Simple Structural Modifications Research Articles

Brønsted ionic liquids: Study of physico-chemical properties and catalytic activity in aldol condensations

A serie of substituted amines based ionic liquids was prepared using an aliphatic linear carboxylic acid (pentanoic acid). The ionic liquids synthesised are 2-hydroxy ethylammonium pentanoate (2-HEAPE), 2-hydroxy diethylammonium pentanoate (2-HDEAPE) and 2-hydroxy triethylammonium pentanoate (2-HTEAPE). FT-IR spectra establishes their ionic salt structure. The influence of structural variations on their thermodynamic properties (density, ultrasonic velocity, ionic conductivity, refractive index, viscosity and surface tension) was investigated, as a function of temperature in the range 278.15–338.15 K. In the compounds studied here, the anion has strong effect on the properties if compared with previous studies of the authors, when shorter chains were used. It was found that the elongation of the alkyl chain causes the pronounced depression of fluidity and ionic conductivity. The observed temperature trend of the studied properties points out the special packing of these ionic liquids, as well as, the strong influence of the steric hindrance among linear aliphatic residues. We also describe the catalytic activity of these type of ionic liquids for a representative serie of aldol condensation processes. Conversions higher than 98% and selectivities higher than 85% were obtained. Moreover the catalysts are easily separated from reaction mixture and re-used, obtaining good conversions for at least three consecutive cycles. As a conclusion, it was found that simple structural modifications into anion length and degree of substitution provide a mechanism to manipulate the catalytic potency of these ionic liquids, as well as, tailor physico-chemical properties for potential end-use applications.

Regular and Irregular Multiple Serially- Concatenated Multiple-Parity-Check Codes for Wireless Applications

Multiple Serially-Concatenated Multiple-Parity-Check (M-SC-MPC) codes are a class of structured Low-Density Parity-Check (LDPC) codes, characterized by very simple encoding, that we have recently introduced. This paper evidences how the design of M-SC-MPC codes can be optimized for their usage in wireless applications. For such purpose, we consider some Quasi-Cyclic LDPC codes included in the mobile WiMax standard, and compare their performance with that of M-SCMPC codes having the same parameters. We also present a simple modification of the inner structure of M-SC-MPC codes that can help to improve their error correction performance by introducing irregularity in the parity-check matrix and increasing the length of local cycles in the associated Tanner graph. Our results show that regular and irregular M-SC-MPC codes, so obtained, can achieve very good performance and compare favorably with standard codes.

Hydrazides as Tunable Reagents for Alkene Hydroamination and Aminocarbonylation

Benzoic hydrazides (R = Ph), which are remarkably bench and thermally stable reagents (often up to 230 degrees C), afford intramolecular hydroamination products upon heating at high temperatures (120-235 degrees C). A concerted Cope-type hydroamination event, followed by a hydrazide-mediated proton transfer step of the hydrazinium ylide intermediate, is proposed and supported by DFT calculations. In contrast, a simple modification of the reagent structure (R = Ot-Bu or NH(2)) favors the formation of aminocarbonylation products at 200 degrees C, and the latter reaction is shown to be stereospecific.

The Photochromism and Fluorescence of Diarylethenes with a Imidazole Bridge Unit: A Strategy for the Design of Turn-on Fluorescent Diarylethene System

A class of diarylethenes with a imidazole bridge unit has been synthesized and shows photochromic properties with UV/vis light irradiation. It is found that electronic properties of substituent in the imidazole bridge unit have a great effect on both photochromism and fluorescence of diarylethenes because of intramolecular charge transfer. Both "turn-on" and "turn-off" fluorescent diarylethenes systems can be achieved by simple modification of molecular structure and electronic properties of substituent, which provides a strategy for the design of new fluorescent diarylethene systems to be used as switches.

Single Organic Microtwist with Tunable Pitch

A facile synthesis of previously unknown, well-separated, uniform chiral microstructures from achiral pi-conjugated organic molecules was developed by simple solution process. Detailed characterization and formation mechanism were presented. By simple structure modification or temperature change, the pitch of the chiral structure can be fine tuned. Our result opens new possibilities for novel materials in which structure chirality is coupled to device performance.

Structural Deign Optimization for A Two-link Robot to Suppress Undesirable Vibration

In this study, we address the case of a horizontal two-link robot with flexible timing belts and present a structural design guideline to reduce its undesirable vibration. First, an equation of motion was constructed using Lagrange's equation, and its validity was examined by comparing the experimental and simulation results using an index to estimate the undesirable vibration. As a result, it was determined that the mathematical model could be used as a simulation tool for design optimization. Then, by a simple structural modification, a design guideline was proposed to reduce the undesirable vibration in the extension motion: namely, a robot arm was designed such that the location of its center of gravity is near the rotation center and its moment of inertia is small. Other optimum structural design may be obtained for the other motion of robot. The points of this study are to propose the design method that includes the definition of objective function for the optimum design and to show a design guideline to reduce the undesirable vibration for a certain motion of robot.

An Inverse Method to Assign Receptances by Using Classical Vibration Absorbers

The classical mass-spring absorber can be thought of as a very simple structural modification. In this paper the inverse problem of assigning receptances to a dynamic system by using one or more simple mass-spring absorbers is considered. The absorber parameters can be determined using selected receptances from the original system. When more than one absorber is applied, the equations that determine the modified-system receptances may be rearranged to form a set of nonlinear algebraic equations, multivariate polynomials in the absorber parameters. The desired absorber parameters are determined by the roots of these equations, which may be found by Newton's method or by using Gröbner bases. Realistic solutions require that positive values be found for the mass and stiffness of each of the added absorbers. Consequently there may be no acceptable solution, a unique solution, or there may be finitely many acceptable solutions. Whenever two receptances are to be assigned at a single frequency by a single absorber, then the available absorber mass and stiffness values are severely restricted. However, arbitrary assignment is possible for many other problems, except for the condition of positiveness on the masses and stiffnesses.

Water-Soluble Porphyrin-Polyethylene Glycol Conjugates with Enhanced Cellular Uptake for Photodynamic Therapy

Water soluble porphyrins were designed and prepared by Williamson ether synthesis reaction between tetrakis(p-bromomethylphenyl)porphyrin and polyethylene glycol (PEG) for photodynamic therapy. The quantum yields for the generation of singlet oxygen of tetra-polyethylene glycol branched porphyrin shows above 80% in D2O. Luminescence of singlet state oxygen was observed from D2O solution under the single-photon excitation at 514 nm. In vitro test, cellular uptake efficiency has been enhanced by simple modification of molecular structure through changing the number of PEG unit without any support such as polymer-encapsulated inorganic nanoparticles.

Molecular Basis of Prodrug Activation by Human Valacyclovirase, an α-Amino Acid Ester Hydrolase

Chemical modification to improve biopharmaceutical properties, especially oral absorption and bioavailability, is a common strategy employed by pharmaceutical chemists. The approach often employs a simple structural modification and utilizes ubiquitous endogenous esterases as activation enzymes, although such enzymes are often unidentified. This report describes the crystal structure and specificity of a novel activating enzyme for valacyclovir and valganciclovir. Our structural insights show that human valacyclovirase has a unique binding mode and specificity for amino acid esters. Biochemical data demonstrate that the enzyme hydrolyzes esters of alpha-amino acids exclusively and displays a broad specificity spectrum for the aminoacyl moiety similar to tricorn-interacting aminopeptidase F1. Crystal structures of the enzyme, two mechanistic mutants, and a complex with a product analogue, when combined with biochemical analysis, reveal the key determinants for substrate recognition; that is, a flexible and mostly hydrophobic acyl pocket, a localized negative electrostatic potential, a large open leaving group-accommodating groove, and a pivotal acidic residue, Asp-123, after the nucleophile Ser-122. This is the first time that a residue immediately after the nucleophile has been found to have its side chain directed into the substrate binding pocket and play an essential role in substrate discrimination in serine hydrolases. These results as well as a phylogenetic analysis establish that the enzyme functions as a specific alpha-amino acid ester hydrolase. Valacyclovirase is a valuable target for amino acid ester prodrug-based oral drug delivery enhancement strategies.

N-Phenylacetanoyl-l-Homoserine Lactones Can Strongly Antagonize or Superagonize Quorum Sensing in Vibrio fischeri

Bacteria monitor their population densities using low-molecular-weight ligands in a process known as quorum sensing. At sufficient cell densities, bacteria can change their mode of growth and behave as multicellular communities that play critical roles in both beneficial symbioses and the pathogenesis of infectious disease. The development of non-native ligands that can block quorum-sensing signals has emerged as a promising new strategy to attenuate these divergent outcomes. Here, we report that N-phenylacetanoyl-L-homoserine lactones are capable of either inhibiting or, in some cases, strongly inducing quorum sensing in the bacterial symbiont Vibrio fischeri. Moreover, simple structural modifications to these ligands have remarkable effects on activity. These studies have revealed one of the first synthetic superagonists of quorum sensing, N-(3-nitro-phenylacetanoyl)-L-homoserine lactone. Together, these ligands represent a powerful new class of chemical probes with the potential to significantly expand the current understanding of quorum sensing and its role in host/bacteria interactions.

A Metabolic Screening Study of Trichostatin A (TSA) and TSA-Like Histone Deacetylase Inhibitors in Rat and Human Primary Hepatocyte Cultures

Hydroxamic acid (HA)-based histone deacetylase (HDAC) inhibitors, with trichostatin A (TSA) as the reference compound, are potential antitumoral drugs and show promise in the creation of long-term primary cell cultures. However, their metabolic properties have barely been investigated. TSA is rapidly inactivated in rodents both in vitro and in vivo. We previously found that 5-(4-dimethylaminobenzoyl)aminovaleric acid hydroxyamide or 4-Me2N-BAVAH (compound 1) is metabolically more stable upon incubation with rat hepatocyte suspensions. In this study, we show that human hepatocytes also metabolize TSA more rapidly than compound 1 and that similar pathways are involved. Furthermore, structural analogs of compound 1 (compounds 2-9) are reported to have the same favorable metabolic properties. Removal of the dimethylamino substituent of compound 1 creates a very stable but 50% less potent inhibitor. Chain lengthening (4 to 5 carbon spacer) slightly improves both potency and metabolic stability, favoring HA reduction to hydrolysis. On the other hand, Calpha-unsaturation and spacer methylation not only reduce HDAC inhibition but also increase the rate of metabolic inactivation approximately 2-fold, mainly through HA reduction. However, in rat hepatocyte monolayer cultures, compound 1 is shown to be extensively metabolized by phase II conjugation. In conclusion, this study suggests that simple structural modifications of amide-linked TSA analogs can improve their phase I metabolic stability in both rat and human hepatocyte suspensions. Phase II glucuronidation, however, can compensate for their lower phase I metabolism in rat hepatocyte monolayers and could play a yet unidentified role in the determination of their in vivo clearance.

Further Insight into the DNA Recognition Mechanism of Trabectedin from the Differential Affinity of Its Demethylated Analogue Ecteinascidin ET729 for the Triplet DNA Binding Site CGA

Trabectedin and its N12-demethylated analogue ET729 bind covalently to the central guanine of selected DNA triplets. Although both drugs equally target several sites, including AGA, we show that covalent modification of CGA is only achieved by ET729. By means of molecular dynamics simulations of the precovalent complexes, we explain in atomic detail how such a simple structural modification brings about this notable change in the DNA-binding selectivity profiles of these two drugs.

Protic Ionic Liquids: Solvents with Tunable Phase Behavior and Physicochemical Properties

The phase behavior, including glass, devitrification, solid crystal melting, and liquid boiling transitions, and physicochemical properties, including density, refractive index, viscosity, conductivity, and air-liquid surface tension, of a series of 25 protic ionic liquids and protic fused salts are presented along with structure-property comparisons. The protic fused salts were mostly liquid at room temperature, and many exhibited a glass transition occurring at low temperatures between -114 and -44 degrees C, and high fragility, with many having low viscosities, down to as low as 17 mPa.s at 25 degrees C, and ionic conductivities up to 43.8 S/cm at 25 degrees C. These protic solvents are easily prepared through the stoichiometric combination of a primary amine and Brønsted acid. They have poor ionic behavior when compared to the far more studied aprotic ionic liquids. However, some of the other physicochemical properties possessed by these solvents are highly promising and it is anticipated that these, or analogous protic solvents, will find applications beyond those already identified for aprotic ionic liquids. This series of protic fused salts was employed to determine the effect of structural changes on the physicochemical properties, including the effect of hydroxyl groups, increasing alkyl chain lengths, branching, and the differences between inorganic and organic anions. It was found that simple structural modifications provide a mechanism to manipulate, over a wide range, the temperature at which phase transitions occur and to specifically tailor physicochemical properties for potential end-use applications.

On-line batch process monitoring using MHMT-based MPCA

A novel technique of on-line batch process monitoring based on the wavelet-based multi-hidden Markov model tree (MHMT) is developed. Unlike most of the existing batch process monitoring methods for only time scale, MHMT cannot only analyze the measurements at multiple scales in time and frequency but also capture the clustering and persistence of the statistical characteristics for practical measured data. This approach provides less signal distortion and better understanding of the principal source of the system variability affecting the process. In order to conduct the on-line batch monitoring, a simple modification of the unfolded structure that trains MHMT to set up the batch-monitoring model is derived. Also, the tying structure of MHMT for increasing the number of training data is developed. The proposed method is developed in this paper to improve the conventional MPCA-based method by extending the time-domain analysis into the time–frequency using the stochastic model analysis. After extracting the essential features of the past operating information, subsequently, two simple monitoring charts are presented to track the progress of each batch run and monitor the occurrence of observable upsets. The applications are discussed through two sets of benchmark data, a DuPont industrial batch polymerization reactor and a fed-batch penicillin production, those of which are characterized by some fault sources to illustrate the advantages of the proposed method in comparison to some conventional methods.

Excimer emission and energy transfer in cofacial boradiazaindacene (BODIPY) dimers built on a xanthene scaffold

Using a rigid xanthene scaffold, a series of boradiazaindacene derivatives were synthesized. In some of these compounds, two boradiazaindacene derivatives were placed cofacially, resulting in significant inter-chromophoric interactions, including excimer emission. A simple modification of boradiazaindacene structure leads to formation of an ICT dye, which has distinct spectral properties. Energy transfer between two BODIPY dyes was demonstrated as well. In addition, the spectral properties of ICT dye can be modulated by the addition of the acid leading to an acid switchable energy transfer cassette.

Evaluation of Website Usability Using Markov Chains and Latent Semantic Analysis

SUMMARY The development of information/communication technology has made it possible to access substantial amounts of data and retrieve information. However, it is often difficult to locate the desired information, and it becomes necessary to spend considerable time determining how to access specific available data. This paper describes a method to quantitatively evaluate the usability of large-scale information-oriented websites and the effects of improvements made to the site design. This is achieved by utilizing the Cognitive Walkthrough for the Web and website modeling using Markov chains. We further demonstrate that we can greatly improve usability through simple modification of the link structure by applying our approach to an actual informational database website with over

Perturbation of the PET Process in Fluorophore−Spacer−Receptor Systems through Structural Modification: Transition Metal Induced Fluorescence Enhancement and Selectivity

Several fluorescent signaling systems are built in the format fluorophore-spacer-receptor with ethylenediamine or N,N-dimethylethylenediamine as the receptor, anthracene as the fluorophore, and a methylene group as the spacer. The receptors are derivatized with different electron-withdrawing groups such as 4-nitrobenzene, 4-nitro-2-pyridine, and 2,4-dinitrobenzene, to perturb the photoinduced intramolecular electron transfer (PET) process from the nitrogen lone-pair to the fluorophore. The photophysical properties of these supramolecular systems and their fluorescence responses toward a number of quenching transition metal ions are reported. It is shown that the PET is highly efficient in the absence of a metal ion. With a metal ion input, the fluorescence can be recovered to a different extent depending on the nature of the metal and on the overall architecture of the system as well. Despite the possibility of strong interaction between the fluorophore and the metal ion, significant fluorescence enhancement is observed with quenching of paramagnetic transition metal ions. The complex stability data show that the stability constants for the metal ions showing fluorescence enhancement are of the order of 10(4) M(-1). This study shows that structurally simple fluorescent signaling systems for quenching transition metal ions can be built by maximizing the PET. It is also shown here that simple structural modification can make these systems highly specific for particular transition metal ions for potential applications in several contemporary areas of research.

BEST PERFORMANCE FROM YOUR SECONDARY CLARIFIERS FAIRFIELD SUISUN SEWER DISTRICT EXPERIENCE

BEST PERFORMANCE FROM YOUR SECONDARY CLARIFIERS FAIRFIELD SUISUN SEWER DISTRICT EXPERIENCEMathematical modeling using the High Accuracy Clarifier Model (HACM) and field testing were applied to investigate the performance and determine the most cost effective modifications of the secondary clarifiers at Fairfield Suisun Sewer District. Simple structural modifications to the flocculation center well and effluent arrangements were identified, designed and constructed. A parallel...Author(s)Marcie BodeauxHany GergesSourceProceedings of the Water Environment FederationSubjectSession 31: Municipal Wastewater Treatment Processes: Primary and Secondary ClarifiersDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2005ISSN1938-6478SICI1938-6478(20050101)2005:13L.2585;1-DOI10.2175/193864705783865370Volume / Issue2005 / 13Content sourceWEFTECFirst / last page(s)2585 - 2595Copyright2005Word count108

Death Rides the Forest: Perceptions of Fire, Land Use, and Ecological Restoration of Western Forests

Abstract: Large wild fires occurring in forests, grasslands, and chaparral in the last few years have aroused much public concern. Many have described these events as “catastrophes” that must be prevented through aggressive increases in forest thinning. Yet the real catastrophes are not the fires themselves but those land uses, in concert with fire‐suppression policies that have resulted in dramatic alterations to ecosystem structure and composition. The first step in the restoration of biological diversity (forest health) of western landscapes must be to implement changes in those factors that have caused degradation or are preventing recovery. This includes changes in policies and practices that have resulted in the current state of wildland ecosystems. Restoration entails much more than simple structural modifications achieved though mechanical means. Restoration should be undertaken at landscape scales and must allow for the occurrence of dominant ecosystem processes, such as the natural fire regimes achieved through natural and/or prescribed fires at appropriate temporal and spatial scales.

Zinc(II)-selective ratiometric fluorescent sensors based on inhibition of excited-state intramolecular proton transfer.

To develop a zinc(II)-selective emission ratiometric probe suitable for biological applications, we explored the cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT) with a series of 2-(2'-benzenesulfonamidophenyl)benzimidazole derivatives. In the absence of Zn(II) at neutral pH, the fluorophores undergo ESIPT to yield a highly Stokes' shifted emission from the proton-transfer tautomer. Coordination of Zn(II) inhibits the ESIPT process and yields a significant hypsochromic shift of the fluorescence emission maximum. Whereas the paramagnetic metal cations Cu(II), Fe(II), Ni(II), Co(II), and Mn(II) result in fluorescence quenching, the emission response is not altered by millimolar concentrations of Ca(II) or Mg(II), rendering the sensors selective for Zn(II) among all biologically important metal cations. Due to the modular architecture of the fluorophore, the Zn(II) binding affinity can be readily tuned by implementing simple structural modifications. The synthesized probes are suitable to gauge free Zn(II) concentrations in the micromolar to picomolar range under physiological conditions.