QM/MM-Based Energy Decomposition Analysis Method for Large Systems

In this work, a QM/MM-based EDA method, called GKS-EDA(QM/MM), is proposed. As an extension of GKS-EDA, this scheme divides the total interaction energy into electrostatic, exchange-repulsion, polarization, and correlation/dispersion terms. GKS-EDA(QM/MM) can be applied to describe the interactions of large-scale systems combined with various QM/MM platforms. By using the examples of a hydrated hydronium ion complex in water solution, the barnase-barstar complex, and MMP-13-pyrimidinetrione in a metalloprotein, the capability of GKS-EDA(QM/MM) for various interactions in large systems is validated.

The Influence of Hydrogen Bonds on the Roaming Reaction

Roaming bypasses the conventional transition state and is a significant reaction pathway due to the unusual energy distributions of its products; however, its reaction pathway under external environmental interactions remains unclear. Herein, we report for the first time the roaming process of nitrobenzene, which is influenced by the hydrogen bonds (H-bonds) between nitro- and phenyl radicals and water molecules in the gas phase. Notably, despite the fact that the single water structure produces a higher but narrower barrier, whereas the double water structure leads to a lower but wider barrier, the roaming reaction still occurs. The underlying mechanism responsible for these influences of H-bonds is ascribed to the dramatically changed polarization and correlation interactions between the roaming radicals. The reaction rates and thermal perturbation probabilities are also remarkably influenced due to the presence of the H-bonds, by approximately 2 orders of magnitude. It is anticipated that this work will encourage the promising feasibility of introducing environmental molecules to modulate the roaming reaction.

Energy decomposition analysis methods for intermolecular interactions with excited states

Intermolecular interactions with excited states play important roles in various photochemical and photophysical processes. In this work, an energy decomposition analysis (EDA) method of intermolecular interactions for systems in which one monomer is in a singly excited state while others are in their ground states, called GKS-EDA(TD), is proposed. Based on the computational results of time-dependent density functional theory (TD-DFT), GKS-EDA(TD) divides the total interaction energy with excited states into electrostatic, exchange-repulsion, polarization, correlation and dispersion. The nature of intermolecular interactions in test examples with their low-lying singly excited states is investigated, which shows that GKS-EDA(TD) can be used for various intermolecular interactions with different excitation modes. Furthermore, GKS-EDA(TD) is employed to explore the non-covalent interactions in a series of C₆₀⋯ nucleic acid base complexes with the decomposition of excitation energy contribution.

Values of optical coherence tomography angiography for diagnosing diabetic retinopathy and evaluating treatment outcomes

PURPOSE

To compare the consistency between fundus fluorescein angiography (FFA) and optical coherence tomography angiography (OCTA) for the diagnosis of diabetic retinopathy (DR).

MATERIALS AND METHODS

Ninety-six diabetic patients (185 eyes) treated from January 2019 to December 2019 underwent OCTA and FFA. The image characteristics of fundus lesions were recorded. Sixty-nine patients (137 eyes) who were diagnosed with DR by both examinations and needed to receive panretinal photocoagulation (PRP) were selected. The retinal nerve fiber layer (RNFL) thickness, macular superficial vascular complex (SVC) and deep vascular complex (DVC) blood flow density, 300μm area surrounding foveal avascular zone (FAZ) (FD300) blood flow density and FAZ parameters were compared.

RESULTS

The Kappa coefficient of FFA and OCTA for diagnosing DR was 0.537 (P=0.000). FFA and OCTA had substantial consistency for detecting retinal microaneurysms and macular edema (Kappa coefficient=0.643/0.616, P=0.000), perfect consistency for detecting retinal neovascularization and retinal non-perfusion area (Kappa coefficient=0.809/0.832, P=0.000), and moderate consistency for detecting structural changes in the macular ring (Kappa coefficient=0.423, P=0.000). The RNFL thickness in the peripapillary and the superior temporal, temporal inferior, inferior nasal and superior nasal regions rose 1 week after PRP but declined 1 year after treatment (P<0.05). The macular SVC, DVC and FD300 blood flow density declined 1 week after PRP but rose 1 year after treatment (P<0.05).

CONCLUSIONS

OCTA shows consistency with FFA for diagnosing DR, which remedies the deficiency of FFA. The reduction in fundus lesions after PRP can be quantified by OCTA.

A general tight-binding based energy decomposition analysis scheme for intermolecular interactions in large molecules

In this work, a general tight-binding based energy decomposition analysis (EDA) scheme for intermolecular interactions is proposed. Different from the earlier version [Xu et al., J. Chem. Phys. 154, 194106 (2021)], the current tight-binding based density functional theory (DFTB)-EDA is capable of performing interaction analysis with all the self-consistent charge (SCC) type DFTB methods, including SCC-DFTB2/3 and GFN1/2-xTB, despite their different formulas and parameterization schemes. In DFTB-EDA, the total interaction energy is divided into frozen, polarization, and dispersion terms. The performance of DFTB-EDA with SCC-DFTB2/3 and GFN1/2-xTB for various interaction systems is discussed and assessed.

λ-DFVB(U): A hybrid density functional valence bond method based on unpaired electron density

In this paper, a hybrid density functional valence bond method based on unpaired electron density, called λ-DFVB(U), is presented, which is a combination of the valence bond self-consistent field (VBSCF) method and Kohn–Sham density functional theory. In λ-DFVB(U), the double-counting error of electron correlation is mitigated by a linear decomposition of the electron–electron interaction using a parameter λ, which is a function of an index based on the number of effectively unpaired electrons. In addition, λ-DFVB(U) is based on the approximation that correlation functionals in KS-DFT only cover dynamic correlation and exchange functionals mimic some amount of static correlation. Furthermore, effective spin densities constructed from unpaired density are used to address the symmetry dilemma problem in λ-DFVB(U). The method is applied to test calculations of atomization energies, atomic excitation energies, and reaction barriers. It is shown that the accuracy of λ-DFVB(U) is comparable to that of CASPT2, while its computational cost is approximately the same as VBSCF.

Metal-Ligand Bonds in Rare Earth Metal-Biphenyl Complexes

A series of theoretical methods, including density functional theory, multiconfiguration molecular orbital theory, and ab initio valence bond theory, are devoted to understanding the metal-ligand bonds in M-BP (BP = biphenyl; M = Sc, Y, or La) complexes. Different from most transition metal-BP complexes, the most stable metal-biphenyl conformers are not half-sandwich but clamshell. Energy decomposition analysis results reveal that the M-BP bonds in the clamshell conformers possess extra-large orbital relaxation. According to the wave function analysis, 2-fold donations and 2-fold back-donations exist in the clamshell M-BP bonds. The back-donations from M to BP are quite strong, while donations from BP to M are quite weak. Our work improves our understanding of the metal-ligand bonds, which can be considered as the "reversed" Dewar-Chatt-Duncanson model.

Exploring the nature of electron-pair bonds: an energy decomposition analysis perspective

In this paper, the nature of electron-pair bonds is explored from an energy decomposition perspective. The recently developed valence bond energy decomposition analysis (VB-EDA) scheme is extended for the classification of electron-pair bonds, which divides the bond dissociation energy into frozen, reference state switch, quasi-resonance and polarization terms. VB-EDA investigations are devoted to a series of electron-pair bonds, including the covalent bonds (H-H, H₃C-CH₃, H₃C-H, and H₂N-NH₂), the ionic bonds (Na-Cl, Li-F), the charge-shift (CS) bonds (HO-OH, F-F, Cl-Cl, Br-Br, H-F, F-Cl, H₃Si-F and H₃Si-Cl), and the inverted central carbon-carbon bond in [1.1.1] propallene. It is shown that the VB-EDA approach at the VBSCF level is capable of predicting the characters of the electron-pair bonds. The perspective from VB-EDA illustrates that a relatively high value of quasi-resonance term indicates a CS bond while a large portion of polarization term suggests a classical covalent bond.

Reliable Prediction of the Protein-Ligand Binding Affinity Using a Charge Penetration Corrected AMOEBA Force Field: A Case Study of Drug Resistance Mutations in Abl Kinase

Protein mutations that directly impair drug binding are related to therapeutic resistance, and accurate prediction of their impact on drug binding would benefit drug design and clinical practice. Here, we have developed a scoring strategy that predicts the effect of the mutations on the protein-ligand binding affinity. In view of the critical importance of electrostatics in protein-ligand interactions, the charge penetration corrected AMOEBA force field (AMOEBA_CP model) was employed to improve the accuracy of the calculated electrostatic energy. We calculated the electrostatic energy using an energy decomposition analysis scheme based on the generalized Kohn-Sham (GKS-EDA). The AMOEBA_CP model was validated by a protein-fragment-ligand complex data set (Abl236) constructed from the co-crystal structures of the cancer target Abl kinase with six inhibitors. To predict ligand binding affinity changes upon protein mutation of Abl kinase, we used sampling protocol with multistep simulated annealing to search conformations of mutant proteins. The scoring strategy based on AMOEBA_CP model has achieved considerable performance in predicting resistance for 8 kinase inhibitors across 144 clinically identified point mutations. Overall, this study illustrates that the AMOEBA_CP model, which accurately treats electrostatics through penetration correction, enables the accurate prediction of the mutation-induced variation of protein-ligand binding affinity.

XEDA, a fast and multipurpose energy decomposition analysis program

A fast and multipurpose energy decomposition analysis (EDA) program, called XEDA, is introduced for quantitative analysis of intermolecular interactions. This program contains a series of variational EDA methods, including LMO-EDA, GKS-EDA and their extensions, to analyze non-covalent interactions and strong chemical bonds in various environments. XEDA is highly efficient with a similar computational scaling of single point energy calculations. Its efficiency and universality are validated by a series of test examples including van der Waals interactions, hydrogen bonds, radical-radical interactions and strong covalent bonds.

Metal Effect Meets Volcano Plots: A DFT Study on Tris(phosphino)borane-Transition Metal Complexes Catalyzed H2 Activation

Bifunctional transition metal complexes are of particular interest in metal-ligand cooperative activation of small molecules. As a novel type of bifunctional catalyst, Lewis acid transition metal (LA-TM) complexes have attracted increasing interest in hydrogen activation and storage. To advance the catalyst design, herein the metal effect of LA-TM complexes on the hydrogen activation has been systematically studied with a series of tris(phosphino)borane (TPB) complexes with V, Cr, Mn, Fe, Co, and Ni as metal centers. The metal effect not only influences the mechanism of hydrogen activation, but also notably casts a volcano plot for the activity. TPB complexes of V, Cr, Mn, Fe, and Co tend to activate H₂ through a stepwise mechanism, while TPB-Ni prefers a synergetic mechanism for H₂ activation. More importantly, the metal effect significantly influences the activity of H₂ activation and the formation of the LA-H-TM bridging hydride. The trend of changes in the LA-H-TM structures, the second-order perturbation stabilization energies, and the Laplacian bond orders, along with different metals (from V to Ni), are all interestingly constitute volcano plots for the performance of TPB-TM complexes catalyzed H₂ activation. TPB-Mn and TPB-Fe are found to be the optimal catalysts among the discussed TPB-TM complexes. The volcano plots disclosed for the metal effects should be informative and instructive for homogeneous and heterogeneous LA-TM catalysts development.

[Well differentiated grade 3 gastroenteropancreatic neuroendocrine tumors:new insights into diagnosis and therapeutic strategy]

Gastroenteropancreatic neuroendocrine tumor G3(GEP-NET G3) is a novel subtype of neuroendocrine neoplasms proposed in 2019,which has unique biological behavior characteristics. However,there are still many challenges and controversies in its diagnosis and treatment. There are obvious differences between GEP-NET G3 and neuroendocrine carcinoma (NEC) in genetic alterations and molecular profiles. The most frequently mutated genes in NET G3 are MEN1,DAXX/ATRX,while in NEC,TP53 and Rb are the most frequently mutated genes. Currently,the mainstream view is that NET G3 and NEC are two distinct diseases with different genetic backgrounds,and NET G3 will not develop into NEC. Several clinical and pathological factors should be considered to distinguish GEP-NET G3 and NEC,which including patients' medical history,histopathological morphology of neoplasms,Ki-67 index,immunohistochemical results of TP53,Rb,DAXX/ATRX and other markers. Multidisciplinary treatment,including radical resection,chemotherapy,targeted therapy,peptide receptor radionuclide therapy,immunotherapy should be applied in patients with GEP-NET G3. Overall,given its relatively indolent biological behavior,the therapeutic strategy should be more actively. Although the cure strategy of NET G3 has many similarities with NET G1/2,it is completely different from NEC.

Understanding intermolecular interactions of large systems in ground state and excited state by using density functional based tight binding methods

A novel energy decomposition analysis scheme, named DFTB-EDA, is proposed based on the density functional based tight-binding method (DFTB/TD-DFTB), which is a semi-empirical quantum mechanical method based on Kohn-Sham-DFT for large-scale calculations. In DFTB-EDA, the total interaction energy is divided into three terms: frozen density, polarization, and dispersion. Owing to the small cost of DFTB/TD-DFTB, DFTB-EDA is capable of analyzing intermolecular interactions in large molecular systems containing several thousand atoms with high computational efficiency. It can be used not only for ground states but also for excited states. Test calculations, involving the S66 and L7 databases, several large molecules, and non-covalent bonding complexes in their lowest excited states, demonstrate the efficiency, usefulness, and capabilities of DFTB-EDA. Finally, the limits of DFTB-EDA are pointed out.

Diabatization around Conical Intersections with a New Phase-Corrected Valence-Bond-Based Compression Approach

In the present work, the valence-bond-based compression approach for diabatization (VBCAD), previously presented in the literature [J. Phys. Chem. Lett. 2020, 11, 5295-5301] in the case of avoided crossings, is extended to the more general situation of conical intersections and their vicinity. A pointwise phase-correction scheme for diabatic states is proposed, based on the explicit use of the peculiarities of the nonorthogonality of ab initio valence bond (VB) theory. Rather than fitting or propagating nonadiabatic couplings, it allows us to determine the phase of diabatic states consistently and automatically at each geometry point. Moreover, it is shown that the undetermination of degenerate states around a conical intersection can be fixed naturally from a straightforward classical VB picture. These are illustrated with two prototypical symmetry-induced (Jahn-Teller) conical intersection models.

A Valence-Bond-Based Multiconfigurational Density Functional Theory: The λ-DFVB Method Revisited

A recently developed valence-bond-based multireference density functional theory, named λ-DFVB, is revisited in this paper. λ-DFVB remedies the double-counting error of electron correlation by decomposing the electron-electron interactions into the wave function term and density functional term with a variable parameter λ. The λ value is defined as a function of the free valence index in our previous scheme, denoted as λ-DFVB(K) in this paper. Here we revisit the λ-DFVB method and present a new scheme based on natural orbital occupation numbers (NOONs) for parameter λ, named λ-DFVB(IS), to simplify the process of λ-DFVB calculation. In λ-DFVB(IS), the parameter λ is defined as a function of NOONs, which are straightforwardly determined from the many-electron wave function of the molecule. Furthermore, λ-DFVB(IS) does not involve further self-consistent field calculation after performing the valence bond self-consistent field (VBSCF) calculation, and thus, the computational effort in λ-DFVB(IS) is approximately the same as the VBSCF method, greatly reduced from λ-DFVB(K). The performance of λ-DFVB(IS) was investigated on a broader range of molecular properties, including equilibrium bond lengths and dissociation energies, atomization energies, atomic excitation energies, and chemical reaction barriers. The computational results show that λ-DFVB(IS) is more robust without losing accuracy and comparable in accuracy to high-level multireference wave function methods, such as CASPT2.

Improving Cross-cultural "Mind-reading" with Electrical Brain Stimulation

A cross-cultural disadvantage exists when inferring the mental state of others, which may be detrimental for individuals acting in an increasingly globalized world. The dorsomedial prefrontal cortex (dmPFC) is a key hub of the social brain involved in ToM. We explored whether facilitation of dmPFC function by focal high-definition tDCS can improve cross-cultural mind-reading. 52 (26 F/M) Singaporeans performed the Caucasian version of the Reading the Mind in the Eyes Test (RMET) and received HD-tDCS to either the dmPFC or a control site (right temporoparietal junction, rTPJ) in sham-controlled, double-blinded, crossover studies. Contact with Caucasians was determined for the Singaporean cohort as a potential mediator of RMET performance and HD-tDCS response. 52 Caucasians completed the RMET during sham-tDCS and served as a comparison group. A cross-cultural disadvantage on the RMET was confirmed in the Singaporean cohort and this disadvantage was more pronounced in those participants who had less contact with Caucasians. Importantly, HD-tDCS to the dmPFC improved RMET performance in those with less contact. No effect was identified for rTPJ HD-tDCS or for the age/sex control task demonstrating task and site specificity of the stimulation effects. Electrical stimulation of the dmPFC selectively improves the rate of cross-cultural ToM inference from facial cues, effectively removing cross-cultural disadvantage that was found in individuals with lower cross-cultural exposure.

An unusual case of pigmented plaques on the sole

Palmoplantar lichen planus is a rare variant of lichen planus with diverse clinical presentations, making the diagnosis challenging. We present an unusual case of a young patient who presented with asymptomatic non-pruritic flat-topped pigmented plaques on his left sole and no other lesions elsewhere. Histology was consistent with lichen planus. We emphasize a high index of suspicion owing to varied clinical presentation and the necessity of a biopsy for diagnosis.

Transcranial MR Imaging-Guided Focused Ultrasound Interventions Using Deep Learning Synthesized CT

BACKGROUND AND PURPOSE

Transcranial MR imaging-guided focused ultrasound is a promising novel technique to treat multiple disorders and diseases. Planning for transcranial MR imaging-guided focused ultrasound requires both a CT scan for skull density estimation and treatment-planning simulation and an MR imaging for target identification. It is desirable to simplify the clinical workflow of transcranial MR imaging-guided focused ultrasound treatment planning. The purpose of this study was to examine the feasibility of deep learning techniques to convert MR imaging ultrashort TE images directly to synthetic CT of the skull images for use in transcranial MR imaging-guided focused ultrasound treatment planning.

MATERIALS AND METHODS

The U-Net neural network was trained and tested on data obtained from 41 subjects (mean age, 66.4 ± 11.0 years; 15 women). The derived neural network model was evaluated using a k-fold cross-validation method. Derived acoustic properties were verified by comparing the whole skull-density ratio from deep learning synthesized CT of the skull with the reference CT of the skull. In addition, acoustic and temperature simulations were performed using the deep learning CT to predict the target temperature rise during transcranial MR imaging-guided focused ultrasound.

RESULTS

The derived deep learning model generates synthetic CT of the skull images that are highly comparable with the true CT of the skull images. Their intensities in Hounsfield units have a spatial correlation coefficient of 0.80 ± 0.08, a mean absolute error of 104.57 ± 21.33 HU, and a subject-wise correlation coefficient of 0.91. Furthermore, deep learning CT of the skull is reliable in the skull-density ratio estimation (r = 0.96). A simulation study showed that both the peak target temperatures and temperature distribution from deep learning CT are comparable with those of the reference CT.

CONCLUSIONS

The deep learning method can be used to simplify workflow associated with transcranial MR imaging-guided focused ultrasound.

Why Can Cationic Halogen Bond Donors Activate the Ritter-Type Solvolysis of Benzhydryl Bromide but Cationic Hydrogen Bond Donors Can Not?

It is found by experiment that the cationic halogen bond donors (cationic iodoimidazolium compounds) can activate the Ritter-type solvolysis of benzhydryl bromide, while the cationic hydrogen bond donors (cationic imidazolium compounds) could not. To understand the activation mechanism, various noncovalent interactions between benzhydryl bromide and a series of activators in solution, including halogen bond, hydrogen bond, lone pair···π/π+, and C-H···π/π+, were explored theoretically. Our study revealed that the activation difference can be contributed by the variation of the noncovalent interactions. For halogen bond donors, the successful activation is attributed by halogen bond and lone pair···π. The halogen bonds mainly provide the stabilization energy of the ion-pair complex with the help of lone pair···π. For hydrogen-bond donors, the contribution of the hydrogen bond is unable to compensate the like-charge repulsion arising from the generation of the carbocation, leading to the unsuccessful activation. In general, lone pair···π makes a difference.

A Novel Valence-Bond-Based Automatic Diabatization Method by Compression

A novel valence-bond-based automatic diabatization method by compression, called valence-bond-based compression approach for dibatization (VBCAD), is presented in this Letter. It is a "black-box" type method that provides an automatic diabatization from a classical valence bond (VB) perspective. In VBCAD, a model space projection is performed by an eigenvalue decomposition algorithm followed by dimensional reduction based on a sequence of Householder transformations. Our diabaticity criterion is implemented in a way that maximizes the diversity of VB structure weights between different diabatic states. Owing to the rigorous Householder transformations employed in this entire procedure, the invariance of the target eigensubspace is preserved. This is illustrated on two prototypical examples.

Energy decomposition analysis based on broken symmetry unrestricted density functional theory

In this paper, the generalized Kohn-Sham energy decomposition analysis (GKS-EDA) scheme is extended to molecular interactions in open shell singlet states, which is a challenge for many popular EDA methods due to the multireference character. Based on broken symmetry (BS) unrestricted density functional theory with a spin projection approximation, the extension scheme, named GKS-EDA(BS) in this paper, divides the total interaction energy into electrostatic, exchange-repulsion, polarization, correlation, and dispersion terms. Test examples include the pancake bond in the phenalenyl dimer, the ligand interactions in the Fe(ii)-porphyrin complexes, and the radical interactions in dehydrogenated guanine-cytosine base pairs and show that GKS-EDA(BS) is a practical EDA tool for open shell singlet systems.

Common and unique effects of HD-tDCS to the social brain across cultural groups

Cultural background influences social cognition, however no study has examined brain stimulation differences attributable to cultural background. 104 young adults [52 South-East Asian Singaporeans (SEA); 52 Caucasian Australians (CA)] received anodal high-definition transcranial direct current stimulation (HD-tDCS) to the dorsomedial prefrontal cortex (dmPFC) or the right temporoparietal junction (rTPJ). Participants completed tasks with varying demands on self-other processing including visual perspective taking (VPT)and episodic memory with self and other encoding. At baseline, SEA showed greater self-other integration than CA in the level one (line-of-sight) VPT task as indexed by greater interference from the alternate perspective. Anodal HD-tDCS to the dmPFC resulted in the CA performing closer to the SEA during egocentric perspective judgements. Baseline performance on level two (embodied rotation) VPT task and the self-reference effect (SRE) in episodic memory was comparable between the two groups. In the combined sample, HD-tDCS to the rTPJ decreased the interference from the egocentric perspective during level two VPT and dmPFC HD-tDCS removed the SRE in episodic memory. Stimulation effects were comparable when baseline performance was comparable. When baseline performance differed, stimulation differences were identified. Therefore, social cognitive differences due to cultural background are an important consideration in social brain stimulation studies.

Highly Enantioselective Cross-Electrophile Aryl-Alkenylation of Unactivated Alkenes

Enantioselective cross-electrophile reactions remain a challenging subject in metal catalysis, and with respect to data, studies have mainly focused on stereoconvergent reactions of racemic alkyl electrophiles. Here, we report an enantioselective cross-electrophile aryl-alkenylation reaction of unactivated alkenes. This method provides access to a number of biologically important chiral molecules such as dihydrobenzofurans, indolines, and indanes. The incorporated alkenyl group is suitable for further reactions that can lead to an increase in molecular diversity and complexity. The reaction proceeds under mild conditions at room temperature, and an easily accessible chiral pyrox ligand is used to afford products with high enantioselectivity. The synthetic utility of this method is demonstrated by enabling the modification of complex molecules such as peptides, indometacin, and steroids.

λ-Density Functional Valence Bond: A Valence Bond-Based Multiconfigurational Density Functional Theory With a Single Variable Hybrid Parameter

A new valence bond (VB)-based multireference density functional theory (MRDFT) method, named λ-DFVB, is presented in this paper. The method follows the idea of the hybrid multireference density functional method theory proposed by Sharkas et al. (2012). λ-DFVB combines the valence bond self-consistent field (VBSCF) method with Kohn–Sham density functional theory (KS-DFT) by decomposing the electron–electron interactions with a hybrid parameter λ. Different from the Toulouse's scheme, the hybrid parameter λ in λ-DFVB is variable, defined as a function of a multireference character of a molecular system. Furthermore, the E_C correlation energy of a leading determinant is introduced to ensure size consistency at the dissociation limit. Satisfactory results of test calculations, including potential energy surfaces, bond dissociation energies, reaction barriers, and singlet–triplet energy gaps, show the potential capability of λ-DFVB for molecular systems with strong correlation.

A cyclic cinnamate dimer mechanophore for multimodal stress responsive and mechanically adaptable polymeric materials

A methanone tethered cinnamate dimer manifests both multimodal stress-responsiveness and mechanical adaptability by light.

σ-Aromaticity in a Fully Unsaturated Ring

Aromaticity is one of the most fundamental and fascinating chemical topics, attracting both experimental and theoretical chemists owing to its many manifestations. Both σ- and π-aromaticity can be classified depending on the character of the cyclic electron delocalization. In general, σ-aromaticity stabilizes fully saturated rings with σ-electron delocalization whereas the traditional π-aromaticity describes the π-conjugation in fully unsaturated rings. Here, we demonstrate a strong correlation between nucleus-independent chemical shift (NICS) values and extra cyclic resonance energies (ECREs), which are used to evaluate the σ-aromaticity in an unsaturated three-membered ring (3MR) of cyclopropene, which were computed by molecular orbital (MO) theory and valence bond (VB) theory, respectively. Further study shows that the fully unsaturated ring in methylenecyclopropene and its metallic analogy is σ-aromatic. Our findings revolutionize the fundamental knowledge of the concept of σ-aromaticity, thus opening an avenue to design σ-aromaticity in other fully unsaturated systems, which are traditionally reserved as the domain of π-aromaticity.

[Clinicopathologic and molecular features of cribriform morular variant of papillary thyroid carcinoma]

Objective: To investigate the clinicopathologic and molecular features of the rare cribriform morular variant of papillary thyroid carcinoma (CMV-PTC). Methods: The clinicopathologic data of 10 patients with CMV-PTC were retrospectively reviewed. Immunohistochemical (IHC) staining was done using LSAB method. DNA sequencing for APC were applied using Sanger method. BRAF V600E mutation was examined using ARMS method. The cytological, morphological, IHC and molecular features were analyzed. Results: All patients were female at an average age of 27 years old. The tumors were mostly located in the right lobe of thyroid. Fine needle aspiration cytology was performed in three patients; two were diagnosed as suspicious for PTC and one as PTC. Nine tumors presented as solitary nodule and two as multiple nodules in both lobes. Infiltration was demonstrated in three cases. The average size was 2.6 cm. The neoplastic cells were arranged in papillary, cribriform, solid and glandular patterns, with rare or without colloid inside the lumen. The number of morula varied, ranging from zero to many. The neoplastic cells were variably enlarged, showing round, oval or spindle shape. Nuclear irregularity was identified as irregular membrane, nuclear grooves or pseudoinclusion, but no typical ground glass feature. Peculiar nuclear clearing could be observed in the morular cells. IHC staining showed the neoplastic cells were negative for thyroglobulin and p63, but positive for TTF1, cytokeratin 19 and estrogen receptor. Diffuse staining with cytokeratin was seen in the neoplastic cells and the morula. Specific cytoplasmic and nuclear staining of β-catenin was seen in the neoplastic cells but not the morula. Ki-67 proliferation index was 1%-30%. No recurrence or metastasis was observed. One patient was demonstrated to harbor both somatic and germline mutations of the APC gene, who was found to have adenomatous polyposis and her mother died of colonic carcinoma. No BRAF V600E mutation was detected. Conclusions: CMV-PTC is rare and shows atypical cytological and clinicopathological features, and it is easily misdiagnosed.TG, TTF1, ER and β-catenin are specific IHC markers for CMV-PTC. The morula is negative for cytokeratin 19, in contrast to squamous metaplasia. Although CMV-PTC has indolent clinical behavior, a definite diagnosis is necessary to rule out the possibility of APC gene mutation and related extra-thyroidal neoplasm, such as FAP and Gardner syndrome.

What kind of neutral halogen bonds can be modulated by solvent effects?

Halogen bonds with a large portion of polarization can be modulated by solvent effects.

Infrared spectroscopy of gas phase alpha hydroxy carboxylic acid homo and hetero dimers

New gas phase infrared spectroscopy is reported for an aromatic alpha hydroxy carboxylic acid homo dimer of 9-hydroxy-9-fluorene carboxylic acid (9HFCA)₂, and the hetero dimer of 9HFCA with glycolic acid.