Proton interactions in chemical-electrochemical and physical systems

The repulsive Coulombic forces exerted between proton wave particles in electrochemical and physical systems are examined, together with the attractive ion-induced dipole forces between protons and neighboring neutral particles, e.g. neutrons in the case of physical systems (nuclei). It is shown that when protons and neutrons are treated as harmonic oscillators with the same kinetic and potential energy, then two roots exist for their vibrational velocity. One root corresponds to negligible relativistic corrections (v/c?1) and unstable nuclei, the other to significant relativistic corrections (v/c≈1) and to formation of stable nuclei. It is shown that the first root corresponds to protons in chemical-electrochemical systems and the second (relativistic) root corresponds to protons in nuclei. In the latter case the formation of stable nuclei is due to the attractive ion-induced dipole forces and to the pronounced increase in mass and gravitational forces. The latter, together with the ion-induced dipole forces, counterbalance the strong repulsive Coulombic forces. This leads to the analytical computation of the energy of formation of the ⁴He and ²H nuclei and of the gravitational constant. All three computed values are in quantitative agreement with experiment.     

A Magic-Angle-Spinning NMR Spectroscopy Method for the Site-Specific Measurement of Proton Chemical-Shift Anisotropy in Biological and Organic Solids

Proton chemical shifts are a rich probe of structure and hydrogen-bonding environments in organic and biological molecules. Until recently, measurements of ¹H chemical-shift tensors have been restricted to either solid systems with sparse proton sites or were based on the indirect determination of anisotropic tensor components from cross-relaxation and liquid-crystal experiments. We have introduced a magic-angle-spinning approach that permits site-resolved determination of chemical-shift-anisotropy tensors of protons forming chemical bonds with labeled spin 1/2 nuclei in fully protonated solids with multiple sites, including organic molecules and proteins. This approach, originally introduced for the measurements of chemical-shift tensors of amide protons, is based on three RN-symmetry-based experiments, from which the principal components of the ¹H chemical-shift tensor can be reliably extracted by simultaneous triple fit of the data. Herein, we expand our approach to a much more challenging system involving aliphatic and aromatic protons. We start with a review of prior work on experimental NMR spectroscopy and computational quantum chemical approaches for measurements of ¹H chemical-shift tensors and relating these to the electronic structures. We then present our experimental results on U-¹³C,¹⁵N-labeled histidine and demonstrate that ¹H chemical-shift tensors can be reliably determined for the ¹H¹⁵N and ¹H¹³C spin pairs in cationic and neutral forms of histidine. Finally, we demonstrate that the experimental ¹H(C) and ¹H(N) chemical-shift tensors are in agreement with DFT calculations; therefore, establishing the usefulness of our method for the characterization of structures and hydrogen-bonding environments in organic and biological solids.     

Chain fluctuations in the amorphous regions of polyethylene as indicated in proton relaxation spectroscopy

The longitudinal relaxation of the residual protons in deuterated polyethylene has been measured with the aim to detect any heterogeneity of the amorphous methylene phase. In order to obtain a clearer distinction between ‘amorphous’ and ‘crystalline’ protons, an oxygen enhancement study has been carried out. The experiments have yielded no hint for a distribution of correlation times within the amorphous methylene phase. Therefore a single correlation function of a non-Markovian type is assumed. A model of two super-imposed defect diffusion mechanisms is suggested as an explanation for the so-called β- and γ- processes. The theoretical curves are compared with relaxation dispersion data measured in the frequency range 10⁴ to 10⁸ Hz by the aid of a special field-cycling apparatus.     

N.m.r. and macromolecular migration in a melt or in concentrated solutions

A procedure of analysis of n.m.r. measurements is proposed as an approach to the observation of a single chain diffusion in a melt. The dynamic screening effect is applied to the definition of a temporary submolecule; this is used as a semi-local probe to investigate collective motions of all parts of a polymer chain. Measurements performed on ¹³C nuclei or protons lead to similar conclusions. The best agreement with experimental results is obtained by combining a M³ dependence of the terminal relaxation time (M is the chain molecular weight) with a multiple-mode relaxation spectrum; all modes have the same statistical weight.     

Hammett-Beziehungen zwischen 1H-NMR- bzw. 31P-NMR-chemischen Verschiebungen und Substituenten-konstanten in ω-Diphenylphosphinyl-und ω-Diphenylthiophosphinyl-trans-styrenen

Hammett Relationships between ¹H-NMR and ³¹P-NMR Chemical Shifts, Respectively, and Substituent Constants in ω-Diphenylphosphinyl and ω-Diphenylthiophosphinyl trans-Styrenes A well linear correlation between the chemical shifts of the ethylenic protons H_B and the ³¹P nuclei, respectively, and the Hammett constants σ_p of substituents R in 4-position for diphenylphosphinyl trans-styrenes 1 and the analogous diphenylthiophosphinyl trans-styrenes 2 has been found. A similar relationship for the proton H_A has been observed in the case of 1 only, but the substituent-induced shifts are not so sensitive. Donor substituents R in 1 and 2 effect an increase in the shielding of H_B and a deshielding of the P atom being connected with shifts of the i. r. PO absorption bands in 1 in the direction of lower wavenumbers. A mesomeric interaction between R and PY substituents (Y = O, S) is concluded to produce polymethin-like π-electron density distribution.     

Synthesis and photophysical behavior of a water‐soluble coumarin‐bearing polymer for proton and Ni2+ ion sensing

BACKGROUND: In recent years, many fluorescent chemosensors with various macromolecular structures have been prepared for the detection of protons or metal cations in the environment. Most of this research is focused on polymer sensors with fluorescent recognition sites in the main chain. In this case, the fluorescent recognition sites are covalently bonded to the polymer chain, and thus the polymer shows photophysical properties as a chemosensor for protons and metal ions. RESULTS: An acrylic monomer bearing coumarin moieties, 7‐hydroxy‐4‐methyl‐8‐(4′‐acryloylpiperazin‐1′‐yl)methylcoumarin, was synthesized. This was then copolymerized with N‐vinylpyrrolidone to obtain a blue fluorescent material. The fluorescent copolymer has good solubility in aqueous solution. Its main photophysical properties were determined in relation to its use as a sensor for protons and metal cations. It is an efficient ‘off‐on’ switcher for pH between 3.02 and 12.08. Additionally, the polymer sensor is selective to Ni²⁺ ions, with the increase in the fluorescence intensity depending on Ni²⁺ ion concentrations in the range 0.33 × 10^?5–7.67 × 10^?5 mol L^?1. CONCLUSION: The results suggest that this copolymer may offer potential as a reusable polymer sensor for protons and Ni²⁺ ions in aqueous solution. Copyright © 2009 Society of Chemical Industry     

Effects of protonation on the conformational characteristics and geometry of the rod-like benzobisoxazole polymers

Recent experiments on model compounds suggest that rodlike polybenzobisoxazole (PBO) and polybenzobisthiazole (PBT) chains are protonated when dissolved in highly acidic solvent. The PBO model compound can exist as a 2H⁺ ion, with one proton on each nitrogen atom, or (depending on the acidity of the medium) as a 4H⁺ ion, with two additional protons on the oxygen atoms. The PBT model compounds generally form 2H⁺ ions, owing to the lower basicity of sulfur atoms relative to oxygen atoms. In the present study, geometry-optimized CNDO/2 calculations have been carried out in an attempt of predict the effect of protonation on the conformational characteristics and geometry of PBO model compounds. Values of the conformational energy vs. rotation of the endphenylenes about the heterocyclic group are calculated for cis-PBO model compounds in the unprotonated form and as 2H⁺ and 4H⁺ ions. All three species prefer the coplanar conformation with maximum barriers, occurring at the perpendicular conformation, of approximately 8.4, 33.6, and 84.0 kJ mol^?1 for the unprotonated form, the 2H⁺ ion, and the 4H⁺ ion, respectively. Steric arguments would suggest that repulsions between the acidic protons and the ortho hydrogens on the phenylenes would render the coplanar conformation more repulsive than other orientations. However, detailed analysis of the optimized geometries reveals that the rotatable bond shortens with protonation, indicating an increased bond strength and, hence, increased conjugation energy.     

Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.     

Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy provides useful data for analyzing fatty acid compositions of edible vegetable oils. Quantitation of each fatty acid was carried out by evaluation of particular peaks. According to the ¹H NMR method, terminal methyl protons, divinyl protons, and allyl protons are useful to calculate linolenic acid, linoleic acid, and oleic acid, respectively. The ω-2 carbon, divinyl carbon, and allylic carbons were used for calculation of these acids by the ¹³C NMR method. Compositional results obtained by NMR coincided well with those of the conventional gas chromatography (GC) method. Results from ¹³C NMR were in better agreement with those from GC than were the results obtained by the ¹H NMR method.     

Rapid determination of iodine value by 1H nuclear magnetic resonance spectroscopy

High-resolution ¹H nuclear magnetic resonance (¹H NMR) has been found to be an effective tool for the direct, rapid, and automated determination of the iodine value (IV) of vegetable oils, including hydrogenated oils (IV=45.9–140.2). The total time required to obtain the ¹H NMR data is about 3 min per sample. The IV is calculated from the number of double-bonded protons and the average molecular weight derived directly from the spectrum. The average of olefinic protons and allylic plus divinyl protons area was used to calculate the absolute number of double-bonded protons. The ¹H NMR results were compared with those obtained by the traditional Wijs-cyclohexane methods. The correlation coefficient between traditional IV and the novel ¹H NMR method was r ²=0.9994 for the regression equation Y=0.9885X + 2.8084, where X was the result given by the traditional method. With the proposed regression equation, IV calculated by the ¹H NMR method was within an error of ± 1 unit of the result obtained by the traditional method. The proposed method is practically viable if one can afford to have the NMR system.     

Activity of Bromelain with Cationic Surfactants and the Correlation with the Change of 1H NMR Signals

This study observed the activities of bromelain in the presence of various cationic surfactants at different temperatures and the conformational changes in bromelain by ¹H NMR spectroscopy. We found that the bromelain activity was enhanced by tens to hundreds of micromoles per liter of the surfactant. In the presence of the surfactants, bromelain exhibited good tolerance to a range of substrate temperatures and its thermal stability was also increased. The ¹H NMR experiments indicated that when the temperature was increased from 25.0 to 45.0 °C, the protons of bromelain having chemical shifts (δ) between 3.7 and 5.2 ppm moved upfield, while those having δ values between 3.2 and 3.7 ppm moved downfield. In the bromelain/cationic surfactant mixture, the values of δ for the protons in both bromelain and the cationic surfactants decreased, accompanied by the broadening of the half-peak width of the surfactant protons. These results indicated that both increasing temperature and adding a cationic surfactant made the bromelain chain more flexible and hence, increased the bromelain activity. To the best of our knowledge, this was the first time that the relationship between the protein activity and the ¹H NMR data was expounded.     

Novel 4-(2,2,6,6-tetramethylpiperidin-4-ylamino)-1,8-naphthalimide based yellow-green emitting fluorescence sensors for transition metal ions and protons

Two novel yellow-green emitting 1,8-naphthalimides, containing a 4-amino-2,2,6,6-tetramethylpiperidinyl moiety, were configured as “fluorophore–spacer–receptor” systems. The photophysical characteristics of the dyes were investigated in both DMF and water/DMF (4:1, v/v) solutions. The ability of the new compounds to detect cations was evaluated by means of the changes in their fluorescence intensity imparted by the presence of transition metal ions (Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺) and protons. The presence of metal ions and protons was found to disallow photoinduced electron transfer resulting in enhanced fluorescence intensity. The results clearly show that only Cu²⁺ ions and protons were effectively detected, indicating the potential of the novel compounds as highly efficient “off–on” switchers for Cu²⁺ ions and protons.     

Spectroscopic Characterization of Ozonated Sunflower Oil

Ozonation reactions are very important in vegetable oil chemistry since their ozonation products are involved in antimicrobial effect in therapeutical uses for several microbiological etiology diseases. Information on the spectroscopic characterization of the products generated by ozonolysis of sunflower oil is limited. In the present study ozonized sunflower oil with 650 mmol-equiv/kg of peroxide index is chemically characterized. Ozonation of sunflower oil produced ozonides, aldehydes and hydroperoxides which were identified by ¹H, ¹³C and two-dimensional ¹H Nuclear Magnetic Resonance (NMR). The virgin sunflower oil and ozonized sunflower oil show very similar ¹H NMR spectra except for the resonances at δ = 9.74 and δ = 9.63 ppm that correspond to both triplet from aldehydic protons, δ = 5.6 ppm (olefinic signal from hydroperoxides), and δ = 5.15 ppm (multiplet from ozonides methylic protons). Other resonance assignments are based on the connectivities provided by the proton scalar coupling constants. These are the following: δ = 3.15 ppm (doublet from methylenic group in α position respect to olefinic proton), δ = 2.45 ppm (multiplet from methylenic group allylic to ozonides methynic protons) and δ = 1.62 ppm (multiplet methylenic protons in β position respect to ozonides methynic protons). From the ¹³C NMR and ¹H-¹³C two- dimensional spectrum of the ozonized sunflower oil, the presence of ozonides was confirmed by the signals δ = 103.43 and δ = 103.49 ppm, respectively. The others new signals found in δ = 42.5 and δ = 42.76 ppm confirm the presence of methylenic carbons from hydroperoxides and ozonides. These results indicate that NMR Spectroscopy can provide valuable information about the amount of reaction compounds of ozonized vegetable oil. From the chemical structural elucidation of ozonated sunflower oils, relevant biochemical and chemical information can be achieved.     

NMR studies of equilibriums in electrolytes: Ionic pairing in glymes

In this article, the formation constants of ionic pairs in salt-low molecular weight analogs of PEO (glyme, diglyme, triglyme) systems are estimated using NMR spectroscopy. The results from ⁷Li, ¹¹B and ¹⁹F NMR titration are compared and the role of the nuclei studied is discussed. It is shown that even in the solvents of very similar coordination (in terms of the donor and acceptor number values) and dielectric properties, the ionic pair formation constant depends on solvent used. The role of the solvent is discussed in terms of effects related to ion agglomerate formation, non-covalent interactions between ions and liquid matrix as well as the number of interacting centers present in the molecules of the solvent. The discrepancies between the results obtained using various nuclei NMR as well as discrepancies between ion pair formation constant calculated for different experimental regimes are also analyzed.     

Sequential distribution of main chain phosphorus-containing copolyesters characterized by 1H NMR

A series of main chain phosphorus-containing copolyesters were synthesized by polycondensation of terephthalic acid (TPA), ethylene glycol (EG) and phenyl phosphonic acid (PPA). Chemical structures of these main chain phosphorus-containing copolyesters were characterized by ¹H NMR. Experimental results show that the resonance intensity of PPA aromatic protons increases with increase of the phosphorus content. The chemical shifts of the ethylene protons in the ethylene glycol units vary with different sequences. The resonance chemical shift of the ethylene protons of the T-E-T unit is higher than those of P-E-T (T-E-P) and P-E-P units. The monomer molar fraction, sequential distribution and degree of randomness of the phosphorus-containing copolyesters were determined through analyses of the ethylene protons in the ethylene glycol units. The molar fractions of the PPA comonomer determined by ¹H NMR analyses are close to the values determined by a UV method. The degree of randomness for the copolyesters was found to be in the range 0·66–0·83. © 1998 SCI.     

Electron spin echo spectroscopy: A tool to probe structural properties of coals

Electron spin echo (e.s.e.) spectroscopy has been used in these laboratories to investigate proton hyperfine interactions in whole coal, separated coal macerals, synthetic lignites and model materials comprising perylene radical ions adsorbed on alumina and silica-alumina catalysts. The e.s.e. technique provides information that is complementary to electron nuclear double resonance in studying such interactions in coal. Coupling constants measured so far in evacuated samples of Illinois No. 6 agree well with models for condensed ring aromatic structures. Analysis of the proton matrix interactions are best fitted by r = 0.75 ± 0.05 nm, A_iso = 0 and n = 40 protons. Matrix interactions from ¹³C nuclei also are seen. Coupling constants observed in a vitrain component separated from Illinois No. 6 coal are similar to those seen in the whole coal; the fact that the maceral does not exhibit all of the interactions found in whole coal suggests molecular structures to be specific to individual maceral types. Differences in the g-values of macerals may provide a direct, non-destructive route to the analysis of maceral-specific structure.     

Synchrotron X-ray microdiffraction analysis of proton irradiated polycrystalline diamond films

X-ray microdiffraction is a non-destructive technique that allows for depth-resolved, strain measurements with submicron spatial resolution. These capabilities make this technique promising for understanding the mechanical properties of MicroElectroMechancial Systems (MEMS). This investigation examined the local strain induced by irradiating a polycrystalline diamond thin film with a dose of 2 × 10¹⁷ H⁺/cm² protons. Preliminary results indicate that a measurable strain, on the order of 10^− 3, was introduced into the film near the End of Range (EOR) region of the protons.     

NMR characterization of dihydrosterculic acid and its methyl ester

Cyclopropane FA occur in nature in the phosphoplipids of bacterial membranes, in oils containing cyclopropene FA, and in Litchi sinensis oil. Dihydrosterculic acid (2-octyl cyclopropaneoctanoic acid) and its methyl ester were selected for ¹H and ¹³C NMR analysis as compounds representative of cyclopropane FA. The 500 MHz ¹H NMR spectra acquired with CDCl₃ as solvent show two individual peaks at −0.30 and 0.60 ppm for the methylene protons of the cyclopropane ring. Assignments were made with the aid of 2D correlations. In accordance with previous literature, the upfield signal is assigned to the cis proton and the downfield signal to the trans proton. This signal of the trans proton is resolved from the peak of the two methine protons of the cyclopropane ring, which is located at 0.68 ppm. The four protons attached to the two methylene carbons α to the cyclopropane ring also show a split signal. Two of these protons, one from each methylene moiety, display a distinct shift at 1.17 ppm, and the signal of the other two protons is observed at 1.40 ppm, within the broad methylene peak. The characteristic peaks in the ¹³C spectra are also assigned.     

Structural Analysis of Hepta-, Nona-, and Undeca-Cyclic Aromatic Hydrocarbons by NMR Spectroscopy

Large condensed polycyclic aromatic hydrocarbons (LCPAHs) generally have distorted structures due to steric repulsion between neighboring hydrogen atoms. The distortion may influence their physicochemical properties such as electric conductivity, photoconductivity, and photochromism. Accordingly we have synthesized LCPAHs and analyzed their structure. In the present study, we synthesized an undecacyclic aromatic compound, dibenzo[a,rst]-dinaphtho[2,1,8-klm:1′,2′-o]pentaphene (DDPP) and determined the structure by use of NMR spectroscopy. To assign the ¹H- and ¹³C-NMR chemical shifts completely, we used the HMQC-TOCSY (Heteronuclear Multiple Quantum Coherence-Total Correlation SpectroscopY) method in which the original proton-carbon correlation is relayed to neighboring protons in the same spin-system. Furthermore, we compared the chemical shifts (δs) of the heptacyclic aromatic hydrocarbon, peropyrene, the nonacyclic, violanthrene B (VEB), and the undecacyclic, DDPP, and investigated correlations between their local structure and δs. For the protons in the bay region, the averaged δs decrease as molecular size increases: 9.23 ppm (hepta-) > 9.07 ppm (nona-) > 8.77 ppm (undeca-). Similar change in the δs is also found for the protons in the cove region: 9.37 ppm (nona-) > 8.81 ppm (undeca-). Thus, it is noted that the averaged δs for the protons in the cove region become downfield than those for the protons in the bay region. The findings are explained in terms of the anisotropic effect of the local magnetic field of benzene rings.     

Modeling the steady-state effects of cationic contamination on polymer electrolyte membranes

When cationic impurities, such as Na⁺, Ca²⁺, or metal cations, are present in a polymer electrolyte membrane fuel cell (PEMFC) the performance of the PEMFC can be significantly reduced. These effects were modeled in a PEM by solving the Nernst-Planck equation for all cationic species in the membrane. The model shows that cationic contaminants will always be more concentrated on the cathode side of the PEM when current is drawn through the PEM. This was attributed to the trade off between diffusion and migration of contaminants in the membrane. It was then theorized that at high currents and contamination levels a maximum current density of protons through the PEM would be encountered. This model allows us to better understand the effects of cationic contamination on PEMFCs. This understanding should lead to development of new modes for diagnosis and better methods to recover fuel cell performance.