Tetramethylguanidine Research Articles

Integrated capture and conversion of CO2 to methane using deep eutectic solvents under mild conditions

Addressing the issues of absorbent regeneration, CO2 compression and purification, and energy consumption during transportation in the integrated carbon capture and utilization (ICCU) process, an integrated technology for CO2 capture and hydrogenation conversion has been proposed. In this study, deep eutectic solvents (DESs) composed of tetramethylguanidine (TMG) and ethylene glycol (EG) were employed to capture and hydrogenate CO2. When a heterogeneous Ru-based catalyst and a TMG:EG DES were used as a catalytic system, CO2 methanation was achieved under mild conditions (170°C and 8 MPa H2 pressure), with a CH4 yield of up to 75 % and a conversion number (TON) of 148. Importantly, the structure of the DES remained unchanged before and after the reaction, and the catalytic system could be reused three times without significantly diminishing the effectiveness of CO2 hydrogenation. This method not only reduces desorption energy consumption but also benefits from the absorbent’s high specific heat capacity, enabling the absorbent to absorb the heat generated during CO2 hydrogenation and addressing issues such as carbon deposition and catalyst deactivation resulting from poor heat transfer.

5-Fluoro uracil mediated transformation of surface-active ionic liquid based micellar nanoaggregates into pH-responsive vesicular nanoaggregates as promising drug delivery vehicle

Surface-active ionic liquids (SAILs) are poised as significant contenders in sustained and targeted drug delivery due to their membrane-like structures and their ability to transport drug molecules regardless of their polarity. In order to design a simple system that an encapsulate the anticancer drug and release it in a sustained manner, herein we designed vesicular nano-aggregates through synergistically interacting chemotherapeutic drug 5-Fluoro Uracil (5-FU) with the biocompatible SAILs, Choline Oleate ([Ch][Ol]) and Tetramethyl guanidine Oleate ([TMG][Ol]). The intention for designing the system is to offers less complexity and improved drug loading efficiency and targeted and sustained release. The molecular interactions have been proven by computational approach and the size of the nanoaggregates was determined using techniques such as Dynamic Light Scattering (DLS), Förster Resonance Energy Transfer (FRET) and Small-Angle Neutron Scattering (SANS). SANS fitting data and TEM images confirmed the transition of prolate ellipsoid micelles at [5-FU] = 0 mM to uni-lamellar ([5-FU] = 1 mM) and multi-lamellar vesicles ([5-FU] = 2 mM). These vesicular nano-aggregates are studied for their stability against temperature, pH-response and ionic strength of solution, revealing stability up to 60 °C, robust at physiological pH 7.4 and remain stable to exposure to Na+ and Ca2+ ions at concentrations up to 180 mM and 50 mM, respectively. The vesicular nano-aggregates ([Ch][Ol]/5-FU and [TMG][Ol]/5-FU) when exposed to physiological pH (i.e., 7.4) released 64.8 % and 61.2 % drug release whereas when the same systems were exposed to cancerous pH (5.2 and 6.7) released 95.9 % and 84.5% (pH 5.2 and 6.7) and 94.8 % and 81.2 % (pH 5.2 and 6.7) for the [Ch][Ol]/5-FU and [TMG][Ol]/5-FU systems, respectively. Results for the studied system encompasses them as a promising candidate for drug release at specific sites. The anticipated research might pave the way for the development of a biocompatible and stimuli-responsive drug carrier that would allow for the localized delivery of an anticancer drug.

Revealing the Roles of Guanidine Hydrochloride Ionic Liquid in Ion Inhibition and Defects Passivation for Efficient and Stable Perovskite Solar Cells.

As a result of full-scale ongoing global efforts, the power conversion efficiency (PCE) of the organic-inorganic metal halide perovskite has skyrocketed. Unfortunately, the long-term operational stability for commercialization standards is still lagging owing to intrinsic defects such as ion migration-induced degradation, undercoordinated Pb2+, and shallow defects initiated by disordered crystal growth. Herein, we employed multifunctional, non-volatile tetra-methyl guanidine hydrochloride [TMGHCL] ionic liquid (IL) as an additive to elucidate defects' passivation effects on organic-inorganic metal halide perovskite. More specifically, the formation of hydrogen bonds between H+ in GA+ and I- and coordinate bonding between Cl- and undercoordinated Pb2+ could significantly passivate these defects. The hypothesis was confirmed by both experimental and DFT simulations displaying that the optimized ratio of IL integration restrains ion migration, improving grains' size, and significantly elongating the carrier lifetime. Remarkably, the modified cell achieved a peak efficiency of 22.00 % with negligible hysteresis, compared to the control device's PCE of 20.12 %. In addition, the TMGHCL-based device retains its 93.29 % efficiency after 16 days of continuous exposure to air with a relative humidity of 35±5% and temperature of 25±5 °C. This efficient approach of adding IL to perovskites absorber can produce high PCE and has strong commercialization potential.

Preparation of functionalized 5H-chromen-5-one catalysed by tetramethyl guanidine

A well-organized, single step, tetramethyl guanidine catalyzed, three-component construction of 5H-chromen-5-one has been established. A variety substrate, together with aromatic, fused aromatic and heterocyclic carbonyl aldehydes, were reacted with CH initiated substrates to give the anticipated derivatives in good yields. This technique affords an ecological another approach to quick fabrication of a diversity-oriented 5H-chromen-5-one. The constructed molecules were confirmed by IR, NMR (1H, and 13C) spectra.

Mechanism of catalyst on morphological evolution of Al(OH)3 during Al–H2O reaction

The morphologies of Al(OH)3 crystals prepared via the Al–H2O reactions with various catalysts and the growth mechanisms of these crystals were investigated. The reaction was carried out with NaOH, KOH, tetramethylguanidine (TMG), and tetramethylammonium hydroxide (TMAH) as catalysts. The evolution of the obtained product was observed in situ, and the products obtained after 120 min of reaction have the shapes of the hexagonal prism, long-hexagonal prism, long rod, and irregular rod, respectively. In the NaOH and KOH systems, the products are gibbsite, and the gibbsite crystals grow along the (110), (001), and (100) faces in the NaOH system, and the (100), (102), and (110) faces in the KOH system. However, in the TMG and TMAH systems, the products are bayerite, and the bayerite crystals grow along the (110), (111), and (001) faces. It is worth mentioning that gibbsite has more Al—O bonds than bayerite, giving rise to the formation of columnar crystals.

Red light activatable photobase generator for rapid thiol-nucleophilic polymerization

Photobase generators (PBGs) are molecules capable of releasing reactive bases when exposed to a photonic field. These compounds have been increasingly used as photolatent catalysts for light-induced polymerization processes such as ionic polymerization and ring opening polymerization. However, most PBGs require UV light trigger, with inherent limitations of low penetration depth, harmful irradiance, and high equipment cost. Herein, we introduce a long-wavelength visible-light responsive PBG based on a tetramethylguanidine (TMG) conjugated with a photoremovable methylene blue moiety. Under irradiation of red light (λmax = 660 nm), TMG is rapidly released, enabling the initiation of thiol nucleophilic addition to a range of electrophilic substrates including (meth)acrylate, propiolate, and glycidyl groups. The photopolymerization was demonstrated by red light-induced crosslinking of resins, prepared by mixing pentaerythritol tetrakis(3-mercaptopropionate) with poly(ethylene glycol) functionalized with electrophilic substrates. We further highlight the advantage of long wavelength visible light initiation by photopolymerization behind a tissue spacer, and fabrication of thick (up to 5 cm) plastic samples.

Structure-Property Relationships of Short Chain (Mixed) Cellulose Esters Synthesized in a DMSO/TMG/CO2 Switchable Solvent System.

Increasing environmental pollution and petroleum resource depletion are important indicators for the necessary and inevitable replacement of fossil-based polymeric materials with more sustainable counterparts. Hence, the development of bio-based materials from renewable resources, such as cellulose, is of great importance. Herein, we introduce a rapid and homogeneous microwave assisted synthesis of high molecular weight (59 kDa ≤ Mn ≤ 116 kDa) short chain (mixed) cellulose esters (CEs) with variable acyl side chain length (2 ≤ C ≤ 8) by using a DMSO/TMG/CO2 switchable solvent system. Accordingly, (mixed) CEs were synthesized by implementing tetramethylguanidine (TMG) into a switchable solvent system (DMSO/TMG/CO2), followed by in-depth structural characterization via IR, 1H NMR, 13C NMR, and SEC. Examination of the structure-property relationships revealed a decrease in the glass transition temperature (177 °C ≤ Tg ≤ 204 °C), an increase in surface hydrophobicity, i.e., water contact angle (WCA) (65° ≤ WCA ≤ 98°), and a decrease of Young's modulus (7.51 MPa ≤ E ≤ 13.6 MPa), with longer alkyl side chains.

Novel BODIPY-Based Photobase Generators for Photoinduced Polymerization.

Photobase generators (PBGs) are compounds that utilize light-sensitive chemical-protecting groups to offer spatiotemporal control of releasing organic bases upon targeted light irradiation. PBGs can be implemented as an external control to initiate anionic polymerizations such as thiol-ene Michael addition reactions. However, there are limitations for common PBGs, including a short absorption wavelength and weak base release that lead to poor efficiency in photopolymerization. Therefore, there is a great need for visible-light-triggered PBGs that are capable of releasing strong bases efficiently. Here, we report two novel BODIPY-based visible-light-sensitive PBGs for light-induced activation of the thiol-ene Michael "click" reaction and polymerization. These PBGs were designed by connecting the BODIPY-based light-sensitive protecting group with tetramethylguanidine (TMG), a strong base. Moreover, we exploited the heavy atom effect to increase the efficiency of releasing TMG and the polymerization rate. These BODIPY-based PBGs exhibit extraordinary activity toward thiol-ene Michael addition-based polymerization, and they can be used in surface coating and polymer network formation of different thiol and vinyl monomers.

Efficient removal of basic heterocyclic nitrogen compounds from fuel oils by functionalized acidic ionic liquids: Extraction experiment and interaction exploration

It is a crucial procedure for eliminating nitrogen compounds from the fuel processing industry. Novel acidic ionic liquids (ILs) with functional groups can enhance the separation process, making it more effective and selective. In this study, two SO3H-functionalized tetramethylguanidine (TMG)-based ILs, namely [TMGPS]HSO4 and [TMGPS]H2PO4, were utilized as extractants to eliminate two common basic heterocyclic nitrogen compounds, pyridine and quinoline, from fuel oils. [TMG]HSO4 was used as a reference to examine and confirm the impact of functional sites on the removal of basic pyridine and quinoline. The extraction efficiency (EE) for the adopted ILs was measured, and their performance was analyzed. The results revealed that [TMGPS]HSO4 had a higher EE value than [TMGPS]H2PO4 under optimal conditions. Additionally, the EE values for pyridine and quinoline using [TMGPS]HSO4 were 99.56 % and 94.36 %, respectively. The polarity relationship during the extraction process was also investigated. Furthermore, the hydrogen bond interaction and acid-base coordination of functionalized acidic ILs with basic pyridine and quinoline were validated. These findings demonstrate the successful development of functional ILs for efficiently eliminating typical heterocyclic base nitrogen compounds from fuel oils.

Characterization and Reactivity Studies of Mononuclear Tetrahedral Copper(II)-Halide Complexes.

Structures, physicochemical properties, and reactivity of the whole series of copper(II)-halide complexes (1X; X = F, Cl, Br, and I) were examined using a TMG3tach tridentate supporting ligand consisting of cis,cis-1,3,5-triaminocyclohexane (tach) and N,N,N',N'-tetramethylguanidine (TMG). The tach ligand framework with the bulky and strongly electron-donating TMG substituents enforces the copper(II) complexes to take a tetrahedral geometry, as inferred from the electron paramagnetic resonance (EPR) spectra, exhibiting relatively large gz and small Az values. The electronic absorption spectra of 1X agreed with the simulation spectra obtained by time-dependent density functional theory (TD-DFT) calculations on a slightly distorted tetrahedral geometry. 1I and 1Br gradually decomposed to generate the corresponding copper(I) complex and halide radical X•, and in the case of 1Br, intramolecular hydroxylation of a methyl group of the TMG substituent took place under aerobic conditions, which may be caused by the reaction of the generated copper(I) complex and dioxygen (O2), generating a reactive oxygen species. 1X except 1I showed hydrogen atom abstraction (HAA) reactivity toward 1,4-cyclohexadiene (CHD), where 1F exhibited the highest reactivity with a second-order rate constant as 1.4 × 10-3 M-1 s-1 at 25 °C. Such an HAA reactivity can be attributed to the higher basicity of F- and/or large bond dissociation free energy of conjugate acid H-F as well as the unstable copper(II) electronic state in the tetrahedral geometry.

Record release of tetramethylguanidine using a green light activated photocage for rapid synthesis of soft materials.

Photocages have enabled spatiotemporally governed organic materials synthesis with applications ranging from tissue engineering to soft robotics. However, the reliance on high energy UV light to drive an often inefficient uncaging process limits their utility. These hurdles are particularly evident for more reactive cargo, such as strong organobases, despite their attractive potential to catalyze a range of chemical transformations. Herein, two metal-free boron dipyrromethene (BODIPY) photocages bearing tetramethylguanidine (TMG) cargo are shown to induce rapid and efficient polymerizations upon exposure to a low intensity green LED. A suite of spectroscopic characterization tools were employed to identify the underlying uncaging and polymerization mechanisms, while also determining reaction quantum efficiencies. The results are directly compared to state-of-the-art TMG-bearing ortho-nitrobenzyl and coumainylmethyl photocages, finding that the present BODIPY derivatives enable step-growth polymerizations that are >10× faster than the next best performing photocage. As a final demonstration, the inherent multifunctionality of the present BODIPY platform in releasing radicals from one half of the molecule and TMG from the other is leveraged to prepare polymers with starkly disparate physical properties. The present findings are anticipated to enable new applications of photocages in both small-molecule photochemistry for medicine and advanced manufacturing of next generation soft materials.

Switchable multipath cascade cyclization to synthesize bicyclic lactams and succinimides via chemodivergent reaction.

Herein, a novel switchable multipath cascade cyclization via chemodivergent reaction between readily available ketoamides and deconjugated butenolides was developed to efficiently synthesize γ-lactone fused γ-lactams and succinimide fused hemiketals. The Aldol/aza-Michael reaction and Aldol/imidation/hemiketalization reaction were enabled by catalytic amounts of two bases, namely tetramethyl guanidine and NaOAc. A wide range of substrate scope with diverse functional group compatibility was demonstrated to deliver the corresponding products with good yield and excellent diastereoselectivity (>60 examples).

Efficient separation of cellulose from bamboo by organic alkali

This study focuses on the effective separation of cellulose from bamboo through a two-step process. Several organic alkalies 2-pyrrolidinone, ethylurea, dibutylamine, N-methylformamide and tetramethyl guanidine were used to remove lignin and isolate cellulose from massive bamboo. The results showed that tetramethyl guanidine can effectively remove lignin and hemicellulose while retaining almost all the cellulose in the residual solid. The removal of lignin and hemicellulose achieved 86.0 and 84.0% after heating for 3 h at 150 °C, respectively. Subsequently, the final removal of lignin and hemicellulose increased to 91.5 and 93.8%, respectively, after a simple alkaline H2O2 bleach treatment. Interestingly, the loss of cellulose was very small after two-step treatments, and 96.9% of the component was still retained. The crystallinity increased from 69.8–75.2% in X-ray diffraction graphs due to the removal of lignin and hemicellulose. The Scanning electron microscopy images indicated that the diameter of cellulose bundles decreased from 80–100 µm to about 50 µm after organic alkali treatment, and then the fiber bundle was completely separated into a single long fiber with a diameter of about 10 µm after H2O2 bleaching. The Fourier transform infrared spectroscopy spectra confirmed the high selective removal of lignin and hemicellulose. Two-dimensional 1H-13 C Heteronuclear singular quantum correlation were analyzed to investigate the lignin structure and found that only the signals of –OCH3, Cγ–Hγ in β-O-4’ (Aγ) and β-β’ (Cγ) structures and C5-H5 in guaiacyl (G5) did not disappear after two-step treatment.

Organocatalyzed Phospha-Michael Addition: A Highly Efficient Synthesis of Customized Bis(acyl)phosphane Oxide Photoinitiators.

Addition of the P-H bond in bis(mesitoyl)phosphine, HP(COMes)2 (BAPH), to a wide variety of activated carbon-carbon double bonds as acceptors was investigated. While this phospha-Michael addition does not proceed in the absence of an additive or catalyst, excellent results were obtained with stoichiometric basic potassium or caesium salts. Simple amine bases can be employed in catalytic amounts, and tetramethylguanidine (TMG) in particular is an outstanding catalyst that allows the preparation of bis(acyl)phosphines, R-P(COMes)2 , under very mild conditions in excellent yields after only a short time. All phosphines RP(COMes)2 can subsequently be oxidized to the corresponding bis(acyl)phosphane oxides, RPO(COMes)2 , a substance class belonging to the most potent photoinitiators for radical polymerizations known to date. Thus, a simple and highly atom economic method has been found that allows the preparation of a broad range of photoinitiators adapted to their specific field of application even on a large scale.

Synthesis of side-chain functional Poly(ε-caprolactone) via the versatile and robust organo-promoted esterification reaction

Side-chain functionalized poly(ε-caprolactone) (PCL) is of much ongoing interest in light of its biocompatible and biodegradable features being widely applied in the field of biomaterials, but the versatile and robust protocols for the preparation of PCL-based (co)polymers with functional pendants remaining a challenge. Herein, an organic base of tetramethylguanidine (TMG) promoted esterification reaction of a variety of carboxylic acids and a-Cl of poly(α-chloro-ε-caprolactone) (P(α-Cl-CL)), enabling the direct synthesis of side-chain functional PCL, is described with wide substrate scope in mild reaction condition. It is noteworthy that this protocol affords one versatile and robust method for the preparation of PCL-based functional polymers, which are of high attraction for their application in biological area.

Insight into catalyst of tetramethylguanidine decorated palygorskite for CO2 conversion assisted with zinc halides

The clay mineral-based catalyst assisted with zinc halides was explored for cycloaddition of CO2, which was fabricated by modifying tetramethylguanidine (TMG) on palygorskite (Pal). More activated sites and oxygen vacancies were generated in Pal particles, and were found to be favorable for loading TMG after thermal/acid treatment. The composite TMG@P-Pal in combination with ZnBr2 showed excellent catalytic performance, and the conversion reached 99.0% (selectively >99.0%) for coupling gaseous CO2 with various epoxides. The kinetics indicated that the catalysis followed a reaction order of one, and the apparent activation energy (Ea = 76.93 kJ·mol−1) was derived by the Arrhenius equation. The catalytic activity of zinc halides was confirmed to follow the order of ZnBr2 > ZnCl2 > ZnI2 in producing cyclic carbonates. Both TMG molecules and Pal were found to activate CO2 based on the DFT calculations. This study elucidates the layer-chain structured palygorskite loaded with ZnBr2 can be a promising material for catalyzing CO2 cycloaddition with aid of guanidine molecules.

A Fruitful Decade of Organofluorine Chemistry: New Reagents and Reactions

A Fruitful Decade of Organofluorine Chemistry: New Reagents and Reactions

Effects of Ionic Liquids on Laccase from Trametes versicolor

Interactions between ionic liquids and biomolecules are of great interest due to the intrinsic properties of ionic liquids and the flexibility allowed by mixing and matching cations and anions to create unique ionic liquids. A number of ionic liquid–biomolecule studies have focused on interactions with proteins, including industrially relevant enzymes. One of these, laccase from Trametes versicolor, is a naturally derived enzyme used in the breakdown of phenolic compounds in a wide variety of industries, especially useful in breakdown of lignocellulosic materials. Here, a combination of experiments and molecular dynamics (MD) simulations was used to investigate the interactions of ionic liquids with laccase. Enzyme kinetics assays indicated that ionic liquids composed of tetramethylguanidine (TMG) and either serine or threonine caused significant reduction in enzymatic activity, while kinetics was not impacted by TMG-Asp or TMG-Glu ionic liquids. Similarly, intrinsic fluorescence of laccase in the presence of TMG-Ser and TMG-Thr exhibited a shift in spectral properties consistent with structural destabilization, but again TMG-Asp and TMG-Glu had no impact. MD simulations of laccase and ABTS with/without TMG-Ser ionic liquid provided insight into the deactivation mechanism of laccase. The simulations indicated that TMG-Ser disrupts laccase’s electron transfer mechanism.

Structure and dynamics of aqueous norspermidine solutions: an in situ ultrasonic relaxation spectroscopic study

An in situ ultrasonic relaxation spectroscopic study is presented in an effort to determine the structural changes and the dynamics involved when norspermidine (NSpd) is dissolved in water. Our aim is to elucidate the mechanism responsible for the observed relaxation mechanism in acoustic spectra and estimate the corresponding thermodynamic parameters and the associated volume change. The experimental spectra of aqueous NSpd solutions revealed a single Debye-type relaxation mechanism attributed to proton-transfer reaction. The concentration and temperature dependence of the acoustic parameters supports this assignment. The activation enthalpy and entropy were estimated equal to ΔH * = 1.79 ± 0.20 kcal mol−1 and ΔS * = −18.31 ± 0.73 cal mol−1 K−1, respectively. The concentration and temperature dependence of the sound velocity and absorption in the solutions exhibit characteristic features that are related to alterations in the network rigidity due to variations in hydrogen-bonding interactions at molecular level. The volume change associated to proton-transfer reaction for NSpd has been estimated and compared with the volume change observed for an analogous guanidine, the 1,1,3,3 tetramethyl guanidine. The obtained results are discussed in the framework of an existing theoretical structural model highlighting the strong molecular association in these liquid mixtures leading to complementary information on the structure and dynamics of guanidine amines. A comprehensive model of the whole relaxation processes is presented and discussed in detail.

A Flexible Synthetic Approach to Fluorescent Chromeno[4,3-b]pyridines and Pyrano[3,2-c]chromenes from Electron-Deficient 3-Vinylchromones.

We report a flexible approach to the synthesis of phenanthrene-like heterocycles through organocatalytic ANRORC (Addition of the Nucleophile, Ring Opening, and Ring Closure) reaction of electron-deficient 3-vinylchromones with cyanoacetamide. Addition of highly basic DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) or tetramethylguanidine (TMG) at 80 °C leads to chromeno[4,3-b]pyridines in good yields, whereas Et3 N at 20 °C made it possible to obtain the less accessible pyrano[3,2-c]chromenes and their 2-imines. The synthesis proceeds in mild conditions (EtOH, 20-80 °C), is versatile and applicable for a wide scope of reactants. The obtained compounds show bright fluorescence in the range 460-595 nm with high quantum yields (up to 0.84) in various solvents (MeCN, DMSO, EtOH, H2 O).