Functional group corrections to the GFN2-xTB and PM6 semiempirical methods for noncovalent interactions in alkanes and alkenes.

Analytical corrections were developed to improve the accuracy of the PM6 and GFN2-xTB semiempirical quantum mechanical methods for the evaluation of noncovalent interaction energies in alkanes and alkenes. We followed the approach of functional group corrections, wherein the atom-atom pair corrections depend on the nature of the interacting functional groups. The training set includes 21 alkane and 13 alkene complexes taken from the Donchev et al.

Electrostatic penetration effects stand at the heart of aromatic π interactions.

The nature of the interaction in benzene-containing dimers has been analysed by means of Symmetry Adapted Perturbation Theory (SAPT). The total interaction energy and the preference for the dimers to adopt slipped structures are, apparently, consequence of the balance between repulsion and dispersion. However, our results indicate that this only holds when trends are analysed using fixed intermolecular distances.

The PM6-FGC Method: Improved Corrections for Amines and Amides.

Recently, we reported a new approach to develop pairwise analytical corrections to improve the description of noncovalent interactions, by approximate methods of electronic structures, such as semiempirical quantum mechanical (SQM) methods. In particular, and as a proof of concept, we used the PM6 Hamiltonian and we named the method PM6-FGC, where the FGC acronym, corresponding to Functional Group Corrections, emphasizes the idea that the corrections work for specific functional groups rather than for individual atom pairs. The analytical corrections were derived from fits to B3LYP-D3/def2-TZVP (reference).

Curvature and size effects hinder halogen bonds with extended π systems.

Curvature and size effects in halogen interactions with extended aromatic species have been evaluated, employing computational methods, in dimers formed by dihalogens Cl2, Br2 and I2 with both planar (coronene and circumcoronene) and curved (corannulene, sumanene and C60) aromatic systems. The main controlling factor in these interactions is dispersion, so they become stronger as the size of the halogen grows. The nature of the interaction with the halogen changes depending on the curvature and the extension of the aromatic system.

The relative position of π-π interacting rings notably changes the nature of the substituent effect.

The substituent effect in monosubstituted benzene dimers mostly follows changes on electrostatics mainly controlled by the direct interaction of the substituent and the other phenyl ring, whereas the contribution from the interacting rings is smaller. As the substituent is located further away the two contributions become of similar magnitude, so the global result is a combination of both effects. These trends are confirmed in larger systems containing a contact between phenyl rings; at closer distances the interaction of the substituent and the other ring clearly dominates over changes associated with the substituted ring, but as the substituent is located further away its contribution decreases and the contribution from the ring becomes more relevant.

The nervous system component of the mesentery of the sea cucumber Holothuria glaberrima in normal and regenerating animals.

The mesenterial tissues play important roles in the interactions between the viscera and the rest of the organism. Among these roles, they serve as the physical substrate for nerves connecting the visceral nervous components to the central nervous system. Although the mesenterial nervous system component has been described in vertebrates, particularly in mammals, a description in other deuterostomes is lacking.

On the Nature of σ-σ, σ-π, and π-π Stacking in Extended Systems.

Stacking interactions have been evaluated, employing computational methods, in dimers formed by analogous aliphatic and aromatic species of increasing size. Changes in stability as the systems become larger are mostly controlled by the balance of increasing repulsion and dispersion contributions, while electrostatics plays a secondary but relevant role. The interaction energy increases as the size of the system grows, but it does much faster in π-π dimers than in σ-π complexes and more remarkably than in σ-σ dimers.

Endohedral alkali cations promote charge transfer transitions in complexes of C with [10]cycloparaphenylenes.

[10]cycloparaphenylene ([10]CPP) effectively encapsulates ionic endofullerenes MC (M = Li, Na, K) as revealed by dispersion-corrected density functional theory methods. The interaction between [10]CPP and these fullerenes is dominated by dispersion, though it is stronger than with pristine C due to a reinforcement of electrostatic and induction contributions to the stability. The C carbon cage effectively shields the cations and distributes the charge among all carbon atoms, so the nature of the endohedral cation has no noticeable effect upon the final stability of the complexes.

Sentinel Lymph Node Biopsy in Patients With Thick Primary Cutaneous Melanoma.

Background: The clinical value of sentinel lymph node biopsy (SLNB) in patients with thick melanoma is uncertain. The purpose of this study was to investigate the correlations between survival and lymph node status in thick melanomas.

Methods: Of a total of 736 melanoma patients registered between 2000 and 2016, 50 presented with thick melanomas (≥ 4.

Characterization of Chickpea ( L.) Flour Films: Effects of pH and Plasticizer Concentration.

The use of flours as a material for biopolymer-based film preparation has gained interest due to the fact that they are a natural mixture of compatible macromolecules and due to their low cost. Chickpea flour shows a promising composition for the development of edible films. The aim of this study was to characterize and evaluate the properties of chickpea flour films as affected by pH (7 or 10) and plasticizer concentration (1% or 3% /) of film-forming solutions.

Assessment of electronic transitions involving intermolecular charge transfer in complexes formed by fullerenes and donor-acceptor nanohoops.

Complexes formed by fullerenes C60/C70 and substituted cycloparaphenylenes with the capability of acting as donor/acceptor pairs ([10]CPAq and [10]CPTcaq nanohoops) have been studied using density functional theory methods empirically corrected for dispersion. All nanohoops form stable complexes with fullerenes, with complexation energies amounting to around -32 kcal mol-1 with C60 and reaching between -36 and -39 kcal mol-1 in the case of C70. According to DFT calculations, the rings are too large to appropriately accommodate the fullerene, which moves from the centre of the ring to a side region (in most cases located on the side opposite the anthracene unit).

Influence of Multiple Conformations and Paths on Rate Constants and Product Branching Ratios. Thermal Decomposition of 1-Propanol Radicals.

The potential energy surface involved in the thermal decomposition of 1-propanol radicals was investigated in detail using automated codes (tsscds2018 and Q2DTor). From the predicted elementary reactions, a relevant reaction network was constructed to study the decomposition at temperatures in the range 1000-2000 K. Specifically, this relevant network comprises 18 conformational reaction channels (CRCs), which in general exhibit a large wealth of conformers of reactants and transition states.

Fullerene size controls the selective complexation of [11]CPP with pristine and endohedral fullerenes.

The ability of the carbon nanoring [11]cycloparaphenylene ([11]CPP) for coordinating fullerenes has been tested using a series of hosts, including the pristine fullerenes C60, C70, C76 and C78, the clusterfullerene Sc3N@C80, monometallic endofullerenes Y@C82 and Tm@C82, and dimetallic endofullerenes Y2@C82 and Lu2@C82. A systematic theoretical study employing dispersion corrected density functional methods has been carried out in order to explore the characteristics of the complexes and the strength of the interaction. Depending on the dimer, complexation energies span from around -36 kcal mol-1 with C60 to -53 kcal mol-1 with the C82 derivatives.

Dissecting the concave-convex π-π interaction in corannulene and sumanene dimers: SAPT(DFT) analysis and performance of DFT dispersion-corrected methods.

The characteristics of the concave-convex π-π interactions are evaluated in 32 buckybowl dimers formed by corannulene, sumanene, and two substituted sumanenes (with S and CO groups), using symmetry-adapted perturbation theory [SAPT(DFT)] and density functional theory (DFT). According to our results, the main stabilizing contribution is dispersion, followed by electrostatics. Regarding the ability of DFT methods to reproduce the results obtained with the most expensive and rigorous methods, TPSS-D seems to be the best option overall, although its results slightly tend to underestimate the interaction energies and to overestimate the equilibrium distances.

A theoretical study of complexes between fullerenes and concave receptors with interest in photovoltaics.

The complexation of the pristine fullerenes C60 and C70 and the endohedral fullerenes Sc3N@C80 and Sc3N@C68 has been tested using a series of hosts of different nature, including the buckybowls corannulene and sumanene, a zinc porphyrin, a chloro boron subphthalocyanine, and a corannulene pentasubstituted with nitrile groups. A systematic theoretical study has been carried out in order to explore both the strength of the interaction and the feasibility for electron transfer of the dimers. Dispersion is the main stabilizing contribution in these dimers, so both molecules orientate so as to maximize the number of close contacts among atoms.

A theoretical study of complexes formed between cations and curved aromatic systems: electrostatics does not always control cation-π interaction.

The present work studies the interaction of two extended curved π-systems (corannulene and sumanene) with various cations (sodium, potassium, ammonium, tetramethylammonium, guanidinium and imidazolium). Polyatomic cations are models of groups found in important biomolecules in which cation-π interaction plays a fundamental role. The results indicate an important size effect: with extended π systems and cations of the size of potassium and larger, dispersion is much more important than has been generally recognized for cation-π interactions.

Carbon-nanorings ([10]CPP and [6]CPPA) as fullerene (C and C) receptors: a comprehensive dispersion-corrected DFT study.

A comprehensive computational analysis of all possible complexes between the carbon-nanorings, CNRs, [10]CPP and [6]CPPA with the fullerenes C and C, was carried out. The B97-D2 functional together with the def2-TZVP basis set was used through the work, although comparisons with other different functionals (BLYP-D2, B3LYP-D3(BJ), TPSS-D3(BJ), PBE0-D3(BJ) and M06-2X) were also performed. In order to find all the possible rearrangements of the fullerenes inside the CNRs, two methods of different complexities and computational costs were employed.

A through-space description of substituent effects leads to inaccurate molecular electrostatic potentials and cationπ interactions in extended aromatic systems.

Non-local effects are crucial in order to give an accurate description of substituent effects in extended aromatic systems. As a consequence, the predictions based on the currently accepted through-space picture can lead to large errors in the strength of cationπ interactions, especially for rings furthest from the substituent.

Evolution of phospholipid contents during the production of quark cheese from buttermilk.

We report the evolution of phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylcholine (PC), phosphatidylserine (PS), and sphingomyelin (SM) contents during the production of quark cheese from buttermilk by successive ultrafiltration concentration, enrichment with cream, concurrent homogenization and pasteurization, fermentative coagulation, and separation of quark from whey by further ultrafiltration. Buttermilk is richer than milk itself in phospholipids that afford desirable functional and technological properties, and is widely used in dairy products. To investigate how phospholipid content is affected by end-product production processes such as ultrafiltration, homogenization, pasteurization or coagulation, we measured the phospholipids at several stages of each of 5 industrial-scale quark cheese production runs.

Comment on "Theoretical studies on a carbonaceous molecular bearing: association thermodynamics and dual-mode rolling dynamics" by H. Isobe, K. Nakamura, S. Hitosugi, S. Sato, H. Tokoyama, H. Yamakado, K. Ohno and H. Kono, , 2015, , 2746.

The LC-BLYP functional accompanied with proper calculations leads to unreliable results for systems governed by π···π interactions. It seems quite clear that a good representation of dispersion interactions is required, so DFT must be supplemented (through the DFT-D formalism or the many-body dispersion method) in order to afford good results.

On the interaction between the imidazolium cation and aromatic amino acids. A computational study.

Complexes formed by the imidazolium cation and the aromatic amino acids, phenylalanine, tyrosine, tryptophan, and histidine have been studied by using computational methods. Complexation energies estimated at the MP2.X level amount to -123.

Fullerene recognition with molecular tweezers made up of efficient buckybowls: a dispersion-corrected DFT study.

In 2007, Sygula and co-workers introduced a novel type of molecular tweezers with buckybowl pincers that have attracted the substantial interest of researchers due to their ideal architecture for recognizing fullerenes by concave-convex π∙∙∙π interactions (A. Sygula et al., J.

Tailoring buckybowls for fullerene recognition. A dispersion-corrected DFT study.

A series of buckybowls with different sizes and structures have been tested as potential receptors of fullerenes C60, C70 and C40. Among these bowls are corannulene (C20H10), sumanene (C21H12), pinakene (C28H14), hemifullerene (C30H12), circumtrindene (C36H12), pentaindenocorannulene (C50H20) and bowl-shaped hexabenzocoronene derivatives. An exhaustive study, taking into account different orientations of fullerenes, was performed in order to obtain the most favourable arrangement for interacting with the bowls.

Milk phospholipids: Organic milk and milk rich in conjugated linoleic acid compared with conventional milk.

The objective of this study was to compare the phospholipid content of conventional milk with that of organic milk and milk rich in conjugated linoleic acid (CLA). The membrane enclosing the fat globules of milk is composed, in part, of phospholipids, which have properties of interest for the development of so-called functional foods and technologically novel ingredients. They include phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylcholine (PC), phosphatidylserine (PS), and the sphingophospholipid sphingomyelin (SM).