Nonionized Carboxyl Groups Research Articles

Membrane Vesicles Are the Dominant Structural Components of Ceftazidime-Induced Biofilm Formation in an Oxacillin-Sensitive MRSA.

Methicillin-resistant Staphylococcus aureus (MRSA) has received increasing attention in recent years. However, the characteristics and relevant mechanisms of biofilm formation in oxacillin-sensitive MRSA (OS-MRSA) are poorly understood. This study was designed to characterize biofilm formation in OS-MRSA BWSA15 in response to ceftazidime (TZ) by comparing the methicillin-sensitive S. aureus (MSSA) strain BWSA23 and the oxacillin-resistant MRSA (OR-MRSA) strain BWSA11. The biofilms and biofilm-forming cells were observed by electron microscopy. Biofilms grown on microtiter plates were chemically decomposed and analyzed by Fourier transform infrared spectroscopy. The transcriptional regulation of genes associated with methicillin resistance, surface adhesion, fatty acid biosynthesis, and global regulation (sigma B) was investigated. A significant increase in biofilm formation ability (10.21-fold) and aggregation ability (2.56-fold) was observed in BWSA15 upon the treatment with TZ (16 μg/ml). The TZ-induced biofilm formation in BWSA15 was characterized by a disappearance of polysaccharide-like extracellular substances and an appearance of a large number of intercellular MVs from extracellular matrix. Few MVs were identified in the biofilms formed by BWSA11 and BWSA23. There was a significant upregulation of mecA, sigB, and fatty acid biosynthesis-associated genes and downregulation of icaA, icaD, clfA, clfB, and fnaA in BWSA15 upon the treatment with TZ. The formation of intracellular junctions of MVs in the biofilms of BWSA15 was mediated by a significant increase in the proportion of proteins as well as by an increase in the proportion of non-ionized carboxyl groups in fatty acids. This study demonstrated that beta-lactam antibiotics can induce biofilm formation in OS-MRSA, and the biofilm induction in OS-MRSA can mainly be attributed to exposed MVs with increased hydrophobicity rather than polysaccharide intercellular adhesins, cell wall-anchored surface proteins, and extracellular DNA.

Nanocrystalline TiO2 Thin Films Fabricated Via a Polyelectrolyte Multilayer‐Assisted Sol–Gel Reaction

Nanostructured anatase titanium dioxide (TiO2) thin films were fabricated with an in situ, sol–gel process in a self‐assembled, polyelectrolyte multilayer (PEM) template. Because the PEM template is formed by the sequential adsorption of appositively charged, weak polyelectrolytes, polyacrylic acid, and polyallylamine, it contains nonionized carboxylic groups that are able to react with the inorganic precursor, resulting in the formation of an inorganic–organic hybrid network. After annealing, nanocrystalline TiO2 films with a controlled surface morphology, crystallite size, and a thickness on the nanometer scale were obtained. The average TiO2 crystallite size was approximately 10 nm. The surface morphology and the roughness of the nanocrystalline films were evaluated by field‐emission scanning electron microscopy and atomic force microscopy. UV‐vis spectroscopy was used to establish the optical parameters of the nanocrystalline TiO2 films. The as‐fabricated, nanostructured TiO2 films showed high absorption in the UV region and the controlled transmission of visible light.

Weak Polyion Multilayer-Assisted in Situ Synthesis as a Route toward a Plasmonic Ag/TiO2 Photocatalyst

Nanocrystalline Ag/TiO(2) composite thin films were synthesized using a two-step synthesis methodology: the in situ precipitation of Ag nanoparticles followed by an in situ sol-gel reaction of titanium iso-propoxide in a weak polyion multilayer (PEM) template formed by the layer-by-layer (LbL) self-assembly of poly(acrylic acid) (PAA) and polyallylamine (PAH). Because the PEM template is assembled from weak polyions, it contains nonionized carboxylic groups that are able to react with the inorganics, resulting in the formation of a homogeneous Ag(x)/TiO(2)-PEM precursor film, where the content of Ag is controlled by repeating the Ag loading cycle. The subsequent annealing of the precursor yields nanostructured Ag(x)/TiO(2) films with thicknesses controlled by the PEM template on the nanometer scale. Transmission electron, field-emission scanning electron, and atomic force microscopy methods were employed to evaluate the morphology and growth characteristics of the metallic and semiconductor nanocrystallites in the Ag(x)/TiO(2) composite thin films. The as-formed Ag(x)/TiO(2) composite thin films exhibited UV-visible photoactivity monitored by the decomposition of methylene blue (MB). In the near-UV range, the expected photocatalytic behavior of TiO(2) is greatly enhanced because it is assisted by the near-field amplitudes of the localized surface plasmon resonance (LSPR) of the Ag nanoparticles in the Ag(x)/TiO(2) films.

Preparation and swelling kinetics of pH-sensitive photocrosslinked hydrogel based on carboxymethyl chitosan

A series of photocrosslinkable carboxymethyl chitosans were synthesized by mixing azidobenzaldehyde and an aqueous solution of carboxymethyl chitosan. Aqueous solutions of the product were photocrosslinked via UV irradiation to afford hydrogels. The morphologies and the mechanical properties of the hydrogels were characterized. Their swelling kinetics were studied. The hydrogels displayed good pH sensitivity in pH 2.2–8.0 buffer solutions and an overshooting effect during swelling in pH <5 buffer solutions. The following three factors may contribute to this overshooting effect: firstly, because of the protonation of amide groups in the network in acidic solution, the formation of ionic bonds between amine ions and partial carboxylic ions causes the release of solvent from the swollen network; secondly, ionized carboxylic groups in the network become protonated and convert into nonionized carboxylic groups, and so the concentration of free counterions within the network gradually decreases in acidic solution, leading to solvent release; finally, hydrogen bonds gradually form between nonionized carboxylic groups on the network, which also leads to solvent release from the swollen network. In pH ≥ 5 buffer solutions, the overshooting effect disappeared and the swelling kinetics followed Schott’s second-order swelling kinetics.

Adhesion properties of physically crosslinked elastic gels of poly(sodium acrylate)–poly(acrylic acid) mixtures evaluated by a point contact method

Adhesion properties of physically crosslinked hydrogels consisting of partially hydrated poly(sodium acrylate) (PSA) and poly(acrylic acid) (PAA) were investigated. The adhesion force and separation energy between the gels in swollen states were measured using a simple tack-evaluation technique by a point contact. As a result, the adhesion properties were significantly affected by the PSA/PAA ratio, which resulted from the fact that the physical and chemical properties of gels were changed through the replacement of PSA by PAA at gelation. The measurements of attenuated total reflectance Fourier transform infrared spectroscopy and the dynamic shear viscoelasticity suggested that the number of nonionized carboxyl groups increased and the stiffness increased with increasing the PAA ratio, respectively. In order to understand the adhesion properties further, the apparent contact area was evaluated by a stamp experiment using vermilion ink. The relationships between the adhesion properties and the physical and chemical features of gels are discussed in terms of the surface molecular interaction, the elastic and viscous properties of the bulk, and the apparent and true contact areas of the present system. From these results, the factors that determine the adhesion curve and the uniqueness and advantages of the present evaluation method are clarified.

Fragmentation pathways of negative ions produced by electrospray ionization of acyclic dicarboxylic acids and derivatives

Fragmentation pathways have been studied on the monoanions formed during electrospray ionization of a wide range of aliphatic dicarboxylic acids and their monoesters. All negative ion spectra were obtained from alcoholic or aqueous methanolic solutions without buffers or adjustment of pH, using either a Finnigan LCQ ion trap or a VG-Micromass Quattro triple quadrupole mass spectrometer. Fragmentation pathways were studied using collision-induced dissociation and isotopic-labelling techniques. Two primary fragmentation pathways of the dicarboxylic acid monoanions were observed, namely decarboxylation of the non-ionized carboxyl group and loss of water from this group. The fragmentations were strongly dependent on the chain lengths of the diacids. In the case of a monoester anion, loss of a molecule of alcohol paralleled the loss of water from the diacid monoanion. Losses of water or alcohol were shown to lead to formation of reactive ynolate anions (HOOC(CH2)xC≡CO–, x = 3–9), which in the ion trap spectrometer engaged in complex ion – molecule reactions consistent with the chemistry of these anions. For the longer chains (x &gt; 6), the interactions between the ionized and non-ionized carboxyl groups led to readily formed ion–neutral complexes, which are described as a neutral molecule (ROH, R = H or alkyl) held by a pair of molecular tweezers.Key words: ESI-MS/MS on negative ions, fragmentation pathways of acyclic carboxylic acid monoanions, ion–molecule reactions in an ion trap mass spectrometer, hydrogen–deuterium exchange in a gas-phase anion–neutral complex.

Formation of hydrogen bonding in ionized poly(N‐isopropylacrylamide) gels by continuous water exchange

AbstractThe effects of continuous water exchange on the swelling behavior of poly(N‐isopropylacrylamide‐co‐sodium acrylate) gel were studied. The diameter of gels and the Na+ concentration in the solvent were measured at several constant intervals after the solvent (the distilled deionized water) was exchanged. The diameter decreased at room temperature as the solvent was exchanged with water, and it continued to decrease even after more than about 97% of the initial Na+ diffused into the water. Thus, the final swelling ratio of the gel was only slightly larger than that of the neutral poly(N‐isopropylacrylamide) gel. To reveal the structural change in molecular level, solid‐state 13C cross‐polarization/magic‐angle spinning, solid‐state 1H combined rotation and multiple‐pulse spectroscopy, and swollen‐state 13C dipolar decoupled/magic‐angle spinning NMR experiments were carried out for several dried and swollen samples by varying the times of water exchange. As a result, the intensity and position of the carboxyl peak changed, and the relative intensity of the nonionized carboxyl groups of gels increased with an increasing number of water exchanges. These results indicated that hydrogen bonding was formed between the two, nonionized carboxyl groups (COOH) and/or between the COOH and CONH groups. The macroscopic polymer network shrinkage is discussed in terms of the replacement of counterions Na+ by H+ and of the formation of intermolecular hydrogen bonding. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1090–1098, 2004

Complexes of 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (4,13-diaza-18-crown-6) with 2,5-pyridinedicarboxylic and 2,2-dithiosalicylic acids

A 1:2:2 complex of 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane with 2,5-pyridinedicarboxylic acid and water (1) and its 1:1:1.75 complex with 2,2′-dithiosalicylic acid and water (2) have been obtained and characterized by x-ray diffraction. C26H40N4O14 (1), triclinic, $$P\bar 1$$ , a = 9.574(1) A, b = 9.632(1) A, c = 9.723(1) A, α = 112.70(1)°, β = 91.07(1)°, γ = 115.45(1)°, V = 728.35(13) A3, Z = 1. C26H39.5N2O9.75S2 (2), M = 600.22, triclinic, $$P\bar 1$$ , a = 10.492(1) A, b = 10.945(1) A, c = 14.535(2) A, α = 102.74(1)°, β = 109.08(1)°, γ = 90.68(1)°, V = 1532.2(3) A3, Z = 2. In complex 1, both N-atoms of the macrocyclic ring are protonated. The following types of H-bonding have been found: (1) between protonated aza groups of the macrocycle and ionized carboxylic groups; (2) between the protonated aza groups and N-atoms of the pyridine nuclei (D–A distance slightly exceeds 3 A); (3) between water molecules and C=O groups of the non-ionized carboxylic groups; and (4) between the nonionized and ionized groups of the carboxylic acid. The above interactions give rise to the formation of a developed supramolecular network in the crystals of 1. In complex 2, despite the presence of several types of hydrogen bonds involving the aza crown, 2,2′-dithiosalicylic acid and water, the aromatic anions are H-bound only to the two other components, and not to each other. The H-bonds found in complex 2 are between (1) one of the protonated aza groups and water, (2) protonated aza groups and O-atoms of the ionized carboxylic groups, (3) water molecule and carboxylic O-atom, (4) water molecule and sulfur atom, and (5) water molecule and O-atom of diaza-18-crown-6.

Swelling and photoelastic behaviour of ionized hydrogels of poly(acrylic acid)

The photoelastic and swelling behaviour of poly(acrylic acid) gels swollen in 1 M NaCl aqueous solution was studied as a function of crosslinking degree (1–5 wt.% ethylene glycol dimethacrylate) and degree of ionization αg = 0 − 1. The degree of swelling passes through a minimum at αg ≐ − 0.15 regardless of the degree of crosslinking, probably due to the formation of hydrogen bonds between ionized and nonionized carboxyl groups. In the same neutralization region, the equilibrium modulus reaches a maximum; on the other hand, the modulus related to the dry state is independent of α for all crosslinker concentrations. Thus the mechanical behaviour of poly(acrylic acid) gels is in accord with the Gaussian theory and no contribution of permanent physical interactions to the modulus is observed. The optical behaviour is more complex — the sign of the stress-optical coefficient Ce changes three times with increasing α due to the orientation of the side groups. The analysis of the optical data shows that the Ce value is controlled by the degree of swelling and by the ionization.

The photoelastic behaviour of the ionized poly(acrylic acid) network

In loosely crosslinked networks of poly (acrylic acid) the degree of swelling passes through a pronounced minimum at a neutralization of about 15% obviously as a result of the formation of hydrogen bonds between ionized and nonionized carboxyl groups. In the same range the equilibrium modulus reaches a maximum, but the modulus related to the dry state is constant, as required by the theory of Gaussian networks. The sign of the stress-optical coefficient changes three times with increasing neutralization, which may be interpreted by the varying degree of orientation of the side group. In spite of this, however, the photoelastic behaviour of poly(acrylic acid) networks is simpler than that of poly(methacrylic acid) networks, and its interpretation does not require an assumption of the existence of correlated structures.

The behavior of linear polymers at interfaces

Monolayers of synthetic linear polymers were studied by means of measurements of interfacial pressure and potential at air/water and oil/water interfaces. The polymers examined were: poly- N-vinyl pyrrolidone, polyvinyl acetate, polyvinyl stearate, polymethyl methacrylate, polymethacrylic acid, copolymers of polymethacrylic acid and diethylaminoethyl vinyl ether, poly-ϵ-caproamide, polyethylene terephthalate, and polyacrylonitrile. All the polymers except polyvinyl acetate give films of the condensed type at the air/water interface, whereas all the polymers except polyethylene terephthalate and polyacrylonitrile give films of the expanded type at the oil/water interface. The film of the condensed type gives a constant surface moment up to a collapse point, and the true molecular weight can be obtained from the surface pressure. The film of the expanded type gives a constant surface moment at larger areas, but the moment changes at a certain area. In this case, a smaller molecular weight than the true one is obtained from the surface pressure. The film of the expanded type at the oil/water interface has segments in the main chain as a statistical kinetic unit, each consisting of about 48 skeletal atoms, and is discussed in the light of the Singer equation of state. The value of surface moment is determined chiefly by the orientation of the CO bond. The behavior of an ampholyte was studied by the measurement of interfacial potential. The results showed that the amine groups could not be ionized more than about 20 mole per cent owing to the strong cohesion between major nonionized carboxyl groups at the air/water interface, but such a restriction was not found at the oil/water interface owing to the sufficiently expanded state. The extension of these conclusions to proteins is suggested.