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Patients with coronavirus disease 19 (COVID-19) have increased susceptibility to secondary respiratory infections including invasive pulmonary aspergillosis (IPA). COVID-19-associated pulmonary aspergillosis (CAPA) is difficult to diagnose and can be associated with increased mortality especially in severe immunodeficiency such as hematological malignancies. Our study evaluates IPA in COVID-19 patients defined as COVID-19-CAPA among patients with acute leukemia (AL). A retrospective single-center study analyzed 46 patients with COVID-19 infection and acute leukemia, admitted to the Clinic for Haematology, Clinical Center of Serbia, Belgrade between the 2 April 2020 and 15 May 2021. During hospitalization, all participants were diagnosed with probable IPA according to the previous consensus definitions. Positive serology and galactomannan (GM) detection values in bronchoalveolar lavage (BAL) and serum were used as microbiological criteria. COVID-19 associated probable IPA was found in 22% (9/41) tested patients, where serum GM and IgM anti-Aspergillus antibodies were positive in 12% (5/41) and 10% (4/41) had positive serology for aspergillosis. One patient died while eight recovered during follow-up. Our study showed that COVID-19 might be a risk factor for IPA development in patients with AL. Early diagnosis and prompt treatment are required as reported mortality rates are high.

IntroductionInsulin and proinsulin autoantibodies (IAA/PAA) are usually the first markers to appear in patients with type 1 Diabetes Mellitus (T1DM) and their prevalence ranges from 10 to 60% in the child-adolescent population. The reference method for IAA/PAA detection is the Radioligand Binding Assay (RBA), a highly specific and sensitive technique, but expensive and polluting. The aim of this work was to develop a novel flow cytometric microsphere-based immunoassay (FloCMIA) for PAA detection, employing recombinant human proinsulin (PI), as an alternative method to RBA, less expensive and harmful to the environment.Materials and MethodsHuman PI was expressed as Thioredoxin fusion protein (TrxPI) in E. coli and a fraction was biotinylated. A double paratope model was used in which samples were incubated with TrxPI–biotin and microspheres adsorbed with TrxPI. The immune complexes were revealed using Streptavidin–Phycoerythrin. The geometric mean of the signals was analyzed, and the results were expressed as Standard Deviation scores (SDs). Sera from 100 normal human control and from 111 type 1 diabetic patients were evaluated by FloCMIA. To correlate the novel assay with RBA, 51 diabetic patients were selected, spanning a wide range of PAA reactivity by RBA.ResultsThe study of ROC curves allowed choosing a cut-off value of 3.0 SDs and the AUC was 0.705, indicating that FloCMIA has fair ability to distinguish between samples from each group. A prevalence of 50% for PAA was obtained in the population of diabetic patients studied. The specificity was 96% and the analytical sensitivity (percentage of patients RBA positive, also positive by FloCMIA) was 69%. There was a substantial agreement between methods (kappa statistic=0.700).ConclusionsA novel immunoassay based on flow cytometry that uses easy-to produce recombinant PI was developed. This assay constitutes an innovative and cost-effective alternative to RBA for the determination of PAA in patients’ sera. The method developed here, presents good performance and a wide dynamic range together with a small required sample volume. Furthermore, these results make it possible to develop multiplex immunoassays that allow the combined detection of autoantibodies present in T1DM and other related autoimmune diseases.

Autoimmune Diabetes Mellitus (DM) is a chronic disease caused by the selective destruction of insulin producing beta cells in human pancreas. DM is characterized by the presence of autoantibodies that bind a variety of islet-cell antigens. The 65 kDa isoform of glutamate decarboxylase (GAD65) is a major autoantigen recognized by these autoantibodies. Autoantibodies to GAD65 (GADA) are considered predictive markers of the disease when tested in combination with other specific autoantibodies. In order to produce reliable immunochemical tests for large scale screening of autoimmune DM, large amounts of properly folded GAD65 are needed. Herein, we report the production of human GAD65 using the baculovirus expression system in two species of larvae, Rachiplusia nu and Spodoptera frugiperda. GAD65 was identified at the expected molecular weight, properly expressed with high yield and purity in both larvae species and presenting appropriate enzymatic activity. The immunochemical ability of recombinant GAD65 obtained from both larvae to compete with [35S]GAD65 was assessed qualitatively by incubating GADA-positive patients’ sera in the presence of 1 μM of the recombinant enzyme. All sera tested became virtually negative after incubation with antigen excess. Besides, radiometric quantitative competition assays with GADA-positive patients’ sera were performed by adding recombinant GAD65 (0.62 nM–1.4 µM). All dose response curves showed immunochemical identity between proteins. In addition, a bridge-ELISA for the detection of GADA was developed using S. frugiperda-GAD65. This assay proved to have 77.3% sensitivity and 98.2% of specificity. GAD65 could be expressed in insect larvae, being S. frugiperda the best choice due to its high yield and purity. The development of a cost effective immunoassay for the detection of GADA was also afforded. Fil: Trabucchi, Aldana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentina Fil: Bombicino, Silvina Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentina Fil: Targovnik, Alexandra Marisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Nanobiotecnología. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Nanobiotecnología; Argentina Fil: Marfía, Juan Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentina Fil: Sabljic, Adriana Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentina Fil: Faccinetti, Natalia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentina Fil: Guerra, Luciano Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentina Fil: Iacono, Ruben Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentina Fil: Miranda, Maria Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Nanobiotecnología. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Nanobiotecnología; Argentina Fil: Valdez, Silvina Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Estudios de la Inmunidad Humoral Prof. Ricardo A. Margni; Argentina

Sabljic, Ivana. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. - CONICET – Universidad de Buenos Aires. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. - GDM, Chacabuco, Buenos Aires, Argentina. Barneto, Jésica Alejandra. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. - CONICET – Universidad de Buenos Aires. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. Balestrasse, Karina Beatriz. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. - CONICET – Universidad de Buenos Aires. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. Zavala, Jorge Alberto. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. - CONICET – Universidad de Buenos Aires. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. Pagano, Eduardo Antonio. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. - CONICET – Universidad de Buenos Aires. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales (INBA). Buenos Aires, Argentina. Southern green stink bugs (Nezara viridula L.) are one of the major pests in many soybean producing areas. They cause a decrease in yield and affect seed quality by reducing viability and vigor. Alterations have been reported in the oxidative response and in the secondary metabolites in different plant species due to insect damage.\nHowever, there is little information available on soybean-stink bug interactions.\nIn this study we compare the response of undamaged and damaged seeds by Nezara viridula in two soybean cultivars, IAC-100 (resistant) and Davis (susceptible), grown under greenhouse conditions. Pod hardness, H2O2 generation, enzyme activities in guaiacol peroxidase (GPOX), catalase (CAT) and superoxide dismutase (SOD) as well as lipoxygenase expression and isoflavonoid production were quantified.\nOur results showed a greater resistance of IAC-100 to pod penetration, a decrease in peroxide content after stink bug attack, and higher GPOX, CAT and SOD activities in seeds due to the genotype and to the genotype-interaction with the herbivory treatment. Induction of LOX expression in both cultivars and higher production of isoflavonoids in IAC-100 were also detected. It was then concluded that the herbivory stink bug induces pathways related to oxidative stress and to the secondary metabolites in developing seeds of soybean and that differences between cultivars hold promise for a plant breeding program. il., tbls., grafs.

Z-drugs such as zopiclone are increasingly involved in forensic cases. Its degradation occurs in solvents and biological fluids. It is assumed that hydrolysis largely accounts for the breakdown of zopiclone in aqueous media. Therefore, a stability study in blood at different storage conditions (-20, 4, 20, and 40A degrees C) was performed to establish changes of the drug's concentration with time, also including its degradation product 2-amino-5-chloropyridine (ACP). As removal of the aqueous phase may stabilize molecules that are prone to hydrolysis, it was assessed whether the use of dried blood spots (DBS) may be an alternative for storing and analyzing zopiclone and ACP. Spiked and authentic blood samples and corresponding DBS were analyzed using fully validated LC-MS/MS assays. There was agreement between the measurement of zopiclone from either blood or matching DBS in freshly prepared samples. Results showed that zopiclone was unstable in blood at all storage temperatures except at -20A degrees C. Stability of zopiclone in spiked and authentic blood was increased in DBS compared to matching blood samples stored at the same condition. About 85 % of the initial concentration of zopiclone was still intact in DBS on day 8 at 20A degrees C. ACP was formed from zopiclone in equimolar amounts in both media. Therefore, determination of both zopiclone and ACP may be helpful to estimate the initial concentration in both media. Pre-analytical conditions have a major impact on the recovery of zopiclone from blood. With respect to its known advantages, DBS can be recommended as a valuable alternative for the determination of zopiclone from blood.

A flow-through sampler (FTS) was codeployed with a super high volume active sampler (SHV) between October 2007 and November 2008 to evaluate its ability to determine the ambient concentrations of pesticides and brominated flame retardants in the Canadian High Arctic atmosphere. Nine pesticides and eight flame retardants, including three polybrominated diphenyl ether (PBDE) replacement chemicals, were frequently detected. Atmospheric concentrations determined by the two systems showed good agreement when compared on monthly and annually integrated time scales. Pesticide concentrations were normally within a factor of 3 of each other. The FTS tended to generate higher PBDE concentrations than the SHV presumably because of the entrainment of blowing snow/ice crystals or large particles. Taking into account uncertainties in analytical bias, sample volume, and breakthrough estimations, the FTS is shown to be a reliable and cost-effective method, which derives seasonally variable concentrations of semivolatile organic trace compounds at extremely remote locations that are comparable to those obtained by conventional high volume air sampling. Moreover, the large sampling volumes captured by the FTS make it suitable for the screening of new and emerging chemicals in the remote atmosphere where concentrations are usually low.

SummaryUse of recombinant human proteins has revolutionized medicine by providing over 200 highly purified hormones and proteins that effectively treat many inherited and acquired peptide hormone and protein deficiencies. With the exception of therapeutic monoclonal antibodies, these biological medicines are synthesized by cultured cells using DNA sequences that would yield proteins with identical amino acid sequences as endogenous human proteins. Therefore, there was the broad expectation that recombinant human biological medicines would be non-immunogenic in patients capable of synthesizing even sub-optimal levels of these therapeutic proteins to which they are innately tolerant. However, the widespread clinical use of recombinant human proteins has demonstrated that nearly all of them are immunogenic. This observation suggests that factors additional to differences in amino acid sequences of endogenous and biotherapeutic proteins contribute to the immunogenicity of therapeutic proteins. The main aim of this review is to summarize some of the factors that are known to contribute to the immunogenicity of recombinant therapeutic proteins.

Dipeptidyl peptidase III (DPP III) is a widely distributed cytosolic zinc peptidase from the M49 family, which hydrolyses dipeptides from the N-termini of its peptide substrates. Until now, most studies on DPP III were done on orthologs from eukaryotic organisms, showing that DPP III participates in the intracellular protein catabolism and oxidative stress response. The knowledge about prokaryotic DPP III is very scarce, particularly data on its catalytic mechanism, physiological function and structural characteristics are lacking. We have been studying two bacterial orthologs: DPP III from the human gut symbiont Bacteroides thetaiotaomicron (Bt) and from Caldithrix abyssi (Ca), which inhabits hydrothermal vents. Both proteins were produced in Escherichia coli and then purified. Diverse crystallization screens were applied and wild-type CaDPP III crystals were obtained. Crystallization experiments with wild-type BtDPP III failed probably due to charge heterogeneity. In order to overcome this problem, specific amino acid replacements (all cysteines were replaced by serines) were introduced and crystals of the variant protein were grown. Datasets for both DPP III proteins were collected at BESY II, Germany. Up to date, all efforts to solve the structures of the two proteins using molecular replacement method and anomalous dispersion of the zinc ions, were unsuccessful. Therefore, selenomethionine labeled BtDPP III, non-cysteine variant, was prepared and the crystals were obtained in the same crystallization condition as the non-labelled protein. Diffraction data up to 1.8 Å resolution were collected at Elettra Trieste, Italy, and the first prokaryotic DPP III structure was solved using single-wavelength anomalous dispersion of the selenium atoms. BtDPP III crystallized in space group P3121 with unit cell dimensions a=103.5 Å and c=141.6 Å and one molecule per asymmetric unit. The overall fold is typical for a member of the M49 family with two domains separated by a wide cleft. The upper domain is mostly helical with a tetracoordinated zinc ion, while the lower domain contains mixed secondary structure elements with a five-stranded β-barrel core. The main structural difference between BtDPP III and eukaryotic DPP III is the absence of a 30 amino acid loop in upper domain. In human DPP III this loop contains the ETGE motif which is supposed to be responsible for binding KEAP1, a repressor protein from the Keap1-Nrf2 signaling pathway.

This study was undertaken to test the ability of the molecular connectivity model to predict the soil sorption coefficients of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, chlorobenzenes, chlorinated alkanes and alkenes, heterocyclic and substituted PAHs, and halogenated phenols. Tests performed on 31 such compounds clearly demonstrate that this simple nonempirical model accurately predicts the soil sorption coefficients for the above classes of compounds. Moreover, the model out performs the traditional empirical models based on 1-octanol/water partition coefficients or water solubilities in accuracy, speed, and range of applicability. Additional tests on approximately 160 polar and ionic compounds show that the above topological model plus a single semiempirical variable is capable of accounting for the soil sorption properties of nearly 95% of all organic chemicals whose soil sorption coefficients have been measured. The results of these tests demonstrate that the molecular connectivity model is a very accurate predictive tool for the soil sorption coefficients of a wide range of organic chemicals and that it can be confidently used to rank potentially hazardous chemicals and thus to create a priority testing list. 55 references, 5 figures, 7 tables.

The ultraviolet absorption spectra of cyclopentadiene and cyclopentadiene‐d6 were measured in the NV1 transition region. The spectra were analyzed to determine the excited state properties. The prominent vibrational progression was identified as a progression in the (predominantly) a1 C=C stretching vibration. A second, unidentified, vibrational interval was observed in the cyclopentadiene spectrum and inferred to exist in the spectrum of cyclopentadiene‐d6. The excited state potential surface was deduced to be displaced 0.2 A from the lower, predominantly along the C=C normal coordinate. The excited state lifetime was determined to be 37 fs at the origin and decrease at a rate inversely related to the excited state vibrational quantum number.

The polarization-selected two-photon resonant multiphoton ionization spectra of cyclopentadiene and cyclopentadiene-d 6 have been measured in the 3p-Rydberg←X region of the spectrum. The spectra were analyzed to provide experimental assignments for all three 3p-Rydberg origins and three a 1 , three b 1 , and one a 2 fundamental vibrational frequencies in the 3p-Rydberg states. The allowed origins of the B 1 and A 1 3p-Rydberg←X transitions were not observed; Herzberg-Teller induced false origins were observed from the ground to these states in their stead

The polarization-selected two-photon resonant multiphoton ionization spectra of cyclopentadiene and cyclopentadiene-d 6 have been measured in the 3p-Rydberg←X region of the spectrum. The spectra were analyzed to provide experimental assignments for all three 3p-Rydberg origins and three a 1 , three b 1 , and one a 2 fundamental vibrational frequencies in the 3p-Rydberg states. The allowed origins of the B 1 and A 1 3p-Rydberg←X transitions were not observed; Herzberg-Teller induced false origins were observed from the ground to these states in their stead

When synthetic, xenobiotic compounds such as agrochemicals and industrial chemicals are utilized, they eventually reach the soil environment where they are subject to degradation, leaching, volatilization, sorption, and uptake by organisms. The simplest assumption is that such chemicals in soil are totally available to microorganisms, plant roots, and soil fauna via direct, contact exposure ; subsequently these organisms are consumed as part of food web processes and bioaccumulation may occur, increasing exposures to higher organisms up the food chain. However, studies in the last two decades have revealed that chemical residues in the environment are not completely bioavailable, so that their uptake by biota is less than the total amount present in soil (Alexander 1995 ; Gevao et al. 2003 ; Paine et al. 1996). Therefore, the toxicity, biodegradability, and efficacy of xenobiotics are dependent on their soil bioavailability, rendering this concept profoundly important to chemical risk assessment and pesticide registration.

The ultraviolet absorption spectra of cyclopentadiene and cyclopentadiene‐d6 were measured in the NV1 transition region. The spectra were analyzed to determine the excited state properties. The prominent vibrational progression was identified as a progression in the (predominantly) a1 C=C stretching vibration. A second, unidentified, vibrational interval was observed in the cyclopentadiene spectrum and inferred to exist in the spectrum of cyclopentadiene‐d6. The excited state potential surface was deduced to be displaced 0.2 A from the lower, predominantly along the C=C normal coordinate. The excited state lifetime was determined to be 37 fs at the origin and decrease at a rate inversely related to the excited state vibrational quantum number.

In this experimental investigation of the valence states of cis- and trans-hexatrienes, two triplet and two singlet valence transitions are observed in each isomer. Differences are observed between the cis- and trans-hexatriene spectra. A comparison of the trans-hexatriene results with the best ab initio and semiempirical calculations suggests that the B,' and Ag+ singlet states are observed and that the A,- state, while not observed, is above the B,+ state. The relation of these results to the polyene problem will be discussed.

The Hel photoelectron (PE) spectra of desmethyldiazepam, diazepam, oxazepam, temazepam, 3-(S)-methyldesmethyldiazepam, 3-(S)-methyldiazepam, 5-methyl-2H-1,4-benzodiazepin-2-one, and benzophenonmethylimine have been measured and analyzed. Their low-energy regions (up to 12.0 eV) have been completely assigned by the composite molecule method using the PE spectra of diphenylmethane, benzophenonmethylimine, acetamide, chlorobenzene, and acetophenonmethylimine to compare the electronic structure of equivalent parts.

The aromatic stabilities of bridged hetero[n]annulenes (n = even, odd) and the parent structures of hetero-[n]annulenes and hetero[n]polycycles have been predicted by the topological resonance energy, TRE, approach. The TRE criterion places bridged structures in all cases studied between the hetero[n]annulenes and hetero[n]polycyclic systems. The extra aromatic stability of the bridged heteroannulenes compared to heteroannulenes is attributed to homoaromatic interaction across the ring at the bridge sites. Available experimental evidence supports the theoretical results.

Comparaison des spectres de perte d'energie electronique des isomeres cis et trans de l'hexatriene

The NV2 valence transition of 2,3‐dimethylbutadiene is demonstrated, by electron energy loss spectroscopy, to occur around 7 eV. The slight NV2 intensity difference between this molecule and butadiene is shown to arise from a ground state vibrational excitation dependent enhancement of the NV2 transition in DMB.

Comparaison des spectres de perte d'energie electronique des isomeres cis et trans de l'hexatriene

To determine the feasibility of developing an expert system for biodegradability assessment, a survey was conducted in which biodegradation experts were asked to estimate rates and products of degradation for 50 chemicals. These chemicals, which varied widely in structure, were considered representative of the spectrum of premanufacture notice chemicals subject to EPA review under the Toxic Substances Control Act. There was substantial agreement among the 22 experts on both sites of initial attack and rates of degradation. The approximate order in which various groups were viewed as contributing to aerobic biodegradability is as follows: ester, amide, anhydride greater than hydroxyl greater than carboxyl, epoxide, site of unsaturation greater than benzene ring, methyl, methylene. Hydrolyzable groups, azo bonds, halogens, and nitro groups were preferred sites of anaerobic attack. Among the negative influences on aerobic biodegradability were molecular mass, branching, halogenation, and nitrogen heterocycles. Results also indicate that estimates of removal by biodegradation in aerobic wastewater treatment and time for aerobic ultimate and primary degradation were well correlated, and that the predictive value of such correlations could be improved using correction factors for certain classes of chemicals. The results lend support to existing rules of thumb, but also offer additional insight that will prove useful in designing a prototype system.

In this experimental investigation of the valence states of cis- and trans-hexatrienes, two triplet and two singlet valence transitions are observed in each isomer. Differences are observed between the cis- and trans-hexatriene spectra. A comparison of the trans-hexatriene results with the best ab initio and semiempirical calculations suggests that the B,' and Ag+ singlet states are observed and that the A,- state, while not observed, is above the B,+ state. The relation of these results to the polyene problem will be discussed.

The NV2 valence transition of 2,3‐dimethylbutadiene is demonstrated, by electron energy loss spectroscopy, to occur around 7 eV. The slight NV2 intensity difference between this molecule and butadiene is shown to arise from a ground state vibrational excitation dependent enhancement of the NV2 transition in DMB.

Experimentally determining soil sorption behavior of xenobiotic chemicals during the last 10 years has been costly, time-consuming, and very tedious. Since an estimated 100,000 chemicals are currently in common use and new chemicals are registered at a rate of 1000 per year, it is obvious that our human and material resources are insufficient to experimentally obtain their soil sorption data. Much work is being done to find alternative methods that will enable us to accurately and rapidly estimate the soil sorption coefficients of pesticides and other classes of organic pollutants. Empirical models, based on water solubility and n-octanol/water partition coefficients, have been proposed as alternative, accurate methods to estimate soil sorption coefficients. An analysis of the models has shown (a) low precision of water solubility and n-octanol/water partition data, (b) varieties of quantitative models describing the relationship between the soil sorption and above-mentioned properties, and (c) violations of some basic statistical laws when these quantitative models were developed. During the last 5 years considerable efforts were made to develop nonempirical models that are free of errors imminent to all models based on empirical variables. Thus far molecular topology has been shown to be the most successful structural property for describing and predicting soil sorption coefficients. The first-order molecular connectivity index was demonstrated to correlate extremely well with the soil sorption coefficients of polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, chlorobenzenes, chlorinated alkanes and alkenes, heterocyclic and heterosubstituted PAHs, and halogenated phenols. The average difference between predicted and observed soil sorption coefficients is only 0.2 on the logarithmic scale (corresponding to a factor of 1.5). A comparison of the molecular connectivity model with the empirical models described earlier shows that the former is superior in accuracy, performance, and range of applicability. It is possible to extend this model, with the addition of a single, semiempirical variable, to take care of polar and ionic compounds and to accurately predict the soil sorption coefficients for almost 95% of all organic chemicals whose coefficients have been reported. No empirical or nonempirical models have ever predicted the soil sorption coefficients to such a high degree of accuracy on such a broad selection of structurally diverse compounds. An additional advantage of the molecular connectivity model is that it is sufficient to know the structural formulas to make predictions about soil sorption coefficients.(ABSTRACT TRUNCATED AT 400 WORDS)