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ABSTRACT The kinetics of formanilides hydrolysis were determined under first-order conditions in hydrochloric acid (0.01-8 M, 20-60°C) and in hydroxide solutions (0.01-3 M, 25 and 40°C). Under acidic conditions, second-order specific acid catalytic constants were used to construct Hammett plots. The ortho effect was analyzed using the Fujita-Nishioka method. In alkaline solutions, hydrolysis displayed both first- and second-order dependence in the hydroxide concentration. The specific base catalytic constants were used to construct Hammett plots. Ortho effects were evaluated for the first-order dependence on the hydroxide concentration. Formanilide hydrolyzes in acidic solutions by specific acid catalysis, and the kinetic study results were consistent with the AAC2 mechanism. Ortho substitution led to a decrease in the rates of reaction due to steric inhibition of resonance, retardation due to steric bulk, and through space interactions. The primary hydrolytic pathway in alkaline solutions was consistent with a modified BAC2 mechanism. The Hammett plots for hydrolysis of meta- and para-substituted formanilides in 0.10 M sodium hydroxide solutions did not show substituent effects; however, ortho substitution led to a decrease in rate constants proportional to the steric bulk of the substituent. [ABSTRACT FROM AUTHOR]

Global quantitative estimations of ecosystem functions are vital. Among those, ecosystem respiration and photosynthesis contribute to carbon cycling and energy flow to food webs. These can be estimated in streams with the open channel diel oxygen method (single or two stations) essentially relying on a mass balance of oxygen over a defined reach. The method is generally perceived as low cost and easy to apply with new drift free optic sensors. Yet, it remains challenging on several key issues reviewed here: measurements of gas transfer at the air-water interface, appropriate mixing of tracers, uncertainty propagation in the calculations, spatial heterogeneity in oxygen concentrations, the derivation of net primary production (NPP) or autotrophic respiration, and the temperature dependence of photosynthesis and respiration. An extremely simple modeling tool is presented in an Excel workbook recommended for teaching the basic principles of the method. The only method able to deal with stream spatial heterogeneity is the method by Demars et al. Example data, Excel workbook, and R script are provided to run stream metabolism calculations. Direct gas exchange determination is essential in shallow turbulent streams, but modeling may be more accurate in large (deep) rivers. Lateral inflows should be avoided or well characterized. New methods have recently been developed to estimate NPP using multiple diel oxygen curves. The metabolic estimates should not be systematically temperature corrected to compare streams. Other recent advances have improved significantly the open channel diel oxygen method, notably the estimation of respiration during daylight hours. [ABSTRACT FROM AUTHOR]

The goal of the research was to study the reactivity of the hydrophobic 2- and 3-pyridineketoximes under exposure to UV-VIS light. The photodegradation was conducted in both toluene and heptane for 10 h under atmosphere of argon. Ten-hour irradiation experiments demonstrated that the pyridineketoximes underwent the facile E-Z photoisomerization, photo-Beckmann rearrangement, and to a lesser extent, the photosubstitution to the pyridine ring. From LC-MS and NMR analysis of the irradiated solutions, it was found that the photosubstitution proceeded to give the corresponding 6- substituted 2- or 3-pyridylketoxime via the replacement of the ring hydrogen by the benzyl or heptyl group. The photo- Beckmann rearrangement led to the formation of the corresponding amides, but also other products formed in the photo-decomposition reaction. [ABSTRACT FROM AUTHOR]

A comprehensive review of quantitative structure-activity relationships (QSAR) allowing the prediction of the fate of organic compounds in the environment from their molecular properties was done. The considered processes were water dissolution, dissociation, volatilization, retention on soils and sediments (mainly adsorption and desorption), degradation (biotic and abiotic), and absorption by plants. A total of 790 equations involving 686 structural molecular descriptors are reported to estimate 90 environmental parameters related to these processes. A significant number of equations was found for dissociation process (pKa), water dissolution or hydrophobic behavior (especially through the KOWparameter), adsorption to soils and biodegradation. A lack of QSAR was observed to estimate desorption or potential of transfer to water. Among the 686 molecular descriptors, five were found to be dominant in the 790 collected equations and the most generic ones: four quantum-chemical descriptors, the energy of the highest occupied molecular orbital (EHOMO) and the energy of the lowest unoccupied molecular orbital (ELUMO), polarizability (α) and dipole moment (μ), and one constitutional descriptor, the molecular weight. Keeping in mind that the combination of descriptors belonging to different categories (constitutional, topological, quantum-chemical) led to improve QSAR performances, these descriptors should be considered for the development of new QSAR, for further predictions of environmental parameters. This review also allows finding of the relevant QSAR equations to predict the fate of a wide diversity of compounds in the environment. [ABSTRACT FROM AUTHOR]

Previous studies have shown that patients with hepatitis B virus-related cirrhosis (HBVRC) without overt hepatic encephalopathy (OHE) are associated with a varying degree of cognitive dysfunction. Several resting-state functional magnetic resonance imaging (fMRI) studies have been conducted to explore the neural correlates of such cognitive deficits, whereas little effort has been made to investigate the cortical integrity in cirrhotic patients without OHE. Here, using cortical thickness, surface area and local gyrification index (lGI), this study performed a comprehensive analysis on the cortical morphometry of patients with HBV-RC without OHE (HBV-RC-NOHE) vs. matched healthy controls. Compared with healthy controls, we found significantly increased cortical thickness in the bilateral lingual and parahippocampal gyrus, right posterior cingulate cortex, precuneus, peri-calcarine sulcus and fusiform gyrus in patient with HBV-RC-NOHE, which may closely relate to be the low-grade brain edema. Cortical gyrification analysis showed significantly increased lGI in the left superior and inferior parietal cortex as well as lateral occipital cortex, which was speculated to be associated with disruptions in white matter connectivity and sub-optimal intra-cortical organization. In addition, the mean cortical thickness/lGI of the regions with structural abnormalities was shown to be negatively correlated with psychometric hepatic encephalopathy score (PHES) of the patients with HBV-RC-NOHE. These morphological changes may serve as potential markers for the preclinical diagnosis and progression of HBV-RC-NOHE. [ABSTRACT FROM AUTHOR]

Air temperature (Ta) is a key input in a wide range of agroclimatic applications. Moderate Resolution Imaging Spectroradiometer (MODIS) Ts (Land Surface Temperature (LST)) products are widely used to estimate daily Ta. However, only daytime LST (Ts-day) or nighttime LST (Ts-night) data have been used to estimate Tmax/Tmin (daily maximum or minimum air temperature), respectively. The relationship between Tmax and Ts-night, and the one between Tmin and Ts-day has not been studied. In this study, both the ability of Ts-night data to estimate Tmax and the ability of Ts-day data to estimate Tmin were tested and studied in the Corn Belt during the growing season (May-September) from 2008 to 2012, using MODIS daily LST products from both Terra and Aqua. The results show that using Ts-night for estimating Tmax could result in a higher accuracy than using Ts-day for a similar estimate. Combining Ts-day and Ts-night, the estimation of Tmax was improved by 0.19-1.85, 0.37-1.12 and 0.26-0.93 °C for crops, deciduous forest and developed areas, respectively, when compared with using only Ts-day or Ts-night data. The main factors influencing the Ta estimation errors spatially and temporally were analyzed and discussed, such as satellite overpassing time, air masses, irrigation, etc. [ABSTRACT FROM AUTHOR]

In recent decades, a large number of reports related to the synthesis of N, O, and S containing heterocycles have appeared owing to a wide variety of their biological activity. The metal catalyzed synthesis of heterocycles is becoming an important and highly rewarding protocol in organic synthesis. Palladium-mediated cyclization reactions have been recognized as some of the simplest and useful tools for regio- as well as stereoselective syntheses of carbo- and heterocyclic compounds. This review focuses on the use of palladium as a catalyst for the synthesis of nitrogen containing five-membered heterocylces fused with other heterocycles. It describes the formation of different types of heterocyclic rings. [ABSTRACT FROM PUBLISHER]

ABSTRACT Guanine-rich DNA sequences that may form G-quadruplexes are located in strategic DNA loci with the ability to regulate biological events. G-quadruplexes have been under intensive scrutiny owing to their potential to serve as novel drug targets in emerging anticancer strategies. Thermodynamic characterization of G-quadruplexes is an important and necessary step in developing predictive algorithms for evaluating the conformational preferences of G-rich sequences in the presence or the absence of their complementary C-rich strands. We use a combination of spectroscopic, calorimetric, and volumetric techniques to characterize the folding/unfolding transitions of the 26-meric human telomeric sequence d[A3G3(T2AG3)3A2]. In the presence of K+ ions, the latter adopts the hybrid-1 G-quadruplex conformation, a tightly packed structure with an unusually small number of solvent-exposed atomic groups. The K+-induced folding of the G-quadruplex at room temperature is a slow process that involves significant accumulation of an intermediate at the early stages of the transition. The G-quadruplex state of the oligomeric sequence is characterized by a larger volume and compressibility and a smaller expansibility than the coil state. These results are in qualitative agreement with each other all suggesting significant dehydration to accompany the G-quadruplex formation. Based on our volume data, 432 ± 19 water molecules become released to the bulk upon the G-quadruplex formation. This large number is consistent with a picture in which DNA dehydration is not limited to water molecules in direct contact with the regions that become buried but involves a general decrease in solute-solvent interactions all over the surface of the folded structure. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 216-227, 2014. [ABSTRACT FROM AUTHOR]

A method for the selective hydration of nitrile to amide by employing commercially available acetaldoxime and inexpensive oxometallate such as molybdate, vanadate, and tungstate in environmentally friendly water is described. Under this protocol, nitriles including aromatic nitriles, heterocyclic nitriles, and aliphatic nitriles were converted into the corresponding amides in good to excellent yields. [Supplementary materials are available for this article. Go to the publisher's online edition ofSynthetic Communications®for the following free supplemental resource(s): Full experimental and spectral details.] [ABSTRACT FROM AUTHOR]

Carefully constructed but fallible historical estimates of GDP and agricultural output inform our understanding of the preindustrial origins of economic growth. Here we review four recent attempts at estimating agricultural output and food availability in England and Wales at different points between the Middle Ages and the Industrial Revolution. We highlight their contrasting implications for trends in well-being and nutritional status over time. Building on these estimates, we propose our own tentative, compromise estimate of food availability. The compromise estimates are more coherent with our understanding of conditions before and during the Industrial Revolution. [ABSTRACT FROM PUBLISHER]

Pressure is a thermodynamic parameter that can induce structural changes in biomolecules due to a volumetric decrease. Although most proteins are denatured by pressure over 100 MPa because they have the large cavities inside their structures, the double-stranded structure of DNA is stabilized or destabilized only marginally depending on the sequence and salt conditions. The thermal stability of the G-quadruplex DNA structure, an important non-canonical structure that likely impacts gene expression in cells, remarkably decreases with increasing pressure. Volumetric analysis revealed that human telomeric DNA changed by more than 50 cm3 mol-1 during the transition from a random coil to a quadruplex form. This value is approximately ten times larger than that for duplex DNA under similar conditions. The volumetric analysis also suggested that the formation of G-quadruplex DNA involves significant hydration changes. The presence of a cosolute such as poly(ethylene glycol) largely repressed the pressure effect on the stability of G-quadruplex due to alteration in stabilities of the interactions with hydrating water. This review discusses the importance of local perturbations of pressure on DNA structures involved in regulation of gene expression and highlights the potential for application of high-pressure chemistry in nucleic acid-based nanotechnology. [ABSTRACT FROM AUTHOR]

The densities of l-alanine and l-serine in aqueous solutions of N, N-dimethylformamide (DMF) have been measured at 298.15 K with an Anton Paar Model 55 densimeter. Apparent molar volumes $$ (V_{\phi } ) $$ , standard partial molar volumes $$ (V_{\phi }^{0} ) $$ , standard partial molar volumes of transfer $$ (\Updelta_{\text{tr}} V_{\phi }^{0} ) $$ and hydration numbers have been determined for the amino acids. The $$ \Updelta_{\text{tr}} V_{\phi }^{0} $$ values of l-serine are positive which suggest that hydrophilic-hydrophilic interactions between l-serine and DMF are predominant. The -CH group of l-alanine has much more influence on the volumetric properties and the $$ \Updelta_{\text{tr}} V_{\phi }^{0} $$ have smaller negative values. The results have been interpreted in terms of the cosphere overlap model. [ABSTRACT FROM AUTHOR]

Stereoelectronic interactions associated with theAEand also the conformational and structural properties of 1,3-oxathianeS-oxide (1), 1,3-dithianeS-oxide (2), 1,3-thiaselenaneS-oxide (3), 1,3-oxaselenaneSe-oxide (4), 1,3-thiaselenaneSe-oxide (5), and 1,3-diselenaneSe-oxide (6) were investigated using quantum mechanical methods. These compounds were fully optimized at the B3LYP/6 – 311 +G** and HF/6 – 311 +G** levels of theory. The Gibbs Free Energy, Enthalpy, and Entropy differences (i.e., ΔG, ΔH, and ΔS) between the axial and equatorial conformations were calculated at the B3LYP/6 – 311 +G** and HF/6 – 311 +G** levels of theory. The decrease of theAEis corresponding to the decreases of calculated Δ(Gax–Geq) value of the above mentioned compounds. The calculatedAEvalues are more significant for the justification of the conformational dominances of the compounds than steric effects. In this work, the relations between the Anomeric Effects, donor and acceptor orbital energies, occupancies, structural parameters, dipole–dipole interactions, and conformational behavior of the compounds have been studied. [ABSTRACT FROM PUBLISHER]

Excess molar volumes V for 40 mixtures of heptane with a liquid alkane and apparent molar volumes in heptane for eight solid alkanes have been obtained at 298.15 K. They include five linear, 30 branched-chain, and 13 cyclic alkanes. Almost all systems exhibit negative V values. For mixtures with open chain alkanes, V increases from C5 to C7 and then decreases. A similar trend is shown by mixtures with cycloalkanes. V values are compared with known H data for mixtures with heptane and tetrachloromethane. Signs and trends of V and H are correlated with the free volume and interactional terms of the Flory theory. The partial molar volumes at infinite dilution in heptane, V°, have also been obtained and discussed together with literature data on other hydrocarbons and polar compounds. The calculated contributions to V° by CH, CH, CH and C groups are compared with previously determined contributions of polar groups. The lower contributions of the latter groups are explained with the volume contraction caused by dipole-induced dipole interaction. The volume effects associated with branching and cyclization have been evaluated and compared with the corresponding effects on solvation enthalpy. The branching effect, in the order of magnitude of few cm·mol, and the larger negative values of cyclization volumes, down to −24 cm·mol, are discussed in terms of packing and solute-solvent interactions, in analogy to polar organic solutes either in heptane and tetrachloromethane. A negative cyclization effect is also exhibited by the solvation enthalpies. [ABSTRACT FROM AUTHOR]

Women educators played an essential role in transforming public museums that had been focused on collections and research into effective educational and informational sites that engaged broad publics. Three significant innovators were Delia Griffin of St. Johnsbury Museum in Vermont who emphasized hands-on learning, Anna Billings Gallup who shaped a distinctive model museum for children in Brooklyn and Laura Bragg of the Charleston Museum who established strong collaboration with the local public schools. Joining museum curatorial staffs and professional associations that were largely male, these women educators and their peers typically provided pedagogical insights and teaching skills that enabled them to work effectively with school systems, teachers, pupils and parents. Genuinely interested in natural science, they shaped careers which included opportunities to engage with science, provided a considerable degree of autonomy and enabled them to experiment with hands-on learning. They built networks of museum educators and influenced the young American Association of Museums. Women museum educators created a bridge between semi-public natural history establishments for collection, preservation and scientific research and an active audience of teachers, pupils, visitors and patrons. Their efforts transformed museums into sites for education and broad public access to science in the early 20th century. [ABSTRACT FROM AUTHOR]

Amide bond formation is one of the most important reactions in both chemistry and biology 1-4 , but there is currently no chemical method of achieving α-peptide ligation in water that tolerates all of the 20 proteinogenic amino acids at the peptide ligation site. The universal genetic code establishes that the biological role of peptides predates life's last universal common ancestor and that peptides played an essential part in the origins of life 5-9 . The essential role of sulfur in the citric acid cycle, non-ribosomal peptide synthesis and polyketide biosynthesis point towards thioester-dependent peptide ligations preceding RNA-dependent protein synthesis during the evolution of life 5,9-13 . However, a robust mechanism for aminoacyl thioester formation has not been demonstrated 13 . Here we report a chemoselective, high-yielding α-aminonitrile ligation that exploits only prebiotically plausible molecules-hydrogen sulfide, thioacetate 12,14 and ferricyanide 12,14-17 or cyanoacetylene 8,14 -to yield α-peptides in water. The ligation is extremely selective for α-aminonitrile coupling and tolerates all of the 20 proteinogenic amino acid residues. Two essential features enable peptide ligation in water: the reactivity and pK aH of α-aminonitriles makes them compatible with ligation at neutral pH and N-acylation stabilizes the peptide product and activates the peptide precursor to (biomimetic) N-to-C peptide ligation. Our model unites prebiotic aminonitrile synthesis and biological α-peptides, suggesting that short N-acyl peptide nitriles were plausible substrates during early evolution.

The origins of life represent one of the most fundamental chemical questions being addressed by modern science. One of the longstanding mysteries of this field is what series of chemical reactions could lead to the molecular biologists dream; a pool of homochiral nucleotides? Here we summarize those results we consider to be historically important and outline our recently published research aimed at understanding the chemoselective origins of the canonical ribonucleotides. 1 Introduction 1.1 Nucleotides: What's the Problem? 2 Synthesis of Activated Pyrimidines 2.1 Pyrimidine Elaboration by Cyanovinylation 2.2 Photochemical Epimerization and Cytidine to Uridine Conversion 2.3 Urea-Mediated Phosphoryl Transfer and Intramolecular Rearrangement 2.4 Pyrimidine Photosanitization 3 Chemoselective Purine Glycosylation 4 Future Scope for Investigation 5 Conclusion [ABSTRACT FROM AUTHOR]

The ability of different stationary phases developed for the analysis of polar compounds (ZIC-HILIC, ZIC-pHILIC and Zorbax SB-Aq) to separate isoniazid, its metabolites (acetylisonazid, pyridoxal isonicotinoyl hydrazone, pyridoxal isonicotinoyl hydrazone 5-phosphate), pyridoxine, pyridoxal and pyridoxal 5-phosphate under MS compatible conditions was systematically investigated using HPLC-UV. The mobile phase strength, pH and buffer concentration were modified to assess their impact on the retention of these compounds. The best available separation of the compounds was achieved using 1 mM ammonium formate (pH≈6) and ACN (20:80, v/v) on ZIC-HILIC and employing 5 mM ammonium formate (pH 3.0) and ACN (40:60, v/v) on ZIC-pHILIC. A gradient profile using 0.5 mM ammonium formate (pH≈6) and MeOH (0-12 min: 10% MeOH, 12-15 min: 10-50% MeOH, 15-35 min: 50% MeOH, 35.0-35.2 min: 50-10% MeOH, 35.2-45.0 min: 10% MeOH) provided the best separation of the compounds on Zorbax SB-Aq. Subsequent LC-MS analysis demonstrated that ZIC-HILIC is useful for the analysis of pyridoxine, pyridoxal and pyridoxal isonicotinoyl hydrazone. However, the chromatographic conditions developed for the analysis of the compounds on Zorbax SB-Aq are capable of achieving the best separation of all compounds in this study with the higher sensitivity for most of the analytes. [ABSTRACT FROM AUTHOR]

This article presents a reoptimization of the GROMOS 53A6 force field for hexopyranose-based carbohydrates (nearly equivalent to 45A4 for pure carbohydrate systems) into a new version 56A (nearly equivalent to 53A6 for non-carbohydrate systems). This reoptimization was found necessary to repair a number of shortcomings of the 53A6 (45A4) parameter set and to extend the scope of the force field to properties that had not been included previously into the parameterization procedure. The new 56A force field is characterized by: (i) the formulation of systematic build-up rules for the automatic generation of force-field topologies over a large class of compounds including (but not restricted to) unfunctionalized polyhexopyranoses with arbritrary connectivities; (ii) the systematic use of enhanced sampling methods for inclusion of experimental thermodynamic data concerning slow or unphysical processes into the parameterization procedure; and (iii) an extensive validation against available experimental data in solution and, to a limited extent, theoretical (quantum-mechanical) data in the gas phase. At present, the 56A force field is restricted to compounds of the elements C, O, and H presenting single bonds only, no oxygen functions other than alcohol, ether, hemiacetal, or acetal, and no cyclic segments other than six-membered rings (separated by at least one intermediate atom). After calibration, this force field is shown to reproduce well the relative free energies of ring conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic linkage conformers. As a result, the 56A force field should be suitable for: (i) the characterization of the dynamics of pyranose ring conformational transitions (in simulations on the microsecond timescale); (ii) the investigation of systems where alternative ring conformations become significantly populated; (iii) the investigation of anomerization or epimerization in terms of free-energy differences; and (iv) the design of simulation approaches accelerating the anomerization process along an unphysical pathway. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011 [ABSTRACT FROM AUTHOR]

The anomeric effect is a chemical phenomenon that refers to an observed stabilization of six-membered carbohydrate rings when they contain an electronegative substituent at the C1 position of the ring. This stereoelectronic effect influences the three-dimensional shapes of many biological molecules. It can be manifested not only in this classical manner involving interaction of the endocyclic oxygen atom (O5) found in such sugars with the C1 substituent (endo-anomeric effect) but also through a corresponding interaction of the electronegative exocyclic substituent with O5 (exo-anomeric effect). However, the underlying physical origin(s) of this phenomenon is still not clear. Here we show, using a combination of laser spectroscopy and computational analysis, that a truncated peptide motif can engage the two anomers of an isolated sugar in the gas phase, an environment lacking extraneous factors which could confound the analysis. (Anomers are isomers that differ in the orientation of the substituent at C1.) Complexes formed between the peptide and the ?- or ?-anomers of d-galactose are nearly identical structurally; however, the strength of the polarization of their interactions with the peptide differs greatly. Natural bond order calculations support this observation, and together they reveal the dominance of the exo- over the endo-anomeric effect. As interactions between oxygen atoms at positions C1 and C2 (O1 and O2, respectively) on the pyranose ring can alter the exo/endo ratio of a carbohydrate, our results suggest that it will be important to re-evaluate the influence, and biological effects, of substituents at position C2 in sugars. [ABSTRACT FROM AUTHOR]

The article discusses the English old poor law (OPL), instituted during the reign of British Queen Elizabeth I and continuing through the 1830s. It explores the historiography of studies of OPL, as well as considering changes in standards of living, the relationship between life expectancy and mortality rates during the seventeenth- and eighteenth-centuries, and changes in real wages between the late medieval and early modern periods. Other subjects considered include British public health policies and public charities, the social impact of the plague, and how the OPL and poor relief benefited women.