Explicitly correlated coupled-cluster theory has developed into a valuable computational tool for the calculation of electronic energies close to the limit of a complete basis set of atomic orbitals. In particular at the level of coupled-cluster theory with single and double excitations (CCSD), the space of double excitations is quickly extended towards a complete basis when Slater-type geminals are added to the wave function expansion. The purpose of the present article is to demonstrate the accuracy and efficiency that can be obtained in computational thermochemistry by a CCSD model that uses such Slater-type geminals. This model is denoted as CCSD(F12), where the acronym F12 highlights the fact that the Slater-type geminals are functions f(r12) of the interelectronic distances r12 in the system. The performance of explicitly correlated CCSD(F12) coupled-cluster theory is demonstrated by computing the atomization energies of 73 molecules (containing H, C, N, O, and F) with an estimated root-mean-square deviation from the values compiled in the Active Thermochemical Tables of σ = 0.10 kJ/mol per valence electron. To reach this accuracy, not only the frozen-core CCSD basis-set limit but also high-order excitations (connected triple and quadruple excitations), core–valence correlation effects, anharmonic vibrational zero-point energies, and scalar and spin–orbit relativistic effects must be taken into account. 相似文献
Cell‐penetrating peptides (CPPs) and their synthetic mimics (CPPMs) represent a class of molecules that facilitate the intracellular delivery of various cargo. Previous studies indicated that the presence of aromatic functionalities improved CPPM activity. Given that aromatic functionalities play prominent roles in membrane biology and participate in various π interactions, we explored whether these interactions could be optimized for improved CPPM activity. CPPMs were synthesized by ring‐opening metathesis polymerization by using monomers that contained aromatic rings substituted with electron‐donating and electron‐withdrawing groups and covered an electrostatic potential range from ?29.69 to +15.57 kcal mol?1. These groups altered the quadrupole moments of the aromatic systems and were used to test if such structural modifications changed CPPM activity. CPPMs were added to dye‐loaded vesicles and the release of carboxyfluorescein was monitored as a function of polymer concentration. Changes in the effective polymer concentration to release 50 % of the dye (effective concentration, EC50) were monitored. Results from this assay showed that the strength of the electron‐donating and electron‐withdrawing groups incorporated in the CPPMs did not alter polymer EC50 values or activity. This suggests that other design parameters may have a stronger impact on CPPM activity. In addition, these results indicate that a wide range of aromatic groups can be incorporated without negatively impacting polymer activity. 相似文献
Pure rotational spectra of the ground vibrational states of eight isotopologues of H(2)S···CuCl and twelve isotopologues of H(2)S···AgCl have been analysed allowing rotational constants and hyperfine coupling constants to be determined. The molecular structures have been determined from the measured rotational constants and are presented alongside the results of calculations at the CCSD(T) level. Both molecules have C(s) symmetry at equilibrium and are pyramidal at the sulphur atom. The chlorine, metal, and sulphur atoms are collinear while the local C(2) axis of the hydrogen sulphide molecule intersects the axis defined by the heavy atoms at an angle, φ = 74.46(2)° for Cu and φ = 78.052(6)° for Ag. The molecular geometries are rationalised using simple rules that invoke the electrostatic interactions within the complexes. Centrifugal distortion constants, Δ(J), and nuclear quadrupole coupling constants, χ(aa)(Cu) and χ(aa)(Cl) for H(2)S···CuCl are presented for the first time. The geometry of H(2)S···AgCl is determined with fewer assumptions and greater precision than previously. 相似文献
We report calculations using a reaction surface Hamiltonian for which the vibrations of a molecule are represented by 3N-8 normal coordinates, Q, and two large amplitude motions, s(1) and s(2). The exact form of the kinetic energy operator is derived in these coordinates. The potential surface is first represented as a quadratic in Q, the coefficients of which depend upon the values of s(1),s(2) and then extended to include up to Q(6) diagonal anharmonic terms. The vibrational energy levels are evaluated by solving the variational secular equations, using a basis of products of Hermite polynomials and appropriate functions of s(1),s(2). Our selected example is malonaldehyde (N=9) and we choose as surface parameters two OH distances of the migrating H in the internal hydrogen transfer. The reaction surface Hamiltonian is ideally suited to the study of the kind of tunneling dynamics present in malonaldehyde. Our results are in good agreement with previous calculations of the zero point tunneling splitting and in general agreement with observed data. Interpretation of our two-dimensional reaction surface states suggests that the OH stretching fundamental is incorrectly assigned in the infrared spectrum. This mode appears at a much lower frequency in our calculations due to substantial transition state character. 相似文献
A direct comparison of two strategies for designing antimicrobial polymers is presented. Previously, we published several reports on the use of facially amphiphilic (FA) monomers which led to polynorbornenes with excellent antimicrobial activities and selectivities. Our polymers obtained by copolymerization of structurally similar segregated monomers, in which cationic and non‐polar moieties reside on separate repeat units, led to polymers with less pronounced activities. A wide range of polymer amphiphilicities was surveyed by pairing a cationic oxanorbornene with eleven different non‐polar monomers and varying the comonomer feed ratios. Their properties were tested using antimicrobial assays and copolymers possessing intermediate hydrophobicities were the most active. Polymer‐induced leakage of dye‐filled liposomes and microscopy of polymer‐treated bacteria support a membrane‐based mode of action. From these results there appears to be profound differences in how a polymer made from FA monomers interacts with the phospholipid bilayer compared with copolymers from segregated monomers. We conclude that a well‐defined spatial relationship of the whole polymer is crucial to obtain synthetic mimics of antimicrobial peptides (SMAMPs): charged and non‐polar moieties need to be balanced locally, for example, at the monomer level, and not just globally. We advocate the use of FA monomers for better control of biological properties. It is expected that this principle will be usefully applied to other backbones such as the polyacrylates, polystyrenes, and non‐natural polyamides. 相似文献
Organic polymers that contain ligated metals offer a variety of unique properties which include luminescence, electro‐ and photochemistry, catalysis, charge, magnetism, and thermochromism. These organic–inorganic hybrid materials have the potential to offer novel active matrixes for advanced devices. Continued progress in synthetic chemistry and molecular characterization will enable such advanced materials. Here the focus is restricted to side‐chain metal complexes with emissive properties that highlight the use of lanthanide ions as opposed to the often‐studied transition metal complexes.
Oligomers based on an o-phenylene ethynylene (oPE) backbone with polar substituents have been synthesized using Sonogashira methods. Folding of these extremely short oligomers was confirmed via 1D and 2D (NOESY) NMR methods. Utilizing electron-rich and electron-poor phenylene building blocks, variations of these oPE oligomers have been synthesized to determine the folded stability of pi-rich vs pi-poor vs pi-rich-pi-poor systems. Slight variations in temperature offer a route, aside from solvent denaturation, to probe the stability of the folded structure. This is the first report of an NMR solution characterization of folding for a PE backbone without hydrogen bonds. 相似文献