Transient Product Research Articles

Spectroelectrochemistry of Non-Aromatic Explosives in Acetonitrile and the Influence of Superoxide

The spectroelectrochemistry of non-aromatic explosive compounds, namely two nitramines (RDX and HMX), a nitrate ester (PETN), and a plastic explosive composite (Semtex 1A) in acetonitrile (AN) is reported. The redox behavior of these compounds is studied using cyclic voltammetry while monitoring changes in UV absorbance to identify transient intermediates and product species. In search of a low-cost solution-phase detection technique for explosives, we compare the spectroelectrochemistry of these compounds in the presence and absence of naturally dissolved oxygen (2 mM in AN), where the superoxide radical is co-electrogenerated during analyte reduction. Free superoxide yields a prominent UV signal in this medium (λmax = 250 nm) that the explosives’ nitro or methylene groups attenuate stoichiometrically. Overlapping UV spectra of multiple species are deconvoluted using a new strategy, spectral regional baselining, for time- and potential-resolved spectroelectrochemical (SEC) analysis. SEC data for nitrite (NO2 -), nitrate (NO3 -), and nitromethane (CH3NO2) were also collected to support proposed reaction mechanisms for the transformation of explosives that include superoxide adducts and dimerized azoxy reduced intermediates. The findings expand the understanding of high-explosive solution-phase chemistry and offer a route to novel signal transduction for (electro-)chemical sensors for energetic materials.Figure 1. Spectroelectrochemistry of PETN in aerated acetonitrile with regions denoted for differential baseline analysis. (a) 3-D projected cyclic voltammogram (black) with UV absorbance from relevant wavelength (red, unscaled) as a function of time and potential; (b) full spectra (time domain) during cyclic voltammogram. Figure 1

Examination of Protonation-Induced Dinitrogen Splitting by in Situ EXAFS Spectroscopy.

The splitting of dinitrogen into nitride complexes emerged as a key reaction for nitrogen fixation strategies at ambient conditions. However, the impact of auxiliary ligands or accessible spin states on the thermodynamics and kinetics of N-N cleavage is yet to be examined in detail. We recently reported N-N bond splitting of a {Mo(μ2:η1:η1-N2)Mo}-complex upon protonation of the diphosphinoamide auxiliary ligands. The reactivity was associated with a low-spin to high-spin transition that was induced by the protonation reaction in the coordination periphery, mainly based on computational results. Here, this proposal is evaluated by an XAS study of a series of linearly N2 bridged Mo pincer complexes. Structural characterization of the transient protonation product by EXAFS spectroscopy confirms the proposed spin transition prior to N-N bond cleavage.

Electroanalysis and Spectroelectrochemistry of Nonaromatic Explosives in Acetonitrile Containing Dissolved Oxygen.

In search of a rapid, low-cost, and solution-phase detection technique for explosives, the (spectro-)electrochemistry of compounds from two major nonaromatic classes, namely nitramines (RDX and HMX) and nitrate esters (pentaerythritol tetranitrate (PETN) and the plastic explosive composite Semtex 1A) in acetonitrile (AN) is reported. In electrochemical screening, 5 μg of explosive material was detectable in 10 s by multicomponent cyclic voltammetric (CV) analysis on unmodified glassy carbon under ubiquitous environmental influences (i.e., trace water and dissolved oxygen). The explosives were identified with high recoveries under a battery of proof-of-concept testing scenarios in various matrices. In AN containing naturally dissolved oxygen (approx. 2 mM), the superoxide radical is co-electrogenerated during analyte reduction. Free superoxide yields prominent signals that the explosives attenuate quantitatively. To gain further insight into the electrochemical transformation mechanism, spectroelectrochemistry was employed to monitor changes in ultraviolet (UV) absorbance during CV and identify transient intermediates and product species, which could be targeted by future chemical sensors. Overlapping UV spectra of multiple species are deconvoluted using a new strategy, spectral regional baselining, for time- and potential-resolved spectroelectrochemical (SEC) analysis. This study shows that dissolved oxygen, hitherto an interferent purposefully removed from the solution, can be exploited advantageously in electrochemical sensing. The work expands our understanding of high-explosive solution-phase chemistry and offers a novel route to signal transduction for the sensing of energetic materials.

Molecular dynamics simulations of singlet oxygen atoms reactions with water leading to hydrogen peroxide

The formation mechanisms of hydrogen peroxide due to the interaction of oxygen atom from the cold atmospheric plasmas in contact with water are not fully understood. Previous work on molecular dynamics (MD) simulations of interactions of O atoms in bulk water based on reactive force field and density-functional tight-binding method did not observe the formation of . In this work we applied density functional theory in MD simulations of 192 trajectories considering system to explore the reaction mechanisms for atomic oxygen radical in water. Our calculations revealed that triplet (ground) state oxygen was not reactive. Oxywater-similar structure was a transient product. Perhydroxyl anion and its counterpart hydronium were formed. In most of simulated cases, hydrogen peroxide was observed as a final product. The formation pathways of hydrogen peroxide exhibited large complexities for the simple hydrogen bonded system. According to the sources and pathways of the hydrogen atom being bonded in hydrogen peroxide molecule, mechanisms can be classified into (1) hydrogen-abstraction, (2) hydrogen-transfer n (n = 3, 4, 5, 6, 7, 8), (3) proton-delivery n = 2, 3, (4) proton-transfer. It was confirmed that for correct prediction of reaction mechanisms is better to use quantum molecular dynamic simulations.

MCM-56 stabilization synthesis using auxiliary tetraethylammounium ions: Its role to inhibit surface Si-O-Al bridged linkage and retain highly delaminated structure

MCM-56 is one important member of MWW type zeolites, which possesses an unique 2D framework structure consisting of one or two MWW monolayers. Due to its high external surface area and large external acid concentration, MCM-56 zeolite exhibits excellent potential catalytic performance in alkylation of aromatics. However, it's a transient product and momentarily convert into MCM-49 zeolite. Herein, we present a facile strategy for stable synthesis of highly delaminated MCM-56 zeolite, denoted MCM-56(D), by using the dual-template system composed of hexamethyleneimine (HMI) and tetraethylammonium hydroxide (TEAOH). The characteristics of extended stable period and higher delamination degree distinguish MCM-56(D) from traditional MCM-56. The phase stabilization period is prolonged by two days or more, which is dependent on the increase of TEAOH amount. The results indicate that HMI acts as a directing agent to promote crystallization of MWW topology, while TEAOH has been proven to be a crystallization regulator by hindering Si-O-Al bridges formation in interlayers, thus forming a highly exfoliated MCM-56(D). Compared with the traditional MCM-56, the external surface area and mesoporous volume (213.6 m2/g, 1.20 cm3/g) of MCM-56(D) increased by more than 60% and 183%, respectively, naturally possessing more accessible Brønsted acid sites favourable for bulky molecule reaction, so it shows a high conversion in cracking of 1, 3, 5-triisopropylbenzene. In the liquid-phase alkylation of benzene with ethylene, MCM-56(D) performs higher reactivity and slower deactivation than MCM-22 and MCM-49 under a WSHV (Ethylene) of 2 h−1. This dual-template method ensures MCM-56(D) a practicable catalyst for processing bulky molecules in petrochemical industry.

Excited state proton transfer processes of pyranine studied by femtosecond stimulated Raman spectroscopy

As one of the most fundamental processes, proton transfer reaction plays an important role in chemical and biological process, and to reveal the choreography of the proton motion intra- and intermolecularly, a spectroscopic technique capable of capturing molecular structural dynamics of excited-state proton transfer motions on an intrinsic time scale is needed. In this study, We utilize wavelength-tunable femtosecond stimulated Raman spectroscopy with a time resolution of ~100 fs, spectral resolution of 15 cm<sup>–1</sup> and spectral range of 400 cm<sup>–1</sup>—1800 cm<sup>–1</sup>, combined with traditional transient absorption spectroscopywith a time window between 0 and 600 ps to simultaneously achieve reaction dynamics for transient reactant and product of the photoacid pyranine (8-hydroxypyrene1, 3, 6-trisulfonic acid, HPTS) molecules undergoing excited-state proton transfer reaction in complex with water and acetate molecules. Marker bands attributed to the deprotonated form of HPTS in a frequency range from 400 cm<sup>–1</sup> to 1700 cm<sup>–1</sup> are obtained under the excitation of 400 nm laser pulses. The marker band at 1516 cm<sup>–1</sup>, which is assigned to phenolic ring carbon carbon double band stretching accompanied with carbon hydrogen in-plane rocking motions, exhibits complex rise and decay dynamics. The simultaneously observed excited-state Raman mode at 920 cm<sup>–1</sup> which is assigned to the excited carbon-carbon single bond stretch mode in the protonated acetic acid root molecule, helps us to clearly resolve the reaction rates of excited-state proton transfer. Based on the multi-exponential fitting results, the dynamics of excited-state Raman mode at 920 cm<sup>–1</sup> exhibits bi-exponential processes with time constants of ~470 fs and ~3 ps. The ultrafast time component indicates that the excited-state proton transfer originates from an HPTS-acetate complex, indicating that part of the ground-state HPTS molecules are in the “tight” hydrogen bonding configuration that can quickly shift the excited-state proton charge toward the acetate acceptor molecule through a direct hydrogen bond. The second slower time component implies a significant subpopulation of HPTS in the ground state, i.e. hydrogen bonds to an acetate ion via an intervening water molecule, and upon photo excitation, the proton transfers to the water solvent before proton is picked up by the acetate ion.

Audiological profile of indoor cycling teachers

ABSTRACT Purpose: to describe the audiological profile and auditory complaints of indoor cycling teachers, as well as to relate the findings with time of noise exposure and presence of tinnitus. Methods: participants were eight teachers of both genders, age ranging from 24 to 36 years, with professional experience in the area for at least one year. Sound pressure level was measured during the class, which lasted from 45 to 50 minutes and an adapted anamnesis questionnaire composed of ten items was applied to each individual to research the auditory symptoms and factors related to noise exposure and the audiological assessment performed. Inferential statistical tests were applied. The level of statistical significance was 0.05. Results: all of them had pure tone audiometry, tympanometry testing and brainstem auditory evoked potential within normal limits. There were alterations in the high frequency audiometry and otoacoustic emissions without a statistical correlation with the time of professional experience. Conclusion: the audiological profile obtained was pure tone audiometry, tympanometry and brainstem auditory evoked potential within normal limits; altered transient otoacoustic and distortion product emissions and high frequency audiometry. The complaints reported were: tinnitus, dizziness, the need to listen at a high volume and being exposed to excessive noise.

The structure-catalytic activity relationship for the transient layered zeolite MCM-56 with MWW topology

Abstract Zeolite MCM-56 is a high alumina, monolayered form of the commercially useful framework MWW but it is a transient product during crystallization, so many factors influence its state and quality. This work examines properties of a series of MCM-56 and MCM-49 samples synthesized for different times using Aerosil, Ultrasil and Ludox as silica sources, hexamethyleneimine as the structure directing agent and additionally aniline as structure promoting agent. It was found that the most important parameter, governing the catalytic activity in the test reaction of Friedel-Crafts alkylation of mesitylene with benzyl alcohol, was availability of the Bronsted acid centers located at the external surfaces of the crystals. The key role in correlating physical characteristic with activity was played by infrared spectroscopy as it enabled the study of many properties of the tested materials, starting from the total concentration of acid centers, and their type (Bronsted or Lewis acids) through the concentration of centers available for the reagent molecules, to investigating the correlation of acidity with the degree of zeolite crystallinity.

Dynamic control analysis of intensified extractive distillation process with vapor recompression

This paper explores the dynamic control of a complex multivariable interacting extractive distillation process with vapor recompression by taking the separation of acetone and methanol using water as separating agent. Results show that the effectiveness of conventional single-end temperature control structure with holding the solvent-to-feed and reflux-to-distillate ratios constant is poor owing to the large product offsets, and a series of improved control structures with composition controller(s) are developed and assessed by inserting the large throughput and feed composition perturbations. In the configuration of composition control loops, there are two crucial issues needed to be solved: one is that which of distillate impurities (methanol and solvent) should be controlled; another is the correspondingly paired manipulated variable (whether solvent-to-feed ratio or reflux ratio). Results illustrate that the effective product quality control is achieved for facing large (20%) disturbances in throughput and feed composition when the distillate methanol and water impurities are controlled by manipulating the solvent-to-feed and reflux-to-distillate ratios for extractive column, while another alternative is infeasible due to the failure of the tuning of the composition controller. And the control scheme with dual-impurity control strategy works better than that with single purity control option in terms of transient product peaks and settling time whether for handling throughput or feed composition disturbances.

In Situ Controlled Syntheses of Electrolyte Additives for High Voltage Lithium Ion Batteries

The development of cathode materials needs concomitant electrolyte developments to accommodate the high voltage to reach high energy and power densities required for electric vehicle and personal electronics. Previously we reported that aging TMSPi (trimethylsilylphosphite) additive in a standard 1.2 M LiPF6 carbonate electrolyte can generate a beneficial transient product, PF2(OSi(CH3)3), which was later proven to mitigate impedance rise during long term cycling in composite cathode-graphite cells. However, the generation of PF2(OSi(CH3)3) is spontaneous and cannot be controlled, and as aging process proceeds to a greater extent, PF2(OSi(CH3)3) disappears gradually and other transient detrimental products form along the way and eventually deteriorate the impedance.1,2 By using molecular engineering to tune functionality, ratio, and stability, we can control the in situ electrolyte additive to selectively synthesize the beneficial component in high yield (> 98%) and maximize the battery performance. The in situ method is particularly of interest to scale up electrolyte preparation since it would alleviate any requirements of extra separation and purification of the desired additives. By varying the structure of the additive precursor, we clearly see a trend that is governed by thermodynamics which determine the product ratio and composition. The electrochemistry of these additives and their application in composite cathodes will be discussed. By introducing the novel in situ synthetic method for electrolyte additive syntheses, avenues for new additives that were previously inaccessible will open up and facilitate the development of the lithium ion batteries toward high energy and high power density. References The Journal of Physical Chemistry C 2018, 122 (18), 9811-9824.RSC Advances 2016, 6 (44), 38342-38349.

Aqueous Dearomatization/Diels–Alder Cascade to a Grandifloracin Precursor

A green laboratory experiment has been developed in which students perform an aqueous oxidation/cycloaddition reaction to convert salicyl alcohol into a pentacyclic diepoxydione that is readily isolated by filtration. Drawing on their knowledge of periodate-mediated 1,2-diol cleavage, students propose a mechanism for the oxidation of salicyl alcohol (which is not a 1,2-diol) and the structure of the transient product (prior to a spontaneous Diels–Alder dimerization). Students then characterize salicyl alcohol and their diepoxide product by mass spectrometry, IR spectroscopy, and 1H, 13C, and two-dimensional NMR spectroscopy. The only organic solvents used are small amounts for IR and NMR spectroscopy.

Effects of Dexmedetomidine Infusion During Sevoflurane Anesthesia on Otoacoustic Emissions.

Background and ObjectivesKnowing the ototoxic potential of the agents used in medical treatments is important for the protection of hearing. Although we have knowledge regarding some effects of dexmedetomidine, which is an anesthetic-sparing drug, its influence over the hearing system has never been studied and is obscure yet. The aim of this study is to determine the effects of intravenous dexmedetomidine application during sevoflurane anesthesia on otoacoustic emissions (OAEs).Subjects and MethodsThis prospective randomized study was performed on 60 patients (34 male, 26 female, mean age: 30.6±9.2 years) who were scheduled for an elective surgery under general anesthesia and the patients were enrolled and randomly divided into 2 groups. They received dexmedetomidine (Group D) or Saline (Group S) infusion during a standardized Sevoflurane anesthesia. Transient and distortion product OAEs were measured preoperatively and postoperatively (24th hour). OAE results were compared within and between groups.ResultsIn group D postoperative OAEs were lower than preoperative OAEs and postoperative levels of group S, especially at low frequencies (p<0.05).ConclusionsDexmedetomidine infusion affects the micromechanical function of cochlea especially in the low-frequency region. Dexmedetomidine should be carefully used during general anesthesia to avoid its probable harmful effects on cochlear micromechanics.

Photochemical Generation and Characterization of Di-tert-butylsilylene (SitBu2) in Solution

Di-tert-butylsilylene (SitBu2) has been detected directly in solution and its reactivity characterized by laser flash photolysis methods. Laser photolysis of 7,7-di-tert-butyl-7-silabicyclo[4.1.0]heptane (5) affords a transient product that exhibits λmax ≈ 520 nm and decays on the microsecond time scale, concurrent with the growth of a second, much longer-lived species exhibiting λmax = 290, 430 nm. The two species are assigned to di-tert-butylsilylene (SitBu2) and its disilene dimer, tetra-tert-butyldisilene (tBu2Si═SitBu2, 8), respectively. Transient absorption spectra recorded by laser photolysis of hexa-tert-butylcyclotrisilane (7) are consistent with the prompt formation of both SitBu2 and 8, the former appearing as a weak shoulder absorption on the red edge of the intense absorption band due to the disilene. Absolute rate constants were determined for the reactions of SitBu2 with a variety of representative silylene substrates in hexanes at 25 °C, including methanol, triethylsilane, acetic acid, acetone, molecular oxygen, and four aliphatic alkenes (1-hexene, cyclohexene, cis-cyclooctene, and 2,3-dimethyl-2-butene). Rate and(or) equilibrium constants for Lewis acid–base complexation of the silylene with diethyl ether, tetrahydrofuran, tetrahydrothiophene, and diethyl- and triethylamine were also determined, along with the UV–vis absorption spectra of the corresponding Lewis acid–base complexes. Rate constants for the reactions of dimethylsilylene (SiMe2) and dimesitylsilylene (SiMes2) with cis-cyclooctene, 2,3-dimethyl-2-butene, and 1-hexene are also reported, enabling a comprehensive assessment to be made of steric effects on the reactivities of simple (transient) dialkyl- and diarylsilylene derivatives in solution. The kinetic data show the reactivity of SitBu2 to be intermediate between that of SiMe2 and SiMes2 under similar conditions, with the (2 + 1)-cycloaddition reactions with alkenes exhibiting the largest variations in rate constant as a function of substitution at Si. Absolute rate constants for the reactions of tetra-tert-butyldisilene (8) with O2 and acetone are also reported.

In vitro and in vivo characterization of Clostridium scindens bile acid transformations

ABSTRACT The human gut hosts trillions of microorganisms that exert a profound influence on human biology. Gut bacteria communicate with their host by secreting small molecules that can signal to distant organs in the body. Bile acids are one class of these signaling molecules, synthesized by the host and chemically transformed by the gut microbiota. Among bile acid metabolizers, bile acid 7-dehydroxylating bacteria are commensals of particular importance as they carry out the 7-dehydroxylation of liver-derived primary bile acids to 7-dehydroxylated bile acids. The latter represents a major fraction of the secondary bile acid pool. The microbiology of this group of gut microorganisms is understudied and warrants more attention. Here, we detail the bile acid transformations carried out by the 7-dehydroxylating bacterium Clostridium scindens in vitro and in vivo. In vitro, C. scindens exhibits not only 7α-dehydroxylating capabilities but also, the ability to oxidize other hydroxyl groups and reduce ketone groups in primary and secondary bile acids. This study revealed 12-oxolithocholic acid as a major transient product in the 7α-dehydroxylation of cholic acid. Furthermore, the in vivo study included complementing a gnotobiotic mouse line (devoid of the ability to 7-dehydroxylate bile acids) with C. scindens and investigating its colonization dynamics and bile acid transformations. Using NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry), we demonstrate that the large intestine constitutes a niche for C. scindens, where it efficiently 7-dehydroxylates cholic acid to deoxycholic acid. Overall, this work reveals a novel transient species during 7-dehydroxylation as well as provides direct evidence for the colonization and growth of 7-dehydroxylating bacteria in the large intestine.

Crossing the great divide between single-crystal reactivity and actual catalyst selectivity with pressure transients

The quantitative prediction of catalyst selectivity is essential to the design of efficient catalytic processes and requires a detailed knowledge of the reaction mechanism and rate constants. Here we present a study that accurately predicts, using the kinetics and a mechanism derived from fundamental studies on single-crystal gold, the product distribution resulting from the complex reaction network that governs the oxidative coupling of methanol, catalysed by nanoporous gold between 360 and 425 K and for a vast range of pressures. Analysis of the transient product responses to micropulses of methanol over nanoporous gold yields a precise understanding of the marked dependence of selectivity on pressure, surface oxygen coverage and temperature. The key to a high selectivity for methyl formate is the surface lifetime and abundance of the methoxy. This successful microkinetic modelling of catalytic reactions across a wide set of reaction conditions is broadly applicable to predicting catalytic selectivity and provides a pathway to designing more efficient catalytic processes. Catalytic studies on single crystals are very insightful, but it is often difficult to extend their conclusions to an actual catalytic process due to gaps in the experimental conditions. Now, Madix and co-workers report a method to bridge these gaps using the oxidative coupling of methanol on gold as an example.

Assessment of auditory functions in chronic hepatitis C patients treated by sofosbuvir

ObjectiveEvaluating the auditory function in patients with chronic hepatitis C treated with sofosbuvir and ribavirin. MethodsThis study involved 80 patients with chronic hepatitis C who agreed to receive sofosbuvir and ribavirin. All participants were subjected to baseline otological and audiological assessment just before treatment. The audiological assessment included standard pure tone audiometry, extended high-frequency audiometry, immitancemetry and otoacoustic emissions (OAEs) (transient and distortion product). According to baseline hearing threshold measurements, the study population was divided into 2 groups. Group 1 included 42 patients with normal hearing sensitivity (250–8000 Hz), and Group 2 included 38 patients with sensorineural hearing loss. After 24 weeks of therapy, otological and audiological assessments were repeated and compared between the two groups and before and after therapy. ResultsPost-treatment hearing threshold evaluation showed no significant difference from pretreatment evaluation at all tested frequencies. There was no statistically significant difference between pre and post-treatment otoacoustic emissions results. ConclusionTherapy with sofosbuvir and ribavirin in chronic hepatitis C has no noticeable effects on cochlear functions.

Assessment of auditory and vestibular functions in vitiligo patients

ObjectivesTo evaluate audiological and vestibular functions via basic audiological evaluation, otoacoustic emissions and videonystagmography (VNG) in vitiligo patients. Material and methods30 vitiligo patients (8 acrofacial and 22 mixed types) as the study group and 30 normal healthy adults as the control group were included in the study. All participants were submitted to basic audiological evaluation, transient and distortion product otoacoustic emmisions (TEOAEs and DPOAEs), vestibular assessment including history taking, office tests and videonystagmography (VNG) and dermatological assessment to determine type, percent of body surface area involvement and duration of vitiligo. ResultsThis study showed statistically significant difference between control and study groups in pure tone audiometry (PTA) and otoacoustic emissions results. Fifty percent of vitiligo patients had peripheral vestibular disorders (10 vestibular neuritis and 5 posterior canal benign paroxysmal positional vertigo. ConclusionThe results in this study showed that 50% of vitiligo patients suffered from peripheral vestibular disorders in addition to auditory affection. Vitiligo patients require routine monitoring for auditory and vestibular functions for early identification and monitoring of changes as the disease progress.

The Enigmatic P450 Decarboxylase OleT Is Capable of, but Evolved To Frustrate, Oxygen Rebound Chemistry.

OleT is a cytochrome P450 enzyme that catalyzes the removal of carbon dioxide from variable chain length fatty acids to form 1-alkenes. In this work, we examine the binding and metabolic profile of OleT with shorter chain length (n ≤ 12) fatty acids that can form liquid transportation fuels. Transient kinetics and product analyses confirm that OleT capably activates hydrogen peroxide with shorter substrates to form the high-valent intermediate Compound I and largely performs C-C bond scission. However, the enzyme also produces fatty alcohol side products using the high-valent iron oxo chemistry commonly associated with insertion of oxygen into hydrocarbons. When presented with a short chain fatty acid that can initiate the formation of Compound I, OleT oxidizes the diagnostic probe molecules norcarane and methylcyclopropane in a manner that is reminiscent of reactions of many CYP hydroxylases with radical clock substrates. These data are consistent with a decarboxylation mechanism in which Compound I abstracts a substrate hydrogen atom in the initial step. Positioning of the incipient substrate radical is a crucial element in controlling the efficiency of activated OH rebound.

Engineered bacteria detect gut inflammation in mice

A new strain of engineered bacteria can detect inflammation in the colon of mice even after more than 1,000 bacterial divisions, researchers report (Nat. Biotechnol. 2017, DOI: 10.1038/nbt.3879). Such a microbe could help doctors diagnose and monitor diseases such as inflammatory bowel disease. Pamela A. Silver and coworkers at Harvard University engineered nonpathogenic Escherichia coli to detect and respond to tetrathionate, a transient product of a reactive oxygen species released by intestinal cells during inflammation. The researchers inserted two genetic circuits into the bacterial genome. The first circuit produces the transcriptional factor Cro in response to tetrathionate, and Cro triggers a second “memory” circuit to produce the protein β-galactosidase. Even when tetrathionate is no longer around, the bacteria “remember” the exposure and continue to produce both proteins. The researchers monitored inflammation in mice treated with the microbes by measuring β-galactosidase in the animals’ feces. ...

Transient detailed balance and product form for reaction networks

ABSTRACTThis paper explores the boundary of the set of reaction networks that have an exact transient (truncated) multidimensional Poisson or product-form distribution for the number of particles of different types. Motivated by the birth–death process, we introduce the notions of transient detailed balance and delay functions, and use these notions to obtain the novel transient product-form distribution in a coagulation-fragmentation process for polymers with a tree-like structure from that of the pure coagulation process.