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PubMed2004

Physical parameters influencing optimization of ultrasound-mediated DNA transfection.

Ultrasound (US) has been shown to transiently disrupt cell membranes and, thereby, facilitate the loading of drugs and genes into viable cells. To address optimization of gene therapy applications, the aim of this work was to systematically determine the influence of physical parameters on transfection and viability of DU145 prostate cancer cells by two different DNA plasmids (pEGFP-N1 and pGL3). By sonicating cells in vitro in the presence of naked DNA, we found that transfection efficiency was increased by: 1. optimizing acoustic energy at 10 to 30 J/cm(2) (for our apparatus, at pressures above the cavitation threshold); 2. using 500-kHz US in the presence of Optison to nucleate cavition, rather than 24-kHz US without Optison; 3. increasing cell concentration from 10(6) to 10(7) cells/mL; and 4. changing temperature during sonication from 21 to 37 degrees C. The best conditions in this study increased transfection by almost 100-fold in the absence of significant DNA damage. Additional measurements indicated that less than one fourth of cells with DNA plasmid uptake into the cytosol showed DNA expression, which suggests that further optimizing transfection by US may require facilitating intracellular DNA trafficking.

Albumins↗

PubMed2003

Correction for oral contrast artifacts in CT attenuation-corrected PET images obtained by combined PET/CT.

UNLABELLED: Recent studies have shown increased artifacts in CT attenuation-corrected (CTAC) PET images acquired with oral contrast agents because of misclassification of contrast as bone. We have developed an algorithm, segmented contrast correction (SCC), to properly transform CT numbers in the contrast regions from CT energies (40-140 keV) to PET energy at 511 keV. METHODS: A bilinear transformation, equivalent to that supplied by the PET/CT scanner manufacturer, for the conversion of linear attenuation coefficients of normal tissues from CT to PET energies was optimized for BaSO(4) contrast agent. This transformation was validated by comparison with the linear attenuation coefficients measured for BaSO(4) at concentrations ranging from 0% to 80% at 511 keV for PET transmission images acquired with (68)Ge rod sources. In the CT images, the contrast regions were contoured to exclude bony structures and then segmented on the basis of a minimum threshold CT number (300 Hounsfield units). The CT number in each pixel identified with contrast was transformed into the corresponding effective bone CT number to produce the correct attenuation coefficient when the data were translated by the manufacturer software into PET energy during the process of CT attenuation correction. CT images were then used for attenuation correction of PET emission data. The algorithm was validated with a phantom in which a lesion was simulated within a volume of BaSO(4) contrast and in the presence of a human vertebral bony structure. Regions of interest in the lesion, bone, and contrast on emission PET images reconstructed with and without the SCC algorithm were analyzed. The results were compared with those for images obtained with (68)Ge-based transmission attenuation-corrected PET. RESULTS: The SCC algorithm was able to correct for contrast artifacts in CTAC PET images. In the phantom studies, the use of SCC resulted in an approximate 32% reduction in the apparent activity concentration in the lesion compared with data obtained from PET images without SCC and a <7.6% reduction compared with data obtained from (68)Ge-based attenuation-corrected PET images. In one clinical study, maximum standardized uptake value (SUV(max)) measurements for the lesion, bladder, and bowel were, respectively, 14.52, 13.63, and 13.34 g/mL in CTAC PET images, 59.45, 26.71, and 37.22 g/mL in (68)Ge-based attenuation-corrected PET images, and 11.05, 6.66, and 6.33 g/mL in CTAC PET images with SCC. CONCLUSION: Correction of oral contrast artifacts in PET images obtained by combined PET/CT yielded more accurate quantitation of the lesion and other, normal structures. The algorithm was tested in a clinical case, in which SUV(max) measurements showed discrepancies of 2%, 1.3%, and 5% between (68)Ge-based attenuation-corrected PET images and CTAC PET images with SCC for the lesion, bladder, and bowel, respectively. These values correspond to 6.5%, 62%, and 66% differences between CTAC-based measurements and (68)Ge-based ones.

Administration, Oral↗

PubMed2005

Application of variational reduced-density-matrix theory to the potential energy surfaces of the nitrogen and carbon dimers.

The acceleration of the variational two-electron reduced-density-matrix (2-RDM) method, using a new first-order algorithm [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)], has shown its usefulness in the accurate description of potential energy surfaces in nontrivial basis sets. Here we apply the first-order 2-RDM method to the potential energy surfaces of the nitrogen and carbon dimers in polarized valence double-zeta basis sets for which benchmark full-configuration-interaction calculations exist. In a wave function formalism accurately stretching the triple bond of the nitrogen dimer requires at least six-particle excitations from the Hartree-Fock reference. Furthermore, cleaving the double bond of C2 should produce a "non-Morse"-like potential curve because the ground state near equilibrium (X 1sigma(g)+) has an avoided crossing with the second excited state (B' 1sigma(g)+) and a level crossing with the first excited state (B 1delta(g)). Because the 2-RDM method variationally optimizes the energy over correlated 2-RDMs on the two-electron space without parametrization of the many-electron wave function, it captures multireference correlations that are difficult to describe with approximate wave functions. The 2-RDM method yields for N2 a potential energy surface with features and spectroscopic constants that are more accurate than those from single-reference methods and similar in accuracy to multireference techniques, and it describes the non-Morse-like behavior of C2 which is not captured by single-reference methods.

Journal Article↗

PubMed2004

Solving and analyzing side-chain positioning problems using linear and integer programming.

MOTIVATION: Side-chain positioning is a central component of homology modeling and protein design. In a common formulation of the problem, the backbone is fixed, side-chain conformations come from a rotamer library, and a pairwise energy function is optimized. It is NP-complete to find even a reasonable approximate solution to this problem. We seek to put this hardness result into practical context. RESULTS: We present an integer linear programming (ILP) formulation of side-chain positioning that allows us to tackle large problem sizes. We relax the integrality constraint to give a polynomial-time linear programming (LP) heuristic. We apply LP to position side chains on native and homologous backbones and to choose side chains for protein design. Surprisingly, when positioning side chains on native and homologous backbones, optimal solutions using a simple, biologically relevant energy function can usually be found using LP. On the other hand, the design problem often cannot be solved using LP directly; however, optimal solutions for large instances can still be found using the computationally more expensive ILP procedure. While different energy functions also affect the difficulty of the problem, the LP/ILP approach is able to find optimal solutions. Our analysis is the first large-scale demonstration that LP-based approaches are highly effective in finding optimal (and successive near-optimal) solutions for the side-chain positioning problem.

Algorithms↗

PubMed2006

Optimized effective potentials yielding Hartree-Fock energies and densities.

It is commonly believed that the exchange-only optimized effective potential (OEP) method must yield total energies that are above corresponding ground-state Hartree-Fock (HF) energies except for one- and two-electron systems. We present a simple procedure for constructing local (multiplicative) exchange potentials that reproduce exactly the HF energy and density in any finite basis set for any number of electrons. For any finite basis set, no matter how large, there exist infinitely many such OEPs, which questions their suitability for practical applications.

Journal Article↗

PubMed2005

Regulation of energy expenditure during prolonged athletic competition.

BACKGROUND: Athletic competitions, such as the Tour de France, demand both momentary bursts of very high power output and the ability to provide high levels of energy expenditure for several weeks. As such, they provide a model of the ability for sustained muscular activity, which is important in terms of how humans are understood, not only as athletes, but also within an evolutionary context. METHODS: Laboratory correlated HR responses were made of elite professional cyclists (N=7) during successive competitions in one of the three grand tours in cycling in successive years, with the intent of evaluating the magnitude and pattern of energy expenditure. HR recordings were normalized into a training impulse (TRIMP) score, summating the intensity and duration of each race, and tracked over the duration of successive tours. RESULTS: Although the day-by-day pattern of HR responses in exercise intensity zones associated with exercise intensities below the first ventilatory threshold, between the first and second ventilatory thresholds, and above the second ventilatory threshold varied in response to the course and competitive situation, the net accumulation of both time in each of the HR zones and TRIMP was remarkably constant from one tour to the next, both within the group at large as well as within individual athletes. The magnitude of accumulation of TRIMP was similar to that of previous reports on elite tour cyclists. CONCLUSIONS: We interpret these results as evidence that humans adopt a pacing strategy designed to optimally distribute energy reserves over the duration of each tour.

Adaptation, Physiological↗

PubMed1997

Criteria to find qualified candidates--professional personnel recruitment methods adapted to neurosurgery.

A neurosurgeon has not received any special training in personnel recruitment at the time he becomes chief of a department. Consequently, a suboptimal personnel policy is most probable. Due to the rapid changes in social behaviour and style of leadership in postwar Europe, he might be ill advised to follow only the example of his successful predecessors, apart from the fact, that this would only be possible if the personalities (of the former and new chief) were similar. To save time and energy for optimal patient care, personnel recruitment can be improved and made more reproducible and reliable by adopting modern, professional non-medical principles. A typical stepwise process of personnel recruitment includes an analysis of the position and function, the definition of demands and offers, the choice of advertising and searching methods, the analysis of the application documents, the interview with the candidate including its re-evaluation and the ongoing evaluation process during the training. This election process is not only conducted by the chief of a department, but also by senior staff-members and even young, competing assistants. It aims to find the candidate who fits best in the requirements, who will be trained and educated with the least effort and who has the best potential to succeed in the long run. The only factors seemingly predicting a good development of a candidate are personality, energy (potential, motivation) and intelligence. Therefore, the search should especially aim to discover these-admittedly difficult to detect-qualities.

Achievement↗

PubMed2006

Variational reduced-density-matrix theory applied to the potential energy surfaces of carbon monoxide in the presence of electric fields.

The variational optimization of the energy with respect to the two-electron reduced-density matrix (2-RDM), constrained by N-representability conditions, can determine the shape of molecular potential energy surfaces with useful accuracy. In this paper, we apply the 2-RDM method with a first-order optimization algorithm [Mazziotti, D. A. Phys. Rev. Lett. 2004, 93, 213001] to investigating the potential energy surfaces of carbon monoxide in the presence and absence of an electric field. Two beneficial characteristics of the 2-RDM method for computing potential energy surfaces include the following: (i) its ability to capture multireference effects without specifying any reference wave function or density matrix and (ii) its guarantee of a global energy minimum in the variational optimization. The 2-RDM method produces electronic ground-state energies with similar accuracy at equilibrium and nonequilibrium geometries in both the presence and the absence of the electric field. Computed dipole moments are similar in accuracy to the values from the computationally expensive configuration interaction with single, double, triple, and quadruple excitations. These surfaces have important applications in quantum molecular control theory.

Carbon Monoxide↗

PubMed1983

Efficiency of energy conversion in model biological pumps. Optimization by linear nonequilibrium thermodynamic relations.

Experimental investigations showed linear relations between flows and forces in some biological energy converters operating far from equilibrium. This observation cannot be understood on the basis of conventional nonequilibrium thermodynamics. Therefore, the efficiencies of a linear and a nonlinear mode of operation of an energy converter (a hypothetical redox-driven H+ pump) were compared. This comparison revealed that at physiological values of the forces and degrees of coupling (1) the force ratio permitting optimal efficiency was much higher in the linear than in the nonlinear mode and (2) the linear mode of operation was at least 10(6)-times more efficient that the nonlinear one. These observations suggest that the experimentally observed linear relations between flows and forces, particularly in the case of oxidative phosphorylation, may be due to a feedback regulation maintaining linear thermodynamic relations far from equilibrium. This regulation may have come about as the consequence of an evolutionary drive towards higher efficiency.

Energy Metabolism↗

PubMed2001

Experimental and clinical results of Er:YAG laser stapedotomy.

BACKGROUND AND OBJECTIVE: At the beginning of the 1980s, different laser types were used for stapes surgery to reduce potential harm to inner ear structures through manipulation with conventional instruments during stapedotomy. Most clinical studies were carried out with the CO2 or the argon laser. The Er:YAG laser has been used rarely in patients with otosclerosis. STUDY DESIGN/MATERIALS AND METHODS: In an experimental study on 54 human petrous bones, the optimal laser energy parameter for dissection of the posterior stapes crus and the footplate perforation were determined. With these parameters, stapedotomy was carried out with the Er:YAG laser in 29 patients with otosclerosis with a conventional dissection of the incudostapedial joint and the stapedius muscle tendon. The Er:YAG laser was used (60 or 100 mJ, 3-6 pulses) for dissection of the posterior stapes crus and footplate perforation. RESULTS: No intra- or postoperative complications were observed in all 29 patients. Vertigo and hearing loss were not observed intra- or postoperatively. The postoperative hearing results (improvement of the air-bone gap) was in all cases satisfactory (median remaining air bone gap, 8.1 dB). The median operation time was 29 minutes (15-42 minutes) and did not show a significant prolongation in comparison to the conventional technique. In 1 of the 29 patients, the footplate perforation needed to be carried out conventionally. CONCLUSION: For the first time, Er:YAG laser parameters have been optimized and refined in a human petrous bone model and were then used in a clinical setting. According to the presented results, the Er:YAG laser seemed to be a very suitable instrument for stapedotomy.

Adult↗

PubMed2002

Ultrasound-assisted method for determination of chemical oxygen demand.

A method for determination chemical oxygen demand (COD) assisted by use of ultrasound has been successfully evaluated for the first time. The method uses instrumentation simpler and cheaper and, in some instances, safer than that used by previous methods for the same purpose. The new device used for sonication is an all-glass cylindrical sonotrode that can be introduced directly into the reaction mixture. Use of this device enables more efficient interaction between sample and ultrasonic energy. The optimized experimental conditions are high ultrasonic power (55% amplitude, 0.9-second pulses each second), high sulfuric acid concentration (>60%), and a sonication time of 2 min. Under these conditions the method has limitations similar to those of the official COD method with regard to the type of organic compound. It works adequately with easily oxidized organic matter (potassium hydrogen phthalate and dextrose) and other organic compounds difficult to oxidize by conventional methods (e.g. phenol and acetic acid) but the COD values obtained with volatile compounds and difficult organic matter are poor. Chloride is tolerated up to a concentration of 7000 mg L(-1) without any masking agent. Gasification of the sample is recommended to improve results; use of air and argon resulted in no significant differences - bubbling with air during sonication resulted in COD values for certified materials and real wastewater samples statistically identical with the certified COD values and those obtained by the classic (open reflux) method. The use of ultrasound energy for COD determination thus seems to be an interesting and promising alternative to conventional oxidation methods used for the same purpose.

Journal Article↗

PubMed2001

Matrix-assisted laser desorption/ionization coupled with quadrupole/orthogonal acceleration time-of-flight mass spectrometry for protein discovery, identification, and structural analysis.

The design and operation of a novel UV-MALDI ionization source on a commercial QqoaTOF mass spectrometer (Applied Biosystem/MDS Sciex QSTAR Pulsar) is described. Samples are loaded on a 96-well target plate, the movement of which is under software control and can be readily automated. Unlike conventional high-energy MALDI-TOF, the ions are produced with low energies (5-10 eV) in a region of relatively low vacuum (8 mTorr). Thus, they are cooled by extensive low-energy collisions before selection in the quadrupole mass analyzer (Q1), potentially giving a quasi-continuous ion beam ideally suited to the oaTOF used for mass analysis of the fragment ions, although ion yields from individual laser shots may vary widely. Ion dissociation is induced by collisions with argon in an rf-only quadrupole cell, giving typical low-energy CID spectra for protonated peptide ions. Ions separated in the oaTOF are registered by a four-anode detector and time-to-digital converter and accumulated in "bins" that are 625 ps wide. Peak shapes depend upon the number of ion counts in adjacent bins. As expected, the accuracy of mass measurement is shown to be dependent upon the number of ions recorded for a particular peak. With internal calibration, mass accuracy better than 10 ppm is attainable for peaks that contain sufficient ions to give well-defined Gaussian profiles. By virtue of its high resolution, capability for accurate mass measurements, and sensitivity in the low-femotomole range, this instrument is ideally suited to protein identification for proteomic applications by generation of peptide tags, manual sequence interpretation, identification of modifications such as phosphorylation, and protein structural elucidation. Unlike the multiply charged ions typical of electrospray ionization, the singly charged MALDI-generated peptide ions show a linear dependence of optimal collision energy upon molecular mass, which is advantageous for automated operation. It is shown that the novel pulsing technique of this instrument that increases the sensitivity for precursor ions scans is applicable to the identification of peptides labeled with isotope-coded affinity tags.

Databases, Factual↗

PubMed1996

A refined model of the thyrotropin-releasing hormone (TRH) receptor binding pocket. Experimental analysis and energy minimization of the complex between TRH and TRH receptor.

Seven transmembrane (TM) spanning, G protein-coupled receptors (GPCRs) appear to bind large glycoprotein hormones predominantly within their extracellular domains, small nonpeptidic ligands within the TM helical bundle, and peptide ligands within the extracellular domains and TM bundle. The tripeptide thyrotropin-releasing hormone (TRH, pyroGlu-His-ProNH2) may bind entirely within the TM bundle of the TRH receptor (TRH-R). We have previously demonstrated direct binding contacts between the pyroGlu of TRH and two residues in TM helix 3 (TM-3) of TRH-R and proposed a model of the binding pocket of TRH-R [Perlman, J. H., Laakkonen, L., Osman, R., & Gershengorn, M. C. (1994) J. Biol. Chem. 269, 23383-23386]. Here, we provide evidence for two additional direct interactions between TRH and TRH-R. One interaction is between the aromatic ring of Tyr 282 of TM-6 and His of TRH. This is based on a large increase in the half-maximally effective concentration (EC50) of TRH for stimulation of inositol phosphate formation by Y282A TRH-R and a loss of selectivity of this mutant receptor for TRH analogs substituted at His. We provide evidence for another interaction between Arg 306 of TM-7 and the terminal carboxamide of TRH. Using four direct interactions as anchors, a refined model of the TRH-R binding pocket was constructed using geometry optimization through energy minimization. A novel method for modeling GPCRs based on Monte Carlo and stochastic dynamics simulations is presented in the accompanying paper [Laakkonen, L. J., Guarnieri, F., Perlman, J. H., Gershengorn, M. C., & Osman, R. (1996) Biochemistry 35, 7651-7663].

Amino Acid Sequence↗

PubMed2026

Multi-omics unveils seasonal remodeling and metabolic crosstalk between testis and abdominal fat body in a non-amplexus stream frog Nanorana taihangnica (Anura: Dicroglossidae).

BACKGROUND: Energy allocation between reproduction and survival represents a fundamental life-history challenge for animals in seasonal environments. Using integrated transcriptomics and metabolomics, we investigated Nanorana taihangnica (Anura: Dicroglossidae), a non-amplexus stream frog endemic to China, to elucidate the seasonal morphological and molecular coordination between the testis and abdominal fat body. RESULTS: Morphological analysis showed that fat body adipocyte cross-sectional area minimized at the end of the breeding season but rapidly recovered thereafter, while testicular volume continued declining post-breeding and only recovered during the non-breeding period. During breeding season, multi-omics analyses revealed that the fat body enhanced fatty acid oxidation, upregulated histidine-carnosine metabolism, activated NAD+ metabolism and FOXO3-mediated antioxidative responses to mitigate metabolic stress, and regulated adipocyte survival and apoptosis via sphingolipid signaling. Seasonal testicular development was centrally regulated by the mTOR signaling pathway, whose activity integrated autophagy levels, NAD+ availability, and aspartate metabolism to coordinate spermatogonial proliferation and spermatogenesis. CONCLUSIONS: This study demonstrates that N. taihangnica optimizes seasonal energy storage, allocation, and reproductive investment through molecular and metabolic crosstalk between the fat body and testis, providing empirical insights into the physiological integration of life-history strategies in animals inhabiting fluctuating environments.

Animals↗

PubMed2006

Monitoring of ketogenic diet for carnitine metabolites by subcutaneous microdialysis.

The ketogenic diet (KD) provides ketones from the degradation of free fatty acids for energy metabolism. It is a therapeutic option for pharmacoresistant epilepsies. Carnitine is the carrier molecule that transports fatty acids across the mitochondrial membrane for degradation into ketones. The integrity of this transport system is a prerequisite for an adequate ketogenic response. For monitoring of tissue metabolism with KD, we used the sampling method of s.c. microdialysis (MD), which permits minimally invasive, frequent, and extensive metabolic monitoring independent of blood tests. By using this new method, we monitored changes in carnitine metabolism induced by KD, particularly in free carnitine (C0), acetylcarnitine (C2), and hydroxybutyrylcarnitine (C4OH). Correlation of microdialysate and tissue concentrations for carnitines in vitro was about 85%. Carnitine metabolism was monitored in seven children started on a KD for pharmacoresistant epilepsy after a conventional initial fasting period. Detected metabolic changes consisted of a slight decrease in s.c. C0 and a marked increase in C2/CO and C4OH/CO levels. The levels of s.c. C4OH strongly correlate with beta-hydroxybutyrate (beta-OHB) levels in plasma providing an additional parameter for the carnitine reserve of the body and reflect an optimal ketogenic energy supply. Subcutaneous MD allows close and extensive monitoring of metabolism with a KD.

3-Hydroxybutyric Acid↗

PubMed1999

Molecular orbital study of complexes of zinc(II) with sulphide, thiomethanolate, thiomethanol, dimethylthioether, thiophenolate, formiate, acetate, carbonate, hydrogen carbonate, iminomethane and imidazole. Relationships with structural and catalytic zinc in some metallo-enzymes.

Geometry optimization and energy calculations have been performed at the density functional B3LYP/LANL2DZ level on hydrogen sulfide (HS-), dihydrogensulfide (H2S), thiomethanolate (CH3S-), thiomethanol (CH3SH), thiophenolate (C6H5S-), methoxyde (CH3O-), methanol (CH3OH), formiate (HCOO-), acetate (CH3COO-), carbonate (CO3(2-)), hydrogen carbonate (HCO3-), iminomethane (NH=CH2), [ZnS], [ZnS2]2-, [Zn(HS)]+, [Zn(H2S)]2+, [Zn(HS)4]2-, [Zn(CH3S)]+, [Zn(CH3S)2], [Zn(CH3S)3]-, [Zn(CH3S)4]2-, [Zn(CH3SH)]2+, [Zn(CH3SCH3)]2+, [Zn(C6H5S)]+, [Zn(C6H5S)2], [Zn(C6H5S)3]-, [Zn(HS)(NH=CH2)2]+, [Zn(HS)2(NH=CH2)2], [Zn(HS)(H2O)]+, [Zn(HS)(HCOO)], [Zn(HS)2(HCOO)]-, [Zn(CH3O)]+, [Zn(CH3O)2], [Zn(CH3O)3]-, [Zn(CH3O)4]2, [Zn(CH3OH)]2+, [Zn(HCOO)]+, [Zn(CH3COO)]+, [Zn(CH3COO)2], [Zn(CH3COO)3]-, [Zn(CO3)], [Zn(HCO3)]+, and [Zn(HCO3)(Imz)]+ (Imz, 1,3-imidazole). The computed Zn-S bond distances are 2.174A for [ZnS], 2.274 for [Zn(HS)]+, 2.283 for [Zn(CH3S)]+, and 2.271 for [Zn(C6H5S)]+, showing that sulfide anion forms stronger bonds than substituted sulfides. The nature of the substituents on sulfur influences only slightly the Zn-S distance. The optimized tetra-coordinate [Zn(HS)2(NH=CH2)2] molecules has computed Zn-S and Zn-N bond distances of 2.392 and 2.154A which compare well with the experimental values at the solid state obtained via X-ray diffraction for a number of complex molecules. The computed Zn-O bond distances for chelating carboxylate derivatives like [Zn(HOCOO)]+ (1.998A), [Zn(HCOO)]+ (2.021), and [Zn(CH3COO)]+ (2.001) shows that the strength of the bond is not much influenced by the substituent on carboxylic carbon atom and that CH3- and HO- groups have very similar effects. The DFT analysis shows also that the carboxylate Ligand has a preference for the bidentate mode instead of the monodentate one, at least when the coordination number is small.

Acetates↗

PubMed2002

The temporal organization of ingestive behaviour and its interaction with regulation of energy balance.

Body weight of man and animals is under homeostatic control mediated by the adjustment of food intake. It is discussed in this review that besides signals reporting energy deficits, optimized programs of body clocks take part in feeding behaviour as well. Circadian light- and food-entrainable clocks determine anticipatory adaptive behavioural and physiological mechanisms, promoting or inhibiting food intake. In fact these clocks form the constraints within which the homeostatic regulation of feeding behaviour is operating. Therefore, a strong interaction between circadian and homeostatic regulation must occur. In this homeostatic control, a wide variety of regulatory negative feedback mechanisms, or satiety signals, play a dominant role. In this respect several gut hormones and body temperature function as 'short-term' satiety factors and determine meal sizes and intermeal intervals. Leptin, secreted by fat cells in proportion to the size of adipose tissue mass, is probably an important determinant of the 'long-term' regulation of feeding behaviour by setting the motivational background level for feeding behaviour. Thus, initiation or termination of meals at any particular point in time, depends on the resultant of all satiety signals and on constraints imposed by circadian light- and food-entrainable oscillators.

Adipose Tissue↗

PubMed2003

Mechanism of 1,3-migration in allylperoxyl radicals: computational evidence for the formation of a loosely bound radical-dioxygen complex.

The three pathways postulated for 1,3-migration of the peroxyl group in the allylperoxyl radical (1a), a key reaction involved in the spontaneous autoxidation of unsaturated lipids of biological importance, have been investigated by means of quantum mechanical electronic structure calculations. According to the barrier heights calculated from RCCSD(T)/6-311+G(3df,2p) energies with optimized molecular geometries and harmonic vibrational frequencies determined at the UMP2/6-311+G(3df,2p) level, the allylperoxyl rearrangement proceeds by fragmentation of 1a through a transition structure (TS1) with a calculated DeltaH++(298 K) of 21.7 kcal/mol to give an allyl radical-triplet dioxygen loosely bound complex (CX). In a subsequent step, the triplet dioxygen moiety of CX recombines at either end of the allyl radical moiety to convert the complex to the rearranged peroxyl radical (1a') or to revert to the starting peroxyl radical 1a. CX shows an electron charge transfer of 0.026 e in the direction allyl --> O(2). The dominant attractive interactions holding in association the allyl radical-triplet dioxygen pair in CX are due chiefly to dispersion forces. The DeltaH(298 K) for dissociation of CX in its isolated partners, allyl radical and triplet dioxygen, is predicted to be at least 1 kcal/mol. The formation of CX prevents the diffusion of its partners and maintains the stereocontrol along the fragmentation-recombination processes. The concerted 1,3-migration in allylperoxyl radical is predicted to take place through a five-membered ring peroxide transition structure (TS2) showing two long C-O bonds. The DeltaH++(298 K) calculated for this pathway is less favorable than the fragmentation-recombination pathway by 1.9 kcal/mol. The cyclization of 1a to give a dioxolanyl radical intermediate (2a) is found to proceed through a five-membered ring transition structure (TS3) with a calculated DeltaH++(298 K) of 33.9 kcal/mol. Thus, the sequence of ring closure 1a --> 2a and ring opening 2a --> 1a' is unlikely to play any significant role in allylperoxyl rearrangement 1a --> 1a'. In the three pathways investigated, the energy of the transition structure is predicted to be somewhat lower in either heptane or aqueous solution than in the gas phase. Although the energy lowering calculated for TS1 is smaller than the calculated for TS2 and TS3, it is very unlikely that the solvent effects may reverse the predicted preference of the fragmentation-recombination pathway over the concerted and stepwise ring closure-ring opening mechanisms.

Allyl Compounds↗