CH2OH Group Research Articles

Detecting a quasi-stable imine species on the reaction pathway of SHV-1 β-lactamase and 6β-(hydroxymethyl)penicillanic acid sulfone.

For the class A β-lactamase SHV-1, the kinetic and mechanistic properties of the clinically used inhibitor sulbactam are compared with the sulbactam analog substituted in its 6β position by a CH2OH group (6β-(hydroxymethyl)penicillanic acid). The 6β substitution improves both in vitro and microbiological inhibitory properties of sulbactam. Base hydrolysis of both compounds was studied by Raman and NMR spectroscopies and showed that lactam ring opening is followed by fragmentation of the dioxothiazolidine ring leading to formation of the iminium ion within 3 min. The iminium ion slowly loses a proton and converts to cis-enamine (which is a β-aminoacrylate) in 1 h for sulbactam and in 4 h for 6β-(hydroxymethyl) sulbactam. Rapid mix–rapid freeze Raman spectroscopy was used to follow the reactions between the two sulfones and SHV-1. Within 23 ms, a 10-fold excess of sulbactam was entirely hydrolyzed to give a cis-enamine product. In contrast, the 6β-(hydroxymethyl) sulbactam formed longer-lived acyl–enzyme intermediates that are a mixture of imine and enamines. Single crystal Raman studies, soaking in and washing out unreacted substrates, revealed stable populations of imine and trans-enamine acyl enzymes. The corresponding X-ray crystallographic data are consonant with the Raman data and also reveal the role played by the 6β-hydroxymethyl group in retarding hydrolysis of the acyl enzymes. The 6β-hydroxymethyl group sterically hinders approach of the water molecule as well as restraining the side chain of E166 that facilitates hydrolysis.

Spectroscopic Investigation and Characterizations of PAM/PEO Blends Films

Polymer blends have been obtained in the form of dimensionally stable and free standing films and their properties were characterized by different techniques. FTIR analysis and Raman spectroscopic analysis cleared the hydrogen bonding intermolecular interaction between –CONH2 groups in Poly Acrylamide (PAM) and C-O-C and –CH2OH group in Poly Ethylene Oxide (PEO). From Differential Scanning Calorimeter (DSC) the study shows that crystallinity is increasing with PEO wt%. From polymer interaction parameter we also show that the polymer blend is miscible. Thermal stability of films is investigated by Thermo Gravimetric Analysis (TGA) and derivative Thermo Gravimetric Analysis (DrTG). From UV-Vis absorption spectra, absorption band edge, direct/ indirect band gap and optical activation energy have been calculated.

Controlling the self-assembly of homochiral coordination architectures of Cu(II) by substitution in amino acid based ligands: synthesis, crystal structures and physicochemical properties.

Through the strategic design of ligands based on amino acids, structural diversity in chiral coordination architectures of CuII is demonstrated with six new examples: {[Cu(L-HTyrbenz)2]·CH3OH·H2O}n (1), {[Cu(L-HSerbenz)2]·3H2O}n (2), {[Cu(L-HTyrthio)2]·H2O}n (3), [Cu(L-HTyr4-pyr)2(H2O)]·2H2O (4), [Cu(L-HSerthio)2(H2O)] (5), and [Cu(L-Phethio)2(H2O)]·3H2O (6) [where L-H2Tyrbenz = L-N-(benzyl)-tyrosine, L-H2Serbenz = L-N-(benzyl)-serine, L-H2Tyrthio = L-N-(methyl-2-thiophenyl)-tyrosine, L-H2Tyr4-pyr = L-N-(methyl-4-pyridyl)-tyrosine, L-H2Serthio = L-N-(methyl-2-thiophenyl)-serine and L-HPhethio = L-N-(methyl-2-thiophenyl)-phenylalanine]. For these 1:2 metal–ligand complexes, the availability of a donor atom (either from the phenolic OH group or the carboxylate group of one of the ligands) for bridging between the CuII centers results in the formation of coordination polymers (1–3), while no such availability allows a water molecule to occupy the fifth site around the CuII center to generate hydrogen bonded supramolecular assemblies (4–6). In 1, a coordination polymer is formed via a syn–anti bridging carboxylate, and the phenolic group has no role in its formation. To further emphasize this point, L-tyrosine in 1 is replaced with L-serine to form 2, in which an anti–anti bridging by the carboxylate group is observed. On the other hand, the formation of {[Cu(L-HTyrthio)2]·H2O}n (3) results from the growth of a spiral polymer via the unique phenolic bridging with a distance of 10.806(9) Å between two CuII centers. On changing from the L-H2Tyrbenz ligand to the L-H2Tyr4-pyr ligand (1vs.4), the strong hydrogen bonding of the pyridyl nitrogen with the phenolic group does not allow the latter to bind to CuII. Similarly, on changing from L-H2Tyrthio to L-H2Serthio (3vs.5), the length of the –CH2OH group in the latter is much less than the distance between the two CuII centers, therefore this group cannot occupy the fifth site and thus a water molecule is coordinated. This is further confirmed by reacting 5 with 2 eq. of L-H2Tyrthio in methanol to form 3, while the reverse is not possible. All these compounds are characterized by a number of analytical methods, such as elemental analysis, FTIR, UV-Vis and circular dichroism spectroscopy, polarimetry, powder and single crystal X-ray diffraction and thermogravimetric analysis. Photoluminescence properties of all ligands containing the L-tyrosine group and their metal complexes (1, 3 and 4) are compared in solution at room temperature.

Liquid–liquid equilibrium data for binary systems containing o-dichlorobenzene and nitrobenzene

The liquid–liquid equilibrium (LLE) data of four binary systems (o-dichlorobenzene(1)+1,2-ethanediol(2)), (o-dichlorobenzene(1)+1,2-propanediol(2)), (nitrobenzene(1)+1,2-ethanediol(2)) and (nitrobenzene(1)+1,2-propanediol(2)) under atmospheric pressure and at temperatures 290–400K were determined in this study. The results indicated the mutual solubility between all the binary systems increased with temperatures. The NRTL and UNIQUAC models were applied to correlate the liquid–liquid equilibrium data. In addition, the data were correlated well by the UNIFAC (Do) group contribution method, in which 1,2-ethanediol was treated as a single DOH group (methodI) or two CH2OH groups (method II), and 1,2-propanediol was divided into groups (CH3, CH2OH, CHOH). The new group interaction parameters for (ACCl–DOH, ACNO2–DOH, ACCl–CH2OH, ACNO2–CH2OH, ACH–CH2OH) were obtained by the experimental LLE data regression. Moreover, all the new interaction parameters except the group ACNO2–DOH were proved reliable, among which the parameters for ACCl–DOH were proved by estimating the binary system (chlorobenzene+1,2-ethanediol) LLE data from literature and the parameters for (ACCl–CH2OH, ACNO2–CH2OH, ACH–CH2OH) were proved by estimating the LLE data of the (o-dichlorobenzene(1)+1,2-ethanediol(2)) and (nitrobenzene(1)+1,2-ethanediol(2)) binary systems in this work.

Tuning Gas Permeability and Selectivity Properties by Thermal Modification of the Side Groups of Poly(oxindolebiphenylylene)s Membranes

This work presents the results of polymer membranes whose permeability and selectivity combination of properties can be defined through the chemical modification, in the solid state, of the repeating unit of a poly(oxindolebiphenylyene) that bears a −CH2OH group, PN–CH2OH. The chemical modifications are promoted by moderate thermal treatments (160–180 °C) and short times (<3.5 h). With TGA and FTIR-ATR, it is demonstrated that at certain levels of carefully controlled temperatures and times, the repeating unit of PN–CH2OH is being probably transformed into random copolymers [(PN–CH2OH)m–(PN–H)p]n and eventually at finite time into a “new” poly(oxindolebiphenylylene) in which the −CH2OH group is replaced by −H to produce a PN–H polymer. The gas permeability–selectivity combination for the gas pairs H2/CH4 and O2/N2, at 35 °C and 2 bar, assessed for the thermally rearranged membranes falls slightly above or on the well-known additive behavior expected for copolymers depending on temperature and time and of course on type of gases to be separated. At 160 °C and short reaction times (5 min), the thermally modified membranes possess both higher permeability and selectivity for the gas pair H2/CH4 than the nonthermally treated PN–CH2OH membranes. At 180 °C and 30 min, the thermally treated membranes possess higher permeability coefficients for H2 and O2, by a factor of 3.3 and 4.0, and still have the selectivity of pure synthesized PN–CH2OH.

Synthesis, immobilization and catalytic activity of a copper(II) complex with a chiral bis(oxazoline).

A chiral bis(oxazoline) bearing CH2OH groups was synthesized from a commercial bis(oxazoline) and characterized by 1H- and 13C-NMR, high resolution ESI-mass spectrometry and FTIR. The corresponding copper(II) complex was immobilized onto the surface of a mesoporous carbonaceous material (Starbon® 700) in which the double bonds had been activated via conventional bromination. The materials were characterized by elemental analysis, ICP-OES, XPS, thermogravimetry and nitrogen adsorption at 77 K. The new copper(II) bis(oxazoline) was tested both in the homogeneous phase and once immobilized onto a carbonaceous support for the kinetic resolution of hydrobenzoin. Both were active, enantioselective and selective in the mono-benzoylation of hydrobenzoin, but better enantioselectivities were obtained in the homogeneous phase. The heterogeneous catalyst could be separated from the reaction media at the end of the reaction and reused in another catalytic cycle, but with loss of product yield and enantioselectivity.

Role of Re Species and Acid Cocatalyst on Ir-ReOx/SiO2in the C-O Hydrogenolysis of Biomass-Derived Substrates

The catalytic performance of ReOx -modified Ir metal catalyst in the hydrogenolysis of C-O bonds is strongly dependent on the choice of solvent. The acidic property of the Re species becomes obvious in the alkane solvent, and the hydrogenolysis reaction proceeds mainly by acid-catalyzed dehydration and the subsequent metal-catalyzed hydrogenation. The acidic property of the Re species is weakened in water; however, the hydrogenolysis reaction proceeds in water via a direct mechanism involving SN 2-like attack of a hydride species at the interface between Ir and ReOx on the adsorbed Re alkoxide species. This mechanism enabled the selective dissociation of the C-O bond neighboring the CH2 OH group.

Alcohol oxidation by flavoenzymes.

This review article describes the occurrence, general properties, and substrate specificity of the flavoenzymes belonging to the glucose-methanol-choline oxidoreductase superfamily and the l-α-hydroxyacid dehydrogenase family. Most of these enzymes catalyze the oxidations of hydroxyl groups, yielding carbonyl moieties. Over the years, carbanion, hydride transfer, and radical mechanisms have been discussed for these enzymes, and the main experimental evidences supporting these mechanisms are presented here. Regardless of the chemical nature of the organic substrate (i.e., activated and non-activated alcohols), a hydride transfer mechanism appears to be the most plausible for the flavoenzymes acting on CH-OH groups. The reaction of most of these enzymes likely starts with proton abstraction from the substrate hydroxyl group by a conserved active site histidine. Among the different approaches carried out to determine the chemical mechanisms with physiological substrates, primary substrate and solvent deuterium kinetic isotope effect studies have provided the most unambiguous evidences. It is expected that the numerous studies reported for these enzymes over the years will be instrumental in devising efficient industrial biocatalysts and drugs.

Optical nonlinearity and electric conductivity origin study on sucrose crystal by using IR, Raman, INS, NMR, and EPR spectroscopies

The supposed importance of hydrogen bonds toward the origin of second harmonic generation (SHG) and electric conductivity in crystalline sucrose was investigated by IR (4000–10cm−1), INS (2000–10cm−1, at 35K), polarized Raman (3600–50cm−1) spectra, and 1H NMR second moment line records in the temperature range 450–80K. The temperature dependence of NIR (7000–5500cm−1) polarized spectra gave information about –CH2 motions complementary to NMR results concerning –CH2OH group rearrangements. The EPR spectra were applied to study the generation of radical ions by exposure to NIR radiation. Density functional theory quantum chemical calculations were performed to reproduce the vibrational spectra in order to complete as far as possible the assignments of bands observed by us and in the literature in sucrose crystals, and to throw more light on the possible reasons of sucrose electric conductivity and optical nonlinearity by the knowledge of theoretical values of dipole moments, polarizabilities, first order hyperpolarizabilities of sucrose molecule and clusters as well as ionization energy and electron affinity. The proton transfer in one specific hydrogen bond parallel to the helical axis b is proposed to be the most important in SHG and conductivity origin.

Quantum chemical studies on solvents for post-combustion carbon dioxide capture: calculation of pKa and carbamate stability of disubstituted piperazines.

Piperazine is a widely studied solvent for post-combustion carbon dioxide capture. To investigate the possibilities of further improving this process, the electronic and steric effects of -CH(3), -CH(2)F, -CH(2)OH, -CH(2)NH(2), -COCH3 , and -CN groups of 2,5-disubstituted piperazines on the pKa and carbamate stability towards hydrolysis are investigated by quantum chemical methods. For the calculations, B3LYP, M11L, and spin-component-scaled MP2 (SCS-MP2) methods are used and coupled with the SMD solvation model. The experimental pK(a) values of piperazine, 2-methylpiperazine, and 2,5-dimethylpiperazine agree well with the calculated values. The present study indicates that substitution of -CH(3), -CH(2) NH(2), and -CH(2) OH groups on the 2- and 5-positions of piperazine has a positive impact on the CO(2) absorption capacity by reducing the carbamate stability towards hydrolysis. Furthermore, their higher boiling points, relative to piperazine itself, will lead to a reduction of volatility-related losses.

A computational evaluation of the steric and electronic contributions to the stability of the structures of α− and β−D‐glucopyanose Part 3: energy versus geometry for α− and β−D‐glucopyanose in the gas phase (593.4)

The cyclic structures of α− and β−D‐glucopyranose differ in energy by less than a kcal (~.3 kcal at 298 K in aqueous solution) and both the α− and β− conformers have several relatively stable rotamers. These rotamers are referred to as gg, gt, and tg according to the position of the ‐OH attached to the ‐CH2 at postion C5 on the ring. While the axial versus equatorial orientation of the hydroxyl group at C1 gives rise to the conformational energy, the energies of the gg, gt, and tg rotamers are based on the orientation of the hydroxymethyl group at C5.Relaxed scans are a series of geometry optimizations carried out at 5° intervals as the terminal ‐OH (of the ‐CH2OH group (the HOCC dihedral), the ‐CH2 ‐ (the OCCO dihedral) and the axial/equatorial ‐OH at C1 (the HOCO dihedral) are rotated. Scans of energy as the rotational angles are changed show that only the orientation of hydroxymethyl substituent at C5 makes any significant contribution to the energy. Rotation about the C‐O bond, the HOCO dihedral for the hydroxyl group at C1, shows a low‐level variation in energy (~6 kcal range). Similarly, rotation about the C‐O bond, the HOCC dihedral in the hydroxymethyl group provides energy changes in the same range. However, rotation about the C5‐C6 bond (the OCCO dihedral) show double that range of energies (~12 kcal) and prominent minima indicating the gg, gt, and tg rotamers. Additionally, comparisons of dihedral scans and conformational energies of 2‐hydroxymethyl 6‐hydroxyl‐tetrahydro‐2H‐pyran and 2‐hydroxymethyl‐tetrahydro‐2H‐pyran with 1,5‐anhydro‐D‐glucitol and glucose indicate that the hydroxyl substituents on the pyran ring make little contribution to the stability of the α−, β− conformers and the gg, gt, and tg rotamers of glucose.Three‐dimensional scans of energy versus the two dihedrals in in the hydroxymethyl group (HOCC and OCCO) were done for both α− and β−D‐glucopyranose to develop a potential energy surface to confirm the geometries, energies and number of the low energy structures.

Quantifying effects of glycerol and low molecular weight polyethylene glycols on Cro repressor folding and dimerization (755.3)

Small solutes affect noncovalent protein processes by their competitive‐with‐water preferential interactions with the chemical functional groups on the protein surface that is buried or exposed during the process. Solute effects on protein processes are exploited by in vitro biochemists to drive folding or binding, but many of these effects are not understood. Here we determine the effects of glycerol and low molecular weight polyethylene glycols (PEGs) on equilibrium folding/unfolding and dimerization of a variant Cro repressor dimer and equilibrium folding/unfolding of a variant Cro repressor monomer (generously provided by Prof. Michael Mossing of University of Mississippi Department of Chemistry and Biochemistry) and dissect the effects of these solutes on each Cro repressor specie into effects from the terminal (‐CH¬2OH) and interior (‐CH2OCH2‐) groups. We find that glycerol and diEG are protein‐stabilizing solutes, triEG has a neutral effect on protein stability, and tetraEG and above are protein‐destabilizing solutes. From this we conclude that the exterior ‐CH2OH groups are stabilizing and the interior ‐CH2OCH2‐ groups are destabilizing. We also find that the effects of each solute scale in an approximate 2:1 ratio between the variant dimer and the variant monomer, showing that the effects of the solutes scale linearly with surface area buried or exposed in the process.Grant Funding Source: Supported by NIH Grant 47022

Facile and rapid thermo-regulated biomineralization of gold by pullulan and study of its thermodynamic parameters

A novel method for the production of gold nanoparticles (AuNPs) using pullulan as reducing and stabilizing agent has been developed. Quasi-spherical shaped AuNPs in the range of 50–100nm were produced at three different temperature regimes 80°C, 90°C and 100°C as characterized using UV–vis spectrophotometer, TEM and DLS. Study of reaction kinetics and thermodynamic parameters indicated that the reaction between pullulan and chloroauric acid for AuNPs formation followed first order reaction kinetics and higher temperature was favorable for the synthesis of smaller sized AuNPs. FT-IR data analyses, provided an insight towards the mechanism of gold nanoparticle formation which suggested that, the free CH2OH groups of pullulan molecule were oxidized to carboxylate ions resulted in formation of AuNPs whereas the basic skeletal structure of pullulan remained unaltered. This study may open up new avenues for synthesis of tailor made biogenic AuNPs with possible application in biomedical field.

Highly selective and controllable pyrophosphate induced anthracene-excimer formation in water

Introducing four –CH2OH groups to an anthracene bridged Zn–DPA complex was found to result in a new highly selective and controllable excimer-based fluorescent sensor for pyrophosphate in water.

Copper(ii) induced oxidative modification and complexation of a schiff base ligand: synthesis, crystal structure, catalytic oxidation of aromatic hydrocarbons and DFT calculation

A mononuclear square planar complex [CuII(L2f)], formed from a Schiff baseH2Laand Cu2+with the concomitant oxidation of two –CH2OH groups to aldehyde, displayed catalytic oxidation of aromatic hydrocarbons.

Bis(μ-2-hydroxymethyl-2-methylpropane-1,3-diolato)bis[dichloridotitanium(IV)] diethyl ether disolvate

The title complex, [Ti2Cl4{CH3C(CH2O)2(CH2OH)}2], lies across a centre of symmetry with a diethyl ether solvent mol­ecule hydrogen bonded to the –CH2OH groups on either side of it. The TiIV atom is coordinated in a distorted octa­hedral geometry by a tripodal ligand and two terminal chloride atoms. There are three coordination modes for the tripodal ligand distinguishable on the basis of their very different Ti—O bond lengths. For the terminal alkoxo ligand, the Ti—O distance is 1.760 (1) Å, the asymmetric bridge system has Ti—O bond lengths of 1.911 (1) and 2.048 (1) Å. The Ti—O bond length for the alcohol O atom is the longest at 2.148 (1) Å.

Deep Level Emission of ZnO and Amorphous SiOC Films by Photoluminescence

Effect of polarity in substrate for ZnO growth was researched. The zinc oxide films were deposited on SiOC/Si wafer by a RF magnetron sputtering system. SiOC film was also deposited by RF magnetron sputtering to obtain a low temperature process. Polarity in SiOC film changed with increasing the oxygen gas flow rates, and the chemical shift in the PL spectra was observed because of lowering the polarity of SiOC film caused by chemical reactions between CH group and OH group as the polar sites by high plasma energy. The chemical shift after ZnO deposition on SiOC film made was attributed to defects owing to the Vo and Zni and the valence band in ZnO at interfaces between ZnO and SiOC films. ZnO grown on SiOC film including polar sites changed the roughness owing to the induction of the trap charge resulted from the defects. The roughness of ZnO increased at SiOC with low polarity. SiOC with polar sites enhanced the level of blue emission deeply, and showed the blue shift in PL spectra.

Direct Microwave-Assisted Hydrothermal Depolymerization of Cellulose

A systematic investigation of the interaction of microwave irradiation with microcrystalline cellulose has been carried out, covering a broad temperature range (150 → 270 °C). A variety of analytical techniques (e.g., HPLC, (13)C NMR, FTIR, CHN analysis, hydrogen-deuterium exchange) allowed for the analysis of the obtained liquid and solid products. Based on these results a mechanism of cellulose interaction with microwaves is proposed. Thereby the degree of freedom of the cellulose enclosed CH2OH groups was found to be crucial. This mechanism allows for the explanation of the different experimental observations such as high efficiency of microwave treatment; the dependence of the selectivity/yield of glucose on the applied microwave density; the observed high glucose to HMF ratio; and the influence of the degree of cellulose crystallinity on the results of the hydrolysis process. The highest selectivity toward glucose was found to be ~75% while the highest glucose yield obtained was 21%.

Kinetics and mechanism of transaldimination of amino acids and aromatic amines with pyridoxal

Kinetics and mechanism of transaldimination of amino acids and aromatic amines with pyridoxal have been studied by means of UV spectroscopy and polarimetry. It has been shown that aminal intermediates are formed in reaction of the Schiff’s bases with p-aminobenzoic acid and β-alanine. The structure of aminal and Schiff’s base is determined by the spatial arrangement of the amino acid and aromatic fragments with respect to the pyridine ring plane. The presence of OH and CH2-OH groups in the o-positions in pyridoxal structure turns amino groups by 90° with respect to the pyridine ring. The scheme of Schiff’s bases transaldimination by amino acids and biological amines has been developed according to stereospecific, energy, and geometric factors.

Sum-Frequency-Generation Vibration Spectroscopy and Density Functional Theory Calculations with Dispersion Corrections (DFT-D2) for Cellulose Iα and Iβ

Sum-frequency-generation (SFG) vibration spectroscopy selectively detects noncentrosymmetric vibrational modes in crystalline cellulose inside intact lignocellulose. However, SFG peak assignment in biomass samples is challenging due to the complexity of the SFG processes and the lack of reference SFG spectra from the two crystal forms synthesized in nature, cellulose Iα and Iβ. This paper compares SFG spectra of laterally aligned cellulose Iα and Iβ crystals with vibration frequencies calculated from density functional theory with dispersion corrections (DFT-D2). Two possible hydrogen-bond networks A and B ( Nishiyama et al. Biomacromolecules 2008 , 9 , 3133 ) were investigated for both polymorphs. From DFT-D2 calculations the energetically favorable structures for cellulose Iα and Iβ had CH2OH groups in tg conformations and network A hydrogen bonding. The calculated frequencies of C-H stretch modes agreed reasonably well with the peak positions observed with SFG and were localized vibrations; thus, peak assignments to specific alkyl groups were proposed. DFT-D2 calculations underestimated the distances between hydrogen-bonded oxygen atoms compared to the experimentally determined values; therefore, the OH stretching calculated frequencies were ~100 cm(-1) lower than observed. The SFG peak assignments through comparison with DFT-D2 calculations will guide the SFG analysis of the crystalline cellulose structure in plant cell walls and lignocellulose biomass.