Relative Stabilization Energies Research Articles

الدراسة التركيبية والطاقية لأيونات الليثيوم مع الأحماض الدهنية ميثيل استر [[FAME (9Z-18:1) + Li+ باستخدام الطريقة الكيميائية الكمومية (PM3)

Lithium (Li) ions are being used in a variety of fields ranging from energy storage to the treatment of mental illnesses including bipolar disorder and schizophrenia. Lithium caton (Li+) is able to form cationic adducts with various compounds and they can stabilize the biomacromolecules that interact with. Here, the interaction of lithium ions with fatty acid methyl ester [FAME (9Z-18:1)] has been theoretically investigated to gain insight into the structure and energetics of [FAME (9Z-18:1) + Li+]. All theoretical calculations were performed using Gaussian09 software via a graphic user interface. Geometry optimisations with harmonic vibrational analysis of conformations for chelated and extended forms of [FAME (9Z-18:1) + Li+] were carried out using semi-empirical method PM3. To obtain accurate energetic, zero-point energy (ZPE) corrections were included in all optimized energies and relative energies between conformers. The calculations indicated that the chelated form is relatively more stable than extended forms by 25 and 118 kJmol-1 when lithium is bound to the carbonyl oxygen (O-Li+) or olefin (C=C-Li+), respectively. The comparison between the relative stabilization energies of extended (O-Li+) versus extended (C=C-Li+) reveals that the lithium cation energetically prefers to bind to with carbonyl oxygen over the carbon-carbon double bond. Keywords: lithium ions, geometry optimization, sim-empirical method, Gaussian 09.

A volumetric, ultraacoustical study and computational study of molecular interactions in 4-aminoantipyrine-aqueous-β-cyclodextrin solutions

Present work reports experimental densities and corresponding apparent and standard partial molar volumes, ultrasonic velocities and isentropic, apparent and standard partial molar compressibilities of 4-Aminoantipyrine-aqueous-β-cyclodextrin (0.000 mol∙kg−1, 0.001 mol∙kg−1, 0.005 mol∙kg−1, 0.010 mol∙kg−1and 0.015 mol∙kg−1) solutions at different temperatures. Transfer properties like transfer volumes and compressions were calculated. The refractive indices of these systems were also measured. The computational properties such as solvation energy (ΔESol), relative stabilization energy (ΔERel), complexation energy (ΔEComp) and change in volume (ΔV) were computed using DFT. The results from volumetric and acoustical studies have been evaluated in terms of molecular interactions and their existence confirmed from experimental and computational studies. The values of transfer volumes and compressibilities indicate the hydrophilic-hydrophilic interactions between polar groups of 4-Aminoantipyrine and hydroxyl groups of β-cyclodextrin dominating over hydrophobic-hydrophobic interactions between the phenyl group of 4-Aminoantipyrine and hydrophobic interior of β-cyclodextrin.

Investigation on the stability of the Enol Tautomer of Favipiravir and its derivatives by DFT, QTAIM, NBO, NLO and 1H-NMR

Relative stability energies of enol and keto forms of Favipiravir drug (6-fluoro-3-hydroxy-2-pyrazine carboxamide) and its twelve derivatives were theoretically envisaged using the B3LYP/6-311 + G(3df,2p)//B3LYP/6-311 + G(d,p) level of theory. Influence of the nature of the substituted groups on the geometric structures, IMHB, vibrational frequencies, dipole moments, and global reactivity descriptors was systematically studied. The enol form was found to be more stable than the keto form, regardless of the nature of the substituted group, by an average of 12.5 and 5.4 kcal/mol in the gas phase and in the aqueous solution, respectively. The role of the IMHB strength in the stability of the enol form compared with the keto form was investigated in terms of QTAIM and NBO analysis and 1H NMR chemical shifts. The NLO properties at CAM-B3LYP with 6-311 + G(d,p) basis set of the two forms and their derivatives were also used to explain the relative stability.

Interaction at a distance: Xenon migration in Mb

The transport of ligands, such as NO or O2, through internal cavities is essential for the function of globular proteins, including hemoglobin, myoglobin (Mb), neuroglobin, truncated hemoglobins, or cytoglobin. For Mb, several internal cavities (Xe1 through Xe4) were observed experimentally and they were linked to ligand storage. The present work determines barriers for xenon diffusion and relative stabilization energies for the ligand in the initial and final pocket, linking a transition depending on the occupancy state of the remaining pockets from both biased and unbiased molecular dynamics simulations. It is found that the energetics of a particular ligand migration pathway may depend on the direction in which the transition is followed and the occupancy state of the other cavities. Furthermore, the barrier height for a particular transition can depend in a non-additive fashion on the occupancy of either cavity A or B or simultaneous population of both cavities, A and B. Multiple repeats for the Xe1 → Xe2 transition reveal that the activation barrier is a distribution of barrier heights rather than one single value, which is confirmed by a distribution of transition times for the same transition from unbiased simulations. Dynamic cross correlation maps demonstrate that correlated motions occur between adjacent residues or through space, residue Phe138 is found to be a gate for the Xe1 → Xe2 transition, and the volumes of the internal cavities vary along the diffusion pathway, indicating that there is dynamic communication between the ligand and the protein. These findings suggest that Mb is an allosteric protein.

A Competition between Relative Stability and Binding Energy in Caffeine Phenyl-Glucose Aggregates: Implications in Biological Mechanisms.

Hydrogen bonds and stacking interactions are pivotal in biological mechanisms, although their proper characterisation within a molecular complex remains a difficult task. We used quantum mechanical calculations to characterise the complex between caffeine and phenyl-β-D-glucopyranoside, in which several functional groups of the sugar derivative compete with each other to attract caffeine. Calculations at different levels of theory (M06-2X/6-311++G(d,p) and B3LYP-ED=GD3BJ/def2TZVP) agree to predict several structures similar in stability (relative energy) but with different affinity (binding energy). These computational results were experimentally verified by laser infrared spectroscopy, through which the caffeine·phenyl-β-D-glucopyranoside complex was identified in an isolated environment, produced under supersonic expansion conditions. The experimental observations correlate with the computational results. Caffeine shows intermolecular interaction preferences that combine both hydrogen bonding and stacking interactions. This dual behaviour had already been observed with phenol, and now with phenyl-β-D-glucopyranoside, it is confirmed and maximised. In fact, the size of the complex's counterparts affects the maximisation of the intermolecular bond strength because of the conformational adaptability given by the stacking interaction. Comparison with the binding of caffeine within the orthosteric site of the A2A adenosine receptor shows that the more strongly bound caffeine·phenyl-β-D-glucopyranoside conformer mimics the interactions occurring within the receptor.

Engineering of TiN (N = 1 – 15) nanoclusters by doping osmium impurity

Bimetallic transition metal nanoclusters have attracted significant attention in recent years due to their wide range of applications such as heterogeneous catalysts, electrochemistry and alloy design. However many studies were reported on pure transition metal nanoclusters and bimetallic of late transition metal nanoclusters. In this study the density functional theory (DFT) with PBEsol exchange correlation functional was employed to investigate the structural and electronic properties of TiN-1Os (N = 2-16) nanoclusters. The calculations showed that osmium impurity mostly prefers to be encapsulated by titanium nanoclusters. The binding energies gradually decrease with the cluster size N. The Os dopant was found to enhance the binding energy of titanium nanoclusters. The relative stability or second order energies showed that Ti6Os and Ti12Os clusters are the most stable. Interestingly, osmium dopant converted the nanocluster with 13 atoms to be the most stable. Furthermore, the dissociation energy or first order energies showed an excellent correlation with the relative stability trend. The HOMO-LUMO revealed the lowest energy gap at Ti12Os (N = 13) which correlates well with the predicted binding energy, relative stability and dissociation energy.

Surface-dependent properties and morphological transformations of rutile GeO2 nanoparticles

Recently, the knowledge of surface-dependent properties has attracted a lot of attention since it is crucial for materials functionalization based on the morphological control of nanoparticles (NPs). This study describes the surface-dependent properties and morphological transformation routes of rutile germanium dioxide (r-GeO2) using the density functional theory (DFT) and the Wulff construction procedure. The calculations revealed the following order of relative surface stability: (110) > (100) > (321) > (311) > (201) > (211) > (101) > (103) > (001) > (111), with the Ge-O bonds being attributed to Ge4p-O2p and Ge4s-O2p interactions. The results demonstrate that the different coordination breakages on the outermost polyhedra are related to atomic charges, band gap, relative stability, and Fermi energy. Additionally, a map of the morphological transformation routes and the band alignment were elaborated, showing that cubic, octahedral, or hexadecahedral morphologies can have photocatalytic activity for H2 production via water splitting. The methodology and results reported herein can help target the synthesis and functionalization of rutile-type materials.

The effect of doping with pt impurity on ti clusters: a density functional theory study

Transition metal nanoclusters have been greatly investigated in various areas such as catalysis, energy conversion and sensing due to their unique chemical, optical, structural, and electronic properties. Doping monometallic clusters with other metals offer the opportunity to enhance these properties. Extensive work has been done on late transition metal clusters i.e., noble and platinum metals. However, less work has been done on titanium metal clusters. The structural properties of TiN-1Pt (N = 2 – 16) clusters have been investigated using the density functional theory method with the PBEsol exchange-correlation functional. Our results showed that the binding energies for both systems decrease with cluster size N. The Ti12Pt cluster was found to be more enhanced in comparison with pure Ti revealed by the binding energy, relative stability and dissociation energy. Furthermore, binding, relative stability and dissociation energies were found to be enhanced as compared to the energies for Ti monometallic clusters.

Oterra (formerly Hansen Natural Colours) buys SECNA & Diana Food businesses

S-benzyl-β-N-(1-(4-fluorophenyl)ethylidene)dithiocarbazate (HL), Schiff base of S-benzyl dithiocarbazate was synthesized by 1:1 condensation between S-benzyl dithiocarbazate and 4-Fluoroacetophenone. The Hard-Soft Schiff base (HL) was characterized by FT-IR, H1-NMR, Raman, and UV-VIS spectroscopic techniques. Theoretical quantum chemical calculations were performed using DFT in combination with B3LYP exchange correlation functional and 6-311++ G (d, p) basis sets level. The calculated values of chemical potential (µ), HOMO-LUMO energy gap, chemical hardness (ɳ), softness (S), ionization energy (IE), electron affinity (EA), dipole moment (D), electronegativity (χ), electrophilicity (ω) and relative stabilization energy of the compound were 0.30852 eV, 0.15928 eV, -0.1492 eV, 1.5341 eV, -0.22890 eV, -0.07962 eV, 3.4689 Debye, -0.30852 eV, -0.31883 eV and -1624.7264 eV respectively. Theoretically calculated parameters like H1-NMR, FT-IR, UV-VIS, Raman, are in good agreement with experimental results. Natural bond orbital analysis (NBO) is performed for HOMO-LUMO, charge delocalization, electrostatic potential and orbital contributions.

Experimental and Quantum chemical analyses of S-benzyl-β-N-(1-(4-fluorophenyl)ethylidene)dithiocarbazate as biologically active agent

S-benzyl-β-N-(1-(4-fluorophenyl)ethylidene)dithiocarbazate (HL), Schiff base of S-benzyl dithiocarbazate was synthesized by 1:1 condensation between S-benzyl dithiocarbazate and 4-Fluoroacetophenone. It's in-vitro cytotoxicity is assayed against two habitually infection causing bacteria strains including gram-positive Staphylococcus aureus and gram-negative Escherichia coli for antibacterial activity. The results showed appreciable biological activity and the activity increased with increase in concentration. The Hard-Soft NS Schiff base (HL) was characterized by FT-IR, H1-NMR, Raman, and UV–VIS spectroscopic techniques. Theoretical quantum chemical calculations were performed using DFT in combination with B3LYP exchange correlation functional and 6–311++ G (d, p) basis sets level. The calculated values of chemical potential (µ), HOMO-LUMO energy gap, chemical hardness (ɳ), softness (S), ionization energy (IE), electron affinity (EA), dipole moment (D), electronegativity (χ), electrophilicity (ω) and relative stabilization energy of the compound were 0.30852 eV, 0.15928 eV, −0.1492 eV, 1.5341 eV, −0.22890 eV, −0.07962 eV, 3.4689 Debye, −0.30852 eV, −0.31883 eV and −1624.7264 eV respectively. VEDA-4 (Vibrational energy distribution analysis) software was employed for theoretical FT-IR spectrum analysis which yielded 103 fundamental vibrational modes along with potential energy distribution percentage (PED%) showing non-linearity of HL.

Synthesis, Spectral and Quantum-Chemical Studies on S-benzyl-β-N-(1-(4-fluorophenyl) ethylidene) dithiocarbazate

S-benzyl-β-N-(1-(4-fluorophenyl)ethylidene)dithiocarbazate (HL), Schiff base of S-benzyl dithiocarbazate was synthesized by 1:1 condensation between S-benzyl dithiocarbazate and 4-Fluoroacetophenone. The Hard-Soft Schiff base (HL) was characterized by FT-IR, H1-NMR, Raman, and UV-VIS spectroscopic techniques. Theoretical quantum chemical calculations were performed using DFT in combination with B3LYP exchange correlation functional and 6-311++ G (d, p) basis sets level. The calculated values of chemical potential (µ), HOMO-LUMO energy gap, chemical hardness (ɳ), softness (S), ionization energy (IE), electron affinity (EA), dipole moment (D), electronegativity (χ), electrophilicity (ω) and relative stabilization energy of the compound were 0.30852 eV, 0.15928 eV, -0.1492 eV, 1.5341 eV, -0.22890 eV, -0.07962 eV, 3.4689 Debye, -0.30852 eV, -0.31883 eV and -1624.7264 eV respectively. Theoretically calculated parameters like H1-NMR, FT-IR, UV-VIS, Raman, are in good agreement with experimental results. Natural bond orbital analysis (NBO) is performed for HOMO-LUMO, charge delocalization, electrostatic potential and orbital contributions.

Diels\u2013Alder reactions and electrophilic substitutions with atypical regioselectivity enable functionalization of terminal rings of anthracene

Reversing the regioselectivity of the renowned Diels–Alder reaction by overriding the usual thermodynamic and kinetic governing factors has always been a formidable challenge to synthetic organic chemists. Anthracenes are well-known to undergo [4 + 2]-cycloadditions with dienophiles at their 9,10-positions (central ring) over 1,4-positions (terminal ring) guided by the relative aromatic stabilization energy of the two possible products, and also by harboring the largest orbital coefficients of the highest occupied molecular orbital (HOMO) at the 9,10-positions. We, herein, report a 1,4-selective [4 + 2]-cycloaddition strategy of 9,10-unsubstituted anthracenes by installing electron-donating substituents on the terminal rings which is heretofore unprecedented to the best of our knowledge. The developed synthetic strategy does not require any premeditated engagement of the 9,10-positions either with any sterically bulky or electron-withdrawing substituents and allows delicate calibration of the regioselectivity by modulating the electron-donating strength of the substituents on the terminal rings. Likewise, the regioselective functionalization of the terminal anthracene ring in electrophilic substitution reactions is demonstrated. A mechanistic rationale is offered with the aid of detailed computational studies, and finally, synthetic applications are presented.

β-Cyclodextrin Inclusion Complexation With Tricyclic Antidepressants Desipramine and Imipramine: A Structural Chemistry Perspective

Single-crystal X-ray diffraction and DFT calculation have been carried out for an atomic-level understanding of β-cyclodextrin (β-CD) inclusion complexation with 2 tricyclic antidepressants (TCAs), desipramine and imipramine. X-ray analysis discloses that the A–C-rings are buried in the β-CD cavity and the side chain is mostly outside the cavity, nearby the O2–H/O3–H side. Hence, the inclusion structures of both complexes are stabilized by host–guest C5–H∙∙∙π interaction and N5′–H∙∙∙O5/O6 H-bonds of twofold-screw-symmetry-related molecules, which are similar to those of the reported complexes of nortriptyline and amitriptyline. The DFT full-geometry optimization in the gas phase reveals an alternative inclusion scenario with the TCA side chain that is embedded in the β-CD cavity and stabilized by intermolecular O6–H∙∙∙N5’ H-bond and O2–H/O3–H∙∙∙π interactions. The β-CD encapsulation of the TCA side chain is more energetically stable by 10.76 and 4.70 kcal mol−1 than that of the aromatic moiety for the respective complexes of DPM and IPM, based on the relative stabilization energies (ΔΔEstb). This suggests the existence of the bimodal β-CD–TCA inclusion complexes as spectroscopically observed in solution, thus explaining the controversy in the inclusion mode and the improvement of TCA therapeutic effect by CD encapsulation.

Interactions of sodium salicylate and β-cyclodextrin in water: A volumetric, ultraacoustic and optical study

Present article reports the thermodynamic studies on standard transfer volumes and compressibilities of non-steroidal anti-inflammatory drug, sodium salicylate in 0.0005, 0.001, 0.004, 0.009, 0.0140 mol·kg−1 aqueous-β-cyclodextrin solutions at 303.15, 308.15 and 313.15 K. The transfer properties have been calculated from the standard partial molar volumes and compressibilities determined form the linear dependence of corresponding apparent molar properties over the drug concentration. Apparent molar properties have been calculated from measured density and ultrasonic velocity data. Further, the optical property, refractive index (n) of the studied drug solutions has been measured. In addition to this, the quantum mechanical calculations were performed using the DFT. The solvation energy (ΔESol), relative stabilization energy (ΔERel), complexation energy (ΔEComp) and change in the volume (ΔV) of the different complexes have been calculated. The results have been discussed in terms of the drug-solvent and drug-β-cyclodextrin interactions. The complex formation of sodium salicylate with β-cyclodextrin with dominating lateral interactions namely ion-hydrophilic/hydrophilic-hydrophilic or hydrogen bonding interactions has been confirmed from standard partial molar properties and computational studies.

Experimental, DFT Studies and Biological Evaluation of S‐methyl‐β‐N‐(3‐(2‐nitrophenyl)allylidene)dithiocarbazate

AbstractS‐Methyl‐β‐N‐(3‐(2‐nitrophenyl)allylidene)dithiocarbazate (HL), Schiff base of S‐methyl dithiocarbazate, was synthesized by 1:1 condensation between S‐methyl dithiocarbazate and trans‐o‐Nitrocinnamaldehyde. It's in‐vitro cytotoxicity is assayed against two habitually infection causing bacteria strains including gram‐positive Staphylococcus aureus and gram‐negative Escherichia coli for antibacterial activity. The results showed appreciable biological activity and the activity increased with increase in concentration. This nitrogen‐sulfur based Schiff base (HL) was characterized by Mass, FT‐IR, 1H‐NMR, 13C‐NMR, Raman, and UV‐Vis spectroscopic techniques. Theoretical quantum chemical calculation has been performed using DFT in combination with B3LYP exchange correlation functional and 6‐311++ G (d, p) basis sets level. The computed parameters were: Chemical potential of compound (μ) −0.174 eV, HOMO‐LUMO energy gap −0.11093 eV, chemical hardness (ɳ) −0.055 eV, softness (S) 2.164 eV, ionization energy (IE) −0.23026 eV, electron affinity (EA) −0.11933 eV, the electronegativity (EN) 0.174 eV, dipole moment (D) 1.3383 Debye and relative stabilization energy −1536.982 eV. In the theoretical FT‐IR spectrum analysis 81 fundamental vibrational modes has be observed because of non‐linear structure of HL, with potential energy distribution percentage (PED%) by using VEDA‐4 (Vibrational energy distribution analysis) software. Theoretically calculated parameters like 1H‐NMR, 13C‐NMR, FT‐IR, UV‐VIS, Raman, electrostatic potential and HOMO‐LUMO energy gap were in conformity with experimental results.

Synthesis, characterization, thermal and DFT studies of S-methyl-β-N-(3-(2-nitrophenyl)allylidene)dithiocarbazate as anti-bacterial agent

S-Methyl-β-N-(3-(2-nitrophenyl)allylidene)dithiocarbazate (HL), Schiff base of S-methyl dithiocarbazate, was synthesized by 1:1 condensation between S-methyl dithiocarbazate and trans-o-nitro cinnamaldehyde. It's in-vitro cytotoxicity is assayed against two habitually infection causing bacteria strains including gram-positive Staphylococcus aureus and gram-negative Escherichia coli for antibacterial activity. The results showed appreciable biological activity and the activity increased with increase in concentration. This nitrogen-sulfur based Schiff base (HL) was characterized by Mass, FT-IR, 1H-NMR, 13C NMR, Raman, and UV–Vis spectroscopic techniques. Theoretical quantum chemical calculation has been performed using DFT in combination with B3LYP exchange correlation functional and 6–311++ G (d, p) basis sets level. The computed parameters were: Chemical potential of compound (μ) −0.174 eV, HOMO-LUMO energy gap −0.11093 eV, chemical hardness (ɳ) −0.055 eV, softness (S) 2.164 eV, ionization energy (IE) −0.23026 eV, electron affinity (EA) −0.11933eV, the electronegativity (EN) 0.174 eV, dipole moment (D) 1.3383 Debye and relative stabilization energy −1536.982 eV. In the theoretical FT-IR spectrum analysis 81 fundamental vibrational modes has be observed because of non-linear structure of HL, with potential energy distribution percentage (PED%) by using VEDA-4 package. Theoretically calculated parameters like 1H-NMR, 13C NMR, FT-IR, UV-VIS, Raman, electrostatic potential and HOMO-LUMO energy gap were in conformity with experimental results. Thermal reactivity of the ligand was studied by TGA decomposes completely to give gaseous products.

Synthesis, characterization, computational studies and biological evaluation of S-benzyl-β-N-[3-(4-hydroxy-3-methoxy-phenylallylidene)]dithiocarbazate

S-Benzyl-β-N-[3-(4-hydroxy-3-methoxy-phenylallylidene)]dithiocarbazate (HL1), Schiff base of S-benzyl dithiocarbazate, was synthesized by 1:1 condensation between S-benzyl dithiocarbazate and 4-hydroxy-3-methoxy cinnamaldehyde. The nitrogen-sulfur Schiff base (HL1) was characterized by Mass, FT-IR, H1-NMR, Raman, and UV-VIS spectroscopic techniques. Theoretical quantum chemical calculations were performed using DFT in combination with B3LYP exchange correlation functional and 6–311++ G (d, p) basis sets level. The calculated values of chemical potential (μ), HOMO-LUMO energy gap, chemical hardness, softness (S), ionization energy (IE), electron affinity (EA), dipole moment (D) and relative stabilization energy of the compound were 0.14881 eV, 0.12542 eV, 0.06271 eV, 3.37299 eV, −0.21152 eV, −0.08610 eV, 4.4090 Debye and −1753.350 eV respectively. Theoretically calculated parameters like H1-NMR, FT-IR, UV-VIS, Raman, electrostatic potential and HOMO-LUMO energy gap are in good agreement with experimental results. Also, in-vitro cytotoxicity studies were done against two habitually infection causing bacteria strains including gram-positive (S. aureus) and gram-negative (E. coli) for antibacterial activity. The results showed appreciable biological activity and the activity increased with increase in dose.

Cu(H2O) n ]2+ (n = 1–6) complexes in solution phase: a DFT hierarchical study

For the theoretical modeling of energy profiles of Cu2+ reactions with biological ligands, it is indispensable to know the structure of its solvation sphere. Not withstanding the experimental and theoretical studies on this topic, nature of Cu–water complexes is still subject of intense debate. In order to gain insight into the structural features and relative stabilities of the [Cu(H2O) n ]2+ (n = 1–6) species, several of their coordination modes considering water molecules in the first and second hydration shell of Cu2+, have been considered. Electronic structure calculations were performed with the G09 quantum chemistry suite of programs. Geometries are optimized by means of DFT functionals (allocate in different rungs of the Jacob’s ladder) and the ab initio MP2 perturbation theory applying the def-SVP valence split basis set; formation of complexes is studied in gas phase and solution by application of CPCM and SMD protocols. Stabilization energies for each stoichiometry are calculated at the MP2/aug-cc-pVTZ level of theory. [Cu(H2O)2]2+, [Cu(H2O)3]2+ and [Cu(H2O)4]2+ complexes show lineal, planar trigonal and square planar structures, respectively; gas phase and CPCM results indicate that [Cu(H2O)5]2+ is isoenergetic with [Cu(H2O)4]2+(H2O), but SMD solvent effects favor formation of intramolecular hydrogen bonds. For sixfold complexes, [Cu(H2O)4]2+(H2O)2 is consistently found to be the most stable compared with [Cu(H2O)6]2+ and [Cu(H2O)5]2+(H2O). For n = 5 and 6, hydrogen bond formation in the second hydration shell competes with coordination in axial positions; results indicate that this intramolecular hydrogen bond stabilizes the complex more than axial coordination of water. In gas phase as well as solution, BHLYP outcomes are always consistent with MP2 results, evidencing the importance of exact exchange in the functional. SMD solvent effects show that water ligands are more loosely bond to the central ion that might explain a variety of complexes coexisting in solution, contrasting with gas phase where releasing a water molecule entails a higher energetic cost. Results indicate a clear tendency to improve the geometry, the symmetry and the relative stabilization energy of the Cu–water complex, toward the MP2 value, when either advancing on the Jacob’s ladder or the percentage of exact exchange in the functional increases.

On the Possibility of Mo Substitution in Mesoporous Materials - Cluster Model Calculations

<p>Scattered Wave SCF-<em>X</em>a calculations were carried out on various Mo-containing cluster models in order to find out the possibility of molybdenum incorporation in a zeolitic framework, containing ring systems as secondary building units. Four and six membered ring clusters were found to stabilize molybdenum in their framework compared to that by linear chain models. Comparison of relative stabilization energies for corner and edge shared MoO<sub>4</sub> moiety favoured the formation of the former one. Calculated HOMO-LUMO electronic transition for tetrahedrally coordinated molybdenum in Mo-containing ring clusters showed a shift of 15 nm from that in Mo-containing linear chain clusters. These results were compared with the experimental results obtained from UV-DRS studies on Mo-MCM-41 catalyst.</p>

Investigation of structures and energy properties of molybdenum carbide clusters: Insight from theory

Density functional theory calculations for (Mo2C)n clusters with n=1–10 are presented. For this study the linear combination of Gaussian-type orbitals auxiliary density functional theory (LCGTO-ADFT) approach has been employed. For each cluster size several dozens of isomers, considering different spin multiplicities were studied to determine the lowest energy structures. Initial starting structures for subsequent geometry optimization were taken along Born–Oppenheimer molecular dynamics (BOMD) simulations at different temperatures. This represents the first systematic study on these clusters based on non-symmetry adapted first-principle calculations. Ground state structures, relative stability energy, vibrational frequencies, dissociation energies, ionization potentials, electron affinities and spin density plots are reported. The analysis of the evolution of the ground state structures with increasing the cluster size demonstrates that these systems are characterized by peculiar structure motives and that interesting structure transitions occur at certain system sizes. The comparison of the obtained results with the experimental data from the bulk reveals that packing effects in these clusters can be observed already at very small system size.