By simply grafting a –CN group and/or a –OCH3 group onto the meta- and/or para-site of the C-ring, a series of Ir(III) complexes bearing a similar molecular platform of bis(1,2-diphenyl-1H-benzimidazolato-N,C2′)iridium(III)(acetylacetonate), but showing fine-tuned phosphorescence covering nearly the whole window of the visible spectrum with a wide color-tuning range of 109 nm was acquired. With the help of DFT calculations, it was revealed that if the C-related arene moiety of the C^N ligand (C-ring) contributes substantially to both the HOMO and LUMO of an Ir(III) complex, the concurrent introduction of an electron-donating –OCH3 and an electron-withdrawing –CN groups on the C-ring at the meta- and para-sites relative to the Ir atom may lead to a favorable synergetic substituent effect on the color-tuning direction. This may represent a facile yet effective molecular design strategy for Ir(III) complexes with a desirous emission color. A bluish green organic light-emitting diode (OLED) based on one of the objective complexes displayed a maximum current efficiency of 62.1 cd A−1, an external quantum efficiency of 19.8%, and a brightness of 48040 cd m−2, implying that high-performance red and blue OLED phosphors as well as libraries of Ir(III) complexes bearing similar molecular platforms may be developed through this –OCH3 and –CN synergetic substitution strategy.

•A facile yet efficient analysis strategy was developed using UV spectrophotometry coupled to multivariate calibration methods.•The method can realize the simultaneously quantitative determination of dinitrobenzene isomers in water samples without any prior separation.•Validation by real water samples confirmed the potential applicability of the method in practice.•The result could be applied to advance analysis strategy in the other complicated systems with multiple components.A facile yet efficient strategy was proposed by means of a combination of ultraviolet (UV) spectrophotometry with multivariate calibration methods, through which 1,2-dinitrobenzene, 1,3-dinitrobenzene and 1,4-dinitrobenzene in water samples could be simultaneously determined without any pre-separation process. The competitive adaptive reweighted sampling combined with successive projections algorithm (CARS–SPA) approach was used to diminish uninformative variables and select the important ones from spectral data measured. The multivariate calibration models were constructed by partial least squares (PLS-1) regression with high accuracy, in which the coefficients of determination of prediction (Rpred2) were 0.9935, 0.9969, and 0.9971 and the root mean square error of prediction (RMSEP) were 0.7850, 0.5411 and 0.5414 for 1,2-dinitrobenzene, 1,3-dinitrobenzene and 1,4-dinitrobenzene, respectively. The optimized model was successfully applied to simultaneously determine the content of the three studied analytes in several real water samples with good recovery close to 100%. Finally, the elliptical joint confidence region (EJCR) tests further confirm that the proposed method has no proportional and constant error in the predicted concentrations, providing a statistic support for the accuracy of the model. These results indicate that it is promise for UV spectroscopy coupled to the multivariate calibration technique to establish a simple, quick, accurate and reliable analysis method for simultaneous determination of some nitroaromatic compounds in real environments. Also, the strategy proposed by the work will advance the analytical methods used in the other complicated sample systems.

Aggregation-induced emission (AIE) compounds with intramolecular charge transfer (ICT) character have attracted considerable interest from experimental and theoretical researchers due to their potential in optoelectronic and sensory applications. However, their deactivation mechanism in solutions has been disputed, limiting their further applications. Therefore, in this work, we combined experimental observations with density functional theory (DFT) and time-dependent DFT (TD-DFT) methods to unveil the deactivation mechanism of a new AIE-active naphthalimide derivative (FNIb) in the polar solution, which was synthesized by us lately. An in-depth investigation on the effects of solvent polarity on its geometrical and electronic structures, and absorption and emission spectra indicates that FNIb would prefer a conformational planarization mechanism to the popular twisted intramolecular charge transfer mechanism (TICT) in the deactivation process. Our findings would add more insights into previous studies to rationalize the controversy on the deactivation mechanism of the AIE ICT-featured compounds in solutions.

G protein coupled receptors (GPCRs) play a crucial role in regulating signal recognition and transduction through their activation. The conformation transition in the activation pathway is of particular importance for their function. However, it has been poorly elucidated due to experimental difficulties in determining the conformations and the time limitation of conventional molecular dynamics (CMD) simulation. Thus, in this work, we employed a targeted molecular dynamic (TMD) simulation to study the activation process from an inactive structure to a fully active one for β2 adrenergic receptor (β2AR). As a reference, 110 ns CMD simulations on wild β2AR and its D130N mutant were also carried out. TMD results show that there is at least an intermediate conformation cluster in the activation process, evidenced by the principal component analysis and the structural and dynamic differences of some important motifs. It is noteworthy that the activation of the ligand binding site lags the G-protein binding site, displaying uncoupled correlation. Comparisons between the CMD and TMD results show that the D130N mutation significantly speeds up ICL2 and key ionic lock to enter into the intermediate state, which to some extent facilitates the activation involved in the NPxxY, DRY region and the separation between TM3 and TM6. However, the contribution from the D130N mutation to the activation of the ligand binding site could not be observed within the scale of 110 ns time. These observations could provide novel insights into previous studies for better understanding of the activation mechanism for β2AR.

Members of the ATP-binding cassette (ABC) transporter family are present in three kingdoms of life and play a vital role in most cellular functions. ABC transporters function as either importers that bring nutrients and other molecules into cells, or as exporters that pump toxins, drugs and lipids across membranes. Currently, the limitation of 3D structures highlights the importance of the functional annotation for transporters using bioinformatics-based methods. In this work, we focused on annotation of substrate specificity for ABC transporters. Three types of the subunit proteins of ABC transporters, namely permease protein, ATP-binding protein and substrate binding protein all contribute much to the transport process, but have unique structures and properties. However previous computational methods have only considered the three subunit proteins in the same way and cannot individually characterize each type of subunit protein. Here, through individual feature evaluation and selection, specific representation for each type of subunit protein was implemented. Then three subunit-specific models were built to consistently analyse four major classes of ABC transporters with different transport targets. Our method achieved a 5-fold cross validation accuracy of 93.35%, 84.34%, 87.24% and 81.96% for sugar transporter, ion transporter, amino acid/protein transporter and others, respectively. Our method also showed an overall prediction accuracy of 88.02% with a Mathew's correlation coefficient of 0.6736 on an independent dataset. The results suggest that considering three subunit proteins separately and developing individual models for three substrate protein groups are recommendable. This method would be an effective tool for computational annotation of substrate specificity for ABC transporters.

The quantitative analysis of explosives is very important for national defence and security inspection. However, conventional analytical methods are complicated and time-consuming because of the complexity of the explosive samples. Herein, we proposed a new quantitative method, which combined ultraviolet (UV) spectrophotometry with partial least squares regression (PLS-1 and PLS-2), to quickly determine the content of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclo-octane (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT) simultaneously from mixed explosive samples. The calibration models were constructed by using 49 reference samples in the calibration set and optimized by full cross-validation. The predictive performance of the optimized models was validated by 21 explosive samples in an independent test set. The standard errors of prediction (SEP) were lower than 1.4 μg mL−1 for HMX, 2.2 μg mL−1 for RDX, and 0.8 μg mL−1 for TNT in both PLS models. Finally, the optimized PLS-1 and PLS-2 models were successfully applied to simultaneously determine the three explosive ingredients in eight polymer bonded explosives (PBXs). The average recovery was close to 100% for each of the three components. Thus, UV spectrophotometry combined with PLS regression can be considered as a promising strategy to conduct the determination of HMX, RDX and TNT in practice.

•A novel, simple, quick and accurate approach was developed using UV spectrophotometry coupled to multivariate calibration methods.•The method can realize the simultaneously determination of PETN, RDX and TNT in binary-component polymer bonded explosive samples.•Validation by the real explosives confirmed the potential applicability of the method in practice.Explosive determination is of great importance in national defense and security fields. Simple, quick and reliable analytical techniques have been highly demanded in the field. In this work, we proposed a novel method for simultaneous determination of pentaerythritol tetranitrate (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 2,4,6-trinaitrotolunene (TNT) in binary-component polymer bonded explosive (PBX) samples by means of a combination of ultraviolet (UV) spectrophotometry with multivariable calibration methods. An orthogonal array design (DAD) was employed to construct the calibration set, which contains 27 reference samples. The calibration models were constructed using Partial Least Square regression (PLS-1) and Multiple Linear Regression (MLR). The variables were selected by the Successive Projection Algorithm (SPA) in MLR model. The predictive ability of the optimized models was validated by a test set including 18 samples. Finally, the two optimized models were successfully applied to simultaneously determine the content of PETN, RDX and TNT in five real binary-component PBX samples. Satisfactory results were obtained for the two models, in which the recovery yields were close to 100% for all the analytes. The computed elliptical joint confidence region (EJCR) further shows that the two models have no proportional and constant errors in the predicted concentrations. In addition, the statistical analysis indicates that MLR model with reasonable variable selection (SPA-MLR) could exhibit a slight superiority toward PLS-1 in the system. In a word, UV-spectroscopy in combination with multivariable calibration techniques has high potential to be a simple, quick and accurate analysis method for explosive determination in practice.

Three conjugated D–A copolymers were found to form well-defined nanopillar arrays through facile spin-casting process when blended with fullerene derivatives. Research results indicate that the presence of large coplanar segments and intramolecular S⋯O attractive interactions in the polymers are both crucial factors for achieving self-assembled nanopatterned pillar arrays.

The use of enzymes in nonaqueous solvent has been one of the most exciting facets of enzymology in recent times; however, the mechanism of how organic solvent and essential water influence on structure and function of enzyme has been not satisfactorily explained in experiments, which limit its further application. Herein, we used molecular dynamics (MD) simulation to study γ-chymotrypsin in two types of media (viz., acetonitrile media with inclusion of 151 crystal water molecules and aqueous solution). On the basis of the MD result, the truncated active site modes containing two specific solvent molecules are furthered studied at the B3LYP/6-31+G(d,p) level of theory within the framework of PCM model. The results show that the acetontrile solvent gives rise to an extent deviation of enzyme structure from the native one, a drop in the flexibility and the total SASA of enzyme. The QM study further reveals that the structure variation of the active pocket caused by acetonitrile would lead to a weakened strength in the catalytic H-bond network, a drop in the pKa value of His57, and an increase in the proton transfer barriers from the Ser195 to the His57 residue, which may contribute to the drop in the enzymatic activity in acetontrile media. In addition, the crystal waters play an importance role in retaining the catalytic H-bond network and weakening the acetonitrile-induced variations above, which may be associated with the fact that the enzyme could retain catalytic activity in microhydration acetonitrile media.

This work mainly studies the effects of the position (there are two possible hydrated sites) and the manner (i.e., whether water acts as a proton donor or acceptor) of hydration by various numbers of water molecules on the stability of 14 solvated N-methylacetamide structures, NMA-(H2O)n (n = 1–3), as well as the binding strength between the NMA and the water cluster, using molecular dynamics (MD) and B3LYP methods. Natural bond orbital (NBO) analysis is used to explore the origin of these effects. Some novel observations are obtained from the work. Our results show that monohydration at the carbonyl site favors stability and binding strength compared to monohydration at the amino site. Similarly, the preferred hydration at the carbonyl site is observed for dihydrated NMAs when the second water is added as a proton donor to the C=O group or the first water is H-bonded to the C=O group. However, unfavorable hydration at the C=O site occurs if the second water acts as a proton acceptor. Trihydration by a ring cluster of three water molecules at either the carbonyl site or the amino one yields relatively stable complexes, but significantly disfavors binding strength. The other trihydrated NMAs show similar behavior to dihydrated NMAs. In addition, our results show that the C=O and N–H frequencies can still be utilized to examine the H-bond effects of the water cluster.

Four novel iridium(III) complexes bearing biphenyl (7a–7c) or fluorenyl (7d) modified benzothiazole cyclometallate ligands are synthesized. In comparison with the yellow parent complex, bis(2-phenylbenzothiozolato-N,C2′) iridium(III) (acetylacetonate) [(pbt)2Ir(acac)] (λPLmax = 557 nm, φPL = 0.26), 7a–7d show 20–43 nm bathochromic shifted orange or red phosphorescence in solution, with maximum photoluminescence (PL) quantum yield of 0.62, and PL lifetime of 1.8–2.0 μs. Meanwhile, the resulting complexes also exhibit intense orange or red phosphorescence of λPLmax = 588–611 nm in solid films. The complex 7c with two tert-butyl substituents possesses the highest phosphorescent efficiency both in dilute solution and thin solid films, therefore may be a prospective candidate for both doping and host emitting electrophosphorescent material. Furthermore, despite the observation of severe oxygen quenching for 7a–7d in solution, 7a and 7c even show efficient emission intensity quenching by oxygen in their solid state due to the existence of void channels in crystals; consequently, they are promising molecular oxygen sensor reagents. Electrochemical measurement and DFT calculation results suggest that all these chelates own declined LUMOs of 0.1 eV relative to that of (pbt)2Ir(acac) owing to the contribution of the phenyl substituents; whereas only 7d shows a more destabilized HOMO (∼0.1 eV) compared with the parent chelate.

Substituent effects (R = F, OH, OCF3, OCH3, CN, CHO, NH2, NO, CH3, CF3, PH2, SH, SiH3) on C-substituted methanimine were investigated using B3LYP and G3 calculations. The physical origin of substituent effects is explored by means of NBO (nature bond orbital) and AIM (atoms in molecules) as well as correlation analysis. The results reveal that the π-withdrawing/donating ability of substituents plays a dominant role in influencing the atomic charge on the CN nitrogen while the charge variation on the CN carbon atom attached by substituents can be well described by the substituent group electronegativity. AIM analysis indicates that the substituent changes the atomic charge adjacent to it through the modification of its interatomic surfaces. In terms of NBO analysis, the effect of substituents on the trans/cis inversion barriers can be attributed to the substitution induced variations on hyperconjugation of lone pair on the inverting nitrogen (nN) into the adjacent σ∗(CR) orbital in the transition state, and displays a strong dependence on the electronegativity of substituent groups. The isodesmic reaction suggests that the highly electronegative substituents along with strong π-donating character would obviously stabilize the C-substituted imines.

A polarizable continuum model (PCM), at the B3LYP/6-311++G (d,p) level of theory, is used to study solvent effects on isolated formamide and its monohydrated complex. Six varying kinds of solvent (viz.water, dimethyl sulfoxide, acetonitrile, ethanol, tetrahydrofuran, carbontetrachloride) are selected to model different polarity environments. The roles of non-specific solvation and specific H-bonding associated with the bound water in influencing geometries, vibrational frequencies, binding energies, 1H chemical shifts and n →π* transition energies are discussed for formamide. Natural bond orbital (NBO) and atoms in molecules (AIM) theories are used to analyze the nature of H-bonding and the origin of solvent effects. Significant red- and blue-shifts are observed for the frequencies of formamide upon solvation and formation of hydrogen bonds, respectively. Both the solvation and the H-bonding increase the 1H chemical shifts of amino protons and the n →π* transition energy, while the chemical shift of formyl proton is nearly insensitive to the two effects. The role of the specific H-bonding in influencing molecular properties is lessened by the solvation since the solvent lowers the binding energy of the complex, while the solvent effect is also modulated by the H-bonding through a specific intermolecular interaction. Compared with non-polar solvents, polar solvents have a more obvious effect on the properties examined. Furthermore, all the variations show a large dependency on the dielectric constant up to a value of ∼10, after which no further changes are observed.

Aggregation-induced emission (AIE) compounds with intramolecular charge transfer (ICT) character have attracted considerable interest from experimental and theoretical researchers due to their potential in optoelectronic and sensory applications. However, their deactivation mechanism in solutions has been disputed, limiting their further applications. Therefore, in this work, we combined experimental observations with density functional theory (DFT) and time-dependent DFT (TD-DFT) methods to unveil the deactivation mechanism of a new AIE-active naphthalimide derivative (FNIb) in the polar solution, which was synthesized by us lately. An in-depth investigation on the effects of solvent polarity on its geometrical and electronic structures, and absorption and emission spectra indicates that FNIb would prefer a conformational planarization mechanism to the popular twisted intramolecular charge transfer mechanism (TICT) in the deactivation process. Our findings would add more insights into previous studies to rationalize the controversy on the deactivation mechanism of the AIE ICT-featured compounds in solutions.

By simply grafting a –CN group and/or a –OCH3 group onto the meta- and/or para-site of the C-ring, a series of Ir(III) complexes bearing a similar molecular platform of bis(1,2-diphenyl-1H-benzimidazolato-N,C2′)iridium(III)(acetylacetonate), but showing fine-tuned phosphorescence covering nearly the whole window of the visible spectrum with a wide color-tuning range of 109 nm was acquired. With the help of DFT calculations, it was revealed that if the C-related arene moiety of the C^N ligand (C-ring) contributes substantially to both the HOMO and LUMO of an Ir(III) complex, the concurrent introduction of an electron-donating –OCH3 and an electron-withdrawing –CN groups on the C-ring at the meta- and para-sites relative to the Ir atom may lead to a favorable synergetic substituent effect on the color-tuning direction. This may represent a facile yet effective molecular design strategy for Ir(III) complexes with a desirous emission color. A bluish green organic light-emitting diode (OLED) based on one of the objective complexes displayed a maximum current efficiency of 62.1 cd A−1, an external quantum efficiency of 19.8%, and a brightness of 48040 cd m−2, implying that high-performance red and blue OLED phosphors as well as libraries of Ir(III) complexes bearing similar molecular platforms may be developed through this –OCH3 and –CN synergetic substitution strategy.

Four novel iridium(III) complexes bearing biphenyl (7a–7c) or fluorenyl (7d) modified benzothiazole cyclometallate ligands are synthesized. In comparison with the yellow parent complex, bis(2-phenylbenzothiozolato-N,C2′) iridium(III) (acetylacetonate) [(pbt)2Ir(acac)] (λPLmax = 557 nm, φPL = 0.26), 7a–7d show 20–43 nm bathochromic shifted orange or red phosphorescence in solution, with maximum photoluminescence (PL) quantum yield of 0.62, and PL lifetime of 1.8–2.0 μs. Meanwhile, the resulting complexes also exhibit intense orange or red phosphorescence of λPLmax = 588–611 nm in solid films. The complex 7c with two tert-butyl substituents possesses the highest phosphorescent efficiency both in dilute solution and thin solid films, therefore may be a prospective candidate for both doping and host emitting electrophosphorescent material. Furthermore, despite the observation of severe oxygen quenching for 7a–7d in solution, 7a and 7c even show efficient emission intensity quenching by oxygen in their solid state due to the existence of void channels in crystals; consequently, they are promising molecular oxygen sensor reagents. Electrochemical measurement and DFT calculation results suggest that all these chelates own declined LUMOs of 0.1 eV relative to that of (pbt)2Ir(acac) owing to the contribution of the phenyl substituents; whereas only 7d shows a more destabilized HOMO (∼0.1 eV) compared with the parent chelate.

G protein coupled receptors (GPCRs) play a crucial role in regulating signal recognition and transduction through their activation. The conformation transition in the activation pathway is of particular importance for their function. However, it has been poorly elucidated due to experimental difficulties in determining the conformations and the time limitation of conventional molecular dynamics (CMD) simulation. Thus, in this work, we employed a targeted molecular dynamic (TMD) simulation to study the activation process from an inactive structure to a fully active one for β2 adrenergic receptor (β2AR). As a reference, 110 ns CMD simulations on wild β2AR and its D130N mutant were also carried out. TMD results show that there is at least an intermediate conformation cluster in the activation process, evidenced by the principal component analysis and the structural and dynamic differences of some important motifs. It is noteworthy that the activation of the ligand binding site lags the G-protein binding site, displaying uncoupled correlation. Comparisons between the CMD and TMD results show that the D130N mutation significantly speeds up ICL2 and key ionic lock to enter into the intermediate state, which to some extent facilitates the activation involved in the NPxxY, DRY region and the separation between TM3 and TM6. However, the contribution from the D130N mutation to the activation of the ligand binding site could not be observed within the scale of 110 ns time. These observations could provide novel insights into previous studies for better understanding of the activation mechanism for β2AR.

G-protein-coupled receptors (GPCRs) are important drug targets and generally activated by ligands. However, some experiments found that GPCRs also give rise to constitutive activity through some mutations (viz., CAM), which are usually associated with different kinds of diseases. However, the mechanisms of CAMs and their roles in interactions with drug-ligands are unclear in experiments. Herein, we used microsecond molecular dynamics simulations to study the effect of one important F282L mutation on β2AR in order to address the questions above. With the aid of principle component and correlation analysis, our results revealed that the F282L mutation could increase the instability of the overall structure, increase the dramatic fluctuations of NPxxY and extracellular loops, and decrease restraint of the helices through weakening interhelical H-bonding and correlations between residues, which could partly contribute to the constitutive activity reported by the experiments. The observations from the protein structure network (PSN) analysis indicate that the mutant exhibits less information flow than the wild β2AR and weakens the role of TM5 and TM6 in the signal transmission, but it enhances the impact of TM3 on the orthosteric pathway and TM4 on the allosteric one. In addition, the results from the virtual screening reveal that the mutant prefers to select agonists rather than antagonists, similar to the active state but opposite of the inactive state, further confirming that the F282L mutation advances the activation of β2AR. Our observations provide valuable information for understanding the mechanism of the mutation-caused constitutive activity of GPCR and related drug-design.