Modulation of Solid-State Chemical Stability of Gabapentin by Pyridinecarboxylic Acid.

PURPOSE: Gabapentin (GBP) is an anticonvulsant drug with poor chemical stability that is particularly sensitive to heat and mechanical stress, which can lead to intramolecular lactamization. The purpose of this study was to enhance the chemical stability of GBP by cocrystallization with organic acids. METHOD: Two novel multicomponent crystals, GBP-2,6-pyridinedicarboxylic acid salt (GBP-2,6PDA salt) and GBP-2,5-pyridinedicarboxylic acid cocrystal (GBP-2,5PDA cocrystal) were synthesized and characterized by various solid-state analytical techniques. The degradation behavior of GBP, GBP-2,6PDA salt and GBP-2,5PDA cocrystals were evaluated under thermal and mechanical stresses. RESULT: Under thermal and mechanical stresses, GBP-2,5PDA cocrystals were found to undergo severer degradation than GBP-2,6PDA salt and neat GBP. GBP-2,6PDA salt exhibited superior chemical stability compared to the others. Furthermore, the crystal structure revealed that the order of atomic distance between the carboxyl group (C7) and amino group (N12) of GBP is as follows: GBP-2,5PDA cocrystal < GBP < GBP-2,6PDA salt, which is consistent with the chemical stability of GBP in different solid forms. Therefore, we believe that the distance between C7 and N12, the reaction active sites leading to dehydrative condensation of GBP, is a key factor determining the chemical stability of GBP in the solid state. CONCLUSIONS: These results provide a potential method to improve the chemical stability of GBP during the manufacturing process and storage.

Influence of the auxiliary acceptor and π-bridge in triarylamine dyes on dye-sensitized solar cells.

Four metal-free organic dyes (AFL7-AFL10) based on triarylamine donors and different π-bridges with or without a benzothiadiazole auxiliary acceptor have been synthesized. The dyes' photophysical and electrochemical properties, theoretical calculations, and dye-sensitized solar cell (DSSC) performances have been investigated. Electrochemical measurement data indicate that varying the π-conjugacy system can tune the HOMO and LUMO energy levels. A high molar extinction coefficient combined with a broad absorption spectrum helps to reinforce the dyes' light harvesting ability; therefore, it could help to increase the JSC of the DSSCs. Among the four dyes, AFL7 bearing the bithiophene bridge achieves the best photocurrent performance with a JSC value of 16.94 mA cm-2, corresponding to an overall conversion efficiency η of 7.92% under standard AM 1.5 G conditions (that of N719 dye was 8.53% under the same conditions). The results show that the dyes based on the triarylamine donor containing fluorenyl and biphenyl moieties are promising candidates for improving the performance of DSSCs.

The effect of Fe vacancies and Cu adhesion on the magnetic properties of Fe3GeTe2.

Fe3GeTe2 is a promising two-dimensional magnetic material that exhibits a high Curie temperature with monolayer geometry. Using the first principles calculation method, the effects of both Fe vacancies and contact with Cu electrodes on the magnetic properties of Fe3GeTe2 are studied. Calculation results determined that Fe vacancies occur preferentially on the FeII site. As a result, the magnetic moment of FeI ions decreases significantly, while the magnetic moment of FeII increases due to the presence of the FeII vacancies. The Cu(111) layers that act as the electrodes have moderately strong bonds with Fe3GeTe2 but they are found not to distort the primary structure of the Fe3GeTe2 monolayers, thus producing a stable Cu(111)/Fe3GeTe2 interface. The magnetic moments of FeI atoms at the Fe3GeTe2 layer surface decrease substantially following the adhesion of Cu(111) layers. The effect for other Fe atoms, however, is relatively weak. These results are useful for experimental studies and can promote the applications of Fe3GeTe2 in spin electronics.

Novel indeno[2,1-b]carbazole donor-based organic dyes for dye-sensitized solar cells.

Four novel metal-free organic dyes (CFB1, CFB2, CFT1 and CFT2) based on indeno[2,1-b]carbazole donors were synthesized and their absorption spectra, photovoltaic performances, and electrochemical properties were evaluated. The differences in linking mode and the number of thiophene units led to variations in absorptivity, electron injection efficiency, and charge recombination. Among the four dyes, CFT1 with a π-bridge at the indeno[2,1-b]carbazole ring and a bridge of thiophene showed the best photovoltaic performance with a JSC of 12.34 mA cm-2, VOC of 0.71 V, and FF of 0.68, corresponding to an overall conversion efficiency η of 5.97% under standard AM 1.5 G irradiation.

Coexistence of piezoelectricity and magnetism in two-dimensional vanadium dichalcogenides.

Akin to three dimensional (3D) multiferroics, two dimensional (2D) piezoelectric materials with intrinsic magnetic properties are promising applications in nanoscale spintronic devices. In this study, 2D magnetic transition metal dichalcogenides (VS2, VSe2, and Janus-VSSe) have been investigated by the first principles method for their structural, magnetic, electronic, and piezoelectric properties. H type Janus-VSSe has been shown to be more stable than the T type, and dynamically stable through phonon frequency analysis. Our calculations show that H type Janus-VSSe is not only a magnetic semiconductor but also exhibits appreciable in-plane and vertical piezoelectricity. Additionally, H type VS2 and VSe2 also show high in-plane piezoelectricity. The calculated values of in-plane piezoelectricity for these magnetic materials are higher than traditional 3D piezoelectric materials such as α-quartz. The coexistence of magnetism and piezoelectricity in H type VS2, Janus-VSSe, and VSe2 makes them promising piezoelectric materials in nanoscale spin devices.

Investigation of magnetic and electronic properties of transition metal doped Sc2CT2 (T = O, OH or F) using a first principles study.

It is well known that two-dimensional Sc2CT2 (where, T = O, OH or F) structures are excellent semiconductors. The results of the present study employing the first principles calculations indicated that the transition metals, including Ti, V, Cr or Mn, can be doped into Sc2AlC, under ScAl-rich conditions, which is the precursor of the Sc2CT2 structures. The resulting TM-doped Sc2C(OH)2 systems are n-type semiconductors, while the TM-doped Sc2CO2 systems are of the p-type. The difference can be attributed to the higher unfilled p orbitals of O than OH. All Cr- and Mn-doped Sc2CT2 structures were found to be magnetic. Those TM-doped Sc2CT2 systems show heterogeneous magnetic and electronic properties, which can be promising for two-dimensional materials in spin electronics applications.

Tuning the Magnetic Properties of Cr2TiC2Tx through Surface Terminations: A Theoretical Study.

Recently, magnetic two-dimensional Cr2TiC2Tx MXenes with promising applications in spin electronics have been experimentally confirmed. However, the underlying magnetic mechanism needs to be further investigated. Along these lines, in this work, the magnetic properties of Cr2TiC2On/4F2-n/4 and Cr2TiC2On/4 structures were simulated through first-principle calculations using the GGA+U approach. The values of 4.1 and 3.1 eV were calculated for the Hubbard U of Cr and Ti, respectively, by applying the linear response method. Interestingly, the Cr2TiC2On/4F2-n/4-based configurations with low O content (n ≤ 4) exhibit antiferromagnetic behavior, while the majority of the respective configurations with high O content (n ≥ 5) are ferromagnetic. As far as the Cr2TiC2O5/4F3/4 structure (n = 5) is concerned, the value of about 2.64 µB was estimated for the magnetic moment of the Cr atom. On top of that, the Curie temperature lies within the range of 10~47 K. The extracted theoretical results are in good agreement with experimental outcomes of the Cr2TiC2O1.3F0.8-based structure. From the simulated results, it can be also argued that the magnetic moment of Cr atoms and the Neel temperature can be directly tuned by the active content of O atoms. The conductivity of both Cr2TiC2On/4F2-n/4 and Cr2TiC2On/4 configurations can be regulated by the externally applied magnetic field, while the density of states around the Fermi level shifted significantly between ferromagnetic and antiferromagnetic arrangements. The acquired results provide important theoretical insights to tuning the magnetic properties of Cr2TiC2Tx-based structures through surface termination mechanisms, which are quite significant for their potential applications in spin electronics.

High magnetoresistance in ultra-thin two-dimensional Cr-based MXenes.

Developing effective magnetoresistance devices has become beneficial due to their extensive applications in electronics such as data storage. One challenge is to reduce the scale of devices while maintaining a high magnetoresistance. Another challenge for the applications of magnetoresistance devices involves synthesizing them with stable interfaces. Antiferromagnetic Cr-based MXenes are similar to tunneling magnetoresistance junctions, and can be synthesized in a straightforward manner. Density functional theory calculations show that the medium adhesion strength between Au electrodes and Cr-based MXene can ensure the formation of stable interfaces. Exchange coupling between Cr atoms in different atomic layers is found to decrease to 0.4 meV with increasing thickness. Magnetoresistance values are higher than 400% with 1.0 V. The results show that Cr-based MXenes are promising magnetoresistance devices with high magnetoresistance values and ultra-thin layers (about 1 nm) and exhibit tunable exchange coupling between Cr atoms through thickness control.