Academic literature on the topic 'Acid-base propertie'

The design of chiral synthetic polymers capable of self-assembling into stable secondary structures represents an attracting approach with important biological applications, such as selective subcellular localization, protein surface mimicry and recognition. Chirality in polymers may be expressed based on the location of the stereogenic centers: i) main-chain chirality; ii) side-chain chirality and iii) self-assembled structures. Synthetic polymers as polyacetylenes, polyolefines and polymethacrylamides showing side-chain chirality may be synthesized by radical polymerization processes starting from modified α-amino acids. In previous work, a new family of biomimetic polymers showing side-chain chirality, named polyamidoamino acids (PAACs), were introduced. The first polymer of this family was named L-ARGO7, derived by the step-wise polyaddition of L-arginine with N,N’-methylenebisacrylamide (MBA). The reaction was carried out in water, at 50°C and pH > 9 for 6 days, yielding a polymer with Mw ≈8000 and PDI 1.4. L-ARGO7 turned to be highly cytocompatible (IC50 ≥ 8 mg mL-1) and easily internalized in mouse embryo fibroblasts balb/3T3 clone A31 cell line proving, in this respects, to share some of the unique biological properties of polyarginine cell-permeating peptides. The objectives of this work were multiple: to obtain a library of PAACs from the reaction of N,N’-methylenebisacrylamide with various natural α-amino acids following the same general procedure adopted for the synthesis of L-ARGO7, thus demonstrating the versatility of the synthetic process devised; to study the solution properties of PAACs, namely as acid-base behavior, ionization state, size and viscosity; to elucidate their conformational properties and ability to fold in aqueous media into compact and stable secondary structures; to study the responsiveness of these conformations to external stimuli; to study the fluorescent properties of PAACs from L-tryptophan; most important, to assess the PAAC ability to exhibit chirality-dependent interactions with biomolecules. The PAACs synthesized in this work can be classified based on the structural features of the α-amino acid residue: i) cationic arginine derived PAACs obtained from D-, L- and D,L-arginine; these polymers are moderately basic, since the guanidine group is internally neutralized by the carboxylate. Basicity is mainly due to the presence of the tert-amine; ii) hydrophobic alkyl-substituted PAACs derived from L-alanine (M-L-Ala), L-valine (M-L-Val) and L-leucine (M-L-Leu); these polymers are obtained by reacting slightly hydrophobic α-amino acids bearing lateral substituents of increased steric hindrance; iii) polar glutamine-derived PAAC obtained from L-glutamine (M-L-Gln); glutamine was chosen for its ability to form hydrogen bonds as protons donor or acceptor; iv) amphipathic homo- and copolymeric L-tryptophan-based PAACs synthesized from, respectively, L-tryptophan (M-L-Trp) and L-tryptophan/glycine mixtures (M-G-L-Trp); tryptophan was chosen for its fluorescence properties, used to characterized conformational and structural features of homo- and copolymers. EXPERIMENTAL PART: PAACs SYNTHESIS The synthetic procedure of the investigated PAACs is reported in Scheme 1. L-, D- and D,L-PAACs were obtained in variable yield (60-70 %) carrying out the polymerization in aqueous solutions at 50 °C and pH > 9 for 6 days. In no case, traces of hydrolytic degradation or formation of aggregates were seen. After 6 days, solutions were acidified to pH 4, purified by ultrafiltering through membranes with 100 and 5 kDa nominal molecular weight cut-off. The intermediated fractions were freeze-dried and structurally analysed by means of 1H and 13C NMR in D2O, at pH 4.5. Molecular weights (Mw and Mn) was measured by means of size exclusion chromatrographic (SEC) analysis, carried out in 0.1 M TRIS buffer pH 8.00 ± 0.05, with 0.2 M NaCl. RESULTS i) ARGO7 and Alkyl-substituted PAACs Circular dichroism (CD) measurements were recorded between 200 – 280 nm in the 3-12 pH interval. Spectra were consistent with the presence of pH-dependent ordered secondary structures, whose changes with pH were rapidly achieved and fully reversible. In addition, conformations resulted thermodynamically stable and reversible in the 3-70°C range. CD spectra were collected at ionic strength up to 2 M NaCl and in presence of denaturating agents, as urea and guanidinium chloride. Conformation of ARGO7 isomers resulted unaffected by ionic strength and presence of denaturants, whereas M-L-Ala, M-L-Val and M-L-Leu conformations changed with the introduction of guanidinium chloride. Molecular dynamics (MD) simulations were performed at Politecnico di Milano (prof. G. Raffaini and F. Ganazzoli) and revealed that ARGO7 and alkyl-substituted PAACs had a compact, coiled structure (Rgs 0.8-1.11 nm). MD showed that PAACs’ main chains were organized into a transoid arrangement characteristics of hairpin-like conformations. Structuring and size were mainly dictated by intramolecular interactions of electrostatic nature in the polymer main chain, with minor dependence from the amino acids side chain. Hydrodynamic radius (Rh) was determined by DLS as a function of pH, time, ionic strength and presence of denaturating agents (urea and guanidinium chloride). Results revealed that these PAACs had monomodal volumetric distributions of 1.5 ± 0.3 nm average radius, stable at 25 °C for at least 1 month and unaffected by pH, ionic strength and presence of denaturants. In addition, nanoparticles’ dimensions did not change by increasing the PAACs concentration in the 0.5 – 20 mg mL-1 range, suggesting these polymers may intramolecularly self-assembled into stable single chain nanoparticles. ii) glutamine-derived PAACs Differently from the other PAACs, M-L-Gln Mw and Mn values were more than two times higher than the others. This was tentatively ascribed to the presence of intra- and intermolecular hydrogen bonding, further studied with CD and NMR spectroscopy. CD spectra resulted sensitive to the presence of urea, a protein denaturant known to form H-bonding, with time dependent spectral variations. DOSY, variable-temperature NMR (VT-NMR) and NOESY were used to obtain the structural and conformational features of M-L-Gln. DOSY showed only one diffusion coefficient, from which a Rh of 3.53 nm was calculated. VT-NMR was carried out at pH 4.5 and revealed that side-chain amide groups were involved in the formation of H-bonding, whereas only a small percentage of amides of the MBA backbone did the same. In addition, NOESY experiments measured two NOEs, both involving CH2 next to the tert-amine and CH2 in β and γ position of the glutamine side chain, respectively. Thus, M-L-Gln showed a coiled structure in which glutamine side chain moved closer to the main chain. iii) tryptophan-based PAACs Polymers bearing tryptophan as side substituent were synthesized by Michael-type polyaddition of MBA with L-tryptophan, its isomer, and different molar ratio of L-tryptophan/glycine mixtures. Differently from the other PAACs, these reactions were carried out under nitrogen flux and by portion wise addition of the base to avoid indole oxidation. UV–Vis absorption and scattering of polarized IR beam tests showed all of them to have composition- and pH-dependent solubility. CD studies and DLS measurements were comparable with the other PAACs. CD were consistent with the formation of pH dependent self-assembled structures, whose conformation was dictated by the polymer main chain and its average ionization degree. Rhs resulted stable for at least 1 month, unaffected by pH but, to some extent, sensitive to concentration in the range 1–30 mg·mL−1. Photoluminescence analyses, quantum yields, steady state and time-resolved fluorescence were measurements at different pH, polymers concentration and tryptophan content. Results indicated that the photoluminescence properties of tryptophan derived polymers were governed solely by tryptophan. All polymers exhibited pH-dependent quantum yields, lifetimes and emission maximum. Interestingly, fluorescence studies conducted on oxygen-free solution gave comparable results, indicating compact conformations where L-tryptophan moieties were not accessible to the quencher. Also, intermolecular quenching by approaching chains was studied and observed in M-L-Trp and M-G-L-Trp10. iv) L- and D-ARGO7 chiral recognition To assess ARGO7 chiral recognition ability, sodium deoxycholate (NaDC), one of the components of bile salts, was chosen as a chiral model surface. Through a stepwise mechanism, NaDC can form chiral micelles, whose self-assembly behaviour is mainly affected by pH. In particular, NaDC showed three main pH dependent behaviour: homogenous solution (pH > 8), gel phase (pH 7 – 7.5), flocculation and aggregation (pH < 7). Pulsed-gradient spin echo NMR (PGSE-NMR), surface tension, circular dichroism (CD), dynamic light scattering (DLS), zeta potential (ZP) and small-angle neutron scattering (SANS) experiments were carried out on NaDC/L- and NaDC/D-ARGO7 mixtures, to assess chirality-dependent interactions. Surface tension, DLS, zeta potential and PGSE NMR measurements were recorded to characterize NaDC behaviour in solutions (CMC and self-assembly) as a function of pH and concentration and will not be considered in this report. CD measurements were carried out on 5 mg mL-1 of NaDC mixed with 0.5 mg mL-1 of either L-, D- or D,L-ARGO7 solutions, in the 190 – 300 nm range in a 1 mm cell. Prior to the analysis, solutions were corrected to pD (pH of D2O solutions) 9.06, and 7.50. At pD 9.06, the addition of NaDC did not result in any significant modification of the polymers’ spectra, in either L- or D- form of the polymers. Thus, no chiral discrimination could be found at this pH. At pD 7.30, CD spectra of NaDC gel phase showed different pattern upon addition of L- and D-ARGO7, whereas no changes were seen with D,L-ARGO7. Thus, the self-reorganization of NaDC into an ordered gel, was likely due to the chiral recognition of the different isomers. Small-angle neutron scattering (SANS) measurements were carried out at the ISIS Neutron and Muon Source facility (Rutherford Appleton Laboratory in Oxfordshire, UK, under the supervision of Prof. Peter Griffiths) to study chiral recognition, by looking at the conformational modifications of NaDC micelles upon introduction of the different isomeric forms of the polymer, at different pHs and concentrations. SANS collected at pD 8.5 - 8.8 for various NaDC concentrations were consistent with the presence of micelles, described by prolate ellipsoids with polar radius of 22 – 28 Å and equatorial radius of 7 – 10 Å. By decreasing pH, NaDC micelles’ structure changed from a prolate ellipsoid (pD 8.80) to an elongated rod (pD 7.30) described by elliptical cylinders of 487.6 ± 21.2 Å length and 2.88 ± 0.19 axis ratio (Figure. 1a, black curve). NaDC/ARGO7 mixtures were prepared adding 5 mg mL-1 of NaDC to 0.5 mg mL-1 solution of D-, L-, D,L-ARGO7 and an equimolar mixture obtained by mixing L- and D-isomer of the polymer (D-/L-ARGO7). All NaDC/ARGO7 mixtures showed superimposable curves. They were fitted with the same model used for NaDC solutions, that is micelles with prolate ellipsoidal morphology (Figure 1a). Only small changes in the total charge and in the semi-minor and semi-major axis were seen. This confirmed the modest effect of the electrostatic interactions between the two components, ARGO7 and NaDC, and the absence of chiral discrimination. Chiral recognition was then assessed collecting SANS data for 5 mg mL-1 NaDC gels (pD 7.3 – 7.5) with 0.5 mg mL-1 of D-, L-, D,L-ARGO7 or an equimolar mixture composed of 0.5 mg mL-1 D-ARGO7 and 0.5 mg mL-1 L-ARGO7. They showed that NaDC structure was differently affected by the chirality of the polymer (Figure 1b), confirming results obtained from CD spectra. In particular, D-, D,L-ARGO7 and the equimolar mixture changed SANS pattern in the same way. They retained the same rod-like structure of NaDC micelles, albeit with a lower axis ratio (1.51 ± 0.41). Different was the case of the NaDC/L-ARGO7 solutions, where L-ARGO7 appeared to trigger the formation of NaDC ellipsoidal clusters. In conclusion, PAACs represent singular examples of synthetic bioinspired chiral polymers that showed potential for biotechnological applications on account of their i) stimuli-responsiveness, ii) self-assembly ability and iii) selective interactions with chiral structures, including biological structures.

Estudaram-se as propriedades ácido base e de complexação com íons Cu(II) dos ácidos húmico (AH) e fúlvico (AF) extraídos de vermicomposto. O isolamento e a purificação foram realizados de acordo com o método descrito pela Sociedade Internacional de Substâncias Húmicas (IHSS). Estudaram-se as propriedades ácido-base por titulação potenciométrica em meio de KNO3 0,10 mol L-1 utilizando-se funções de Gran modificadas. Caracterizaram-se cinco classes de grupos ionizáveis, constatando-se predominância de grupos carboxílicos sobre grupos fenólicos e amínicos, especialmente para o AF, cuja acidez total foi maior do que a do AH. Estudaram-se as propriedades complexantes com íons Cu(II) nos pH 4, 5 e 6 por titulação potenciométrica com um eletrodo íon-seletivo para Cu(II), adotando-se os métodos de Scatchard e de regressão não linear com a equação de Langmuir para tratamento de dados. Em pH 5 e 6 caracterizaram-se duas classes de sítios de complexação, enquanto em pH 4, apenas uma classe foi caracterizada. De maneira geral, a estabilidade e a capacidade de complexação aumentaram com o pH, indicando a competição de prótons pelos sítios de complexação. Os resultados indicam maior estabilidade e capacidade para a complexação com AH em relação ao AF. Esta tendência foi verificada por funções diferenciais de equilíbrio diferenciais aplicadas em baixos graus de ocupação de sítios.
Acid base and complexation with Cu(II) ions were studied for humic (AH) and fulvic (AF) acids extracted from vermicompost. The isolation and purification was performed according the procedure described by the International Humic Substances Society (IHSS). The acid base properties were studied by potentiometric titration in 0,10 mol L-1 KNO3 using modified Gran functions. Five classes of ionizable sites were characterized, showing a predominance of carboxylic over phenolic and aminic groups, especially for AF, which has total acidity larger than the one determined for AH. Complexing properties with Cu(II) ions were studied by potentiometric titration at pH 4, 5 and 6 using Cu(II) ion-selective electrode. Data treatment was performed using the Scatchard method, as well as non-linear regression with the Langmuir equation. At pH 5 and 6, two classes of binding sites were characterized, but at pH 4 only a single complexing site was characterized. Stability and capacity increased with pH, suggesting competition of protons by the binding sites. The results indicate larger stability and capacity for complexation with AH in comparison with AF. This trend was also verified by differential equilibrium functions at low degree of site occupation.

The release of toxic metal species is of concern due to their detrimental effects on the environment and human health. Industrial effluents are a major source of mobilised metal species. Suitable technologies are needed to sequester toxic metal species at the point of source. Biosorption, which is based on the passive adsorption of contaminants onto biological materials, promises to offer an effective alternative or complementary step to existing treatment methods. However, to date there has been no widespread commercialisation of the technique. This is partly due to an insufficient understanding of the complex underlying mechanisms which makes it difficult to select suitable biomass for specific remediation problems and to predict process performance. This study characterised two gram-positive, thermophilic bacteria, Anoxybacillus flavithermus (BF) and Geobacillus stearothermophilus (BS), harvested at two different growth times, with regard to their acid-base and Cd�⁺ adsorption behaviour. The aim was to investigate the metal cation adsorption properties of thermophilic bacteria which has not been studied previously, and to gain a better understanding of the interactions responsible for bacterial metal cation adsorption. Experimental techniques employed in this study included microscopy to establish cell and cell wall morphology, batch acid-base and Cd�⁺ adsorption experiments to quantify proton active surface functional groups and Cd�⁺ adsorption, electrophoretic mobility measurements to assess the overall surface charge of the bacteria and in situ attenuated total reflection infrared (ATR-IR) spectroscopy to reveal the chemical identities of functional groups. Chemical equilibrium models based on batch acid-base titration and electrophoretic mobility data were developed to quantitatively describe proton active surface functional groups. These groups can also interact with metal cations. It was found that growth time was an important factor in all experiments with the differences between growth times often being more pronounced than the differences between the two bacterial strains. Microscopy revealed a gram-positive cell wall structure with different widths and staining behaviour for exponential phase cells of BF and BS. Stationary / death phase cells showed disintegrating cell walls. Acid-base titrations indicated that all cells possessed buffering capacity over the whole investigated pH range (pH 2 - 10). From electrophoretic mobility measurements, isoelectric points of ~ 3.2 for BF and < 1.8 and ~ 4.2 for exponential and stationary / death phase cells of BS respectively were estimated. Chemical equilibrium models including a Donnan electrostatic model were derived which described both the batch acid-base titration data and the electrophoretic mobility data reasonably well, although a comparison with IR data suggested room for further improvement. In situ ATR-IR spectroscopy of hydrated bacterial cells at various pH values revealed amide and carboxyl groups and a contribution from phosphate / polysaccharide moieties. Group specific interactions with Cd�⁺ were not detected, however, a partially reversible absorbance increase of all peaks suggested conformational changes in the presence of Cd�⁺. BF and BS adsorbed ~ 70 [mu]mol Cd�⁺ (g dry bacterial)⁻� at pH 5 in 0.01 M NaNO₃. Release of major cations occurred concomitantly with Cd�⁺ adsorption. The buffering and Cd�⁺-binding capacities of BF and BS were found to be comparable to those of mesophilic bacteria and ion exchange was identified as an important adsorption mechanism.

[Truncated abstract] The influence of environmental conditions and properties of pyritic shale in the mining waste from Mt. Whaleback in Western Australia, in particular the inclusions and encapsulation of pyrite on the oxidation of pyritic shale and its subsequent acid mine drainage, was studied by employing an isothermal batch reactor system and QEMSCAN technique. The experimental technique was validated by comparing the experimental results obtained in this study with the literature data. It was found that the presence of water significantly accelerates the rate of shale oxidation. Weathering of the shale samples was found to influence the O2 consumption rate. It was also found that shale properties have a major effect on the oxidation rate and thereby affect the acid generation. Static test methods (Sobek and Lawrence) were employed to test the Neutralisation Potential (NP) of more than 100 actual and composite samples including pyritic shale samples, rock samples, mineral samples, various pyrite-mineral, pyrite-shale, and pseudo-shale blends. The influence of sample properties (bulk elemental composition, and mineralogy), test technique (Sobek and Lawrence) and associated variables (acid strength and volume) on the acid neutralisation potential of the samples was studied. It was found that the Sobek method produced consistently higher NP results under comparable acid conditions to those obtained with the Lawrence method. The theoretical NP values of individual minerals were calculated based on the mineral composition combined with the acid neutralising equations and ideal chemical formula. ... To experimentally model the major mineral phases, 11 minerals were used to produce pyrite-mineral blends and pseudo-shales, whose compositions mimic those of the actual shales studied. Mineral blends were employed to evaluate and contrast their individual acid generation or neutralisation behaviour with binary and higher order interactions. Blends of pyrite with some selected shales were also employed in this study. It was found that interactions can occur between the multiple mineral components which can enhance the rate of acid generation beyond that of the individual behaviour. It was found that the products from the pre-oxidation of shales, the properties and morphology of a sample such as the surface area, encapsulation, the mineralogy and pH all play a significant role in the acid generation and neutralisation rates. However, the absolute rate of acid generation appears to be most sensitive to the components such as Fe3+, which contribute to its reaction mechanisms. This investigation has provided a scientific insight into the acid generation and neutralisation behaviour of pyritic shale in relation to its mineralogy. It was found that the relative instantaneous rates of acid generation and consumption for individual minerals can be significantly different to that of their total potentials for acid generation and neutralisation. The significantly different behaviour of the actual and pseudo shales suggests that at low pH, there may be other mechanisms underlying the net capacity and rates of shales to generate or consume acid than bulk mineralogy. These findings have significant implications to the mining industry operating in reactive grounds.

This dissertation covers the studies of two major topics: the photochemistry of mononuclear and multinuclear gold(I) complexes and synthetic approaches to tailor photophysical properties of cyclic trinuclear d10 complexes. First a detailed photochemical examination into the photoreactivity of neutral mononuclear and multinuclear gold(I) complexes is discussed, with the aim of gold nanoparticle size and shape control for biomedical and catalysis applications. Next is a comprehensive systematic synthetic approach to tailor the photophysical properties of cyclic trinuclear d10 complexes. This synthetic approach includes an investigation of structure-luminescence relationships between cyclic trinuclear complexes, an examination into their π-acid/π-base reactivity with heavy metal cations and an exploration into the photophysical properties of new heterobimetallic cyclic trinuclear complexes. These photophysical properties inspections are used to screen materials for their employment in molecular electronic devices such as organic light-emitting diodes (OLEDs) and thin film transistors (OTFTs).

When two or more drugs are administered simultaneously, the pharmacological response may be greater or less than the sum of the effects of the individual drugs. One drug may antagonize or potentiate the effects of the other and there may be also qualitative differences in response. Although some drug interactions increase the toxicity or result in loss of therapeutic effect, others are beneficial. Indeed, modern anaesthetic techniques depend on beneficial drug interactions. A sound combination of drugs helps clinicians to increase both the efficacy and safety of drug treatment. Drugs may interact on a pharmaceutical, pharmacodynamic, or pharmacokinetic basis. Many pharmacodynamic interactions are predictable and can be avoided by the use of common sense. However, it is much more difficult to predict the likelihood of pharmacokinetic and pharmaceutical interactions despite good prior knowledge of pharmacokinetics and chemical properties of individual drugs. Pharmaceutical drug interactions usually occur before the drug is given to the patient and they are caused by chemical (such as acid–base, salt formation, oxidation–reduction, hydrolysis, or epimerization) or physical (such as adsorption/absorption or emulsion breaking) reactions. When drugs have a pharmacokinetic interaction, one drug alters the absorption, distribution, or the elimination of the other drug. Many pharmacokinetic drug interactions are due to inhibition or induction of cytochrome P450 enzymes. Pharmacodynamic drug interactions are caused by drugs having an effect on the same receptors or the same physiological system. This chapter gives anaesthetists an overview of clinically relevant perioperative drug interactions.

The characteristics of the soil cover of the city Cherkassy and the sources of anthropogenic changes of its acidbase properties are presented. The results of the research of soils from different functional zones of the city Cherkassy showed that its reaction is mainly alkaline. The cartographic model of experimental data was made with the program SURFER showing acid-base regime characteristics of soils in different functional zones of the city. This mapping allowed to identify the following soils: fertile (рН = 6.5–7.0) and potentially fertile (рН = 7.0–7.5), hardly suitable (рН = 7.5–8.0), moderately (рН = 8.0–8.5) and highly (рН = 8.0–8.5) toxic. It is concluded that only 60% of urban soils can be identified as fertile or potentially fertile in terms of characteristics of acid-base regime. The results of the evaluation of acid-base regime of urban soilsare correlated with the results of the previous studies of pollution of snow cover in the areas of permanent emissions and the anionic composition of soils. The analysis of the cause-effect relationships in the impact of adverse environmental factors on urban landscapes showed that the formation of acid-base regime of soils is influenced both by the natural landscape, i.e. geochemical, and anthropogenic factors.

The spectral and luminescent properties of trans-2-(4’-dimethylaminebenzylideneacetyl)-5,5-dimethylcyclohexane-1,3-dione and 10-hydroxy-3,3,6,6,9-pentamethyl-1,2,3,4,5,6,7,8,9,10-decahydroacridine-1,8-dione have been studied depending on the acid-base properties of the medium. It has been shown that the first compound can exist in the form of three different structural forms, while the second compound exhibits dual fluorescence in solvents with a high basicity parameter. These properties of chromophores can be used in chemical analysis to indicate the acid-base equilibrium of the medium.

Effect of chemical structure of the aliphatic acid on rust-inhibiting properties and tribological behaviors of the water-based cutting fluid was studied in systematically. It was obtained that (1) the rust-inhibiting property became better with increase of the length of alkyl-chain of the aliphatic acid salts of triethanolamine. (2) The rust-inhibiting property of the aliphatic binary acid triethanolamine salts was better than that of the aliphatic monoacid triethanolamine salts. But the tribological behavior of the aliphatic monoacid triethanolamine salts was favor. Compared with base water, anti-wear and friction-reducing abilities of the soluble aliphatic acid triethanolamine salts would be improved greatly. (3) The adsorption and tribo-reaction films on the metal wear scar surface were monitored by auger energy spectrum.

The research carried out showed that the amount of the buffering capacity of soil in acid and alkaline ranges varied within 27–98% (from low to very high) and 31–81% (from medium to very high) respectively. The specific features of acid-base buffering capacity of soils are in asymmetry with buffering areas. For the first time the computer generated models were created using the software package SURFER that will allow to monitor the urban soils’ state in time and space, to estimate the degree of their degradation under the influence of growing technogenic load, to specify the peculiarities of the formation of ecogeochemical situation in the city. The city map was zoned by acid-base buffering properties of soils based on the theoretical, statistical and visual interpretation of cartographic data.