scholarly journals The time course of the heat effects in rapid chemical changes. Part II.—Some reactions of acids, bases, amino-acids and proteins

1930 ◽  
Vol 126 (802) ◽  
pp. 470-486 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Chemical Reactions ◽  
Time Course ◽  
Carbonic Acid ◽  
Total Heat ◽  
Physical Factors ◽  
Single Experiment ◽  
Temperature Changes ◽  
Heat Effects ◽  
Acids And Bases

During the last 20 years the time relationships of the rapid heat changes in muscle and nerve have been the subject of exhaustive study, by Hill, Hartree, Meyerhof and many of their collaborators. The changes involved in such processes have turned out to be dependent both on physical factors and on the heat effects of a number of separate rapid chemical reactions. Hitherto, however, there seems to have been but little attempt, either by physical chemists or by physiologists, to study the time relationships involved in the heat effects of individual rapid chemical reactions themselves. Investigators, for instance, have contented themselves with measuring the total heat of such reactions, merely by mixing together in thermos flasks, or other suitable calorimeters, the reagents required, and by noting the temperature changes which ensue over the period subsequent to mixing. Since, as a rule, observations of this kind have to be extended over a period of some minutes in order to ensure that the heat liberated in the change is uniformly distributed through the calorimeter and its contents, no information is obtained as to whether the heat change under investigation is complete within say one minute or within the merest fraction of a second. Such information ought in certain cases to prove to be of great interest to chemistry, but of its importance in physiology when attempts are made to assess the rôle of separate chemical reactions in the rapid changes known to occur in muscle, nerve and blood there would seem to be no question. Recently a method has been worked out for this purpose, and a description of its experimental details and testings have been described fully above. It is sufficient to state here that the method has made it possible to mix together completely within a period of 0∙001 second or less the reagents, whose interaction it is desired to study, and to measure accurately the total heat evolved within a period of only 0·01 to 0·002 second after the reaction has been started by mixing the reagents. It has been shown that the total temperature change involved in such heat effects can be measured to an accuracy of 0·001°C., whilst in the case of “time” reactions in which the evolution or absorption heat takes place gradually over a period of 0·01 second or more the temperature changes between instants of time t 1 and t 2 can be determined almost to a further place of decimals, viz., 0·0001°C. to 0·0002°C. The present paper is of a preliminary kind and contains a description of the first applications of the method to the following rapid reactions: (α) the neutralisations of typical acids and bases (strong and weak); (β) the reactions of the simplest amino-acid, glycine, with acids, bases and buffers; (γ) the reactions of the blood proteins with acids and bases; and (δ) a single experiment on the reaction between carbon monoxide and hæmoglobin. It was to be anticipated that of the above reactions only those of carbonic acid with bases, of bicarbonate with acid, and of hæmoglobin with carbon monoxide, would fail to show completion of the heat change within 0·01 to 0·015 second. The experimental observations confirmed this expectation.

scholarly journals The time course of the heat effects in rapid chemical changes. Part I. - Apparatus and methods. Part II. - Some reactions of acids, bases, amino-acids and proteins

1930 ◽  
Vol 106 (743) ◽  
pp. 251-252 ◽  
Keyword(s):  
Amino Acids ◽  
Chemical Reactions ◽  
Time Course ◽  
Absolute Temperature ◽  
Chemical Changes ◽  
Sources Of Error ◽  
Heat Effects ◽  
Extensive Test ◽  
The Absolute

(1) The method of Hartridge and Roughton for following the velocity of rapid chemical reactions has been extended to the measurement of the amount of heat liberated in rapid reactions within periods of 0.01 second or less from the commencement of such reactions. For this purpose it has been necessary to carry out an extensive test of the physical sources of error involved in the measurement of temperature of rapidly moving fluids by means of thermojunctions. As the result of numerous controls and computations it is concluded that with the apparatus described in the text it is possible to measure the absolute temperature of the fluid travelling down the observation tube of the Hartridge-Roughton apparatus to an accuracy of 0.001° C. This claim is confirmed by experiments on the heat evolved in numerous rapid reactions, the values obtained agreeing very closely with the standard accepted values of the heat of such reactions.

scholarly journals Role of mechanical cues and hypoxia on the growth of tumor cells in strong and weak confinement: A dual in vitro–in silico approach

2020 ◽  
Vol 6 (13) ◽  
pp. eaaz7130 ◽  
Author(s):  
V. Le Maout ◽  
K. Alessandri ◽  
B. Gurchenkov ◽  
H. Bertin ◽  
P. Nassoy ◽  
...  
Keyword(s):  
In Silico ◽  
Time Course ◽  
Growth Dynamics ◽  
Tumor Model ◽  
Mechanistic Modeling ◽  
Physical Factors ◽  
Factors Affecting ◽  
Numerical Studies

Characterization of tumor growth dynamics is of major importance for cancer understanding. By contrast with phenomenological approaches, mechanistic modeling can facilitate disclosing underlying tumor mechanisms and lead to identification of physical factors affecting proliferation and invasive behavior. Current mathematical models are often formulated at the tissue or organ scale with the scope of a direct clinical usefulness. Consequently, these approaches remain empirical and do not allow gaining insight into the tumor properties at the scale of small cell aggregates. Here, experimental and numerical studies of the dynamics of tumor aggregates are performed to propose a physics-based mathematical model as a general framework to investigate tumor microenvironment. The quantitative data extracted from the cellular capsule technology microfluidic experiments allow a thorough quantitative comparison with in silico experiments. This dual approach demonstrates the relative impact of oxygen and external mechanical forces during the time course of tumor model progression.

scholarly journals XII. Thermal properties of carbonic acid low temperatures

1915 ◽  
Vol 215 (523-537) ◽  
pp. 353-381 ◽  
Keyword(s):  
Thermal Properties ◽  
Low Temperatures ◽  
Constant Pressure ◽  
Carbonic Acid ◽  
Total Heat ◽  
Thermodynamic Equations

In a former paper (1) the authors described a series of measurements on the thermal properties of Co 2 and the construction of a θ ø chart embodying those results. It was pointed out that the superheated area of the chart was incomplete, the constant pressure lines being only approximately accurate and the total heat (I) lines omitted. It was also pointed out that throttling experiments on the superheated gas would form a valuable check on the accuracy of the chart, and the construction of an Iø chart was postponed till more accurate measurements should have been made on the superheated gas and the whole had been checked by throttling experiments. The present paper describes the additional experiments required to complete and check the θ ø chart, including a re-measurement of the total heat of the liquid for which some extrapolated values had been used before, and finally the construction of the Iø chart. This chart has been constructed graphically, as the θø chart was, directly from the observed data and its accuracy checked in various ways by thermodynamic equations. These equations apply quite generally to all Iø charts and are independent of tire particular properties of carbonic acid.

scholarly journals Chemical reactions during sintering of Fe-Cr-Mn-Si-Ni-Mo-C-steels with special reference to processing in semi-closed containers

2015 ◽  
Vol 47 (1) ◽  
pp. 61-69 ◽  
Author(s):  
A. Cias
Keyword(s):  
Mechanical Properties ◽  
Carbon Monoxide ◽  
Special Reference ◽  
Water Vapour ◽  
Chemical Reactions ◽  
Thermodynamic Data ◽  
Alloying Elements ◽  
Bearing Steels ◽  
Kinetics Of

Sintering of Cr, Mn and Si bearing steels has recently attracted both experimental and theoretical attention and processing in semiclosed containers has been reproposed. This paper brings together relevant thermodynamic data and considers the kinetics of some relevant chemical reactions. These involve iron and carbon, water vapour, carbon monoxide and dioxide, hydrogen and nitrogen of the sintering atmospheres and the alloying elements Cr, Mn, Mo and Si. The paper concludes by presenting mechanical properties data for three steels sintered in local microatmosphere with nitrogen, hydrogen, nitrogen-5% hydrogen and air as the furnace gas.

scholarly journals The chronoarchitecture of the cerebral cortex

2005 ◽  
Vol 360 (1456) ◽  
pp. 733-750 ◽  
Author(s):  
Andreas Bartels ◽  
Semir Zeki
Keyword(s):  
Cerebral Cortex ◽  
Time Course ◽  
A Priori ◽  
Spatial Location ◽  
Connectivity Pattern ◽  
Anatomical Connectivity ◽  
Natural Conditions ◽  
Single Experiment ◽  
New Approach ◽  
Spatio Temporal

We review here a new approach to mapping the human cerebral cortex into distinct subdivisions. Unlike cytoarchitecture or traditional functional imaging, it does not rely on specific anatomical markers or functional hypotheses. Instead, we propose that the unique activity time course (ATC) of each cortical subdivision, elicited during natural conditions, acts as a temporal fingerprint that can be used to segregate cortical subdivisions, map their spatial extent, and reveal their functional and potentially anatomical connectivity. We argue that since the modular organisation of the brain and its connectivity evolved and developed in natural conditions, these are optimal for revealing its organisation. We review the concepts, methodology and first results of this approach, relying on data obtained with functional magnetic resonance imaging (fMRI) when volunteers viewed traditional stimuli or a James Bond movie. Independent component analysis (ICA) was used to identify voxels belonging to distinct functional subdivisions, based on their differential spatio-temporal fingerprints. Many more regions could be segregated during natural viewing, demonstrating that the complexity of natural stimuli leads to more differential responses in more functional modules. We demonstrate that, in a single experiment, a multitude of distinct regions can be identified across the whole brain, even within the visual cortex, including areas V1, V4 and V5. This differentiation is based entirely on the differential ATCs of different areas during natural viewing. Distinct areas can therefore be identified without any a priori hypothesis about their function or spatial location. The areas we identified corresponded anatomically across subjects, and their ATCs showed highly area-specific inter-subject correlations. Furthermore, natural conditions led to a significant de-correlation of interregional ATCs compared to rest, indicating an increase in regional specificity during natural conditions. In contrast, the correlation between ATCs of distant regions of known substantial anatomical connections increased and reflected their known anatomical connectivity pattern. We demonstrate this using the example of the language network involving Broca's and Wernicke's area and homologous areas in the two hemispheres. In conclusion, this new approach to brain mapping may not only serve to identify novel functional subdivisions, but to reveal their connectivity as well.

Diffusion and chemical reaction velocity in cylindrical and spherical systems of physiological interest

1952 ◽  
Vol 214 (1119) ◽  
pp. 564-564 ◽  
Keyword(s):  
Carbon Monoxide ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Soleus Muscle ◽  
Infinite Medium ◽  
Zero Order ◽  
The Body ◽  
Blood Capillaries ◽  
Reaction Velocity ◽  
First Order

Equations are developed for the rate of penetration of a substance into (or egress from) the zone included between two coaxial cylinders. In the most general case the penetrating substance is assumed to engage in diffusion, a chemical reaction of the first order and a zero-order reaction (e. g. metabolism). The rate of elimination of nitrogen from the tissues into the blood capillaries is considered as an example of diffusion alone, without any accompanying chemical reactions. Application of the simplified equations to this case strongly supports the view that the rate of elimination of nitrogen from the body when breathing oxygen is not conditioned by diffusion factors, but depends only on the volume of the various systems of the body and the rate of blood flow through them. The rate of passage of carbon monoxide from the blood to the myoglobin of red mammalian muscles is next considered as an example of diffusion accompanied by a first-order chemical reaction velocity. Calculations for resting and active muscles indicate that in the latter case certainly, and in the former case probably, the rate of up take of carbon monoxide by the red muscles should be fast enough to affect appreciably the measurement of blood volume by the carbon monoxide method. Millikan’s experiments on the rates of change of oxymyglobin concentration in the resting soleus muscle of the cat are used as an example of the most general case, in which diffusion and chemical reactions, both of first order and zero order, are all involved. The application of the equations of this paper to his data are shown to lead to reasonable conclusions as to the number of open blood capillaries in the resting soleus muscle. Similar equations, with examples, are also developed for the case of a cylinder suspended in an infinite medium and for a sphere suspended in an infinite medium.

scholarly journals Efficient and selective molecular catalyst for the CO2-to-CO electrochemical conversion in water

2015 ◽  
Vol 112 (22) ◽  
pp. 6882-6886 ◽  
Author(s):  
Cyrille Costentin ◽  
Marc Robert ◽  
Jean-Michel Savéant ◽  
Arnaud Tatin
Keyword(s):  
Carbon Monoxide ◽  
Carbonic Acid ◽  
Water Soluble ◽  
Turnover Frequency ◽  
High Turnover ◽  
Molecular Catalyst ◽  
Electrochemical Conversion ◽  
Production Of Hydrogen ◽  
Soluble Molecule ◽  
Neutral Water

Substitution of the four paraphenyl hydrogens of iron tetraphenylporphyrin by trimethylammonio groups provides a water-soluble molecule able to catalyze the electrochemical conversion of carbon dioxide into carbon monoxide. The reaction, performed in pH-neutral water, forms quasi-exclusively carbon monoxide with very little production of hydrogen, despite partial equilibration of CO2 with carbonic acid—a low pKa acid. This selective molecular catalyst is endowed with a good stability and a high turnover frequency. On this basis, prescribed composition of CO–H2 mixtures can be obtained by adjusting the pH of the solution, optionally adding an electroinactive buffer. The development of these strategies will be greatly facilitated by the fact that one operates in water. The same applies for the association of the cathode compartment with a proton-producing anode by means of a suitable separator.

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