Orientation Of Carboxyl Group Research Articles

4-Nitrophenol imprinted core-shell poly(N-isopropylacrylamide-acrylic acid)/poly(acrylic acid) microgels loaded with cadmium nanoparticles: A novel catalyst

4-nitrophenol imprinted poly(N-isopropylacrylamide-acrylic)/poly(acrylic acid) [p(NIPAM-AAc)/p(AAc)] microgels are synthesized by precipitation polymerization. 1 and 95 mol % of AAc is incorporated in core and shell of synthesized microgels respectively, so that shell can be swollen up to large extent instead of core part. Cd nanoparticles are synthesized within core using in situ reduction. Size of Cd nanoparticles and structure of microgels are analyzed by STEM, FTIR and UV–Vis spectroscopy. Series of 4-NP and its derivatives (nitroarenes and azo dyes) are reduced by using synthesized microgel as catalyst in aqueous medium. Significant difference in apparent rate constant (kapp), percentage reduction and reduction time among 4-NP and its derivatives is observed. This shows that 4-NP imprinting has affected the sieve of microgels and orientation of carboxyl groups (COOH) of AAc. Effect of solvents on catalytic reduction of 3-NP is also studied using synthesized microgel as catalyst. Significant difference in kapp, percentage reduction and reduction time of 3-NP in different solvents is also observed. 95% AAc in imprinted shell is observed as capable catalyst for reduction of 4-NP template and its derivatives. Synthesized microgel has multiple features: 4-NP imprinting, core-shell structure and 95% AAc in shell. All of these features are helped in the catalytic reduction of nitro compounds. The compounds similar to 4-NP are reduced more as compared to other compounds due to 4-NP imprinting. This shows that synthesized MIP is more effective for reduction of compounds similar to 4-NP. High mol percentage of AAc monomer within shell is facilitated the diffusion of substrates towards nanoparticles embedded in core. Possible product formation of nitroarenes and azo dyes in the presence of microgel was reported. Effect of different solvents on catalytic reduction of 3-NP is also observed.

Conformational flexibility and pseudosymmetric aggregation in a betainium salt hydrate

The cation of 3-(trimethylammonium)-benzoic acid exhibits a considerable conformational flexibility connected to the orientation of carboxyl group, coupled to the proton position, and rotations of the trimethylammonium group. This conformational flexibility considerably affects the aggregation of ions and molecules of 3-(trimethylammonium)-benzoic acid iodide hydrate, which crystallizes in a low-symmetry structure with four symmetry-independent formula units (monoclinic space group Pc, Z’ = 4, model I). However this structure approximates the symmetry of space group P21/c in the same unit cell (Z’ = 2, model II), and also even a still more highly symmetric structure of space group P21/c in a half-smaller unit cell (Z’ = 1, model III). The independent formula units are differentiated by the conformations of trimethylammonium groups (ordered in model I, but disordered in models II and III), conformations of the carboxyl groups and positions of OH···O bonded water molecules (ordered in molecules I and II, and disordered in model III), while the bulks of the cations and iodide anions are consistent for all models. While the calorimetric study and varied-temperature structural determinations exclude phase transitions of the highly pseudosymmetric model I. This pseudosymmetry is independent of temperature between 100 K and the m.p. at 463 K, and illustrates subtle structural effects leading complex molecular aggregation in the crystal. Theoretical computations confirm the low energy differences between the conformers.Graphical abstractᅟ

Single-Use Disposable Electrochemical Label-Free Immunosensor for Detection of Glycated Hemoglobin (HbA1c) Using Differential Pulse Voltammetry (DPV).

A single-use disposable in vitro electrochemical immunosensor for the detection of HbA1c in undiluted human serum using differential pulse voltammetry (DPV) was developed. A three-electrode configuration electrochemical biosensor consisted of 10-nm-thin gold film working and counter electrodes and a thick-film printed Ag/AgCl reference electrode was fabricated on a polyethylene terephthalate (PET) substrate. Micro-fabrication techniques including sputtering vapor deposition and thick-film printing were used to fabricate the biosensor. This was a roll-to-roll cost-effective manufacturing process making the single-use disposable in vitro HbA1c biosensor a reality. Self-assembled monolayers of 3-Mercaptopropionic acid (MPA) were employed to covalently immobilize anti-HbA1c on the surface of gold electrodes. Electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) confirmed the excellent coverage of MPA-SAM and the upward orientation of carboxylic groups. The hindering effect of HbA1c on the ferricyanide/ferrocyanide electron transfer reaction was exploited as the HbA1c detection mechanism. The biosensor showed a linear range of 7.5–20 µg/mL of HbA1c in 0.1 M PBS. Using undiluted human serum as the test medium, the biosensor presented an excellent linear behavior (R2 = 0.999) in the range of 0.1–0.25 mg/mL of HbA1c. The potential application of this biosensor for in vitro measurement of HbA1c for diabetic management was demonstrated.

Cobalt(II) metal–organic framework micro-nanoparticles: Molecular self-assembly from layers to micropores showing the conjunctive orientation of carboxyl groups

Cobalt metal–organic framework (MOF) materials CoL(1,4-chdc)·mH2O (1,4-chdc=1,4-cyclohexanedicarboxylic acid, L1=1,2-di(4-pyridyl)ethylene, and m=0 for 1Co; L2=1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene and m=2 for 2Co) were assembled in a MeOH–H2O solvent system. They crystallized in a monoclinic system with space group P2(1)/c, Z=4, a=9.479(4)Å, b=13.704(6)Å, c=14.455(6)Å, and β=99.424(6)° for 1Co, and a=14.349(11)Å, b=12.088(9)Å, c=26.62(2)Å, and β=97.255(11)° for 2Co. It was shown that N-ligand can regulate and control the conjunctive orientation of carboxyl groups in these MOFs; thus, the MOFs exhibited structures that ranged from layers to micropores. Furthermore, the micro-nanoparticles of 1Co and 2Co were investigated for new potential applications of micro-nano MOFs.

Chemoselective Hydrogenation of Benzoic Acid over Ni–Zr–B–PEG(800) Nanoscale Amorphous Alloy in Water

A Zr and polyethylene glycol 800 [PEG(800)] modified Ni–B [Ni–Zr–B–PEG(800)] amorphous alloy catalyst showed excellent catalytic performance, comparable to noble metal catalysts, in the chemoselective hydrogenation of benzoic acid to cyclohexane carboxylic acid. The synergistic effect between Zr and PEG(800) is suggested to decrease significantly the agglomeration of the active Ni species, causing the Ni–Zr–B–PEG(800) to have a larger BET area, smaller particle size, and the greatest number of Ni active centers, accounting for its high activity in water. The solvent effect on the selectivity was studied in detail. The high polarity of the water favors the orientation of carboxyl group toward the solvent, resulting in the selective hydrogenation of the aromatic ring, thus leading to a high selectivity for production of cyclohexane carboxylic acid compared to that occurring in the low polarity cyclohexane.

2-(4-Phenyl-5-pyridin-2-yl-4H-1,2,4-triazol-3-yl)cyclohexanecarboxylic Acid and Its DMSO Solvate: Synthesis, Crystal Structure and Biological Activity

A new 1,2,4-triazole derivative, 2-(4-phenyl-5-pyridin-2-yl-4H-1,2,4-triazol-3-yl)cyclohexanecarboxylic acid, C20H20N4O2 (I), and its dimethyl sulfoxide solvate 1:1 (II) have been synthesized and their crystal structure was established. Compound (I) was screened for its antiproliferative and antiinflammatory activity. Structural analysis indicated the substantial difference between two symmetry independent molecules in (I) and this in (II), it manifests in the relative orientation of pyridine/phenyl and triazole rings, as well as in the orientation of carboxyl group with respect to cyclohexane ring. The molecules A and B in the crystal (I) form two hydrogen-bonded chains through O–Hcarboxyl and Ntriazole atoms, giving separate catemers of symmetry independent molecules. The catemer of (IA) running along the 21 axis is homochiral, while the catemer (IB) is racemic—formed about the c glide plane. In the crystalline solvate (II) complexation of (I) with DMSO induced enantiomeric self-resolution. Obtained crystals are racemic twins, in which each part is built of one enantiomer of (I) having the relative configuration 11S,12R or 11R,12S. A pair of host–guest molecules is linked by the O–Hcarboxyl⋯ODMSO hydrogen bond.

Syntheses, Structural Characterization, and Properties of {[Cu(bpp)2(H2O)2](tp)·7H2O} and {[Cu(bpp)2(H2O)](ip)·7H2O} Complexes. New Examples of the Organic Anionic Template Effect on Induced Assembly of Water Clusters (bpp = 1,3-Bis(4-pyridyl)propane, tp = Terephthalate, ip = Isophthalate)

A unique zero-dimensional (0D) discrete (H2O)14 cluster containing a rare hanging-ladder-like water octamer and an infinite one-dimensional (1D) loose-string-like water chain, respectively, was observed in the coordination polymeric solids {[Cu(bpp)2(H2O)2](tp)·7H2O} (1) and {[Cu(bpp)2(H2O)](ip)·7H2O} (2) (bpp = 1,3-bis(4-pyridyl)propane, tp = terephthalate, and ip = isophthalate), obtained by similar solution phase ultrasonic synthesis techniques, in which 1 (C34H50CuN4O13) crystallized in the monoclinic P21/n space group, Z = 4 (a = 12.824(3) A, b = 16.867(3) A, c = 17.660(4) A; β = 94.50(3)°; V = 3808(1) A3) and 2 (C34H48CuN4O12) was attributed to the monoclinic P21 chiral space group, Z = 2 (a = 10.439(2) A, b = 16.863(3) A, c = 11.302(2) A; β = 107.84(3)°; V = 1893.9(6) A3), respectively. Of particular interest, the shapes of water clusters have been obviously well-tuned by modulating different relative orientations of carboxylate groups based on the tp2− and ip2− dianions, demonstrating that water a...

Orientations of Carboxylate Groups Coupled to the Mn Cluster in the Photosynthetic Oxygen-Evolving Center As Studied by Polarized ATR-FTIR Spectroscopy

It is essential to clarify the structures and interactions of amino acids surrounding the Mn cluster in photosystem II (PSII) to understand the molecular mechanism of photosynthetic oxygen evolution. In this study, polarized attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was applied for the first time to PSII to investigate the orientation of carboxylate groups coupled to the oxygen-evolving Mn cluster. PSII membranes from spinach were oriented on the surface of a silicon ATR crystal, and flash-induced polarized ATR-FTIR difference spectra for the S(1) --> S(2) transition (S(2)/S(1) spectra) were obtained. The distribution of membrane orientations by mosaic spread was estimated from the semiquinone CO peak in polarized Q(A)(-)/Q(A) difference spectra recorded using the same oriented sample by buffer exchange. The orientations of carboxylate groups coupled to the Mn cluster were estimated from the dichroic ratios of the symmetric COO(-) bands in the polarized S(2)/S(1) ATR-FTIR spectra. We found that most of the carboxylate groups perturbed during the S(1) --> S(2) transition, due to direct ligation to the Mn cluster or though a hydrogen bond network, have orientations in a relatively narrow angle range of 34-48 degrees with respect to the membrane normal. Implications of the obtained orientations and the changes upon formation of S(2) are discussed on the basis of the information from previous FTIR studies and the X-ray structures. The results in this study show that polarized ATR-FTIR difference spectroscopy is a fruitful method for investigating the orientations and their reaction-induced changes in redox cofactors and coupled amino acid side chains in photosynthetic proteins.

Structural Interactions in Chondroitin 4-Sulfate Mediated Adherence of Plasmodium falciparum Infected Erythrocytes in Human Placenta during Pregnancy-Associated Malaria

Infection with Plasmodium falciparum during pregnancy results in the adherence of infected red blood cells (IRBCs) in placenta, causing pregnancy-associated malaria with severe health complications in mothers and fetuses. The chondroitin 4-sulfate (C4S) chains of very low sulfated chondroitin sulfate proteoglycans (CSPGs) in placenta mediate the IRBC adherence. While it is known that partially sulfated but not fully sulfated C4S effectively binds IRBCs, structural interactions involved remain unclear and are incompletely understood. In this study, structurally defined C4S oligosaccharides of varying sulfate contents and sizes were evaluated for their ability to inhibit the binding of IRBCs from different P. falciparum strains to CSPG purified from placenta. The results clearly show that, with all parasite strains studied, dodecasaccharide is the minimal chain length required for the efficient adherence of IRBCs to CSPG and two 4-sulfated disaccharides within this minimal structural motif are sufficient for maximal binding. Together, these data demonstrate for the first time that the C4S structural requirement for IRBC adherence is parasite strain-independent. We also show that the carboxyl group on nonreducing end glucuronic acid in dodecasaccharide motif is important for IRBC binding. Thus, in oligosaccharides containing terminal 4,5-unsaturated glucuronic acid, the nonreducing end disaccharide moiety does not interact with IRBCs due to the altered spatial orientation of carboxyl group. In such C4S oligosaccharides, 14-mer but not 12-mer constitutes the minimal motif for inhibition of IRBC binding to placental CSPG. These data have important implications for the development and evaluation of therapeutics and vaccine for placental malaria.

Ab Initio Molecular Dynamics of Heme in Cytochrome c

Ab initio molecular dynamics (AIMD) calculations, based on the Car-Parrinello method, have been carried out for three models of heme c that is present in cytochrome c. Both the reduced (Fe(II)) and oxidized (Fe(III)) forms have been analyzed. The simplest models (1R and 1O, respectively) consist of a unsubstituted porphyrin (with no side chains) and two axially coordinated imidazole and ethylmethylthioether ligands. Density functional theory optimizations of these models confirm the basic electronic features and are the starting point for building more complex derivatives. AIMD simulations were performed after reaching the thermal stability at T = 300 K. The evolution of the Fe-L(ax) bond strengths is examined together with the relative rotations of the imidazole and methionine about the axial vector, which appear rather independent from each other. The next models (2R and 2O) contain side chains at the heme to better simulate the actual active site. It is observed that two adjacent propionate groups induce some important effects. The axial Fe-Sdelta bond is only weakened in 2R but is definitely cleaved in the oxidized species 2O. Also the mobility of the Im ligand seems to be reduced by the formation of a strong hydrogen bond that involves the Im Ndelta1-Hdelta1 bond and one carboxylate group. In 2O the interaction becomes so strong that a proton transfer occurs and the propionic acid is formed. Finally, the models 3 include a free N-methyl-acetamide molecule to mimic a portion of the protein backbone. This influences the orientation of carboxylate groups and limits the amount of their hydrogen bonding with the Im ligand. Residual electrostatic interactions are maintained, which are still able to modulate the dissociation of the methionine from the heme.

Rotational orientation of carboxyl groups in cyclohexane systems revision of Simon's pK a-rule

Rotational orientation of carboxyl groups in cyclohexane systems revision of Simon's pK a-rule

Surface Chemistry of High Polymers. VII Polyacids and Some Vinyl Polymers

Abstract The films of polyacids (poly-l-glutamic acid and the copolymer of maleic acid and vinyl acetate) and some related compounds were studied in order to know the behaviour of carboxyl groups in the linear polymer at the interface. The principal results obtained are as follows. The orientation of carboxyl group is affected considerably by other accompanying groups in polymer. Hence, the surface moment of carboxylic compounds is various according to the surface orientation of respective groups in the polymer. Accordingly, the surface moment of copolymer cannot be explained by the simple additivity of the moment of constituent polar groups. The surface moment of polyacids abruptly decreases nearly at the pH of aqueous phase equal to the pK of corresponding structural unit.