A model for the plateau in the relaxation modulus for linear chain polymer melts

A simple model is considered for the free energy associated with the relaxation of a linear chain polymer melt. The relaxation of the chain configurations results in an adjustment of the locations of the interchain contacts. The change in the distribution of the positions of the contacts between a pair of relaxing chains is hindered by the presence of other nearby chains in the melt. There is less configuration space available to the relaxing chains, due to the noncrossability of the chain backbones, than would be the case for phantom chains. This results in an increase in the free energy of the relaxing system. The analysis presented indicates that, given the free energy models considered, the extent of relaxation decreases as the length scale for relaxation increases. This results in a plateau in the relaxation modulus. This qualitative prediction of a plateau does not rely on the assumption of a specific mechanism for the chain dynamics, and is relatively insensitive to the form chosen for the terms in the free energy. If reasonable assumptions are made concerning the form of the free energy, then it is shown that the plateau which results depends on monomer length, Kuhn length, the monomer density for the melt, and, for solutions, the polymer concentration in a manner consistent with experimental data.     

Microchip capillary electrophoresis instrumentation for in situ analysis in the search for extraterrestrial life

The search for signs of life on extraterrestrial planetary bodies is among NASA's top priorities in Solar System exploration. The associated pursuit of organics and biomolecules as evidence of past or present life demands in situ investigations of planetary bodies for which sample return missions are neither practical nor affordable. These in situ studies require instrumentation capable of sensitive chemical analyses of complex mixtures including a broad range of organic molecules. Instrumentation must also be capable of autonomous operation aboard a robotically controlled vehicle that collects data and transmits it back to Earth. Microchip capillary electrophoresis (μCE) coupled to laser-induced fluorescence (LIF) detection provides this required sensitivity and targets a wide range of relevant organics while offering low mass, volume, and power requirements. Thus, this technology would be ideally suited for in situ studies of astrobiology targets, such as Mars, Europa, Enceladus, and Titan. In this review, we introduce the characteristics of these planetary bodies that make them compelling destinations for extraterrestrial astrobiological studies, and the principal groups of organics of interest associated with each. And although the technology we describe here was first developed specifically for proposed studies of Mars, by summarizing its evolution over the past decade, we demonstrate how μCE-LIF instrumentation has become an ideal candidate for missions of exploration to all of these nearby worlds in our Solar System.     

On the contact conditions for the charge profile in the theory of the electrical double layer for nonsymmetrical electrolytes

In this paper, we generalize a recently derived expression of the contact value of the charge profile for the case of nonsymmetrical electrolytes. For the electrolytes with a single type of cation and anion, this relation can be presented as the sum of three contributions. One of them is the normal component of the Maxwell electrostatic stress tensor. The second one is the surface electrostatic property, which is defined as the integral of the product of the gradient of the electrical potential and the density distribution function of coions. The third term is the bulk contribution, which is defined by the sum for anions and for cations of the product of their charge and their partial pressure. For noncharged surfaces, only the last two terms are present and have the same sign in the case of size asymmetry. In the case of charge asymmetry, the contact value of the charge profile is the result of the competitions of bulk and surface terms in which the bulk term is dominant. Using both the contact theorems for the density and the charge profiles, the exact expressions for the contact values of the profiles of coions and counterions are obtained and some related properties are discussed. A semiempirical expression of the contact value of the charge profile is discussed in relation to our exact result.     

Expressions for the C-term in the presence of pore flow

In the course of our work on capillary electrochromatography (CEC) we, as others, have found strong evidence that flow in pores of particles can be significant. Its magnitude relative to the interstitial flow is characterized by the flow reduction factor, omega. Indirect evidence for pore flow was obtained much earlier by others, when it was noted that plate height, especially the C-term part, was significantly smaller in electrically driven (ED) than in pressure drive (PD) systems. This was interpreted as enhanced mass transfer, for which the intra-particle flow was held responsible. More direct evidence was produced by us when the size-exclusion (SEC) behaviour of polymers was studied in ED systems. It was found that the effect of exclusion on migration velocity could vanish entirely, and large and small molecules were co-eluted. This can only be explained if omega approaches 1; flow within the pores being as large as the interstitial flow. Indeed, consideration of double layer overlap indicated that omega-values close to 1 can often be expected in CEC. These large values omega inspired us to reconsider the effect of pore flow on the mass transfer term. We have arrived at the conclusion that enhanced mass transfer cannot explain in itself the extremely small values for the reduced plate height, h, (<1) observed especially for weakly retained solutes. In fact, when the pore flow is equal in magnitude to the interstitial flow, an unretained solute moves as fast within the particle as in the interstices; there is no non-equilibrium generated and a mass transfer term in h is not expected. For the migration of the solute the system is essentially uniform. Thus, apart from the mass transfer enhancement, another factor plays a role in the decrease of the h-values. We have attempted to derive a suitable expression for this effect. Some results are presented here. In one approach the situation is compared to that of an open tubular column with moving pseudo-stationary phase on the wall, an experiment that has actually been carried out by Krejci et al., or with micellar electrokinetic chromatography. In that case the plate height is easily derived. The result says that the plate height is proportional to the square of velocity difference between the two zones. However, the analogy is not perfect, and another approach suggests a direct proportionality rather than a square law one. Finally, a more refined treatment could be made only for a slab, not for a sphere. Extrapolation of this result to a sphere is put forward as a tentative expression for this effect.     

Specific method for the determination of ozone in the atmosphere

A simple, sensitive and specific method for the determination of ozone in the atmosphere is described. Reactions of ozone with several 1-alkenes were studied at room temperature (25°). Eugenol(4-allyl-2-methoxyphenol), when reacted with ozone, was found to produce relatively large amounts of formaldehyde compared to other 1-alkenes tested. The method described was compared with alkaline iodide method for the determination of various concentrations of ozone in the range 0.05–2.0 p.p.m. Hydrogen peroxide, peracetic acid, sulfur dioxide and various reducing agents commonly present in the air, do not interfere. Formaldehyde when present in the air, must be determined simultaneously and the concentration of formaldehyde subtracted from that of the ozone. Any formaldehyde monitoring equipment can be easily adapted for the determination of ozone.     

Information requirements for chemists in the pharmaceutical industry

The principal information needs of chemists in the pharmaceutical industry center around a substance, methods used for its characterization, its reactions, its physicochemical and biomedical properties, and its metabolic fate in biological media. Novelty searches for a specific chemical are critical because of the need for patent protection for product candidates. Chemical relatives are important, necessitating substructure searching. Therapeutic neighbors may give insight into its biological mode of action. The phases of drug discovery and development are used to indicate the diversity of the information needs of chemists and to emphasize the dual process of generation and use of information.     

生物油中酚类化合物加氢脱氧催化剂研究进展

随着化石能源日益匮乏,生物质热裂解制备生物油广受关注.然而,生物油中含有大量酚、呋喃、醛、酮等含氧化合物,含氧量高达50%,导致其热值低、化学稳定性差等,因而阻碍了它的广泛应用,必须对其进行加氢脱氧精制降低含氧量.在生物油中众多含氧化合物中,酚羟基氧被认为是最难被脱除的.对酚类含氧化合物加氢脱氧催化剂及反应进行了简单综述,并提出了如何进一步提高催化剂性能的有效方法.     

Recent Developments in Electrochemical Sensors for the Detection of Neurotransmitters for Applications in Biomedicine

Neurotransmitters are important biological molecules that are essential to many neurophysiological processes including memory, cognition, and behavioral states. The development of analytical methodologies to accurately detect neurotransmitters is of great importance in neurological and biological research. Specifically designed microelectrodes or microbiosensors have demonstrated potential for rapid, real-time measurements with high spatial resolution. Such devices can facilitate study of the role and mechanism of action of neurotransmitters and can find potential uses in biomedicine. This paper reviews the current status and recent advances in the development and application of electrochemical sensors for the detection of neurotransmitters. Measurement challenges and opportunities of electroanalytical methods to advance study and understanding of neurotransmitters in various biological models and disease conditions are discussed.     

Prospects for combinatorial chemistry in the agrosciences

The recent progress and future prospects for the successful application of combinatorial chemistry and high throughput screening within the agrochemical lead discovery process are outlined and discussed. Solid and solution phase library synthesis technologies are reviewed and compared, and the role and importance of bioavailability, diversity and virtual screening in rational library design are detailed.     

Thomas-Fermi theory for the ion cloud in the trap

Using Thomas-Fermi Theory, we deal with the motion of a trapped ion cloud with conserved total angular momentum in thermal equilibrium at zero temperature. It is shown that in the case of high magnetic field (≧600 kG) the motion of an electron cloud trapped in a Penning trap would be modified by quantum effects. Under the present laboratory conditions the quantum effects are negligible for the motion of a Mg⁺²⁴ ion cloud trapped in a Paul trap.     

Variational formula for the relaxation time in the Boltzmann equation

The relaxation time approximation (RTA) is commonly employed in nonequilibrium statistical mechanics to approximate solutions to the Boltzmann equation in terms of an exponential relaxation to equilibrium. Despite its common use, the RTA suffers from the drawback that relaxation times commonly employed are independent of initial conditions. We derive a variational principle for solutions to the Boltzmann equation, which allows us to extend the standard RTA using relaxation times that depend on the initial distribution. Tests of the approach on a calculation of the mobility for a one-dimensional (1D) tight-binding band indicate that our analysis typically provides a better approximation than the standard RTA.     

聚合物膜燃料电池用电催化剂研究进展

综述了聚合物膜燃料电池（ＰＥＭＦＣ）用电催化剂最新的研究进展,包括阳极甲醇催化剂有机螯合物催化剂及其它的还原催化剂。     

Elemental carbon in the atmosphere: challenges for the trace analyst

Summary Elemental carbon is an ubiquitous part of the atmospheric aerosol, originating from all combustion processes. It influences the radiative transfer by its absorbing properties leading to influences on regional climate. While its importance in air chemistry seems to be small there may exist hygienic aspects due to absorbed mutagenic and cancerogenic substances which are not understood completely yet. Soot has unique properties as a tracer for atmospheric transport processes. The mostly hydrophobic character of soot particles influences its life time because it impedes an incorporation into clouds and thus a rapid removal by wet deposition processes. From a literature review a number of tasks for the analyst are formulated concerning improvement of analytical measurement techniques, understanding the change of the surface properties from hydrophobic to hydrophilic, and the use of absorbed substances for source identification which is of importance for a better use of soot as a tracer for atmospheric transport processes.     

NACE for the analysis of acrylamide in food

An NACE method was developed for the quantitative determination of acrylamide in processed food. The method is premised on the modification of the aqueous acid-base character of acrylamide in an organic solution. Acrylamide, which is a polar molecule in aqueous solution, in a low-pH environment in ACN acquires a proton, and thereby migrates under its own electrophoretic mobility in CE. Thus, nonaqueous separation of acrylamide was achieved by employing 30 mmol/L HClO(4) in ACN as the running electrolyte. The detection limit of the method for acrylamide was found as 0.041 mg/L using UV detection at 200 nm. The run-to-run and day-to-day precisions for the corrected peak areas were calculated as 1.65 and 3.90%, respectively. The applicability of the method has been demonstrated by analyzing acrylamide in the samples of potato chips and French fries. The method is simple, rapid, inexpensive, and widely applicable for the determination of acrylamide in food samples.     

Receptor-Based Pharmacophore Modeling in the Search for Natural Products for COVID-19 Mpro

Considering the urgency of the COVID-19 pandemic, we developed a receptor-based pharmacophore model for identifying FDA-approved drugs and hits from natural products. The COVID-19 main protease (M^pro) was selected for the development of the pharmacophore model. The model consisted of a hydrogen bond acceptor, donor, and hydrophobic features. These features demonstrated good corroboration with a previously reported model that was used to validate the present model, showing an RMSD value of 0.32. The virtual screening was carried out using the ZINC database. A set of 208,000 hits was extracted and filtered using the ligand pharmacophore mapping, applying the lead-like properties. Lipinski’s filter and the fit value filter were used to minimize hits to the top 2000. Simultaneous docking was carried out for 200 hits for natural drugs belonging to the FDA-approved drug database. The top 28 hits from these experiments, with promising predicted pharmacodynamic and pharmacokinetic properties, are reported here. To optimize these hits as M^pro inhibitors and potential treatment options for COVID-19, bench work investigations are needed.     

A statistical model for the optimization of dsc performance in the evaluation of drugs for preformulation studies

Differential scanning calorimetry (DSC) is a thermal analytical tool for preformulation studies. Extrapolated melting temperature (T_P) and heat of fusion (ΔH_f) can be used as parameters for optimizing the DSC performance. Two model pharmaceuticals acetaminophen and nicotinamide are used in this study. Using a factorial design for the experimental model and matrix analysis the results, the effect of sample mass, heating rate and the nitrogen flow rate were evaluated on the ΔH_f values and T_P values. Two levels for each of the procedural variables were used as a balanced experimental design with two sample sizes, two heating rates and two nitrogen flow rates. It was found that the change in the heating rate caused significant changes in the ΔH_f values but not the T_p values for acetaminophen. However, no significant effect was found for the T_p value but ΔH_f value was affected to a certain extent for nicotinamide.     

New method for allowance for the activity of the nucleophile in calculations of the reactivities of heteroaromatic compounds

A new method for allowance for the activity of the nucleophile in calculations of the reactivities of heteroaromatic compounds that is based on the special application of the valence molecular orbital (VMO) theory in the form of Dewar reactivity numbers is proposed. It is shown that there is a correspondence between the proposed method and the general VMO theory. The 5-azacinnoline molecule was calculated by both methods. According to the calculations, the 6-C atom should be the most active in reactions with hard bases, whereas the 4-C atom should be the most active in reactions with soft bases. A qualitative correspondence between the proposed method and the DMTS (delocalization model of the transition state) method is also demonstrated in the case of the quinolinium cation.More complex computational methods are presently not applicable to many-atom systems and not found in the literature.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 403–405, March, 1979.     

Contact conditions for the charge in the theory of the electrical double layer

In this paper, from the Born-Green-Yvon equations of the liquid-state theory, we derive a general expression for the charge-density contact value at charged interfaces. This relation is discussed, in particular, for symmetrical electrolytes. We emphasize an essential coupling between the electric properties and the density profile. Limiting behavior at small and large charges at the interface is discussed.     

Method for estimating the largest Lyapunov exponent for the chaotic regime in chemical reactions

Based on the Belousov-Zhabotinskii reaction in CSFR we observe that the mixing rate decrease in the reaction volume of the mixture to the value ₀ leads to a qualitative change in the nature of the chaotic regime, similar to a second order phase transition. We show that the largest Lyapunov exponent for the system is directly proportional to ₀ ².Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 52–56, January–February, 1992.     

Encouragements for the Use of Microwaves in Industrial Chemistry

Microwave travels at the speed of light, and transfers energy solely to materials. This holds great promise for energy conservation in industrial processes. However, due to differences with common heating principles, and misunderstanding of the correct way to handle them, the effectiveness of microwaves has been underestimated, and development of technologies using microwaves often stops due to this. This paper has focused on the use of microwave heating for organic/polymer synthesis, specifically for a highly effective condensation reaction and for use with ionic reactants. In addition to covering the process of ascertaining which reactions are suitable for the application of microwave heating, and introducing studies on scaling these up, this paper covers points of caution, especially those relating to the all‐important measurement/control of temperature. Based on their accumulation of expertise in the area, the authors present the design for equipment/plants for industrial use and introduce their research into the practical application of such technology.