Degree Of Oligomerization Research Articles

A role for leucoanthocyanidin reductase in the extension of proanthocyanidins

Proanthocyanidins (PAs) are the second most abundant plant polyphenolic compounds after lignin. PAs affect taste, mouth feel and astringency of many fruits, wines and beverages1,2, have been associated with reduced risks of cardiovascular disease, cancer and Alzheimer's disease3-5, can improve nutrition and prevent bloat in ruminant animals6 and enhance soil nitrogen retention7. PAs are oligomers and polymers of flavan-3-ols, primarily (-)-epicatechin and (+)-catechin, but the mechanism by which the monomers polymerize and become insoluble is currently unknown. Leucoanthocyanidin reductase (LAR) has been shown to convert leucocyanidin to (+)-catechin8,9. Here, we report that loss of function of LAR in the model legume Medicago truncatula leads unexpectedly to loss of soluble epicatechin-derived PAs, increased levels of insoluble PAs, and accumulation of 4β-(S-cysteinyl)-epicatechin, which provides the 4→8 linked extension units during non-enzymatic PA polymerization. LAR converts 4β-(S-cysteinyl)-epicatechin back to epicatechin, the starter unit in PAs, thereby regulating the relative proportions of starter and extension units and consequently the degree of PA oligomerization.

Equilibria of oligomeric proteins under high pressure – A theoretical description

High pressure methods have become a useful tool for studying protein structure and stability. Using them, various physico-chemical processes including protein unfolding, aggregation, oligomer dissociation or enzyme-activity decrease were studied on many different proteins. Oligomeric protein dissociation is a process that can perfectly utilize the potential of high-pressure techniques, as the high pressure shifts the equilibria to higher concentrations making them better observable by spectroscopic methods. This can be especially useful when the oligomeric form is highly stable at atmospheric pressure. These applications may be, however, hindered by less intensive experimental response as well as interference of the oligomerization equilibria with unfolding or aggregation of the subunits, but also by more complex theoretical description. In this study we develop mathematical models describing different kinds of oligomerization equilibria, both closed (equilibrium of monomer and the highest possible oligomer without any intermediates) and consecutive. Closed homooligomer equilibria are discussed for any oligomerization degree, while the more complex heterooligomer equilibria and the consecutive equilibria in both homo- and heterooligomers are taken into account only for dimers and trimers. In all the cases, fractions of all the relevant forms are evaluated as functions of pressure and concentration. Significant points (inflection points and extremes) of the resulting transition curves, that can be determined experimentally, are evaluated as functions of pressure and/or concentration. These functions can be further used in order to evaluate the thermodynamic parameters of the system, i.e. atmospheric-pressure equilibrium constants and volume changes of the individual steps of the oligomer-dissociation processes.

Gas-Phase Analysis of the Complex of Fibroblast GrowthFactor 1 with Heparan Sulfate: A Traveling Wave Ion Mobility Spectrometry (TWIMS) and Molecular Modeling Study.

Fibroblast growth factors (FGFs) regulate several cellular developmental processes by interacting with cell surface heparan proteoglycans and transmembrane cell surface receptors (FGFR). The interaction of FGF with heparan sulfate (HS) is known to induce protein oligomerization, increase the affinity of FGF towards its receptor FGFR, promoting the formation of the HS-FGF-FGFR signaling complex. Although the role of HS in the signaling pathways is well recognized, the details of FGF oligomerization and formation of the ternary signaling complex are still not clear, with several conflicting models proposed in literature. Here, we examine the effect of size and sulfation pattern of HS upon FGF1 oligomerization, binding stoichiometry and conformational stability, through a combination of ion mobility (IM) and theoretical modeling approaches. Ion mobility-mass spectrometry (IMMS) of FGF1 in the presence of several HS fragments ranging from tetrasaccharide (dp4) to dodecasaccharide (dp12) in length was performed. A comparison of the binding stoichiometry of variably sulfated dp4 HS to FGF1 confirmed the significance of the previously known high-affinity binding motif in FGF1 dimerization, and demonstrated that certain tetrasaccharide-length fragments are also capable of inducing dimerization of FGF1. The degree of oligomerization was found to increase in the presence of dp12 HS, and a general lack of specificity for longer HS was observed. Additionally, collision cross-sections (CCSs) of several FGF1-HS complexes were calculated, and were found to be in close agreement with experimental results. Based on the (CCSs) a number of plausible binding modes of 2:1 and 3:1 FGF1-HS are proposed. Graphical Abstract ᅟ.

Empirical power laws for the radii of gyration of protein oligomers.

The radius of gyration is a fundamental structural parameter that is particularly useful for describing polymers. It has been known since Flory's seminal work in the mid-20th century that polymers show a power-law dependence, where the radius of gyration is proportional to the number of residues raised to a power. The power-law exponent has been measured experimentally for denatured proteins and derived empirically for folded monomeric proteins using crystal structures. Here, the biological assemblies in the Protein Data Bank are surveyed to derive the power-law parameters for protein oligomers having degrees of oligomerization of 2-6 and 8. The power-law exponents for oligomers span a narrow range of 0.38-0.41, which is close to the value of 0.40 obtained for monomers. This result shows that protein oligomers exhibit essentially the same power-law behavior as monomers. A simple power-law formula is provided for estimating the oligomeric state from an experimental measurement of the radius of gyration. Several proteins in the Protein Data Bank are found to deviate substantially from power-law behavior by having an atypically large radius of gyration. Some of the outliers have highly elongated structures, such as coiled coils. For coiled coils, the radius of gyration does not follow a power law and instead scales linearly with the number of residues in the oligomer. Other outliers are proteins whose oligomeric state or quaternary structure is incorrectly annotated in the Protein Data Bank. The power laws could be used to identify such errors and help prevent them in future depositions.

Self-assembly and rheological behaviors of dynamic pseudo-oligomeric surfactant

Oligomeric surfactants possess superior physicochemical properties making them a promising future in applications, but cumbersome covalent synthesis and purification seriously impede their development. Recently, dynamic surfactants fabricated via non-covalent interaction have attracted considerable attention. Here, we developed a dynamic oligomeric surfactant by simple neutralization reaction in situ without extra inorganic salts, and the degree of oligomerization can be flexibly changed in 1 ~ 3 by controlling the molar ratio. Through surface activity, dynamic light scattering, rheology, and freeze-fracture transmission electron microscopy, it was found that the pseudo-gemini or trimeric surfactants are readily to form viscoelastic wormlike micelles and show remarkable thickening ability, as similar to that of conventional covalent oligomeric counterparts. However, due to the nature of non-covalent bond, the viscoelastic fluid based on pseudo-oligomeric surfactant is highly thermosensitive compared with common oligomeric surfactant systems. Additionally, a scaling law of correlating C * with the degree of oligomerization was revealed for the first time in viscoelastic oligomeric surfactant system, which is convenient for forecasting the overlapping concentration and controlling the viscoelasticity of solution.

Enzyme-Regulated Supramolecular Assemblies of Cholesterol Conjugates against Drug-Resistant Ovarian Cancer Cells.

We report that phosphotyrosine–cholesterol conjugates effectively and selectively kill cancer cells, including platinum-resistant ovarian cancer cells. The conjugate increases the degree of noncovalent oligomerization upon enzymatic dephosphorylation in aqueous buffer. This enzymatic conversion also results in the assembly of the cholesterol conjugates inside and outside cells and leads to cell death. Preliminary mechanistic studies suggest that the formed assemblies of the conjugates not only interact with actin filaments and microtubules but also affect lipid rafts. As the first report of multifaceted supramolecular assemblies of cholesterol conjugates against cancer cells, this work illustrates the integration of enzyme catalysis and self-assembly of essential biological small molecules on and inside cancer cells as a promising strategy for developing multifunctional therapeutics to treat drug-resistant cancers.

A study of the structure-activity relationship of oligomeric ellagitannins on ruminal fermentation in vitro.

The aim of this study was to investigate how the degree of oligomerization of ellagitannins (ET) influences their ability to alter ruminal fermentation. Dimeric to heptameric ET were isolated from rosebay willowherb (Epilobium angustifolium) flowers and purified. Ellagitannins were tested in vitro on a mixture of grass silage and buffered rumen fluid. Total gas production was measured in real time using an automated pressure evaluation system. Methane production was monitored at regular interval by gas chromatography for 72h. The effect of ET was evaluated on 2 sources of rumen fluid using a randomized block design. Ammonia nitrogen, volatile fatty acid concentration, and pH were measured at the end of the experiment. Results show that oligomeric ET decreased gas production and total volatile fatty acid concentration proportionally to their degree of oligomerization. Methane production was also decreased by all the tested compounds and dimer was less effective than the larger ET, which showed similar levels of activity. Additionally, willowherb's oligomeric ET decreased ammonia-nitrogen and branched-chain volatile fatty acid concentrations, thus indicating reduced protein degradation by ruminal bacteria. This effect showed a quadratic relationship with the degree of oligomerization and was maximal with the tetramer. In conclusion, this study shows that the degree of oligomerization of ET has more than a simple linear effect on fermentation parameters in vitro. Large oligomers, in fact, have more detrimental effects on volatile fatty acid and gas production than small ones, while being similarly effective at inhibiting methane production.

Effect of Oligomerization of Counterions on Water Activity in Aqueous Cationic Surfactant Systems

A sorption calorimetry study of cationic cetyltrimethyl ammonium surfactants with four different counterions was performed. The counterions were acetate, succinate, citrate, and butyl tetracarboxylate with formal charges ranging from 1 to 4, respectively. The counterions with 2-4 charges can be considered as oligomers. In all the cases, hydration experiments started with dry solid phases that upon water uptake went through solid-state phase transitions and hexagonal to micellar cubic phase transitions. It was found that in liquid-crystalline phases the activity of water increased with the degree of oligomerization or, equivalently, the formal charge of the counterions. The results are discussed in terms of the forces acting between the colloidal aggregates. It is argued that under the conditions investigated, the so-called strong-coupling theory can be used to describe the electrostatic forces between the charged colloidal objects. Therefore, we suggest that the observed dependence of water activity on the degree of polymerization is due to the entropy of mixing of the counterions in the water volume, which we describe using Flory-Huggins theory.

Sol-gel synthesis of mesoporous aluminosilicates with a narrow pore size distribution and catalytic activity thereof in the oligomerization of dec-1-ene

Porous aluminosilicates with Si/Al ratio of 80 have been prepared by the sol-gel synthesis using tetraethyl orthosilicate (TEOS) and aluminum nitrate (Al(NO3)3*9H2O). It has been shown that the precipitation pH value and the gelation conditions strongly affected characteristics of the porous structure, the incorporation of aluminum into the silicate framework, and the surface acidity. It has been found that the implementation of the sol-gel synthesis initially in the acidic medium followed by the alkaline one allowed producing the mesoporous aluminosilicate with the specific surface area SBET of 660 m2 g−1, the mesopore volume V of 0.74 cm3 g−1, and the pore size distribution within the range of 2–5 nm. The high activity and selectivity of synthesized aluminosilicates in the oligomerization of dec-1-ene have been revealed.The conversion of dec-1-ene reached 92%. The formation selectivity of dec-1-ene oligomers with the oligomerization degree n = 2–3 amounted 87%.

Onset of the Electronic Absorption Spectra of Isolated and π-Stacked Oligomers of 5,6-Dihydroxyindole: An Ab Initio Study of the Building Blocks of Eumelanin.

Eumelanin is a naturally occurring skin pigment which is responsible for developing a suntan. The complex structure of eumelanin consists of π-stacked oligomers of various indole derivatives, such as the monomeric building block 5,6-dihydroxyindole (DHI). In this work, we present an ab initio wave-function study of the absorption behavior of DHI oligomers and of doubly and triply π-stacked species of these oligomers. We have simulated the onset of the electronic absorption spectra by employing the MP2 and the linear-response CC2 methods. Our results demonstrate the effect of an increasing degree of oligomerization of DHI and of an increasing degree of π-stacking of DHI oligomers on the onset of the absorption spectra and on the degree of red-shift toward the visible region of the spectrum. We find that π-stacking of DHI and its oligomers substantially red-shifts the onset of the absorption spectra. Our results also suggest that the optical properties of biological eumelanin cannot be simulated by considering the DHI building blocks alone, but instead the building blocks indole-semiquinone and indole-quinone have to be considered as well. This study contributes to advancing the understanding of the complex photophysics of the eumelanin biopolymer.

Polypeptides with Pendant Porphyrins: From the Recognition of Bidentate Bases to Inter-Digitated Photo-Active Strands

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short a-helical polypeptides.1 When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached within the cell membrane, where the solar energy is converted into chemical energy used by the cell to grow. In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest. Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires.2 An octapeptide3 and an hexadecapeptide4 derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement. Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration.5 The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide via host/guest interactions. Acknowledgements This work was supported by the CNRS and the French Ministry of Research. References W. Kühlbrandt, Nature 1995, 374, 497-498.a) R. W. Wagner, J. S. Lindsey, J. Seth, V. Palaniappan, D. F. Bocian, J. Am. Chem. Soc. 1996, 118, 3996-3997 and ref. cited therein. b) M. J. Crossley, P. L. Burn, S. J. Langford, J. K Prashar, J. Chem. Soc., Chem. Commun. 1995, 1921-1923. c) A. Osuka, H. Shimidzu, Angew. Chem. Int. Ed. Engl. 1997, 36, 135-137. N. Solladié, A. Hamel, M. Gross, Tet. Lett. 2000, 41, 6075-6078.Unpublished results.a) M. Fujitsuka, M. Hara, S. Tojo, A. Okada, V. Troiani, N. Solladié, T. Majima, J. Phys. Chem B. 2005, 109, 33-35. b) M. Fujitsuka, D. W. Cho, N. Solladié, V. Troiani, H. Qiu, T. Majima, J. Photochem. Photobiol. A 2007, 188, 346-350. Figure 1

Heterogeneously-acid catalyzed oligomerization of glycerol over recyclable superacid Aquivion® PFSA

This manuscript explores the catalytic activity, selectivity and stability of Aquivion® PFSA PW98 in the oligomerization of glycerol. Aquivion® PFSA PW98 is a solid superacid catalyst with a Hammett acidity function of −12. Furthermore, the perfluorinated structure allows this polymer to stand quite high operating temperature (up to 150–160°C) without loss in mechanical and chemical integrity which is of huge interest for glycerol conversion. In this context, we discovered that Aquivion® PFSA PW98 was nearly fully selective to oligoglycerols up to 80% conversion of glycerol. The oligomerization degree of oligoglycerol and the regioselectivity of the reaction (linear vs branched and cyclic isomers) were fully analyzed by means of GC and SEC chromatographies. In contrast to conventional solid acid catalysts, Aquivion® PFSA PW98 was found highly robust in glycerol and was sucessfully recycled at least 10 times without apparent decrease in activity or selectivity. A comparison with Nafion NR 50 is also included to shed light on the potential of Aquivion® PFSA PW98 for acid-catalyzed conversion of glycerol.

Structure-Based Statistical Mechanical Model Accounts for the Causality and Energetics of Allosteric Communication.

Allostery is one of the pervasive mechanisms through which proteins in living systems carry out enzymatic activity, cell signaling, and metabolism control. Effective modeling of the protein function regulation requires a synthesis of the thermodynamic and structural views of allostery. We present here a structure-based statistical mechanical model of allostery, allowing one to observe causality of communication between regulatory and functional sites, and to estimate per residue free energy changes. Based on the consideration of ligand free and ligand bound systems in the context of a harmonic model, corresponding sets of characteristic normal modes are obtained and used as inputs for an allosteric potential. This potential quantifies the mean work exerted on a residue due to the local motion of its neighbors. Subsequently, in a statistical mechanical framework the entropic contribution to allosteric free energy of a residue is directly calculated from the comparison of conformational ensembles in the ligand free and ligand bound systems. As a result, this method provides a systematic approach for analyzing the energetics of allosteric communication based on a single structure. The feasibility of the approach was tested on a variety of allosteric proteins, heterogeneous in terms of size, topology and degree of oligomerization. The allosteric free energy calculations show the diversity of ways and complexity of scenarios existing in the phenomenology of allosteric causality and communication. The presented model is a step forward in developing the computational techniques aimed at detecting allosteric sites and obtaining the discriminative power between agonistic and antagonistic effectors, which are among the major goals in allosteric drug design.

Selective Antimicrobial Activities and Action Mechanism of Micelles Self-Assembled by Cationic Oligomeric Surfactants.

This work reports that cationic micelles formed by cationic trimeric, tetrameric, and hexameric surfactants bearing amide moieties in spacers can efficiently kill Gram-negative E. coli with a very low minimum inhibitory concentration (1.70-0.93 μM), and do not cause obvious toxicity to mammalian cells at the concentrations used. With the increase of the oligomerization degree, the antibacterial activity of the oligomeric surfactants increases, i.e., hexameric surfactant > tetrameric surfactant > trimeric surfactant. Isothermal titration microcalorimetry, scanning electron microscopy, and zeta potential results reveal that the cationic micelles interact with the cell membrane of E. coli through two processes. First, the integrity of outer membrane of E. coli is disrupted by the electrostatic interaction of the cationic ammonium groups of the surfactants with anionic groups of E. coli, resulting in loss of the barrier function of the outer membrane. The inner membrane then is disintegrated by the hydrophobic interaction of the surfactant hydrocarbon chains with the hydrophobic domains of the inner membrane, leading to the cytoplast leakage. The formation of micelles of these cationic oligomeric surfactants at very low concentration enables more efficient interaction with bacterial cell membrane, which endows the oligomeric surfactants with high antibacterial activity.

Lipid Mediated Oligomeric Assembly of the Serotonin Transporter at the Plasma Membrane

The human serotonin transporter (hSERT) is responsible for the termination of synaptic serotonergic signaling. Using single molecule microscopy, we have shown previously that SERT forms higher oligomers at the plasma membrane of living cells; we found a variety of aggregation states of membrane-associated transporters, revealing molecular associations at least up to pentamers and demonstrating the coexistence of different degrees of oligomerization in a single cell. The oligomerization was found to be independent of SERT surface density, indicating a stable interaction of the subunits. We developed a special bleaching protocol to decipher the interaction kinetics of SERT oligomers; the complexes remained stable over several minutes in the live cell plasma membrane. Together, the results indicate kinetic trapping of SERT oligomers at the plasma membrane, subsequent to an equilibration which occurs at an unknown subcellular organelle.By evaluating the subunit stoichiometry of SERT in the endoplasmic reticulum (ER) we show here that the oligomerization is indeed chemically equilibrated at ER membranes; after trafficking to the plasma membrane, the SERT stoichiometry remains fixed. Furthermore, we show that the stabilization of the transporter complexes can be ascribed to the differences in the lipid composition of the plasma membrane and the ER. Upon alteration of the lipid composition the SERT complexes are liberated from kinetic trapping at the plasma membrane and their oligomeric size is significantly reduced. In conjunction with the use of SERT mutants exhibiting altered lipid binding capability, we could thus show that stable oligomerization of SERT at the plasma membrane is lipid-mediated.

Detailed Investigation of Detergent Micelle Formation using Molecular Dynamics Simulations

Surfactants are amphiphilic molecules with the ability to self-assemble into micelles and are commonly used in membrane protein extraction and solvation. Recent studies have shown that detergent type and concentration have a direct impact on the degree of oligomerization and function of membrane proteins [1], further extending their usefulness as a tool for investigating the structure-function relationship of membrane proteins. Despite their widespread use, the biophysical properties of detergent micelles at the atomistic level are poorly understood. We have conducted a systematic study on the physical characteristics of surfactant micelles using all-atom and coarse-grained molecular dynamics (MD) simulations. The commonly used detergents n-dodecylphosphochiline (DPC) and n-dodecyl-β-D-maltoside (DDM) were chosen. Our results agree in general with small angle X-ray scattering (SAXS) experiments and provide valuable insights into the relationship between micelle shape and aggregation number. Cluster analysis of self-assembled micelles reveal a wide distribution of micellar size and shape. This is consistent with the large range of aggregation numbers for DPC and DDM that have been experimentally determined. The shape of DPC micelles was more spherical due to its lower aggregation number, whereas DDM micelles tended to be ellipsoidal. In addition, micelle shape strictly obeys behavior based on theoretical packing factor considerations [2] such that both DPC and DDM surfactants formed ellipsoid micelles and larger preformed micelles (up to 300 detergent molecules) deformed to a hexagonal shape. Our results allow us to more accurately estimate the number of molecules and the effective thickness of the detergent layer surrounding membrane proteins. These insights in turn add to our understanding of the relationship between detergent properties and membrane protein oligomerization. [1] Hussain, S. 2015 J. Mol. Biol. 427:1278. [2] Israelachvili. J. N. et. al., 2011 Academic Press, 3rd ed.

Statistical Physics of the Causality and Energetics in Allosteric Communication

Allostery is one of the pervasive mechanisms through which proteins in living systems carry out enzymatic activity, cell signaling, and metabolism control. The effective modeling of protein function regulation requires a synthesis of the thermodynamic and structural views of allostery. We present here a structure-based statistical mechanical model of allostery, allowing to observe causality of communication between regulatory and functional sites and to estimate per-residue free energy changes. Based on the notions of ligand free and ligand occupied systems in the context of protein harmonic representation, corresponding sets of characteristic normal modes are obtained and used as inputs for the allosteric potential. The latter quantifies mean elastic work exerted on a residue because of the local motion of its neighbors. Subsequently, in a statistical mechanical framework the entropic contribution to allosteric free energy of a residue is directly calculated from the comparison of the conformational ensembles in the ligand free and occupied systems. The method is a systematic approach for analyzing the energetics of allosteric communication based on a single structure, and its feasibility was tested on a variety of allosteric proteins particularly heterogeneous in terms of size, topology, and degree of oligomerization. The allosteric free energy calculations show diversity of ways and complexity of scenarios existing in the phenomenology of allosteric causality and communication. Achieving the discriminative power between agonist and antagonists and developing computational techniques for on-demand design of desired allosteric effectors are among the major goals of future theoretical studies towards allosteric drug design.

Assembly of synthetic Aβ miniamyloids on polyol templates.

Covalent dynamic chemistry is used to mimic the first steps of the highly cooperative fibril formation of Aβ peptides. For that purpose, Aβ peptide pentapeptide boronic acids 1 and 2 were synthesized by solid-phase peptide synthesis and studied in esterification experiments with polyhydroxylated templates. The bis-hydroxylated dipeptide Hot=Tap serves as a template of adjustable degree of oligomerization which spontaneously forms boronic esters with peptides of type 1 and 2. Nuclear magnetic resonance can differentiate between regioisomeric boronic esters and identifies preferred sites of esterification on the dimeric template 9. 2-Formylphenylboronic acid (14) is used to link the parent pentapeptide Leu-Val-Phe-Phe-Ala to the template 16 to obtain threefold boronic ester 17. The miniamyloid 17 assembles from seven components by imine and boronic ester bonds between the peptides and the template. The relative orientation and spacing of the peptides mimic the assembly of peptides in Alzheimer β-amyloids.

The molecular designs and properties of asymmetric heterocycles (HBrBN3) n (n = 1-4)

The structures and properties of asymmetric heterocycles (HBrBN3) n (n = 1-4) are systematically studied at the B3LYP/6-31G* level. The molecules (HBrBN3) n (n = 2-4) have the core structures of a 2n-membered ring with alternating boron and α-nitrogen atoms. The relationships between geometrical parameters and oligomerization degree n are discussed. The calculated IR spectra have four main characteristic regions. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed. Thermodynamic analysis of the gas-phase oligomerizations shows that formation of the most stable heterocycles (HBrBN3) n (n = 2-4) is enthalpy driven in the range of 200-800 K.

Theoretical studies of the structures and properties of (Cl2InN3) n (n = 1–6) clusters

The equilibrium geometries, stabilities, IR spectra, and thermodynamic properties of (Cl2InN3) n (n = 1–6) clusters are systematically investigated at the DFT-B3LYP level. Harmonic vibrational analysis has been performed to assure that the optimized geometries are stable. The optimized results suggest that the core structures of 2n-membered ring with alternating indium and a-nitrogen atoms are observed in clusters when n ≥ 2. The relative stabilities of (Cl2InN3) n (n = 1–6) clusters were analyzed by means of the dependent relationships between the averaged binding energies, the second-order difference of energies, the HOMO–LUMO energy gaps and the cluster size n, and a local odd-even alternation phenomenon was found. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. Thermodynamic analysis of the gas-phase oligomerizations shows that formations of the most stable clusters (Cl2InN3) n (n = 2–6) from the monomer are thermodynamically favorable by the enthalpies and Gibbs free energies in the range of 200–700 K.