely reduced glutathione. Rats were exposed to MeCl concentrations of 1500, 500, or 100 ppm. A 6-hr exposure to 1500 ppm of MeCl decreased the NPSH content of liver, kidney, and lungs to 17, 27, and 30% of control values, respectively, while 500 ppm MeCl lowered the liver, kidney, and lung NPSH to 41, 59, and 55% of control values, respectively, demonstrating a concentration-related effect. Blood NPSH did not differ from controls in either of these groups. No statistically significant changes from controls in tissue or blood NPSH were observed following a 100-ppm MeCl exposure. The extent of tissue NPSH loss was dependent on exposure duration. Liver and kidney NPSH returned to control NPSH concentrations within 8 hr following exposure of 1500 ppm MeCl. Pretreatment of rats with Aroclor-1254 or SKF-525A did not alter the MeCl-induced decrease in tissue NPSH. These data indicate that MeCl reacts extensively with tissue NPSH in vivo in a concentration-related fashion following acute inhalation exposure. The most likely NPSH constituent with which MeCl reacts is reduced glutathione. The finding that blood NPSH was not affected, in contrast to liver, kidney, or lung NPSH, indicates a tissue-specific reaction between MeCl and sulfhydryl groups, a reaction in which the tissue enzyme glutathione- S -alkyltransferase may play a role.

Inhalation exposure for 2 years to 14.3 ppm formaldehyde (HCHO) induced a 50% incidence of squamous cell carcinoma in the nasal cavity of F-344 rats but only a 3.3% incidence in B6C3F1 mice. Since the response was concentration and species dependent, species differences in nasal cavity “dose” were examined as a possible mechanism for the differences in tumor incidence. Naive (nonpretreated) and HCHO-pretreated (6 or 15 ppm, 6 hr/day, 4 days) mice and rats were exposed to HCHO for 6 hr during which respiratory rate and tidal volume were recorded to calculate the theoretical deposition (μg/min/cm2) of HCHO on the nasal epithelium. Species differences in delivered “dose” were further assessed by comparative autoradiography, histopathology, and cell turnover studies. Because mice were better able to reduce minute ventilation upon repeated exposures, they had less HCHO available for deposition than rats, resulting in less tissue damage and a lower rate of cell turnover in the nasal epithelium. The correlation between calculated “dose” and observed nasal toxicity, including nasal tumor incidence, demonstrates that by normalizing the dosimetry to nasal surface area, species differences in nasal toxicity may be better understood.

Modular polyketide synthases (PKSs) produce numerous structurally complex natural products that have diverse applications in medicine and agriculture. PKSs typically consist of several multienzyme subunits that utilize structurally defined docking domains (DDs) at their N and C termini to ensure correct assembly into functional multiprotein complexes. Here we report a fundamentally different mechanism for subunit assembly in trans-acyltransferase (trans-AT) modular PKSs at the junction between ketosynthase (KS) and dehydratase (DH) domains. This mechanism involves direct interaction of a largely unstructured docking domain (DD) at the C terminus of the KS with the surface of the downstream DH. Acyl transfer assays and mechanism-based crosslinking established that the DD is required for the KS to communicate with the acyl carrier protein appended to the DH. Two distinct regions for binding of the DD to the DH were identified using NMR spectroscopy, carbene footprinting, and mutagenesis, providing a foundation for future elucidation of the molecular basis for interaction specificity.

A Dynamic Nuclear Polarisation (DNP) enhanced solid-state Magic Angle Spinning (MAS) NMR spectrometer which uses a 187 GHz (corresponding to 1H NMR frequency of 284 MHz) Extended Interaction Klystron (EIK) amplifier as the microwave source is briefly described. Its performance is demonstrated for a biomolecule (bacteriorhodopsin), a pharmaceutical, and surface functionalised silica. The EIK is very compact and easily incorporated into an existing spectrometer. The bandwidth of the amplifier is sufficient that it obviates the need for a sweepable magnetic field, once set, for all commonly used radicals. The variable power (CW or pulsed) output from the EIK is transmitted to the DNP-NMR probe using a quasi-optic system with a high power isolator and a corrugated waveguide which feeds the microwaves into the DNP-NMR probe. Curved mirrors inside the probe project the microwaves down the axis of the MAS rotor, giving a very efficient system such that maximum DNP enhancement is achieved with less than 3 W output from the microwave source. The DNP-NMR probe operates with a sample temperature down to 90 K whilst spinning at 8 kHz. Significant enhancements, in excess of 100 for bacteriorhodopsin in purple membrane (bR in PM), are shown along with spectra which are enhanced by ≈25 with respect to room temperature, for both the pharmaceutical furosemide and surface functionalised silica. These enhancements allow hitherto prohibitively time consuming experiments to be undertaken. The power at which the DNP enhancement in bR in PM saturates does not change significantly between 90 K and 170 K even though the enhancement drops by a factor of ≈11. As the DNP build up time decreases by a factor 3 over this temperature range, the reduction in T1n is presumably a significant contribution to the drop in enhancement.

Plasmas from 30 normals, 46 patients with von Willebrand's disease (vWd) and 17 with hemophilia A were examined for levels of Total Progressive Antithrombin (TPA) and for three Factor VIII-related activities: coagulant (VIII:C), antigenic (VIIIR:Ag) and Willebrand factor (VIIIR:WF). The mean of TPA for the normals was 102.1%, and for the hemophiliacs 102.6% while that for the vWd group was 133.4%. The difference was statistically highly significant. The 1 3 elevation of TPA in vWd was accompanied by reduction to 44% of the average of all the F. VIII activities. The normal TPA in hemophilia A plasmas suggests that the inverse relationship between TPA and F. VIII in vWd is not the result of the reduced coagulant activity.

Upper respiratory tract irritation (sensory irritation) by airborne chemicals in animals causes a decrease in respiratory rate with no compensatory increase in tidal volume. This condition is an important respiratory tract defense mechanism. The purpose of this investigation was to determine whether sensory irritation tolerance would develop in F-344 rats following repeated Cl 2 inhalation. Male, F-344 rats were divided into four groups (40 to 50 animals/group) and exposed to 0, 1, 5, or 10 ppm Cl 2 , 6 hr/day, 5 days/week for 2 weeks. Sensory irritation was quantified 16 to 24 hr following the last day of Cl 2 pretreatment by measuring respiratory rate depression during exposure of groups of three to four animals for 10 min to various Cl 2 concentrations (1 to 760 ppm). Concentration-response curves were compared to the curve obtained from rats receiving no pretreatment (naive group). Tolerance was seen after all Cl 2 pretreatments and was greatest in the 10-ppm group. When compared to the non-pretreated group, all Cl 2 -pretreated rats had concentration-response curves with decreased slopes demonstrating increasing tolerance with increasing Cl 2 challenge concentration. The concentration of Cl 2 needed to elicit a reflex decrease in respiratory rate of 50% (RD 50 ) was 25 ppm in non-pretreated rats whereas Cl 2 pretreatments of 1, 5, or 10 ppm increased the RD 50 values to 90, 71, and 454 ppm, respectively. Tolerance development to sensory irritation is important because an organism's ability to perceive the presence or lung damaging concentrations of irritants may be compromised. Since the current threshold limit value for Cl 2 is 1 ppm, indications of tolerance development of rats exposed to Cl 2 at 1 ppm may be relevant to humans exposed repeatedly to this concentration.