Search results for " Force"

Thermal Degradation of Green Asparagus Texture

2019

A cutting cell was developed to evaluate the texture of green asparagus by measuring its resistance to being cut with a wire. The cell was used in conjunction with a universal texturometer and improved on the single-point method of the Wilder fibrometer. Experimental conditions were determined for using the cell to measure the cutting resistance of asparagus subjected to different extents of heat treatment. Better discrimination between samples was obtained than with a Kramer cell. The fresh asparagus spears. were heated at temperatures between 70 and 100°C for different lengths of time and the kinetics of the degradation of texture was studied. A biphasic (two-component) behavior was obser…

Force probe measurements of antibody-antigen interactions.

2000

The surface force apparatus has been used to quantify directly the forces that govern the interactions between proteins and ligands. In this work, we describe the measured interactions between the antigen fluorescein and the Fab' fragment of the monoclonal 4-4-20 anti-fluorescyl IgG antibody. Here we first describe the use of the surface force apparatus to demonstrate directly the impact of the charge composition in the region of the antibody binding site on the antibody interactions. Several approaches are described for immobilizing antigens, antibodies, and proteins in general for direct force measurements. The measured force profiles presented are accompanied by an extensive discussion o…

ChemInform Abstract: Diastereoselective Synthesis of Spongian Diterpenes. Total Synthesis of the Furanoditerpene (-)-Spongia-13(16),14-diene.

2010

Abstract An effective diastereoselective synthesis of the marine-sponge metabolite (−)-spongia-13(16),14-diene 1 is achieved starting from S-(+)-carvone via a homochiral phenanthrenone as the key intermediate for the construction of the furan ring system. S-(+)-Carvone was transformed into the phenanthrenone 2a in six steps (53% overall yield), using an intramolecular Diels-Alder reaction as the key step. Conversion of the enone function in 2a into an epoxyaldehyde function followed by cyclisation and aromatisation in acid conditions completed the construction of ring D.

1-Methyl-4-nitraminopyridinium nitrate and 4-nitraminopyridinium methanesulfonate

2001

In the title compounds, C6H8N3O2+*NO3- and C5H6N3O2+*-CH3SO3-, respectively, the cations are almost planar; the twist of the nitramino group about the C-N and N-N bonds does not exceed 10 degrees. The deviations from coplanarity are accounted for by intermolecular N-H...O interactions. The coplanarity of the NHNO2 group and the phenyl ring leads to the deformation of the nitramino group. The C-N-N angle and one C-C-N angle at the junction of the phenyl ring and the nitramino group are increased from 120 degrees by ca 6 degrees, whereas the other junction C-C-N angle is decreased by ca 5 degrees. Within the nitro group, the O-N-O angle is increased by ca 5 degrees and one O-N-N angle is decr…

Hydrogen-bonded dimers of tetra-urea calix[4]arenes stable in THF.

2007

[structure: see text]. Whereas tetra-urea derivatives of tetra-alkoxy calix[4]arenes 1 exist as single molecules in THF, dimeric hydrogen-bonded capsules are exclusively found for the corresponding calix[4]arene derivatives 3 and 2 with two or four free hydroxyl groups. Comparison with the rigidified tetra-urea 5 suggests that this increased stability of the dimers is due to the stabilization of their four-fold symmetry by intramolecular hydrogen bonds between the phenolic hydroxyl groups.

Computational Modeling of Biological Systems: The LDH Story

2010

Lactate dehydrogenases, LDH, catalyzed reaction has been used in this chapter as a conductor wire to present the evolution and difficulties on computing methods to model chemical reactions in enzymes, since the early calculations based at semiempirical level carried out in gas phase to the recent sophisticated simulations based on hybrid Quantum Mechanical/Molecular Mechanics Dynamics (QM/MM MD) schemes. LDH catalyzes the reversible transformation of pyruvate into lactate. The chemical step consists in a hydride and a proton transfer from the cofactor (NADH) and a protonated histidine (His195), respectively. This fact has generated a lot of controversy about the timing of both transfers in …

2015

Chemical ligation has been used to alter motions in specific regions of dihydrofolate reductase from E. coli and to investigate the effects of localized motional changes on enzyme catalysis. Two isotopic hybrids were prepared; one with the mobile N-terminal segment containing heavy isotopes (2H, 13C, 15N) and the remainder of the protein with natural isotopic abundance, and the other one with only the C-terminal segment isotopically labeled. Kinetic investigations indicated that isotopic substitution of the N-terminal segment affected only a physical step of catalysis, whereas the enzyme chemistry was affected by protein motions from the C-terminal segment. QM/MM studies support the idea th…

Synthetic/ECM-inspired hybrid platform for hollow microcarriers with ROS-triggered nanoporation hallmarks

2017

Reactive oxygen species (ROS) are key pathological signals expressed in inflammatory diseases such as cancer, ischemic conditions and atherosclerosis. An ideal drug delivery system should not only be responsive to these signals but also should not elicit an unfavourable host response. This study presents an innovative platform for drug delivery where a natural/synthetic composite system composed of collagen type I and a synthesized polythioether, ensures a dual stimuli-responsive behaviour. Collagen type I is an extracellular matrix constituent protein, responsive to matrix metalloproteinases (MMP) cleavage per se. Polythioethers are stable synthetic polymers characterized by the presence o…

Smart switching in feedforward control of grip force during manipulation of elastic objects

2017

AbstractSwitching systems are common in artificial control systems. Here, we suggest that the brain adopts a switched feedforward control of grip forces during manipulation of objects. We measured how participants modulated grip force when interacting with soft and rigid virtual springs when stiffness varied nearly continuously between trials. We identified a sudden phase transition between two forms of feedforward control that differed in the timing of the synchronization between the anticipated load force and the applied grip force. The switch occurred several trials after a threshold stiffness level. These results suggest that in the control of grip force, the brain acts as a switching c…

Factors related to excessive patellofemoral loading in rearfoot running

2015

Running is recognized as one of the most popular exercise methods. Furthermore, running related injuries have been under the scope for the last few decades. Synchronous function between the segments of the lower limbs is necessary for efficient locomotion. Patellofemoral pain syndrome is a common exercise related syndrome and multifactorial in nature. The purpose of this study was to measure contact forces and frontal plane moments to detect the factors that are associated with atypically high patellofemoral joint loading in rearfoot striking (RFS) running pattern, and moreover, which could possibly contribute to development of the patellofemoral pain syndrome. 39 team sport female athletes…