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PubMed2005

Ab initio study of cyclobutane: molecular structure, ring-puckering potential, and origin of the inversion barrier.

The structure and ring-puckering properties of cyclobutane and its perdeuterated isotopomer are studied using high-level ab initio methods and complete basis set extrapolations. Calculations reveal significant coupling between the ring-puckering (theta) and CH(2)-rocking (alpha) motions, with equilibrium angles (theta(eq) = 29.59 degrees and alpha(eq) = 5.67 degrees) that are within the range of experimentally determined values. Our best estimate of the inversion barrier is 482 cm(-1), in excellent agreement with recent experimental determinations. Ring-inversion transition frequencies are evaluated from the eigenstates of the intrinsic reaction coordinate potentials for cyclobutane and cyclobutane-d(8). Natural bond orbital analysis shows that sigma(CC) --> sigma(CH)* and sigma(CH) --> sigma(CH)* hyperconjugative interactions are strengthened as cyclobutane puckers, thereby suggesting that inversion barriers in four-membered ring systems are a consequence of electronic delocalization rather than torsional strain.

Journal Article↗
PubMed2006

Transformation of hydrogel-based inverse opal photonic sensors from FCC to L1(1) during swelling.

The structural evolution of Bragg diffracting inverse opal hydrogel sensors during swelling is directly observed by two-photon laser scanning fluorescence microscopy and compared to predictions from finite element analysis. A fluorescently labeled pH-sensitive hydrogel is UV-polymerized in a dried polystyrene colloidal crystal template, which is etched to yield an inverse opal. Fluorescence imaging of the hydrogel at different pH values reveals an inhomogeneous deformation of the FCC array of aqueous pores. The pores elongate along the sample normal direction and collapse along the sample parallel directions, consistent with the Bragg response, which indicates a 1-D increase in the interlayer distance. Interconnects between the pores serve as anchor points during hydrogel expansion into the pores. Pinning of the hydrogel to the substrate causes a change of the hydrogel lattice symmetry during deformation, from FCC (ABC stacking) to L1(1) (ABCA'B'C' stacking). Reconstructed cross-sections confirm that a 1-D increase in the interlayer distance along the substrate normal direction is responsible for the diffraction response of an inverse opal hydrogel sensor. Comparison with predictions from finite element analysis shows qualitative agreement, although the experimental mesostructure is significantly more deformed than the calculated data, due to buckling in the experimental system that is not captured by the model.

Biosensing Techniques↗
PubMed2002

A theoretical investigation into the inversion barrier of dipole-stabilized alpha-aminoorganolithiums.

[reaction: see text] Results from density functional theory calculations (B3LYP/6-31+G) suggest that inversion of the monomer of 2-lithio-N-formylpyrrolidine (2) in coordinating ethereal solvent occurs with an activation barrier of 15.7 kcal/mol, while the inversion of the monomer in a noncoordinating hydrocarbon solvent is considerably slower. However, aggregation into a trimer in hydrocarbon solvent restores the low inversion barrier. This study suggests that solvation and aggregation may influence the mechanism and rate of racemization of dipole-stabilized alpha-aminoorganolithiums.

Journal Article↗
PubMed2000

Acid-catalyzed inversion of sucrose in the amorphous state at very low levels of residual water.

PURPOSE: Factors affecting the solid-state acid-catalyzed inversion of amorphous sucrose to glucose and fructose in the presence of colyophilized citric acid, with less than 0.1% w/w residual water, have been studied. METHODS: Samples of citric acid and sucrose were lyophilized at a weight ratio of 1:10 citric acid:sucrose from solutions with initial pH values of 1.87, 2.03, and 2.43, as well as at a weight ratio of 1:5, at an initial pH of 1.87. Glass transition temperatures, Tg, were measured by DSC and the presence of any possible residual water was monitored by Karl Fischer Titrimetry. The inversion of sucrose was measured by polarimetric analysis after reconstitution of solid samples stored at 50 degrees C under P2O5. RESULTS: Samples of 1:10 citric acid:sucrose at an initial pH of 1.87, 2.03, and 2.43 exhibited the same Tg. The initial rate of reactivity was affected at a 1:10 ratio by the solution pH before lyophilization in the order: 1.87 > 2.03 > 2.43 and by citric acid concentration at pH 1.87 in the order 1:5 > 1:10. CONCLUSIONS: Sucrose, colyophilized with an acid such as citric acid, undergoes significant acid-catalyzed inversion at 50 degrees C despite the very low levels of residual water, i.e., <0.1% w/w. At the same ratio of citric acid to sucrose (1:10), and hence the same Tg, the rate of reaction correlates with the initial solution pH indicating that the degree of ionization of citric acid in solution is most likely retained in the solid state. That protonation of sucrose by citric acid is important is shown by the direct relationship between maximum extent of reaction and citric acid composition. It is concluded that colyophilization of acidic substances with sucrose, even in the absence of residual water, can produce reducing sugars capable of further reaction with other formulation ingredients susceptible to reaction with reducing sugars.

Citric Acid↗
PubMed2001

MRI prior computation and parallel tempering algorithm: a probabilistic resolution of the MEG/EEG inverse problem.

Since the MEG inverse problem is ill-posed and admits many possible solutions, it is not possible to give it a single "true" answer. Therefore, we propose here to use a specific probabilistic algorithm to map the full probability distribution of the MEG sources with Markov Chain Monte Carlo methods. Using a Bayesian approach, the probability of the MEG solutions is expressed as the product of the likelihood by the prior probability. To compute the prior and constrain the MEG inverse problem resolution, MRI data are also acquired and automatically processed to determine the brain position and volume. We then use Parallel Tempering algorithm to estimate the full posterior probability and determine the likely solutions of the inverse problem. We illustrate the method with results obtained from the analysis of somatosensory data. This illustrates both the MRI processing for the prior computation, and how the knowledge of the full posterior probability distribution can be used to estimate the position of the sources, as well as their likely extension.

Adult↗
PubMed2000

Electromagnetic inverse solutions in anatomically constrained spherical head models.

Two classes of functional neuroimaging methods exist: hemodynamic techniques such as PET and fMRI, and electromagnetic techniques such as EEG/ERP and MEG. In order to fusion these images with anatomical information, co-registration with volumetric MRI is needed. While such co-registration techniques are well established for hemodynamic images, additional steps are needed for electromagnetic recordings, because the activity is only recorded on the scalp surface and inverse solutions based on specific head models have to be used to estimate the 3-dimensional current distribution. To date most of the experimental and clinical studies use multi-shell concentric sphere models of the head, solve the inverse problem on this simplistic model, and then co-register the solution with the MRI using homogeneous transform operations. Contrary to this standard method, we here propose to map the MRI to the spherical system by defining transformation operations that transform the MRI to a best-fitting sphere. Once done so, the solution points are defined in the cerebral tissue of this deformed MRI and the lead field for the distributed linear inverse solutions is calculated for this solution space. The method, that we call SMAC (Spherical Model with Anatomical Constrains) is tested with simulations, as well as with the following real data: 1) estimation of the sources of visual evoked potentials to unilateral stimulation from data averaged over subjects, and 2) localization of interictal discharges of two epileptic patients, one with a temporal, the other with an occipital focus, both confirmed by seizure freedom after resection of the epileptogenic region.

Brain↗
PubMed1995

What causes the face inversion effect?

What is it about the way faces are represented by the visual system that makes them so much harder to recognize when inverted? The authors tested the hypothesis that the "face inversion" effect results from the use of holistic shape representations. This suggests that the susceptibility of nonface patterns to inversion should be a function of their degree of part decomposition. In Experiment 1 this was tested and confirmed with dot patterns in which the degree of part decomposition was manipulated by grouping and segregation on the basis of dot color. The hypothesis also predicted that the face inversion effect can be eliminated with face stimuli if participants are induced to recognize the faces in terms of their component parts. In Experiment 2 this was tested and confirmed with whole, intact faces, in which the degree of part decomposition was manipulated by allowing participants to study them, initially, in either whole, intact versions or versions with parts presented separately.

Adult↗
PubMed1995

The dorsal raphe nucleus is a site of action mediating the behavioral effects of the benzodiazepine receptor inverse agonist DMCM.

Systemic administration of benzodiazepine receptor inverse agonists leads to behavioral changes similar to those produced by inescapable shock (IS). The dorsal raphe nucleus (DRN) is a critical structure mediating IS effects. The present experiments determined whether the DRN is a site mediating the behavioral changes produced by benzodiazepine receptor inverse agonists. Microinjection of the inverse agonist Methyl 6,7-Dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) in the region of the DRN produced enhancement of fear conditioning as assessed by the amount of freezing in the presence of shock cues as well as interference with shuttlebox escape learning assessed 24 hr later. Furthermore, lesion of the DRN blocked the effects of systemic DMCM on fear conditioning and escape learning. These data suggest that the DRN is indeed critical in mediating these behavioral consequences of DMCM and further support a role for the DRN in producing the behavioral changes induced by IS.

Animals↗
PubMed2004

Linear theory, dimensional theory, and the face-inversion effect.

We contrast 2 theories within whose context problems are conceptualized and data interpreted. By traditional linear theory, a dependent variable is the sum of main-effect and interaction terms. By dimensional theory, independent variables yield values on internal dimensions that in turn determine performance. We frame our arguments within an investigation of the face-inversion effect--the greater processing disadvantage of inverting faces compared with non-faces. We report data from 3 simulations and 3 experiments wherein faces or non-faces are studied upright or inverted in a recognition procedure. The simulations demonstrate that (a) critical conclusions depend on which theory is used to interpret data and (b) dimensional theory is the more flexible and consistent in identifying underlying psychological structures, because dimensional theory subsumes linear theory as a special case. The experiments demonstrate that by dimensional theory, there is no face-inversion effect for unfamiliar faces but a clear face-inversion effect for celebrity faces.

Computer Simulation↗
PubMedDate not supplied

Selective population inversion in NMR.

Population inversion of a selected region of a spectrum is a concept which has wide application in both NMR spectroscopy and imaging. While inversion of population at any one frequency is a trivial matter, ensuring an accurate inversion over a specified bandwidth, with negligible perturbation of the magnetization outside that bandwidth, is a major problem. However, by using as a driving function a complex radiofrequency (r.f.) pulse with an envelope of the form (sech beta t)1+5i where 1/beta is the temporal width and t is time, we have found that above a critical r.f. power threshold, magnetization is accurately inverted over a very sharply defined bandwidth, while outside that region, magnetization is returned to its initial position, and population is unaffected. Within the broad limits imposed by our equipment, we have also discovered that the phenomenon is independent of the incident r.f. power.

Magnetic Resonance Spectroscopy↗
PubMed2001

'Inverse' melting of a vortex lattice.

Inverse melting is the process in which a crystal reversibly transforms into a liquid or amorphous phase when its temperature is decreased. Such a process is considered to be very rare, and the search for it is often hampered by the formation of non-equilibrium states or intermediate phases. Here we report the discovery of first-order inverse melting of the lattice formed by magnetic flux lines in a high-temperature superconductor. At low temperatures, disorder in the material pins the vortices, preventing the observation of their equilibrium properties and therefore the determination of whether a phase transition occurs. But by using a technique to 'dither' the vortices, we were able to equilibrate the lattice, which enabled us to obtain direct thermodynamic evidence of inverse melting of the ordered lattice into a disordered vortex phase as the temperature is decreased. The ordered lattice has larger entropy than the low-temperature disordered phase. The mechanism of the first-order phase transition changes gradually from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures.

Journal Article↗
PubMed2001

Review of the inverse Knapp procedure: indications, effectiveness and results.

PURPOSE: To evaluate the indications and results of inverse Knapp procedures performed at one institution over a 10 year period between 1987 and 1996. METHODS: The records of patients who had undergone inverse Knapp procedures were retrospectively reviewed. Demographic data were collected, pre- and post-operative orthoptic assessments were evaluated, and pre- and post-operative binocular single vision (BSV) charts and Hess charts were scored. RESULTS: Twenty-one patients were identified and records were available in 17. The main indication for the operation was orbital trauma. The mean vertical deviation in primary position and downgaze improved from 16.06 prism dioptres (PD) to 7.35 PD and 26.45 PD to 6.66 PD respectively. The pre-operative average score for BSV was 42%, increasing to 62% post-operatively. The Hess chart error scores improved on average from 848.8 pre-operatively to 296.4 post-operatively. Further operations were required for 8 patients. CONCLUSIONS: Inverse Knapp procedure is an uncommon strabismus operation but an extremely useful one in selected cases. We recommend it for the treatment of marked inferior rectus weakness, congenital or acquired, for post-traumatic inferior rectus underaction with or without orbital blow-out fracture and for residual large hypertropia in patients with poor binocular functions. The extent of inferior rectus underaction should be assessed very carefully to avoid overcorrecting.

Adolescent↗
PubMed2005

Inverse magnetocaloric effect in ferromagnetic Ni-Mn-Sn alloys.

The magnetocaloric effect (MCE) in paramagnetic materials has been widely used for attaining very low temperatures by applying a magnetic field isothermally and removing it adiabatically. The effect can also be exploited for room-temperature refrigeration by using giant MCE materials. Here we report on an inverse situation in Ni-Mn-Sn alloys, whereby applying a magnetic field adiabatically, rather than removing it, causes the sample to cool. This has been known to occur in some intermetallic compounds, for which a moderate entropy increase can be induced when a field is applied, thus giving rise to an inverse magnetocaloric effect. However, the entropy change found for some ferromagnetic Ni-Mn-Sn alloys is just as large as that reported for giant MCE materials, but with opposite sign. The giant inverse MCE has its origin in a martensitic phase transformation that modifies the magnetic exchange interactions through the change in the lattice parameters.

Alloys↗
PubMed2004

Inverse relationship between ER-beta and SRC-1 predicts outcome in endocrine-resistant breast cancer.

The oestrogen receptor (ER) interacts with coactivator proteins to modulate genes central to breast tumour progression. Oestrogen receptor is encoded for by two genes, ER-alpha and ER-beta. Although ER-alpha has been well characterized, the role of ER-beta as a prognostic indicator remains unresolved. To determine isoform-specific expression of ER and coexpression with activator proteins, we examined the expression and localisation of ER-alpha, ER-beta and the coactivator protein steroid receptor coactivator 1 (SRC-1) by immunohistochemistry and immunofluorescence in a cohort of human breast cancer patients (n=150). Relative levels of SRC-1 in primary breast cultures derived from patient tumours in the presence of beta-oestradiol and tamoxifen was assessed using Western blotting (n=14). Oestrogen receptor-beta protein expression was associated with disease-free survival (DFS) and inversely associated with the expression of HER2 (P=0.0008 and P<0.0001, respectively), whereas SRC-1 was negatively associated with DFS and positively correlated with HER2 (P<0.0001 and P<0.0001, respectively). Steroid receptor coactivator 1 protein expression was regulated in response to beta-oestradiol or tamoxifen in 57% of the primary tumour cell cultures. Protein expression of ER-beta and SRC-1 was inversely associated (P=0.0001). The association of ER-beta protein expression with increased DFS and its inverse relationship with SRC-1 suggests a role for these proteins in predicting outcome in breast cancer.

Adult↗
PubMed1999

Inverse agonist activities of beta-adrenoceptor antagonists in rat myocardium.

1. Negative inotropic effects of several beta-adrenoceptor (betaAR) antagonists on electrically-stimulated right atria, left atria, right ventricles and left ventricular papillary muscles from reserpine-treated rats were used as a measure of their inverse agonist activities. 2. Beta1AR antagonists acebutolol, atenolol and metoprolol, beta2AR antagonist ICI-181,551 and nonselective betaAR antagonists alprenolol, nadolol, propranolol and timolol produced negative inotropic effects, which were most marked on the right atria. 3. The nonselective betaAR antagonist pindolol did not exhibit inverse agonist activity but inhibited the negative inotropic activities of ICI-118,551, atenolol and propranolol. 4. The negative inotropic effects of lidocaine, nifedipine and pentobarbitone were similar on all the four myocardial preparations. 5. The positive inotropic efficacy of salbutamol on right and left atria but not on right ventricles and papillary muscles was comparable to that of isoprenaline. The antagonist activity of ICI-118,551 against isoprenaline was greater on right atria than on other cardiac regions. 6. Beta1AR proteins were expressed in all regions of the heart but of beta2AR were primarily localized in the right atrium. 7. It is concluded that beta2AR play a greater role in right atria than in other cardiac regions and almost all betaAR antagonists behave as inverse agonists.

Adrenergic beta-Agonists↗
PubMed2001

Differential modulation by GTPgammaS of agonist and inverse agonist binding to h5-HT(1A) receptors revealed by [3H]-WAY100,635.

1. The interaction of serotonergic ligands at human (h) 5-HT(1A) receptors expressed in Chinese hamster ovary cells was examined with the selective 'neutral' 5-HT(1A) antagonist [(3)H]-WAY100,635. Its binding was saturable (K(D)=0.056 nM) with a B(max) (3.65 pmol mg(-1)) significantly higher than that of two other selective 5-HT(1A) radioligands: the partial agonist, [(3)H]-S15535 (2.77 pmol mg(-1)) and the agonist, [(3)H]-8-OH-DPAT (2.02 pmol mg(-1)). 2. The influence of GTPgammaS (100 microM) on the binding affinity of 15 serotonergic agonists, partial agonists, antagonists and inverse agonists was investigated in competition binding experiments with [(3)H]-WAY100,635. 3. Agonists, including 5-HT, 8-OH-DPAT and buspirone, displayed biphasic isotherms which shifted to the right in the presence of GTPgammaS. In contrast, isotherms of the inverse agonists, methiothepin, (+)butaclamol and spiperone, were shifted to the left in the presence of GTPgammaS. Unlabelled WAY100,635 was the only ligand that was unaffected by GTPgammaS, consistent with 'neutral' antagonist properties. 4. The magnitude of affinity changes induced by GTPgammaS for 13 ligands was highly correlated (r = 0.98) with their efficacy (positive and negative) previously determined by [(35)S]GTPgammaS binding. 5. In contrast, the napthylpiperazine derivative and high efficacy agonist, S14506, displayed only a modest GTPgammaS shift, in accordance with previous indications of 'atypical' binding properties of this ligand. A further full agonist, S14671, which is chemically closely-related to S14506, also displayed a minimal GTPgammaS shift, underpinning this observation. 6. In conclusion, [(3)H]-WAY100,635 constitutes a useful neutral antagonist radioligand for the characterization of drug actions at h5-HT(1A) receptors. GTPgammaS-induced affinity changes of agonist and inverse agonist competition isotherms generally correlate well with ligand efficacy, with the notable exception of two chemically-similar agents, S14506 and S14671, which are efficacious agonists, yet relatively insensitive to h5-HT(1A) receptor/G-protein coupling changes.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2005

Anxiogenic properties of an inverse agonist selective for alpha3 subunit-containing GABA A receptors.

Alpha3IA (6-(4-pyridyl)-5-(4-methoxyphenyl)-3-carbomethoxy-1-methyl-1H-pyridin-2-one) is a pyridone with higher binding and functional affinity and greater inverse agonist efficacy for GABA(A) receptors containing an alpha3 rather than an alpha1, alpha2 or alpha5 subunit. If doses are selected that minimise the occupancy at these latter subtypes, then the in vivo effects of alpha3IA are most probably mediated by the alpha3 subtype. Alpha3IA has good CNS penetration in rats and mice as measured using a [(3)H]Ro 15-1788 in vivo binding assay. At doses in rats that produce relatively low levels of occupancy (12%) in the cerebellum (i.e. alpha1-containing receptors), alpha3IA (30 mg kg(-1) i.p.), like the nonselective partial inverse agonist N-methyl-beta-carboline-3-carboxamide (FG 7142), not only caused behavioural disruption in an operant, chain-pulling assay but was also anxiogenic in the elevated plus maze, an anxiogenic-like effect that could be blocked with the benzodiazepine antagonist Ro 15-1788 (flumazenil). Neurochemically, alpha3IA (30 mg kg(-1) i.p.) as well as FG 7142 (15 mg kg(-1) i.p.) increased the concentration of the dopamine metabolite 3,4-dihydroxyphenylacetic acid in rat medial prefrontal cortex by 74 and 68%, respectively, relative to vehicle-treated animals, a response that mimicked that seen following immobilisation stress. Taken together, these data demonstrate that an inverse agonist selective for GABA(A) receptors containing an alpha3 subunit is anxiogenic, and suggest that since alpha3-containing GABA(A) receptors play a role in anxiety, then agonists selective for this subtype should be anxiolytic.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2005

Physical activity is inversely related to waist circumference in 12-y-old French adolescents.

BACKGROUND AND OBJECTIVE: Waist circumference (W) has been shown to be a good predictor of cardiovascular risk. The aim of this study was to investigate whether physical activity (PA) is related to W in adolescents as previously shown in adults. DESIGN AND SUBJECTS: Cross-sectional population-based survey of 2,714 12-y-old adolescents from the eastern part of France. MEASUREMENTS: Body mass index (BMI) and W were measured. Structured PA, active commuting to and from school and sedentary activities (SED), for example television viewing, computer/video games and reading and different potential confounders (dietary habits, parental overweight, family annual income tax and educational level) were assessed by a questionnaire. RESULTS: The adolescents had a mean BMI of 19.0+/-3.4 kg/m2, and 20.2% of them were overweight, with no gender difference. Boys had a greater W than girls (67.6+/-9.1 vs 65.7+/-8.9 cm, P<0.0001). In all, 42% of the girls and 25% of the boys did not practice any structured PA outside school and less than 40% of the adolescents commuted actively to school more than 20 min/day. About one-third of the adolescents devoted more than 2 h/day to SED. In univariate analyses, BMI was negatively associated with structured PA but significantly only for girls (P<0.01) and positively associated with SED for both genders (P<0.0001 for girls, P<0.01 for boys). W was negatively associated with structured PA and positively associated with SED both in girls (P<0.0001 and P=0.03, respectively) and boys (P<0.01 and P=0.08, respectively). Multiple general linear models show that SED is associated with BMI, independently of structured PA, in both genders. On the other hand, structured PA was inversely associated with W, independently of SED. The inverse relation between structured PA and W persisted after additional adjustment on BMI, with a greater effect of PA for the adolescents with higher BMI. CONCLUSIONS: In 12-y-old adolescents, structured PA is inversely associated with W, an indicator of total adiposity but also more specifically of abdominal fat. This suggests that PA may have a beneficial effect on youth metabolic and cardiovascular risks, in particular in the presence of overweight..

Abdomen↗