The synthesis and characterization of six new substituted guanidium tetrahydroxidohexaoxidopentaborate(1-) salts are reported: C(NHsub.2)sub.2(NHMe)Bsub.5Osub.6(OH)sub.4·Hsub.2O (1), ...C(NHsub.2)sub.2(NH{NHsub.2})Bsub.5Osub.6(OH)sub.4 (2), C(NHsub.2)sub.2(NMesub.2)Bsub.5Osub.6(OH)sub.4 (3), C(NHsub.2)(NMesub.2)sub.2Bsub.5Osub.6(OH)sub.4 (4), C(NHMe)(NMesub.2)sub.2Bsub.5Osub.6(OH)sub.4·B(OH)sub.3 (5), and TBDHBsub.5Osub.6(OH)sub.4 (6) (TBD = 1,5,7-triazabicyclo 4.4.0dec-5-ene). Compounds 1-6 were prepared as crystalline salts from basic aqueous solution via self-assembly processes from B(OH)sub.3 and the appropriate substituted cation. Compounds 1-6 were characterized by spectroscopic (NMR and IR) and by single-crystal XRD studies. A thermal (TGA) analysis on compounds 1-3 and 6 demonstrated that they thermally decomposed via a multistage process to Bsub.2Osub.3 at >650 °C. The low temperature stage (<250 °C) was endothermic and corresponded to a loss of Hsub.2O. Reactant stoichiometry, solid-state packing, and H-bonding interactions are all important in assembling these structures. An analysis of H-bonding motifs in known unsubstituted guanidinium salts C(NHsub.2)sub.3sub.2Bsub.4Osub.5(OH)sub.4·2Hsub.2O, C(NHsub.2)sub.3Bsub.5Osub.6(OH)sub.4·Hsub.2O, and C(NHsub.2)sub.3sub.3Bsub.9Osub.12(OH)sub.6 and in compounds 1-6 revealed that two important H-bonding Rsub.2 sup.2(8) motifs competed to stabilize the observed structures. The guanidinium cation formed charge-assisted pincer cation-anion H-bonded rings as a major motif in C(NHsub.2)sub.3sub.2Bsub.4Osub.5(OH)sub.4·2Hsub.2O and C(NHsub.2)sub.3sub.3Bsub.9Osub.12(OH)sub.6, whereas the anion-anion ring motif was dominant in C(NHsub.2)sub.3Bsub.5Osub.6(OH)sub.4·Hsub.2O and in compounds 1-6. This behaviour was consistent with the stoichiometry of the salt and packing effects also strongly influencing their solid-state structures.
Long-lived organic room-temperature phosphorescence (RTP) materials have recently drawn extensive attention because of their promising applications in information security, biological imaging, ...optoelectronic devices, and intelligent sensors. In contrast to conventional fluorescence, the RTP phenomenon originates from the slow radiative transition of triplet excitons. Thus, enhancing the intersystem crossing (ISC) rate from the lowest excited singlet state (S
) to the excited triplet state and suppressing the nonradiative relaxation channels of the lowest excited triplet state (T
) are reasonable methods for realizing highly efficient RTP in purely organic materials. Over the past few decades, many strategies have been designed on the basis of the above two crucial factors. The introduction of heavy atoms, aromatic carbonyl groups, and other heteroatoms with abundant lone-pair electrons has been demonstrated to strengthen the spin-orbit coupling, thereby successfully facilitating the ISC process. Furthermore, the rigid environment is commonly constructed through crystal engineering to restrict intramolecular motions and intermolecular collisions to decrease excited-state energy dissipation. However, most crystal-based organic RTP materials suffer from poor processability, flexibility, and reproducibility, becoming a thorny obstacle to their practical application.Amorphous organic polymers with long-lived RTP characteristics are more competitive in materials science. The intertwined structures and long chains of polymers not only ensure the rigid environment with multiple interactions but also protect triplet excitons from the surroundings, which are conducive to realizing ultralong and bright RTP emission. Exploring the fabrication strategies, intrinsic mechanisms, and practical applications of organic long-lived RTP polymers is highly desirable but remains a formidable challenge. In particular, intelligent organic RTP polymer systems that are capable of dynamically responding to external stimuli (e.g., light, temperature, oxygen, and humidity) have been rarely reported. To develop multifunctional RTP materials and expand their potential applications, a great amount of effort has been expended.This Account gives a summary of the significant advances in amorphous organic RTP polymer systems, especially smart stimulus-responsive ones, focusing on the construction of a rigid environment to suppress nonradiative deactivation by abundant inter/intramolecular interactions. The typical interactions in RTP polymer systems mainly include hydrogen bonding, ionic bonding, and covalent bonding, which can change the molecular electronic structures and affect the energy dissipation channels of the excited states. An in-depth understanding of intrinsic mechanisms and an extensive exploration of potential applications for excitation-dependent color-tunable, ultraviolet (UV) irradiation-activated, temperature-dependent, water-responsive, and circularly polarized RTP polymer systems are distinctly illustrated in this Account. Furthermore, we propose some detailed perspectives in terms of materials design, mechanism exploration, and promising application potential with the hope to provide helpful guidance for the future development of amorphous organic RTP polymers.
The intermolecular H‐bonding density heavily influences the gelation and rheological behavior of hydrogen‐bonded supramolecular polymer hydrogels, thus offering a delicate pathway to tailor their ...physicochemical properties for meeting a specific biomedical application. Herein, one methylene spacer between two amides in the side chain of N‐acryloyl glycinamide (NAGA) is introduced to generate a variant monomer, N‐acryloyl alaninamide (NAAA). Polymerization of NAAA in aqueous solution affords an unprecedented ultrasoft and highly swollen supramolecular polymer hydrogel due to weakened H‐bonds caused by an extra methylene spacer, which is verified by variable‐temperature Fourier transform infrared (FTIR) spectroscopy and simulation calculation. Intriguingly, poly(N‐acryloyl alaninamide) (PNAAA) hydrogel can be tuned to form a transient network with a self‐fused and excellent antifouling capability that results from the weakened dual amide H‐bonding interactions and enhanced water‐amide H‐bonding interactions. This self‐fused PNAAA hydrogel can completely inhibit postoperative abdominal adhesion and recurrent adhesion after adhesiolysis in vivo. This transient hydrogel network allows for its disintegration and excretion from the body. The molecular mechanism studies reveal the signal pathway of PNAAA hydrogel in inhibiting inflammatory response and regulating fibrinolytic system balance. This self‐fused, antifouling ultrasoft supramolecular hydrogel is promising as a barrier biomaterial for completely preventing postoperative tissue adhesion.
One more methylene makes a difference: introducing one extra methylene between two amides in the side chain of poly(N‐acryloyl alaninamide) weakens the H‐bonding interaction, resulting in an ultrasoft and highly swollen supramolecular polymer hydrogel that can be tuned to form a transient network with a self‐fused and antifouling ability, which is harnessed to completely prevent postoperative tissue adhesion.
The functionalization of unactivated carbon-hydrogen bonds is a transformative strategy for the rapid construction of molecular complexity given the ubiquitous presence of C-H bonds in organic ...molecules. It represents a powerful tool for accelerating the synthesis of natural products and bioactive compounds while reducing the environmental and economic costs of synthesis. At the same time, the ubiquity and strength of C-H bonds also present major challenges toward the realization of transformations that are both highly selective and efficient. The development of practical C-H functionalization reactions has thus remained a compelling yet elusive goal in organic chemistry for over a century.Specifically, the capability to form useful new C-C, C-N, C-O, and C-X bonds via direct C-H functionalization would have wide-ranging impacts in organic synthesis. Palladium is especially attractive as a catalyst for such C-H functionalizations because of the diverse reactivity of intermediate palladium-carbon bonds. Early efforts using cyclopalladation with Pd(OAc)
and related salts led to the development of many Pd-catalyzed C-H functionalization reactions. However, Pd(OAc)
and other simple Pd salts perform only racemic transformations, which prompted a long search for effective chiral catalysts dating back to the 1970s. Pd salts also have low reactivity with synthetically useful substrates. To address these issues, effective and reliable ligands capable of accelerating and improving the selectivity of Pd-catalyzed C-H functionalizations are needed.In this Account, we highlight the discovery and development of bifunctional mono-N-protected amino acid (MPAA) ligands, which make great strides toward addressing these two challenges. MPAAs enable numerous Pd(II)-catalyzed C(sp
)-H and C(sp
)-H functionalization reactions of synthetically relevant substrates under operationally practical conditions with excellent stereoselectivity when applicable. Mechanistic studies indicate that MPAAs operate as unique bifunctional ligands for C-H activation in which both the carboxylate and amide are coordinated to Pd. The
-acyl group plays an active role in the C-H cleavage step, greatly accelerating C-H activation. The rigid MPAA chelation also results in a predictable transfer of chiral information from a single chiral center on the ligand to the substrate and permits the development of a rational stereomodel to predict the stereochemical outcome of enantioselective reactions.We also describe the application of MPAA-enabled C-H functionalization in total synthesis and provide an outlook for future development in this area. We anticipate that MPAAs and related next-generation ligands will continue to stimulate development in the field of Pd-catalyzed C-H functionalization.
Chemical kinetic studies of the β-scission reaction class of hydroperoxyl alkyl hydroperoxyl radicals (•P(OOH)sub.2) from normal-alkyl cyclohexanes are carried out systematically through high-level ...ab initio calculations. Geometry optimizations and frequency calculations for all species involved in the reactions are performed at the B3LYP/CBSB7 level of theory. Electronic single-point energy calculations are calculated at the CBS-QB3 level of theory. Rate constants for the reactions of β-scission, in the temperature range of 500–1500 K and the pressure range of 0.01–100 atm, are calculated using transition state theory (TST) and Rice-Ramsberger-Kassel-Marcus/Master-Equation (RRKM/ME) theory taking asymmetric Eckart tunneling corrections and the one-dimensional hindered rotor approximation into consideration. The rate rules are obtained by averaging the rate constants of the representative reactions of this class. These rate rules can greatly assist in constructing more accurate low-temperature combustion mechanisms for normal-alkyl cyclohexanes.
Lithium, as a green energy metal used to promote world development, is an important raw material for lithium-ion, lithium–air, and lithium–sulfur batteries. It is challenging to directly extract ...lithium resources from brine with a high Mg/Li mass ratio. The microstructure study of salt solutions provides an important theoretical basis for the separation of lithium and magnesium. The changes in the hydrogen bond network structure and ion association of the Lisub.2SOsub.4 aqueous solution and Lisub.2SOsub.4-MgSOsub.4-Hsub.2O mixed aqueous solution were studied by Raman spectroscopy. The SOsub.4 sup.2− fully symmetric stretching vibration peak at 940~1020 cmsup.−1 and the O-H stretching vibration peak at 2800~3800 cmsup.−1 of the Lisub.2SOsub.4 aqueous solution at room temperature were studied by Raman spectroscopy and excess spectroscopy. According to the peak of the O-H stretching vibration spectrum, with an increase in the mass fraction of the Lisub.2SOsub.4 solution, the proportion of DAA-type and DDAA-type hydrogen bonds at low wavenumbers decreases gradually, while the proportion of DA-type hydrogen bonds at 3300 cmsup.−1 increases. When the mass fraction is greater than 6.00%, this proportion increases sharply. Although the spectra of hydrated water molecules and bulk water molecules are different, the spectra of the two water molecules seriously overlap. The spectrum of the anion hydration shell in a solution can be extracted via spectrum division. By analyzing the spectra of these hydration shells, the interaction between the solute and water molecules, the structure of the hydration shell and the number of water molecules are obtained. For the same ionic strength solution, different cationic salts have different hydration numbers of anions, indicating that there is a strong interaction between ions in a strong electrolytic solution, which will lead to ion aggregation and the formation of ion pairs. When the concentration of salt solution increases, the hydration number decreases rapidly, indicating that the degree of ion aggregation increases with increasing concentration.
We present a study of the intermolecular interactions in van der Waals complexes of methane and neon dimers within the framework of the CCSD method. This approach was implemented and applied to ...calculate and examine the behavior of the contracted two-particle reduced density matrix (2-RDM). It was demonstrated that the region near the minimum of the two-particle density matrix correlation part, corresponding to the primary bulk of the Coulomb hole contribution, exerts a significant influence on the dispersion interaction energetics of the studied systems. As a result, the bond functions approach was applied to improve the convergence performance for the intermolecular correlation energy results with respect to the size of the atomic basis. For this, substantial acceleration was achieved by introducing an auxiliary basis of bond functions centered on the minima of the 2-RDM. For both methane and neon dimers, this general conclusion was confirmed with a series of CCSD calculations for the 2-RDM and the correlation energies.
The tetrel bond (TB) between 1,2-benzisothiazol-3-one-2-TFsub.3-1,1-dioxide (T = C, Si) and the O atom of pyridine-1-oxide (PO) and its derivatives (PO-X, X = H, NOsub.2, CN, F, CHsub.3, OH, ...OCHsub.3, NHsub.2, and Li) is examined by quantum chemical means. The Si∙∙∙O TB is quite strong, with interaction energies approaching a maximum of nearly 70 kcal/mol, while the C∙∙∙O TB is an order of magnitude weaker, with interaction energies between 2.0 and 2.6 kcal/mol. An electron-withdrawing substituent on the Lewis base weakens this TB, while an electron-donating group has the opposite effect. The SiFsub.3 group transfers roughly halfway between the N of the acid and the O of the base without the aid of cooperative effects from a third entity.
The dual binding behavior of the metallylenes THsub.2 (T = Si, Ge, Sn, Pb) with some selected Lewis acids (T'Hsub.3F, T' = Si, Ge, Sn, Pb) and bases (Nsub.2, HCN, CO, and Csub.6Hsub.6) has been ...investigated by using the high-level quantum chemical method. Two types (type-A and type-B) of tetrel-bonded complexes can be formed for THsub.2 due to their ambiphilic character. THsub.2 act as Lewis bases in type-A complexes, and they act as Lewis acids in type-B ones. CO exhibits two binding modes in the type-B complexes, one of which is THsub.2···CO and the other is THsub.2···OC. The THsub.2···OC complexes possess a weaker binding strength than the other type-B complexes. The THsub.2···OC complexes are referred to as the type-B2 complexes, and the other type-B complexes are referred to as the type-B1 complexes. The type-A complexes exhibit a relatively weak binding strength with Esub.int (interaction energy) values ranging from -7.11 to -15.55 kJ/mol, and the type-B complexes have a broad range of Esub.int values ranging from −9.45 to −98.44 kJ/mol. The Esub.int values of the type-A and type-B1 complexes go in the order SiHsub.2 > GeHsub.2 > SnHsub.2 > PbHsub.2. The AIM (atoms in molecules) analysis suggests that the tetrel bonds in type-A complexes are purely closed-shell interactions, and those in most type-B1 complexes have a partially covalent character. The EDA (Energy decomposition analysis) results indicate that the contribution values of the three energy terms go in the order electrostatic > dispersion > induction for the type-A and type-B2 complexes, and this order is electrostatic > induction > dispersion for the type-B1 complexes.
Hydrogen-bonding catalytic reactions have gained great interest. Herein, a hydrogen-bond-assisted three-component tandem reaction for the efficient synthesis of N-alkyl-4-quinolones is described. ...This novel strategy features the first proof of polyphosphate ester (PPE) as a dual hydrogen-bonding catalyst and the use of readily available starting materials for the preparation of N-alkyl-4-quinolones. The method provides a diversity of N-alkyl-4-quinolones in moderate to good yields. The compound 4h demonstrated good neuroprotective activity against N-methyl-ᴅ-aspartate (NMDA)-induced excitotoxicity in PC12 cells.
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