Constant Ion Concentration Research Articles

Mass/heat transfer analogy method in the research of convective fluid flow through channels with a specific geometry

The present work contains the results of the comparative analysis of the literature data and the own investigations on mass and heat transfer coefficients occurring under conditions of the convective fluid flow through channels characterised by a specific geometry. The authors focused on the available experimental investigations on mass transfer. The considered experiments were carried out using the electrochemical method named limiting current technique. Two channel geometries were discussed: the annular channel of the conventional size and the long minichannel with a square cross-section area. Taking into consideration dimensionless numbers: Schmidt and Nusselt – analogical for mass and heat transfer – the formulas describing the phenomena under consideration were included. In the case of the annular channel the laminar and turbulent range of Reynolds numbers was studied. For the square minichannel – the laminar flow is considered. The analogy between mass and heat transfer introduced by Chilton and Colburn was applied in the analysis. An equivalent boundary condition is included in considerations concerning the mass and heat transfer. It is the Dirichlet boundary condition characterised by constant temperature of the wall which corresponds to the situation of constant ion concentration at the cathode surface in the limiting current technique. The main purpose of the present work was to verify the method for the determination of heat transfer coefficients using the analogy between mass and heat transfer processes in the case of convective fluid flow through the annular and square channels. The problem discussed in the present work is important and actual due to the possibility of the elimination of temperature measurements in the investigations of heat transfer processes occurring in channels characterised by a specific geometry. It should be noted that sometimes temperature measurement may be difficult or even impossible. This situation also causes high uncertainty of the obtained results. Due to this problem, the presented analysis was performed also with the use of thermal results based on the analytical solution. The verification of the use of mass/heat transfer analogy method in specific cases gives the extended knowledge of correct application of the limiting current technique in heat transfer research. The main objective of the work was achieved by conducting a comparative analysis of the adequate mass and heat transfer results. The existing literature data do not provide an answer to the question about the correctness of using the limiting current technique in the case of discussed annular channels or long square minichannels. The received results make us be critical of applying the mass/heat transfer analogy method in some heat transfer cases.

Temporal dynamics of Na/K pump mediated memory traces: insights from conductance-based models of Drosophila neurons.

Sodium potassium ATPases (Na/K pumps) mediate long-lasting, dynamic cellular memories that can last tens of seconds. The mechanisms controlling the dynamics of this type of cellular memory are not well understood and can be counterintuitive. Here, we use computational modeling to examine how Na/K pumps and the ion concentration dynamics they influence shape cellular excitability. In a Drosophila larval motor neuron model, we incorporate a Na/K pump, a dynamic intracellular Na+ concentration, and a dynamic Na+ reversal potential. We probe neuronal excitability with a variety of stimuli, including step currents, ramp currents, and zap currents, then monitor the sub- and suprathreshold voltage responses on a range of time scales. We find that the interactions of a Na+-dependent pump current with a dynamic Na+ concentration and reversal potential endow the neuron with rich response properties that are absent when the role of the pump is reduced to the maintenance of constant ion concentration gradients. In particular, these dynamic pump-Na+ interactions contribute to spike rate adaptation and result in long-lasting excitability changes after spiking and even after sub-threshold voltage fluctuations on multiple time scales. We further show that modulation of pump properties can profoundly alter a neuron's spontaneous activity and response to stimuli by providing a mechanism for bursting oscillations. Our work has implications for experimental studies and computational modeling of the role of Na/K pumps in neuronal activity, information processing in neural circuits, and the neural control of animal behavior.

Chemical Force Microscopy Study on the Interactions of COOH Functional Groups with Kaolinite Surfaces: Implications for Enhanced Oil Recovery

Clay–oil interactions play a critical role in determining the wettability of sandstone oil reservoirs, which, in turn, governs the effectiveness of enhanced oil recovery methods. In this study, we have measured the adhesion between –COOH functional groups and the siloxane and aluminol faces of kaolinite clay minerals by means of chemical force microscopy as a function of pH, salinity (from 0.001 M to 1 M) and cation identity (Na+ vs. Ca2+). Results from measurements on the siloxane face show that Ca2+ displays a reverse low-salinity effect (adhesion decreasing at higher concentrations) at pH 5.5, and a low salinity effect at pH 8. At a constant Ca2+ concentration of 0.001 M, however, an increase in pH leads to larger adhesion. In contrast, a variation in the Na+ concentration showed less effect in varying the adhesion of –COOH groups to the siloxane face. Measurements on the aluminol face showed a reverse low-salinity effect at pH 5.5 in the presence of Ca2+, whereas an increase in pH with constant ion concentration resulted in a decrease in adhesion for both Ca2+ and Na+. Results are explained by looking at the kaolinite’s surface complexation and the protonation state of the functional group, and highlight a more important role of the multicomponent ion exchange mechanism in controlling adhesion than the double layer expansion mechanism.

Influenza of the Cu Ion on the Structural and Optical Properties in Cu + Ce Co-Doped ZnO Compounds

This article showed and explained the effects of the Cu2+ ions on the structural and photoluminescent properties of Ce3+ doped ZnO compounds (ZnO: Ce3+) in Cu2+ + Ce3+ co-doped ZnO (ZnO: Cu2+ + Ce3+) solid solutions powders. The samples were synthesized by a solution combustion method maintaining the Ce3+ ion concentration constant in 3%wt and varying the Cu2+ ion concentration in 0%wt, 1%wt, 2%wt, 3%wt, 10%wt and 20%wt. However, pristine ZnO and Ce3+ doped ZnO were synthesized by the same method for comparison. After the synthesis process all the samples were annealed at 900°C by 24 h. The pure ZnO, ZnO: Ce3+ and ZnO/Cu2+ + Ce3 powders were structurally characterized using X-ray diffraction (XRD) technique, the XRD patterns showed that for either undoped and doped with the Cu2+ ion both exhibited the hexagonal wurtzite ZnO crystalline structure, also the diffraction peaks of both samples types showed a little change toward lesser angles. The morphology and particle size of the samples were observed by means of a scanner electron microscopy (SEM); from SEM imagen is observed that the crystallites of the samples are agglomerated forming cage-like hollow structures caused by the combustion process. The cage-like structures have approximate size of 800 nm. In addition, the photoluminescence of pure ZnO, ZnO: Ce3+and ZnO: Cu2+ + Ce3+ compounds was measurement as a function of Cu2+ ion concentration under a excitation wavelength of 378 nm in the UV region. As an important result, it is observed that by Auger phenomena of non-radiative recombination, the UV emission of the ZnO is quenching.

城市小型湖泊浮游植物群落结构特征及演替规律——以武汉沙湖为例

PDF HTML阅读 XML下载 导出引用 引用提醒 城市小型湖泊浮游植物群落结构特征及演替规律——以武汉沙湖为例 DOI: 10.5846/stxb201606211215 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41331174）；江西省水利厅重大科技项目（KT201412）；水利部科技推广项目（TG1520） Distribution and succession pattern of phytoplankton communities in a small urban lake, Sand Lake in Wuhan City, China Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:城市小型湖泊具有对环境变化的高敏感性，其浮游植物群落特征和演替规律对湖泊生态系统的监测与管理有重要意义。本研究于2015年3-12月，对武汉市沙湖进行了生态和水质监测，共鉴定出藻类10门312种，绿藻、硅藻和蓝藻种类数占优。为探究富营养化城市小型湖泊浮游植物群落时空异质性及其演替驱动力，选取了4个多样性指数（Shannon-Wiener指数、Simpson指数、Pielou均匀度指数和Whittaker指数），并进行了多样性指数与环境因子的相关性分析、主成分分析和聚类分析，计算了优势种在监测时段的3个种间联结性指数和校正χ2检验系数。结果表明，夏秋季节浮游植物群落处于演替的稳定状态，环境因子驱动作用明显，其中离子浓度的影响大于温度的影响，钠、镁离子浓度为主要影响因素；蓝藻门和绿藻门优势种联结性较高，硅藻门优势种内部联结性较高而与其他门类相关性较低，从季节上看，夏秋季节的优势种种间联结性较高，春冬季优势种与其他时段优势种相关性低，可能为群落在冬春季不稳定的原因。 Abstract:Small urban lakes are highly sensitive to changes in their environment and are closely associated with the surrounding urban systems. The distribution and succession pattern of phytoplankton can significantly influence the entire ecosystem in a small urban lake. From March to December 2015, phytoplankton and water quality were monitored in Sand Lake, Wuhan city, China. In total, 312 species were detected representing 10 phyla, with Chlorophyta, Bacillariophyta, and Cyanophyta being the major phyla represented. Biodiversity indices were calculated using the methods of Shannon-Wiener, Simpson, Pielou, and Whittaker. The biodiversity indices and environmental factors were subjected to correlation analysis, principal component analysis, and cluster analysis. Three interspecific association indices and the calibrated coefficients of χ2 test were calculated. The results showed that the phytoplankton reached a stable state in summer and autumn, during which the environmental factors were the main influence; the effect of constant ion concentration was greater than that of temperature, particularly those of sodium and magnesium. Analysis of the data for the dominant species showed that Chlorophyta and Cyanophyta were significantly correlated, whereas Bacillariophyta showed no significant correlation with other phyla. A significant correlation occurred between summer and autumn dominant species, while dominant species in winter and spring showed no significant correlation with those in other seasons, which could be attributed to the low stability of the phytoplankton during this period. 参考文献 相似文献 引证文献

Structural and Optical Properties of Cu<sup>2+</sup> + Ce<sup>3+</sup> Co-Doped ZnO by Solution Combustion Method

In this work, ZnO, Ce3+ doped ZnO (ZnO/Ce3+) and Cu2+ + Ce3+ co-doped ZnO (ZnO/Cu2+ + Ce3+ ) solid solutions powders were synthesized by a solution combustion method maintaining the Ce3+ ion concentration constant in 3%Wt while the Cu2+ ion concentration was varied in 1, 2, 3, 10 and 20%Wt. After its synthesis, all the samples were annealed at 900?C by 24 h. The ZnO, ZnO/Ce3+ and ZnO/Cu2+ + Ce3+ powders were structurally characterized using X-ray diffraction (XRD) technique, and the XRD patterns showed that for pure ZnO, Cu2+ undoped ZnO/Ce3+ and ZnO/Ce3+ doped with the Cu2+ ion, the three samples exhibited the hexagonal wurtzite ZnO crystalline structure. However, the morphology and particle size of both samples were observed by means of a scanning electron microscopy (SEM); from SEM image, it is observed that the crystallites of both samples are agglomerated forming bigger amorphous particles with an approximate average size of 1 μm. In addition, the photoluminescence of the ZnO, Ce3+ doped ZnO and Cu2+ + Ce3+ doped ZnO samples was measurement under an illumination of 209 nm wavelength (UV region): for the ZnO/Ce3+ sample, your emission spectrum is in the visible region from blue color until red color; the UV band of the ZnO is suppressed. The multicolor emission visible is attributed to the Ce3+ ion photoluminescence, while for the ZnO/Cu2+ + Ce3+, its emission PL spectrum is quenching by the Cu2+ ion, present in the ZnO crystalline.

Metal ion sorption dynamics in a foamed chitosan structure

Industrial processes are responsible for heavy metal releases into the environment. Removal of excessive heavy metals has become a major concern, therefore, new economical and efficient methods of water treatment are now being explored. The experiments described in this paper relate to the removal of heavy metal cations from water. The adsorption process was carried out in a packed column containing foamed chitosan. Initially, a method of production of the foamed structure was developed. Subsequently, the foamed structure was properly prepared for testing. The adsorption process was continuous with constant ion concentration at the column inlet. Parameters such as sorption capacity of the chitosan bed, as well as influence of the initial ion concentration and feed flow rate were investigated. The Bohart–Adams model was used to describe the sorption dynamics.

Enhanced multiple vibrational resonances by Na+ and K+ dynamics in a neuron model.

Some neuronal receptors perceive external input in the form of hybrid periodic signals. The signal detection may be based on the mechanism of vibrational resonance, in which a system's response to the low frequency signal can become optimal by an appropriate choice of the vibration amplitude of HFS. The vibrational resonance effect is investigated in a neuron model in which the intra- and extra-cellular potassium and sodium concentrations are allowed to evolve temporally, depending on ion currents, Na+-K+ pumps, glial buffering, and ion diffusion. Our results reveal that, compared to the vibrational resonances in the model with constant ion concentrations, the significantly enhanced vibrational multi-resonances can be observed for the single neuron system where the potassium and sodium ion concentrations vary temporally. Thus, in contradiction to a popular view that ion concentrations dynamics play little role in signal detection, we indicate that the neuron's response to an external subthreshold signal can be largely improved by sodium and potassium dynamics.

Ion-isotopic exchange reaction kinetics using organic base anion exchange resins Indion-102 and Indion GS-400

The present study deals with the kinetic study of iodide and bromide ion-isotopic exchange reactions in organic based anion exchange resins Indion-102 (nuclear grade) and Indion GS-400 (non-nuclear grade) using radiotracer isotopes. The resins in iodide and bromide form were equilibrated respectively with iodide and bromide ion solutions which were previously spiked with 131I and 82Br radiotracer isotopes. For both bromide and iodide ion-isotopic exchange reactions, it was observed that the values of specific reaction rate increase with increase in ion concentration from 0.001 to 0.004 M at a constant temperature of 40.0°C. However, at constant ion concentration of 0.003 M, the specific reaction rate was observed to decrease with rise in temperature from 30.0 to 45.0°C. Also it was observed that for iodide ion-isotopic exchange reaction by using Indion-102 resin, the values of specific reaction rate, amount of iodide ion exchanged, initial rate of iodide ion exchange and logK d were 0.258 min−1, 0.492 mmol, 0.127 mmol/min and 19.2, respectively, which were higher than 0.208 min−1, 0.416 mmol, 0.087 mmol/min and 17.6, respectively, obtained by using Indion GS-400 resin under identical experimental conditions of 40.0°C, 1.000 g of ion exchange resin and 0.003M labeled iodide ion solution. The same trend was observed for the two resins during bromide ion-isotopic exchange reaction. The overall results indicate that, under identical experimental conditions, Indion-102 resin shows higher performance than Indion GS-400 resin.

P‐140: The Ion Adsorption on SiOx Alignment Film Used for the Low Power LCDs Using Variable Frame Frequency

Abstractliquid crystal displays(LCDs) are the dominant display technology in today's mobile devices. For the battery life of mobile devices, it is very demanding to lower the power consumption of mobile displays. Operating active‐matrix liquid‐crystal displays (AMLCDs) with an ultra‐wide refresh‐rate range, down to ∼1 Hz, can lower the power consumption and offer video rate as well. It has been shown that a SiOx‐based liquid crystal (LC) alignment technique can overcome the ion problems typically encountered with low‐refresh‐rate devices because of its adsorption ability. In this paper, a further study is taken on the adsorption property of SiOx alignment film. To estimate the structure of ionic impurities in LC, a new model given constant ion concentration is implemented to simulate the voltage holding profiles, which shows that the ionic impurities adsorbed by the SiOx film are probably associated with water. Besides, it is found that adding salt into LC can help the adsorption of SiOx film, and thus lower the ion concentration in LC more effectively.

Prediction of the effects of methanol and competing ion concentration on retention in the ion chromatographic separation of anionic and cationic pharmaceutically related compounds

The mixed-mode separation of a selection of anionic and cationic pharmaceutically related compounds is studied using ion-exchange columns and eluents consisting of ionic salts (potassium hydroxide or methanesulfonic acid) and an organic modifier (methanol). All separations were performed using commercially available ion-exchange columns and an ion chromatography instrument modified to allow introduction of methanol into the eluent without introducing compatibility problems with the eluent generation system. Isocratic retention prediction was undertaken over the two-dimensional space defined by the concentration of the competing ion and the percentage of organic modifier in the eluent. Various empirical models describing the observed relationships between analyte retention and both the competing ion concentration and the percentage of methanol were evaluated, with the resultant model being capable of describing the separation, including peak width, over the entire experimental space based on six initial experiments. Average errors in retention time and peak width were less than 6% and 27%, respectively, for runs taken from both inside and outside of the experimental space. Separations performed under methanol gradient conditions (while holding the competing ion concentration constant) were also modelled. The observed effect on retention of varying the methanol composition differed between analytes with several analytes exhibiting increased retention with increased percentage methanol in the eluent. An empirical model was derived based on integration of the observed t R vs. %methanol plot for each analyte. A combination of the isocratic and gradient models allowed for the prediction of retention time using multi-step methanol gradient profiles with average errors in predicted retention times being less than 4% over 30 different 2- and 3-step gradient profiles for anions and less than 6% over 14 different 2- and 3-step gradient profiles for cations. A modified peak compression model was used to estimate peak widths under these conditions. This provided adequate width prediction with the average error between observed and predicted peak widths being less than 15% for 40 1-, 2- and 3-step gradients for anions and less than 13% over 14 1-, 2- and 3-step gradients for cations.

Flow splitting at the inlet electrode as a method for decreasing the electric current in electric field assisted liquid chromatography

The combination of pressurized flow and electric field offers, with the use of capillary columns, several options for retention control. However, it has been shown that the utility of this technique is strongly limited by the high electric current that is generated at the high electric field strengths that are needed. We have earlier shown that the high current is a result of locally increased mobile phase ion concentration in the electric field, particularly around the inlet electrode. In this paper, we report that by splitting the mobile phase flow around the inlet electrode a relatively constant ion concentration around the electrode can be obtained and the high currents are there by reduced.

Cytotoxicity of Copper Ions Released from Metal: Variation with the Exposure Period and Concentration Gradients

The aim of this work is to contribute to the elucidation of the cytotoxic process caused by the copper ions released from the biomaterials. Clonal cell lines UMR106 were used in the experiments. Copper ions were obtained from two different sources: copper salts and metal dissolution. Experiments carried out with constant ion concentrations (copper salts) were compared with those with concentrations that vary with time and location (dissolution of the metal). Present results and others previously reported could be interpreted through mathematical models that describe: (1) the variation of concentration of copper ions with time and location within a biofilm and (2) the variation of the killing rate with the concentration of the toxic ion and time. The large number of dead cells found near the copper sample with an average ion concentration below the toxic limit could be interpreted bearing in mind that these cells should be exposed to a local concentration higher than this limit. A logarithmic dependence between the number of cells and exposure time was found for nearly constant ion concentrations. Apparent discrepancies, observed when these results and those of different researchers were contrasted, could be explained considering the dissimilar experimental conditions such as the source of the ions and their local concentration at real time.

Controlling of the adsorption and dispersing force of polycarboxylate-type superplasticizer by sulfate ion concentration in aqueous phase

The dispersing force of polycarboxylate-type superplasticizer (PC) with poly(ethyleneoxide) (PEO) graft chain has been known to degrade by the sulfate ion in the aqueous phase of concrete. Alkaline sulfate contents and calcium sulfates in cement, mixing temperature and time elapsed after mixing, and other various material characteristics as well as environmental conditions affect the sulfate ion concentration. Therefore, it is generally very difficult to keep the sulfate ion concentration constant. In this study, the active control of the sulfate ion concentration in aqueous phase by adding soluble salts containing multiple-charged cations, such as CaCl 2 and alkaline sulfate, has been attempted. The adsorption of PC is able to be controlled by adding salts such as CaCl 2 and Na 2SO 4. The change of the PC adsorption ratio results directly in the variation of the dispersing force of superplasticizer. It is also indicated that ionic strength in the aqueous phase affects the dispersing force of PC. The dispersing force degrades with the increase in ionic strength and sulfate ion concentration.

Calcium permeability of neuronal nicotinic acetylcholine receptor channels in PC12 cells

The conductance properties of neuronal nicotinic acetylcholine receptors (neuronal nAChR channels) in PC12 cells were studied using single channel and whole cell gigaohm seal voltage clamp techniques. Acetylcholine receptor agonists were applied using external pipettes. Neuronal nAChR channels were selective for monovalent cations, and were impermeable to anions. Based on measurements of shifts in reversal potential with changes in external Na and K ion concentrations and evaluation of the GHK constant field relation, P K/P Na was 1.45 (ignoring Ca permeability). P Ca/P K was 1.75 based on the shift in reversal potential seen when raising the external Ca concentration from 2 to 50 mM (holding the external Na ion concentration constant), and determining the best fit to the extended GHK constant field relation using ionic activities. This value is larger than that determined for the muscle-type nAChR channel. Evaluation of the extended GHK current equations using these permeability coefficients indicated that at subthreshold voltages approximately 5% of total current through neuronal nAChR channels will be carried by Ca ions. Thus, these channels may be important mediators of activity-dependent Ca influx in the nervous system.

Halophytes

Halophytes are plants adapted to live in a saline environment, be it seawater, a salt-water marsh, or a salt-desert; nearly all are angiosperms. The growth of dicotyledonous halophytes is frequently stimulated by salt, although that of most monocotyledonous halophytes is not. Survival requires osmotic adjustment, which is commonly achieved by using the ions present in the environment and which is associated with succulence in dicotyledons but generally not in monocotyledons. At the cellular level, survival depends on the ability of the plant to compartmentalize, in vacuoles, the ions used for osmotic adjustment, particularly sodium and chloride. A vital feature of the physiology of these plants is their ability to accumulate sufficient ions to maintain growth while avoiding either a water deficit or an excess of ions, either of which could prove toxic. The means by which relatively constant ion concentrations in the shoot are maintained are considered. The conclusion is drawn that ion uptake by the roots is not controlled by the shoots; rather, shoot growth is regulated by the supply of ions from the roots. The agricultural importance of halophytes in a world where most of the water is salty at any given moment is emphasized.

Geochemical evidence of chemical equilibria in the South Meager Creek geothermal system, British Columbia, Canada

Meager geothermal reservoir appears to be in “thermochemical” equilibrium as indicated by constant ion-concentration ratios (B/Li, B/K, Na/Li, Na/CI etc.). The Na/Li ratio describes the thermal conditions of the first and the deepest equilibrium reached by the thermal waters, whereas the Na/K indicates a secondary and shallower equilibrium. Analysis of the correlations between K, Na and CI indicate that discharge from well MC1 is probably a mixture between a single brine and high-chloride cool waters.

Effects of solvent viscosity and different guanidine salts on the kinetics of ribonuclease A chain folding

AbstractThe kinetics of folding of the two forms of unfolded ribonuclease A have been measured as a function of solvent viscosity by adding either glycerol or sucrose. The aim is to find out if either reaction is rate limited by segmental motion whose rate depends on external friction. The fast folding reaction (U2 ⇄ N) is known to be the direct folding process, and the slow folding reaction (U1 ⇌ N) is known to be rate limited by an interconversion between two forms (U1 ⇌ U2) which are present after unfolding in strongly denaturing conditions. No dependence on solvent viscosity is found, either for the direct folding reaction or for the interconversion reaction. Each folding reaction has also been tested to see if its rate depends on the concentration of one or more partly folded intermediates, by adding denaturants destabilize any partly folded structures. Different guanidine salts are used as denaturants to vary the denaturing effectiveness of the salt while holding the guanidinium ion concentration constant. The rates both of the direct folding reaction and of the interconversion reaction decrease in relation to the denaturing effectiveness of the salt. However, there is a basic difference between the responses of the fast and slow folding reactions to low concentrations of denaturants. Although each folding reaction produces native protein, there is an 800‐fold decrease in the rate of the fast folding reaction in 1M guanidine thiocyanate and only a 13‐fold decrease in the rate of the slow folding reaction. This is consistent with the fast reaction being the direct folding process and the slow reaction being rate limited by the initial conversion of the slowrefolding to the fast‐refolding form. Both the lack of viscosity dependence and the effects of denaturants indicate that the formation of structure is rate limiting in the direct folding reaction, U2 ⇌ N. The failure to find a viscosity dependence for the interconversion reaction, U1 ⇌ U2, indicates that in this reaction also friction‐limited segmental motion is not the rate‐limiting process. Since the U1 ⇌ U2 interconversion still occurs when the polypeptide chain is completely unfolded, the surprising result is that its rate in refolding conditions depends significantly on a reaction intermediate which is “denatured” by guanidine salts.

Paper-electrophoretic studies of the solution chemistry of RaD ( 210Pb), RaE ( 210Bi) and RaF ( 210Po) : II. In nitric acid and perchloric acid

An attempt has been made to define the concentration range of nitric and perchloric acids which give separations of RaD, RaE and RaF in electrophoresis on paper. The effect on the ionic nature of these elements of varying the concentration of these acids and also of the progressive replacement of nitric acid by potassium nitrate, keeping the NO 3 − ion concentration constant, has been examined.

Relaxation enhancement by paramagnetic ion binding in deoxyribonucleic acid solutions.

THE effect of paramagnetic ions on proton relaxation times depends not only on their concentration but also on the binding of the ion to other molecules which may be present in the same solution. By measuring longitudinal relaxation times (T1) by nuclear magnetic resonance we have compared the proton relaxation-rates at constant ion concentration with and without deoxyribonucleic acid (DNA) present. In this way it was possible to detect binding and to distinguish between interior and exterior DNA binding sites for different transition metal ions.