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At least 163 records · Page 9Linked to original sources
PubMed1979

Classification of drugs by discriminant analysis using fragment molecular connectivity values.

An investigation was made into the use of linear and quadratic discriminant analysis, along with K nearest-neighbor analysis, in the classification of a set of 51 compounds which were divided into five therapeutic categories. By superimposing each compound on a pattern structure, as first proposed by Cammarata, eight positions were assigned on the molecule. Each position was coded with the numerical value of a descriptor index. Relative molar refraction, which was the index used by Cammarata, was compared with a number of molecular connective indices. For each of the indices studied, it was found that only four of the eight positions contributed significantly to between-class differences. It was also found that first-order molecular connectivity, calculated as the sum of the contributions of each of the bonds joining a given position, resulted in consistently fewer misclassifications as compared with the other indices. Using first-order molecular connectivity, validation procedures were performed on the original set of compounds, on random samples drawn from this set, and on a set of ten compounds not included in the analysis. The results obtained were highly data dependent, but they, nevertheless, suggest that molecular connectivity indices should prove useful in structural classification procedures.

Analysis of Variance↗
PubMed1990

[A comparison of statistical methods for quantal analysis in computer and physiological experiments].

Amplitude distributions of postsynaptic potentials were simulated in computer experiments on the basis of binomial statistics. Influences of the sample size (N) and noise standard deviation (Sn) on the determination of the quantal content (m) and quantal size (v) were studied. Four methods of the quantal parameter estimation were modified and used: histogram, variance, failure and combined method. Three last methods gave satisfactory estimations (within +/- 10%) at N = 500-1000 and Sn less than 2v. The histogram method was adequate at Sn less than or equal to v. Similar results were obtained at N = 50-200, when the experiment was repeated about ten times. Applicability of similar methods was confirmed by the analysis of an intracellular record of inhibitory postsynaptic potentials (N = 1333) from the sensorimotor cortex of rabbit.

Action Potentials↗
PubMedDate not supplied

Three-dimensional computerized tomography: a quantum leap in diagnostic imaging?

Ever since the discovery of radium by Madame Curie, men and women of vision and science have labored to improve radiation technology. Over a period of approximately 85 years, we have gone from this initial discovery to three-dimensional computerized transmission tomography; one of the latest techniques in modern day x-ray imaging. Its uses are vast and unparalleled in many facets of medicine and surgery, outlining pathology as never before seen, and possibly, never before completely understood. Three-dimensional computerized tomography is rapidly gaining popularity in cross-sectional imaging of the foot and ankle. It has proven invaluable in elucidating osseous and soft tissue pathology. Abnormalities of the musculoskeletal system that exhibit complex anatomy are often difficult to interpret using standard radiographic techniques. Overall, three-dimensional computerized tomography has established itself as a means by which clinicians may appreciate the three-dimensional disposition of anatomy and disease.

Ankle↗
PubMed1986

Estimating the time course of evoked quantal release at the frog neuromuscular junction using end-plate current latencies.

The use of end-plate current (e.p.c.) latency measurements to estimate the time course of the stochastic probabilistic process governing evoked release was investigated in the sciatic nerve-sartorius muscle preparation of the frog, Rana pipiens. We also examined the possibility that the release of a quantum depresses or enhances the subsequent release of additional quanta. Muscle end-plates were voltage clamped at 3-4 degrees C. Quantal release was restricted to a short, or localized, region of the nerve terminal using Ca2+-free, EGTA Ringer solution and a Ca2+-filled micropipette. The number of e.p.c.s containing 0, 1, 2, etc. quanta were totalled and compared to numbers predicted using Poisson's theorem. The differences between the actual and predicted numbers of events were not significant at the nineteen junctions studied (P less than 0.05). The latency of the first quantum observed in several hundred e.p.c.s was measured and used to calculate an estimate, alpha 1(t), of the time-dependent, probabilistic process, alpha (t), governing all evoked quantal release (Barrett & Stevens, 1972b). In three experiments, all quantal latencies were measured to obtain the actual alpha (t). The alpha 1(t) function gave an excellent approximation of alpha (t) (P greater than 0.2), in real and simulated latency data. The latency of the second quantum in the e.p.c.s was measured and used to provide another estimate, alpha 2(t), of alpha (t). The alpha 2(t) function was lower (depressed) during the first few milliseconds of the evoked release period, relative to alpha 1(t). The difference was significant (P greater than 0.01) in all experiments. Our measurement procedures were tested using computer-generated 'e.p.c.s' containing randomly occurring 'quanta'. These tests showed that the early depression was due to inadequate detection of the second quantum in the e.p.c.s. The effect of Sr2+ on evoked release was examined using double-barrelled pipettes containing 1 M-SrCl2 and CaCl2 solutions. The major result was that the durations of alpha 1(t) and alpha 2(t) were equally lengthened in Sr2+, relative to Ca2+.

Animals↗
PubMed1993

Mechanisms of post-traumatic seizures: a quantum pharmacological analysis of the molecular properties of an epileptogenic focus following iron-induced membrane peroxidation.

Late post-traumatic epilepsy following severe head trauma has been well documented. While there is increasing evidence suggesting that iron-induced lipid peroxidation of neural membranes may accompany cerebral haemorrhage, the pathogenic processes of post-traumatic epileptogenesis remain unknown. Furthermore, the effective prophylactic use of standard anticonvulsant drugs is unsubstantiated. The rational design of therapeutic agents specific for the prevention and treatment of post-traumatic epilepsy hinges on understanding the molecular membrane events at the epileptogenic focus. This study employs the techniques of theoretical quantum pharmacology to provide a structural analysis of neural phospholipid membranes, investigating changes in membrane integrity at the epileptogenic focus as the molecular basis for seizure activity. Molecular mechanics calculations and molecular dynamics simulations were used to model the biochemical events of the epileptogenic focus. We predict that applications of quantum pharmacological techniques to model biochemical events may provide an understanding of proconvulsive pathogenic mechanisms in post-traumatic epilepsy.

Aspartic Acid↗
PubMed1991

Fractal and chaotic dynamics in nervous systems.

The chaotic aspects of brain structure and dynamics have been discussed. The relation of chaos to fractal processes in the brain from the neurosystems level down to the molecule has been explored. It is found that chaos appears to play an integral, though not necessarily exclusive role in function at all levels of organization from the neurosystems to the molecular and quantum levels. An interesting consequence involving the possible interface between chaotic dynamics and quantum physics has been discussed because of its potential significance is resolving several of the most intractable conceptual problems to do with computability, the brain and the mind (Blakemore and Greenfield, 1987; Hooper and Teresi, 1987; Rose, 1973; Searle, 1979; Penrose, 1986, 1989).

Action Potentials↗
PubMed1985

Profiles of evoked release along the length of frog motor nerve terminals.

In order to determine the relative probability of evoked transmitter release from different parts of frog motor nerve terminals, a technique has been developed in which single quantum end-plate potentials (e.p.p.s) are recorded by two intracellular electrodes, located at opposite ends of identified junctions. The log of the ratio of the amplitudes recorded simultaneously at the two electrodes is a linear function of the distance of the site of origin of the event from each of the two electrodes. Using online computer data acquisition and analysis, and current pulses at known locations for spatial calibration, it is possible to localize the site of single quantum e.p.p.s to within +/- 10-20 micron. Using the frog cutaneous pectoris neuromuscular preparation and a low calcium, high magnesium Ringer solution to ensure mostly single quantum events and failures, several thousand responses were recorded from each junction, allowing construction of a profile of the numbers of single quantum events arising from each portion of the junction. By comparison of junctional morphology and release profiles, it is possible to construct a probability of release per unit length profile for the entire junction. This technique has several advantages over localization of release events by measurements of extracellular synaptic currents. It was found that, for most junctions, the central 60-90% of the terminal exhibited relatively uniform probability of release, with highest levels typically near the point where the axon first contacted the muscle fibre, or in regions with many short terminal branches. However, no instances have been found in which a small region of terminal (10% or less) showed extraordinarily high release levels (30-50% of the total release from the junction). Characteristically, but not invariably, there is reduced release near the ends of terminal branches, especially the longer branches, where release per unit length could be as little as 5-10% of that in proximal portions. Some junctions had large regions of terminal that released very little transmitter. These also showed multiple myelineated axonal inputs, and may have been polyneuronally innervated junctions in which one of the inputs was much weaker than the other.

Animals↗
PubMed1995

Theory of electrostatic interactions in macromolecules.

In the past year, substantial progress has been made in the modeling of electrostatic interactions in biomolecules. This review highlights advances in the following areas: first, the efficient computation of long-range electrostatic interactions in detailed molecular simulations; second, the application of the Poisson-Boltzmann electrostatic model in conformational analysis; third, the application of the Poisson-Boltzmann model in quantum chemistry calculations; fourth, the development of atomic parameters; and finally, the modeling of ionization equilibria in proteins.

Computer Simulation↗
PubMedDate not supplied

[Cell molecular computer. VII. Cell biophysics and realistic or information physics (1)].

Living organisms measure many parameters in order to have orientation in the outer medium. That is why biophysics cannot use the ordinary laws of physics and must take into account the influence on the phenomena to be studied not only of a measurement but also of a calculation process in the real physical and biophysical device predicting the future. Science taking into account the effects of the calculating process-realistical or informative (RI) physics-has different (laws) for different times, distances and numbers of measuring and predicting parameters. RI-physics deals with unreproducible events and considers only such time intervals and distances for which the prediction can be made on the basis of earlier measurements and calculations according to the laws with optimal difficulty. It is suggested that the living cell uses the laws which are close to these optimal (limiting) laws of RI-physics. Physics and quantum mechanics can be considered as a limiting case of RI-physics. In this case values of distances and times are large enough and the number of simultaneously measured independent parameters is such that the heat effect of the calculating device would become negligible. Molecular cell computer (MCC) [I] cannot calculate the interaction of a great quantity of different molecules, using the equations of quantum mechanics because the expense of the (price of action) would be very large and both MCC and the surrounding world could change.

Cell Physiological Phenomena↗
PubMed1976

Analysis of pairs of individual Ia-E.P.S.P.S in single motoneurones.

1. Recordings of individual e.p.s.p.s evoked by the action of single medial gastrocnemius Ia fibres have been made from medial gastrocnemius motoneurones. In many motoneurones the action of two Ia fibres has been observed and the properties of the e.p.s.p.s compared. 2. For sixty-three pairs of averaged e.p.s.p.s, each from the same motoneurone, the ratio of half-widths was plotted against the ratio of rise times. These results were compared with theoretical values derived from the Rall compartmental model. It was found that variations in synaptic current time courses and differences in the termination of localized synaptic terminals were not sufficient to account for all the data. 3. Amplitude and rise time were inversely related but the correlation coefficient was very low. For pairs of e.p.s.p.s in the same motoneurone the e.p.s.p. with the fast rise time was larger than that with the slow rise time in forty-eight of sixty-three cases. 4. In a given motoneurone individual e.p.s.p.s evoked by the action of different Ia fibres did not vary greatly in amplitude. The ratio of peak amplitudes was less than 3 for 86% of the pairs of e.p.s.p.s examined, and the maximum was 4-8. 5. Amplitude histograms were constructed for individual e.p.s.p.s at thirty-three synapses. Twenty-two of them could be shown to satisfy the Poisson law. The others satisfied the binomial law or neither. 6. Within a given motoneurone the amplitude of an e.p.s.p. is closely related to the mean number of quanta released but not to the amplitude of the unit e.p.s.p. produced by the action of a single quantum of transmitter.

Animals↗
PubMedDate not supplied

[Organization of the background activity of rabbit visual cortex neurons].

Algorithm of calculation of consitent approximation to real entropy and redundancy which helps to understand the connection of two or more related states was realized by means of electronic computer BECM-6. Different laws of changes of information estimates dependeing on the number of approximation and the pitch of temporary quantum of messages corresponded to every type of cell impulsation of rabbits' visual cortex--arrhithimical, grouping and regular. The connections between the laws of impulse succession organization and some of its parameters were revealed. The results of studying the models of casual and deterministic pulse trains were compared.

Animals↗
PubMedDate not supplied

Software tools and databases for bacterial systematics and their dissemination via global networks.

The dynamic expansion of the taxonomic knowledge base is fundamental to further developments in biotechnology and sustainable conservation strategies. The vast array of software tools for numerical taxonomy and probabilistic identification, in conjunction with automated systems for data generation are allowing the construction of large computerised strain databases. New techniques available for the generation of chemical and molecular data, associated with new software tools for data analysis, are leading to a quantum leap in bacterial systematics. The easy exchange of data through an interactive and highly distributed global computer network, such as the Internet, is facilitating the dissemination of taxonomic data. Relevant information for comparative sequence analysis, ribotyping, protein and DNA electrophoretic pattern analysis is available on-line through computerised networks. Several software packages are available for the analysis of molecular data. Nomenclatural and taxonomic 'Authority Files' are available from different sources together with strain specific information. The increasing availability of public domain software, is leading to the establishment and integration of public domain databases all over the world, and promoting co-operative research projects on a scale never seen before.

Amino Acid Sequence↗
PubMed1996

Computed radiography X-ray exposure trends.

RATIONALE AND OBJECTIVES: Computed radiography provides correct optical density on film, independent of the incident radiation exposure, but it can result in under- or overexposure of the imaging plate. In the current study, we evaluated the radiation exposure trends of computed radiography over a 2-year period for portable chest examinations to determine and compare the radiographic techniques of the computed radiography system relative to conventional screen-film detectors. METHODS: A Fuji computed radiography system was interfaced to a digital workstation to track system usage and examination demographics, including examination type and sensitivity number. Hard-copy films were used for diagnosis. The sensitivity number, a value inversely related to incident exposure on the imaging plate, was used to determine whether the proper techniques were used by the technologists. RESULTS: The initial use of the computed radiography system revealed a broad distribution of exposures being used; complaints regarding noisy films (e.g., underexposure) resulted in subsequent overexposure for a significant number of films. A quality-control audit indicating excessive exposure resulted in educational feedback and a tighter distribution of exposures within the optimal range as determined by our radiologists. The average technique was approximately equivalent to a 200-speed system. CONCLUSION: Computed radiography provides excellent dynamic range and rescaling capabilities for proper film optical density, and thus fewer repeat examinations. However, underexposure results in suboptimal image quality that is related to excessive quantum mottle. Overexposure requires film audits to limit unnecessary radiation exposure. In general, the optimal exposures are achieved with approximately 1.5-2 times the incident detector exposure of a 400-speed rare-earth system. The ability of computed radiography to reduce radiation exposure is unlikely when compared with a typical rare-earth screen-film combination (400 speed) in terms of adequate image quality for the diagnosis of subtle, low-contrast findings. For certain diagnostic procedures (e.g., nasogastric tube placement verification), lower exposures can be tolerated.

Humans↗
PubMed1996

Structural and quantum chemical factors affecting mutagenic potency of aminoimidazo-azaarenes.

A set of 16 mutagenic aminoimidazo-azaarenes, including four that have been isolated from cooked foods and identified as bacterial mutagens and rodent carcinogens, was selected from a larger series previously published [Hatch et al. (1991): Environ Mol Mutagen 17:4-19] for an in-depth structure-activity study using computational methods. Structural features believed to affect mutagenic potency were tabulated. Molecular orbital energies and other electronic properties of these compounds were calculated using Huckel, semiempirical AM1, and ab initio quantum mechanical methods. Factor interrelationships were studied by multiple linear regression and canonical correlation analyses. Our goal was an improved understanding of the chemical basis of mutagenicity for this class of heterocyclic amines. The major findings were as follows: 1) mutagenic potency is related to the size of the aromatic ring system; 2) potency is enhanced by the presence and location of an N-methyl group; 3) potency is enhanced by addition of ring nitrogen atoms in pyridine, quinoline, and quinoxaline configurations; 4) potency is inversely related to the energy of the LUMO (lowest unoccupied molecular orbital) of the parent amines; 5) potency is directly, though weakly, related to the LUMO energy of the derived nitrenium ions; and 6) the calculated thermodynamic stability of the nitrenium ions (relative to the parent amine) is directly correlated with nitrenium LUMO energy and with the negative charge on the exocyclic nitrogen atom. Although this study raises several intriguing issues relating mutagenicity to chemical properties, further study will be required to determine the plausibility of the nitrenium ion as the ultimate mutagen for binding to DNA.

Benzimidazoles↗
PubMed1994

Influence of slight sequence changes on the free energy of a single stranded ribonucleic acid molecule.

Single-stranded ribonucleic acid molecules take a variety of secondary structures. The free energy (g) of a given secondary structure of a molecule is calculated from the Boltzmann weighted summation over the states of this molecule taking this secondary structure. Likewise, the free energy (G) of a molecule is calculated from the summation over the states of this molecule, which takes various secondary structures. The g-value can be evaluated by Salser's method (1977, Cold Spring Harbor Symp. Quantum Biol. 42, 985-1002). By use of these values, the G-value can also be obtained. Computer studies utilizing this method reveal that there is a particular class of molecules whose G-values tend to increase when the sequences are slightly changed. As far as we examined, such molecules take few secondary structures that fulfill the following two conditions simultaneously: (i) The g-value is close to that of the optimal secondary structure. (ii) The structure is very different from the optimal secondary structure. Here, the optimal secondary structure means the one with the lowest g-value among all the secondary structures taken by the molecule.

Base Sequence↗
PubMed1990

Theoretical calculations on calcium channel drugs: is electron transfer involved mechanistically?

Theoretical studies were done on calcium channel drugs in order to gain insight into the mode of action. Empirical force field calculations with nifedipine, a calcium channel antagonist, indicate that the E-conformation at the ring juncture is lower in energy than the Z-conformation. This energy difference is only 0.2 kcal/mol when the esters in the 3- and 5-positions of the dihydropyridine (DHP) ring are both synperiplanar (sp, sp). Molecular orbital calculations on the ground and excited states in the Z-conformation with the esters in the (ap, sp) conformation show a low lying excited state with substantial intramolecular electron transfer (ET) character. This excited state is only 1.8 eV higher in energy than the ground state and corresponds to a transfer of approximately 0.3 electron from the DHP ring to the nitrobenzene moiety. We suggest that ET may play an important role in the mechanism of action, either intramolecular or, as previously proposed, intermolecular, along with lipophilicity and steric effects.

Calcium Channel Blockers↗