Single Bond Lengths Research Articles

Sulfur Switches for Responsive Peptide Materials.

There is considerable recent interest in the synthesis and development of peptide-based materials as mimics of natural biological assemblies that utilize proteins and peptides to form organized structures and develop beneficial properties. Due to their potential compatibility with living organisms, synthetic peptide materials are also being developed for applications such as cell grafting, therapeutic delivery, and implantable diagnostic devices. One desirable feature for such applications is the ability to design materials that can respond to stimuli by changes in their structure or properties under biologically relevant conditions. Peptide and protein assemblies can respond to stimuli, such as changes in temperature, solution pH, ions present in media, or interactions with other biomacromolecules. An exciting area of emerging research is focused on how biology uses the chemistry of sulfur-containing amino acids as a means to regulate biological processes. These concepts have been utilized and expanded in recent years to enable the development of peptide materials with readily switchable properties.The incorporation of sulfur atoms in polypeptides, peptides, and proteins provides unique sites that can be used to alter the physical and biological properties of these materials. Sulfur-containing amino acid residues, most often cysteine and methionine, are able to undergo a variety of selective chemical and enzyme-mediated reactions, which can be broadly characterized as redox or alkylation processes. These reactions often proceed under physiologically relevant conditions, can be reversible, and are significant in that they can alter residue polarity as well as conformations of peptide chains. These sulfur-based reactions are able to switch molecular and macromolecular properties of peptides and proteins in living systems and recently have been applied to synthetic peptide materials. Naturally occurring "sulfur switches" can be reversible or irreversible and are often triggered by enzymatic activity. Sulfur switches in peptide materials can also be triggered in vitro using oxidation/reduction and alkylation as well as photochemical reactions. The application of sulfur switches to peptide materials has greatly expanded the scope of these switches due to the ability to readily incorporate a wide variety of noncanonical sulfur-containing synthetic amino acids.Sulfur switches have been shown to provide considerable potential to reversibly alter peptide material properties under mild physiologically relevant conditions. An important molecular feature of sulfur-containing amino acid residues was found to be the location of sulfur atoms in the side chains. The variation of sulfur atom positions from the backbone by single bond lengths was found to significantly affect polypeptide chain conformations upon oxidation-reduction or alkylation/dealkylation reactions. With the successful adaptation of sulfur switches to peptide materials, future studies can explore how these switches affect how these materials interact with biological systems. This Account provides an overview of the different types of sulfur switch reactions found in biology and their properties and the elaboration of these switches in synthetic systems with a focus on recent developments and applications of reversible sulfur switches in peptide materials.

Self-driven carbon atom implantation into fullerene embedding metal–carbon cluster

Hundreds of members have been synthesized and versatile applications have been promised for endofullerenes (EFs) in the past 30 y. However, the formation mechanism of EFs is still a long-standing puzzle to chemists, especially the mechanism of embedding clusters into charged carbon cages. Here, based on synthesis and structures of two representative vanadium-scandium-carbido/carbide EFs, VSc2C@Ih (7)-C80 and VSc2C2@Ih (7)-C80, a reasonable mechanism-C1 implantation (a carbon atom is implanted into carbon cage)-is proposed to interpret the evolution from VSc2C carbido to VSc2C2 carbide cluster. Supported by theoretical calculations together with crystallographic characterization, the single electron on vanadium (V) in VSc2C@Ih (7)-C80 is proved to facilitate the C1 implantation. While the V=C double bond is identified for VSc2C@Ih (7)-C80, after C1 implantation the distance between V and C atoms in VSc2C2@Ih (7)-C80 falls into the range of single bond lengths as previously shown in typical V-based organometallic complexes. This work exemplifies in situ self-driven implantation of an outer carbon atom into a charged carbon cage, which is different from previous heterogeneous implantation of nonmetal atoms (Group-V or -VIII atoms) driven by high-energy ion bombardment or high-pressure offline, and the proposed C1 implantation mechanism represents a heretofore unknown metal-carbon cluster encapsulation mechanism and can be the fundamental basis for EF family genesis.

Imprinted polymeric nanoparticles as artificial enzymes for ester hydrolysis at room temperature and pH 7

Replication of the extraordinary catalysis of enzymes in synthetic systems is a long-standing goal of scientists. Here we report a synthetic mimic of carbonic anhydrase capable of hydrolyzing nonactivated alkyl esters at room temperature and neutral pH, while more reactive aryl esters stay intact in the same solution. This type of catalysis normally occurs only in enzymes but becomes possible with synthetic catalysts when a basic group is placed accurately near a zinc-bound water molecule to activate the latter for the nucleophilic attack on the ester substrate. Basicity and charge character of the proton acceptor determine the catalytic mechanism and its window of operation, as well as the type of esters to be hydrolyzed. The distance between the catalytic groups dictates the rate of hydrolysis for the benchmarking p -nitrophenyl ester, with a change by a single bond length impacting the rate more than changing the basicity of the active site base by20 orders of magnitude. • Hydrolysis of alkyl ester at room temperature and pH 7 • Enzyme-like catalytic proficiency • Selective transformation of less reactive esters over more reactive ones • Biomimetic cooperative catalysis Enzymes are characterized by their extraordinary catalytic efficiency and specificity but tend to denature easily under adverse conditions. If synthetic catalysts having similar catalytic capabilities but greater stability can be rationally designed and made, many fields of research and technology will benefit. This report describes synthetic enzymes that rival their biological counterparts in catalytic proficiency. As crosslinked polymeric nanoparticles, they become more active at higher temperatures and can potentially function under conditions totally impossible for natural biocatalysts. Their ability to selectively hydrolyze nonactivated esters under ambient conditions may facilitate chemical recycling of hydrolyzable plastics such as polyester and polycarbonate. Natural esterases hydrolyze esters under physiological pHs, but chemists often have to use strongly acidic or basic conditions for the same hydrolysis. We report synthetic nanoparticle catalysts that hydrolyze nonactivated alkyl esters at room temperature and neutral pH, with enzyme-like catalytic mechanisms and exquisite substrate selectivity. Unlike natural enzymes that denature easily at elevated temperatures, the synthetic catalysts become more active at higher temperatures.

Synthesis, Spectroscopic, Crystal Structure, DFT, Hirshfeld Surface and Molecular Docking Analysis of Hexahydroquinoline Derivative (HQ)

The synthesis of a HQ derivative using a one-pot multicomponent synthesis is reported. Single crystal X-Ray diffraction at 293 K was used to characterize the material, which was then investigated theoretically using the DFT method. The 3 D Hirshfeld surface and 2 D fingerprint plots were created and linked with the XRD results to elucidate intermolecular interactions in the crystal lattice. In addition, FT-IR, UV-Vis, 1H, and 13 C were used to support the synthesis. Theoretical data calculated via DFT/6-311++G(d,p) level, matched to experimental single crystal X-ray diffraction bond lengths and bond angle parameters, NMR and FT-IR spectra, coincides with experimental data. The time dependent (TD-DFT) results correlates with the experimental electronic absorption measurements. Mulliken population analysis, Molecular Electrostatic Potential analysis (MEP), and Electron Localization Function (ELF) study were also performed. TD-DFT and HOMO/LUMO computations were used to examine the electron transport. Molecular docking using 7 protein receptors and drug Likeness were used to find the best ligand-protein interactions.

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Computational Studies of the Role of Substituents on the Reactivity and Biological Activities of Naphthoic Acid

Substituents play a major role in influencing the reactivity and biological activity of aromatic compounds. Substituents affect the conductivity of molecular electronic and photoresponsive switches, light harvesting dye-sensitized solar cells and organic electroluminescent devices. A number of quantum mechanical methods corresponding to stabilization energy, charge of substituent active region, energy dispersive analysis, and molecular electrostatic potential help in the description of substituent effect in aromatic systems. In the present work we carried out computational studies for the estimation of chemical and structural properties of a chemical library of nine <i>ortho</i> substituted naphthoic acids. The chemical reactivity of the selected substituted naphthoic acids was assessed from a number of physicochemical properties such as total energy, HOMO-LUMO gap, chemical hardness, binding energy, ionization potential, electron affinity, electronegativity, electrochemical potential, global softness, electrophilicity and dipole moment. The effect of the electron-donor groups on conjugation of <i>ortho</i> substituted naphthoic acid was investigated by correlating the calculated rotational barriers of transition state of <i>cis</i> and <i>trans</i> <i>ortho</i>-substituted naphthoic acids to observe change in single bond length, double bond length, bond angle, dihedral angle, and rotational frequency of carboxylic group of substituted napthoic acids. The rotational barrier correlated with the geometric, atomic, molecular, and spectroscopic parameters. Moreover, quantitative structure–activity relationship (QSAR) analyses was performed and the obtained structural properties were linked with biological activities.

Implications of Nitrogen Doping on Geometrical and Electronic Structure of the Fullerene Dimers

Main observation and conclusionBecause of its unsaturated bonds, C60 is susceptible to polymerize into dimers. The implications of nitrogen doping on the geometrical and electronic structure of C60 dimers have been ambiguous for years. A quarter‐century after the discovery of azafullerene dimer (C59N)2, we reported its single crystallographic structure in 2019. Herein, the unambiguous crystal structure information of (C59N)2 is elucidated specifically, revealing that the inter‐cage C—C single bond length of (C59N)2 is comparable with that of an ordinary C(sp3)‐C(sp3) single bond, and that the most stable conformer of (C59N)2 is gauche‐conformer with a dihedral angle of 66°. To amend the structural deviations, geometrical structure of (C59N)2 is optimized by a B3LYP‐D3BJ function, which is proved to be more consistent with its single crystal structure than those by the commonly used B3LYP function. Moreover, the calculation method is also suitable for other representative fullerene dimers, such as (C60)2 and its divalent anion. Additionally, the dissociation of (C59N)2 at 473 K under mass spectrometric conditions suggests the inter‐cage C—C bond is relatively weaker than an ordinary C—C single bond, which can be explained by the interaction energies of inter‐cages.

Interception of Elusive Cationic Hf-Al and Hf-Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions.

Heterobimetallic complexes with inequivalent bridging alkyl chains are very often invoked as key intermediates in many catalytic processes, yet their interception and structural characterization are lacking. Such complexes have been prepared from reactions of the cationic cyclometalated hafnocene [CpPr Cp Hf][B(C6 F5 )4 ] (1) with main group metal alkyls to afford the corresponding hetero-bridged cationic products, [CpPr Cp Hf(μ-R)E(R)n ][B(C6 F5 )4 ] (E=Al or Zn; R=Me, Et, or iBu). NMR and DFT studies demonstrate that both bridging alkyls establish agostic interactions with Hf, which are appreciably stronger for ethyl rather than methyl groups. Hf-Al and Hf-Zn distances are surprisingly short and only slightly longer than computed Hf-Al or Hf-Zn single bond lengths (2.80 Å). Finally, a reaction of [CpPr Cp Hf(μ-Me)Zn(Me)][B(C6 F5 )4 ] with excess ZnMe2 yields an unprecedented heterotrimetallic species, [(CpPr )2 Hf(μ-Me)(ZnMe)(μ3 -CH2 )ZnMe][B(C6 F5 )4 ], the detailed structure of which is elucidated by a combination of NMR spectroscopic methods and molecular calculations.

Aqueous pKa prediction for tautomerizable compounds using equilibrium bond lengths

The accurate prediction of aqueous pKa values for tautomerizable compounds is a formidable task, even for the most established in silico tools. Empirical approaches often fall short due to a lack of pre-existing knowledge of dominant tautomeric forms. In a rigorous first-principles approach, calculations for low-energy tautomers must be performed in protonated and deprotonated forms, often both in gas and solvent phases, thus representing a significant computational task. Here we report an alternative approach, predicting pKa values for herbicide/therapeutic derivatives of 1,3-cyclohexanedione and 1,3-cyclopentanedione to within just 0.24 units. A model, using a single ab initio bond length from one protonation state, is as accurate as other more complex regression approaches using more input features, and outperforms the program Marvin. Our approach can be used for other tautomerizable species, to predict trends across congeneric series and to correct experimental pKa values.

A Modular Access to Divinyldiphosphenes with a Strikingly Small HOMO–LUMO Energy Gap

The olefinic C-H bond functionalization of (NHC)CHPh (NHC=IPr=C{(NAr)CH}2 1; SIPr=C{(NAr)CH2 }2 2; Ar=2,6-iPr2 C6 H3 ), derived from classical N-heterocyclic carbenes (NHCs), with PCl3 affords the dichlorovinylphosphanes {(NHC)C(Ph)}PCl2 (NHC=IPr 3, SIPr 4). Two-electron reduction of 3 and 4 with magnesium leads to the formation of the divinyldiphosphenes [{(NHC)C(Ph)}P]2 (NHC=IPr 5, SIPr 6) as crystalline solids. Unlike literature-known diphosphenes, which are mostly yellow or orange, 5 is a green whereas 6 is a purple solid. Although the P=P bond lengths of 5 (2.062(1)) and 6 (2.055(1) Å) are comparable to those of the known diphosphenes (2.02-2.08 Å), the C-P bond lengths of 5 (1.785(1)) and 6 (1.797(1) Å) are, however, considerably shorter than a C -P single bond length (1.85 Å), indicating a considerable π-conjugation between C=C and P=P moieties. The HOMO-LUMO energy gap for 5 (4.15) and 6 (4.52 eV) is strikingly small and thus the narrowest among the diphosphenes (>4.93 eV) reported as yet. Consequently, 5 readily undergoes P=P bond cleavage at room temperature on treatment with sulfur to form the unique dithiophosphorane {(IPr)C(Ph)}P(S)2 7. Interestingly, reaction of 5 with selenium gives the selenadiphosphirane [{(IPr)C(Ph)}P]2 Se 8 with an intact P-P bond.

Single and dual adhesive bond strength analysis of single lap joint between dissimilar adherends

The emerging trends for joining of aircraft structural parts made up of different materials are essential for structural optimization. Adhesively bonded joints are widely used in the aircraft structural constructions for joining of the similar and dissimilar materials. The bond strength mainly depends on the type of adhesive and its properties. Dual adhesive bonded single lap joint concept is preferred where there is large difference in properties of the two dissimilar adherends and demanding environmental conditions. In this work, Araldite-2015 ductile and AV138 brittle adhesives have been used separately between the dissimilar adherends such as, CFRP and aluminium adherends. In the dual adhesive case, the ductile adhesive Araldite-2015 has been used at the ends of the overlap because of high shear and peel strength, whereas in the middle of the bonded region the brittle adhesive AV138 has been used at different dimensions. The bond strength and corresponding failure patterns have been evaluated. The Digital Image Correlation (DIC) method has been used to monitor the relative displacements between the dissimilar adherends. Finite element analysis (FEA) has been carried-out using ABAQUS software. The variation of peel and shear stresses along the single and dual adhesive bond length have been captured. Comparison of experimental and numerical studies have been carried-out and the results of numerical values are closely matching with the experimental values. From the studies it is found that, the use of dual adhesive helps in increasing the bond strength.

Crystal structure of 1,3-di-tert-butyl-2-chloro-1,3,2-di-aza-phospho-rinane - a saturated six-membered phospho-rus nitro-gen heterocycle with a partially flattened chair conformation and a long PIII-Cl bond.

Colourless blocks of 1,3-di-tert-butyl-2-chloro-1,3,2-di-aza-phospho-rinane, C11H24ClN2P (1), were obtained by sublimation in vacuo slightly above room temperature. The asymmetric unit of the monoclinic crystal structure of the six-membered N-heterocyclic compound is defined by one mol-ecule in a general position. The six-membered ring of the mol-ecule adopts a cyclo-hexane-like chair conformation; the chair at one side is to some extent flattened as a result of the approximately trigonal-planar coordination of both nitro-gen atoms. In detail, this modified chair conformation is characterized by an angle of 53.07 (15)° between the plane defined by the three carbon atoms and the best plane of the two nitro-gen atoms and the two carbon atoms bound to them, and an angle of 27.96 (7)° between the latter plane and the plane defined by the nitro-gen and phospho-rus atoms. The tert-butyl groups are oriented equatorially and the chloro substituent is oriented axially. The P-Cl bond length of 2.2869 (6) Å is substanti-ally longer than the P-Cl single-bond length in PCl3 [2.034 Å; Galy & Enjalbert (1982 ▸). J. Solid State Chem. 44, 1-23]. Inspection of the inter-molecular distances gives no evidence for inter-actions stronger than van der Waals forces. The closest contact is between the Cl atom and a methyl-ene group of a neighbouring mol-ecule with a Cl⋯C distance of 3.7134 (18) Å, excluding a significant influence on the P-Cl bonding.

Novel N-heterocyclic carbene silver(I) complexes: Synthesis, structural characterization, and anticancer activity

In this study, we synthesized four novel unsymmetrically substituted NHC ligands (1a-d) and their Ag(I) complexes (2a-d). All new compounds were characterized using elemental analysis, FT-IR, 1H NMR, and 13C NMR spectroscopy and X-ray crystallography. The molecular structure of complex 2d was elucidated through single crystal X-ray diffraction analyses. Single crystal structural studies for complex 2d show that the benzene rings (C9–C14) and the central benzimidazole ring system make dihedral angles of 85.65(11)°. The Ag–Cl and Ag–C single bond lengths are 2.3553(7) and 2.096(2) Å, respectively. The C–Ag–Cl bond angle is 168.27(7)°. Both salts and complexes were tested for their anti-cancer potential against three human cancer cell lines (DU-145, MCF-7, and MDA-MB-231) and non-cancer cells adipose from mouse (L-929) for 24 h, 48 h and 72 h using the MTT assays. However, the Ag(I)–NHC complexes (2a-d) showed a dose and time-dependent cytotoxic activity against all cell lines. MDA-MB-231 human breast carcinoma cells were the most sensitive to the Ag(I)–NHC complex displaying IC50 lower than 1 μM all time points. Further, the IC50s for Ag(I)–NHC were higher in non-cancer cells, suggesting that complexes possessed noteworthy selectivity for human cancer cells.

Synthesis, characterization and anticancer activity of allyl substituted N-Heterocyclic carbene silver(I) complexes

Metal N-heterocyclic carbene (NHC) complexes have attracted considerable attention in biological fields for their potential applications in cancer and antimicrobial therapies. In this study, four new benzimidazole-based N-heterocyclic carbene salts (1a-d) and their silver (I) complexes (2a-d) were synthesized. All new compounds were characterized by elemental analysis, FT-IR, 1H NMR and, 13C NMR spectroscopy. Additionally, single crystal structural studies for complex 2d show that the benzene rings (C9C14) and the central benzimidazole ring system make dihedral angles of 83.58(13)°. The AgCl and AgC single bond lengths are 2.3267(8) and 2.087(3) Å, respectively. The CAgCl bond angle is 175.20(7)°. The prop-1-ene moiety attached at the second N-atom of benzimidazole is disordered at two set of sites with an occupancy ratio of 0.592(6): 0.408(6). There is one intramolecular hydrogen bond interaction between C22A-H22A … N2. The salts and Ag-complexes were further evaluated for their in vitro anticancer activities against DU-145 human prostate cancer cells, MCF-7, MDA-MB-231 human breast cancer cells and L-929 non-cancer cell for 24 h, 48 h and 72 h using the MTT assay. The Ag(I)NHC complexes (2a-d) showed a dose and time-dependent cytotoxic activity against all cell lines. The IC50s for all Ag(I)NHC complexes lower than 1 μM for 72 h time points on cancer cells. The results showed that complex 2d exhibited the highest activity against all cancer cell lines studied. Further, the complexes had relatively higher cytotoxicity to cancer cells than to non-cancer cell lines.

Linearly Two-Coordinated Silicon: Transition Metal Complexes with the Functional Groups M≡Si—M and M═Si═M

A detailed experimental and theoretical analysis is presented of unprecedented molybdenum complexes featuring a linearly coordinated, multiply bonded silicon atom. Reaction of SiBr2(SIdipp) (SIdipp = C[N(C6H3-2,6- iPr2)CH2]2) with Na[Tp'Mo(CO)2(PMe3)] (Na-1) in the ratio 1:2 afforded the reddish-brown metallasilylidyne complex [Tp'(CO)2Mo≡Si-Mo(CO)2(PMe3)Tp'] (Tp' = κ3- N, N', N″-hydridotris(3,5-dimethylpyrazolyl)borate) (2), in which an almost linearly coordinated silicon atom (∠(Mo1-Si-Mo2) = 162.93(7)°) is bridging the 15VE metal fragment Tp'Mo(CO)2 with the 17VE metal fragment Tp'Mo(CO)2(PMe3) via a short Mo1-Si bond (2.287(2) Å) and a considerably longer Mo2-Si bond (2.438(2) Å), respectively. The reddish-orange silylidyne complex [Tp'(CO)2Mo≡Si-Tbb] (3) was also prepared from Na-1 and the 1,2-dibromodisilene ( E)-Tbb(Br)Si═Si(Br)Tbb (Tbb = C6H2-2,6-[CH(SiMe3)2]2-4- tBu) and contains as 2 a short Mo-Si bond (2.2614(9) Å) to an almost linearly coordinated Si atom (∠(Mo-Si-CTbb) = 160.8(1)°). Cyclic voltammetric studies of 2 in diglyme revealed an irreversible reduction of 2 at -1.907 V vs the [Fe(η5-C5Me5)2]+/0 redox couple. Two-electron reduction of 2 with potassium graphite yielded selectively the 1,3-dimetalla-2-silaallene dianion [Tp'(CO)2Mo═Si═Mo(CO)2Tp']2- (42-), which was isolated as the bright yellow dipotassium salt [K(diglyme)]2-4. Single crystal X-ray diffraction analysis revealed a centrosymmetric structure of 42-. The Mo-Si bond length of 42- (2.3494(2) Å) compares well with those of Mo-Si double bonds and lies in-between the Mo1-Si triple bond and Mo2-Si single bond length of 2. Compounds 2, 3 and [K(diglyme)2]-4 were characterized by elemental analyses, IR and multinuclear NMR spectroscopy. Comparative ELF (electron localization function), NBO (natural bond orbital) and NRT (natural resonance theory) analyses of 2, 3 and 42- shed light into the electronic structures of these compounds.

Effect of cerium on structure, magnetism and magnetostriction of Fe81Ga19 alloy

FeGa alloy is a new kind of magnetostrictive material, and rare-earth cerium can improve its magnetostrictive property. (Fe81Ga19)100–xCex (x = 0, 0.3 at%, 0.7 at%, 1 at%) samples were prepared by doping cerium in Fe81Ga19 alloy. Their microstructures and phases were studied, and valence electronic structures were investigated. Electromagnetic parameters, such as coercivity, saturation magnetization, remnant magnetization and saturation magnetostrictive coefficients (λs) of every sample were measured. Cerium atoms are distributed at grain boundaries, and the Ce-doped alloys remain the A2 structure of FeGa alloy. When x is 0.7, the value of saturation magnetism is 217.08 emu/g, which is the maximum in the Ce-doped samples. The equivalent half length of single bond is the maximum also, and reaches to 0.11380 nm. At the same time, the number of covalent electrons is 3.5672, and is the minimum of the Ce-doped samples. Its λs is the largest in the four samples. The change of λs results in the change of equivalent half length of single bond in Ce-doped alloy.

Substituent effects on the basicity (pKa) of aryl guanidines and 2-(arylimino)imidazolidines: correlations of pH-metric and UV-metric values with predictions from gas-phase ab initio bond lengths

The AIBLHiCoS method accurately predicts the pKa values of 2-(arylimino)imidazolidines using only a single ab initio bond length.

Infrared Spectra and Density Functional Calculations for Singlet CH2═SiX2 and Triplet HC-SiX3 and XC-SiX3 Intermediates in Reactions of Laser-Ablated Silicon Atoms with Di-, Tri-, and Tetrahalomethanes.

Reactions of laser-ablated silicon atoms with di-, tri-, and tetrahalomethanes in excess argon were investigated, and the products were identified from the matrix infrared spectra, isotopic shifts, and density functional theory energy, bond length, and frequency calculations. Dihalomethanes produce planar singlet silenes (CH2═SiX2), and tri- and tetrahalomethanes form triplet halosilyl carbenes (HC-SiX3 and XC-SiX3). The Si-bearing molecules identified are the most stable, lowest-energy product in the reaction systems. While the C-Si bond in the silene is a true double bond, the C-Si bond in the carbene is a shortened single bond enhanced by hyperconjugation of the two unpaired electrons on C to σ*(Si-X) orbitals, which contributes stabilization through a small amount of π-bonding and reduction of the HCSi or XCSi angles. The C-Si bond lengths in these carbenes (1.782 Å for HC-SiF3) are between the single-bond length in the unobserved first insertion intermediate (1.975 Å for CHF2-SiF) and the double-bond length in the silene (1.704 Å for CHF═SiF2). The silicon s(2)p(2) and titanium s(2)d(2) electron configurations produce similar primary products, but the methylidyne with Ti has a bond to carbon stronger than that of the halosilyl carbene.

Charge transport and localization in atomically coherent quantum dot solids.

Epitaxial attachment of quantum dots into ordered superlattices enables the synthesis of quasi-two-dimensional materials that theoretically exhibit features such as Dirac cones and topological states, and have major potential for unprecedented optoelectronic devices. Initial studies found that disorder in these structures causes localization of electrons within a few lattice constants, and highlight the critical need for precise structural characterization and systematic assessment of the effects of disorder on transport. Here we fabricated superlattices with the quantum dots registered to within a single atomic bond length (limited by the polydispersity of the quantum dot building blocks), but missing a fraction (20%) of the epitaxial connections. Calculations of the electronic structure including the measured disorder account for the electron localization inferred from transport measurements. The calculations also show that improvement of the epitaxial connections will lead to completely delocalized electrons and may enable the observation of the remarkable properties predicted for these materials.

The AIBLHiCoS Method: Predicting Aqueous pKa Values from Gas-Phase Equilibrium Bond Lengths.

The proposed AIBLHiCoS method predicts a given compound's pKa in aqueous solution from a single ab initio bond length only, after geometry optimization in the gas phase. Here we provide simple and predictive equations for naphthols and chemically similar biomolecules. Each linear equation corresponds to a High-Correlation Subset (HiCoS) that expresses the novel type of linear free energy relationship discovered here. The naphthol family exhibits a clear and strong relationship with the phenol family, with the "active" C-O bond always producing the highest correlations. The proposed method can isolate erroneous experiments and operate in non-aqueous solution and at different temperatures. Moreover, the existence of "active fragments" is demonstrated in a variety of sizable biomolecules for which the pKa is successfully predicted.