Interplay of π-stacking and inter-stacking interactions in two-component crystals of neutral closed-shell aromatic compounds: periodic DFT study

This paper bridges the gap between high-level ab initio computations of gas-phase models of 1 : 1 arene–arene complexes and calculations of the two-component (binary) organic crystals using atom–atom potentials. The studied crystals consist of electron-rich and electron-deficient compounds, which form infinite stacks (columns) of heterodimers. The sublimation enthalpy of crystals has been evaluated by DFT periodic calculations, while intermolecular interactions have been characterized by Bader analysis of the periodic electronic density. The consideration of aromatic compounds without a dipole moment makes it possible to reveal the contribution of quadrupole–quadrupole interactions to the π-stacking energy. These interactions are significant for heterodimers formed by arenes with more than 2 rings, with absolute values of the traceless quadrupole moment (Q_zz) larger than 10 D Å. The further aggregation of neighboring stacks is due to the C–H⋯F interactions in arene/perfluoroarene crystals. In crystals consisting of arene and an electron-deficient compound such as pyromellitic dianhydride, aggregation occurs due to the C–H⋯O interactions. The C–H⋯F and C–H⋯O inter-stacking interactions make the main contribution to the sublimation enthalpy, which exceeds 150 kJ mol⁻¹ for the two-component crystals formed by arenes with more than 2 rings.

The interplay of π-stacking and inter-stacking interactions in two-component organic crystals without conventional hydrogen bonds.     

Proline derived guanidine catalysts forge extensive H-bonded architectures: a solution and solid state study

The preparation of a range of amino acid derived guanidine organocatalysts is reported together with their application to the Michael addition of 2-hydroxy-1,4-napthoquinone to β-nitrostyrene, achieving a maximum ee of 56%. Some insight into the mechanism was sought by using X-ray crystallography and a detailed study of the intra- and intermolecular hydrogen bonding is reported.

Catalysts assemble! We present the design and synthesis of a large family of amino acid derived guanidine organic moieties as catalysts in the solution state and building blocks towards extended H-bonded architectures upon crystallisation.     

Intensified primary cancer care: a randomized study of home care nurse contacts

Newly diagnosed cancer patients (n=527) were randomised to intensified primary care or a control group. Intensified primary care comprised routines to improve general practitioners' and home care nurses' possibilities to support and monitor patients, i.e. increased information from specialist care, education and supervision in cancer care. The aims of this paper are to evaluate the effects of intensified primary care on cancer patients' home care nurse contacts, and to study if patients' use of home care services 6 months after diagnosis can be predicted. The intervention resulted in a marked increase of follow-up contacts. About 90% of intensified primary care patients reported such contacts, compared to 26% of control patients. The results indicate that standard care does not routinely include follow-up contacts, not even for the oldest (80+ years) or those with advanced disease. Only 27% and 36% of these groups of control patients reported follow-ups. Logistic regression analysis identified intensified primary care as the strongest predictor for reporting a continuing contact 6 months after diagnosis. Intensified primary care patients were 14 times more likely than controls to report a such contact. The strongest predictor of a continuing contact in the intensified primary care group was high age. Patients with advanced disease were more likely than patients with non-advanced disease to report a continuing contact, and living in a rural district was positively associated with reporting a contact. A majority of the patients (70%) assessed the time for the first contact as the 'right time' and estimated that the nurse gave expected support to a very large or large extent (67%). The results suggest that routines like those implemented through intensified primary care may be an effective strategy to increase the accessibility and continuity of care, especially for elderly people and for patients with a need for long-term contacts.     

The function of oxybuprocaine: a parachute effect that sustains the supersaturated state of anhydrous piroxicam crystals

Polymers have been recognized to have the function of sustaining the supersaturated state of drugs. This function has been widely studied because it will improve the absorption of poorly water-soluble drugs. However, clarifying the mechanism of this sustaining pharmaceutical effect (parachute effect) on the supersaturated state as a result of polymers is remains a task. We have found that oxybuprocaine, which is a small molecule, has a parachute effect on the supersaturated state (due to an anhydrate-to-hydrate transformation) of piroxicam-anhydrate in the aqueous phase. We consider that oxybuprocaine controls the environment of the solution and the network of polymers is unnecessary. Therefore, oxybuprocaine not only becomes a clue for elucidating the essential mechanism of the parachute effect of polymers but also enables us to rationally propose a new type of solubilizer.

A small molecule, oxybuprocaine, has a parachute effect on the supersaturated state of piroxicam anhydrous crystals.     

Effect of surface morphology on methane interaction with calcite: a DFT study

Natural gas, consisting primarily of methane, is found in carbonate reservoirs of which calcite is major component. However, the complexity and heterogeneity of carbonate reservoirs remain a major challenge in estimating ultimate recovery. Herein, density functional theory calculations are employed to study the effect of surface morphology on the adsorption of CH₄ on the surface of CaCO₃ (calcite). Among the 9 different surface symmetries considered, the strongest adsorption (and consequently the largest adsorption capacity) of methane is found for the 110 surface of the material. In fact, the adsorption capacity of this surface is more than an order of magnitude larger than the one for the 104 surface, which is the lowest energy surface for the calcite. The obtained results are explained by structural analysis and charge calculations. These findings can be useful for the estimation of the ultimate gas recovery taking into account heterogeneous porosity and permeability of the carbonate reservoirs.

Adsorption and surface energies of methane on different calcite morphologies.     

The role of the solvent and the size of the nanotube in the non-covalent dispersion of carbon nanotubes with short organic oligomers – a DFT study

Among different dispersants of single-walled carbon nanotubes (SWCNTs), conjugated organic oligomers have the ability to interact strongly with SWCNTs and allow for effective dispersion in several organic solvents. Recently, we have carried out two computational investigations on the intermolecular interactions between conjugated organic oligomers and SWCNTs in order to gain insight into an important process of the non-covalent dispersion of carbon nanotubes with short oligomers. These studies highlighted the fact that two additional factors, namely, the effects of the solvent and the carbon nanotube''s size on these interactions need further investigation. In this work, with the help of model compounds (which are molecular fragments of the short oligomers used in our previous investigations), we analyze the significance of these two factors. We employ three dispersion corrected density functional theory (D-DFT) approximations (B97D, wB97XD, and B3LYP-D3) to assess the effect of the DFT method, and two basis sets (6-31G(d) and 6-31++G(d,p)) to assess the importance of using a higher basis set in our computations. The main focus of this work is to assess the effect of solvation and nanotube''s size on the structure, electronic properties, and binding energies of the respective pairs of model compounds and segments of carbon nanotubes. No significant differences are found between the results of (6,5) and (8,7) SWCNTs in either the geometrical parameters of interacting oligomers or the general tendency of wrapping of their long side chains (SCs) around the nanotubes. However, we find that the binding energies per atom between nanotubes and model compounds are larger for nanotubes with the smaller diameter. The results of electronic properties also show that all model compounds interact more strongly with the (6,5) SWCNT than with the (8,7) SWCNT. Polar solvents such as chloroform show lower binding energies relative to those obtained without a solvent or with non-polar solvents such as hexane. It appears that the presence of a solvent weakens the oligomer/nanotube interactions and, presumably, strengthens the oligomer/solvent and nanotube/solvent interactions to facilitate dispersion of SWCNTs.

Among different dispersants of single-walled carbon nanotubes (SWCNTs), conjugated organic oligomers have the ability to interact strongly with SWCNTs and allow for effective dispersion in several organic solvents.     

Structural diversity in the coordination compounds of cobalt,nickel and copper with N-alkylglycinates: crystallographic and ESR study in the solid state

Reactions of N-methylglycine (HMeGly), N-ethylglycine-hydrochloride (H₂EtGlyCl) and N-propylglycine-hydrochloride (H₂PrGlyCl) with cobalt(ii), nickel(ii) and copper(ii) ions in aqueous solutions resulted in ten new coordination compounds [Co(MeGly)₂(H₂O)₂] (1), [{Co(MeGly)₂}₂(μ-OH)₂]·2H₂O (1d), [Cu(MeGly)₂(H₂O)₂] (2α), [Co(EtGly)₂(H₂O)₂] (3), [Ni(EtGly)₂(H₂O)₂] (4), [Cu(μ-EtGly)₂]_n (5p), [Co(PrGly)₂(H₂O)₂] (6), [Ni(PrGly)₂(H₂O)₂] (7), and two polymorphs of [Cu(PrGly)₂(H₂O)₂] (8α and 8β). Compounds were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, thermal analysis and X-band electron spin resonance (ESR) spectroscopy. These studies revealed a wide range of structural types including monomeric, dimeric and polymeric architectures, as well as different polymorphs. In all monomeric compounds, except 2α, and in the coordination polymer 5p hydrogen bonds interconnect the molecules into 2D layers with the alkyl chain pointing outward of the layer. In 2α and in the dimeric compound 1d hydrogen bonds link the molecules into 3D structures. 1d with cobalt(iii), and 4 and 7 with nickel(ii) are ESR silent. The ESR spectra of 1, 3 and 6 are characteristic for paramagnetic high-spin cobalt(ii). The ESR spectra of all copper(ii) coordination compounds show that the unpaired copper electron is located in the d_x²−y² orbital, being in agreement with the elongated octahedral geometry.

Interactions in copper, nickel and cobalt complexes with N-methyl-, N-ethyl- and N-propylglycinate: monomers, dimer and polymers.     

Infections after the use of alemtuzumab in solid organ transplant recipients: a comparative study

We undertook a retrospective cohort study comparing infection in solid organ transplant recipients receiving alemtuzumab (n = 726) versus basiliximab (n = 215) or antithymocyte globulin (ATG) (n = 85). Eighty-one percent of patients had kidney transplants. Overall, 33% of patients in the alemtuzumab group (240/724) developed infection compared with 40% (87/215) in the basiliximab group (odds ratio [OR], 0.72; 95% confidence interval [CI], 0.53–0.99; P = .04). The frequency of infection was similar in the alemtuzumab and ATG groups (33% versus 36%, respectively, P = .53). The frequency of fungal infections, most caused by Candida spp., was similar in the alemtuzumab and basiliximab groups (10% versus 9%); disseminated fungal infection occurred in 68% of the patients with fungal infection receiving alemtuzumab and in 30% of the patients with fungal infection receiving basiliximab (OR, 4.76; 95% CI, 1.58–14.28; P = .003). Basiliximab posed a higher risk than alemtuzumab for infection. Disseminated candidal infections were more common in patients receiving alemtuzumab.     

Photolysis of carboxymethylflavin in aqueous and organic solvent: a kinetic study

This is the first study on the photolysis of carboxymethylflavin (CMF), an intermediate in the photolysis of riboflavin (RF). CMF is photodegraded by removal of side-chain to lumichrome (LC) in acid solution and to LC and lumiflavin (LF) in alkaline solution. It also undergoes alkaline hydrolysis to 1,2-dihydro-1-methyl-2-keto-3-quinoxaline carboxylic acid (KA) and 1,2,3,4-tetrahydro-1-methyl-2,3-dioxoquinoxaline (DQ) by cleavage of isoalloxazine ring. CMF degrades to LC in organic solvents. The formation of LC in acid solution and organic solvents takes place by second-order reaction and those of LC, LF, KA and DQ in alkaline solution by first-order reactions. The values of second-order rate constants for the photolysis of CMF at pH 2.0 to 7.0 are in the range of 1.13 to 2.45 M⁻¹ s⁻¹ and those of first-order rate constants (k_obs) at pH 8.0–12.0 from 1.53 to 4.18 × 10⁻⁴ s⁻¹ and for the formation of photoproducts from 0.37 to 16.6 × 10⁻⁵ s⁻¹. The photolysis of CMF is enhanced, with pH, in the alkaline region since the excited state is sensitive to alkaline hydrolysis. The photolysis and fluorescence quantum yields of CMF in aqueous and organic solvents have been reported. CMF and photoproducts have been assayed spectrofluorimetrically. The mode of CMF photolysis is discussed.

Carboxymethylflavin (CMF) undergoes photolysis in acid solution to form lumichrome (LC) and in alkaline solution, LC and lumiflavin (LF) by side-chain cleavage and β-keto acid and a dioxoquinoxalaine (DQ) compound by isoalloxazine ring cleavage.     

Efficient tuning of zinc phthalocyanine-based dyes for dye-sensitized solar cells: a detailed DFT study

The growing energy demand speed up the designing of competent photovoltaic materials. Herein, five zinc phthalocyanine-based donor materials T1–T5 are designed by substituting various groups (isopropoxy, cyano, fluoro, methoxycarbonyl, and dicyanomethyl) around zinc phthalocyanine. B3LYP/6-31G (d,p) level density functional theory (DFT) was used to investigate the optoelectronic properties of five zinc phthalocyanine-based dyes T1–T5 for dye-sensitized solar cells. The designed molecule T1 shows maximum absorption wavelength (λ_max) in the absorption spectrum at 708.89 and 751.88 nm both in gaseous state and in THF (tetrahydrofuran) solvent. The E_g value of T1 (1.86 eV) is less than reference R, indicating a greater charge transfer rate for T1 among the molecules. The values of open-circuit voltages achieved with acceptor polymer PC₇₁BM are higher than R except for T1 and are 0.69 V, 1.95 V, 1.20 V, 1.44 V, and 1.84 V for T1, T2, T3, T4, and T5, respectively. The lower the reorganization energy, the higher the charge transfer for T1 due to its lower hole mobility (0.06297 eV) than R. Thus, the designed T1–T5 molecules are expected to exhibit superior performance in dye-sensitized solar cells.

We used a quantum chemical approach to investigate the optoelectronic properties of dyes T1–T5 for dye-sensitized solar cells using DFT and TD-DFT computation. The newly designed molecules exhibited outstanding photovoltaic and optoelectronic properties.     

Enhanced hydrogen storage performance of graphene nanoflakes doped with Cr atoms: a DFT study

The hydrogen storage performances of novel graphene nanoflakes doped with Cr atoms were systematically investigated using first-principles density functional theory. The calculated results showed that one Cr atom could be successfully doped into the graphene nanoflake with a binding energy of −4.402 eV. Different from the H₂ molecule moving away from the pristine graphene nanoflake surface, the built Cr-doped graphene nanoflake exhibited a high affinity to the H₂ molecule with a chemical adsorption energy of −0.574 eV. Moreover, the adsorptions of two to five H₂ molecules on the Cr-doped graphene nanoflake were studied as well. It was found that there were a maximum of three H₂ molecules stored on the graphene nanoflake doped with one Cr atom. Also, the further calculations showed that the numbers of the stored H₂ molecules were effectively improved to be six (or nine) when the graphene nanoflakes were doped with two (or three) Cr atoms. This research reveals that the graphene nanoflake doped with Cr atom could be a promising material to store H₂ molecules and its H₂ storage performance could be effectively enhanced through modifying the number of doped Cr atoms.

Our study reveals that the H₂ storage performance of a graphene nanoflake based material could be significantly enhanced through doping with Cr atoms.     

The electronic structures and magnetic properties of mixed-valence Fe-based metal–organic VNU-15 frameworks: a theoretical study from linear response DFT+U calculations

The crystal symmetries, electronic structures, and magnetic properties of metal–organic VNU-15 frameworks (VNU = Vietnam National University) were investigated using density functional calculations (DFT) with an on-site Coulomb repulsion approximation, U_eff, of 4.30 eV, determined via the linear response method. Two different orientations of dimethylammonium (DMA⁺) cations in VNU-15 were investigated. Antiferromagnetic configurations were predicted to be the ground states, with Fe ions in high-spin states for both phases. Furthermore, VNU-15 had intrinsic semiconductor electronic behavior with a small band gap of about 1.20 eV. The change in the orientation of DMA⁺ led to changes in the dispersion of the band structure, the band gap, and the Fe contributions to the valence band and conduction band. A fascinating feature was found involving exchange of oxidation numbers between two adjacent Fe atoms in the two phases. Our results revealed that VNU-15 has strong oxidation activity and predicted the important role of an anisotropic effect on the hole and electron effective masses. The findings presented that the electronic and magnetic properties could be controlled via hydrogen bonds and proved VNU-15 to be a prospective material for photocatalytic applications.

The effects of DMA⁺ cation orientation on the electronic structures and magnetic properties of the metal–organic framework VNU-15 are investigated, and VNU-15 is proved to be a prospective material for photocatalytic applications.     

Mobile devices and weak ties: a study of vision impairments and workplace access in Bangalore

Purpose: To explore ways in which social and economic interactions are changed by access to mobile telephony. Method: This is a mixed-methods study of mobile phone use among 52 urban professionals with vision impairments in Bangalore, India. Results: Interviews and survey results indicated that mobile devices, specifically those with adaptive technology software, play a vital role as multi-purpose devices that enable people with disabilities to navigate economically and socially in an environment where accessibility remains a significant challenge. Conclusions: We found that mobile devices play a central role in enabling and sustaining weak ties, but also that these weak ties have important gender-specific implications. We found that women have less access to weak ties than men, which impacts women’s access to assistive technology (AT). This has potential implications for women’s sense of safety and independence, both of which are strongly related to AT access.

• Implications for Rehabilitation

• Adaptive technologies increase individuals’ ability to keep in contact with casual connections or weak ties through phone calls or social media.

• Men tend to have stronger access to weak ties than women in India due to cultural impediments to independent access to public spaces.

• Weak ties are an important source of assistive technology (AT) due to the high rate of resale of used AT, typically through informal networks

     

Amplitude low-frequency oscillation abnormalities in the heroin users: a resting state fMRI study

Functional neuroimaging studies have revealed abnormal functional organization of the heroin users' brain, including reward circuit, cognitive control circuit, memory circuit, motivation and salience evaluation circuits and so on. In the current study, we aimed to explore the functional changes in the regional brain of heroin users using the amplitude of low-frequency oscillations in the Blood Oxygenation Level Dependent (BOLD) signals. With fMRI data acquired during resting state from 24 chronic heroin users (all subjects were being treated with methadone) and 24 non-addicted controls, we investigated addiction related altered in the amplitude low-frequency fluctuate (ALFF) between the two groups. Compared with controls, we found that heroin addicts had decreased ALFF in the bilateral dorsal anterior cingulate cortex (dACC), bilateral medial orbit frontal cortex (mOFC), left dorsal lateral prefrontal cortex (dlPFC), left middle temporal gyrus, left inferior temporal gyrus, posterior cingulate cortex and left cuneus as well as increased ALFF in the bilateral angular gyrus, bilateral precuneus, bilateral supramarginal gyrus, left post cingulate cortex and left middle frontal gyrus. Moreover, we also found that the increased ALFF in the bilateral parietal lobe had a significantly positive correlation with the methadone does, thus we inferred that the reduced ALFF may due to heroin consumption, nevertheless, the increased ALFF in the bilateral parietal lobe may have resulted from the methadone treatment. This resting-state fMRI study suggests that the changed spontaneous neuronal activity of these regions may be implicated in the underlying pathophysiology of heroin addicts.     

2-Bromoanthraquinone as a highly efficient photocatalyst for the oxidation of sec-aromatic alcohols: experimental and DFT study

Anthraquinones are recognized as high efficiency photocatalysts which can perform various redox reactions in aqueous or organic phases. We have experimentally proven that 2-BrAQ can undergo hydrogen transfer with an alpha-aromatic alcohol under light conditions, thereby efficiently oxidizing the aromatic alcohol to the corresponding product. The yield of 1-phenethanol to acetophenone can reach more than 96%. In subsequent catalyst screening experiments, it was found that the electronegativity of the substituent at the 2 position of the anthraquinone ring and the acidity of the solvent affect the photocatalytic activity of anthraquinones. After using various aromatic alcohol substrates, 2-BrAQ showed good conversion and selectivity for most aromatic alcohols, but showed C–C bond cleavage and low selectivity with non-α-position aromatic alcohols. In order to explore the mechanism of the redox reaction of 2-BrAQ in acetonitrile solution, the corresponding free radical reaction pathway was proposed and verified by density functional theory (DFT). Focusing on calculations for 2-BrAQ during the reaction and the first-step hydrogen transfer reaction between the 2-BrAQ triplet molecule and the 1-phenylethanol molecule, we recognized the changes that occurred during the reaction and thus have a deeper understanding of the redox reaction of anthraquinone compounds in organic systems.

Anthraquinones are recognized as high efficiency photocatalysts which can perform various redox reactions in aqueous or organic phases.     

Temperature-dependence on the optical properties of chitosan carbon dots in the solid state

We report the synthesis of chitosan-derived aminated carbon dots with dual fluorescence bands and their influence on the morphology, absorption and emission spectral profiles as well as on the band gap energy in relation to thermal treatment after synthesis. To unravel these changes, we performed spectroscopic measurements in the solid state on two stages at temperatures ranging from 303 to 453 K. For the first heating stage, the emission spectrum showed a 20 nm red shift and a new absorption band at 350 nm, possibly related to new bonds and/or nitrogenous molecular fractions. For the second heating stage in the same temperature range, no displacements in the emission spectrum were observed and both the energy gap and bandwidths for the two emission bands are practically constant, indicating a change nitrogen moiety exposed on the surface. Furthermore, through atomic force microscopy it was noted that the morphology and size of the CDs were not significantly affected by the increase in temperature. It is noteworthy that the values of the Huang–Rhys factor, respectively, 2.584 × 10⁻¹⁰ and 2.315 × 10⁻⁹ for band I and II emission after the second heating indicate a mechanism of weak electron–phonon interactions. This work may open a novel perspective for the development of new surface modulation strategies for carbon dots subjected to thermal treatment in the solid state.

Effect of thermal treatment on chitosan CDs in the solid state causes a redshift of PL emission and changes in surface states.     

Novel A-π-D-π-A type non-fullerene acceptors of dithienyl diketopyrropopyrrole derivatives to enhance organic photovoltaic applications: a DFT study

To boost the photovoltaic attributes of organic photovoltaic cells, seven dithienyl diketopyrropopyrrole (TDPP) donor-based A-π-D-π-A (acceptor-bridge-donor-bridge-acceptor) type molecules (TM1–TM7) were formulated by modifying the electron accepting ends of the reference molecule (TMR). Optical and quantum chemical parameters of seven synthesized molecules were investigated using density functional theory with the MPW1PW91/6-31G(d,p) functional. Several parameters that can be used to measure and improve the efficiency of solar cells have been analyzed and summed up. These parameters include binding energy of exciton, excitation energy of electron, reorganization energies, dipole moment, molecular electrostatic potential, charge mobility, wavelength of maximum absorption, open circuit voltage, short circuit current, fill factor, density of states, transition density matrices, as well as iso-surface and non-covalent interactions. Thus, all of our proposed structures are perceived to be superior to the reference in terms of the maximum possible solar energy yield in solar cells with bulk heterojunctions, as determined by analyses of our designed molecules for the aforementioned parameters.

The investigated non-fullerene acceptor molecules TM1, TM2, TM3, TM4, TM5, TM6, and TM7 that are fashioned by making alterations at the terminal position of reference molecule TMR demonstrate significant absorption in the visible region.     

Janus transition metal dichalcogenides in combination with MoS2 for high-efficiency photovoltaic applications: a DFT study

Exotic features of two-dimensional materials have been demonstrated, making them particularly appealing for both photocatalytic and photovoltaic applications. van der Waals corrected density functional theory calculations were performed on AAII-Se MoSSe, AAII-Te MoSTe, and AAII-Se WSSe heterostructures in this study. Our findings reveal that the heterostructures have high stability due to the tiny lattice mismatch and binding energy, which is extremely favorable for epitaxial growth of these heterostructures. According to the electronic band gap calculation, AAII-Se MoSSe and AAII-Se WSSe are semiconducting materials, while AAII-Te MoSTe has metallic properties. Interestingly, all three heterostructures have type II band gap alignment, which is advantageous for photovoltaic and photocatalytic applications. Furthermore, it was discovered that AAII-Se MoSSe and AAII-Se WSSe heterostructures exhibit high power conversion efficiency of up to 12.15% and 9.37%, respectively. Based on these intriguing features, the two heterostructures are excellent prospects for photovoltaic applications. The heterostructures have no appropriate band edge sites for overall water splitting at pH = 0, but they are good for the oxygen evolution process. It is feasible to alter the position of the band edges using strain resulting in improved overall water splitting by the heterostructures.

MoS₂/Janus TMDC heterostructure stacking patterns with different stacking orientations.