Electronic HOMO-LUMO Research Articles

Investigation of the adsorption of miglitol anti-diabetic drug on the surface of X12Y12 (X = B, Al; Y = N, P) nanocages: A DFT and COSMO insights

A DFT investigation has been carried out to understand the adsorption nature of the miglitol (MT) anti-diabetic drug on the surface of B12N12, B12P12, Al12N12, and Al12P12 nanocages in the gas and water phase. MT drug is physically adsorbed on the surface of B12N12 and B12P12 while chemisorption is observed for Al12N12 and Al12P12 nanocages. Al12N12 shows the highest adsorption energy of −2.08 eV in gas and −1.96 eV in water media respectively. The electronic HOMO–LUMO energy gaps were extremely reduced by about 48.21 %, 41.67 %, 4.02 %, and 9.92 % in the gas phase after the adsorption of MT drug onto the surface of the studied nanocages respectively which implies the increase in electrical conductivity of these nanocages. Dipole moment and COSMO surface analysis forecasted that Al12N12 and Al12P12 show more solubility in water media. Therefore, all the studied nanocages are favorable drug carriers and among them, Al12N12 can be used as a promising nano-vehicle for MT drug.

Structural, spectroscopic, electronic, Hirshfeld, QTAIM and biological predications of a hybrid 2,6-dichloropurine compound: A detailed density functional theoretical study

Extensive research into the optimized structure, spectroscopic and biological properties of 2,6-dichloropurine (6DCP) was conducted using IR/Raman and NMR techniques, as well as theoretically using the DFT approach with B3LYP, CAM-B3LYP, and PBEPBE function levels at 6-311++G(d, p) basis set. The computational results from DFT approaches such as geometrical, IR/Raman and NMR spectra were compared with the experimental results. All our theoretical calculations were in good agreement with observed data. The electronic HOMO-LUMO, H-bonding and strong conjugative interactions across different molecular entities are discussed to reveal the accompanying pharmaceutical intermediate. The molecular properties such as chemical reactivity descriptors, mapped ESP, dipole moment, mean polarizability, and first order hyperpolarizability of the title molecule were calculated by quantum mechanical calculations. The high value of the electronic dipole moment and polarizability estimate for the 6DCP molecule may improve its biological activity. The NBO study has enabled researchers to investigate hyper-conjugate interactions, intramolecular bonding, and strong H-bonding interactions. Strong H-bonding interaction energies of 120.47 kcal/mol have been performed at the DFT/PBEPBE level.

Anisotropic charge transport and optoelectronic properties of wide band gap organic semiconductors based on biphenyl derivatives: A computational study

The electronic structures and the charge transport properties of the biphenyl derivatives were calculated using density functional theory (DFT). The values of ionization potential (IP) of all the compounds were found in the range of 5.4–6.6 eV inferring the fact that the studied compounds held considerable air-stability properties. Moreover, lower values of hole-injection barrier as compared to those of electron-injection barrier implied that the investigated compounds were p-type semiconductors. The Hirshfeld Surface analysis depicting the distribution of surface charge in between the molecular layers of the crystals revealed that the principal interactions were mostly due to the C⋯H/H⋯C and H⋯H contacts for all the studied crystals. Bathochromic shifts were observed in absorption spectra of the compounds due to the substitution of different functional groups. The excitation energy and electronic HOMO–LUMO gap > 3 eV inferred the compounds to be wide band gap semiconductors. Further, the electronic band structure calculations for all the crystals ensued the band gap of the studied crystals in the range of 2.3–2.4 eV.

Tuning the Optoelectronic Properties of Stannoles by the Judicious Choice of the Organic Substituents.

Stannoles are organometallic rings in which the heteroatom is involved in a form of conjugation that is called σ*-π* conjugation. Only very little is known about how the substituents on the Sn atom or substituents on the stannole ring determine the optoelectronic properties of these heterocycles. In this work, this question has been studied experimentally and theoretically. Calculations of optimized equilibrium geometries, energy gaps between the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs), and of the absorption spectra of a wide range of compounds were performed. The computational data showed that the substituents on the Sn atom influence the optoelectronic properties to a lower extent than the substituents in the 2 and 5 positions of the ring. These substituents in the 2 and 5 positions of the stannole ring can also have a strong influence on the overall planarity of the structure, in which mesomeric effects can play a substantial role only if the structure is planar. Thus, only structures with a planar backbone are of interest in the context of tuning the optoelectronic properties. These were selected for the experimental studies. On the basis of this information, a series of six novel stannoles was synthesized by the formation of a zirconium intermediate and subsequent transmetalation to obtain the tin compound. The calculated electronic HOMO-LUMO energy gaps varied between 2.94 and 2.68 eV. The measured absorption maxima were located between 415 and 448 nm compared to theoretically calculated values ranging from 447 nm (2.77 eV) to 482 nm (2.57 eV). In addition to these optical measurements, cyclic voltammetry data could be obtained, which show two reversible oxidation processes for three of the six stannoles. With this study, it could be demonstrated how the judicious choice of the substituents can lead to large and predictable bathochromic shifts in the absorption spectra.

Solubility of amide functionalized single wall carbon nanotubes: A quantum mechanical study

The electronic structure and solubility of aminotriethylene glycol (ATG) functionalized single walled carbon nanotubes (fSWCNTs) were examined using density functional theory (DFT). According to DFT formalisms, the ATG-fSWCNTs increases its structural distortion and solubility both for the zigzag and armchair configurations as the concentration of ATG groups increases. The energy pattern is size dependent, as the size of the (n,0) and (n,n) tube is incrementally increased the binding energy (BE) and solvation free energy (SFE) decreases. The BE and SFE profile of the ATG-(n,0) fSWCNTs was found out to display a repeating high (for even n) and low (for odd n) pattern due to π bonding structures manifested in the corresponding electronic HOMO-LUMO gaps.

Structure and dynamics of a dl-homocysteine functionalized fullerene-C60-gold nanocomposite: a femtomolar l-histidine sensor.

A functionalized fullerene-C60-thiol mediated gold nanocomposite was realized using dl-homocysteine as a bifunctional ligand. The nanocomposite was designed by following electronic structure calculations via the DFT formalism. The computed electrostatic potential profile and the electronic HOMO-LUMO energy gap implied enhanced electron transport across the nanocomposite skeleton. Accordingly, synthesis of the nanocomposite proceeded with the hydrophilic fullerene-C60 thiol derivative via in situ reduction of gold(iii), resulting in sterically full gold clusters bound to the fullerene-C60 core. Molecular dynamics simulations with the MM+ force field provided insight into the mode of interaction and direction of electron transfer in the nanocomposite-histidine ensemble. Subsequently, an electrochemical strategy for l-histidine sensing was proposed; the nanocomposite-modified glassy carbon electrode exhibited electrocatalytic activity towards l-histidine sensing, studied via cyclic and square wave voltammetry and impedance spectroscopy. A femtomolar l-histidine sensor, the first of its kind with orders of magnitude enhanced performance in its detection limit, linear range, sensitivity, stability and specificity, and free of interference, thus emerged.

Focus on Partnership

The electronic structures and the charge transport properties of the biphenyl derivatives were calculated using density functional theory (DFT). The values of ionization potential (IP) of all the compounds were found in the range of 5.4–6.6 eV inferring the fact that the studied compounds held considerable air-stability properties. Moreover, lower values of hole-injection barrier as compared to those of electron-injection barrier implied that the investigated compounds were p-type semiconductors. The Hirshfeld Surface analysis depicting the distribution of surface charge in between the molecular layers of the crystals revealed that the principal interactions were mostly due to the C⋯H/H⋯C and H⋯H contacts for all the studied crystals. Bathochromic shifts were observed in absorption spectra of the compounds due to the substitution of different functional groups. The excitation energy and electronic HOMO–LUMO gap > 3 eV inferred the compounds to be wide band gap semiconductors. Further, the electronic band structure calculations for all the crystals ensued the band gap of the studied crystals in the range of 2.3–2.4 eV.

Molecular and Electronic Structure of the Cluster [Au8(PPh3)8](NO3)2

AbstractWe present a detailed structural discussion of [Au8(PPh3)8](NO3)2, crystallized as a CH2Cl2 solvate. Its structure is compared with closely related triphenylphosphine‐stabilized gold clusters. Characterization by optical extinction spectroscopy, luminescence spectroscopy, voltammetry and DFT calculations was performed to determine the electronic HOMO–LUMO gap. Comparison of its characteristic energies with those of structurally related clusters revealed that the evolution of the HOMO–LUMO gap does not follow a simple scaling law but depends on specific structural features.

Hückel theory and optical activity.

Optical rotations and rotatory strengths are calculated for achiral, conjugated hydrocarbons with the aim of determining to what extent the sum-over-π → π* rotatory strengths are sufficient to account for nonresonant optical activity. The separability of σ and π electrons might provide a short cut to the interpretation of chiroptical structure-property relations in some cases. It is shown that by restricting the analyses to planar, C(2v)-symmetric π-systems and their one electron HOMO-LUMO excitations, an intuitive understanding of the vexing property of optical activity is forthcoming for the following reasons: Hückel wave functions are simply calculated, and in some cases, they can even be approximated by inspection of structure. Wave functions of planar molecules can be multiplied with one another graphically or, in the mind's eye, to yield transition electric and magnetic moments. The gyration tensors have just one independent component. Transition dipole moments are orthogonal to one another. And, the most optically active directions are found at their bisectors. Throughout, emphasis is on the evaluation of long wavelength optical rotation, consistent with quantum chemical computation, using simple models that are part of the fabric of organic chemistry pedagogy.

Au67(SR)35 Nanomolecules: Characteristic Size-Specific Optical, Electrochemical, Structural Properties and First-Principles Theoretical Analysis

The preparation of gold nanomolecules with sizes other than Au(25)(SR)(18), Au(38)(SR)(24), Au(102)(SR)(44), and Au(144)(SR)(60) has been hampered by stability issues and low yields. Here we report a procedure to prepare Au(67)(SR)(35), for either R = -SCH(2)CH(2)Ph or -SC(6)H(13), allowing high-yield isolation (34%, ~10-mg quantities) of the title compound. Product high purity is assessed at each synthesis stage by rapid MALDI-TOF mass-spectrometry (MS), and high-resolution electrospray-ionization MS confirms the Au(67)(SR)(35) composition. Electronic properties were explored using optical absorption spectroscopy (UV-visible-NIR regions) and electrochemistry (0.74 V spacing in differential-pulsed-voltammetry), modes of ligand binding were studied by NMR spectroscopy ((13)C and (1)H), and structural characteristics of the metal atom core were determined by powder X-ray measurements. Models featuring a Au(17) truncated-decahedral inner core encapsulated by the 30 anchoring atoms of 15 staple-motif units have been investigated with first-principles electronic structure calculations. This resulted in identification of a structure consistent with the experiments, particularly, the opening of a large gap (~0.75 eV) in the (2-) charge-state of the nanomolecule. The electronic structure is analyzed within the framework of a superatom shell model. Structurally, the Au(67)(SR)(35) nanomolecule is the smallest to adopt the complete truncated-decahedral motif for its core with a surface structure bearing greater similarity to the larger nanoparticles. Its electronic HOMO-LUMO gap (~0.75 eV) is nearly double that of the larger Au(102) compound and it is much smaller than that of the Au(38) one. The intermediary status of the Au(67)(SR)(35) nanomolecule is also reflected in both its optical and electrochemical characteristics.

Molecular and Electronic Structure of the Peptide Subunit of Geobacter sulfurreducens Conductive Pili from First Principles

The respiration of metal oxides by the bacterium Geobacter sulfurreducens requires the assembly of a small peptide (the GS pilin) into conductive filaments termed pili. We gained insights into the contribution of the GS pilin to the pilus conductivity by developing a homology model and performing molecular dynamics simulations of the pilin peptide in vacuo and in solution. The results were consistent with a predominantly helical peptide containing the conserved α-helix region required for pilin assembly but carrying a short carboxy-terminal random-coiled segment rather than the large globular head of other bacterial pilins. The electronic structure of the pilin was also explored from first principles and revealed a biphasic charge distribution along the pilin and a low electronic HOMO-LUMO gap, even in a wet environment. The low electronic band gap was the result of strong electrostatic fields generated by the alignment of the peptide bond dipoles in the pilin's α-helix and by charges from ions in solution and amino acids in the protein. The electronic structure also revealed some level of orbital delocalization in regions of the pilin containing aromatic amino acids and in spatial regions of high resonance where the HOMO and LUMO states are, which could provide an optimal environment for the hopping of electrons under thermal fluctuations. Hence, the structural and electronic features of the pilin revealed in these studies support the notion of a pilin peptide environment optimized for electron conduction.

Altering the electronic properties of diamondoids through encapsulating smallparticles

The stability, optimized structure, and electronic gap of four diamondoid complexes, adamantane,C10H16, diamantane,C14H20, triamantane,C18H24 and theTd-symmetry isomerof pentamantane, C26H32, incorporating cage-centered small atoms and ions (X@cage, whereX = H+,Li0,+,Be0,+,2+,Na0,+,Mg0,2+, He, Ne,and F−) havebeen studied at the B3LYP hybrid level of theory. All adamantane complexes, except those encapsulatingH+ and Mg, are endohedral minima. In contrast no diamantane complexes are minima. A widevariety of atoms and ions can be encapsulated by triamantane and pentamantanemolecules. The complexes are more stable for smaller and more highly charged metallicguest species. The electronic HOMO–LUMO gaps of diamondoid complexes aresignificantly affected by the inclusion of charged particles. The stability of the structures,the amount of the charges which are transferred between small particles and diamondoidscages, and the change in the HOMO–LUMO gaps of diamondoids are nearly the same forthe corresponding possible complexes. All these features mostly depend on the charge, thesize and the type of the encapsulated particle, and not on the type of diamondoid.

Gd3N@C2n (n = 40, 42, and 44): Remarkably Low HOMO−LUMO Gap and Unusual Electrochemical Reversibility of Gd3N@C88

High-performance liquid chromatography was used to isolate two new trimetallic nitride endohedral fullerenes, Gd3N@C2n (n = 42 and 44), and they were characterized by MALDI-TOF mass spectrometry, UV-vis-NIR, and cyclic voltammetry. It was found that their electronic HOMO-LUMO gaps depend pronouncedly on the size of the cage, from a large band gap for Gd3N@C80 (2.02 V) to a small band gap for Gd3N@C88 (1.49 V). The electrochemical properties also change dramatically with the size of the cage, going from irreversible for the C80 cage to reversible for Gd3N@C88. The latter is the largest trimetallic cluster inside C88 isolated and characterized to date. Gd3N@C88 has one of the lowest electrochemical energy gaps for a nonderivatized metallofullerene.