399 research outputs found
Enzymatic Synthesis of Nucleoside Triphosphates. Does It Involve An Ion-Radical Path ?
Accumulation and release of energy in the nucleoside triphosphate enzymatic synthesis and hydrolysis does not limited to a routine energy consuming nucleophilic mechanism. These processes require an overcoming the large energy barrier exceeding a total value of accumulated or released energy level by at least 3 – 4 times (~10 kcal/mol). This energy is supposed to be taken from the mechanical compression of the catalytic site and used to form P–O chemical bond by a direct nucleophilic addition of phosphate to nucleoside diphosphate (ADP as an example). A new, energetically “cheapâ€, ion-radical mechanism of the ATP biosynthesis has been proposed due to the observation of magnetic isotope and magnetic field effects on the ATP synthesis. This mechanism is about to generate a compression energy to “spend†on a partial dehydratation of magnesium ion inside the nucleotidyl transferase catalyric site (energy cost of this process is 3-5 kcal/mol, i.e. by 2-3 times less than a total accumulated or released energy). Dehydration of this ion is to increase its electron affinity and hence to stimulate an electron transfer from ADP3- to Mg2+. This reaction is a starting point of the ion-radical mechanism considering the molecular mechanics of enzymatic machines and its quantum chemistry background as well. To the contrast of a hardly controllable nucleophilic path, the ion-radical mechanism might be turned on/off by a targeted delivery of  paramagnetic magnesium ions, 25Mg2+, towards the phosphate transferring enzyme catalytic site. The magnesium isotope substitution is easily reachable by the endo-osmotic pressure techniques, which makes it attractive for further biotechnological and/or pharmacological application(s)
Large magnetoresistance at room-temperature in semiconducting polymer sandwich devices
We report on the discovery of a large, room temperature magnetoresistance
(MR) effect in polyfluorene sandwich devices in weak magnetic fields. We
characterize this effect and discuss its dependence on voltage, temperature,
film thickness, electrode materials, and (unintentional) impurity
concentration. We usually observed negative MR, but positive MR can also be
achieved under high applied electric fields. The MR effect reaches up to 10% at
fields of 10mT at room temperature. The effect shows only a weak temperature
dependence and is independent of the sign and direction of the magnetic field.
We find that the effect is related to the hole current in the devices.Comment: 3 pages, 4 figure
Properties of the B+-H2 and B+-D2 complexes: a theoretical and spectroscopic study
The rotationally resolved infrared spectrum of the B+-D2 ion-neutral complex is recorded in the D-D stretch vibration region (2805–2875 cm−1) by detecting B+ photofragments. Analysis of the spectrum confirms a T-shaped equilibrium geometry for the B+-D2 complex with a vibrationally averaged intermolecular bond length of 2.247 Å, around 0.02 Å shorter than for the previously characterised B+-H2 complex [V. Dryza, B. L. J. Poad, and E. J. Bieske, J. Am. Chem. Soc. 130, 12986 (2008)10.1021/ja8018302]. The D-D stretch band centre occurs at 2839.76 ± 0.10 cm−1, representing a −153.8 cm−1 shift from the Q1(0) transition of the free D2 molecule. A new three dimensional ab initio potential energy surface for the B++H2 interaction is calculated using the coupled cluster RCCSD(T) method and is used in variational calculations for the rovibrational energies of B+-H2 and B+-D2. The calculations predict dissociation energies of 1254 cm−1 for B+-H2 with respect to the B++H2 (j = 0) limit, and 1313 cm−1 for B+-D2 with respect to the B++D2 (j = 0) limit. The theoretical approach reproduces the rotational and centrifugal constants of the B+-H2 and B+-D2 complexes to within 3%, and the magnitude of the contraction of the intermolecular bond accompanying excitation of the H2 or D2 sub-unit, but underestimates the H-H and D-D vibrational band shifts by 7%–8%. Combining the theoretical and experimental results allows a new, more accurate estimation for the B+-H2 band origin (3939.64 ± 0.10 cm−1)
Magnetostimulated Chandges of Microhardness in Potassium Acid Phthalate Crystals
A decrease in microhardness along the (010) cleavage in potassium acid
phthalate single crystals by 15--18% after the application of a permanent
magnetic field was revealed for the first time. It is shown that the effect
revealed is of the volume character. The role of interlayer water in the
processes stimulated by a magnetic field is studied., Interlayer water plays
does not cause the observed changes it only plays the part of an indicator of
these changes in potassium acid phthalate crystals in a magnetic field. It is
established that microhardness in the (100) plane of the crystal in an applied
a magnetic field first increases by 12--15% and then remains constant in time
within the accuracy of the experiment. The possibility of varying the crystal
structure of potassium acid phthalate crystals by applying magnetic fields
inducing rearrangement in the system of hydrogen bonds or in the defect
structure is discussed.Comment: 6 pages, 7 figure
Hybrid nanoparticles based on sulfides, oxides, and carbides
The methods for synthesis of hybrid nanoparticles based on sulfides, oxides, and carbides of heavy and transition metals were considered. The problem of the influence of the method of synthesis of the hybrid nanoparticles on their atomic structure, morphology of the nanomaterials, and functional properties was analyzed. The areas of practical use of the hybrid nanoparticles were proposed. © 2013 Springer Science+Business Media New York
Magnetism, entropy, and the first nano-machines
The efficiency of bio-molecular motors stems from reversible interactions
; weak bonds stabilizing intermediate states (enabling
conversion of chemical into mechanical energy). For their (unknown) origins, we
suggest that a magnetically structured phase (MSP) formed via accretion of
super-paramagnetic particles (S-PPs) by magnetic rocks on the Hadean Ocean
floor had hosted motor-like diffusion of ligand-bound S-PPs through its
template-layers; its ramifications range from optical activity to quantum
coherence. A gentle flux gradient offers both detailed-balance breaking
non-equilibrium and to a magnetic dipole, undergoing infinitesimal
spin-alignment changes. Periodic perturbation of this background by local
H-fields of template-partners can lead to periodic high and low-template
affinity states, due to the dipole's magnetic degree of freedom. An
accompanying magnetocaloric effect allows interchange between system-entropy
and bath temperature. We speculate on a magnetic reproducer in a setting close
to the mound-scenario of Russell and coworkers that could evolve bio- ratchets.Comment: 17 pages, 1 figur
Photolysis Kinetics, Mechanisms, and Pathways of Tetrabromobisphenol A in Water under Simulated Solar Light Irradiation
Carbon dioxide/methanol conversion cycle based on cascade enzymatic reactions supported on superparamagnetic nanoparticles
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