Methylene Bridge Research Articles

Impurity absorption sites and parity effects: A deviation from Simmons's model in methylene bridges with an even number of carbons and its consequences in the conductance

This work presents a new kind of odd–even effect involving an adsorbed impurity in methylenic bridges with an even number of carbons that causes a deviation in the Simmons model. The systems studied are composed of an extended molecule containing an even number of carbons forming a dopped methylenic bridge with an impurity, attached to two gold clusters. Changing the sites of an acceptor impurity (NO2) in the even methylenic bridges containing M carbon atoms (M = 8, 10, 12, and 14), an oscillating behavior of the energies' gap between HOMO/HOMO-1 and LUMO/LUMO + 1 molecular orbitals was observed. The gaps oscillate as a function of the site's parity where the impurity was adsorbed and can be explained by considering multiple avoided-crossing phenomena. The results show a strong dependence of the electrical conductance as a function of the adsorbed site with a deviation of the Simmons model due to the impurity.

Performance and characterization of phenol-formaldehyde resin with crude bio-oil by model compound method.

In order to clarify the effects of crude bio-oil for phenol-formaldehyde resin, the phenol-formaldehyde resin with bio-oil model compounds (BMPF) were prepared by model compound method. The bonding strength and aging resistance of BMPF were determined, and their microstructure and chemical bonds were also analyzed by scanning electron microscope, Fourier transform infrared spectroscopy, and nuclear magnetic resonance analysis, respectively. The results showed that the components of crude bio-oil had various degrees of effects on the BMPF performance, and the most obvious one is the phenols. The phenols and the ketones of bio-oil had positive effects on the bonding strength. The ketones had the biggest effect on the surface smoothness of BMPF film. But all components of bio-oil could inordinately improve the aging resistance of BMPF. The structural analysis indicated that the effects of bio-oil components on the BMPF performance by changing the resin structure. The CH2 peak in FT-IR and the methylene bridges intensity in NMR of phenol-free BMPF and ketone-free BMPF were smaller, while the results of aldehyde-free BMPF and acid-free BMPF were opposite. And the influence degree of BMPF structure was basically consistent with that of BMPF performance. These results could provide a basis for the modification of phenol-formaldehyde resin by crude bio-oil.

Mannich bases derivatives of 2-Phenyl-5-Benzimidazole sulfonic acid; Synthesis, Characterization, Computational studies and Biological evaluation

A new series of N-Mannich bases of 2-Phenyl-5-benzimidazole sulfonic acid have been synthesized through amino methylation reaction with secondary amines. The two moieties were held together through a methylene bridge, which comes from formaldehyde (Formalin Solution 37%) used in the reaction. Chemical structures of the newly synthesized compounds have been confirmed using FT-IR, 1HNMR and 13CNMR. Different in vitro assays including Anti-oxidant, Enzyme inhibition, Anti-microbial and Cytotoxicity assay were performed to evaluate the biological potential with reference to the standard drug. Among the synthesized library, compound 3a shows maximum alpha-glucosidase inhibition with an IC50 value of 66.66 μg/ml, compound 3d was found most toxic with LC50 value of 10.17 μg/ml. ADME evaluation studies were performed with the help of Molinspiration online software. Docking calculations were also performed. Given the importance of the nucleus involved, the synthesized compound might find extensive medicinal applications as reported in the literature.

Squaramides for colorimetric and fluorescent anion sensing.

A series of fluorophore-containing squaramides were synthesised to investigate the fluorescent and colorimetric response to anions of squaramides containing large aromatic substituents. Squaramides in which the fluorophores were conjugated directed to the squaramide motif were found to have highly acidic NH protons, giving rise to complicated fluorescence behaviour and colour changes upon addition of anions. In contrast, squaramides incorporating a methylene spacer to electronically insulate the fluorophore from the squaramide gave a relatively simple fluorescence response upon addition of anions, which was attributed to a decrease in excimer emission relative to monomer emission intensity, likely due to a disaggregation mechanism. The ratio of excimer : monomer emission was used to provide a ratiometric fluorescent response to anions, with the most selective molecules demonstrating a preference for binding to sulfate over other anions.

Water-soluble pillar[6]arene bearing pyrene on alternating methylene bridges for direct spermine sensing.

This paper describes the design and synthesis of a conjugate, which is composed of a percarboxylated water-soluble pillar[6]arene and three fluorescent pyrene chromophores on alternating methylene bridges. The optical characteristics are investigated. This conjugate is capable of encapsulating polycationic guest spermine, which results in an enhancement in the fluorescence intensity of pyrene. This host-pyrene conjugate is used for direct sensing of spermine, which shows selectivity towards a variety of biological analytes. The detection of spermine is demonstrated in live cells.

Enhancing allosteric inhibition of dihydrodipicolinate synthase through the design and synthesis of novel dimeric compounds.

The synthesis of the first dimeric inhibitor of E. coli dihydrodipicolinate synthase (DHDPS) is reported herein. Inspired by 2,4-thiazolidinedione based ligands previously shown to inhibit DHDPS, a series of dimeric inhibitors were designed and synthesised, incorporating various alkyl chain bridges between two 2,4-thiazolidinedione moieties. Aiming to exploit the multimeric nature of this enzyme and enhance potency, a dimeric compound with a single methylene bridge achieved the desired outcome with low micromolar inhibition of E. coli DHDPS observed. This work highlights the continued importance of investigation into DHDPS as an antibacterial target. Furthermore, we demonstrate the design of dimeric ligands can provide a promising strategy to improve potency in the search for novel bioactive compounds.

Pyrolysis mechanism of composite binder composed of coal tar pitch and phenolic resin for carbon materials

The composite binder consisting of coal tar pitch (CTP) and phenolic resin (PR) has both low viscosity and high char yield, and it has great potential in the preparation of advanced carbon materials. However, the lack of understanding of its synergetic behavior and mechanism hinders the optimization of the preparation process. In this work, the co-pyrolysis of CTP and PR was systematically investigated. The char yield of the composite binder was confirmed to be remarkably higher than the weighted average of the two single binders. Furthermore, the calculated activation energy for the pyrolysis of the composite binder was higher than that of CTP and PR after 400 °C. The interaction and structure evolution mechanisms of composite binder were clarified. Specifically, the ortho-position of the phenoxy carbon in CTP cross-link with the para-position of the phenoxy carbon in PR by the methylene bridge, and the free polycyclic aromatic hydrocarbons stack onto the as-crosslinked polycyclic aromatics driven by the pancake bonds.

Tuning of the Supramolecular Helicity of Peptide-Based Gel Nanofibers.

Helical supramolecular architectures play important structural and functional roles in biological systems. The helicity of synthetic molecules can be tuned mainly by the chiral manipulation of the system. However, tuning of helicity by the achiral unit of the molecules is less studied. In this work, the helicity of naphthalimide-capped peptide-based gel nanofibers is tuned by the alteration of methylene units present in the achiral amino acid. The inversion of supramolecular helicity has been extensively studied by CD spectroscopy and morphological analysis. The density functional theory (DFT) study indicates that methylene spacers influence the orientation of π-π stacking interactions of naphthalimide units in the self-assembled structure that regulates the helicity. This work illustrates a new approach to tuning the supramolecular chirality of self-assembled biomaterials.

Placing CF2 in the Center: Major Physicochemical Changes Upon a Minor Structural Alteration in Gem-Difunctional Compounds.

Fluorine atoms play an important role in all branches of chemistry and accordingly, it is very important to study their unique and varied effects systematically, in particular, the structure-physicochemical properties relationship. The present study describes exceptional physicochemical effects resulting from a H/F exchange at the methylene bridge of gem-difunctional compounds. The Δlog P(CF2-CH2) values, that is, the change in lipophilicity, observed for the CH2 /CF2 replacement in various α,α-phenoxy- and thiophenoxy-esters/amides, diketones, benzodioxoles and more, fall in the range of 0.6-1.4 units, which for most cases, is far above the values expected for such a replacement. Moreover, for compounds holding more than one such gem-difunctional moiety, the effect is nearly additive, so one can switch from a hydrophilic compound to a lipophilic one in a limited number of H/F exchanges. DFT studies of some of these systems revealed that polarity, conformational preference as well as charge distributions are strongly affected by such hydrogen to fluorine atom substitution. The pronounced effects described, are a result of the interplay between changes in polarity, H-bond basicity and molecular volume, which were obtained with a very low 'cost' in terms of molecular weight or steric effects and may have a great potential for implementation in various fields of chemical sciences.

Supramolecular self-assembly between symmetric tetramethyl cucurbit[6]uril and dimethylphenylpiperazine hydrochloride

The interaction between symmetric tetramethyl cucurbit[6]uril (TMeQ[6]) and 2,3-dimethylphenylpiperazine hydrochloride (PMY) has been studied in the presence of [CdCl4]2−. Each port of the TMeQ[6] is connected to PMY through weak interactions such as ion dipole interactions and CH⋯O hydrogen bonding interactions, whilst the [CdCl4]2− is connected with the portal carbonyl oxygen, glycoside urea methylene and a bridging methylene of a TMeQ[6] molecule via ion–dipole interactions. These interactions were evident from a single crystal X-ray diffraction study of TMeQ[6]-PMY-[CdCl4]2−. In addition, the complex can form a one-dimensional supramolecular chain structure, and then assemble into a two-dimensional supramolecular framework, which can be described as a TMeQ[6]-PMY-[CdCl4]2− based supramolecular framework (QSF).

Synthesis and Fabrication of a Betulin-Containing Polyolefin Electrospun Fibrous Mat for Antibacterial Applications.

Biocompounds play a significant role in the area of renewable polymers in terms of sustainability, as they can be employed or converted into monomers for polymerization in a manner similar to many petroleum-derived monomers. In this work, betulin, a plant-derived triterpene with antibacterial and antiviral properties, was converted to two kinds of α,ω-diene derivatives with different methylene spacer lengths between the olefin and the ester group via an esterification reaction. Polyolefins were subsequently made by acyclic diene metathesis (ADMET) polymerization of betulin-based α,ω-diene. The polymer consists of rigid betulin and flexible unsaturated aliphatic segments, which was confirmed by NMR spectroscopy and gel permeation chromatography (GPC). The influence of different parameters including temperature, catalysts, and catalyst loading on ADMET polymerization was investigated. These polyolefins with high molar mass (up to 20.0 kg/mol) were obtained in an elevated yield (≥95%). Thermal analysis of these (co)polymers showed excellent thermal stability (up to 360 °C) and tunable glass transition temperatures depending on the nature of betulin and alkene segments. To evaluate the antimicrobial potential of betulin-containing polymers, the fabrication of polyolefin fibrous mats (ca. 400 nm diameter) via the electrospinning technique was successfully achieved. Their morphology and hydrophobicity were studied by scanning electron microscopy (SEM) and water contact angle analyses. The fibrous mats possessed broad-spectrum antibacterial property, providing a feasible strategy to design betulin-based polymeric fibers for many applications in the biomedical field.

Neat Protein Single-Chain Nanoparticles from Partially Denatured BSA.

The main challenge for the preparation of protein single-chain nanoparticles (SCNPs) is the natural complexity of these macromolecules. Herein, we report the suitable conditions to produce "neat" bovine serum albumin (BSA) single-chain nanoparticles (SCNPs) from partially denatured BSA, which involves denaturation in urea and intramolecular cross-linking below the overlap concentration. We use two disuccinimide ester linkers containing three and six methylene spacer groups: disuccinimidyl glutarate (DSG) and disuccinimidyl suberate (DSS), respectively. Remarkably, the degree of internal cross-linking can be followed simply and efficiently via 1H NMR spectroscopy. The associated structural changes-as probed by small-angle neutron scattering (SANS)-reveal that the denatured protein has a random-like coil conformation, which progressively shrinks with the addition of DSG or DSS, thus allowing for size control of the BSA-SCNPs with radii of gyration down to 5.4 nm. The longer cross-linker exhibits slightly more efficiency in chain compaction with a somewhat stronger size reduction but similar reactivity at a given cross-linker concentration. This reliable method is applicable to a wide range of compact proteins since most proteins have appropriate reactive amino acids and denature in urea. Critically, this work paves the way to the synthesis of "neat", biodegradable protein SCNPs for a range of applications including nanomedicine.

DFT Studies on the Early-Transition-Metal-Catalyzed Polymerization of Polar Monomers with a Methylene Spacer between Vinyl and Functional Groups

DFT Studies on the Early-Transition-Metal-Catalyzed Polymerization of Polar Monomers with a Methylene Spacer between Vinyl and Functional Groups

Development and Evaluation of a Novel Sulfonated Phenol-Formaldehyde Resin with High Dispersion Stability.

Sulfonated phenol-formaldehyde (SPF) resin used as a cross-linker for petroleum reservoir conformance control was synthesized under alkaline conditions. The reaction process of SPF resin was evaluated by measuring the solution's viscosity with respect to phenol-formaldehyde (PF) resin. The molecular structure of SPF resin was characterized by both FTIR and HPLC-MS/MS. The influence of the formaldehyde/phenol molar ratio (F/P) and the sodium formaldehyde sulfoxylate/phenol molar ratio (S/P) on the properties of SPF were analyzed in terms of the storage time, coagulation value, molecular size, and zeta potential. The results indicate that the presence of formaldehyde sodium bisulfite could slow down condensation reaction. Phenol rings were connected by methylene bridges in the position of o-p, and sulfonated SPF resin molecules all had one sulfonate group on the oligomer structure. The storage time decreased from 87 to 6 days, and the zeta potential decreased from -3.02 to -7.70 mV with the increase in F/P (1.2-2.0). Meanwhile, the sedimentation value and the diameter increased from 3.291 × 104 to 5.045 × 104 mg/L and from 2.7 to 5.3 nm, respectively. Sulfonation could significantly increase the storage time and dispersion stability. With the increase in S/P (0.1-0.35), the storage time increased from 15 to 86 days, the sedimentation value increased from 1.927 × 104 to 5.269 × 104 mg/L, and the diameter decreased from 6.3 to 3.0 nm. This paper can present new ideas for improving the storage stability and salt tolerance of phenol-formaldehyde resin and further improving the range of its applications, which has essential reference significance.

Bridging and Fixing Metal–Organic Cages

Despite their well-defined and intrinsic porous structures, metal–organic cages (MOCs) readily lose their crystalline arrangement upon solvent exchange and desolvation, which significantly reduces their porosity. Herein, we report a novel bridging and fixing strategy for retaining the ordered arrangement of MOCs. In the bridging process, electrophilic aromatic substitution reactions involving the 4,6-dihydroxy-1,3-benzenedicarboxylate (m-DOBDC2–) ligands of cuboctahedral MOCs and formaldehyde connect the cages by methylene bridges, which are among the shortest linkers. In the subsequent fixing process, pore-filling and coordinating solvents are exchanged with or removed by low surface tension, noncoordinating solvents (such as mesitylene) in which MOCs are poorly soluble. This mild activation process avoids altering the cage arrangement, thereby further increasing the porosity of the bridged MOCs. The general applicability of this fixing process is demonstrated using cuboctahedral MOCs with different functional groups. As a result, after the fixing process, MOP-1-H displays the highest surface area of 1090.7 m2/g among Cu-paddlewheel-based MOCs. This study extends the potential applications of MOCs as functional porous materials by providing a simple and pragmatic method for preserving their porosities.

Phenolic hydroxyl-functionalized hyper-cross-linked polymers for efficient adsorptive removal of aniline

Herein, three phenolic hydroxyl-functionalized hyper-cross-linked polymers were synthesized according to two sequential Friedel-Crafts alkylation reactions at two different temperatures and they were used to adsorb aniline. The first reaction at 293 K brought abundant phenolic –OH (up to 17.95 wt%) to the intermediates, and the followed reaction at 353 K offered the resultant products with a hyper-cross-linked frameworks composed of plentiful rigid methylene bridges. The resulting polymers were promising for the adsorption of aniline, and the maximum capacities (qmax) arrived at 210.9 mg/g. As the initial concentration of aniline was<100 mg/L, the adsorption efficiency reached>95 %, and the final concentration was lower than 0.1 mg/L, much lower than the emission concentration limit of aniline in China (1.0 mg/L). The adsorption mechanism discovered that acid-base interaction, electrostatic interaction and hydrogen bonding, especially the micropore-filling were important for the adsorption.

Synthesis and Physicochemical Properties of Cryptophazane—A Soluble and Functionalizable C1‐Symmetrical Cryptophane

AbstractThe first example of a cryptophazane, a cryptophane functionalized with a nitrogen atom replacing one of the methylene bridges, is obtained with a 28 % overall yield over 8 steps, through the preparation of a C1‐symmetrical aza‐cyclotriveratrylene (aza‐CTV). Herein, we demonstrate that the introduction of a nitrogen atom on this part of the cryptophane core enhances the solubility in organic media of both the cryptophane and the synthetic intermediates, while presenting the same conformation as known cryptophanes. Cryptophazane was prepared on a multigram scale and easily functionalized. We also investigated its ability to encapsulate xenon atoms using hyperpolarized 129Xe (HP 129Xe) NMR spectroscopy. We found that both its affinity and exchange kinetics were in the appropriate range for applications in 129Xe magnetic resonance imaging (MRI). Combined with the wide range of possible functionalization, this makes cryptophazane an excellent candidate for targeted HP 129Xe MRI.

Synthesis and Physicochemical Properties of Cryptophazane-A Soluble and Functionalizable C1 -Symmetrical Cryptophane.

The first example of a cryptophazane, a cryptophane functionalized with a nitrogen atom replacing one of the methylene bridges, is obtained with a 28 % overall yield over 8 steps, through the preparation of a C1 -symmetrical aza-cyclotriveratrylene (aza-CTV). Herein, we demonstrate that the introduction of a nitrogen atom on this part of the cryptophane core enhances the solubility in organic media of both the cryptophane and the synthetic intermediates, while presenting the same conformation as known cryptophanes. Cryptophazane was prepared on a multigram scale and easily functionalized. We also investigated its ability to encapsulate xenon atoms using hyperpolarized 129 Xe (HP 129 Xe) NMR spectroscopy. We found that both its affinity and exchange kinetics were in the appropriate range for applications in 129 Xe magnetic resonance imaging (MRI). Combined with the wide range of possible functionalization, this makes cryptophazane an excellent candidate for targeted HP 129 Xe MRI.

Conformational Effects on the Threading Kinetics of Dumbbell-Shaped Guests into the Cavity of Oxatub[4]arene.

Unprecedented threading kinetics were revealed between viologen-based guests and conformationally adaptive oxatub[4]arene. Three representative conformations of oxatub[4]arene are involved in the kinetic and thermodynamic products which follow the opposite orders in their rankings. Consequently, error correction was involved and a complex kinetic process was observed in a simple two-component system. Moreover, it was found that some viologen-based guests have much faster threading kinetics than those of DABCO-based with the same stoppers. This was enabled by an unprecedented threading mechanism in which a tilted conformation of the guests is adopted by involving one linear alkyl group on the 3,5-dialkoxybenzyl stoppers, the viologen core, and the methylene spacers in the transition states. This new mechanism even allows the viologen-based guests with the 3,5-dicetyloxybenzyl stoppers to form a pseudorotaxane with oxatub[4]arene.

Conformational Effects on the Threading Kinetics of Dumbbell‐Shaped Guests into the Cavity of Oxatub[4]arene

AbstractUnprecedented threading kinetics were revealed between viologen‐based guests and conformationally adaptive oxatub[4]arene. Three representative conformations of oxatub[4]arene are involved in the kinetic and thermodynamic products which follow the opposite orders in their rankings. Consequently, error correction was involved and a complex kinetic process was observed in a simple two‐component system. Moreover, it was found that some viologen‐based guests have much faster threading kinetics than those of DABCO‐based with the same stoppers. This was enabled by an unprecedented threading mechanism in which a tilted conformation of the guests is adopted by involving one linear alkyl group on the 3,5‐dialkoxybenzyl stoppers, the viologen core, and the methylene spacers in the transition states. This new mechanism even allows the viologen‐based guests with the 3,5‐dicetyloxybenzyl stoppers to form a pseudorotaxane with oxatub[4]arene.