Transition Species Research Articles

CO2 Capture by Diamines in Dry and Humid Conditions: A Theoretical Approach.

This work is a mechanistic study of the CO2 reaction with diamines under both dry and wet conditions. All protic α,ω-diamines R1H1N1-(CH2)n-N2H2R2, with n = 1-5 and R1 and R2 = H and/or CH3, were investigated. Depending on the nature of the diamine, the reaction was found to follow one of two concerted asynchronous reaction mechanisms with a zwitterion hidden intermediate. Both mechanisms involved two processes. The first process consisted of a nucleophilic attack of the nitrogen N1 of the first amine group on the carbon of CO2, accompanied by the transfer of a hydrogen atom H1 from N1 to the nitrogen N2 of the second amine group, leading to the formation of a carbamate zwitterion. The subsequent process corresponds to the transfer of a hydrogen atom H2 from the second amine group N2 to an oxygen atom of CO2, thus ending the reaction by the formation of carbamic acid. The structure of the zwitterion hidden intermediate was determined using the reactive internal reaction coordinates (RIRC), a reaction pathway visualization tool, consisting of a 3D representation of the potential energy versus the internuclear distances N2-H1 and N2-H2, which correspond to the bond being formed and the bond being broken, respectively. The life span of the transitory species, i.e., the zwitterion, was found to depend on the nature of the second amine group. For primary amines, the life span of the zwitterion was "short", whereas for secondary amines, it was "long". The corresponding mechanisms were termed the "early" and "late" asynchronous mechanism, respectively. Regardless of the mechanism, the activation barriers were found to decrease with the length of the carbon chain linking the two amine groups, with an asymptotic behavior from n = 4. Involvement of a water molecule generates a significant catalytic effect for diamines with short carbon chains (n < 4), whereas for longer chain diamines, water has a slightly adverse effect.

Advanced oxidation processes and nanomaterials -a review

Water related problems are expected to further increase considerably due to climate changes and population growth. Conventional wastewater treatment can be either a physical, chemical, and/or biological processes, or in some cases a combination of these operations. Current wastewater treatment technologies are deemed ineffective in the complete removal of pollutants, particularly organic matter. In many cases, these organic compounds are resistant to conventional treatment methods, thus creating the necessity for secondary treatment. Advanced Oxidation Processes (AOPs) are chemical oxidation processes that use powerful transitory species such as hydroxyl radicals and sulphate radicals. These species can be generated from water using energy for instance solar energy, electrical energy, sound energy etc or simply by chemicals like H2O2, ozone etc with or without the use of an appropriate catalyst. In many such methods, nanomaterials have been effectively used as catalysts for the generation of the transitory species. The large-scale commercialization of AOPs can lead to reduction of cost favorable to environmental applications as AOPs are based on physicochemical processes that produce intense changes in the structure of chemical species. The majority of AOPs can be applied to the remediation and detoxification of low or medium volumes of waters. This review summarises the major Advanced Oxidation Processes reported in recent literature with emphasis on the latest advances in the use of nanomaterials employed in various processes.

Variation of Density and Biomass of the Ichthyofauna Associated to Soft Bottoms of a Western Coastal Lagoon of B.C.S., Mexico

An analysis of the variation of the density and biomass of the fish communities of the lagoon of La Paz, Mexico was carried out from November 2016 to September 2017. A total of 2763 organisms were collected with a total biomass of 211,422.93 g in an area of 5022 m2, a density and biomass of 0.550 lnd/m2 and 44.091 g/m2. The site with the largest biomass was recorded in Zacatecas (11.179 g/m2) located north of the lagoon, while Grand Plaza recorded the lowest biomass (2.732 g/m2). Regarding the density, the maximum value was recorded in the site Yate Hundido, located northwest of the lagoon (0.129 lnd/m2) and the lowest was Las Palmas (0.036 lnd/m2) located north of the lagoon. The most abundant species was Diapterus peruvianus with 683 individuals and a biomass of 37,507.57 g. The physicochemical variables showed two seasons with significant change where we can observe higher temperatures in the summer (average of 27.45°C) and minimum in winter (average of 22.49°C). The Shannon-Weaver diversity index showed a difference (p = 0.050) between months, with the highest value recorded in April (H' = 2.133 bits/ind) and the lowest in June (H' = 1.041 bits/ind). The biomass and density values recorded in the lagoon were found to be associated with the spatio-temporal variation of temperature of the lagoon, as well as the resident and transitory species located in the area of study. In addition, the body sizes recorded corresponded to juvenile and young adult individuals.

Macrocyclic Lactones Act as a Queen Pheromone in a Primitively Eusocial Sweat Bee.

Eusociality is characterized by the reproductive division of labor between two castes: fertile queens and largely sterile workers. Queen pheromones are known to influence worker behavior and reproductive physiology and are therefore key components in regulating complex eusocial behavior [1]. Recent studies indicate that cuticular hydrocarbons (CHCs) act as queen pheromones in various eusocial hymenopteran species [2-8]. However, almost all species investigated to date are highly eusocial and do not include extant transitory stages from solitary to eusocial behavior [9]. Indeed, primitively eusocial species, which largely lack morphologically distinct castes, are thought to control worker reproduction through the physical aggression of the queen rather than via pheromones [10-12]. Halictid or sweat bees exhibit a high variability of eusociality including solitary and facultatively eusocial species [9, 13-16]. However, the mechanisms controlling worker reproduction in these transitory species are unknown. The results of a recent correlative study based on caste-specific chemical profiles in various halictid bees of different social levels have revealed an overproduction of macrocyclic lactones in queens compared with workers [17]. Using chemical analyses and behavioral experiments in which we simulated below-ground nests of the primitively eusocial sweat bee Lasioglossum malachurum, we identified a queen pheromone and found that macrocyclic lactones, not CHCs, influence worker behavior and decrease ovarian activation in this species. Our data suggest that the evolution of queen pheromones is more complex than previously inferred from highly eusocial species and shed new light on the complexity of the evolution of queen pheromones.

Morphological tunable three-dimensional flower-like zinc oxides with high photoactivity for targeted environmental Remediation: Degradation of emerging micropollutant and radicals trapping experiments

Abstract Zinc oxide (ZnO) with a high potentiality for tunable morphology is gaining immense research interests for targeted environmental remediation of emerging micropollutants in source waters. Various three-dimensional (3D) flower-like nanostructures of ZnO were synthesized by following a facile and low-temperature hydrothermal synthesis approach, using Zn(CH3COO)2∙2H2O as the starting precursor reagent, in the presence of different bases at varying concentrations as the structure-directing reagents. BET studies indicated that the ZnO-flowers 1 were more superior than ZnO-flowers 2 and 3, as it possessed the highest specific surface area (10.83 m2/g), pore volume (0.054 cm3/g) and pore size (23.52 nm). Subsequently, the photoactivities of ZnO-flowers on the degradation of emerging salicylic acid micropollutant under UV-A illumination were examined. Batch studies suggested that the ZnO-flowers were photoactive and photocatalysed optimally under neutral pH condition that are aligned with the cost-effective and practical implementation for water/wastewater treatment. ZnO-flowers 1 demonstrated the highest photoactivity according to its reaction rate constant, where the kinetics data was well-fitted using the pseudo-first order Langmuir-Hinshelwood rate equation. This finding was well correlated to the BET studies, where the high photoactivity in ZnO-flowers 1 could be ascribed to its exceptional surface morphology that maximises the surface contact area with salicylic acid during photodegradation. Finally, the radicals trapping experiments were carried out in order to validate the role of primary photogenerated holes (h+) and various secondary reactive oxygen species (ROS) in the photodegradation of salicylic acid using ZnO-flowers photocatalysts. It was confirmed that the active species of photogenerated h+, •OH, and •O2− were responsible for the photodegradation process. The plausible mechanistic pathways for the reaction between scavenging reagents and the reactive transitory species to form by-products and intermediates were also proposed.

Stabilizing of the Transitory Species (TiO2)2 by Encapsulation Into Carbon Nanotubes.

The aim of this paper is studying the encapsulation effect of carbon nanotubes (CNTs ) on the stabilizing process of titanium dioxide molecule dimers (TiO2)2. First, a theoretical study was performed concerning the guest species that are various titanium dioxide dimers. Five structures were treated as following: i) Cis (C) or ii)Trans (T) relatively to a square shaped fragment Ti2O2, iii) a mixed Tetrahedral/Pyramidal (T/P) disposition while two titanium atoms are sharing three oxygen atoms, and finally not bonded dimers in iv) parallel (P) and v) orthogonal (O) positions respectively. Only the (T), (C) and (T/P) isomers may be considered as stable compounds. The structure of the T-dimer is more stable than the Cis one by only 6.5 kcal mol-1. Typically, intra and extracyclic Ti-O bond lengths are 1.84Å and 1.61Å respectively. (T/P) dimer can be described as a metastable structure since its energy is higher than (T) one by 19 kcal mol-1. NBO analysis highlights the participation of dative bonding between oxygen lone pair and vacant titanium 3d orbitals. (P) and (O) structures represent transitory species that transform into the more stable structure which is the T-dimer. The second and principal part of this work concerns the re-optimization of the studied structures placed inside the CNT (12,0). Only (T), (C) and (P) dimers are stabilized by encapsulation through the establishment of strong interactions with the CNT wall. The (T / P) and (O) isomers which are converted into (T) and (P) dimers respectively, are leaving the nanotube while they still interacting with its edge. These favorable results are indicating in one hand the possibly detection of (T) and (C) isomers, and in another hand that the process of polymerization of the TiO2 molecule which is leading to nanostructured materials could be controlled by encapsulation within the CNTs.

Multistep π dimerization of tetrakis(n-decyl)heptathienoacene radical cations: a combined experimental and theoretical study.

Radical cations of a heptathienoacene α,β-substituted with four n-decyl side groups (D4T7(.) (+) ) form exceptionally stable π-dimer dications already at ambient temperature (Chem. Comm. 2011, 47, 12622). This extraordinary π-dimerization process is investigated here with a focus on the ultimate [D4T7(.) (+) ]2 π-dimer dication and yet-unreported transitory species formed during and after the oxidation. To this end, we use a joint experimental and theoretical approach that combines cyclic voltammetry, in situ spectrochemistry and spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The impact of temperature, thienoacene concentration, and the nature and concentration of counteranions on the π-dimerization process is also investigated in detail. Two different transitory species were detected in the course of the one-electron oxidation: 1) a different transient conformation of the ultimate [D4T7(.) (+) ]2 π-dimer dications, the stability of which is strongly affected by the applied experimental conditions, and 2) intermediate [D4T7]2 (.) (+) π-dimer radical cations formed prior to the fully oxidized [D4T7]2 (.) (+) π-dimer dications. Thus, this comprehensive work demonstrates the formation of peculiar supramolecular species of heptathienoacene radical cations, the stability, nature, and structure of which have been successfully analyzed. We therefore believe that this study leads to a deeper fundamental understanding of the mechanism of dimer formation between conjugated aromatic systems.

Biodiversidad de aves en México

We present an update to the knowledge of bird diversity in México. We assembled a list of the birds of Mexico including all species for which presence, recent or historical, has been confirmed, and incorporating recent taxonomic viewpoints. From this list, we obtained numbers of species and taxonomic richness, seasonal status, ecological distribution, and conservation status. Of the roughly 10 500 bird species currently recognized, 1 123 to 1 150 (11%) are found in Mexico, what ranks the country in the 11th position in bird species richness, and in 4th in the proportion of endemic species. Mexican avifauna is largely composed of resident species; however, migratory and transitory species are also important components. Similarly, a large proportion (77%) of the species breed in Mexico. Endemism levels are high: 194 to 212 species are included in some endemism category. Between 32-44% of the Mexican bird species has been rated with some level of threat according to national and international listings. Geographically, the highest species richness is located in contact areas between lowland and mountains in both slopes and along the lowlands of the in Gulf slope and the Yucatan Peninsula; endemism is mainly located in western Mexico: mainly along the Pacific slope and in mountains in the Transvolcanic Mexican Belt, the Sierra Madre Occidental, and the Sierra Madre del Sur; in the Atlantic slope, endemism is higher along the Sierra Madre Oriental.

Effects of O2 and H2O2 on TiO2 Photocatalytic Efficiency Quantified by Formaldehyde Formation from Tris(hydroxymethyl)aminomethane

AbstractThe impact of O

Who is who in the understory: the contribution of resident and transitory groups of species to plant richness in forest assemblages

The forest understory is made up of resident and transitory species and can be much richer than the canopy. With the purpose to describe the contribution of these groups to the woody understory, five Atlantic Forest fragments were selected and studied in Northeastern Brazil. In order to analyze the understory's structure, the sample included woody individuals with circumference at breast height (CBH) smaller than 15cm and circumference at ground level (CGL) greater than 3cm, regardless of height. The recorded species were quantified and classified into functional stratification categories (resident and transitory), and the floristic similarity between the understory and the tree stratum was calculated. Species' importance in the understory was analyzed by height and total natural regeneration classes based on a regeneration index. The understory was richer in species (median=63.8, SD=21.72, n=5 fragments) than the tree stratum (43.8, 18.14, 5), and the similarity between these components was relatively high (median=0.54, SD=0.09). The results also showed that the studied understory in the forest fragments was mainly composed by transitory species (median=67.01%, SD=3.76), that were well distributed among height classes and had the highest densities, which may favor their future presence in the canopy's structure and composition. The typical understory species were grouped into two strata: the lower understory, made up of species that generally do not reach more than 4m in height (mostly species from families Piperaceae, Rubiaceae and Melastomataceae); and the upper understory, with intermediate heights between the lower understory and the canopy, but with average heights that were not higher than 10m (mainly of species from families Anonnaceae, Clusiaceae and Myrtaceae). These families' richness was commonly used as an indicator of the vegetation's successional stage; however, such results must be seen with caution as they show that these families co-occurred and were highly important in different strata. Studying the understory is fundamental because it represents a floristically rich stratum with a unique structure, which promotes the natural regeneration of the tree stratum.

Seasonal variation in seagrass biomass in Northern Palk Bay, India

Seagrass meadows are highly productive and serve as shelter and feeding areas for a variety of marine animals. Luxuriant seagrass beds are found in specific regions along the Indian coast. One of the largest contiguous seagrass ecosystems is located on the shallow continental shelf adjacent to the east coast of India and is comprised of four seasonally transitory species of seagrass. An extensive survey was carried out during the period from August 2009 to November 2010 on the physico-chemical variability and biomass of seagrass in the Adiramapattinam and Manalmelkudi coastal areas along Palk Bay, Bay of Bengal. There was a distinct seasonal and spatial variation of the above ground and below ground biomass between the stations. Seasonal variation in the seagrass biomass could be influenced by independent abiotic variables such as air temperature, salinity, pH, dissolved oxygen, particulate organic carbon and nutrients. The present investigation concluded that all the seagrass species were highly influenced by temperature, salinity, dissolved oxygen and total dissolved organic nitrogen in both the study areas.

The species–area relationship and confounding variables in a threatened monkey community

This study investigates the species-area relationship (SAR) for forest monkeys in a biodiversity hotspot. The Udzungwa Mountains of Tanzania are well-suited to investigate the SAR, with seven monkey species in a range of fragment sizes (0.06-526 km(2)). We test the relationship between species richness and forest fragment size, relative to human and environmental factors. We distinguish resident and transitory species because the latter have an "effective patch size" beyond the area of forest. Forest area was the strongest (log-linear) predictor of species richness. However, forest area, elevation range and annual moisture index were intercorrelated. Previous knowledge of the relationship between elevation and tree communities suggests that the SAR is largely a result of habitat heterogeneity. Isolation by farmland (matrix habitat) also had a significant negative effect on species richness, probably exacerbated by hunting in small forests. The effect of area and isolation was less for transitory species. The human influence on species' presence/absence was negatively related to the extent of occurrence. Weaker relationships with temperature and precipitation suggest underlying climatic influences, and give some support for the influence of productivity. A reduced area relationship for smaller forests suggests that fragment sizes below 12-40 km(2) may not be reliable for determining SAR in forest monkeys. Further practical implications are for management to encourage connectivity, and for future SAR research to consider residency, matrix classification and moisture besides precipitation.

The surface analytical characterization of carbon fibers functionalized by H 2SO 4/HNO 3 treatment

A systematic, time-dependent, surface-sensitive study has, for the first time, given new insights into the mechanism of the often-used, but unexplained, sulfuric/nitric acid oxidation of graphene-containing materials, such as carbon fibers and carbon nanotubes. We used X-ray photoelectron, photoacoustic FTIR and Raman spectroscopies to follow the evolution of the functionalization of carbon fibers sonicated in a 3:1 (v/v) mixture of concentrated acids at 60 °C. The study has revealed that oxidation occurs subsequent to acid attack, the attack serving to prepare sites for the ensuing oxidation, as witnessed by the presence of four O1s, two N1s and two S2p XPS peaks during the site preparation process. Their intensities varied discontinuously with treatment time, particularly in the early stages, rather than constantly increasing with time. Two of the O1s, and all the S2p and N1s peaks diminished in intensity with treatment time, eventually disappearing. The only nontransitory oxidized carbon functionality was COOH, confirmed by the two remaining O1s XPS peaks, which continued to increase long after the disappearance of the transitory species. This slow carboxylic acid production indicates that COOH formation is the rate-controlling step of the process, occurring subsequent to the site preparation initiated by the transitory species.

Factors influencing the production and stability of xanthylium cation pigments in a model white wine system

The influence of various wine parameters on the production and stability of xanthylium cation pigments in a wine-like medium is reported. The xanthylium pigments have an absorbance maximum in the visible region at 440 nm that is close to the measured absorbance used by the wine industry to indicate the browning of wine (i.e. 420 nm). The results of this study show that iron is more efficient than copper in both the colouration and production of xanthylium cation pigments in wine-like solutions of tartaric acid and (+)-catechin. The non-flavonoid caffeic acid can inhibit the accumulation of the xanthylium cation pigments, despite the presence of metal ions, and also influence the stability of the pigment. Sunlight leads to a decrease in the concentration of xanthylium cation pigments while a temperature difference of 20°C in the absence of light was observed to have little influence on concentration. The results suggest that the xanthylium cations are more likely to be a transitory species during white wine oxidation rather than accumulating pigments based on their instability with caffeic acid.

Control of Morphology of Silver Clusters Coated on Titanium Dioxide during Photocatalysis

Supported metal catalysts have been used extensively in many current industrial processes. The morphology of coated metal on a support is usually an important factor affecting the efficiency of the catalyst. In this study, the investigation is focused on a photocatalytic process to coat silver clusters on titania (P-25 TiO2) with an emphasis on the morphology control of coated silver clusters. For the first time, the particle size and the deployment intervals of silver clusters are controlled with an innovative method that involves the in-situ formation of water-insoluble transitory species such as AgBr, AgCl, or Ag2O on the surface of titanium dioxide. Experimental results demonstrated that the transitory particles function as physical spacers, which temporarily occupy some of the active site on the titanium dioxide surface and act as reservoirs for Ag+ ions to keep the local Ag+ concentration on TiO2 extremely low. The silver clusters coated on titania are found to be stable in the spherical silver-3c syn crystalline form indicated by TEM, XRD, and XPS measurements.

Evidence of ionic components in vulcanization mixtures by means of electric current measurements: Investigations with natural rubber/sulfur/zinc bis(dimethyldithiocarbamate) and comparison mixtures

Continuous low-level current (CLLC) measurements for detecting ionic species in the course of vulcanization reactions were applied to investigate the vulcanization of a mixture of natural rubber (NR), sulfur (S), and zinc bis(dimethyldithiocarbamate) (ZnDMTC). A dc voltage was applied to the reaction mixture in a special vulcanization mold and the current (e.g., in the range of 10−9 A) was measured. Temperature-dependent current maxima were found after reaction times tmax. The simplest explanation is that transitory ionic species occur during vulcanization. An activation energy (Ea ) = 116.4 kJ/mol, similar to that obtained in previous chemical investigations, was determined from the decrease of tmax with increasing temperature. The maxima corresponded to reaction times where a strong increase of polymer crosslinking was observed, as measured using vulcametry. For comparison, dc measurements were carried out with the corresponding mixture without elemental sulfur (NR/ZnDMTC) and mixtures containing zinc stearate (ZnST) instead of zinc bis(dimethyldithiocarbamate) (NR/S/ZnST and NR/ZnST). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2206–2212, 2000

Absolute concentration measurements by pulsed laser-induced fluorescence in low-pressure gases: allowing for saturation effects

We present a simple method to account for the inevitable partial saturation of the excitation process in pulsed laser-induced fluorescence. The method allows the absolute concentration of a transitory species in a low-pressure gas to be determined by comparing the signal with that from a calibrating (stable) species of known concentration: the two species are excited with different laser powers, in the inverse ratio of their transition strenghts. The validity of the method is justified both theoretically and experimentally, and is applied to the measurement of CF radicals in a fluorocarbon discharge.

SPECTROSCOPY AND STRUCTURE OF PENTACOORDINATED MOLECULES

Abstract Many proposed reaction mechanisms involve a transitory pentacoordinate intermediate. For example, the change in optical activity accompanying bimolecular displacement at tetrahedral carbon has reasonably been explained as resulting from the formation of a trigonal-bipyramidal transient with the entering and leaving groups occupying apical positions.1 Also reasonable are mechanisms advanced to account for relative rates and products formed in the hydrolysis of phosphate esters' or displacements in phosphonium' systems. Certain hypotheses4 governing the stability of the transitory trigonal-bipyramidal species are applied, and a specific intramolecular exchange process is stipulated to occur in order to account for some of the experimental information.' Mechanisms proposed to proceed via pentacoordinate species involving transition metal compounds5,6 are more speculative, whether they be dissociative (involving octahedral structures) or bimolecular (involving four-coordinate geometries).

On Defining Assembly Space: A Reply to Grover and Lawton

We appreciate the concerns raised by Grover & Lawton (p. 484) regarding our recent work. The central issue raised by Grover & Lawton is the primacy of stability as a property which maintains the status quo-an issue with which ecologists and evolutionary biologists have grappled for a very long time. There is little doubt that thought about the nature of stability strongly influences the design and interpretation of ecological experiments, as well as the form of prevailing paradigms. As a result, investigations exploring different realms of a system's behaviour often expose dynamics and behaviour which cannot be reconciled within the framework of current ecological thought. Rather than being at odds with Grover & Lawton, we find our respective approaches complementary if not integral to the development of a broader framework of community phenomenology, particularly given the emerging characterization of the community assembly state space (Drake 1990, 1991; Drake et al. 1993; Luh & Pimm 1993). To address Grover & Lawton's concerns, we begin by defining an assembly map as a convoluted mesh of variously crossing, and sometimes intersecting, trajectories. Trajectories are defined by a given set of species and associated environmental effects moving through space and time. Hence, a trajectory is one of many sequences of community states or configurations which exist and move through time (cf. assembly, succession). The form any trajectory can take is initially limited by environmental and geological vagaries. Subsequently, however, the direction a community assembly trajectory can take is richly varied. Factors such as the sequence and timing of species invasion and reinvasion, and the evolutionary and real-time dynamical interactions which occur therein, are all capable of directing a system along different, though equally plausible, trajectories. The assembly map as described above has several specific geometric properties which tie together studies such as ours. First, there are unreachable portions of the assembly map (e.g. Diamond 1975; Sugihara 1985); these regions represent community configurations which simply cannot exist. Secondly, the map of trajectories contains alternative pathways (some shorter than others) between distant community states. The system can reach state C by traversing states A-B-D in sequence, but the sequence AD-C might also exist containing very different mechanisms responsible for the organization of state C. Some trajectories have the same solution, while others traverse very different portions of the assembly space despite identical initial conditions. Disturbance can reset a trajectory onto another or simply back up the current trajectory. So defined, we have a map which is woven together into a mesh of trajectories or permissible states. Viewed in this manner we believe that our respective approaches simply focus on different portions of the assembly space-an essential difference if we are to develop a more general framework of community organization. It appears as though Grover & Lawton believe that some aspects of the assembly space offer more information than others. If this were a general rule nature should have relatively few assembly trajectories with which to define community organization. In the laboratory and in nature we often find a wide range of trajectories producing both transitory and persistent species ensembles-even within the confines of very similar environments. We also wish to reiterate that the trajectories we observed were the results of invasion timing, dynamics, and the interplay between the two. On a more technical side, our experimental design involved a relatively rapid sequence of invasions without maintenance of constant nutrient levels. However, Grover & Lawton suggest that the slowest meaningful invasion schedule, invasion only at successive equilibria (implicitly maintaining nutrient levels) is preferable. One feature of natural freshwater systems, particularly those in temperate regions, is quite rapid seasonal variation. This feature was a major concern in the design of our experiment because maintaining relatively constant conditions for an extended period would surely reduce environmental variation from our assembly trajectories. We chose to focus on the historical assembly processes which are capable of altering the expression of the mechanisms (e.g. predation, competition) often posited as the causal agent. To suggest, as Grover & Lawton do, that only certain time intervals are interesting is simply not justifiable by any scientific evidence we are aware of. Rather than 'rapid' invasions being extreme we feel that such a schedule is more likely to be the norm than 488

A new transitory product in the ozonolysis of trans-2-butene at atmospheric pressure

A previously unidentified transitory species, tentatively assigned as hydroxyethyl formate, CH 3CH (OH)-O-CHO, was formed as a major product in the ozonolysis of trans-2-butene at atmospheric pressure. A continuous stirred-tank reactor was used to analyze reaction products via molecular-beam sampling and matrix isolation FTIR spectroscopy. CH 3CHO, HCHO, CO 2, CO, CH 3OH, CH 4 and H 2O were the main, HCOOH and CH 2CO the minor, products. CH 3COOH and propene ozonide were detected as trace components.