Length Of Substituent Research Articles

Paving the way to solubility through volatility: Thermodynamics of imidazolium-based ionic liquids of the type [CnC1Im][I

Ionic liquids are effectively used for manufacturing of nanoparticles for thermoelectric generators and in the field of hydrogen storage. Development and optimization of these processes require knowledge of the thermodynamic properties of ionic liquids. Thermochemical study of the series of 1-alkyl-3-methylimidazolium iodides is presented in this work. Vapor pressures and vaporization enthalpies have been measured by using quartz-crystal microbalance. Solution enthalpies were measured by using solution calorimetry. Thermodynamics of aqueous solutions, solubility parameters and miscibility of ILs in eleven organic solvents were derived and discussed. The absence of thermal decomposition of [C4C1Im][I] under vaporization conditions has been demonstrated experimentally and theoretically. It has been shown that vaporization enthalpies are linearly dependent on the chain length of the alkyl substituent and linearly dependent on the surface tension. Aqueous-phase enthalpies of formation of alkyl imidazolium cations have been derived with help of solution calorimetry.

Synthesis of Super Hydrophobic Disperse Dyes Having Long Alkyl Substituents and Their Dyeability onto Unmodified Polypropylene Fibers

The new series of super hydrophobic disperse dyes having different length of alkyl substituents was synthesized to dye pure polypropylene fibers. From butyl to dodecyl groups were introduced to an anthraquinoid chromophore. The adsorption interaction of the dyes toward the polypropylene fiber was increased with the increase of the length of alkyl chains due to enhancement of hydrophobicity of the dyes. The optimum alkyl group was determined as the longest dodecyl group in this study. Their absorption spectra in the visible range appeared almost the same regardless of the length of alkyl groups, which meant that the length of alkyl groups did not influence on optical properties of the dyes relating to color appearances. The color fastnesses of the dyed fabrics to washing, rubbing, and light were good enough for practical application.

Quantitatively Assessing the Salting-Out Capacity of Inorganic Salts with Respect to Ethoxylated Surfactants

The results from assessing the salting-out capacity of inorganic salts with respect to poly(ethylene glycol) monoalkyl ethers (DS-10 and ALM-10 synthanols) are summarized. The effect the length of the aliphatic substituent in a molecule of a surfactant has on the salting-out capacity is determined. The correlation dependences between the energy of hydration of ions and their salting-out capacity are determined for poly(ethylene glycol) monoalkyl ethers and ethoxylated nonylphenols (AF 9-12 and AF 9-25 neonols).

Влияние природы растворителя на самосборку монозамещённых пиллар[5]аренов, содержащих N-(аминоалкил)амидный фрагмент

Chemistry of macrocyclic compounds is one of the rapidly developing areas of modern organic chemistry. These macrocycles have become widespread due to the high availability of parents compounds, the possibility of synthesis of ligands based on them for highly selective recognition, ion-selective membranes, electrodes, sensors and nanocontainers for targeted drug delivery. Moreover, in the past few years, attention of researchers has again been riveted on mechanically interlocked molecules (rotaxanes and pseudorotaxans) and supramolecular polymers, which can be explained by their potential application as molecular machines and materials. Mechanically interlocked molecules are molecular architectures consisting from two or more components which mechanically bind due to their own topology. Supramolecular polymers are comprise ordered monomer units combined via non-covalent bonds (hydrogen bonds or electrostatic interactions). Thus, this manuscript presents an approach to the synthesis of monosubstituted pillar[5]arenes containing N-(aminoalkyl)amide fragments with various substituent lengths. The formation of self-inclusion complexes by synthesized macrocycles was established by one- and two-dimensional NMR spectroscopy. According to NMR data, only four carbon atoms of the alkyl fragment were included in the macrocyclic cavity regardless of the alkyl chain length. Formation of self-inclusion complexes becomes possible due to the intramolecular hydrogen bond between the NH protons and the oxygen atom of methoxyl fragment, which is confirmed by IR spectroscopy. It was shown by dynamic light scattering that the synthesized pillar[5]arenes in chloroform form aggregates with an average hydrodynamic diameter of 316-640 nm and polydispersity index from 0.18 to 0.20, while polydisperse systems are formed in dimethyl sulfoxide.

Bulky-substituted phthalodinitriles and cobalt and copper phthalocyanines based on them: synthesis, thermal analysis and spectroscopic properties

By the nucleophilic substitution of the nitro group in 4-nitrophthalononitrile for the residues of alkoxy-substituted phenols, the synthesis of alkoxyphenoxyphthalonitriles was carried out. By template condensation of the substituted phthalonitriles obtained with copper and cobalt acetates at 200 °C, the corresponding phthalocyaninates were obtained. The conditions for the isolation and purification of the complexes synthesized were selected. The stability of substituted phthalonitriles and phthalocyaninates synthesized based on them regarding to heating in an argon–oxygen medium was evaluated (1:1 ratio). It was found the compounds obtained are thermally stable, and the destruction of phthalocyanines begins at lower temperatures compared to the corresponding phthalonitriles. For the complexes synthesized, the spectroscopic properties in organic solvents and concentrated sulfuric acid were studied. The influence of the nature of the substituent, metal complexing agent and solvent on the nature of the spectroscopic curves and the position of the main absorption band of phthalocyanine complexes has been established. It is noted passing from polar aprotic solvents to nonpolar ones, a shift of the maximum of the Q absorption band for the studied macrocycles was observed. Electronic absorption spectra in sulfuric acid show a significant bathochromic shift of the absorption band. An increase in the length of the alkyl substituent practically was found not to affect the position of the absorption maximum. Passing from complexes with Co(II) to Cu(II), a bathochromic shift of the absorption maximum was observed.

Effect of Ionic Liquid Structure on the Electrochemical Response of Dopamine at Room Temperature Ionic Liquid‐modified Carbon Paste Electrodes (IL–CPE)

AbstractIn this work 12 different ionic liquids (ILs) have been used added as co‐binders in the preparation of modified carbon paste electrodes (IL–CPEs) used for the voltammetric analysis of dopamine in Britton‐Robinson buffer. The ionic liquids studied were selected based on three main criteria: (1) increasing chain length of alkyl substituents (studying 1‐ethylimidazolium and ethyl, propyl, butyl, hexyl and decylmethylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids); (2) nature of the counter ion (dicyanamide, bis(trifluoromethylsulfonyl)imide and hexafluorophosphate) in 1‐butyl‐3‐methylimidazolium ionic liquids; and (3) cation ring structures (1‐butyl‐3‐methylimidazolium, 1‐butyl‐1‐methylpiperidinium, 1‐butyl‐1‐methylpyrrolidinium and 1‐butyl‐3‐methylpyridinium) in bis(trifluoromethylsulfonyl)imide or hexafluorophosphate (1‐butyl‐3‐methylimidazolium or 1‐butyl‐3‐methylpyridinium as cations) ionic liquids. The use of IL as co‐binders in IL–CPE results in a general enhancement of both the sensitivity and the reversibility of dopamine oxidation. In square wave voltammetry experiments, the peak current increased up to a 400 % when 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide was used as co‐binder, as compared to the response found with the unmodified CPE. Experimental data provide evidence that electrostatic and steric effects are the most important ones vis‐à‐vis these electrocatalytic effects on the anodic oxidation of dopamine on IL–CPE. The relative hydrophilicity of dicyanamide anions reduced the electrocatalytic effects of the corresponding ionic liquids, while the use of 1‐ethyl‐3‐methylimidazolium hexafluorophosphate or 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (two relatively small and highly hydrophobic ionic liquids) as co‐binders in IL–CPE resulted in the highest electrocatalytic activity among all of the IL–CPE studied.

Self-Assembly Properties of Solution Processable, Electroactive Alkoxy, and Alkylthienylene Derivatives of Fused Benzoacridines: A Scanning Tunneling Microscopy Study.

Self-organization in mono- and bilayers on HOPG of two groups of benz[5,6]acridino[2,1,9,8-klmna]acridine derivatives, namely, 8,16-dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines with an increasing alkoxy substituent length and 8,16-bis(3- or 4- or 5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines, i.e., three positional isomers of the same benzoacridine, is investigated by scanning tunneling microscopy. The layers were deposited from a solution of the adsorbate (in hexane or dichloromethane) and imaged ex situ at molecular resolution. In all cases, the resulting two-dimensional (2D) supramolecular organization is governed by the interactions between large, fused heteroaromatic cores that form densely packed rows separated by areas covered by substituents. In 8,16-dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines, the alkoxy substituents, separating the rows of densely packed cores, are interdigitated. An increasing substituent length leads to an intuitively expected increase in this 2D unit cell parameter that corresponds to the orientation of the substituent in the monolayer. In the case of 8,16-bis(3- or 4- or 5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine positional isomers, the self-assembly processes are more complex. Although the determined 2D unit cell is in all cases essentially the same, the role of alkylthienylene substituents in layer formation is distinctly different. Thus, the formation of monolayers and bilayers is very sensitive to isomerism. 8,16-Bis(5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine is capable of forming the most stable monolayer and the most labile bilayer. In the case of 8,16-bis(3-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine, an inverse phenomenon is observed leading to the most labile monolayer and the most stable bilayer. These differences are rationalized in terms of dissimilar molecular geometries of the studied isomers and different interdigitation patterns in their 2D supramolecular structures.

Tissue-specific analysis of lipid species in Drosophila during overnutrition by UHPLC-MS/MS and MALDI-MSI

Diets high in calories can be used to model metabolic diseases, including obesity and its associated comorbidities, in animals. Drosophila melanogaster fed high-sugar diets (HSDs) exhibit complications of human obesity including hyperglycemia, hyperlipidemia, insulin resistance, cardiomyopathy, increased susceptibility to infection, and reduced longevity. We hypothesize that lipid storage in the high-sugar-fed fly's fat body (FB) reaches a maximum capacity, resulting in the accumulation of toxic lipids in other tissues or lipotoxicity. We took two approaches to characterize tissue-specific lipotoxicity. Ultra-HPLC-MS/MS and MALDI-MS imaging enabled spatial and temporal localization of lipid species in the FB, heart, and hemolymph. Substituent chain length was diet dependent, with fewer odd chain esterified FAs on HSDs in all sample types. By contrast, dietary effects on double bond content differed among organs, consistent with a model where some substituent pools are shared and others are spatially restricted. Both di- and triglycerides increased on HSDs in all sample types, similar to observations in obese humans. Interestingly, there were dramatic effects of sugar feeding on lipid ethers, which have not been previously associated with lipotoxicity. Taken together, we have identified candidate endocrine mechanisms and molecular targets that may be involved in metabolic disease and lipotoxicity.

Synthesis and antibacterial activity of new dimeric pyridinium chlorides based on 2,2-bis(hydroxymethyl)propane-1,3-diyl spacer

New bispyridinium dichlorides based on 2,2-bis(hydroxymethyl)propane-1,3-diyl spacer were synthesized from pentaerythritol, 4-aminopyridine, and carboxylic acids. The resulting biocides possess a high antibacterial effect. The minimal inhibitory concentration (MIC) of these compounds against pathogenic bacteria, namely, gram-positive Methicillin-resistant Staphylococcus aureus (strain ATCC 25923) and gram-negative Escherichia coli (ATCC 25922) and Pseudomonas aeruginosa (ATCC 27853), was established. The influence of the alkyl substituent length in salts on their microbiological activity was studied.

Fluorescent bent-core mesogens with thiophene-based central unit

ABSTRACT New bent-core mesogens with thiophene central ring were designed to obtain fluorescent and conductive liquid crystlline phases. Depending on the number of terminal chains and the length of lateral substituent at central unit either calamitic or columnar phases were formed. All the synthesised compounds showed high quantum efficiency of fluorescence in solution, ~0.9, that was however reduced to ~0.15 in condensed state. The light emitted from nematic or columnar phase was linearly polarised. Quenching of fluorescence in condensed state, together with observed red shift of emission maximum wavelength, evidenced formation of J-aggregates or weak excimers. Aggregation was also monitored by dynamic light scattering in water/tetrahydrofuran (THF) solutions.

Surface-Confined Macrocyclization via Dynamic Covalent Chemistry.

Surface-confined synthesis is a promising approach to build complex molecular nanostructures including macrocycles. However, despite the recent advances in on-surface macrocyclization under ultrahigh vacuum, selective synthesis of monodisperse and multicomponent macrocycles remains a challenge. Here, we report on an on-surface formation of [6 + 6] Schiff-base macrocycles via dynamic covalent chemistry. The macrocycles form two-dimensional crystalline domains on the micrometer scale, enabled by dynamic conversion of open-chain oligomers into well-defined ∼3.0 nm hexagonal macrocycles. We further show that by tailoring the length of the alkyl substituents, it is possible to control which of three possible products-oligomers, macrocycles, or polymers-will form at the surface. In situ scanning tunneling microscopy imaging combined with density functional theory calculations and molecular dynamics simulations unravel the synergistic effect of surface confinement and solvent in leading to preferential on-surface macrocyclization.

Optimizing the monomer structure of polyhedral oligomeric silsesquioxane for ion transport in hybrid organic–inorganic block copolymers

ABSTRACTPoly(ethylene oxide)‐b‐polyhedral oligomeric silsesquioxane (PEO–POSS) mixed with lithium bis(trifluoromethanesulfonyl)imide salt is a nanostructured hybrid organic–inorganic block copolymer electrolyte that may enable lithium metal batteries. The synthesis and characteristics of three PEO–POSS block copolymer electrolytes which only differ by their POSS silica cage substituents (ethyl, isobutyl, and isooctyl) is reported. Changing the POSS monomer structure results in differences in both thermodynamics and ion transport. All three neat polymers exhibit lamellar morphologies. Adding salt results in the formation of a disordered window which closes and gives way to lamellae at higher salt concentrations. The width of disordered window decreases with increasing length of the POSS alkyl chain substituent from ethyl to isobutyl and is absent in the isooctyl sample. Rheological measurements demonstrate good mechanical rigidity when compared with similar all‐organic block copolymers. While salt diffusion coefficient and current ratio are unaffected by substituent length, ionic conductivity increases as the length of the alkyl chain substituent decreases: the ethyl substituent is optimal for ion transport. This is surprising because conventional wisdom suggests that ion transport occurs primarily in the PEO‐rich domains, that is, ion transport should be unaffected by substituent length after accounting for the minor change in conducting phase volume fraction. © 2020 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2020 © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 363–371

Evaluation of Electrochemical Stability and Li-ion Interactions in Ether Functionalized Pyrrolidinium and Phospholanium Ionic Liquids

Potential electrolytes for lithium ion batteries (LIB) depicting high electrochemical stability and ionic conductivity still represents a great challenge. Herein, we investigate the reduction stability and Li+ cation interactions with substituted cyclic phospholanium (CylP5+) and pyrrolidinium (Pyr+) ionic liquids (ILs) with bis(trifluoromethanesulfonyl)imide (TFSI−) anion. The cations CylP5+ and Pyr+ are functionalized with varying chain lengths of alkyl and alkoxy substituents and their reduction potentials evaluated with respect to Li+/Li. CylP5+ cations, in general have better stability than Pyr+ based ILs, while the alkoxy substitution is found to lower the reduction stability compared to alkyl substituents in both ILs. Furthermore, the interaction energies between the substituent modified-cations (C), Li+ cation and the anion (A) were evaluated. The ion-pair (C-A) interaction energies on addition of Li+ cation is shown to decrease for both Pyr+ and CylP5+ cations with shorter alkoxy chain lengths, thereby implying faster diffusion of ions due to weaker interactions. Similarly, among the two cations, lowest ΔE were noted between alkoxy substituted [Li(CylP5)]2+ cation and TFSI−, signifying faster diffusion of ions in CylP5+ based electrolytes than that of Pyr+ based ILs. These results govern the synthesis of novel ILs with promising base cation and functionalization for LIB.

Effect of new water-soluble phenolic antioxidants on the activity of Nrf2-driven enzymes, glutathione system, and Nrf2 translocation into the nucleus

Understanding the role of reactive oxygen and nitrogen species in eustress (redox balance) and distress (oxidative stress) development poses new challenges for biomedical scientists and pharmacologists in the search for compounds that can not only have a direct antioxidant (antiradical) effect, but also affect redox-sensitive signaling pathways, primarily Keap1/Nrf2/ARE system. Aim of the study was to investigate the influence of novel water-soluble structurally related monophenols on key elements of Keap1/Nrf2/ARE system induction (activity of Nrf2-driven enzymes, the state of the glutathione system, and intracellular redistribution of transcription factor Nrf2). Material and methods . Five original hydrophilic structurally related monophenols, differing in the number of tert-butyl ortho-substituents, the length of the para-alkyl substituent, and the presence of a divalent sulfur or selenium atom in it were investigated (phenoxane, the potassium salt of phenosan acid, was used as a reference compound). Cell lines U937 and J774 were cultured for 24 h in the presence of tested compounds, and comparative analysis was performed of its ability to induce the synthesis of Nrf2-driven enzymes of phase II xenobiotic detoxification pathway and antioxidant enzymes (NAD(P)H: quinone oxidoreductase 1 (NQO1), glutathione S-transferases (GST), glutathione peroxidases, glutathione reductase (biochemical spectrophotometric methods were used to study their activity), as well as to influence the state of glutathione system (spectrophotometry) and translocation of transcription factor Nrf2 into the nucleus (immunofluorescent staining, confocal microscopy) (key events of Keap1/Nrf2/ARE signaling system activation). Results and discussion . Monophenol TS-13 have found to be the most effective inducer of tested enzymes in U937 cells among the structural analogs, while the structure of the para-alkyl substituent and the degree of OH group hindrance are important for the implementation of this effect; TS-13 also effectively enhanced Nrf2 import into J774 cell nucleus. The NQO1- and GST-inducing abilities of structurally related monophenols are closely interrelated, which indicates the possibility of coordinated induction of these enzymes and the presence of a common regulatory system that ensures their activation in response to cell treatment with phenolic antioxidants.

Steady state charge conduction through solution processed liquid crystalline lanthanide bisphthalocyanine films

In-plane electrical characteristics of non-peripherally octyl(C[Formula: see text]H[Formula: see text]- and hexyl(C[Formula: see text]H[Formula: see text]-substituted liquid crystalline (LC) double decker lanthanide bisphthalocyanine (LnPc[Formula: see text] complexes with central metal ions lutetium (Lu), and gadolinium (Gd) have been measured in thin film formulations on interdigitated gold (Au) electrodes for the applied voltage ([Formula: see text] range of [Formula: see text]. The conduction mechanism is found to be Ohmic within the bias of [Formula: see text] while the bulk limited Poole–Frenkel mechanism is responsible for the higher bias. The compounds show individual characteristics depending on the central metal ions, substituent chain lengths and their mesophases. Values of 67.55 [Formula: see text]cm[Formula: see text] and 42.31 [Formula: see text]cm[Formula: see text] have been obtained for room temperature in-plane Ohmic conductivity of as-deposited octyl lutetium (C[Formula: see text]LuPc[Formula: see text] and hexyl gadolinium (C[Formula: see text]GdPc[Formula: see text] films, respectively while C[Formula: see text]GdPc[Formula: see text] films exhibit nearly two orders of magnitude smaller conductivity. On annealing at 80[Formula: see text]C, Ohmic conductivities of C[Formula: see text]LuPc[Formula: see text] and C[Formula: see text]GdPc[Formula: see text] are found to have increased but the conductivity of C[Formula: see text]GdPc[Formula: see text] decreased by more than one order of magnitude to 1.5 [Formula: see text]cm[Formula: see text]. For physical interpretation of the charge transport behavior of these three molecules, their UV-vis optical absorption spectra in the solution and in as-deposited and annealed solid phases and atomic force microscopy study have been performed. It is believed that both orientation and positional reorganizations are responsible, depending upon the size of the central ion and side chain length.

Reversible control of enantioselectivity by the length of ketone substituent in biocatalytic reduction.

Enzyme engineering has been widely employed to tailor the substrate specificity and enantioselectivity of enzymes. In this study, we mutated Trp288, an unconserved residue in the small binding pocket of an acetophenone reductase from Geotrichum candidum NBRC 4597 (GcAPRD). Trp288 mutants showed substrate specificity expansion towards bulky-bulky ketones and enantioselectivity alteration which was highly dependent on the substrate substituent length. In aliphatic ketone reduction, enantioselectivity inverted from (S) to (R) when one of the substituents to the carbonyl carbon was elongated from propyl to butyl or pentyl. The best (R)-selective mutant, Trp288Val, achieved the reduction of 3-heptanone to its corresponding (R)-alcohol with 97% ee. Our docking simulation suggested that when enantioselectivity inverted to (R), only pro-R binding poses were productive. Gly94 played an important role to stabilize the butyl or pentyl group for their productive pro-R poses. Interestingly, when the substituent was further elongated, the enantioselectivity inverted back to the (S) form.

A Study of the Products of Alkylation of Turbine Oil Distillate with Catalytic Cracking Gases

The main physicochemical properties and structural parameters of the products of alkylation of the turbine oil distillate with catalytic cracking gases on Zeokar-600 and Omnikat-210P zeolite catalysts have been determined using IR, 1H NMR, and UV spectroscopy techniques. Alkylation has been carried out in the temperature range of 50–150°C at oil : gas ratios of 1 : 1 and 1 : 2. The reaction products have been studied. The products have been obtained under optimal conditions, ensuring the maximum increase in the viscosity index of the oil fraction from 32 to 75 and 53 on the Zeokar-600 and Omnikat-210P catalysts, respectively. It has been shown that the kinematic viscosity and viscosity index of the oil fraction are increased by the alkylation. This is due to an increase in the length and quantity of alkyl substituents of aromatic hydrocarbons by adding propylene and butylene units of olefin hydrocarbon gases of catalytic cracking.

Strategy for the Construction of Diverse Poly-NHC-Derived Assemblies and Their Photoinduced Transformations.

A series of supramolecular assemblies of types [Ag8 (L)4 ](PF6 )8 and [Ag4 (L)2 ](PF6 )4 , obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4-triazolium) salts H4 -L(PF6 )4 and AgI ions, is described. The assembly type obtained dependends on the N-wingtip substituents of H4 -L(PF6 )4 . Changes in the lengths of the N4-wingtip substituents enables controlled formation of assemblies with either [Ag4 (L)2 ](PF6 )4 or [Ag8 (L)4 ](PF6 )8 stoichiometry. The molecular structures of selected [Ag8 (L)4 ](PF6 )8 and [Ag4 (L)2 ](PF6 )4 assemblies were determined by X-ray diffraction analyses. While H4 -L(PF6 )4 does not exhibit fluorescence in solution, their tetra-NHC (NHC=N-heterocyclic carbene) assemblies do upon NHC-metal coordination. Upon irradiation, all assemblies undergo a light-induced, supramolecule-to-supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties.

Photophysical properties and immobilisation of fluorescent pH responsive aminated benzimidazo[1,2-a]quinoline-6-carbonitriles.

This work presents a systematic evaluation of 2-amino, 5-amino and 2,5-diamino substituted benzimidazo[1,2-a]quinoline-6-carbonitriles as novel pH probes with a potential application in pH sensing materials or as H+ fluoroionophores in bulk optode membranes. The study was carried out by varying the length, type and position of amino substituents in ten fluorescent dyes with the same benzimidazo[1,2-a]quinoline-6-carbonitrile core. The photophysical and acid-base properties of the dyes were investigated by the UV/Vis absorption and fluorescence spectroscopies, and interpreted by the electronic structure DFT calculations. pH sensing mechanisms and structure-property relations affecting the fluorescence response were discussed through a detailed analysis of the piperidine substituted derivatives 1-4. Push-pull donor-acceptor interactions stimulate strong fluorescence in the visible spectral range (up to Φ = 0.65 for 7) and induce significant changes in the photophysical properties associated with the acid-base equilibria (up to a 50-fold increase in the fluorescence intensity). pKa values in aqueous and mixed solutions (v/v H2O:EtOH 99:1, 50:50), appear suitable for monitoring acidic pH in solution. The most promising candidates were immobilised in thin polymer matrices by the spin coating technique to form fluorescent sensing materials - optodes, and examined as novel pH-sensitive fluoroionophores. In the liquid membrane environment, dyes exhibited significant increase of the apparent pKas by almost 4 units. Bright and blue emissive thin films showed pH response and dynamic range around pKa = 5, making them suitable for a wide range of optical sensing applications.

PH-Sensitive N,N-Dimethylalkane-1-amine N-Oxides in DNA Delivery: From Structure to Transfection Efficiency.

pH-sensitive liposomes composed of homologues of series of N,N-dimethylalkane-1-amine N-oxides (CnNO, n = 8-18, where n is the number of carbon atoms in the alkyl substituent) and neutral phospholipid dioleoylphosphatidylethanolamine (DOPE) were prepared at two molar ratios (CnNO/DOPE = 0.4:1 and 1:1) and tested for their in vitro transfection activity. Several techniques (SAXS/WAXS, UV-vis, zeta potential measurements, confocal microscopy) were applied to characterize the system in an effort to unravel the relationship among the transfection efficiency, structure, and composition of the lipoplexes. The transfection efficiency of CnNO/DOPE for plasmid DNA in U2OS cells follows a quasi-parabolic dependence on CnNO's alkyl substituent length with a maximum at n = 16. The transfection efficiency of CnNO/DOPE (n = 12-18) lipoplexes was found to be higher than that of commercially available Lipofectamine 2000. C16NO/DOPE also positively transfected HEK 293T and HeLa cells. Small-angle X-ray scattering (SAXS) shows large structural diversity depending on the complex's composition and pH. Transfection efficiencies mediated by two structures, either a condensed lamellar (Lαc) or epitaxially connected Lαc and a condensed inverted hexagonal (HIIc) phase (Lαc & HIIc), were found to be very similar. The change in pH from acidic to neutral induces phase transition Lαc & HIIc → QII + Lα, with cubic phase QII of the Pn3m space group. QII detected in lipoplexes of most efficient composition CnNO/DOPE (n = 16 and 18) facilitates DNA release and promotes its internalization in the cell.