Restricted rotation about partial C,N double bonds

The restricted rotation about the partial C,N double bond in 2-chloro-6-NR₂-pyran-4-ones is discussed in the light of NMR spectroscopic data and theoretical calculations.Ab initio calculations at the HF/6-31G^* level were carried out using a continuum model to take solvent effects into account. The delocalization of-electron density [described by natural bond orbital analysis (NBO)] was applied to determine the degree of conjugation in the ground state (GS) and in the transition state (TS) for the restricted rotation of the compounds studied. The reason for the different barriers to rotation of the NR₂ substituents (pyrrolidino > dimethylamino > morpholidino > piperidino) at the 2-chloro-pyran-4-one ring appears to be the different steric hindrance of the NR₂ substituents in the GS for the restricted rotation.     

Multimodal Interfaces for Cell Phones and Mobile Technology

By modeling users' natural spoken and multimodal communication patterns, more powerful and highly reliable interfaces can be designed that support emerging mobile technology. In this paper, we highlight three different examples of research that is advancing state-of-the-art mobile technology. The first is the development of fusion-based multimodal systems, such as ones that combine speech and pen or touch input, which are substantially improving the robustness and stability of system recognition. The second is modeling of multimodal communication patterns to establish open-microphone engagement techniques that work in challenging multi-person mobile settings. The third is new approaches to adaptive processing, which are able to transparently guide user input to match system processing capabilities. All three research directions are contributing to the design of more reliable, usable, and commercially promising mobile systems of the future.     

Mathematical modeling of controlled-release systems of herbicides using lignins as matrices

The herbicides applied in soils can be easily lost, owing to leaching, volatilization, and bio-and photodegradation. Controlled-release systemsusing polymeric matrices claim to solve these problems. The movement of the herbicides in the soilisalso an important phenomenon to be studied in order to evaluate the loss processes. The development of mathematical models is a relevantrequirement for simulation and optimization of such systems. This study reviews mathematical models as an initial step for modeling data obtained for controlled-release systems of herbicides (diuron, 2,4-dichlorophenoxyacetic acid, and ametryn) using sugarcane bagasse lignin as a polymeric matrix. The release kinetic studies were carried out using several acceptorsystems includinga water bath, soil, and soil-packed columns. Generally, these models take into account phenomena such as unsteady-state mass transfer by diffusion (Fick'slaw) and convection, consumption by several processes, and partitioning processes, resulting in partial differential equations with respect to time and space variables.     

[13C]Dynamic NMR and Molecular Modeling of 2,4-Bis(N-Pyrrolidinyl)-6-chloro-s-triazine

The room temperature [¹³C]NMR spectrum of 2,4-bis(N-pyrrolidinyl)-6-chloro-s-triazine shows doubled signals for the pyrrolidine rings, which suggests restricted rotation about the Ar-C—N bond. The rotational barrier around this bond was determined by [¹³C]dynamic NMR (DNMR) spectra run at different increasing temperatures and also by the PM3 Hamiltonian contained in the MOPAC package. The values thus obtained, 16.6 and 13.6 kcal mol^–1, respectively, are in good agreement.     

Electron density distribution in the crystal of the Meisenheimer complex of potassium 3-methyl-5′, 7′-dinitro-5′, 8′-dihydrospiro(1,3-oxazolidine-2,8′-quinolinide) based on X-ray diffraction data at 153 K

The electron density distribution in the crystal of the Meisenheimer complex of potassium 3-methyl-5′, 7′-dinitro-5′, 8′-dihydrospiro(1,3-oxazolidine-2,8′- quinolinide) (1) was studied based on the data of precision X-ray diffraction study. The experimental data were compared with the results of quantum-mechanical calculations. The electron density distributions in the regions of the nitro groups are substantially different in spite of the similarity in the geometric parameters of these groups. In addition, there is a discrepancy between the exprimental and theoretical data on this distribution. The effect of the cation on the electronic strucure of the anion in the crystalline phase is the most probable cause of the differences observed. To reveal this effect.ab initio calculations of different anion1-K⁺ systems were performed and a topological analysis of the electron density distributions was carried out. Depending on the mode of coordination of the cation to the anion, the former determines the contribution of alternative resonance forms to the structure of the anion. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 451–458, March, 2000.     

Modeling of the DTG Curves for Oxidation of a Nanosized Molybdenum Ferrite Coupling Mechanics and Diffusion

From a model for isothermal oxidation kinetics in nanosized ferrite spinels based on a diffusion-induced stress effect, the authors present a modeling of the DTG curves for the oxidation of Fe²⁺ and Mo³⁺ cations on octahedral sites of a molybdenum ferrite. This has been made by considering that the chemical diffusion coefficient is given by the relation , when D _o is a pre-exponential factor, E _a ^′ an activation energy and V _a an activation energy induced by the oxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Error of Atomic Charges Derived from Electrostatic Potential

The purpose of this article is to show that CHELP, CHELPG, and Merz and Kollman undergo error for the charge on atoms of HCOO^– (H₂O) _n for n = 1 6. We also demonstrate that the CHELP, CHELPG, and Merz and Kollman show error for the tendency toward change in the charges on carbons for CH₃NH⁺ ₃ (CH₃)₂NH⁺ ₂ (CH₃)₃NH⁺ (CH₃)₄N⁺.     

A Systematic Quantum Chemistry Study on Cyclodextrins

Summary.  AM1 and PM3 modeling of β-hydroxyethyl ether and α-(1→4)-glucobiose indicated that PM3 is advantageous to AM1 in cyclodextrin (CD) chemistry. The conclusion was supported by direct structure optimization of α- and β-CD with AM1 and PM3, in which AM1 gave badly distorted geometries due to unreasonable hydrogen bonding, whereas PM3 reproduced the crystalline structures rather well. Ab initio calculation was for the first time performed on CD, demonstrating the feasibility of this method for future studies concerning CD chemistry. The results also provided valuable insights into the driving forces in CD molecular recognition. Received January 7, 2000. Accepted (revised) March 22, 2000     

A genetic algorithm for the automated generation of small organic molecules: Drug design using an evolutionary algorithm

Rational drug design involves finding solutions to large combinatorial problems for which an exhaustive search is impractical. Genetic algorithms provide a novel tool for the investigation of such problems. These are a class of algorithms that mimic some of the major characteristics of Darwinian evolution. LEA has been designed in order to conceive novel small organic molecules which satisfy quantitative structure-activity relationship based rules (fitness). The fitness consists of a sum of constraints that are range properties. The algorithm takes an initial set of fragments and iteratively improves them by means of crossover and mutation operators that are related to those involved in Darwinian evolution. The basis of the algorithm, its implementation and parameterization, are described together with an application in de novo molecular design of new retinoids. The results may be promising for chemical synthesis and show that this tool may find extensive applications in de novo drug design projects.     

Synthesis and in Vitro Evaluation of N-[[4-[2-(Carboxyl)-1-Cycloalken-1-yl]Phenyl]Methyl]Imidazoles as Nonpeptide Angiotensin II Receptor Antagonists

A series of nonpeptide angiotensin II receptor antagonists was synthesized via palladium-assisted cross coupling of aryl stannane and cycloalkenyl triflates and subsequent alkylation of silyl-protected imidazole. Our compounds, which have a terminal five- to seven-membered cycloalkenyl ring, are compared to DuPont EXP7711, an N-[(2′-carboxybiphenylyl)methyl]imidazole, which has a terminal phenyl moiety. Physicochemical properties of the compounds, such as lipophilicity, steric bulk, conformation, and the relative spatial proximity of the 2-carboxyl and the middle phenyl, are quantitated by computational chemistry. Potency in terms of binding affinity to AT₁ receptors in rat adrenal glomerulosa and rabbit aorta is maximized when the terminal ring is aromatic.