Non-protonated Form Research Articles

Direct Synthesis of Controlled-Structure Primary Amine-Based Methacrylic Polymers by Living Radical Polymerization

We report the direct homopolymerization and copolymerization of a primary amine-based methacrylic monomer, 2-aminoethyl methacrylate (AMA), in its hydrochloride salt form by living radical polymerization. Linear PAMA homopolymer and AB diblock copolymers (where A = AMA and B = 2-(diisopropylamino)ethyl methacrylate, or DPA) were prepared with reasonably narrow polydispersities (Mw/Mn ∼ 1.2−1.3) in either DMSO or DMSO/1,4-dioxane mixtures at 70 °C using cumyl dithiobenzoate (CDB) as a reversible addition−fragmentation transfer (RAFT) chain transfer agent. AMA monomer is highly unstable in its nonprotonated form, undergoing rapid internal rearrangement to afford 2-hydroxyethyl methacrylamide. PAMA homopolymer proved to be significantly more stable than AMA monomer, but nevertheless slow chemical degradation occurred over long time scales (days) in alkaline solution. Initial 1H NMR studies confirm that (i) this PAMA degradation involves the elimination of 2-aminoethanol and (ii) at least some of its repeat u...

An XPS analysis of the interaction ofmeso-tetrakis(N-methylpyridinium-4-yl)porphyrin with exfoliated manganese thiophosphate

Composite thin films of (C72H66N8O12S4)yLi2xMn1−xPS3 have been obtained through a solution approach by interacting the tosylate salt of the cationic water soluble5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin(H2T4)and MnPS3 exfoliated in the presence of lithium ions. The thin films have been investigated throughx-ray diffraction (XRD), ultraviolet/visible (UV/vis) absorption and mainly x-rayphotoemission spectroscopy (XPS). N 1s core-level XPS spectra emphasize thepresence of three non-equivalent nitrogen atoms, similarly to the film of the pureH2T4 salt. This result, together with the interlayer spacing determined by the XRD pattern and theevidence from absorption measurements, indicates that the porphyrin is intercalated intoMnPS3 layers in a non-protonated form and substantially flattened with respect to the free molecule. Thestriking likeness between the N 1s core levels in the XPS spectra of the composite material, of theH2T4 salt and of the neutral meso-tetrapyridylporphyrin(H2TPyP) suggests thatH2T4 is presentbetween the MnPS3 nanosheets together with its counter-ion (tosylate). This hypothesis is confirmed by theobservation of a structure which can be attributed to the sulfur of the counterion in the S2p core-level XPS spectra of the composite material. An analysis of the Mn 2p and 3p, Sand P 2p core-level regions through XPS reveals a strong similarity between the startingMnPS3 and the composite material, suggesting that no charge transfer occurs from the guest(H2T4-tosylate) tothe host species (MnPS3).

Using "Basic Principles" To Understand Complex Science: Nicotine Smoke Chemistry and Literature Analogies

The Henderson–Hasselbalch equation calculates the equilibrium distribution of 50:50 for nicotine in its nonprotonated (free base form), relative to its monoprotonated form, at pH of 8 in dilute aqueous solution. This ratio has then been used in the literature to predict the effect of ammonia compounds in tobacco and in smoke on nicotine pyrolysis and smoke chemistry. Experiments demonstrate that neither the thermal chemistry of tobacco alkaloids nor the transfer of nicotine from tobacco to smoke can be explained by the position of the nonprotonated versus monoprotonated form equilibrium in aqueous extracts of tobacco. The high thermal stability of nicotine in air allows nicotine salts to be converted to nonprotonated nicotine and volatilize during heating prior to any substantial decomposition of the nicotine moiety. In contrast, cocaine hydrochloride is thermally unstable and will rapidly decompose upon heating; cocaine hydrochloride must first be converted to its nonprotonated form prior to heating and ...

Studies of intramolecular hydrogen bonding in protonated and non-protonated hexahydropyridinobenzodioxins

The conformational stability of hexahydropyridobenzodioxin and related derivatives in both protonated and non-protonated forms have been investigated by means of ab initio molecular orbital methods as well as semi-empirical AM1 and PM3 methods. One of the cis conformers ( cis2e) has been found to be most stable due to the formation of an intramolecular hydrogen bond, other conformers including the trans isomer cannot form this interaction but are of different stability because of the orientation of the polar oxygens and the nitrogen. The effect of the intramolecular hydrogen bonding on the stability of hexahydropyridobenzodioxin and its methylated derivatives has been examined using various basis sets levels. In protonated form, both the semi-empirical and ab initio calculations give excellent agreement in energetic order; however, different orderings of conformer stabilities are observed by different computational methods in non-protonated form. The results provide insight into the intramolecular hydrogen bonding in computational studies of biologically important molecules.

Surface-enhanced Raman spectroscopy and electrochemistry of 2,2′-bipyridine adsorbed at copper electrode

The adsorption of 2,2′-bipyridine (22BPY) on the surface of polycrystalline copper electrode was studied by means of surface-enhanced Raman spectroscopy (SERS) and cyclic voltammetry in a wide range of electrode potential. Experiments were carried out in both acidic and neutral solutions, as well as in presence of two kinds of supporting electrolyte (KCl and LiClO 4) in order to examine the influence of molecule protonation and specifically adsorbed anions. It was found that a molecule orientation with respect to the surface changes from perpendicular to more tilted in the neutral perchlorate solution followed by the conformation change from cis to trans in strongly negative potentials. This conformational transition occurs gradually, probably through a series of intermediate states. The SERS features due to trans conformers are uniquely observed in presence of perchlorate anions. In the presence of chloride the molecular plane is at least slightly inclined towards the surface in the whole potential range. In acidic solutions the SERS results indicate that 22BPY adsorbs in non-protonated form independent on the present anion with the molecular plane tilted although it becomes more perpendicular with respect to the surface at negative potentials. The cyclic voltammetry measurements revealed that the hydrogen evolution is inhibited in presence of 22BPY in both neutral and acidic solutions. It suggests strong adsorption of this molecule in a wide range of electrode potentials.

Cooperative Effects in the Binding of Substrates to Nickel(II) and Nickel(III) Complexes with a Bis(macrocyclic) Ligand

Nickel(II) complexes of mono- and bis(macrocyclic) ligands are the products of a nickel(II)-assisted template reaction with 2,3,2-tet, melamine and formaldehyde [2,3,2-tet = bis−N,N′-(2-aminoethyl)propane-1,3-diamine; melamine = 2,4,6-triamino-1,3,5-triazine]. The structures of two four-coordinate, diamagnetic nickel(II) complexes (protonated and non-protonated form) and of a six-coordinated paramagnetic nickel(II) compound with the protonated ligand have been determined by X-ray crystallography. Electronic spectroscopy was used to analyze the equilibrium between the paramagnetic and diamagnetic forms, and the electrochemical properties have been studied extensively (NiIII/II and NiII/I couples). The equilibrium between the paramagnetic and diamagnetic forms and the nickel(III/II) couple are strongly dependent on the electrolyte, and sulfate is found to be coordinated selectively to the apical positions of both the nickel(II) and nickel(III) centers of the dinuclear compound. The structural, thermodynamic and electrochemical studies suggest that cooperative effects, involving coordination of sulfate to one nickel center, assisted by hydrogen bonding to an axially coordinated water molecule of the other nickel center, is responsible for the recognition of this anion. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Phenazine-2,3-diamine.

The planar electron-rich heterocyclic diamine 2,3-diaminophenazine (DAP), C12H10N4, is of particular interest to both chemists and biochemists because of its rich organic chemistry and intense luminescence. In this paper, we report the first structure of DAP in its non-protonated form and describe the intriguing crystal packing, which features pi-pi, hydrogen- and T-bonded interactions.

Double effect of organic amines (activation and inhibition) on the phosphotriesterase

The kinetic behavior of the phosphotriesterase in the presence of organic amines (diethylamine, diisopropylamine, triethylamine, pyridine and others) capable of activating the enzyme at the concentration up to 0.10 M and inhibiting it at higher concentrations is described. The form acting as activator in a solution is the nonprotonated form of amines and the value of activation effect depends on p K a of amine and its structure. The activation by amines at the above concentrations has a noncompetitive character, whereas the inhibition at higher concentrations has competitive one. The mechanism of phosphotriesterase action in the presence of amines is discussed.

Thermal stability of polyaniline

Among conducting polymers with metallic characteristics, polyaniline (PANI) is claimed to have one of the highest environmental stability. From an industrial point of view it would be useful to be able to thermally process this material into useful products using conventional techniques such as extrusion, stretching, rolling, etc., which generally are carried out at elevated temperatures. Somewhat surprisingly, relatively few studies have addressed the thermal stability of PANI, in particular that of the non-protonated emeraldine base form. Therefore, a study of the thermal properties was performed to examine the thermal stability of this material and to identify the optimum processing and maximum application temperatures.

Characterisation of bifunctional ruthenium(II) complexes, potential DNA photo-probes. Presence of folded and unfolded conformers †

Novel bifunctional ruthenium(II) complexes, [Ru(TAP)2(POQ-Nmet)]2+ and [Ru(BPY)2(POQ-Nmet)]2+ (1a, 2a), containing a metallic and an organic moiety, have been prepared as photoprobes and photoreagents of DNA (TAP = 1,4,5,8-tetraazaphenanthrene, POQ-Nmet = 5-[6-(7-chloroquinolin-4-yl)-3-thia-6-azaheptanamido]-1,10-phenanthroline). The ES mass spectrometry and 1H NMR data in organic solvents indicate that the quinoline moiety exists in both the protonated and non-protonated form. Moreover, the comparison of the NMR data with those of the corresponding monofunctional complexes (without quinoline) evidences that [Ru(TAP)2(POQ-Nmet)]2+ and [Ru(BPY)2(POQ-Nmet)]2+ are unfolded when the quinoline unit is protonated whereas deprotonation permits folding of the molecule. In the folded state the spatial proximity of the electron donor (the organic moiety) and electron acceptor (the metallic moiety) in [Ru(TAP)2(POQ-Nmet)]2+ favours intramolecular photo-induced electron transfer, which has been shown in a previous study to be responsible for the very low luminescence of 1a in non-protonating solutions. The restoration of the luminescence by protonation of the quinoline moiety as observed previously is in agreement with the unfolding of the molecule demonstrated in this work. The existence of such folding–unfolding processes related to protonation is crucial for studies of 1a with DNA.

X-ray photoelectron spectroscopy study of silane-treated newsprint-fibers

The nature of adhesion in multicomponent materials such as cellulosic fibers/thermoplastic composites is strongly dependent on the surface properties of the components. X-ray Photoelectron Spectroscopy (XPS) was used to characterize the surfaces of untreated and treated newsprint-fibers. Gamma-aminopropyltriethoxysilane and dichlorodiethylsilane were used for the surface modification of the fibers. The XPS analysis indicated that coupling between the silanes and the newsprint-fibers has occurred, and that silanols were adsorbed to the surface of newsprint-fibers by two different mechanisms: (1) an ether linkage between the silanols and the hydroxyl groups of the fibers and (2) a hydrogen bonding between the amine and the hydroxyl groups of the fibers. The formation of the hydrogen bonding was evidenced by the two observed amino states, i.e., a covalent non-protonated form and an ionic protonated form.

Polyaniline pH Electrodes

Polyaniline-coated Pt, Pd, and graphite electrodes have been studied. Their potential relationship to pH follows the same principle as the pH glass electrode. They are solid state involving no redox reactions. The potential is derived from the surface charge density caused by protonation or deprotonation. They act as capacitors. The nonprotonated form of polyaniline was used for pH 6.8 to 1.2 and the protonated form of polyaniline was used for pH 6.8 to 13.0. Three regions of curves (acid, neutral, and alkaline) were obtained. The polyaniline-coated graphite electrode is recommended. It offers the advantage of sturdiness and may be used in microscale in HF solution, at high pressure. At pH 2.2, approximately 4,200 H+ions were adsorbed by polyaniline per nm2. An insignificant number of H+ions were adsorbed by polyaniline at pH 6.2; this is close to its isoelectric point.

Inner-Sphere and Outer-Sphere Complexation of a Polycarboxylic Acid at the Water−Boehmite (γ-AlOOH) Interface: A Combined Potentiometric and IR Spectroscopic Study

Speciation and equilibria of 1,2,4,5-benzenetetracarboxylate (pyromellitate) at the water-boehmite (gamma-AlOOH) interface were studied in 0.1 M Na(Cl) at 298 K. Surface equilibrium analyses were based upon potentiometric and adsorption measurements in the range 4.5 < pH < 10.0. To characterize the surface complexes at the molecular level, attenuated total reflectance infrared spectra were recorded. The IR data provided information on the structure and composition of the complexes. This information could then be used to constrain the thermodynamic surface complexation model. The acid/base properties of pyromellitate in solution and its complexation with. Al(III) mere also studied by means of potentiometric titrations in 0.1 M Na(Cl) at 298 K. The results of these measurements were primarily used to investigate the effect of pyromellitate on the dissolution of boehmite. In aqueous solution Al(III) forms a series of mononuclear complexes, namely, AlHL, AlL-, and Al(OH)L2-. No indication of polynuclear complexes was found within the concentration ranges studied. IR spectra of pyromellitate sorbed at the water-boehmite interface suggested the existence of one dominating surface complex over a wide pH range (4.4 less than or equal to pH less than or equal to 8.1). The IR spectroscopic characteristics of this complex were in agreement with an enter-sphere nonprotonated pyromellitate ion. No evidence was found fur protonation of the sorbed ion. Thus, the nonprotonated form is greatly stabilized at the interface as compared to the speciation in the aqueous solution. The IR data also showed some indications of a second minor surface complex. This was tentatively assigned to an inner-sphere species. According to the constraints provided by the IR data, the potentiometric and adsorption data were modeled with two surface complexes, =AlOH2+L4- (outer-sphere) and =AlL- (inner-sphere). The extended constant capacitance mod.el was used to account for the electrostatic effects at the interface. The agreement between the experimental data and the model was satisfactory. Furthermore, the model was also in agreement with the minor changes observed in the IR spectra as a function of pH. (Less)

EPR and ENDOR spectroscopy studies on α-aminoanthraquinone radical cations in solution

EPR and ENDOR spectra of the radical cations of 1,4-diamino-9,10-anthraquinone, 1,4-bis(methylamino)9,10-anthraquinone, 1,4-bis(ethylamino)-9,10-anthraquinone, 1,4-bis(butylamino)-9,10-anthraquinone and 1,4-bis(hexylamino)-9,10-anthaquinone were measured in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP), with (bis(trifluoroacetoxy)iodo)benzene (PIFA) as oxidizing agent, in the temperature range 260–300 K. The isotropic hyperfine coupling constants (hcc) of the labile amino protons were assigned by deuterium exchange with deuterated trifluoroacetic acid (d-TFA) in HFP as solvent. The results are compared with the radical cations of 1,4-diamino-9,10-anthraquinone and 1,4-bis(methylamino)-9,10-anthraquinone produced in acetonitrile by electrolytic oxidation. A tentative assignment of the hcc constants by MO calculations was made for 1,4-diamino-9,10-anthraquinone. The results indicate that deuteration is restricted entirely to the amino protons and that the obtained radical cation of aminoanthraquinone occurs in the non-protonated form (Q+˙).

Photophysics of Bifunctional Ru(II) Complexes Bearing an Aminoquinoline Organic Unit. Potential New Photoprobes and Photoreagents of DNA

[Ru(BPY)2POQ−Nmet]2+ and [Ru(TAP)2POQ−Nmet]2+ (1 and 3) are bifunctional complexes composed of a metallic unit linked by a flexible chain to an organic unit. They have been prepared as photoprobes or photoreagents of DNA. In this work, the spectroscopic properties of these bifunctional complexes in the absence of DNA are compared with those of the monofunctional analogues [Ru(BPY)2Phen]2+, [Ru(BPY)2acPhen]2+, [Ru(TAP)2Phen]2+, and [Ru(TAP)2acPhen]2+ (2 and 4). The electrospray mass spectrometry and absorption data show that the quinoline moiety exists in the protonated and nonprotonated form. Although the bifunctional complex containing 2,2‘-bipyridine (BPY) ligands exhibits photophysical properties similar to those of the monofunctional compounds, the bifunctional complex with 1,4,5,8-tetraazaphenanthrene (TAP) ligands behaves quite differently. It has weaker relative emission quantum yields and shorter luminescence lifetimes than the monofunctional TAP analogue when the quinoline unit is nonprotonated. This indicates an efficient intramolecular quenching of the 3MLCT (metal to ligand charge transfer) excited state of the TAP metallic moiety. When the organic unit is protonated, there is no internal quenching. In organic solvent, the nonquenched excited metallic unit (bearing a protonated quinoline) and the quenched one (bearing a nonprotonated organic unit) are in slow equilibrium as compared to the lifetime of the two emitters. In aqueous solution this equilibrium is faster and is catalysed by the presence of phosphate buffer. Flash photolysis experiments suggest that the intramolecular quenching process originates from a photoinduced electron transfer from the nonprotonated quinoline to the excited Ru(TAP)22+ moiety.

The interaction of aliphatic amines with safranine T in aqueous solution

The photophysics of the excited states of safranine T and its reactions with aliphatic amines were studied in aqueous solution. The fluorescence lifetime of the singlet state was found to be 1.3 ns at 20 °C in water, and increasesin non-hydroxylic solvents. This state is quenched by trialkylamines with nearly diffusional rate constants. In addition to the intense absorption of the monoprotonated form of the triplet state at 820 nm, a weaker absorption at 420 nm was detedted. The non-protonated form also has a residual absorption at 820 nm. The lifetime of the non-protonated triplet was found to be around 15 μs. The monoprotonated triplet state of the dye is quenched by amines with rate constants of about 1×10 9 M −1 s −1, too high to be ascribed to a charge transfer mechanism. Similar to the reaction in organic solvents, this reaction proceeds by a proton transfer mechanism, leading to the non-p3otonated form of the triplet state. This form is then quenched by another amine molecule to give the corresponding semireduced species.

General model for the steady-state response properties of fiber-optic ammonia gas sensors

A mathematical model is derived to describe the steady-state response properties of the fiber-optic ammonia sensor. Unlike our previous model, the present model permits any concentration of total ammonia nitrogen initially present in the internal solution of the sensor. A cubic equation is solved to give the magnitude of the nonprotonated form of the indicator dye under equilibrium conditions. For the first time, the effect of the initial ammonia nitrogen concentration in the internal solution is evaluated. In addition, the response equation is differentiated with respect to the sample ammonia concentration to give an expression that can be used to evaluate the effects of critical experimental parameters on the measurement sensitivity. This model is verified by comparing predicted and actual responses for several different fiber-optic sensor configurations. The model is used to generate surface maps that allow evaluation of the interrelationships between key experimental parameters such as the indicator concentration, sample ammonia concentration, internal ammonium chloride concentration and indicator acid dissociation constant. Results of this analysis indicate that optimal responses and maximal sensitivity require careful selection of values for these parameters.

Origin of the high-energy emission of 1,1′-diethyl-2,2′-cyanine dye

In addition to the yellow emission ascribed to the J aggregates of 1,1′-diethyl-2,2′-cyanine, this compound also exhibits a high-energy emission around 400 nm in dilute aqueous solutions (c<10−3 mol 1−1. It was using time-resolved emission measurements that protonation of 1,1′-diethyl-2,2′-cyanine is responsible for this emission. At pH<4, the excited state protolytic reaction competes with ground state protonation. Both pathways give the same excited species, luminescing at 400nm. The non-protonated form shows only weak flourescence. The excited state lifetime of the protonated form is 4.5 ns.

Medium effects on the ionization constants of some quinoline derivatives

The deprotonation and acid ionization constants of some quinoline derivatives in aqueous organic solvents were determined. The organic solvents used include methanol and ethanol as amphiprotic solvents andDMF andDMSO as dipolar aprotic solvents. The obtainedpK1 andpK2 values are discussed with respect to the nature and the amount of the organic component. The high stabilization of the non-protonated form by dispersion forces and of the proton by its interaction with the solvent are the main factors responsible for the increase in the ionization constants of the protonated forms of the quinolines under investigation. On the other hand, H-bonding interactions (in addition to the electrostatic effect) seem to play the major role in determining the second acid-base equilibrium of 8-hydroxyquinoline. The deprotonation constants of the examined quinolines are correlated with their experimentally determined lone-pair ionization potential values.

PH-dependence of warfarin binding to alpha 1-acid glycoprotein (orosomucoid).

The binding of warfarin to alpha 1-acid glycoprotein (AAG) was found to increase with decreasing pH. The u.v.-visible difference spectra generated upon binding to AAG at pH 5.0 or 7.4 showed warfarin to bind as the anion. Warfarin-binding data were satisfactorily fitted to a model that incorporates the effect of pH and discriminates the association constants of the non-protonated and protonated binding site of the protein. It was shown that AAG-binding site in the protonated form had a markedly higher affinity for warfarin than the non-protonated form, with a pK value of 7.7 +/- 0.1, which is likely to be a histidine residue. Among other possible interactions, it is suggested that ligand binding to AAG involves a reinforced hydrogen bond.