Base Adducts Research Articles

Mechanism of B‐H Redistribution during Reduction of Polyborazylene by Hydrazine

AbstractDensity functional theory has been used to elucidate the mechanistic underpinnings of the regeneration of ammonia‐borane (H3B−NH3, AB) from polyborazylene (BxNxHx, PBz) in the presence of hydrazine (H2N−NH2, Hz). Herein, borazine (B3N3H6, Bz) is used as the simplest relevant model of PBz for the regeneration process. Digestion of Bz using Hz was found to occur by a string of Lewis acid base adduct (between B atoms of Bz and Hz molecule) formation and Hz assisted proton transfer processes. Later, B−H bonds of HB(NHNH2)2, the Bz digested product, are redistributed to form hydrazine‐borane (H3B−NH2NH2, HzB) and B(NHNH2)3. Redistribution of B−H bonds occurs through hydroboration and concerted proton‐hydride transfer. Another B−H redistributed product, B(NHNH2)3, produces HzB as a result of proton and hydride transfer from cis‐diazene (Dz), the oxidized product of Hz in presence of O2.

The Potential Role of Lewis Acid–Base Adducts in Enhancing Stereoselectivity in Ziegler–Natta Catalysts: A DFT Study

Ziegler–Natta (Z–N) systems have been well established as heterogeneous catalysts that produce isotactic polypropylene and polyethylene with great efficiency. Such systems benefit considerably from donors (Lewis bases), whose addition significantly improves the stereoselectivity of polymerization. There is a consensus that the primary role of the external donors is to coordinate at the vacant site created by the extraction of internal donors and thus maintain the stereoselectivity. However, the bite difference between internal donors such as phthalates or succinate derivatives and external donors such as alkoxysilanes raises the question of how external donors can effectively replace internal donors. In order to investigate this, we have chosen four external alkoxysilane donors: (1) diisopropyl dimethoxysilane, (2) dicyclopentyl dimethoxysilane, (3) disec-butyl dimethoxysilane, and (4) sec-butyl(methyl) dimethoxysilane. DFT studies reveal that the bite difference problem can be overcome by the favorable formation of adducts between the alkoxysilane external donors and AlEt2Cl in the Z–N systems. These adducts tend to coordinate in the vicinity of the active site. Furthermore, our findings demonstrate the potential of these Lewis acid–base adducts to enhance the stereoselectivity of Z–N catalysts significantly.

Genotoxic Risks to Male Reproductive Health from Radiofrequency Radiation.

During modern era, mobile phones, televisions, microwaves, radio, and wireless devices, etc., have become an integral part of our daily lifestyle. All these technologies employ radiofrequency (RF) waves and everyone is exposed to them, since they are widespread in the environment. The increasing risk of male infertility is a growing concern to the human population. Excessive and long-term exposure to non-ionizing radiation may cause genetic health effects on the male reproductive system which could be a primitive factor to induce cancer risk. With respect to the concerned aspect, many possible RFR induced genotoxic studies have been reported; however, reports are very contradictory and showed the possible effect on humans and animals. Thus, the present review is focusing on the genomic impact of the radiofrequency electromagnetic field (RF-EMF) underlying the male infertility issue. In this review, both in vitro and in vivo studies have been incorporated explaining the role of RFR on the male reproductive system. It includes RFR induced-DNA damage, micronuclei formation, chromosomal aberrations, SCE generation, etc. In addition, attention has also been paid to the ROS generation after radiofrequency radiation exposure showing a rise in oxidative stress, base adduct formation, sperm head DNA damage, or cross-linking problems between DNA & protein.

Roles of electrostricted and structural hydration in the stability of nucleic acid duplexes.

To understand the mechanisms that govern the many biological roles of nucleic acids, it is essential to have a complete physical description of the folding of nucleic acids, including ion and water binding. To investigate the role of water in the stability of nucleic acid duplexes, we use biophysical techniques such as differential scanning calorimetry (DSC and PPC), density, ultrasound and temperature-dependence UV spectroscopy to measure complete thermodynamic profiles for the unfolding of DNA hairpins and duplexes containing chemical modifications. The favorable folding of a DNA duplex (negative ΔGo) results from a compensation between a favorable ΔH and unfavorable TΔS contributions. The resulting compensating temperatures are characteristic of the type of hydration, electrostricted or structural. DSC and UV melting curves of DNA duplexes as a function of salt and osmolyte concentrations show ion and water releases. Therefore, the favorable folding of each DNA molecule results from the formation of base-pair stacks and uptake of both counterions and water molecules. Furthermore, the comparison of the signs of ΔΔGo (or ΔΔH-Δ(TΔS) compensation) with ΔΔV of the Hess cycles for pairs of duplexes with and without a chemical modification (base pair, bulge, mismatch or adduct), allow us to indicate the type of hydration of the chemical modification: similar signs indicate electrostricted hydration while opposite signs indicate structural hydration. The main conclusion is the incorporation of stabilizing chemical modifications in DNA is accompanied by an immobilization of electrostricted water while the incorporation of destabilizing modifications immobilizes structural water. Supported by Grant MCB-1912587 from National Science Foundation.

Aromatic 1,2-Azaborinin-1-yls as Electron-Withdrawing Anionic Nitrogen Ligands for Main Group Elements.

The 2-aryl-3,4,5,6-tetraphenyl-1,2-azaborinines 1-EMe3 and 2-EMe3 (E=Si, Sn; aryl=Ph (1), Mes (=2,4,6-trimethylphenyl, 2)) were synthesized by ring-expansion of borole precursors with N3 EMe3 -derived nitrenes. Desilylative hydrolysis of 1- and 2-SiMe3 yielded the corresponding N-protonated azaborinines, which were deprotonated with nBuLi or MN(SiMe3 )2 (M=Na, K) to the corresponding group 1 salts, 1-M and 2-M. While the lithium salts crystallized as monomeric Lewis base adducts, the potassium salts formed coordination polymers or oligomers via intramolecular K⋅⋅⋅aryl π interactions. The reaction of 1-M or 2-M with CO2 yielded N-carboxylate salts, which were derivatized by salt metathesis to methyl and silyl esters. Salt metathesis of 1-M or 2-M with methyl triflate, [Cp*BeCl] (Cp*=C5 Me5 ), BBr2 Ar (Ar=Ph, Mes, 2-thienyl), ECl3 (E=B, Al, Ga) and PX3 (X=Cl, Br) afforded the respective group 2, 13 and 15 1,2-azaborinin-2-yl complexes. Salt metathesis of 1-K with BBr3 resulted not only in N-borylation but also Ph-Br exchange between the endocyclic and exocyclic boron atoms. Solution 11 B NMR data suggest that the 1,2-azaborinin-2-yl ligand is similarly electron-withdrawing to a bromide. In the solid state the endocyclic bond length alternation and the twisting of the C4 BN ring increase with the sterics of the substituents at the boron and nitrogen atoms, respectively. Regression analyses revealed that the downfield shift of the endocyclic 11 B NMR resonances is linearly correlated to both the degree of twisting of the C4 BN ring and the tilt angle of the N-substituent. Calculations indicate that the 1,2-azaborinin-1-yl ligand has no sizeable π-donor ability and that the aromaticity of the ring can be subtly tuned by the electronics of the N-substituent.

A DNA Cleavage Assay Using Synthetic Oligonucleotide Containing a Single Site-Directed Lesion for In Vitro Base Excision Repair Study.

Many chemicals cause mutation or cancer in animals and humans by forming DNA lesions, including base adducts, which play a critical role in mutagenesis and carcinogenesis. A large number of such adducts are repaired by the DNA glycosylase-mediated base excision repair (BER) pathway, and some are processed by nucleotide excision repair (NER) and nucleotide incision repair (NIR). To understand what structural features determine repair enzyme specificity and mechanism in chemically modified DNA in vitro, we developed and optimized a DNA cleavage assay using defined oligonucleotides containing a single, site specifically placed lesion. This assay can be used to investigate novel activities against any newly identified derivatives from chemical compounds, substrate specificity and cleavage efficiency of repair enzymes, and quantitative structure-function relationships. Overall, the methodology is highly sensitive and can also be modified to explore whether a lesion is processed by NER or NIR activity, as well as to study its miscoding properties in translesion DNA synthesis (TLS).

Enhancing the stability of the polymeric Lewis-base-assisted dual-phase 3D CsPbBr3–Cs4PbBr6 perovskite by molecular engineering and self-passivation

Self-ordered polymeric Lewis acid–base adduct formation for a dual role of passivated CsPbBr3–Cs4PbBr6 perovskite grain morphology modulation and exciton dielectric confinement, thereby exhibiting high performances and stability in PeLEDs.

A thermo-regulated highly regioselective mono and dihalogenations of phenols and anilines in water employing new Lewis base adducts (LBAs) [DBUBr]+Br− and [DBUI]+I− as green reagents: a simple approach

A temperature regulated easy to handle aqueous phase regioselective halogenation of phenols and anilines employing New Lewis base adducts (LBAs) is reported.

Synthesis of 10B-Enriched Borane Lewis Base Adducts

Synthesis of ¹⁰B-Enriched Borane Lewis Base Adducts

In situ post-synthesis of luminescent Lewis acid-base adducts.

Inkjet printing has drawn widespread attention and is considered as one of the most promising technologies for mass manufacturing of optoelectronic devices. Herein, we elaborate a novel strategy to modulate the morphologies of inkjet-printed thin films by optimizing the ink formulation and suppressing the coffee-ring effect, combining the approach of in situ post-synthesis based on Lewis acid-base interactions. Luminescent Lewis acid-base adducts are created immediately during inkjet printing, i.e., in situ post-synthesis based on coordination chemistry. The electron-deficient aryl borane was employed as Lewis acid to trigger the coordination interaction with a Lewis base of a nitrogen-containing fluorescent material, which resulted in the rearrangement of the frontier molecular orbitals. Most likely, a reduced singlet-triplet energy gap and charge transfer would be detectable if the Lewis base is a conjugated fluorophore. This exemplifies the great potential of In situ post-synthesis strategy in the design of new luminescent materials for light-emitting diodes and encryption via inkjet printing.

How Bulky of Base Adducts can be Responsible for Clastogenicity rather than Mutagenicity?

Two types of TK mutants are induced by genotoxic factors; normally growing (NG) TK mutants due to point mutations of targeted TK locus, and slowly growing (SG) mutants due to gross structural changes involving the growth-regulating gene outside targeted TK locus. In this study, human lymphoblstoid WTK1 cells were used to consider how bulky n- alkylated bases can induce SG mutants. For this purpose, n-alkyl methanesulfonates (AMS) having an n-alkyl group with 3-7 carbons [n-propy methanesulfonate (PMS), n-butyl methanesulfonate (BMS), n-pentyl methanesulfonate (PeMS), n- hexyl methanesulfonate (HexMS), and heptyl methanesulfonate(HepMS)] were synthesized. n-alkyl methanesulfonates having n-alkyl groups with 1-7 carbons induced NG mutants, but n-alkyl methanesulfonates having n-alkyl groups with ≥4 carbons but not with ≤3 carbons induced SG mutants. n-Alkyl methanesulfonates having n-Alkyl groups with ≥4 carbons have been shown to induce bulky adducts that cause disturbances to the helical DNA structure and are removed by nucleotide excision repair. It could be considered that n-alkyl groups with ≥4 carbons causing disturbances to the helical DNA structure induce SG mutants to result in clastogenicity rather than mutagenicity.

Lewis Acid-Base Adducts for Efficient and Stable Cesium-Based Lead Iodide-Rich Perovskite Solar Cells.

All-inorganic cesium-lead-iodide (CsPbI3 Br3- x (2 < x< 3)) perovskite presents preeminent photovoltaic performance and chemical stability. Unfortunately, this kind of material suffers from phase transition to a nonperovskite phase under oxidative chemical stresses. Herein, the introduction of a low concentration of Lewis acid-base adducts (LABAs) is reported to synergistically reduce defect density, optimize interfacial energy alignment, and improve device stability of CsPbI2.75 Br0.24 Cl0.01 (CsPbTh3 ) solar cells. Both theoretical simulations and experimental measurements reveal that the noncoordinating anions, PF6 - , as a Lewis base can more effectively bind with undercoordinated Pb2+ to passivate iodide vacancy defects than the BF4 - and absorbed I- , and thus the point defects are well suppressed. In addition, N-propyl-methyl piperidinium (NPMP+ ) is selected to assemble with PF6 - in CsPbTh3 film. The NPMP+ can regulate the crystal growth and finally homogenize the grain size and decrease the trap density. Consequently, the LABAs strategy can improve the power conversion efficiency of CsPbTh3 solar cells to 19.02% under 1-sun illumination (100mW cm-2 ). Fortunately, the NPMP+ and PF6 - -treated CsPbTh3 film shows great phase stability after storage in ambient air for 250 days, and the power conversion efficiency of corresponding solar cells is almost 76% of the initial value after 60 days aging under ambient conditions.

Characterization and Quantification of Acrolein-Induced Modifications in Hemoglobin by Mass Spectrometry─Effect of Cigarette Smoking.

Exposure to acrolein, the smallest α, β-unsaturated aldehyde, in humans originates from cigarette smoking and other environmental sources, food cooking, and endogenous lipid peroxidation and metabolism. The protein modification caused by acrolein is associated with various diseases, including cancer, cardiovascular, and neurodegenerative diseases. In this study, acrolein-modified human hemoglobin was reduced by sodium borohydride. Thus, three types of modifications, that is, Schiff base, Michael addition, and formyl-dehydropiperidion adducts, were converted to the corresponding stable adducts, leading to mass increases of 40.0313, 58.0419, and 96.0575 Da, respectively. These stable acrolein-modified hemoglobin peptides were identified by nanoflow liquid chromatography coupled to a high-resolution nanoelectrospray ionization tandem mass spectrometry. Among the 26 different types and sites of modifications, 15 of them showed a dose-dependent increase with increasing concentrations of acrolein. To investigate the role of acrolein-induced modifications in smoking and oral cancer, the 15 dose-responsive acrolein-modified peptides, together with three ethylated peptides previously identified, were quantified in oral cancer patients, healthy smokers, and healthy nonsmokers. The results reveal that the relative extents of the Michael-type adduct at α-Lys-16, α-His-50, and β-Lys-59 are significantly higher in smokers (oral cancer and healthy) than in nonsmokers. Areas under the receiver operating characteristic curve of these peptides range from 0.7500 to 0.9375, indicating the ability to discriminate smokers from nonsmokers. Additionally, these acrolein-modified peptides correlate with three ethylated peptides at the N-termini of α- and β-globin, as well as β-His-77, and with the number of cigarettes smoked per day. Therefore, measuring the reduced Michael adducts at α-Lys-16, α-His-50, and β-Lys-59 of hemoglobin from one drop of blood by this sensitive and specific method may reflect the increase of acrolein exposure due to cigarette smoking.

N‐Benzoyl‐4‐dimethylaminopyridinium Chloride: A Lewis Base Adduct for Efficient Poly and Monobenzoylation

AbstractN‐benzoyl‐4‐dimethylaminopyridinium chloride [DMAPBz]+Cl− was efficiently employed for polybenzoylation of triols and tetrols without epimerization and elimination products. This Lewis base adduct has also been employed for regioselective monobenzoylation of polyols obtained from D‐pentoses. Further an eco‐friendly monobenzoylation of phenols, amines and alcohols was achieved in water as a solvent without using a base and chromatographic purification of the products. Chemoselective monobenzoylation and recovery of the DMAP is an added advantage of our protocol.

Amplification, Enrichment, and Sequencing of Mutagenic Methylated DNA Adduct through Specifically Pairing with Unnatural Nucleobases.

3-Methylthymine (m3T) is a long-known chemically stable but strongly mutagenic DNA base adduct; however, the sequencing method to determine m3T is lacking so far. Two of the main obstacles include the capacity of m3T to stall DNA elongation and its low abundance. To address the challenges, we report an unnatural base pairing strategy in this paper. A new m3T-TPT3 base pair was developed with a Vmax/Km value 82-fold higher than that of the m3T-A pair. The TPT3 nucleobase can be specifically incorporated opposite the m3T base, and the resulting m3T-TPT3 base pair can be effectively extended to give full-length products in the presence of commercial DNA polymerases. Importantly, the feature of the m3T-TPT3 pair enables a replacement PCR amplification to transfer m3T lesions at the exact positions into unnatural base pairs, which permits Sanger sequencings as well as biotin-streptavidin-based enrichments of m3T lesions. Taken together, this work offers a simple, convenient, and practical method for amplification, enrichment, and sequencing of m3T for the first time.

Lewis Base Adducts of Phosphine-Stabilized Pb(II) Cations: Synthesis and Catalytic Hydroamination of Alkynes.

Phosphine-stabilized Pb(II) cations, generated by chloride abstraction from chloroplumbylene 1, readily react with Lewis bases (L) such as phosphines and amines to give the corresponding donor-acceptor complexes 3. These complexes 3 react with phenylacetlylene via alkyne insertion into the Pb-L bond to afford the corresponding vinylplumbylenes 4. Of particular interest, the stable complex 4-HNiPr2 (with a secondary amine) can be used as a hydroamination catalyst of phenylacetylene.

Solvent engineering for two-dimensional perovskite of guanidium lead iodide

Guanidinium lead tri-iodide-based perovskite (GAPbI3) is considered a potential candidate for stable structural template of future perovskite solar cells (PSCs) due to the high molecular symmetry of the GA cation, leading to a near-zero dipole moment, along with a high thermodynamic stability. However, a very low power conversion efficiency (PCE) has been reported for GAPbI3 PSC due to its low-dimensionality, comparatively large band gap, and significant trap states due to large grain boundaries and severe aggregation. In the present study, a two-dimensional (2D) GA2PbI4 perovskite is prepared via a one-step Lewis acid–base adduct approach in which a 7:3 ratio of 4-tert-butylpyridine (tBP) and thiourea in dimethylformamide is employed as the Lewis base. It is observed that the tBP promotes the layer-by-layer growth of 2D perovskite in two directions by guiding multiple PbI2 layers more effectively. The optimized GA2PbI4 perovskite film exhibits better uniformity, large grain size, reduced trap states, and a lower band gap of 2.03 eV. The device containing the GA2PbI4 perovskite exhibits a PCE of ca. 1.74%, along with long-term durability under ambient conditions, and hysteresis-free current density-voltage behavior. The significant enhancement in the PCE of the GA cation-based PSC leaves scope for further improvement in the perovskite-based devices.

Crystal structures of the Lewis acid-base adducts {[(C6H11)2N]3Ti-LB}+[MeB(C6F5)3]-·1.5C7H8; LB = (C6H5)3PO (1), p-F-C6H4CN (2).

The reaction of [(C6H11)2N]3Ti-CH3 with the Lewis acid B(C6F5)3, followed by addition of the Lewis bases (C6H5)3PO and p-F-C6H4CN led to the complex salts tris-(di-cyclo-hexyl-amido)(tri-phenyl-phosphine oxide)titanium methyl-tris(penta-fluoro-phen-yl)borate toluene sesquisolvate, [Ti(C12H22N)3(C18H15OP)](C19H3F15B)·1.5C7H8, (1), and tris-(di-cyclo-hexyl-amido)(4-fluoro-benzo-nitrile)-titanium methyl-tris-(penta-fluoro-phen-yl)borate toluene sesquisolvate, [Ti(C12H22N)3(C7H4FN)](C19H3F15B)·1.5C7H8, (2), both crystallizing with 1.5 equivalents of toluene solvent mol-ecules. The Lewis acid-base adducts (1) and (2) can be described by dative donor bonds. The packing of the complex cations, anions and solvent mol-ecules in the crystal structure is consolidated by an intricate three-dimensional network of non-classical C-H⋯F inter-actions. Disorder of some of the cyclo-hexyl groups and the toluene solvent mol-ecules is observed.

Carbonyl functional group assisted crystallization of mixed tin–lead narrow bandgap perovskite absorber in ambient conditions

Tin–lead (Sn–Pb) perovskite solar cells are receiving growing interest due to their applications in tandems and lead mitigation. Nonetheless, fast crystallization and facile Sn2+ oxidation restrict their ambient fabrication, which increases fabrication costs. This Letter presents an experimental study on additive assisted growth of FA0.2MA0.8Sn0.5Pb0.5I2.4Br0.6 narrow bandgap perovskite films employing a Lewis-base molecule, caffeine (1,3,7-trimethylpurine-2,6-dione), having two carbonyl functional groups (C = O) in ambient conditions (relative humidity &amp;lt; ∼10%). The C = O interacts with metallic ions (Sn2+ and Pb2+) via chelation to form an acid–base adduct, slowing down the fast crystallization of FA0.2MA0.8Sn0.5Pb0.5I2.4Br0.6 perovskite films. As a result, the grain size improves resulting in better structural and optical properties. In contrast, Urbach energy values showed higher electronic disorder near the band edges even upon caffeine doping implying Sn4+ doping in an ambient environment. This work accentuates the potential of the acid–base adduction to regulate uncontrolled crystallization of Sn–Pb perovskites in the ambient environment.

Six-Membered Saturated NHC-Stabilized Borenium Cations: Isolation of a Cationic Analogue of Borinic Acid.

The reaction of six-membered saturated NHC [1,3-di(2,6-diisopropylphenyl) tetrahydropyrimidine-2-ylidene; henceforth abbreviated as 6-SIDipp] with PhBCl2 yields a Lewis base adduct, 6-SIDipp·PhBCl2 (1), which readily undergoes nucleophilic substitution reaction with AgNO3, leading to the single (2) and double (3) substitution of both chlorides with ONO2 moieties at the boron atom. The reaction of 1 with 1 equiv of AlCl3 resulted in a borenium cation of composition [6-SIDipp·B(Ph)Cl]+ (4) with AlCl4- as the counteranion. Although borenium cations with different substituents on boron have been reported, a structurally characterized phenylchloroborenium cation remains unknown. Similarly, the reaction of 1 with triflic acid provides the first representative of a new class of borenium cations bearing one hydroxyl and one phenyl group on boron (5), a cationic analogue of borinic acid.