Application of error-ranked singular value decomposition for the determination of potential-derived atomic-centered point charges

The present work provides a detailed investigation on the use of singular value decomposition (SVD) to solve the linear least-squares problem (LLS) for the purposes of obtaining potential-derived atom-centered point charges (PD charges) from the ab initio molecular electrostatic potential (V(QM)). Given the SVD of any PD charge calculation LLS problem, it was concluded that (1) all singular vectors are not necessary to obtain the optimal set of PD charges and (2) the most effective set of singular vectors do not necessarily correspond to those with the largest singular values. It is shown that the efficient use of singular vectors can provide statistically well-defined PD charges when compared with conventional PD charge calculation methods without sacrificing the agreement with V(QM). As can be expected, the methodology outlined here is independent of the algorithm for sampling V(QM) as well as the basis set used to calculate V(QM). An algorithm is provided to select the best set of singular vectors used for optimal PD charge calculations. To minimize the subjective comparisons of different PD charge sets, we also provide an objective criterion for determining if two sets of PD charges are significantly different from one another.     

A combined electronegativity equalization and electrostatic potential fit method for the determination of atomic point charges

We report an approach for the determination of atomic monopoles of macromolecular systems using connectivity and geometry parameters alone. The method is appropriate also for the calculation of charge distributions based on the quantum mechanically determined wave function and does not suffer from the mathematical instability of other electrostatic potential fit methods.     

Generation of OPLS-like charges from molecular electrostatic potential using restraints

A new method for generating atom-centered charges for use in condensed phase computer simulations is presented, which is based on a restrained electrostatic potential (RESP) procedure. Charges are calculated from a least-squares fit to the quantum mechanical electrostatic potential with a restraint applied to reduce their magnitude. The restraint developed here offers advantages over that used in RESP. The magnitude of the restraint is optimized to yield charges as close to the equivalent OPLS values as possible while still reproducing the molecule's electrostatic potential. A cross-validation analysis is used to show that the restraint is insensitive to the selection of OPLS molecules from which it is derived. Thus, with this method, OPLS-like charges may be produced from the electrostatic potential for atom types not in the OPLS force field. In addition, the restraint is shown to reduce the conformational dependence of the charges. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 483–498, 1999     

Off‐atomic site charges in some anions,metal cations,and complexes: Significance for electrostatic properties and binding

Electronic structures and properties of several anions, metal cations, and their complexes with neutral molecules were investigated at the HF/6‐31G** and B3LYP/6‐31G** levels of theory. Charges shifted from atomic sites due to atomic orbital hybridization called hybridization displacement charges (HDC) were investigated in detail. It has been found that many components of HDC are associated with each atom of ion that are shifted from the atomic sites, those associated with metal cations being shifted by large distances as found previously in electrically neutral systems. It is shown that atomic orbitals are appreciably rehybridized in going from neutral molecules to anions and cations. Molecular dipole moments and surface molecular electrostatic potentials (MEP) are obtained satisfactorily using HDC for the various types of species mentioned above. In the OH^?? H₂O complex, reversal of direction of shift of an HDC component associated with the hydrogen atom of H₂O involved in hydrogen bonding, indicates that the hydrogen bond between OH^? and H₂O would have some covalent character. Other atomic site‐based point charge models cannot provide such information about the nature of bonding. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem 2007     

A practical procedure for the determination of electrostatic charges of large molecules

Summary A practical procedure for the precise determination of electrostatic charges, which are evaluated by fitting the rigorous quantum mechanical molecular electrostatic potential to a monopole-monopole expression, is presented. The proposal of this procedure arises from the study of the minimum requirements necessary to obtain reliable electrostatic charges. Such a study is focused on: (i) the dependence of the electrostatic charges on the set of points where the quantum mechanical and the monopole-monopole molecular electrostatic potentials are fitted; thus, both the influence of the number of points and their distribution in layers located out of the van der Waals radii of the atoms are examined, and (ii) the reliability of the use of fractional models for the evaluation of electrostatic charges of large molecules. Results point out that the optimum number of points is defined by a density of points ranging from 0.45 to 0.60 points/Ų when four layers (separated by 0.2 Å) are considered. Nevertheless, the use of only two layers (separated by 0.4 Å) for large molecules is recommended, thus enabling one to obtain reliable charges at a reduced computational cost. Moreover, results justify the use of fractional models for the determination of electrostatic charges of extremely large molecules, even when aromatic structures exist.     

Fast tools for calculation of atomic charges well suited for drug design1

Two novel approaches to construct empirical schemes for partial atomic charge calculation were proposed. The charge schemes possess important benefits. First, they produce both topologically symmetrical and environment dependent charges. Second, they can be parameterised to reasonably reproduce ab initio molecular electrostatic potential (MEP), which guarantees their successful use in molecular modelling. To validate the approaches, the parameters of the proposed charge schemes were fitted to best reproduce MEP simultaneously on grids around a set of 227 diverse organic compounds. The residual errors in MEP reproduction due to calculated atomic charges were compared to those due to charges from known charge schemes.     

Conformational dependence of charges in protein simulations

We have studied the conformational dependence of molecular mechanics atomic charges for proteins by calculating the charges fitted to the quantum mechanical (QM) electrostatic potential (ESP) for all atoms in complexes between avidin and seven biotin analogues for 20 snapshots from molecular dynamics simulations. We have studied how various other charge sets reproduce those charges. The QM charges, even if averaged over all snapshots or all residues, in general have a larger magnitude than standard Amber charges, indicating that the restraint toward zero in the restrained ESP method is too strong. This has a significant influence on the electrostatic conformational energies and the interaction energy between the biotin ligand and the protein, giving a difference between the QM and Amber charges of 43 and 8 kJ/mol for the negatively charged and neutral biotin analogues, respectively (3-4%). However, this energy difference is strongly reduced if the solvation energy (calculated by the Poisson-Boltzmann or Generalized Born methods) is added, viz., to 7 kJ/mol for charged and 3 kJ/mol for uncharged ligand. In fact, charges need to be recalculated with a QM method only for residues within 7 or 4 A of the ligand, if the error should be less than 4 kJ/mol. Unfortunately, the QM charges do not give significantly better MM/PBSA estimates of ligand-binding affinities than standard Amber charges.     

Calculation of the electrostatic charges and energies for intercalation of aromatic drug molecules with DNA

In this work, we analyzed the influence of the charge model on the magnitudes of atomic charges and electrostatic energies for the binding of aromatic drug molecules with DNA. The dependence of the charge and energy on the level of theory (HF, DFT (B3LYP), MP2, semi‐empirical methods), basis set (STO‐3G, 3‐21G, 6‐31G, 6‐31G*, 6‐31G**), method of charge computation (Mulliken, Natural Population Analysis, CHelpG, Merz–Kollman), and force field charge (CHARMM27, AMBER99) has been tracked for typical aromatic drugs of different structure and charge state. Recommendations and restrictions have been formulated for the use of particular approaches in charge/electrostatic energy calculations. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Fast,efficient generation of high‐quality atomic charges. AM1‐BCC model: I. Method

The AM1‐BCC method quickly and efficiently generates high‐quality atomic charges for use in condensed‐phase simulations. The underlying features of the electron distribution including formal charge and delocalization are first captured by AM1 atomic charges for the individual molecule. Bond charge corrections (BCCs), which have been parameterized against the HF/6‐31G* electrostatic potential (ESP) of a training set of compounds containing relevant functional groups, are then added using a formalism identical to the consensus BCI (bond charge increment) approach. As a proof of the concept, we fit BCCs simultaneously to 45 compounds including O‐, N‐, and S‐containing functionalities, aromatics, and heteroaromatics, using only 41 BCC parameters. AM1‐BCC yields charge sets of comparable quality to HF/6‐31G* ESP‐derived charges in a fraction of the time while reducing instabilities in the atomic charges compared to direct ESP‐fit methods. We then apply the BCC parameters to a small “test set” consisting of aspirin, d ‐glucose, and eryodictyol; the AM1‐BCC model again provides atomic charges of quality comparable with HF/6‐31G* RESP charges, as judged by an increase of only 0.01 to 0.02 atomic units in the root‐mean‐square (RMS) error in ESP. Based on these encouraging results, we intend to parameterize the AM1‐BCC model to provide a consistent charge model for any organic or biological molecule. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 132–146, 2000     

Accurate molecular electrostatic potentials based on modified PRDDO/M wave functions. I. Electrostatic potential derived atomic charges

A new approach for the calculation of electrostatic potential derived atomic charges is presented. Based on molecular orbital calculations in the PRDDO/M approximation, the new parametrized electrostatic potential (PESP) method is parametrized against ab initio MP2/6-31G** calculations. For a data set of 820 atoms in 145 molecules containing H, C, N. O, F, P, S, Cl, and Br (including hypervalent species), the PESP method achieves a mean absolute error of 0.037 e⁻ with a correlation coefficient of 0.990. Unlike other approximate approaches, no scaling factor is required to improve the agreement between PESP charges and the underlying ab initio results. PESP calculations are an order of magnitude faster than the simplest ab initio calculation (STO-3G) on large molecules while achieving a level of accuracy that rivals much more elaborate ab initio methods. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 955–969, 1997     

Quick scheme for evaluation of atomic charges in arbitrary aluminophosphate sieves on the basis of electron densities calculated with DFT methods

It is demonstrated that unique and simple analytical functions are justified for the atomic charge dependences q of the T (T = Al, P) and O atoms of aluminophosphates (AlPOs) using DFT calculations with several basis sets, starting from STO-3G to 3-21G and 6-21G**. Three internal (bonds, angles, ...) coordinates for the charge dependences of the T atoms and four coordinates for the O are sufficient to reach a precision of 1.8% for the fitted q(Al), 1.0% for q(P), and 2.5% for q(O) relatively to the values calculated at any basis set level. The proposed strategy consists in an iterative scheme starting from charge dependences based on the neighbor's positions only. Electrostatic potential values are computed to illustrate the differences between the calculated and fitted charges in the considered AlPO models.     

基于细胞膜表面电势探讨Ca与毒性离子在植物根膜表面的相互作用

有毒重金属离子的自由离子活度已被广泛认为是重金属最直接的活性形态,可以用来预测重金属的生物效应,而事实上生物体表的重金属离子浓度由于细胞表面膜电势的静电效应而与本体溶液中重金属的自由离子活度存在显著差异.细胞膜表面电势随溶液中离子组成变化而发生变化,本体介质中钙离子能通过电荷屏蔽和离子键结合来降低膜表面电势的电负性,从而减少阳离子如Al3+、Cu2+和Ni2+在膜表面的活度,增加阴离子如SeO42-和H2AsO4-在膜表面的活度,这种电负性降低的程度能通过Gouy-Chapman-Stern模型来量化.基于植物根表重金属离子活度可以更好地预测其生物效应.细胞膜表面电势为研究离子之间交互作用机制及其与植物效应之间的关系提供了一个全新的角度.     

Constructing irregular surfaces to enclose macromolecular complexes for mesoscale modeling using the discrete surface charge optimization (DISCO) algorithm

Salt-mediated electrostatics interactions play an essential role in biomolecular structures and dynamics. Because macromolecular systems modeled at atomic resolution contain thousands of solute atoms, the electrostatic computations constitute an expensive part of the force and energy calculations. Implicit solvent models are one way to simplify the model and associated calculations, but they are generally used in combination with standard atomic models for the solute. To approximate electrostatics interactions in models on the polymer level (e.g., supercoiled DNA) that are simulated over long times (e.g., milliseconds) using Brownian dynamics, Beard and Schlick have developed the DiSCO (Discrete Surface Charge Optimization) algorithm. DiSCO represents a macromolecular complex by a few hundred discrete charges on a surface enclosing the system modeled by the Debye-Hückel (screened Coulombic) approximation to the Poisson-Boltzmann equation, and treats the salt solution as continuum solvation. DiSCO can represent the nucleosome core particle (>12,000 atoms), for example, by 353 discrete surface charges distributed on the surfaces of a large disk for the nucleosome core particle and a slender cylinder for the histone tail; the charges are optimized with respect to the Poisson-Boltzmann solution for the electric field, yielding a approximately 5.5% residual. Because regular surfaces enclosing macromolecules are not sufficiently general and may be suboptimal for certain systems, we develop a general method to construct irregular models tailored to the geometry of macromolecules. We also compare charge optimization based on both the electric field and electrostatic potential refinement. Results indicate that irregular surfaces can lead to a more accurate approximation (lower residuals), and the refinement in terms of the electric field is more robust. We also show that surface smoothing for irregular models is important, that the charge optimization (by the TNPACK minimizer) is efficient and does not depend on the initial assigned values, and that the residual is acceptable when the distance to the model surface is close to, or larger than, the Debye length. We illustrate applications of DiSCO's model-building procedure to chromatin folding and supercoiled DNA bound to Hin and Fis proteins. DiSCO is generally applicable to other interesting macromolecular systems for which mesoscale models are appropriate, to yield a resolution between the all-atom representative and the polymer level.     

核酸、蛋白质的电荷数随pH的变化规律

从理论上推导出核酸、蛋白质的正电荷数随pH的变化关系式:Y=∑(i=1-3)[H^+]~n~i/([H^+]+K~b~i),负电荷数随pH的变化关系式:X=∑(i=1-5)K~a~im~i/([H^+]+k~a~i)、净电荷数随pH变化关系式以及等电点计算关系式,并从关系式中导出核苷酸、碱基、中性氨基酸、酸性氨基酸、碱性氨基酸的等电点关系式,表明理论推导是正确、可靠的。用表面活性剂沉淀肌酸激酶、不同pH的溶菌酶电泳方法验证了计算结果的可靠性。同时,计算了人DNA、蚕DNA、β-乳球蛋白带电荷数随pH的变化规律,并估计了计算误差。     

Accurate molecular electrostatic potentials based on modified PRDDO/M wave functions: III. Extension of the PESP method for calculation of electrostatic potential-derived atomic charges to compounds containing Li+, Na+, Mg2+, K+, Ca2+, Zn2+, and I

The PESP (Parameterized ElectroStatic Potential) method for calculating molecular electrostatic potentials, previously parameterized for H, C, N, O, F, P, S, Cl, and Br, is extended to molecules containing Li⁺, Na⁺, Mg²⁺, K⁺, Ca²⁺, Zn²⁺, and I. For a collection of 166 molecules containing 1668 atoms with at least one metal or iodine atom, PESP achieves an average absolute deviation in electrostatic potential-derived atomic charges of 0.042e⁻ compared with ab initio MP2/6-31G** calculations, with a correlation coefficient of 0.996. For a larger data set, consisting of 311 molecules encompassing all of the 16 elements just listed (2488 total atoms), PESP achieves an average absolute deviation of 0.040e⁻ and a correlation coefficient of 0.995. PESP calculations are an order of magnitude faster than the simplest ab initio method (STO-3G) on large molecules, while achieving a level of accuracy that rivals much more elaborate ab initio methods. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1456–1469, 1998     

Fabrication,structure and surface charges of albumin-chitosan hybrids

Protein-polymer hybrids consisting of protein and natural polymers or synthetic polymers exhibit superior properties to unmodified proteins,generating a high demand for these materials in the fields of medicine,biotechnology,and nanotechnology.Herein,protein-polysaccharide hybrids were fabricated via the formation of an amide bond between bovine serum albumin(BSA) and chitosan(CS) using N-ethyl-N-(3-dimethylaminopropyl) carbodiimide hydrochloride(EDC) as the couple reagent.FTIR spectrum reveals that the carboxyl group of BSA conjugated with the amino group of chitosan backbone.The molecular weight of BSA-CS hybrids was identified by matrix-associated laser desorption ionization time of flight mass spectra(MALDI-TOF MS) and sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE).The maximum number of chitosan chains binding to each BSA molecule was estimated as 6,and the optimal number was estimated as 2.In addition,the secondary structure and surface property of BSA were dependent upon the number of polymer conjugating on protein.The secondary structure of BSA was not significantly changed,if a few chitosans were coupled with BSA.By further increasing the molar ratio of chitosan to BSA,the secondary structure of BSA was markedly damaged.The surface’s negative charges of modified BSA also decreased.The result of native polyacrylamide gel electrophoresis(native-PAGE) also demonstrated the changes in surface charges and molecular weight of BSA-CS hybrids.     

A study of solvent effects on the stereoselectivity of Diels-Alder reactions through molecular surface electrostatic potentials

Statistical models for the study of solvent effects on the endo/exo selectivity of Diels-Alder reactions using molecular surface electrostatic potentials was obtained. The models show that hydrogen bond interactions of solvent molecules favor the predominance of the endo isomer for the reaction of methyl acrylate, methyl methacrylate and methyl trans-crotonate with cyclopentadiene whereas the effect of solvophobicity seems to be negligible.