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I claim that Wittgenstein's reference to Hertz's "dynamical models" at 4.04 in the Tractatus provides evidence for the view that the Tractatus does not explain the sense of propositions by offering an account of the fundamental structure of reality. Just as Hertz's dynamical models capture what all mechanical descriptions of the same system have in common, so Tractarian analysis captures what all propositions that express the same sense have in common, and in neither case is there a need to appeal to an underlying ontology. [ABSTRACT FROM AUTHOR] more...

Heinrich Hertz dedicated the last four years of his life to a systematic reformulation of mechanics. One of the main issues that troubled Hertz in the customary formulation of mechanics was a 'logical obscurity' in the notion of force. However, it is unclear what this logical obscurity was, hence it is unclear how Hertz took himself to have avoided it. In this paper, I argue that a subtle ambiguity in Newton's original laws of motion lay at the basis of Hertz's concerns; an ambiguity which led to the development of two slightly different notions of force. I then show how Hertz avoided this ambiguity by deriving a unitary notion of force, thus dispelling the obscurity that lurked in the customary representation of mechanics. [ABSTRACT FROM AUTHOR] more...

Fluctuations in the second harmonic intensity were observed in a number of insoluble amphilphiles spread at an air/aqueous interface. The fluctuations, which depend on the polarization of both the incident light and the second harmonic light generated, indicate a new phase transition for which the orientation of the head group is the order parameter. It is found that the phase transition occurs in certain long chain aromatic species but not in others of the same chain length with different head groups. The phase transition is identified as a weak first order transition. Agreement is obtained with a modified Landau–Ginzburg equation in which the chain–chain interactions provide a friction for the motions of the head groups. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR] more...

In our efforts to examine the validity of the Kramers’ equation, the rate constants of the excited state isomerization of 1,1’-binaphthyl in n-alkane solvents were measured at room temperature using picosecond spectroscopy. These data, and data measured previously in n-alcohols, were compared with Kramers’ model using two forms for the friction. When a hydrodynamic model for the friction was used, good agreement was found for the alcohol data only. When the isomerization friction is assumed to scale linearly with the friction for overall reorientational motion, we find excellent agreement for both the alcohol and alkane solvents. In addition, the friction in alkanes is found to be considerably larger than that of alcohols of comparable viscosity. This provides a direct indication that the molecular aspects of the solute–solvent interaction play a role in the barrier crossing process. [ABSTRACT FROM AUTHOR] more...

The rates of optically induced conformational changes of excited state 1,1’-binaphthyl in a series of alcohol solvents were measured by a picosecond laser technique. Excellent agreement with experiment is found for the Kramers model for both the intermediate and high friction regimes using a frequency independent friction coefficient evaluated from classical hydrodynamics. This is the first observation of Kramers behavior in the intermediate friction regime and indicates that deviations from Kramers behavior is not a universal phenomenon in the conformational dynamics of flexible molecules in solution. It also emphasizes the possibility that the observed deviations from the Kramers model can be due to effects other than non-Markovian friction. [ABSTRACT FROM AUTHOR] more...

At the time of Heinrich Hertz's premature death in 1894, he was regarded as one of the leading scientists of his generation. However, the posthumous publication of his treatise in the foundations of physics, Principles of Mechanics , presents a curious historical situation. Although Hertz's book was widely praised and admired, it was also met with a general sense of dissatisfaction. Almost all of Hertz's contemporaries criticized Principles for the lack of any plausible way to construct a mechanism from the “hidden masses” that are particularly characteristic of Hertz's framework. This issue seemed especially glaring given the expectation that Hertz's work might lead to a model of the underlying workings of the ether. In this paper I seek an explanation for why Hertz seemed so unperturbed by the difficulties of constructing such a mechanism. In arriving at this explanation, I explore how the development of Hertz's image-theory of representation framed the project of Principles . The image-theory brings with it an austere view of the “essential content” of mechanics, only requiring a kind of structural isomorphism between symbolic representations and target phenomena. I argue that bringing this into view makes clear why Hertz felt no need to work out the kinds of mechanisms that many of his readers looked for. Furthermore, I argue that a crucial role of Hertz's hypothesis of hidden masses has been widely overlooked. Far from acting as a proposal for the underlying structure of the ether, I show that Hertz's hypothesis ruled out knowledge of such underlying structure. [ABSTRACT FROM AUTHOR] more...

We develop a model to probe the relativeorientation of two second-orderpolarizable daunomycin molecules that are intercalated into a DNAduplex using optical second-harmonic (SH) generation. The SH fieldgenerated by the daunomycin molecules interfere with each other. Becausethe interference depends on the relative orientation of the daunomycinmolecules, we can control the interference by changing the numberof base pairs separating them. The relative orientation changes asthe number of base pairs separating them, multiplied by 36°,which is the twist angle between neighboring base pairs. In this paper,we derive a set of relationships between the relative angle of themolecules and the nonlinear susceptibility elements, and we calculatethe SH field generated by the DNA/molecular-pair complex attachedto an isotropic dielectric sphere. Calculations reveal that the SHintensity varies periodically with the relative orientation of thetwo chromophores in the plane perpendicular to the helical axis. Thepredicted periodicity is in close agreement with experimental results.Structural changes induced by foreign molecules binding to DNA willchange the relative orientation of the two chromophores and therebychange the SH interference pattern. We discuss the potential of thisSH interference method in providing a new way to probe structuralchanges induced by the formation of biomolecule complexes. An importantfeature of the method is that it is label-free, that is, the bindingmolecule, in this case, daunomycin, is not tagged. [ABSTRACT FROM AUTHOR] more...

Abstract: Quality assurance has become an integral part of surgical pathology. Despite the development of interdisciplinary quality systems, however, the means for objective analysis in surgical pathology are limited. Immunohistostaining is a multi-factorial procedure that depends on the quality of reagents and antibodies employed in the process and on technical methodology. In the present study, we aim to establish a straightforward procedure for objective quality evaluation of the components involved in immunohistostaining. The quality of two of these components, the primary antibody and the automated staining device, was assessed by employing each component from two different sources, one serving as the test substance and the second as the reference. Assessment was performed by at least two pathologists in a blinded fashion using pre-established quality criteria and scores. The quality analysis of two automated devices revealed a significant difference between the reference and tested devices (3.5±1.7 and 4.2±1.5, respectively, P>0.05), while the analysis of two selected antibodies did not reveal any statistical difference. The described method provided objective quality assessment of selected components affecting immunohistostaining by elaborating numeric values that enabled statistical analysis. This approach is applicable to any given component in various surgical pathology procedures. [Copyright &y& Elsevier] more...

In mammalian cortex, most excitatory inputs occur on dendritic spines, avoiding dendritic shafts. Although spines biochemically isolate inputs, nonspiny neurons can also implement biochemical compartmentalization; so, it is possible that spines have an additional function. We have recently shown that the spine neck can filter membrane potentials going into and out of the spine. To investigate the potential function of this electrical filtering, we used two-photon uncaging of glutamate and compared the integration of electrical signals in spines vs. dendritic shafts from basal dendrites of mouse layer 5 pyramidal neurons. Uncaging potentials onto spines summed linearly, whereas potentials on dendritic shafts reduced each other's effect. Linear integration of spines was maintained regardless of the amplitude of the response, distance between spines (as close as <2 μm), distance of the spines to the soma, dendritic diameter, or spine neck length. Our findings indicate that spines serve as electrical isolators to prevent input interaction, and thus generate a linear arithmetic of excitatory inputs. Linear integration could be an essential feature of cortical and other spine-laden circuits. [ABSTRACT FROM AUTHOR] more...

The way that enzymes respond to temperature is fundamental to many areas of biotechnology. This has long been explained in terms of enzyme stability and catalytic activation energy, but recent observations of enzyme behaviour suggest that this picture is incomplete. We have developed and experimentally validated a new model to describe the effect of temperature on enzymes; this model incorporates additional fundamental parameters that enable a complete description of the effects of temperature on enzyme activity. In this article, we consider the biotechnological implications of this model in the areas of enzyme engineering, enzyme reactor operation and the selection and/or screening of useful enzymes from the environment. [Copyright &y& Elsevier] more...

The article investigates the aqueous interfaces of nano-and microparticle systems. Applications of the interface-selective methods of second harmonic and sum frequency spectroscopy to the investigation equilibrium and time-dependent properties of interfaces are increasing at an explosive rate. The aqueous interfaces of nano-and microsize particles are suspended in aqueous solutions. more...

Background : A variety of molecules produced by both tumor cells and normal cells reduce the activity of lymphokine-activated killer (LAK) cells. We tested the possible cross-regulation of mel-624 melanoma cells and adherent peripheral blood mononuclear cells (PBMCs) in affecting LAK cell activity. Methods : PBMC adherent cells were cultured together with mel-624 melanoma cells. Supernatant was transferred to a 4-day LAK cells generation culture consisted of PBMC nonadherent cells and interleukin-2. LAK cytotoxic activity was tested in a 4-hour assay against Daudi tumor cells prelabeled with sodium 51 chromate. Results : The supernatant produced within the first 48 hours of mixed mel-624 melanoma cell and adherent PBMC culture substantially (by 69 percent) reduced the generation of LAK cells, whereas the supernatant from either tumor culture or adherent PBMC culture had no effect. The inhibitory effect was manifested on the generation of LAK cells when autologous nonadherent cells were cultured with 1,000 units/ml IL-2, but there was no effect on mature LAK cell cytotoxic activity. Inhibition of LAK cell generation was partially dependent on protein synthesis and was not mediated by transforming growth factor ß (TGF- ß ). Conclusion : Our results point toward the production of soluble, yet unidentified proteins, in mixed tumor-adherent PBMC cultures, which substantially reduced the induction of LAK cells in culture. [ABSTRACT FROM AUTHOR] more...

This work presents a novel study of the notion of facial attractiveness in a machine learning context. To this end, we collected human beauty ratings for data sets of facial images and used various techniques for learning the attractiveness of a face. The trained predictor achieves a significant correlation of 0.65 with the average human ratings. The results clearly show that facial beauty is a universal concept that a machine can learn. Analysis of the accuracy of the beauty prediction machine as a function of the size of the training data indicates that a machine producing human-like attractiveness rating could be obtained given a moderately larger data set. [ABSTRACT FROM AUTHOR] more...

Two established thermal properties of enzymes are the Arrhenius activation energy and thermal stability. Arising from anomalies found in the variation of enzyme activity with temperature, a comparison has been made of experimental data for the activity and stability properties of five different enzymes with theoretical models. The results provide evidence for a new and fundamental third thermal parameter of enzymes, Teq, arising from a subsecond timescale-reversible temperature-dependent equilibrium between the active enzyme and an inactive (or less active) form. Thus, at temperatures above its optimum, the decrease in enzyme activity arising from the temperature-dependent shift in this equilibrium is up to two orders of magnitude greater than what occurs through thermal denaturation. This parameter has important implications for our understanding of the connection between catalytic activity and thermostability and of the effect of temperature on enzyme reactions within the cell. Unlike the Arrhenius activation energy, which is unaffected by the source (’evolved’) temperature of the enzyme, and enzyme stability, which is not necessarily related to activity, Teq is central to the physiological adaptation of an enzyme to its environmental temperature and links the molecular, physiological, and environmental aspects of the adaptation of life to temperature in a way that has not been described previously. We may therefore expect the effect of evolution on Teq with respect to enzyme temperature/activity effects to be more important than on thermal stability. Teq is also an important parameter to consider when engineering enzymes to modify their thermal properties by both rational design and by directed enzyme evolution. [ABSTRACT FROM AUTHOR] more...

In the present study, we analyzed the immunological characteristics of mononuclear cells (MNC) isolated from both neonatal umbilical cord blood (UCB) and maternal peripheral blood (MPB) during the delivery. The in vitro proliferative response of UCB T lymphocytes was significantly reduced compared to the maternal response to phytohemagglutinin A, pokeweed mitogen, and alloantigen stimulation, in correlation with the lower percentage of UCB than MPB lymphocytes, but not with that of B cells. The mean cytotoxic activity level of interleukin-2 (IL-2)-activated natural killer (NK) was higher in UCB than in MBP, whereas the percentage of CD56+ NK cell count was similar. Our results show differences in the immune reactivity of T and B lymphocytes from neonate and adult isolated under similar physiological conditions. [Copyright &y& Elsevier] more...

Reports on angiogenesis which is essential for tumor growth and metastases. Assessment of the number of endothelial cells in blood microvessels by immunohistostaining on paraffin-embedded tumor tissue sections using vascular endothelial growth factor; Establishment of murine sarcoma by the antitumor in vivo effect exerted by tumor necrosis factor alpha. more...

A novel method of estimating the kinetic parameters of Taq DNA polymerase during rapid cycle PCR is presented. A model was constructed using a simplified sigmoid function to represent substrate accumulation during PCR in combination with the general equation describing high substrate inhibition for Michaelis–Menten enzymes. The PCR progress curve was viewed as a series of independent reactions where initial rates were accurately measured for each cycle. Kinetic parameters were obtained for allele-specific PCR (AS-PCR) amplification to examine the effect of mismatches on amplification. A high degree of correlation was obtained providing evidence of substrate inhibition as a major cause of the plateau phase that occurs in the later cycles of PCR. [Copyright &y& Elsevier] more...

Target cells adsorbed in affinity separation processes need to be effectively recovered from the adsorption matrix once contaminating cell types have been removed. Although tangential flow can be used to generate detachment forces, the resultant dilution is excessive. In this study, three alternative detachment protocols have been assessed using a membrane-based adsorption surface.Back flushing buffer through the membrane to generate greater detachment forces was studied. However, at the maximum back flush velocity obtainable less than 50% of attached cells were removed and recovered cell concentrations were low.Controlled transmembrane delivery of hydrochloric acid as a non-specific eluent was also investigated. While this allowed complete recovery of cells the effective acid concentration was excessive. The upstream dilution required to maintain cell viability again leads to considerable dilution.Injection of air bubbles into the tangential flow stream to generate elevated detachment forces was found to be the most effective approach. Detachment was found to be a function of both number and size of bubbles. Under optimal conditions, 80% of attached cells can be removed to give a detached cell concentration of 108 cells ml−1. This leads to an essentially reagentless detachment protocol allowing the development of an isocratic affinity cell separator where cells can be attached, washed, and detached in the same buffer. [Copyright &y& Elsevier] more...

This paper presents a multidimensional CSG geometric modeller. It then shows how this modeller can be used to produce a compact representation of the complete configurationspace map of a mechanism composed of polyhedral parts. The map is derived directly from the three-dimensional geometric model that describes the mechanism, and allows more degrees of freedom than any other current system. Methods of exploring the map to give the kinematics of the mechanism will also be described and examples will be given. We will then go on to show how geometric constraints can be reformulated as a multidimensional CSG expression describing the constraints problem in a space similar to the configuration space above. Geometric constraints representing mechanisms will be described and the resulting mechanisms shown. Finally we will show how the two techniques, which are both coded using the same multidimensional modeller, can be combined. This allows parts of a machine that are known (such as slides and hinges) to be described explicitly using constraints, and parts that are unknown (such as interferences between moving parts) to be coded as a configuration-space map. The entire mechanism can then be simulated and its behaviour examined. [ABSTRACT FROM AUTHOR] more...

Employing cell fractionation with the aid of peanut agglutinin, it was found that at least two subpopulations of T cells are required for the generation of suppressor T lymphocytes in culture. The co-operation of these two subpopulations, the medullary and the cortical types of thymocytes, is required for the induction phase but it apparently plays no role in the expression of the suppressive effect. With the aid of genetic markers, it was found that the medullarytype, cortisone-resistant, PNA-negative T cell was the progenitor of the suppressor lymphocytes, while the cortical type cells performed an accessory (regulatory?) function. Finally, it was observed that allostimulation oft cells in culture gives rise to both 'helper' and suppressor cells. The generation of 'helper' lymphocytes requires allostimulation for less than 24 hr while the induction of suppressor cells requires a longer period of stimulation which leads in the end to predominance of the suppressor effect. [ABSTRACT FROM AUTHOR] more...

Human xanthine oxidase was purified from breast milk. The dehydrogenase form of the enzyme, which predominates in most mammalian tissues, catalyses the oxidation of NADH by oxygen, generating superoxide anion significantly faster than does the oxidase form. The corresponding forms of bovine enzyme behave very similarly. The steady-state kinetics of NADH oxidation and superoxide production, including inhibition by NAD, by the dehydrogenase forms of both enzymes, are analysed in terms of a model involving two-stage recycling of oxidised enzyme. Established inhibitors of xanthine oxidoreductases (allopurinol oxypurinol, amflutizole and BOF 4272), which block all other reducing substrates, were ineffective in the case of NADH. Diphenyleneiodonium, on the other hand, was a powerful inhibitor of NADH oxidation. The potential involvement of reactive oxygen species arising from NADH oxidation by xanthine oxidoreductase in ischaemia-reperfusion injury and other disease states, as well as in normal signal transduction, is discusssed. [ABSTRACT FROM AUTHOR] more...

Electronic energy transfer dynamics at the air/liquid interface have been studied by surface second harmonic techniques. The effects of dimensionality on the dynamics are discussed. [ABSTRACT FROM AUTHOR] more...

The ratio k cat/K M – often referred to as the ‘specificity constant’ – is a useful index for comparing the relative rates of an enzyme acting on alternative, competing substrates. However, an alternative description, ‘catalytic efficiency’, is frequently used, and on occasions misused, to compare the reactivity of two enzymes acting on the same substrate. Here, we highlight the pitfalls in using k cat/K M to compare the catalytic effectiveness of enzymes. [Copyright &y& Elsevier] more...

This article focuses on the correlation between the Raven Progressive Matrices Scale and the Shipley Institute of Living Scale. The two tests were compared with respect to mental deterioration, socio-economic status, diagnosis and age. Comparisons were made between the total number of correct answers on the Matrices with the following scores of the Shipley such as total mental age, abstraction age, vocabulary age, and conceptual quotient. In comparing the two scales, attention was drawn to the following variables: mental deterioration, socio-economic status, diagnosis, and age. Results indicated substantial correlation between the two scales, but they were not sufficiently similar to be interchangeable. more...

Surface second harmonic generation has been used to study the adsorption of alkyl phenols and anilines and their respective ions to the air/water interface. The free energies of adsorption of the neutral molecules were obtained using a simple Langmuir model. The quantitative effects of the opposing hydrophobic and solvations forces on molecular adsorption were investigated by varying the chain length of alkylphenolate and alkylanilinium ions. An alkyl chain of at least five carbons was found to be necessary to balance the bulk ionic solvation and thereby bring the ion interface population to a level above the water background. The adsorption of the ions can be described quantitatively by using a modified Langmuir model that includes the electrostatic free energy of the electric double layer as given by the Gouy–Chapmann theory. From the excellent fit of the second harmonic data to this treatment, the chemical and electrostatic free energies of adsorption, interface electric potential, and interface pH were obtained. [ABSTRACT FROM AUTHOR] more...

The article presents an obituary for Herman Bachelard who gained his BSc in Chemistry and Microbiology from Melbourne University in 1951.

This presents an investigation of intermolecular electron transfer (ET) in the asymmetric environment of liquid/liquid interfaces. The time-resolved ultrafast excited state ET at the dimethylaniline (DMA)/aqueous interface is presented. The role of acceptor and donor molecules is performed by photoexcited coumarin 314 (C314) and DMA respectively. Changes in the C314 ground- and excited-state populations with time can be traced through the photoexcitation of C314 with a 120 fs laser pulse at 424 nm. This change in the excited-state C314 can be characterized by a biexponential curve which is convoluted to include the instrument response time. more...

Pays tribute to Brian Edward Bent a former professor of chemistry at Columbia University, who died on July 23, 1996.

We report the first observation of a sharp structural change in an air/acetonitrile–water interface as the solution composition varies; the abruptness of which suggests an interfacial phase transition. The structural change is manifested by shifts in the frequency and in the polarization of the signal from the acetonitrile molecules in the interface observed using infrared+visible surface sum frequency generation. [ABSTRACT FROM AUTHOR] more...

The first measurement of the geminate electron–hole recombination times of two neat octane isomers has been studied using femtosecond techniques. The recombination times were found to be 2.2±1.0 ps in n-octane and 470±40 fs in iso-octane, thus showing that the rates are strongly dependent on the structure of the alkane solvents. [ABSTRACT FROM AUTHOR] more...

The article reports on an item analysis of the progressive matrices (PM) test for a sample of hospitalized schizophrenics. The Raven PM Scale is a non-verbal test of immediate observation and reasoning. The PM consists of 5 sets of 12 matrices (60 problems) arranged in order of difficulty. A previous study has reported an item analysis of the PM for samples of male schizophrenic patients drawn from the wards of both state and private mental institutions. The PM test was administered to 52 male schizophrenic patients at a Veterans Administration Hospital. The results of an item analysis indicated that sets C and D discriminated satisfactorily. more...

This paper presents the first study of the rotations of rigid molecules in 3 dimensions at the air/water interface, using the femtosecond time resolved sum frequency generation (SFG) technique. For the purpose of this research, the aromatic dye molecule C153 was chosen as an example of a molecule having two functional groups that are SFG active, one being the hydrophilic —C=O group and the other the hydrophobic —CF3 group. From polarized SFG measurements, the orientations of the two chromophores with respect to the surface normal were obtained. On combining these results with the known relative orientation of the two chromophores in the molecule yields the absolute orientation of C153 at the air/water interface. It was found that the —CF3 axis projected towards the bulk air at an angle of 59° with respect to the interface normal and the —C=O group projected towards the bulk water at an angle of 144°. In order to observe the rotational motions of C153 at the air/water interface, the approach was used to perturb the ground electronic state equilibrium orientational distribution using a polarized resonant pump pulse, which preferentially excites ground state molecules that have their electronic S0 → S1 transition moment aligned closely to the electric field of the incident pump pulse. As a consequence of the photoselection perturbation, the orientational distribution of the remaining ground state molecules was not the equilibrium distribution. Similarly, the orientational distribution of the excited state molecules that were created by the polarized pump pulse was not in their final equilibrium orientational distribution. The rotational motions of the interfacial molecules towards equilibrium were obtained from time dependent measurements of the intensities of the SFG signal generated by the simultaneous incidence at the air/water interface of a visible probe pulse plus an IR probe pulse. In this way, the recovery times to achieve the orientational equilibrium of the two chromophores including the orientation of the normal of the C153 plane with respect to the interface were obtained. The photo-selection process shifts the average orientation angle of the hydrophilic —C=O group by an increase of 4° ± 0.6° with a rotational recovery time constant of 130 ± 20 ps, which is the time to return to an orientational equilibrium distribution. The hydrophobic –CF3 group undergoes a shift that increases its angle by 8° ± 1.5° with a rotational recovery time constant of 210 ± 38 ps. We find that the orientational change of the molecular normal is 4° ± 0.5° and has a rotational recovery time constant of 125 ± 26 ps. The interface-specific time-dependent polarized measurements allowed us to monitor the orientational motions of molecules at interfaces, both in 3 dimensions and in real time. [ABSTRACT FROM AUTHOR] more...

Second harmonic generation (SHG) spectroscopy has been applied to probe the fused silica/water interface at pH 7 and the uncharged 1 1 ¯ 02 sapphire/water interface at pH 5.2 in contact with aqueous solutions of NaCl, NaBr, NaI, KCl, RbCl, and CsCl as low as several 10 μM. For ionic strengths up to about 0.1 mM, the SHG responses were observed to increase, reversibly for all salts surveyed, when compared to the condition of zero salt added. Further increases in the salt concentration led to monotonic decreases in the SHG response. The SHG increases followed by decreases are found to be consistent with recent reports of phase interference and phase matching in nonlinear optics. By varying the relative permittivity employed in common mean field theories used to describe electrical double layers and by comparing our results to available literature data, we find that models recapitulating the experimental observations are the ones in which (1) the relative permittivity of the diffuse layer is that of bulk water, with other possible values as low as 30, (2) the surface charge density varies with salt concentration, and (3) the charge in the Stern layer or its thickness varies with salt concentration. We also note that the experimental data exhibit sensitivity depending on whether the salt concentration is increased from low to high values or decreased from high to low values, which, however, is not borne out in the fits, at least within the current uncertainties associated with the model point estimates. [ABSTRACT FROM AUTHOR] more...

The binding of EcoR1 to a 90-bp DNA duplex attached to colloidal microparticles and the subsequent cleavage by the enzyme was observed in real time and label-free with time-resolved second harmonic (SH) spectroscopy. This method provides a unique way to investigate biomolecular interactions based on its sensitivity to changes in structure and electrical charge on formation of a complex and subsequent dynamics. The binding of EcoR1 to the recognition sequence in DNA appears as a rapid increase in the SH signal, which is attributed to the enzyme-induced change in the DNA conformation, going from a rod-like to a bent shape. In the presence of the cofactor Mg2+, the subsequent decay in the SH signal was monitored in real time as the following processes occurred: cleavage of DNA, dissociation of the enzyme from the DNA, and diffusion of the 74-bp fragment into the bulk solution leaving the 16-bp fragment attached to the microparticle. The observed decay was dependent on the concentration of Mg2+, which functions as a cofactor and as an electrolyte. With SH spectroscopy the rehybridization dynamics between the rehybridized microparticle bound and free cleaved DNA fragments was observed in real time and label-free following the cleavage of DNA. Collectively, the experiments reported here establish SH spectroscopy as a powerful method to investigate equilibrium and time-dependent biological processes in a noninvasive and label-free way. [ABSTRACT FROM AUTHOR] more...

The two established thermal properties of enzymes are their activation energy and their thermal stability. Arising from careful measurements of the thermal behaviour of enzymes, a new model, the Equilibrium Model, has been developed to explain more fully the effects of temperature on enzymes. The model describes the effect of temperature on enzyme activity in terms of a rapidly reversible active-inactive transition, in addition to an irreversible thermal inactivation. Two new thermal parameters, T eq and Δ H eq, describe the active–inactive transition, and enable a complete description of the effect of temperature on enzyme activity. We review here the Model itself, methods for the determination of T eq and Δ H eq, and the implications of the Model for the environmental adaptation and evolution of enzymes, and for biotechnology. [ABSTRACT FROM AUTHOR] more...

Arising from careful measurements of the thermal behaviour of enzymes, a new model, the Equilibrium Model, has been developed to explain more fully the effects of temperature on enzymes. The model describes the effect of temperature on enzyme activity in terms of a rapidly reversible active–inactive (but not denatured) transition, revealing an additional and reversible mechanism for enzyme activity loss in addition to irreversible thermal inactivation at high temperatures. Two new thermal parameters, Teq and ΔHeq, describe the active–inactive transition, and enable a complete description of the effect of temperature on enzyme activity. We describe here the Model and its fit to experimental data, methods for the determination of the Equilibrium Model parameters, and the implications of the Model for the environmental adaptation and evolution of enzymes, and for biotechnology. [ABSTRACT FROM AUTHOR] more...

Dendritic spines mediate most excitatory synapses in the brain. Past theoretical work and recent experimental evidence have suggested that spines could contain sodium channels. We tested this by measuring the effect of the sodium channel blocker tetrodotoxin (TIX) on depolarizations generated by two-photon uncaging of glutamate on spines from mouse neocortical pyramidal neurons. In practically all spines examined, uncaging potentials were significantly reduced by TTX. This effect was postsynaptic and spatially localized to the spine and occurred with uncaging potentials of different amplitudes and in spines of different neck lengths. Our data confirm that spines from neocortical pyramidal neurons are electrically isolated from the dendrite and indicate that they have sodium channels and are therefore excitable structures. Spine sodium channels could boost synaptic potentials and facilitate action potential backpropagation. [ABSTRACT FROM AUTHOR] more...

Dendritic spines receive most synaptic inputs in the forebrain. Their morphology, with a spine head isolated from the dendrite by a slender neck, indicates a potential role in isolating inputs. Indeed, biochemical compartmentalization occurs at spine heads because of the diffusional bottleneck created by the spine neck. Here we investigate whether the spine neck also isolates inputs electrically. Using two-photon uncaging of glutamate on spine heads from mouse layer-5 neocortical pyramidal cells, we find that the amplitude of uncaging potentials at the soma is inversely proportional to neck length. This effect is strong and independent of the position of the spine in the dendritic tree and size of the spine head. Moreover, spines with long necks are electrically silent at the soma, although their heads are activated by the uncaging event, as determined with calcium imaging. Finally, second harmonic measurements of membrane potential reveal an attenuation of somatic voltages into the spine head, an attenuation directly proportional to neck length. We conclude that the spine neck plays an electrical role in the transmission of membrane potentials, isolating synapses electrically. [ABSTRACT FROM AUTHOR] more...

The effect of charge on the rotational dynamics of the molecular probe coumarin 314 (C314) at air/water interfaces covered with the negatively charged surfactant sodium dodecyl sulfate (SDS) was investigated using femtosecond time-resolved second harmonic spectroscopy. The out-of-plane orientational time constant at the highest SDS surface coverage of 100 Å2per molecule is 383 ± 9 ps. The rotational dynamics is slower than at the air/water interface where the out-of-plane reorientational time constant is 336 ± 6 ps. At the air/water interface the rotational dynamics is over three times slower than the bulk orientational diffusion time of 100 ps. The relatively small effect of the surfactant charge density on the C314 rotation time constant is surprising, considering the marked dependence of the C314 orientation, spectra, and surfactant phase diagram on surfactant density. [ABSTRACT FROM AUTHOR] more...

A method to determine the absolute orientation of molecules at liquid interfaces by sum frequency generation (SFG) is reported. It is based on measurements of the orientations of two nonparallel vibrationally active chromophores in the molecule of interest combined with a rotation matrix formulation to obtain the absolute molecular orientation. We chose m-tolunitrile, a planar molecule adsorbed to the air/water interface, as a proof-of-method experiment. Quantitative analysis of different polarization sum frequency intensities facilitate unique peak assignments of the methyl and nitrile groups of m-tolunitrile. The SFG analysis of the measurement yields a nitrile group tilting at 53° to the surface normal, and the C3 axis of the methyl group is almost upright at 23° with respect to the surface normal. Using a rotation matrix formulation, we found that the angle between the surface plane and the m-tolunitrile molecular plane is 70°. [ABSTRACT FROM AUTHOR] more...

Patterns of utilization and effects of participation in Overeaters Anonymous (OA) in 40 individuals meeting DSM-III criteria for bulimia are described. All were abstinent from compulsive overeating for a mean of 3 years, with 21 (52.5%) initiating sustained abstinence within the first month of membership. Most attended meetings 5 times per week and called their sponsors daily, and 25 (62.5%) were in psychotherapy concurrently. The authors describe the nature and philosophy of OA and discuss factors which might explain the symptomatic control achieved by this group. [ABSTRACT FROM AUTHOR] more...