Search

Vibrational force fields for the ground states of 1,3-butadiene, 1,3,5-hexatriene, and 1,3,5,7-octatetraene are calculated from extended Pariser–Parr–Pople CI theory. For the ground state of butadiene, the principal π-system force constants are compared to those determined by empirical, other semiempirical, and ab initio methods. The calculated vibrational frequency shifts for a series of deuterium substituted butadienes are found to be in good agreement with experiment. Trends in the principal π-system force constants of the polyenes for the ground states of ethylene through octatetraene are described, including the effects of introducing cis linkages in the polyene chain and of using single- vs single-plus-double-excitation CI. Correlations between the force constants and the calculated vibrational frequencies are discussed, and current assignments of the vibrational spectra of the polyenes are examined in view of the theoretical results. [ABSTRACT FROM AUTHOR]

CHARMM (Chemistry at HARvard Molecular Mechanics) is a highly versatile and widely used molecular simulation program. It has been developed over the last three decades with a primary focus on molecules of biological interest, including proteins, peptides, lipids, nucleic acids, carbohydrates, and small molecule ligands, as they occur in solution, crystals, and membrane environments. For the study of such systems, the program provides a large suite of computational tools that include numerous conformational and path sampling methods, free energy estimators, molecular minimization, dynamics, and analysis techniques, and model-building capabilities. The CHARMM program is applicable to problems involving a much broader class of many-particle systems. Calculations with CHARMM can be performed using a number of different energy functions and models, from mixed quantum mechanical-molecular mechanical force fields, to all-atom classical potential energy functions with explicit solvent and various boundary conditions, to implicit solvent and membrane models. The program has been ported to numerous platforms in both serial and parallel architectures. This article provides an overview of the program as it exists today with an emphasis on developments since the publication of the original CHARMM article in 1983. © 2009 Wiley Periodicals, Inc.J Comput Chem, 2009. [ABSTRACT FROM AUTHOR]

Explores strategies to develop mosaic chemotherapeutic approaches for amyotrophic lateral sclerosis/motor neurone disease (ALS/MND). Inclusion of beta-2 adrenergic agonists for ALS/MND treatment; Pathogenesis-based and symptom-directed therapies in ALS/MND; Effect of beta-2 adrenergic agonists in the central nervous system and muscular system; Side-effects of beta-2 adrenergic agonists.

The bifunctional aldehydes glyoxal and malondialdehyde, known to be toxic products of the radiolysis of sugar and other food constituents, interact with DNA in vitro and in vivo as demonstrated by thermal denaturation profiles, chromatographic behavior, and incomplete degradation of the reaction product by deoxyribonuclease. After irradiation of DNA in diluted radioactive glucose solution followed by incubation at slightly acid pH, the radioactivity is found in the core of the enzymic digest only. Attempts to locate the binding site proved that the radiolytic compound is associated preferentially with the guanine and cytidine moiety of the DNA core. [ABSTRACT FROM AUTHOR]

In a previous paper [Ghysels et al., J. Chem. Phys. 126, 224102 (2007)] the mobile block Hessian (MBH) approach was presented. The method was designed to accurately compute vibrational modes of partially optimized molecular structures. The key concept was the introduction of several blocks of atoms, which can move as rigid bodies with respect to a local, fully optimized subsystem. The choice of the blocks was restricted in the sense that none of them could be connected, and also linear blocks were not taken into consideration. In this paper an extended version of the MBH method is presented that is generally applicable and allows blocks to be adjoined by one or two common atoms. This extension to all possible block partitions of the molecule provides a structural flexibility varying from very rigid to extremely relaxed. The general MBH method is very well suited to study selected normal modes of large macromolecules (such as proteins and polymers) because the number of degrees of freedom can be greatly reduced while still keeping the essential motions of the molecular system. The reduction in the number of degrees of freedom due to the block linkages is imposed here directly using a constraint method, in contrast to restraint methods where stiff harmonic couplings are introduced to restrain the relative motion of the blocks. The computational cost of this constraint method is less than that of an implementation using a restraint method. This is illustrated for the α-helix conformation of an alanine-20-polypeptide. [ABSTRACT FROM AUTHOR]

The cerebral cortex reorganizes in response to central or peripheral lesions. Although basal ganglia and cerebellum are key components of the network dedicated to movement control, their role in motor reorganization remains elusive. We therefore tested if slowly progressive neurodegenerative motor disease alters the subcortical functional anatomy of the basal ganglia-thalamo-cerebellar circuitry. Ten patients with amyotrophic lateral sclerosis (ALS) and ten healthy controls underwent functional magnetic resonance imaging (fMRI), while executing a simple finger flexion task. Cued by an acoustic trigger, they squeezed a handgrip force transducer with their right hand at 10% of their maximum voluntary contraction force. Movement frequency, amplitude, and force were controlled. Statistical parametric mapping of task-related BOLD-response revealed increased activation in ALS patients as compared to healthy controls. The main activation increases were found in the supplementary motor area, basal ganglia, brainstem, and cerebellum. These findings suggest that degeneration of cortical and spinal motor neurons in ALS leads to a recruitment of subcortical motor structures. These subcortical activation patterns strongly resemble functional activation in motor learning and might therefore represent adaptations of cortico-subcortical motor loops as a—albeit finally ineffective—mechanism to compensate for the ongoing loss of motor neurons in ALS. [ABSTRACT FROM AUTHOR]

Motor fatigue, during 30 seconds of maximum voluntary isometric contraction (MVIC) was simultaneously evaluated by the decline in mechanical force output, and from the compression in the power spectrum obtained from surface electromyogram (sEMG). Measurements were performed in patients diagnosed with amyotrophic lateral sclerosis (ALS) and normal control (NC) in two muscle groups, elbow flexors (EF) and ankle dorsiflexors (DF). The decline in force output, as a manifestation of mechanical fatigue, was digitally calculated online by partitioning the force versus time curve to determine the percent of MVIC reduction over a 30 sec period and was expressed as force fatigue index (FFI). The compression in the sEMG power spectrum, as a manifestation of myoelectrical fatigue, was tracked by calculating the median frequency shift (MFS) from the first 5 sec to the last 5 sec of the 30 sec MVIC using digital Fast Fourier Transformation. In ALS patients, the significantly higher reduction in mechanical force output during the 30 sec MVIC (higher FFI) was accompanied with significantly less compression in the sEMG power spectrum (less MFS) as compared to NC ( P ≤0.005) in the two muscle groups. This dissociation between the mechanical and myoelectrical manifestation of muscle fatigue in ALS indicates that a reduction in muscle fiber conduction velocity (MFCV) may be a contributing peripheral factor in the pathogenesis of muscle fatigue in ALS. Alterations in motor unit functionality, especially in type II fast motor unit muscle fibers, and structural damage in denervated muscle fibers may contribute to the lower MFCV during motor fatigue in ALS patients. [ABSTRACT FROM AUTHOR]